| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 95 === The Sn-Zn based solder exhibits unsatisfactory oxidation resistance. It is very prone to oxidation that decreases the life of products. This study investigated the oxidation behavior of Sn-8.5Zn-xAg-0.01Al-0.1Ga(x= 0~1.0wt％) solders at high temperatures and during heat/humidity exposure. During the experiment, some whiskers formed on the surface of the solder. Therefore, the observation of Sn whisker growth behavior was also investigated in this study.
The microstructure of Sn-8.5Zn-xAg-0.01Al-0.1Ga(x=0~1.0wt％) shows that the AgZn3 compound was formed after the addition of Ag to the solder. The results of thermal gravimetric analysis(TGA) showed that the oxidation rate and oxide decreased as the Ag content of Sn-8.5Zn-xAg- 0.01Al-0.1Ga(x=0~0.5wt％) increase. The major composition of the oxide was ZnO. Because the oxidation layer blocked the reaction and diffusion between Zn and O2, the oxidation reaction reaches saturation after 25 minutes.
The content of Zn-rich phase decreased in the matrix. After heat/humidity exposure at 85℃/85％RH(relative humidity), the major oxide formed are ZnO and a few SnO2. The thickness of oxidation layer increases with increasing Ag content. Sn whisker growth was driven by the compressive stress in the solder. The compressive stress is introduced due to the volume expansion when ZnO formed at the grain boundary of Sn.
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