Sciencemadness Discussion Board

Filling in hole in heat sink

Foeskes - 27-5-2018 at 05:24

So I bought a heatsink from a market and when I got home I realized I accidentally bought one for a TO-3 power transistor. So I decided to fill in the hole.
At first I wanted to use Zinc which is a decent thermal conductor, but it freezes before filling the hole so I used pure tin instead(tin seems to conduct better than 60/40 alloy).
Is this good enough for use?
I could technically just use the area without holes but that would make my circuit bigger and I prefer to have a smaller circuit.
I will be using this for heat sinking igbts.

image.jpeg - 1.8MB

coppercone - 27-5-2018 at 09:07

If you are neurotic you can heat up the whole thing in the oven first, as hot as you can go, then buy some aluminum brazing rod from home depot and try to fill it in using a mapp torch.

I thought you might have a torch, but in general the aluminum brazing rods are fairly expensive, especially at home depot, and I don't know if it will work much better then zinc, I think they are zinc based... and they are kind of a bitch to use honestly, I don't like welding or brazing aluminum, though I found welding the shit easier then brazing! I had zero success brazing aluminum. Even with oxy/acetylene and liberal use of flux and doing shit like hitting it with the wire brush when its hot.

Welding with oxy/acetylene is nice and easy, looks decent, welding with oxy/hydrogen (from tanks) adjusted to correct ratio is easy but I get a nasty weld, which is supposed to be nicer because of the hydrogen (!? why i dont know), I think maybe I just need more practice, then it will be better then oxy/acetylene

When it comes to brazing though, I had better luck using the benzomatic brazing rods from home depot then the supposedly good aluminum brazing rods from the welding store!

But anyway,

Best bet with power electronics if course is to buy the best parts so you don't need a good heat sink, I don't know where the h40n60 stands, I have some myself, but I believe its an older part.

Those IGBT come in generations basically, so, i think the industry is on generation 8, maybe 9, I don't know where that part you have falls into place

For me it is especially difficult to justify using older generation power electronics... I feel like a fool dealing with the losses...

I think that the silicon carbide/GaN versions are not considered to be IGBT generations but separate shoot outs, I think their specifications are even better but expect to pay twice as much

If you look through IGBT manufacturer corporate literature you will find basically heirchies of generations and applications to help you determine how to choose the part with the lowest losses.

Just a suggestion, I did not analyze your part, but I found myself in the situation before trying to design around some scrap-box thing I had to realize that its basically outdated and unless you have a very good reason to use it for some particular parameter, its not worth the extra engineering... I just keep them around for curiosities sake.

[Edited on 27-5-2018 by coppercone]

[Edited on 27-5-2018 by coppercone]

[Edited on 27-5-2018 by coppercone]

coppercone - 27-5-2018 at 09:25

May be of help:



gets you an idea of the lay of the land.

Its manufacturer specific, but you can basically look at your application, and look at the recommended part by that table, then compare the specifications to see if you are in the right ballpark, I think the technologies used by the different manufacturers so the groupings of parts will be similar.

There are other tables that I saw, similar to that one, generated by different manufacturers, but I don't feel like looking for them right now.

Infenion has a really nice table somewhere, better then the one I linked, that also lists stuff like CoolMos.. cant find it tho

for like 100KHz or more you will want the carbide or nitride ones (forgot what it was) they are $$$

this is for mosfet I think, but very nice

[Edited on 27-5-2018 by coppercone]

sodium_stearate - 27-5-2018 at 10:07

Why not just purchase some 1/8 inch thick aluminum
plate or bar of the proper size, and make your own heat
sink? That way you can drill whatever size holes you
need, at the exact locations needed.

Foeskes - 27-5-2018 at 10:25

There are other heat sinks the same size for sale(with no holes), but I just have this one currently and I don't plan on going there for at least a month.

Also I don't live in the us so brazing and welding tools are limited. It took me 6 months before I can find a way to buy a butane torch(not online). Mapp and propane are unavailable. It is also hard to find any welding machines other than stick welders. Aluminium Blazing rods are available though.

stamasd - 28-5-2018 at 06:36

You could use indium. It's expensive but very soft, easy to mold and it's actually used in thermal management, as a heatsink "paste"
I use it for making vacuum gaskets.

[Edited on 28-5-2018 by stamasd]

Fulmen - 28-5-2018 at 09:35

You could use a copper heat spreader, this should provide enough area.

sodium_stearate - 28-5-2018 at 10:00

ALuminum works great for heat sinks.
Thicker is better. The more massive, the better the
cooling. It takes a combination of mass and area
exposed to the air. A plain hunk of 1/8 inch aluminum
4 inches wide and 6 inches long makes a fairly robust
heat sink. Mount the semiconductor near the center
making sure to use some heat sink grease.

Generally, those tiny heat sinks which are commercially
available are not massive enough to provide decent cooling.

The larger, more expensive ones, you will notice, have
a combination of a thick plate that has cast cooling fins
on one side. That way, both the area exposed to the air
and the mass are maximized.

But, a big piece of 1/4 inch thick aluminum plate
works very nicely too.