Basic Research of 20.MU.m-Pitch Micro Au Bump Interconnection

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The three-dimensional (3D) chip stacking LSI under development in ASET uses new SIP (systemin-a-package) packaging technologies to realize high-density and high-speed transmission. Superfine flip-chip bonding utilizing micro bumps on Cu through-chip via (TCV) with a 20-μm-pitch is an important technology for realizing vertical interconnection, and ultrasonic flip chip bonding (UFB), utilizing Au bumps to connect the Cu TCV, is expected to enable a low-temperature and high-throughput process. In a basic study of the 20-μm-pitch Au bump interconnection, a thermo-compression bonding process was evaluated on a chip-on-chip (COC) structure. First, the mechanism of Au-Au thermo compression bonding with a recrystallization phenomenon across the bonding interface was confirmed. Second, it was confirmed that in the case of COC interconnections, the plastic strain range of the interconnections during temperature cycling tests (TCT) was mainly determined by the thermal mismatch in the thickness direction between the Au bump and the underfill resin. Finally, we developed a finite element method (FEM) analysis that corresponds well with the TCT results on the assumption that Au bump interconnection was composed of inhomogeneous crystal structure.
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