Thermo-mechanical reliability aspects and finite element simulation in packaging

Computer-based thermo-mechanical design and performance optimization are in widespread use and mainly work with finite-element analyses (FEA). Concepts of FEA-based theoretical investigations on the failure of the precision material compounds used in microsystem technology are briefly introduced. The phenomenon of stresses at interfaces between dissimilar materials is of special importance within the variety of failure criteria and is therefore discussed in more detail. The stress state at interfacial edges is shown to be strongly localized as has to be expected from the often singular elastic solution at an interface edge. Aspects of the failure analysis for three important material classes, i.e. polymeric materials, thin electrodeposited metallic layers and soft solders are considered. The different appropriate constitutive models and related failure criteria are given. They require a certain amount of input material parameters, for which measuring results are provided. For polymeric materials, standard thermo-elastic data, isothermal relaxation data, and fracture toughness data is exemplified. Elastic-plastic modeling is looked at for copper thin films. Finally, soft solder characteristics and failure data are presented.