Experimental And Correlated Studies On Thermal Conductivity Of Beryllium Oxide Particles Filled Polymer As Thermal Interface Material For Dynamic Heat Flow In Leds Package

BeO nanoparticles were synthesized by polyacrylamide gel route with varied calcination temperature; 800, 900 and 1000 0C. Structural characterization and surface morphology between synthesized BeO nanoparticles and commercial BeO microparticles were analyzed by X-ray diffraction analysis (XRD) and Scanning electron microscope analysis (SEM) in order to study the crystallinity and structural properties as well as surface morphology of BeO particles that would be beneficial for filler application. Thermal conductivity measurement analysis was carried out on both synthesized (800 0C) and commercial BeO particles filled epoxy matrix in order to figure out the effect of particle size on the thermal conductivity of epoxy composites. The structural properties and surface morphology that yielded the best crystallinity quality for BeO particles as well as the optimum size which enhanced the thermal conductivity of filled epoxy composites were observed at commercial BeO microparticles. BeO particles filled epoxy composite has been prepared with varied filler loading (10, 30 and 50 wt%) by mixing using the mechanical stirrer. Then, X-ray diffraction analysis (XRD), dynamic mechanical analysis (DMA) and Thermo-mechanical analysis (TMA) were carried out in order to study the crystallinity, thermal and mechanical properties of the composites

Synthesis And Characterization Of MgO And MgO/ZnO Multilayer Thin Films For Heat Spreading Application In Light Emitting Diode Packaging

This research was carried out to synthesize magnesium oxide (MgO) and magnesium oxide - zinc oxide (MgO/ZnO) multilayer thin film as a TIM cum heat spreader for efficient thermal management in LEDs packaging system. MgO (10 layers) and MgO/ZnO multilayer (stacked separately in a configuration of 9:1, 8:2, 7:3, 6:4 and 5:5 layers) thin films are coated over aluminum (Al 5052 grade) and copper (Cu) substrates using spin coating technique. In the first part, MgO thin film was synthesis using 0.6 M, 10 coating cycles, preheated at 200 °C for 20 minutes, and finally annealed at 600 °C for 1 hour. Structural characterization by XRD shows the presence of (200), (220), and (222) MgO phases with crystalline size (37.47 nm), reduced microstrain (2.5 x 10-3) and dislocation density (7.0 x 10-4 lines/m2) for 0.6 M MgO coated Al. Uniform distribution of 74 nm size grains and surface roughness of 19.11 nm were confirmed by FESEM and AFM analysis. A significant difference in junction temperature (ΔTJ = 24.7%) and total thermal resistance (ΔRth-tot = 3.86 K/W) were recorded for LED fixed on 0.6 M MgO coated Al compared to that of bare Al. In the second part, ZnO was added to the monolithic MgO to improve the structural, surface, and thermal transport properties of MgO. Among the studied MgO/ZnO multilayers, 6:4 L MgO/ZnO displayed larger crystalline sizes of 52 nm (Al) and 35 nm (Cu) with thermal conductivity of 24.31 W/mK (Al), and 15.13 W/mK (Cu) respectively. 6:4 L MgO/ZnO multilayer films showed lower surface roughness (9.6 nm (Al) and 2.6 nm (Cu)) with uniformly distributed grains and presence of large numbers of contact points to the LEDs packag

Challenging thermal management by incorporation of graphite into aluminium foams

The recent progress made in active thermal management for electronics demands the development of new open-pore foam materials with excellent thermal performance that result from the combination of high thermal conductivity (≥70 W/mK) and the lowest possible fluid pressure drop. The foams considered to date in the literature do not meet these conditions. In this work, a new class of two-phase composite foam materials, which contain graphite flakes and aluminium, were fabricated by the gas pressure liquid metal infiltration method. These materials were fabricated in two main microstructures: i) aluminium foam with oriented graphite flakes in struts; ii) alternating layers of oriented graphite flakes and aluminium foam. The resulting materials exhibited thermal conductivities within the 60–290 W/mK range, and power dissipation capacities up to 325% higher than those for conventional aluminium foams, with pressure drops kept at convenient values for the most demanding active thermal management applications.The authors acknowledge partial financial support from the “Ministerio de Ciencia e Innovación, Spain” (grant MAT2016-77742-C2-2-P)

