The virtue of making resistors out of ceramic is that they can run really hot.
AlN surface-mount resistors are good because they can conduct a lot of heat into PCB copper pours, or into aluminum heat sinks.
Either way, you need heat spreading and surface area to cool things.
One thing I like is punched copper disks, like jewelry makers use. Cheap on Amazon or Ebay. Epoxy one to a part and it spreads the heat laterally and increases surface area. Any air flow sweeps the top and the bottom.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
That almost cries for oil cooling. Of course, when I did that with a larger setup the container began to weep. I must have botched one of the solder seams.
-- Regards, Joerg http://www.analogconsultants.com/
Oil is nasty. If you get water on your jeans, it evaporates.
I was thinking about a cavity and some water channels machined in an aluminum block. The Cree would push into a cavity with an o-ring seal. Water would flow on the bottom of the fet. Cooling would be awesome and capacitance minimal.
My average drain voltage is low (I'm making narrow positive pulses) so electrolysis might be managable. One could bond a very thin AlN slab to the fet tab too.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Getting low capacitive conduction and radiation from something heatsunk to a conductive surface is both clumsy and expensive.
I wonder where the target market is? Curious mixture of old school thinking and . . . In a low labor price market, it will be a hard sell.
Why are simple AlO2 wafers still so $$$ ? Even sourced off-shore?
RL
And necessary to make fast amps and pulse generators. Radiation doesn't do much to cool a small part, and fast circuits need small parts.
Making a small, 7 ns, 1KV, 4 MHz pulse generator is hardly old-school. It is a serious thermal-capacitive challenge.
That one was *hard*, electrically and especially thermally.
They are cheap, but alumina conducts at about 25 w/mK. Alumium nitride is maybe 5x better, close to common aluminum alloys.
The only reasonably affordable better insulator is BeO, and beryllium is toxic.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Philips used to offer a ~2in x 4in Alox plate laser-cut to accept a to220 spring clip. It mounted to printed wiring using folded tinned metal grips on the edges. MOQ ~ 1 gazillion.
RL
Epoxy is not great with heat though. What product do you use?
Clifford Heath
Some thermally conductive stuff,
AAVID 4952G
The thermal conductivity is only mediocre, 1.4 w/mK. The trick is to keep it thin.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Joerg wrote in news: snipped-for-privacy@mid.individual.net:
Fluorinert is dielectric and a lot less messy. (and a lot more expensive) Not better than water thermally, but far better than water around electrical circuits!
Nah, sapphire becomes opaque around 5 um, and polycrystalline alumina will be worse.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Every once in a whie one of my people will suggest oil cooling or potting. A few hours alone locked in a dark closet seems to help them.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
We sometimes want to thermal image a board in a box. If we remove the top cover, the air flow all changes. FLIR sells a thermally-transparent (looks like glass) window for some kilobucks that we could install in the cover, or use to replace the cover.
We use the black plastic from the cheapest, thinnest garbage bags.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Wouldn't clingfilm work?
-- Regards - Rodney Pont The from address exists but is mostly dumped, please send any emails to the address below e-mail rpont (at) gmail (dot) com
I have used oil cooling over decades. It works. You just have to make sure there is no mess. At least when married.
-- Regards, Joerg http://www.analogconsultants.com/
Not a problem if people dress accordingly :-)
Really hoppy India Pale Ale might also work.
-- Regards, Joerg http://www.analogconsultants.com/
Some of it does. Again, the cheapest stuff is the thinnest.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
The compatible garments are wool; oil just diffuses in, doesn't leave a spot. Wool shirt is great for machine shop (but roll up the sleeves before using power tools, of course).
Garbage bags are low-density polyethylene, which works pretty well in
1-mil gauge. I used that in my Footprints sensors to suppress convection near the sensor film.HDPE is better if you can get it thin enough.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
there's
ut
ive,
Why, what is better about it? HDPE is milk jugs and kayaks. Both pretty t hick. Where do you find it thin?
-- Rick C. +++ Get 1,000 miles of free Supercharging +++ Tesla referral code - https://ts.la/richard11209
You could melt a bleach bottle and smear it out into a thin layer. Commercially? Dunno.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.