Development and Implementation of C4NP Technology for 300 mm Wafers

Considerable work is ongoing worldwide on developing lead-free solutions for electronics industry to meet the needs of RoHs requirements. This paper describes the development and implementation of lead-free C4 interconnects for 300 mm wafers using, C4NP technology at IBM with equipment partnership with Suss MicroTech Inc. Key process modules of C4NP technology are: (a) UBM pads fabrication using simple unit processes in back end of the line semiconductor manufacturing facility, (b) Solder melt filling of glass molds with cavities in solder fill tool and inspection, (c) C4 bump transfer to UBM pads on wafers using vaporized flux process in solder transfer tool, (d) Final inspections and electrical tests. This process technology for C4 bumping eliminates the need for solder or solder alloy plating and provides wider latitude for selecting solder composition. For example, solders can be selected for improved mechanical properties and, or low alpha emission requirements. This can be accomplished by simple changing of mold fill head. Primary efforts of this study are focused on four key elements: (1) Development of unit processes for UBM pad patterning and solder transfer processing, (2) chip/organic laminate module builds, using industry standard bond and assembly processes, (3) selection of specific test vehicle wafers with 200 um pitch pads and over 1.25 million C4 bumps, and (4) extensive reliability testing of modules with JDEC and IBM internal standards. Modules with test vehicle chips as well as product chips have shown excellent reliability data, comparable to that of high lead electroplated C4 bumps, and meet application requirements. In order to assess manufacturing robustness and yields, sector partitioning studies were undertaken to understand the effects of unit process windows and defect densities. Results show that C4NP technology can produce yields comparable to that of electroplated C4 Bumps. Technology qualification studies have been successfully completed. Thus, enabling the path for manufacturing ramp up. This technology is extendable to higher density C4 interconnects and product qualifications studies on C4 bumps on 150 um pitch are ongoing. IBM is adapting this technology for 300 mm lead-free applications.