Thermal interface materials - a review of the state of the art

The past few decades have seen an escalation of power densities in electronic devices, and in particular in microprocessor chips. Together with the continuing trend of reduction in device dimensions this has led to dramatic increase in the thermal issues within electronic circuits. Thermal management is therefore becoming increasingly more critical and fundamental to ensuring that electronic devices operate within their specification. Although a thermal management system may make use of all modes of heat transfer to maintain temperatures within their appropriate limits and to ensure optimum performance and reliability, conductive heat transfer is typically used to spread the heat out from its point of generation and into the extended surface area of a heat sink. To minimise the contact resistance, thermal interface materials (TIMs) are introduced to the joint to fill the air gaps and are an essential part of an assembly when solid surfaces are attached together. This paper reviews the conventional interface materials and then goes on to present a comprehensive review of the emerging state-of-the-art research in the use of carbon nanotube based materials. The paper also outlines the advantages and disadvantages of each TIM category and the factors that need to be considered when selecting an interface materia

ANALYSIS OF RELIABILITY AND CONDUCTION MECHANISMS IN EMBEDDED PLANAR CAPACITORS

An embedded planar capacitor is a thin laminate embedded in a multilayered printed wiring board (PWB) that functions both as a power-ground plane and as a parallel plate capacitor. The capacitor laminate consists of a dielectric material (epoxy-BaTiO3 composite dielectric is widely used) sandwiched between two Cu layers. These capacitors have gained importance with an increase in the operating frequency and a decrease in the supply voltage in electronic circuits since it can lead to PWB miniaturization. Further, the use of embedded planar capacitor leads to better electrical performance of the PWB. Although embedded planar capacitors have various advantages there are some issues such as lack of reliability information and a high leakage current in the epoxy-BaTiO3 composite dielectric. This dissertation aims in investigating these issues that needs to be investigated for wide scale commercialization of these capacitors. The reliability of embedded planar capacitors is critical since these capacitors are not reworkable and its failure can lead to PWB failure. In this work the reliability of an embedded planar capacitor (with epoxy-BaTiO3 composite dielectric) is investigated under environmental stress conditions in the presence of an applied bias. Temperature-humidity-bias (THB) tests and highly accelerated life test (HALT) was performed at multiple stress levels to investigate the reliability under these conditions. The failure modes and mechanisms during THB and HALT are investigated. Further, during HALT the life time is also modeled using the Prokopowicz model and regression of the in-situ capacitor data. The loading of BaTiO3 in the epoxy-BaTiO3 composite dielectric should be as high as possible (until the theoretical maximum packing density is achieved) to maximize the effective dielectric constant of the composite. But as the loading of BaTiO3 in the composite dielectric increases, the undesirable leakage current also increases. The mechanism of current conduction in this composite dielectric is investigated in this work. The effect of various factors such as BaTiO3 loading, BaTiO3 particle diameter, temperature, and voltage on the resulting leakage current has been modeled. Measurements of leakage current were performed on embedded capacitors with varying BaTiO3 loading and varying particle diameters over a range of temperature and voltage. The consistence of the leakage current data with standard conduction models is compared to investigate the conduction mechanism

Comparison Of Thermal And Optical Behaviors Of Pre-Molded And Ceramic Package Light Emitting Diodes

The project signifies thermal and optical characterizations of pre-molded and ceramic package light emitting diodes (LEDs) that are conducted by using thermal transient and light emission recording techniques. It was observed that the luminous intensity of the LEDs is dependent on the input current. However, the LEDs efficiency is reduced for about 15% with the current increases, which due to the high current density and heating of LED junction. In terms of package-level and system-level, pre-molded package LED shows approximately to 13% and 15% lower in junction-to-case and junction-to-ambient thermal resistances respectively than ceramic package LED. Despite, the heat dissipation of ceramic package LED is improved after mounting on a metal-core board (board-level). Here, the effects of packaging material properties and ratio of contacting surface area are applied. Next, the results shows that the application of thermal compound as thermal interface material yields about 6% lower junction-to-ambient thermal resistance than thermal tape. Further investigation shows that the optimum heat convection for pre-molded package LED in an open-air environment is obtained as the cooling fan facing upward; while in terms of still-air environment, it is achieved as the cooling fan facing downward. Lastly, the accuracy of the captured thermal transient is improved by considering the optical power into the determination of real thermal resistance. In sequence, it was seen that the use of direct current reveals more accurate and reliable measurement results where the occurrence of electrical disturbance is minimized

