Hey science folks 
I have 2 TO-220 cased MOSFETs here, one bad, and one I think is counterfeit. Is there someone who can help me dissolve away the plastic casing on these to reveal the silicon dies inside?
(Left one is suspected counterfeit. Middle one is bad, but genuine. The one on the right is genuine and new stock and won’t be part of this.)
Thanks!
Raymond
The covers are made of Bakelite. Dissolving it is right out. Popping it loose from the metal base is possible, but you might damage the chip underneath. You could fry it in a kiln at about 500’C, and it might drip off the base or at least become soft enough to dislodge, so perhaps jig it upside down.
I think once you get the cover off, the Indium soldered leads underneath will be melted away, but the silicon could still be intact.
What not to do: put it in a vice, place a flat screwdriver on the plastic cover on the back, whack screwdriver 1 with handle of screwdriver 2.
This was a 2955. The cover took 2 pins and split the silicon wafer. Oops!
Fuming nitric acid is what the semiconductor companies use. Here is a link from Hackaday https://hackaday.com/2020/10/21/learn-ic-decapping/
Might try using a end mill in one of the Sherline mills in Machine Shop. Shave a little off at a time till you get to the die cavity.
What makes you think the part is counterfeit?
There’s a post explaining it in show and tell. Fwiw, the logo looks different on the left, so maybe it is a counterfeit.
If they end up decapping them, post some die shots, it’d be cool to see the differences.
Hmmm… this -
Heated too. I don’t have the necessary gear to do it - or the chemicals - and was hoping someone in science would be willing to help. I don’t mind making a donation to the committee.
We’ll be meeting around 3pm Sunday. Drop by.
I’ll be having afternoon dinner with Mom and MIL starting at 2. 
Raymond
