What the hell is a shim, and do I need one?

What exactly does a shim do? Do I need one? When I buy my mobo or cpu, will either one of them come with a shim?
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  1. Shims are only used on amd cpus. They are designed to help keep from crushing the core when a heatsink is put on. Also help stabilize the heatsink. I dont use one on my old athlon 1.4ghz. Sometimes the shim can actually keep the heatsink from sitting all the way down. You dont really need one if your carefull when installing the heatsink.
    Anyone correct me if i am wrong
  2. You don't need one whatsoever if you can put a HSF on straight. They are for people that don't know how to install big HS like the Swiftech MCX462+. They greatly hurt thermal conductivity, bringing a .24 c/w HSF into the .40 c/w area, in my informal tests.

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  3. You are mostly right...

    The idea behind <i>non-conductive</i> shims is that of keeping the heatsink stable on top the CPU.

    Here's an example of shim-done-right... <A HREF="http://www.casecooler.com/unnonmicshim.html" target="_new">http://www.casecooler.com/unnonmicshim.html</A>

    The problem is pretty simple... the spring clip mounting method relies upon pressure between the flat bottom of the heatsink and the flat top of the CPU to keep things in place. This works very well <b>if</b> there is enough pressure, the heatsink is flat, the cpu is flat and the system is not moved or is moved very gently.

    However:

    AMD's silly rubber feet do next to nothing to stabilize the assembly.

    Of 19 AMD XP series cpus I have in stock here, none of the heat islands are flat. The heat island on every one of them is slightly domed.

    Of the half dozen heatsinks I have here, only 3 are truly flat bottomed (the others will be before I sell them :smile: )

    There is no amount of single point pressure that will stabilize an object on a curved surface and in fact pressure tends to de-stabilize them. Given that spring clips create a pressure point about the size of a pin head and the sides of the spring clips are uneven in length, the expansion due to heat is also unequal, so the heatsink will actually move on top of the CPU as it warms up... which can repeatedly break the thermal bond between heatsink and cpu.

    Of course ALL computers get moved from time to time... dusting, rearranging, bumps and drops, etc. With nothing more than those silly rubber feet to keep things from tipping, rocking or bouncing, it is a pretty simple matter to disturb the heatsink even in drops as small as 1/4"... like when you are getting your fingers out from under the case.


    The non-conductive shim serves no real cooling purpose. It's job is to eliminate this mechanical instability inherrent in the mounting method. With a correctly made shim (.75mm thick, contacting the edges of the chip) when the heat sink is put on an AMD processor the chip will flex just a bit and some, not all, of the pressure of the clip is transferred onto the shim, creating the far more stable mounting situation of having a single point of pressure applied in the center of a large outer rim.

    By way of a somewhat extreme analogy... try putting a ruler on top of a pingpong ball and then holding it in place with the point of a pencil, note what happens when you increase the pressure... Now put the ruler on top of a glass and try holding it in place with a pencil with varying pressures... see the difference?


    Conductive shims are nothing but a really good way to short out your CPU.


    --->It ain't better if it don't work<---
  4. The MCX 462+ has four mounting screws to secure the CPU. Why would anyone buy a shim for that? It's actually for people who buy big HSF's with the 3 clip or 1 clip to secure the CPU to the socket evenly.

    And a .24 to .40?? I mean, shims do very very little to the temps to a CPU, unless you got a shim that's more crooked than a US politician. Can you post some websites of this "test" that brought a .24 TR to a .40??

    <P ID="edit"><FONT SIZE=-1><EM>Edited by fo_sho on 04/18/03 07:27 PM.</EM></FONT></P>
  5. Why would you use a shim under a heatsink that fastens with 4 screws?

    To keep the heatsink level.


    Old engineering adage: The wider the base the stronger the tower.


    --->It ain't better if it don't work<---
  6. if you researched shims you would know that they are not 100% level with the CPU core.

    "Because this spacer was made to leave a fraction of an inch between it and the CPU core, before installing it you must check to ensure that it is as flat as it can get. "

    taken from tweakmonster: http://www.tweakmonster.com/spacers/page_2amd.htm

    You don't need a shim for a HSF with spring loaded mounting screws. Shims are MOSTLY used so you don't CRACK your core.

    New engineering adage: The wider the base the stronger the tower, unless there's a space between the tower and the ground, and a concrete block supporting it.

    <P ID="edit"><FONT SIZE=-1><EM>Edited by fo_sho on 04/18/03 11:15 PM.</EM></FONT></P>
  7. I've not only researched shims, I have had custom designed ones made to solve a heat problem I've run into with a whole mess of AMD machines. I have one on "the mother board from hell" as my customer calls it and it's solving the problem just fine.

