As a manufacturer of high-rel and Mil Printed Circuits, we have
seen an increasing number of board designs  that require the use 
of (LPI)Liquid Photo Imageable soldermask.  The LPI masks perform 
well in most cases, but many of these designs incorporate tented 
via's. In the past, Dryfilm soldermasks have been used for boards 
with tented via's, but many customers are moving away from the dryfilm 
soldermask. 

We are currently using a "via fill" process in which we fill the 
holes with an epoxy s/m by screen printing.  This is followed by 
application of the Liquid Photo Imageable (LPI) soldermask over
the surface of the board.  The result is an LPI mask with tented
via's.  

To me, this process seems to be a step backward on the technology
curve.  It requires more process steps and more time.   
We would like to get away from the screen printing and pursue a 
100% Photo process.  I have discussed this issue with several 
soldermask suppliers, and I have been told that this is a very 
common procedure and that many other board shops use the same 
process.  None of our suppliers have offered a more effective 
solution.

I would be interested in any feedback related to the use of LPI
soldermask when tented via's are required.  Would anyone like to 
share their "success" stories or recommend a supplier that could
help with this issue.

Thank you in advance for your comments.

Sincerely,

Jim McNeal  


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Jim McNeal  Q.A.and Eng. Mgr.
Electro Plate Circuitry, Inc.
Carrollton, Tx
Ph. 214-466-0818
EMAIL  [log in to unmask]