GB2120466A - Printed circuit board connector - Google Patents

Abstract

A printed circuit board connector includes a thermoplastic body (14,15) having two extended generally parallel jaws (18,19), at least one of which contains a plurality of laterally spaced conductive leaf springs (20,21,22, 23) in an arrangement congruent with a corresponding plurality of circuit traces (12, 13) at the edge of a circuit board (11) to which it is desired to make electrical connections. A U- shaped metal return spring (24) biases the jaws towards each other, this spring bias serving to provide a compressive clamping force against the circuit board. A linear cam or plunger (25) slides within the U- shaped spring to prise it open for zero- insertion force connection to the circuit board, that is, with little or no sliding friction. Once in place, the linear cam or plunger is moved outwardly, permitting the U-shaped spring to bring the noses at the extremity of the jaws into a compressive grip against the circuit board. The elongated conductive strips within at least one of the jaws overtravel resiliently when jaw contact is made and thereby exert a contact force against the circuit board traces which is substantially independent of circuit board thickness variations. <IMAGE>

Description

SPECIFICATION Printed circuit board connector This invention relates to printed circuit board connectors and in particular to multi conductor electrical connectors for use with electronic circuit boards.

It is well known in the art that substantial force is required to insert a printed circuit board into a connector having a large number of spring contacts therein, due to the resilient engaging force of the contacts with the edge of the board.

As the number of contacts is increased in a connector, the amount of force required to insert the printed circuit board into the connector, or to withdraw it from the connector, may become excessive for practical use. In addition, direct insertion of boards into connectors having spring contacts therein results in a heavy wiping action occurring between the contacts and the conductive traces on the edge of the board, which may cause excessive wear of the traces over lengthy periods of use of the connector. It is, therefore, a common practice in the art to provide a "zero insertion force" printed circuit board connector in which the contacts are mounted out of the path of movement of the board when it is inserted into the connector whereby little or no resistance is encountered upon inserting the board thereinto.

There are two general types of zero insertion force connectors, one in which the contacts are normally closed and the other in which the contacts are normally open. In the case of a connector having normally open contacts, the contacts are normally unloaded (that is, no stresses are applied to the contacts) and the contacts are calmed against the printed circuit board. In a connector having normally closed contacts, the contacts are preloaded in the connector housing in a position to engage resiliently a printed circuit board mounted therein and a cam actuator is provided for retracting the contracts away from the standard engagement position so that a board may be inserted into the housing with zero insertion force.

U.S. Patent Nos. 3,899,234 and 3,963,317 disclose normaily-closed contact-type zero insertion force printed circuit board connectors in which the cam-actuating mechanism for retracting the two rows of contacts in each connector is disposed between the two rows. This arrangement has the disadvantage that it necessarily requires that the two rows of contacts be spaced apart a greater distance than would otherwise be required if the actuator were not employed.

U.S. Patent Nos. 3,537,063 and 3,818,419 also disclose normaliy-closed contact-type zero insertion force printed circuit board connectors, but in these connectors the cam actuators are not disposed between the two rows of contacts therein thus permitting a closer spacing between the two rows of contacts in the connectors.

However, the cam-actuating mechanism in U.S. Patent No. 3,537,063 comprises two rotatable cam shafts which act independently and are subject to high torsional forces, which does not permit uniform actuation of the contacts. The connector disclosed in U.S. Patent No. 3,818,419 has the disadvantage that the cam-actuating mechanism moves laterally thereby necessitating a relatively wide connector housing. Another prior connector of interest is disclosed in our U.S.

Patent No. 4,050,758.

Another more recent zero insertion force connector of the normally-closed contact-type is described in our U.S. Patent No. 4,159,861.

