Improved modeling for solder joint geometry and self-alignment in flip chip bonding

Prediction of solder joint geometry is one of key steps for achieving accurate alignment in optoelectronic packaging. An improved modeling is developed to predict the solder joint geometry. The wetting angle of molten solder in pad as well as that out of pad is taken into account in this model. Therefore, the molten solder geometry overflowed pads can be successfully predicted. The simulation result is corroborated by our experimental tests. This method is also applied for modeling of multiple solder joints. Moreover, the restore force of the misaligned solder joint, determined by various parameters, could be calculated in the self-alignment process based on the above-mentioned model. In addition, a polynomial regression model is accomplished to clearly understand the relationships between the restore force and the parameters of solder joints. And the alignment accuracy is expected to be improved thanks to optimization of solder joint geometry and restore force.