From LED to Solid State Lighting E-Book

S. W. Ricky Lee

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 417

Veröffentlichungsjahr: 2021

Beschreibung

FROM LED TO SOLID STATE LIGHTING

A comprehensive and practical reference complete with hands-on exercises and experimental data

In From LED to Solid State Lighting: Principles, Materials, Packaging, Characterization, and Applications, accomplished mechanical engineers Shi-Wei Ricky Lee, Jeffery C. C. Lo, Mian Tao, and Huaiyu Ye deliver a practical overview of the design and construction of LED lighting modules, from the fabrication of the LED chip to the LED modules incorporated in complete LED lighting fixtures. The distinguished authors discuss the major advantages of solid-state lighting, including energy savings, environmental friendliness, and lengthy operational life, as well as the contributions offered by the packaging of light-emitting diodes in the pursuit of these features.

Readers will discover presentations of the technical issues that arise in packaging LED components, like interconnection, phosphor deposition, and encapsulation. They’ll also find insightful elaborations on optical design, analysis, and characterization. Discussions of LED applications, technology roadmaps, and IP issues round out the included material.

This important book also includes:

• Thorough introductions to lighting, photometry, and colorimetry, the fundamentals of light-emitting diodes, and the fabrication of LED wafers and chips
• Practical discussions of the packaging of LED chips, wafer-level packaging of LED arrays, and optical and electrical characterization
• Comprehensive explorations of board-level assembly and LED modules and optical and electrical characterization
• In-depth examinations of thermal management, reliability engineering for LED packaging, and applications for general lighting

Perfect for post-graduate students and practicing engineers studying or working in the field of LED manufacturing for solid state lighting applications, From LED to Solid State Lighting: Principles, Materials, Packaging, Characterization, and Applications is also an indispensable resource for managers and technicians seeking a one-stop guide to the subject.

Leseprobe

Table of Contents

Cover

Title Page

Copyright

Preface

About the Authors

1 LEDs for Solid‐State Lighting

1.1 Introduction

1.2 Evolution of Light Sources and Lighting Systems

1.3 Historical Development of LEDs

1.4 Implementation of White Light Illumination with an LED

1.5 LEDs for General Lighting

References

2 Packaging of LED Chips

2.1 Introduction

2.2 Overall Packaging Process and LED Package Types

2.3 Chip Mounting and Interconnection

2.4 Phosphor Coating and Dispensing Process

2.5 Encapsulation and Molding Process

2.6 Secondary Optics and Lens Design

References

3 Chip Scale and Wafer Level Packaging of LEDs

3.1 Introduction

3.2 Chip Scale Packaging

3.3 Enabling Technologies for Wafer Level Packaging

3.4 Designs and Structures of LED Wafer Level Packaging

3.5 Processes of LED Wafer Level Packaging

References

4 Board Level Assemblies and LED Modules

4.1 Introduction

4.2 Board Level Assembly Processes

4.3 Chip‐on‐Board Assemblies

4.4 LED Modules and Considerations

References

5 Optical, Electrical, and Thermal Performance

5.1 Evaluation of Optical Performance

5.2 Power Supply and Efficiency

5.3 Consideration of LED Thermal Performance

References

6 Reliability Engineering for LED Packaging

6.1 Concept of Reliability and Test Methods

6.2 Failure Analysis and Life Assessment

6.3 Design for Reliability

References

7 Emerging Applications of LEDs

7.1 LEDs for Automotive Lighting

7.2 Micro‐ and Mini‐LED Display

7.3 LED for Visible Light Communication

References

8 LEDs Beyond Visible Light

8.1 Applications of UV‐LED

8.2 Applications of IR‐LEDs

8.3 Future Outlook and Other Technology Trends

References

Index

End User License Agreement

List of Tables

Chapter 1

Table 1.1 Recipes of semiconductor compounds for LEDs.

Chapter 2

Table 2.1 Thermal conductivity of common packaging materials.

Chapter 3

Table 3.1 KOH vs. TMAH.

Table 3.2 Effect of angular misalignment on incline plane roughness.

Chapter 4

Table 4.1 PCB core material properties.

Table 4.2 Dielectric layer filler material properties [13].

Table 4.3 Experiment test matrix (MCPCB and FR4 with thermal vias thermal pe...

Table 4.4 Solder paste type (according to particle size) [27].

Table 4.5 Reflow profile parameters (for Cree XLamp XB‐D) [17].

Chapter 5

Table 5.1 Radiometric quantities (SI).

Table 5.2 Photometric quantities (SI).

Table 5.3 The original test color samples (TCS) for evaluating the color‐ren...

Chapter 6

Table 6.1 The meaning of different

β

values.

Chapter 8

Table 8.1 Band gap energy and emission wavelength ranges that can be achieve...

Table 8.2 Feature of mercury lamps and UV‐LED lamps.

Table 8.3 The performance of Blue LEDs and UV‐LEDs.

Table 8.4 Crystal lattice mismatch and thermal mismatch between AlN and vari...

Table 8.5 Some performance parameters of the IR‐LED [75].

List of Illustrations

Chapter 1

Figure 1.1 Structure of a typical diode.

Figure 1.2

I

–

V

characteristics of a typical diode.

Figure 1.3 LED under forward bias.

Figure 1.4 Mechanism of electroluminescence.

Figure 1.5 Four generations of lighting systems.

Figure 1.6 Edison's patent of incandescent lightbulb.

Figure 1.7 Edison's first successful lightbulb demonstrated to the public....

Figure 1.8 Examples of LED applications.

Figure 1.9 The first demonstration of electroluminescence with SiC crystal....