Although relatively successful, this latter device and all of the other prior art devices of which the aforementioned are typical, tend to provide connector contact pressure against the edge board traces which are not independent of the circuit board thickness. Due to printed circuit board thickness variations, both intentional and due to manufacturing tolerances, prior art edge board connectors utilise contacts which must take into consideration those variations and are therefore compromised in design. This is because effective contact normal force to be achieved for reliable electrical interface at a minimum circuit board thickness is necessarily higher for circuit boards of greater thickness.The design compromise results from the need to provide the aforementioned reliable electrical interface without making the insertion forces unduly high for thicker boards with the attendant hazard of board damage.

It is an object of the invention to deal with the prior art disadvantage by providing a zero insertion force edge board connector in which the electrical contact interface is virtually independent of circuit board thickness variations within a reasonable range.

According to the invention in its broadest aspect, there is provided a zero insertion force, clamp on, board connector for a printed circuit board including at least one conductive trace accessible adjacent an edge of the board and comprising an insulating body having a pair of resilient opposing jaws extending therefrom for clamping on to the circuit board, first means comprising at least one elongated leaf spring contact member having a cantilevered outward end within at least one of the jaws for contacting a corresponding conductive trace of the circuit board when the jaws are clamped on to the circuit board, the spring contact projecting resiliently from the jaw toward the opposing jaw by a predetermined amount in a first condition when the connector is not clamped to the board, second means for deflecting the jaws toward each other to clamp on to the circuit board with a first predetermined compressive force, and third means comprising an overtravel space within each of the jaws corresponding to each of the first means spring contact members, whereby each of the contact springs bears on the corresponding one of the conductive traces with a second compressive force as a function substantially only of the spring characteristic of the first means and independent of the first compressive force.

The device according to the invention eliminates printed circuit board tolerance problems by articulating the housing in such a way that the actual printed circuit board surface becomes a datum for contact deflection. The ends of the housing jaws which are brought into compressive contact with the circuit board are independent of the contact member leaf spring deflection. The leaf springs always overtravel by the same amount regardiess of the spacing variations between opposing jaw member nose portions during the compressive engagement. The overtravel deflection of the leaf spring contacts provides a small amount of longitudinal wiping action as the said overtravel occurs.

The housing itself comprises a base portion of thermoplastic material and two jaw members extending therefrom, these jaw members being articulated or "live hinged". In an initial position, these jaws are open by an amount sufficient to provide the zero force insertion of the connector jaws over the accessible circuit board edge.

The apparatus according to the invention originated from a requirement for a test probe connector for electronic systems checkout; however, the invention is also applicable in other zero insertion force edge board connector applications including front- or side- board entry configurations.

Another object of the present invention is to provide a zero insertion force connector as aforementioned, which is immune to the design compromises necessary in prior art devices of the type because of circuit board variations or tolerances.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a pictorial representation of a connector according to the invention with jaws open (initial condition) showing a vestigial portion of a circuit board to which it is to be mated; Fig. 2 is a plan view of the connector of Fig. 1; Fig. 3 is a sectional view of one of the two connector body halves taken as indicated in Fig. 2; Fig. 4 is a section taken through the connector assembly of Fig. 1 in the initial condition; Fig. 5 is a section taken as in Fig. 4 except that the connector is shown mated in compressive relationship to the thicker of two alternative corresponding circuit boards;; Fig. 6a is a plan view of the actuating member (plunger) of Figs.1,4 and 5; Fig. sub is an end view of the actuating member of Fig. 6a; Fig. sic is a cross-sectional view of the actuator of Fig. 6a, taken as indicated on Fig. Sb: Fig. 7a is an end view of the resilient biasing spring shown in Figs.1,4 and 5, in its open condition; Fig. 7b is a cross-section of Fig. 7a, also illustrating open and closed conditions of the biasing spring; Fig, 8 is a cross-section of a typical contact leaf spring from a jaw of Figs. 1, 4 or 5.

