Effect And Measurement Of Thermal Mismatch On MEMS Upper Chip Deformation

MEMS devices are widely used in aerospace,automobile,medical and consumer electronics because of their miniaturization and high integration.In the process of MEMS sensor manufacturing,its packaging requirements and cost account for a large proportion of the whole device.As one of the most popular chip packaging methods,the on-board chip is fixed on the substrate by the packaging adhesive.Micro accelerometer such as MEMS devices continue to the thermal load of work condition,because of the silicon chip and encapsulated inside glue,substrates,such as packaging materials,the coefficient of thermal expansion mismatch between causes because hot chip structure caused by the mismatch of thermal stress and thermal deformation,and even stripping of encapsulation structure and separation,serious when can cause the failure of the whole MEMS devices.Aiming at the thermal deformation and strain of silicon chip surface caused by thermal mismatching of package structure,we analyze the distribution of surface deformation and strain by finite element method and experiment.Firstly,the finite element analysis model of baseboard-binder layer-silicon chip is established,and the influence of the thickness change of packaging adhesive,ceramic substrate and the upper silicon chip on the surface thermal deformation and strain of the upper silicon chip is analyzed by using the finite element method.Then,the surface deformation and strain of the packaging structure of the upper layer of the silicon chip were measured experimentally.The experimental results reached the expected goal and requirements,and also provided a method to measure the surface strain of the upper layer of the MEMS chip on a micro scale.The experimental results are consistent with the results of finite element analysis,which proves the feasibility of the experiment.The main work of the paper is as follows:(1)By establishing the finite element model of the substrate-bonding layer-silicon chip thermal deformation analysis,the thickness of the bonding layer,the thickness of the ceramic substrate and the heat of the upper silicon chip surface of the MEMS package structure under different thicknesses of the silicon chip were studied.The effects of deformation and strain distribution;(2)Aiming at the surface strain measurement of MEMS upper silicon chip under micro-scale condition,a method combining optical micro-vision,lithography technology of silicon chip surface feature pattern and digital image processing technology is proposed.By measuring the thermal expansion coefficient of the silicon chip,the average relative error value of the measured value and the theoretical value is within 10%.It shows that the method can be successfully applied to the measurement of surface strain of MEMS upper silicon chip.Therefore,using this method to test,the thermal deformation and strain distribution of the surface of the silicon chip are finally obtained.Compared with the simulation analysis under the same conditions,the results are basically consistent,indicating that the experiment is authentic and feasible.