Abstract
The microstructural evolutions and shear properties of the Sn–3.5Ag (in wt%) BGA solder joints were investigated in terms of the effects of various substrate metallization methods with multiple reflows. A continuous scallop-shaped Cu 6Sn 5 intermetallic compound (IMC) layer was formed at the solder/Cu interface, whereas a reaction layer between the solder and electrolytic Ni/Au substrate was analyzed to be a continuous Ni 3Sn 4 IMC layer. The thickness of the IMC layers increased with the number of reflows. The reaction products between the solder and electroless Ni/immersion Au (ENIG) substrate were three distinctive layers consisting of Ni 3Sn 4, Ni–Sn–P and Ni 3P. The spalling of the Ni 3Sn 4 IMC and the growth of Ni–Sn–P and Ni 3P layers were observed with the number of reflows. The shear properties of the Sn–3.5Ag/Cu solder joints were nearly consistent with the multiple reflows. The electrolytic Ni/Au substrate provided the excellent mechanical properties of the Sn–3.5Ag BGA solder joints. The shear properties of the Sn–3.5Ag/ENIG solder joints significantly decreased with the multiple reflows.
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