Effects of Indium content on interfacial reaction and microstructure evolution of Cu/SAC-xIn/ENEPIG BGA solder joints

The effects of Indium (In) content on interfacial reaction and microstructure evolution of Cu/Sn-3.0Ag-0.5Cu-xIn/ENEPIG (SAC-xIn, x = 0, 1, 2, 5 wt.%) ball grid array (BGA) solder joints were investigated. The growth of intermetallic compounds (IMCs) were suppressed by the solid dissolution of In into (Cu,Ni)₆(Sn,In)₅, which further inhibited the growth of Cu₃Sn. The IMCs at the SAC/Cu interface exhibited the typical scallop-like morphology. As the In content increased, the IMCs became flatter while their grain size increased slightly. At the ENEPIG side, the IMCs changed from large rod-like to small needle-like shapes. Notably, the effects of In addition on the inhibition of the IMC growth and the microstructure refinement of the IMCs were most pronounced when the In content was 2 wt.%. While, the inhibition effect was weakened due to the formation of the Ag₂In phase in the Cu/SAC-5In/ENEPIG BGA solder joints. Also, In addition promoted the dissolution of the Cu substrate and inhibited the dissolution of the ENEPIG substrate, which further affected the Cu-Ni cross-interaction in the Cu/SAC-xIn/ENEPIG BGA solder joints. The growth, microstructure evolution and suppression mechanism of the interfacial IMCs in the Cu/SAC-xIn/ENEPIG BGA solder joints were probed and discussed.