Thermal grease theory

Thermal grease theory

Summary: There's a theory making the rounds that the MacBook Pro's high temperatures are attributed to a misapplication of "thermal grease" that's applied to the CPU and GPU chips during the manufacturing process.

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TOPICS: Processors
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MBP-thermal-grease.jpgThere's a theory making the rounds that the MacBook Pro's high temperatures are attributed to a misapplication of "thermal grease" that's applied to the CPU and GPU chips during the manufacturing process.

A post by Interrupting Moss on the Something Awful forums mentions that "it just takes a slight misapplication of thermal grease on a MacBook Pro to make the temperatures skyrocket."

The amazing part is that if true, Apple techs are assembling MacBook Pro's with too much thermal paste because the MBP service manual tells them to! According to MacBook Pro service manual "0.2-0.3cc" of thermal grease should be applied to all three chip mating surfaces. Interrupting Moss however, states that reapplying thermal grease "properly" dropped the running temperature of his MBP by 14 degrees Celsius.

Jean-Cyril posts on the Apple support discussion boards that he "replaced the thermal compound with sparing quantities of Arctic Silver 5" and that "a small drop is sufficient."

MixedBag posted detailed before and after photos of his MacBook pro after removing the thermal grease and replacing it with "a fraction of a fraction of a millimeter thick layer of Arctic Silver 5 on the three chips." He goes on to say that it now runs much cooler.

The thermal grease modification is not for the faint of heart as it requires almost complete disassembly of your MacBook Pro. It will most likely void your warranty and most have said that it causes the fan to run more often. But for some it's a fair price to pay for a cooler running machine.

Should Apple have done this in the first place, or is the MacBook Pro designed with the extra thermal grease to keep the fan from coming on?

Topic: Processors

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14 comments
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  • I hope you were kidding...

    I hope you were kidding with the question "Should Apple have done this in the first place, or is the MacBook Pro designed with the extra thermal grease to keep the fan from coming on?"

    Let?s see, design a system that won't conduct heat away from the hot chips so the machine runs quieter...

    Error, does not compute.

    Sorry, got overheated... :)
    dbaelegance
    • HAHAHA

      Yeah I was thinking the same thing. Okay, Jason, here's how this works: thermal grease is designed to fill in the microscopic bumps between the chip and the heatsink. It also transfers heat energy from the chip to the heatsink; naturally, the fan takes over from there.

      However: you can't pile on extra thermal paste to keep the fan from coming on. Too much paste causes a rise in temperature, which would turn the fans on. OF COURSE Apple should have applied thinner layers of thermal paste to begin with. That's the problem!
      anythingbutmine0
      • actually

        the fans come on when they sense extra heat in the heat exchanger, not the CPU. So, in this case, the fans do run more often after application of a proper amount of thermal grease, because more heat is being transferred to the exchanger and needing to be vented by the fans.

        With the huge hulking globs of thermal grease the way apple built the thing, a large portion of the heat is being channeled out via the physical connection to the motherboard and making the case of the laptop hotter.

        Given a choice, I'd much rather have a machine that runs cooler with more fan noise than one that I have to worry about getting burnt should I sit it on my lap. :)
        Sxooter_z
        • No temp sensor on CPU?

          You're saying there is no temperature sensor on the CPU? Or rather, there is no temperature sensor on the CPU that is tied to the fans?
          anythingbutmine0
          • the latter

            The latter. The heat exchanger cranks up when it detects heat being put into it. So, the better insulated the CPU is from the heat exchanger, the less the fans would run.
            Sxooter_z
    • Makes sense

      Since Apple is always touting how quiet its machines are over PCs.
      DarthRidiculous
  • Thermal Grease

    I have been and continue to use thermal paste for the last 30
    years. I have, also, been mildly amused by the misinformation
    published by the original report and the readers responses.
    1. Thermal paste is not electrically conductive.

    2. Excess paste on the MB, while unsightly will not affect it's
    operation.

    3. The reduction in temperature, using Arctic Silver is probably
    do to it's superior thermal conducting properties.

    4. I have used Wakefield Compound for years and still use it
    today on CPU chips w/o any noticeable over heating problems. I
    monitor heatsink temperatures quite closely on all my
    customer's machines.
    macaroo_z
    • Are you saying this story is fud?

