GB2276502A

GB2276502A - Anisotropic conductive elastic connector

Info

Publication number: GB2276502A
Application number: GB9404009A
Authority: GB
Inventors: Toru Takahashi
Original assignee: Yamaichi Electronics Co Ltd
Current assignee: Yamaichi Electronics Co Ltd
Priority date: 1993-03-04
Filing date: 1994-03-02
Publication date: 1994-09-28
Anticipated expiration: 2014-03-02
Also published as: JPH06260234A; GB2276502B; GB9404009D0; JPH07123057B2

Abstract

An anisotropic conductive elastic connector (1) comprising an insulative elastic sheet (10) formed of a foam synthetic resin material and having a number of electrically conductive wires (11) embedded in the insulative elastic sheet (10). The insulative elastic sheet (10) may be formed by a laminate of foamed and non-foamed synthetic resins. The non-foamed synthetic resin may form the outer surfaces of the sheet. <IMAGE>

Description

TITLE OF THE INVENTION ANISOTROPIC CONDUCTIVE ELASTIC CONNECTOR BACKGROUND OF THE INVENTION 1. Field of the invention This invention relates to an anisotropic conductive elastic connector, in which an electrical connection is achieved by means of compression by a member to be connected.

2. Prior Art With the progress of the tendency of shifting the circuit mounting method for electronic devices and instruments to a surface mounting, the IC package mounting method is gradually needed to fulfil the requirement for the surface mounting as a mainstream.

Particularly, among semiconductor IC packages, LGA packages and BGA packages are each provided with a number of wiring patterns and soldering balls arranged on a rear surface of the IC package in an XY grit. In case an IC package of khis type is to be connected using a socket, if the IC package is connected under compression, with an elastic connector interposed between the rear surface of the IC package and a printed wiring board pattern, the mounting height can be reduced thereby enabling to achieve a high density electrical connection.

The conventional elastic connectors commercially available are insufficient in flexibility. In case the entire compressing force acting surface is to be compressed flat, a force required for compressing the surface about 0.1 mm is 30 kg. or more per 25.4 mm2 (one inch). Therefore, acceptable elastic connectors are limited to those having an elongated rod-like configuration because a compressive load can be comparatively small. Sheet-like connectors having a large dimension are, in most cases, not employed as a connector.

Generally, it is essential for elastic connectors that an insulative elastic member is compressed. If a compressing area is large, the compression force required is unduly increased and so such elastic connectors are unusable. For example, if the compression force is about 30 kg., there is a possibility that a wiring board to be pressed against the elastic connectors is damaged.

A conventional clamp type elastic connector, which is interposed between two connecting members (members to be connected), comprises an insulative elastic member having number of electrically conductive wires embedded therein in such a manner as to vertical to the compressive force acting surface. This type of conventional elastic connectors are commercially available as anisotropic conductive elastic connectors.

However, the conventional devices require a very large compressive load and have many difficulties in respect of use, and therefore, various techniques are proposed as mentioned above. However, a fundamental solution is not yet reached and the prior art is limited when it is applied to the surface mounting.

The fundamental reason for the above can be found in the pressure connection type clamping structure of the elastic connector in which a compressive load is applied to the entire surface of the compressing force acting surface of the elastic member. In case the conventional elastic member is compressed, even if flexibility thereof is increased for example, a compressive load for an amount of deformation which occurs when the thickness of the elastic member is flatly depressed and spread in all directions, is sometimes increased in a geometrically progressing manner.

Furthermore, owing to the fact that when the sheet-like elastic connector having a large dimension is clamped and compressed in a direction of the thickness, the plane dimension of the connector is spread in all directions as a result of reduction of the sectional dimension, a positional displacement occurs between the electrically conductive wire of the elastic connector and the contacting points of the connecting member.

The spread in plane dimension of the elastic connector does not always occur simultaneously with the compression. It sometimes remains inside the insulative elastic member as a stress-strain and appears in the form of releasing the internal strain of the elastic connector when a heat stress, a mechanical stress, etc. are applied. In this sense, therefore, it occurs irrespective of time.

The present invention has been accomplished in view of the above problems.

OBJECT AND SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an anisotropic conductive elastic connector in which a compressive load can be reduced and a highly reliable electrical connection can be obtained.

Another object of the present invention is to widely spread a sheet-like elastic connector having a large dimension and enhance its practice.

