How to decap a chip to expose the die?

Question

Any suggestions to open a surface mount package (TSOP, QFN etc) to expose the die?

Possibilities tried or considered:

• Split the package using wire cutters - sometimes works and sometimes doesn't
• Grind the top off with grinder - Some chips have no cavity between the die and the cap.
• Soak in MEK - I heard this works but haven't tried it.

Why would I want to do this? To photograph for forensics purposes - to look for damage or to get die numbers. I don't expect the part to function afterward. Electronic forensics labs seem to be able to open chips easily but I'm not sure what tools/techniques they use.

Answer 1

Travis Goodspeed has the tutorial: http://travisgoodspeed.blogspot.com/2009/06/cold-labless-hno3-decapping-procedure.html Basically you put the part in a test tube with NO3 and swirl it around and leave it overnight until the encapsulation is dissolved.

Only slightly related, but look through Travis's Flickr stream for a lot of interesting dieshots.

Answer 2

Hot red fuming nitric acid is the stuff to use, it dissolves the plastic. It's rather nasty, several kids in my class at school got acid burns when an experiment performed by our chemistry teacher went wrong and there was an explosion.

Answer 3

Your safest option is to stick with ceramic eproms and chips that have the thin glass layer between the brown ceramic parts. I heat them with a heat gun, then gently drive a sharp chisel (the chip I mount horizontally in a table vise) to split the chip in half. You can do this same procedure with ceramic chips that have a gold cap over the die. The gold cap is held down with solder, so the heat weakens it.
I have not been able to mechanically expose the die in an epoxy chip, and don't plan to use any nitric acid. From what I have seen, the epoxy has no open space between it and the top of the die inside.