Abstract
Evolution behaviors of Cu6Sn5 and Cu3Sn layers were studied upon Sn–xZn (x=0, 0.2, 0.5, and 0.8wt%) and electroplated Cu (EPC) joints. The Cu6Sn5 and much thicker Cu3Sn layers were observed at a Sn/EPC interface during thermal aging at 180°C. Zn addition was found to suppress the growth of whole intermetallic compound (IMC) layer, while the suppression effect was weakened with increase of Zn content. Though Zn addition suppressed growth of the Cu3Sn layer, it also promoted the Cu6Sn5 growth. Moreover, the grains of IMC layer near the solder were observed to be refined by Zn; it is beneficial in increasing atom diffusion through the Cu6Sn5 layer. Hence, Cu atom accumulation decreased while Sn atom accumulation increased at Cu3Sn/Cu6Sn5, further promoting 2Cu3Sn+3Sn→Cu6Sn5. Therefore, the refining upon grain size of the IMC layer as well as stabilizing upon the Cu6Sn5 phase by a small amount of Zn contributed to Cu6Sn5 growth and Cu3Sn consumption in the solder joints.
Published Version
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