Study of wetting reaction between eutectic AuSn and Au foil

Wetting reactions between eutectic AuSn solder and Au foil have been studied. During the reflow process, Au foil dissolution occurred at the interface of AuSn/Au, which increases with temperature and time. The activation energy for Au dissolution in molten AuSn solder is determined to be 41.7 kJ/mol. Au₅Sn is the dominant interfacial compound phase formed at the interface. The activation energy for the growth of the interfacial Au₅Sn phase layer is 54.3 kJ/mol over the temperature range 360–440°C. The best wettability of molten AuSn solder balls on Au foils occurred at 390°C (wetting angle is about 25°). Above 390°C, the higher solder oxidation rate retarded the wetting of the molten AuSn solder.