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Lapping - yet again, how smooth is smooth ??

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choke man
Jan 2, 2001
still kinda stuck in the same old spot, asking for (hopefully informed) opinions

the question is: how smooth is (really) smooth ?

I have read for several years the pros and cons of lapping to 600 grit (40 micron), or continuing on to 2000 grit (<3 micron)

and I am not confusing smooth, by which I mean without scratches, with flat
(which is presumed by good technique and equipment)

not having a profilometer I can only LOOK at the surface

--> if one holds the surface at an angle to the light the 'scratches', or 'burnishing marks' are quite visible
- with a 3X glass there are a lot more that can be seen

has anyone actually made the SAME setup 20 or 30 times to
1) determine the goop application induced variation ?
2) measure the effect, given the natural variation, of the surface finish ?

some info:
my wb test rig enables the placement of (matched/calibrated) thermocouples of either side of the TIM layer, so its easy to measure the temp drop across the TIM layer

and the variation is driving me nuts

any experience to share would be appreciated
(but please, no theory - just the facts)

be cool

[posted in several forums as I'm fishing for info]