Some optimum processing properties for anisotropic conductive adhesives for flip chip interconnection

In terms of electrical properties, the optimum interconnect packaging option for a bare semiconductor die is to attach directly the chip to the substrate — flip chip attach. This strategy has been followed for high complexity/cost boards in the past, but recently considerable interest has grown in the possible use of this technology for lower cost substrates and processes. Anisotropic conductive adhesives offer one possible route for low-cost flip chip technology, and in this paper, we use models to determine some of the optimum material properties required, and compare them against the properties of some representative current-generation materials to identify where improvements can be made. The materials properties examined in this paper include rheology of the adhesive resin, and type, size and volume fraction of conductive filler particles. The models developed deal with the time required to process the adhesive, changes in particle densities on the pads, and probabilities of electrical opens and shorts.