Figure 1.10 Nobel Prize in Physics 2014 honored the blue light LED inventors...

Figure 1.11 White light illumination with RGB LEDs.

Figure 1.12 White light illumination with phosphor‐converted LED.

Figure 1.13 Blue light LED with yellow phosphor for white light illumination...

Figure 1.14 Mechanism of white light generation with blue–yellow color mixin...

Figure 1.15 Percentage of lighting energy consumption in overall electricity...

Figure 1.16 Application of solid‐state lighting in a Hong Kong subway train....

Figure 1.17 Energy saving due to the implementation of SSL in the subway sys...

Chapter 2

Figure 2.1 Functions of the package.

Figure 2.2 Overall LED packaging process.

Figure 2.3 Typical PTH components.

Figure 2.4 Typical PTH LED component.

Figure 2.5 LED lead frame and typical SMD LED components: (a) LED lead frame; ...

Figure 2.6 Ball grid array (BGA) and land grid array (LGA).

Figure 2.7 High‐power LED package.

Figure 2.8 Cross‐section inspection of die attach adhesive with less metal con...

Figure 2.9 Cross‐section inspection of die attach adhesive with more metal con...

Figure 2.10 Die attach adhesive dispensing pattern.

Figure 2.11 Insufficient die attach adhesive material.

Figure 2.12 Effect of chip misalignment: (a) well aligned; (b) misaligned by 1...

Figure 2.13 Die mounting process (die attach adhesive).

Figure 2.14 Solder wire dispensing method.

Figure 2.15 Solder paste method.

Figure 2.16 Solder preforms.

Figure 2.17 Solder preform method.

Figure 2.18 Au20Sn eutectic die bonding.

Figure 2.19 Effect of bonding surface roughness [13]: (a) AFM inspection of le...

Figure 2.20 Typical gold wire bonds.

Figure 2.21 Stitch bond on gold stud.

Figure 2.22 Reverse wire bond.

Figure 2.23 Schematic layout of flip‐chip LEDs.

Figure 2.24 Adhesive type flip‐chips: (a) conductive adhesive; (b) anisotropic...

Figure 2.25 Flip‐chip LED with Au20Sn eutectic solder bonded on silicon substr...

Figure 2.26 Gold stud bump (before coining).

Figure 2.27 Gold stud bump (after coining).

Figure 2.28 Flip‐chip with gold stud bump (thermo‐sonic).

Figure 2.29 Phosphor particles.

Figure 2.30 Dispersed dispensing method: (a) in‐cup; (b) lens type.

Figure 2.31 Dripping and stringing in needle dispensing.

Figure 2.32 Dispensing vs. jetting.

Figure 2.33 Compression molding.

Figure 2.34 Conformal coating: (a) in‐cup; (b) lens type.

Figure 2.35 Electrophoretic deposition setup.

Figure 2.36 Spray coating setup.

Figure 2.37 Spray coating [45].

Figure 2.38 Stencil printing method.

Figure 2.39 Conformal phosphor coating by stencil printing method.

Figure 2.40 Conformal coating with phosphor preform.

Figure 2.41 Quasi‐conformal coating: (a) 3528; (b) K1.

Figure 2.42 Effect of temperature on phosphor emission spectrum.

Figure 2.43 Remote phosphor configuration.

Figure 2.44 Package level remote phosphor configuration: (a) in‐cup; (b) lens ...

Figure 2.45 Plastic lens for K1 emitter.

Figure 2.46 Encapsulant filling with lens.

Figure 2.47 Lens formation by compression molding: (a) mold; (b) silicone lens...

Figure 2.48 Secondary optics (total internal reflection lens).

Figure 2.49 TIR lenses: (a) collimating lens; (b) side‐emitting lens.

Figure 2.50 Optical simulation procedures.

Figure 2.51 Optical processes involve in simulation.

Figure 2.52 Effect of number of rays on radiant power calculation.

Figure 2.53 Effect of number of rays on light pattern.

Chapter 3

Figure 3.1 Miniaturization trend in the LED industry.

Figure 3.2 Current industrial practice of LED WLP [6].

Figure 3.3 LED wafer level packaging process.

Figure 3.4 Samsung PoC LED, LM101A.

Figure 3.5 Schematic diagram of PoC LED.

Figure 3.6 APT white LED chip CSP.

Figure 3.7 Schematic diagram of FEC LED.

Figure 3.8 Samsung FEC LED, LH181B.

Figure 3.9 Nonuniform PR thickness by spin coating on a wafer with cavities.

Figure 3.10 Standard photolithography process.

Figure 3.11 Lift‐off process.

Figure 3.12 Silicon crystal structure.

Figure 3.13 Anisotropic vs. isotropic etching.

Figure 3.14 Crystal plan orientations.

Figure 3.15 Anisotropic silicon wet etching process flow.

Figure 3.16 Anisotropic silicon wet etching result.

Figure 3.17 Typical DRIE process flow.

Figure 3.18 Through silicon via by DRIE.

Figure 3.19 Via filling process.

Figure 3.20 Copper‐filled TSV.

Figure 3.21 Electro‐copper and solder plating process flow.

Figure 3.22 Zincation process.

Figure 3.23 Electroless nickel plating results.

Figure 3.24 Silicon stencil.

Figure 3.25 Stencil design.

Figure 3.26 Regular and reverse wire bond.

Figure 3.27 Reverse wire bond without gold stud (side view).

Figure 3.28 Reverse wire bond without gold stud (close‐up at LED die bond pad)...

Figure 3.29 Reverse wire bond with gold stud (side view).

