Compositions – Electrically conductive or emissive compositions
Reexamination Certificate
2000-10-20
2003-03-04
Mullis, Jeffrey (Department: 1711)
Compositions
Electrically conductive or emissive compositions
C525S088000, C525S094000, C525S242000
Reexamination Certificate
active
06527984
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a low temperature-curable connecting material for anisotropically electroconductive connection to be used for bonding and connecting elements together, each element having a plurality of electrodes opposite to those on a counter element, in particular, a low temperature-curable connecting material containing a polymerizable component subject to radical polymerization.
DESCRIPTION OF THE RELATED TECHNIQUES
It has become a practical trend to use, as a material for connecting an element having a plurality of electrodes confronting correspondingly to electrodes on another element to be connected therewith, an anisotropically electroconductive connecting material, such as an anisotropically electroconductive film (ACF) and an anisotropically electroconductive paste (ACP) as a substitute for conventional solder. The anisotropically electroconductive material is prepared by dispersing electroconductive particles in an adhesive component constituted mainly of a thermosetting resin and is used for bonding and electroconductively connecting elements together, each element being provided on an opposing face with a plurality of electrodes, by interposing the anisotropically electroconductive material between the elements and subjecting the resulting assemblage to a heat-pressing, in order to effect electroconductive connection between the correspondingly confronting electrodes by establishment of frictional contact of the confronting electrodes with the electroconductive particles bridging therebetween, on the one hand, and to build up an assured insulating separation between the neighboring electrodes, on the other hand, together with firm mechanical bonding of the elements with each other by causing the thermosetting resin to cure. When the electrodes have a smaller connecting surface area, a connecting material not containing electroconductive particles may be used. Here also, the electroconductive connection and the mechanical bonding are realized in the same manner.
The anisotropically electroconductive connecting material can provide secure electroconductive connection between the correspondingly confronting electrodes and build up an assured insulating separation between the neighboring electrodes. The anisotropically electroconductive connecting material has been used for assembling a semiconductor element or package on a printed circuit board or for connecting a printed circuit board with another printed circuit board, such as a flexible printed circuit board or, further, in an ordinary liquid crystal display arrangement.
On realizing an electroconductive connection between the electrodes on, for example, printed circuit boards having micronous circuits using conventional anisotropically electroconductive connecting material, a sufficient connection reliability and a satisfactory bonding strength are attained by effecting the curing reaction of the thermosetting resin at a temperature of 150-200° C. for a time period of about 20 seconds to cause the curing reaction to proceed sufficiently. Recently, however, demand for connecting between micronous circuits with each other has become increased due to the general trend to precise and thin design of electronic devices and instruments. In order to meet this requirement, it has highly been expected to develop an anisotropically electroconductive connecting material capable of both establishing a highly insulating separation between the neighboring micronous electrodes and reducing the occurrence of damage upon heat-pressing. In addition, it has in recent years become practiced increasingly to assemble a circuit board or the like having micronous circuits on a large connecting substrate panel, where a connection by heating at a temperature over 150° C. may cause a large thermal deformation or warp, resulting in a considerable disorder in the dimensional stability, which has been taken up as a troublesome problem and, thus, a demand for an anisotropically electroconductive connecting material operable at a lower temperature has been brought about.
It has been proposed, for example, in Japanese Patent Kokai Hei 10-147762 A, a connecting material permitting such a lower temperature connection, in which a radical polymerization resin is incorporated. The connecting material is in a form of an anisotropically electroconductive film and comprises an adhesive mass and, dispersed therein, electroconductive particles, wherein the adhesive mass comprises a polymerizable component subject to cross-linking and to radical polymerization, an organic peroxide and a thermoplastic elastomer. This connecting material can attain a low temperature connection by heating at a lower temperature or by irradiation of light to cause radical polymerization and cross-linking, whereby a low temperature curing is realized.
However, use of such a polymerizable material subject to radical polymerization may tend to cause the cured mass to fall off due to accumulation of internal stresses at the bonded site after the curing, since the shrinkage of the cured resin by radical polymerization is greater than that of a conventionally used thermosetting resin, such as an epoxy resin or the like, so that an increase in the bonding strength may not be expected. This leads also to a difficulty in increasing the reliability of establishment of electric continuity and, in addition, tends to cause deterioration of these characteristic properties for a successive long term service. Thereto is further added the fact that the adhesive used for bonding the electrode onto the printed circuit substrate board softens on such a connection procedure, so that the electrodes are apt to displace in accompaniment with the shrinkage of the connecting material. When the electrodes are arranged at a small interval, the shrinkage of the connecting material causes a further reduction of the electrode interval, whereby the electroconductive particles present within the interval space may, on certain occasions, come into frictional contact with the neighboring electrodes to bridge therebetween, resulting in short circuiting. For obviating such a difficulty, a thermoplastic elastomer is incorporated. However, there may occur a possible phase separation of the thermoplastic elastomer from the polymerizable component subject to radical polymerization, resulting also in a reduction of the bonding strength.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a low temperature-curable anisotropically electroconductive connecting material which can be cured at a lower temperature with a reduction of shrinkage of the material upon the curing, whereby an accumulation of internal stresses is avoided to thereby increase the bonding strength and the reliability of electric continuity at the junction while securing electric insulating separation between the neighboring electrodes and maintaining these characteristic features for a long time.
The present invention resides in the following low temperature-curable anisotropically electroconductive connecting material:
(1) A low temperature-curable connecting material for anisotropically electroconductive connection, comprising an adhesive mass for bonding and connecting elements, each having electrodes thereon in a correspondingly confronting relationship, wherein the adhesive mass comprises
a polymerizable component subject to radical polymerization and cross-linking,
a polymerization initiator and
an A-B-type block-copolymer having a segment compatible with the polymerizable component and a segment incompatible with the polymerizable component.
(2) The low temperature-curable connecting material as defined in the above (1), wherein the polymerizable component comprises a polymerizable coupling agent.
(3) The low temperature-curable connecting material as defined in the above (1) or (2), wherein the block-copolymer is a polystyrene/polyvinyl acetate block-copolymer or a polystyrene/poly(meth)acrylate block-copolymer.
(4) The low temperature-curable connecting material as defined in any
Flynn ,Thiel, Boutell & Tanis, P.C.
Mullis Jeffrey
Sony Chemicals Corporation
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