Milling a hole in IC's package and filling with Sulfuric acid or Nitric acid basically do the job. We can reveal the die while terminals still intact. This is great result but one thing is still missing the bond wires they simply gone. 

My assumption was that hot temperature has dissolved the tiny copper wires. So, I smashed some ICs and started to test at which temperature thier bond wires will be dissolved. (Same place different temperatures)

It looks like 180-220°c with Sulfuric Acid is safe for tiny wires. 

So, if hot temperature doesn't destroy bond wires what does? 

To answer this let's take another approach, instead of manually milling we will use CNC with raster scan pattern. 

And milling it 

First by 0.3mm and then by 0.1mm we get this

We see the top of (one of many) bond wires.

Now, if we add Sulfuric acid with temperature of 220°c nothing will happen. But if we rise to 240-260°c bond wires will be dissolved.

Same happens with Nitric acid with temperature if 200°c 

The white things are the 'shell' of what used to be bond wires. 

Added ceramic cup instead of thin metallic one

Now Nitric acid will not try to burn through the tray. 

Nitric acid is amazing, only 15 minutes and some structures started to emerge.

And the bond wires? Totally intact 

We can see the bond wires intact with higher temperatures. (Although at 200°c they will be totally dissolved)

It's worth trying 160&180°c but this is very good starting point.

Bad news, after much testing it look like in Nitric acid, bond wires are dissolved at temperature of 120°c after about an hour.

We can see the difference as bond wires get thin and disappear eventually.