Mail*Link¨ SMTP               RE>[TECHNET] [T]:Dewetting

Hi Poh,
No, dewetting can not be caused by component misalignment as such. However,
if the misalignment occurs together with thin solder coating over copper and
the solder paste somehow does not cover that area, than dewetting can occur.
But, the real reason for the dewetting, which is likely a wetting problem
rather than a de-wetting problem, is the thin HASL solder coverage.
It is not a good idea to reduce the peak reflow temperatures or time at
reflow temperatures (about 25C above Liquidus of the involved solder) to less
than 5 seconds anywhere on the assembly. More product problems are created
with inadequate wetting than with de-wetting.
The solution is a thicker solder coat on the  Cu surface (take it easy at
HASL) or OSP.

Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ  07945  USA
Phone & Fax: 973-543-2747
E-mail: [log in to unmask]