Interfacial reaction and intermetallic compound formation of Sn–1Ag/ENIG and Sn–1Ag/ENEPIG solder joints

• Interfacial reactions of Sn–1Ag/ENIG and ENEPIG joints are investigated.
• Their interfacial reactions and solder/substrate compatibility are estimated.
• The results are compared with those of Sn–3Ag–0.5Cu solders.
• ENEPIG performed very well with Sn–Ag–Cu solder.
• ENEPIG proved not to be a suitable surface finish for Sn–Ag solder.

Interfacial reactions and intermetallic compound (IMC) formation of Sn–1 wt.%Ag solder with two different surface finishes, electroless nickel–immersion gold (ENIG) and electroless nickel–electroless palladium–immersion gold (ENEPIG), were evaluated during a reflow process. We first compared the interfacial reactions of the two solder joints and identified a relationship between the interfacial reaction behavior and solder/substrate compatibility. The Sn–1Ag/ENIG joint exhibited stable IMC growth and superior interfacial stability compared with the Sn–1Ag/ENEPIG joint. The growth rate of the interfacial IMC layer and consumption rate of the Ni(P) layer were closely related to the interfacial microstructure and morphology of the IMCs. The layer-type well-attached interfacial IMCs had advantages with respect to IMC growth rate and Ni(P) consumption rate. Compared to the previous Sn–3.0Ag–0.5Cu study, ENEPIG performed very well with Sn–Ag–Cu solder alloy. On the other hand, ENEPIG proved not to be a suitable surface finish for Sn–Ag solder alloy in this study.