Figure 3.30 Reverse wire bond with gold stud (close‐up at LED die bond pad).

Figure 3.31 Aligned submount and stencil.

Figure 3.32 Stencil printing process flow.

Figure 3.33 Stencil printing results.

Figure 3.34 Three‐dimensional X‐ray inspection.

Figure 3.35 Schematic diagram of waffle pack design.

Figure 3.36 Remote phosphor layer fabrication process flow.

Figure 3.37 Waffle pack molds.

Figure 3.38 Prefabricated remote phosphor film.

Figure 3.39 Waffle pack assembly process flow.

Figure 3.40 LED panel with waffle pack phosphor film.

Figure 3.41 Cross‐section inspection.

Figure 3.42 Uniform white light from LED WLP with waffle pack.

Figure 3.43 Chromaticity coordinates of waffle packs panels with different ble...

Figure 3.44 LED WLP with remote phosphor layer.

Figure 3.45 Mold design.

Figure 3.46 Silicone lens with a step.

Figure 3.47 Remote phosphor deposition results.

Figure 3.48 LED array panel with remote phosphor.

Figure 3.49 Uniform white light from LED array panel.

Figure 3.50 Moldless encapsulation method.

Figure 3.51 Silicone dome array (2.8 mm × 2.8 mm).

Figure 3.52 LED WLP with moldless encapsulation.

Figure 3.53

H

/

L

measurement.

Figure 3.54 Silicone dome geometry control (2.8 mm × 2.8 mm).

Figure 3.55 Silicone dome geometry control (5 mm × 5 mm).

Figure 3.56 Effect of silicone volume on geometry (2.8 mm × 2.8 mm).

Figure 3.57 Effect of silicone volume on geometry (5 mm × 5 mm).

Figure 3.58 4 × 4 LED panel array mask layout.

Figure 3.59 4 × 4 LED panel microfabrication process.

Figure 3.60 4 × 4 LED panel array.

Figure 3.61 Rough (1 0 0) plane.

Figure 3.62 Effect of angular misalignment (

scanning electron microscope

(

SEM

)...

Figure 3.63 Effect of angular misalignment on incline plane roughness.

Figure 3.64 Effect of angular misalignment (undercut).

Figure 3.65 LED WLP with copper‐filled TSVs.

Figure 3.66 Multichip LED WLP with through silicon slots.

Figure 3.67 LEDs connection methods.

Figure 3.68 Through silicon slots by DRIE.

Figure 3.69 Aluminum layer deposition and patterning.

Figure 3.70 Passivation layer deposition and patterning.

Figure 3.71 Plating results.

Figure 3.72 Singulated package assembled on a PCB.

Figure 3.73 Cross‐section inspection.

Figure 3.74 LED WLP with a cavity (schematic cross‐section view).

Figure 3.75 LED WLP with a cavity (schematic top view).

Figure 3.76 Submount microfabrication process flow.

Figure 3.77 Copper pillars exposed from the cavity bottom.

Figure 3.78 Solder bumps on the copper pillars after reflow.

Figure 3.79 Submount with copper‐filled TSVs and a cavity.

Figure 3.80 LED chip mounted in the cavity.

Figure 3.81 After phosphor printing.

Figure 3.82 Cross‐section inspection of final package.

Figure 3.83 Uniform white light from the package.

Figure 3.84 Lightbulb with LED WLP panel.

Figure 3.85 LED WLP panel vs. COB.

Figure 3.86 Radiation power distribution.

Figure 3.87 Color temperature distribution.

Figure 3.88 Illuminance measurement results.

Chapter 4

Figure 4.1 Heat dissipation paths of conventional IC assemblies.

Figure 4.2 Heat dissipation path of LED assemblies.

Figure 4.3 MCPCB schematic diagram.

Figure 4.4 MCPCB cross‐section.

Figure 4.5 MCPCB with PTH.

Figure 4.6 Cree XLamp bond pad layout [17].

Figure 4.7 FR4 PCB with thermal vias.

Figure 4.8 PTH with conformal copper layer.

Figure 4.9 Void trapped in thermal vias.

Figure 4.10 Thermal vias filling defects.

Figure 4.11 Full‐filled thermal via by LuMac Copper Systems.

Figure 4.12 FR4 PCBs with thermal vias.

Figure 4.13 Cross‐section inspection of test samples.

Figure 4.14 Junction temperature measurement results.

Figure 4.15 Overall thermal resistance measurement results.

Figure 4.16 PCB thermal resistance measurement results.

Figure 4.17 PTH LED assembly.

Figure 4.18 Typical wave soldering process [26].

Figure 4.19 Wave soldering [26].

Figure 4.20 Solder particles in solder paste.

Figure 4.21 Solder paste printing results.

Figure 4.22 Typical reflow profile [28].

Figure 4.23 Board level assembly with multiple LED components.

Figure 4.24 LED COB assembly structure.

Figure 4.25 Multiple shadows from LED assembly with discrete LED components....

Figure 4.26 LUXEON COB [32].

Figure 4.27 SMD vs. COB (heat dissipation path).

Figure 4.28 Al

2

O

3

vs. AlN (radiant flux comparison) [40].

Figure 4.29 Glob top dispensing [41].

Figure 4.30 Dam on COB substrate.

Figure 4.31 LED COB assembly fabrication process.

Figure 4.32 COB assembly with remote phosphor layer.

Figure 4.33 COB assembly with remote phosphor plate.

Figure 4.34 COB encapsulant by molding.

Figure 4.35 Effect of housing size on temperature.

Figure 4.36 Effect of inclination on temperature.

