Are holes in the heatsink under the IGBT brick baseplate a problem?

[Phoenix]

Hello

As you may know, it is very hard to find new large heatsinks without any holes. I am trying to find a heatsink for my large DRSSTC with at least 30x30cm dimensions, but all the offers I can find have holes in them.

Is it a big problem if there are for example a few M5 and M6 holes under the baseplates of the IGBTs? I personally do not really think that this is a big issue, because the heat will get spreaded by the highly thermally conductive baseplate, but I would like to hear your thoughts.

And do you know where I could get such a heatsink?

With best regards
Phoenix

[oneKone]

In many of my projects I've used heatsinks with holes in them. I have the same perspective as you, with large devices like igbt bricks there's quite a large surface area to dissipate heat.

The 2 sources that I can think of for heatsinks are rs components (expensive) or depending on where you live a scrapyard or solar company for old house inverters.

[Mads Barnkob]

I would not worry too much about a few holes underneath a CM300, with a area of about 70 square-centimeter, a M6 hole is properly around 1/280 (guess) of the total area.

You could fill the holes with brass screws and gently and carefully cut them off with a grinder and sand the surface down to be level, this could however ruin the very even surface and make heat transfer even worse.

I got enough heat sinks so that I could sell you a large one, but it is very expensive to ship. I guess its around 70-80 Euro to another country in Europe.

[Phoenix]

Thank you for your replies 

I really didn't knew that RS components sells such large heatsinks, but they are quite expensive as you said, oneKone.

My IGBT Bricks are way larger than CM300 Bricks and they have an area of about 182cm² each, so a few small M6 holes shouldn't really be a problem like you said, Mads.

I think I could still close the holes with some metal epoxy (JB Weld). I just need to be careful that nothing protrudes from the hole, because then the baseplate wouldn't make perfect contact. With the epoxy there also would be no need for grinding, because I can simply wipe away the excess before the whole thing cures.

Greetings
Phoenix

[Teravolt]

if you want to order from US I get thease

https://www.mpja.com/High-Power-Aluminum-Heatsink/productinfo/34881+HK/

or

https://www.mpja.com/5-7_8-X-2-3_4-Aluminum-Heatsink/productinfo/32088+HK/


or ebay

[oneKone]

@phoenix

If you haven't mounted the modules yet you could loctite in some M6 grubscrews and fill the smaller void with heatsink paste. Obviously it's not the best solution but it would stop the paste from leaking out (assuming the holes are drilled through) and it might and a tiny bit more thermal transfer?

[Bambinz]

Probably some small holes will not be a big problem because the surface of the IGBT is very large compared to the hole area.
The very important things is that the hole do not compromise the planarity of the heatsink, therefore a little countersink can be a good things.