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Following the discussion in another thread, I would like to post some practical information how to check flatness of the CPU heatspreades or cooler base.
The INK METHOD
Simply place a drop of ink (I used black fountain pen ink) on the surface and press against a glass. I used a 10mm thick plate of glass, which I use for lapping, which is really stiff and does not deform, you may get some useful info even with a lot thinner glass.
You can see the results:
![flat1.jpg flat1.jpg](https://tpucdn.com/forums/data/attachments/320/320292-a88fce7e7dbf4cd6f2117fb5b86b05cd.jpg)
![flat2.jpg flat2.jpg](https://tpucdn.com/forums/data/attachments/320/320293-cda9898f98e1586fc40cd5476a87f14b.jpg)
The lapped surface in nearly perfectly flat, except the two right corners.
The CPU excluding a few milimetres on the edges and upper corners is also acceptably flat and I would not feel any need to lap it for normal use. You can even clearly see the grinding marks after it has been ground flat.
The OPTICAL INTERFERENCE METHOD
Under certain conditions you can see a rainbow pattern (with broad spectrum light) or light and dark pattern (with monochromatic light) between a reflective surface of the object and flat glass.
If you had a green light with wavelenght of 0.5 μm (micrometer), each neighboring dark (or light) stripe would mean, that the distance between the two surfaces changed by 0.25 μm between these stripes.
I quickly lapped and polished the above photographed CPU (and destroyed a valuable historic artefact) and got this picture:
![int 1.jpg int 1.jpg](https://tpucdn.com/forums/data/attachments/320/320317-7e38689192561d8a7c9182c9f8fa076c.jpg)
![int2.jpg int2.jpg](https://tpucdn.com/forums/data/attachments/320/320318-45060afbbd0ed17e77c55c9fc418ebec.jpg)
![int3.jpg int3.jpg](https://tpucdn.com/forums/data/attachments/320/320390-b2e77024ad3a75938661e3eda2de138c.jpg)
You can see, that in the indicated area there is something like 8 stripes from top to bottom. That should mean that in this area the heatspreader is flat within 8 x 0.25 μm, that is two micrometers! (two thousands of a milimeter)
WARNING: Lapping a CPU voids the warranty.
ANOTHER WARNING: Do not decide to lap the cpu only after seeing in out of the socket, you need to see what is happening with it when it is mounted in the socket!
EDIT:
If somebody wondered, why the interference pattern does not look very nice, it is because the surface itself in less than perfect - the plating started to wear off and how I said I lapped it just very quickly. I also did not have a proper monochromatic light and no special equipment. This sort of stuff can require special lens to capture it, special shape of the light beam etc.
However it proves clearly, that you can even with a very dirty quick lapping job get to 2 micrometer flatness on a large portion of the CPU.
Here is a picture of how the surface really looks:
![cpu after lp.jpg cpu after lp.jpg](https://tpucdn.com/forums/data/attachments/320/320382-3d4efa7197d50fc5732decceeec78c0f.jpg)
EDIT 2:
I should add that I put the CPU under the middle of the glass piece and left it press against the CPU only by its weight (2.44kg). In reality coolers press the CPU with much larger force. While changing the force you can observe changing of the pattern, it also depends on how you hold or support the CPU. So if the shape of the CPU looks like "an unimpressive hill", this shape could improve under the pressure of the cooler.
I do not believe this optical interference method has much practical use for a normal consumer, the ink method is so much more easy and convenient...
The overall result - the thickness of the gap between the CPU and cooler base and resulting thermal resistance of this thermal interface depends on many factors: shape of the mating surfaces, flexibility of the mating bodies, contact force, mounting of the CPU and cooler, TIM, etc.
EDIT 3: For anyone wanting to post pictures in this thread: can you PLEASE INPUT THUMBNAILS in the text, not whole pictures? I have no idea why the forum inputs large pictures as a default.
The INK METHOD
Simply place a drop of ink (I used black fountain pen ink) on the surface and press against a glass. I used a 10mm thick plate of glass, which I use for lapping, which is really stiff and does not deform, you may get some useful info even with a lot thinner glass.
