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July 2009

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Subject:
From:
"Croslin, Robert" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Croslin, Robert
Date:
Fri, 10 Jul 2009 15:04:56 -0400
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text/plain
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text/plain (69 lines)
Jack, we actually have a library shape 'test point' that we insert on
every net during the normal layout process, then let the engineer
challenge it if he/she feels there's a problem. Spectra is an excellent
tool to use for doing that if you have it. When they do, I tell them I
want to see calculated data on the issue before we delete it entirely,
then we would move to using a via. We only move one or two a year,
excepting for under BGA's of course. I also require the math when one
of them claims they need to violate good manufacturing clearances for
some performance benefit. I've never lost one of those arguments.


Bob

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Olson
Sent: Friday, July 10, 2009 1:20 PM
To: [log in to unmask]
Subject: [TN] ICT and SolderMask

I'm wading into deeper water these days...

(As a circuit board designer,)
We have vias that can be used as test points that are 40mil pads with
13mil holes. Normally we would like mask to cover most of the pad but
not the hole, so we have an 18mil aperture on the mask layer.
Whenever these vias are USED as test points, we have to open up the mask
and leave them fully exposed.

The problem is, no matter how hard we try to generate test point data,
during test fixture development they end up inserting a few more, moving
them around, etc. which means we either have to modify the mask or leave
ALL of them exposed. to minimize the possibility of solder shorts, we
are discussing now to modify the mask instead of leaving them all open,
preferably without having to change the board revision.

Has anyone else had to deal with this situation?

I would be interested to know if you are generating test point data, Is
it really good enough?
Or,
Are they modifying it in production?
If so, do they make an effort to get the TP changes back to you?

the man with the mask,
Jack

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