Anisotropically conducting adhesive, and process for producing a

Details Anisotropically conducting adhesive, and process for producing a Anisotropically conducting adhesive, and process for producing a

1996-12-27

1999-04-06

Kopec, Mark

Compositions

Electrically conductive or emissive compositions

Free metal containing

252512, 25251921, 156 731, 1562728, 1562739, H01B 122, B32B 3126, B32B 3128

Patent

active

058913661

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to an anisotropically conducting adhesive with particles dispersed in a thermoplastic base material and to a process for producing an anisotropically conducting adhesive.
2. Description of the Related Art
Anisotropically conducting adhesives are known. In a base material, for instance a thermoplastic base material, they have finely dispersed conductive particles. The conductive particles are dispersed in the form of particulate powder in the base material. The anisotropically conducting adhesives are in sheet form, for instance, and are suited for electrically conductively gluing together two contacts, for instance two conductor tracks. The tracks are pressed under pressure and temperature action onto the opposed sides of the adhesive, so that the base material deformed and the conductive particles distributed in it establish an electrically conductive connection between the applied tracks. The base material performs an adhesive action between the parts having the conductor tracks that are to be glued together.
It becomes clear that the resolution of the anisotropically conducting adhesive, that is, the minimum possible distance between two adjacent electrically conductive connections, depends on the structure of the dispersed electrically conductive particles. In order that the conductive particles will enable the electrically conductive connection in only one direction, they must be spaced apart sufficiently from one another so that an undesired isotropically electrically conductive connection is avoided. This can happen for instance from accidental coagulation, or in other words clumping together of the electrically conductive particles in the base material. As a result, the known anisotropically conducting adhesives can be used only for contacting contacts that are located relatively far apart from one another, because otherwise an adequately high contact reliability is not achieved.


SUMMARY OF THE INVENTION

The anisotropically conducting adhesive of the invention has particles dispersed in a thermoplastic base material, which particles are finely distributed below a percolation temperature, characterized in that the particles are metal particles and metal ions, and has the advantage over the prior art that by means of a purposeful coagulation of the electrically conductive particles, the contact reliability between two adjacent electrically conductive connections extending through the adhesive is improved. Because the conductive particles are formed by metal particles finally dispersed below a percolation threshold and dispersed metal ions, and these can be purposefully coagulated to form anisotropically electrically conductive paths, anisotropy of the contact connection is assured with high certainty. The term percolation threshold is understood to mean the state in which the conductive particles each occupy a random position in the base material, and in which there is just barely still no metallically conductive connection between two adjacent particles. Because of the coagulation of the conductive particles to form the electrically conductive paths, the adhesive has regions, advantageously between two adjacent conductive paths, of improved insulation capacity, since here the number of conductive particles is reduced as a result of the coagulation into the conductive paths.
As a result of the process according to the invention for producing the anisotropically conducting adhesive, it is highly advantageously possible in a simple way to employ process steps, known per se from the structuring of integrated circuits, in modified fashion. Because a thermoplastic base material with conductive particles dispersed in it is preferably exposed to light via a mask, causing local heating in the exposed regions of the base material, and anisotropically electrically conductive paths are created in the exposed regions, any arbitrary layout of anisotropically conductive paths can be created via a large process window, and very high res

REFERENCES:
patent: 3708387 (1973-01-01), Turner et al.
patent: 3834373 (1974-09-01), Sato
patent: 4735847 (1988-04-01), Fujiwara et al.
patent: 4740657 (1988-04-01), Tsukagoshi et al.
patent: 5362421 (1994-11-01), Kropp et al.
patent: 5670251 (1997-09-01), Difrancesco
patent: 5685939 (1997-11-01), Wolk et al.

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