1. Discoloration of Passitivation
Before wire bonding
Discoloration of passitivation under wire bonds occur during wire bonding process. With old UCSB TOB bond shapes, it occurs under both channel and bias bonds
With different bond geometries, discoloration smaller/bigger
It is not clear what this discoloration is caused by, if it is potentially dangerous, or if it will get worse with time
Dots and metal lines do not appear with bonding only; appears to be HV effect
After wire bonding
Bias Ring
Guard Ring

2. Channel Bonds
After wire bonding, the channel wires have divots that match to locations of passitivation edges on sensor
Bonds looked at previously looked more pocked. Not clear if caused by powering module for ~8 hours

3. FNAL vs. UCSB FNAL UCSB FNAL bonds towards back of bond pad
UCSB bonds towards front of bond pad
Strength of discoloration appears to be correlated with nearness of bond feet and height of bond wire
New bond shapes result in much less discoloration