Electronupdate did a teardown and analysis of a cheap four function calculator:
It’s such an amazingly old looking die.
Even with 400x magnification it would not be too hard to reverse engineer back to a schematic! This must be a very old design indeed. When one thinks of high-tech it’s always the new-new thing… however some designs can be very old indeed and still be in production.
Reverse Engineering a Simple Four Function Calculator: die decap – [Link]