I posted another thread about getting silicon MOSFET dice with no practical solution found yet.
Therefore, I decided to use SiC devices, and I've already designed accordingly.
However, out of curiosity, I just want to see what if I can get dice from packaged devices.
I decapped a Toshiba TK32V60X MOSFET (from its 8mm*8mm DFN package), and the result is here.
During the process, acid etched bonding wire and permeated through bonding pad, leaking into die internally, and created discoloration.
I haven't tested those bare dice yet, but I bet they won't work properly, and even if they work, I won't be comfortable to apply 400V to it.
So the question is, is there a good way of decapping copper wire bonded silicon power devices?
I used 3:1 mixture of 98% H2SO4 and saturated NaNO3. Apparently this stuff is not as good as real HNO3, but buying HNO3 is too expensive, I don't want to spend $50 on its shipping.
I used a 200C hot plate to decap the chip, the chip lies on hot plate, pads side down, marking side up, and I applied acid mixture drop wise and cleaned foaming using the side (not tip) of a pair of tweezers.
It took about 20 minutes to reveal the die, I then cleaned it up a bit using IPA, then desoldered the die from its copper substrate. I did another cleaning and shot the photos.