Lead Production Research Articles

A decision support methodology for embodiment design and process chain selection for hybrid manufacturing platforms

This paper presents a methodology for the transformation of a product concept into a detailed design and manufacturing process chain for hybrid manufacturing platforms. Hybrid platforms offer new capabilities and opportunities for product design. However, they require high levels of process expertise for effective design and effective process selection. Design for hybrid manufacture is challenging as there is a requirement to understand a number of technologies, which may be highly varied. To address this challenge, a knowledge-based decision support system developed in this paper enables manufacturing expertise to be integrated into procedures for product design and process chain selection. This formalised numerical methodology is able to consider a wider range of varied manufacturing processes than any previous study. A feature-based design method is developed, which guides the designer towards an optimised product design during the embodiment design phase, and a process chain selection program is utilised to enable the effective analysis of a product design based on product evaluation criteria. The methodology has been successfully applied to the design of an LED product with internal geometries and electronics.

LED 칩 제조용 사파이어 웨이퍼 절단을 위한 내부 레이저 스크라이빙 시스템 개발

LED has added value as a lighting source in the illμminating industry because of its high efficiency and low power consμmption. In LED production processes, the chip cutting process, which mainly uses a scribing process with a laser has an effect on quality and productivity of LED. This scribing process causes problems like heat deformation, decreasing strength. The inner laser method, which makes a void in wafer and induces self-cracking, can overcome these problems. In this paper, cutting sapphire wafer for fabricating LED chip using the inner laser scribing process is proposed and evaluated. The aim is to settle basic experiment conditions, determine parameters of cutting, and analyze the characteristics of cutting by means of experimentation.

An explanation for catastrophic failures of GaN-based vertical structure LEDs subjected to thermoelectric stressing

Both accelerated life tests and engineering practices present a common behavior: LED products may encounter catastrophic failure under thermo-electric co-stressing. The present work proposes that the applied thermoelectric stresses themselves are not necessary conditions but pre-conditions for LED breakdown. The deformation and sliding of the metal lines on n-GaN under thermoelectric co-stressing cause electrodes to become dilapidated. Such dilapidated electrodes with rough edges will help to generate localized high electrical fields. The catastrophic failure occurs during the de-trapping process of space charges in and around threading dislocations when the applied electric field is removed and short circuits form between the charged dislocation cores and the tips of the dilapidated electrodes. A phenomenological relationship is given to describe the interactions between temperatures and applied electric currents on the diffusion-flux-accommodated sliding and deformation of patterned metal electrodes on vertical LEDs. Such a law is coincident with the practical trend of LED failure rates observed in accelerated life tests and engineering applications.

형광램프 대체 컨버터 내장형 LED램프의 안전성 확보방안

As products using LEDs are developed actively, also there has been large request for LED products that can replace traditional lamps like fluorescent lamps and metal halide lamps. But so far there is no proper standard that manufacturer can use and test it. As a result manufacturer can't develop retrofit LED lamps and sell it even they have technology. In this study, by analyzing control gear for fluorescent lamp that is currently used in market which is magnetic or electronic ballast, I'd like to develop proper test method by investigating compatibility between all-type control gear and LED retrofit products.

Energy efficiency: A proposal

Increase of energy efficiency in Serbia is one of the priority tasks. Sector of electric lighting offers great opportunities for increasing energy efficiency due to the rapid development of LED technology. Nowadays LED lighting is still expensive and have relatively little application in the domain of electric lighting. However, it is anticipated that LED products would soon greatly transform the electric lighting market. In recent years, LED technology has significantly improved, and constantly evolving. It is expected that advanced and future LED bulbs / lamps to be getting cheaper and with a better technical characteristics and that they will soon be dominant on the lighting market. Serbia must prepare for the LED future, creating appropriate legislation and promotion of appropriate incentive measures.

Silver plating for LED applications, technology, processes and production experience.

How the metal finishing (plating) market is meeting the technical demands of this LED market will be the subject of this paper. Specially designed Silver Plating processes for LED in order to achieve high brightness (1.8 GAM or higher) whilst also giving deposits with high reflectance will be discussed. The use of specially developed Drum Plating (Stripe plating) equipment enabling spot plating with high brightness and wider current density area will be documented as well as how these products are moving towards more Environmentally Friendly low and non-cyanide systems.

High-brightness LEDs of big chip size on multi-layer interconnects with optimized thermal dissipation and optical performance

