The EMC material employed to package the pressure sensor is a typical epoxy-based polymer, and
therefore it shows viscoelastic behavior [22]. Several assumptions are used to develop the FE model. The
total stress applied to each piezoresistor is the sum of the average stresses acting on each of the elements
within it [23,24]. With the data of dynamic mechanical analysis (DMA) and thermal mechanical analysis
(TMA) examinations, the material properties of the EMC are described below. The elastic modulus
linearly decreased with temperature from room temperature to 150 °C, and then it dropped dramatically
when the EMC was heated up to between 150 °C and 198 oC. Finally, the elastic modulus of the EMC
was almost a constant value of 1.5 × 109 Pa when the temperature was over 198 °C. Therefore, the current
FE analysis models the EMC as a temperature-dependent linear isotropic material and assumes a stress
free temperature at 165 °C (transfer molding temperature). The material properties of the dam-ring are
assumed to be isotropic/linear material properties. The package-induced stress is caused by the
coefficient of thermal expansion (CTE) mismatch of the packaging materials. In simulating the response
of the pressure sensor, the deformation of the piezoresistors is modeled using commercial ANSYS®
software (Version 9). Figures 4 and 5 show the mesh structures of the FE models employed for the
sacrifice-replacement and dam-ring approaches, respectively