C4NP Technology for Lead Free Solder Bumping

C4NP is a novel solder bumping technology developed by IBM that addresses the limitations of existing bumping technologies by enabling low-cost, fine pitch bumping using a variety of lead-free solder alloys. It is a solder transfer technology where molten solder is injected into pre-fabricated and reusable glass molds. The glass mold contains etched cavities which mirror the bump pattern on the wafer. Filled mold and wafer are brought into close proximity/soft contact at reflow temperature and solder bumps are transferred onto the entire 300 mm (or smaller) wafer in a single process step without the complexities associated with liquid flux. The simplicity of the process makes it a low cost, high yield and fast cycle time solution for bumping with a variety of high performance lead free alloys. The focus of this paper is on the mold fabrication, solder fill and inspection steps prior to solder transfer including high volume manufacturing tool designs. Yield improvements from the mold suppliers and mold specs are discussed. Finally, the results from a detailed cost model are reviewed. This cost model includes a comparison of C4NP versus alternative bumping techniques and includes capital, materials, and labor cost factors. The data in this paper are provided by the IBM Systems and Technology Group in the Hudson Valley Research Park, NY.