Investigation of interfacial reactions between Sn–Zn solder with electrolytic Ni and electroless Ni(P) metallization

In this study, interfacial reactions of electrolytic Ni and electroless Ni(P) metallization of the ball-grid-array (BGA) substrate with the molten Sn–9Zn (wt.%) eutectic solder alloy were investigated, focusing on the shear strengths and the identification of the intermetallic compound (IMC) phases at various reflow periods. Zn-containing Pb-free solder alloys were kept in molten condition (240 °C) on the bond pads for different durations ranging from 1 to 60 min to render the ultimate interfacial reaction and to observe the consecutive shear strength. After the shear test, fracture surfaces were investigated by scanning electron microscopy equipped with an energy dispersive X-ray spectrometer. Cross-sectional studies of the interfaces were also conducted to correlate with the fracture surfaces. The solder ball shear-load for the Ni(P) system during extended reflow increased with the increase of reflow time. The consumption of the electroless Ni(P) layer in Sn–9Zn was also lower than that of the electrolytic Ni. It was evident that the Sn–Zn solder/electrolytic Ni system was more vulnerable than the Sn–Zn solder/electroless Ni(P) system in high temperature long time liquid state annealing. Sn–Zn solder with electroless Ni(P) metallization appeared as a good combination in soldering technology.