Referring firstly to Fig. 1, a typical connector according to the invention is shown generally at 10, poised for connection with the representative circuit board 11, shown in vestigial form. The circuit board 11 includes a plurality of conductive traces typically 12 and 1 3 on at least one face thereof, but since the leaf spring contacts of the connector 10 are shown in both jaws 18 and 19, it may be presumed that the circuit board 11 also includes conductive traces on its bottom side, not visible from the illustration.

The body of connector 10 comprises a pair of facing halves 14 and 15 which may be identical parts turned essentially to "face" each other. It is not strictly necessary that these body halves 14 and 1 5 be identical parts, but from the point of view of manufacturing economy and basic symmetry of the device, such identity is highly desirable.

The structure illustrated at 16 and 1 7 affords alignment in that the bore in 1 6 and 17 can pass over corresponding posts fixed with respect to the structure supporting the circuit board 11.

Although a number of options are available as to the method of securing the connector body halves 14 and 15 to each other, it will be seen to be possible to associate this assembly step with the structure of 16 and 1 7. The body halves 14 and 15, including the extended jaw portions 18 and 19, respectively, are formed of resilient thermoplastic material and can be joined at 34 by means of a suitable adhesive.

The jaw portions 18 and 19 may be formed so as to be mechanically biased toward each other in the absence of other influences, or the gripping action required of these jaws against the circuit board 11 may be affected entirely through a spring clip 24, this spring clip being shown by itself in Figs. 7a and 7b. In Fig. 7a, the view of spring clip 24 is as it would be looking normally into the connector between jaws 1 8 and 19 and ignoring the presence of the actuating member (plunger) 25. The central slot 29 in the bend of the spring clip shown in both Figs. 7a and 7b permits the stem 28 to pass through to the rear of the connector as illustrated in Fig. 1. This stem 28 provides actuation between the initial condition illustrated in Figs. 1 and 4, and the locked-on or engaged condition represented in Fig. 5. The sectional views of Figs. 4 and 5 will be described in more detail hereinafter.

From Fig. 7b, it will be understood that the spring clip 24 is constructed to have a quiescent position where the outward ends are together or nearly so, as illustrated at 24a. Where these ends are laterally outwardly-spaced as at 24b and as shown in Fig. 1, the jaws 18 and 19 are open or in an initial condition pursuant to the positioning of the actuating member 25. This actuating member 25 is shown in detail in Figs. 6a, 6b and 6c, and from these figures it can be seen to be a form of linear or sliding cam member which can prise open the spring clip 24 as in Fig. 1 or permit clip 24 to pull the jaws 18 and 1 9 resiliently toward each other at their outward extremities.Typical spring clip gripping fingers 26 and 27 are shown in the lower jaw 1 9, and it is to be understood that similar gripping fingers would be employed in the upper jaw 18. These gripping fingers will be seen to operate to transfer the inwardly directed force of the spring clip 24 to the jaws themselves, producing a relatively uniform compression force between the jaws and the board in the mated or engaged condition. The articulation of the thermoplastic body members 14 and 1 5 occurs generally about a line 33 as illustrated in Fig. 1 for the upper jaw 1 8 and in a similar location for the lower jaw 1 9.

In Figs. 1 and 2, four of the leaf spring contact members are arbitrarily identified as 20, 21,22 and 23. All of these contact members are of substantially the same shape with alternate ones having slightly greater length in order to produce staggered connection loops such as illustrated at 22b and 23b on Fig. 1. These loops would normally project through eyelets in an overlaying planar member for the purpose of effecting conventional electrical connection to a wire harness or the like.

Each of the leaf spring contact members has a shape shown in more detail in the cross-section of Fig. 8, with "hooked back" end loops such as 21 a and 22a arbitrarily identified on Fig. 1. For the purposes of Fig. 8, the leaf spring contact member is arbitrarily identified as 31, as is the case in Figs.

4 and 4.

