Though it is never desirable, we have used polyimide (Kapton) cover coat even on rigid boards. Of course this adds labor to the process since the cover coats will need to be tooled so as not to cover everything. (Drilled, die blanked or even more costly/time consuming...laser skived).

Karl

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Phil Nutting
Sent: Wednesday, August 15, 2007 10:59 AM
To: [log in to unmask]
Subject: [TN] Solder mask as an insulator


Let me start with, I know that we should not rely on the LPI solder mask
as an insulator.  So I need recommendations for a simple and cost
effective solution.

Problem parameters; 0.062 thick FR-4 with 2 oz copper and LPI mask.  PTH
components laying on traces that go under the parts.  PTH parts are
shorting to the traces.

Our fab house is against adding a second layer of LPI mask.  On face
value a second layer sounds good and easy, but I know there are issues
too long to list.

Short of raising the components above the board, applying an insulator
under the components or a new board layout is there a better way of
preventing this shorting problem?

Thanks in advance.

Phil Nutting
Design for Manufacturing Engineer
Kaiser Systems, Inc.
126 Sohier Road
Beverly, MA 01915
voice: 978-922-9300 x1310
fax: 978-922-8374
e-mail: [log in to unmask] 
www.kaisersystems.com

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