Tin-Plated Pin Terminal Structure for Low-Force Connector Insertion

The plating layer is segmented into multiple layers with different functions: a first plating layer (Sn-Pd alloy) that prevents whisker formation and provides baseline solder wettability, and a second plating layer (pure Sn or Sn-based) that enhances solder wettability. This segmentation allows each layer to perform its specific function without causing localized thickening that would increase insertion force.

The patent applies different plating compositions and thicknesses at different locations and depths. The first plating layer has a specific Pd content (0.01-5 mass%) distributed throughout, while the second plating layer is applied only on the outer surface where solder contact occurs. This local differentiation ensures solder wettability is enhanced where needed without creating excessive thickness that would impede insertion.

The patent creates a composite plating structure where a Sn-Pd alloy layer (first plating layer) is combined with a pure Sn or Sn-based layer (second plating layer). The Sn-Pd alloy provides whisker resistance while the outer Sn layer provides solder wettability. This composite structure achieves both reliability functions in a single integrated plating system that can be manufactured using standard electroplating processes.

The patent extracts the whisker prevention function into a dedicated first plating layer with controlled Pd content, while the second plating layer focuses solely on providing solder wettability. This functional extraction allows each layer to be optimized independently and simplifies the manufacturing process by using sequential electroplating steps rather than requiring complex multi-material assembly.