WO2021113148A1

WO2021113148A1 - Connector with top-and bottom-stitched contacts

Info

Publication number: WO2021113148A1
Application number: PCT/US2020/062389
Authority: WO
Inventors: Randall E. Musser; Jonathan E. Buck
Original assignee: Samtec, Inc.
Priority date: 2019-12-06
Filing date: 2020-11-25
Publication date: 2021-06-10

Abstract

To help maintain and improve signal integrity, an electrical connector includes a connector housing; and at least three parallel, spaced apart, immediately adjacent, linear arrays of electrical contacts.

Description

CONNECTOR WITH TOP- AND BOTTOM-STITCHED CONTACTS

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The entire contents of each of U.S. Patent Application No. 62/694,832 filed on July 6, 2018; U.S. Patent Application No. 62/704,031 filed on November 5, 2018; U.S. Patent Application No. 62/704,038 filed on December 17, 2018; U.S. Patent Application No.

62/704,069 filed on December 6, 2019; U.S. Patent Application No. 29/716,201 filed on December 6, 2019; and U.S. Patent Application No. 29/716,202 filed on December 6, 2019 are hereby incorporated by reference in their entireties.

BACKGROUND

1. Field of the Invention

[0002] The present invention relates to electrical connectors.

2. Description of the Related Art

[0003] Connectors are used to place electrical devices in communication with one another. A connector includes contacts that transmit signals to an electrical device or another connector and a housing to support the contacts. The contacts of a connector can each include a raised portion to help secure and position the contacts within the housing. Further, solder can be attached to the contacts. The solder is used to form electrical and mechanical connections between the contact and a pad on a printed circuit board (PCB).

[0004] Fig. 1 is an end view and Fig. 2 is a side view of a known contact 20. Fig. 1 shows the contact 20 without a fusible member 40, and Fig. 2 shows the contact 20 with the fusible member 40. The contact 20 includes a head 21 and a tail 22 at the opposite end from the head 21. The head 21 includes the contact beam 23. A medial portion of the contact 20 includes wings 24, wedges 25, lead-ins 26, and a bump 27. The wings 24 engage the bottom of a core of a connector housing to maintain a consistent distance between the tail portion 22 of the contact 20 and the housing. The wedges 25 engage a side wall of the core in order to fix the position of the contact 20 and retain the contact 20 in the core of the housing. The wedges 25 fix the contact 20 in the core in the width direction of the housing to prevent stress from being applied in a length direction of the housing to prevent problems with co-planarity that can lead to an unreliable connection. The lead-ins 26 are formed by coined edges that facilitate insertion of the contacts or terminals 20 into the cores of the housing. The bump 27 positions and stabilizes the contact 20 in a desired position and orientation relative to the housing.

[0005] As shown in Fig. 3, known connectors can have an array of contacts 30 arranged in rows. The contacts 30 shown in Fig. 3 are different than the contact 20 shown in Figs. 1 and 2. As shown in Fig. 3, the contact 30 includes a head 31 and a tail 32 at the opposite end from the head 31. The head 31 includes the contact beam 33. A medial portion of the contact 30 includes wedges 35 and lead-ins 36, and the tail 32 includes a fusible member 40. However, the contact 30 shown in Fig. 3 does not include wings 24 or bumps 27 as included in the contact 20 shown in Figs. 1 and 2. It is also possible that the contact 20 shown in Figs. 1 and 2 can be used in the connector shown in Fig. 3. Because of the orientation of wedges 25 and lead-ins 26 (and the wings 24 of the contact 20 shown in Figs. 1 and 2 is used), the contact 20 is designed to be stitched or inserted from the bottom of the housing. The contact 20 is usually part of a contact ribbon that is included on a spool. The contacts 20 are stitched, or loaded, from the bottom, one row at a time. In a single row, the contacts 20 can be loaded sequentially or simultaneously.

[0006] In small connectors, contacts with wider beams can provide better electrical performance. However, wider beams limit the pitch of the contacts. When the beams of the contacts are widened, there is less material from the housing that contacts can engage with, making smaller pitches even more difficult.

SUMMARY OF THE INVENTION

[0007] To overcome the problems described above, embodiments of the present invention provide connectors and methods of making connectors, which each achieve improved impedance and return loss, smaller pitches, and contacts with wider beams.

[0008] In one embodiment of the present invention, an electrical connector includes a connector housing and at least three parallel, spaced apart, immediately adjacent, linear arrays of electrical contacts.

[0009] A longitudinal centerline and a median centerline can divide the electrical connector into four quadrants, and each of the four quadrants can define a structure that is different from each of the other quadrants. There can be an equal number of electrical contacts on either side of the longitudinal centerline, and there can be an equal number of electrical contacts on either side of the median centerline. The electrical connector can further include first and second keying features such that the first and second keying features can be positioned on the same side of the connector housing, can be spaced apart from each other, can each have a same shape, and can each be positioned as a mirror image of the other. The electrical connector can further include first and second keying features such that the first and second keying features can be positioned on the same side of the connector housing, can be spaced apart from each other, can each have a same shape, and can each be positioned as a mirror image of the other and such that the first and the second keying features can be on opposite sides of the longitudinal centerline or the median centerline. Each of the first and the second keying features can define a post; the connector housing can include ribs; and each of the first and the second keying features can be located between two adjacent ribs. Each of the first and second keying features can define a recess; the connector housing can include ribs; and each of the first and the second keying features can be located at an end of one of the ribs.

[0010] In another embodiment of the present invention, an electrical connector includes a receptacle housing, the receptacle housing having a longitudinal centerline and including first, second, and third inner ribs that are oriented parallel to one another and are spaced apart from one another, a first keying structure positioned adjacent to a second end of the second inner rib, a second keying structure positioned adjacent to a first end of the first inner rib, and a third keying structure positioned adjacent to a first end of the third inner rib.

[0011] In another embodiment of the present invention, an electrical connector includes a receptacle housing, the receptacle housing having a longitudinal centerline and including first, second, third, fourth, fifth, sixth, and seventh inner ribs that are oriented parallel to one another and are spaced apart from one another, a first keying structure positioned adjacent to a second end of the second inner rib, a second keying structure positioned adjacent to a second end of the sixth inner rib, a third keying structure positioned adjacent to a first end of the first inner rib, and a fourth keying structure positioned adjacent to a first end of the seventh keying structure. [0012] In another embodiment of the present invention, an electrical connector includes a plug housing having a longitudinal centerline and including first, second, third, and fourth plug ribs that are each oriented parallel to one another and are spaced apart from one another, a first plug keying structure positioned adjacent to a second end of the connector housing and between the second and third plug ribs, a second plug keying structure positioned adjacent to a first end of the connector housing and between the first and second plug ribs, and a third plug keying structure positioned adjacent to the first end of the connector housing and between the third and fourth plug ribs.

[0013] In another embodiment of the present invention, an electrical connector includes a plug housing having a longitudinal centerline and including a first, second, third, fourth, fifth, sixth, seventh, and eighth plug ribs that are each oriented parallel to one another and are spaced apart from one another, a first plug keying structure positioned adjacent to a second end of the connector housing and between the second and third plug ribs, a second plug keying structure positioned adjacent to second end of the connector housing and between the sixth and seventh plug ribs, a third plug keying structure positioned adjacent to a first end of the connector housing and between the first and second plug ribs, and a fourth plug keying structure positioned adjacent to the first end of the connector housing and between the seventh and eighth plug ribs.

[0014] The first keying structure can include a canted side wall that abuts the longitudinal centerline of the receptacle housing. The first keying structure can include a second side wall and a fifth side wall, and the longitudinal centerline of the receptacle housing can pass through the second side wall and the fifth side wall. The first keying structure can include a second side wall and a canted wall, and the longitudinal centerline of the receptacle housing can pass through an intersection of the second side wall and the canted wall. The second keying structure and the third keying structure can each be positioned on opposite sides of the longitudinal centerline of the receptacle housing. The first, second, third, and fourth keying structures can all be spaced away from the longitudinal centerline and a median centerline of the receptacle housing. [0015] The electrical connector can further include a first alignment peg positioned on the longitudinal centerline. The electrical connector can further include a second alignment peg spaced away from the longitudinal centerline.

[0016] The first plug keying structure can include a second plug side wall and a fifth plug side wall, and the longitudinal centerline can pass through both the second plug side wall and the fifth plug side wall. The second plug keying structure and the third plug keying structure can both be positioned on opposite sides of the longitudinal centerline of the plug housing. The first and second plug keying structures and the third and fourth plug keying structures can be positioned on opposite sides of the longitudinal centerline. The electrical connector can be an open pin field electrical connector, and all of the mating ends of all of the electrical contacts all have the same shape. The electrical connector can be a mezzanine connector.

[0017] The electrical connector can further include a first row of electrical contacts positioned immediately adjacent to a second row of electrical contacts, and a third row of electrical contacts positioned immediately adjacent to the second row of electrical contacts, wherein the first and second rows can be separated by a first row pitch of approximately 2.2 mm and the second and third rows can be separated by a second row pitch of approximately 2.4 mm. The first, second, third, and fourth keying structures can define four points of a trapezoid, and the trapezoid can be symmetrical about a median centerline of the receptacle housing. The first, second, third, and fourth plug keying structures can define four points of a trapezoid, and the trapezoid can be symmetrical about a median centerline of the receptacle housing.

[0018] The above and other features, elements, characteristics, steps, and advantages of the present invention will become more apparent from the following detailed description of embodiments of the present invention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figs. 1 and 2 show a known electrical contact that can be stitched into a connector housing from one direction.

[0020] Fig. 3 is a close-up sectional view of a known connector housing with electrical contacts stitched from one direction. [0021] Fig. 4 is a close-up sectional view of a connector housing with electrical contacts stitched from two different directions.

[0022] Figs. 5 and 6 show an electrical contact that can be stitched from the top of a connector housing.

[0023] Figs. 7 and 8 show another electrical contact that can be stitched from the bottom of a connector housing.

[0024] Fig. 9 is a perspective view of a mating pair of mezzanine connectors according to an embodiment of the present invention.

[0025] Figs. 10 and 11 are perspective views of a receptacle connector according to an embodiment of the present invention.

[0026] Fig. 12 is a partial sectional view of the receptacle connector shown in Figs. 10 and 11.

[0027] Fig. 13 is a top view of the receptacle connector shown in Figs. 10-12.

[0028] Fig. 14 is a bottom view of the receptacle connector shown in Figs. 10-13.

[0029] Fig. 15 is a side view of the receptacle connector shown in Figs. 10-14.

[0030] Fig. 16 is a perspective view of a plug connector according to an embodiment of the present invention.

[0031] Fig. 17 is a bottom perspective view of the plug connector shown in Fig. 16.

[0032] Fig. 18 is a top view of the plug connector shown in Figs. 16 and 17.

[0033] Fig. 19 is cross-sectional view of the plug connector shown in Figs. 16-18.

[0034] Fig. 20 is a side view of the plug connector shown in Figs. 16-19.

[0035] Fig. 21 is a top view of a receptacle connector according to an embodiment of the present invention.

[0036] Fig. 22 is a bottom view of the receptacle connector shown in Fig. 21.

[0037] Fig. 23 is a top perspective view of the receptacle connector shown in Figs. 21-22.

[0038] Fig. 24 is a top view of a plug connector according to an embodiment of the present invention.

[0039] Fig. 25 is a bottom view of the plug connector shown in Fig. 24.

[0040] Fig. 26 is a bottom perspective view of the plug connector shown in Figs. 24-25. [0041] Fig. 27 shows a top view of a receptacle connector according to an embodiment of the present invention.

[0042] Fig. 28 shows a bottom view of the receptacle connector shown in Fig. 27.

[0043] Fig. 29 shows a top view of a plug connector according to an embodiment of the present invention.

[0044] Fig. 30 shows a bottom view of the plug connector shown in Fig. 29.

[0045] Figs. 31-35 show various substrate footprint patterns according to various embodiments of the present invention.

[0046] Fig. 36 is a top view of a receptacle connector according to an embodiment of the present invention.

[0047] Fig. 37 is a bottom view of the receptacle connector shown in Fig. 36.

[0048] Fig. 38 is a top perspective view of the receptacle connector shown in Figs. 36-37.

[0049] Fig. 39 is a top view of a receptacle connector according to an embodiment of the present invention.

[0050] Fig. 40 is a bottom view of the receptacle connector shown in Fig. 39.

[0051] Fig. 41 is a top perspective view of the receptacle connector shown in Figs. 39-40.

[0052] Fig. 42 is a top view of a plug connector according to an embodiment of the present invention. [0053] Fig. 43 is a bottom view of the plug connector shown in Fig. 42. [0054] Fig. 44 is a top perspective view of the plug connector shown in Figs. 42-43. [0055] Fig. 45 is a top view of a plug connector according to an embodiment of the present invention. [0056] Fig. 46 is a bottom view of the plug connector shown in Fig. 45. [0057] Fig. 47 is a top perspective view of the plug connector shown in Figs. 45-46.

DETAILED DESCRIPTION

[0058] Embodiments of the present invention can include, but are not limited to: alternatively stitched electrical contacts, in series, along a common row of cores in a connector housing to increase electrical contact density without degrading signal integrity to commercially useless levels; optimized row to row spacing in an electrical connector and corresponding substrate footprint to reduce crosstalk, to permit more ground vias in a substrate, such as a printed circuit board, to maintain electrical conductor density, to aid in alternatively stitching of electrical contacts, and to make differential signal routing in a printed circuit board easier; and air void placement in ribs that helps to improve single-ended or differential impedance and reduce near-end crosstalk (NEXT) between adjacent rows of electrical contacts by reducing coupling between adjacent rows of electrical contacts at or above approximately 32 Gbits/sec. Row to row spacings described herein also permit electrical contacts in adjacent rows to carry more power or current or voltage at a 30°C rise time.

[0059] Alternatively stitched electrical contacts 110, 120 are discussed first. Fig. 4 shows a portion of a single contact row in a housing 102 of a receptacle connector 100. As shown, the receptacle connector 100 can include recesses 104 defined by ribs 106. The ribs 106 each extend beyond contact mating ends 116 of electrical contacts 110, 120. The ribs 106 can be positioned between two immediately adjacent electrical contacts 110, 120 along a row. Electrical contacts 110 can each be stitched into the housing 102 from the top or mating side 108 of the housing 102, in a first direction toward a bottom or mounting side 112 of the housing 102. Electrical contacts 120 can be stitched from the bottom or mounting side 112 of the housing 102 in a second direction toward the top or mating side 108 of the housing 102. Each row of electrical contacts 110, 120 can include any number of electrical contacts 110, 120, including three or more electrical contacts. The first and second directions oppose each other. [0060] The electrical contacts 110, 120 can each include securing structures. Securing structures can include structures that engage with cores 118 in the housing 102 to prevent the electrical contacts 110, 120 from being removed from the cores 118 and/or to position the electrical contacts 110, 120 within the cores 118 and include, for example, wings, wedges, protrusions, lead-ins, and bumps. Electrical contacts 110, 120 can be held in the housing 102 by an interference fit.

[0061] Electrical contacts 110 can include securing structures that are oriented to allow the electrical contacts 110 to be inserted into the cores 118 of the housing 102 from the mating side 108. As shown in Fig. 4, the electrical contacts 110 can include wings 114 that engage with the housing 102 to secure the electrical contacts 110 in the housing 102. Electrical contacts 120 can include securing structures that are oriented to allow the electrical contacts 110 to be inserted into the cores 118 of the housing 102 from the mounting side 112. As also shown in Fig. 4, the electrical contacts 120 can include wedges 125 that engage with the housing 102 to secure the electrical contacts 120 in the housing 102.

[0062] An example electrical contact 110 is shown in Figs. 5 and 6. Figs. 5 and 6 show an electrical contact 110 that includes a mating end 116 and wings 54. Fig. 5 shows that a retention portion 56 of the electrical contact 110 can define a first width Wl, a second width W2, a third width W3, and a fourth width W4. The first width Wl can be greater in length than any one of the second width W2, the third width W3, or the fourth widths W4. The second width W2 can be greater in length than any one of the third width W3 or the fourth widths. The third width W3 can greater in length than the fourth width W4. A mounting end 58 of the electrical contact 110 can have a fifth width W5 that is shorter in length than any one of the first width Wl, the second width W2, the third width W3, or the fourth width W4. Alternatively, the second width W2 and the third width W3 can be the same length or approximately the same lengths.

[0063] An example electrical contact 120 is shown in Figs. 7 and 8. Figs. 7 and 8 show an electrical contact 120 that includes a mating end 116 and one or more wedges 75 that each protrude in the same direction from a material thickness MT of the electrical contact 120. Wedges 75 can each include a portion 78 that has a portion width PW that is shorter in length than the material thickness MT of the electrical contact 120.

[0064] The electrical contacts 110, 120 can include other securing structures. For example, although not shown in Fig. 4, the electrical contacts 110, 120 can include bumps that position the contact within the core 118 of the housing 102. In Fig. 4, the electrical contacts 110, 120 include different securing structures, i.e., wings 114 and wedges 125, but it is possible that electrical contacts 110, 120 can include the same securing structures, e.g., both having wings 114 or both having wedges 125. As shown in Fig. 4, the cores 118 in the housing 102 can be shaped to receive the electrical contacts 110, 120. Thus, the cores 118 that receive electrical contacts 110 can be shaped differently than the cores 118 that receive electrical contacts 120. Regardless of the shapes or widths of the dissimilarly shaped retention portions 56, 56A of electrical contacts 110, 120, as shown in Figs. 5-8, the intermediate portions 60 of two immediately adjacent electrical contacts 110, 120 can be the same sixth width W6. The same can be true for two or more or for three or more immediately adjacent recesses 104, which can each define approximately equal seventh widths W7. Electrical contacts 110, 120 can define differently shaped retention portions 56, 56A, but the same shaped intermediate portions 60 and same shaped mating ends 116.

[0065] Fusible members 130, 140 can be attached to the mounting ends 58 of the electrical contacts 110, 120 in any suitable manner. Fusible members 130, 140 can include solder or any other suitable material that can be used to form electrical and mechanical connections to another device such as a substrate, e.g. PCB, flexible circuit board, or a cable.

[0066] By stitching electrical contacts 110, 120 from the mating side 108 and mounting side 112 of the housing 102, the electrical contacts 110, 120 can be located closer together than allowed by the prior art, decreasing the pitch of the electrical contacts 110, 120, even if the electrical contacts 110, 120 have intermediate portions 60 or mating ends 116 that are wider than electrical contacts that are only stitched in one direction. A sixth width W6 to contact pitch ratio can be 50-75% of the contact pitch. As shown in Fig. 4, top and bottom stitching allows the electrical contacts 110, 120 to include securing structures or retention portions 56, 56A that engage at different heights in the cores 118 so that retention portions 56, 56A of adjacent electrical contacts 110, 120 do not interfere with each other. In Fig. 4, the wings 114 engage the top of the cores 118, and the wedges 125 engage the middle of the cores 118, which allows the cores 118 to be placed closer together, decreasing the pitch of the receptacle connector 100 without sacrificing signal integrity at a data transfer rate at or above 32 Gbits/sec.

