Influence of materials data on the performance modelling in the design of MEMS packages

To predict the performance and the reliability of microsystems in the development process, simulation is a powerful tool which is still gaining greater importance. The accuracy of the simulation results depends substantially on the quality of the available materials data. Realistic results can only be achieved in thermo-mechanical computations when the temperature dependency as well as the nonlinearities and the time-dependence of the materials properties are taken into account. The first part of the work reported here is dedicated to the data and materials models for the simulation of MEMS assemblies. As part of this work measured materials data as well as suitable models for their numerical representation are demonstrated. In the presentation, the results of the measurements of most of the relevant properties of package and assembly materials are presented. These comprise bonding wires, moulding compounds and conductive adhesives under typical service conditions. The corresponding materials modelling for finite element simulations will be shown. Furthermore, the procedure to predict the performance of MEMS assemblies and interconnections is regarded. On the basis of such an analysis the necessary models and data for prediction of the thermo-mechanical behaviour are presented. It will be demonstrated how these can be utilized in designing MEMS. The finite-elements-simulations will present coupled physical problems as induced by interactions of thermal and mechanical effects. In that way, it will be possible to take into account complex load profiles under realistic service conditions. In a representative example of an industrial pressure sensor the influence of the attachment material and its viscoelasticity-plasticity on the accuracy of the device will be calculated.