Fig. 8 shows a cross-section taken through a typical one of the leaf springs, for example, from left to right through one of the leaf spring contacts illustrated in Fig. 2. This typical contact leaf spring has the contact loop 31a equivalent to 22b or 23b as discussed in connection with Fig. 1 and for the same purpose. A cross-section of body member with jaw 18, as shown in Fig. 3, illustrates the general area about which the bending (articulation) occurs as discussed previously and also shows a nose 30. In Fig. 4 leaf contact spring 31 is shown in place, this illustrating being readily reconciled with Figs. 1 and 2. In Fig. 4 it will be noted that leaf spring contact 31 has a bend or inflection point 31 c from which it is deflected inwardly toward point 31c.The top end of the nose 30 catches and restrains the loop (hooked back) in 31 d, so that the point 31 IL; which is the point of electrical contact with the corresponding conductive trace on the circuit board 11 during full engagement as illustrated in Fig. 5. It will be noted that in Fig. 5 the point 31 b is automatically outwardly deflected, the spring constant of the leaf spring contact member 31 providing a predetermined contact pressure. The inside surface of the jaw 14a, shown in both Figs. 4 and 5, comes into contact with the circuit board as shown in Fig. 5.However, the contact pressure at point 31 b is only a function of this resilient deflection about point 31 c, the inside surface 1 4a of jaw 18 having established a datum plane so that the contact pressure at 316 will be seen to be independent of variations in the thickness of circuit board 11. The function of the corresponding parts within jaw 1 9 is identical. In the initial condition shown in Fig. 4, the notched surface of the actuating member (plunger) 25 permits the parts 26 to be accommodated. A typical slot for this purpose is shown at 33 in Fig.

6b.

From Figs. 6a and 6b, it will be realised that more of the finger parts 26 which capture the edge of the spring clip 24 are contemplated than are shown in Fig. 1. The showing of Fig. 1 is simplified in that respect for clarity.

Spring 32, although it is inverted vis-a-vis 31, will be understood to be an identical part.

The position of the actuating member 25 in Fig.

4 may be referred to as a first operating condition.

In Fig. 5, the position of the actuating member 25 may be referred to as the second operating position or condition in which the spring clip 24 is free to exert inwardly directed pressure from both sides. That is, the open ends of spring clip 24 attempt to assume a position such as 24a in Fig.

7b and thereby effect articulation of the thermoplastic housing as hereinbefore indicated. It is important to note that this inward jaw pressure produced by spring clip 24 does not determine the contact pressure at point 31 b, but only the compressive force of the jaw surface typically at 1 4a against the surface of circuit board 11. To reemphasise, the actual contact pressure at 316 is determined by the deflection about point 31 c of the leaf contact spring 31 (and 32, of course, in the same manner). Spring clip 24 must, of course, exert sufficient jaw-closing force to overcome the resistance of the sum of the individual contact leaf springs of both jaws up to the point of clamp-on.

Referring once again to Fig. 8, it will be noted that the point 31 b may be thought of as rotating about point 31 c as it is depressed against the circuit board conductive trace. This provides a sufficient wiping action which is generally regarded as important in making reliable electrical connections in devices of the character described.

Modifications and variations in the specific structure described could be made by those of skill in the art once the invention is understood. For one example, other cam type configurations will suggest themselves in lieu of the linearly displaced operating member 25.

Suitable materials for the various parts of the structures illustrated can readily be selected by those of skill in this art. A spring metal material such as beryllium alloy of copper might be employed for spring clip 24 and for the elongated leaf contact springs of which 31 is typical. A variety of thermoplastics suitable for the housing and jaw members is well known.

Claims (11)

1. A zero insertion force, clamp on, board connector for a printed circuit board including at least one conductive trace accessible adjacent an edge of the board and comprising an insulating body having a pair of resilient opposing jaws extending therefrom for clamping on to the circuit board, first means comprising at least one elongated leaf spring contact member having a cantilevered outward end within at least one of the jaws for contacting a corresponding conductive trace of the circuit board when the jaws are clamped on to the circuit board, the spring contact projecting resiliently from the jaw toward the opposing jaw by a predetermined amount in a first condition when the connector is not clamped to the board, second means for deflecting the jaws toward each other to clamp on to the circuit board with a first predetermined compressive force, and third means comprising an overtravel space within each of the jaws corresponding to each of the first means spring contact members, whereby each of the contact springs bears on the corresponding one of the conductive traces with a second compressive force as a function substantially only of the spring characteristic of the first means and independent of the first compressive force.

