Characterization of adhesive materials for high circuit density applications

Abstract

This report presents the results of the evaluation of isotropic and anisotropic conductive adhesives for flip chip and chip size package applications. Samples consist of bumped testchips mounted on fine pitch rigid and flexible substrates. The finest pitch of the rigid glass substrates is 70 /spl mu/m and for the flexible substrates 100 /spl mu/m. Promising candidate for adhesive joining technique are the isotropic conductive adhesives. These adhesives are isotropic, which means that they conduct electricity equally in all directions. To use such adhesives in flip chip applications, the material has to be applied precisely onto the points to be connected, and is not allowed to flow and short circuit between circuit lines. The anisotropicaliy conductive adhesive materials are prepared by dispersing electrically conductive particles in an adhesive matrix at a concentration that is high enough to assure reliable conductivity between the substrate and the IC electrodes. The reliability evaluation was performed with special regard to the degradation and to the interface reactions between polymers and metal surfaces in adhesive contacts. The electrical and mechanical performance of the adhesive bonds were studied by evaluating initial contact resistance and mechanical adhesion as a function of temperature and humidity. A detailed thermo-mechanical analysis was used to determine the optimal cure schedule and to characterize the materials according to their physical properties. This kind of analysis method has also been used to optimize the curing profile, i.e. to shorten the curing time.