Transistor Paste

[Bimphert]

Just wondering IF there is any difference between the thermal paste used for transistors (typically white) and the thermal paste used for mounting CPU's (typically grey, ie. Arctic Silver)

I'm guessing NO but maybe someone out there knows more about this!






PS: I'm aware that the paste's are sold in "other colors" BUT typically the CPU paste = grey and TX paste = white.


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[modge]

Just wondering IF there is any difference between the thermal paste used for transistors (typically white) and the thermal paste used for mounting CPU's (typically grey, ie. Arctic Silver)

I'm guessing NO but maybe someone out there knows more about this!






PS: I'm aware that the paste's are sold in "other colors" BUT typically the CPU paste = grey and TX paste = white.


`

You can use either it doesn't matter.

 

[avionic]

Beware some of those other than white pastes are not only heat conductive but also electrical conductive..Not a good thing to use on a electrically "hot" transistor case(collector).

 

[RossW]

DO NOT USE GRAY GREASE UNLESS YOU KNOW EXACTLY WHAT KIND OF GREASE IT IS AND HAVE READ THE SPEC SHEET.

Gray grease is very often gray because it contains a large amount of silver which makes it an excellent thermal conductor and an excellent electrical conductor. Mis-using electrically conductive grease is a good way to very quickly cause alot of damage. We use both at work and every now and then someone uses the wrong one, it's not pretty.

 

[Hyperion]

Which is why I always use the white stuff - perfectly adequate - when it is correctly applied !

 

[Bimphert]

DO NOT USE GRAY GREASE UNLESS YOU KNOW EXACTLY WHAT KIND OF GREASE IT IS AND HAVE READ THE SPEC SHEET.

Gray grease is very often gray because it contains a large amount of silver which makes it an excellent thermal conductor and an excellent electrical conductor.

Beware some of those other than white pastes are not only heat conductive but also electrical conductive..Not a good thing to use on a electrically "hot" transistor case(collector).

YES, thank you both for that verification! I suspected that initially but I read somewhere that "Arctic Silver" was one of the "better" brands of Tx grease and is therefore preferred. It ALSO contains something like 99% PURE silver, which immediately sparked a RED flag, but just thought I'd check here since I've only ever used the "white stuff."

The website (for Arctic Silver) claims that it is NOT electrically conductive BUT that it is slightly capacitive. Interesting!!!
http://www.arcticsilver.com/as5.htm


When in doubt, use the WHITE stuff! :thmbsp:



On another note, Which is preferred, Silicon Base OR Silicon Free grease???




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[avionic]

Quoted from Rod Elliot of ESP

9 - Thermal Compounds
One of the most common mistakes made by hobby electronics enthusiasts (and quite a few professionals too), is to assume that if a little thermal compound is good, a lot must be better. Absolutely not so! The amount of thermal compound should be exactly that amount which ensures that an air-free join is made between the mating surfaces. If too much is applied it will cause an increase in thermal resistance, since it is not really that good at conducting heat. Generally speaking, any electrical insulator is also a thermal insulator, so the thinner the final composite insulation - including thermal "grease" - the better.

Having said that, one must ensure that the electrical insulation is sufficient for the applied voltage or disaster will surely follow - usually in a spectacular fashion - especially if high voltages or currents are available.

A quick note on the application of thermal compounds is in order. This is the method I generally use, and it works very well once you have a copious supply of workshop rags to clean the mess from your fingers.

Apply a small quantity of the thermal compound to one finger, then gently rub with your thumb to create an approximately even coating on finger and thumb. Now rub the thermal compound onto a washer, held between thumb and finger, ensuring that the coating is just thick enough to be opaque, but thin (and even) enough to ensure that the contact will be absolute on both surfaces (transistor and heatsink). Test your skill until with moderate pressure, you can leave a perfectly formed outline of the transistor, with no blobs or gaps, on the heatsink surface.

 

[markn2wae]

Here is my experience with the gray stuff.

I work for a company that repair and re-cones speakers (powered and passive) and some of our customers really beat them up and often the amp. driving the tweeter gets fried.

The LM3886 amplifier IC is rated for 68W, that is a lot of Watts in a small IC and it will get quite hot when driven hard.

