Hello Krishna,

Is the secondary side in contact with the oven's conveyor rack?  SMDs
and primary side thru-hole leads can bind and slip during transport.
Support the board with a fixture or use the rails if you're not doing so
already.

You can also check the solderability of your pads.  Print some paste at
the problem site on a bare board and look for good wetting after
reflow.  If the solder balls-up, you've found the culprit.  Choose a
sample with grainy-looking pads from the problem lot if possible.  That
is one indicator of exposed, unsolderable intermetallic on a hot air
solder leveled board (HASL).  There should be at least 80 microinches of
Sn63/Pb37 coating the pads for good solderability in a JIT process.
I've used Trace Labs in Chicago for this kind of testing before.

John Balchunas

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