The market share of high-brightness LEDs in general lighting has been rapidly expanding mainly owing to the continued technological advances on internal quantum efficiency, light extraction and wavelength conversion. In spite of these promising advances, there remain some key breakthroughs to be made before LED lighting technology can be fully adopted into the broad market, with emphasis on efficient thermal dissipation, higher efficacy at high brightness, and low manufacturing cost. Higher brightness requires LEDs to be operated at higher current density which results in efficacy degradation due to droop behavior and thus higher power loss into heat and shorter lifetime. Therefore a highly efficient mechanism of thermal dissipation is needed for timely conduction of heat away from the high-power LED chip. For general lighting at high brightness, a large chip size is preferable. More importantly, with larger chip size, higher brightness can be achieved at much lower current density which leads to less degradation of efficacy. However simply increasing the die size of LEDs in wafer fabrication causes significant yield loss and thus hinders the adoption of big-chip LEDs. In this paper we propose a scalable approach to enable larger chip sizes for manufacturing high efficacy & high brightness LEDs at high yield and low cost. The metric of lower cost per lumen is necessary for LEDs to be competitive to traditional light sources like fluorescent lights in the consumer market segment. About 50% of the total LED production cost is consumed by the packaging processes after the emissive device stack being fabricated. Also given the minimal thickness of the device stack, the key bottleneck for thermal dissipation resides in the packaging structure and its interface to the device stack. We address these two key challenges with a novel wafer-level packaging structure of metal contacts forming a perimeter that is integrated into the device stack, which optimizes the thermal dissipation rate from the active device stack to substrate while allowing high aperture ratio and improved light output. Our approach applies a wafer-level batch process starting from LED fabrication to packaging for internal and external light extraction as well as wavelength conversion, in order to achieve high throughput and high yield in a scalable and inexpensive manner. To improve the overall power efficiency, different materials have been selected for ohmic contacts and high reflectivity at p and n electrodes, and further developments continue to be implemented, including a current-spreading layer, large-area light extraction structure and integrated phosphor material. Flip chip packaging is chosen due to its advantage of full front-side emission, maximized aperture ratio, compact form factor, higher integration density and ease of wafer level processing. The substrates for flip chip packaging of LED chips are made of Si which was selected due to its relatively high thermal conductivity (149 W/m/K) and ease of fabrication with standard semiconductor processes. Multi-layer interconnects are patterned over the Si substrate with solder bumps built over the passivation openings for flip-chip assembly of multiple LED dies. The multi-layer dielectric stack of the substrate is designed to form dielectric mirror maximizing the reflection of emitted light back into the LED side for improved light output.

Development and future of ultraviolet light-emitting diodes: UV-LED will replace the UV lamp

Ultraviolet light-emitting diodes (UV-LEDs) have started replacing UV lamps. The power per LED of high-power LED products has reached 12 W (14 A), which is 100 times the values observed ten years ago. In addition, the cost of these high-power LEDs has been decreasing. In this study, we attempt to understand the technologies and potential of UV-LEDs.

Wafer-scale surface roughening for enhanced light extraction of high power AlGaInP-based light-emitting diodes

A new approach to surface roughening was established and optimized in this paper for enhancing the light extraction of high power AlGaInP-based LEDs, by combining ultraviolet (UV) assisted imprinting with dry etching techniques. In this approach, hexagonal arrays of cone-shaped etch pits are fabricated on the surface of LEDs, forming gradient effective-refractive-index that can mitigate the emission loss due to total internal reflection and therefore increase the light extraction efficiency. For comparison, wafer-scale FLAT-LEDs without any surface roughening, WET-LEDs with surface roughened by wet etching, and DRY-LEDs with surface roughened by varying the dry etching time of the AlGaInP layer, were fabricated and characterized. The average output power for wafer-scale FLAT-LEDs, WET-LEDs, and DRY3-LEDs (optimal) at 350 mA was found to be 102, 140, and 172 mW, respectively, and there was no noticeable electrical degradation with the WET-LEDs and DRY-LEDs. The light output was increased by 37.3% with wet etching, and 68.6% with dry etching surface roughening, respectively, without compromising the electrical performance of LEDs. A total number of 1600 LED chips were tested for each type of LEDs. The yield of chips with an optical output power of 120 mW and above was 0.3% (4 chips), 42.8% (684 chips), and 90.1% (1441 chips) for FLAT-LEDs, WET-LEDs, and DRY3-LEDs, respectively. The dry etching surface roughening approach developed here is potentially useful for the industrial mass production of wafer-scale high power LEDs.

Study on Reliability and Lifetime Prediction of High Power LEDs

With the rapid development of semiconductor lighting technology, the LED will gradually replace the traditional lighting to be the lighting market-led. However, the reliability life of LED products is the key to restrict its development. For further study on the reliability in this paper, the stress accelerated test was adapt to explore the reliability of LED, meanwhile, the failure of failure devices in the test was analyzed, and to study the correlation between the contact thermal resistance change of the LED device structure and the light fades. The finite element software was applied to simulate the work load impact on LED, and the corresponding changes in the internal structure was analyzed as well , then the establishment of the internal structure of the strain and thermal resistance were built . Ultimately, a method which is significant to short the cycle of the LED life prediction was proposed based on the ANSYS simulation. DOI : http://dx.doi.org/10.11591/telkomnika.v12i2.4415

Multiphysical Simulation of ns-Laser Ablation of Multi-material LED-structures

Structuring of multilayer stacks with ns-laser pulses is widely used in the industrial production of LEDs. These stacks are built up from several different materials each one layered upon each other. In order to thoroughly understand the physics of the structuring process a multiphysical simulation model has been developed. This model is capable to handle the beam propagation and the energy coupling into the work piece both for transparent and for absorbing materials as well as phase transitions (melting, solidifying, evaporation, condensation) of multiple different materials within the calculation domain. Furthermore a modified volume of fluid approach has been developed to calculate the material and energy flow within both the liquid and vapor phases and thus to track the free surface of the material during laser ablation. The paper gives an insight into this model illuminating the physical background of the ablation process and shows the excellent correspondence of the simulations with experimentally obtained results.

