Effect of Rare Earth Metals on the Properties of Zn-20Sn High-Temperature Lead-Free Solder

Cerium–lanthanum mixed rare earth (RE) (0.5 wt.%) was added to Zn-20Sn high-temperature lead-free solder to study the effect of RE on the solder properties. The Zn-20Sn-0.5RE solder has a better corrosion resistance than that of Zn-20Sn alloy. RE addition increases the γ-Cu5Zn8 layer thickness, promotes growth of a e-CuZn5 layer shaped like bamboo shoots, and increases the roughness of the e-CuZn5 layer, which increases the shear strength of the solder joints. Compared with the Zn-20Sn alloy, the creep resistance of the Zn-20Sn-0.5RE solder was improved after soldering. The indentation hardness increases in an order of Zn-20Sn-0.5RE solder, Zn-20Sn solder, e-CuZn5 layer, and γ-Cu5Zn8 layer.