Effects of Minor Addition of Zn on Interfacial Reactions of Sn-Ag-Cu and Sn-Cu Solders with Various Cu Substrates during Thermal Aging

The effects of Zn addition to Sn-0.7Cu and Sn-3.8Ag-0.7Cu (all in wt.%) Pb-free solders on the interfacial reaction with Cu substrates were investigated. The study was focused on the intermetallic compound (IMC) growth, Cu consumption and void formation as a function of thermal aging and solder composition. Four different kinds of Cu substrates (high-purity Cu, oxygen-free Cu, vacuum-sputtered Cu, and electroplated Cu) were prepared to compare their interfacial reaction behaviors with Zn-added solders. Thermal aging was performed at 150°C for up to 1000 hours to accelerate the interfacial reactions between solders and Cu substrates. Growth of IMCs (Cu6Sn5 and Cu3Sn) in Zn-added solders was slower than those without Zn addition. The growth of the Cu3Sn phase, in particular, was drastically reduced in the Zn-added solders on all four Cu substrates. On an electroplated Cu, numerous voids were observed in the Cu3Sn phase for Sn-Cu and Sn-Ag-Cu solders aged at 150°C for 1000 hours. However, these voids were largely eliminated in the Zn-added solders. On other three Cu substrates, the conditions which produce a high density of voids were not found after the aging in both solders with and without Zn. The Cu consumption with Zn-added solders was also significantly lower. The beneficial effects of Zn-addition on interfacial reactions are reported and the corresponding mechanisms in suppressing void formation and Cu consumption due to Zn addition are discussed.

By: Moon-Gi Cho; Sung K. Kang; Da-Yuan Shih; Hyuck Mo Lee

Published in: Journal of Electronic Materials, volume 36, (no 11), pages 1501-1509 in 2007

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