Re: The goo inside of IGBT modules.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Steve Ward" <steve.ward-at-gmail-dot-com> 

Hey Terry,


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:
 > >Hi,
 > >
 > >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 
6101:
 >
 > http://hot-streamer-dot-com/temp/Dow-6101.pdf

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!

Steve

 >
 > Cheers,
 >
 >         Terry
 >
 >
 >
 >
 > >Steve
 > >
 > >PS. anyone have any IGBT bricks for sale?  Im always looking for
 > >spares for my big coil!  Contact me off-list.
 >
 >