Design And Fabrication Of Wafer Level Package For Micro Thermal Conductivity Detectors

Thermal Conductivity Detector(TCD),as a commonly used sensitive gas concentration detector in the gas chromatography field,has become an indispensable detection instrument in metallurgy,petroleum,and chemical industries.Moreover,miniaturization and facilitation of the conventional instruments are required in today’s society,in which the miniaturization of the internal sensors and detectors of the instruments is the critical factor.As a key component of the micro gas chromatograph,the micro thermal conductivity detector(μTCD)is widely used,owing to its small size,high sensitivity,fast response speed,and low power consumption.Therefore,the realization of the mass fabrication ofμTCDs has important practical significance for promoting the domestic independent development of portable micro gas chromatographs.In this thesis,the wafer-level packaging fabrication ofμTCDs was chosen as the research object,and the Micro-Electro-Mechanical-Systems(MEMS)technology was ultilized in realizing the wafer-level packaging of the self-fabricatedμTCDs.The main contents of this work involve the study onμTCD packaging method,the design and production of capped wafers,bonding and packaging technologies,and packaging quality inspection.(1)The structural characteristics of the miniature thermal conductivity detectors were investigated.Accordingly,the wafer-level packaging ofμTCDs was designed and manufactured,and miniature thermal conductivity detector units with the sizes of5×5 mm~2have been successfully fabricated on 4-inch wafers in batches.Particularly,the as-packagedμTCDs can be integrated into the chromatographic system,and consequently,gas detection was realized.(2)The advantages and disadvantages of wet etching and dry etching for fabricating the capped wafers were investigated and compared.Results show that although the fabrication cost in wet etching is relatively low,long-term immersion corrosion will damage the metal mask,thus affecting the surface flatness of the capped wafer and being not conducive to the subsequent bonding process.In contrast,these problems can be overcome in fabrication of the capped wafers by the dry etching process,where the process is easy controlled,and the repeatability is good.(3)The parameters forμTCD anode bonding package were optimized,and the bonding quality of the as-packagedμTCDs was investigated.Combined with different detection methods,the packaging performance of the self-fabricatedμTCDs was evaluated.Results reveal that the packaging quality of the fabricatedμTCDs is high,and the anodic bonding strengthes of all the tested samples are higher than 10 MPa.In the air tightness test,80%of the test samples reached the qualified helium leakage standard value of the Chinese military standard GJB 548B-2005 for the volume of the sealed cavity V<0.05 cm~3.