Title:
ELECTRICAL CONNECTOR DEVICES
United States Patent 3795037
Abstract:
An electrical connector comprises a plurality of elongated flexible conductors embedded in, and extending between surface of, a block of elastomeric insulating material.
US Patent References:
Sealing and conducting gasket material
Pulsifer et al. - May 1959 - 2885459
Multiple segment array making
Gannoe - July 1968 - 3391456
Relay
Nelsen - September 1958 - 2852639
Method of brazing
Hack - October 1962 - 3056195
/3613230.html
Griff - October 1971 - 3613230
Sealing and conducting gasket material
Pulsifer et al. - May 1959 - 2885459
Multiple segment array making
Gannoe - July 1968 - 3391456
Relay
Nelsen - September 1958 - 2852639
Method of brazing
Hack - October 1962 - 3056195
/3613230.html
Griff - October 1971 - 3613230
Application Number:
05/311602
Publication Date:
03/05/1974
Filing Date:
12/11/1972
View Patent Images:
Export Citation:
Assignee:
International Computers Limited (London, EN)
Primary Class:
Other Classes:
333/260, 439/591, 174/541
International Classes:
H01R13/64; H01R43/00
Field of Search:
174/35GC,68.5 339/59M,61M 29/627,628,629,631
US Patent References:
| 3722053 | METHOD OF MAKING WELL PRESSURE SEALING CUP REINFORCING STRUCTURE | March 1973 | Berry et al. |
Primary Examiner:
Lanham, Charles W.
Assistant Examiner:
Duzan, James R.
Attorney, Agent or Firm:
Misegades, Douglas & Levy
Parent Case Data:
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is a divisional application of Ser. No. 135,674, filed Apr. 20, 1971, in Group Art Unit 353 now abandoned; and is filed under 37 C.F.R. 1.60. In the present application, applicant claims the benefits of 35 U.S.C. 120 and 121 as to the filing date of Apr. 20, 1971; and the benefits of 35 U.S.C. 119 as to the British filing date of May 5, 1970 and Sept. 23, 1970, respecting British application Nos. 21609/70 and 45196/70.
Claims:
I claim
1. A method of making an elastomeric electrical connector element comprising the steps of:
2. A method of making an electrical connector element, comprising the steps of:
1. A method of making an elastomeric electrical connector element comprising the steps of:
2. A method of making an electrical connector element, comprising the steps of:
Description:
BACKGROUND OF THE INVENTION
Field of the Invention and Cursory Prior Art
The present invention is an improvement and a departure from at least the following:
Patent Patentee Class Subclass 2,885,459 Pulsifer et al. 174 35 GC 2,967,216 Zablocki et al. 339 59 M 2,454,567 Pierson, Jr. 174 35 GC 3,324,445 Miller 339 61 M 940518/63 Burndy (Gr. Britain) 174 68.5
The invention relates to electrical connector devices.
Recent advances in micro-circuit techniques have allowed the size of individual micro-circuit elements to be significantly reduced. While a large number of circuits may be packaged in a very small volume by such techniques, a corresponding number of electrical connections must be made to such micro-circuit packages. One problem with forming such electrical connections is that the dimensions and physical tolerances of the connections to microcircuit packages are extremely small and such connections are difficult to produce by conventional techniques. Also, it is desirable that micro-circuit packages be easily replaceable and if such a micro-circuit has a large number of permanent connections to external circuitry, the time and effort to break and re-establish such electrical connections becomes extremely expensive. Thus, problems arise in replacing micro-circuit packages which are soldered to external circuits as the solder must be carefully removed from each lead or wire.
With conventional electrical components it is possible to secure electrical contact between components, many times by providing a spring made from an electrically conductive material and moulded in a suitable insulating material. Each end of such a spring is held in contact with anelectrically conducting portion of a component and when a pressure is exerted against one of the components the spring is compressed to assure an electrical connection therebetween. However, with the development with micro-circuit techniques, and the requirement of electrically connecting a large number of very small conductors on a micro-circuit device, it has been found that such spring contacts do not readily lend themselves to miniaturisation. In many cases it has become necessary to mount micro-circuit devices on subcarriers of much larger dimensions to make the devices compatible with conventional electrical connectors. This however, increases the cost of packaging and reduces many advantages of miniaturisation techniques.
