Numerical analysis of microwave underfill cure in ball-grid packages

Microwave cure of thermosetting polymer underfill material in a simplified ball grid array package is assessed using a multiphysics analysis approach. A dual section microwave oven system capable of heating individual surface mount components on a printed circuit board assembly is described and its integration into a microelectronics manufacturing line is briefly outlined. Due to the complexity of measuring key process parameters in situ, a numerical approach, briefly described in this article, has been adopted to analyse and optimise the curing process. The numerical model comprises an unstructured finite volume thermophysical solver that is linked, through a Eulerian-Lagrangian mapping process, to a conformal finite difference time domain electromagnetic solver. A sample analysis focusing on the curing of an underfill material in a simplified ball grid array package is considered. Results obtained for a range of temperatures, microwave power density and thermomechanical stress development are presented.