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| From [log in to unmask] Wed Apr 3 17: |
02:10 1996 |
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Tue, 02 Apr 1996 14:08:41 -0800 |
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by ipc.org (Smail3.1.28.1 #2)
id m0u44my-00006eC; Tue, 2 Apr 96 06:02 CST |
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TED JONES wrote:
>
> The Navy has recently experienced field failures (shorts) on three
> 7-layer polyimide PWBs. The boards had operated for 300 hours in a
> sealed chamber. The chamber is maintained at 50C, with constant
> humidity.
>
> The shorts (about 8 ohms of resistance) developed between a PTH and
> ground plane on layer 5. There is a voltage potential of 30 volts
> (+15/-15) between the PTH and plane. The clearance between the PTH's
> pad and the plane is 10 mils.
>
> Horizontal microsections of the failed areas do not show any obvious
> migration path. The only anomaly noted on the failed pad is that it
> demonstrates much more pink ring than pads on adjacent PTHs.
>
> We're looking for ideas on the most likely cause of the shorts.
>
> Have there been any studies done that indicate pink ring will or will
> not contribute to this type of failure?
>
> Has anyone seen similar failures?
Is there a chance that you are seeing the CAF phenomenon ?
good luck
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