SUMMARY OF THE INVENTION
According to one aspect of the invention there is provided an electrical connector comprising a plurality of elongated flexible conductive members embedded in, and each extending between surface areas of, a block of elastomeric insulating material with the extremities of the conductive members being exposed at said surface areas.
In use such a connector can provide several conductive paths between two conductors each in contact with an appropriate part of a different one of said surface areas. Conveniently, these surface areas are substantially parallel opposite faces of a slab constituting said block. Then, it is generally most useful for said appropriate parts to be in register with each other through the block. A small clamping pressure is sufficient for good contact.
Preferably, the extremities of the conductive members project from the block surface. The projection may be of a different material, e.g. an intermediate required for good bonding with a final layer of a noble metal.
According to another aspect of the invention there is provided a method of making an electrical connector using metal blanks having side rails interconnected by uniformly spaced parallel strip members, comprising the steps of making a stack of said blanks in register with each other and disposed alternately with spacer blanks of similar shape to said metal blanks but without the strip members, and filling the space between the side rails of the stack with liquid, settable elastomeric, insulating material, setting said material, and removing said side rails.
BRIEF DESCRIPTION OF THE DRAWING
A device for electrically connecting different electrical conductors embodying the present invention will now be described by way of example, with reference to the accompanying drawing which,
FIG. 1 shows a resilient member of the invention having a rectilinear configuration;
FIG. 2 shows a resilient member of the invention having a curvilinear configuration;
FIG. 3 shows resilient member of the invention embedded in an elastomeric material;
FIG. 4 shows the electrical connectors of the invention in a practical configuration;
FIG. 5 shows the resilient members as part of a frame;
FIG. 6 shows a metallic frame which serves as a temporary spacer;
FIG. 7 shows a stack comprised alternatively of elements shown in FIGS. 5 and 6;
FIG. 8 shows another connector; and
FIG. 9 shows the connector of FIG. 8 in use.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1 there is shown a resilient connector 10 of the present invention having surfaces 11 and 12 at the top and bottom of the member, respectively. Member 10 may be formed from any suitable electrically conductive resilient material such as, for example, phosphor bronze. In FIG. 2 another similar resilient member 40 is shown having opposed contact surfaces 41 and 42. The resilient members 10 and 40 having cross-sectional dimensions of the order of 25 microns and may have a free length of 2 millimeters.
A device 1 in which a plurality of resilient members 10 or 40 may be employed is shown in FIG. 3. Each resilient member 10 is embedded in an elastomeric material 21 which both physically and electrically separates each resilient member 10 from one another to form device 1. The elastomeric material 21 may be subjected to a grinding process to improve the flatness of the surface thereof and during this process the level of resilient members 10 may be reduced somewhat below that of the surface of material 21 as shown. In such cases, it may be convenient to electrolessly plate a conductive material on the opposed contact faces 11 and 12, this material being shown as contacts 13, 18, 19, 20, 22 and 23. A conductive land portion 14 of micro-circuit 15 is arranged to form an electrical connection with contacts 13, 18 and 19. Similarly, a raised conductor element 16 is arranged to electrically connect contacts 20, 22 and 23 with external electrical circuits (not shown). For example, conductor 16 may be a conductive portion of a printed circuit board. Thus, by maintaining conductor 16 on a rigid member and by applying a force of say, 50 grams, to micro-circuit 15, a resilient and reliable electrical connection between conducting land 14 and conductor 16 is formed by the device 1.
It will be appreciated that such a device 1 will not be subject to the requirement of accurately controlling the height of electrically conductive portions thereon, as is the case when pillars are used as electrical interconnection members. This problem is avoided as a result of the deivce 1 being completely resilient. Also, since no part of device 1 is bonded or fixedly attached to conductor lands 14 and 16, it will be seen that replacement of particular components such as micro-circuit 15, will be easily accomplished by removing the desired component from contact with the device 1.
