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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