Manufacturing Of Light Emitting Diodes Research Articles

Sapphire Substrate Geometrical Effects on III-N Blue LED Material Properties

Solid-state lighting modules based upon III-N light-emitting diodes (LEDs) are now progressing towards widespread adoption in residential and commercial applications. LED manufacturers are driving die performance and yield upwards while reducing cost. However, color binning due to the sensitivity of the human eye response, which can resolve differences in dominant wavelength within a 2 nm range, remains one of the primary yield and cost limiters. As we continue to improve and understand growth process-related reproducibility, we have observed that some of the within-wafer and wafer-to-wafer characteristics cannot be explained through known physical phenomena from the epitaxy, and are more likely related to substrate properties.In this presentation, we will analyze a set of experiments designed to understand the effect of (0001) sapphire c-plane substrate physical dimensions (thickness, diameter, bow/warp/TTV, edge beveling) and crystal properties (misorientation, surface roughness) on uniformity and reproducibility of constituent LED layers. Our initial studies have found that precisely controlled crystal misorientation (offcut) towards the m-plane is a significant factor influencing wafer-to-wafer peak wavelength variation, GaN surface roughness, and p-doping levels. Quantitative analysis of these results with respect to variation in typical substrate manufacturing capabilities will be presented; the trends are in agreement with the materials characteristics explored in our previous studies [1, 2]. Warp and bow are critical parameters for control over GaN material characteristics. Furthermore, tight control over the total thickness variation (TTV) is needed to obtain highly uniform, repeatable sub-micron dimensions used to create current patterned substrate (PSS) wafers. [1] D. Lu, D.I. Florescu, D.S. Lee, V. Merai, J.C. Ramer, A. Parekh, and E.A. Armour, “Sapphire substrate misorientation effects on GaN nucleation layer properties”, J. Crystal Growth 272:353, (2004).[2] D. Lu, D.I. Florescu, D.S. Lee, V. Merai, A. Parekh, J.C. Ramer, S.P. Guo, and E. Armour, “Advanced characterization studies of sapphire substrate misorientation effects on GaN-based LED device development”, Phys. Stat. Sol.(a) 200:71, (2003).

Enhancing mathematical programming models to account for demand priorities increasing as a function of delivery date

Linear and mixed integer programs are frequently used to allocate resources to support a prioritized statement of demands or needs. This paper describes how to enhance these mathematical programming formulations to reflect the dynamic relative importance of demands, namely the priorities of demands – relative to other objectives – increasing as a function of the time of demand fulfillment. We illustrate the modeling using data from a light-emitting diode manufacturer from Taiwan.

Research progress of substrate materials used for GaN-Based light emitting diodes

GaN-based light emitting diodes (LEDs) as the third generation of lighting devices, have been rapidly developed in recent years. Substrate materials, serving as the LED manufacturing basis, have great influences on the production and application of LED. The critical characteristics of substrate affecting the design and fabrication of LED are its crystal structure, thermal expansion coefficient, thermal conductivity, optical transmittance, and electrical conductivity. In this paper, we compare several common substrate materials, namely, sapphire, silicon carbide, silicon, gallium nitride and gallium oxide, review the research progress of the substrate materials in the aspects of high quality epitaxial growths, high performance device designs and preparations of substrates, and comment on their further development.

Optimization Models for Production Planning in LG Display

This paper introduces an application for production planning based on multiple linear programming models for a light-emitting diode (LED) array assembly. The proposed method, multirank mixing (MRM) optimization, focuses on reducing the inventory level of the LED parts used for various electronic devices, while also meeting customer demands. In this industry, high inventory levels result in high scrap rates for LED parts because product models change frequently. Therefore, maintaining low inventory levels is critical. MRM optimization determines the best combination of LED parts for each assembly step, given inventory levels of LED parts with varying quality characteristics. The results of our performance testing show that our proposed method outperforms a heuristic method that requires intensive effort by human planners. When LG Display used MRM optimization at one of its LED manufacturing facilities, the scrap rate for LED packages decreased substantially.

