Abstract
The multiple reflow reliability of Au-20 wt%Sn solder has attracted great interests in optoelectronic and high power electronic industries. But the growing dendrite in the solder has a negative effect on the reliability of the solder joint. In this study, to control the microstructure and improve the reliability of the Au-20Sn electronic-packaging solders, we successfully designed and prepared a (Au-20 wt%Sn)-2wt.%Ag solder using micro-alloying method. It was found that the addition of 2 wt%Ag can change the heterogeneous nucleation conditions and refine the grains of primary Au5Sn phase, forming globular-shaped (Au,Ag)5Sn phase and eutectic (AuSn + (Au,Ag)5Sn) lamellar structure. The (Au-20Sn)-2Ag solder showed a strong reflow reliability even after 200 times of reflow (the shear strength of (Au-20Sn)-2Ag/Au/Ni(P)/Kovar joint maintained 88.33% of that measured after one reflow, and the shear strength of Au-20Sn/Au/Ni(P)/Kovar joint only maintained 63.37% of that measured after one reflow). The interface of (Au-20Sn)-2Ag/substrate joint after 200 times of reflow consisted of less accumulated (Ni,Au)3Sn2 grains and thick (Au,Ni)5Sn phase, so the refined microstructure can reduce the stress concentration and thus hinder the crack initiation and propagation, thereby significantly improving the reliability of the joint.
Published Version
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