      Why are MacBook Pros running so hot? Is it because of the
      aluminum cases or because of thermal grease?
      mlindl
      • No

        No, he is saying that the thermal grease's job, is to provide a thermal conductive surface between the heat sink and the chip. Understand, it CONDUCTS heat. That means, if you GLOP it on so that a large amount of the surface is NOT in contact with the heatsink, it will in fact, because it conducts heat, become hot itself. Basically, the heat is not being removed, and is retained, allowing it to keep increasing in temp, because there is no heat removal.
        Troll Hunter
        • you don't understand heat flow

          go find out, then post.

          What you've posted here is against the laws of physics.
          If you have a grasp of electricity, imagine the cpu is a big battery
          full of heat energy.
          The temperature is equivalent to voltage, and the heat flow is
          equivalent to current.
          All substances have thermal "resistance" (the opposite of thermal
          conductivity).

          The overall resistance to the flow of heat is a function of the
          thermal resistance, it's diameter and thickness.

          With a given substance, eg: the thermal paste applied by Apple,
          if it is a thicker layer, then the thermal resistance will be higher.

          If a smaller cross sectional area of paste conducts to the fan
          module, then resistance will be higher.

          If a less efficient conductive paste is used, the resistance will be
          higher.

          If the resistance is higher, the CPU temperature will he higher.

          This is how it works.
          Are Apple guilty here? I don't know. I'm not sure this article
          posts any useful information to determine this.

          The fan being on more tells you nothing unless you know where
          the temperature sensor for the fan control is. Is it on the fan or
          is it on the CPU?

          If the sensor is on the fan, and more heat reaches the fan, by
          optimising the thermal paste then the fan will go on more.

          If the sensor is in the cpu and the fan goes on more, then you've
          made the heat flow worse.
          stevey_d
    • moreover the thermal control system doesn't seem to be coping

      dependant on the placement of thermal sensors, and the logic
      over when they cause the fan to do on, by moving heat more
      efficiently from point A (CPU) to point B (fan), perhaps the
      temperature-throttled CPU is generating more heat energy that
      it otherwise would, causing the fans to operate almost
      continuously.
      Attempting to re-engineer a complex system without the
      functional specification can cause unexpected results.

      Looking at it from a user perspective: (1) I lose my warranty (2)
      the fans operate more and are therefore more noisy.....
      WHY would you want to do this again?
      stevey_d
  • Thermal Grease Purpose

    Thermal grease should have high thermal conductivity and only enough should be used to fill the air gap between the hot part and it's mounting surface and heat sinks. The thinner the layer used the better. The thermal conductivity of the grease is better than air, and worse than than the case of the part or a heat sink or metallic mounting surface. The original heat sink greases were made with a silicone grease or fluid base. These can prevent conformal coating of the assembly if required to prevent corrosion.
    Jay_in_OK
  • I had this happen to an linux workstation.

    The heat sink compund or thermal grease really does help with the conduction of heat from the chips. Looking at an mechanical engineer's standpoint this true if you look at the surfaces of the heat sink and chip they are not prefectly flat and even. The heat sink compound or thermal grease fills in the tiny gaps and to help transfer the heat from the chip to the heat sink.
    I had an linux workstation that the manufacture that shall go nameless forgot to put thermal grease on the chips and when we got to use the machine to it max it would warn and then crash the system. I had remove the heat sink from the CPU and discovered there was no thermal grease and I had to put the thermal grease and it had reduced the temperatures from 35C to 25C.
    It is strange that the system could of passed QC without but I think with current need of these machine they are not as stringent on burn-in (excuse the pun) and QC.
    phatkat
  • several notebook 'mods' in online groups for better cooling

    I am not running a Macbook, but I recently removed the heatpipe in my notebook, pitched the foam thermal pad over the GPU and substituted a copper shim of equal thickness. I cleaned the overwhelming amount of thermal goop from the CPU.

    All contact surfaces received JUST enough new quality thermal paste to completely cover each mating surface.

    As my notebook's temp sensors are part of the motherboard and not the heatpipe, I can unequivally state that my typical CPU temp dropped by ~6C and my typical GPU temp dropped by ~15C.

    I have since seen similar modifications for other brands of notebooks claiming similar results.

    I will also admit that proper application of thermal paste is a labor intensive task. The factory line just puts a dollop of paste on a chip and hopes the compression from the heatsink installation properly spreads it.
    Jim Johnson