Thermomechanical Reliability of SAC/SB Mixed Solder Containing Sn-58Bi Eutectic Solder

초록

This study investigated the thermo-mechanical reliability of Sn-3.0Ag-0.5Cu (SAC)/Sn-58Bi (SB) mixed solder joints with comparing SAC solder. To investigate the effect of SB addition on the thermo-mechanical reliability of SAC solder joints, thermal shock testing was conducted for 1000 cycles (-55 to 125 °C). The mechanical bonding properties were evaluated through solder ball shear and microhardness tests before and after thermal shock testing. In addition, the microstructure and fracture mode were analyzed. The SAC/SB mixed solder joints showed higher initial shear strength and microhardness than that of SAC solder joints. After thermal shock testing, both solder joints exhibited decreased mechanical properties. However, the reduction in shear strength and microhardness was lower in the SAC/SB mixed solder joints. This result is attributed to the precipitation hardening and dispersion strengthening effects of the Bi-rich phase and Ag3Sn and Cu6Sn5 intermetallic compound (IMC) particles formed in the SAC/SB mixed solder joints. Microstructural analysis showed that the coarsening of internal phases and excessive growth of the interfacial IMC layer were relatively suppressed in the SAC/SB mixed solder joints. Furthermore, fracture mode analysis indicated that the fracture surface of SAC/SB mixed solder joints indicated mixed ductile–brittle fracture mode involving both the solder bulk and interfacial IMC before and after thermal shock testing. Therefore, SAC mixing with SB improved the reliability of SAC solder joints during thermal shock testing.

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