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Old 2005-10-18, 20:31   #1
ewmayer
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Sep 2002
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Default CPUs as Art - How to Expose the Bare Silicon?

I have a small collection of bare CPUs which I add to from time to time - I've always enjoyed looking at the bare silicon of the chip, and the colorful diffraction patterns given off by the features etched into same. Up until several years ago it was usually pretty easy to wedge the tip of a knife blade under a corner of the metal cap covering the chip and pop the cap off, but there are 2 cases that have me stumped:

1) Heavy use of solder - if the metal cover is really heavily soldered onto the "box" containing the CPU, it's impossible to wedge anything between the cap and the box. Is it safe to heat the solder to a temperature high enough to melt it (e.g. using a propane torch)? Note that I'm not at all concerned about preserving the functional properties of the CPU, just its physical appearance. (Also the fine gold-wire connections if possible, but I fear gold may have a melting point similar to that of the solder - anybody know the numbers on that?)

2) I have some FPGA chips from a company I worked for a couple years ago (now defunct) which I'd like to mount and display. The problem here is that the chips don't have any kind of removable cap protecting the silicon wafer - instead that is covered with a flat blob of some kind of black epoxy-like goop that looks like it was just smeared onto the silicon and allowed to harden. Anybody have any idea what this stuff is, and how it might be removed without damaging the silicon beneath?

Thanks,
-Ernst
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