While it is shown in FIG. 3 that conductor 16 is in contact with three contacts of respective resilient members 10, conductor 16 could be in contact with a greater number of contacts, say five or six, without affecting the connection existing between conductor 16 and conductive land 14 as any other resilient members in contact with conductor 16 would not be in contact with either conductive land 14 or those resilient members in contact with conductive land 14. Also while domed contacts 13, 18 and 19 are shown it will be realised that such contacts may be flush with the surface of elastomeric material 21, and the domed contacts may be dispensed with.
An electrical assembly in which the resilient electrical connector device 1 is employed, is shown in FIG. 4. A micro-circuit 15 is mounted on a liquid cooled heat sink 25 with the resilient connector device 1 mounted on circuit 15. A printed circuit board 17 is appropriately aligned with various micro-circuits 15 by means of dowel pins 26 and 27 while nut and bolt arrangements 28 and 29 act to hold circuit board 17 in contact with device 1 and apply a steady pressure against the resilient connector device 1. Particular conductors 30 on the printed circuit board 17 may then be connected to the resilient electrical connector device 1 by means of interconnecting elements 31 on the printed circuit board 17.
A method for producing the resilient electrical connector device 1 shown in FIG. 3 will now be described. A pattern in the form of a thin metal having a frame 32 with a plurality of resilient members 10 may be produced by a conventional chemical milling technique. A hold or aperture 36 is provided in each corner of the frame for purposes of registration. By employing a chemical milling process, a large number of frames may be produced in one operation, all having accurate dimensions. Next, a spacer member 33 which is shown in FIG. 6, is placed in registration with frame 32. A stack which alternately consists of frame 32 and spacer member 33 is then built up with the thickness of the spacer member accurately determining the spacing between any two frames. The assembly is clamped between end plates 34 and 35 by pins 37 as shown in FIG. 7 with the cavity containing a large number of accurately spaced resilient members 10. The cavity is then filled with a suitable liquid elastomer, which for example, may be silicone rubber. The elastomer is then polymerised and then end plates 34 and 35 and spacer members 33 are removed. The frames 32 are then removed by a chemical etching technique to leave a large number of resilient members 10 (FIG. 1) accurately spaced in an elastomeric material 21. As stated previously, the surface of material 21 may be subjected to a grinding process to improve the flatness thereof.
Thus it will be seen that a resilient electrical connector device 1 is produced in which a large number of electrically conducting and mutually insulated paths are provided between one side of a sheet of flexible material and another. In this way the device 1 attains anisotropically conductive characteristics as a high degree of conductance is achieved in one direction and a low or negligible degree of conductance is achieved in a direction orthogonal to the first direction.
Also, as a result of such characteristics, a micro-circuit having contact or conductive lands, each of which encompasses a small number of resilient members 10 in elastomer 21 may be electrically connected with external circuitry, say, in the form of a printed circuit interconnecting network provided with similar contacts or conductive lands of the same geometry and displacement as the micro-circuit. The required electrical connection between a micro-circuit and a printed circuit board is simply achieved by inserting the device 1 between the micro-circuit and printed circuit board and subjecting the assembly to a small pressure to ensure reliable electrical connections.
While the resilient member 10 has been shown in two different forms in FIGS. 1 and 2 it will be appreciated that these forms are exemplary only and that other shapes may be employed. In each case however individual resilient members 10 or 40 alone will have insufficient strength to support a micro-circuit element 15 but by being embedded in a elastomeric material 21, sufficient strength is imparted to a number of such resilient members 10.
Another method for producing the device of the present invention is to provide a resilient porous member. Suitable metals are selectively deposited in the pores to provide a plurality of electrically conductive paths from one surface of the resilient member to another surface.
It will be noted that FIG. 3 shows the domed contact portions 13, 18, etc., to project slightly beyond the surface of the block 21 of elastomeric material adjacent thereto. Such projections facilitate obtaining adequate contact pressure at the contact portions without unduly loading adjacent circuit elements to displace the elastomeric block. This is particularly so where the conductive contact areas of the associated micro-circuit and/or circuit board are flush. The elastomeric material is not readily displaceable in practice, because of soft material will tend to have a fairly high co-efficient of friction, with the result that the face of the block in contact with a circuit element tends to resist any lateral movement relative to the face of the element. This tendency increases as the pressure is increased with the result that practicable pressures applied to the elements tend only to produce a slight bulge at the ends of the block 1.
