WO1989002664A1 - Interconnection system - Google Patents

Abstract

An interconnection system is described for interconnecting two circuit carrying elements such as printed circuit boards, substrates, carriers and the like. The basic connecting device is an elastomeric insert (252) having wire strands around three sides which is supported in a slot (250) in a rigid frame (238), itself adapted to be secured between the two circuit carrying elements with the wires in contact with conductive circuit elements (260) (pads or tracks) on the two separate elements. The frame is secured in position relative to the two elements by means of studs (246, 248) which are secured in and extend perpendicularly from one of the elements. The protruding ends of the studs are threaded to receive nuts for securing the assembly together. The corners and where necessary the side edges of the frame are cutaway to accommodate the studs (246, 248) and the slots (250, 256) are located out of alignment with the cutaway regions so that if required the slots can extend over a distance which is greater in length than the distance between adjacent studs.

Description

Title: Interconnection System

DESCRIPTION

Field of Invention

This invention concerns interconnecting devices by which, a plurality of electrical interconnec ions may be made between two circuit carrying elements, and having a plurality of electrical conductive traces. The invention is of particular application in 'the field of interconnecting one printed circuit board to ano her or carrier mounted components such as integrated circuits, to a printed circuit board.

The reference to circuits herein includes both passive and active circuits and may include merely one or more conductive tracks on a circuit board.

Background to the invention

With the trend towards smaller and more sophisticated components and assemblies in the electronics industry, a demand has been generated for reliable but small scale electrical connectors. Many attempts have been made to solve this problem and in an article in ELECTRONICS of May 3rd 1984 pages 135 to 136 there is described a compression contact connector for interconnecting a 132 pin leadless chip carrier to a printed circuit board. The connector employs elastomer devices each located in a slot in one of the sides of a square frame which is adapted to sit on the circuit board. The frame is secured to the board by screws which extend through an upper pressure plate, and the frame and the board are secured to an underlying stiffener. The chip carrier is sandwiched between the frame and the pressure plate and is electrically connected to the board via conductive tracks on the elastomeric devices. Compression of the latter is obtained by tightening the screws.

Likewise U.S. Patent 4593961 illustrates an electrical compression connector particularly appropriate for interconnecting two sets of electrical traces one set on a printed circuit board and the other set on a chip ^* carrier. , .

The devices described in the aforementioned references are essentially designed to enable a multiple pin leadless chip carrier to be connected to a printed circuit board. No attempt has been made to design the frame in which the elastomer elements are located in such a way as to enable not only a variety of differently shaped and sized frames to be located on a printed circuit board but also to allow for high packing, density where a number of frames are to be located on a single printed circuit board.

Additionally neither of the prior art references deals with the possibility of stacking circuit carrying elements one above the other and providing for multiway interconnectio .

It is, therefore, an object of the present invention to provide an improved multiway compression connector for interconnecting conductive tracks or pads on parallel circuit carrying elements e.g. printed circuit boards, substrates, carriers or the like.

Summary of the Invention

According to the present invention in a compression connector of the type comprising an elongate frame having slots therein which is sandwiched between circuit carrying elements and which contain elastomeric inserts bearing a plurality of conductive tracks for interconnecting conductive regions on the two circuit carrying elements, the external wall of the frame is cutaway to accommodate joining devices for securing the frame between the two circuit carrying elements.

The cutaway regions are preferably formed in external corners of the frame out of alignment with the slots.

The invention allows two frames to abut either along their length or at a corner without increasing the number of joining devices required at junctions where they abut.

The invention also permits a slot to be longer in extent than the distance between two joining members.

Neither of these features has hitherto been possible since the known insert containing frames have included circular holes through their corners, through which securing pins or studs have extended, for securing the frames to the printed circuit board and ot er backing members, and the slots for retaining the inserts have extended between the holes and in alignment therewith, so that the maximum length of a slot has been determined by the spacing between adjoining holes.

Preferably the conductive elements on the elastomeric inserts comprise spaced apart lengths of conductive wire typically formed from or at least coated with gold or other previous metal. i i A key may be provided to prevent one circuit carrying element from being placed incorrectly relative to another by providing a protruding lug for example at one corner or along one of the edges of the frame and an appropriate cutout in the corner or edge region of the said one element. Only when the said one element is correctly aligned with the protruding lug so that the latter can engage the cutout is the said one element capable of being fitted into the frame.

