Thermal Grease/Adhesive (?)

I'm betting it's epoxy of some sort, designed to keep the screws from vibrating loose. Don't know how you'd identify it for sure.

If it's white, and gets all over your trousers as soon as you walk in the same room as it, then it's silicon grease, also known as thermal grease, or heatsink compound. Contrary to what you believe, the surface tension exhibited by this stuff over a large area, causes it to stick surfaces together like the proverbial, and it is often necessary to get a screwdriver in between the two sheets of metal to get some air in between to ' break ' the bond.

Thermal adhesive, on the other hand, is just that. It sticks heatsinks directly to the tops of ICs, with a thermal conductivity similar to that of silicon grease. The difference is that once it has done this, you would need a crowbar to separate them again.

Provided there is still a reasonably even film of grease on both surfaces, and it has not dried out and gone ' chalky ', then you can go ahead and just reassemble with the old grease. However, be aware that this stuff seems to attract workshop debris, and you should examine both surfaces CAREFULLY before reassembly, as anything that stops the surfaces bolting back together totally flat, will ruin the heat conductivity between the two surfaces, through the grease.

Arfa

"CitizenRuth" wrote ... ....

Not advisable. The act of disassembly looses the "excess" that squeezed out from the surfaces, and you can't really effectively recover all of it to reuse. Besides if it got very hot, the compound may have partially "dried up" making it more difficult to get the thermal coupling the second time around.

Should be able to use standard heatsink compound (gooey, white stuff) which is widely sold to people constructing their own PCs. It is used between the CPU chip and the heat sink in the computer. Should be able to buy this stuff anywhere computer CPUs, heatsinks, etc. are offered.

I usually clean off the old stuff with alcohol and a rag (or Kleenex, etc.)

Ifg the heatsink was also screwed on, then probably NOT tthermal adhesive, but thermal heatsink compound which could be either silicon or Berrylium Oxide based. If the latter, it is highly toxic.

geoff

Sorry if this seems pedantic, but silicone (not silicon) grease and heatsink compound are not the same thing at all. The former is a clear grease, often used for HV insulation and sometimes for lubricating plastic gears. The latter is a silicone *based* compound with additives for conducting heat efficiently.

That is true.

I would advise against this. It is by far the best course of action to thoroughly clean both surfaces of old heatsink compound and reapply new. It is after all rather cheap and readily available. Semiconductors OTOH can be pricey, difficult to obtain and can cause widespread damage when they short ;-)

Dave

What you have there is very common, it's just silicone heatsink compound, used to increase the efficiency of transfer of heat from component to heatsink. If it were thermal *adhesive*, they probably wouldn't have used screws to secure the assembly. Thermal adhesive is generally used instead of mechanical fixing methods, and the adhesive itself is rather pricey. It is very common for thermal heatsink compound to age and can become quite stubborn to break, which might lead one to believe it's adhesive, but it's easy to spot the difference as thermal heatsink compound will be softish and sticky as opposed to rock hard. Thermal adhesive is *very* sturdy though, it's epoxy based, sets rock hard and can require serious force to remove.

You should clean off all the old compound and reapply new. You *might* get away with reassembly without new compound, but I don't think it's worth the gamble. If it isn't convenient to get to an electronics shop for a tube of heatsink compound, the stuff available for CPU heatsinks, which is readily available from computer shops, is the same thing. White or silver compound will work great. You don't have to plaster it on like mortar as some people believe, just apply a nice even coat to one surface and reassemble.

Dave

It is "thermal grease" aka "heat-sink compound". Remarkably poor epoxy if he could just pry it apart.

Your political "thinking" needs work as well. Thought about just moving to the PRC? I'm sure you'd love it. Curious why all those people spend 10s of thousands of US$ to get away from there, though. Makes you wonder.

"Richard Crowley" wrote in news:dieuno$keb$ snipped-for-privacy@news01.intel.com:

WHITE HS compound contains either alumina or beryllium [oxide?];that's what makes it white and thermally conductive(no silicone,AFAIK),and there are clear -silicone- greases made by Dow Corning.The white compound has some solvent that dries out after some time. Silicone grease will not dry out.

"Dave D" wrote in news:P7GdnZ6 snipped-for-privacy@pipex.net:

If the white compound had silicone grease in it,it would not dry out. I believe the white compound has some other petro-based grease.

There is a silver-loaded thermal epoxy adhesive,and 3M(IIRC) makes a thermal 2-part adhesive for gluing on heat sinks.

It's heatsink grease, you can get it anywhere that sells electronic components, even Radio Shack has it in little tubes.

This is almost always a grease made of silicone oil and zinc oxide powder, and some is thick enough to hold the parts together firmly to require tools to separate them. Don't substitute it with a heatsink grease containing silver powder, commonly sold for computer CPU cooling, in case there's high voltage (silver powder is also very messy).

I'd be very surprised if any consumer product made in the past 30 years contained anything as toxic as beryllium. Even the oxide form seems to be considered hazardous.

Mackie used to be a very service oriented company.. I haven't dealt with them lately, but I suspect if you called them up they'd send you a little of whatever it is they use free of charge. They should at least telll you what it is and where to get some. Especially since you paid like 1500 bucks for those speakers.

Shouldn't be an issue with the voltages one would expect to see in a transistor amp. Cheap white compound will dry out over time and lose its effectiveness, whereas something like arctic silver shouldn't. I wouldn't necessarily recommend silver loaded compound mind, but I see no reason not to use it for this kind of job. It's possible in this case that the transistor is directly mounted anyway, ie without an insulating pad.

Dave

That's probably true, I often wondered how a silicone based product could 'dry out'. I read somewhere these compounds were based on silicone/synthetic oils, maybe there's something else added as well which dries out.

Dave

Hi Dave

Yeah Yeah - you're right ! The missing ' e ' on the end of silicone was a typo. I probably should have put it the other way around like " It's heatsink compound, otherwise known as thermal grease or silicone grease ". I know that it's not actually the same stuff as silicone grease - I have a big tub of that which I use for all sorts of plastic lubricating. But I think that you've gotta agree that for as long as any of us in the business can remember, this hateful stuff has been known generically ( albeit erroneously ) as ' Silicone Grease '. ( probably because it's based on silicone, and greasy ... )

As far as replacing the compound goes, I would absolutely, definitely and without question, agree with you to always always always replace compound between semiconductors and their heatsinks, first cleaning off all traces of the old, chemically. However, where the compound is between a true heatsink, and a secondary ' belt and braces ' piece of metal such as a back panel, like the OP seems to be suggesting, then in my experience, there is no need to cover yourself, the kids and next door's cat ( for if any of them are within 30 yards of you, they will get covered ... !! ) in the stuff, just for the hell of cleaning it off and replacing it. Compound in this sort of position doesn't normally get to a high enough temperature to dry out and go powdery. : -))

Arfa

You must be a silicone't (!)

geoff

Ohhhh That's baaaad !!!!

Arfa ;-)

For some reason I appear to have missed a few clues in his text. I got the impression that the stuff was between the mounting brackets and the speaker cabinet, and missed where he said it was gooey stuff.

Not at all. The Dems will be running a socialist. If the Repubs run a leftist like McCain, then I figure I might as well go all the way.

You've got the wrong guy. I'm busy trying to keep the PRC from moving in here.