Comparison of spreading behaviour and interfacial microstructure in Sn–0·7Cu, Sn–0·3Ag–0·7Cu and Sn–2·5Ag–0·5Cu lead free solder alloys on Fe–42Ni substrate

Abstract

In the present work, spreading behaviour and development of interfacial microstructure in Sn–0·7Cu, Sn–0·3Ag–0·7Cu and Sn–2·5Ag–0·5Cu lead free solder alloys on Fe–42Ni substrates having two different surface textures were investigated. Smooth textured surfaces yielded better wettability than rough surfaces particularly for Sn–0·7Cu solder alloy. Wettability of Sn–0·7Cu solder on rough textured surfaces was found to be poor compared to other solder alloys. Spreading of Sn–0·7Cu solder on substrate surface showed longer viscous regime, Sn–2·5Ag–0·5Cu solder exhibited shortest viscous regime. Sn–0·3Ag–0·7 solder showed intermediate behaviour. Sn–Cu solder alloy exhibited needle and coarse shaped (Cu,Ni)6Sn5 intermetallics at the interface and in the matrix of the solder alloy on smooth substrate, whereas on rough substrate, formation of only coarse shaped (Cu,Ni)6Sn5 intermetallic compounds (IMCs) was observed. For Sn–0·3Ag–0·7Cu solder alloy, Fe–Ni–Sn and FeSn2 IMCs identified at the interface. (Cu,Ni)6/Sn5 IMCs were found to be less coarser than as observed at Sn–0·7Cu/substrate interface. Sn–2·5Ag–0·5Cu alloy exhibited (Cu,Ni)3Sn4 and (Cu,Ni)6 Sn5 IMCs at the interface and in the bulk of solder alloy.