Analysis of vapor pressure and void volume fraction evolution in porous polymers: A micromechanics approach

Abstract A novel micromechanics model is proposed, aimed at evaluating vapor pressure and void volume fraction of moisture absorbed polymeric materials during solder reflow process in electronic packaging. This model takes into account contributions of both thermal expansion and vapor pressure to the deformation of moisture absorbed polymers so that it is capable of predicting vapor pressure and void volume fraction simultaneously provided the initial conditions of vapor pressure and void volume fraction are prescribed. The novelty of the present model lies in that it can tackle problems where the void volume fraction is variable and unknown. An incremental algorithm based on this model is formulated to facilitate the numerical calculation. The effective properties (Young's modulus, Poisson's ratio and apparent thermal expansion coefficient) and vapor pressure obtained by this model can be used as initial loading condition and material properties for analyzing vapor pressure induced interfacial delamination and evaluating reliability of electronic packages.