High rate electrodeposition of near-eutectic PbSn solders

A study on the improvement of deposition rate for near-eutectic PbSn solder plating was performed. This research focused on (1) the effect of process parameters on the diffusion-limited current density (LCD) to extend the operating zone, (2) the process optimization at 4 μm/min with a modified bath, and (3) the trouble-shooting procedures for abnormal and non-conformal growths. The effect of waveform on surface morphology, growth pattern, film composition and thickness uniformity was also examined. The LCD was increased by increasing metal concentration, bath temperature and agitation, or by decreasing the concentration of methane sulfonic acid (MSA). The effect of additives on LCD was not significant. No significant change in morphology and growth pattern was observed up to approximately 10 μm/min with a modified bath. Process results obtained at optimized conditions showed smooth surfaces, conformal growth and good repeatability of thickness and composition. The probability of abnormal growth was increased with increasing deposition rate, but it was prominently suppressed by increasing MSA concentration and temperature or by decreasing duty cycle. The growth conformality along the resist was improved at a fixed deposition rate by decreasing wafer rotation speed and duty cycle or by increasing MSA concentration