It is desirable for each of the ends of the embedded conductive members to project slightly from the surface of the block. Pressure applied to the circuit elements is then more directly related only to the establishment of effective pressures between the embedded members and the conductive areas on the circuit elements.
As shown in FIG. 8 it is preferred for the contact portion to have at least an outer layer 71 of a noble metal, e.g., gold. It may of course be necessary to use an intervening portion 70 of another conductive material to ensure good bonding, depending on the material used for the embedded conductive members 72. The intervening portion 70 may, conveniently, constitute the projections desired for the embedded members 72.
The block 21 may support members 72 of, say, beryllium-copper, or phosphor-bronze alloy, bent into a V-shape to provide the required flexibility in the direction in which pressure is to be applied. The ends of the members 72 are initially arranged to be substantially level with faces 79, 79a respectively. A layer of, say, copper 70 is then formed over the ends of the members 72 by, for example, electrolytic deposition. In the process of deposition the copper layer 70 forms a dome at each end of a member 72. A second dome-like layer 71 of, say gold is then deposited over the copper domes 70 by a similar process, so that the contact forming layers of gold project from the surfaces 79, 79a respectively.
FIG. 9 illustrates the effect of assembling a contact block similar to that of FIG. 8, between a pair of circuit elements 74 and 75 carrying conductive areas 76 and 77 respectively and applying pressure to urge the elements together. It will be seen that in addition to the formation of a bulge 72 at the ends of the block 21, the elastomeric material of the block is free to be displaced, as indicated at 73, for example, into the small spaces between the surfaces 74, 74a of the elements 74 and 75 and the originally flat surfaces 79, 79a of the block.
It is also to be noted that because there is no initial contact between the surfaces 79, 79a of the block and the surfaces 74, 74a of the elements when they are initially assembled before pressure is applied, there is little friction to prevent some slight relative movement between the block and the elements 74 and 75.
It will be seen, therefore, that effective electrical contact between the conducting areas 76 and 77 is potentially improved in three ways. Firstly the individual contact pressures between the contact-forming ends of the members 72 and the areas 76 and 77 respectively are less dependent upon the resistance to compression of the elastomeric material of the block 21. Further, the deposition of a noble metal on the ends of the members 72 secures a second improvement, and thirdly any tendency for lateral displacement of the block 21 produces a sliding action between the contact-forming ends of the members 72 and the conductive areas 76 and 77 respectively. It is also to be noted from FIG. 9 that a degree of tolerance in relative lateral positioning of the circuit elements 74 and 75 is permissible using this form of contact block assembly. For example, it will be seen that the member designated 72a is in contact with a conductive area 77 in the element 75 but not with an area 76 in the element 74. Conversely, the member designated 72b is in contact with an area 76 in element 74 but not with an element 77 in the element 75. Thus a lateral relative displacement of the order indicated in the figure between the elements 74 and 75 is permissible without either short-circuiting of adjacent areas 76 or 77 and without any corresponding areas 76 and 77 being unconnected.
Field of the Invention and Cursory Prior Art
The present invention is an improvement and a departure from at least the following:
Patent Patentee Class Subclass 2,885,459 Pulsifer et al. 174 35 GC 2,967,216 Zablocki et al. 339 59 M 2,454,567 Pierson, Jr. 174 35 GC 3,324,445 Miller 339 61 M 940518/63 Burndy (Gr. Britain) 174 68.5
The invention relates to electrical connector devices.
Recent advances in micro-circuit techniques have allowed the size of individual micro-circuit elements to be significantly reduced. While a large number of circuits may be packaged in a very small volume by such techniques, a corresponding number of electrical connections must be made to such micro-circuit packages. One problem with forming such electrical connections is that the dimensions and physical tolerances of the connections to microcircuit packages are extremely small and such connections are difficult to produce by conventional techniques. Also, it is desirable that micro-circuit packages be easily replaceable and if such a micro-circuit has a large number of permanent connections to external circuitry, the time and effort to break and re-establish such electrical connections becomes extremely expensive. Thus, problems arise in replacing micro-circuit packages which are soldered to external circuits as the solder must be carefully removed from each lead or wire.