Control of vapor feed from liquid precursors to the OMVPE process

Since the perfection of the blue light emitting diode twenty years ago, LED production by MOCVD has seen strong growth. The luminous efficacy of current LED lamps is now among the highest for all light sources. In order to obtain highest efficacy, brightness and color trueness, the control of the epitaxial process by which the LED epi film is produced is crucial. As for any chemical reaction, the product of the reaction depends on the composition of the educts, the reaction temperature and pressure. The better the control of process parameters the better controlled are the properties of the product.For liquid organometallic precursors, controlled evaporation is employed to generate a vapor. To ensure that the intended concentration is delivered to the reactor with the greatest precision, it is important to understand and control three critical parameters: the temperature of the liquid, total pressure and carrier gas flow. While carrier gas flow and total pressure can be controlled with high precision, the temperature of the liquid precursor shifts considerably with carrier gas flow, fill level, and geometric factors of the thermal bath and the cylinder. We analyzed the performance of a commonly used cylinder filled with trimethylgallium (TMGa) to quantify the typical performance of on-board sources. After turning on the carrier gas, the TMGa cools by more than 1°C which results in a concentration decrease, i.e. TMGa delivery error of more than 6%. It takes about 90min or circa 50g of TMGa to reach steady state with a stable concentration. We will show how central delivery from an engineered evaporation device reduces the TMGa delivery error to less than ±0.5% allowing instant use of the vapor without waiting for a source to stabilize.

Concentration and temperature dependences of the liquid-vapor separation factor for ammonia with impurities of hydrocarbons and permanent gases

The phase equilibria for systems of ammonia-impurity (oxygen, nitrogen, methane, propane, ethane, n-butane, isobutane, propylene, carbon monoxide) were examined and concentration and temperature dependences of a separation factor, which are required for deep purification of ammonia used in the production of energy-efficient LEDs, were determined between liquid and vapor for the systems in a region of low concentrations of an impurity at an elevated pressure.

Thermal analysis of remote phosphor in LED modules

Phosphor plays an important role in LED packages by converting the wavelength of light and achieving specific color. The property and degradation of phosphor are strongly affected by the temperature. Some structural factors have been investigated in this paper and their effects are evaluated. Remote phosphor is an effective approach to improve the performance and reliability of LED modules and products. It is a trade-off that the final product design depends on both the thermal performance and the cost.

Comparing the light quality of retrofit LED products

Comparing the light quality of retrofit LED products

Efficient LED Package Design Scheme Based on Mathematical Model

The light distribution simulation of LED is very important before the production. In order to obtain the customer requirements of the light extracting rate, emitting angle, to make the LED parameters ( include chip inserted depth, reflecting bowl angle, resin encapsulation form and so on) control, it is necessary to do meaningful light distribution simulation before the production of LED. At present, in the market, there are very few companies which can produce LED chips, because of less investment, low threshold into line, most of the companies are doing package and application of LED, it is needed to do the design of LED light distribution. In this paper, based on analysis of LED thermal baseboard heat conduction equation, LED package thermal issues are explored. And an efficient LED package design scheme is proposed based on mathematical model, and the MFC simulation program of LED designed by C++ language can run in every operating system, moreover, the design of the program is of high practicability. Detailed experimental results prove the effectiveness of the proposed scheme, which will bring meaningful and valuable reference and guidance for some enterprises.

Life cycle assessment of light-emitting diode downlight luminaire—a case study

Purpose Light-emitting diode (LED) technology is increasingly being used for general lighting. Thus, it is timely to study the environmental impacts of LED products. No life cycle assessments (LCA) of recessed LED downlight luminaires exist in the literature, and only a few assessments of any type of LED light source (component, lamp and luminaire) are available.

Compression molding solutions for various high end Package and Cost savings for standard Package applications

There has been great progress on compression molding technology and equipment. This technology is used not only for most advanced semiconductor package, but also regular MAP Package which BGA type substrate and QFN molding to reduce CoO. And achieve to good reliability to each component by no resin flow. There is wide range of applications including LED production. The system is fully developed and started selling is ready to support for the mass production. Compression Molding is the next Defacto standard product in mold industry.

一种基于伪失效寿命的LED可靠性快速评价方法

An efficient and rapid reliability evaluation method of LED has been proposed.The pseudo-failure lifetime is tested and the lifetime data is analyzed by Minitab.The results show that the pseudo-failure lifetime of all samples are Weibull distribution.The reliability evaluation of LED products are made by comparing the scale parameters of Weibull distribution.This method has a certain reference value to reliability evaluation and life prediction of LED.

Activities of IEC Special View : Standardization of LED Products(<Special Issue>Towards Standardization of LED Lighting-Direction of Japan's Strategy for Globalization)

Activities of IEC Special View : Standardization of LED Products(<Special Issue>Towards Standardization of LED Lighting-Direction of Japan's Strategy for Globalization)