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, AuSn2,
and AuSn4 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.