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The electrochemical behaviors, microstructures, and corroded products of Sn-9Zn-xAg lead-free solders were investigated in this study. The 63Sn-37Pb and Sn-3.5Ag solder alloys were also tested for comparison. The Sn-3.5Ag solder alloy had a higher equilibrium potential (Ϫ0.44 V SCE ) than the ones of 63Sn-37Pb (Ϫ1.10 V SCE ) and Sn-9Zn (Ϫ1.43 V SCE ). The Ag addition enhanced the corrosion resistance of the Sn-9Zn solder alloy. Passivation behavior occurred in the solder alloys used in this study except the 63Sn-37Pb one. X-ray diffraction patterns showed that the Zn segregated in the Sn-9Zn solder alloy as solidified, but it dissolved when 0.5 wt % Ag was added to the solder alloy. The AgZn 3 and Ag 5 Zn 8 were found in the Sn-9Zn-1.5Ag solder alloy but they were substituted by the Ag 3 Sn when the Ag content in the solder alloy was above 2.5 wt %. However, they were the initial sites for pits formation. The corroded product of SnCl 2 was observed in all solder alloys tested. In addition, the ZnCl 2 , ZnO, and SnO were observed in the Sn-9Zn-xAg solder alloys.The 63Sn-37Pb solder alloy is the most widely used interconnecting material in microelectronic packaging due to its low melting point of 183°C, excellent wettability on substrate, and suitable mechanical properties. 1 But it will be limited to use after 2006 because of its toxicity. 2 Therefore, it is an urgent mission to develop a suitable lead-free solder for using in practice.Many factors have to be considered for developing a new leadfree solder, such as wettability, melting point, solder joint reliability, and corrosion resistance. 3 The Sn-9Zn solder alloy is a promising material to use in lead-free packaging processes because its melting point of 198°C is close to that of the 63Sn-37Pb solder alloy. However, it is sensitive to corrosion and oxidation due to the high activity of Zn and an inferior wettability on Cu substrate as soldered. Although the disadvantages can be resolved by soldering in a protective atmosphere, the increased cost and complicated process are not accepted.Lin et al. have shown that Al addition enhances the corrosion and oxidation resistance of the Sn-Zn-Al solder alloy. 4,5 However, the Al addition also decreases the ductility of the Sn-Zn-Al solder alloy. 6 Besides, the Kirkendall voids form at the Sn-Zn-Al/Cu interface after aging and deteriorate the solder joint reliability. 7 Takemoto et al. 8 have reported that adding Ag to the Sn-9Zn solder alloy inhibits the anodic dissolution of Zn and enhances the wettability of solder alloy on Cu substrate. A wetting time of 1.4 s was obtained when Cu was fluxed in a rosin mildly activated ͑RMA͒ solution then soldered in the Sn-9Zn-0.5Ag solder alloy at 230°C as reported by Lin and Shih, 9 which could be acceptable for the practical process. Chang et al. 10 have demonstrated that the Sn-9Zn-0.5Ag solder alloy has a higher melting temperature than that of the Sn-9Zn just for 1.2°C, which is acceptable for practical usage. Kirkendall voids formation was hindered by the Ag addition as re...

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