With conventional electrical components it is possible to secure electrical contact between components, many times by providing a spring made from an electrically conductive material and moulded in a suitable insulating material. Each end of such a spring is held in contact with anelectrically conducting portion of a component and when a pressure is exerted against one of the components the spring is compressed to assure an electrical connection therebetween. However, with the development with micro-circuit techniques, and the requirement of electrically connecting a large number of very small conductors on a micro-circuit device, it has been found that such spring contacts do not readily lend themselves to miniaturisation. In many cases it has become necessary to mount micro-circuit devices on subcarriers of much larger dimensions to make the devices compatible with conventional electrical connectors. This however, increases the cost of packaging and reduces many advantages of miniaturisation techniques.
SUMMARY OF THE INVENTION
According to one aspect of the invention there is provided an electrical connector comprising a plurality of elongated flexible conductive members embedded in, and each extending between surface areas of, a block of elastomeric insulating material with the extremities of the conductive members being exposed at said surface areas.
In use such a connector can provide several conductive paths between two conductors each in contact with an appropriate part of a different one of said surface areas. Conveniently, these surface areas are substantially parallel opposite faces of a slab constituting said block. Then, it is generally most useful for said appropriate parts to be in register with each other through the block. A small clamping pressure is sufficient for good contact.
Preferably, the extremities of the conductive members project from the block surface. The projection may be of a different material, e.g. an intermediate required for good bonding with a final layer of a noble metal.
According to another aspect of the invention there is provided a method of making an electrical connector using metal blanks having side rails interconnected by uniformly spaced parallel strip members, comprising the steps of making a stack of said blanks in register with each other and disposed alternately with spacer blanks of similar shape to said metal blanks but without the strip members, and filling the space between the side rails of the stack with liquid, settable elastomeric, insulating material, setting said material, and removing said side rails.
BRIEF DESCRIPTION OF THE DRAWING
A device for electrically connecting different electrical conductors embodying the present invention will now be described by way of example, with reference to the accompanying drawing which,
FIG. 1 shows a resilient member of the invention having a rectilinear configuration;
FIG. 2 shows a resilient member of the invention having a curvilinear configuration;
FIG. 3 shows resilient member of the invention embedded in an elastomeric material;
FIG. 4 shows the electrical connectors of the invention in a practical configuration;
FIG. 5 shows the resilient members as part of a frame;
FIG. 6 shows a metallic frame which serves as a temporary spacer;
FIG. 7 shows a stack comprised alternatively of elements shown in FIGS. 5 and 6;
FIG. 8 shows another connector; and
FIG. 9 shows the connector of FIG. 8 in use.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1 there is shown a resilient connector 10 of the present invention having surfaces 11 and 12 at the top and bottom of the member, respectively. Member 10 may be formed from any suitable electrically conductive resilient material such as, for example, phosphor bronze. In FIG. 2 another similar resilient member 40 is shown having opposed contact surfaces 41 and 42. The resilient members 10 and 40 having cross-sectional dimensions of the order of 25 microns and may have a free length of 2 millimeters.
A device 1 in which a plurality of resilient members 10 or 40 may be employed is shown in FIG. 3. Each resilient member 10 is embedded in an elastomeric material 21 which both physically and electrically separates each resilient member 10 from one another to form device 1. The elastomeric material 21 may be subjected to a grinding process to improve the flatness of the surface thereof and during this process the level of resilient members 10 may be reduced somewhat below that of the surface of material 21 as shown. In such cases, it may be convenient to electrolessly plate a conductive material on the opposed contact faces 11 and 12, this material being shown as contacts 13, 18, 19, 20, 22 and 23. A conductive land portion 14 of micro-circuit 15 is arranged to form an electrical connection with contacts 13, 18 and 19. Similarly, a raised conductor element 16 is arranged to electrically connect contacts 20, 22 and 23 with external electrical circuits (not shown). For example, conductor 16 may be a conductive portion of a printed circuit board. Thus, by maintaining conductor 16 on a rigid member and by applying a force of say, 50 grams, to micro-circuit 15, a resilient and reliable electrical connection between conducting land 14 and conductor 16 is formed by the device 1.
