Solder bumping consists in manufacturing metal spheres acting as interconnections for flip-chip. Those spheres are composed of a Sn/Ag/Cu alloy (SAC). Before the sphere can be deposited, the deposition of an Under Bump Metalization (UBM) layer is required.
This post-process is not operated by the ICs foundry but by an external subcontractor. This is a two-steps process: first, an electro less UBM (Ni/Au) is deposited on the pads of the die, then solder balls are individually placed over the pads. The minimum pitch is 150 µm.
The price of this option depends on the design, you must request a quotation at the early stage of your project. As an example, the customer is invoiced 10800 € for the solder bumps depositions on a die with 84 pads. This option is available on any CMP MPW runs.
Electroless UBM deposition step is strongly design-dependent. For this reason, this service is offered for R&D purposes only, with a best effort delivery from CMP.