### Pillar component lead

Copper pillar bump is a made of a pillar of copper and a solder cap. The pillar is non reflowable in nature whereas the cap can reflow. These leads are electroplated on a copper seed layer at the base and photoresist defines the diameter of the pillar. Nickel diffusion forms a barrier between the cap and the pillar limiting formation of micro voids and preventing any inter-connection between layers at the interface.

Copper pillar bumps is becoming common in flip-chip connections because they provide a higher pitch compared to spherical solder bumps.