I'd expect the OSP to have a "blotchy" finish to it prior to solder
paste deposition if there is a contaminant and it is solder mask
residue.  If this is the case, then you can send the bare boards out to
an analysis lab to determine whether the contaminant on the blotchy
areas is indeed solder mask residue or its due to some fault with OSP.
I suppose OSP is not the best finish for your situation because the
color change on the pad would not be nearly as dramatic as it would be
with some kind of plated board finish.

As it is, you can't tell whether the contamination occurred before or
after OSP.  If it was after, it could be some consequence of shipping or
storage conditions.

>>> [log in to unmask] 4/20/2006 2:03:51 pm >>>
Mike & Wayne,
I checked the process flow, it is using OSP Coating for the Surface
Finishing.

If the resist is of green color covering the solder pad, I can
understand
the defect but clear color? This is what the Customer claimed to me,
they
said is solder resist deposit on the pad, that's why I am inquiry more
details here. Later, I will check with the Supplier again on their
opinion
of this issue. But most likey is Supplier problem as their quality
really
sucks,haha.

Anyway, Thank you for the kind responds, Hope to exchange more
informations here with you guys in the future. Cheers~


On Thu, 20 Apr 2006 09:22:04 -0700, Barmuta, Mike
<[log in to unmask]>
wrote:

>SJ: The soldermask if thin enough will appear clear even if it has
>coloring pigmentation.
>
>Residual photo imageable soldermask is normally caused by under
>developing after exposure. The cause can be in the developing process
>itself or in upstream processes i.e. excessive coating thickness,
uneven
>tack dry, photo tools etc.
>It is also possible that a thin layer of mask can re-deposit in the
>final cure step.
>
>Are you sure this is soldermask? It's hard to tell from the pictures
but
>it could also be poor activation in the assembly process. It looks
like
>you are using an OSP coating. If this is not activated properly by
the
>flux you could see a similar result.
>
>
>Regards
>
>Michael Barmuta
>
>Staff Engineer
>
>Fluke Corp.
>
>Everett WA
>
>425-446-6076
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Saint Jerky
>Sent: Thursday, April 20, 2006 8:42 AM
>To: [log in to unmask]
>Subject: [TN] Solder Resist Question
>
>I received some PWB photo from my customer which they claim the
present
>of "Solder Resist(Clear Color)" on the Solder Pad thus preventing the
>solder from wetting. In your opinion, what's that clear color layer
of
>substance that is preventing it from wetting? Is it really solder
>resist?
>Picture:
>http://img115.imageshack.us/img115/6089/untitled3or.jpg
>http://img126.imageshack.us/my.php?image=untitled16ut.jpg
>
>This PWB is coated with Green Color Solder resist,if it is really
solder
>resist, shouldn't it be Green color instead of Clear? I am puzzle why
>the
>resist turn clear instead of Green when adhere to the solder pad. Can
>someone teach me?
>
>Sorry if you feel this is a noob question as I am new.
>
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