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.