Directional Atmospheric Plasma De-oxidation for Ultra Small Passive Component Assembly

The use of flux in electronic component assembly, while effective for solder oxide removal, faces increasing challenges with continued miniaturization. The risk of corrosive residues, and the higher intricacy of rinsing steps to avoid same, represent impediments to reliability and environmental responsibility, underscoring the need for alternative approaches. In this study, we investigate the potential of atmospheric pressure (AP) plasma technology for SAC305 deoxidation and resultant solder assembly. Two approaches are explored, namely in-line (before component placement) and insitu (during placement), with the latter shown to provide superior oxide removal in a more cost-effective manner. In-situ process parameters were investigated for both the plasma treatment (Ar vs Ar+H2 gas, standoff distance, treatment time) and thermal profile (temperature, N
2
flow), including interactions between the two. XPS analysis was used to correlate oxide levels to solder joint quality, the latter being validated by both optical inspection to IPC criteria and cross-sectional SEM- EDX analysis. The findings indicated that AP plasma can indeed deoxidize Sn based and SAC solder surfaces, said deoxidation enhanced by the use of Ar+H
2
to impart a reductive nature to the mechanism. The selection of an appropriate standoff distance, a corresponding treatment duration and profile adjustment were all critical in determining a process window that would balance acceptable solder joint formation and adjacent component integrity. This is due to the temperature contributions of an in-situ plasma. Resultant joint integrity appears as good or better than those formed by flux deoxidation. The atmospheric plasma approach therefore appears to be an effective alternative for solder surface deoxidation in component assembly, positioning it as a more scalable and environmentally friendly option compared to the traditional use of flux.