It will be appreciated that such a device 1 will not be subject to the requirement of accurately controlling the height of electrically conductive portions thereon, as is the case when pillars are used as electrical interconnection members. This problem is avoided as a result of the deivce 1 being completely resilient. Also, since no part of device 1 is bonded or fixedly attached to conductor lands 14 and 16, it will be seen that replacement of particular components such as micro-circuit 15, will be easily accomplished by removing the desired component from contact with the device 1.
While it is shown in FIG. 3 that conductor 16 is in contact with three contacts of respective resilient members 10, conductor 16 could be in contact with a greater number of contacts, say five or six, without affecting the connection existing between conductor 16 and conductive land 14 as any other resilient members in contact with conductor 16 would not be in contact with either conductive land 14 or those resilient members in contact with conductive land 14. Also while domed contacts 13, 18 and 19 are shown it will be realised that such contacts may be flush with the surface of elastomeric material 21, and the domed contacts may be dispensed with.
An electrical assembly in which the resilient electrical connector device 1 is employed, is shown in FIG. 4. A micro-circuit 15 is mounted on a liquid cooled heat sink 25 with the resilient connector device 1 mounted on circuit 15. A printed circuit board 17 is appropriately aligned with various micro-circuits 15 by means of dowel pins 26 and 27 while nut and bolt arrangements 28 and 29 act to hold circuit board 17 in contact with device 1 and apply a steady pressure against the resilient connector device 1. Particular conductors 30 on the printed circuit board 17 may then be connected to the resilient electrical connector device 1 by means of interconnecting elements 31 on the printed circuit board 17.
A method for producing the resilient electrical connector device 1 shown in FIG. 3 will now be described. A pattern in the form of a thin metal having a frame 32 with a plurality of resilient members 10 may be produced by a conventional chemical milling technique. A hold or aperture 36 is provided in each corner of the frame for purposes of registration. By employing a chemical milling process, a large number of frames may be produced in one operation, all having accurate dimensions. Next, a spacer member 33 which is shown in FIG. 6, is placed in registration with frame 32. A stack which alternately consists of frame 32 and spacer member 33 is then built up with the thickness of the spacer member accurately determining the spacing between any two frames. The assembly is clamped between end plates 34 and 35 by pins 37 as shown in FIG. 7 with the cavity containing a large number of accurately spaced resilient members 10. The cavity is then filled with a suitable liquid elastomer, which for example, may be silicone rubber. The elastomer is then polymerised and then end plates 34 and 35 and spacer members 33 are removed. The frames 32 are then removed by a chemical etching technique to leave a large number of resilient members 10 (FIG. 1) accurately spaced in an elastomeric material 21. As stated previously, the surface of material 21 may be subjected to a grinding process to improve the flatness thereof.
Thus it will be seen that a resilient electrical connector device 1 is produced in which a large number of electrically conducting and mutually insulated paths are provided between one side of a sheet of flexible material and another. In this way the device 1 attains anisotropically conductive characteristics as a high degree of conductance is achieved in one direction and a low or negligible degree of conductance is achieved in a direction orthogonal to the first direction.
Also, as a result of such characteristics, a micro-circuit having contact or conductive lands, each of which encompasses a small number of resilient members 10 in elastomer 21 may be electrically connected with external circuitry, say, in the form of a printed circuit interconnecting network provided with similar contacts or conductive lands of the same geometry and displacement as the micro-circuit. The required electrical connection between a micro-circuit and a printed circuit board is simply achieved by inserting the device 1 between the micro-circuit and printed circuit board and subjecting the assembly to a small pressure to ensure reliable electrical connections.
