Anisotropically conductive polymer films with a uniform dispersion of particles

Anisotropically conductive films consisting of a single layer of magnetically separated conductor spheres in a polymer matrix are described. In a vertical magnetic field, ferromagnetic spheres in a viscous medium become parallel magnetic dipoles and repel one another to produce a uniform, two-dimensional particle distribution. This structure is then frozen in by cooling or curing of the polymer matrix. In order to prevent the formation of undesirable dendritic particle protrusions, the magnetic force on the particles has to be balanced against the surface tension of the polymer and the gravity effect. As an interconnection material placed between circuit devices, the present conductive polymer films with uniformly distributed particles exhibit, as compared to the conventional, random distribution, a reduced tendency for electrical shorts and pad-to-pad variations in contact resistance values especially for fine pitch interconnections. Since the percolation stringers are no longer present in the magnetically distributed structure, it is anticipated that electric-field-induced isolation failures observed in some adhesive films will be substantially diminished.<
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