Modeling of micropitch shift of a magnetoelectrical sensor during laser solder ball bonding process

With the development of optoelectronics and microelectromechanical systems (MEMS) packaging, laser soldering has become an extensively used interconnection technique in electronic manufacturing industry. Postsolder shift in assembling of such components is the most challenging issue to affect the packaging yields. To maintain a high coupling efficiency or accuracy, tight control of postsolder shift is required. In the present work, a 3-D thermal-mechanical coupled finite element model was developed to investigate the time-dependent pitch shift induced by the laser solder ball bonding process. This model accounted for the laser interaction, the heat conduction, the thermal induced deformation and the phase change of the solder and could reflect the actual laser soldering process. The modeling results show different deformation mechanisms in the prebumping and reflow processes. The pitch shift is mainly induced by the thermal shrinkage of solder. The pitch angles obtained from the finite element analysis are in good agreement with those from the measurement using laser goniometer.