Fluxless Soldering of Laminated Thin Metal Plates Using Au-Sn Alloy Solder

Abstract

Au-Sn solder has relatively high reliability because of the higher corrosion resistance and high temperature strength compared with Pb-Sn solder. It is, however, difficult to form Au-Sn alloy solder layer in the wet plating process on bonding surfaces. In this study, Au-Sn solder is provided as laminated Au-Sn-Au plating formed in a wet process on thin metal plates. Ni plating is formed prior to laminated Au-Sn-Au plating in order to improve wettability of the solder. Soldering process for thin metal plates without flux is investigated at the view point of soldering conditions and outgassing from the solder. Experimental result shows that Au plating contains larger amount of gas compared with Ni or Sn plating and the gas causes the solder layer to form voids. Forming many small holes around the specimen surface, amount of voids can be reduced. Peeling test shows that the peel strength of bonded specimen is influenced by the residual Ni thickness on the bonding interface rather than the bonding time or bonding pressure.