Cheng-Nan Han

Analysis of Thermal and Luminous Performance of MR-16 LED Lighting Module

Light emitting diode (LED) with a long lifetime, low power consumption, and low pollution has been successfully applied in many products. However, due to its low electro-optical conversion efficiency, high percentage of input power transformed to redundant heat, thus increasing the LED temperature. This phenomenon decreases the luminous flux, changing light color, and useful life span of LED. Therefore, thermal management becomes an important issue in high power LED. In this paper, the variation of luminous flux and light color for different LED lighting modules under long time operation has been measured and discussed. In addition, a detailed finite element model of LED lighting module, MR-16, with a corresponding input power and suitable boundary conditions is established by using the ANSYS finite element analysis program. Furthermore, to validate the simulation results, the current-voltage-temperature method for characterization of a diode is utilized to measure the junction temperature of LED chip indirectly and compare with simulation results. After the simulation is validated, various thermal performance assessments under the different design parameters of the LED package and lighting module are also investigated in this paper. The methodology and analysis results of this paper can provide a guideline for the LED lighting module such as MR-16 design in the future.

Analysis of Thermal Performance of High Power Light Emitting Diodes Package

This paper reports on the thermal characteristics of the high power LED package. The increment of input power generates more heat in the chip, decreasing the luminance and life span of LEDs. To enhance the efficiency of high power LEDs, challenges related to thermal management need to be addressed. In this research, a detailed finite element model of the high power LED package with proper input power and boundary condition is established using the ANSYS@ finite element analysis program. The applied input power is 1W on GaN, and the convection coefficient is adopted from Williams experimental results. Radiation is also included in the FEM model. Additionally, forward voltage methods used to indirectly measure the junction temperature are also performed to validate the finite element model with predicted input power. The simulation results closely match the experimental data, with only 5% error. Various thermal performances under different design parameters of the high power LED package are developed following verification of the simulation analysis. Five design factors including (a) the substrate of the chip, (b) the thickness of the die attach material (c) the electro-optical conversion efficiency (d) the thickness of the copper slug and (e) the area of the copper slug are chosen to determine themost dominant factor in this study. The factorial design provides a guide line for the compromise between thermal enhanced design and manufacturing process in the future.

Mechanical characteristic of ssDNA∕dsDNA molecule under external loading

The elasticity and extensibility behaviors of sequence-dependent single stranded and double stranded DNA (ssDNA∕dsDNA) under various external loading conditions are studied by the clustered atomistic-continuum mechanics (CACM). The proposed numerical CACM is based on the finite element method, and it comprises both the atomistic-continuum and clustered atomistic-continuum (the clustered atoms are treated as a single super atom) mechanics. Through the CACM simulation, the transient mechanical response of the DNA could be revealed, including the stretching and rotating of the DNA backbone. Moreover, good agreement was achieved between the numerical simulation and single molecule experimental results.

Thermal Performance Assessment and Validation of High-Concentration Photovoltaic Solar Cell Module

A high-concentration photovoltaic (HCPV) system with high optic-electric transition efficiency was developed in order to increase the electrical energy generated by a photovoltaic system. However, device temperature rises quickly because of the solar cell operating under concentrated-light operation conditions. Therefore, system output power or energy-conversion efficiency decreases as the temperature of the cell incorporated within the system increases. Consequently, thermal management has become an important issue for HCPV solar cell package. In this paper, the finite element (FE) analysis was used to initially establish a detailed FE model of the HCPV solar cell package as a baseline model. Moreover, the dissipation power of the solar cell obtained by employing a predicted function is applied. Outdoor experiments were also performed to validate the baseline FE model with the estimated dissipation power. After validation of the simulation, an analysis of the thermal performance variations under different HCPV solar cell package design parameters was performed. Simulation results of different design parameters revealed that the geometry of the heat sink plate played an important role in the thermal management of the HCPV solar cell package.

Factorial Analysis of Chip-on-Metal WLCSP Technology with Fan-Out Capability

In this study, a wafer level chip scaled packaging (WLCSP) having the capability of redistributing the electrical circuit is proposed to resolve the problem of assembling a fine-pitched chip to a coarse-pitched substrate. In the fan-out WLCSP, the solder bumps could be located on both the filler polymer and chip surface. The concept of the fan-out WLCSP and the processes of fabricating the novel fan-out WLCSP would be described. In addition, the reliability characteristic of the fan-out WLCSP in packaging level is described by using the two-dimensional finite element model. The 25 factorial designs with the analysis of variance (ANOVA) are conducted to obtain the sensitivity information of the packaging

Fabrication process simulation and reliability improvement of high-brightness LEDs

Abstract To enhance the light extraction efficiency and thermal performance of AlGaInP light-emitting diodes (LEDs), the wafer bonding technique which can replace the GaAs substrate with other high thermal conductivity substrates was applied. However, this technique may make the film crack during either the removal etching process of the GaAs substrate or the annealing process after the GaAs removal. Therefore, this crack problem is an important issue in the reliability/yield of high-brightness LEDs. In this research, a detailed finite element model of the high-brightness AlGaInP LED, which is replaced by the GaAs substrate with high thermal conductivity substrate through the Au–In metal bonding technique, was developed and fabricated. In addition, the mechanical behavior of wafer-level metal bonding was also simulated by finite element analysis (FEA) and validated by experimental measurements. Hence, the above validated simulation technique combined with process modeling is used to understand the stress variation of the multilayer structure of AlGaInP LED during the fabrication process and to find the principal cause of the film crack.

