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Mac mini 2018 Hexa Core Cooling Analysis

Aiding the stock cooling of the CPU in a 2018 Mac mini

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The cooling solution for the new Mac Mini 2018 is insufficient for sustained loads. Not only will the thermal interface material need to be changed to something better, but analyzing the specifics of the setup Apple has manufactured and checking to see what can be improved is what this project is about.

Publicly, the following is known:

  • 8th & 9th "generation" processors marketed TDP is not a fixed, maximum TDP
    • TDP for these "generations" have two, separate parts: PL1 & PL2.
    • PL1 is the marketing TDP that ranges from 35 W to 95 W for desktop-class processors.
    • PL 2 is PL1 * 1.25, or 25% above the marketed target.
  • Apple's stock thermal paste is dried crap.
    • Not literally, but figuratively
    • If it was literally, you'd have an awful stink when you used the computer under any moderate or heavy workload.
  • Replacing a base model's, on with an i3-8100B, TIM with Arctic's MX-2 prevents sitting at 98-100 °C load temps on the i3 quad core.
  • What will happen with an i7-8700B? I plan on finding out
  • Since I will be attempting to correct a design flaw and restoring the performance of the machine, I have a legitimate defense under Right to Repair legislation if Apple gives me grief in the future.

Mac mini (Late 2018) Cold Plate - EHP Mod.scad

Modified for aftermarket heat pipes with 3 pairs listed. Will update when material reduction is present to lower cost of manufacturing.

scad - 4.78 kB - 01/15/2019 at 23:08

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Mac mini (Late 2018) Cold Plate - SA Mod - Sine Wave.scad

Modified cold plate for thicker and louvered cold plate for greater surface area and all copper construction. Code cleanup & heat pipes added.

- 5.90 kB - 01/10/2019 at 04:15

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Mac mini (Late 2018) Cold Plate - Clearance.scad

Stock cold plate with EMI cage clearance added.

- 2.31 kB - 01/10/2019 at 04:14

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PwrData_2018-12-25_17-30-00 - MM i7-8700B MX-2 & Lapping.csv.bz2

Lapped Heatsink & MX-2 TIM Hardware Thermals, bzip2 compression

Bzip2 Archive - 23.30 MB - 12/26/2018 at 03:40

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PwrData_2018-12-25_17-30-00 - MM i7-8700B MX-2 & Lapping.csv.xz

Lapped Heatsink & MX-2 TIM Hardware Thermals, xz compression

xz - 17.83 MB - 12/26/2018 at 03:40

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  • Plans A1/A2, Plan B, & Plan C Details

    Michael O'Briena day ago 0 comments

    As I've been working on the project, I've been able to figure out what needs to be done and what I can do in order to try and achieve it. As such, I've been developing backup plans concurrently to each other. What I'll be discussing here is the figurative fleshing out of the said ideas and bringing up the rationalization of that has cause me to pump over to the "next level" of cooling, thus the next plan. Most of what I've already written thus far is regarding Plan A. What I'd like to achieve is a solution that fits inside the mini if at all possible.

    Note: I'm not providing many links in this log right now due to the WIP-state a lot of the research I'm conducting. With whichever plan(s) I execute, I will have full documentation.

    Read more »

  • Models Updated & Further Development

    Michael O'Brien6 days ago 0 comments

    Adjusted a couple little parameters of the CAD files based on inaccuracies of the model that printed. Just widening the space between the threaded posts and adjusting the cutout for the heat pipes.

    To do list:

    • Place general markers in the CAD files for the fin stack and tie down points and some other clearance objects.
    • Develop a 5 pipe setup to provide a thermal capacity of over 200 W via the heat pipes and a copper interconnect.
    • Develop a larger cold plate with integrated barbs for possible water cooling.

    While spending more time reading up and playing with variables, it appears that the fin stack may also be insufficient. If that proves to be the case, then I will escalated things. In order to prove it, using two, short heat pipes to conduct up to 200 W of heat off the cold plate into a remote copper slug will be used. This will be right next to the speaker. 3 heat pipes will connect the slug to the fin stack. Despite the thermal resistance of the additional slug, it'll be modeled for all 5 pipes and in a way such that they can touch and be soldered to each other. If that doesn't provide my 50 °C temperature delta, then I have a last resort.

    Not practical on the machining side, but great for DIY, I will then enlarge and create a cavity in the cold plate. Enough room for a 1.5-2 mm thick copper foam sheet. After bolting and sandwiching, a cold plate with a larger thermally conductive surface area will have been made. Trim a few fins on the fin stack and you can create a custom, rather mini, water cooling loop.

  • Test Print Ordered

    Michael O'Brien01/10/2019 at 04:57 0 comments

    STL files don't translate well over to a machine shop for making prototypes. In my travels, I came across https://print.all3dp.com/. There are probably other, better sites, but this works well enough for what I seem to need. I took the OpenSCAD model, outputted a STL model with angles aliased to every 10 degrees, and have an SLS print in nylon on the way and it will be here Friday. I'm serious about "fixing" the cooling solution.

