Investigation of the Thermal Drift of MEMS Capacitive Accelerometers Induced by the Overflow of Die Attachment Adhesive

Abstract

Packaging stress has significant influence on the thermal stability of microelectromechanical system (MEMS) devices, which utilize the die-on-substrate packaging method to connect the chips and the package shell. A certain adhesive, during the packaging process, is deposited on the package shell by hands or machines to shape an intermediate layer for gluing die and substrate. Due to the uncontrollability of deposition amount, the adhesive always flow out to form overflow structure on the side of die chip. The adhesive overflow will change the distribution of thermal stress induced by the changed temperature and further impact the thermal stability of devices, which is characterized by the quantity of thermal drift. This paper investigates the contribution of adhesive overflow to the thermal drift of comb MEMS capacitive accelerometers. The accelerometers with different levels of overflow are modeled by chip-adhesive–substrate models to study the deformation of sensitive component induced by temperature change. The thermal drift is acquired by an analytical method using the structure deformation and the calculation of the differential capacitance. The thermal drift theory for accelerometers with adhesive overflow is verified by a series of experiments. The results indicate that the adhesive overflow can lead to 10% increase of thermal drift compared with accelerometers without adhesive overflow. In addition, this increase can be extended by the asymmetry of supporting beams of accelerometer. Therefore, the overflow phenomenon should be carefully considered in the packaging process for highly accurate MEMS accelerometers.