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Low Temperature Wafer Level Packaging Technology of Bulk-Micromachined MEMS Device
Keywords: mems, sensor, wafer-level bonding
New low temperature, low cost, small size packaging technology of novel bulk-micromachined MEMS sensor for mobile applications was developed. The developed package is a kind of 24 leads QFN and the dimension of the package is 4.0mmx4.0mmx1.2mm. Recently, it has been increased to use accelerometers to hand held phones for changing image directions, games and free-fall detection. It is also has been increased to use micro-compasses for navigation and LBS. Recently multi-axes gyroscopes has been developed for motion UI, games and image stabilizations. Electro-static comb actuators are widely used for most of the sensors and they should be hermetically packaged with frit glass or metal eutectic adhesives to increase Q at higher than 300 degreeC. The developed sensor is fabricated with bulk-micromachining process of SOI substrates and composed with only one proof mass. It is needed that the low temperature (below 250 degreeC) packaging technology and passivation of top and bottom sides of the sensor for keeping the sensor performances and preventing the proof-mass stiction during the molding process, respectively. An ASIC chip should be also packaged with the sensor for the driving and the sensing. In this paper, to meet the above requirements, newly developed packaging structure was developed. The sensor device was capped with very thin (130um-thickness) top and bottom silicon cap wafers which have a cavity. Top and bottom cap wafers were bonded with the sensor wafer with a low temperature polymer adhesive at 200 degreeC. After bonding the three substrates, the top cap silicon was dry etched to expose bonding pads for the signal inter-connection. The ASIC chip was polished to 75um-thickness, diced and die attached on a lead-frame with a DAF. The diced wafer-level-capped sensor was stacked on the ASIC, wire bondings were accomplished between the sensor and the ASIC, and the ASIC and the lead-frame and finally transfer molding process was done.
Heung Woo Park, Principal Engineer
Samsung Electro-Mechanics Co., Ltd.
Suwon, Gyunggi-Do 443-743,
Republic of Korea

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