Experimental investigation of microheat pipes for high‐power light‐emitting diode modules

A light-emitting diode (LED) is a novel electronic light source that provides a direct conversion of electrical energy into light. A typical LED power package has a heat flux of 100 W/cm2, thus high power LEDs face severe thermal challenges because of their small size and general lack of a proper thermal path. The advantage of microheat pipes (MHPs) which are largely used in heat dissipation of microdevices is based on phase change. With the trend of using a silicon wafer as the substrate in LED manufacturing, a silicon-glass MHP was fabricated for the quick spread of heat from the LEDs. Flat plate grooved MHPs are introduced. The grooves were fabricated on the silicon wafer and followed by bonding with Pyrex 7740 glass. Water was selected as the working liquid and the charge rate was 40%. The temperature test experiments were carried out to test the feasibility of the MHPs in LED heat conduction, and the preliminary experimental results indicate that the heat conductivity of MHPs without a vapour chamber is better than that of MHPs with a vapour chamber, which is even better than that of the silicon wafer.

Evaluating the impact of LED bulb development on the economic viability of ultraviolet technology for disinfection

Ultraviolet (UV) technologies have been very successful in disinfection applications due to their ability to inactivate microorganisms without producing harmful disinfection by-products. However, there have been a number of concerns associated with the use of conventional UV systems such as hazardous mercury content, high capital investment and reduced electrical efficiency. These concerns have set limitations for the use of UV processes. The study evaluates the development of light emitting diode (LED) technology as an alternative UV source over the last 5 years, analyses the projections provided by the researchers and UV LED manufacturers and presents the information in a cost model with the aim to predict the timeline at which UV LED will compete with traditional UV low pressure high output technology in the commercial market at full-scale residential and industrial disinfection applications.

The Design of High Power LED Headlamp

With the continuous development of LED(Light-Emitting Diode) manufacturing technology, the high power white LED is gradually applied in the field of all kinds of lighting .But with working time increasing of LED chips, their junctions temperature continue increasing, which lead to decrease light-emitting efficiency and reliability of LED chip, and even be failure. According to the serious heating of LED chip, this paper has been designed a fin-type aluminum radiator panels using Pro/E software. A LED constant current drive circuit is designed by using LTC3783 chip. With the ANSYS software, thermal analysis was carried out on the fin-type aluminum radiator panels, and eventually the mode of high power LED headlamps is determined. The stability of the LED constant current drive circuit is verified through experiments. The LED headlamps of 90W worked for ten hours, and the results of the experiments showed that the LED chip junctions temperature measured are less than 75°Cso we can solve heat dissipation of high power LED headlamps effectively.

Non-Destructive Inspection Methods for LEDs Using Real-Time Displaying Optical Coherence Tomography

In this study, we report the applicability of two different Optical Coherence Tomography (OCT) technologies for inspecting Light Emitting Diode (LED) structures. Sectional images of a LED were captured using a Spectral Domain OCT (SD-OCT) system and a Swept Source OCT (SS-OCT) system. Their center wavelengths are 850 and 1,310 nm, respectively. We acquired cross-sectional two dimensional (2D) images of a normal LED and extracted sectional profiles to inspect possible wire disconnection that may be present in the LED manufacturing process. The SD-OCT and SS-OCT images were compared with each other in the same sample to study their advantages. The distribution of fluorescence material was observed more clearly with the SD-OCT of 850 nm wavelength, whereas the status of wire connection was clearer in the SS-OCT images with 1,310 nm wavelength. In addition, the volume of the fluorophore space was calculated from the OCT images. This is the first report that a nondestructive optical imaging modality such as OCT can be applied to finding screen defects in LED. We expect this method can improve the inspection efficacy over traditional inspection methods such as Charged Coupled Device (CCD) camera or X-ray instruments.

Manufacturability of high power ultraviolet-C light emitting diodes on bulk aluminum nitride substrates

As the technological challenges in obtaining high power ultraviolet-C light emitting diodes (LEDs) on bulk AlN substrates are being overcome, the next challenge faced is the manufacturability. One of these challenges consists of introducing a 10×10mm substrate into a fabrication facility that is processing 2” and larger diameter substrates. This has been successfully carried out using a standard visible LED production facility that is involved in high volume manufacturing of blue LEDs. By introducing specifications on the substrates, the epitaxial wafers, and the fabrication process, the establishment of a pilot production process with pathways to high volume manufacturing has been established.

