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Modelling and characterisation of a grease pump-out test stand and its use for accelerated stress testing of thermal greases

: Wunderle, B.; Heilmann, J.; May, D.; Arnold, J.; Hirscheider, J.; Bauer, J.; Schacht, R.; Vogel, J.; Ras, M.A.


Volz, S. ; Institute of Electrical and Electronics Engineers -IEEE-:
THERMINIC 2017, 23rd International Workshop Thermal Investigations of ICs and Systems : September 27-29, 2017, Amsterdam, the Netherlands; Proceedings
Piscataway, NJ: IEEE, 2017
ISBN: 978-1-5386-1928-5
ISBN: 978-1-5386-1929-2
International Workshop on Thermal Investigations of ICs and Systems (THERMINIC) <23, 2017, Amsterdam>
Conference Paper
Fraunhofer ENAS ()
Fraunhofer IZM ()

Thermal greases allow a low stress bond at low bond line thicknesses (BLT) at medium thermal conductivities and simple application, all of which make it an alternative to solders, thermal adhesives or pads. It is widely used in power and microprocessor applications, most of which involve large areas to be used for heat transfer. However, for years thermal overload failure of power modules and chips has been a pressing problem due to pump-out of thermal grease as die or module thermal interface material (TIM): Most thermal greases are Bingham fluids and thus no solids, so they can be squeezed out from in between the gap, driven by thermo-mechanical action of the adjacent layers as e.g. DCB substrate or silicon chip with the heat sink. Today, thermal greases have to be qualified in lengthy stress tests in a product relevant environment which consumes substantial resources as often a system test is required. Therefore, a fast test is necessary which accelerates testing and thus allows a fast screening of market-available greases on one hand, and guidelines for material development on the other. For that purpose this paper addresses this topic in a combined simulative and experimental manner, where at the same time a novel test procedure is proposed for accelerated grease pump-out testing (GPOT) in the framework of a completely new approach, combining loading with in-situ failure analytical techniques and decoupling thermal from mechanical loading.