removing heat with thermal tape and small heatsinks

Most IR imagers are designed for architectural use; they won't focus closer than a few feet, and the pixel counts are pitiful. The low-end Flir units aren't much good for electronics.

My Flir E45 can resolve the hot spot on an 0603 resistor. It has a $3000 germanium lens that will focus on a part that it touches.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

I *hate* it when that happens.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

I presume that you know that "thermally conductive" means "slightly better than nothing". Aluminum has a natural insulator on the surface; anodizing "properly" could increase the voltage standoff.

Winfield Hill

My personal [tm] view is that using the board to funnel away heat from high temperature components is a no-no. As somebody else pointed out, it will heat up the whole board.

An example I encountered is my USB Terratec satellite USB TV tuner. To drive the LNB and dish motor it uses a LM317, and they also use the LM317 as a 22 kHz amplifer for the LNB control signals.. The LM317 is soldered on a small PCB.. with the rest of teh parts, and after replacing that LM317 about 6 times PLUS the heat damaged electrolytics around it (it has a small switcher from 12V to 20 V) finally decided it sucked, and fixed it my way:

It is still working...

50 cent heatsink...

I was going to say I'd be more worried about the transistors, and not the resistors. I made this heater thing with R's in TO-220 packs. During testing I 'unsoldered' the bus wire to the resistors a few times... with something like an 75% resistor survival rate. (It happened ~4 times and once a resistor 'not so good' afterwards.)

George H.

So what are you using exactly? 6 W/m/k is quite decent.

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

Q-dope is polystyrene, so I gather you sold it pretty fast.

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

Actually you cackle maniacally and post pictures on Dropbox. ;)

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

6 W/m/k is pretty good--normal zinc oxide paste (as used on heat sinks and babies' bottoms) comes in around 0.85.

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

Only when I blow things up on purpose.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Hard anodize seems safe up to about 200 volts. You've got to be very careful about machining... any tiny bumps or burrs will be lethal. An aluminum nitride insulator is generally better.

I have some thermal putty that claims 10.

The virtue of the filled silicone grease is that (given flat surfaces) it will squish down below 100 uinches thickness (my measurement resolution.)

Incidentally, don't automatically believe anybody's thermal specs. Lying is standard in this biz, even by the big names. And this thermal stuff is a nuisance to measure yourself.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

TW-T600-2MM from 3G Shielding. I start with 2mm material and squash it down to 1mm, which doesn't take a lot of force.

I've tested it and the thermal conductivity really is close to 6, compressed. The other virtue of compressing it, is that it gets thinner!

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Yup. It's also history dependent--back at IBM we had problems with some special Shin Etsu paste packed with silver flakes, which formed stacks when compressed. Under thermal cycling the silicone oil washed the fines out from between the stacks of flakes, which trashed the thermal conductivity.

Silver epoxy's alpha depends very sensitively on the mixing ratio and the bake time and temperature--you really want it to shrink by a percent or so to improve the electrical and thermal conductivity.

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

Interesting. I sent for a sample kit.

Do they have distributors? Octopart never heard of them.

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

Okay, so it's good to go except for the possibility of stress crack failure due to 20o->150oC temperature cycling.

I guess that flakes could stack up flat and make an almost solid thermal path. Grains don't do that. We got some diamond filled thermal epoxy and it wasn't dramatically better than plain epoxy.

We avoid epoxy, especially potting; it's a mess in production.

We do use some thermal cure 1-part glob-top stuff, which is a lot easier to use than mixed goop.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Air is a good insulator. Thermal conductivity is terrible, but a small fan fixes that. It's hard to get a dielectric constant much below

1.0006.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Life sucks, don't it.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

I got some T600 samples last week. I wonder, does the thermal conductivity have full inverse proportionality to squashed thickness? They don't address compression on the datasheet, although thickness is in the formula.

--
 Thanks, 
    - Win