Immersion, Non-electrolytic Tin lead Plating Process

The technological development and characteristics of an innovative process and composition for immersion plating and fusing of a solderable tin lead deposit over copper are discussed. The process offers a viable alternative to hot air solder levelling, electrodeposition selective stripping, or inhibitor coatings for maintaining solderability of printed wiring boards. A flat, uniform solderable tin lead coating on all feature surfaces and edges is achieved. A number of important benefits are derived. The ability to coat any copper surface uniformly, including fine pitch features, is substantially enhanced. Solderability is improved because of a thick, flat, co-planar and uniform tin lead deposit on all copper surfaces. Typical thickness and composition of the fused alloy are 150 to 300 microinches (4 to 8 microns) and 65 to 75% tin.