[0067] For a fixed pitch, electrical contacts 110, 120 with wider width W6, intermediate portions 60 and mating ends 116 provide improved electrical performance, including improved impedance/improved return loss. For example, if differential signals are transported, i.e., transmitted and/or received, through electrical contacts 110, 120, then a time domain impedance can be between about 85 W and about 100 W at 17 ps (10%-90%) or between about 86 W and about 99 W at 17 ps (10%-90%). Simulated insertion loss is between 0 dB and -1.5 dB at frequencies from 1 GHz up to and including 17 GHz (approximately 34 Gbits/sec or 2 times the frequency) and between 0 dB and -3dB through 23 GHz (approximately 46 Gbits/sec). Simulated differential return loss is between -10 dB and -60 dB at frequencies from 1 GHz up to and including 23 GHz. Simulated differential vector sum crosstalk is between -40 dB and -100 dB at frequencies from 1 GHz up to and including 19 GHz with excursions, is between -30 dB and -100 dB at frequencies from 1 GHz up to and including 34 GHz, and is between -20 dB and - 100 dB at frequencies from 1 GHz up to and including 50 GHz. Data rate per channel is approximately 32 Gbits/sec, an aggregate data rate can be approximately 4096 Gbits/sec, and the data rate density can be approximately 2088 Gbits/sec per square inch at any of the at least 32 Gbit/sec capable impedance, insertion loss, differential return loss, vector sum crosstalk values listed above. Because electrical connectors can be devoid of metal, metal crosstalk shields, power contacts, and lossy crosstalk shields, electrical connectors can have an open pin field. Electrical contacts 110, 120 can be electrically arranged in patterns of signal-ground- signal (S-G-S), S-S-G-S-S, S-S-G-G-S-S or can electrically carry or be assigned as power, reference, or ground electrical contacts 110, 120.

[0068] In a single row, different stitching processes can be used. For example, the electrical contacts 110 or 120 can all be stitched, and then the remaining electrical contacts 120 or 110 can all be stitched. Alternatively, the electrically contacts 110, 120 can be alternatively stitched in series: a single electrical contact 110 or 120 can be stitched, then a single electrical contact 120 or 110 can be stitched, etc., until the entire row is stitched.

[0069] The fusible members 130, 140 can be attached to the electrical contacts 110, 120 after the electrical contacts 110, 120 have been stitched into the receptacle connector 100. [0070] The receptacle connector 100 can be any suitable connector, including, for example, a mezzanine connector that can be used to connect two substrates, e.g., printed circuit boards, together in parallel or substantially parallel within manufacturing tolerances. The receptacle connector 100 can be a hermaphroditic connector that connects with a connector that has contacts that are only stitched from one direction.

[0071] Fig. 9 shows examples of such mezzanine connectors, in which receptacle connector 200 has electrical contacts that are stitched from two directions and the plug connector 300 has electrical contacts that are only stitched from one side. Optionally, the connector can be a right angle connector. The plug connector 300 can have stitched electrical contacts and the receptacle connector 200 can have electrical contacts that are only stitched from one side, such as the mounting side 212 of the receptacle housing 202.

[0072] Fig. 9 shows a receptacle connector 200 and a plug connector 300 mounted on respective substrates 400. As shown, the receptacle connector 200 in the bottom portion of Fig. 9 can include four parallel, spaced apart receptacle rows 204, 210, 220, 206 of electrical contacts 110, 120. A first receptacle row 204 of electrical contacts 110, 120 and a fourth receptacle row 206 of electrical contacts 110, 120 extend along the inside of the outer sides of the receptacle housing 202. A second receptacle row 210 of electrical contacts 110, 120 and a third receptacle row 206 of electrical contacts 110, 120 are back-to-back and extend along an inner rib 250 that extends from end to end down a middle of the receptacle connector 200 along longitudinal centerline CL (not shown). Although the receptacle connector 200 in Fig. 9 is shown with four parallel, spaced apart, shieldless rows, any number of rows of electrical contacts 110, 120 can be used. The electrical contacts 110, 120 of the receptacle connector 200 can be stitched from two directions as described with respect to Figs. 4-8. The receptacle connector 200 can be devoid any of crosstalk shields and magnetic absorbing lossy material or can include any number of crosstalk shields or electrically conductive or non-conductive magnetic absorbing lossy material. Fusible members 230, 240, such as solder balls, can be attached to respective ones of the electrical contacts 110, 120.

[0073] The plug connector 300 in the top portion of Fig. 9 can include a plug housing 302 four parallel, spaced apart plug rows 304, 310, 320, 306 of electrical plug contacts 308. A first plug row 304 of electrical plug contacts 308 and a second plug row 310 of electrical plug contacts 308 each extend along a respective plug rib 350 that extends from end to end of the plug connector 300. A third plug row 320 of electrical plug contacts 308 and a fourth plug row 306 of electrical plug contacts 308 each extend along a respective plug rib 350 that extends from end to end of the plug connector 300.

[0074] Although the plug connector 300 in Fig. 9 is shown with four parallel, spaced apart, shieldless rows of electrical plug contacts 308, any number of rows can be used. The electrical plug contacts 308 of the plug connector 300 can be stitched from two directions as described with respect to Figs. 4-8. The plug connector 300 can be devoid any of crosstalk shields and magnetic absorbing lossy material or can include any number of crosstalk shields or electrically conductive or non-conductive magnetic absorbing lossy material. Fusible elements 330, 340, such as solder balls, can be attached to each respective one of the electrical plug contacts 308. Typically, the numbers of rows and electrical plug contacts 308 in the plug connector 300 and receptacle connector 200 are the same.

[0075] As shown in Fig. 9, fusible members 230, 240, 330, 340 are used to attach the electrical plug contacts 308 to the substrates 400. The electrical plug contacts 308 carried by the plug connector 300 can be stitched from one side or only from the mounting side 312 of the plug housing 302.

[0076] Figs. 10 and 11 show a receptacle connector 200A of an embodiment of the present invention that includes a first receptacle row 204A, a second receptacle row 210A, a third receptacle row 220A, and a fourth receptacle row 206A of stitched electrical contacts, such as electrical contacts 110, 120. As shown in Fig. 11, the first receptacle row 204A and the second receptacle row 210A can be spaced apart by a first row pitch RP1. The second receptacle row 210A and the third receptacle row 220A can be spaced apart by a second row pitch RP2 that is numerically greater than the first row pitch RP1. The third receptacle row 220A can be spaced apart from the fourth receptacle row 206A by a third row pitch RP3 that is equal to or approximately equal to the first row pitch RP1. The first row pitch can be 2.2±0.05 mm, 2.2±0.1 mm, or some other value approximately equal to 2.2 mm, such as 2.2±0.05 mm or 2.2±0.005mm. The second row pitch can be 2.4±0.005 mm, 2.4±0.05 mm, 2.4±0.1 mm, or some other value approximately equal to 2.4 mm. The third row pitch can be the same as the first row pitch, such as 2.2±0.005 mm, 2.2±0.05 mm, 2.2±0.1 mm, or some other value approximately equal to 2.2 mm. Making the row pitches unequal to each other in an electrical connector and corresponding substrate footprint helps to reduce crosstalk in the electrical connector and the footprint, permit more ground vias in a substrate, such as a printed circuit board, maintain electrical conductor density, and ease differential signal routing in a printed circuit board so that data rates of at least 32 Gbits/sec can be maintained with acceptable levels of impedance, insertion loss, differential return loss, or crosstalk. [0077] The top perspective view of Fig. 10 shows that the receptacle connector 200A includes a first receptacle row 204A and a fourth receptacle row 206A that each extend along the inside of the outer sides of the receptacle housing 202A. A second receptacle row of electrical contacts 110, 120 and a third receptacle row of electrical contacts 110, 120 are positioned back-to-back extending along an inner rib 250A that extends from end to end down the middle of the receptacle connector 200A along longitudinal centerline CL.

[0078] In Figs. 10 and 11, the receptacle connector 200A or receptacle housing 202A includes four rows of electrical contacts 110, 120, but any number of rows can be used. In Figs. 10 and 11, each row of electrical contacts 110, 120 can include at least one hundred, evenly spaced contacts positioned on a 0.63±0.1 mm or 0.065±0.05 contact pitch PI, but any number of electrical contacts can be used per row.

[0079] As shown in Fig. 10, mating ends 116A of three immediately adjacent electrical contacts 110, 120 can be on the same pitch, but two of the three electrical contacts, such as electrical contacts 110, can be inserted into the receptacle housing 202A in a first direction from a mating side 108A of the receptacle housing 202A and the third one of the three electrical contacts, such as electrical contact 120 can be inserted into the receptacle housing 202A from a second direction opposite to the first direction.

[0080] The receptacle housing 202A can be defined by two parallel, spaced apart longitudinal walls, such as first longitudinal wall 260A and second longitudinal wall 260B, and two parallel, spaced apart end walls, such as first end wall 262A and second end wall 262B. The two parallel, first and second spaced apart end walls 262A, 262B are shorter in length than the two parallel, first and second spaced apart longitudinal walls 260A, 260B. A centerline CL extends through the two parallel, spaced apart end walls 262A, 262B, parallel to the two parallel, spaced apart first and second longitudinal walls 260A, 260B. A receptacle mating side 208A of the receptacle housing 202A can include a first keying structure 270A and a second keying structure 270B. The first keying structure 270A lies on one side of the centerline CL, and can abut the centerline CL or cross the centerline CL such that the centerline CL passes through at least a portion, but does not bisect the total bounded area, of the first keying structure 270A. The second keying structure 270B can be positioned at the receptacle mating side 208A of the receptacle housing 202A on an opposite side of the centerline compared to the first keying structure 270A, and can abut the centerline CL or cross the centerline CL such that the centerline CL passes through at least a portion, but does not bisect the total bounded area, of the second keying structure 270B.

[0081] Each of the first and second keying structures 270A, 270B can be a respective first recess 272A and second recess 272B, with at least three sides or surfaces defined by the receptacle housing 202A and respective portions of the two parallel, spaced apart end first and second end walls 262A, 262B. Each of the at least three-sided, first and second recesses 272A, 272B can be defined by or include a first side wall, line, or surface 274, a second side wall, line, or surface 276 that can perpendicularly intersect the first side wall 274, and a canted side wall, line, or surface 278 that intersects with the second side wall 276. Each of the first and second keying structures 270A, 270B, which can be recesses, are configured to receive a corresponding first keying structure or second keying structure, which can be posts, of a mating plug connector. The first keying structure 270A and the second keying structure 270B can be positioned non-symmetrically about both the longitudinal centerline CL and the median centerline ML. One benefit of the offset is to position plastic and air, present in the first and second keying structures 270A, 270B and their mating counterparts, in places that help with signal integrity.

[0082] On one side of the receptacle housing 202A, adjacent to first end wall 262A, the canted side wall 278 can abut the centerline CL, be spaced from the centerline CL, or pass through centerline CL. On an opposed side of the receptacle housing 202A, adjacent to the second end wall 262B, the first side wall 274 can abut, be coincident with, be parallel to, or be positioned adjacent to, but spaced away from, the centerline CL. The first keying structure 270A and the second keying structure 270B can be identically shaped, can be mirror images about a centerline that is perpendicular to the centerline CL and spans the receptacle rows 204, 210, 220, 206, or can be offset mirror images.

[0083] Fig. 11 is a bottom perspective view of the receptacle connector 200A shown in Fig. 10. Fusible members 230, 240 can be attached to the electrical contacts 110, 120 in any suitable manner. The receptacle connector 200A can include one or more standoffs 201. As shown in Fig. 11, the standoffs 201 can be located at one or more of the four corners of the receptacle housing 202A. Any number and any location of standoffs 201 can be used. The standoffs 201 ensure that the receptacle connector 200A is a fixed distance from a substrate when the fusible members 230, 240 are re-flowed to connect the receptacle connector 200A to the substrate. The receptacle connector 200A can include alignment pegs 280A, 280B that can be inserted into corresponding alignment holes in a substrate to self-align the receptacle housing 202A on a substrate and roughly align the fusible members 230, 240 with respect to solder pads on a substrate. Fig. 11 shows a first alignment peg 280A and a second alignment peg 280B, but any number of alignment pegs can be used. The first and second alignment pegs 280A, 280B can have any suitable shapes, including, for example, a circular shape, an oval shape, a square shape, etc. The shape of the first and second alignments pegs 280A, 280B can be the same or different. Portions of one or more of the first or second alignment pegs 280A, 280A can intersect the centerline CL, or both the first and second alignment pegs 280A, 280B can be spaced from the centerline CL. Four receptacle rows 204A, 210A, 220A, 206A of electrical contacts 110, 120 is are shown, but one or more receptacle rows can be used.

[0084] Fig. 12 shows four electrical contacts 110A, 120A carried by the receptacle housing 202A of the receptacle connector 200A. The receptacle housing 202 can include cores 118A into which the electrical contacts 110A, 120A can be stitched. The electrical contacts 110A can include mating ends 116A and can be stitched from the mating side 108A of the receptacle housing 202A, and the electrical contacts 120A can be stitched from the mounting side 212A of the receptacle housing 202, as described above.

[0085] Figs. 13-15 show a receptacle connector 200B that includes four receptacle rows 204B, 210B, 220B, 206B of electrical contacts 110, 110A, 120, 120A. As shown in Fig. 13, the contact pitch PI between adjacent electrical contacts 110, 110A, 120, 120A in any receptacle row can be between approximately 0.62±0.1 mm, such as 0.635 mm. A longitudinal length LI of a receptacle housing 202B carrying four receptacle rows of one hundred electrical contacts 110, 110A, 120, 120A can be between approximately 67.6±2 mm. A receptacle cavity length at a mating interface can be between approximately 64.7±2 mm. A receptacle cavity depth of the mating interface can be between approximately 7.0±2 mm. A contact area distance CD between two facing mating ends 116B is approximately 1.7±0.1 mm. A depth or width DW of the receptacle housing 202B is approximately 8.5±0.5 mm. The receptacle connector 200B can be devoid of shields, devoid of power contacts, can have metallic crosstalk shields, can have electrically conductive on non-conductive magnetic absorbing material, or can be devoid of magnetic absorbing material.

[0086] The receptacle connector 200B can include a receptacle housing 202, which can define two parallel, spaced apart longitudinal walls, such as a first longitudinal wall 260C and a second longitudinal wall 260D, and two parallel, spaced apart end walls, such as first end wall 262C and second end wall 262D. The two parallel, spaced apart first and second end walls 262C, 262D can each be shorter in width than the two parallel, spaced apart first and second longitudinal walls 260C, 260D. A centerline CL extends through the two parallel, spaced apart first and second end walls 262C, 262D, parallel to the two parallel, spaced apart first and second longitudinal walls 260C, 260D. A median centerline ML cuts a longitudinal length of the receptacle connector 200B in half, intersects the centerline CL at a ninety degree angle, and extends across first, second, third, and fourth receptacle rows 204, 210, 220, 206. A mating interface of the receptacle connector 200B can include a first keying structure 270C and a second keying structure 270D. The first keying structure 270C can lie on one side of the centerline CL. The first keying structure 270C can abut the centerline CL, or intersect the centerline CL such that the centerline CL passes through at least a portion of the first keying structure 270C, but does not bisect the total bounded area, of the first keying structure 270C. The second keying structure 270D can be positioned at the mating interface or mating side 214 of the receptacle connector 200B on an opposite side of the centerline compared to the first keying structure 270C. The second keying structure 270D can abut the centerline CL or cross the centerline CL, such that the centerline CL passes through at least a portion, but does not bisect the total bounded area, of the second keying structure 270D.

[0087] The receptacle housing 202, also called a connector housing, defines a first end wall 262A, an opposed second end wall 262C, extends along a longitudinal centerline CL, and has median centerline ML that is perpendicular to the longitudinal centerline CL. The respective first, second, third, and fourth spaced apart, parallel receptacle rows 204, 210, 220, 206 of electrical contacts can be carried by the receptacle housing 202. Each of the first, the second, the third, and the fourth receptacle rows of 204, 210, 220, 206 of electrical contacts 110, 120 each extend parallel to the longitudinal centerline CL. The first receptacle row 204 or first row of electrical contacts 110, 120 is spaced from the second receptacle row 210 or second row of electrical contacts 110, 120 by a first row pitch RP1. The third receptacle row 220 or third row of electrical contacts 110, 120 is spaced from the second receptacle row 210 of electrical contacts 110, 120 by a second row pitch RP2 that is numerically greater than the first row pitch RP1. The fourth receptacle row 206 or fourth row of electrical contacts 110, 120 is spaced from the third receptacle row 220 of electrical contacts 110, 120 by a third row pitch RP3 that is equal to or with manufacturing tolerance of the first row pitch RP1. The first keying structure 270A is positioned adjacent to the first end wall 262A of the receptacle housing 202, adjacent to a mating side 214 of the receptacle housing 202. The second keying structure 270B is positioned adjacent to the second end wall 262B of the receptacle housing 202, adjacent to the mating side 214 of the receptacle housing 202. The first keying structure 270A and the second keying structure 270B can be positioned non-symmetrically about both the longitudinal centerline CL and the median centerline ML. The first and second keying structures 270A and 270B can be offset with respect to each other along the median centerline ML.

[0088] Each of the first and second keying structures 270C, 270D can be a respective first recess 272C and second recess 272D with at least three sides or surfaces defined by the receptacle connector 200B and respective portions of the two parallel, spaced apart first and second end walls 262C, 262D. Each of the at least three-sided first and second recesses 272C, 272D can be defined by or include a first side wall, line, or surface 274A, a second side wall, line, or surface 276A that can perpendicularly intersect the first side wall 274A, and a canted side wall, line, or surface 278A that intersects with the second side wall 276A. A fourth side wall, line, or surface 282 can intersect the canted side wall, line, or surface 278A. A fifth side wall, line, or surface 284 can intersect the first side wall, line, or surface 274A and the fourth side wall, line, or surface 282. Each of the first and second keying structures 270C, 270D, which can be recesses, are configured to receive a corresponding first keying structure or second keying structure, which can be posts, of a mating plug connector. [0089] On one end of the receptacle housing 202B, adjacent to the second end wall 262D, the canted side wall 278A can abut the centerline CL, be spaced from the centerline CL, or pass through centerline CL. On an opposed side of the receptacle housing 202B, adjacent to the first end wall 262C, the first side wall 274A can abut, be coincident with, be parallel to, or be positioned adjacent to, but spaced away from, the centerline CL. The first keying structure 270C and the second keying structure 270D can each be identically shaped, can be positioned as mirror images about a centerline that is perpendicular to the centerline CL and spans the receptacle rows 204B, 210B, 220B, 206B, or can be positioned as offset mirror images.

