Thermo-mechanical finite element analysis in a multichip build up substrate based package design

This paper presents a thermo-mechanical analysis of a multichip module (MCM) package design, with emphasis on the package warpage, thermally induced stress and the second level solder joint reliability. The MCM package contains four flip chips which are mounted on a build up substrate. First, the effect of the positioning of four silicon dice within the MCM package on the warpage of the package is studied. Second, the effect of package dimensions (the heat spreader thickness, the structural adhesive thickness and the substrate thickness) on the maximum residual stress as well as the warpage of the package is performed. Finally, this paper presents a 3D sliced model for solder joint reliability of the MCM assembly. A creep constitutive relation is adopted for the 63Sn/37Pb solder to account for its time and temperature dependence in thermal cycling. The fatigue life of solder joint is estimated by the Darveaux's approach. A series of parametric study is performed by changing the package dimensions. The results show that the largest die tends to experience highest stresses at its corner and has more influence on the warpage of the package than smaller dice. The results also show the most sensitivity factors that affect the package warpage and the second level solder joint reliability are the substrate thickness and the heat spreader thickness. The structural adhesive thickness has no major effect on the package warpage, the maximum von Mises stress of the package and the second level solder joint reliability.