[SI-LIST] Re: Effect of Epoxies on Ethernet Magnetics
- From: Gene Glick <gglick@xxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Fri, 17 Jul 2015 13:41:58 -0400
On 7/17/2015 1:23 PM, Dave Cuthbert wrote:
KHD, I once had a small transformer potted in epoxy and at low temperature
(0 deg C) the epoxy compressed the transformer core thereby reducing its
permeability by a factor of four. This cause the core to saturate. The
solution was to first dip the core/windings in a soft potting material,
allow it to set up, and then pot the assembly in epoxy.
Dave Cuthbert
Consultant, EMC, Analog, SI, power
NARTE Certified EMC Engineer
Sometimes very small ferrite cores develop cracks as the potting
material cures. So it actually introduces air-gaps into the core, which
lowers the permeability. Ultimately, we had an outside vendor make the
parts for us, and they somehow manage this problem (for all I know, they
throw away the rejects).
Look into 3M 2216 epoxy for gluing down parts to your board, and is also
very good for filling in holes in toroid. Stuff is easy to work with, is
good to very high temperatures, and can withstand enough G-force to hold
parts onto our boards when tested in a HALT chamber.
gene
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