Chapter 5

Figure 5.1 Photopic (black) and scotopic (gray) luminosity functions. The so...

Figure 5.2 The CIE 1931 color matching function.

Figure 5.3 Comparison between the response of M cone cell and the

y

tristimu...

Figure 5.4 The CIE 1931 chromaticity diagram.

Figure 5.5 MacAdam ellipses on CIE 1931 chromaticity diagram.

Figure 5.6 MacAdam ellipses on CIE 1976 chromaticity diagram.

Figure 5.7 The Planckian locus on CIE 1931 chromaticity diagram [5].

Figure 5.8 Comparison of the color presented by high pressure sodium lamp (o...

Figure 5.9 Philips research lab. 12 V 16A tungsten ribbon calibration lamp [...

Figure 5.10 Philips' commercial desktop spectrometer (Instruments System® CA...

Figure 5.11 The light path from the light source under test to the photodete...

Figure 5.12 Typical polar light pattern of a 5050 LED component [15].

Figure 5.13 Typical integrating sphere system including a spectrometer (Inst...

Figure 5.14 Typical calibration procedures for the

K

‐factor.

Figure 5.15 Junction temperature measurement procedures by the forward volta...

Figure 5.16 Typical thermal resistor–capacitor pair network.

Figure 5.17 Mentor Graphic T3Ster

®

for the measurement of the forward v...

Figure 5.18 Electrical configuration for the driving current, sense current,...

Chapter 6

Figure 6.1 Three major steps of reliability engineering.

Figure 6.2 Comparison of max temperature on LED surface and junction tempera...

Figure 6.3 The real‐time on‐site light output monitoring system for LED reli...

Figure 6.4 Typical thermal cycling chamber (left) and humidity chamber (righ...

Figure 6.5 Three‐dimensional X‐ray imaging of voids in a thermal via of a PC...

Figure 6.6 A simple fishbone example for the cause of gold wire bond breakin...

Figure 6.7 The failure rate versus time of a common product.

Figure 6.8 Key activity in design for reliability [7].

Chapter 7

Figure 7.1 Forecast about the development of micro‐LED displays [25].

Figure 7.2 Schematic diagram of the model for the LCD with a mini‐LED backli...

Figure 7.3 Light modulation of mini‐LED backlit liquid crystal display (LCD)...

Figure 7.4 Conceptual diagram of scaling up display size based on same angul...

Figure 7.5 The 27 “gaming monitor and the 2” VR display of AUO [25].

Figure 7.6 (a) The 16.7 in curved automotive display with direct backlight s...

Figure 7.7 Optical microscope image (a) of a micro‐display fabricated from a...

Figure 7.8 Representative micro‐displays programmed onto the flip‐chip blue ...

Figure 7.9 Model of LED display unit [33].

Figure 7.10 Schematic diagram for configuration of full color micro‐LED disp...

Figure 7.11 Two approaches used to build micro‐LED displays. Both methods st...

Figure 7.12 Integral imaging based on a mini‐LED [33].

Figure 7.13 Typical automotive application [43].

Chapter 8

Figure 8.1 The electromagnetic spectrum of light [1].

Figure 8.2 Structural diagram of a face‐up (top) and flip‐chip (bottom) UV‐L...

Figure 8.3 Emission spectra of AlGaN, InAlGaN, and InGaN

more quantum well

(

Figure 8.4 Cross‐sectional diagram of lead‐frame‐based plastic (LFP) packagi...

Figure 8.5 Thermal resistance network for LFP (up) and COB packaging (down) ...

Figure 8.6 Packaging‐free UV‐LED solidification light source module [15]....

Figure 8.7 “UV‐LEDs: Technology & Application Trends”, a report from Yole Dé...

Figure 8.8 Engineering prototype of UV‐curing system [32].

Figure 8.9 The power degradation of packaged deep UV‐LED at 20 mA dc and 25 ...

Figure 8.10 The electromagnetic spectrum of light.

Figure 8.11 (a) Photograph of a standard detector and the lensed detector; (...

Figure 8.12 (a) LED and PD detector structure; (b) LED and PD detector mount...

Figure 8.13 Experimental setup employed to assess the

quantum well infrared

...

Figure 8.14 Concept of proposed system [81].

Figure 8.15 An example of a street intersection and traffic controller [83]....

Figure 8.16 Electronic adjustable current circuit driver for LED and IR/RED ...

Guide

Cover

Table of Contents

Title Page

Copyright

Preface

About the Authors

Begin Reading

Index

WILEY END USER LICENSE AGREEMENT

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From LED to Solid State Lighting

Principles, Materials, Packaging, Characterization, and Applications

Shi‐Wei Ricky Lee

Chair Professor, Department of Mechanical and Aerospace EngineeringDirector, HKUST Foshan Research Institute for Smart ManufacturingChairman, HKUST SZ-HK Collaborative Innovation Research InstituteActing Dean, Systems Hub, HKUST (GZ)The Hong Kong University of Science and TechnologyKowloon, HKSAR, China

Jeffery C.C. Lo

Assistant Director, HKUST Foshan Research Institute for Smart ManufacturingProgram Manager, Electronic Packaging LaboratoryThe Hong Kong University of Science and TechnologyKowloon, HKSAR, China

Mian Tao

Lead Engineer, Technology Division, Group of Integrated Circuits and SystemsHong Kong Applied Science and Technology Research InstituteNew Territories, HKSAR, China

Huaiyu Ye

Associate Professor, School of MicroelectronicsSouth University of Science and TechnologyShenzhen, Guangdong, China

