Investigation of Shear Strength and Temperature Cycling Performance of Bi-doped Sn-Ag-Cu Solder Joints

The shear strength, shear fracture mode, and interfacial reaction of Bi-doped SnAgCu solder ball under thermal aging at 150°C and 175°C for up to 250h were investigated in this study. Five different combinations of solder balls and substrate finishes were fabricated and tested including: SAC405Ni005-Bi and SAC105Ni005 on organic solderability preservative (OSP); SAC405Ni005-Bi, SAC305, and SAC302 on electrolytic NiAu (eNiAu). The interfacial intermetallic compound (IMC) of SAC105Ni005 on Cu-OSP, SAC305 on eNiAu, SAC405Ni005-Bi on Cu-OSP, SAC305 on eNiAu, SAC405Ni005-Bi on Cu-OSP and eNiAu are identified as (Cu, Ni)6Sn5, which confirms that Bi atom is not involved in the interfacial reaction. Whereas the IMC of SAC302 on eNiAu is identified as (Ni, Cu)3Sn4, which significantly differs from the other combinations. In addition, the formation of second phase IMC Cu3Sn and (Ni, Cu)3Sn4 were further observed on SAC405Ni005-Bi with Cu-OSP and eNiAu after thermal aging for 250h, respectively. The result of ball shear test at 600 um/sec shear speed showed that as-assembled SAC405Ni005-Bi gives approximately 70% bulk strength increase as compared to SAC305 and SAC302, which confirms the strengthening effect of Bi addition. Furthermore, the shear test after thermal aging indicated that the interfacial shear strength of SAC405Ni005-Bi on Cu-OSP is approximately 40% greater than SAC405Ni005-Bi on eNiAu, which confirms that IMC combination of (Cu, Ni)6Sn5 and Cu3Sn is more robust than that of (Cu, Ni)6Sn5 and (Ni, Cu)3Sn4 to resist interfacial shear stressing. As a result, temperature cycling is performed to validate the performance of Bi-doped solder alloy.