Hi, friends

I am trying to do flip chip bonding using Indium as soldering material. The
indium is electroplated for 2um thick and then patterned with the feature
size about 30um. I tried the bonding temperature about 250C for 5 minutes,
but the bonding strength is so weak and it is easily break apart.

As I know the oxide formed on the indium is the reason for the weak and
unreliable bonding, so i tried to etch off the oxide by dipping it in HCl
for 5 minutes, but apparently it doesn't improve the bonding.

I am wondering anyone can give me some suggestion on the selection of
solder material, and Indium solder process.

Thank you so much,

Zhiyan