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October 2013

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Subject:
From:
Reuven Rokah <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Reuven Rokah <[log in to unmask]>
Date:
Wed, 30 Oct 2013 20:09:17 +0200
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What kind of failure mode?


On Wed, Oct 30, 2013 at 7:04 PM, Ed Popielarski
<[log in to unmask]>wrote:

> Good Morning Esteemed Colleagues,
>
> We have recently been experiencing increasing failure rates of an SMT (5.2
> X 5.2 X 1.2 mm) transformer. The first build in September showed about 6%
> fallout. Subsequent builds from the same reel have increased to 25% most
> recently. These components have been stored in a normal ambient
> environment. I have verified and re-verified reflow conditions are well
> within manufacturer's specifications (confirmed by the manufacturer).
>
> When this problem was first identified, I "dissected" one of the failing
> devices and found the wire pair (primary and secondary) in good condition
> on the outer windings, but as I continued to unwind down to about 1/3 deep,
> the insulation began to stick both side by side and to subsequent layers
> which would "fuzz" as it was pulled apart with exposed copper implied.
>
> I am beginning to suspect "cold flow", a problem that was prevalent in the
> days of wire wrapped backplanes.
>
> Has anyone experienced a similar condition? The manufacturer has been
> "working on it" since mid-September and has yet to provide any root cause
> and/or solution.
>
> Any insight would be appreciated.
>
>
> Ed Popielarski
> Engineering Manager
>
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>
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-- 

Best Regards,

*Reuven Rokah*

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