While most of the industries are striving very hard to produce totally lead-free electronic products, many concerns remain regarding lead-free solder joint reliability. One major concern is the robustness of gold metallization of the electronic components for lead-free soldering. Most of the electronic components are plated with thin gold flesh on a Ni barrier layer to improve wettability and corrosion resistance. During the soldering process, the gold readily dissolves into bulk solder. However, studies [1, 2] of such solder joints have shown that the gold precipitates back to the interface after high-temperature aging, forming a Au-Sn intermetallic, AuSn_4. This binary Au-Sn intermetallic is a weak, brittle compound that degrades the thermal fatigue life when present in high concentration in solder [3] and results in embrittlement and early failure in electronic assemblies during thermal shocks or mechanical shocks and/or bending. Therefore, information about the lead-free solder/gold metallization interdiffusion during high-temperature applications is very important for controlling the technological processes for the reliability of the electronic interconnects. Gold concentration in Pb-Sn solder has been explored by several investigators [3-5]. According to these works, gold has a propensity to embrittle solder joints when present in a range of concentrations that extends from 2 to 7 wt.%. Other investigators [6] stated that, as a rule of thumb, gold concentration of more than 3 wt.% in a PbSn solder joint causes considerable degradation.
展开▼
