Three-dimensional hybrid method using optical interferometry and nonlinear FEM for electronic packaging applications

A three dimensional hybrid method which combines optical interferometry and nonlinear finite element analysis is developed for electronic applications. Several optical interferometry techniques with high sensitivities capable of capturing full field displacement patterns in all three orthogonal directions are outlined with samples of packages tested. Combining moire interferometry with finite element analysis, a two dimensional hybrid method is used to analyze thermal strains in a column grid array package. After a successful two dimensional feasibility study, the three dimensional hybrid method which uses moire interferometry and the Twyman/Green interferometer to produce global displacements of an electronic package under a thermal loading, in combination with a three dimensional local nonlinear finite element model is developed. The localized stress/strain distributions in critical areas of a solder joint are determined using this hybrid model. This method eliminates the need for a complicated global finite element model, whose accuracy depends on materials properties and mesh geometries used in the model. Optical interferometries by themselves produce full field global displacements, but do not have enough sensitivity and resolution to produce localized strains. Combining the optical methods with the finite element models provides good sensitivity in local regions. The thermal strains in the solder joint of a plastic ball grid array package are determined using the hybrid model developed in this investigation.