AN OVERVIEW AND EVALUATION OF ANISOTROPICALLY CONDUCTIVE ADHESIVE FILMS FOR FINE-PITCH ELECTRONIC ASSEMBLY

Conductive adhesives have been used in the electronics industry for se veral years to attach chips to package lead frames in the semiconducto r industry and for general interconnection of components to flexible c ircuits for various consumer products. Generally, these materials cond uct equally in all directions. To obtain pad isolation, the adhesives are screen printed to the pattern of the circuit pads. In the last few years, a new class of adhesives that are conductive in a single direc tion have been developed. These are referred to as anisotropic conduct ive adhesive films (ACAF's). These anisotropically conductive adhesive s provide electrical as well as mechanical interconnections for fine p itch applications. The conductivity of ACAF materials is only in the Z -direction (perpendicular to the plane of the board) while electrical isolation is maintained in the X - Y plane. Currently, at least 15 ACA F materials are commercially available. We have developed a methodolog y for evaluating these materials for their mechanical and electrical p roperties and interconnection use in the 8 to 15 mil pitch range. In a ddition, we characterized the materials according to their physical pr operties and cure characteristics. This paper details our findings wit h a comparison of physical form to assembly/cure and final electrical properties. We include in this study data from scanning electron micro scopy, thermal analysis of the ACAF's, and cure and assembly studies o n mixed substrate test vehicles. Information on initial electrical tes ting and long-term reliability testing is also given.