According to a preferred feature of the invention the joining members comprise elongate circular, section studs one end of each of which is secured to a first circuit carrying element and the opposite ends of which are threaded to receive nuts or the like for securing a second circuit carrying element and backing plate thereto.

Where it is desired .that the securing studs are located at a regular pitch in rows and columns, and the frame size is such that it will encompass three or more studs, cutaway regions are preferably provided at appropriate intervals along the length of each side wall which extends by more than the said pitch.

Conveniently a cutaway region in the side wall of a frame is semicircular in cross section, with a radius of curvature equal to half the diameter of a stud.

At the corners of the frame the cutaway regions comprise quadrant^' section cutaways, again of similar radius, so that where appropriate,, four frame members can be located about a single stud with the four cutaways cooperating to embrace the stud. j i

According to a preferred feature of the invention, the circuit carrying element to which the frame is to be attached, is provided with a regular array of equally spaced apart studs on a square matrix having a constant pitch and the frames are of standard size just corresponding to the pitch between two studs or a whole number multiple of the stud pitch.

According to another preferred feature of the invention, each frame is preferably in the form of a square or rectangle in which the minimum size corresponds to the spacing between four adjoining studs and the maximum size is comme.nsurate with the size of the circuit carrying element on which it is to be mounted.

The frames may simply provide interconnection between conductive elements on opposed faces of two parallel spaced apart carrying elements such. as, printed circuit boards, or may provide multiple connections between for example a mother-board and a smaller element which may, for example, be a chip carrier on which one or more integrated circuits or other devices are mounted and which require multiple connections to the mother-board.

Preferably the frame includes upstanding lugs at least at the corners thereof and the smaller circuit carrying element is demensioned so as to just fit within the lugs.

Where integrated circuits are mounted on a circuit carrying element, the latter is often referred to as a substrate .

Considerable heat may be generated and to this end a thermally conductive heat dissipating plate is conveniently provided to overlie the substrate or substrates and conduct heat away.

Transfer of heat may be assisted by locating pads of thermally conductive material on the rear surface of each substrate, to make contact with the heat dissipating plate .

Preferably a heat sink is provided for example along one edge region of the conductive heat dissipating plate.

In the case of a double sided motherboard, having conductive tracks formed on both faces, the studs may extend from both faces of the board so as to allow an assembly of frames and substrates (and if required, heat dissipating plates), to be mounted on both faces of the motherboard.

Two or more substrates may be mounted one above another with an appropriate frame or frames sandwiched between the motherboard and the substrates, and between one substrate and the next .

By using frames of half height when one substrate is to be mounted above another, the overall height of the double substrate mounting may be kept the same as a single substrate mounting. In this event, half height resiliently deformable inserts must also be provided for use with the half height frames. Where two substrates are to be mounted one above the other in one region of a motherboard and only one substrate in another region, frames of half height may be used to advantage for mounting the two substrates one above the other.

The frames are preferably formed from injection moulded plastics material.

Typically the slots are of standard length and extend between stud positions along the length of each frame, and the resiliently deformable inserts are also of standard length for fitting within standard size slots. However, the invention allows longer slots to be employed and correspondingly longer resiliently deformable inserts without any substantial weakening of the frame, since the latter can still be secured by studs at each appropriate position along it's length.

The circuit carrying elements to which the invention can be applied may be single sided, or double sided or multilayer boards, with through hole connections between tracks on one side and the other, where required.

The invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 is a diagrammatical illustration showing how a substrate can be interconnected to conductive tracks on a printed circuit mother-board by means of a wire on elastomer (WOE) insert,

Figure 2 illustrates a square frame assembly into which WOE inserts can be slotted and which provides corner support and location for a square substrate with the frame mounted on a printed circuit mother-board,

Figure 3 illustrates an arrangement of two different frames on a mother-board,

Figure 4 shows an 'L' shaped substrate adapted for fitting to the frame arrangement of Figure 3,

Figure 5 is an exploded side view of an assembly of parts which enable a number of substrates to be mounted side by side on a motherboard, with provision for heat dissipation,

Figure 6 is a side view of the assembly of side by side substrates and a motherboard of Figure 5,

Figure 7 is an exploded perspective view showing four different substrates mounted on a single printed circuit board in accordance with the invention,

Figure 8 shows how two substrates can be mounted one above the other using interconnecting compression connectors in support frames in accordance with the invention,

Figure 9 illustrates an arrangement in which a double sided mother-board provides support for a stack of four substrates two on one face and two on the other face, again interconnected by means of compression connectors in accordance with the invention,

Figure 10 is a side view partly in cross section through the assembly of parts shown in Figure 7,

Figure 11 is a side view partly in cross section, and partly cutaway, of the assembly of parts shown in Figure 8

Figure 12 is a side view again partly in cross section and partly cutaway, of the assembly of parts shown in Figure 9, and

Figure 13 is a plan view to an enlarged scale showing how three compression contact retaining frames can cooperate in close juxtaposition on a printed circuit board, using single stud fixing, in accordance with the invention.

Referring to the drawings, Figures 1 and 2 illustrate how compression contact elements can be used to make electrical connection between a mother-board and a substrate.

Referring in particular to Figure 1, the motherboard shown at 10 contains a plurality of electrically conductive tracks such as 12, 14 and 16. A substrate 18 bearing, for example, one or more integrated circuits contains similar tracks or conductive pads on it's underside, which correspond in position to the conductive tracks 12, 14, 16 but cannot be seen in the perspective view of Figure 1.

Electrical connection between the hidden pads on substrate 18 and the tracks on the otherrboard is achieved by means of conductive filaments or wires, of which one is shown at 20, which extend three parts around an elongate rectilinear block of elastomeric material 22.'- The wires 20 are separated laterally one from another so that each represents a single conductive path around the elastomeric block.

When sandwiched between the conductive tracks on the mother-board 10 and the pads on substrate 18, wires which are in alignment with conductive pads above tracks and below, provide an electrical path between the pads and the tracks, and those wires which align with gaps between conductive tracks on the mother-board (or pads on the substrate 18) serve no purpose as far as interconnection is concerned.

The elastomeric block 22 must be held in position relative to the printed circuit board and substrate and to this end a frame is provided such as shown at 24 in Figure 2, having four slots 26, 28, 30, 32 into which elastomeric blocks such as 22 can be fitted. The height of the walls of the frame is selected to be a little less than the corresponding dimension of the block 22, so that the latter will protrude above and below a slot into which it is inserted.

To facilitate assembly, the blocks are dimensioned width wise so as to be a snug fit in a slot, so that if one or more blocks have been inserted into the slots and the frame 24 is lifted, the blocks do not fall out of the slots.

The corners of the frame 24 protrude upwardly and downwardly below .the general upper and lower faces of the frame, the upward protrusions such as 34 having corner cutouts to receive the corners of a substrate (not shown) such as 18, which is dimensioned so as to be a snug fit within the four corners so defined. The cutaway region is denoted by reference numeral 36 in the upstanding protrusion 34 and it will be noted that each of the cutout regions such as 36 only extends over one half the width of the cooperating slots such as 28, 30.

Where it is important a the substrate such as 18 can only be inserted in one particular orientation relative to the frame, the latter is provided with a key to prevent incorrect insertion of a substrate. The simplest form 'of key is shown in Figure 2 where the corner upstand 38 is not cutaway as at 36 but instead protrudes so as to define an inwardly directed corner 40. By cutting away the appropriate corner of the substrate which is to be inserted into the frame, so as to just accommodate the inwardly directed corner 40, so the substrate is prevented from being inserted into the frame except with the cutout corner in alignment with the inwardly directed corner 40.

As previously mentioned the corner regions of the frame extend in a downward direction as well as in an upward direction relative to the side wall containing the slots, so as to form feet, as at 42.

In accordance with the invention, the external corners of the frame are cutaway as at 44 to define a concave curved recess- The radius and extent of the recess 44 is such that if four frames such as 24 were positioned so as to define a square, the four concave recesses 44 at the centre would define a circular aperture.

