On chip micro stress test circuit for miniature component

Abstract

Adhesive bonding is a popular assembly method for miniaturized component composed of parts with different materials. However, it also inevitably introduces assembly stresses in some stress-sensitive structures, which adversely influence the accuracy of the performance, as well as the long-term stability of the component. An on chip piezoresistive micro stress test circuit was designed and tested in this paper. Piezoresistors were fabricated by doping Boron to n-type silicon wafer. The sensitive structure on the micro part was a flexible beam which had a thickness of 50 μm. Silver epoxy adhesive and double epoxy adhesive were used in the assembly process and the stresses parallel and perpendicular to the flexible beam were calculated. The experimental results showed that silver epoxy adhesive introduced larger stress because the difference in thermal expansion coefficients between silver epoxy adhesive and silicon are larger than that of double epoxy adhesive. Aging tests were also carried out and 46 percent of stress on average was released in 100 days at room temperature. This preliminary work implied that the stress distribution of the sensitive structure at all stages of the assembly could be measured using on chip micro stress test circuit.