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With the miniaturization of electronic devices, electronic packaging has become increasingly precise and complex, which presents a significant challenge in terms of heat dissipation. Electrically conductive adhesives (ECAs), particularly silver epoxy adhesives, have emerged as a new type of electronic packaging material, thanks to their high conductivity and stable contact resistance. However, while there has been extensive research on silver epoxy adhesives, little attention has been paid to improving their thermal conductivity, which is a critical requirement in the ECA industry. In this paper, we propose a straightforward method for treating silver epoxy adhesive with water vapor, resulting in a remarkable improvement in thermal conductivity to 9.1 W/(m·K), three times higher than the sample cured using traditional methods (2.7 W/(m·K)). Through research and analysis, the study demonstrates that the introduction of H2O into the gaps and holes of the silver epoxy adhesive increases the path of electron conduction, thereby improving thermal conductivity. Furthermore, this method has the potential to significantly improve the performance of packaging materials and meet the needs of high-performance ECAs. [ABSTRACT FROM AUTHOR]

The Ångström method is a promising thermal diffusivity measurement method for microfibers. Based on the heat-loss Ångström method and micro-Ångström method, the FFT (Fast Fourier Transform) Ångström method can be used to shorten the testing time and enhance the testing robustness of thermal conductivity. The FFT Ångström uses multi-frequency superimposed input signals and then uses the FFT for frequency division analysis. Since different frequencies are input at the same time, the measuring time is greatly reduced. Moreover, because different frequencies are input in the same environment, the random and environmental perturbations of the frequencies are the same, enhancing the fitting robustness. In contrast, the single feeding strategy is relatively time-consuming, and its measurement homogeneity for different frequencies cannot be guaranteed. By comparing the measurement results from a multi-frequency input and separated single-frequency input, the FFT shows good feasibility and robustness. It may also have great potential in other types of thermal wave measurements. [ABSTRACT FROM AUTHOR]

Thermal composites are widely used in thermal management. Usually, they consist of polymers and fillers. In pursuit of higher thermal conductivity, the fillers are mostly spherical particles for higher packing density. In previous work, the relationship between particle size distribution (PSD) and packing density was studied, especially the parameters such as polydispersity δ and the skewness S are defined to characterize the PSD. However, in our observation, for sieving process, which is very helpful in manipulating PSD and thus tuning thermal conductivity, δ and S are not good enough to explain most of the compositing results. Here, we suggest a new set of indices (bias-normal indices) to evaluate the sieving efficacy. Three kinds of ceramic powders (MgO, Al 2 O 3 , and AlN) and their single- and triple-order composites materials were prepared. The results show that the explanations based on bias-normal ratio index agree well with all the experiments. Thus, this new indicator is competent in guiding the recipe design of the thermal composite materials, and when well-designed recipes are employed, sieving is proven an efficient and simple way to promote the thermal performance, which is of great practical value. [ABSTRACT FROM AUTHOR]

l A novel design of microscale heat flux meter composed of a micro-hotwire and an infrared thermal microscopy is demonstrated. l By applied this microscale heat flux meter in heat-loss modified Angstrom method, low-dimensional thermal measurement for simultaneous measurement of thermal diffusivity, thermal conductivity and specific heat can be realized. l This microscale heat-flux meter is a general technique, which is promising for extensions to other thermal measurements. A microscale heat-flux meter is designed based on micro-hotwire and infrared thermal microscopy. Its feasibility in low-dimensional thermal measurement is verified by its application in heat-loss modified Angstrom method for simultaneous measurement of thermal diffusivity, thermal conductivity and specific heat. The hotwire and the sample under test are placed in a vacuum chamber. Through an observation window, the infrared microscopy can capture the thermal image including the hotwire and the sample. When the hotwire is heated, the temperature distribution along the wire is acquired by the readings extracted from the thermal image, which enables the determination of nonlinear and local temperature gradient. This gradient, according to Fourier's Law, can be used to calculate the local heat flux. When a sample is attached to the middle of the hotwire, the attached point is appeared to be a singularity in the temperature distribution along the hotwire, which poses a rigorous challenge to calculate the heat flux flowing into the sample. Here we tried some approaching strategies and verified that the local heat flux at second derivative minima around the singularity is a good enough approximation. The mathematical and physical origins for this approximating strategy are also discussed. This microscale heat-flux meter is a general technique, which is promising for an extension to other thermal measurements. [ABSTRACT FROM AUTHOR]

Annular thermoelectric power generator has been increasingly considered in application of ambient energy harvesting owing to the advantages of simple structure and no pollution. To improve thermal stability and energy harvesting performance of this system, the latent heat of phase change materials to improve thermal management and the high thermal conductivity of the heat sink to enhance heat transfer with the ambient are harness to annular thermoelectric power generator. Motivated by this, a phase change material based annular thermoelectric energy harvester (PCM-ATEH) with fins is developed for ambient energy harvesting and its three-dimensional transient model is also built up through jointly with thermo-electric and phase change processes. This paper considers the influence of key parameters such as temperature fluctuation amplitude, temperature fluctuation period, height ratio of PCM and thermoelectric generator (TEG) and melting temperature on liquid fraction, temperature difference, voltage and power density. Moreover, the comparison of PCM-ATEH and PCM based thermoelectric energy harvester (PCM-TEH) with/without fins is further conducted in this study to explore thermal management and energy harvesting performance. The energy harvesting characteristics of PCM-ATEH with fins is developed concerning the combination of power generation of TEG and melting process of PCM. Based on the results, it is found that the temperature difference and power density of PCM-ATEH with fins vary periodically with the sinusoidal temperature boundary, and results show that increasing temperature fluctuation period is not always feasible. Additionally, the comparative results indicate that the peak power density and energy efficiency of PCM-ATEH with fins are increased by 0.126 W/m2 and 0.02 % compared with PCM-TEH with fins, and increased by 0.195 W/m2 and 0.041 % compared with PCM-ATEH without fins. The results of energy harvesting characteristics show that a maximum of 0.77$ per watt can be reached to power generation cost of PCM-ATEH with fins. This paper can provide theoretical guidance for thermal management and energy conversion of energy harvesting system. [ABSTRACT FROM AUTHOR]