Hygroscopic Swelling Effect on Polymeric Materials and Thermo-hygro-mechanical Design on Finger Printer Package

The objective of this paper is focused on the hygroscopic swelling effect on polymeric material used in electronic package and thermo-hygro-structure coupled design and reliability analysis for finger printer package. For moisture absorption/desorption analysis, the ambient environment for temperature and humidity are set to be 60degC60%RH, 85degC60%RH and 85degC85%RH, respectively. The transient moisture diffusion analysis described by Fick's equation is performed to evaluate the overall moisture distribution. Hygroscopic swelling properties such as coefficient of saturation (Csat), coefficient of moisture expansion (beta) and activation energy (Q) can be extracted through TMA (Thermal Mechanical Analysis) and TGA (Thermal Gravitational Analysis). A three-dimensional solid model of finger printer package based on finite element ANSYS software is developed to predict the thermal-induced strain, hygroscopic swelling and the residual stress distributions. The predicted thermal-induced displacements were found to be very good agreement with the Moire interferometer experimental in-plane deformation. The developed finite element 3D model, therefore, is applied to predict the mechanism of thermo-hygro-mechanical induced stress in accordance with JEDEC pre-condition standard JESD22-A120. An analytical expression for the total expansion strain due to thermo-hygro-mechanical coupled effect was proposed and the implementation procedures using software ANSYS were described in details. A series of comprehensive parametric studies were conducted in this paper.