Ultrasonic Fluxless Soldering of Eutectic SnPb and SnAgCu Alloys: A Feasibility Study

Compared with the traditional eutectic SnPb soldering, lead-free soldering has been a focal point for electronics packaging research in order for the industry to meet the regulations on environment protection. By eliminating the lead element from soldering process, the concerns on environmental pollution can be significantly reduced. However, the current lead-free soldering processes usually still require the flux chemicals for promoting wetting. The use of flux chemicals is not environmentally friendly. In this study, motivated by the potential benefits of soldering using ultrasonic energy, we carry out a feasibility study of ultrasonic fluxless soldering experiments on both the regular eutectic SnPb soldering alloy, Sn63Pb37 and the popular SnAgCu alloy, SAC305. By developing the appropriate testing conditions, the solder joints are successfully formed using the dipping ultrasonic soldering method regardless if chemical flux is applied. The effects of soldering time, temperature, and ultrasonic power are investigated. The results from SEM observation and EDS element analysis indicate that the use of chemical flux produces thicker intermetallic compound (IMC) layers for Sn63Pb37 alloy, and a longer soldering time leads to thicker IME layers for both solder alloys. However, a higher soldering temperature may not be beneficial to the growth of IME layer in ultrasonic soldering of SAC305 alloy. However, the driving mechanisms behind the phenomena remain to be investigated in the future.