Characterization of Multifunctional Nanomaterials for Electronics Thermal Management and Sintering Applications

The science of manipulating materials at their nanoscale level is nowadays allowing endless possibilities to disrupt the current limitations on the conventional production processes and products. In electronics, the need for more capable thermal management strategies led to the exploration of advanced approaches and focus on new materials and allowed to push further the thermal dissipation capabilities of each generation of products. In this thesis, we investigate different thermal management concepts and propose new solutions based on carbon and metallic nanomaterials, while we explore the possibility to combine the size effect with the composition effect of the nanoscale materials.Due to their high surface to volume ratio, nanoscale particles show different thermodynamics properties that led to their potential implementation in electronics fabrication processes. More specifically, silver nanoparticles (Ag NPs) have been under focus in recent years for applications to replace lead-free solder and contribute to energy saving. Due to a poor trade-off between the process parameters, the production costs, and the reliability of the silver related application, different strategies are being suggested to optimize its applications. In this present study, we investigate multiple sintering parameters of Ag NPs and use the nanoscale effect in a hybrid approach for the sintering of microscopic powder. The results of the sintering parameters are correlated to the density of the samples and their properties in terms of thermal and electrical conductivity. While the sintering of Ag NPs occurs at low temperatures and allows to obtain relatively high densities, the thermal and electrical properties are still limited and the increase in the temperature and fraction of the NPs higher than 400 degrees and 2wt.% has a much- pronounced effect to improve the physical properties of the samples.The sintering of Ag NPs was also explored in this thesis to propose a novel approach to use graphene foam as a heat sink. While graphene is known for its outstanding physical, chemical, and mechanical properties, its integration as a practical solution in electronics is still missing. The use of Ag NPs in this work allowed to successfully attach the 3D graphene foam on its substrate and further improve both its mechanical and thermal properties by coating the graphene with Ag NPs. Also, the integration of Ag NPs as a die-attach for the 3D porous structure allowed its further use as a container for Phase Change Materials (PCM). Different amounts of PCM were introduced in the lightweight foam and the junction temperature of the hot spot was correlated to the power and the presence of the PCM. We found that graphene foam presents a real advantage for its use in thermal dissipation strategies.2D graphene material is developed herein as a coating for micro-and nanoscale particles. Using Chemical Vapor Deposition (CVD) and Arc Discharge (AD) methods, we introduce the possibility to produce graphene coating on copper particles for application in thermal management. In addition, we explore the possibility to introduce a doping effect on the coated NPs to further study its effect on the thermal performances of NPs. The morphology and the composition of the coating were investigated and correlated with the bottom-up production process of CVD and AD. The thermal conductivity and chemical stability of the produced particles were studied for their use as fillers in thermally conductive pastes and additives water-based nanofluids. The thermal properties of the different systems were linked to the fraction of the additives and nanofillers. The graphene-coated particles were found to have a multifunctional effect. In both micro-and nanoscale particles, the graphene coating was found to act as a corrosion resistance that stabilizes the metallic core of the particles. The graphene coating also was found to act as a carbon source to reduce the microparticles in a bimodal powder at high temperatures. Finally, the encapsulation of the nanoscale powder allowed to observe a melting point depression related to the composition of the core of the nanoparticles and their nanoscale size.In an effort to combine the size effect of the nanoparticles and their compositions, different alloyed nanoparticles were produced using AC. The morphology, the composition, and their sintering properties were compared to highlight their composition effect. The produced nanopowders were also used as a sintering aid in the spark plasma sintering approach (SPS) and the results show a positive contribution of the nanopowders in the reduction of the sintering temperature and the densification of the samples. An additional effect is also reported and arises from the possibility to use those particles to fine-tune the chemical composition of the bimodal particles

Development and characterization of cotton and cotton fabric reinforced geopolymer composites

Sustainable geopolymer composites reinforced with natural cotton fibres have been developed and their mechanical and durability properties are evaluated in this research. Results showed that the mechanical properties (flexural strength, flexural modulus, fracture toughness, compressive strength, impact strength and hardness) of woven cotton fabric-reinforced geopolymer composites were superior to those of geopolymer composites with short cotton fibres. Exposure to water and elevated temperatures (200 to 1000°C) severely reduced the mechanical properties of the composites