Authored By:
J. Trodler Dipl.-Ing.
Heraeus Deutschland GmbH&Co.KG,
Hanau Germany
R. Dudek Dr.-Ing., Fraunhofer ENAS, Chemnitz Germany
M. Rollig Dr.-Ing., Fraunhofer IKTS, Dresden Germany
Summary
New solder alloy development for high temperature applications have increased the last few years; for example, automotive applications now use both Innolot and/or HT1 alloys, especially when the devices have to work at temperatures up to 170 Celsius. For the solder alloy and the interconnection itself, there are some fatigue life advantages when using Innolot, especially for thermal cycles - 40/+150 Celsius. On the other hand, by using Innolot there is a relatively high thermo-mechanical stress induced which can create ceramics defects at the passive components. The paper will compare and discuss the differences of the alloy, based stress in ceramic components due to passive cycle tests, real customer tests, and stress analyses based on the finite element method.
Conclusions
During physical testing, standard SAC alloys show fatigue, while both high temperature alloys produced acceptable results for the solder joint, and the IL alloy produced a ceramic crack after TCT. Due to additional active TCT tests, utilizing other alloys, there were also similar results detected. Field test conditions that seems to be non-critical. By an FEM it has been analyzed the stress on the passive components with different alloys. With regard to component stress, IL was determined to be the most critical alloy, with HT1 producing the lowest stress. Therefore, when there is a risk of ceramic cracks, using an alloy with a higher shear rate may provide a possible solution. Further activities will analyze other combinations such as devices with conformal coating etc. In addition, the knowledge can influence the quality of the ceramic passive components.
Initially Published in the SMTA Proceedings
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