Abstract
In this paper, the microstructure evolution and shear performance of aged BGA structure Cu/Sn-58Bi/Cu and Cu/Sn-57.6Bi-0.4Ag/Cu solder joints with the same volume and different thicknesses were studied. The results show that phase coarsening occurred in both solder joints after aging, and the addition of Ag was beneficial to fine the microstructure of solder joints. However, the added Ag did not mitigate the growth of intermetallic compound (IMC) layer in the aged solder joint. Moreover, the shear strength of Cu/Sn-57.6Bi-0.4Ag/Cu solder joints is greater than that of Cu/Sn-58Bi/Cu solder joints. The shear strength of both joints increased with the decrease in joint thickness at the same aging time. Interestingly, the shear strength decreased first and then increased with aging time at the same thickness. Finally, it can be known from the fractographies that the fracture positions of the two solder joints with different thicknesses after aging all happened in the solder matrix, showing a prominent ductile fracture.
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