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June 2006

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Subject:
From:
Steve Gregory <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Steve Gregory <[log in to unmask]>
Date:
Fri, 9 Jun 2006 13:14:04 -0500
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text/plain
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Hi Peter!

I would think that it's bound to lose a little of the strength since the
PEM deforms the laminate around the hole going in, and the laminate
doesn't really spring back once the old PEM is removed. How much
strength that is, I don't have a clue. I would think that if you applied
a thin coat of good two-part epoxy on the inside surface of the hole,
then press a new PEM nut in would give you a PEM nut that you wouldn't
have to worry about.

Check this out: http://www.circuittechctr.com/guides/3-3-1.shtml

This a guide that mirrors the IPC - 7721 non-plated hole repair method.
If you should significantly damage any of the laminate removing the PEM
nuts, this would be the procedure you would use repairing the holes
anyway.

-Steve Gregory- 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Peter Lee
Sent: Friday, June 09, 2006 12:57 PM
To: [log in to unmask]
Subject: [TN] Reworking PEM nut on PCBA

Does anyone have recommendation on a process to remove self-clinching
PEM nut from the board? An incorrect 4-40 size and 1/4" long nut was
mistakenly installed and needs to be removed and replaced with a similar
but shorter nut.

Would I lose much of the clinching strength by re-using the hole? Is
there any work-around to reinforce the hole to achieve the similar pull
strength as before?

Any suggestion is appreciated.

Rgds,
Peter

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