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Trouble mounting IGBT

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Dosinski

Thu Jun 03 2010, 08:08PM

Registered Member #2680 Joined: Wed Feb 10 2010, 09:23PM
Location:
Posts: 45

So far I have been using cheap IGBTs for my DRSSTC which i ordered from china(right). Those weren't so good so i ordered some nice high current IGBTs (left). Unfortunately i didn't notice the IGBTs weren't in a TO-247 package case until it was too late. For the TO-247 IGBTs, i've been mounting them to a heatsink using a 3mm screw. How can i mount these new IGBTs (without using superglue or magic)?

The only good idea i have is to clamp the IGBTs to the heatsink. My only other idea is to drill a hole through the igbt (which probably won't go over so well).

Mads Barnkob

Thu Jun 03 2010, 08:19PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Clamp seems to be your solution.

IGBT Heatsink Clamp

Avalanche

Thu Jun 03 2010, 08:42PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

yes, don't try drilling holes in them

Herr Zapp

Fri Jun 04 2010, 12:37AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Dosinski -

You didn't specify the device P/N, or show a photo of the front of the device, but this is probably the Super-247 package, which is designed to be mechanically clamped against the heat sink.

Aavid makes several compatible heat-sink clips, like the MAX 07 or MAX 08. This clip is secured to the heat sink with a single screw, and clamps the device against the heat sink with relatively high force. Use a thermal transfer compound between device and the heatsink. This can be used to clamp a Super-247 device against just about any type of flat plate or heatsink that would accommodate a normal TO-247 device.

Detailed information is available on the Aavid website:

The "bolt-on" Max Clips are shown on page 15.

Regards,
Herr Zapp

Daniel Uhrenholt

Fri Jun 04 2010, 06:17AM

Registered Member #125 Joined: Fri Feb 10 2006, 01:52PM
Location: Aalborg, Denmark
Posts: 155

Hi Dosinski,

I recall seeing some IGBT`s like that some years ago when Terry Fritz made the SISG. As I remember, Finn Hammer glued the IGBT`s on the heat sink with some kind of thermal adhesive glue, and the glue is usually a two-part epoxy resin... I dont know where buy it, but try Google:-)

Cheers, Daniel

GeordieBoy

Fri Jun 04 2010, 12:42PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

Regardless of whether the package has a "mounting hole" or not, you really should be using a clamp to mount TO-220 or TO-247 type power semiconductors to their heatsink if they are dissipating more than a few watts.

Using a bolt through the hole in the package is really not suitable unless the power dissipation is very small. It tends to pull the top of the package where no heat is generated down against the heatsink. Whilst lifting the area of the backplate on which the actual die is located away from the heatsink! This greatly increases thermal resistance between the silicon die and the heatsink. The end result is that the heatsink stays relatively cool, the backplate quickly gets very hot, and the die cooks causing the MOSFET/IGBT to fail. Then when the power is turned off, the heatsink and device feel stone-cold to the touch. The small thermal mass of the tiny metal TO-247 backplate means that any heat is quickly conducted away to the heatsink once the source of heat is turned off (or the device fails.) You are then left scratching your head for an explanation of the device failures!

So if you have "unexplained" IGBT or MOSFET failures of devices mounted with an M3 through the hole in the package try mounting them properly with a clamp that provides positive pressure over the location of the die inside the package.

You can buy spring steel clips like these:

or clamp a couple of devices down with a piece of metal bar as shown:

-Richie,

Sulaiman

Fri Jun 04 2010, 10:10PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I repaired a bit of kit recently that used a cheap simple method;

Mount the transistors on the underside of your pcb with no space between pcb and transistor, metal plate facing away from the pcb.
Screw the pcb to your heatsink, the pcb can bend a little with no problems.
You will need one hole each side of the transistor.

For many transistors clamp them to a long heatsink with a metal bar that has holes for screws each side of each transistor. The bar bends minutely allowing continuous even pressure.

By far the most common method is a ready made heatsink with matching clip(s)
as noted above.

There are other techniques, invent your own.

Conundrum

Sat Jun 05 2010, 12:28PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

i've used epoxy mixed with dried out thermal paste before now.

if you evaporate off the silicone you are left with very fine aluminium and silver oxides it seems.

-A

Dosinski

Sun Jun 06 2010, 01:35AM

Registered Member #2680 Joined: Wed Feb 10 2010, 09:23PM
Location:
Posts: 45

Thank you for the replies. Due to the haphazard design of my full bridge, my best bet are steel clamps from Aavid. I ordered some today, i'll test them out next week.
-Dave

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