Thermal and Mechanical Properties of Flip Chip Package with Au Stud Bump

Abstract

The Au stud bumps offer a low cost flip chip solution for low I/O (input/output) count ICs and fine pitch packaging applications. The thermo-mechanical reliability of the flip chip package with Au stud bump was investigated in this study. Flip chip solder joints were fabricated using the Au stud bumps and Sn surface finish. And two different types of reliability test was done with and without the underfill process. Isothermal aging study was performed to investigate the formation and growth of the intermetallic compound (IMC) layer at the solder/metallization interface. The micro structural change of the Au stud solder joints were characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy. Results showed that before aging for 250 h, AuSn₄ and (Cu,Au)₃Sn IMC formed and after aging for 250 h Cu₃Sn IMC formed and grew as the aging time got longer. Effect on the mechanical reliability of the Au stud solder joints was also studied using shear (bonding) tester, and the temperature cycle test was chosen for the thermo-mechanical reliability evaluation of the Au stud solder joints.