Abstract:
The invention relates to apparatus for clamping superimposed conductive elements (11, 13) disposed in aligned groups by means of a clip device (22, 23) such that an integrated circuit device may be removably connected to a printed circuit card with a predetermined force being applied uniformly across all the superimposed elements. In accordance with the invention, at least one of the clips (22, 23), in the free state, has a cambered form, equivalent to the elastic deformation of an initially straight beam of uniform section and of the same length mounted on two simple supports spaced this length and uniformly charged over this length. 
     The invention is primarily used for the electrical interconnection of integrated circuit devices to printed circuit cards.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The subject matter of this invention is related to applications for patent, Ser. No. 326,820 of Gerard Dehaine and Ser. No. 326,530 of Jean Bonnefoy, all filed concurrently herewith and assigned to the assignee of the present invention. The subject matter of said applications are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a clamping device for clamping superimposed elements of aligned groups and relates more particularly to clamping of electrically superimposed conductor elements for interconnection of integrated circuit devices to printed circuit cards. 
     2. Description of the Prior Art 
     The clamping of two elements which may later have to be separated has the advantage of providing a convenient means of connection relatively adaptable to configurations of the elements and to the different clamping conditions, while leaving the elements practically unchanged, appropriate to any future utilization. Further, it is less costly and more efficient to clamp two elements than joining them by a solid connector such as solder. 
     The connection of elements by clamping is carried out throughout the electrical arts. A connection device which is well known for two superimposed conductive elements is the clamping wire or clamp cables found in the form of a shell associated with a clamping screw. Its utilization is, however, limited by the fact that for such clamps, it is necessary that there be as many clamp-wires as pairs of conductive elements to be connected. 
     The common collection of aligned groups of conductive elements may be made generally by two clips or straps which rectilinear clamp the groups of elements in the direction of their alignment. Two clamping members, notably a bolt, disposed at the respective extremities of the two clips while being spaced one from the other for a given length greater than that of the aligned groups, exercise on the extremities of the clips a predetermined clamping force. This connection device if simple and cheap, but it has the disadvantage of not exercising a uniform pressure on the spaced elements of each group. In effect, in adjusting the bolts mounted at the extremities of the two clips to apply the desired clamping force, the clips act as levers bearing on the elements of the extreme groups and flexing between them in accordance with the clamping force and the configuration of the clips. Such an arrangement is not useful for the uniform clamping of numerous aligned groups of superimposed elements even while employing thick and rigid clips. 
     In the area of electronics for example, the integration of endless crossing of circuits leads to the miniaturizing and the multiplication of the conductor elements for input and output of the electronic devices. For example, high density integrated circuit devices ordinarily have, at the present time, on the order of fifty output points, of 70 um width and spaced at 120 um about, while the substrates provided to receive these devices and the interconnector provided to receive these devices are provided, on each side, with 150 output points of 0.3 mm of width and spaced at about 0.5 mm. The points of the integrated circuit devices and of the substrates are in general associated with connecting conductors respectively and connected by them to the areas of connection disposed on the substrate for the connection of the integrated circuit devices and on printed circuit cards and for the interconnection of the substrates. It is necessary to exert an effort on the order of 100 grams per contact. In the case where a substrate has 150 points on a side of 75 mm, a force increasing to 1.5 kg must be exercised uniformly on this length. 
     In such circumstances, it is evident that the wire clamps are inapplicable and, on the other hand, it follows that the clamping device with clips mentioned above does not assure an efficient connection with the desired force of the elements of all the groups. It should also be noted that such a clamping device with clips is efficient only if the groups of elements are aligned in parallel to the clips. But, the deposit by serigraphie of an interconnection network of a substrate requires as many heatings of the substrate as there are conductive and insulating layers for the solidification of these layers. The successive heating and coolings result in distortion of the substrate and even more if the substrate has an elevated surface. It follows that the straight and rigid clips would be disadvantageous and less desirable as the substrate surface increases and the interconnection network and points of input and output become more dense. 
