Effect of Al2O3 addition in Sn-Ag-Cu solder balls on the microstructure and shearing strength of BGA packages with immersion Sn surface finish

Sn-Ag-Cu solders have been widely used as lead-free candidates for the Ball-Grid-Array (BGA) interconnection in the microelectronic packaging industry. However, widely used Sn-Ag-Cu solders such as with 3.0-4.0 wt% Ag in microelectronics exhibit significantly poorer reliability than SnPb solder. For the improvement of the problem by SAC solder alloys, the IMC control at the interface are needed. In order to identify the effect of the addition of 0.25 wt.% Al₂O₃ nanoparticles to Sn3.5Ag0.5Cu (SAC) solder, the interfacial microstructure between the solder with immersion Sn pad BGA substrates has been investigated as a function of multiple reflow cycles. Also the strength of the solder joints was evaluated by a ball shear test. The SAC composite solder joints consistently displayed a higher shear strength than that of the SAC solder joints as well as a function of reflow cycles due to a second phase dispersion strengthening mechanism. Another, the presence of a small amount of Al₂O₃ nanoparticles is effective in suppressing the growth of the intermetallic compounds layer.