What is the best chemistry for wet-etching polyimide?

The polyimide is chemically activated by a UV photopackage and derived from polyamic acid monomers. The poly is also hard-cured (‘baked’). I need to remove the polyimide (10 microns thick) from a thin copper film (10-30 microns) without damaging or corroding the copper.

I’ve had some input that 8M Hydroxide at 95 degrees C will work, but I’d like to avoid the use of such a hazardous chemical. I would also like to avoid anything that is explosive or carcinogenic as it is difficult to convince the lab supervisor to let those chemicals through the door.

Thanks for your input!
I already searched the US patents, I’m hoping for personal experience (including concentrations).