Low Profile Packaging for MEMS Aero-acoustic Sensors
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Low Profile Packaging for MEMS Aero-acoustic Sensors
John R. Burns1, Robert D. White1, and Joshua S. Krause1 1
Department of Mechanical Engineering, Tufts University, 200 College Ave., Medford, MA 02155
Abstract: This paper describes a semi-automated conductive ink process used for packaging MEMS devices. The method is applied to packaging of MEMS sensors for wind tunnel testing. The primary advantage of the method is a reduction in surface topology between the package and the integrated MEMS sensors. In this paper we explore the relationship between trace dimensions, resistivity, and deposition parameters such as feed rate, tip-substrate separation and tip diameter. Using this procedure it is possible to generate interconnects between a PC board and MEMS sensor chip with a topology of less than 25 micrometers. Introduction: The ability to produce low-profile connections easily and effectively allows for a simple integration of MEMS devices into low topology packages. In this work, we explore the possibility of using an automated micropositioning stage and computer-controlled pressure driven syringe to draw interconnects between a PC board and a MEMS chip using conductive silver filled ink. By optimizing the flow characteristics of the conductive ink through the syringe and the velocity of the micro-positioning stages, the height of the silver traces can be reduced to fewer than 25 micrometers in order to achieve low profile, low resistance, and versatile connections for a wide variety of applications. The previous packaging approach employed by our group, which is similar to other methods commonly used for surface mounting MEMS sensor chips, used gold wire bonds with potting epoxy fill. With careful application of this procedure, including computer numerically controlled milling of the epoxy cavities; a minimum surface topology of approximately 100 micrometers was achieved. For flow measurement applications under turbulent boundary layers with Reynold’s numbers on the order of 106 and flow speeds on the order of 200 m/s, a surface roughness of less than 25 micrometers is desired. This is a lower surface topology than could be achieved with the wirebonding method. In addition, for large arrays of MEMS microphones, yield issues were dominated by wire bond integrity problems. These two issues were the primary motivation for developing the low profile conductive ink process [4]. However, the process is generally useful and can be applied to the packaging of various types of sensor systems that require low profile interconnects. Since the material properties of the silver conductive ink are suitable from a low profile (10µm-15µm silver particles), low volumetric resistivity, and material compatibility standpoint, it serves as a good candidate for making interconnections easily and effectively. There are multiple applications where precise placement of silver conductive ink can be useful. Some applications include the production of
active and passive components such as transistors, resistors, capacitors, diodes, and
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