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A Numerical Study on Optimization of Stresses Occured During Chip to Wafer Bonding in Vacuum
Keywords: Wafer Bonding, Chip to Wafer, FEM modelling
The transition of MEMS companies on 8-inch process lines, is clearly observed since 2001, and it is expected that the 8-inch revenue share of the MEMS market more than double from $1.4 billion this year to $3.5 billion in 2011. In reality, the development of new technologies and new facilities for as large as 8-inch wafer production becomes a great challenge. The System-in-Package (SiP) solutions for inertial measurement units (gyroscopes, accelerometers) based on direct wafer bonding of MEMS on ASIC devices, and in parallel, the implementation of a two step Chip to Wafer (C2W) packaging process which has strong throughput advantages, is a main goal of the European FP6 project DAVID. In this paper Authors report the implementation of a Finite Element Method (FEM) in modelling the heat flow and the deformation of the main part of the bonding machine, the work undertaken in order to develop and optimize the technology for innovative waferlevel vacuum packaging process, addressed to high volume System-in-Package (SiP) production. The investigated new approach is based on two-step MEMS (Micro Electro-Mechanical Systems) to ASIC (Application Specific Integrated Circuit) integration, realised by means of prototyped bonding station, the EVG540, developed by EVG Group. The design of experiment was carried out by Taguchi method. The relation between heat flow in analyzed system and bonding setups configuration (different compliant conditions), unit design (heat sinks, thermal insulation), materials properties (heat conductivity, emissivity, and coefficient of thermal expansion - CTE) and process conditions (vacuum level, heaters power supply, force load, and process duration) was identified and studied. The experimental results proved the correctness of the developed model. The numerical calculations confirmed usability of compliant layers. As a result, the process conditions (temperature, force load, setup configuration) were determined, and the overall bonding process can be optimized.
Krzysztof Malecki,
Wroclaw University of Technology
Wroclaw, Dolnoslaskie 50-372,
Poland


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