Impact of Thermal Variations and Soldering Process on Performance and Behavior of MEMS Capacitive Accelerometers

This work presents an analysis of performance and multiple parameters of microelectromechanical system (MEMS) capacitive accelerometers in applications with large thermal variations and the effects of the soldering process on them. The proposed test consists of a thermal characterization phase performed between two mechanical calibrations. The test is performed on multiple units before and after the soldering process. Mechanical, thermal, and performance parameters are analyzed and compared among all tests. The ranges and relative variations of these characteristics, both during the soldering process and the tests, have been identified and characterized individually. Mechanical bias shows greater variability than other parameters in both the soldering process and thermal tests. On the contrary, the thermal characteristic parameters show great stability in all cases. The thermal drifts, which are the main source of error in environments with large thermal variations, are successfully compensated for using a model with only two characteristic parameters. According to the observed behaviors, negative thermal variations (toward cooler temperatures) might be more suitable for thermal calibration due to other effects, such as creep, taking place primarily at hotter temperatures. The creep effect at constant temperature is analyzed according to the Kelvin–Voigt model with promising results, and a possible link between thermal drift and creep effects is presented. Performance results are calculated in multiple compensation scenarios. Using the proposed compensation techniques, the average maximum error is reduced from over 70 to 7 mg and the uncertainty is also reduced to a third of the initial value.