Effects of adhesive material on the output characteristics of pressure sensor

The attachment of the silicon piezoresistive pressure sensor die to the substrate is one of the most critical steps in the production of highly accurate pressure sensor. In this paper, single parameter of the adhesive affecting the silicon piezoresistive pressure sensor's output characteristics has been studied. Shear strength of the adhesive with optimized parameters also has been evaluated. Material (adhesive) parameters and package-induced residual stress are analyzed to investigate how these factors influence the sensor's performance. Finite element analysis (FEA) is used to predict the distribution of the residual stress induced by coefficient of thermal expansion (CTE) mismatch between the glass base (Pyrex7740), polymer adhesive and substrate (Kovar), and experiments are carried out to verify the FEA. Results show that thicker die-attaching adhesive that has a lower Young's modulus generates lower residual stress and smaller zero offset as well as smaller temperature drift to the sensor. Based on FEA and experiments data the optimized die-attaching process parameters are proposed. Shear test is introduced to verify the reliability of the bonding strength of the optimized die-attachment process. Test results show that the minimum shear force is 42N, and the ratio of the smallest area of the residual adhesive to the whole area of the adhesive layer is larger than 60%, which meets the U.S. military standard.