Low stress packaging of a micromachined accelerometer

A packaging study of an acceleration microelectromechanical systems (MEMS) sensor is presented. The sensor consists of two silicon chips: a surface micromachined capacitive transducer (g-cell), which converts acceleration into signals of capacitance variation, and a microprocessor control unit (MCU) for signal conditioning. The two chips are die-bonded into a single piece of leadframe, connected via wire bonding, and finally molded with an epoxy compound. The primary goals of this paper are to provide insight and guidance for designing a package with low stress and low deformation. In particular, two die-bonding schemes: full die attach and four-dot die attach are presented in detail and their impact on performance of the transducer is discussed. Both the numerical simulation and testing data indicated that the four-dot-die-attach process results in a significantly lower packaging stress to the transducer, and is appropriate for stress-sensitive MEMS devices.