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I have an Asus eee pc 1015ped. Upon disassembly I've found out the heat sink cools 2 chips. The one on the left is obviously the CPU and the one on the right is the integrated GPU I assume.

The big chips are the CPU and (presumably) GPU

And the detached heat sink looks like this:

enter image description here

The left square is thermal paste for the CPU. The right (bigger) one bothers me. Is it thermal paste too? If so, why is it different? Also, why doesn't the GPU have this shiny mirror thing?

I want to change the paste for the CPU. Will the same paste do for the GPU (if my assumptions are correct at all)?

  • Nobody mentioned this so far, but I think that a warning is in order: If you actually want to replace pads with grease, make sure that the grease is making proper contact. It could very easily happen that you remove the pads and find out that there's too much space for grease to work efficiently. – AndrejaKo Sep 22 '15 at 16:05
  • @AndrejaKo, thank you for the heads up. Do those pads go bad and need replacement? – Vladislav Ivanishin Sep 22 '15 at 16:09
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    I know that they can physically fall apart if squished too much. I don't know if their thermal properties change over time, so I can't say if you need to replace them or not. In my personal experience, they seem to "work" fine even if old. – AndrejaKo Sep 22 '15 at 16:11
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There is no grease. As pjc50 has pointed out, an integrated GPU is part of the die along with the CPU.

The two packages are different approaches to BGA packaging. This document gives examples of your packages on page 14-4. The left package is an HL-PBGA die-up package, and the "shiny mirror thing" is actually the bottom of the die. The other package is an H-PBGA die-down package - if you were to dismount the package you'd see a well in the underside with the chip inside.

In both cases, thermal contact with the heat sink is made by thermal conductive pads rather than thermal grease. Thermal pads are not quite as good (thermally) as a good grease, but they can be much thicker, and they have much more tolerance for differences in separation between the IC and heat sink. This allows adequate performance at much lower cost than would be needed to handle multiple chips, each with a different surface height. And you can see that two different pads (with different nominal thicknesses) have been used for the two chips. Note also that the left-hand pad has compressed around the die, evidence of good mechanical contact and pressure.

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"Integrated" GPUs are on the same die as the processor itself. So the left heatsink works for both. The "shiny mirror" is a heat spreader, made of ceramic or possibly just regular epoxy that has been polished flat.

The thing on the right looks more like an eMMC Flash device to me. It has the normal slightly rough epoxy surface normally used for chip packaging. The pad on top of it looks like a thermally-transmissive sticky pad.

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  • It could be the back of the die - I'd forgotten until the other answer reminded me that the die can be upside down in BGA packages - but dies are very thin (few hundred microns) and vulnerable, hence the assumption that it's a piece of packaging rather than the silicon itself. – pjc50 Sep 22 '15 at 15:45
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    It IS the back of the die. That's what silicon looks like, I know, I design these things ;-) OK, smaller ones but anyway. Indeed it is very brittle but as long as you do not put excessive force on it nothing will break. Oh, that IC package (left one) is called a BGA, see en.wikipedia.org/wiki/Ball_grid_array – FakeMoustache Sep 22 '15 at 15:48
  • @FakeMoustache - They're both BGA packages. See the link in my answer. – WhatRoughBeast Sep 22 '15 at 17:28
  • The one on the right didn't have anything shiny so I completely ignored it ;-) Of course it is also a BGA. – FakeMoustache Sep 22 '15 at 19:19

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