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 option, available on ams 0.35 & 0.18 runs only, is operated at wafer-level within ams cleanroom after CMOS process. It allows the deposition of an array of solder balls at wafer-level, with an I/O pitch compatible with traditional printed circuit board (PCB) assembly processes. For mechanical reasons solder balls are usually evenly distributed over the whole chip surface and electrically connected to the IC‘s CMOS pads by means of a redistribution layer (RDL) included in the option.
Single die flip-chip packaging
Option supported by ams hitkit 4.10 ISR15, through an add-on