- Sample prep
It is often necessary to re-bond a bare die. Typical reasons include:
Several firms sell refurbished wire bonders and provide service, support, and parts. Some of these companies will also do custom bonding projects for single dies or small lots.
If any existing bonds, or pieces of them, are still on the pads these must be removed first.
Pads should be clean and relatively undamaged. A small amount of cratering from a previous bond is OK as long as there is still sufficient metal underneath to make a solid connection.
The die must be secured firmly to its new package to keep it from moving around. AZ has had good experiences using a tiny dot of cyanoacrylate adhesive, although silver epoxy or Crystalbond would likely work fine as well. Make sure the volume of adhesive is low enough that it doesn't squeeze out and get on the top of the die.
Bonding to a clean, once-bonded pad should be essentially the same as bonding to a never-bonded pad. Contact resistance may be a little higher and reliability reduced, but this isn't a big concern if you just want to dump the firmware.
Bondable surfaces are generally soft metals with minimal oxidation (thin native oxide will be penetrated by the “scrubbing” action of the ultrasound, but thicker oxides will cause problems)