@misc{WunderleMayHeilmannetal., author = {Wunderle, Bernhard and May, Daniel and Heilmann, Jens and Arnold, J{\"o}rg and Hirscheider, Josef and Lee, Yi and Bauer, J{\"o}rg and Schacht, Ralph and Abo Ras, Mohamad}, title = {Accelerated Pump Out Testing for Thermal Greases}, series = {20th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE)}, journal = {20th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE)}, publisher = {IEEE}, isbn = {978-1-5386-8040-7}, doi = {10.1109/EuroSimE.2019.8724540}, pages = {11}, abstract = {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 a die or module thermal interface material (TIM): Most thermal greases are Bingham fluids and thus not 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 commercial 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 way, 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. This allows for the first time a realistic loading of greases during accelerated testing with testing times below one hour. The method is demonstrated on various commercial and custom greases, varying their composition and structure, and benchmarked against industry standard thermal cycling tests. Further, two fundamental failure mechanisms have been identified being at work simultaneously, notably fluid transport (which constitutes actually a pump-in phenomenon) and air entrapment. We were able to identify key properties of the materials and loading variables, on which their intensity depends.}, language = {en} } @misc{KoberKuehhornRademannetal., author = {Kober, Markus and K{\"u}hhorn, Arnold and Rademann, J{\"o}rg and M{\"u}ck, Bernhard}, title = {Nonlinear topology optimization of centrifugally loaded aero-engine part with newly developed optimality-criteria based algorithm}, series = {Aerospace Science and Technology}, volume = {Vol. 39}, journal = {Aerospace Science and Technology}, doi = {10.1016/j.ast.2014.09.005}, pages = {705 -- 711}, abstract = {In this paper a successful topology optimization of a centrifugally loaded aero-engine part is presented. For the topology optimization, which is a nonlinear problem due to several contact regions, a self-developed topology optimization algorithm in combination with a commercial FE-solver is used. The goal of the optimization was the reduction of stresses in the structure. ©2014 Rolls-Royce Deutschland Ltd \& Co. KG. Published by Elsevier Masson SAS. All rights reserved.}, language = {en} } @misc{SchachtGruenNowaketal., author = {Schacht, Ralph and Gruen, Tobias and Nowak, Torsten and Arnold, J{\"o}rg and May, Daniel and Wunderle, Bernhard}, title = {Experimental investigation of pumped two-phase flow boiling using different finned and pin finned structures on interchangeable heater modules}, series = {29th International Workshop on Thermal Investigations of ICs and Systems (THERMINIC)}, journal = {29th International Workshop on Thermal Investigations of ICs and Systems (THERMINIC)}, doi = {10.1109/THERMINIC60375.2023.10325896}, abstract = {This paper introduces an industry-grade, multipurpose closed loop flow boiling cooler test stand for rapid experimental characterization and parameter variation. A flow boiling chamber with interchangeable plug-in heater module was designed that allows for the investigation of different finned cooler structures and surface topologies and chemistry respectively to enhance small bubble formation and release. In this experimental investigation a finned and a pin finned cooler structure using mm-size dimensions were used. It could be shown that the pin finned and finned cooler structure show for low flow rates at low pressure drop the same performance. Furthermore, it could be observed that the heat transfer coefficient could be increased for both cooler structure in the two-phase regime as opposed to single-phase convective liquid cooling.}, language = {en} }