Reflowable anisotropic conductive adhesives for flipchip packaging

Anisotropic conductive adhesive (ACA) is an interconnect material providing electrical connection and mechanical bonding between two substrates. The application of this interconnect process has increased tremendously in LCD module assembly, for interconnection between the TAB package and LCD cell, and also the flip-chip on glass substrate bonding process. This paper presents ACA development trends, the advantages and limitations of current ACA materials and ACA application to flip chip bonding. This paper also discusses new developments in ACA, including the reflowable ACA bonding application. The reflowable ACA enables ACA bonding prior to the surface mount reflow process. The new application simplifies the current flip chip bonding process as compared to C4, COB, etc., and improves the system cost by eliminating the expensive IC bumping process. The ACA resin is also a good element for chip encapsulation. The gang bonding process provides very short process cycle times for high pin count devices, and can interconnect IC chips down to 75 μm pad pitch and 5000 μm sq. contact area. ACA bonding is a new interconnect process generation, providing the potential to replace current IC packaging processes and the soldering process. At present, the application is limited by the interconnection reliability, since ACA is a polymeric resin based material. As the new material was developed to withstand multiple thermal reflow, the interconnection reliability shall be acceptable as a viable solution for future IC packaging processes