Solder Volume Effect on Interfacial Reaction between Sn-Ag-Cu/ENImAg Substrate

The purpose of this study is to investigate the effect of solder volume on interfacial reaction during reflow soldering between Sn-3.0Ag-0.5Cu (SAC305) and Sn-4.0Ag-0.5Cu (SAC405), and electroless nickel/immersion silver (ENImAg) surface finish. Different solder balls with sizes of 300 μm, 500 μm and 700 μm diameters were used. The characteristics of intermetallic compound (IMC) were analysed by using field emission scanning electron microscopy (FESEM), scanning electron microscopy (SEM), optical microscope and energy dispersive x-ray (EDX). After the plating process, the result showed that ENImAg surface finish was free from black line nickel. After reflow soldering, a thin layer Ni3P or P-rich layer was formed. The result also revealed that an IMC layer was formed at the interface of (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 as well as Ag3Sn platelet. In term of morphologies, the grains type of IMC layer appeared as chuck, needles, rode, plate, diamond and bar shape. The result also indicated that, the solder volume can influence the IMC thickness, where the smaller size of solder balls produced a thinner IMC layer compared with a larger solder ball during the reflow soldering process. Meanwhile, a total of the IMC thickness for SAC305 was thinner than SAC405 solder ball.