Hi Rich -
To add to Phil's input - I also suspect the condition you see is crazing.
Remember the glass weave in FR-4 and similar materials will not allow a
"crack" to propogate (run). Our internal standards addressed this condition
in a manner similar to flared terminals, etc., by stating that the visible
condition should come no closer than .030" to an internal circuit when
viewed in the Z axis.
Regards - Kelly
-----Original Message-----
From: Phil Nutting <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Thursday, November 09, 2000 9:22 AM
Subject: Re: [TN] Stress Cracks on PCB
Rich,
I don't know about specifications, but my experience with PEM fasteners in
circuit boards is as follows. Using the KPS6 "FoilgardŽ Fasteners" requires
a fairly tight tolerance hole. Using the KF series of inserts in plated
thru holes will usually rip the plating out of the hole. If inserted in a
non-plated hole there will be some "board damage" around the hole because
the process of pressing in the fastener requires that the material "move and
adjust shape" to accommodate the fastener. G10 or FR4 don't "move" like
steel or aluminum and will probably show some signs of crazing or haloing.
Regards,
Phil Nutting
Manufacturing Engineer
Kaiser Systems, Inc.
126 Sohier Road
Beverly, MA 01915
ph: 978-922-9300
fx: 978-922-8374
[log in to unmask]
-----Original Message-----
From: Rich Lasko [mailto:[log in to unmask]]
Sent: Thursday, November 09, 2000 9:40 AM
To: [log in to unmask]
Subject: [TN] Stress Cracks on PCB
Good morning everyone.
I need some input from you guys. We have a product (pcb assembly) in which
we needed to "press in" a PEM spacer. Unfortunately when we pressed in the
spacer, it has caused stress cracks in the pcb. I have looked in the
IPC-A-610 to find out acceptable and rejectable criteria for stress cracks,
however, I have not been able to find any. The closest I can come is
crazing. However, the defect appears to be more of a stress crack then
crazing.
Need help. Is there any other accept/reject criteria or anyone else
experience with stress cracks from pressing in hardware.
Please advise.
Rich
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