HP-C5 1FI1-0001 USA 10/87
The package itself looks like it might have an “E” stamped on it but otherwise no markings
Somewhat unusual, the die did not have any overglass. Instead, it had an (epoxy?) protective coat on it.
The top metal is greenish. My theory is that its related to copper traces left from removing the copper slug. H2SO4 was used to do final decap kept at very high concentration due to the very small amount of epoxy. Primarily its intent was to dissolve the die attach epoxy.