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Lowering the Cost of Flip Chip Interconnections using a Single Chamber, Multi-Metal, Bump Plating Tool
Keywords: Interconnections, Flip Chip, Bumping
The growth of flip chip packaging has been hindered by lack of infrastructure and tools for producing low cost bumps. Currently 83% of bumped wafers are plated [1]. The plating equipment base for bumping today is older multi-tank technology. This equipment typically requires significant floor space and is not capable of handling the small lots and quick changeovers required by the back end assembly facilities. The wire bonding equipment model has been well accepted within back end assembly. This model is built around individual machines with small footprints that are justified based on incremental capacity increases and fast ROI. The user friendly GUI, the ease of programmability and the quick changeover capability make this model the standard to emulate for new equipment designed for package assembly. This design concept has been used to develop an innovative single-chamber plating tool, capable of producing multi-metal layered bumped wafers. This plating tool has a footprint similar to that of a wire bonder, the tool handles one wafer at a time and plates at high speed through improved reaction kinetics and control. The single wafer chamber is designed to enable quick changeovers, efficient chemical usage, and require decreased rinsing volume (less waste water treatment). Custom designed PLC and software provides easy programmability and recipe portability enabling flexibility in process definition and recipe management. Data logging and acquisition provides data collection of both key mechanical and process metrics. The tool is capable of plating a wide range of metals and alloys providing a broad range of application in the market. Using the multi-layered metal stacks allows development of a full range of lead-free and high performance metal systems. Copper pillar structures can be capped by a solder layer and then reflowed to provide a reliable solder connection. Both electrolytic and electroless nickel-gold bumping are currently available chemistries with this single chamber approach. Both process development and process capability experiments are currently underway. The presentation will provide DOE data describing the process and the capabilities achieved.
Lee Levine, Principal Consultant
Surfect Technologies
New Tripoli, PA

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