High frequency thermosonic flip chip bonding for gold to gold interconnection

Our main objective is to compare the process windows under different ultrasonic frequencies for thermosonic flip chip application. The interaction effects of bond power and bond force on the die shear strength and package standoff height are elucidated. The effects due to different substrate materials (FR-4 and ceramic substrates) are also included. It is interesting to notice that, apparently, the vibrating amplitude and thence the bonding frequency play a key role in determining the robustness of the thermosonic flip chip bond. Based on our findings, the process windows of 63 kHz and 109 kHz bonding on FR-4 and ceramic substrates are established, respectively, and compared. Unlike some earlier studies on high frequency bonding in wirebonding, the findings in this work suggests that the process window of the 109 kHz bonding is in fact wider than the 63 kHz bonding on both substrate materials, where rigid ceramic substrates allowed larger process windows for both frequencies bonding than FR-4 substrates.