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Thermo-mechanical reliability during technology development of power chip-on-board assemblies with encapsulation

: Wunderle, B.; Becker, K.-F.; Sinning, R.; Wittler, O.; Schacht, R.; Walter, H.; Schneider-Ramelow, M.; Halser, K.; Simper, N.; Michel, B.; Reichl, H.


Microsystem Technologies 15 (2009), Nr.9, S.1467-1478
ISSN: 0946-7076
Fraunhofer IZM ()

In this paper we examine the thermo-mechanical reliability of polymer-encapsulated chip-on-board (COB) assemblies for power applications by simulation and experiment. Thereby the focus is set on the low cycle fatigue failure behaviour of the die-attach material under thermal cycling conditions. As die-attach material different solder materials and Ag-filled thermal adhesives have been used. The encapsulation was performed with a soft silicone-based and hard silica-reinforced epoxy-based material, respectively. An other process variable takes into account die-tilt. The study was carried out as a feasibility analysis in the course of a COB technology development. To this end lifetime models have been employed to correlate crack growth in the, i.e. attach to a computational accumulative failure criterion which allows to consistently describe ad predict quantitatively the lifetime of the assemblies. Thereby a considerable influence of the encapsulation was found. In particular it could be shown that a hard encapsulation largely increases reliability for solder die-attach.