I am impressed at the bravery of some to take apart their MacBook Pros and handle the heat issue themselves. Even to go so far as to use an infrared thermometer to document the temperatures. However, there are some things that don't seem to jive with what's known regarding thermal transfer between materials. I'm starting this thread in hopes that we might try to come to a better understanding of what's really causing the high temps in the MBPs (besides the fact that there's a Core Duo in a confined space). [Disclaimer: I do not own a MBP, so I can't comment on whether I think they are hot. I'm just working on the assumption that enough people have complained to make it a legitimate problem.]
First a question: Among those that have taken apart their MBPs, how many can document the temp change before and after? That is, have actually measured the temps at the processor or on the heat pipes (i.e., feeling warmer or cooler with your hands or lap doesn't count). The more documented info we have, the better.
From what I've read in forums here and elsewhere, the success of that procedure seems to be 50-50. Some have improvements, others don't. This brings me to my most important point: Contrary to what everyone seems to say about applying thermal compound between an electronic device and a heatsink, it really doesn't matter if you use a large amount of compound.
Flame me if you must, but the only reason to be sparing is because you would like the application to look nice, because the compound may interfere with nearby devices, or simply because using more than necessary is wasteful. i.e., using more should not reduce heat transfer. On the other hand, the pressure applied between heatsink and device is crucially important, as is the thermal conductivity of the compound. So, could it be possible that those who have replaced the thermal compound on their MBPs, and noted an improvement, are either inadvertently applying more pressure or are using better-quality compound?
OK, now for why this is so (thermal physics of materials). If you take two reasonably flat surfaces, say even optically polished flat, and you lay one on top of the other, they will at most make contact at 3 distinct points. This follows from a consideration of the geometry involved, and the fact that only extremely rarely are materials atomically flat. For definiteness, suppose one of the objects is copper, and the other is a ceramic, like that used in processor packaging. The hot ceramic is only transferring its thermal energy at those 3 very small points. This is why the surface area of the two objects does not significantly affect the heat transfer characteristics. Note that at temps ~ 100 C, thermal transfer due to radiation is negligible compared to thermal conduction.
Now, suppose we clamp the two objects together with some pressure. Copper is pretty soft, and so will more or less deform to give you additional points of contact. Also, as the pressure is increased, the points that are already in contact can transfer additional heat because those connections are more intimate. However, even with an absurd, unrealistic pressure, we can never bring the two objects to make contact along their entire surface. Here is where thermal interface materials enter. By applying a thermally-conductive, paste-like material, we can fill in all the microscopic gaps, and allow heat transfer across the whole surface. So, even if you put a glob of thermal coumpound on, as long as you mash the two pieces together (say, with the force of a single finger), the excess should be squeezed out, and the interface should be sufficient for good thermal transfer. My guess is that Apple may have messed up by not designing the heat transfer blocks to be parallel and in intimate contact with the processors, or the thermal compound is of poor quality.
Sorry for the long diatribe. Any thoughts?
-RendIt
First a question: Among those that have taken apart their MBPs, how many can document the temp change before and after? That is, have actually measured the temps at the processor or on the heat pipes (i.e., feeling warmer or cooler with your hands or lap doesn't count). The more documented info we have, the better.
From what I've read in forums here and elsewhere, the success of that procedure seems to be 50-50. Some have improvements, others don't. This brings me to my most important point: Contrary to what everyone seems to say about applying thermal compound between an electronic device and a heatsink, it really doesn't matter if you use a large amount of compound.
Flame me if you must, but the only reason to be sparing is because you would like the application to look nice, because the compound may interfere with nearby devices, or simply because using more than necessary is wasteful. i.e., using more should not reduce heat transfer. On the other hand, the pressure applied between heatsink and device is crucially important, as is the thermal conductivity of the compound. So, could it be possible that those who have replaced the thermal compound on their MBPs, and noted an improvement, are either inadvertently applying more pressure or are using better-quality compound?OK, now for why this is so (thermal physics of materials). If you take two reasonably flat surfaces, say even optically polished flat, and you lay one on top of the other, they will at most make contact at 3 distinct points. This follows from a consideration of the geometry involved, and the fact that only extremely rarely are materials atomically flat. For definiteness, suppose one of the objects is copper, and the other is a ceramic, like that used in processor packaging. The hot ceramic is only transferring its thermal energy at those 3 very small points. This is why the surface area of the two objects does not significantly affect the heat transfer characteristics. Note that at temps ~ 100 C, thermal transfer due to radiation is negligible compared to thermal conduction.
Now, suppose we clamp the two objects together with some pressure. Copper is pretty soft, and so will more or less deform to give you additional points of contact. Also, as the pressure is increased, the points that are already in contact can transfer additional heat because those connections are more intimate. However, even with an absurd, unrealistic pressure, we can never bring the two objects to make contact along their entire surface. Here is where thermal interface materials enter. By applying a thermally-conductive, paste-like material, we can fill in all the microscopic gaps, and allow heat transfer across the whole surface. So, even if you put a glob of thermal coumpound on, as long as you mash the two pieces together (say, with the force of a single finger), the excess should be squeezed out, and the interface should be sufficient for good thermal transfer. My guess is that Apple may have messed up by not designing the heat transfer blocks to be parallel and in intimate contact with the processors, or the thermal compound is of poor quality.
Sorry for the long diatribe. Any thoughts?
-RendIt
