Hi Technetters:

I need some help resolving a solderability dispute.  One of my customers
claims to have poor solderability with one part number (2 sided board)
utilizing mixed technology, surface mount on the top side and through
hole components.  The customer is using water soluble flux.  The problem
spans two production lots.  Their testing consisted of passing bare
boards over the solder wave.  The soldered boards had pads that did not
wet (skips) the remaining pads exhibited good wetting.  There was no
pattern to the skips i.e. they occurred within SOIC patterns with pads
on either side accepting solder.  At my request the customer applied
solder paste to a bare board and reflowed it.  This board exhibited
dewetting on all pads.

The tested boards and samples from these production lots were returned
for failure analysis.  Solder floats and vertical edge dips of the
boards exhibited good wetting.  A friend at a contract assembler hand
dispensed solder paste on one of the untested boards and coated some
pads with a water soluble flux.  The soldered pads wet completely, and
the flux coated pads did not exhibit dewetting.

Is there any testing that can be performed to resolve the problem?  What
could be the cause of the differing results?  Any assistance is
appreciated.

Thanks,

Don Vischulis
QA Manager
ITO Industries

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