> 
> The soldermask was so thin as to be non-existant in many places on
> the board.  It looked like the board was contaminated prior to the
> soldermask application or the soldermask liquid itself was bad.
> We had caps and resistors shorting to traces THROUGH the soldermask
> even though when examined under a microscope there was no apparent
> break in the mask.
Don

It sounds as though the resist is breaking down along the track edge where it is 
thinnest. This could be more to do with the method of application than the type 
of ink used. If the LPISM was applied with curtain coating, this problem could 
be due to too low a coating weight being used to give good coverage. If the 
copper thickness on thin tracks is high due to overplating, or using 2oz copper 
base, a higher coating weight is needed. In areas of high track density, a 
patchy appearance can result due to the way the ink flows off the tracks into 
the gaps.

It is not possible to go above a certain weight of ink with curtain coating and, 
in some instances, a double coat is necessary to give good coverage over tracks. 
We have to use double coat on come 2oz panels to achieve 0.5 mil coverage over 
the track edge as it is impossible to achieve this with a single pass. The 
method of application is more important than the matte or glossy question.

If the ink looks thin and patchy and more coppery than green in areas, then it 
is too thin. I agree that semi-matte is better for assembly than high gloss 
although our semi-matte comes out pretty glossy in appearance due to the method 
of application. Screen printing is more capable of producing a truly matte 
finish.
-- 
Paul Gould
Teknacron Circuits Ltd
EMail [log in to unmask]

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