WO2006062911A1

WO2006062911A1 - Test socket and method for making

Info

Publication number: WO2006062911A1
Application number: PCT/US2005/043969
Authority: WO
Inventors: Scott R. Williams
Original assignee: K & S Interconnect, Inc.
Priority date: 2004-12-08
Filing date: 2005-12-06
Publication date: 2006-06-15

Abstract

A test socket for use with test equipment to test an electronic component is provided. The test socket includes a conductive body (130) defining a plurality of through holes (160), and a plurality of contact elements (170), each of the contact elements extending at least partially through a respective one of the through holes.

Description

TEST SOCKET AND METHOD FOR MAKING

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No.

60/634,217, filed December 8, 2004, the contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The invention is generally directed to test sockets, and more specifically, to high density test sockets suitable to provide interconnection between (1) contact pads of a device to be tested, and (2) test equipment.

BACKGROUND OF THE INVENTION

[0003] In the testing of integrated circuit components (e.g., packaged integrated circuits), a test socket (e.g., a test socket for high frequency applications) may be used to provide interconnection between contacts on the component to be tested (e.g., land grid array (LGA) contact pads) and the test equipment. Such a socket may include, for example, an insulated housing having cavities therein for receiving electrical contact assemblies (e.g., coaxial spring pins assemblies). Such electrical contact assemblies may include a contact element having contact surfaces at opposite surfaces of the test socket, where a solid dielectric layer is disposed in the insulated housing and surrounds the respective contact elements. Further, a ground shield layer is often disposed in the insulated housing and surrounds the solid dielectric layer.

[0004] Several problems exist in the current socket technology. Often, after the contact elements wear due to excessive connection/disconnection cycling, the entire electrical contact assembly is replaced. Further, a pitch of conventional test sockets is often limited by a thickness of the solid dielectric layer. Further still, the thickness of the solid dielectric layer of each of the electrical contact assemblies is primarily influenced by the dielectric constant of the solid dielectric layer and a maximum level of a signal (i.e., with respect to ground potential on the ground shield) introduced on the corresponding contact element and should be sufficient to prevent dielectric breakdown from occurring. The solid dielectric layer also influences the characteristic impedance of the test socket. [0005] Moreover, since the ground shield layer of the electrical contact assemblies is typically tied to an external ground of the test equipment (and a ground pad or pads of the component under test), the assembly of the test socket may be quite complicated.

[0006] Thus it would be desirable to provide a test socket overcoming one or more of the above-identified deficiencies.

SUMMARY OF THE INVENTION

[0007] According to an exemplary embodiment of the present invention, a test socket for use with test equipment to test an electronic component is provided. The test socket includes a conductive body defining a plurality of through holes, and a plurality of contact elements, each of the contact elements extending at least partially through a respective one of the through holes.

[0008] According to another exemplary embodiment of the present invention, a test socket for testing an electronic component is provided. The test socket includes a conductive body defining a plurality of through holes, and a plurality of contact elements. Each of the contact elements extends at least partially through a respective one of the through holes. The contact elements include contact elements of (1) a first type having a first diameter, and (2) a second type having a second diameter, the first diameter and the second diameter being different from one another.

[0009] According to yet another exemplary embodiment of the present invention, a method of assembling a test socket is provided. The method includes mounting an alignment fixture to a conductive body to align an array of holes of the alignment fixture with an array of through holes of the conductive body. The method also includes inserting an array of contact elements into respective, selected through holes of the conductive body such that a projecting portion of each of the array of contact elements protrudes into a respective hole of the alignment fixture.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention. [0011] It is emphasized that, according to common practice, the various features of the drawings are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawing are the following figures:

Fig. 1 is a partial perspective view illustrating portions of a test socket according to an exemplary embodiment of the present invention;

Fig. 2A is a cross sectional view taken along line X of assembled the test socket of Fig. 1, and includes contact elements;

Figs. 2B and 2C are plan views of exemplary contact elements for use in a test socket according to an exemplary embodiment of the present invention;

Fig. 3 is a partial exploded perspective view of a test socket according to another exemplary embodiment of the present invention;

Fig. 4 is a partial cross sectional view of the test socket of Fig. 3;

Fig. 5A is a detailed view of portion 5A of Fig. 4;

Fig. 5B is a detailed view of portion 5B of Fig. 4;

Fig. 6 is a partial cross sectional view of the test socket of Fig. 3;

Fig. 7A is an exploded side view of the test socket of Fig. 3;

Fig. 7B is a detailed view of portion B of Fig. 7A;

Figs. 8-9 are schematic views of contact elements and alignment structures configured for use in test sockets according to exemplary embodiments of the present invention;

Fig. 10 is a graph illustrating an exemplary operating range of exemplary contact elements according to an exemplary embodiment of the present invention; and

Fig. 11 is a flow diagram illustrating a method of assembling the test socket of Fig. 3 according to an exemplary embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] In the figures like numerals represent like features.

[0013] As will be described in greater detail below, and unlike the prior art which utilizes socket bodies made of a dielectric material, the present invention relates to a socket which includes a conductive body for receiving the contact elements (e.g., conductive pins) of the socket. Such a structure may desirably have a "coaxial" effect in that the conductive body corresponds to an outer shell conductor of the coax, and the contact elements correspond to the core conductor of the coax. Such a structure allows for high speed sockets, with the desired characteristic impedance and improved bandwidth. For example, an air gap is provided between certain of the contact elements and the conductive body (e.g., using spacers, bushings, or the like) to control the characteristic impedance. Further, different sized contact elements (e.g., contact elements having different diameters) may be used in the socket to effect the desired characteristics.