Light emitting diodes: Light engines to simplify and economize advanced microscopy

THE old adage, ‘‘A picture is worth a thousand words,’’ is especially true in biological research, with microscopic images serving to mark the development of key concepts in biology since Hooke first described ‘‘cells’’ in thin slices of cork (1). More than 400 years later, microscopic imaging still serves as a primary data source for biological research, with increasingly advanced techniques that provide information on molecular scale interactions and dynamics. Such advanced molecular imaging techniques take advantage of ever more sophisticated light sources, optics, detectors, and image processing methods, many of which can be quite complex and expensive. At the same time, new technologies and production methods, many driven by the consumer market, have resulted in key components of imaging systems becoming smaller, simpler, and cheaper. The convergence of these effects is having profound effects on our options for light sources for microscopic imaging. The properties of the illumination source are critical to many advanced optical microscopy methods. Lasers play a key role in many of these owing to the monochromatic and coherent nature of their light, plus their ability to be pulsed and otherwise controlled. However, illumination with high-pressure mercury gas discharge or xenon lamps is still the standard for most imaging applications. These light sources provide bright, broad-spectrum excitation (300–900 nm) that can be easily selected by excitation filters for fluorescent imaging applications. However, there are quite a few disadvantages that limit the wide-spread of mercury or xenon lamps-based microscopy system in biological applications. First, sometimes these traditional light sources are too bright and harmful for the living organisms being studied. Excessive brightness can cause rapid photo-bleaching of the dyes used to stain the cells/ tissues. UV light especially, if not blocked, can have significant deleterious effects on live cells. Second, there are substantial costs involved in using mercury or xenon lamps because of their relatively short lifespan. The life of a mercury lamp is usually several hundred hours, and the intensity of these lamps decays progressively during this time. In addition, gas discharge lamps require some time to warm up before lamp intensity reaches steady state. Therefore, once mercury lamps are turned on, they have to be left on for hours to enable fluorescent measurements as needed without delay, thereby further shortening the lamp lifetime. Third, there are also some hazards issues of using mercury or xenon lamps. These lamps generate a significant amount of heat and therefore introduce complications when used in a confined space. When mercury lamps die, they can explode and damage the lenses or mirrors within the lamp housing. These factors combine to make gas discharge lamps inconvenient for lab-based applications and impractical for field applications, including use in portable, miniature, or low cost imaging devices. By contrast, light-emitting diodes (LEDs) show great pro

Modeling and Simulation of LED Manufacturing Process with ExtendSim

LED (Light Emitting Diode) has many excellent features as a new lighting device, and has been widely used by far. The structure and light-emitting principle are introduced. The LED manufacturing process is explained and dynamically shown with FLASH CS. The processing line is modeled and simulated through dynamics software ExtendSim. The simulation result is analyzed and the processing line is balanced. The throughput is improved with the simulation.

Light emitting diodes reliability review

The increasing demand for light emitting diodes (LEDs) has been driven by a number of application categories, including display backlighting, communications, medical services, signage, and general illumination. The construction of LEDs is somewhat similar to microelectronics, but there are functional requirements, materials, and interfaces in LEDs that make their failure modes and mechanisms unique. This paper presents a comprehensive review for industry and academic research on LED failure mechanisms and reliability to help LED developers and end-product manufacturers focus resources in an effective manner. The focus is on the reliability of LEDs at the die and package levels. The reliability information provided by the LED manufacturers is not at a mature enough stage to be useful to most consumers and end-product manufacturers. This paper provides the groundwork for an understanding of the reliability issues of LEDs across the supply chain. We provide an introduction to LEDs and present the key industries that use LEDs and LED applications. The construction details and fabrication steps of LEDs as they relate to failure mechanisms and reliability are discussed next. We then categorize LED failures into thirteen different groups related to semiconductor, interconnect, and package reliability issues. We then identify the relationships between failure causes and their associated mechanisms, issues in thermal standardization, and critical areas of investigation and development in LED technology and reliability.

