Correct modelling of geometry and of materials properties in the thermo-mechanical finite-elements-simulation of Chip Scale Packages

The first part of the work reported here is dedicated to the 3D finite-elements modelling of CSP. It will take into account both thermal-mechanical characteristics of the assembly materials and geometric factors. Here an approach of modular and parametric modelling with standardised modules linked via contact elements is proposed. Also the aspects of CAD systems for parameterised modelling are treated. The modular concept of modelling also will allow for efficient calculations with a variable number of bumps. The second part of the paper is dedicated to the materials descriptions which is necessary for the simulation of CSP assemblies. Measured materials data as well as suitable models for numerical representation are discussed. The relevant thermo-mechanical properties of package and assembly materials are presented. Besides actual solder alloys also polymers like moulding compounds are treated. In order to calibrate and check the simulation results, an ESPI sensor was used for measuring the thermal deformations of specimens under thermal loads in comparison to finite elements simulations. FE-models validated by experimental results present the deformations and stress state of the package under thermal cycling.