Foam dam barriers for Liquid Metal safety insurance guide.

Discussion in 'Hardware Components and Aftermarket Upgrades' started by Falkentyne, May 21, 2018.

  1. Falkentyne

    Falkentyne Notebook Virtuoso

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    When using liquid metal pastes on laptops that are often transported or carried in backpacks often (e.g. for students or travelers), it is a good idea to have free insurance against liquid metal runoff escaping the CPU/heatsink/GPU areas, getting on the PCB and destroying your hardware. Do not allow conductive balls of doom to run amok in your laptops!

    You are STILL going to have to deal with possible dislodging or runoff even if you do use Super 33+ tape or decent Kapton tape. Tape won't prevent runoff at all.

    Runoff is spare traces of LM balls that escape from the housing, do NOT get trapped on insulated SMD resistors and slide ACROSS the CPU or GPU housing and off onto the motherboard, where it WILL eventually fry something by shorting. That's where barriers come in. A common barrier first used by an airline pilot over here (who takes his laptop with him, and who NEEDS a barrier) is highly compressible foam.

    The foam must be VERY porous and not dense at all and *MUST* compress to the width of a human hair, with your fingers, with MINIMAL resistance, with a cutout shape in the shape of the CPU or GPU, with a few millimeters to spare for proper clearance (you don't want the foam blocking the heatsink from touching the cores). THESE DAMS ARE NOT EVER, EVER TO BE USED IN SUBSTITUTION FOR NAIL POLISH INSULATION COATINGS, OR SUPER 33+/KAPTON TAPES, EVER, but in COMBINATION with them.

    The job of the foam is to catch any spare LM balls that escape the chips, and block them from going anywhere else. They will sit on the foam with nowhere to go. If you had a bad mount and the temps started skyrocketing, you will have saved your hardware.

    Suitable foam is best sourced locally so you can test it in person, rather than trying to find it online. Hardware stores or hobby shops are excellent places for finding foam. These foam materials are often used in packing sensitive objects.

    The cutout foam MUST be very thin. On high pressure heatsinks like desktop heatsinks or AIO's, if foam happens to be used, that is not important, just compressible. But laptop heatsinks have atrocious mounting pressure so ANY resistance from foam will decrease resistance even further and not give you desired temps--you want the temps with foam to be identical to without foam. So do your work.

    Let's say your foam is 3mm thick and highly compressible.
    You MAY get away with this, but to be safe, you should CUT the foam width in half to 1.5mm. This will be ideal. If you're good and OCD, or just plain pro, go for 1mm. Thinner is better. Just don't have it so thin that it breaks apart.

    Don't try to cut an 'uncut' (meaning: square shape of foam, that has not had the CPU or GPU layout trimmed from it yet to trim it, that will be too difficult. Instead cut out your shape first, trim the outside to the exact shape of the CPU and GPU housings, and THEN use extremely precise scissors like titanium scissors, and then start working around both the inside and the outside to trim some of the thickness away. Once you start this, you will see why the "cutout" is much easier to trim than an uncut block :)

    To secure the foam dams so they don't shift and move when applying the heatsinks, put a dab of transparent nail polish (the same stuff you used for insulating the SMD resistors) in each corner and secure it.

    Left image is original cutout foam dam, 3mm for BGA CPU. Right three images are trimmed 1mm cutout foam dams for BGA CPU and GPU's.
    Trying to use 3mm (or thicker) foam requires VERY low density. The thinner the better.

    Some substitutions for foam dams can possibly be thin compressed layers of silicone gasket sealer--the same stuff used for relidding IHS's, although this requires preparation--this MUST sit BELOW the level of the CPU or GPU as this otherwise adds resistance! There are ways to prep this, such as @Mr. Fox 's experiment,--and even extremely thick (VERY thick) pastes like that super old Radio shack thermal paste, or partially dried or old Arctic Ceramique (NOT dried out, just very hard to squeeze) will also work as barriers too, when used carefully around the silicon housings, although this will be messy, and a pain to clean up if you have to redo your LM application. A VERY big pain. Feel free to list tested foam dam alternatives which are safe and work well for you.

    Note that trying to use foam dams for LGA processors will require extra planning.

    Picture: 3mm cutout BGA foam dam, 1mm cutout CPU and 1mm GPU foam dams.

    foamdam_forum.jpg
     
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  2. yrekabakery

    yrekabakery Notebook Deity

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    Haven't tested it yet, but I was thinking this would work well:

    [​IMG]
     
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  3. Mobius 1

    Mobius 1 nͫiͤcͫeͤ

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    too much density I think

    the foam that I got from a dell replacement part box was perfect for this purpose, not sure what they're called in the commercial market
     
  4. Dr. AMK

    Dr. AMK The Strategist

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    Thank you for sharing, take care guys, I lost 3 laptops motherboards and 2 GPU's because of sellers shipping laptops to me with LM without any protections, no taps, no silicon, no foam nothing, I have total lost almost $3000, along with wasted more than 7~8 months of repairing, asking for support and ordering parts internationally. all of that because of LM and unprofessional thermal paste for traveling and shipping activities, and I don't like anyone of you to feel what I felt, face what I faced or lose what I lost.
     
  5. Mr. Fox

    Mr. Fox Undefiled BGA-Hating Elitist

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    It might be too dense, but it seems pretty thin (1/8"). If it is not too expensive to buy for testing (or if someone already has it on hand) it would be worth trying. If the temps are crazy high, it will be an obvious indication it is too dense.

     
  6. Dr. AMK

    Dr. AMK The Strategist

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    @Mr. Fox method works perfect, @Mobius 1 shipped his KM1 to me and he did this method and the laptop arrived without any problems.
     
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  7. yrekabakery

    yrekabakery Notebook Deity

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    I already have it. It was like $3 for that bag at an ACE Hardware. It's for sealing, so it's definitely not very porous. It's 3mm in its normal state and can compress down to about .5mm when applying some finger pressure. I would probably leave it at 3mm for sectioning around the IHS, and cut it in half (1.5mm) for placing around the GPU die.

    The thicker versions of this in the store were actually much more porous, like the ones in the OP. But they would need to be cut into thinner sections as well.
     
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  8. Mr. Fox

    Mr. Fox Undefiled BGA-Hating Elitist

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    You may end up needing to cut it down for the CPU as well. Even if it feels very compressible between your fingertips. There is not much air space between the CPU retention bracket and heat sink at the hinged end of the bracket. Try it with full thickness first. You will feel how much resistance when tightening down the heat sink. It may feel very soft between your fingers, but when compressed evenly the length of the foam using the heat sink it becomes more resistance to compression. You will be able to tell right away by the temps if it is too stiff. For only $3 it is definitely worth trying. The self-adhesive part would also be nice.
     
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  9. yrekabakery

    yrekabakery Notebook Deity

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    Good point.

    I was thinking of sticking it on the motherboard around the socket as well. That way the retention bracket is basically sandwiched between two layers of foam.
     
  10. Falkentyne

    Falkentyne Notebook Virtuoso

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    Indeed. Trimming it down to 1mm (width of a CD) completely prevents the foam from interfering with anything at all. Then you have to make sure you don't use too much nail polish, since if that hardens, it can actually be thicker than the foam :)
     
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