In this study, the effect of epoxy based molding compound packaging on a micro-electro-mechanical system (MEMS) pressure sensor performance is investigated. A series of experiments were conducted to characterize the MEMS sensor over temperature and pressure changes by measuring output voltage signals. The sensor was modeled by a finite element method to investigate the stress developments. The molding compound was assumed as elastic and viscoelastic material to examine the material modeling effect on the calculation results. The model was verified by comparing the calculated results with experimental data. It was found that the stress induced by the molding compound had significant influence on the sensor performance, and the accuracy of the calculations was highly dependent on the modeling of the molding compound. Based on the results, the mechanism of the stress development and its effect on the sensor signal were discussed

Packaging Effect on MEMS Pressure Sensor Performance

The silicon-based pressure sensor is one of the major applications in the MEMS device. Nowadays, the silicon piezoresistive pressure sensor is a mature technology in the industry, but its requirement in terms of sensing accuracy and stability is more rigorous than that of many advanced applications. The major factor affecting the sensing stability of the piezoresistive pressure sensor is its thermal and packing effects. For a packaged pressure sensor, silicone gel is usually used to protect the die surface, so the thermal and packaging effects caused by the silicone gel should be taken into consideration to obtain better sensing sensitivity and stability. For fast design and optimization purpose, a finite element method (FEM) is adopted for sensor performance evaluation, packaging-induced signal variation, and thermal/packaging effects will be examined in this research. Several experiments are also performed to validate the finite element model. After the simulation is validated, an optimization analysis is carried out under different packaged pressure sensor design parameters. The simulation results show that the different geometry of the protection gel will influence pressure sensitivity significantly; base on analysis results, this research will conclude a design guideline for pressure sensor packages with concave and convex type of protection gel.

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Sensitivity analysis of packaging effect of silicon-based piezoresistive pressure sensor

https://hal.archives-ouvertes.fr/hal-00730848/document

Finite Element analysis of a shape memory alloy actuator for a micropump

A novel plastic packaging of a piezoresistive pressure sensor using a patterned ultra-thick photoresist is experimentally and theoretically investigated. Two pressure sensor packages of the sacrifice-replacement and dam-ring type were used in this study. The characteristics of the packaged pressure sensors were investigated by using a finite-element (FE) model and experimental measurements. The results show that the thermal signal drift of the packaged pressure sensor with a small sensing-channel opening or with a thin silicon membrane for the dam-ring approach had a high packaging induced thermal stress, leading to a high temperature coefficient of span (TCO) response of −0.19% span/°C. The results also show that the thermal signal drift of the packaged pressure sensors with a large sensing-channel opening for sacrifice-replacement approach significantly reduced packaging induced thermal stress, and hence a low TCO response of −0.065% span/°C. However, the packaged pressure sensors of both the sacrifice-replacement and dam-ring type still met the specification −0.2% span/°C of the unpackaged pressure sensor. In addition, the size of proposed packages was 4 × 4 × 1.5 mm3 which was about seven times less than the commercialized packages. With the same packaging requirement, the proposed packaging approaches may provide an adequate solution for use in other open-cavity sensors, such as gas sensors, image sensors, and humidity sensors.

https://www.mdpi.com/1424-8220/9/8/6200/pdf

Yeong K. Kim

Papers

Finite element simulation of package stress in transfer molded MEMS pressure sensors