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Just got a D14 in, not super-happy with the finish on the contact surface. - Page 4  

post #31 of 39
Quote:
Originally Posted by AMD4ME View Post

Lapping is intended to make a surface flat.

actually lapping is intended to make the contact surface convex so the middle of the HSF and the middle of the cpu heat spreader has the highest direct contact pressure (hence more metal to metal contact surface)
post #32 of 39
Quote:
Originally Posted by psyclum View Post

actually lapping is intended to make the contact surface convex so the middle of the HSF and the middle of the cpu heat spreader has the highest direct contact pressure (hence more metal to metal contact surface)

No that is incorrect. PC enthusiasts have been lapping CPU heat spreaders and heatsinks FLAT - to improve the metal-to-metal contact area for 20+ years to gain slight improvements in thermal cooling. You would not want to make a surface convex if you understand that more surface contact AREA is required to improve heat transfer - NOT more pressure.

That is why I have corrected this mis-information several times in numeorus threads. More pressure beyond a reasonable amount does NOT improve thermal conduction. A convex base often results in poor contact on the total heat spreader surface and lowers the HSFs performance as a number of HSF tests have demonstrated.

Why people perpetuate this false info. is beyond me. I guess they've never actually conducted proper testing.

The link I posted of the microscopic surfaces illustrates that increased pressure can't increase metal-to-metal contact unless it's so high as to smash the metal, which could also destroy the CPU.
Edited by AMD4ME - 3/3/12 at 8:28pm
post #33 of 39
Quote:
Originally Posted by psyclum View Post

actually lapping is intended to make the contact surface convex so the middle of the HSF and the middle of the cpu heat spreader has the highest direct contact pressure (hence more metal to metal contact surface)

so true, a convex shape makes sure that you get the best and highest possible pressure to the DIE of the chip which is in the middle.
tim is only used to fill microscopic scratches, thats all

same as saying that a convex shape from a hs results from bad machinery. There is a reason why - common logic!
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post #34 of 39
Quote:
Originally Posted by AMD4ME View Post

No that is incorrect. PC enthusiasts have been lapping CPU heat spreaders and heatsinks FLAT - to improve the metal-to-metal contact area for 20+ years to gain slight improvements in thermal cooling. You would not want to make a surface convex if you understand that more surface contact AREA is required to improve heat transfer - NOT more pressure.
That is why I have corrected this mis-information several times in numeorus threads. More pressure beyond a reasonable amount does NOT improve thermal conduction. A convex base often results in poor contact on the total heat spreader surface and lowers the HSFs performance as a number of HSF tests have demonstrated.
Why people perpetuate this false info. is beyond me. I guess they've never actually conducted proper testing.
The link I posted of the microscopic surfaces illustrates that increased pressure can't increase metal-to-metal contact unless it's so high as to smash the metal, which could also destroy the CPU.

we are only talking about a convex surface where the highest point is maybe 1/10th of a millimeter taller from the lowest point... people don't use electric grinders to lap their HSF/chip... fine grit sandpaper wont take huge chunks out of the heat spreader or the HSF... the convex shape only ensures that the middle of the CPU(where most of the heat is generated) has maximum contact. humans aren't going to do a perfect job in smoothing a surface to perfectly even. the alternative is to achieve a convex shape where the most important part (middle of the chip) makes contact with good pressure while the rest will have to be taken care of by the TIM.

remember, we aren't talking about a magnifying glass type of convex. we are talking about a VERY slight convex that you can achieve with maybe a 2000 to 5000 grit sandpaper... lapping is supposed to make sure the contact surface isn't concave where the edges of the chip is making maximum contact. that's pretty much it. convex shape only ensures the center of the chip makes maximum contact since that's where the heat is generated. it's NOT supposed to be so convex that it's visible w/o the use of a surface plate and light.
post #35 of 39
damn i always mix it up with convex and concave, edited my previous post
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post #36 of 39
^^^^ As I stated people have been lapping HSFs and CPUs FLAT for over 20 years to improve surface AREA contact for better thermal heat transfer to the HSF.

You do NOT want a convex surface on the HSF base as the clamp pressure is center mounted and more than adequate. With a convex surface you end up with thicker TIM in the outer surfaces of the CPU/heat spreader that do not contact the heat spreader with sufficient force to be metal-to-metal. Testing of HSFs that come with convex bases from poor machining illustrate the loss in heat transfer and efficiency.

There is no advantage to excessive force in the center of the heat spreader. Ideally you'd want uniform pressure over the entire heat spreader and HSF base. This is preceisely why people lap the CPU and HSF as flat as possible.

If you believe convex is the way to go, so be it. Careful HSF testing shows this to be untrue, which is why I have corrected this mis-information numerous times. Anyone serious about this issue could certainly perform careful testing themselves and see that full contact flat surfaces perform best.
Edited by AMD4ME - 3/4/12 at 2:07pm
post #37 of 39
i dont see any high detailed technical documentation about that. its your opinion. dont try again to force people to think what you claim to be true.

thanks
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post #38 of 39
Quote:
Originally Posted by justanewguy View Post

i dont see any high detailed technical documentation about that. its your opinion. dont try again to force people to think what you claim to be true.
thanks

You comments are typically personal attacks of no value. No one can force anyone to believe anything. wink.gif

People believe whatever makes them happy even if untrue... http://theflatearthsociety.org/cms/


As I suggested in the above post - everyone is free to conduct their own testing to see what works for them. I suggest they do so and then they will see the merit of my post.

No matter what references I post you and a few other people here try to find fault with them so it's a waste of time to argue when a simple test by any objective PC enthusiasts will show them what works best.
Edited by AMD4ME - 3/4/12 at 1:53pm
post #39 of 39
The OP's question has been answered, so I'm locking this. If you want to discuss the reasoning behind lapping CPUs please do so in another thread.
    
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