1. What we learned today
Made test bonds on Al plate using bonding parameters of channel and bias bonds
Inspected 10 bonds of each type
None of them showed any damage, dotting, divots, etc.
So damage to bonds before voltage NOT due to clamps (Huh??)
Found that damage to bonds before voltage matches to location of blue marks on sensors
Checked this match on old UCSB TOB bonds, new UCSB TOB bonds, bonds on sensor test structure
Only does not match on bias bonds
How can this be true??
CMS week, Dec 8th, 2005

2. How bonding damages bonds/sensors?
Photos of path of bond wire when bonding to second sensor
Notice curve of wire through wedge hits surface
Rolls wire over sensor’s surface
Reproduces blue marks exactly 1 3 2
CMS week, Dec 8th, 2005

3. Encapsulation Study n+ metal n+ metal Guard ring
So all damage seen made during bonding, including blue marks, metal lines and metal dots
Encapsulated portion looks exactly the same as unencapsulated portion
But I have seen metal lines and metal dots develop after HV and wire bonds become more pocked
Does any of this have anything to do with explosive damage?
Does metal at edge of n+ increase chance of catastrophic failure?
Does damage to bonds increase chance of sparking, corona, more Al deposits?
Does increase in damage seen in bonds indicate corona?
But encapsulation, raising bond heights is still good idea as it decreases potential for sparking that blows channels, increases the bias current, and damages passitivation
n+ metal
n+ metal
Guard ring
CMS week, Dec 8th, 2005