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1995

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Subject:
From:
"Wally Doeling (wallyd)" <[log in to unmask]>
Date:
Mon, 12 Jun 95 10:23:00 PDT
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     In regard to tenting vias.
     Several years ago we asked ourselves why we tented.
     The answers were :
          ICT
          Design.

     We solved the ICT reason by going to mechanical fixtures instead of 
vacuum.  Or by the use of a lidded fixture.

          Design (turned out to be a imagination item) because it was not 
required as at the same time we were
     minimizing the use of flow solder process and going to two reflow 
processes.
          As it turned out, with attention to the wave process, there was 
not a need to tent in wave either....
          
     You need to look at your processes in assembly and see if you have a 
real need!

     [log in to unmask]

 ----------
From: TechNet-request
To: technet
Subject: LPI Soldermask with Tented Via's
Date: Friday, June 09, 1995 6:28PM

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


=====================================================

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



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