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Library of Congress Cataloging‐in‐Publication Data

Names: Lee, Shi‐Wei Ricky, author. | Lo, Jeffery C. C., author. | Tao,  Mian, author. | Ye, Huaiyu, author.Title: From LED to solid state lighting : principles, materials, packaging,  characterization, and applications / Shi‐Wei Ricky Lee, Jeffery C. C. Lo,  Mian Tao, Huaiyu Ye.Description: Hoboken, NJ : Wiley, 2022.Identifiers: LCCN 2021003853 (print) | LCCN 2021003854 (ebook) | ISBN  9781118881477 (hardback) | ISBN 9781118881583 (adobe pdf) | ISBN  9781118881552 (epub)Subjects: LCSH: Light emitting diodes.Classification: LCC TK7871.89.L53 L4365 2022 (print) | LCC TK7871.89.L53  (ebook) | DDC 621.32/8–dc23LC record available at https://lccn.loc.gov/2021003853LC ebook record available at https://lccn.loc.gov/2021003854

Cover Design: WileyCover Image: © ModernewWorld/DigitalVision/Getty Images

Preface

The light‐emitting diode (LED) is a semiconductor device based on the effect of electroluminescence, which is a form of energy conversion from electrons directly to photons. Although the fundamental principle of physics was discovered more than 100 years ago, devices for actual applications were not invented until the 1960s. It took another 30 years for researchers to complete the visible light spectrum of LEDs with various recipes of semiconductor compounds. By the turn of the century, owing to the development of high‐brightness and high‐power LEDs with white light illumination, the era of solid‐state lighting (SSL) began. LED evolved to be the light source of the fourth generation of lighting systems since the turn of the millennium.

Although diodes seem to be the simplest solid‐state device, the manufacturing of LED light sources actually involves many fabrication processes and supply chains. Starting from the preparation of substrate wafers and the growth of epitaxial layers, sophisticated semiconductor processing control must be enforced in order to ensure good internal quantum efficiency. LED chip design and fabrication are essential elements that can substantially affect light extraction efficiency. The subsequent packaging will define the luminous efficiency, and the power supply at the system level will determine the overall lighting efficiency. There are a number of books on LEDs, but most of them are on sciences and technologies before packaging. This book intends to cover the mid‐ to downstream topics related to LEDs and so is mainly based on the research outcomes and teaching materials of authors over the past decade. The selected subjects are for postgraduate students in universities and professional engineers in the industries involved in the design, material development, packaging and assembly processes, reliability testing, and applications of LEDs for SSL. This book is aimed at the introductory to intermediate levels. A bachelor's degree or equivalent in a relevant engineering or science discipline greatly help the reader's understanding of its contents.

Chapter 1 of this book is a concise review of LEDs and lighting systems for readers who have not had former exposure to these areas. Chapter 2 introduces the fundamentals of packaging processes and materials for conventional LEDs. Chapter 3 covers more advanced topics on chip scale and wafer level packaging for LEDs, which are mainly based on the authors' research outcomes. Chapter 4 provides information on board level assembly including chip‐on‐board and LED modules. Chapter 5 reviews the approaches to evaluating the optical, electrical, and thermal performance of LEDs. Chapter 6 covers the topic of reliability engineering for LED packaging, with detailed test methods and failure analyses. Chapter 7 introduces emerging applications of LEDs, such as automotive lighting, micro/mini‐LED displays, and visible light communications. Chapter 8 discusses LEDs beyond visible light, including ultraviolet and infrared applications, and relevant technology trends.

As mentioned in the first chapter of this book, the gap between the onset of generations of lighting systems is approximately 60 years. It is the consensus that the dawn of SSL occurred in the late 1990s. Twenty years have gone by and there is no hint of new sciences that may lead to the fifth generation of lighting systems in the future. Some people tend to believe LEDs may be the last form of light source for general lighting applications for human societies. Nevertheless, there are always surprises in scientific and technological development. We will see whether there is to be a new form of light source for general lighting in four decades' time. In the meantime, the authors hope this book will contribute to the education and training of students and professionals for the improvement of LED packaging and its relevant applications in terms of reliability and performance. The 2014 Nobel Prize in Physics highlighted that the award was conferred “for the invention of efficient blue light‐emitting diodes which has enabled bright and energy‐saving white light sources.” The most significant word in this award citation is “energy‐saving.” Lighting accounts for 20% of electricity consumption on earth. Any saving on energy in lighting is meaningful. Let's work together harder and further to achieve more efficient lighting through the design, materials, and packaging of LEDs.

March 2021

Shi‐Wei Ricky Lee

Jeffery C. C. Lo

Mian Tao

Huaiyu Ye

About the Authors

Shi‐Wei Ricky Lee, PhD, FIEEE, LFASME, LFIMAPS, FInstP

Chair Professor, Department of Mechanical & Aerospace Engineering

Director, HKUST Foshan Research Institute for Smart Manufacturing

Director, Electronic Packaging Laboratory

Acting Dean, Systems Hub, HKUST (GZ)

The Hong Kong University of Science and Technology

Kowloon, HKSAR, China

Ricky Lee received his PhD degree in Aeronautical and Astronautical Engineering from Purdue University in 1992. Currently, he is Chair Professor of Mechanical and Aerospace Engineering and Director of Foshan Research Institute for Smart Manufacturing, and Director of Electronic Packaging Laboratory, at the Hong Kong University of Science and Technology (HKUST). He also has concurrent appointments as Acting Dean of Systems Hub of the HKUST Guangzhou Campus and Director of HKUST LED‐FPD Technology R&D Center at Foshan, Guangdong, China. Dr. Lee has been focusing his research on the development of packaging and assembly technologies for electronics and optoelectronics. His R&D activities include wafer level packaging and 3D IC integration, additive manufacturing for microsystems packaging, LED packaging for solid‐state lighting and applications beyond lighting, lead‐free soldering, and reliability analysis. Dr. Lee is a Fellow of IEEE, ASME, IMAPS, and Institute of Physics (UK). He is also Editor‐in‐Chief of ASME Journal of Electronic Packaging.