[0090] As shown in Fig. 14, a mounting contact field MF can have a width of approximately 6.8±1 mm and can have a contact field length MFL approximately 62.8±1 mm, for an approximate overall contact area between approximately 427.04 mm² and approximately 440.22 mm², including these areas and any area therebetween. Four hundred individual electrical contacts can fit within these areas. First, second and third row pitches RP1, RP2, RP3 of the receptacle connector 200B can be approximately 2.1 to 2.3 mm, approximately 2.3 to 2.5 mm, and approximately 2.1 to 2.3 mm, respectively. For example, first, second, and third row pitches RP1, RP2 and RP3 can be 2.2±0.05mm, 2.4±0.05mm, and 2.2±0.05mm, respectively.

The first row pitch RP1 is a distance between centerlines of the first receptacle row 204A and the second receptacle row 210A. The second row pitch RP2 is a distance between centerlines of the second receptacle row 210A and the third receptacle row 220A. A third row pitch RP3 is a distance between the third receptacle row 220A and the fourth receptacle row 206A. A distance between respective centers of the first and second alignment pegs 280A, 280B and the centerline CL along the length of the receptacle connector 200B can be approximately 1.2±0.1 mm. The diameter of the circular alignment peg and the larger diameter of the oval-shaped alignment peg can be approximately 0.6±0.1 mm to 0.8±0.1 mm. The smaller diameter of the oval-shaped second alignment peg 280B can be approximately 0.5±0.1 mm to 0.7±0.1 mm. [0091] As shown in Fig. 15, a receptacle height RH of the receptacle connector 200B, measured from a receptacle mating side 208B of the receptacle housing 202B to bottom surface of a fusible member 230, such as a solder ball, can be between approximately 3.7±0.1 mm. A standoff distance SD between the bottom of the connector standoff and the bottom of the adjacent alignment peg can be approximately 0.74±0.05 mm.

[0092] Figs. 16 and 17 illustrate an exemplary plug connector 300A of an embodiment of the present invention. As shown in Fig. 16, the plug connector 300A can have a plug housing 302A, or connector housing, that defines two parallel, spaced apart longitudinal walls, such as first longitudinal plug wall 360A and second longitudinal plug wall 360B, and two parallel, spaced apart end walls, such as first plug end wall 362A and second plug end wall 362B. The two parallel, spaced apart first and second plug end walls 362A, 362B are shorter in length than the two parallel, spaced apart first and second longitudinal plug walls 360A, 360B. A centerline CL extends through the two parallel, spaced apart plug end walls 362A, 362B, parallel to the two parallel, spaced apart longitudinal plug walls 360A, 360B. The plug connector 300A can include a first plug row 304A, a second plug row 310A, a third plug row, 320A and a fourth plug row 306A of electrical plug contacts 308A that are configured to mate with the receptacle connector 200B shown in Figs. 13-15. The top perspective view of Fig. 16 shows that the plug connector 300A can include a first plug row 304A and a second plug row 310A of back-to-back electrical plug contacts 308A carried by a plug rib 350A adjacent to a mating interface of the plug housing 302A. The plug connector 300A can further include a third plug row 320A and a fourth plug row 306A of back-to-back electrical plug contacts 308A carried by a plug rib 350A adjacent to a mating interface of the plug housing 302A. The first plug row 304A of electrical plug contacts 308A can be positioned immediately adjacent to the second plug row 310A of electrical plug contacts 308A. The third plug row 320A of electrical plug contacts 308A is positioned adjacent to the second plug row 310A of electrical plug contacts 308A. A fourth plug row 306A of electrical plug contacts 308A is positioned adjacent to the third plug row 320A of electrical plug contacts 308A.

[0093] The plug ribs 350A can be spaced apart, be positioned parallel to each other, and extend in a direction from the first plug end wall 362A to the second plug end wall 362B. Fig.

16 also shows that the plug ribs 350A and mating ends 116C protrude above the plug housing 302A so they extend into and mate within recesses defined by the receptacle connector 200B shown in Figs. 13-15. [0094] The plug connector 300A mating interface 314 can include at least two keying structures, such as first plug keying structure 370A and second plug keying structure 370B. The first plug keying structure 370A can lie on one side of the centerline CL, can abut the centerline CL, or can cross the centerline CL such that the centerline CL passes through at least a portion, but does not bisect the total bounded area, of the first plug keying structure 370A. The second plug keying structure 370B can be positioned at the mating interface of the plug connector 300A on an opposite side of the centerline CL compared to the first plug keying structure 370A, and can abut the centerline CL or can cross the centerline CL such that the centerline CL passes through at least a portion, but does not bisect the total bounded area, of the second plug keying structure 370B. One of the first and second plug keying structures 370A, 370B can partially lie along the same line as the third plug row 320A of electrical plug contacts 308A, but not lie along lines of the first, second and third plug rows 304A, 310A, 320A of electrical plug contacts 308A. One of the remaining first and second plug keying structures 370A, 370B can partially lie along the same line as the second plug row 310A of electrical contacts, but not lie along lines of the first, third and fourth plug rows 304A, 320A, 306A of electrical contacts.

[0095] Each of the first and second plug keying structures 370A, 370B can be a respective protrusion defined by the plug housing 302A or positioned adjacent to the plug housing 302A. Each of the first and second plug keying structures can define three or more sides and can include a first plug side wall, line, or surface 374, a second plug side wall, line, or surface 376 that can perpendicularly intersect the first plug side wall 374, a canted plug side wall, line, or surface 378 that intersects with the second plug side wall 376, and fourth plug side wall, line, or surface 380 can intersect the canted plug side wall, line, or surface 378 and the first plug side wall, line, or surface 374. Each of the first and second plug keying structures 370A, 370B is configured to receive a corresponding first keying structure 270A, 270C or second keying structure 270B, 270D, which can be recesses or cavities of a mating receptacle connector 200, 200A, 200B. A fifth plug side wall, line, or surface 382 can be positioned between the canted plug side wall, line, or surface 378 and the fourth plug side wall, line, or surface 380.

[0096] On one side of the plug connector 300A, adjacent to first plug end wall 362A, the canted plug side wall 378 can abut the centerline CL, be spaced from the centerline CL, or pass through centerline CL. On an opposed side of the plug connector 300A, adjacent to the second plug end wall 362B, the first plug side wall 374 can abut, can be coincident with, can be parallel to, or can be positioned adjacent to, but spaced away from, the centerline CL. The first plug keying structure 370A and the second plug keying structure 370B can each be identically shaped, can be positioned as mirror images about a centerline that is perpendicular to the centerline CL and spans the first plug row, the second plug row, the third plug row, and the second plug row 304A, 310A, 320A, 306A, or can be positioned as offset mirror images, as shown.

[0097] Fig. 17 is a bottom perspective view of the plug connector 300A. Fusible members, not shown in Fig. 17, can be attached to the electrical plug contacts 308A in any suitable manner. The plug connector 300A can include plug standoffs 301. The plug standoffs 301 can be located at the four corners of the plug housing 302A. Any number and any location of plug standoffs 301 can be used. The plug standoffs 301 help ensure that the plug connector 300A is spaced a fixed distance from a mounting surface of a substrate when the fusible members (not shown) are re-flowed to connect the plug connector 300A to a substrate. The plug connector 300A can include a first plug alignment peg 384A and a second plug alignment peg 384B that are configured to be received in pre-drilled alignment holes to roughly align fusible elements of the plug connector 300A with corresponding solder pads on a mounting surface of a substrate. Fig. 17 shows two plug alignment pegs, but any number of plug alignment pegs 384A, 384B can be used. The first and second plug alignment pegs 384A, 384B can have any suitable shapes, including, for example, a circular shape, an oval shape, a square shape, etc. The shapes of the first and second plug alignments pegs 384A, 384B can be the same or different. All of the first and second plug alignment pegs 384A, 384B can be positioned on the same side of the centerline CL, such that all of the first and second plug alignment pegs 384A, 384B and one of the first and second plug keying structures 370A, 370B are all positioned on the same side of the centerline CL. At least two alignment pegs can lie on the same line as one of the second plug row 310A of electrical plug contacts 308A and the third plug row 320A of electrical plug contacts 308A. A mated height of the receptacle connector 200, 200A, 200B and plug connector 300, 300A can be approximately 10±1 mm. Both the plug connector 300, 300A and the receptacle connector 200, 200A, 200B can include open pin field contacts.

[0098] Fig. 18 illustrates an exemplary plug connector 300B of an embodiment of the present invention. The plug connector 300B shown in Fig. 19 is similar to the plug connector 300A shown in Figs. 16 and 17. One difference is that the first plug keying structure 370C shown in Fig. 19 lies on the same line as the third plug row 320B and the first plug keying structure 370A shown in Fig. 16 lies along the same line as the third plug row 320A. Another difference is that the second plug keying structure 370D shown in Fig. 19 lies on the same line as the third plug row 320B, and the second plug keying structure 370B shown in Fig. 16 lies along the same line as the second plug row 310A.

[0099] Fig. 19 shows two first electrical plug contacts 308B and two second electrical plug contacts 308C, and any of the plug connectors 300, 300A, 300B. The plug housing 302, 302A includes cores 118C and recesses 104A into which the first and second electrical plug contacts 308B, 308C can be stitched from the mounting side 386 of the plug housing 302, 302A. Plug securing structures 388, 390 can engage the plug housing 302, 302A at different heights. In addition, the first electrical plug contacts 308B can include indents 392, 394 that oppose the plug securing structures 388, 390 of the adjacent first or second electrical plug contacts 308B, 308C. Fusible elements 330, 340 can be attached to mounting ends of first or second electrical plug contacts 308B, 308C.

[0100] As shown in Fig. 20, a plug height PH of the plug connector 300, 300A, 300B, measured from a top surface of the plug connector 300, 300A, 300B to a bottom surface of a fusible element 330, such as a solder ball, can be between approximately 8.4±0.5 mm.

[0101] As shown in Fig. 21, a receptacle connector 405 can have a receptacle housing 406 that defines two parallel, spaced apart longitudinal walls, such as first longitudinal wall 407A and second longitudinal wall 407B and two parallel, spaced apart end walls, such as first end wall 409A and second end wall 409B. The two parallel, spaced apart first and second end walls 409A, 409B are shorter in length than the two parallel, spaced apart first and second longitudinal walls 407 A, 407B. A centerline CL extends through the two parallel, spaced apart first and second end walls 409A, 409B, parallel to the two parallel, spaced apart first and second longitudinal walls 407 A, 407B. A mating interface of the receptacle connector 405 or receptacle housing 406 can include a first keying structure 410A and a second keying structure 410B. The first keying structure 410A can lie on one side of the centerline CL, and can abut the centerline CL or cross the centerline CL such that the centerline CL passes through at least a portion, but does not bisect a total bounded area or perimeter, of the first keying structure 410A. The second keying structure 410B can be positioned at the mating interface of the receptacle housing 406 on an opposite side of the centerline CL compared to the first keying structure 410A, and can abut the centerline CL or cross the centerline CL such that the centerline CL passes through at least a portion, but does not bisect a total bounded area or perimeter, of the second keying structure 410B.

[0102] Each of the first and second keying structures 410A, 410B can be a respective first recess 408A and second recess 408B with at least three wall sides or surfaces and four or five total sides or surfaces defined by the receptacle housing 406 and respective portions of the two parallel, spaced apart first and second end walls 409A, 409B. Each of the first and second recesses 408A, 408B can have a bounded area or perimeter defined by a first side wall, line, or surface 412A, a second side wall, line, or surface 414B, a canted side wall, line, or surface 416, a fourth side wall, line, or surface 412B, and a fifth side wall, line, or surface 414A. It should be understood that, with respect to the first and second keying structures 410A, 410B, "wall" can also include a line, surface or partial wall. The first side wall 412A and the fourth side wall 412B can be parallel to each other. The second side wall 414B and the fifth side wall 414A can be parallel to each other. The first side wall 412A and the second side wall 414B can intersect to form a right angle. The canted side wall 416 can intersect the second side wall 414B. The fourth side wall 412B can be parallel to the first side wall 412A and can intersect the canted side wall 416. The fifth side wall 414A can be parallel to the second side wall 414B and can intersect the first side wall 412A and the fourth side wall 412B. The second sidewall 414B can be shorter in length than the first side wall 412A and the fifth side wall 414A. The fourth side wall 412B can be the shortest sidewall in length. Each of the first and second keying structures 410A, 410B, which can be recesses, are configured to receive a corresponding first plug keying structure 510A or second plug keying structure 510B shown in Fig. 24, which can be posts or first or second protrusions 508A, 508B defined by plug housing 505 or positioned adjacent to a plug housing 505. For example, the first keying structure 410A of the receptacle connector 405 can receive the second plug keying structure 510B of the plug housing 505, and the second keying structure 410B of the receptacle housing 406 can receive the first plug keying structure 510A of the plug housing 505.

[0103] The receptacle connector 405 or receptacle housing 406 can include four parallel, spaced apart receptacle rows 420, 422, 424, 426 of electrical contacts 110, 110A, 120. A first receptacle row 420 of electrical contacts 110, 110A, 120 and a fourth receptacle row 426 of electrical contacts 110, 110A, 120 extend along the inside of the respective first longitudinal wall 407A and the second longitudinal wall 407B of the receptacle housing 406. A second receptacle row 422 of electrical contacts 110, 110A, 120 and a third receptacle row 424 of electrical contacts 110, 110A, 120 are back-to-back extending along an inner rib 428 that extends from end to end down a middle of the receptacle connector 405 or receptacle housing 406. Although the receptacle connector 405 is shown with four parallel, spaced apart, shieldless rows, any number of rows of electrical contacts 110, 110A, 120 can be used. The electrical contacts 110, 110A, 120 of the receptacle connector 405 can be stitched from two directions as described with respect to Figs. 4-8. The receptacle connector 405 can be devoid any of crosstalk shields and magnetic absorbing lossy material or can include any number of crosstalk shields or electrically conductive or non-conductive magnetic absorbing lossy material. Fusible elements, such as solder balls, can be attached to respective ones of the electrical contacts 110, 110A, 120. The electrical contacts 110, 110A, 120 can also terminate in press-fit pins, eye-of- the needles, J-lead, or other configurations.

[0104] On one side of the receptacle connector 405 or receptacle housing 406, adjacent to first end wall 409A, the fourth side wall 412B can abut, be coincident with, or be positioned adjacent to, but spaced away from, the centerline CL. The first side wall 412A can be positioned parallel to and spaced away from the centerline CL. On an opposed side of the receptacle connector 405 or receptacle housing 406, adjacent to the second end wall 409B, the first side wall 412A can abut, be coincident with, or be positioned adjacent to, but spaced away from, the centerline CL. The fourth side wall 412B can be positioned parallel to and spaced away from the centerline CL. The first keying structure 410A and the second keying structure 410B can be identically shaped. The second keying structure 410B can be a mirror image of the first keying structure 410A with respect to a median centerline ML that is perpendicular to the centerline CL.

[0105] As shown in Fig. 22, a mounting interface of the receptacle connector 405 can include first alignment peg 401 and second alignment peg 402. The centerline CL can pass through the first alignment peg 401, and the first alignment peg 401 can have a center point CP that the centerline CL passes through. The second alignment peg 402 can be positioned on either side of the centerline CL, such that the centerline CL does not intersect the second alignment peg 402. In one embodiment, the second alignment peg 402 can be positioned, completely or partially, under the first keying structure 410A. The first alignment peg 401 can be positioned, completely or partially, under the second keying structure 410B. The second alignment peg 402 and the second receptacle row 422 of electrical contacts 110, 110A, 120 can both lie along a centerline CL2 that is parallel to and spaced away from the centerline CL, such that the centerline CL2 passes through the second receptacle row 422 of electrical contacts 110, 110A, 120 and the second alignment peg 402. The first alignment peg 401 can have a circular shape with a diameter of approximately 0.8±0.05 mm, and the second alignment peg 402 can have an oval shape with diameters of approximately 0.8±0.05 mm and 0.6±0.05 mm. The first alignment peg 401 can be positioned adjacent to the first end wall 409A of the receptacle housing 406 or connector housing and adjacent to a mounting interface 430 of the receptacle housing 406. The second alignment peg 402 can be positioned adjacent to the second end wall 409B of the receptacle housing 406 and adjacent to the mounting interface 430 of the receptacle housing 406. The first alignment peg 401 and the second alignment peg 402 can both be positioned non-symmetrically about both the longitudinal centerline CL and the median centerline ML. The first row pitch RP1 between respective electrical contact centers of the first receptacle row 420 and the second receptacle row 422 can be approximately 2.2±0.005 mm, 2.2±0.1 mm or 2.2±0.05mm. A second row pitch RP2 between respective electrical contact centers of the second receptacle row 422 and the third receptacle row 424 can be approximately 2.4±0.005 mm, 2.4±0.1 mm or 2.4±0.05 mm. A third row pitch RP3 between respective electrical contact centers of the third receptacle row 424 and the fourth receptacle row 426 can be approximately 2.2±0.005 mm, 2.2±0.1 mm or 2.2±0.05 mm. [0106] Fig. 23 is a top perspective view of the receptacle connector 405 shown in Figs. 21 and 22. Immediately adjacent electrical contacts 110, 110A, 120 can be spaced apart on 0.65±0.05 centerlines. The receptacle connector 405 can carry 400 electrical contacts 110, 110A, 120 in four rows of one-hundred electrical contacts.