[0014] In certain exemplary embodiments of the present invention, the conductive body may be used in conjunction with one or more "retainer" layers, where the retainer layers may (1) be conductive, (2) be non-conductive, or (3) include a conductive retainer layer and a non-conductive retainer layer.

[0015] Fig. 1 is a partial perspective view illustrating portions of test socket 100; however, Fig. 1 does not show contact elements 170 which are shown in the cross sectional view of Fig. 2A. Fig. 2A is a cross sectional view taken along line X of assembled test socket 100. More specifically, conductive body 130 of test socket 100 defines through holes 160 and 165 for receiving contact elements 170. Contact elements 170 illustrated in Fig. 2A may be, for example, input/output (I/O) elements or power elements whose function is understood by those of skill in the art.

[0016] As shown in Figs. 1 and 2A, test socket 100 includes top and bottom retainers 110 and 120, and conductive body 130. Top and bottom retainers 110 and 120 may be made from, for example, glass epoxy (e.g. an FR4 material), ridge plastic materials or other materials used to make conventional circuit boards, among others. Exemplary functions of top and bottom retainers 110 and 120 are (1) to be sufficiently rigid to maintain alignment of contact elements 170, and (2) to have a sufficiently low dielectric constant to prevent discharge from contact elements 170 to conductive body 130 when predetermined gaps are set. An exemplary thickness of top and bottom retainers 110 and 120 may be within a range of about 5 to 20 mils to reduce impedance variations.

[0017] Top and bottom retainers 110 and 120 may each include conductive layer

125 (see Fig. 2A) on external surfaces thereof, for example, to reduce cross talk between neighboring contact elements 170 and noise emanating from test socket 100. Conductive layers 125 may be, for example, a noble metal, a gold material, a silver material, among others, and may be conductively coupled to conductive body 130 through a portion of contact elements 170 that are used for grounding or directly contact conductive body 130 at locations adjacent to contact elements 170. Further, conductive layers 125 may be, for example, etched away from locations adjacent to remaining contact elements 170 that are not used for grounding and may be insulated from conductive body 130 so that these remaining contact elements 170 may be insulated from conductive layers 125.

[0018] Top and bottom retainers 110 and 120, respectively, define , a plurality of through holes 140 and 150 therethrough. Each through hole 140 of top retainer 110 corresponds to a respective through hole 150 of bottom retainer 120 to form through hole pairs 140; 150. Moreover, an array of contact elements 170 may be provided and each contact element 170 may correspond to and may extend through a respective through hole pair 140; 150 and may be retained thereby. That is, each contact element 170 includes end sections 190 and 200 (and body 195 therebetween) such that end sections 190 and 200 may have a diameter smaller than a diameter of body 195. Moreover, the diameter of each end section 190 and 200 of the array of contact elements 170 may correspond to and may desirably fit within respective through holes 140 and 150 of top and bottom retainers 110 and 120.

[0019] For example, the array of contact elements 170 may be pressure fit into and extend from through holes 140 and 150 of top and bottom retainers 110 and 120 so that the array of contact elements 170 are substantially held in place via top and bottom retainers 110 and 120.

[0020] The array of contact elements 170 may be resilient, and lengths of bodies

195 of respective contact elements 170 may be longer than conductive body 130 such that the array of contact elements 170 may be compressed (i.e., preloaded) by top and bottom retainers 110 and 120 during assembly of test socket 100. For example, the preloaded displacement may be in the range of about 20 to 30 mils. [0021] Lengths of end sections 190 and 200 of the array of contact elements

170, respectively, may be longer than a thickness of top and bottom retainers 110 and 120 so as to project therefrom. For example, each of the array of contact elements 170 may extend out of top and bottom retainers 110 and 120 by about 5 to 20 mils.

[0022] Figs. 2A-2C illustrate exemplary contact elements 170 including contact element 170a and contact element 170b. For example, contact element 170a may be an I/O contact element while contact element 170b may be a power contact element (e.g., a V_cc contact element, a V_ss contact element, etc.). Note that in Fig. 2A contacts elements 172a, 172b, and 174 and illustrated as being of like size and dimension; however, it is understood that the contacts elements may be of substantially the same size and shape, or may be of different sizes and shapes. For example, in a single socket, contact elements 170a and 170b may be utilized.

[0023] For example, each contact element 170 may be configured as a substantially cylindrical shaped compliant contact element. Such a substantially cylindrical shaped compliant contact element 170 may be, for example, a spring pin, a coiled spring, a woven/braided wire, among others, such that the substantially cylindrical shaped compliant contact element 170 is compliant enough to be preloaded and retainable in the top and bottom retainers 110 and 120. As will be described in greater detail below, each of contact elements 170 may be configured as a spring pin, for example, including a barrel engaged with a plunger, where a spring element is disposed within a cavity formed by the engaged barrel and plunger.

