Optimal Hot-Dipped Tinning Process Routine for the Fabrication of Solderable Sn Coatings on Circuit Lead Frames.

Previous studies merely focus on the hot dipping properties of lead frame materials used in electronic industry. Yet, the environmentally friendly and cost-efficient traits of hot-dipped tinning process make it a possible promising surface modification technique compared with electroplating. As a result, the optimal hot-dipped tinning process routine is proposed in this paper. The hot-dipped tinning process of four different types of copper foils (C11000, C19400, C19210, and C70250), pretreatment parameters, mechanical properties of Cu substrates, thickness of IMC (intermetallic compound) layers and coatings, and microstructure of coatings were investigated to determine the copper substrate suitable for hot-dipped tinning and the optimized tinning procedures. The results indicate that a proper increase in alloying elements (e.g., Cu-Fe-P series alloys) towards Cu substrate leads to a decrease in hot dipping performance. The proper process routine is determined as alkaline cleaning→water scrubbing→accelerant solvent dipping→drying→hot-dipped tinning→cooling. The appropriate dipping temperature range is 260 to 280 °C, which assists to maintain acceptable micro hardness (i.e., maintaining at least 95% of the original hardness). The optimal dipping time should be set as 6-10 s. The proposed hot-dipped tinning process routine may present a guideline for the fabrication of tin coating in electronic industry.