[0107] Figs. 24-26 illustrate an exemplary plug connector 500. As shown in Fig. 24, a plug housing 505 or connector housing can be defined by two parallel, spaced apart longitudinal walls, such as first longitudinal plug wall 507A and second longitudinal plug wall 507B and two parallel, spaced apart end walls, such as first plug end wall 509A and second plug end wall 509B. The first and second plug end walls 509A, 509B are shorter in length than the two first and second longitudinal plug walls 507A, 507B. A longitudinal centerline CL3 extends through the first and second plug end walls 509A, 509B, parallel to the first and second longitudinal plug walls 507 A, 507B. A mating interface of the plug connector 500 or plug housing 505 can include a first plug keying structure 510A and a second plug keying structure 510B. The first plug keying structure 510A can be on one side of the longitudinal centerline CL3 and can be spaced away from the longitudinal centerline CL3, can abut the longitudinal centerline CL3, or can cross the longitudinal centerline CL3 such that the longitudinal centerline CL3 passes through at least a portion of the first plug keying structure 510A but does not bisect the total bounded area or perimeter of the first plug keying structure 510A. The second plug keying structure 510B can be positioned at the mating interface of the plug connector 500 or plug housing 505, on an opposite side of the longitudinal centerline CL3 as compared to the first plug keying structure 510A, and can be spaced away from the longitudinal centerline CL3, abut the longitudinal centerline CL3 or cross the longitudinal centerline CL3 such that the longitudinal centerline CL3 passes through at least a portion of the second plug keying structure 510B without bisecting the total bounded area or the perimeter of the second plug keying structure 510B.

[0108] The plug connector 500 can include a first plug row 520 of electrical plug contacts 308, 308A, 308B, 308C, a second plug row 522 of electrical plug contacts 308, 308A, 308B,

308C, a third plug row 524 of electrical plug contacts 308, 308A, 308B, 308C, and a fourth plug row 526 of electrical plug contacts 308, 308A 308B, 308C. Plug connector 500 can include a first plug row 520 and a second plug row 522 of back-to-back electrical plug contacts 308, 308A, 308B, 308C carried by a plug rib 528 adjacent to a mating interface of the plug housing 505.

The plug connector 500 can further include a third plug row 524 and a fourth plug row 526 of back-to-back electrical plug contacts 308, 308A, 308B, 308C carried by a plug rib 528 adjacent to a mating interface of the plug housing 505. The first plug row 520 of electrical plug contacts 308, 308A, 308B, 308C can be positioned immediately adjacent to the second plug row 522 of electrical plug contacts 308, 308A. 308B, 308C. The third plug row 524 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the second plug row 522 of electrical plug contacts 308, 308A, 308B, 308C. A fourth plug row 526 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the third plug row 524 of electrical plug contacts 308, 308A, 308B, 308C.

[0109] The plug ribs 528 can be spaced apart, can be positioned parallel to each other, and can extend in a direction from the first plug end wall 509A to the second plug end wall 509B. As shown in Fig. 26, plug ribs 528 and mating ends 116C at mating interface 518 can protrude above a step defined by the plug housing 505 so plug ribs 528 and mating ends 116C extend into and mate within recesses defined by a mating receptacle connector.

[0110] Referring again to Fig. 24, the mating interface 518 of the plug connector 500 can include at least two keying structures, such as first plug keying structure 510A and second plug keying structure 510B. The first plug keying structure 510A can lie on one side of the longitudinal centerline CL3, can abut the longitudinal centerline CL3, or can cross the longitudinal centerline CL3 such that the longitudinal centerline CL3 passes through at least a portion, but does not bisect the total bounded area, of the first plug keying structure 510A. The second plug keying structure 510B can be positioned at the mating interface 518 of the plug connector 500 on an opposite side of the longitudinal centerline CL3 compared to the first plug keying structure 510A, and can abut the longitudinal centerline CL3 or cross the longitudinal centerline CL3 such that the longitudinal centerline CL3 passes through at least a portion, but does not bisect the total bounded area, of the second plug keying structure 510B. The first plug keying structure 510A can partially lie along the same line as the third plug row 524 of electrical plug contacts 308, 308A, 308B, 308C, but not lie along lines of the first, second and fourth plug rows 520, 522, 526 of electrical plug contacts 308, 308A, 308B, 308C. The second plug keying structure 510B can partially lie along the same line as the second plug row 522 of electrical plug contacts 308, 308A, 308B, 308C, but not lie along lines of the first, third and fourth plug rows 520, 524, 526 of electrical plug contacts 308, 3008A, 308B, 308C.

[0111] Each of the first and second plug keying structures 510A, 510B can be a respective first protrusion 508A or second protrusion 508B defined by the plug housing 505 or positioned adjacent to the plug housing 505. Each of the first and second plug keying structures 510A, 510B can define three or more sides and can include a first plug side wall, line, or surface 512A, a second plug side wall, line, or surface 514B that can perpendicularly intersect the first plug side wall 512A, a canted plug side wall, line, or surface 516 that intersects with the second plug side wall 514B, a fourth plug side wall, line, or surface 512B, and a fifth plug side wall 514A. The fourth plug side wall, line, or surface 512B can intersect the canted plug side wall, line, or surface 516 and the fifth plug side wall, line, or surface 514A. The fifth plug side wall, line, or surface 514A can intersect the fourth plug side wall, line, or surface 512B and the first plug side wall, line, or surface 512A.

[0112] Each of the first and second plug keying structures 510A, 510B are configured to receive a corresponding first keying structure 270A, 270C or second keying structure 270B,

270D of a mating receptacle connector 200, 200A, 200B.

[0113] On one side of the plug connector 500 or plug housing 505, adjacent to first plug end wall 509A, first plug side wall 512A can abut the longitudinal centerline CL3, can be spaced away from the longitudinal centerline CL3, or can pass through longitudinal centerline CL3. On an opposed side of the plug connector 500 or plug housing 505, adjacent to the second plug end wall 509B, the fourth plug side wall 512B can abut, can be coincident with, can be parallel to, or can be positioned adjacent to, but spaced away from, the longitudinal centerline CL3.

The first plug keying structure 510A and the second plug keying structure 510B can each be identically shaped, can be positioned as mirror images about a centerline ML that is perpendicular to the longitudinal centerline CL3 and spans the first plug row, the second plug row, the third plug row, and the fourth plug row 520, 522, 524, 526, or can be positioned as offset mirror images about centerline ML, as shown.

[0114] Fig. 25 is a bottom view of the plug connector 500A. Fusible members, not shown, can be attached to the electrical plug contacts 308, 308A, 308B, 308C in any suitable manner. Alternatively, the electrical plug contacts 308, 308A, 308B, 308C can terminate in J-leads, press- fit pins, eye-of-needles, or other suitable termination. The plug connector 500 can include plug standoffs 530. The plug standoffs 301 can be located at the four corners of the plug housing 505. Any number and any location of plug standoffs 530 can be used. The plug standoffs 530 help ensure that the plug connector 500A is spaced a fixed distance from a mounting surface of a substrate when the fusible members (not shown) are re-flowed to connect the plug connector 500A to a substrate. The plug connector 500 can include first plug alignment peg 532 and a second plug alignment peg 534 that are configured to be received in pre-drilled alignment holes to roughly align fusible elements of the plug connector 500 with corresponding solder pads on a mounting surface of a substrate.

[0115] Fig. 25 shows first and second plug alignment pegs 532, 534, but any number of plug alignment pegs can be used. The first and second plug alignment pegs 532, 534 can have any suitable shapes, including, for example, a circular shape, an oval shape, a square shape, etc. The shapes of the first and second plug alignments pegs 532, 534 can be the same or different. All of the first and second plug alignment pegs 532, 534 can be positioned on the same side of the longitudinal centerline CL3, such that all of the first and second plug alignment pegs 532, 534 and one of the first and second plug keying structures 510A, 510B are all positioned on the same side of the longitudinal centerline CL3. The first alignment peg 532, which can be positioned adjacent to the first plug end wall 509A can lie on the same line as the third plug row 524 of electrical plug contacts 308, 308A-C.

[0116] Longitudinal centerline CL3 can pass through the second plug alignment peg 534, and the second plug alignment peg 534 can have a center point CP2 that the longitudinal centerline CL3 passes through. The first plug alignment peg 532 can be positioned on either side of the longitudinal centerline CL3, such that the longitudinal centerline CL3 does not intersect the first plug alignment peg 532. In one embodiment, the first plug alignment peg 532 can be positioned, completely or partially, under the perimeter of the first plug keying structure 510A. The second plug alignment peg 534 can be positioned, completely or partially, under the perimeter of the second plug keying structure 510B. The first plug alignment peg 532 and the third plug row of electrical plug contacts can both lie along a centerline CL4 that is parallel to the longitudinal centerline CL3 and spaced away from the longitudinal centerline CL3.

[0117] The second plug alignment peg 534 can be aligned with the longitudinal centerline CL3 of the plug connector 500, while the first plug alignment peg 532 can be a distance between approximately 1.2±0.05 mm to approximately 1.3±0.05 mm from the longitudinal centerline CL3 of the plug connector 500. The first plug alignment peg 532 can have a circular shape with a diameter of approximately 0.8±0.05 mm, and the second plug alignment peg 534 can have an oval shape with diameters of approximately 0.8±0.05 mm and 0.6±0.05 mm. A first row pitch RP1 between respective electrical contact centers of the first plug row 520 and the second plug row 522 can be approximately 2.2±0.1 mm, 2.2±0.05, or 2.2±0.005 mm. A second row pitch RP2 between respective electrical contact centers of the second plug row 522 and the third plug row 524 can be approximately 2.4±0.1 mm, 2.4±0.05 mm or 2.4±0.005 mm. A third row pitch RP3 between respective electrical contact centers of the third plug row 524 and the fourth plug row 526 can be approximately 2.2±0.1 mm, 2.2±0.05 mm or 2.2±0.005 mm.

[0118] Referring to Fig. 27, a receptacle connector 600 can include a receptacle housing 605 can be defined by two parallel, spaced apart first and second longitudinal walls 607A, 607B and two parallel, spaced apart first and second end walls 609A, 609B. The two parallel, spaced apart first and second end walls 609A, 609B can be shorter in length than the two parallel, spaced apart first and second longitudinal walls 607 A, 607B. Longitudinal centerline CL5 extends through the two parallel, spaced apart first and second end walls 609A, 609B, parallel to the two parallel, spaced apart first and second longitudinal walls 607 A, 607B. A mating interface 604 of the receptacle housing 605 can include a first receptacle keying structure 610A and a second receptacle keying structure 610B. The first receptacle keying structure 610A lies on the longitudinal centerline CL5 such that the first receptacle keying structure 610A is non- symmetrical about the centerline CL5. The second keying structure 610B can be positioned at the mating interface 604 of the receptacle housing 605, on an opposite side of the longitudinal centerline CL5 compared to the first receptacle keying structure 610A, and can lie on the longitudinal centerline CL5 such that the second longitudinal keying structure 610B is non- symmetrical about the longitudinal centerline CL5 and non-symmetrical about median centerline ML5. The first receptacle keying structure 610A and the second receptacle keying structure 610B can be offset with respect to each other and the median centerline CL5. The first and second receptacle keying structures 610A, 610B can be offset mirror images of each other.

[0119] Each first and second receptacle keying structure 610A, 610B can be a respective first and second recess 608A, 608B, each with four or five sides or surfaces defined by the receptacle housing 605 and respective portions of the two parallel, spaced apart first and second end walls 609A, 609B. Each five-sided first and second recess 608A, 608B can have a perimeter defined by a first side wall, line, or surface 612A, a second side wall, line, or surface 614B, a canted side wall, line, or surface 616, a fourth side wall, line, or surface 612B, and a fifth side wall, line, or surface 614A. It should be understood that, with respect to the first and second keying structures 610A, 610B, the term wall can also include line or surface. Fifth and second side walls 614A, 614B can form respective right angles with first side wall 612A. Fourth side wall 612B can form a right angle with fifth side wall 614A. Fourth side wall 612B is shorter in length than any of the other side walls 612A, 614B, 616, 614A. Each of the first and second receptacle keying structures 610A, 610B, which can be recesses, are configured to receive a corresponding first plug keying structure 710A or second plug keying structure 710B as shown in Fig. 29, which are posts or protrusions of a plug housing 705.

[0120] On one side of the receptacle housing 605, adjacent to first end wall 609A, the first and fourth side walls 612A, 612B can be evenly spaced away from the longitudinal centerline CL5. On an opposite end of the receptacle housing 605, adjacent to second end wall 609B, the longitudinal centerline CL5 can intersect an intersection I of second side wall 614B and the canted side wall 616. First side wall 612A and fourth side wall 612B can be unevenly spaced or can be non-uniformly spaced away from the longitudinal centerline CL5. The first keying structure 610A and the second keying structure 610B can be identically shaped or have the same perimeter shape. The first keying structure 610B can be offset from the second keying feature 610A with respect to the longitudinal centerline CL, with respect to the median centerline ML5, or both the longitudinal centerline CL and the medial centerline ML5. The first receptacle keying structure 610A can be a mirror image of the second keying structure 610B with respect to median centerline ML5 that is perpendicular to the longitudinal centerline CL5. [0121] As shown in Fig. 28, a mounting side or interface 620 of the receptacle housing 605 can include a first alignment peg 601 and a second alignment peg 602. The longitudinal centerline CL5 can pass through the first alignment peg 601, and the first alignment peg 601 can have a center point CP3 that the longitudinal centerline CL5 passes through. The second alignment peg 602 can be positioned on either side of the longitudinal centerline CL5, such that the longitudinal centerline CL5 does not intersect the second alignment peg 602. In one embodiment, the second alignment peg 602 can be positioned, completely or partially, under a perimeter defined by the first receptacle keying structure 610A shown in Fig. 27. The first alignment peg 601 can be positioned, completely or at least partially, under a perimeter defined by the second keying structure 610B of Fig. 27. The second alignment peg 602 can also be positioned so that the second alignment peg 602 is not even partially positioned under the first receptacle keying structure 610A. The first alignment peg 601 can have a circular shape with a diameter of approximately 0.8±0.05 mm, and the second alignment peg 602 can have an oval shape with dimensions of approximately 0.8±0.05 mm and 0.6±0.05 mm.

[0122] As shown in Fig. 29, a plug connector 700 having a plug housing 705 can be defined by two parallel, spaced apart, opposed first and second longitudinal plug walls 707 A, 707B and two parallel, spaced apart first and second plug end walls 709A, 709B. The two parallel, opposed spaced apart first and second plug end walls 709A, 709B can be shorter in length than the two parallel, spaced apart first and second longitudinal plug walls 707A, 707B. A longitudinal centerline CL6 extends through the two parallel, spaced apart first and second plug end walls 709A, 709B, parallel to the two parallel, spaced apart first and second longitudinal plug walls 707 A, 707B. A mating interface 704 of the plug housing 705 can include a first plug keying structure 710A and a second plug keying structure 710B. The first plug keying structure 710A can lie on the longitudinal centerline CL6 such that the first plug keying structure 710A is non-symmetrical about the longitudinal centerline CL6. The second plug keying structure 710B can be positioned at the mating interface 704 of the plug housing 705, on an opposite side of the longitudinal centerline CL6 compared to the first plug keying structure 710A, and can lie on the longitudinal centerline CL6 such that the second plug keying structure 710B is non- symmetrical about the longitudinal centerline CL6. The first plug keying structure 710A and the second plug keying structure 710B can be offset with respect to each other about the longitudinal centerline CL6. Each first and second plug keying structure 710A, 710B can each define respective four-sided or five-sided first and second projections 708A, 708B that each extend in a direction perpendicular to the longitudinal centerline CL6 and perpendicular to a first, second, third, and fourth plug rows 730, 740, 750, 760. The first plug row of electrical contacts 308, 308A, 308B can be spaced away from the second plug row by a first row pitch RP1. The second plug row of electrical contacts 308, 308A, 308B can be spaced away from the third plug row of electrical contacts 308, 308A, 308B by a second row pitch RP2. The third plug row of electrical contacts 308, 308A, 308B can be spaced away from the fourth plug row of electrical contacts 308, 308A, 308B by a third row pitch RP3. As discussed above, the first row pitch RP1 and the third row pitch RP3 can be substantially the same. The second row pitch RP2 is greater than the first row pitch RP1 or the third row pitch RP3.

[0123] Each of the first and second plug keying structures 710A, 710B are configured to receive a corresponding first receptacle keying structure 610A or second receptacle keying structure 610B of the receptacle connector 600 shown in Figs. 27 and 28. The first and second protrusions 708A, 708B of the plug housing 705 are configured to fit into the respective first and second recesses 608A, 608B of the receptacle connector 600. For example, first receptacle keying feature 610A of the receptacle housing 605 can receive the second plug keying feature 710B of the plug connector 700, and second receptacle keying feature 610B of the receptacle housing 605 or receptacle connector 600 can receive the first plug keying feature 710A of the plug connector 700.

[0124] Each of the first and second plug keying structures 710A, 710B can have a four-sided or five-sided perimeter or other geometric shaped perimeter that includes a first plug side wall, line, or surface 712A, a second plug side wall, line, or surface 714B, a canted plug side wall, line, or surface 716, a fourth plug side wall, line, or surface 712B, and a fifth plug side wall, line, or surface 714A. Fifth and second plug side walls 714A, 714B can form right angles with first plug side wall 712A. Fourth plug side wall 712B can form a right angle with fifth plug side wall 714A. Fourth plug side wall 712B can be shorter in width or thickness than any of the other plug side walls 712A, 714A, 714B, 716. Each of the first and second receptacle keying structures 610A, 610B of the receptacle housing 605, discussed earlier, which can be first and second recesses 608A, 608B, are configured to receive a corresponding first plug keying structure 710A or second plug keying structure 710B. The first plug keying structure 710A and the second plug keying structure 710B can both be posts or first and second protrusions 708A, 708B defined by, or positioned adjacent to, plug housing 705.

[0125] On one side of the plug housing 705, adjacent to first plug end wall 709A, the longitudinal centerline CL6 can intersect the first protrusion 708A at an intersection I of second plug side wall 714B and the canted plug side wall 716. First and fourth plug side walls 712A, 712B can be unevenly spaced or can be non-uniformly spaced away from the longitudinal centerline CL6. On an opposite end of the plug housing 705, adjacent to plug end wall 709B, the first and fourth plug side walls 712A, 712B can be evenly spaced away from the longitudinal centerline CL6. The first plug keying structure 710A and the second plug keying structure 710B can be identically shaped. The first plug keying structure 710B can be a mirror image of the second plug keying structure 710B, with respect to median centerline ML6 that is perpendicular to the longitudinal centerline CL6 and perpendicular to the first and second plug rows 730, 740. The first plug keying structure 710A and the second plug keying structure 710B can be offset with respect to each other about the centerline CL6, can be offset with respect to each other with respect to the median centerline ML6, or can be both. The first plug keying structure 710A can be a mirror image of the second plug keying structure 710B with respect to median centerline ML6 that is perpendicular to the longitudinal centerline CL6.