[0024] Referring again to Fig. 2A, it is contemplated that to align certain of the plurality of contact elements 170 (i.e., those contact elements which are surrounded by the predetermined gaps and are not in direct physical contact with conductive body 130) in their respective through holes 160 of conductive body 130, insulated aligners/ bushings 185 are provided. For example, such contact elements 170 may be pressure fit into insulated aligners/bushings 185 and may be disposed in through holes 160 having predetermined air gaps surrounding contact elements 170. Insulated aligners/bushings 185 may comprise, for example, a thermoplastic material such as TEFLON® or TORLON®, as an example TORLON® 4203. For example, insulated aligners/bushings 185 may be designed to have a dielectric constant in the range of about 1 to 10.

[0025] For example, the array of contact elements 170 may be constructed of high conductivity material such as a noble metal, gold, copper, a silver compound, etc. Further, the array of contact elements 170 may have their surfaces treated, for example, with a noble metal, a gold plating, a silver plating, etc., to increase a surface conductivity thereof.

[0026] Conductive body 130 is sandwiched between top and bottom retainers

110 and 120, and in the exemplary embodiment illustrated in Figs. 1 and 2A, a portion of conductive body 130 circumferentially surrounds each of the contact elements 170. For example, certain of contact elements are received by through holes 160 such that predetermined gaps are formed between the contact elements and conductive body 130.

[0027] Thus, conductive body 130 includes an array of through holes 160 and

165, each of which may correspond to a respective through hole pair 140; 150 formed , in top and bottom retainers 110 and 120, respectively. Each contact element 170 is disposed in a respective through hole 160 and 165 such that an axis of each contact element 170 may be coaxially aligned with a center axis of the respective through hole 160 and 165.

[0028] Surfaces of conductive body 130 which define the array of through holes

160 and 165 may be surface treated to increase the conductivity thereof. For example, the surfaces around through holes 160 and 165 of conductive body 130 may include a noble metal, a gold plating, a silver plating, etc., among others, to increase a surface conductivity thereof.

[0029] The array of contact elements 170 may be a substantially uniform array of contact elements 170, or the contact elements 170 may be of different types. In Fig. 2A, contact elements 170 include contact element 172a (e.g., a V_cc type contact element electrically isolated from conductive body 130), contact element 172b (e.g., a V_ss type contact element electrically coupled to conductive body 130), and contact element 174 (e.g., an I/O signal type contact element electrically isolated from conductive body 130). Certain of contact elements 172 may directly contact conductive body 130 (with no bushings 185 and/or an intentional air gap providing electrical isolation from conductive body 130), while others of contact elements 172 may be electrically insulated from conductive body 130 (e.g., by a first respective predetermined air gap and/or bushings), while contact elements 174 may be insulated from conductive body 130 by a second respective predetermined air gap. The first respective predetermined air gaps may be different in size from the second respective predetermined air gaps. That is, for example, power contact elements (e.g., contact elements of 172a having power signals introduced thereon such as V_cc contact elements) may be insulated from conductive body 130 by the respective first predetermined air gaps, while signal contact elements (e.g., contact elements of second type 174 having test and/or data signals introduced thereon) are insulated from conductive body 130 by the second respective predetermined air gaps, and grounded contact elements (e.g., contact elements of first type 172b which may be electrically coupled to conductive body 130 such as V_ss contact elements) may not have any predetermined air gaps. The grounded contact elements may be configured to electrically connect conductive body 130 to an external ground. Thus, the ground contact elements may provide a ground connection for conductive body 130 and a ground connection to the component under test (not shown).

[0030] While certain of the contact elements 170 may have a diameter that is greater than a diameter of other of the contact elements (e.g., to allow for increased current carrying capacity), a pitch of the contact elements 170 may remain , substantially constant regardless of the diameters of contact elements 170.

[0031] As shown in Fig. 1, through holes 165 of conductive body 130

(corresponding to at least a portion of contact elements 172b) have a diameter that is smaller than a diameter of through holes 160 of conductive body 130 (corresponding to contact elements 172a and 174).

[0032] The second predetermined gaps for contact elements 174 may be in the range of, for example, about 10 to 30 mils with a switching frequency of the test/data signal introduced on contact elements 174 being in the range of, for example, about 1 GHz to 40 GHz. The first predetermined gaps for insulated contact elements 172a may be in the range of about, for example, 5 to 20 mils with a switching frequency of signals introduced on contact elements 172a in the range of, for example, 0 to 1 GHz.

[0033] The first and second predetermined gaps for insulated contact elements

172a and 174 may be sized to maintain a predetermined characteristic impedance, for example, 50, 75 or 93 ohms. That is, the predetermined characteristic impedance of test socket 100 may be configured in consideration of a size of the first and second predetermined gaps corresponding to insulated contact elements 172a and 174. This allows impedance matching between the test equipment, test socket 100, and the component under test to reduce or eliminate losses due to impedance mismatch.

[0034] It is contemplated that the characteristic impedance of the test socket

100 may be mixed (i.e., have difference values) across the test socket 100. That is, predetermined gaps of differing sizes may be used such that impedance zones in the test socket 100 are created.

[0035] In the exemplary embodiment illustrated in Fig. 1, test socket 100 is shown having a 10 x 6 array of contact elements 170, however, it is understood that the array may be of any shape or size (e.g., an N x M array, where N and M are integer numbers). For example, the number of contact elements 170 may be in a range of about 600 to 1200.

