Controlling Ag3Sn Plate Formation in Near-Ternary-Eutectic Sn-Ag-Cu Solders by Minor Zn Alloying Addition

As a result of extensive studies, near-ternary-eutectic Sn-Ag-Cu (SAC) alloys have been identified as the leading Pb-free solder candidate to replace Pb-bearing solders for ball grid array (BGA) module assembly. However, recent studies on the processing behaviors and solder joints reliability assessment have revealed several potential reliability risk factors associated with the alloy system. The formation of large Ag3Sn plates in solder joints, especially when solidified in a relatively slow cooling rate, possesses potential reliability concern. In previous studies, several methods were developed to suppress the formation of large Ag3Sn plates and its implications on solder joint reliability were reported. In this study, the effect of adding a minor amount of Zn in SAC alloy was investigated. The minor Zn addition was shown to effectively reduce the amount of undercooling during solidification and thereby suppress the formation of large Ag3Sn plates. The Zn addition is shown to cause changes in both the microstructure and interfacial reaction of the solder joint. The interaction of Zn with other alloying elements in the solder was also investigated which helps understand the role of Zn during solidification of the near-ternaryeutectic alloys.

By: Sung K. Kang, Da-Yuan Shih, Donovan Leonard, Donald W. Henderson, Timothy Gosselin, Sung-il Cho, Jin Yu, Won K. Choi

Published in: JOM - Journal of the Minerals Metals and Materials Society, volume 56, (no 6), pages 34-38 in 2004

Please obtain a copy of this paper from your local library. IBM cannot distribute this paper externally.

Questions about this service can be mailed to .