Hi All,
We shipped 52 bare boards to our customer, who hand assembled 2, and then
sent 50 to a contract manufacturer for assembly.  The assembly house
soldered the surface mount caps (paste & oven) and stopped because the
solder was not "wetting".  (there were apparently no problems with the hand
assembled boards).  I saw 4 of the partially assembled boards- they look
ugly.  The HASL solder covers the entire pad (no copper showing), but the
paste solder doesn't flow to the pad edges.  It looks like the two solders
don't want to combine.
The bare board HASL finish (vertical HASL) looks typical, the HASL solder
content was analyzed (ok) the previous week, and the solder pot was skimmed
that morning.

So, we sent a spare bare board from the same lot to a test house for J-std
3, test A (dip test), which it passed.

The assembly house says the bare boards are at fault, and that the dip test
is less demanding than the paste/ I/R oven process used on these boards.

Any ideas as to the root cause?

Is there a straight forward way to verify this?

It's been a year since we received our last solderability complaint.  That
ended in inconclusive discussion regarding "intermetallics".  I'm hoping to
resolve this one more logically.


Thanks,
Mark Hargreaves

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