[0126] As shown in Fig. 30, a mounting side 720 interface of the plug connector 700 or plug housing 705 can include a first plug alignment peg 701 and second plug alignment peg 702. The longitudinal centerline CL6 can pass through the first plug alignment peg 701, and the first plug alignment peg 701 can have a center point CP4 that the longitudinal centerline CL6 passes through. The second plug alignment peg 702 can be positioned on either side of the longitudinal centerline CL6, such that the longitudinal centerline CL6 does not intersect the second plug alignment peg 702. In one embodiment, the first plug alignment peg 701 can be positioned, completely or partially, under a perimeter defined by the first plug keying structure 710A or the second plug keying structure 710B of Fig. 29. Second plug alignment peg 702 can be positioned, at least partially or not at all, under a perimeter defined by the first plug keying structure 710A of Fig. 29. The first plug alignment peg 701 can define an oval shape with diameters of approximately 0.8±0.05 mm and 0.6±0.05 mm. The second plug alignment peg 702 can have a circular shape with a diameter of approximately 0.8±0.05 mm. The first and second plug alignment pegs can be reversed, so that the first plug alignment peg 701 defines an oval shape and the second plug alignment peg 702 defines a circular shape. The first and second plug alignment pegs 701, 702 can be positioned asymmetrically about the longitudinal centerline CL6, asymmetrically about the median centerline ML6, or asymmetrically about the longitudinal centerline CL6 and the median centerline ML6.

[0127] Fig. 31 shows an example of a layout of a substrate 800, such as a printed circuit board, daughtercard, or backplane, including pads 802 that can be used to electrically connect with fusible elements of the receptacle connectors or the plug connectors described herein. A first pad row pitch PRP1, measured between respective centers of pads in a first pad row 804 and respective centers of pads in a second pad row 806, can be 2.2±0.2mm, or any other pitch that corresponds to a mounting receptacle row or plug row. A second pad row pitch PRP2, measured between respective centers of pads in the second pad row 806 and respective centers of pads in a third pad row 808, can be 2.4±0.2mm, or any other pitch that corresponds to a mounting receptacle row or plug row. A third pad row pitch PRP3, measured between respective centers of pads in the third pad row 808 and respective centers of pads in a fourth pad row 810, can be 2.2±0.2mm, or any other pitch that corresponds to a mounting receptacle row or plug row.

[0128] The first pad row 804 can contain at least at least one hundred pads 802. The second pad row 806 can contain at least one hundred pads 802. The third pad row 808 can contain at least one hundred pads 802. The fourth pad row 810 can contain at least one hundred pads. Pads 802 can be any number greater than sixty, at least one hundred, at least one hundred and fifty, or any whole number of pads greater than sixty and less than one hundred and fifty pads per pad row. A first alignment hole 812 can be 0.8±0.05 mm by 0.6±0.05 mm and can lie along a same line as the second pad row 806 of pads 802 or can be coincident with the second pad row 806 of pads 802. A second alignment hole 814 can be 0.8±0.05 mm in diameter, can be positioned on a centerline CL positioned equidistant between and parallel to the second and third pad rows 806, 808, and can be positioned adjacent to the first pad 816 in the second pad row.

[0129] Fig. 32 shows an example of a footprint layout of a substrate 800A, such as a printed circuit board, daughtercard, or backplane, including pads 802A that can be used to electrically connect with fusible elements of the receptacle connectors or the plug connectors described herein. A first pad row pitch PRP1, measured between respective centers of pads in a first pad row 804A and respective centers of pads in a second pad row 806A, can be 2.2±0.2mm, or any other pitch that corresponds to a mounting receptacle row or plug row. A second pad row pitch PRP2, measured between respective centers of pads in the second pad row 806A and respective centers of pads in a third pad row 808A, can be 2.4±0.2mm, or any other pitch that corresponds to a mounting receptacle row or plug row. A third pad row pitch PRP3, measured between respective centers of pads in the third pad row 808A and respective centers of pads in a fourth pad row 810A, can be 2.2±0.2mm, or any other pitch that corresponds to a mounting receptacle row or plug row.

[0130] A first alignment hole 812A can lie on the same line as a third pad row 808A of pads 802A. A second alignment hole 814A can be positioned between the second pad row 806A and the third pad row 808A, adjacent to a first pad 816A in the second pad row 806A and the third pad row 808A.

[0131] The first pad row 804A can contain at least at least one hundred pads 802A. The second pad row 806A can contain at least one hundred pads 802A. The third pad row 808A can contain at least one hundred pads 802A. The fourth pad row 810A can contain at least one hundred pads. The first alignment hole 812A can be 0.8±0.05 mm in diameter and can lie along a same line as the third pad row 808A of pads 802A or be coincident with the third pad row 808A of pads 802A. The second alignment hole 814A can be 0.8±0.05 mm by 0.6±0.05 mm, can be positioned on a centerline CL positioned equidistant between and parallel to the second and third pad rows 806A, 808A, and can be positioned adjacent to a first pad 816A in the second pad row 806A.

[0132] Fig. 33 shows an example of a layout of a substrate 800B, such as a printed circuit board, daughtercard, or backplane, including pads 802B that can be used to electrically connect with fusible elements of the receptacle connectors or the plug connectors described herein. A first pad row pitch PRP1, measured between respective centers of pads in a first pad row 804B and respective centers of pads in a second pad row 806B, can be 2.2±0.2mm, or any other pitch that corresponds to a mounting receptacle row or plug row. A second pad row pitch PRP2, measured between respective centers of pads in the second pad row 806B and respective centers of pads in a third pad row 808B, can be 2.4±0.2mm, or any other pitch that corresponds to a mounting receptacle row or plug row. A third pad row pitch PRP3, measured between respective centers of pads in the third pad row 808B and respective centers of pads in a fourth pad row 810B, can be 2.2±0.2mm, or any other pitch that corresponds to a mounting receptacle row or plug row.

[0133] A first alignment hole 812B can be positioned between the second pad row 806B and the third pad row 808B, adjacent to a last pad 818 in the second pad row 806B and the third pad row 808B. A second alignment hole 814B can lie on the same line as a second pad row 806B of pads 802A.

[0134] Fig. 34 shows an example of a layout of a substrate 800C, such as a printed circuit board, daughtercard, or backplane, including pads 802C that can be used to electrically connect with fusible elements of the receptacle connectors or the plug connectors described herein. A first pad row pitch PRP1, measured between respective centers of pads in a first pad row 804C and respective centers of pads in a second pad row 806C, can be 2.2±0.2mm, or any other pitch that corresponds to a mounting receptacle row or plug row. A second pad row pitch PRP2, measured between respective centers of pads in the second pad row 806C and respective centers of pads in a third pad row 808C, can be 2.4±0.2mm, or any other pitch that corresponds to a mounting receptacle row or plug row. A third pad row pitch PRP3, measured between respective centers of pads in the third pad row 808C and respective centers of pads in a fourth pad row 810C, can be 2.2±0.2mm, or any other pitch that corresponds to a mounting receptacle row or plug row.

[0135] A first alignment hole 812C can be positioned between the second pad row 806C and the third pad row 808C, adjacent to a last pad 818C in the second pad row 806C and the third pad row 808C. A second alignment hole 814C can lie on the same line as a third pad row 808C of pads 802C.

[0136] Fig. 35 shows an example of a layout of a substrate 800D, such as a printed circuit board, daughtercard, or backplane, including pads 802D that can be used to electrically connect with fusible elements of the receptacle connectors or the plug connectors described herein. A first pad row pitch PRP1, measured between respective centers of pads in a first pad row 804D and respective centers of pads in a second pad row 806D, can be 2.2±0.2mm, or any other pitch that corresponds to a mounting receptacle row or plug row. A second pad row pitch PRP2, measured between respective centers of pads in the second pad row 806D and respective centers of pads in a third pad row 808D, can be 2.4±0.2mm, or any other pitch that corresponds to a mounting receptacle row or plug row. A third pad row pitch PRP3, measured between respective centers of pads in the third pad row 808D and respective centers of pads in a fourth pad row 810D, can be 2.2±0.2mm, or any other pitch that corresponds to a mounting receptacle row or plug row.

[0137] A first alignment hole 812D can be positioned on the same line as second the second pad row 806D. A second alignment hole 814D can be positioned on the same line as a third pad row 808D of pads 802D and the first alignment hole 812D.

[0138] As shown in Fig. 36, a receptacle connector 1005 can have a receptacle housing 1006 that defines two parallel, spaced apart longitudinal walls, such as first longitudinal wall 1007A and second longitudinal wall 1007B and two parallel, spaced apart end walls, such as first end wall 1009A and second end wall 1009B. The two parallel, spaced apart first and second end walls 1009A, 1009B are shorter in length than the two parallel, spaced apart first and second longitudinal walls 1007A, 1007B. The first and second end walls 1009A, 1009B can also be referred to as a first end and a second end, respectfully, of the receptacle or connector housing 1006. A centerline CL extends through the two parallel, spaced apart first and second end walls 1009A, 1009B, parallel to the two parallel, spaced apart first and second longitudinal walls 1007A, 1007B. A mating interface of the receptacle connector 1005 or receptacle housing 1006 can include a first keying structure 1010A, a second keying structure 1010B, and a third keying structure 1010C. The first keying structure 1010A can lie on the longitudinal centerline CL such that the longitudinal centerline CL bisects a total bounded area or perimeter of the first keying structure 1010A, passes through two sides or surfaces of the first keying structure 1010A, or passes through one side or surface and one point of intersection between two sides or surfaces of the first keying structure 1010A. The second keying structure 1010B and third keying structures 1010C can be positioned on opposite sides of the centerline CL such that the centerline CL does not intersect with either of the second keying structure 1010B or of the third keying structure 1010C.

[0139] Each of the first, second, and third keying structures 1010A, 1010B, 1010C can be a respective first recess 1008A, second recess 1008B, and third recess 1008C, each having three or more wall sides or surfaces and four or five total sides or surfaces defined by the receptacle housing 1006 or respective portions of the two parallel, spaced apart first and second end walls 1009A, 1009B. Each of the first, second, and third recesses 1008A, 1008B, 1008C can have a bounded area or perimeter defined by a first side wall, line, or surface 1012A, a second side wall, line, or surface 1014B, a canted side wall, line, or surface 1016, a fourth side wall, line, or surface 1012B, and a fifth side wall, line, or surface 1014A. It should be understood that, with respect to the first, second, and third keying structures 1010A, 1010B, 1010C, "wall" can also include a line, surface, or partial wall. The first side wall 1012A and the fourth side wall 1012B can be parallel to each other. The second side wall 1014B and the fifth side wall 1014A can be parallel to each other. The first side wall 1012A and the second side wall 1014B can intersect to form a right angle. The canted side wall 1016 can intersect the second side wall 1014B. The fourth side wall 1012B can be parallel to the first side wall 1012A and can intersect the canted side wall 1016. The fifth side wall 1014A can be parallel to the second side wall 1014B and can intersect the first side wall 1012A and the fourth side wall 1012B. The second sidewall 1014B can be shorter in length than the first side wall 1012A and the fifth side wall 1014A. The fourth side wall 1012B can be the shortest sidewall in length. The second and third keying features 1010B, 1010C can be mirror images of each other with respect to the centerline CL. Each of the first, second, and third keying structures 1010A, 1010B, 1010C, which can be recesses, are configured to receive a corresponding first plug keying structure 1210A, second plug keying structure 1210B, or third plug keying structure 1210C shown in Fig. 42, which can be posts or first, second, or third protrusions 1208A, 1208B, 1208C defined by plug housing 1205 or positioned adjacent to a plug housing 1205. For example, the first keying structure 1010A of the receptacle connector 1005 can receive the first plug keying structure 1210A of the plug housing 1205, the second keying structure 1010B of the receptacle housing 1006 can receive the second plug keying structure 1210B of the plug housing 1205, and the third keying structure 1010C of the receptacle housing 1006 can receive the third plug keying structure 1210C of the plug housing 1205.

[0140] The receptacle connector 1005 or receptacle housing 1006 can include eight parallel, spaced apart receptacle rows 1020, 1021, 1022, 1023, 1024, 1025, 1026, 1027 of electrical contacts 110, 110A, 120. A first receptacle row 1020 of electrical contacts 110, 110A, 120 and an eighth receptacle row 1027 of electrical contacts 110, 110A, 120 extend along the inside of the respective first longitudinal wall 1007A and the second longitudinal wall 1007B of the receptacle housing 1006. A second receptacle row 1021 of electrical contacts 110, 110A, 120 and a third receptacle row 1022 of electrical contacts 110, 110A, 120 are positioned back-to- back, and extend along a first inner rib 1030 that extends in an end to end direction of the receptacle connector 1005 or receptacle housing 1006. A fourth receptacle row 1023 of electrical contacts 110, 110A, 120 and a fifth receptacle row 1024 of electrical contacts 110, 110A, 120 are positioned back-to-back, and extend along a second inner rib 1031 that extends in the end to end direction along a middle of the receptacle connector 1005 or receptacle housing 1006. A sixth receptacle row 1025 of electrical contacts 110, 110A, 120 and a seventh receptacle row 1026 of electrical contacts 110, 110A, 120 are positioned back-to-back, and extend along a third inner rib 1032 that extends in the end to end direction of the receptacle connector 1005 or receptacle housing 1006. The first and second inner ribs 1030, 1031 can be oriented parallel to one another. The second and third inner ribs 1031, 1032 can each be oriented parallel to one another. Each of the first, second, and third keying structures 1010A, 1010B, 1010C can be located at an end of the ribs 1030, 1031, 1032. Although the receptacle connector 1005 is shown with eighth parallel, spaced apart, shieldless rows, any number of rows of electrical contacts 110, 110A, 120 can be used. The electrical contacts 110, 110A, 120 of the receptacle connector 1005 can be stitched from two directions as described with respect to Figs. 4-8. The receptacle connector 1005 can be devoid any of crosstalk shields and magnetic absorbing lossy material or can include any number of crosstalk shields or electrically conductive or non-conductive magnetic absorbing lossy material. Fusible elements, such as solder balls, can be attached to respective ones of the electrical contacts 110, 110A, 120. The electrical contacts 110, 110A, 120 can also terminate in press-fit pins, eye-of-the needles, J- lead, or other configurations.

[0141] The first keying structure 1010A can lie on the longitudinal centerline CL, adjacent to a second end of the second inner rib 1031, adjacent to the second end wall 1009B, such that the longitudinal centerline CL bisects a total bounded area or perimeter of the first keying structure 1010A, or only intersects the second side wall, line, or surface 1014B and the fifth wall, line, or surface 1014A, or only intersects the fifth wall, line, or surface 1014A and the canted wall, line, or surface 1016, or only intersects the fifth wall, line, or surface 1014A and an intersection of the canted wall 1016 second side wall, line, or surface 1014B. The second keying structure 1010B can lie on a second centerline of the first inner rib 1030, adjacent to a first end of the first inner rib 1030 and adjacent to the first end wall 1009A, such that the second centerline bisects a total bounded area or perimeter of the second keying structure 1010B, or only intersects the second side wall, line, or surface 1014B and the fifth wall, line, or surface 1014A, or only intersects the fifth wall, line, or surface 1014A and the canted wall, line, or surface 1016, or only intersects the fifth wall, line, or surface 1014A and an intersection of the canted wall 1016 second side wall, line, or surface 1014B. The third keying structure 1010C can lie on a third centerline of the third inner rib 1032, adjacent to a first end of the first inner rib 1030 and adjacent to the first end wall 1009A, such that the third centerline bisects a total bounded area or perimeter of the third keying structure 1010C, or only intersects the second side wall, line, or surface 1014B and the fifth wall, line, or surface 1014A, or only intersects the fifth wall, line, or surface 1014A and the canted wall, line, or surface 1016, or only intersects the fifth wall, line, or surface 1014A and an intersection of the canted wall 1016 second side wall, line, or surface 1014B. The first keying structure 1010A, the second keying structure 1010B, and the third keying structure 1010C can each be identically shaped and/or can each have an asymmetrical shape of a completely asymmetrical perimeter. The second keying structure 1010B or the third keying structure 1010C can each be a mirror image of the first keying structure 1010A with respect to a median centerline ML that is perpendicular to the longitudinal centerline CL. The longitudinal centerline CL and the median centerline ML divide the receptacle connector 1005 into four quadrants, with each quadrant having a structure that is different from each of the other quadrants such that no quadrant can be a substitute for the other quadrants. There can be an equal number of electrical contacts 110, 110A, 120 on either side of the longitudinal centerline CL, and there can be an equal number of electrical contacts 110, 110A, 120 on either side of the median centerline ML.

[0142] As shown in Fig. 37, a mounting interface of the receptacle connector 1005 can include first alignment peg 1001 and second alignment peg 1002. The longitudinal centerline CL can pass through the first alignment peg 1001, and the first alignment peg 1001 can have a center point CP that the longitudinal centerline CL passes through. The second alignment peg 1002 can be positioned on either side of the longitudinal centerline CL, such that the longitudinal centerline CL does not intersect any portion of the second alignment peg 1002. In one embodiment, the second alignment peg 1002 can be positioned, completely or partially, under the first keying structure 1010A or can be positioned not to be underneath the first keying structure 1010A. The first alignment peg 1001 can be positioned, completely or partially, under the second keying structure 1010B or the third keying structure 1010C or can be positioned not to be underneath the second keying structure 1010B or the third keying structure 1010C. The second alignment peg 1002 can lie along a fourth centerline between the third and fourth receptacle rows 1022, 1023 that is parallel to and spaced away from the longitudinal centerline CL. The first alignment peg 1001 can have a circular outer or cross- sectional shape with a diameter of approximately 0.8±0.05 mm, and the second alignment peg 1002 can have an oval shape with diameters of approximately 0.8±0.05 mm and 0.6±0.05 mm. The first alignment peg 1001 can be positioned adjacent to the first end wall 1009A of the receptacle housing 1006 and adjacent to a mounting interface 1040 of the receptacle housing 1006. The second alignment peg 1002 can be positioned adjacent to the second end wall 1009B of the receptacle housing 1006 and adjacent to the mounting interface 1040 of the receptacle housing 1006. The first alignment peg 1001 and the second alignment peg 1002 can both be positioned non-symmetrically about both the longitudinal centerline CL and the median centerline ML. Row pitch distances, measured in length, between some adjacent rows of electrical contacts can be dissimilar from one another. The first row pitch RP1 between respective electrical contact centers of the first receptacle row 1020 and the second receptacle row 1021 can be approximately 2.2±0.005 mm, 2.2±0.1 mm, or 2.2±0.05mm. A second row pitch RP2 between respective electrical contact centers of the second receptacle row 1021 and the third receptacle row 1022 can be approximately 2.4±0.005 mm, 2.4±0.1 mm, or 2.4±0.05 mm. A third row pitch RP3 between respective electrical contact centers of the third receptacle row 1022 and the fourth receptacle row 1023 can be approximately 2.2±0.005 mm, 2.2±0.1 mm, or 2.2±0.05 mm. A fourth row pitch RP4 between respective electrical contact centers of the fourth receptacle row 1023 and the fifth receptacle row 1024 can be approximately 2.4±0.005 mm, 2.4±0.1 mm, or 2.4±0.05 mm. A fifth row pitch RP5 between respective electrical contact centers of the fifth receptacle row 1024 and the sixth receptacle row 1025 can be approximately 2.2±0.005 mm, 2.2±0.1 mm, or 2.2±0.05 mm. A sixth row pitch RP6 between respective electrical contact centers of the sixth receptacle row 1025 and the seventh receptacle row 1026 can be approximately 2.4±0.005 mm, 2.4±0.1 mm, or 2.4±0.05 mm. A seventh row pitch RP7 between respective electrical contact centers of the seventh receptacle row 1026 and the eighth receptacle row 1027 can be approximately 2.2±0.005 mm, 2.2±0.1 mm, or 2.2±0.05 mm.

