Effective viscoelastic plastic material modeling for faster and reliable calculations

Finite Element Simulations of highly integrated and large electronics packages with detailed elastic-plastic material modeling of thousands of solder balls are still challenging tasks on today's computation systems. The complex geometry and mesh and the usage of time-consuming creep laws for solder materials make it nearly impossible to calculate different geometries or process parameters. This paper describes a method to reduce the complexity of the mesh in the region of the solder balls and surrounding underfill with one simple block physically described as a viscoelastic material. Therefore a viscoelastic/plastic behavior of a complex unit cell was modeled in a temperature dependent harmonic frequency sweep or relaxation simulation. The reaction of the unit cell was utilized to synthesize the master curve, Prony coefficients and shift function to an effective material model. Finally, an error estimation of the unit cell approach was carried out. The results show that effective material approach can be used to cut down computation time significantly.