Effects of moisture exposure on the mechanical behavior of polycarbonate materials used in electronic packaging

The mechanical properties of polymer materials are often a key concern of the microelectronic packaging industry. The theoretical analysis of stress, strain, and deformation induced in electronic assemblies due to environmental exposures such as moisture adsorption, isothermal aging, and thermal cycling require the complete characterization of mechanical properties and constitutive behavior of the constituent materials. In this work, an experimental investigation has been performed on the effects of moisture adsorption on the stress-strain behavior of polycarbonate materials used in electronic packaging. Uniaxial test specimens were exposed in a controlled temperature and humidity chamber to combined hygrothermal exposures at 60 C and 90% RH, 60 C and 50% RH, and 40 C and 50% RH for various durations. After moisture preconditioning, a microscale tension-torsion testing machine was used to evaluate the complete stress-strain behavior of the material at several temperatures (T = 20 C, 40 C, and 60 C). It was found that moisture exposure strongly affected the mechanical properties of the tested polycarbonate, especially ultimate strain limit. Reversibility tests were also conducted to evaluate whether the degradations in the mechanical properties were recoverable. Upon fully redrying, the material was found to recover most of its original mechanical properties. In addition, optical microscopy was utilized to examine the fracture surfaces of the failed specimens, and observe the influence of moisture exposure.