The provision of the concave recesses 44 allows close juxtaposition of frames on a printed circuit board as is best seen in Figure 3 where a large rectangular frame 46 having eight slots, one of which is denoted by reference numeral 48, is shown butted up against a square frame 50 which contains only four slots, one of which is denoted by reference numeral 52, one along each side.

For simplicity the larger frame is referred to as a 2 x 3 frame and the small square frame a 1 x 1 frame.

Studs 54, 56,58 and 60 secure the l x l frame 50 in position and two of the studs, 54 and 56 additionally co¬ operate with other studs 62, 64, 66, 68, 70, 72, 74, and 76 to secure the 2 3 frame in position. It will be seen that there, is no waste space between frames which can therefore be butted in close relationship, and other frames may, if desired, be butted against either the 2 x 3 or the l l frame at any convenient position as required, using two or more of the bolts already in place, as common fixing points.

This feature represents a great advantage when attempting to achieve the maximum number of connections to tracks on printed circuit boards and substrates.

The two frames 46 and 50 shown in Figure 3 can be used to support and interconnect to two separate substrates, a small square one fitting within the frame 50 and a rectangular one fitting within the frame 46.

Alternatively an 'L' shaped substrate such as shown in Figure 4 at 78, may be fitted over the two frames.

The purpose of Figure 3 is to show how a system using a small number of basic shaped frames such as square frames and rectangular "frames, can be used to conform to many different shapes of substrate and/or mother-board.

Figure 5 shows by way of an exploded elevation the various component parts of a completed assembly in which is shown in it's assembled form in Figure 6.

The printed circuit board or mother-board 80 is provided with upstanding studs or pillars such as 82 which have enlarged heads 84 and are bonded through the board 80 so as to protrude in a fixed and rigid manner above the surface bearing the tracks which are to be interconnected with substrates. The upper end of each pillar is threaded at 86 to receive a nut or like securing member.

A number of different frames 88, 90, 92, and 94 are shown which can be fitted to the board 80 by fitting the frames between the appropriate pillars. The concave recess 96 (corresponding to the recess 44 of Figure 2) is shown at the left hand end of frame 88 whilst a similar concave cutaway is shown at 98 at the opposite corner. Similar cutaways are provided on all of the other frames with the exception of 92 where semicircular section cutaways are provided half way along the longer dimension of the frame as at 100.

Blocks of elastomeric material are shown at 102, 104, 106, 108 and 110 respectively, each of the blocks being covered on three sides by means of wires such as 112. The wires are only shown over part of the length of each of the blocks 104 to 110 but in practice each of the blocks will be covered fully with the wires as is 102.

The blocks fit into slots of which one is shown in hidden detail at 114 in frame 88.

Although not shown, additional elements may be provided for fitting into other slots in other sides of the frames 88, 90 etc., not visible in Figure 5.

The substrates designed to fit into the frame 88 etc., are shown at 116, 118, 120 and 122. It will be seen that the substrate 120 is double size and fits in the double size frame 92. Components such as 124 and 126 (see substrate 116) extend downwardly from the substrates, and tracks for making connection with the wire interconnections 112 extend in the underside surface of the substrate, away from the devices 124, 126 etc.

All electrical connections and tracks are provided on the underside of each substrate, so that the upper surface 128 of each substrate is component and electrical connection f ee.

A final element making up the assembly is a heat dissipting plate 130 typically of metal which is fitted over the substrates and rests on the corners of each of the frames so that when secured in position by tightening nuts threaded on the threaded ends such as 86 of the pillars 82, the heat plane is brought into intimate contact with the substrates but does not crush them. A compressible sheet of thermally conductive material may be located between the plate 130 and each substrate to improve heat transfer.

A heat dissipating member may be provided at one or both ends as at 132, and appropriate concave recesses 134 are provided in the corners and along the face of the element to cooperate with the line of pillars of which 136 can be seen in Figures 5.

The final completed assembly is shown in Figure 6 where nuts such as 138 have been threaded onto the protruding threaded ends of the pillars 82, and tightened so as to hold the assembly together.

It will be seen from Figure 6 that all the components are now totally protected by the walls of the frames and only the edges of the substrate are visible between the upstanding corners of the frame.

