This method is direct continuation of previous one with some tricks. 

First we use no screws between tray and heat end head. Just 'artctic silver' for better heat transfer and dots of glue to hold everything together. 

Second thing is using 60 Watts hot end instead of standard 20 Watts. Unfortunately, some 3d boards, such as BTT SKR 1.4V, doesn't support such high Wattage. I've made a trick and use hot bed connection instead. (Changed pins of hotend and hotbed) (It's impossible to use hotbed connection as is since hotbed range doesn't goes beyond 100+ something.)

Now, heating to 200°c was only 90 seconds instead of 5 minutes. 

And was able to reach 260°c easily. 

I've run different configurations regarding Potassium nitrate vs Sulfuric acid. It loks like the more Potassium nitrate the better. The result was nice 

I was happy for a while but then I saw this

The bond wires are empty I have compared with some old picture where I performed decapping using plasma. The pods where there with remains of bond wires.

So, "operation was successful, the patient is dead". 

We now know that with 260°c the so called 'diy home made Nitric acid' works and decapping the IC. 

Now we have to find the lowest temperature where where decapping is possible without dissolving bond wires.