Rich,
Depending on the locations of the Pems, you might consider taking a few
cross-sections from the areas around the damaged sites. You'll be able to
evaluate what the impact was on inner layers, especially with respect to
distortions - and the potential for shorts between the vcc-gnd planes.
Bruce Tostevin
Benchmark Electronics
Hudson, NH
> -----Original Message-----
> From: Rich Lasko [SMTP:[log in to unmask]]
> Sent: Thursday, November 09, 2000 10:49 AM
> To: [log in to unmask]
> Subject: Re: [TN] Stress Cracks on PCB
>
> My guess is that the set-up of the pressing operation was not done
> correctly
> and the operator used too much force when inserting the PEM spacer. I
> guess
> what I am looking for is criteria to make an accept or reject decision on
> the product that exhibits this condition.
>
> Thoughts? Are there test methods, examples, or is this purely a judgement
> decision?
>
> Thanks for your help everyone.
>
> Rich
>
> -----Original Message-----
> From: Boldt, Mike (msd) USX [mailto:[log in to unmask]]
> Sent: Thursday, November 09, 2000 9:40 AM
> To: [log in to unmask]
> Subject: Re: [TN] Stress Cracks on PCB
>
>
> Hi Rich,
> We routinely use press-in hardware and I'm not aware that we've ever had a
> PWB cracking problem. Have you double checked your hole size, both
> specification and actual, to make certain they're correct?
> Mike
>
> Michael E. Boldt
> Electronic Packaging Engineer
> Moog Inc., Motion Systems Division
>
> -----Original Message-----
> From: Rich Lasko [SMTP:[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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