Figure 7 illustrates, by way of an exploded perspective view, the component parts of one embodiment, in which a substrates in a single plane are to be interconnected to a mother-board. The latter is denoted by reference numeral 140 and the board is generally covered with lines of spaced conductive pads, one line of which is denoted by reference numeral 142. The lines are arranged in square arrays between a rectilinear matrix of apertures such as 144, into which pillars such as 146 can be inserted and bonded.

The pads are of half width around the outside of the mother-board 140 but are of double width as at 148 at all intermediate positions within the board.

Four different holders or frames as they have been described hitherto, are arranged to be carried by the mother-board. These comprise a large 4 4 frame 150, a smaller square 2 x-2 frame 152 a smaller rectangular 2 x 1 frame 154 and the smallest frame which can be fitted namely a 1 x 1 frame, 156.

Pillars are provided through all of the holes which register with a cutaway at a corner or along the side of a frame, and elastomeric blocks coated with conductive wires as denoted by reference numeral 158 are inserted into the slots 160 in the frames.

A 4 x 4 substrate 162 a 2 x 2 substrate 164 a 2 x 1 substrate 166 and a square l x l substrate 168 are fitted over the respective frames 150 etc., so that the conductive pads on the undersides of the substrates mak'e contact with the wires on the elastomeric blocks 158 and thereby the conductive pads of the lines of pads such as 142 and 148 on the mother-board 140.

A heat dissipating plate 170 is fitted over the substrate and heat dissipating pads as at 172, 174, 176 and 178 ensure good thermal transfer between the substrates and the plate 170.

A heat sink 180 is fitted between the protruding edge of the plate 170 and a protruding edge of the mother-board 140 by means of fixing screws such as 182 secured through additional holes in the heat plate such as 184.

One of the nuts which is used to secure the heat plate and remainder of assembly in place by being threaded and tightened over the protruding threaded ends of the pillars 146 is denoted by reference 186.

Figure 8 is similar to Figure 7 but illustrates a mother¬ board 189 and the use of half height frames at 188 and 190 with intermediate substrates 192 sandwiched between the two frames and a further upper layer of substrates 194 fitted to the upper layer of frame 190.

As in Figure 7, a heat dissipating plate 196 is fitted over the upper substrates and heat pads such as shown at 198 are provided to ensure good heat dissipation between the substrates 194 and the heat dissipating plate 196. A heat sink 200 is provided as previously described.

Figure 9 illustrates a more complex arrangement in which a double sided mother-board is employed and sandwiched substrates are mounted on both sides of the mother-board. The double sided mother-board is shown at 202 and a first set of half height frames are shown at 204 with substrates at 206, with the tracks on the underside and track pads on both sides. A second layer of half height frames 208 is fitted over the substrates 206 and because of the track pads on both sides of the substrates 206, the wire on elastomeric elements 210 interconnect the mother-board through the substrates 206 to the substrates 212 which are mounted above the second deck of half height frames 208. A heat dissipating jplate 240 completes the upper part of the assembly.

The above is mirrored below the mother-board 202 and to this end two layers of half height frames 216 and 218 are mounted on the underside of the mother-board 202 with two sets of substrates 220 and 222 carried thereon. In this case the tracks and components are mounted on the upper side of the substrates 220 but track pads are provided on boths sides so as to provide for comminication between the mother-board and the wire on elastomeric element 224 located in the lower frames 218, and thereby to the substrates 222.

Heat pads such as 225 serve to communicate heat -from the substrates 222 to a heat dissipating plate 226.

Double ended pillars such as 228 are secured in appropriate holes in the mother-board 202, and the assemblies on opposite sides of the mother-board are secured in place by means of nuts (preferably NYLOC nuts) .

Figure 10 shows the: assembly of the parts shown in Figure 7 in end view.

The possible position for an edge connector is shown at 230. Otherwise the same reference numerals are used as in Figure 7. Figure 11 shows how by using half height frames, two layers of substrates can be fitted in the same height as the j single layer of Figure 7. In this regard Figure 11 is an end view of the assembly of the parts shown in Figure 8 and{again a typical edge connector position is shown at 2321

The same reference numerals are other wise used as were used in Figure 8.

