Abstract
The exemption of Pb-bearing automobile electronics in the End of Life Vehicle (ELV) directive has recently expired, bring an urgent need to find Pb-free alloys that can maintain good performance under high-temperature and vibration conditions for automobile application. In this study, a new lead-free solder, Sn-0.7Cu-0.2Cr (wt.%) alloy, was developed. To evaluate the thermomechanical reliability of the new solder alloy in automobile electronics, a thermal shock test was performed. The results show that the presence of Cr in solder inhibits the growth of interfacial Cu3Sn layer and the formation of Kirkendall voids, which effectively improves the joint reliability under intense thermal shock condition compared with the commercial SAC305 and SC07 solders. Specifically, the shear strength of the Sn-0.7Cu-0.2Cr/Cu solder joints was higher by 23% and 44% than that of SAC305 and SC07 solder joints after 2000 cycles of thermal shock at 1 m/s shear speed.
Highlights
Due to environmental concerns, legislation has come into effect, which was passed by the European Union in 2002, to ban the use of Pb and other toxic materials in electronic packaging [1,2].Extensive searches for Pb-free solder alloys have been conducted over the past two decades.Nowadays, a Pb-free process has been successfully achieved in consumer electronics production, whereas Pb-bearing solders are still used in the vehicles industry because of the reliability and safety concerns of Pb-free solder alternatives [3,4]
Very few Cu3 Sn intermetallic compounds (IMC) and Kirkendall voids were detected at the SC-Cr/Cu interface, even after 2000 cycles of thermal shock testing, whereas the Cu3 Sn and Kirkendall voids were significant at the SAC305/Cu and SC07/Cu interfaces after 1000 cycles
The addition of Cr effectively slowed down the growth rate of the interfacial IMC layer during thermal shock compared with the Sn-0.7Cu solder
Summary
Legislation has come into effect, which was passed by the European Union in 2002, to ban the use of Pb and other toxic materials in electronic packaging [1,2]. Commercial imperatives to reduce costs have raised considerable interest in lowering the Ag content of SAC solder alloys to reduce the base alloy cost, especially in the context of decreasing profits in electronics manufacturing due to intense competition [7,8,9]. In this context, Ag-free solders, the eutectic SC07 solder, has attracted much attention in automotive electronic applications because of the low cost and good drop reliability. Sn-0.7Cu-0.2Cr solder in the automobile electronics application, the microstructure and shear strength variation of the commercial SAC305 and SC07 solders under thermal shock conditions were evaluated for comparison
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