Tom: There are certain types of epoxies that could show this condition at
180F. These epoxies are typically room temperature cured and have
flexibilizer agents. These can have service temperatures and heat deflection
temperatures(HDT)that fall into this temperature range and possibly show the
condition you saw.

However it is very possible that the potting material will stand up to the
bake out temperature and there could be something wrong in how it was
processed i.e. proportioning of components, improper mixing, insufficient
cure, shelf life, etc.

Typically most epoxies used for electronic applications these days have a
temperature rating of at least 220F. Check with the component
supplier/manufacturer and see what the thermal rating is for this potting
material. If it's in the 220 range or above then I would suspect something
was not processed correctly with this batch of material. If it's below that,
have  them change to a higher temp material if possible or you're going to
have to dry at a lower temperature.


                                                                Regards

Michael Barmuta

Staff Engineer

Fluke Corp.

Everett WA

425-446-6076

-----Original Message-----
From: Tom Parkinson [mailto:[log in to unmask]]
Sent: Wednesday, December 31, 2003 7:24 AM
To: [log in to unmask]
Subject: [TN] Epoxy Potting - Leaks


We're a CM and building an assembly using a potted transformer. One of our
steps in the manufacturing process after aqueous washing is to put the
assemblies in a dry heat oven at approximately 180 degrees F for 2 hours to
ensure any water left over from washing is evaporated.
This is the first time we have seen where a potted transformer has leaked
the epoxy filling after being dried, and in some cases, has swollen the
plastic housing that the transformer is encased in.  We double checked the
temp. Is this something anyone else has seen? Should we have a lower
temperature???

Tom Parkinson - Quality System Manager
WinTronics, Inc.

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