COFFIN-MANSON FATIGUE MODEL OF UNDERFILLED FLIP-CHIPS

The fatigue life of an underfilled flip-chip package has been evaluate d using the Coffin-Manson relation and finite element modeling (FEM)-c omputed solder shear strain for typical flip-chip structures, In the c ourse of this effort, numerical simulations were performed for underfi ll materials of varying thermo-structural properties, two chip sizes, and two solder bump heights, The results were used to examine the para metric sensitivity of the thermal strain in the solder joints and the axial, as well as shear, stress in the underfill material, The predict ed improvement in the number of cycles-to-failure of the underfilled f lip-chip was found to agree with empirical observation, However, the m aximum improvement achievable by underfilling was found to be limited by the adhesion strength of the underfill material.