Reduction of test effort. Looking for more acceleration for reliable components for automotive applications
Introduction
Standard procedures for product qualification do not aim at generating fails or showing weaknesses of a component. They are used to provide a certain confidence that no fails will occur under use conditions. Contrary to this point of view is the technology development. Here tests are done to find weaknesses of the component under well defined stress. Therefore, it is absolutely necessary to test until failures are clearly detectable. In Fig. 1, the possible impacts due to temperature are illustrated. Not only temperature must be taken into account but also the temperature gradient and the temperature swing.
Temperature cycling of electronic components is a highly accepted test method to prove the reliability of a component [1], [2], [3], [4]. The today often accepted number of 1000 cycles passed with no objection concerning the defined failure criterion is not any more sufficient for future applications. End of life tests will be obligatory and will increase the test effort and cost significantly.
Temperature swings address phenomena as delamination at interfaces as die attach or adhesion of moulding compound. Accelerated testing can be performed by using thermal cycling (air to air) or thermal shock (liquid–liquid).
Therefore new approaches are necessary to reduce the test effort. Modelling based on physics of failure must be improved to be able to predict precisely time to failure under use conditions.
Section snippets
Simulation and experiments
Based on the assumption that heat conductance and heat capacity are well known parameters of the used materials to build the components, simulations of the heat transfer during cycling were performed. Especially the aspect how long it takes to reach thermal equilibrium and what kind of stress is induced due to the temperature gradient (Fig. 2) during cycling was of interest.
Using the finite-element-method (Software: ANSYS) the thermo-mechanical stress during both conventional thermal cycling
Results
A comparison of failure modes and failure mechanisms induced by thermal cycling was presented. Test methods like preconditioning, thermal cycling and thermal shock were assessed based on experiments on P-DSO-36 and TO220 like packages. For the observed delaminations a test procedure was proposed to provoke the failure mode in a short time (<1 day). It has been demonstrated that lead (Pb) as a die attach material is the root cause for the observed failure mode. Substitution of lead shows a
Conclusion
For the observed failure modes TS calibrated with a thermal simulation can speed up test time significantly by factors of 50 and even more. This allows turnaround times for product development of less than 1 day to judge the robustness of the component against temperature swings.
The here described procedure should also be applied to other temperature tests like active cycling. Anyway the demand for shorter test cycles especially for long lasting end of life tests should stimulate the research
References (4)
- AEC-Q100. Failure mechanism based stress test qualification for integrated...
- JESD47. Stress-test-driven qualification of integrated circuits (JEDEC solid state technology...
Cited by (2)
Temperature cycling and thermal shock correlation in DPAK & DSO packages
2012, 2012 10th IEEE International Conference on Semiconductor Electronics, ICSE 2012 - ProceedingsElectrical /electronics for reliable systems for automotive applications
2009, SAE Technical Papers