How can I figure the just-right amount of Silver compound?

The fan on my ancient but still working Core 2 Duo MacBook seems to be whirring more than usual. This may be purely subjective, since it's been years since I've heard the "regular" whirring. Anyhow, I suspect it's time to reapply the thermal paste.

I chose a silver compound, namely

Arctic Silver 5 High-Density Polysynthetic Silver Thermal Compound

over the carbon-based compound because it is a better thermal conductor.

But then I read the fineprint. It's also somewhat electrically conducting. If I add too much, it will short the pins of the CPU.

The trouble is that I cannot add too little either, or else it will not cover the CPU/heatsink connection.

How can I possibly get it "just right", neither too much for shorting, nor too little to leave an air gap?

Calaf

Posted 2017-09-26T03:11:37.270

Reputation: 205

Answers

The answers provided are good. But I have a couple issues with both of them.

First, it was not mentioned that you should thoroughly clean the old compound off. And, it's actually quite hard to get off unless you know the secret - Use electrical Contact Cleaner - it will dissolve the compound instantly and leave your surfaces clean and shiny. Use a q-tip or tissue. Alcohol does not work. You should NOT touch the surfaces with your fingers at all after cleaning them.

My recommended method of application (the one I have used probably hundreds of times now without issue) is to gently push the plunger of the Arctic Silver tube while you wipe the tip across the surface of the CPU. You want as thin of a layer as possible across the entire surface of the CPU while thoroughly covering all surface area.

The next trick to perfect the seat between the CPU and Heatsink is to install the heatsink. On Desktop computers you would clamp the heatsink down usually, but mobile computers and some desktops are screwed down. If it screws down, don't tighten the screws all the way. Then gently push down with pressure and gently twist (only slightly, a couple of degrees) back and forth on the heatsink. If using screws, finish tightening the heatsink screws down in a cross-diagonal pattern. Do not lift the heatsink back away from the CPU at any point after mating them together. This technique will squeeze the thermal compound down and make a perfect seal between the heatsink and the CPU.

If you doubt this, pull the heatsink back off. You'll see a perfect mate was made, as evidenced by the heatsink compound, between the CPU and heatsink. If you really pulled it off because you were curious, guess what, START OVER at step 1. :)

Appleoddity

Posted 2017-09-26T03:11:37.270

Reputation: 9 360

Very informative, but I'm still not clear on how I can be sure it will not spill out and short the pins. Do designers give installers a little margin for error (the height of the chip itself, perhaps?), or is this part of the gamble and if a little spews out while tightening the screws then the logic board is toasted? – Calaf – 2017-09-26T15:38:50.523

1There is not a gamble here. I said specifically, in bold, "You want as thin of a layer as possible..." The whole purpose of this stuff is to simply fill in the microscopic imperfections on the two surfaces. Also, this stuff doesn't "spill" out. It is thick and doesn't flow. Just use some common sense, less is more. – Appleoddity – 2017-09-26T18:18:27.490

Maybe it's easy after I've done it once or twice. One last clarification: I understand I shouldn't wiggle it, but should I at least feel some tack? Should I feel that the heatsink is sticking, in a very mild way, before knowing that it's a tight seal? – Calaf – 2017-09-26T18:59:05.317

Yes, with fresh compound it will feel a little sticky when you are wiggling. – Ben Franske – 2017-09-26T20:55:56.297

Essentially you want to cover the top of the CPU die with as thin a layer as possible so use a very small dab of compound and then spread it with your finger so that it more or less evenly covers the highest part of the CPU. Keep it back from the edges a little bit so that it does not spill down the sides of the CPU where you are more likely to short something out.

As an aside it's unlikely there was a problem with your old thermal compound. It doesn't really go bad. Most likely the nosier fan in your system was due to the bearings in the fan wearing out over time and/or dust getting into the bearings of the fan.

Ben Franske

Posted 2017-09-26T03:11:37.270

Reputation: 591

You add a blob the size of a BB pellet.

You want the blob to be in the middle. The pressure of the heatsink on the CPU will spread the paste and cover the surface.

You don't need to worry about the paste being applied evenly because the paste will flow around and equalize the distribution due to the pressure. You just need to make sure it is a blob in the middle so it spreads without air pockets.

If you put it on as a ring around the CPU, that's guaranteed to mess it up.

Source

Nelson

Posted 2017-09-26T03:11:37.270

Reputation: 1 199