Effect of isothermal aging on intermetallic compounds and Kirkendall void growth kinetics of Au stud bumps

Intermetallic compounds (IMCs) and Kirkendall void growth kinetics at various interfaces in Au stud bumps were studied in terms of isothermal aging at 120 °C, 150 °C, and 180 °C for 300 h. Phases of AuSn, AuSn 2 , and AuSn 4 form at the interface of Au studs and Sn after a reflow. The thickness of an Au-Sn IMC was quantified with an image analyzer as a function of aging temperature and time. The growth of the Au-Sn IMC increases linearly with the square root of the aging time at 120 °C, 150 °C, and 180 °C. The growth of the Au-Sn IMC at 180 °C differs from the growth of the Au-Sn IMC at 120 °C and 150 °C because of excessive Au consumption by the Au studs. Kirkendall voids form at the interface of the Au stud and the Au-Sn IMC and increase linearly with the square root of the aging time. The apparent activation energies for the growth of the Au-Sn IMC and the Kirkendall voids were determined to be 0.57 eV and 0.2 eV, respectively, from measurement of the thickness of the Au-Sn IMCs and the width of the Kirkendall voids in relation to the aging temperature and time.