ABSTRACT
This chapter discusses the fundamentals of thermally induced deformations, strains, and stresses and explains some specific examples of thermal deformations and high-temperature fatigue in the context of electronic packaging design. It aims to develop prediction capabilities for the reliability of microelectronic devices and packaging accessories. The differences in the coefficients of thermal expansion of many different materials result in significant thermomechanical strains. Insight into thermomechanical behavior of orthotropic materials is important for proper design of printed circuit boards (PCBs) made from laminated fiber-reinforced composites. Analysis of the thermomechanical stress distribution in any specific situation depends not only on the geometry of the problem but also on the elastic symmetries of the constituent materials. Various testing methods are used to generate fatigue failure data for PCBs. For the most part in PCB design, plastic and anelastic deformations occur in ductile components such as solders, copper platings in plated through holes, and wire bonds.