[0143] Fig. 38 is a top perspective view of the receptacle connector 1005 shown in Figs. 36 and 37. Immediately adjacent electrical contacts 110, 110A, 120 can be spaced apart on 0.65±0.05 mm centerlines. The receptacle connector 1005 can carry electrical contacts 110, 110A, 120 such that 800 electrical contacts can be arranged in eight rows each of one-hundred electrical contacts. [0144] As shown in Fig. 39, a receptacle connector 1105 can have a receptacle housing 1106 that defines two parallel, spaced apart longitudinal walls, such as first longitudinal wall 1107A and second longitudinal wall 1107B and two parallel, spaced apart end walls, such as first end wall 1109A and second end wall 1109B. The two parallel, spaced apart first and second end walls 1109A, 1109B can be the same length as the two parallel, spaced apart first and second longitudinal walls 1107A, 1107B. A longitudinal centerline CL extends through the two parallel, spaced apart first and second end walls 1109A, 1109B, parallel to the two parallel, spaced apart first and second longitudinal walls 1107 A, 1107B. A mating interface of the receptacle connector 1105 or receptacle housing 1106 can include a first keying structure 1110A, a second keying structure 1110B, a third keying structure 1110C, and a fourth keying structure 1110D.

The first, second, third, and fourth keying structures 1110A, 1110B, 1110C, 1110D can form four points of a trapezoid that is symmetrical about a median centerline ML of the receptacle housing 1106.

[0145] The first keying structure 1110A and the second keying structure 1110B can be positioned on opposite sides of the longitudinal centerline CL such that the longitudinal centerline CL does not intersect with either of the first keying structure 1110A or of the second keying structure 1110B. The third keying structure 1110C and fourth keying structures 1110D can be positioned on opposite sides of the longitudinal centerline CL such that the longitudinal centerline CL does not intersect with either of the third keying structure 1110C or of the fourth keying structure 1110D. The third keying structure 1110C and the fourth keying structure 1110D can be separated by a larger distance, measured in length, than the first keying structure 1110A and the second keying structure 1110B.

[0146] Each of the first, second, third, and fourth keying structures 1110A, 1110B, 1110C, 1110D can be a respective first recess 1108A, second recess 1108B, third recess 1108C, and fourth recess 1108D each including three or more wall sides, lines, or surfaces or four or five total sides, lines, or surfaces defined by the receptacle housing 1106 and respective portions of the two parallel, spaced apart first and second end walls 1109A, 1109B. Each of the first, second, third, and fourth recesses 1108A, 1108B, 1108C, 1108D can have a bounded area or perimeter defined by a first side wall, line, or surface 1112A, a second side wall, line, or surface 1114B, a canted side wall, line, or surface 1116, a fourth side wall, line, or surface 1112B, and a fifth side wall, line, or surface 1114A. It should be understood that, with respect to the first, second, third, and fourth keying structures 1110A, 1110B, 1110C, 1110D, "wall" can also include a line, surface, or partial wall. The first side wall 1112A and the fourth side wall 1112B can be parallel to each other. The second side wall 1114B and the fifth side wall 1114A can be parallel to each other. The first side wall 1112A and the second side wall 1114B can intersect to form a right angle. The canted side wall 1116 can intersect the second side wall 1114B. The fourth side wall 1112B can be parallel to the first side wall 1112A and can intersect the canted side wall 1116. The fifth side wall 1114A can be parallel to the second side wall 1114B and can intersect the first side wall 1112A and the fourth side wall 1112B. The second sidewall 1114B can be shorter in length than the first side wall 1112A and the fifth side wall 1114A. The fourth side wall 1112B can be the shortest sidewall in length. The first and second keying features 1110A, 1110B can be mirror images of each other with respect to the longitudinal centerline CL, and the third and fourth keying features 1110C, 1110D can be mirror images of each other with respect to the longitudinal centerline CL. Each of the first, second, third, and fourth keying structures 1110A, 1110B, 1110C, 1110D, which can be recesses, are configured to receive a corresponding first plug keying structure 1410A, second plug keying structure 1410B, third plug keying structure 1410C, or fourth keying structure 1410D shown in Fig. 45, which can be posts or first, second, third, or fourth protrusions 1408A, 1408B, 1408C, 1408D defined by plug housing 1405 or positioned adjacent to a plug housing 1405. For example, the first keying structure 1110A of the receptacle connector 1105 can receive the second plug keying structure 1410B of the plug housing 1405, the second keying structure 1110B of the receptacle housing 1106 can receive the first plug keying structure 1410A of the plug housing 1405, the third keying structure 1110C of the receptacle housing 1106 can receive the fourth plug keying structure 1410D of the plug housing 1405, and the fourth keying structure 1110D of the receptacle housing 1106 can receive the third plug keying structure 1410C of the plug housing 1405.

[0147] The receptacle connector 1105 or receptacle housing 1106 can include sixteen parallel, spaced apart receptacle rows 1120, 1121, 1122, 1123, 1124, 1125, 1126, 1127, 1140, 1141, 1142, 1143, 1144, 1145, 1146, 1147 of electrical contacts 110, 110A, 120. A first receptacle row 1120 of electrical contacts 110, 110A, 120 and an sixteenth receptacle row 1147 of electrical contacts 110, 110A, 120 extend along the inside of the respective first longitudinal wall 1107A and the second longitudinal wall 1107B of the receptacle housing 1106. A second receptacle row 1121 of electrical contacts 110, 110A, 120 and a third receptacle row 1122 of electrical contacts 110, 110A, 120 are positioned back-to-back, and extend along a first inner rib 1130 that extends in an end to end direction of the receptacle connector 1105 or receptacle housing 1106. A fourth receptacle row 1123 of electrical contacts 110, 110A, 120 and a fifth receptacle row 1124 of electrical contacts 110, 110A, 120 are positioned back-to-back, and extend along a second inner rib 1131 that extends in an end to end direction of the receptacle connector 1105 or receptacle housing 1106. A sixth receptacle row 1125 of electrical contacts 110, 110A, 120 and a seventh receptacle row 1126 of electrical contacts 110, 110A, 120 are positioned back-to-back, and extend along a third inner rib 1132 that extends in an end to end direction of the receptacle connector 1105 or receptacle housing 1106. An eight receptacle row 1127 of electrical contacts 110, 110A, 120 and a ninth receptacle row 1140 of electrical contacts 110, 110A, 120 are positioned back-to-back, and extend along a fourth inner rib 1133 that extends in an end to end direction down a middle of the receptacle connector 1105 or receptacle housing 1106. A tenth receptacle row 1141 of electrical contacts 110, 110A, 120 and an eleventh receptacle row 1142 of electrical contacts 110, 110A, 120 are positioned back-to- back, and extend along a fifth inner rib 1134 that extends in an end to end direction of the receptacle connector 1105 or receptacle housing 1106. A twelfth receptacle row 1143 of electrical contacts 110, 110A, 120 and a thirteenth receptacle row 1144 of electrical contacts 110, 110A, 120 are positioned back-to-back and extend along a sixth inner rib 1135 that extends in an end to end direction of the receptacle connector 1105 or receptacle housing 1106. A fourteenth receptacle row 1145 of electrical contacts 110, 110A, 120 and a fifteenth receptacle row 1146 of electrical contacts 110, 110A, 120 are positioned back-to-back and extend along a seventh inner rib 1136 that extends in an end to end direction of the receptacle connector 1105 or receptacle housing 1106. The first and second inner ribs 1130, 1131 can be oriented parallel to one another. The second and third inner ribs 1131, 1132 can each be oriented parallel to one another. The third and fourth inner ribs 1032, 1133 can each be oriented parallel to one another. The fourth and fifth inner ribs 1133, 1134 can each be oriented parallel to one another. The fifth and sixth inner ribs 1134, 1135 can each be oriented parallel to one another. The sixth and seventh 1135, 1136 inner ribs can each be oriented parallel to one another. Each of the first, second, third, and fourth keying structures 1110A, 1110B, 1110C, 1110D can be located at one end of a respective one of the ribs 1130, 1131,

1132, 1133, 1134, 1135, 1136. Although the receptacle connector 1105 is shown with sixteen parallel, spaced apart, shieldless rows, any number of rows of electrical contacts 110, 110A, 120 can be used. The electrical contacts 110, 110A, 120 of the receptacle connector 1105 can be stitched from two directions as described with respect to Figs. 4-8. The receptacle connector 1105 can be devoid any of crosstalk shields and magnetic absorbing lossy material or can include any number of crosstalk shields or electrically conductive or non-conductive magnetic absorbing lossy material. Fusible elements, such as solder balls, can be attached to respective ones of the electrical contacts 110, 110A, 120. The electrical contacts 110, 110A, 120 can also terminate in press-fit pins or eye-of-the needles, J-lead, or other configurations.

[0148] The first keying structure 1110A can lie on a second centerline of the second inner rib 1131, adjacent to a second end of the second inner rib 1131 and adjacent to the second end wall 1109B, such that the second centerline bisects a total bounded area or perimeter of the first keying structure 1110A, or only intersects the second side wall, line, or surface 1114B and the fifth wall, line, or surface 1114A, or only intersects the fifth wall, line, or surface 1114A and the canted wall, line, or surface 1116, or only intersects the fifth wall, line, or surface 1114A and an intersection of the canted wall 1116 second side wall, line, or surface 1114B. The second keying structure 1110B can lie on a sixth centerline of the sixth inner rib 1135, adjacent to a second end of the sixth inner rib 1135 and adjacent to the second end wall 1109B, such that the sixth centerline bisects a total bounded area or perimeter of the second keying structure 1110B, or only intersects the second side wall, line, or surface 1114B and the fifth wall, line, or surface 1114A, or only intersects the fifth wall, line, or surface 1114A and the canted wall, line, or surface 1116, or only intersects the fifth wall, line, or surface 1114A and an intersection of the canted wall 1116 second side wall, line, or surface 1114B. The third keying structure 1110C can lie on a first centerline of the first inner rib 1130, adjacent to a first end of the first inner rib 1130 and adjacent to the first end wall 1109A, such that a centerline bisects a total bounded area or perimeter of the third keying structure 1110C, or only intersects the second side wall, line, or surface 1114B and the fifth wall, line, or surface 1114A, or only intersects the fifth wall, line, or surface 1114A and the canted wall, line, or surface 1116, or only intersects the fifth wall, line, or surface 1114A and an intersection of the canted wall 1116 second side wall, line, or surface 1114B. The fourth keying structure 1110D can lie on a seventh centerline of the seventh inner rib 1136, adjacent to a first end of the seventh inner rib 1136 and adjacent to the first end wall 1109A, such that the seventh centerline bisects a total bounded area or perimeter of the fourth keying structure 1110D. The first keying structure 1110A, the second keying structure 1110B, the third keying structure 1110C, and fourth keying structure 1110D can each be identically shaped and/or can each have an asymmetrical shape or a completely asymmetrical perimeter. The first keying structure 1110A can be a mirror image of the third keying structure 1110C with respect to a median centerline ML that is perpendicular to the longitudinal centerline CL. The second keying structure 1110B can be a mirror image of the fourth keying structure 1110D with respect to the median centerline ML. The first plug keying structure 1110A, the second plug keying structure 1110B, the third plug keying structure 1110C, and the fourth plug keying structure 1110D can be arranged symmetrically about the longitudinal centerline CL and asymmetrically about the median centerline ML, or vice versa. [0149] The longitudinal centerline CL and the median centerline ML divide the receptacle connector 1105 into four quadrants, with each quadrant having a structure that is different from each of the other quadrants such that no quadrant can be a substitute for the other quadrants. There can be an equal number of electrical contacts on either side of the longitudinal centerline CL, and there can be an equal number of electrical contacts on either side of the median centerline ML.

[0150] As shown in Fig. 40, a mounting interface of the receptacle connector 1105 can include first alignment peg 1101 and second alignment peg 1102. The longitudinal centerline CL can pass through the first alignment peg 1101, and the first alignment peg 1101 can have a center point CP that the longitudinal centerline CL passes through. The second alignment peg 1102 can be positioned on either side of the longitudinal centerline CL, such that the longitudinal centerline CL does not intersect the second alignment peg 1102. In one embodiment, the second alignment peg 1102 can be positioned, completely or partially, under the first keying structure 1110A or the second keying structure 1110B or can be positioned not to be underneath the first keying structure 1110A or the second keying structure 1110B. The first alignment peg 1101 can be positioned, completely or partially, under the third keying structure 1110C or the fourth keying structure 1110D or can be positioned not to be underneath the third keying structure 1110C or the fourth keying structure 1110D. The second alignment peg 1102 can lie along a centerline between the seventh and eighth receptacle rows 1126, 1127 that is parallel to and spaced away from the longitudinal centerline CL. The first alignment peg 1101 can have a circular shape with a diameter of approximately 0.8±0.05 mm, and the second alignment peg 1102 can have an oval shape with diameters of approximately 0.8±0.05 mm and 0.6±0.05 mm. The first alignment peg 1101 can be positioned adjacent to the second end wall 1109B of the receptacle housing 1106 and adjacent to a mounting interface 1140 of the receptacle housing 1106. The second alignment peg 1102 can be positioned adjacent to the first end wall 1109A of the receptacle housing 1106 and adjacent to the mounting interface of the receptacle housing 1106. The first alignment peg 1101 and the second alignment peg 1102 can both be positioned non-symmetrically about both the longitudinal centerline CL and the median centerline ML. The first row pitch RP1 between respective electrical contact centers of the first receptacle row 1120 and the second receptacle row 1121 can be approximately 2.2±0.005 mm, 2.2±0.1 mm, or 2.2±0.05mm. A second row pitch RP2 between respective electrical contact centers of the second receptacle row 1121 and the third receptacle row 1122 can be approximately 2.4±0.005 mm, 2.4±0.1 mm, or 2.4±0.05 mm. A third row pitch RP3 between respective electrical contact centers of the third receptacle row 1122 and the fourth receptacle row 1123 can be approximately 2.2±0.005 mm, 2.2±0.1 mm, or 2.2±0.05 mm. A fourth row pitch RP4 between respective electrical contact centers of the fourth receptacle row 1123 and the fifth receptacle row 1124 can be approximately 2.4±0.005 mm, 2.4±0.1 mm, or 2.4±0.05 mm. A fifth row pitch RP5 between respective electrical contact centers of the fifth receptacle row 1124 and the sixth receptacle row 1125 can be approximately 2.2±0.005 mm, 2.2±0.1 mm, or 2.2±0.05 mm. A sixth row pitch RP6 between respective electrical contact centers of the sixth receptacle row 1125 and the seventh receptacle row 1126 can be approximately 2.4±0.005 mm, 2.4±0.1 mm, or 2.4±0.05 mm. A seventh row pitch RP7 between respective electrical contact centers of the seventh receptacle row 1126 and the eighth receptacle row 1127 can be approximately 2.2±0.005 mm, 2.2±0.1 mm, or 2.2±0.05 mm. An eighth row pitch RP8 between respective electrical contact centers of the eighth receptacle row 1127 and the ninth receptacle row 1140 can be approximately 2.4±0.005 mm, 2.4±0.1 mm, or 2.4±0.05 mm. A ninth row pitch RP9 between respective electrical contact centers of the ninth receptacle row 1140 and the tenth receptacle row 1141 can be approximately 2.2±0.005 mm, 2.2±0.1 mm, or 2.2±0.05 mm. A tenth row pitch RP10 between respective electrical contact centers of the tenth receptacle row 1141 and the eleventh receptacle row 1142 can be approximately 2.4±0.005 mm, 2.4±0.1 mm, or 2.4±0.05 mm. An eleventh row pitch RP11 between respective electrical contact centers of the eleventh receptacle row 1142 and the twelfth receptacle row 1143 can be approximately 2.2±0.005 mm, 2.2±0.1 mm or 2.2±0.05 mm. A twelfth row pitch RP12 between respective electrical contact centers of the twelfth receptacle row 1143 and the thirteenth receptacle row 1144 can be approximately 2.4±0.005 mm, 2.4±0.1 mm, or 2.4±0.05 mm. A thirteenth row pitch RP13 between respective electrical contact centers of the thirteenth receptacle row 1144 and the fourteenth receptacle row 1145 can be approximately 2.2±0.005 mm, 2.2±0.1 mm or 2.2±0.05 mm. A fourteenth row pitch RP14 between respective electrical contact centers of the fourteenth receptacle row 1145 and the fifteenth receptacle row 1146 can be approximately 2.4±0.005 mm, 2.4±0.1 mm, or 2.4±0.05 mm. A fifteenth row pitch RP15 between respective electrical contact centers of the fifteenth receptacle row 1146 and the sixteenth receptacle row 1147 can be approximately 2.2±0.005 mm, 2.2±0.1 mm or 2.2±0.05 mm.

[0151] Fig. 41 is a top perspective view of the receptacle connector 1105 shown in Figs. 39 and 40. Immediately adjacent electrical contacts 110, 110A, 120 can be spaced apart on 0.65±0.05 mm centerlines. The receptacle connector 1105 can carry electrical contacts 110, 110A, 120 such that 800 electrical contacts can be arranged in sixteen rows each of fifty electrical contacts. [0152] Figs. 42-44 illustrate an exemplary plug connector 1200. As shown in Fig. 42, a plug housing 1205 or connector housing can be defined by two parallel, spaced apart longitudinal walls, such as first longitudinal plug wall 1207A and second longitudinal plug wall 1207B and two parallel, spaced apart end walls, such as first plug end wall 1209A and second plug end wall 1209B. The first and second plug end walls 1209A, 1209B can be shorter in length than the two first and second longitudinal plug walls 1207 A, 1207B. A longitudinal centerline CL3 extends through the first and second plug end walls 1209A, 1209B, parallel to the first and second longitudinal plug walls 1207 A, 1207B. A mating interface of the plug connector 1200 or plug housing 1205 can include a first plug keying structure 1210A, a second plug keying structure 1210B, and a third keying structure 1210C. The first keying structure 1210A can lie on the centerline CL3 such that the centerline bisects a total bounded area or perimeter of the first keying structure 1210A. The second keying structure 1210B and third keying structures 1210C can be positioned on opposite sides of the centerline CL3 such that the centerline CL3 does not intersect with either of the second keying structure 1210B or of the third keying structure 1210C.

