LED Packaging for Lighting Applications

Design, Manufacturing, and Testing

Sheng Liu, Xiaobing Luo

• Publisher: Wiley
• Year: 2011
• Print ISBN: 9780470827833
• eBook ISBN: 9780470828403
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Since the first light-emitting diode (LED) was invented by Holonyak and Bevacqua in 1962, LEDs have made remarkable progress in the past few decades with the rapid development of epitaxy growth, chip design and manufacture, packaging structure, processes, and packaging materials. LEDs have superior characteristics such as high efficiency, small size, long life, low power consumption, and high reliability. The market for white LED is growing rapidly in various applications. It has been widely accepted that white LEDs will be the fourth illumination source to substitute the incandescent, fluorescent, and high-pressure sodium lamps. With the development of LED chip and packaging technologies, the efficiency of high power white LED will broaden the application markets of LEDs while changing the lighting concepts of our lives.

In LED Packaging for Lighting Applications, Professors Liu and Luo cover the full spectrum of design, manufacturing, and testing. Many concepts are proposed for the first time, and readers will benefit from the concurrent engineering and co-design approaches to advanced engineering design of LED products.

• One of the only books to cover LEDs from package design to manufacturing to testing
• Focuses on the design of LED packaging and its applications such as road lights
• Includes design methods and experiences necessary for LED engineers, especially optical and thermal design
• Introduces novel LED packaging structures and manufacturing processes, such as ASLP
• Covers reliability considerations, the most challenging problem for the LED industry
• Provides measurement and testing standards, which are critical for LED development, for both LED and LED fixtures
• Codes and demonstrations available from the book's Companion Website

This book is ideal for practicing engineers working in design or packaging at LED companies and graduate students preparing for work in industry. This book also provides a helpful introduction for advanced undergraduates, graduates, researchers, lighting designers, and product managers interested in the fundamentals of LED design and production.

Color version of selected figures can be found at www.wiley.com/go/liu/led

Chapter 1

Introduction

1.1 Historical Evolution of Lighting Technology

In the history of human development, lighting sources have experienced numerous changes initially from collecting natural fire sources to making fire by drilling wood. The development of lighting has witnessed the progress of human history. Fire plays an important role in human history in that it provides humans with food, warmth, and brightness. The use of fire follows the tremendous progress of human civilization. Prior to the eighteenth century, fire had always been a lighting tool for humans, the form of which developed from torch, animal oil lamp, and vegetable oil lamp to the candle, and later to the widely used kerosene lamp. Humans have never stopped exploring new lighting methods. During the use of oil lamps, the wick developed from grass to cotton to multi-strand cotton. Around the third century BC, people made candles with beeswax. In the eighteenth century, candles had been made with paraffin, and mass production of candles was enabled by using machines. In the ninteenth century, the British invented the gas lamp that was originally used as a street lamp. Because of its flickering flame, and the harmful gases that would be produced when it was extinguished, the gas lamp was not very safe and was very dangerous for indoor uses. However, through improvements, the gas lamp replaced the kerosene lamp in tens of thousands of households. These light sources all depended on the flames of the burning materials to provide light. In the eighteenth century, the invention of electricity greatly promoted the development of society, bringing new opportunities for the provision of lighting. In 1809, David Humphrey in Britain invented the arc light, using an electrical light source that was produced by the separation of two contacting carbon rod electrodes after electrifying the electrodes in the air [1]. It was used in public and was the first electric light source for practical lighting before the invention of the incandescent lamp. However, because burning produced a hissing sound and the light was too bright, it was not appropriate for indoor lighting. In 1877, a Russian invented the electric candle by modifying the structure of the arc light, but its performance was not improved. At that time, many scientists began to explore a new, safe, and warm light source.

After a long time trial, the US inventor Thomas Edison lit the world's first lamp that had practical value in October 21, 1879. During this process, Edison conscientiously summarized the failures of previous trials in the manufacturing of electrical light and developed a detailed experimental plan. Edison experimented with a variety of plants, and decided to use bamboo thread after it had been carbonized. The available lighting time after the production of the electric bulb increased to 1200 hours. The use of this bamboo thread light lasted for more than 20 years. In 1906, Edison used a tungsten filament to improve the quality of the electric bulb, and this is the incandescent lamp that has been used till now.

In 1959, the halogen tungsten circulation theory was discovered to help invent halogen tungsten lamp. Its luminous efficiency was better than the ordinary incandescent lamp.

The invention of the incandescent lamp illuminated the world, but from the perspective of energy utilization, there existed a serious drawback. Only 10–20% of the power had been converted into light, the remaining power being dissipated in the form of heat. Scientists began a new journey to explore new lighting lamps in order to make better use of energy. In 1902, Peter Cooper Hewitt invented the Mercury lamp, the photovoltaic efficiency of which was then greatly enhanced, but with obvious drawbacks. It radiated a large amount of ultra-violet rays, which was harmful to the human body and the light was too strong. Therefore it was not widely used.

