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“found in several calculators but this specific one was from an SR7949D (only sold in the UK)”

“”“

The two GHU chips are made of a (high silicate?) epoxy I've never seen before.  
The silicate content makes chemically decapping them extremely difficult.  
Although I can get acid to penetrate a few mm to remove the epoxy it leaves 
a strong skeleton behind that so far I've only been able to remove mechanically.  
So this is where they stand:

GHU-01A: was dipped in hot acid for a few hours (contrast to minutes for the
other chips) to take out a lot of the epoxy.  I haven't done any further
processing on it, looks like this if you are curious (picture below)  I may be
able to mechanically lap it to expose the chip surface but this will be somewhat
labor intensive (same with above if I got another copy)...

”“”

Package

GHU-01A
ESR-Y
7623

Die

References