Microstructure of interfacial reaction layer in Sn–Ag–Cu/electroless Ni (P) solder joint

This study examined the interfacial reaction in Sn-3.5Ag-0.7Cu/electroless Ni (P) solder joints using various TEM techniques. TEM confirmed that three types of intermetallic compounds (Ag3Sn, (Cu, Ni)6Sn5 and (Ni, Cu)3Sn4) formed in the solder joints. In addition, interfacial reaction layers between the IMCs and the electroless Ni (P) are composed of two reaction layers (ternary and P-rich Ni layers). The ternary layer is composed of orthorhombic Ni2SnP phase and the P-rich Ni layer is dominantly composed of Ni3P. Furthermore, Kirkendall voids were clearly observed in the ternary layer and P-rich Ni layer. The Sn has diffused preferentially along the grain boundaries in the (Ni,Cu)3Sn4 IMCs.