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Reliable Encapsulation of Microsystems for Automotive Use

: Becker, K.-F.; Braun, T.; Koch, M.; Bauer, J.; Wunderle, B.; Sommer, J.-P.; Aschenbrenner, R.; Reichl, H.

Michel, B.:
MicroCar 2008: Micro materials, nano materials for automotives. Volume of abstracts : Leipzig, 27.2.2008
Berlin: Fraunhofer IZM, 2008 (Micromaterials and Nanomaterials 8.2008)
Fachkongress Microcar <3, 2008, Leipzig>
Konferenzbeitrag, Zeitschriftenaufsatz
Fraunhofer IZM ()

Typical scenario for the integration of electronics into a car is a control unit in the engine compartment, where ambi-ent temperatures are around 150 °C and package junction temperatures may range from 175 °C to 200 °C, peak temperature may exceed these values. Apart from the high temperature load, electronics in automotive applications can be exposed to harsh environment conditions as e.g. to gas oil, brake fluid or accumulator acid.
If advanced packaging technologies are used under harsh environment conditions, it is clear that especially the polymeric materials, i.e. Epoxy Molding Com-pound, Underfiller, solder mask or the organic substrate base material, are challenged. Generally, the development goal for encapsulants compatible with high temperature applications are materials with high Tg and low degradation even at temperatures beyond 200 °C. For these polymeric encapsulants the material suppliers provide basic information about thermo-mechanical and mechanical prop-erties directly after processing, but no information about material data after a certain time of use especially in a harsh environment is given. To yield more insight in transient material parameter changes, material properties of typical encapsulants used for high reliable pack-aging are studied in initial state and after aging under various harsh environment conditions relevant for automotive applications. With these data an evaluation of the material degradation and the related influence on package reliability should be possible. To do this encapsulants need to be robust in terms of chemical inertness when subjected to harsh environment, the second section of this paper is describing the reliability potential of epoxy encapsulants. An example for the reliability potential of such encapsulants is given in the third section, where direct Flip Chip encapsulation leads to extreme thermal cycling performance of 14.000 cycles without electrical failure. The fourth section describes the most advanced options of encapsulation - i.e. the em-bedding of components or submodules into a printed circuit board - in this case of a 77 GHz Radar module for automotive use.