Properties and Reliability of Sn-Pb and Lead-free Mixed Soldering

During the transition from Sn-Pb solder to lead-free solder, it is inevitable to encounter the reliability difficulties when lead-free and Sn-Pb materials were used within the same mounting process. To solve the problem in the mixed soldering, two methods were adopted that is improving the soldering temperature and electroplating Sn-Pb on the surface of the devices then soldering in a lower temperature. Mechanical strength of the solder joint, fracture morphology and the intermetallic compound (IMC) at the interface between solder and board materials were investigated. The experimental results showed the inclination of pores evolving when improving the solder temperature reduces the reliability. However, symmetrical solder joint with high reliability was obtained in the second method.