2019 Volume 60 Issue 700 Pages 142-146
In this paper, we describe the robustness of thermosonic flip chip bonding when the bottom chip is tilted in the chip-on-chip assembly. Experiments were carried out using a bottom chip with 12 Au ball bumps and a top chip with Al pads. A bonding condition that causes gross sliding at the bonding interface was chosen to improve the robustness to chip tilt. The bottom chip was tilted around the axis perpendicular to the direction of the ultrasonic vibration. We found that die-shear force and the sum of the contact area between bumps and the top chip electrodes were constant in spite of tilting of the bottom chip. Although the contact area between each bump and top chip electrode depended on different bonding forces generated by bottom chip tilting, the fractional area of Au-Al alloy of each bonding area became nearly equal. These were caused by the deformation stress of the gold ball bump under the application ofultrasonic vibration being constant in the deformation range in this study.