@Bill,

Yeah, I'm pretty sure we're talking about the same thing (with the exception of my brother's moronic, ham-fisted heat sink mounting story). That picture of nicozeg's is pretty darn good and I don't think it takes much of a leap to "hunch" that the ridges resulting from the laser are significantly larger than the Ra of the remaining die face.

I'm sticking to my original conclusion. Namely that the effective surface area amounts to little more than the "outline" of the letters on such a die until those letters begin working their imprint into the copper. Only then does the peak pressure drop below the yield strength of copper. Granted, we're talking on the order of microns here (perhaps less), so the indentations in the copper should be easily removable via lapping.

If this is indeed the case, one would expect a central spring clip to be slightly more prone to indenting than a pure four-bolt heat sink due to the deflected shape of the baseplate. And in addition to the earlier time aspect I mentioned, there is also the factor of extruding excess TIM before the ridges could indent the copper.

Am about to jump on a plane. Just some anecdotal experience to report. With regards to the imprint. My experience is that it is removable by using a jeweller's rouge (ala ~6000-10000 grit equivalent). I haven't been able to remove it using something that's completely non-abrasive. I believe myv65/Dave is correct about the ridged edges, but the issue here is that of size. To take just a jeweller's rouge to remove the imprint in the space of seconds, we're talking some extremely small imprints going on here (sub-micron's?)

BillA, interesting! I was wondering how you plan on using the information you gather.

I understand that flatness is one effect that influences contact resistance between the cpu and hs but there are several factors that are typically recognized including surface roughness and contact pressure. I'm interested in if and how you see intergrating your measurements into a possible representation of contact behavior that will include the influence of a TIM material.

A good paper that developed a lot of the basic theory for contact resistance between two surfaces is by A. Mujumdar and C. L. Tien, “Fractal Network Model for Contact Conductance,” ASME J. Heat Transfer Vol. 113, pp. 516-525 (1991). There are others also.

Keep up the good work! :)

deeppow
for the moment just gathering and looking
then I'll hope to achieve some understanding (of what I'm 'looking' at)
then - hopefully - to an assessment of influence
etc etc
but I will always be handicapped by a lack of means to quantify roughness

I am used to N8's superlative stuff, he works in the field and has the knowledge and equip
but today I saw a pip, a prototype wb

http://thermal-management-testing.com/no%20name.jpg

the CPU contact area is about that darker patch in the center

truly FLAT, amazing for a commercial product (in 'our' industry)
sorry. no name available - yet

Looks nice and flat, did you ask how they did it? Also do you check them after you've mounted and tested them? I'm really curious if a block needs to be relapped after every use. Also I have a question about your comments re:Cooling Flow. Did you mean there is some abrasive characteristics to it, that does a bit of eroding to the baseplate after removing multiple times? Thats been my compound of choice for a while, I've got AS and Shin Etsu but I prefer the CF for its ease of apllication and removal, and all seem to give similar results for me.

peace.
unloaded