[0036] In Fig. 1, conductive body 130 is sandwiched by top and bottom retainers

110 and 120, respectively. It is contemplated, however, that at these locations top and bottom retainers 110 and 120 may be removed and conductive body 130 may be projected, respectively, toward external surfaces of top and bottom retainers 110 and 120 such that conductive body 130 may make direct contact with ground connections of the test equipment and/or the circuit board or component under test.

[0037] Proper registration of the arrays of through holes 140 and 150 of top and bottom retainers 110 and 120, and the array of through holes 160 and 165 of conductive body 130 may be provided by engaging alignment members 270 and 275 retainer 110 and conductive body 130, and by engaging alignment members 280 and 285 of retainer 120 and conductive body 130. Although alignment members 270, 275, 280 and 285 are shown on two sides of the test socket 100 for simplicity, any number of alignment structures (of any shape or configuration) may be provided.

[0038] Coupling holes 210, 220 and 230 are provided to fixedly couple top 110 retainer, conductive body 130, and bottom retainer 120 together via coupling member 215. While illustrated as a threaded screw, coupling member 215 may be a pressure fit device, a clamping device, or any other coupling structure.

[0039] In Fig. 1, conductive body 130 defines through holes 160 and 165 with diameters of different sizes in a specific configuration, however, the size of each through hole 160 and 165 and the configuration of through holes 160 and 165 may vary based on signal frequencies and magnitudes (e.g., voltage and current magnitudes) of the signals (e.g., test/data signals, power signals, ground signals, etc.) to be introduced on the respective contact element 170, and may be of any diameter and in any configuration.

[0040] According to an exemplary embodiment of the present invention, a portion of contact elements 172 (e.g., ground contact elements) may be arranged in a substantially uniform distribution throughout the array of contact elements 170 so as to provide a common ground potential throughout conductive body 130. Moreover, contact elements 174 may be spaced apart such that these contact elements 174 are located between certain contact elements 172 to reduce crosstalk from neighboring contact elements 174.

[0041] Figs. 3-4, 5A-5B, 6, and 7A-7B are various views of portions of test socket 500 according to an exemplary embodiment of the present invention. Test socket 500 includes conductive retainer 510, conductive body 520 and alignment frame 530. Conductive retainer 510 may be made from, for example, any electrically conductive material such as beryllium copper. Conductive retainer 510 is desirably (1) sufficiently rigid to maintain alignment of contact elements 570, 580 and 590, and/or (2) has a coefficient of thermal expansion which is sufficiently close to that of conductive body 520 to retain the alignment over potential temperature ranges (e.g., 0 to 120 ⁰C). Conductive body 520 may be from any electrically conductive material, for example, brass. Conductive body 520 is desirably (1) sufficiently rigid to maintain alignment of contact elements 570, 580 and 590, and/or (2) has a coefficient of thermal expansion which is sufficiently close to that of conductive retainer 510 to retain the alignment over potential temperature ranges (e.g., 0 to 120 ⁰C).

[0042] Conductive retainer 510 and conductive body 520, respectively, define a plurality of through holes 515 and 525 therethrough (see Fig. 5A). Each through hole 515 of conductive retainer 510 corresponds to a respective through hole 525 of , conductive body 520 to form a plurality of through hole pairs 515;525. Moreover, each of an array of contact elements (e.g., contact elements 570, 580 and 590) extend through a respective through hole pair 515;525. A set of insulated bushings 581;582 and 591; 592 is disposed at opposite ends of respective contact element 580 and 590 to surround portions of contact elements 580 and 590 for at least a portion of the plurality of through hole pairs 515;525. Each insulated bushing 581, 582, 591 and 592 may be seated between the respective contact element 580 and 590 and one of conductive retainer 510 or conductive body 520 to insulate contact elements 580 and 590 that have signals (e.g., power signals or test/data signals) introduced thereon from conductive retainers 510 and conductive body 520.

[0043] Each contact element 570, 580 and 590 includes end sections 574;575,

584;585 and 594;595 at opposite ends of contact elements 570, 580 and 590 and body 573, 583 and 593 disposed therebetween, respectively. Diameters of each end section 574;575, 584;585 and 594;595 of the array of contact elements 570, 580 and 590 may correspond to and may fit within the respective through hole pairs 515;525 formed by conductive retainer 510 and conductive body 520. Moreover, the diameters of end sections 584;585 and 594;595 of the contact elements 580 and 590 may extend through respective sets of insulated bushings 581;582 and 591;592, respectively.

[0044] For example, contact elements 580 and 590 may be pressure fit into, and have portions of end sections 584;585 and 594;595 project from, the corresponding set of insulated bushings 581;582 and 591;592, respectively, so that the array of contact elements 580 and 590 may be fixed to the corresponding set of insulated bushings 581;582 and 591;592 to reliably maintain spacings (e.g., air gaps) between contact elements 580 and 590 and corresponding surfaces of the respective through hole pairs 515;525 to predetermined sizes (e.g., sizes of the predetermined air gaps). The contact elements 580 and 590 may be thereby retained in the respective through hole pair 515;525.

[0045] Contact elements 570 may be pressure fit (e.g., directly contact) to, and have portions of end sections 574;575 project from, respective surfaces defining through hole pairs 515;525.

[0046] Contact elements 570, 580 and 590 may be resilient, and lengths of bodies 573, 583 and 593 of the contact elements 570, 580 and 590 may be longer than the conductive body 520 such that the array of contact elements 570, 580 and 590 may be compressed (i.e., preloaded) by an assembly unit 510;520 of conductive retainer 510 mounted to conductive body 520. For example, the preloaded compression length of the array of contact elements 570, 580 and 590 may be in a range of about 10 to 30 mils.

[0047] Lengths of end sections 574;575, 584;585 and 594;595 of the array of contact elements 570, 580 and 590, respectively, may be designed such that portions of each end section 574, 575, 584, 585 594 and 595 of the array of contact elements 570, 580 and 590 project from one (or both) of conductive retainer 510 or conductive body 520. For example, each of the array of contact elements 570, 580 and 590 may extends out of one of conductive retainer 510 or conductive body 520 by about 5 to 20 mils.

[0048] For example, contact elements 570, 580 and 590 may be made of a high conductivity material such as a noble metal, gold, copper, silver compound, etc. Further, contact elements 570, 580 and 590 may have their surfaces treated, for example, with a noble metal plating, a gold plating, a silver plating, etc., to increase a surface conductivity thereof.

[0049] Conductive retainer 510 and conductive body 520, as assembly unit

510; 520 may circumferentially surround each of contact elements 570, 580 and 590 such that predetermined gaps 560 and 561 are defined around contact elements 580 and 590, respectively. Assembly unit 510;520 defines an array of through holes pairs 515;525, a portion of which may have a set of respective insulated bushings 581;582 and 591;592 disposed with contact elements 580 and 590 therein. Each contact element 570, 580 and 590 may be disposed such that a center axis thereof coaxially aligns with a center axis of the respective through hole pair 515;525.

[0050] Conductive retainer 510 may be, for example, a retaining plate that is configured to be substantially coplanar with one side of conductive body 520.

[0051] Surfaces which define the array of through holes pairs 515;525 formed by assembly unit 510; 520 may be surface treated to increase a conductivity thereof. That is, the surface around through holes pairs 515;525 may include, for example, a noble metal plating, a gold plating or a silver plating, among others, to increase a surface conductivity thereof.

[0052] Each contact element 570, 580 and 590 may be configured as a substantially cylindrical shaped compliant contact element that may be retained within the air gap, and may be embodied as a spring pin, a coiled spring, a woven/braided wire, among others, such that each of the substantially cylindrical shaped compliant contact elements is compliant enough to be preloaded and retainable in the assembly unit 510;520.

[0053] In the illustrated spring pin embodiment of Fig. 5A, each contact element

570, 580 and 590 includes a barrel (part of body portions 573, 583 and 593), a plunger (see length adjacent end sections 574, 584 and 594), and a spring element 576, 586 and 596 (see Fig. 6) disposed within a cavity formed by the engaged barrel and plunger. Each spring element 576, 586 and 596 may act as a biasing unit and provides an electrical path between the barrel and the plunger. In this configuration, each barrel and respective plunger slides relative to each other and may be compressed thereby.

[0054] Figs. 3, 5A-5B also illustrate certain exemplary alternative contact elements 570a, 570b, 570c, 590a, 590b, 590c, which vary from contact elements 570 and 590 primarily in terms of their size relative to the conductive body and retainer. [0055] Figs. 8-9 are partial cross sectional views of configurations of contact elements 580 within a test socket. More specifically, Figs. 8-9 illustrate two exemplary types of insulative aligners/bushings (i.e., insulated bushing 581, insulated aligner 600) that may be used with contact elements 580 on the conductive retainer side of test socket 500.

[0056] To align contact elements 580 which are surrounded by predetermined gaps in their respective through holes pairs 515;525, insulated bushings 581 or insulated aligners 600 (or other alignment structures) may be used. Contact elements of the second type 580 may be pressure fit into insulated bushings 581 or insulated aligners 600 and may be disposed in their respective through holes pairs 515; 525. Insulated bushings 581 or insulated aligners 600 may be formed of a material with has a dielectric constant, for example, in the range of about 1 to 10. Insulated bushings 581 or aligners 600 may be made from, for example, thermoplastic such as TEFLON® or TORLON®, as an example TORLON® 4203. Insulated bushings 581 or insulated aligners 600 may be used with elements 590.

[0057] Each contact element 570 may directly contact assembly unit 510;520 of conductive retainer 510 and conductive body 520, and each contact element of second and third types 580 and 590 may be insulated from assembly unit 510; 520 of conductive retainer 510 and conductive body 520 by a respective predetermined air gaps/and insulative bushings or the like. For example, the predetermined air gaps for contact elements 580 may be different in size from the predetermined air gaps for contact elements 590.

[0058] For example, power contact elements (e.g., contact elements 590 having power signals introduced thereon such as V_cc signals) may be insulated from assembly unit 510;520 by the predetermined air gaps of a first size, signal contact elements (e.g., contact elements 580 having test/data signals introduced thereon) may be insulated from assembly unit 510;520 by predetermined air gaps of a second size, and grounded contact elements (e.g., contact elements 590 such as V_ss signals) may be configured to be electrically coupled to assembly unit 510;520 and may not have any corresponding intentional predetermined air gaps. That is, the grounded contact - elements may electrically connect assembly unit 510;520 to an external ground and may be configured to provide a ground connection for the component under test.

