In it's plain form Electroless tin is not very popular
with many assembly companies. As a thin layer it quickly combines with
the copper. Often within weeks of manufacture the resultant finish
becomes very difficult to solder. This short life span can be increased
by increasing the thickness of the tin layer. Traditionally a thicker
layer was always rejected as it known to regularly result in tin
whiskers forming, which given time would result in short circuits on the
PCB.
If used with the tin thickness in a safe range and assembled within a
fast timescale, Electroless tin is a very workable finish cost
effective. It also has the advantage that if the individual circuit
boards are still panelised, should they be too old to assemble the
panels can be reworked by stripped off and replating the tin.
Follow
this link for more up to date information on Tin whiskers to
the
NASA Goddard Tin Whisker Homepage.
http://www.nepp.nasa.gov/whisker/index.html
