Au bump interconnection with ultrasonic flip-chip bonding in 20 μm pitch

Superfine flip-chip bonding technologies in 20 μm pitch microbumps on copper through-hole electrodes are substantial technologies for three-dimensional (3D) chip stacking LSI. As the advanced interconnection technology to connect the through-hole electrodes at low temperature and low bonding force, the ultrasonic flip-chip bonding (UFB) was verified by the total evaluation and the atomic-level analysis of the bonding interface on the chip-on-chip (COC) structure utilizing electroplated Au microbumps in 20 μm pitch. First, the lower limit bonding conditions were confirmed to be a bonding force of 20 N and an amplitude of 3 μm; the bonding accuracy achieved was within ±2μm, the electrical interface resistance was stable about 0.57 Ω, and no damage around the interconnection structure was observed. Secondly, the mechanism of solid phase bonding interface formation at the atomic level without solid phase diffusion was confirmed as the Au-Au solid phase UFB bonding mechanism, and the orientation geometry of such bonding was apparently different from that of thermo compression bonding, which showed solid phase diffusion across the boundary. The achievement of this research will enable the realization of the 3D chip stacking LSI in the near future, which is characterized by scalabilities and high-performance. The subjects are the elucidation of the real oscillation contributes to bonding to optimize the process conditions and the establishment of the micro joint reliabilities utilizing UFB process.