Effect of Thermal Aging on Intermetallic Compound Growth Kinetics of Au Stud Bump
Microstructural evolution and the intermetallic compound (IMC) growth kinetics in an Au stud bump were studied via isothermal aging at 120, 150, and 180˚C for 300hrs. The AlAu4 phase was observed in an Al pad/Au stud interface, and its thickness was kept constant during the aging treatment. AuSn, AuSn2, and AuSn4 phases formed at interface between the Au stud and Sn. AuSn2, AuSn2/AuSn4, and AuSn phases dominantly grew as the aging time increased at 120˚C, 150˚C, and 180˚C, respectively, while (Au,Cu)6Sn5/Cu3Sn phases formed at Sn/Cu interface with a negligible growth rate. Kirkendall voids formed at AlAu4/Au, Au/Au-Sn IMC, and Cu3Sn/Cu interfaces and propagated continuously as the time increased. The apparent activation energy for the overall growth of the Au-Sn IMC was estimated to be 1.04 eV.