Jeffery C. C. Lo, PhD

Assistant Director, HKUST Foshan Research Institute for Smart Manufacturing

Program Manager, Electronic Packaging Laboratory

The Hong Kong University of Science and Technology

Kowloon, HKSAR, China

Jeffery Lo received his bachelor (first class honors) and MPhil degrees in Mechanical Engineering Department from the Hong Kong University of Science and Technology (HKUST) in 2002 and 2004, respectively. He then joined Electronic Packaging Laboratory of HKUST as a Senior Technical Officer and provided professional technical support to various users, including undergraduate and postgraduate students, from different departments and industrial partners around the world. To further develop his R&D career, he completed his PhD degree at HKUST in 2008 and continued offering support to the lab at the same time. He is now the Program Manager of Electronic Packaging Laboratory and Assistant Director of Foshan Research Institute for Smart Manufacturing, focusing on R&D projects with various international companies. The topics of his research interests include flip‐chip technologies, wafer level packaging, and LED packaging. He was granted the 2004 ECTC Best Poster Paper Award (May 2005), Young Award in IEEE 9th VLSI Packaging Workshop in Japan (December 2008), and IEEE‐CPMT Outstanding Young Engineer Award in 2015. He was the IEEE‐CPMT Hong Kong Chapter Chairman in 2015/16.

Mian Tao, PhD

Lead Engineer, Technology Division, Group of Integrated Circuits and Systems

Hong Kong Applied Science and Technology Research Institute

New Territories, HKSAR, China

Mian Tao received his MSc degree from the Hong Kong University of Science and Technology (HKUST) in Mechanical Engineering in 2010. He then worked in HKUST LED‐FPD Technology R&D Centre at Foshan from 2011 to 2013 focusing on the optical, thermal, and electrical characterization of light‐emitting diode (LED) chips and devices. He received his PhD degree in 2016 from HKUST. His research topic focused on the effect of nonuniformity junction temperature on the performance of an LED device. Afterward, he worked as a research associate in HKUST's Electronic Packaging Laboratory and later joined the Hong Kong Applied Science and Technology Research Institute (ASTRI) as a lead engineer. His research interests include thermal characterization and the management of high‐power electronics and the development of advanced microelectronic packages.

Huaiyu Ye, PhD

Associate Professor, School of Microelectronics

South University of Science and Technology

Shenzhen, Guangdong, China

Huaiyu Ye received his PhD degree from the Department of Microelectronics of Delft University of Technology in 2014. He is Associate Professor of Southern University of Science and Technology (SUSTech). He won the Outstanding Innovation Youth Award in 2017 and Alliance Contribution Award in 2018 of the China Advanced Semiconductor Industry Innovation Alliance and was selected as the Shenzhen Overseas High‐Caliber Personnel in 2019. He mainly conducts his research on advanced packaging of solid‐state lighting and power electronic devices, focusing on materials, technology, structure, testing, thermal management, and reliability. He is also responsible for the construction of advanced packaging platforms, R&D, and industrialization. He chaired and participated in 16 projects in China and overseas. He has served as an academic committee member of several international conferences and participated in Technology Roadmap for Wide Band Gap Power Semiconductor 2018.

1LEDs for Solid‐State Lighting

1.1 Introduction

A light‐emitting diode (LED) is one kind of semiconductor that can emit light. A diode is the simplest solid‐state device in electronics [1]. It consists of a p‐doped and an n‐doped semiconductor, as illustrated in Figure 1.1. The two types of semiconductors form a junction which has the current–voltage (I–V) characteristics given in Figure 1.2. An LED is a diode that can emit photons when it is subject to the forward bias, as shown in Figure 1.3[2]. In the twentieth century, LEDs were mainly used as signal indicators on instrument panels or simple displays for commercial signages. Owing to the development of white light illumination and the improvement in power rating/efficiency, LEDs have been widely used for general lighting since the 1990s [3].

As an opening, in this chapter the classification of light sources is defined first and the four generations of artificial lighting systems introduced. Subsequently, the historical development of LEDs will be reviewed. Afterward, the implementation of white light illumination with LEDs is given as background information for the subsequent chapters. Finally, certain examples are given to illustrate the applications of LEDs for general lighting.

1.2 Evolution of Light Sources and Lighting Systems

In principle, the light sources on earth may be classified into two main categories: hot light sources and cold light sources. Hot light sources include combustion (e.g. candles) and thermal radiation (e.g. incandescent lamps). The former is a chemical reaction, while the latter is a physical phenomenon. Cold light sources include chemiluminescence (e.g. fireflies), electrical discharge (e.g. fluorescent tubes), and electroluminescence (e.g. LEDs) [4]. Electroluminescence is direct energy conversion from electrons to photons [5]. As illustrated in Figure 1.4, when mobile electrons and holes meet at the p–n junction, photons are emitted due to radiative recombination [6]. This is the lighting mechanism of the LED.