To achieve the above objects, from one aspect of the invention, there is provided an anisotropic conductive elastic connector comprising an insulative elastic sheet formed of a foam synthetic resin material and having a number of electrically conductive wires embedded the insulative elastic sheet.

From another aspect of the invention, there is provided an anisotropic conductive elastic connector comprising an insulative elastic sheet formed of a foam synthetic resin material and having a number of electrically conductive wires embedded in the insulative elastic sheet, the insulative elastic sheet comprising an insulative elastic sheet having a larger rigidity than the insulative elastic sheet formed of non-foam synthetic resin material laminated on a compressing force acting surface thereof.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an exploded perspective view of a surface mounting device for an IC package in which a sheet-like anisotropic conductive elastic connector formed of a foam synthetic resin material is used; Fig. 2 is a perspective view showing a semi-manufactured product of the foam sheet-like anisotropic conductive elastic connector; Fig. 3 is an enlarged cross-sectional view of the above connector; Fig. 4 is a side view schematically showing a surface mounting of the surface mounting device of Fig. 1: Fig. 5 is an enlarged cross-sectional view showing another example of the foam sheet-like anisotropic conductive elastic connector; and Fig. 6 is an enlarged view showing a further example of the above connector.

DETAILED DESCRIPTION OF THE EMBODIMENT As described previously, the present invention relates to an anisotropic conductive elastic connector which is capable of achieving an electrical connection by compression.

As shown in Fig. 4, this connector is interposed between an IC package 2 and a wiring board 3 thereby to constitute a sheetlike flat anisotropic conductive elastic connector 1 having a wide dimension, in which an electrical connection is achieved by compression in the width direction. A foam synthetic resin material is applied as a material of an insulative elastic sheet which is used as this connector base. Then, as shown in Fig. 3, a number of very fine electrically conductive wires having an elastic property are embedded in a base material of the foam insulative elastic sheet 10, thereby to constitute a sheet-like connector of a foam construction.

Referring back to Fig. 1, a connector frame 5 is placed on the surface of the wiring board 3 having a wiring pattern applied thereto. A foam sheet-like elastic connector 1 is fitted in the connector frame 5 so as to be superimposed upon the wiring board 3. An IC package 2 is superimposed upon the surface of this elastic connector 1 and a pressure plate 7 is placed on the elastic connector 1. Then, fastening screws 8 are inserted into mounting holes 9 formed in four corners of the pressure plate 7 and further through mounting holes 9' formed in four corners of the connector frame 9' and tightened in order to tighten the IC package 2 and the elastic connector 1 interposed between the wiring board 3 and the pressure plate 7, thereby to compress the foam insulative elastic sheet 10.

Owing to the effect of this compression, the elastic connector 1 is connected both to the IC package 2 which is placed on the compression acting surface of the elastic connector 1 and to the wiring board 3 on which the elastic connector 1 is placed. Thus, the IC package 2 is electrically connected to the wiring board 3 through the elastic connector 1.

As previously described, the anisotropic conductive elastic connector 1 uses the foam insulative elastic sheet 10 as a base, and as shown in Fig. 3, the electrically conductive wires 11 embedded in the foam insulative elastic sheet 10 are arranged in such a manner as to be vertical to the compression active surface of the foam insulative elastic sheet 10. Upon compression, the electrically conductive wires 11 are deflected and one end portions of the conductive wires 11 are exposed from the compression active surface so as to be connected to the contacting points of the IC package 2 and the wiring pattern of the wiring board 3.

The electrically conductive wires 11 embedded in the foam insulative elastic sheet 10 are essentially a flexible conductive member having a low spring constant and penetrating opposite compression active surfaces of the elastic connector.

As shown in Fig. 3 for example, the electrically conductive wires 11 may be very fine wires twisted so as to have flexibility or may be a flexible conductive member formed by twisting and spirally winding the very fine wires. The conductive wire(s) 11 may be a single wire of the very fine wire or a bundle of the very fine wires.

In order to make the sheet-like foam anisotropic conductive elastic connector 1, prism blocks 1' of Fig. 2 are formed by casing a number of the electrically conductive wires 11 in predetermined position of the foam insulative elastic member, and sliced with a predetermined thickness, thereby to form the anisotropic conductive elastic connector 1 having a small thickness of about 0.5 mm to 2 mm.

The configuration of the prism block 1' is not limited to a regular square, but it may also be a triangular prism, a trapezoidal prism, a diamond prism, a picture-frame-like prism, or the like. Therefore, sheet-like foam connectors 1 having a variety of shapes can be formed.