     On the other hand, soldering of connecting conductors as fine and as close as those defined above has the disadvantage of requiring a very delicate operation, particularly in the replacement of an integrated circuit device on a substrate or of a substrate on a card. In this case, it is necessary in effect to resolder all of the connecting conductors without deforming them, while maintaining them equally spaced leaving them undamaged, as well as the areas to which they were soldered. In view of their reutilization, it is necessary then to resolder without there being any alteration of the quality of the solder and the adjacent elements (caused notably by the heat discharge and propagated by the conductors, the points or the areas) and creation of short circuits due to lapping solders. 
     The immovability of the connection device of the conductor elements (points, connecting contacts, areas) present in the preceding example is thus an important factor. The high density integrated circuit devices are actually relatively costly products, and the interconnection substrates are also very costly. Accordingly, their replacement in view of their repair and reutilization is desirable. It can be seen that clamping is apt to allow replacement, but traditional clamping arrangements using rigid and rectilinear clips are unsuitable for this purpose. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the disadvantages of prior art clamping devices. 
     A device in accordance with the present invention for clamping superimposed elements of groups arranged along a given line is of the type comprising two clamping means arranged for clamping the said groups and two force adjusting means for the said clamping means disposed at their respective extremities and being spaced one from the other by a given length and exercising on them a clamping force which has been predetermined and is characterized in that at least one of the said clamping means has in its free state, not constrained, a cambered form relative to the said line, equivalent to the elastic deformation of a beam having initially the form of the said line, of uniform section and resting on two simple supports spaced the said length and uniformly subjected on this length with a total value corresponding substantially to double that of the said clamping force applied to each extremity of the clip, so that the deformation of the clamping means caused by the said force adjusting means takes the form of the said line and produces a uniform clamping of the elements of each group. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The characteristics and advantages of the invention will appear more clearly in the description which follows with reference to the accompanying drawings. 
     FIG. 1 is a schematic view from above and in perspective of an interconnection substrate for integrated circuit devices connected to a printed circuit card by means of clamping devices conforming to the invention. 
     FIG. 2 is an enlarged fragmentary view in section along the line II--II of FIG. 1. 
     FIG. 3 is a fragmentary cross-sectional view on the line III--III of FIG. 1, illustrating in detail a clamping device conforming to the invention in the clamping state. 
     FIG. 4 is a view similar to that of FIG. 3 illustrating the embodiment of a device conforming to the invention in the non-clamping state. 
     FIG. 5 is a view analogous to that of FIGS. 3 and 4 illustrating a variant of the embodiment of a device conforming to the invention in the non-clamping state. 
     FIGS. 6a and 6b are schematics illustrating the deformed elastic equivalent of a clamping clip conforming to the invention and 
     FIG. 7 is a perspective view of a variant of the embodiment of a device conforming to the invention for replacing the four clamping devices shown in FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The example serving to illustrate the structure and the advantages of a clamping device conforming to the invention will be described in connection with connecting leads of an interconnection substrate supporting integrated circuit devices to a printed circuit card, it being understood that the inconveniences of the prior art clamping devices have been discussed above with respect to such a connection. This example will illustrate the principal advantages of the invention. 
     FIG. 1 illustrates in perspective an embodiment conforming to the invention with four identical clamping devices (10) connecting, as will be better seen in FIG. 2, the connecting leads (11) of a substrate (12) with areas of connection or contact pads (13) disposed on a printed circuit card (14) (illustrated in FIG. 1 in partial form) serving to interconnect the substrate (12) between circuit connections on the card as well as to the input and output connections of the card, not shown. 
     Substrate (12), fragmentarily shown in FIGS. 1 and 2 comprises a support plate (15), of which one face has an interconnection network (16) in the form of printed circuits, connecting integrated circuit devices (17) between them as well as the input and ouput contacts (18), and of which the other face comprises a finned radiator (19) for the thermal dissipation of heat created in the integrated circuit devices (17). The connecting leads (11) are soldered at one of their extremities to the contacts (18) as well as the corresponding contacts (18&#39;) insulated electrically on the other face of the support plate (15). 