[0153] The plug connector 1200 can include a first plug row 1220 of electrical plug contacts 308, 308A, 308B, 308C, a second plug row 1221 of electrical plug contacts 308, 308A, 308B, 308C, a third plug row 1222 of electrical plug contacts 308, 308A, 308B, 308C, a fourth plug row 1223 of electrical plug contacts 308, 308A 308B, 308C, a fifth plug row 1224 of electrical plug contacts 308, 308A, 308B, 308C, a sixth plug row 1225 of electrical plug contacts 308, 308A, 308B, 308C, a seventh plug row 1226 of electrical plug contacts 308, 308A, 308B, 308C, and an eighth plug row 1227 of electrical plug contacts 308, 308A 308B, 308C. The plug connector 1200 can include a first plug row 1220 and a second plug row 1221 of back-to-back electrical plug contacts 308, 308A, 308B, 308C carried by a first plug rib 1230 positioned adjacent to a mating interface of the plug housing 1205. The plug connector 1200 can include a third plug row 1223 and a fourth plug row 1224 of back-to-back electrical plug contacts 308, 308A, 308B, 308C carried by a second plug rib 1231 adjacent to a mating interface of the plug housing 1205. The plug connector 1200 can include a fifth plug row 1224 and a sixth plug row 1225 of back-to- back electrical plug contacts 308, 308A, 308B, 308C carried by a third plug rib 1232 adjacent to a mating interface of the plug housing 1205. The plug connector 1200 can include a seventh plug row 1226 and an eighth plug row 1227 of back-to-back electrical plug contacts 308, 308A, 308B, 308C carried by a fourth plug rib 1233 adjacent to a mating interface of the plug housing 1205. The first plug row 1220 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the second plug row 1221 of electrical plug contacts 308, 308A. 308B, 308C. The third plug row 1222 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the second plug row 1221 of electrical plug contacts 308, 308A, 308B, 308C. The fourth plug row 1223 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the third plug row 1222 of electrical plug contacts 308, 308A, 308B,

308C. The fifth plug row 1224 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the fourth plug row 1223 of electrical plug contacts 308, 308A. 308B, 308C. The sixth plug row 1225 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the fifth plug row 1224 of electrical plug contacts 308, 308A, 308B, 308C. The seventh plug row 1226 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the sixth plug row 1225 of electrical plug contacts 308, 308A, 308B, 308C. The eighth plug row 1227 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the seventh plug row 1226 of electrical plug contacts 308, 308A, 308B, 308C.

[0154] The first, second, third, and fourth plug ribs 1230, 1231, 1232, 1233 can be spaced apart, can be positioned parallel to each other, and can extend in a direction from the first plug end wall 1209A to the second plug end wall 1209B. As shown in Fig. 44, the first, second, third, and fourth plug ribs 1230, 1231, 1232, 1233 of plug connector 1200 and mating ends 116C at mating interface 1218 can protrude above a step defined by the plug housing 1205 so plug ribs 1230, 1231, 1232, 1233 and mating ends 116C extend into and mate within recesses defined by a mating receptacle connector.

[0155] Referring again to Fig. 42, the mating interface 1218 of the plug connector 1200 can include at least three keying structures, such as first plug keying structure 1210A, second plug keying structure 1210B, and third keying structure 1210C. The first plug keying structure 1210A can lie on one the longitudinal centerline CL3 such that the longitudinal centerline CL3 passes bisects the total bounded area of the first plug keying structure 1210A. The second plug keying structure 1210B and the third plug keying structure 1210C can be positioned at the mating interface 1218 of the plug connector 1200 on opposite sides of the longitudinal centerline CL3 such that the longitudinal centerline CL3 does not intersect with either of the second keying structure 1210B or of the third keying structure 1210C. The first plug keying structure 1210A can lie along the longitudinal centerline CL3, adjacent to second ends of second and third plug ribs 1231, 1232, adjacent to second plug end wall 1209B, between the fourth plug row 1223 and the fifth plug row 1224, and between the second and third plug ribs 1231, 1232, such that a first line that passes through an entirety of the fourth plug row 1223 abuts or is coincident with or is positioned adjacent to a portion of the first plug keying structure 1210A and such that a second line through an entirety of the fifth plug row 1224 abuts or is coincident with or is positioned adjacent to a portion of the first plug keying structure 1210B. The second plug keying structure 1210B can lie along a centerline between the second plug row 1221 and the third plug row 1222, adjacent to first end of first and second plug ribs 1230, 1231, adjacent to first plug end wall 1209A, and between the first and second plug ribs 1230, 1231, such that a third line that passes through an entirety of the second plug row 1221 abuts or is coincident with or is positioned adjacent to a portion of the second plug keying structure 1210B and such that a fourth line that passes through an entirety of the third plug row 1222 abuts or is coincident with or is positioned adjacent to a portion of the second plug keying structure 1210B. The third plug keying structure 1210C can lie along a centerline between the sixth plug row 1225 and the seventh plug row 1226, adjacent to first end of third and fourth plug ribs 1232, 1233, adjacent to first plug end wall 1209A, and between the third and fourth plug ribs 1232, 1233, such that a fifth line that passes through an entirety of the sixth plug row 1225 abuts or is coincident with or is positioned adjacent to a portion of the third plug keying structure 1210C and such that a sixth line that passes through an entirety of the seventh plug row 1225 abuts or is coincident with or is positioned adjacent to a portion of the third plug keying structure 1210C. Each of the first, second, and third plug keying structures 1210A,

1210B, 1210C can be located between two of the adjacent plug ribs 1230, 1231, 1232, 1233. [0156] Each of the first, second, and third plug keying structures 1210A, 1210B, 1210C can be a respective first protrusion 1208A, second protrusion 1208B, or third protrusion 1208C defined by the plug housing 1205 or positioned adjacent to the plug housing 1205. Each of the first, second, and third plug keying structures 1210A, 1210B, 1210C can define three or more walls, lines, or sides, four or more walls, lines, or sides, at least four or more walls, lines, or sides, or at least five walls, lines, or sides and can include a first plug side wall, line, or surface 1212A, a second plug side wall, line, or surface 1214B that can perpendicularly intersect the first plug side wall 1212A, a canted plug side wall, line, or surface 1216 that intersects with the second plug side wall 1214B, a fourth plug side wall, line, or surface 1212B, and a fifth plug side wall 1214A. The fourth plug side wall, line, or surface 1212B can intersect the canted plug side wall, line, or surface 1216 and the fifth plug side wall, line, or surface 1214A. The fifth plug side wall, line, or surface 1214A can intersect the fourth plug side wall, line, or surface 1212B and the first plug side wall, line, or surface 1212A.

[0157] Each of the first, second, and third plug keying structures 1210A, 1210B, 1210C are configured to engage a corresponding first, second, and third keying structure of a mating receptacle connector.

[0158] The first plug keying structure 1210A, the second plug keying structure 1210B, and the third plug keying structure 1210C can each be identically shaped and/or can each have an asymmetrical shape or an asymmetrical outer perimeter. The second keying structure 1210B and/or the third keying structure 1210C can be a mirror image of the first keying structure 1210A with respect to a median centerline ML3 that is perpendicular to the longitudinal centerline CL3. The longitudinal centerline CL3 and the median centerline ML3 divide the plug connector 1205 into four quadrants, with each quadrant having a structure that is different from each of the other quadrants such that no quadrant can be a substitute for the other quadrants. There can be an equal number of electrical contacts on either side of the longitudinal centerline CL3, and there can be an equal number of electrical contacts on either side of the median centerline ML3.

[0159] Fig. 43 is a bottom view of a mounting interface 1240 of the plug connector 1200. Fusible members, not shown, can be attached to the electrical plug contacts 308, 308A, 308B, 308C in any suitable manner. Alternatively, the electrical plug contacts 308, 308A, 308B, 308C can terminate in J-leads, press-fit pins or eye-of-needles, or other suitable termination. The plug connector 1200, and any connector embodiment described herein, can include plug standoffs. The plug standoffs can be located at the four corners of the plug housing 1205. Any number and any location of plug standoffs can be used. The plug standoffs help ensure that the plug connector 1200 is spaced a fixed distance from a mounting surface of a substrate when the fusible members are re-flowed to connect the plug connector 1200 to a substrate. The plug connector 1200 can include first plug alignment peg 1201 and a second plug alignment peg 1202 that are configured to be received in pre-drilled alignment holes to roughly align fusible elements of the plug connector 1200 with corresponding solder pads on a mounting surface of a substrate.

[0160] First and second plug alignment pegs 1201, 1202 are shown, but any number of plug alignment pegs can be used. The first and second plug alignment pegs 1201, 1202 can have any suitable shapes, including, for example, a circular shape, an oval shape, a square shape, etc. The shapes of the first and second plug alignments pegs 1201, 1202 can be the same or different. The longitudinal centerline CL3 can pass through the first alignment peg 1201, and the first alignment peg 1201 can have a center point CP that the longitudinal centerline CL3 passes through. The second alignment peg 1202 can be positioned on either side of the longitudinal centerline CL3, such that the longitudinal centerline CL3 does not intersect the second alignment peg 1202. In one embodiment, the first plug alignment peg 1201 can be positioned, completely or partially, under the perimeter of the first plug keying structure 1210A. The second plug alignment peg 534 can be positioned, completely or partially, under the perimeter of the second plug keying structure 1210B or the third plug keying structure 1210C.

[0161] The first plug alignment peg 1201 can be aligned with the longitudinal centerline CL3 of the plug connector 1200, while the second plug alignment peg 1202 can be a distance between approximately 1.2±0.05 mm to approximately 1.3±0.05 mm from the longitudinal centerline CL3 of the plug connector 1200. First and second plug alignment pegs 1201, 1202 can be positioned asymmetrically about median centerline ML3. The first plug alignment peg 1201 can have a circular shape with a diameter of approximately 0.8±0.05 mm, and the second plug alignment peg 1202 can have an oval shape with diameters of approximately 0.8±0.05 mm and 0.6±0.05 mm. A first row pitch RP1 between respective electrical contact centers of the first plug row 1220 and the second plug row 1221 can be approximately 2.2±0.1 mm, 2.2±0.05, or 2.2±0.005 mm. A second row pitch RP2 between respective electrical contact centers of the second plug row 1221 and the third plug row 1223 can be approximately 2.4±0.1 mm, 2.4±0.05 mm or 2.4±0.005 mm. A third row pitch RP3 between respective electrical contact centers of the third plug row 1222 and the fourth plug row 1223 can be approximately 2.2±0.1 mm, 2.2±0.05 mm or 2.2±0.005 mm. A fourth row pitch RP4 between respective electrical contact centers of the fourth receptacle row 1223 and the fifth receptacle row 1224 can be approximately 2.4±0.005 mm, 2.4±0.1 mm, or 2.4±0.05 mm. A fifth row pitch RP5 between respective electrical contact centers of the fifth receptacle row 1224 and the sixth receptacle row 1225 can be approximately 2.2±0.005 mm, 2.2±0.1 mm, or 2.2±0.05 mm. A sixth row pitch RP6 between respective electrical contact centers of the sixth receptacle row 1225 and the seventh receptacle row 1226 can be approximately 2.4±0.005 mm, 2.4±0.1 mm, or 2.4±0.05 mm. A seventh row pitch RP7 between respective electrical contact centers of the seventh receptacle row 1226 and the eighth receptacle row 1227 can be approximately 2.2±0.005 mm, 2.2±0.1 mm, or 2.2±0.05 mm.

[0162] Figs. 45-47 illustrate an exemplary plug connector 1400. As shown in Fig. 45, a plug housing 1405 or connector housing can be defined by two parallel, spaced apart longitudinal walls, such as first longitudinal plug wall 1407A and second longitudinal plug wall 1407B and two parallel, spaced apart end walls, such as first plug end wall 1409A and second plug end wall 1409B. The first and second plug end walls 1409A, 1409B are shorter in length than the two first and second longitudinal plug walls 1407 A, 1407B or can be the same length as first and second longitudinal plug walls 1407 A, 1407B. A longitudinal centerline CL3 extends through the first and second plug end walls 1409A, 1409B, parallel to the first and second longitudinal plug walls 1407A, 1407B. A mating interface 1406 of the plug connector 1400 or plug housing 1405 can include a first plug keying structure 1410A, a second plug keying structure 1410B, a third plug keying structure 1410C, and a fourth plug keying structure 1410D. The first, second, third, and fourth plug keying structures 1410A, 1410B, 1410C, 1410D can form four points of a trapezoid that is symmetrical about a median centerline ML3 of the plug housing 1405. [0163] The first plug keying structure 1410A and the second plug keying structure 1410B can be positioned on opposite sides of the centerline CL3 such that the longitudinal centerline CL3 does not intersect with either of the first plug keying structure 1410A or of the second plug keying structure 1410B. The third plug keying structure 1410C and fourth plug keying structures 1410D can be positioned on opposite sides of the longitudinal centerline CL3 such that the longitudinal centerline CL3 does not intersect with either of the third plug keying structure 1410C or of the fourth plug keying structure 1410D. The third plug keying structure 1410C and the fourth plug keying structure 1410C can be separated by a larger distance, in length, than the first plug keying structure 1410A and the second plug keying structure 1410B.

[0164] The plug connector 1400 can include a first plug row 1420 of electrical plug contacts 308, 308A, 308B, 308C, a second plug row 1421 of electrical plug contacts 308, 308A, 308B, 308C, a third plug row 1422 of electrical plug contacts 308, 308A, 308B, 308C, a fourth plug row 1423 of electrical plug contacts 308, 308A 308B, 308C, a fifth plug row 1424 of electrical plug contacts 308, 308A, 308B, 308C, a sixth plug row 1425 of electrical plug contacts 308, 308A, 308B, 308C, a seventh plug row 1426 of electrical plug contacts 308, 308A, 308B, 308C, an eighth plug row 1427 of electrical plug contacts 308, 308A 308B, 308C, a ninth plug row 1440 of electrical plug contacts 308, 308A, 308B, 308C, a tenth plug row 1441 of electrical plug contacts 308, 308A, 308B, 308C, an eleventh plug row 1442 of electrical plug contacts 308, 308A, 308B, 308C, a twelfth plug row 1443 of electrical plug contacts 308, 308A 308B, 308C, a thirteenth plug row 1444 of electrical plug contacts 308, 308A, 308B, 308C, a fourteenth plug row 1445 of electrical plug contacts 308, 308A, 308B, 308C, a fifteenth plug row 1446 of electrical plug contacts 308, 308A, 308B, 308C, and a sixteenth plug row 1447 of electrical plug contacts 308, 308A 308B, 308C. The plug connector 1400 can include a first plug row 1420 and a second plug row 1421 of back-to-back electrical plug contacts 308, 308A, 308B, 308C carried by a first plug rib 1430 adjacent to a mating interface of the plug housing 1405. The plug connector 1400 can include a third plug row 1423 and a fourth plug row 1424 of back-to-back electrical plug contacts 308, 308A, 308B, 308C carried by a second plug rib 1431 adjacent to a mating interface of the plug housing 1405. The plug connector 1400 can include a fifth plug row 1424 and a sixth plug row 1425 of back-to-back electrical plug contacts 308, 308A, 308B, 308C carried by a third plug rib 1432 adjacent to a mating interface of the plug housing 1405. The plug connector 1400 can include a seventh plug row 1426 and an eighth plug row 1427 of back-to-back electrical plug contacts 308, 308A, 308B, 308C carried by a fourth plug rib 1433 adjacent to a mating interface of the plug housing 1405. The plug connector 1400 can include a ninth plug row 1440 and a tenth plug row 1441 of back-to-back electrical plug contacts 308, 308A, 308B, 308C carried by a fifth plug rib 1434 adjacent to a mating interface of the plug housing 1405. The plug connector 1400 can include a eleventh plug row 1443 and a twelfth plug row 1444 of back- to-back electrical plug contacts 308, 308A, 308B, 308C carried by a sixth plug rib 1435 adjacent to a mating interface of the plug housing 1405. The plug connector 1400 can include a thirteenth plug row 1444 and a fourteenth plug row 1445 of back-to-back electrical plug contacts 308, 308A, 308B, 308C carried by a seventh plug rib 1436 adjacent to a mating interface of the plug housing 1405. The plug connector 1400 can include a fifteenth plug row 1446 and an sixteenth plug row 1447 of back-to-back electrical plug contacts 308, 308A, 308B, 308C carried by an eighth plug rib 1437 adjacent to a mating interface of the plug housing 1405. The first plug row 1420 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the second plug row 1421 of electrical plug contacts 308, 308A. 308B, 308C. The third plug row 1422 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the second plug row 1421 of electrical plug contacts 308, 308A, 308B, 308C. The fourth plug row 1423 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the third plug row 1422 of electrical plug contacts 308, 308A, 308B, 308C. The fifth plug row 1424 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the fourth plug row 1423 of electrical plug contacts 308, 308A. 308B, 308C. The sixth plug row 1425 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the fifth plug row 1424 of electrical plug contacts 308, 308A, 308B, 308C. The seventh plug row 1426 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the sixth plug row 1425 of electrical plug contacts 308, 308A, 308B, 308C. The eighth plug row 1427 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the seventh plug row 1426 of electrical plug contacts 308, 308A, 308B, 308C. The ninth plug row 1440 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the eighth plug row 1426 of electrical plug contacts 308, 308A. 308B, 308C. The tenth plug row 1441 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the ninth plug row 1440 of electrical plug contacts 308, 308A, 308B, 308C. The eleventh plug row 1442 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the tenth plug row 1441 of electrical plug contacts 308, 308A, 308B, 308C. The twelfth plug row 1443 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the eleventh plug row 1442 of electrical plug contacts 308, 308A. 308B, 308C. The thirteenth plug row 1444 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the twelfth plug row 1443 of electrical plug contacts 308, 308A, 308B, 308C. The fourteenth plug row 1445 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the thirteenth plug row 1444 of electrical plug contacts 308, 308A, 308B, 308C. The fifteenth plug row 1446 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the fourteenth plug row 1445 of electrical plug contacts 308, 308A, 308B, 308C. The sixteenth plug row 1447 of electrical plug contacts 308, 308A, 308B, 308C can be positioned adjacent to the fifteenth plug row 1446 of electrical plug contacts 308, 308A, 308B, 308C.