For the repeat "offenders" I will substitute the gray grease for the normal white stuff and have not gotten any back for repair for LM chip failure.

As for the TO-3 case transistor, I use the following method with good results.

1) Clean all surfaces of the heat sink\transistor\(mica) insulator.

2) Hold the transistor body up with the pins up, place a SMALL dab of grease on the "wide" side of the pin offset, working it from there to all other surfaces without getting a big bunch near the pins, just enough to cover without any lumps or "trails" of excess compound being pushed around.

3) Place a cleaned (or new) mica insulator onto the transistor and apply the same way as before, working out to the edges of the insulator, "top side" only, don't get any underneath next to the transistor.

4) Put the transistor back on the heat sink, tighten the hardware firmly, you should not see any GREAT amount of oozing out, just enough to see a TINY BEAD around the transistor and heat sink joints.

5) Check for shorts with a meter from the transistor case to the heat sink, there should not be any, you might read SOME leakage if the wires of the emitter and base are connected to the circuit.

I did this to an amplifier that uses germanium transistors that are known to "run away" if they get too hot, I will test this amp. shortly to see how the transistor case temperature differs from the heat sink under load.:scratch2:

Another "experiment" I will try is to see if the paste will conduct with high Voltage applied and see what the "breakdown point" (if any) using a junk regulator mounted to a heat sink with the usual hardware.:scratch2:

Mark T.

 

[Jailtime]

Get some Dow Corning 340 for your audio gear transistors. Most amps I've seen have way too much compound applied. I don't like seeing "bird ****" all over the heatsink.

 

[dodog]

YES, thank you both for that verification! I suspected that initially but I read somewhere that "Arctic Silver" was one of the "better" brands of Tx grease and is therefore preferred. It ALSO contains something like 99% PURE silver, which immediately sparked a RED flag, but just thought I'd check here since I've only ever used the "white stuff."

The website (for Arctic Silver) claims that it is NOT electrically conductive BUT that it is slightly capacitive. Interesting!!!
http://www.arcticsilver.com/as5.htm

So, is Arctic Silver not an acceptable paste to use for, say, mounting an STK module to a heatsink? I'd read, as well, that it's not conductive, but is there still a risk of failure/electrocution/fire? Say I already re-mounted STK to heatsinks, using Arctic Silver, and have been running for a few weeks without issues. Should I feel safe.... or lucky?ara:

 

[RossW]

I'd say lucky, but I am paranoid.

 

[markn2wae]

Follow up on my last post.

The amplifier I used the Arctic silver past on dissipates heat well, I find (by touch) that the TO-3 transistors do not get hotter than than the heat sink, keep in mind I use only a thin film on all surfaces (you have to use magnification to see any "bead" between surfaces)

As for conductivity, I put a small bead on a metal plate, (grounded) and touched a "hot" wire to the top of the bead with a high Voltage power supply (adjustable in Voltage, with a 10 Ma. max. current limit) to just over 1100 Volts DC and saw NO conductivity or shorting out.:thmbsp:

The above applies to the paste sold by Radio shack (#28-1099) the item is marked "Arctic Silver 5", OTHER PRODUCTS MAY DIFFER.

I might hesitate to use the stuff in a switch mode power supply or the horizontal output stage in a TV, but would try it out for a test on a "junker" TV that was still working.

Mark T.

 

[JBL GUY]

Hey Mark from one ham to another...Leave it to a ham to break out
the high voltage power supply to check the electrical conductivity of
heat sink compound :thmbsp::thmbsp:

Once years ago when I was working in the engineering lap building
a prototype...I found I was out of heat sink compound.

So I put in an order from the lab to stores for some more.

They delivered it and it did not say specifically non-conductive but I asked around and was told it worked ok in the past.

So..Well ok wait for it...You know what is coming.

I used it and it was not non-conductive:cry:

But it was the same brand and SKU number...

So I always make sure it says non-conductive on the package.

And I have even done your test with a high voltage power supply.

Hams always have spare HV supply or two on the shelf:yes:

Bottom line is always be sure before you use it...Unless you want
to let the magic smoke out the devices in your unit under repair.

 

[Mchaz]

If you want something better than standard "white paste", but is still an electric insulator try Arctic Silver Céramique.

http://www.arcticsilver.com/ceramique.htm

I've used it in the past with great results.

