Reliability Assessment with FEM
Based on the geometry and material data, the mechanical and thermal behaviour can be simulated. Additionally, it is possible to take thermal-mechanical, electrical-thermal and electrical-mechanical couplings into account. By making use of failure models, the assessed stress limits or the lifetime can be determined and or predicted.
Important aspects are:
- Determination of geometry: the geometry is determined on the basis of CAD-data or as part of the process and technology development.
- Selecting material data: good materials data is a key element for reliability assessment. Material data is already available for several materials. For new materials or extended fields of application (e.g. high temperature), additional material properties can be characterised and prepared for the simulation.
- Assessing production quality: stresses at the various stages of assembly can be investigated by simulation. Typical evaluation criteria are fracture stress and maximum permissible thermo-mechanical deformation.
- Determining hot spot temperatures: simulating the temperature distribution and identifying hot spots for various operational states (power loss: static and transient), and cooling parameters as elements of thermal management.
- Determining the lifetime: to evaluate long-term effects, mechanisms such as thermo-mechanical fatigue (e.g. at soldered joints, through vias), fracture processes, moisture diffusion, delamination, and electro-migration, are determined by using lifetime models– if necessary new lifetime models are developed.