Sapphire-removed induced the deformation of high power InGaN light emitting diodes

Thick copper films on vertically structures InGaN LEDs play a critical role after sapphire removed. The most commonly used GaN thin film growth technique is metal-organic chemical vapor deposition (MOCVD), which provides a high growth temperature, as a result, high intrinsic stress takes place between sapphire and InGaN surface. If the aforementioned metal supporter experiences a large warpage induced from intrinsic stress after sapphire removed, the subsequent processes would be very difficult to carried out. To solve the above issue, a finite element (FE) numerical simulation was employed for stress-strain behavior analysis of the LED device, the results reveal that, increasing the thickness of metal layer or implementing a pre-metal deposition buffer layer can apparently reduce the device warpage after sapphire removal. Based on the above design concepts, the experimental result depicts that, the warpage of LED wafer can be effectively reduced by 25% when metal layer increased from 62.5 um to 82.5 um, which shows good agreements with FE result, hence validates the established research methodology. And more importantly, based on the process modelling and sapphire-removal simulation-technique developed in this study, an optimal novel LED structure is designed for the reduction of process induced warpage. To conclude, a LED chip structural design-process modeling-fabrication methodology was successfully developed, and can be further contributed to the LED industry.

Numerical simulation on the mechanical characteristics of double-stranded DNA under axial stretching and lateral unzipping

The mechanical characteristics of the long-chain double-stranded DNA (dsDNA) molecule under the axial stretching and lateral unzipping are studied by the clustered atomistic-continuum method (CACM). The CACM consisted of the clustered atom method (CAM) and the atomistic-continuum method (ACM). The CAM treats the specific atomic group as the superatom, and the ACM describes the chemical binding energies between (super)atoms by virtual elements. The Newtonian based model of the dsDNA includes the superatoms of the backbones?base pairs and the virtual elements of the stacking energies?hydrogen bonds. The effective properties of the superatoms are numerically extracted from the single-stranded DNA experiments. Good agreements were achieved between the dsDNA numerical results and the single molecular experimental results. Via the simulation of stretching dsDNA, the mechanical responses, including the twisting of the backbone and variation of the elastic deformation energy and stacking energy, can be elucidated. Moreover, the predictive capability of the dsDNA CACM model is then examined. Furthermore, the dsDNA model with sequential information is subjected to the unzipping loading, and the in silico results reveal that the sliding of the backbones and the sequential dependent mechanical responses.

Measurement and simulation of interfacial adhesion strength between SiO2 thin film and III–V material

Silicon oxide material, which has low-refractive index and high isolation characteristic, has been extensively adopted into high-brightness LED structures. However, the interfacial delamination problem between GaP and SiO2 was observed in the high-brightness AlGalnP LED structure during fabrication process. It indicates that the weak adhesion strength of the GaP/SiO2 interface is a significant issue for manufacturing of LEDs. Therefore, in this study, the interfacial adhesion strength between SiO2 and III–V materials, such as GaP and GaAs, were measured by four-point bend test (4-PBT). In addition, the correspondence of the finite element models with the 4-PBT specimens was also established to predict the interfacial adhesion strength, G value, using the modified virtual crack closure technique (MVCCT) simulation technique. Comparing the predicted G value by MVCCT with experiment results of 4-PBT, the simulation results have good agreement with the experimental data.

Investigation of ssDNA molecule using clustered atomistic method and its application to the dsDNA analysis

A novel single-stranded DNA (ssDNA) model based on the clustered atomistic method is conducted to simulate the meso-mechanics of ssDNA molecule. Through the validation of the single molecular experiment, the proposed ssDNA model could represent the ssDNA molecule in different counter length, and the mechanical characteristic of the ssDNA molecule in external tensile loading could be elucidated. Furthermore, the characteristic of the validated ssDNA model is adapted in the double-stranded DNA (dsDNA) model. The simulation result of the dsDNA model under external loading reveals mechanical behavior of the dsDNA B-S structural transition. Good agreement is achieved between the numerical simulation and single molecular manipulation experimental result, and the mechanical behavior of stretching nicked dsDNA could be revealed.