While the resilient member 10 has been shown in two different forms in FIGS. 1 and 2 it will be appreciated that these forms are exemplary only and that other shapes may be employed. In each case however individual resilient members 10 or 40 alone will have insufficient strength to support a micro-circuit element 15 but by being embedded in a elastomeric material 21, sufficient strength is imparted to a number of such resilient members 10.
Another method for producing the device of the present invention is to provide a resilient porous member. Suitable metals are selectively deposited in the pores to provide a plurality of electrically conductive paths from one surface of the resilient member to another surface.
It will be noted that FIG. 3 shows the domed contact portions 13, 18, etc., to project slightly beyond the surface of the block 21 of elastomeric material adjacent thereto. Such projections facilitate obtaining adequate contact pressure at the contact portions without unduly loading adjacent circuit elements to displace the elastomeric block. This is particularly so where the conductive contact areas of the associated micro-circuit and/or circuit board are flush. The elastomeric material is not readily displaceable in practice, because of soft material will tend to have a fairly high co-efficient of friction, with the result that the face of the block in contact with a circuit element tends to resist any lateral movement relative to the face of the element. This tendency increases as the pressure is increased with the result that practicable pressures applied to the elements tend only to produce a slight bulge at the ends of the block 1.
It is desirable for each of the ends of the embedded conductive members to project slightly from the surface of the block. Pressure applied to the circuit elements is then more directly related only to the establishment of effective pressures between the embedded members and the conductive areas on the circuit elements.
As shown in FIG. 8 it is preferred for the contact portion to have at least an outer layer 71 of a noble metal, e.g., gold. It may of course be necessary to use an intervening portion 70 of another conductive material to ensure good bonding, depending on the material used for the embedded conductive members 72. The intervening portion 70 may, conveniently, constitute the projections desired for the embedded members 72.
The block 21 may support members 72 of, say, beryllium-copper, or phosphor-bronze alloy, bent into a V-shape to provide the required flexibility in the direction in which pressure is to be applied. The ends of the members 72 are initially arranged to be substantially level with faces 79, 79a respectively. A layer of, say, copper 70 is then formed over the ends of the members 72 by, for example, electrolytic deposition. In the process of deposition the copper layer 70 forms a dome at each end of a member 72. A second dome-like layer 71 of, say gold is then deposited over the copper domes 70 by a similar process, so that the contact forming layers of gold project from the surfaces 79, 79a respectively.
FIG. 9 illustrates the effect of assembling a contact block similar to that of FIG. 8, between a pair of circuit elements 74 and 75 carrying conductive areas 76 and 77 respectively and applying pressure to urge the elements together. It will be seen that in addition to the formation of a bulge 72 at the ends of the block 21, the elastomeric material of the block is free to be displaced, as indicated at 73, for example, into the small spaces between the surfaces 74, 74a of the elements 74 and 75 and the originally flat surfaces 79, 79a of the block.
It is also to be noted that because there is no initial contact between the surfaces 79, 79a of the block and the surfaces 74, 74a of the elements when they are initially assembled before pressure is applied, there is little friction to prevent some slight relative movement between the block and the elements 74 and 75.
It will be seen, therefore, that effective electrical contact between the conducting areas 76 and 77 is potentially improved in three ways. Firstly the individual contact pressures between the contact-forming ends of the members 72 and the areas 76 and 77 respectively are less dependent upon the resistance to compression of the elastomeric material of the block 21. Further, the deposition of a noble metal on the ends of the members 72 secures a second improvement, and thirdly any tendency for lateral displacement of the block 21 produces a sliding action between the contact-forming ends of the members 72 and the conductive areas 76 and 77 respectively. It is also to be noted from FIG. 9 that a degree of tolerance in relative lateral positioning of the circuit elements 74 and 75 is permissible using this form of contact block assembly. For example, it will be seen that the member designated 72a is in contact with a conductive area 77 in the element 75 but not with an area 76 in the element 74. Conversely, the member designated 72b is in contact with an area 76 in element 74 but not with an element 77 in the element 75. Thus a lateral relative displacement of the order indicated in the figure between the elements 74 and 75 is permissible without either short-circuiting of adjacent areas 76 or 77 and without any corresponding areas 76 and 77 being unconnected.