 

[dodog]

The amplifier I used the Arctic silver past on dissipates heat well, I find (by touch) that the TO-3 transistors do not get hotter than than the heat sink, keep in mind I use only a thin film on all surfaces (you have to use magnification to see any "bead" between surfaces)

As for conductivity, I put a small bead on a metal plate, (grounded) and touched a "hot" wire to the top of the bead with a high Voltage power supply (adjustable in Voltage, with a 10 Ma. max. current limit) to just over 1100 Volts DC and saw NO conductivity or shorting out.:thmbsp:

The above applies to the paste sold by Radio shack (#28-1099) the item is marked "Arctic Silver 5", OTHER PRODUCTS MAY DIFFER.

I might hesitate to use the stuff in a switch mode power supply or the horizontal output stage in a TV, but would try it out for a test on a "junker" TV that was still working.

Mark T.

Thanks for the info Mark! The heatsinks are cool to the touch, even after a few hours of playing. The STK modules aren't really hot either. I'll keep an eye (and nose) on things but I won't be as paranoid now.

 

[JBL GUY]

Im

portant Reminder:
Due to the unique shapes and sizes of the particles in Céramique, it will take a minimum of 25 hours and several thermal cycles to achieve maximum particle to particle thermal conduction and for the heatsink to CPU interface to reach maximum conductivity. (This period will be longer in a system without a fan on the heatsink.) On systems measuring actual internal core temperatures via the CPU's internal diode, the measured temperature will often drop slightly over this "break-in" period. This break-in will occur during the normal use of the computer as long as the computer is turned off from time to time and the interface is allowed to cool to room temperature. Once the break-in is complete, the computer can be left on if desired.

It has to be good because it has to "Break In" just like the
best audio components and tweaks

Sorry just could not resist.

And before I get flamed about break in..I recently pulled a pair of Koss
PRO 4AAA headphones out of storage and the more I listen to them the
better they sound:yes:

Mchaz thank you for the link. It looks like some very good thermal compound.

Looks like they take their thermal compound very seriously.

 

[avionic]

Call me old fashioned..I'll stick with the white stuff.:thmbsp:

"break in" Yeah right..

 

[Bimphert]

Quoted from Rod Elliot of ESP

AWESOME! Appreciate that Avionic.... Rod Elliot's site is indispensable!!!

PS: Nice to see your current avatar... Last one was UUUGGGLY!!!

... As for the TO-3 case transistor, I use the following method with good results.

1) Clean all surfaces of the heat sink\transistor\(mica) insulator.

2) Hold the transistor body up with the pins up, place a SMALL dab of grease on the "wide" side of the pin offset, working it from there to all other surfaces without getting a big bunch near the pins, just enough to cover without any lumps or "trails" of excess compound being pushed around.

3) Place a cleaned (or new) mica insulator onto the transistor and apply the same way as before, working out to the edges of the insulator, "top side" only, don't get any underneath next to the transistor.

4) Put the transistor back on the heat sink, tighten the hardware firmly, you should not see any GREAT amount of oozing out....

Mark T.

Great tip..... The transistors I'm replacing are the TO-3PL type (TO-264) and not the typical TO-3 (round) type. Although I'm sure it can be applied (with slight modifications).

TOO many transistor case styles out there!!!!!





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[markn2wae]

Best way to not get too messy.

AWESOME! Appreciate that Avionic.... Rod Elliot's site is indispensable!!!

PS: Nice to see your current avatar... Last one was UUUGGGLY!!!







Great tip..... The transistors I'm replacing are the TO-3PL type (TO-264) and not the typical TO-3 (round) type. Although I'm sure it can be applied (with slight modifications).

TOO many transistor case styles out there!!!!!





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I do it this way to not get too messy and apply just the right amount and not having to "butter" both sides of the insulator at the same time YUCKY!

Mark T.

 

[avionic]

I do it this way to not get too messy and apply just the right amount and not having to "butter" both sides of the insulator at the same time YUCKY!

Mark T.

I do it similar.But use a single edged razor blade to apply a thin film on the transistor first - then lay down the mica insulator - then apply another thin film on the mica bottom. But its a messy job anytime you deal with compound. Paper towels at the bench.And soap and water at the sink.