[0165] The plug ribs 1430, 1431, 1432, 1433, 1434, 1435, 1436, 1437 can be spaced apart, can be positioned parallel to each other, and can extend in a direction from the first plug end wall 1409A to the second plug end wall 1409B. As shown in Fig. 47, plug ribs 1430, 1431, 1432, 1433, 1434, 1435, 1436, 1437 and mating ends 116C at mating interface 1418 of plug connector 1400 can protrude above a step defined by the plug housing 1405 so plug ribs 1430, 1431,

1432, 1433, 1434, 1435, 1436, 1437 and mating ends 116C extend into and mate within recesses defined by a mating receptacle connector.

[0166] Referring again to Fig. 45, the mating interface 1418 of the plug connector 1400 can include at least four keying structures, such as first plug keying structure 1410A, second plug keying structure 1410B, third keying structure 1410C, and fourth keying structure 1410D. The first keying structure 1410A and the second keying structure 1410B can be positioned on opposite sides of the centerline CL3 such that the longitudinal centerline C3L does not intersect with either of the first keying structure 1410A or of the second keying structure 1410B. The third keying structure 1410C and fourth keying structures 1410D can be positioned on opposite sides of the longitudinal centerline CL3 such that the longitudinal centerline CL3 does not intersect with either of the third keying structure 1410C or of the fourth keying structure 1410D. The third keying structure 1410C and the fourth keying structure 1410D can be separated by a larger distance, in length, than the first keying structure 1410A and the second keying structure 1410B. The first plug keying structure 1410A can lie along a centerline positioned parallel to and between the fourth plug row 1423 and the fifth plug row 1424, adjacent to second ends of the second and third plug ribs 1431, 1432, adjacent to the second plug end wall 1409B, and between the second and third plug ribs 1431, 1432, such that a first line that passes entirely through the fourth plug row 1423 abuts or is coincident with or is positioned adjacent to a portion of the first plug keying structure 1410A and such that a second line that passes entirely through the fifth plug row 1424 abuts or is coincident with or is positioned adjacent to a portion of the first plug keying structure 1410A. The second plug keying structure 1410B can lie along a centerline positioned parallel to and between the twelfth plug row 1443 and the thirteenth plug row 1444, adjacent to second ends of the sixth and seventh plug ribs 1435, 1436, adjacent to the second plug end wall 1409B, and between the sixth and seventh plug ribs 1435 136, such that a third line that passes entirely through the twelfth plug row 1443 abuts or is coincident with or is positioned adjacent to a portion of the second plug keying structure 1410B and such that a fourth line that passes entirely through the thirteenth plug row 1444 abuts or is coincident with or is adjacent to a portion of the second plug keying structure 1410B. The third plug keying structure 1410C can lie along a centerline positioned parallel to and between the second plug row 1421 and the third plug row 1422, adjacent to first ends of the first and second plug ribs 1430, 1431, adjacent to the first plug end wall 1409A, and between the first and second plug ribs 1430, 1431, such that a fifth line that passes entirely through the second plug row 1421 abuts or is coincident with or is positioned adjacent to a portion of the third plug keying structure 1410C and such that a sixth line that passes entirely through the third plug row 1422 abuts or is coincident with or is positioned adjacent to a portion of the third plug keying structure 1410C. The fourth plug keying structure 1410D can lie along a centerline positioned parallel to and between the fourteenth plug row 1445 and the fifteenth plug row 1446, adjacent to first ends of the seventh and eighth plug ribs 1436, 1437, adjacent to the first plug end wall 1409A, and between the seventh and eighth plug ribs 1436, 1437, such that a seventh line that passes entirely through the fourteenth plug row

1445 abuts or is coincident with or is positioned adjacent to a portion of the fourth plug keying structure 1410D and such that an eighth line that passes entirely through the fifteenth plug row

1446 abuts or is coincident with or is positioned adjacent to a portion of the fourth plug keying structure 1410D. Each of the first, second, third, and fourth plug keying structures 1410A, 1410B, 1410C, 1410D can located between two of the adjacent plug ribs 1430, 1431, 1432,

1433, 1434, 1435, 1436, 1437. Any plug keying structure or other keying structure defined herein can be positioned entirely within a corresponding end width of any corresponding plug rib or inner rib.

[0167] Each of the first, second, third, and fourth plug keying structures 1410A, 1410B, 1410C, 1410D can be a respective first protrusion 1408A, second protrusion 1408B, third protrusion 1408C, or fourth protrusion 1408D defined by the plug housing 1405 or positioned adjacent to the plug housing 1405. Each of the first, second, third, and fourth plug keying structures 1410A, 1410B, 1410C, 1410D can define three or more sides, four or more side, five or more sides, at least four sides, only five sides, or at least five sides, and can include a first plug side wall, line, or surface 1412A, a second plug side wall, line, or surface 1414B that can perpendicularly intersect the first plug side wall 1412A, a canted plug side wall, line, or surface 1416 that intersects with the second plug side wall 1414B, a fourth plug side wall, line, or surface 1412B, and a fifth plug side wall 1414A. The fourth plug side wall, line, or surface 1412B can intersect the canted plug side wall, line, or surface 1416 and the fifth plug side wall, line, or surface 1414A. The fifth plug side wall, line, or surface 1414A can intersect the fourth plug side wall, line, or surface 1412B and the first plug side wall, line, or surface 1412A.

[0168] Each of the first, second, third, and fourth plug keying structures 1410A, 1410B, 1410C, 1410D are configured to engage a corresponding first, second, third, and fourth plug keying structure of a mating receptacle connector.

[0169] The first plug keying structure 1410A, the second plug keying structure 1410B, the third plug keying structure 1410C, and the fourth plug keying structure 1410D can each be identically shaped and/or can each have an asymmetrical shape, entirely asymmetrical perimeter or entirely asymmetrical cross-section. The third plug keying structure 1410C can be a mirror image of the first plug keying structure 1410A with respect to a median centerline ML3 that is perpendicular to the longitudinal centerline CL3. The fourth plug keying structure 1410D can be a mirror image of the second plug keying structure 1410B with respect to the median centerline ML3. The first plug keying structure 1420A and the second plug keying structure 1420B can be mirror images about the longitudinal centerline CL3. The third plug keying structure 1420C and the fourth plug keying structure 1420D about the longitudinal centerline CL3. The first plug keying structure 1410A, the second plug keying structure 1410B, the third plug keying structure 1410C, and the fourth plug keying structure 1410D can be arranged asymmetrically about the centerline CL3 and asymmetrically about the centerline ML3. The longitudinal centerline CL3 and the median centerline ML3 divide the plug connector 1405 into four quadrants, with each quadrant having a structure that is different from each of the other quadrants such that no quadrant can be a substitute for the other quadrants. There can be an equal number of electrical contacts on either side of the longitudinal centerline CL3, and there can be an equal number of electrical contacts on either side of the median centerline ML3. [0170] Fig. 46 is a bottom view of the plug connector 1400. Fusible members can be attached to the electrical plug contacts 308, 308A, 308B, 308C in any suitable manner. Alternatively, the electrical plug contacts 308, 308A, 308B, 308C can terminate in J-leads, press- fit pins or eye-of-needles, or other suitable termination. The plug connector 1400 can include plug standoffs. The plug standoffs can be located at the four corners of the plug housing 1405. Any number and any location of plug standoffs can be used. The plug standoffs help ensure that the plug connector 1400 is spaced a fixed distance from a mounting surface of a substrate when the fusible members are re-flowed to connect the plug connector 1400 to a substrate. The plug connector 1400 can include first plug alignment peg 1401 and a second plug alignment peg 1402 that are configured to be received in pre-drilled alignment holes to roughly align fusible elements of the plug connector 1400 with corresponding solder pads on a mounting surface of a substrate.

[0171] First and second plug alignment pegs 1401, 1402 are shown, but any number of plug alignment pegs can be used. The first and second plug alignment pegs 1401, 1402 can have any suitable cross-section or exterior shapes, including, for example, a circular shape, an oval shape, a square shape, etc. The shapes of the first and second plug alignments pegs 1401, 1402 can be the same or different. The longitudinal centerline CL3 can pass through the first alignment peg 1401, and the first alignment peg 1401 can have a center point CP that the longitudinal centerline CL3 passes through. The second alignment peg 1402 can be positioned on either side of the longitudinal centerline CL3, such that the longitudinal centerline CL3 does not intersect the second alignment peg 1402. In one embodiment, the second alignment peg 1402 can be positioned, completely or partially, under the third plug keying structure 1410C or the fourth plug keying structure 1410D or may not be positioned underneath the third plug keying structure 1410C or the fourth plug keying structure 1410D. The first alignment peg 1401 can be positioned, completely or partially, under the first plug keying structure 1410A or the second plug keying structure 1410B or can be positioned not to be underneath the first plug keying structure 1410A or the second plug keying structure 1410B.

[0172] The first plug alignment peg 1401 can be aligned with the longitudinal centerline CL3 of the plug connector 1400, while the second plug alignment peg 1402 can be spaced a distance between approximately 1.2±0.05 mm to approximately 1.3±0.05 mm from the longitudinal centerline CL3 of the plug connector 1400. The second plug alignment peg 1402 can have a circular cross-sectional shape with a diameter of approximately 0.8±0.05 mm, and the first plug alignment peg 1401 can have an oval cross-sectional shape with diameters of approximately 0.8±0.05 mm and 0.6±0.05 mm. A first row pitch RP1 between respective electrical contact centers of the first plug row 1420 and the second plug row 1421 can be approximately 2.2±0.1 mm, 2.2±0.05, or 2.2±0.005 mm. A second row pitch RP2 between respective electrical contact centers of the second plug row 1421 and the third plug row 1423 can be approximately 2.4±0.1 mm, 2.4±0.05 mm or 2.4±0.005 mm. A third row pitch RP3 between respective electrical contact centers of the third plug row 1422 and the fourth plug row 1423 can be approximately 2.2±0.1 mm, 2.2±0.05 mm or 2.2±0.005 mm. A fourth row pitch RP4 between respective electrical contact centers of the fourth receptacle row 1423 and the fifth receptacle row 1424 can be approximately 2.4±0.005 mm, 2.4±0.1 mm, or 2.4±0.05 mm. A fifth row pitch RP5 between respective electrical contact centers of the fifth receptacle row 1424 and the sixth receptacle row 1425 can be approximately 2.2±0.005 mm, 2.2±0.1 mm, or 2.2±0.05 mm. A sixth row pitch RP6 between respective electrical contact centers of the sixth receptacle row 1425 and the seventh receptacle row 1426 can be approximately 2.4±0.005 mm, 2.4±0.1 mm, or 2.4±0.05 mm. A seventh row pitch RP7 between respective electrical contact centers of the seventh receptacle row 1426 and the eighth receptacle row 1427 can be approximately 2.2±0.005 mm, 2.2±0.1 mm, or 2.2±0.05 mm. An eighth row pitch RP8 between respective electrical contact centers of the eighth receptacle row 1427 and the ninth receptacle row 1440 can be approximately 2.4±0.005 mm, 2.4±0.1 mm, or 2.4±0.05 mm. A ninth row pitch RP9 between respective electrical contact centers of the ninth receptacle row 1440 and the tenth receptacle row 1441 can be approximately 2.2±0.005 mm, 2.2±0.1 mm, or 2.2±0.05 mm. A tenth row pitch RP10 between respective electrical contact centers of the tenth receptacle row 1441 and the eleventh receptacle row 1442 can be approximately 2.4±0.005 mm, 2.4±0.1 mm, or 2.4±0.05 mm. An eleventh row pitch RP11 between respective electrical contact centers of the eleventh receptacle row 1442 and the twelfth receptacle row 1443 can be approximately 2.2±0.005 mm, 2.2±0.1 mm or 2.2±0.05 mm. A twelfth row pitch RP12 between respective electrical contact centers of the twelfth receptacle row 1443 and the thirteenth receptacle row 1444 can be approximately 2.4±0.005 mm, 2.4±0.1 mm, or 2.4±0.05 mm. A thirteenth row pitch RP13 between respective electrical contact centers of the thirteenth receptacle row 1444 and the fourteenth receptacle row 1445 can be approximately 2.2±0.005 mm, 2.2±0.1 mm or 2.2±0.05 mm. A fourteenth row pitch RP14 between respective electrical contact centers of the fourteenth receptacle row 1445 and the fifteenth receptacle row 1446 can be approximately 2.4±0.005 mm, 2.4±0.1 mm, or 2.4±0.05 mm. A fifteenth row pitch RP15 between respective electrical contact centers of the fifteenth receptacle row 1446 and the sixteenth receptacle row 1447 can be approximately 2.2±0.005 mm, 2.2±0.1 mm or 2.2±0.05 mm.

[0173] It should be understood that the foregoing description is only illustrative of the present invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the present invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications, and variances that fall within the scope of the appended claims. Any description of any one embodiment can be combined with of the description of any other embodiment disclosed herein.

Claims

WHAT IS CLAIMED IS:

1. An electrical connector comprising: a connector housing; and at least three parallel, spaced apart, immediately adjacent, linear arrays of electrical contacts.

2. The electrical connector of claim 1, wherein a longitudinal centerline and a median centerline divide the electrical connector into four quadrants; and each of the four quadrants defines a structure that is different from each of the other quadrants.

3. The electrical connector of claim 2, wherein there are an equal number of electrical contacts on either side of the longitudinal centerline, and there are an equal number of electrical contacts on either side of the median centerline.

4. The electrical connector of claim 1-3, further comprising first and second keying features; wherein the first and second keying features are positioned on a same side of the connector housing, are spaced apart from each other, each have a same shape, and each are positioned as a mirror image of the other.

5. The electrical connector of claim 2 or 3, further comprising first and second keying features; wherein the first and second keying features are positioned on a same side of the connector housing, are spaced apart from each other, each have a same shape, and each are positioned as a mirror image of the other; and the first and the second keying features are on opposite sides of the longitudinal centerline or the median centerline.

6. The electrical connector of claim 4 or 5, wherein each of the first and the second keying features define a post; the connector housing includes ribs; and each of the first and the second keying features are located between two adjacent ribs.

7. The electrical connector of claim 4 or 5, wherein each of the first and second keying features define a recess; the connector housing includes inner ribs; and each of the first and the second keying features are located at an end of one of the ribs.

8. An electrical connector comprising: a receptacle housing, the receptacle housing having a longitudinal centerline and including first, second, and third inner ribs that are oriented parallel to one another and are spaced apart from one another, a first keying structure positioned adjacent to a second end of the second inner rib, a second keying structure positioned adjacent to a first end of the first inner rib, and a third keying structure positioned adjacent to a first end of the third inner rib.

9. An electrical connector comprising: a receptacle housing, the receptacle housing having a longitudinal centerline and including first, second, third, fourth, fifth, sixth, and seventh inner ribs that are oriented parallel to one another and are spaced apart from one another, a first keying structure positioned adjacent to a second end of the second inner rib, a second keying structure positioned adjacent to a second end of the sixth inner rib, a third keying structure positioned adjacent to a first end of the first inner rib, and a fourth keying structure positioned adjacent to a first end of the seventh keying structure.

10. An electrical connector comprising: a plug housing having a longitudinal centerline and including first, second, third, and fourth plug ribs that are each oriented parallel to one another and are spaced apart from one another

, a first plug keying structure positioned adjacent to a second end of the connector housing and between the second and third plug ribs, a second plug keying structure positioned adjacent to a first end of the connector housing and between the first and second plug ribs, and a third plug keying structure positioned adjacent to the first end of the connector housing and between the third and fourth plug ribs.

11. An electrical connector comprising: a plug housing having a longitudinal centerline and including a first, second, third, fourth, fifth, sixth, seventh, and eighth plug ribs that are each oriented parallel to one another and are spaced apart from one another, a first plug keying structure positioned adjacent to a second end of the connector housing and between the second and third plug ribs, a second plug keying structure positioned adjacent to second end of the connector housing and between the sixth and seventh plug ribs, a third plug keying structure positioned adjacent to a first end of the connector housing and between the first and second plug ribs, and a fourth plug keying structure positioned adjacent to the first end of the connector housing and between the seventh and eighth plug ribs.

12. The electrical connector of claim 8 or 9, wherein the first keying structure includes a canted side wall that abuts the longitudinal centerline of the receptacle housing.

13. The electrical connector of claim 8 or 9, wherein the first keying structure includes a second side wall and a fifth side wall, and the longitudinal centerline of the receptacle housing passes through the second side wall and the fifth side wall.

14. The electrical connector of claim 8 or 9, wherein the first keying structure includes a second side wall and a canted wall, and the longitudinal centerline of the receptacle housing passes through an intersection of the second side wall and the canted wall.

15. The electrical connector of claim 8, wherein the second keying structure and the third keying structure are each positioned on opposite sides of the longitudinal centerline of the receptacle housing.

16. The electrical connector of claim 9, wherein the first, second, third, and fourth keying structures are all spaced away from the longitudinal centerline and a median centerline of the receptacle housing.

17. The electrical connector of one of claims 8-16, further comprising a first alignment peg positioned on the longitudinal centerline.

18. The electrical connector of one of claims 8-17, further comprising a second alignment peg spaced away from the longitudinal centerline.

19. The electrical connector of claim 10, wherein the first plug keying structure includes a second plug side wall and a fifth plug side wall, and the longitudinal centerline passes through both the second plug side wall and the fifth plug side wall.

20. The electrical connector of claim 10 or 19, wherein the second plug keying structure and the third plug keying structure are both positioned on opposite sides of the longitudinal centerline of the plug housing.

21. The electrical connector of claim 11, wherein the first and second plug keying structures and the third and fourth plug keying structures are positioned on opposite sides of the longitudinal centerline.

22. The electrical connector of one of claims 8-21, wherein the electrical connector is an open pin field electrical connector, and all of the mating ends of all of the electrical contacts all have a same shape.

23. The electrical connector of one of claims 8-22, wherein the electrical connector is a mezzanine connector.

24. The electrical connector of one of claims 8-23, further comprising: a first row of electrical contacts positioned immediately adjacent to a second row of electrical contacts, and a third row of electrical contacts positioned immediately adjacent to the second row of electrical contacts, wherein the first and second rows are separated by a first row pitch of approximately 2.2 mm and the second and third rows are separated by a second row pitch of approximately 2.4 mm.

25. The electrical connector of claim 9, wherein the first, second, third, and fourth keying structures define four points of a trapezoid, and the trapezoid is symmetrical about a median centerline of the receptacle housing.

26. The electrical connector of claim 11, wherein the first, second, third, and fourth plug keying structures define four points of a trapezoid, and the trapezoid is symmetrical about a median centerline of the receptacle housing.