Analysis of wetting behavior in solder joint process via Ar/H₂ atmospheric pressure plasma treatment

Solder pad oxidation presents a significant challenge in electronic packaging, reducing solder wettability and compromising solder joint reliability. This study investigates the enhancement of solder joints through atmospheric pressure plasma (APP) cleaning, employing both pre- and post-treatment methods. Using a mixture of argon gas and 5% hydrogen, the APP system effectively eliminates oxides, as confirmed by the H_α peak observed in Optical Emission Spectroscopy analysis, indicating successful hydrogen radical induction. Cross-sectional analysis via Scanning Electron Microscopy demonstrated that samples subjected to both pre- following post-treatment achieved optimal wettability, with a minimum contact angle of 29.5° between solder balls and copper substrates. The pre-treatment promoted the formation of intermetallic compounds at the interface, while the post-treatment effectively removed the tin oxide shell, facilitating proper solder wetting onto the substrate and enhancing overall wetting performance. During plasma post-treatment, the oxide removal rate reached 87.47 nm/min, which is significantly faster than the copper oxide formation rate (2.29 nm/min) during reflow leading to low oxygen content (1.23%) at copper substrate surface. Electron Probe Micro-Analyzer (EPMA) analysis confirmed the absence of continuous oxide layers on both tin balls and copper surfaces, further validating the improvement in wettability. This study underscores the efficiency of APP cleaning in minimizing oxidation and enhancing solder wettability, providing valuable insights for optimizing plasma cleaning techniques to ensure superior solder ability and reliability in electronic packaging.