[0059] Contact elements 580 may have signals (e.g., test/data signals) introduced thereon which have a switching frequency in the range of, for example, about 1 GHz to 40 GHz, and contact elements 590 may carry signals (e.g., power signals) between the component under test (not shown) and the test equipment (not shown), where the switching frequency of the power signals may be, for example, less than 1 GHz (the switching frequency of the power signals may be less than 10 KHz).

[0060] Certain contact elements 570 and 590 (e.g., for power signals) desirably may be of a common design or may have common diameters such that a common diameter thereof is greater than a diameter of other contact elements 570 (e.g., for I/O signals) to allow for increased current carrying capacity in such contact elements 570 and 590.

[0061] A pitch of the array of contact elements 570, 580 and 590 of the test socket 500 may be substantially constant regardless of the diameter of the contact elements 570, 580 and 590. For example, the through hole pairs 515;525 corresponding to contact elements 570, 580 and 590, respectively, may be substantially similar size and/or spacing such that the pitch remains constant regardless of the diameter or diameters of contact elements 570, 580 and 590.

[0062] In certain embodiments of the present invention, through hole 525 of conductive body 520 corresponding to certain contact elements 570 may have a diameter that is smaller than a diameter of through hole 525 of conductive body 520 corresponding to certain contact elements 580. Further, through holes 525 of conductive body 520 corresponding to contact elements 590 may have a diameter that is substantially similar in size to the diameter of the through holes 525 of conductive body 520 corresponding to contact elements 580.

[0063] In such a configuration, contact elements 570 and 590 may have substantially similar diameters, while contact elements 580 may have a diameter that is smaller than contact elements 570 and 590, such that certain contact elements 570 may be pressure fit (i.e., directly contact) into and extend out of opposite ends of the assembly unit 510;520 and contact elements of second and third types 580 and 590 may be insulated from assembly unit 510;520 by respective predetermined air gaps and/or insulative bushings or the like.

[0064] Moreover, the respective gap for each contact element (e.g., contact elements 580 and 590) may be sized according to magnitudes (e.g., voltage and current magnitudes) of a signal to be introduced on the respective contact element 580 and 590, and a desired characteristic impedance. For example, the desired characteristic impedance for test socket 500 may be controlled at least partially based on a size of the predetermined gap 560 and 561 between the respective contact element 580 and 590 and the assembly unit 510;520 and a dielectric constant of material disposed therebetween. The predetermined gaps for contact elements 580 may be in the range of, for example, about 10 to 30 mils and the predetermined gaps for contact elements 590 may be in the range of, for example, about 5 to 20 mils.

[0065] The predetermined gaps 560 and 561 for contact elements 580 and 590 may be sized to provide a characteristic impedance of test socket 500, for example, of 50, 75 or 93 ohms. That is, the characteristic impedance may be set in consideration of a size of the predetermined air gaps 560 and 561. This allows impedance matching between the test equipment, test socket 500 and the component under test to reduce or eliminate losses due to impedance mismatch.

[0066] It is contemplated that the characteristic impedance of test socket 500 may be mixed (i.e., have difference values) across test socket 500. That is, combinations of contact elements of differing diameters and/or assembly unit 510;520 defining differing diameters may be used such that impedance zones in the test socket 500 are created.

[0067] Test socket 500 may have any of a number of different configurations in terms of the array design (e.g., a peripheral array, different lengths and widths of the inner and outer portions defining the periphery of the peripheral array) or any other structure of a different shape or size (e.g., an N x M array, where N and M are integer numbers). For example, the number of contact elements in the test socket be in a range of about 600 to 1200. For example, the composite force to insert the contact elements 570, 580 and 590 may be, for example, 80 lbs or less. Contact elements 570 and 590 may have a substantially common compressive (i.e., insertion) force, and the ratio of compressive force between contact elements 580 and 590 may be in a ratio of between about 1:2 and 2:1. That is, the force to compress contact elements 570, 580 and 590 in test socket 500 may be 80 lbs or less, and that any two contact elements 570, 580 and 590 used in test socket 500 does not have a force which differs substantially (e.g., is greater than the 1:2 ratio). In such a configuration, contact elements 570, 580 and 590 exert enough force to make good electrical contact but not so much that the compressive force exceeds 80 lbs to compress (e.g., to insert) all contact elements 570, 580 and 590 into test socket 500.

[0068] Proper registration of conductive retainer 510 and conductive body 520 may be provided by the alignment frame 530 using alignment dowels 540 and 560 (which may be of different diameters), and which may be press fit through conductive retainer 510 and conductive body 520 and, thereby, may ensure alignment of conductive retainer 510 with conductive body 520.

[0069] Plural coupling holes 507 may be provided to couple conductive retainer

510, conductive body 520 and alignment frame 530 together via a coupling member 550 (e.g., a threaded screw or any other appropriate coupling structure such as a pressure fit device, a clamping device, a housing to hold the test socket, etc.)

[0070] While the assembly unit 510;520 (and other embodiments described herein) is shown having a specific configuration for the array of through hole pairs 515;525 and contact elements, however, it is contemplated that the invention can be practiced with any number of other configurations, for example, by varying the relative positions of contact elements, the total number of contact elements, the relative number of each type of contact element, and/or the number of different contact types, among others.

[0071] Certain contact elements 570 (e.g., ground contact elements) may have a substantially uniform distribution throughout the array so as to provide a common ground potential throughout conductive body 520. Moreover, contact elements 580 may be spaced apart such that contact elements 570 and 590 may be located between contact elements of second type 580 to reduce crosstalk from neighboring contact elements 580.

