Haiying Yang

Experimental and numerical approach on junction temperature of high-power LED

Abstract The understanding of thermal resistance and junction temperature is important in the area of designing efficient, long-lasting high-power Light Emitting Diodes (LEDs) and diode stacks. This paper developed a systematic evaluating program for investigating the effect of location and thickness on the thermal resistance and junction temperature of LED on an aluminum substrate. Structure function measurements were implemented by Thermal Transient Tester (T3ster) and Integrating Sphere on LED placed on an aluminum plate. The temperature distribution of LED was analyzed to understand the relationship between thermal resistance and location of the LED on the aluminum base. Meantime, to evaluate the validity of the test, the simulation is developed by considering structure properties. The simulation curve basically has a similarity with the experimental curve in the overall. It implies that the evaluating method can provide guidance in understanding thermal reliability of LED lamps and designing thermal management techniques.

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.

Investigation on thermal conductivity of bilayer graphene nanoribbons

We investigated the thermal conductivity of bilayer graphene nanoribbons (BGNs) using nonequilibrium molecular dynamics method (NEMD). The relationships among thermal conductivity, different ways of stacking, size, interfacial temperature and edge shape were studied. Two different stacking ways for BGNs are AA-stacked type and AB-stacked type. The results show that the thermal conductivities of AA-stacked BGNs are slightly higher than those of AB-stacked BGNs under the same simulation conditions because of different crystal structures. The thermal conductivity of zigzag BGNs (ZBGNs) first increases and then decreases with increasing width. However, the thermal conductivity of armchair BGNs (ABGNs) monotonously increases with increasing width. The thermal conductivity of BGNs increases with the length of the simulation system. In addition BGNs show temperature dependence and edge-shape dependence for thermal conductivity. We have explained the simulation results by the inter-layer phonon coupling and the phonon scattering, which have been shown to significantly affect the thermal conductivity of BGNs. The systematic analysis of thermal conductivity of BGNs did not only help to obtain conclusions regarding the achievable thermal performance, but also provided the possibility to design different dimensional BGNs for different BGNs-based thermal and microelectronic components.

Optimal approach on net routing for VLSI physical design based on Tabu-ant colonies modeling

Abstract To get a more efficient program for net routing design in VLSI physical design, a new mixed algorithm is presented by combining ant colonies algorithm and Tabu search algorithm for improving net routing design scheme in VLSI physical design. The models by considering different structure property such as two-terminal, multiple-terminal, multi-layers and gridless net routing are developed with introducing the proper parameters matching which can be obtained by computer experiments. The results show that the new algorithm can avoid the low convergence rate in the initial stage of basic ant colonies system. The efficiency of the Tabu-ant colonies is improved about 16.667%; meantime, the Tabu-ant colonies system can also avoid the local optimal solution effectively. It builds a basis for future work in solving multiple-terminal, multiple-layers and gridless net routing problems with high efficiency.

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.

Fatigue Analysis on Thermal Characteristics for PBGA by Using Finite Element Method

The stress and strain of Plastic Ball Grid Array (PBGA) is investigated for reliability evaluation, failure analysis, or manufacturing. A one-eighth model is built to estimate the thermal stress and strain of PBGA under thermal cycling temperature (0°C–100°C). The different 3D elements such as Visco107 and Solid45 were selected for modeling of material 37Sn63Pb and Print Circuit Board (PCB), silicon die, substrate, and Epoxy Molding Compound (EMC), respectively. The results show that the maximum equivalent stress and equivalent plastic strain occur in the second outer solder joint and close to the position of chip. The key solder joint can be obtained and the key node of solder joint is 41402. The results indicate that the integrating 3D model can provide a more comprehensive profile for the thermal investigation of the PBGA package than from using any 2D model. The investigation provides a basis for improving reliability of PBGA product in engineering design.

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...

Experiment and Prediction on Thermal Conductivity of Al2O3/ZnO Nano Thin Film Interface Structure

We predict that there is a critical value of Al2O3/ZnO nano thin interface thickness based on two assumptions according to an interesting phenomenon, which the thermal conductivity (TC) trend of Al2O3/ZnO nano thin interface is consistent with that of relevant single nano thin interface when the nano thin interface thickness is > 300 nm; however, TC of Al2O3/ZnO nano thin interface is higher than that of relevant single nano thin interface when the thin films thickness is < 10 nm. This prediction may build a basis for the understanding of interface between two different oxide materials. It implies an idea for new generation of semiconductor devices manufacturing.

INVESTIGATION FOR MOLECULAR ATTRACTION IMPACT BETWEEN CONTACTING SURFACES IN MICRO-GEARS

The aim of this research work is to provide a systematic method to perform molecular attraction impact between contacting surfaces in micro-gear train. This method is established by integrating involute profile analysis and molecular dynamics simulation. A mathematical computation of micro-gear involute is presented based on geometrical properties, Taylor expression and Hamaker assumption. In the meantime, Morse potential function and the cut-off radius are introduced with a molecular dynamics simulation. So a hybrid computational method for the Van Der Waals force between the contacting faces in micro-gear train is developed. An example is illustrated to show the performance of this method. The results show that the change of Van Der Waals force in micro-gear train has a nonlinear characteristic with parameters change such as the modulus of the gear and the tooth number of gear etc. The procedure implies a potential feasibility that we can control the Van Der Waals force by adjusting the manufacturing parameters for gear train design.

Test investigation on interfacial characteristics of Cr/Al nanofilms structure

The objective of this paper is to provide a systematic test for fabrication or evaluation of a bilayer film structure between Cr and Al in micro/nanoelectronic manufacturing. The Cr/Al bilayer film is fabricated by using the magnetron sputtering. To understand the basic mechanical properties of the Cr/Al bilayer films, the elastic modulus and the hardness of the sample are investigated by using a nanoindenter test. The test can show the changing trend of the Cr/Al sample structure. To investigate the integrating characteristics of the sample in progress, the effect of the thermal cycling loading and no-thermal cycling loading on the integrating force of the Cr/Al samples is tested by using nanoscratch. The interfacial binding force in the films can be obtained for understanding the integrating characteristics. It builds a basis for future work on progress investigation of physical property of Cr/Al bilayer film structure.