Human history has witnessed four generations of lighting systems, as shown in Figure 1.5. Owing to the development of gas pipelines in the early nineteenth century, gas lamps were considered the first generation of lighting systems. In 1879, Thomas Edison filed his patent (Figure 1.6) of an incandescent lightbulb with a service life of 40 hours (Figure 1.7). In the ensuing year he improved the filament materials and increased the service life to more than 1000 hours. Together with the distribution of electrical power lines, the incandescent lightbulb became emblematic of the second generation of lighting systems. In the middle of the twentieth century, fluorescent light tubes appeared and were considered the third generation of lighting systems [7]. Starting from the late 1990s, following the invention of the blue light LED and the implementation of white light illumination with a phosphor‐converted LED (pc‐LED), it became possible to use LEDs for general lighting applications. This marked the onset of the fourth generation of lighting systems. After two decades of development and improvement, LEDs have been widely used in all kinds of applications (Figure 1.8). Nowadays, people also term the fourth generation of lighting systems with LEDs as solid‐state lighting (SSL) or semiconductor lighting [8]. It is interesting to note that the gap between generations of lighting systems appears to be approximately 60 years.

Figure 1.1 Structure of a typical diode.

Figure 1.2I–V characteristics of a typical diode.

Figure 1.3 LED under forward bias.

Figure 1.4 Mechanism of electroluminescence.

Figure 1.5 Four generations of lighting systems.

Source: Chronicle/Alamy Stock Photo.

Figure 1.6 Edison's patent of incandescent lightbulb.

Source: T. A. Edison, Electric Lamp. 1880. US Patent No. 223,898.

Figure 1.7 Edison's first successful lightbulb demonstrated to the public.

Source: https://commons.wikimedia.org/wiki/File:Edison_Carbon_Bulb.jpg#/media/File:Edison_Carbon_Bulb.jpg.

Figure 1.8 Examples of LED applications.

1.3 Historical Development of LEDs

The literature traces back the LED to the beginning of the twentieth century. The British scientist Henry Joseph Round of Marconi Labs discovered the electroluminescence phenomenon in 1907 using a crystal of silicon carbide (SiC) and a cat's whisker detector (Figure 1.9) [9]. In the mid‐1920s, the Russian engineer Oleg Losev independently invented a diode that could emit light and filed the first patent for an LED [10]. For decades afterwards, there was little development of the LED.

The next milestone for the development of the LED occurred in 1962 when Dr. Nick Holonyak Jr. of General Electric invented the red light LED [11]. Subsequently, Dr. M. George Craford of Monsanto introduced an LED that could emit yellow light in 1972 [12]. The last piece of the jigsaw appeared 20 years later when Shuji Nakamura of Nichia demonstrated the first high brightness blue light LED based on indium gallium nitride (InGaN) in 1993 [13]. The presence of the blue light LED implied the completion of the visible light spectrum and the feasibility of implementing white light illumination using LEDs with color mixing schemes [14]. The holy grail of LED development was bestowed on the “three musketeers” who contributed the most to the blue light LED: Professors Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura became the 2014 Nobel Prize Laureates in Physics (Figure 1.10). The award citation was “for the invention of efficient blue light‐emitting diodes which has enabled bright and energy‐saving white light sources” [15].

Figure 1.9 The first demonstration of electroluminescence with SiC crystal.

Source: https://es.wikipedia.org/wiki/Led#/media/Archivo:SiC_LED_historic.jpg.

Figure 1.10 Nobel Prize in Physics 2014 honored the blue light LED inventors [15].

Source: © Nobel Media AB, Photo Alexander Mahmoud.

Nowadays, LEDs can cover the whole visible light spectrum with various kinds of semiconductor compounds, as shown in Table 1.1. Although II–VI compounds may be used, most of them belong to the III–V compounds family. There are two main categories. The aluminum gallium indium phosphide (AlGaInP) quaternary compound may cover from red to green light and the InGaN ternary compound may cover from green to violet light [16]. Although infrared (IR) and ultraviolet (UV) emissions are possible as well, they are for nonlighting applications.

Table 1.1 Recipes of semiconductor compounds for LEDs.

Color

Wavelength

λ

(nm)

Forward Δ

V

(V)

Semiconductor materials

Infrared

λ

 > 760

Δ

V <

 1.63

GaAs, AlGaAs

Red

610 < 

λ

 < 760

1.63 

<

 Δ

V <

 2.03

AlGaAs, GaAsP, AlGaInP,GaP

Orange

590 < 

λ

 < 610

2.03 

<

 Δ

V <

 2.10

GaAsP, AlGaInP,GaP

Yellow

570 < 

λ

 < 590

2.10 

<

 Δ

V <

 2.18

GaAsP, AlGaInP,GaP

Green

500 < 

λ

 < 570

1.9 

<

 Δ

V <

 4.0

Traditional green: GaP AlGaInP, AlGaP Pure green: InGaN/GaN

Blue

450 < 

λ

 < 500

2.48 

<

 Δ

V <

 3.7

ZnSe, InGaN, SiC

Violet

400 < 

λ

 < 450

2.76 

<

 Δ

V <

 4.0

InGaN

Ultraviolet

λ

 < 400

3 

<

 Δ

V <

 4.1

InGaN, Diamond, BN, AlN, AlGaN, AlGaInN

1.4 Implementation of White Light Illumination with an LED

The basic principle for generating white light is to mix red, green, and blue (RGB) lights. With various mixing ratios, different degrees of white light may be achieved. Such an RGB color mixing scheme will involve three kinds of LEDs that can emit red, green, and blue lights, respectively, as shown in Figure 1.11. Since different kinds of LEDs have different forward bias voltages, different chip sizes, different compound materials, and different service lives, the RGB color mixing scheme usually leads to a more complicated and expensive system which is more suitable for display applications [17]. For general lighting, it is often more cost sensitive. Therefore, a cost‐effective approach for white light illumination is needed.

