Thermomechanical Reliabilities of Pb-Free Solder Joints According to Ag Content in Harsh Environment

Pb-free solders based on Sn-Ag-Cu are currently applied to electronic devices. This article investigates the thermomechanical reliability of three different compositions of Pb-free solder joints, Sn-1.0Ag-0.5Cu, Sn-1.2Ag-0.5Cu, and Sn-3.0Ag-0.5Cu in a harsh environment. First, we perform a temperature cycling test (TCT) and a thermal shock test (TST) at temperatures from –55 to 125 °C. In addition, we conduct a combined thermal shock and vibration test (TSVT) using a HALT chamber, at –65 to 150 °C and an acceleration of up to (15 ± 1) Grms, considering the automotive underhood environment. We then analyze the mean lifetimes for each test of Pb-free solder joints dependent on the Ag contents. Finally, we present the lifetime ratios of three different Pb-free solders between TCT and TST, and show that SAC1205 has a similar mean lifetime to SAC305 within about 0.34% in combined TSVT. The results of this article could provide a reference for selecting suitable Pb-free solders in industrial use over harsh environments.