     The printed circuit card (14) comprises a support plate (20) provided with an interconnection network (21) in the form of printed circuits, comprising areas of connection or contact pads (13). 
     FIGS. 2 and 3 illustrate in great detail an embodiment of the clamping device (10) conforming to the invention, respectively in transverse section and in longitudinal section. The clamping of the connectors (11) against the areas (13) is made by means of device (10) comprising two clamping means in the form of clips (22, 23) provided with force adjusting means (24) for the clips, disposed at their respective extremities and being spaced one from the other by a given length and exercising on them a predetermined clamping force. In the example illustrated, the force means (24) comprises threaded bolts (25) passing through the extremities of the clips (22) and (23) through openings (26) and being provided with nuts (27) which exert on the extremities of the clips a predetermined clamping force. 
     FIG. 4 illustrates the essential characteristic of the invention which is found in the fact that one of the clips (22) has a cambered form relative to the line formed by the group of elements (11) and (13), this line being straight in the example illustrated. As shown schematically in FIGS. 6a and 6b, the cambered form of clip (22) is equivalent to the elastic deformation of a beam having initially the form of the line formed by the elements (straight line of the example illustrated) of uniform section and mounted on two supports (28) separated substantially the same length separating the force means (24) and uniformly burdened on this length with a total value corresponding substantially to double that of the clamping force applied to each extremity of the clip by the bolts (25). The shape of the curve taken by the clip (22) corresponds thus to a catenary curve. Deformation of clip (22) exercised by the force means (24) finally to give it the rectilinear form of alignment of the elements (11) and (13) provides a uniform clamping of all the elements (11, 13) of each pair between the clips. 
     In FIG. 4, clip (23) takes the form of alignment of the elements (11 and 13). In this regard, it is not there only to serve as reaction surface of bearing sufficient to exert the predetermined clamping force. Consequently, in the case where the support plate (20) of card (14) has a sufficient rigidity to be able to support without damage the clamping force, this plate (20) can take the place of clip (23), which then need not be used. 
     On the other hand, the two clips (22 and 23) can take the same cambered form as that of clip (22) shown in FIG. 4, as is illustrated in FIG. 5. This gives the assurance of having a uniform clamping pressure due to the concomitant action of the deformation of the clips (22) and (23). Actually, in the device shown in FIG. 4, clip (23) can undergo forces tending to curve it, with a result that a uniform clamping action produced by clip (22) can be altered in certain areas because of the disengagement of the surface of bearing reaction formed by plate (20) and the clip (23). 
     As shown in FIGS. 2 to 5, a supple joint (29) can be interposed between the clip (22) and a series of elements, such as the contacts (11) in the example illustrated. This supple joint permits absorption of the forces due to the fact that the line of the groups of elements (11) and (13) cannot be perfectly straight, that the thickness of the elements (11) and (13) of a same group can vary from groups to others, primarily. In other words, the joint (29) advantageously distributes the clamping force on the assembly of the groups of elements (11) and (13). 
     Further, being given that the connectors are very thin elements and very fragile, but will be to advantage to maintain their desired spacing by means of a rigid band (30), fixed to elements (11) corresponding. 
     As seen in FIG. 7, the assembly of the four clips (22) or of the four clips (23) of the clamping devices (10) seen in FIG. 1, can be formed of a single piece (31). More generally when the substrate (12) is provided with contacts on adjacent sides, the corresponding clips can be formed of a single piece. In the case where the force means (24) are formed by threaded bolts, piece (31) can be provided with corresponding orifices (26). It should be understood, the means for fixation (24) can be formed by other means, such as for example clamps, etc. 
     It follows from the above description that a clamping device conforming to the invention can be adapted to the connection between whatever elements disposed in groups following a line of any form, the principles of cambering of one of the clips at least remaining the same and the resulting effects of the deformation equally. 
     It is to be noted also that the same device (10) or (31) can be applied to the connection of connectors of integrated circuit devices (17) of large dimensions to the support plane (15) of substrate (12).