Monthly Science: Mystery Chip

Dragorn of Kismet gave me a handful of identical mystery chips that might date back to the 1980s. They’re surprisingly large and covered with contacts:

Mystery IC - overview
Mystery IC – overview

There are no logos or identification anywhere on the chip. The back side is blank silicon.

The visible patterns don’t suggest anything obvious:

Mystery IC - detail 1
Mystery IC – detail 1

The metallization layers aren’t particularly intricate:

Mystery IC - detail 2
Mystery IC – detail 2

Surely there’s something tucked under the top metallization; I have neither the materials nor inclination to dissolve the thing one layer at a time.

I gave a sampling to our Larval Engineer, who says she may turn them into fancy jewelry. I’m sure the solder bumps contain lead, but …