along the bottom ~30, and about the same vertically on the left
counting from lower left to upper right is what will define the 'depth' and the fringes become too dense to count,
their curvature can be seen going from upper left to lower right, the upper right corner is quite 'high'
- will be very apparent from the grease (assuming the die is flat)
added a detail image with more contrast
compare to this
http://www.thermal-management-testing.com/PF3fringe.jpg
(a 10mm sq is not much larger than that central area)
of course this is only half of the equation, the die/CPU relative flatness is an issue of equal significance
- consider the case of one convex and the other concave ?
- what is the more typical case is both convex (
certain if hand lapped - other than by N8 or Steve at PolarFlo)
the effect on the wb's apparent C/W is what is huge, more so than the actual dimensions might suggest (w/o testing)
any appraisal of wb C/Ws is incomplete w/o understanding the contribution of flatness,
could be due to this or that or whatever, assumptions are a tricky business