Medical studies have been shown that Pb is a heavy metal toxin that can damage the kidney, liver, blood and the central nervous system. Therefore, rapid switching and great effort for seeking Pb-free solder alloys with a balance of thermal, mechanical and soldering properties as a replacement for Sn–Pb eutectic alloy. From January, 2004, European nations will adopt Pb-free solder alloys in all electronic assemblies, according to Directive on Waste from Electrical and Electronic Equipment (WEEE). In addition, other environmental protection legislation was also made to inhibit the disposal of Pb-containing garbage in the dump. The new lead-free solders need to have a similar melting temperature to existing Sn–Pb solders and adequate mechanical properties to preserve the reliability of the electronic packaging products. Also, the new lead-free solders need to be nontoxic.