The generalized theory of thermoelasticity was employed to characterize the coupled thermal and mechanical wave propagation in high performance microelectronic packages. Application of a Gaussian heat source of spectral profile similar to high performance devices was shown to induce rapid thermal and mechanical transient phenomena. The stresses and temporal gradient of stresses (power density) induced by the thermal and mechanical disturbances were analyzed using the Gabor Wavelet Transform (GWT). The arrival time of frequency components and their magnitude was studied at various locations in the package. Comparison of the results from the classical thermoelasticity theory and generalized theory was also conducted. It was found that the two theories predict vastly different results in the vicinity of the heat source but that the differences diminish within a larger time window. Results from both theories indicate that the rapid thermal-mechanical waves cause high frequency, broadband stress waves to propagate through the package for a very short period of time. The power density associated with these stress waves was found to be of significant magnitude indicating that even though the effect, titled short time scale effect, is short lived, it could have significant impact on package reliability. The high frequency and high power density associated with the stress waves indicate that the probability of sub-micron cracking and/or delamination due to short time scale effect is high. The findings demonstrate that in processes involving rapid thermal transients, there is a non-negligible transient phenomenon worthy of further investigation.

The generalized theory of thermoelasticity was employed to characterize the coupled thermal and mechanical wave propagation in high performance microelectronic packages. Application of a Gaussian heat source of spectral profile similar to high performance devices was shown to induce rapid thermal and mechanical transient phenomena. The stresses and temporal gradient of stresses (power density) induced by the thermal and mechanical disturbances were analyzed using the Gabor Wavelet Transform (GWT). The arrival time of frequency components and their magnitude was studied at various locations in the package. Comparison of the results from the classical thermoelasticity theory and generalized theory was also conducted. It was found that the two theories predict vastly different results in the vicinity of the heat source but that the differences diminish within a larger time window. Results from both theories indicate that the rapid thermal-mechanical waves cause high frequency, broadband stress waves to propagate through the package for a very short period of time. The power density associated with these stress waves was found to be of significant magnitude indicating that even though the effect, titled short time scale effect, is short lived, it could have significant impact on package reliability. The high frequency and high power density associated with the stress waves indicate that the probability of sub-micron cracking and/or delamination due to short time scale effect is high. The findings demonstrate that in processes involving rapid thermal transients, there is a non-negligible transient phenomenon worthy of further investigation.

In this study, transient dynamic response of viscoelastic cylinders enclosed in filament wound cylindrical composites is investigated. Thermal effects, in addition to mechanical effects, are taken into consideration. A generalized thermoelasticity theory which incorporates the temperature rate among the constitutive variables and is referred to as temperature-rate dependent thermoelasticity theory is employed. This theory predicts finite heat propagation speeds. The body considered in this thesis consists of n+1-layers, the inner layer being viscoelastic, while the outer fiber reinforced composite medium consist of n-different generally orthotropic, homogeneous and elastic layers. In each ply, the fiber orientation angle may be different. The body is a hollow circular cylinder with a finite thickness in the radial direction, whereas it extends to infinity in the axial direction. The multilayered medium is subjected to uniform time-dependent dynamic inputs at the inner and/or outer surfaces. The body is assumed to be initially at rest. The layers are assumed to be perfectly bonded to each other. The case in which the inner surface of the viscoelastic cylinder is a moving boundary is further investigated in this study. This is similar to the solid propellant rocket motor cases. The solid propellant is modelled as a viscoelastic material which in turn is modelled as standard linear solid / whereas, the rocket motor case is a fiber-reinforced filament wound cylindrical composite. Method of characteristics is employed to obtain the solutions. Method of characteristics is suitable because the governing equations are hyperbolic. The method is amenable to numerical integration and different boundary, interface and initial conditions can be handled easily.