Ceramic heat spreaders

Oh, you mean *aloominum* - just a note for our non-British readers.

Alumina is not a very good heat conductor. Those thin things don't look like very good spreaders. I bet their theta numbers are fudged, specifically by applying heat uniformly across the surface, which is not how a "spreader" works.

I use aluminum pin-fin heat sinks as spreaders for FPGAs and such. The pins are useless, but the baseplate does suck heat out the central chip hot-spot and spread it around. Aluminum conducts heat 5 or so times better than alumina.

Everybody lies about heat sinks.

I thought the IUPAC deal was that the septics were to use 'Aluminium' in return for us spelling Sulphur as 'Sulfur'.

But 'sodder' instead of solder. That's just weird.

Cheers

Is it meant to run withut a chassis?

Simpler alumina plate shapes have been used with transistor clip fastener (and physical retainer) detail pre-punched. I've never seen it with sigificant 3rd dimensional detail.

If it physically attaches to the heat source alone, I see no advantage to going to the added expense of using an electrical insulator material, unless it's a special safety or EMC issue.

RL

Nobody over here got the memo. (They'd have burst out laughing if they had.)

Pretty amusing from the folks that gave us Featherstonehaugh, Cholmondeley, and Pontefract. ;) (*)

Jibbing at 'sodder', forsooth.

Cheers

Phil Hobbs

(For non-Commonwealth leftpondians: these are pronounced roughly "Fanshaw", "Chumley", and "Pumfrey".)

PS: It's weird how Aussies think that references to their own primitive plumbing makes a clever way to insult Americans.

How many watts is the TO3P package dissipating and what's your target operating temperature? You can use those numbers to calculate how many C/W the heat sink will need to handle. That will give you the approximate size of the heat sink.

How much vertical room do you have for the added heat sink? Any air flow?

Since you didn't bother specifying the transistor device number, I looked up a variety of TO3P packages devices and found that the highest operating temperature mentioned is 150C. At 200C, you transistor should have died from self immolation.

Are you trying to clamp that to the top of the TO3P package? That's all plastic and won't conduct much heat out of the package. It needs to go under the TO3P package or flip the TO3P package over so that the metal is on top.

TO3P package

Actually, I hadn't seen anything like that either, probably because it's a lousy idea. If the heat sink were made from Aluminum Nitride, it has a chance of working. But this one is Aluminum Oxide (alumina), so forget it.

W/m*K Diamond 1000 h-BN 600 c-BN 740 Silver 406 Copper 385 Gold 314 AlN 285 (aluminum nitride ceramic) Aluminum 205 Graphite 200 Carbon 150 SiC 120 Brass 109 Al2O3 25 (aluminum oxide ceramic)

Now that's perphectly phunny.

The fact the material is an electrical insulator is the only real novelty - you will still need to use a thermal compound to exclude air and get good coupling to the "spreader" from the device.

FYI:

I see increasing use of Beryllium Oxide as a heat spreader and insulator for TO220 devices. Used in rectangular strips about 2mm thick it provide massive insulation and conducts heat better than Aluminium.

The TO220 pak is then clamped to the heatsink, a far better way than using 3mm bolts and plastic bushes that crush over time.

.... Phil

BeO is toxic and must be handled carefully. AlN is almost as good a heat conductor as BeO and is safe.

Just to clarify, the transistors are 'upside down'. I just need to operate outside the chassis for debugging purposes, and was looking for a heatsink when I came across the ceramic type and wondered.

In fact, the device works at an ambient of 180'C and these transistors will then be above 200'C, so I'm not too worried about them, but running cooler pleases Mr Arrhenius and they last longer.

The specified operating temperature was passed with a cheery wave, sometimes you just have to.

Hmmm. Diamond.

Thanks

.... Phil

Probably slightly inside the planet. ;)

Cheers

Phil Hobbs

On Sun, 17 Apr 2016 21:40:09 -0700, John Larkin Gave us:

The "handling carefully" amounts to not letting it touch an open wound.

Otherwise it is safer than an old Nickel Cadmium plated part.

IF it does get in one's blood, it id far more deadly and carcinogenic than Nickel Cadmium ever was. Likely even more deadly than pure Cadmium.

So take a purple BeO heat sink tab and cut your finger with it, John... please.

On Mon, 18 Apr 2016 09:19:22 +0100, Syd Rumpo Gave us:

I am sure they'll come up with some graphene matrix film that beats everything short of pure diamond.

On Mon, 18 Apr 2016 04:13:36 -0700 (PDT), Phil Hobbs Gave us:

Like at the (lower)end of an oil derrick drill string?

Yes, /in/ rather than /on/, unless you count the inside of a test oven as 'ambient'.

Cheers

Got nothing better to do ?

No answer necessary.

.... Phil

Oh dear, preconceptions challenged. I can feel the pressure building.

You gonna blow?

Cheers

Or just too stupid know any better.

.... Phil