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→7.1.2.5 Immersion Deposition of Tin
====7.1.2.5 Immersion Deposition of Tin====
A tin coating by ion exchange is usually not possible since copper is the more precious metal. By adding thio-urea the electro-chemical potential of copper is reduced to a level (approx. 450 mV, significantly lower than tin) that allows the exchange reaction. Using a suitable electrolyte composition and enhancer solutions like with the DODUSTAN process ''<xr id="fig:Process flow for electroless tin deposition using the DODUSTAN process"/> (Fig. 7.4)'' tin coatings can be produced that, even under usually unfavorable conditions of copper concentrations of 7 g/l in the electrolyte, are well solderable.
The immersion tin deposition is suitable for the production of a well solderable surface on printed circuit boards and electronic components. It is also used as an etch resist against ammonia based solutions or as corrosion and oxidation protection of copper surfaces.