We are assembling boards from two different vendors and seeing two
completely different results.  Looking internally before approaching the

vendors we have done the following:

a.  Sent both boards unpopulated through IR, both boards look identical
in solderability characterics.
b.  Applied solder paste to both boards, both boards look identical in
solderability characterics.

This is where it gets interesting:

a.  Company's "A"'s boards solder profile was bumpy and un-uniform, and
they contracted to have the boards re-leveled.
b.  Company "B" boards were used as is.
c.  We are using other boards from Company "B", and having no problems
whatsoever.
d.  The board solder surfaces from Company "A" & "B" are inconsistent in

color exhibiting both bright and dull spots on the same solder surface.
e.  Company "A" reworked boards are working fine; Company "B" boards
have solderability issues on one side only in areas of dense SMT pads.
f.  Company "B" boards have been sent to an independent test lab for
evaluation returning a positive report on solderability.
g.  Ionic contamination testing proves that both boards from Company "A"

& "B" are contaminent-free.
h.  Solderability concerns are isolated to one side of the board only
even though it is a double sided SMT assembly process.

Based on the above statements, my questions are:

a.  If boards from both companies have been sent through IR unpopulated
without any solderability concerns, why is one board having negative
results whilst the other is fine?
b.  If we are seeing problems on one board supplied by one vendor, why
aren't we seeing similar problems on other boards being supplied by the
same company?
c.  Why are we having problems with the board lot even though the test
lab has given these boards a passing grade?
d.  Does the surface appearance (dull or bright spots) have an affect on

solderability?  If so, why?

Given the mixed opinions and results on this project, I don't know who
or what to turn to and hope that the accumulated talent of Technet can
offer a guiding light.  Any and all assistance would be greatly
appreciated.

Regards

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