Optimization of UV laser scribing process for light emitting diode sapphire wafers

Billions of light emitting diodes (LEDs) are used today in traffic control, automotive headlights, flat panel display technology, mobile devices, back lighting, projection, and general illumination applications. With the dramatic growth in LEDs, manufacturers are looking for technologies to increase production yield and decrease cost. Sapphire wafer singulation into miniature dies is one of the critical steps used in blue LED manufacturing. Typical dicing techniques used in wafer singulation process include laser dicing, laser scribing and breaking, mechanical scribing and breaking, and diamond blade sawing. In recent years, laser scribing and breaking has proven to be very efficient for volume LED manufacturing. In this paper, we have characterized the effect of 355 nm Q-switched diode-pumped solid-state (DPSS) laser parameters such as fluence, pulse width, and repetition rate on laser scribing process by measuring sapphire wafer cutting depth and scribe kerf width. Furthermore, we have also explored the techniques to increase process efficiency while maintaining quality of scribes using different laser sources.

ChemInform Abstract: Synthesis and Properties of Polysilanes: Versatile New Organic Materials

The most important synthetic methods including the Wurtz reaction, the activated alkali metal mediated reductive coupling, the electrochemical polymerization of dichlorosilanes using sacrificial anodes, the anionic ring-opening polymerization of tetrasilacyclobutanes and of masked disilenes, and the transition metal (Ti, Zr, Hf) catalyzed dehydrogenative coupling of hydrosilanes are briefly overviewed. A short discussion of the thermal and electronic properties of polysilanes allows for anticipating respectively their excellent processability and their technological applications. Among the latter, the most important ones appear to be microlithography for electronics, manufacture of light-emitting diodes (LEB) for various display devices, and fabrication of high tensile strength silicon carbide fibers, as well as heat resistant machineable objects. Other promising potential applications in optoelectronics are based on the interesting nonlinear optical (NLO) and photoconductive properties of suitably substituted polysilanes.

THERMAL MANAGEMENT SOLUTIONS FOR THE LED MARKET

High-brightness light emitting diodes (LEDs) are challenged with thermal management issues due to increased power and reduced surface area. This has led to the need for new materials with higher thermal conductivity that can quickly remove the heat from the active layer. LORD Corporation has developed two new thermal management materials, a “no pump-out” thermal grease and a low modulus die attach adhesive, as solutions to the heat dissipation problems facing LED manufacturers. These innovative technologies will help engineers solve complex fundamental thermal management problems. A new 4 W/mK silicone thermal grease has been developed with significant resistance to in-package bleed-out or pump-out eliminating the reliability problem most commonly encountered with traditional thermal greases. A new 10–20 W/mK thermal epoxy adhesive has also been developed creating a new class of flexible adhesives with high adhesion. This combination allows the new LORD die attach adhesive to not only effectively transfer heat out of the package, but also to dissipate the stress caused by thermal expansion and contraction during thermal cycling thereby affording improved package reliability.

UV enhanced substrate conformal imprint lithography (UV-SCIL) technique for photonic crystals patterning in LED manufacturing

The global LED (light emitting diode) market reached 5 billion dollors in 2008 and will be driven towards 9 billion dollors by 2011 [1]. The current applications are dominated by portable device backlighting, e.g. cell phones, PDAs, GPS, laptop etc. In order to open the general lighting market doors the luminous efficiency needs to be improved significantly. Photonic crystal (PhC) structures in LEDs have been demonstrated to enhance light extraction efficiency on the wafer level by researchers [2]. However, there is still a great challenge to fabricate PhC structures on LED wafers cost-effectively. Nanoimprint lithography (NIL) [3] has attracted considerable attentions in this field due to its high resolution, high throughput and low cost of ownership (CoO). However, the current NIL techniques with rigid stamps rely strongly on the substrate flatness and the production atmosphere. Those factors hinder the integration of NIL into high volume production lines. UV-NIL with flexible stamps [4], e.g. PDMS stamps, allows the large-area imprint in a single step and is less-sensitive to the production atmosphere. However, the resolution is normally limited due to stamp distortion caused by imprint pressure. A novel NIL technique developed by Philips Research and Süss MicroTec, substrate conformal imprint lithography (SCIL), bridges the gap between UV-NIL with rigid stamp for best resolution and soft stamp for large-area patterning. Based on a cost-effective upgrade on Süss mask aligner, the capability can be enhanced to nanoimprint with resolution of down to sub-10 nm on an up to 6 inch area without affecting the established conventional optical lithographic processes on the machine. Benefit from the exposure unit on the mask aligners, the SCIL process is now extended with UV-curing option, which can help to improve the throughput dramatically. In this paper, the fabrication of photonic crystal structures with SCIL technique on Süss MA6 mask aligner is demonstrated. In addition, the industrialization considerations of UV-SCIL process in high volume manufacturing are briefly discussed.

