Yunqing Tang

Thermal management performance of bent graphene nanoribbons

The models of graphene nanoribbons (GNRs) with angles 0°, 30°, 60°, 90° and 120° were constructed to investigate the thermal conduction by using the reverse non-equilibrium molecular dynamics method. A substantially negative correlation between the thermal conductivity and the bent angle shows a nonlinear decline from 0° to 90°. It also shows that there is a little increase from 90° to 120° due to the edge effect. To weaken the edge effect, the nitrogen doping method is adopted to recompose the bent GNRs. The results show that it is effective for the thermal management, and a strict monotonous relationship between the thermal conductivity and bent angle can be obtained. In the meantime, an interesting phenomenon is observed that the GNRs with edge modification by N-doping can get a much better thermal conduction than original GNRs without edge modification. We can understand the physical mechanism by phonon analysis for these GNRs. The investigation implies that we can change the thermal conductivity of GNRs by design by N-doping.

Approach on the Life-Prediction of Solder Joint for Electronic Packaging Under Combined Loading

A life-prediction approach of solder joints for electronic packaging under combined loading is presented in this paper. The deformations of solder joints are calculated under vibration and thermal cycling loading based on the finite element method. The calculated results are used as the boundary condition of the multi-axial loading to investigate the strain and stress of the solder joints. Then the life of solder joints can be evaluated by using a linear damage superposition approach. The result reveals that the life of solder joints can be divided into three regions according to the vibration amplitude at the same temperature: the life of solder joints in the first region is affected by creep damage; the life of solder joints in the second region is greatly influenced by the combined loading damage; the life of solder joints in the third region is impacted by the fatigue damage. The trend of the simulation results approximately agrees with the experimental results of other researchers.

Effect of forming factors on surface temperature and residual deformation of the plate in line heating

Parameters of line heating input are key factors which determine temperature field and deformation field in line heating for ship hull plate manufacturing. Two coupling variables named as qs (average energy input per unit area), qs·t (average energy input per unit area and time) are constructed with line heating input parameters to describe relations between final deformation of plate and acetylene flux, heating velocity, heat source radius, heat source efficiency, and length of heating line in line heating. The relation between the new variables and residual deformation is revealed via numerical simulation. The results show that the new variables can reflect the relation between heating parameters and final residual deformation.

Thermal Effects on LED Lamp With Different Thermal Interface Materials

Thermal performances of light-emitting diode (LED) lamp with three types of thermal interface materials (TIMs) under different convection coefficients and input powers are investigated by using finite-element method. Three types of TIMs are conductive silver, Sn63Pb37 of tin alloy solder, and graphene in this paper. The results demonstrate that the temperature of the LED lamp decreases sharply using the interface material of graphene. With the increasing convection coefficient in a certain range, the junction temperature will be effectively decreased. When under high input powers, graphene has a much better performance than other two TIMs. It implies that graphene may be a possible potential for thermal design, which can effectively prolong the life of LED, especially for high power devices. The simulation offers a test of LED heat dissipation using different TIMs, and the results can provide a reference for the application of graphene in LED thermal design as TIMs and build a motivation for future material research directions. It builds a basis for progressive study of physical property for LED lamp. The obtained results may give insight to the reliability of the LED lamp.

Experimental and numerical approach on interfacial properties of W/Al bilayer films for electronic devices manufacturing

The aim of this article is to provide a systematic method for performing experimental tests and theoretical evaluations on interfacial adhesion properties of the W/Al bilayer thin films interface. Samples W/Al bilayer thin films assembly is deposited on the quartz glass by using radio frequency magnetron sputtering. Based on the analysis of the experimental indentation data, the elastic modulus and hardness of the sample are investigated. The test results show that both of the values are easily influenced by the indentation depth. At the meantime, a finite element model is built to simulate the interface mechanical properties. The analysis shows that stress is mainly centralized close to the indenter and the maximum stress occurs in the lower layer Al film, not in the upper W film. The comparison between the experiment and the simulation shows the validity of the test and the modeling of each other to a certain extent. The investigation builds a basis for future work such as the fabrication of W/Al bilayer thin films for micro/nano manufacturing.

A review on design of interface structure in micro/nano manufacturing

Interface structure is a critical part of electronic components in computers, smart phones, automotive components and other electronic devices. Along with the development of technologies, the demand for electronic devices and their quality has increased rapidly in recent years. Thus, it is indispensable to research the design and reliability of interface structure. In this article, we give a review of recent investigations on the design and reliability of interface structure. Some academic developments on design and reliability of interface structure by considering thermal characteristics under different loading conditions are discussed.

Mechanical characteristics approach on W/Cr nano-interface structure

Abstract The objective of this article is to provide an experimental test and evaluation on mechanical characteristics of the W/Cr interface. The elastic modulus and hardness of the sample are measured by a nanoindentation tester. The test results show that the elastic modulus and hardness of the sample are nonlinear with respect to the depth h of the interface structure, unlike the usual approximate horizontal linear relationship as expected. To understand the bonding characteristics between W and Cr in nanoscale, the nano-scratch test is conducted considering the influence of thermal cycling load on the sample. The test results show that interfacial bonding strengths are different between samples under different thermal cycling loading conditions. It implies that the thermal loading has the potential probability to reduce the bonding reliability of the W/Cr interface. It builds a basis for future work of further investigations on mechanical properties of W/Cr interface structure.

Numerical simulation of thermal properties at Cu/Al interfaces based on hybrid model

Purpose – The purpose of this paper is to investigate thermal properties at Cu/Al interfaces. Design/methodology/approach – A hybrid (molecular dynamics-interface stress element-finite element model (MD-ISE-FE) model is constructed to describe thermal behaviors at Cu/Al interfaces. The heat transfer simulation is performed after the non-ideal Cu/Al interface is constructed by diffusion bonding. Findings – The simulation shows that the interfacial thermal resistance is decreasing with the increase of bonding temperature; while the interfacial region thickness and interfacial thermal conductivity are increasing with similar trends when the bonding temperature is increasing. It indicates that the higher bonding temperature can improve thermal properties of the interface structure. Originality/value – The MD-ISE-FE model proposed in this paper is computationally efficient for interfacial heat transfer problems, and could be used in investigations of other interfacial behaviors of dissimilar materials. All the...

Interfacial heat transfer properties of the typical interconnection structures in IC packaging: a multiscale study

A multiscale analysis method is put forward to evaluate the interfacial properties. The finite element method is used to estimate the thermodynamics properties of the Al-Cu interface structure in the macroscale, and the non-equilibrium molecular dynamics method is used to investigate the interfacial heat transfer in the nanoscale. The deformation and nanocracks always appear at the outside edge of interface owing to the dissimilar thermal expansion coefficients. The diffusion thickness of different atoms increases with the increase of temperature. The diffusion enhances the heat transfer with the increase of temperature in the nanoscale. The results reveal the mechanism of the interfacial heat transfer, which is helpful in the design and manufacture of IC assembly.

Investigation on the electronic and optical properties of Al-doped ZnO nanostructures

In order to investigate the electronic structures and optical properties of Al-doped ZnO materials, the characteristics such as band structure, density of states, complex dielectric constant of pure ZnO nanowires and Al-doped ZnO were studied by using first-principle method based on the density function theory (DFT). With the Al doping increasing, the band gap of Al-doped ZnO narrows, which is different from that of Al-doped ZnO nano-thin films. It supplies the theoretical reference value for the modulation of the band gap and optical properties of Al-doped ZnO.