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  • Preliminary Results, Notes, & Conclusion

    Michael O'Brien12/30/2018 at 05:41 0 comments

    It has taken a few days to look at the data I've collected and tried to figure out what is going on. Why did I not see a notable increase in performance via reduced temperatures or faster clock speeds? Why did the quad core version have its thermals mostly sorted, albeit they are still high? Why do I have a 8-10 ˚C delta between half of my cores? What is my power consumption of the CPU more than 1.5 times that of the rated TDP? Did Apple fsck up or did Intel? Yes, Intel.

    Read more »

  • Mac mini i7-8700B Lapped CSV Files

    Michael O'Brien12/27/2018 at 04:07 0 comments

    Here are the CSV files of the thermal results from lapping the heatsink and using MX-2 TIM, compressed with 7-zip & bzip2, for others to look at on their own.

    Mac mini i7-8700B Lapped Thermals (bzip, ~23 MB)

    Mac mini i7-8700B Lapped Thermals (xz, ~18 MB)

  • Stock Thermal Solution

    Michael O'Brien12/26/2018 at 10:32 0 comments

    The following dimensions will be on the cold plate only, and not including the solderd-on heat pipes. The bottom side of the cold plate is recessed - maybe due to shielding - but anyhow, if you assume the corners are not radiused, this cavity is 1.25" by 1.8", or 31.5 mm by 100 mm. The depth of the cavity is 0.03655" or ~0.9284 mm. The external thickness of the cold plate is 0.11585" or 2.9426 mm, including paint.

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  • TDP, Cooling, & Thermals

    Michael O'Brien12/26/2018 at 05:57 0 comments

    TDP, Thermal Design Power

    Very recently, the enthusiast community has dug into Intel's TDP ratings and performance. Even since Multicore Enhancement, aka MCE, the performance of Intel's CPUs has varied depending on the motherboard manufacturer. The frequency at which a CPU operates is dependent upon a number of factors and even some limitations like T-Junction, which is 100 ˚C for all three CPUs in this configuration.

    If you want to dive into the discussion of Intel's TDP ratings and how they fluctuate, you can read a number of articles such as this on over on Anandtech.com. More or less, TDP is allowed to be fairly high for some time frame before throttling down for thermal reasons inside the die. This upper limit is called the PL2 state, which is 125% the rating of the listed, marketed TDP, which is called PL1. For all three CPUs in the Mac mini 2018, the PL1 TDP is 65 W, thus PL2 is 81.25 W.

    Read more »

  • Mac mini i7-8700B Factory CSV Files

    Michael O'Brien12/26/2018 at 03:18 0 comments

    I've uploaded the CSV file of the factory thermal results, compressed with 7-zip & bzip2, for others to look at on their own.

    Mac mini i7-8700B Factory Thermals (bzip, ~23 MB)

    Mac mini i7-8700B Factory Thermals (xz, ~17 MB)

  • Testing Proceedure

    Michael O'Brien12/24/2018 at 21:03 0 comments

    Testing State

    The Mac mini is functionally stock. It has been manually updated to macOS 10.14.2, automatic updates are disabled. Most automatic features driven by the OS are disabled or hidden if they can be accessed via System Preferences. One HDMI cable is plugged into a 1920x1200 monitor, and both USB ports are occupied by HID devices. The Mac mini is configured with an i7-8700b, 8 GB of RAM, 2 TB SSD, and 10 Gigabit ethernet.

    Room temperature was approximated at 71-72 ˚F, aka ~22 ˚C, with the surrounding surface temperature of 72-73 ˚F. HVAC was utilized to stabilize the environment, though no vent was within 16 feet of the setup, nor were said vents pointed at the setup.

    Read more »

  • Initial Notes

    Michael O'Brien12/18/2018 at 17:05 0 comments

      The Mac mini (Late 2018) come with one of 3 processors: i3-8100B, i5-8500B, or i7-8700B. All 3 CPUs have a TDP of 65W. The base model quad core will thermal throttle under stock conditions as many, like Snazzy Labs (whole video), have shown (thermal throttling). However, the little quad core's thermal performance can be fixed, as he also also showed. But will that work for the most powerful configuration? I haven't been able to find reviews of the high(er) end models so I'm looking at the problem myself.

      What will be attempted?

      1. Polishing/hand lapping the heatsink for better contact
      2. Measuring the contact pressure of the heatsink mounting, which should not be higher than the max range of 15-25 lbf, or ~65-108 psi
      3. Measuring the load of the mounting springs
      4. Shimming the springs and/or the mounting screws to increase the die mounting compressive load to ~25 lbf or just a smidge under, if possible
      5. Measuring the die height of the i7-8700B - it will be the same as the non-B part, but it is on a different PCB
      6. Incorporating a custom, reversible material addition to the underside of the heat sink to form a custom heat spreader, and, hopefully, increase the thermal resistance of the cooling solution

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