Wetting and soldering behaviour of eutectic Au-Ge alloy on Cu and Ni substrates

Au-Ge based alloys are interesting as novel high temperature lead free solder alloys because of their low melting point, good thermal and electrical conductivity and high corrosion resistance. In the present work, the wetting and soldering behaviour of the eutectic Au-28 at.% Ge alloy on Cu and Ni substrates have been investigated. A good wetting on both substrates with final contact angles of 13-14° was observed. In addition, under controlled conditions good solder joints could be produced. Cu substrates exhibit a pronounced dissolution into the Au-Ge filler metal. This was referred to the formation of a reaction layer at the interface with a fcc structure, which allows fast diffusion of Cu and Au. On Ni substrates, the NiGe intermetallic compound was formed at the filler /substrate interface which prevents dissolution of Ni into the solder. Using thin filler metal foils (25 µm), a complete consumption of Ge in the reaction at the Ni interface was observed, leading to the formation of almost pure Au layer in the soldering zone.