Evaluation of Wettability of Composite Solder Alloy Reinforced with Silver and Copper Particles

Composite solder pastes were made so that composite solders can be manufactured using the reflow process. Using this approach, the wettability of Sn-3.0Ag-0.5Cu (SAC) composite solder reinforced with micro-sized Ag and Cu particles was investigated by three methods: temperature profile, solder beading and copper clad laminate (CCL) wetting. The composite solder on copper coupon showed less wetting force in the temperature profile test than that of SAC due to the depression of flow of the molten solder by the Ag or Cu particles. It is also noted that during the soldering dwell time, the wetting force changed with time in either small step-wise force changes, or mild force increase, indicating some dynamical occurrence in the molten solder with reinforcing particles. The solder beading test revealed that the solder beading duration of the composite solder is fast than that of the SAC solder, possibly due to the excellent thermal conductivity of reinforcing particles. The CCL wetting tests pointed out that with the increase in weight proportion of reinforcing particles, the composite solder exhibited either smaller spreading area, or dull appearance with Ag particles added paste, and leaching of Cu particles into flux residues when Cu particles were used as reinforcement. The examination of the microstructure of SAC reinforced with 1% Ag particles revealed that although Ag particles quickly reacted with the molten solder and formed Ag₃Sn intermetallic compounds, which distributed 11011-uniformly through the thickness of the solder. When reinforced with 1% Cu particles, the latter reacted with SAC to form Cu₆Sn₅ reinforcing particles, which dispersed also non-uniformly in the solder matrix. It is also noted that leaching of Cu particles through the flow of flux occurred. In view of the present results, further exploration for improvement in the manufacturability of the composite solder alloys is needed.