[0072] Fig. 10 is a graph illustrating an exemplary operating range of contact elements 570 or 590 according to a current flowing therethrough and ambient temperature. To model the exemplary operating range of contact elements 570 or 590, a direct current was applied to the contact elements and the temperature rise over the ambient temperature is measured. Since an exemplary test socket is desired to operate in a range between 0 and 12O⁰C, the ambient temperate should be desirably less than 12O⁰C according to the magnitude of current flowing through contact elements 570 or 590. Base operating curve 900 represents the operating range of contact elements 570 or 590 in free air. Moreover, derated operating curve 910 represents the operating range of contact elements 570 or 590 in accordance with thermal considerations regarding contact elements 570 or 590 being enclosed within test socket 500.

[0073] Fig. 11 is a flow diagram illustrating an exemplary method of assembling a test socket according to the present invention (e.g., test socket 500 illustrated in Fig. 3). At operation 1000, an alignment fixture (e.g., alignment fixture 530) is mounted to a conductive body (e.g., conductive body 520) to form an alignment fixture/conductive body assembly. The alignment fixture may be configured to increase a retained length of plungers of the array of contact elements (e.g., contact elements 570, 580 and 590) to increase alignment precision (i.e., registration) of the contact elements (e.g., relative to through holes such as holes 515 of conductive retainer 510), thereby improving ease of assembly and increasing assembly throughput.

[0074] Referring to the exemplary embodiment illustrated in Fig. 6, alignment fixture 530 defines an array of holes 506 corresponding to the array of through holes 525 of conductive body 520 such that a depth of each hole 506 is configured to receive a respective contact element extending from conductive body 520. The mounting of the alignment fixture at operation 1000 may include aligning of plural corresponding sets of alignment holes of the alignment fixture and of the conductive body (e.g., see holes 501/507 and holes 502/508 in Fig. 3) by using plural dowels (e.g., dowels 540 and 560). For example, such dowels may be press fit into the corresponding set of alignment holes.

[0075] At operation 1010, insulated bushings (e.g., bushings 592, bushings

582) corresponding to the appropriate contact elements are inserted into preassigned through holes (e.g., through holes 525) of the conductive body (e.g., conductive body 520) (see Fig. 6). The insertion of the insulated bushings may include press fitting each insulated bushing into a corresponding preassigned through holes of the conductive body to a predetermined depth.

[0076] At operation 1020, the contact elements (e.g., contact elements 570, 580 and 590) are inserted into preassigned through holes (e.g., through holes 525) of the conductive body (e.g., conductive body 520). For example, the insertion may include (1) press fitting each contact element 570 into and directly contacting a surface of conductive body 520 adjacent the corresponding preassigned through hole 525 to a first predetermined depth, (2) press fitting each contact element 580 into a corresponding through hole of bushing 582 to a second predetermined depth, and (3) press fitting each contact element 590 into a corresponding through hole of first insulated bushing 592 to a third predetermined depth.

[0077] At operation 1030, second bushings (e.g., bushings 591 corresponding to contact elements 590, bushings 581 corresponding to contact elements 580) are inserted into preassigned through holes (e.g., through holes 515) of conductive retainer (e.g., conductive retainer 510). The insertion of the second bushings may include press fitting each into a corresponding preassigned through hole of the conductive retainer to a predetermined depth.

[0078] At operation 1040, the conductive retainer (e.g., conductive retainer

510) is mounted to the alignment fixture/conductive body assembly. The mounting of the conductive retainer may include aligning of a plural corresponding alignment holes (e.g., alignment holes 511 and 512) of the conductive retainer with the conductive body/alignment fixture assembly using protrusions of the plural dowels (e.g., dowels 540 and 560) from the conductive body/alignment fixture assembly, and temporarily press fitting the plural corresponding alignment holes of the conductive retainer to the conductive body/alignment fixture assembly.

[0079] At operation 1050, the conductive retainer (e.g., conductive retainer

510) is coupled with alignment fixture/conductive body assembly (e.g., alignment fixture/conductive body assembly 530;520). The coupling of the conductive retainer with the alignment fixture/conductive body assembly may be by screw coupling (e.g., using plural threaded screws 550 through coupling holes 551 and 552 of conductive retainer 510 and conductive body 520, respectively) or other coupling means.

[0080] At operation 1060, the alignment fixture (e.g., alignment fixture 530) is removed from the conductive body to provide a conductive body/conductive retainer assembly (e.g., assembly 510; 520). At operation 1070, the alignment frame is coupled with the conductive body/conductive retainer assembly.

[0081] Although this exemplary embodiment illustrates operations 1000 to 1070 in a specific succession, it is contemplated that these operations may be performed in any number of different orders. Further, various of these steps may be omitted (or replaced with other steps) as desired.

[0082] While preferred embodiments of the invention are illustrated and described herein, it should be understood that such embodiments are provided by way of example only. Numerous variations, changes and substitutions can occur without departing from the scope and spirit of the invention.

Claims

What is Claimed:

1. A test socket for use with test equipment to test an electronic component, the test socket comprising:

a conductive body defining a plurality of through holes; and

a plurality of contact elements, each of the contact elements extending at least partially through a respective one of the through holes.

