Influence of cerium on microstructure of Sn-Ag-Cu lead-free solder

The microstructures of Sn-3.8Ag-0.7Cu lead-free solder with different contents of cerium were studied. The studied results showed that the microstructures can be refined and the inter metallic compounds can be suppressed because of addition of small amounts of cerium into the lead-free solder. When cerium is 0.03wt.%, the microstructure of the solder is fine and distributed uniformly, and which possess the best mechanical properties of soldered joints and better wettability. When cerium is over 0.03wt.%, the black cerium-rich phase appears and increases with the content of cerium. The microstructure analyses and theoretical calculation indicated that the black cerium-rich phase is a compound of Sn and Ce.