Three-dimensional Finite Element Analysis of Thermomechanical Behavior in Flip-chip Packages under Temperature Cycling Conditions

Flip-chip packaging provides a high-performance low-cost approach for the development of electronic packages. A three-dimensional viscoelastic-plastic finite element analysis using the commercial software ANSYS has been performed to study the thermomechanical behavior in flip-chip assemblies, i.e., the four components, chip, solder ball, underfill, and substrate. The viscoelastic behavior of the underfill is modeled on the Maxwell constitutive equation while the viscoplastic behavior of the solder balls is modeled by the Anand model. Both the chip and the substrate are assumed to be elastic materials modeled by the Hooke's law. As in standard industry practice, temperature cycling from 125 to 55°C is used. Simulated thermomechanical behavior is presented for the solder balls. Subsequently, the effects of underfill-material properties, such as elasticity and coefficient of thermal expansion are also investigated.