IMC formation on BGA package with Sn-Ag-Cu and Sn-Ag-Cu-Ni-Ge solder balls

Solder balls were attached to the Cu/Ni-P/Au metallized BGA substrate. The two solder ball used in this study are Sn-3.2Ag-0.5Cu and Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge. The package was subjected to thermal aging at 150 °C for 100-1000 h in order to investigate IMC formation behavior. Cross sections and the surface of the IMC layer, revealed through etching of the unreacted solder, were inspected and analyzed with SEM and EDX. The IMCs mainly consist of two morphologies, hexagonal and whisker. The hexagonal crystal was identified as (Cu, Ni)6Sn5 and the whisker crystal is (Ni, Cu)3Sn4. The dissolution of Ni in Cu6Sn5 results in a synergistic effect that enhances the growth of the compound, and a similar effect was not observed when dissolved Cu was present in Ni3Sn4. This phenomenon is possibly due to the vacant energy band of the 3d-orbital of Ni. Ag3Sn was also detected in the solder region near the interfacial IMC. The Ag3Sn was not in direct contact with the BGA substrate.