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November 2013

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Subject:
From:
Robert Kondner <[log in to unmask]>
Reply To:
Date:
Fri, 1 Nov 2013 11:21:05 -0400
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Ok, That says there was not only a failure of the wire insulation but also
of any tape layers between the windings. 

 So three failures in the same location:

  Primary Wire Insulation

 Secondary Wire Insulation

insulation tape between layers. (I assume this was there)

Sounds like someone was doing a high pot test, destroying the transformers,
and then putting them in the "Good" bin? I doubt that.

Now another likely failure is a circuit failure where they are being used. A
simple short on a board or other assembly / component failure might result
in excessive current melting down a section of internal windings. That would
be my guess. This might also explain the "Bad" insulation you saw coming off
the wires.

Bob K. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ed Popielarski
Sent: Friday, November 01, 2013 11:02 AM
To: [log in to unmask]
Subject: Re: [TN] SMT transformer failures

Functional test fails on power up (no DCV SEPIC app) and ohmmeter confirms
short between primary and secondary windings. Disassembled the transformer
under a microscope, it's only 5mm X 5mm including the outer frame.

Ed Popielarski
Engineering Manager


                               970 NE 21st Ct.
                              Oak Harbor, Wa. 98277

                              Ph: 360-675-1322
                              Fx: 206-624-0965
                              Cl: 949-581-6601

https://maps.google.com/maps/myplaces?hl=en&ll=48.315753,-122.643578&spn=0.0
11188,0.033023&ctz=420&t=m&z=16&iwloc=A


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Thursday, October 31, 2013 5:42 PM
To: [log in to unmask]
Subject: Re: [TN] SMT transformer failures

I would ask again:

 What lead someone to suspect a transformer as bad? What lead to disassembly
in the first place?

Bob K.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Don Vischulis
Sent: Thursday, October 31, 2013 7:36 PM
To: [log in to unmask]
Subject: Re: [TN] SMT transformer failures

Yes, this is a polyurethane based insulation system. My experience is with
MW16C (polyimide).  Based on general knowledge, polyurethanes are not very
sensitive to solvents.  I think that the fuzzy finish you observed is
failure of the wire insulation because the coils are impregnated and the
adhesion within the insulation is less than the adhesion within the
impregnant.

My experience is that breaks inside the coil are due to flaws in the
conductor. One failure mechanism is from expansion and contraction from
thermal cycling.  Usually it takes small diameter (39 awg) and some pretty
extreme conditions with hundreds of cycles to cause this to happen. Another
possibility is defective wire or handling damage. Does the manufacturer have
any record of unplanned interruptions during the winding cycle?  Is the
manufacturer purchasing from a low cost source?

Sorry I can't offer more.

Don Vischulis

Sent from my iPad

> On Oct 31, 2013, at 10:07 AM, Ed Popielarski 
> <[log in to unmask]>
wrote:
> 
> NEMA MW82-C Class 180 C
> 
> Ed Popielarski
> Engineering Manager
> 
> 
>                               970 NE 21st Ct.
>                              Oak Harbor, Wa. 98277
> 
>                              Ph: 360-675-1322
>                              Fx: 206-624-0965
>                              Cl: 949-581-6601
> 
> https://maps.google.com/maps/myplaces?hl=en&ll=48.315753,-122.643578&s
> pn=0.011188,0.033023&ctz=420&t=m&z=16&iwloc=A
> 
> 
> -----Original Message-----
> From: Don Vischulis [mailto:[log in to unmask]]
> Sent: Thursday, October 31, 2013 4:10 AM
> To: TechNet E-Mail Forum; Ed Popielarski
> Subject: Re: [TN] SMT transformer failures
> 
> Any idea what type insulation is on the magnet wire or the NEMA
designation of the magnet wire?
> 
> Don Vischulis
> 
> Sent from my iPad
> 
>> On Oct 30, 2013, at 12:04 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
>> 
>> [Description: FullLogo]
>>                              970 NE 21st Ct.
>>                             Oak Harbor, Wa. 98277
>> 
>>                             Ph: 360-675-1322
>>                             Fx: 206-624-0965
>>                             Cl: 949-581-6601
>> 
>> https://maps.google.com/maps/myplaces?hl=en&ll=48.315753,-122.643578&
>> s pn=0.011188,0.033023&ctz=420&t=m&z=16&iwloc=A
>> 
>> 
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