In situ measurement of thermomechanical effects and properties in thin-film polymers

Results of in situ measurements of the thermomechanical properties of polyimides used in the microelectronic packaging industry are presented. During the formation of polymer layers and their subsequent use, there are several thermomechanical effects which can affect the electronic packages performance. Specifically, thermal loading of the structure results in elastic and inelastic effects such as relaxation. The time and temperature dependent relaxation behavior of polyimides in multilayer structures were investigated to determine their thermomechanical properties. Both a numerical model and experimental analysis were used to determine the curvature change of multilayer structures during manufacturing. The numerical model, which is based on Maxwell's model, characterizes the stress relaxation behavior of thermoplastics. The changes in stress over time for quartz-polyimide-aluminum and quartz-polyimide-germanium heterostructures were obtained. From these observations, the relaxation time constant, activation energy, and viscosity-to-shear-modulus ratio were determined for the polyimide.