The influence of exchange rate gains or losses on the operational efficiency of the Taiwanese LED industry — an application of DEA

This study evaluates the efficiency of twenty one manufacturers of Light Emitting Diodes (LED) in Taiwan from 2003 to 2006 through three types of DEA models, BCC, Super-SBM, and Malmquist index. Due to the fact that the traditional DEA model can not address the problem of ranking when many DMUs have efficiency value of 1, Super-SBM-V model has been adopted. Furthermore, since the Taiwan LED manufacturers have depended on foreign trade, exchange rate gains or losses have a great influence on their operations. Reviewing both domestic and abroad studies show that the Malmquist productivity index has rarely been used to evaluate the influence of exchange rate gains or losses on LED manufacturers performances. This study adopted exchange rate gains or losses as a variable to examine the impact of these manufacturers’ productivity due to exchange rate gains or losses. Hopefully, the findings can serve as a reference for manufacturers to modify their developmental strategies. The findings of this study shows that exchange rate gains or losses in fact influenced performance. The connection between exchange rate gains or losses and operational efficiency has been strengthened on a yearly basis.

A case-based decision support system for product development

Companies that are developing new products are now facing increasing global competition. Continual success in the marketplace depends upon how efficiently and effectively a company is able to respond to customers' ever changing needs. In this article, a Case-based Product-development Enhancement System (CPES) is designed to help manufacturing industry to support product development by retrieving and analysing useful knowledge and solutions in a timely and cost-effective manner. CPES provides important support for, and information on product development, and enhances effectiveness in product development strategies by integrating techniques such as data warehouse, Online Analytical Processing and Case-Based Reasoning. When applying CPES in a light emitting diode manufacturer, it was possible to maximise resource utilisation, increase work efficiency and greatly reduce cost in product development.

Shadow-Free Moire Interferometer with Dual Projection for In-Line Inspection of Light Emitting Diodes

In small-sized liquid crystal display markets, small light-emitting diodes (LEDs) are generally used for the illumination part of backlight units. For their uniform light-emitting, the volumetric size control of each pocket is crucial to the LED manufacturing process because the pocket fills with the transparent encapsulating material which plays a role in focusing the emitted light ray from the LED chip and protecting the LED wafer chip and wire-bonding. A special three-dimensional vision system is presented for volumetric inspection of the LED pocket with concave shape. Conventional measurement techniques of measuring the LED pocket easily produce noisy results due to the shadow problem-induced geometric configuration of the imaging part and pattern projecting part. In order to prevent this effect, the proposed sensor system utilizes a dual projection system. By using two measurement results acquired from pattern projections switching with different incident angles, shadow-free results can be acquired. In this article, we will describe the sensor system's principle and the sensor fusion algorithm combining two measurement results efficiently. A series of experiments is conducted to verify the performance of this proposed system. The measurements results show very satisfactory inspection performance and they are discussed in depth.

The Neural‐Network Approach to Recognize Defect Pattern in LED Manufacturing

This paper presents neural network‐based recognition system for automatic light emitting diode (LED) inspection. The back‐propagation neural network (BPNN) is proposed and tested. The current‐voltage (I‐V) characteristic data of LED from the inspection process is used for the network training and testing. This study selects 300 random samples as network training and employs 100 samples as network testing. The experimental results show that if the classification work is doen well, the accuracy of recognition is 100 per cent, and the testing speed of the proposed recognition system is amost one half faster than the traditional inspection system does. The proposed neural‐network approach is successfully demonstrated by real data sets and can be effectively developed as a recognition system for a practical application purpose.