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The ball shear strength of BGA solder joints during isothermal aging was studied with Sn-3.5Ag-0.75Cu solder on three different pads (Cu, electroless Ni-P/Cu, immersion Au/Ni-P/Cu) at temperature between 70 and 170 • C for times ranging from 1 to 100 days. The reliability of solder ball attachment was characterized by mechanical ball shear tests. As a whole, the shear strength of BGA joints decreased with increasing temperature and time. The shear strength for both the immersion Au/Ni-P/Cu and electroless Ni-P/Cu pads was consistently higher than that of the Cu pad for all isothermal aging conditions. The fracture surface showed various characteristics depending on aging temperature, time, and the types of BGA pad. The P-rich Ni layer formed at the interface between (Cu, Ni) 6 Sn 5 and Ni-P deposits layer after aging, but fracture at this interface was not the dominant site for immersion Au/Ni-P/Cu and electroless Ni-P/Cu pad.

The present study is aimed at the assessment on the reliability of solder ball attachment to the bond pads of BGA substrate with various plating schemes. The reliability of solder ball attachment is characterized by mechanical ball shear tests. In addition to the ball shear tests, SEM is performed to inspect the cross-section and the fracture surface of the tested specimens for failure analysis. The aging was conducted in convection ovens in air at 343, 393, 423 and 443 K respectively for times ranging 8.64 × 10 4 to 864 × 10 4 s. Without regard to the deposited layer, the shear strength of BGA joints decreased with the increasing temperature and time. After isothermal aging, the fracture surface shows various characteristics depending on aging temperature and time, and the types of BGA pad.