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Re: The goo inside of IGBT modules.
Original poster: "Steve Ward" <steve.ward-at-gmail-dot-com>
On Wed, 15 Sep 2004 13:04:34 -0600, Tesla list <tesla-at-pupman-dot-com> wrote:
> Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>
> Hi Steve,
> At 10:52 PM 9/14/2004, you wrote:
> >Since there seem to be a handful of experienced power engineers
> >around, i was just curious, what is the true function of the gel type
> >stuff they put inside of big power semiconductors (ive seen it in
> >IGBTs as well as SCRs).
> "Experienced power engineers" use the gel for a wide variety of practical
> jokes! If you throw it on the ceiling above you pal's chair, it will fall
> on him after a few minutes. A paper towel stuck to it makes nice "lawn
> darts" for walls and ceilings too! :-)) It can be left around in odd
> places for people to unexpectedly grab onto...
I will keep these uses in mind... ive got quite a bit of this goo
around now ;-).
> The gel has no thermal use. It just protects the die and bond wires from
> moisture and thermal expansion and cycling. It also vastly increases the
> flash over voltage on the device surface. It does allow for an airspace
> above the die that does actually "cushion" the explosions (as opposed to a
> full hard plastic case). There is really no way they could fill large
> devices with solid plastic since it would shrink during cure and the
> thermal expansion over such a large area would crack it all up.
Ah, that makes perfect sense.
> It is somewhat more thermally conductive than air. But there is no "sink"
> for the heat to go to.
Yeah, i sorta wondered if maybe it was exceptionally conductive and
the heat would end up at the base plate again... but i guess not.
It's thermal contribution is slightly more than
> zero (I don't think they even bother to spec it...). We always used Dow
Cool, thanks for the information... it confirms my speculations.
> E-bay is certainly the best place to find big IGBTs for the hobbyist.
Well... used to be, but i suppose its better than buying new!
> >PS. anyone have any IGBT bricks for sale? Im always looking for
> >spares for my big coil! Contact me off-list.