Steve makes some good points (must that good Navy training).  Another thing
to find out is what their cleaning process is.  I have seen boards from
several quick-turn prototype houses and one of the points they shortcut to
save time is post-HASL or post-plating cleaning.  Warning flags should be
cleaning with water only.   Red warning flags if using tap water.  Neon
glowing red warning flags if cold tap water.  You get the idea.  Also look
at the flow rates through the cleaning process.  4-8 feet per minute good.
20 feet per minute, be alarmed.  They might be optimized for these flow
rates, but color me skeptical.

One quick test you can do to see if they gave you a cheap solder mask.
Take two boards, scrap from the same run is OK.  Run one through your ionic
cleanliness tester (or ion chromatography if you have it).  Run the second
scrap over the wave solder with no flux added and do the same test.  If you
see dramatically higher ionic readings in the second sample, the mask
likely has absorbed residues you don't want.  If you are doing engineering
builds, you may be tuning your circuits around the parasitic values
represented by those residues, that won't appear in good production boards.
It has happened (errr, elsewhere of course).

Doug Pauls
Rockwell Collins

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