Hi Jack,
We had exactly the same problem with white solder mask and are in the 
process of getting it resolved.  I will let you know what we find. 
Just as you stated, we baked the boards and were able to temporarily 
resolve the issue.  However, the problem returned even after baking. 
I know in the past I have heard of problems with white solder mask due to 
incompatibility with flux.  My suspicions are leaning towards a 
combination of the boards not being clean enough prior to solder mask 
application along with insufficient cure.  The jury is in deliberation.

Tom Burek, CID+




From:   Jack Olson <[log in to unmask]>
To:     <[log in to unmask]>
Date:   08/08/2011 08:47 AM
Subject:        [TN] White SolderMask
Sent by:        TechNet <[log in to unmask]>



Greetings,

Have any of you experienced mask problems like the ones shown in these
pictures?

http://frontdoor.biz/PCBportal/WhiteMask.jpg

The bottom picture shows exposed copper, and I believe there is a copper
plane on the top layer.
(this has happened to different boards, different lot codes, but MIGHT be
the same batch of mask)

What I'm wondering is, is it more likely that the problem is related to 
the
fact that the mask is WHITE, or that it is some other problem?
If the properties of white mask are different, maybe it doesn't adhere as
well to the surface? I remember back in the olden days they used to ask us
to break up solid copper planes so the mask would stick better to the
laminate, but I haven't heard of anyone having problems with that for a 
long
time.

The supplier said they baked some bare boards and ran them through the 
oven,
and the problem went away, but we are reluctant to just blindly add a
permanent baking step if there are other considerations.

Jack


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