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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.

As a part of IBM movement from Pb-rich solders to Pbfree solder, a new low cost process has been developed to deposit the solder to a capture, or under bump metal (UBM) pad, with Suss MicroTech Inc as the equipment partner. The controlled collapsed chip connection new process (C4NP) has moved, over the last 2 years, from development into manufacturing for 300 mm wafers. During this transition, a great number of process improvements have resulted in high fabrication yields. Manufacturing robustness has been achieved by clearly identifying the processes which affect the C4 structural integrity. The solder composition has been optimized to improve its mechanical properties as well as low alpha emission rate requirement.Sector partitioning methodology was used to obtain root cause for various defects which then, through replication studies, were confirmed. Key process improvements in the capture pad build, mold fabrication, and mold fill tool have been accomplished as the process has matured. Thermal undercut was identified as a mechanism of Cu seed consumption when no top Cu was available on top of the Ni UBM.C4NP technology can produce yields comparable to that of electroplated C4 Bumps. Yield learning model shows a 15% defect reduction per month since the start of the C4NP program. Technology qualification for 300 mm wafers with 200um and 150 um pitch Pb-free C4 bumps has been successfully completed. Introduction:

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