A clean, solderable, rough surface wets much better than a smooth one
and the resultant solder joint is better, because there are more IMs
formed during the short wetting period. There are also surface tension
factors, best illustrated by a ground glass surface being more wettable
by water than a smooth one. However, as David points out, if oxidised,
the rough surface will place a greater chemical load on the flux.
More important is to know HOW the surface is roughened. If it is a
result of chemical or electrochemical (with reservations) means, well
and good. If produced by abrasion, then there is every chance that
abrasive particles will be physically implanted in the metal. If this
happens, dewetting will certainlt occur, maybe even non-wetting in
severe cases. My reservations re electrochemical deposits are that there
are frequently organic additives co-deposited with the metal that may
inhibit good wetting.
Hope this helps
Brian
Bev Christian wrote:
> TechNetters,
> Can gross (and I mean gross) surface roughness of a component
> termination be enough to almost completely retard solderability compared
> to one with a smooth finish? No, this is NOT a case of the roughness
> being a result of a thin coating being completely oxidized or having the
> intermetallic "come through". That is not to say that the coating isn't
> oxidized on the surface, though.
> regards,
> Bev Christian
> Research in Motion
>
>
>
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