    4 point mounts do not quarantee that the heatsink is exactly level on the cpu, if even one of the springs has more or less tension than the others misalignments can occur.

    The surface area of the AMD cpu is simply not large enough to provide a stable base for a heatsink that is a couple of dozen times it's own surface area and those silly rubber feet do exactly nothing to help the situation.

    As for your new engineering adage... try standing a 40 gallon barrel on a single cement block under it's center and see how steady it is. Now stand it on 4 cement blocks at it's edges and see what you get... It's a simple matter of physics... the larger the base the more stable the assembly.

    Why do you think they don't stand large buildings on small foundations? Well.. that would be because they'd fall over...


    --->It ain't better if it don't work<---
  8. just to clarify the physics aspect: Four mounting points (if rigid) are not stable. The stablest mounting system is three mounting points. Sit on a stool with three legs and it won't ever wobble but with four... Having said that, AMDs pads are flexible to ensure stability but they were designed with stock HSFs in mind. I don't use a shim myself but a non conductive shim designed for the CPU it's used on can't hurt.

    The aim of military training is not just to prepare men for battle, but to make them long for it. <A HREF="http://forums.btvillarin.com/index.php?act=ST&f=41&t=327&s" target="_new"><b>MY SYSTEM</b></A>
  9. So why don't they make SUV's with 3 wheels instead of 4 (wouldn't it cause more stability or somethin?)... that would actually be a very funny sight...LOL

    anyways, I just wanted to say that the shim is not 100% flush with the core. So when you put a flat hunk of metal on, only the core touches the HSF.
  10. LOL... if you can figure out how to do it with 3 points on a square CPU chip I'm all ears...

    Actually, you are right the 3 legged stool won't be tippy... but, when pushed, it falls over much more easily than it's 4 legged cousin.


    --->It ain't better if it don't work<---
  11. Not true... a <i>properly designed</i> shim will be .05mm below the top of the core. When you clip or bolt the cooler in place the chip itself actually flexes downward slightly transferring some of the pressure to the shim. I've tested it with machinist's blue and all 4 sides of the shim do get in contact with the heatsink.

    The correct thickness for an AMD XP shim is .75mm, the heat island is .80mm above the carrier surface.


    --->It ain't better if it don't work<---
  12. "LOL... if you can figure out how to do it with 3 points on a square CPU chip I'm all ears..."

    Picture a triangle over top a square. Problem solved lol...


    As for tipping the stools it will depend on the rake of the supports (angle of the legs).

    The aim of military training is not just to prepare men for battle, but to make them long for it. <A HREF="http://forums.btvillarin.com/index.php?act=ST&f=41&t=327&s" target="_new"><b>MY SYSTEM</b></A>
  13. Somehow I'd rather stick with an all the way around the outside edge of the chip shim... Thanks anyway.


    --->It ain't better if it don't work<---
  14. a shim also helps protect the chip from chiping when transporting your computer. why is every one so against them? they dont do anything for heat transfer good or bad. it will not keep the hsf off the chip unless you start chewing on it before you use it.

    my computer is so fast, it completes an endless loop in less than 4 seconds!
  15. HEY!
    I have a mcx-462 and it absolutely DOESNT need a shim! Sure its heavy but u just rest the cooler in the approx position, line up the bolt holes and screw in the bolts while holding the cooler in position.

    shim my bum!

    <b>Now can someone explain how we ever got the idea that baby bunnies lay multicolored eggs made of chocolate in our living rooms?" :lol: </b>
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  16. Quote:
    What exactly does a shim do?

    Basically limits the downward force that can be applied to the CPU CORE.
    Good thing, if the CPU CORE DIE is manufactured dead parallel to the substrate,
    Bad thing, if its not, not all CPU DIEs are manufactured perfectly level with the substrate, so if its not, the little pads AMD provides on their processors, will allow the heatsink to sit flat on the DIE, but not flat to the substrate, so under those circumstances, a shim will keep the heatsink from sitting flat on the DIE, which could cost you a CPU, I know because I ran across one that wasn't level.


    Quote:
    Do I need one?

    No you do not!


    Quote:
    When I buy my mobo or cpu, will either one of them come with a shim?

    No they will not! AMD does not supply shims, and never will, they will not reccommend a shim supplier to you, because they know theres manufacturing + and - tolerances of the DIEs to the substrates, thats the reason for the little rubber pads, to stabilize the heatsink even if its cocked a little to the substrate. And no M/B manufacturer is going to risk a lawsuit by including shims with their products either.

    Shims are aftermarket products period, and a waste of time and money, and in certain circumstances, can cost you your Processor, because when one burns up, you can see the heatsinks contact points, and if you don't have a properly seated heatsink, you have no warranty. If shims were necessary, AMD would package them with their processors.


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