Mike, just a few minutes ago as I was looking over my new copy of IPC-7095,
"Design and Assembly Process Implementation for BGAs", I noticed on page 30
there is a statement "Most photoimageable wet film masks will not even tent
0.35 mm via holes because it is difficult to cure polymer in via holes".
We have been having trouble at ICT from untented, unplugged vias. The
board designer is helping us out now. We have one board with 0.028" vias
that is worst. By the way, I did a quick calculation that suggested if the
vias were 0.020", the pull-down force at ICT would be increased by a factor
of 6 over the 0.028" version.
Here's a question for TechNetters in general, in the same vein, that may
help Mike and me. Page 31 of 7095 refers to Tenting and Capping. What is
capping? 7095 says "Via capping is the preferred method since tenting
reliability is dependent on the finished hole size". Never heard of it
before, and although I'm not an old timer by TechNet standards, I've been
around a few days. Thanks for assitance. Lou Hart
-----Original Message-----
From: Hiteshew, Michael [SMTP:[log in to unmask]]
Sent: Friday, December 21, 2001 3:29 PM
To: [log in to unmask]
Subject: [TN] Soldermask: LPI vs Dry Film
Techies,
I have a circuit board with 0.024" diameter (finished size) vias.
I'd like to tent them in the final design. My question: Am I better off
specifying dry-film soldermask as opposed to LPI? Is there a cost tradeoff
with dry film? Is it hard to work with or hard to get? It seems to have
fallen out of favor lately, so that's why I'm asking. Thanks in advance.
~Mike
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