C4NP Cu-cored Pb-free flip chip interconnections

We report here preliminary results on a new Cu-cored flip chip structure combining C4NP (Controlled Collapse Chip Connect New Process) with Cu spheres for high density interconnections. C4NP is a new wafer bumping technology developed by IBM in which molten solder is injected into a mold and then transferred to the UBM (Under Bump Metallurgy) pads on the wafer. This simple and parallel process has shown the capability to combine low cost attributes with high performance capabilities. C4NP allows a larger number of interconnections with finer pitch than screen printing methods because it eliminates the volume reduction problem of solder paste. Also, C4NP allows more freedom in selecting the composition of solder bumps when compared with the electroplating method.