In the context of chip technology, bumps are small bond pads used for contacting chips to the substrate and also for making the electrical connections between the packages to the PCB. They are contact bumps or solder balls made of solder or metal alloys with low melting points.
The technique with bump contacting is used in a wide range of packages. For better contacting, the bumps are underlaid with metal pads, which is called underbump metallization (UBM). Bump contacting is used in bump chip carriers( BCC), in leadless leadframe packages( LLP), in flip chips and in bumped tape automated bonding (BTAB).
Inmicro- SMD technology, where bumps are also used for contacting, the bump size is about 75 µm to 200 µm. These are then referred to as microbumps. Such microbumps can be routed through the substrate as silicon through-silicon vias(TSVs). The interconnect paths are thus shorter and the fabrication of multilayer packages is simplified compared to wire bonding.
As an alternative to solder-based bumps, there are copper pillars, Copper Pillars or Cu Pillars. These are cylindrical connectors made of copper with a cap made of solder. Compared to solder bumps, they have better electrical and thermal properties and can be installed in a higher connection density. At 50 µm to 100 µm, Cu pillars are about half the size of solder bumps. With fine pitch, the diameter of the Cu pillars is between 20 µm and 40 µm with a height of about 40 µm.