Advancement in modeling vapor pressure induced stresses in electronic packaging

Reliability defect associated with thermal and humidity environment is not a new issue in modern electronics packaging. Moisture entrapment causes localized vapor pressure build up and leads to pop-corning or delamination in the internal structures when subjected reflow temperature. It was normally assumed that moisture entrapped inside the polymeric material is in saturated vapor state where vapor pressure can raised up to ~5MPa at 260°C which may and may not cause any resultant stress field change that leads to catastrophic failure. The approach proposed here utilized the Pressure-specific volume-Temperature (P-v-T) properties of water to determine the state of the water properties and corresponding vapor pressure induced. This open up the possibility that the pressure developed can be higher than 5MPa which can potentially explain the catastrophic failure such as pop-corning. The modeling framework leverage sequential moisture diffusion analysis and stress analysis with custom subroutine to incorporate vapor pressure induce strain in finite element computation. Two case studies demonstrated the feasibility of this advance methodology to describe the failure mechanism.