One option is to have the stencil supplied etch relief pocket on contact side of the stencil allowing the stencil to gasket to the board.  Photo Stencil provides this type of stencil on a routine basis with good results.

Regards, 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Matt Kehoe
Sent: Friday, March 09, 2007 10:01 AM
To: [log in to unmask]
Subject: [TN] Paste Volume, off contact vs non off contact


We have been processing a family of boards for 3 years. No issues. New PCB
Vendor and the boards suddenly will not print very well. Sloppy printing
definition. Heavy heavy deposition.

Closer inspection reveals that the soldermask is built up .0012-.0019 over
the vias, preventing the stencil from gasketing. Vendor claims they are
built to print.. Opinions? 

Pictures at ;
http://www.sipad.com/ssiqa/3942vias.pdf
http://www.sipad.com/ViasBuildup.pdf

The question we are trying to answer is, if your boards came in with mask
this thick over the vias would you feel confident in running them without
modifing the stencil? Would you expect a significant increase in solder volume?


mk

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