1,721,310 research outputs found
Comparative study of thermally conductive fillers in underfill for the electronic components
No full textGeneral underfill for the flip-chip package had a low thermal conductivity of about 0.2 W/mK. Thermal properties of underfill were measured with various fillers, such as silica, alumina, boron nitride, (BN) and diamond. Coefficient of thermal expansion (CTE) was changed by filler content and CTE of silica 60 wt.% was 28 ppm; BN 30 wt.%, 25 ppm; alumina 60 wt.%, 39 ppm; and diamond 60 wt.%, 24 ppm. The viscosity of underfill was measured with the cone and plate rheometer. Thermal diffusivity was measured with the laser flash method. Diamond filler loaded underfill showed the highest thermal conductivity 60 wt.%; 1.17 W/mK at 55 degrees C. Thermal conductivity of underfill was changed with a transition of heat capacity by the temperature increment in same filler content. In case of different filler content, thermal conductivity was changed with a transition of the thermal diffusivity. (c) 2005 Elsevier B.V. All rights reserved
Topology optimization of rubber isolators considering static and dynamic behaviours
No full textA topology optimization for the design of rubber vibration isolators is proposed. Many vibration isolators are made of rubbers and they operate under small oscillatory load superimposed on large static deformation. Vibration isolators must have a certain degree of static stiffness in order to endure the static loading due to large gravitational and inertial forces. On the other hand, isolators must have a small dynamic stiffness in order to reduce the force transmission from vibrating systems to base structures. Therefore both the static and dynamic behaviours of rubber should be simultaneously considered in the design process. The static behaviours of rubber under large and slow loads are generally treated with hyperelastic constitutive models. Rubber under fast dynamic loads can be modelled as a viscoelastic material. In this paper, the steady state viscoelastic model, which is suggested by Kim and Youn and correctly predicts the influence of the pre-strain on the relaxation function, is applied for the dynamic analysis. The continuum-based design sensitivity analyses (DSA) of both the static hyperelastic model and dynamic viscoelastic model are developed. The topology optimization formulation is proposed in order to generate the system layouts considering both the static and dynamic performance. The density distribution approach and sequentially linear programming (SLP) are used as the optimization algorithms. Some design examples are presented in order to verify the proposed approach.This work was supported by grant No. R01-2001-000-00393 from the Basic Research Program of the Korea Science & Engineering Foundation
Large area interfacing of ZnO nanowire with various metal electrodes using thermocompression bonding
No full textA constitutive model and FEA of rubber under small oscillatory load superimposed on large static deformation
No full textA heuristic constitutive equation and an FE formulation for rubber under small oscillatory loads superimposed on large static deformations are presented. The viscoelastic constitutive model, [9], is implemented in an FE code to analyze the dynamic characteristics of rubber elements under general loading conditions. Dynamic tests in which the rubber specimens endure steady-state harmonic motion superimposed on large static deformation are performed in order to verify the proposed model. Compression and complex-stress tests are included in the tests to check the proposed model under multi-axial stress states. The FEA results are compared with the experimental results. The proposed model successfully predicts dynamic stiffness peak in the complex-stress test, which cannot be explained by conventional models. The model shows a better performance than existing models in predicting the behavior of rubber specimens that are subject to complex pre-strain
Finite element analysis of the flow and heat transfer of solid particles in moving beds
No full textA numerical analysis for the flow and heat transfer of solid particles in moving beds of heat exchangers is presented. The solid particles pass through a bundle of heat source tubes as the result of the gravitational force. Heat energy is transferred through direct contact of particles with the heat source tubes. A viscous-plastic fluid model and a convective heat transfer model are employed in the analysis. The flow field dominantly determines the total heat transfer in the heat exchanger. As the velocities of solid particles around the heat source tubes increase, the heat transfer from the tubes also increases. Examples are presented to show the performance of the numerical model. The effect of how on heat transfer has also been studied. (C) 1998 John Wiley & Sons, Ltd
Thermocompression transfer printing process for improved bonding between nanowires and metal electrodes
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