The requirement that the fastener needs to be retained in the PWB during   
SMT reflow makes this pretty messy. I would question this requirement, at   
least to make sure that the correct tradeoff is being made. Would   
riveting after SMT reflow be a possibility?

Nick Wander
Unisys, Roseville, MN

 ----------
From:  Gagnon, Gerry[SMTP:[log in to unmask]]
Sent:  Monday, February 03, 1997 7:03 PM
To:  'Technet (IPC)'
Subject:  Mechanical fasteners for multilayer PWBs

We have an application that requires fastening surface hardware through
non-plated through holes in a multilayer PWB. A counterbore on the
opposite side of the PWB is necessary so that the fastener does not
protrude above the surface. For assembly reasons, the fastener needs to
be retained in the PWB and successfully survive SMT reflow until the
hardware is attached.

We have tried PEM nuts and were not happy with the resulting laminate
damage. The current thinking is to try tapping the non-plated through
holes and inserting helicoils.

I was wondering if anyone out there has successfully accomplished a
similar design task?

Also, I was wondering if there are board shops out there that have done
this (i.e. tap/install helicoils)?  To do this at module level would
probably destroy the PWB solderability, etc..

Thanks in advance.

Gerry

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