Morimasa Tanimoto, Hitoshi Tanaka, Satoshi Suzuki, Akira Matsuda
The authors have developed Pb-free tin alloy plating materials. Preliminary screen tests showed that several alloy candidates had some shortcomings. Sn-Ag plating had high costs, Sn-Bi plating had shortcomings in both thermal stability and workability, and Sn-Zn plating in wettability and jointing capability.
In the Sn-Bi plating, thermal stability and workability have been improved by adopting a double-layer plating, i.e., an Sn-Bi surface layer/Sn undercoat layer. The double-layer plating reduces the total amount of Bi and hence reduces pollution of the soldering material. Also reflow-process improves the environmental resistivity of the plating.