In 1910, the Neon light was put into use. The light was emitted by the cold cathode glow discharge in the high-voltage field of a low pressure inert gas in the glass tube. The spectral properties of the inert gas determined the color of the neon.

Mercury lamps aroused many scientists' interests further. They found that as long as the inner wall of the mercury lamp tube was painted with a fluorescent material, then, when the ultraviolet rays of mercury were projected on it, the large amount of harmful ultraviolet rays would be excited into visible light. However, due to the poor start-up device of mercury, the scientists encountered serial failures during actual operation. In 1936, George E. Inman and other researchers produced fluorescent lamps which were different from mercury lamps by using a new start-up device. This fluorescent lamp was made by filling a glass tube with a certain amount of mercury steam, coating phosphor inside the tube wall, and installing one filament at each end of tube as an electrode. This light was brighter than the incandescent. It had a higher efficiency of power energy conversion, larger illumination area, and could be adjusted into different light colors, therefore it went into the homes of ordinary people right after it came out. Because the ingredients of fluorescent lamp were similar to those in daylight, it had been called the “daylight lamp”.

Mercury in the fluorescent tube caused environmental pollution, therefore, scientists and manufacturers of lighting began to seek new lighting sources. In the late 1960s, a high pressure gas discharge lamp such as a high pressure sodium lamp and metal halide lamp emerged, which are shown in Figure 1.1.

Figure 1.1 High-pressure sodium lamp.

1.2 Development of LEDs

As far back as 1907, Henry Joseph Round found that the SiC crystal emitted yellow light when studying the non-symmetrical current path on the contacting point of silicon carbide. The first diode should be called the Schottky diode instead of the p–n junction diode. The real application of the principles of semiconductor light-emitting into a light-emitting diode (LED) began in the early 1960s. The General Electric's Nick Holonyak Jr. used GaAs to develop the first commercial red GaAsP LED by using vapor-phase epitaxy. At that time, production yield was very low and the price was very high. In 1968, Monsanto in the USA became the first commercial entity to produce LEDs. It began to establish a factory to produce low-cost GaAsP LEDs, opening a new era of solid-state lighting. Between the years of 1968 and 1970, sales of LEDs doubled every few months. During this period, this company cooperated with Hewlett-Packard to reduce the LED production costs and improve performance. Commercialized GaAsP/GaAs LED devices produced by them became the leading products on the market. However, the luminous output of these red LEDs in that period was 0.l lm/W, much lower than 15 lm/W of the average incandescent. Monsanto's technological backbone, M. George Craford, has made great contribution to the development of LEDs. He and his colleagues successfully developed yellow LED in 1972. The method they adopted was to grow a nitrogen-doped GaAsP excitation layer on the GaAs substrate. Almost at the same time, ZnO doped red GaP LED and the N-doped GaP green LED devices appeared with a liquid phase epitaxy (LPE) growth. Therefore, Monsanto's research team could produce red, orange, yellow, and green LED devices through doping nitrogen to GaAsP by adopting vapor phase epitaxy method.

In 1972, the Hamilton Company produced the first digital watch with an LED display. In the mid-1970s, the portable digital calculator was produced by the Texas Instrument Company, and Hewlett-Packard had a seven-segment digital display composed of red GaAsP LEDs. However, the power consumption of an LED display at that time was very large. Therefore, the demand for power consumption of the liquid crystal display screen (LCDs) that appeared in the late 1970s was very strong. In the early 1980s, LCDs soon replaced LEDs in calculators and watches display.

The company producing the first color televisions, Radio Corporation of America (RCA) in July 1972 adopted metal halide vapor phase epitaxy growth (MHVPE) and Mg-doped GaN film to obtain blue, violet light with the 430 nm emission wavelength. A major technical breakthrough in the early 1980s was the development of an AlGaAs LED that could emit light with a light-emitting efficiency of 10 lm/W. This technology progress enabled LED to be used in outdoor sports information displays, as well as installation of light equipment such as a center high mount stop lamp (CHSML) in cars.

From the late 1980s to 2000, as a result of new LED technologies such as AlGaInP material technology, multi-quantum wells excitation region, and GaP transparent substrate technology, the size and shape of the naked chip (that is, a chip not packaged with other materials) have been further developed. In the early 1990s Hewlett-Packard and Toshiba successfully developed GaAlP LED devices by using metal organic chemical vapor deposition (MOCVD) technology. Because of its h...

Table of contents

• Cover
• Title Page
• Copyright
• Foreword by Magnus George Craford
• Foreword by C. P. Wong
• Foreword by B. J. Lee
• Preface
• Acknowledgments
• About the Authors
• Chapter 1: Introduction
• Chapter 2: Fundamentals and Development Trends of High Power LED Packaging
• Chapter 3: Optical Design of High Power LED Packaging Module
• Chapter 4: Thermal Management of High Power LED Packaging Module
• Chapter 5: Reliability Engineering of High Power LED Packaging
• Chapter 6: Design of LED Packaging Applications
• Chapter 7: LED Measurement and Standards
• Appendix: Measurement Method for Integral LED Road Lights Approved by China Solid State Lighting Alliance
• Index