2. A connector according to claim 1 in which a stop is included within the end of the jaw for each of the spring contact members to restrain the extent of the projection of the spring contact member cantilevered end toward the opposing jaw, the cantilevered end exerting a predetermined initial spring force against the stop.

3. A connector according to claim 2 in which the contact leaf spring is so shaped that the projection in the first condition includes a slope toward the opposing jaw as the spring contact extends outwards toward the end of the jaw from a bearing point within the jaw, the bearing point acting as a fulcrum about which the outward end of the spring contact is deflected when the jaws are clamped on to the board.

4. A connector according to claim 2 or 3 in which the outward end of the spring contact includes a loop formed in a plane normal to the circuit board and oriented with the elongated dimension of the leaf spring, the portion of the loop facing the opposing jaw comprising the contact with the corresponding conductive trace, the stop engaging the inside of the loop in the first condition but not when the jaws are clamped on to the board.

5. A zero insertion force, multiple contact, printed circuit board edge connector for a printed circuit board having a plurality of conductive traces extending outwardly and spaced laterally with respect to an externally accessible edge of the board, the connector comprising a clamp-on, resilient, insulating body member having first and second opposing jaws arranged to contact corresponding opposite surfaces of the board in a distributed compressive engagement at least over the lateral extent of the board having the conductive traces, first means for resiliently biasing the jaws toward each other, an actuating member arranged to control the opening clearance of the jaws by elastically deflecting the jaws, the actuating member having first and second operating positions, the jaws being in the initial condition during the second operating condition of the actuating member and being separated by an amount at least equal to the thickness of the board during first operating condition of the actuating member, and a plurality of discrete contact leaf springs associated with at least one of the jaws, each of the springs being arranged to make discrete contact with a corresponding one of the board traces during the compressive engagement effected by the second operating condition, the leaf springs being deflected toward the opposite jaw inwardly with respect to the corresponding nose portion when the actuating member is in the first operating condition, the leaf springs being elastically deflected to produce a contact pressure against the conductive traces which is a function of the spring factor of the leaf springs and is independent of the thickness of the circuit board.

6. A connector according to claim 5 in which the leaf springs of each of the jaws are arranged to be deflected toward the other jaw and in which stop means are included for limiting the deflection of the leaf springs to a predetermined amount toward the opposite jaw when the actuating member is in its first operating condition, the stop means restraining the leaf springs at a deflection with respect to the corresponding nose portiun at which a predetermined spring force is extant against the stop means.

7. A connector according to claim 5 or 6 in which overtravel space is provided in each of the jaws having the leaf springs associated therewith such that in the compressive engagement extant during the second operating condition of the actuating means, the contact pressure between the leaf springs and the conductive traces is that produced by the elastic deformation of the leaf springs away from the stop means.

8. A connector according to claim 5 or 6 in which the jaws extend from a base portion of the body member, the body member is fabricated from resilient, insulating plastics material, and the actuating means is a linear cam device arranged to spread the jaws when moved from the second to the first operating position.

9. A connector according to claim 5 in which a U-shaped spring clip is mounted within the jaws, extends outwardly from the body member and engages the inner surfaces of the jaws at its open end, the clip providing a force tending to draw the jaws toward each other, and in which the actuating member acts against the inside surface of the clip.

10. A connector according to claim 9 in which the actuating member is a generally cylindrical plunger having a diameter substantially equal to the inside dimension of the clip at its interior extremity.

11. A zero insertion force, clamp on, board connector for a printed circuit board substantially as described with reference to the accompanying drawings.