Effect of Pd(P) thickness on the soldering reaction between Sn–3Ag–0.5Cu alloy and ultrathin-Ni(P)-type Au/Pd(P)/Ni(P)/Cu metallization pad

Abstract The strong effect of the Pd(P) thickness ( δ Pd(P) ) on the interfacial reaction between Sn–3Ag–0.5Cu solder and ultrathin-Ni(P)-type Au/Pd(P)/Ni(P)/Cu pad was revealed. We observed that the P of the Pd(P) film would redeposit over the Ni(P) platings and formed layered Ni 2 SnP in the early stage of soldering reaction. An excessive growth of Ni 2 SnP inhibited the formation of layered (Cu,Ni) 6 Sn 5 , which is argued to be an effective diffusion barrier of Ni. Thus, an extremely fast depletion of the Ni(P) film accompanied by a substantial dissolution of the Cu pad might be induced for large δ Pd(P) . These observations demonstrated that δ Pd(P) plays a dominant role in determining the interfacial microstructure of solder joints and that a precise control on the δ Pd(P) value is required for microelectronic packaging reliability.