Controlled Collapse Chip Connection -New Process (C4NP) technology is a novel solder bumping technology developed by IBM to address the limitations of existing bumping technologies. Through continuous improvements in processes, materials and defect control, C4NP technology has been successfully implemented at IBM in the manufacturing of all 300mm Pb-free solder bumped wafers. Both 200 µm and 150 µm pitch products have been qualified and are currently ramping up volume production.Extendibility of C4NP to 50 µm ultra-fine pitch microbump application has been successfully demonstrated with the existing C4NP manufacturing tools. Targeted applications for microbumps are three-dimensional (3D) chip integration and the conversion of memory wafers from wirebonding (WB) to C4 bumping. The metrology data on solder volume, bump height, defect and yield have been characterized by RVSI inspection. This paper reviews the C4NP processes from mold manufacturing, solder fill and solder transfer onto 300 mm wafers, along with defect and yield analysis. Reliability challenges as well as solutions in the development and qualification of flip chip Pb-free solder joint are also reviewed. In addition to a suitable under bump metallurgy (UBM), a robust lead-free solder alloy with precisely controlled composition and special alloy doping is needed to enhance performance and reliability.

Controlled collapse chip connection new process (C4NP) is currently used in IBM manufacturing for all 300 mm Pbfree wafer bumping for flip chip packages. In this study, the extendibility of C4NP technology to ultra fine pitch applications has been explored. Reusable C4NP glass molds were fabricated and characterized for 50µm pitch application. Mold fill and wafer transfer with Pb-free solders have been demonstrated using both 200mm and 300mm wafers in a manufacturing environment. Significant improvement in bump yield was achieved for these early demonstations of fine pitch interconnections through process optimization and contamination control. Challenge in wafer inspection metrology is discussed for the 50µm pitch micro-bumps. Mechanical strength of the C4NP micro-bumps has been characterized using test dies with a full area array of microbumps.

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