The electrically conductive wires may be properly arranged in accordance with necessity. They may be arranged in one row, two rows, zigzag rows, or picture-frame-like arrangement.

In any case, the configuration of the connector 1 is firmed by dies or mold. A predetermined number of electrically conductive wires 11 are placed in predetermined position within the dies or mold, and then a foam synthetic resin is charged therein to form the prism blocks 1'. These prism blocks 1' are sliced as indicated by imaginary lines to form the sheet-like foam elastic connector 1.

Acceptable synthetic resin for the foam insulative elastic sheet of the present invention includes, polybutadiene, polyisoprene, chloroprene rubber, silicon rubber, etc. An insulative material having excellent flexibility and hardly susceptible to permanent deformation such as, for example, foam member of silicon rubber, is most preferable.

The foam structure of the foam insulative elastic sheet is of a communication foam structure, for example, a partly communication foam structure consisting of a combination or mixture of independent foams and a communication foam structure.

Figs. 5 and 6 show an anisotropic conductive elastic connector comprising a combination of the insulative elastic sheet 10 formed of a foam synthetic resin material and an insulative elastic sheet 4 formed of a non-foam synthetic resin material as a surface layer material. Reference numeral 11 denotes electrically conductive wires which are embedded in the respective sheets 10 and 4.

The insulative elastic sheet 4 formed of a non-foam synthetic resin material uses a material having a larger rigidity than that of the foam insulative elastic sheet 10.

The insulative elastic sheet 4 is laminated to each surface of the upper and lower surfaces of the foam insulative elastic sheet 10 as shown in Fig. 5, or the elastic sheet 4 is laminated to only one surface of the foam insulative elastic sheet 10 as shown in Fig. 6.

This non-foam insulative elastic sheet(s) 4 has the functions for adjusting the compressive efficiency (elasticity) of the foam insulative elastic sheet 10, increasing the surface strength and firmly holding the electrically conductive wires 11 within the foam insulative elastic sheet 10.

As mentioned above, the sheet-like foam anisotropic conductive elastic connector 1 can be compressed with an extremely reduced force. Therefore, the anisotropic conductive elastic connector 1 can be prevented from being unduly stretched in the direction perpendicular to the compressing direction and a reliable electrical connection can be obtained.

For example, there was prepared a sheet-like foam anisotropic conductive elastic connector 1 having electrically conductive wires embedded in sheet having a foam of about 0.5 0 average obtained by foaming a silicon rubber and a thickness of 0.5 mm to 2 mm, such that the electrically conductive wires were arranged at 0.5 mm pitches in the XY directions per square inch. Such obtained anisotropic conductive elastic connector 1 was compressed about 0.1 mm. The compressive force required for it was so small as about 4 kg to 6 kg. The amount of stretch seen in the anisotropic conductive elastic connector 1 at that time was entirely negligibly small relative to the arrangement pitches of the electrically conductive wires.

As described in the foregoing, a sheet-like foam anisotropic conductive elastic connector according to the present invention can extensively reduce a compressive load to the insulative elastic sheet serving as a connector base and distribute a large part of the compressive load to the amount of deflection of the electrically conductive wires embedded in the sheet. Therefore, a highly reliable electrical connection can be obtained. Moreover, the insulative elastic sheet can be prevented from being unduly stretched when it is compressed and therefore, the reliable electrical connection is more enhanced.

Furthermore, the present invention will enhance the practice of the highly reliable, flat and thin elastic connector. As seen, an anisotropic conductive elastic connector according to the present invention can effectively fulfil the requirement for surface mounting of an IC package which tendency is coming to be a mainstream.

The present invention is not limited to the above embodiments but many modifications can be made.

Claims

WHAT IS CLAIMED IS:

1. An anisotropic conductive elastic connector comprising an insulative elastic sheet formed of a foam synthetic resin material and having a number of electrically conductive wires embedded said insulative elastic sheet.

2. An anisotropic conductive elastic connector comprising an insulative elastic sheet formed of a foam synthetic resin material and having a number of electrically conductive wires embedded in said insulative elastic sheet, said insulative elastic sheet comprising an insulative elastic sheet having a larger rigidity than said insulative elastic sheet formed of non-foam synthetic resin material laminated on a compressing force acting surface thereof.

3. An anisotropic conductive elastic connector substantially as hereinbefore described with reference to the accompanying drawings.