Thermal Grease

[Tone Meister]

I'm in a bind and need to source thermal grease locally for use with TO-220, Multiwatt15, etc transistors, and I need to source it TODAY. The local electronics supply has nothing, nada, zilch. So that leaves Radio Shack, and all they have that might work is the Arctic Silver Ceramique, which is non-conductive.

Arctic Silver Incorporated - Céramique

In short, will it work in a pinch?

[soundguruman]

Arctic silver is the best one, by far.
It is way more efficient than cheap zinc grease.
I would rather use it than anything else.

However are you sure it's non-conductive?

I have used it on a bunch of stuff. Superior for sure, and expensive.

[Tone Meister]

Arctic silver is the best one, by far.
It is way more efficient than zinc grease.
I would rather use it than anything else.

However are you sure it's non-conductive?

I have used it on a bunch of stuff. Superior for sure, and expensive.

Well, there are several types of Arctic Silver, and a conductive one would be a disaster. I am installing a TDA7293 in a Marshall amp for a friend who's leaving tonight. But, yes, I am certain the Ceramique version is non-conductive; here is an excerpt I extracted from the website that I linked above:

Electrical Insulator: Céramique does not contain any metal or other electrically conductive materials. It is a pure electrical insulator, neither electrically conductive nor capacitive.

I just need something that will work in a pinch and not cause more harm than good. Anyone else with direct experience with this particular type of Arctic Silver?

[km6xz]

Did the old part have any clean grease on it? Now, they usually use a silicone pad instead of grease. Almost everyone uses way too much so there is excess around the old part, which is enough for it to function at its highest effectiveness by spreading it thinly but evenly over the mating surfaces. I found that using a small 1/2" wide nylon spatula made for coating small photographic plates, also surplus($0.10), to spread a thin bead across the matting surface in 1-2 passes, was very effective and kept hands and work space clean. The result was a smooth even spread a fraction of a millimeter thick. The amount most techs use on one transistor could mount a dozen or more if done properly.
The grease needs to be very thin, only thick enough to fill sight unevenness of the mating surfaces, like scratches. If you can see it as white, it is too much and actually lowers thermal transfer. More transistors die of heat related problems from too much grease than too little.
Years ago I got a Air Force surplus can of silicone clear heat compound for $5 that was in a 1 gallon can. Best stuff I ever used and when I moved and left all the the employees, it was still 90% full after thousands of power transistor replacements. I'm sure it cost us taxpayers many hundreds or maybe a $1k.

[Tone Meister]

The grease on the old part was crusty and likely unusable. I cleaned the all the old compound off the heatsink and picked up a small tube of non-conductive silicon-based thermal compound to tide me over.

[km6xz]

Yes, good not to reuse if it has any dirt in it. The portion under the device, not that excess squeezed out the sides that is exposed to air, is often clean and still usable.

[Tone Meister]

Yes, it too was dirty and would have created more problems than it solved. I did follow your advice and used a very thin layer on the back of the transistor. At that rate, if the tube I have doesn't dry out on me, I have enough to install several dozen more components.

[J M Fahey]

In emergencies such as yours, typical Saturday afternoon jobs: "I NEED to play *tonight* , I'll come back on Monday for the proper job", I have used standard red Lithium car engine grease .
It always worked.
Guess what?
Many musicians never came back ..... and none ever complained that their amp overheated and burnt , at least within the 90 day to a year warranty period, so I guess it's not that useless.
Definitely "better than nothing".
I have autopsied some such amps *years* later, red grease was sort of hardened (imagine a soapbar) , so if transistor was pulled for measurement and reseated it would probably not reflow to fill surface irregularities ... but if left undisturbed it seemed to do its job adequately.
Just sayin'.

As a side note, I guess "ceramic" type Arctic Silver must be plain zinc oxide based.
Out of all available non conducting fillings, it was chosen because of best performance, not chance.
There must be some reason for it to be the industry standard, some 50 (or more) years after introduction.

[Tone Meister]

Thanks for weighing in Juan. I feel sure the run-of-the-mill silicon based compound will suffice. I just couldn't see paying $8.00 for a one shot deal when I can order a 10-year supply for the same money from Mouser.

[km6xz]

You may find that the generic bulk cheap items in chemicals are the same base ingredient for the "audiophile grade" costing 1000 times as much.
A good example, I am into photography and so have detachable lens cameras. The sensor needs to be cleaned occasionally since even micron level dust particles are visible in prints. A couple companies sell cleaning kits that include a small 10ml vial of special sensor cleaning fluid. The kit sells for about $27 and is good for a couple cleanings. I did not believe the wild claims the manufacturer of the making so just used what was available, reagent grade methyl-alcohol and add a drop of a surfactant for spreading. A gallon costs $18 for the best, or simply 97% is about $6. The 3% is mostly water in suspension which is also a very good organic solvent. A friend was berating me for endangering my 36mpx pro camera by using non-authorized cleaner when for only $10 a cleaning I could get the superior and safer real deal. I watched him clean his with the magic sauce and noticed it smelled very familiar. I sent off for the material safety data sheet (MSDS) for the super stuff and found it had one ingredient, only one......Methanol, the common name for methyl-alcohol.
The maker of the super special magic cleaner was buying in 50gal drums at less than $100(actually the current NA contract price on the Methanol Exchange is $1.80/gal or $599/ metric ton), and putting a few drops into plastic vials and selling it directly on their web site for $20-27 x 18927.1(the number of 10ml portions in a drum) for a gross retail total of $378,540, or 378440% markup.
That makes more profit than the $3000 a meter "interconnect" con-men could dream of, with millions more potential customers.
I am in the wrong business....

[R.G.]

The whole point of heat sink goo is that practically anything you can put in there that will fill gaps and exclude air from the crevices is an improvement over leaving the air in place.

See: Thermal grease - Wikipedia, the free encyclopedia

Silicone grease is about 100 times as good a thermal conductor as air, and most greases are 50-100 times better. The best thermal soups are up to about 4000 times better than air.

But not as good as metal to metal contact. Lapping the surfaces smooth to one another or filling the gaps with liquid metal or phase change metal is even better, but obviously introduces electrical connection too.

[Enzo]

I think that is part of why some amp makers - notably QSC - design their amp circuits "inside out" so the power transistor collectors are bolted to the grounded heat sink directly.

[Mick Bailey]

The gap-filler sheet material seems pretty good to me, but it isn't easy to work out what spec material is installed in some of the new amps. It can be insanely expensive for the high-end stuff.

[J M Fahey]

Dear RG, thanks for your post and link.
FWIW a few years ago we were (in Argentina) through one of our periodical crises and no thermal grease was available in bulk, only ridiculous little syringes.
I went to my trusty chemicals supplier, (no , not the one in a dark alley), and bought one kilo of white stuff (NO, I repeat, NOT what you imagine)
Technical grade Zinc Oxide , 2.2 pounds for about U$10 or 20 .
Passed it through a flour sieve into a pot where 1 kilo of red Lithium grease was already molten.
It absorbed about half a kilo before becoming too thick.
So for the last 5 and the next 30 years all my amps leave with pink thermal grease.
And I still have 1/2 kilo of raw ZnO left for extra 35 years backup.

As of RG's link, NOW I can confess that I have used toothpaste once.
Which his table shows as better than thermal grease !!!!!!!!!!!!!!!

[Enzo]

Well, of course. Heat sink compound is designed not to have gaps or holes in the coverage, and toothpaste is also designed to fight cavities, so.....