You can see the results:
![flat1.jpg flat1.jpg](https://tpucdn.com/forums/data/attachments/320/320292-a88fce7e7dbf4cd6f2117fb5b86b05cd.jpg)
![flat2.jpg flat2.jpg](https://tpucdn.com/forums/data/attachments/320/320293-cda9898f98e1586fc40cd5476a87f14b.jpg)
The lapped surface in nearly perfectly flat, except the two right corners.
The CPU excluding a few milimetres on the edges and upper corners is also acceptably flat and I would not feel any need to lap it for normal use. You can even clearly see the grinding marks after it has been ground flat.
The OPTICAL INTERFERENCE METHOD
Under certain conditions you can see a rainbow pattern (with broad spectrum light) or light and dark pattern (with monochromatic light) between a reflective surface of the object and flat glass.
If you had a green light with wavelenght of 0.5 μm (micrometer), each neighboring dark (or light) stripe would mean, that the distance between the two surfaces changed by 0.25 μm between these stripes.
I quickly lapped and polished the above photographed CPU (and destroyed a valuable historic artefact) and got this picture:
![int 1.jpg int 1.jpg](https://tpucdn.com/forums/data/attachments/320/320317-7e38689192561d8a7c9182c9f8fa076c.jpg)
![int2.jpg int2.jpg](https://tpucdn.com/forums/data/attachments/320/320318-45060afbbd0ed17e77c55c9fc418ebec.jpg)
![int3.jpg int3.jpg](https://tpucdn.com/forums/data/attachments/320/320390-b2e77024ad3a75938661e3eda2de138c.jpg)
You can see, that in the indicated area there is something like 8 stripes from top to bottom. That should mean that in this area the heatspreader is flat within 8 x 0.25 μm, that is two micrometers! (two thousands of a milimeter)
- Post the results using ink method of your brand new CPU and cooler base, of the CPU before and after spending some time mounted in the socket with normal mounting mechanism.
- Post your results before and after lapping cooler base and CPUs.
- If you had a small piece of glass, you can easily test the CPU while being mounted in the socket.
- Post the difference between stock mounting mechanism of the LGA1700 socket and the mounting frame. (In my experience an LGA1700 CPU remains slightly bent even after being removed from the socket with stock mounting mechanism, which may affect your results.)
WARNING: Lapping a CPU voids the warranty.
ANOTHER WARNING: Do not decide to lap the cpu only after seeing in out of the socket, you need to see what is happening with it when it is mounted in the socket!
EDIT:
If somebody wondered, why the interference pattern does not look very nice, it is because the surface itself in less than perfect - the plating started to wear off and how I said I lapped it just very quickly. I also did not have a proper monochromatic light and no special equipment. This sort of stuff can require special lens to capture it, special shape of the light beam etc.
However it proves clearly, that you can even with a very dirty quick lapping job get to 2 micrometer flatness on a large portion of the CPU.
Here is a picture of how the surface really looks:
![cpu after lp.jpg cpu after lp.jpg](https://tpucdn.com/forums/data/attachments/320/320382-3d4efa7197d50fc5732decceeec78c0f.jpg)
EDIT 2:
I should add that I put the CPU under the middle of the glass piece and left it press against the CPU only by its weight (2.44kg). In reality coolers press the CPU with much larger force. While changing the force you can observe changing of the pattern, it also depends on how you hold or support the CPU. So if the shape of the CPU looks like "an unimpressive hill", this shape could improve under the pressure of the cooler.
I do not believe this optical interference method has much practical use for a normal consumer, the ink method is so much more easy and convenient...
The overall result - the thickness of the gap between the CPU and cooler base and resulting thermal resistance of this thermal interface depends on many factors: shape of the mating surfaces, flexibility of the mating bodies, contact force, mounting of the CPU and cooler, TIM, etc.
EDIT 3: For anyone wanting to post pictures in this thread: can you PLEASE INPUT THUMBNAILS in the text, not whole pictures? I have no idea why the forum inputs large pictures as a default.
Last edited: