Found it

A project log for Home IC Decapping

Decapping chips with easily obtainable tools and chemicals.

Generic HumanGeneric Human 05/18/2019 at 03:520 Comments

I've found the YouTube video that said rosin (aka colophony) could decap chips, which is what started this project. There's a number of different techniques given and relevant information, the rosin method is at 30:17.