Direct chip powering and enhancement of proximity communication through Anisotropic Conductive adhesive chip-to-chip bonding

Proximity communication (PxC) technology has attracted great attention in recent years for its potential in low power, high bandwidth multi-chip module applications. In our previously demonstrated PxC MCM package, a 3-chip sub-assembly with two Active chips communicated through a Bridge chip and was flip-chip bonded to the substrate. The Bridge and Active chips overlap, and are face-to face bonded with silicone-based adhesive. The low pin count Bridge chip (face-up) relied on the bonded Au wire to deliver power and low speed I/Os. The parasitic inductance of the bondwires limited bandwidth on the Bridge, which motivated an alternative way to power the face-up Bridge chip. In this paper, we report chip-to-chip bonding using Anisotropic Conductive Film (ACF) as the dielectric adhesive between PxC channels. ACF provided direct vertical conductive path to power the Bridge chip. In addition, the introduction of conductive particles could increase the effective dielectric constant of the adhesive which benefits capacitively- signal coupling for proximity communications. The bonding experiment was carried out using a two-stage alignment and bonding/cure process at Sony Chemical & Information Device Corporation. Physical characterizations such as SAT, SEM, EDX were carried out to investigate bond line, alignment and quality of the adhesive interfaces. The effect of the floating metallic particles inside the ACF material on the local capacitive channels was simulated using a commercial FEM solver Q3D Extractor from ANSYS. We also tested conductive channel continuity through boundary scan-chain test of the Island chips. The initial results indicates that ACF sandwiched between two chips formed a uniform, void free bondline.