2. Description of the flip chip process

Bumping is at the heart of flip chip technology. As already mentioned, the electrical connection between the chips is ensured by introducing a conductive microbead between the two chip connection pads, which are covered by a suitable layer known as UBM (Under Bump Metallurgy). One of the most important points in this process is to limit the size of the bead and the UBM on the aluminum chip pad. One of the reasons why flip chip solder alloy technology is not yet widely used is its high cost. In recent years, new, more economical wafer-level connection solutions have been proposed, making its use more attractive.

To fully understand the characteristics of the process, it is necessary to identify the different components of this technique. There are four of them:

• under bump metallurgy — UBM;

• ...