A High-reliability Au Stud Bump Bonding Strategy Based on Au Pads for Flip-chip Bonding Applications

Flip-chip bonding technology has been widely used in advanced packaging applications, where the Au stud bump bonding shows advantages in both the simple and flexible fabrication process and the good electrical performance. However, conventional Al pads suffer from long-term reliability risks due to the Au-Al inter metallic compounds (IMCs). In this paper, Au pads are fabricated on Al pads to provide an inherently stable Au-Au bonding interface for the Au stud bump bonding. The key parameters in the bonding process are investigated by the orthogonal experiments based on the bonding pressure, ultrasound power, and bonding time. According to the results of the shear force tests, the bonding time has the largest influence on the bonding strength, and the optimal process parameters are bonding pressure of 35 gf, ultrasonic power of 390 mW, and bonding time of 20 ms. Furthermore, reliability tests including the high-temperature storage tests (HTSTs) and the temperature cycling tests (TCTs) are carried out on the fabricated heterogeneous bonding structure, which demonstrates good reliability with average shear strengths of 42.65 gf and 43.30 gf after the HTSTs and the TCTs, respectively. This stable and reliable bonding strategy is beneficial to enhancing the reliability of the flip-chip bonding applications.