Main Articel: [[Electroless Plating| Electroless Plating]]
====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 ''(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.
Fig. 7.4: Process flow for electroless tin deposition using the DODUSTAN process
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.
==7.2 Coatings from the Gaseous Phase (Vacuum Deposition)==