Figure 12 shows the end view of the assembly of parts shown in Figure 9 and indicates how four substrates are mounted on either side of a double sided mother-board. A double sided edge connector is shown at 234 and otherwise the same reference numerals are used as have been employed in Figure 9, with the exception of the heat sink 236 which is not shown in Figure 9.

Figure 13 illustrates to an enlarged scale the relation¬ ship between the slots and the external pillar or stud receiving recesses. The top left hand corner of a frame 238 is shown bounded on two sides by two other frames 240 and 242, and pillars 244, 246 and 248 serve as supports for all three frames. Slots such as 250 contain wire on elastomeric blocks 252 but because of the spacing between the slots 250 and the recesses, one of which is shown at 254, a longer slot and consequently longer elastomeric insert may be inserted as shown at 256. In the longer slot, a double or triple length elastomeric element 258' can be fitted.

Conductive pads can be seen on the mother-board where the frames 238 and 242 have been cutaway and one of these is denoted by reference numeral 260.

Claims

1. In a compression connector of the type comprising an elongate frame having slots therein which is sandwiched between circuit carrying elements and which contains elastomeric inserts bearing a plurality of conductive tracks for interconnecting conductive regions on the two circu.it carrying elements, the external wall of the frame is cutaway to accommodate joining devices for securing the frame between the two circuit carrying elements.

2. A compression connector as claimed in claim 1 in which the cutaway regions are formed in external corners of the frame out of alignment with -the slots.

3. A compression connector as claimed in claim 1 in which the conductive elements on the elastomeric inserts comprise spaced apart lengths of conductive wire.

4. A compression connector as claimed in claim 1 in which a key is provided to prevent one circuit carrying element from being positioned incorrectly relative to another.

5. A compression connector as claimed in claim 1 in which the joining members comprise elongate circular section studs one end of each of which is secured to a first circuit carrying element and the opposite ends of which are threaded to receive threaded securing members for securing a second circuit carrying element thereto.

6. A compression connector as claimed in claim 5 wherein the corner cutaways are of quadrant section of radius equal to half the diameter of the studs, so that where appropriate, four frames can be located about a single stud with the four cutaways cooperating to embrace the stud.

7. A compression connector as claimed in claim 5 for interconnecting to circuit carrying elements on one of which the securing studs are located at a regular pitch in rows and columns, and wherein the frame size is such that it will encompass three or more studs, along a row or columns, the external face of the side wall of the frame is cutaway at appropriate intervals along its length to accommodate any intermediate studs.

8. A compression connector as claimed in claim 7 wherein a cutaway in ^"the side, wall of the frame is semi-circular in cross section, with a radius of curvature equal to half the diameter of a stud.

9. A compression connector ^"as claimed in claim 1 wherein the circuit carrying element to which the frame is to be attached-, is provided with a regular array of equally spaced apart studs on a square matrix having a constant pitch and the frames are of differing standard size having sides of length corresponding to a whole number multiple of the stud pitch.

10. A compression connector as claimed in claim 1 wherein the frame includes upstanding lugs at least at the corners thereof and one of the circuit carrying elements is demensioned so as to just fit within the lugs'.

11. A compression connector as claimed in claim 5 wherein - 23 - the studs extend from both faces of the said first circuit carrying element so as to allow an assembly of frames and substrates to be mounted on both faces thereof.

12. A compression connector as claimed in claim 1 wherein three elements are mounted one above another with a frame sandwiched between a first circuit carrying element and the second element and another similar frame sandwiched between the latter and the third element.

13. A compression connector as claimed in claim 13 wherein frames of half height are employed when three circuit carrying elements are to be interconnected by mounting one above the other, so that the overall height of the sandwich is kept the same as that wher.e only two elements are involved element and half height elastomeric inserts are provided for use with the half height frames.

14. A compression connector as claimed in claim 1 wherein the slots are of standard length and the elastomeric inserts are also of standard length for fitting within the standard size slots.

15. A compression connector as claimed in claim 1 wherein the lengthwise extent ^' of a slot is greater than the spacing between two. adjacent joining positions when measured parallel to the side of the frame containing the slot and the cutaways for accommodating the joining devices.

16. Compression connectors conducted arranged and adapted to operate substantially as herein described with reference to the accompanying drawings.