Methoden und Technologien zur Optimierung der Entwärmung aktiver und passiver Komponenten auf keramischen Mehrlagensubstraten

Die Entwicklung der Elektronik schreitet stetig voran. Durch die steigende Funktionsdichte einzelner Baugruppen und die damit einhergehende Miniaturisierung gewinnt das thermische Management zunehmend an Bedeutung. Die hierdurch wachsenden Anforderungen an den Schaltungsträger hinsichtlich der thermischen Performance erfordern die Verbesserung von bestehenden und die Entwicklung von neuen Entwärmungskonzepten. Diese Arbeit beschäftigt sich mit der Optimierung der Entwärmung von Komponenten auf keramischen Schaltungsträgern. Die Arbeit umfasst dabei drei Schwerpunkte: Chipmontage, Wärmespreizung und Wärmeableitung. Die thermische Performance von Chipmontageverfahren wie Silbersintern und reaktives Löten wird ermittelt. Neuartige Silberstrukturen werden im Keramiksubstrat integriert und die Wärmespreizfähigkeit dieser simulativ und messtechnisch qualifiziert. Zudem werden Flüssigkeitskühlkonzepte für keramische Schaltungsträger vorgestellt und mittels Simulation und Messung bewertet.This thesis deals with the thermal path in a multilayer module based on low temperature co-fired ceramic (LTCC). The thermal path describes the path of heat flowing from a heat generating component to a heat sink. The thesis focuses on new materials, technologies and methods, which improve the thermal performance of the multilayer module. The thermal path can be subdivided into three critical parts. The first part contains the joining between the chip and the substrate. So called thermal interface materials (TIM) are used as bonding agent to ensure a strong and thermally conducting bond between chip and substrate. The thesis addresses the pressure less silver sintering technology, which provides a high thermally conducting bond between chip and substrate. Moreover reactive soldering is investigated as potential chip and substrate bonding technology. This technology utilizes a reactive multilayer foil, which reacts fast exothermically after a short thermal pulse. The delivered heat can be used to join materials with different coefficient of thermal expansion (CTE), like copper and LTCC or silicon. The thermal resistance, the mechanical strength and reliability of bonds based on reactive solders and silver pastes are characterized and compared to conventional bonding agents like solders and adhesives. The second part addresses the entire ceramic substrate. To enhance the poor thermal conductivity of the ceramics metals in form of cylinders are integrated in the substrate. These so called thermal vias consist mostly of gold or silver based materials and are integrated below the chip bond area. The influence of the via geometry, via material and sinter process on the thermal performance and the hermeticity of the substrate are evaluated within the scope of this thesis. Furthermore new silver foils are integrated in the LTCC substrate during co-firing, to form a LTCC substrate with massive silver structures. Therefore, the LTCC is locally replaced by the silver foil, which forms areas with a very high thermal conductivity inside the substrate. The thermal performance of these silver structures inside LTCC substrates is investigated on the basis of two demonstrators. The third part of the thermal path deals with the heat sink. The possibility to integrated fluidic channels inside the LTCC substrate, which can be utilized for active cooling with a coolant, is discussed within the scope of this thesis. The investigations cover the design and the fabrication of the fluidic channels and the fluidic interfaces. Moreover the thermal performance of these cooling concepts is evaluated

Simulation of heat transfer by cooling channels in LTCC substrate

The thermal resistance, flow analysis, pressure drop and distribution of coolant inside multilayer LTCC (Low Temperature Co-fired Ceramics) substrate are detailed investigated in this paper. For this reason four various structures of internal channels in the multilayer LTCC substrates were designed and simulated. The simulation 3D model consist of 6 LTCC of DuPont 951® layer with cooling microchannel in middle of substrate, power chips paced on top of LTCC and silver sintered joints under power chips. The impact of the structure of channels, volume flow and power loss of die was simulated, calculated and analyzed by using the simulation software Mentor Graphics FloEFDTM. The structure and size of channels have the significant impact on thermal resistance, pressure of coolant as well as the effectivity of cooling power components which can be placed on LTCC substrate. The thermal resistance was calculated from the temperature gradient among chip junction, the inlet fluid and the thermal load of chip. Optimizing and comparison of cooling channels structure inside LTCC substrates and analyzing the effect of volume flow for achieving the least thermal resistance of LTCC multilayer substrate is the main contribution of this paper

Brazilian Flora 2020: Leveraging the power of a collaborative scientific network

International audienceThe shortage of reliable primary taxonomic data limits the description of biological taxa and the understanding of biodiversity patterns and processes, complicating biogeographical, ecological, and evolutionary studies. This deficit creates a significant taxonomic impediment to biodiversity research and conservation planning. The taxonomic impediment and the biodiversity crisis are widely recognized, highlighting the urgent need for reliable taxonomic data. Over the past decade, numerous countries worldwide have devoted considerable effort to Target 1 of the Global Strategy for Plant Conservation (GSPC), which called for the preparation of a working list of all known plant species by 2010 and an online world Flora by 2020. Brazil is a megadiverse country, home to more of the world's known plant species than any other country. Despite that, Flora Brasiliensis, concluded in 1906, was the last comprehensive treatment of the Brazilian flora. The lack of accurate estimates of the number of species of algae, fungi, and plants occurring in Brazil contributes to the prevailing taxonomic impediment and delays progress towards the GSPC targets. Over the past 12 years, a legion of taxonomists motivated to meet Target 1 of the GSPC, worked together to gather and integrate knowledge on the algal, plant, and fungal diversity of Brazil. Overall, a team of about 980 taxonomists joined efforts in a highly collaborative project that used cybertaxonomy to prepare an updated Flora of Brazil, showing the power of scientific collaboration to reach ambitious goals. This paper presents an overview of the Brazilian Flora 2020 and provides taxonomic and spatial updates on the algae, fungi, and plants found in one of the world's most biodiverse countries. We further identify collection gaps and summarize future goals that extend beyond 2020. Our results show that Brazil is home to 46,975 native species of algae, fungi, and plants, of which 19,669 are endemic to the country. The data compiled to date suggests that the Atlantic Rainforest might be the most diverse Brazilian domain for all plant groups except gymnosperms, which are most diverse in the Amazon. However, scientific knowledge of Brazilian diversity is still unequally distributed, with the Atlantic Rainforest and the Cerrado being the most intensively sampled and studied biomes in the country. In times of “scientific reductionism”, with botanical and mycological sciences suffering pervasive depreciation in recent decades, the first online Flora of Brazil 2020 significantly enhanced the quality and quantity of taxonomic data available for algae, fungi, and plants from Brazil. This project also made all the information freely available online, providing a firm foundation for future research and for the management, conservation, and sustainable use of the Brazilian funga and flora