2. The test socket of claim 1 further comprising at least one retainer defining a plurality of retainer holes therein, the at least one retainer being positioned adjacent the conductive body such that respective ones of the plurality of through holes are aligned with corresponding ones of the plurality of retainer holes thereby defining passages through which respective ones of the plurality of contact elements are configured to extend, the at least one retainer being configured to at least partially retain the contact elements within the test socket.

3. The test socket of claim 2 wherein at least a portion of the plurality of retainer holes have a diameter that is smaller than a diameter of the corresponding portion of the plurality of through holes.

4. The test socket of claim 2 wherein the at least one retainer includes a first retainer and a second retainer, the conductive body being positioned between the first retainer and the second retainer.

5. The test socket of claim 4 wherein each of the first retainer and the second retainer is formed of an electrically insulative material.

6. The test socket of claim 2 wherein the at least one retainer is formed of an electrically conductive material.

7. The test socket of claim 6 further comprising insulative bushings positioned adjacent a portion of at least one of the retainer openings or the through holes to electrically isolate a corresponding portion of the contact elements from at least one of the conductive body or the at least one retainer.

8. The test socket of claim 1 wherein gaps are defined between (1) at least a portion of the contact elements, and (2) corresponding surfaces of the conductive body adjacent the respective through holes.

9. The test socket of claim 8 wherein the gaps are sized to control a characteristic impedance of the test socket.

10. The test socket of claim 9 wherein the characteristic impedance of the test socket is selected from the group consisting of (1) about 50 ohms, and (2) 75

- ohms.

11. The test socket of claim 8 wherein the gaps are sized to provide a plurality of characteristic impedance zones in the test socket, wherein at least one of the characteristic impedance zones has a characteristic impedance that is different from a characteristic impedance of another of the characteristic impedance zones.

12. The test socket of claim 8, wherein the contact elements include contact elements of a first type and contact elements of a second type, wherein the gap associated with the contact elements of the first type is in the range of about 10 to 30 mils, the gap associated with the contact elements of the second type is in the range of about 5 to 20 mils.

13. The test socket of claim 1 wherein at least a portion of the contact elements are in electrical contact with the conductive body.

14. The test socket of claim 1 further comprising insulative bushings positioned adjacent a portion of the through holes to electrically isolate a corresponding portion of the contact elements from the conductive body.

15. The test socket of claim 1 wherein the contact elements include contact elements of a first type and contact elements of a second type, wherein the contact elements of the first type are electrically isolated from the conductive body and the contact elements of the second type are electrically coupled to the conductive body.

16. The test socket of claim 1 wherein a surface of the conductive body adjacent at least a portion of the through holes is coated with a material having a conductivity that is higher than that of the conductive body.

17. The test socket of claim 1 wherein the contact elements include contact elements of different sizes.

18. A test socket for testing an electronic component, the test socket comprising: I

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a conductive body defining a plurality of through holes; and

a plurality of contact elements, each of the contact elements extending at least partially through a respective one of the through holes, the contact elements including contact elements of (1) a first type having a first diameter, and (2) a second type having a second diameter, the first diameter and the second diameter being different from one another.

19. The test socket of claim 18 further comprising at least one retainer defining a plurality of retainer holes therein, the at least one retainer being positioned adjacent the conductive body such that respective ones of the plurality of through holes are aligned with corresponding ones of the plurality of retainer holes thereby defining passages through which respective ones of the plurality of contact elements are configured to extend, the at least one retainer being configured to at least partially retain the contact elements within the test socket.

20. The test socket of claim 19 wherein the at least one retainer includes a first retainer and a second retainer, the conductive body being positioned between the first retainer and the second retainer.

21. The test socket of claim 20 wherein each of the first retainer and the second retainer is formed of an electrically insulative material.

22. The test socket of claim 19 wherein the at least one retainer is formed of an electrically conductive material.

23. The test socket of claim 18 wherein gaps are defined between (1) at least a portion of the contact elements, and (2) corresponding surfaces of the conductive body adjacent the respective through holes.

24. The test socket of claim 18 wherein the gaps are sized to control a characteristic impedance of the test socket.

25. The test socket of claim 18 wherein at least a portion of the contact elements are in electrical contact with the conductive body.

26. The test socket of claim 18 further comprising insulative bushings positioned adjacent a portion of the through holes to electrically isolate a corresponding portion of the contact elements from the conductive body. I

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27. The test socket of claim 18 wherein the contact elements include contact elements of a first type and contact elements of a second type, wherein the contact elements of the first type are electrically isolated from the conductive body and the contact elements of the second type are electrically coupled to the conductive body.

28. The test socket of claim 18 wherein a surface of the conductive body adjacent at least a portion of the through holes is coated with a material having a conductivity that is higher than that of the conductive body.

29. A method of assembling a test socket, the method comprising the steps of:

mounting an alignment fixture to a conductive body to align an array of holes of the alignment fixture with an array of through holes of the conductive body; and

inserting an array of contact elements into respective, selected through holes of the conductive body such that a projecting portion of each of the array of contact elements protrudes into a respective hole of the alignment fixture.

30. The method of claim 29 further comprising the step of inserting a respective insulated bushing into a respective, selected through hole of the conductive body prior to inserting the corresponding contact element into the respective, selected through hole.

31. The method of claim 29 further comprising the step of aligning a conductive retainer to the conductive body by inserting the array of contact elements into respective, selected retainer holes of the conductive retainer.