Immersion plating appears like electroless, sorta, but is different chemically.
Plating is converting metal ions in solution to metal on the board. Those metal ions are "converted" by adding electrons to them. The source of these electrons defines the type of plating. * Electroplating: When the electrons come from a rectifier. * Electroless plating: When the electrons come from another, unrelated chemical in solution. * Immersion plating: When the electrons come from the substrate you are plating on to, as the substrate dissolves, goes into solution, and donates its electrons to the metal already in solution.
The big difference you see is that the immersion bath is one helluva lot more stable, and easier to run, AND, the plating thickness. * Electroless plating can, in theory, go on forever, so you can build up any thickness you want. * Immersion plating stops when the substrate gets fully covered (self limiting).
There are NO known tin electroless plating baths, only immersion tin.
In general, immersion plating gives VERY light finishes, from as low as 3 microinches to a maximum of 40 or so, with tin. While this is not an easy process to manipulate, generally increasing plating temperature tends to increase immersion plating thickness.
Get started by searching the fine SMTnet Archives. We've been talking about immersion tin for a couple of years. In conducting your search: * Immersion has two M * Sometimes 'immersion' is shortened to 'imm' and such.
reply »