There is one known variable, the new inline cleaner. Is the
water pressure the same? One more likely problem could be a bad batch of
parts. Perhaps these parts were not sealed properly. Buy some more from
a different batch and process them on a dummy card and compare.
	Ramon

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David Greig
Sent: Friday, April 27, 2007 11:55 AM
To: [log in to unmask]
Subject: Re: [TN] Metalized Poly Caps

Ken,

Is the failure immediate after assembly, or after use?

I had a metallization migration problem many years ago with a custom
built polyprop cap. It was used in a resonant conversion circuit, 360nF,
500Arms @ 200kHz switching. Turned out that 40% of the available free
electrons were being used.

Halfing the value suggests metallization might be missing, or very thin
and migrating at one end of the cap.

Best Regards
 
David Greig

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bloomquist, Ken
Sent: 27 April 2007 16:29
To: [log in to unmask]
Subject: Re: [TN] Metalized Poly Caps

Thanks Steve for putting up the pictures, now here's the situation.

We are having a higher than expected failure rate on these capacitors.
They are supposed to be .22 mfd and are testing at around .12 mfd after
assembly.

The manufacturer is saying that it is because we are getting water
inside of them during the cleaning process. A possible cause is that we
are breaking the "seal" on the end or possibly putting them into the
cleaning process while they are still hot from the wave solder.

We've built assemblies using these types of parts for decades and
haven't seen this sort of problem in the past.

We pulled a couple of these caps apart and that is what the photos are
showing. It appears that the metallization is missing on part of the
film. They say that this is due to the wash process. The wash is an
inline wash system using DI water, no saponifier. The contractor got a
new wash system a few months ago but it's a typical inline wash using
the same temps and speeds that they used on the old system.

Have any of you been seeing problems with these caps lately or have any
insight into this problem? See the photos below.

http://stevezeva.homestead.com/files/cap1.jpg 

http://stevezeva.homestead.com/files/cap2.jpg 

Thanks,

KennyB

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