Re: The goo inside of IGBT modules.

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

Original poster: "Jan Wagner" <jwagner-at-cc.hut.fi> 


On Wed, 15 Sep 2004, Tesla list wrote:
>Original poster: "Steve Ward" <steve.ward-at-gmail-dot-com> 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).  My thoughts were that it was to help contain
>the explosion when they fail.  Also, that it may prevent moisture from
>getting on the dies and shorting it all out (since the module casing
>is not completely air tight).
>
>But what was more important to me was whether or not the goo serves
>any use in removing heat from the dies?  Im not sure if this gel is a
>thermal insulator or a conductor really... its hard to say.  Does
>anyone know for sure?

The monkey snort is silicone gel. Which is not silicon, but the bathroom 
fixture type sealant resin. Not a good thermal conductor really. It just 
helps keep moisture and corrosives outside. Heat is mainly removed via the 
substrate and baseplate. The low-hardness gel also reduces thermal stress 
on the bonding wires as they can move more freely than in e.g. hard epoxy fill.

Btw, it doesn't damp those explosions, the gel is too "soft" for this, 
shrapnel just shoots right through it, with a nasty little scorched crater 
left behind... :) (at work, one wall is decorated with some dramatically 
exloded 3-phase IGBT modules, some with all gel and guts sticking out, 
quite gory... ;-)

You're not by any chance contemplating to remove the gel and adding a pump 
and internal forced oil cooling to your IGBT modules, are you?  ;-)

cheers,
  - Jan

-- 
****************************************************
  Helsinki University of Technology
  Dept. of Electrical and Communications Engineering
  http://www.hut.fi/~jwagner/ - jwagner-at-cc.hut.fi



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