Another way of generating white light is by fluorescence with phosphor powders. The conventional fluorescent lamp is an example of this. The phosphors may be excited by blue light or UV emitted from an LED, as illustrated in Figure 1.12. Such an approach is termed phosphor‐converted LED (pc‐LED) [18]. If the light source is UV, the phosphors must be a mixture of RGB powders. Although this may offer more flexibility for various color tuning, it may also lead to higher cost and less uniformity.

The most cost‐effective method for generating white light is to use a blue light LED to excite yellow phosphor, as shown in Figure 1.13. The relevant mechanism is illustrated in Figure 1.14 with the CIE 1931 chromaticity diagram. The blue light emitted from the LED has a color coordinate at the “blue corner” of the diagram. When the phosphor is added on the top of the LED, the excited yellow light will make the mixed light move toward the “yellow edge”. This is a one‐dimensional path and the degree of progress from blue to yellow depends on how much yellow light is excited. Therefore, the amount of yellow phosphor may be adjusted so that the resulting color coordinate lands at a precise location in the “white zone”. This is the most convenient and cost‐effective way to generate white light for general lighting applications [19].

Figure 1.11 White light illumination with RGB LEDs.

Figure 1.12 White light illumination with phosphor‐converted LED.

Figure 1.13 Blue light LED with yellow phosphor for white light illumination.

Figure 1.14 Mechanism of white light generation with blue–yellow color mixing.

1.5 LEDs for General Lighting

The benefits of the LED – its high brightness, low power consumption, vivid color spectrum, compact size, and long service life – are well known. These make the LED suitable for many industrial and consumer applications. In particular, people have very much emphasized the general lighting applications of the LED in the 2010s [20]. According to the International Energy Agency, lighting accounts for nearly a fifth of electrical energy consumption worldwide (Figure 1.15). The efficiency of conventional incandescent lightbulbs is typically less than 5%. Therefore, tremendous amounts of energy have been wasted on lighting in the past. Although the efficiency of fluorescent lamps has been improved to some extent, the mercury contents in the light tube impose substantial threats to the environment. Therefore, both incandescent and fluorescent lamps must be banned. Many countries have enforced government policies to phase out the second and third generation lighting systems with very aggressive schedules. Eventually, SSLs with LEDs will be the only allowable and affordable lighting system [21].

Figure 1.15 Percentage of lighting energy consumption in overall electricity supply.

Figure 1.16 Application of solid‐state lighting in a Hong Kong subway train.

Figure 1.17 Energy saving due to the implementation of SSL in the subway systems.

In addition to consumer and household applications, there exist many examples of the use of LEDs for general lighting in the public domain. Figure 1.16 shows the first application of an SSL in a subway system, which was a collaborative project between the Mass Transit Railway Corporation (MTRC) of Hong Kong and the Hong University of Science and Technology (HKUST). LED lighting modules were developed and used to replace the fluorescent light tubes on the trains for saloon interior lighting [22]. The first trial batch of prototypes was installed in 2007. After three years of pilot runs, the MTRC decided to launch massive scale deployment. Besides saloon interior lighting on trains, SSLs are now used for interior ceiling lighting and for advertisement box back lighting in all subway stations. The energy saving due to the implementation of SSL in the subway systems of Hong Kong over the years is given in Figure 1.17. The merit of SSL in terms of energy saving has been evidenced by numerous general lighting applications. This is also the best testimony to the award citation of 2014 Nobel Prize in Physics!

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2Packaging of LED Chips

2.1 Introduction

Packaging is a fundamental step in the manufacture of microelectronics and LED components. Devices which are fabricated on a wafer will not work without being packaged into a component and assembled as a system. The overall packaging process is categorized into different levels. The first level refers to the chip level packaging process which packages chips to components. Burn‐in testing or sorting can be performed on the packaged components. In the second level, which refers to the board level assembly process, different packaged components are assembled onto a board, normally a printed circuit board (PCB). Finally, the board assemblies and other relevant accessories are integrated into a system as a final product for the end user.

Traditional integrated circuit (IC) packaging is commonly used for providing power, electrical connections with other components, mechanical support, protection from the environment, and heat dissipation paths. The performance and reliability of the components depend heavily on the package type, packaging process, and packaging materials. In LED chip packaging, extracting light emitted from the chip to the outside world and color tuning are other important considerations. These directly determine the performance of the LED component. Upon packaging of the LED components, burn‐in testing, sorting, screening, binning, and other necessary processes can be performed thereon. Components with similar optical performance (e.g. lumen output, color temperature, color rendering index, etc.) are selected for the subsequence board level assembly. The overall functions of the package are illustrated in Figure 2.1.

This chapter discusses the LED chip packaging process in detail. Different types of LED packages currently available in the market are introduced. This chapter also covers various types of chip mounting and interconnection methods, as well as several phosphor deposition methods which are commonly adopted. The phosphor coating configurations of the latter will have a big influence on the optical performance of LED components.

In a traditional IC package, the IC is protected by a molding compound which is usually flat and not transparent. Such a molding compound is not suitable for LED packaging. Rather, transparent epoxy or silicone is generally used. The encapsulant material protects the chip and interconnects in the package and serves as a light‐transmitting medium. In some applications, the encapsulation also serves as an optical lens to achieve the designed light output pattern. This chapter briefly discusses various types of encapsulation and molding methods.

Figure 2.1 Functions of the package.

For packaging LED chips, some major considerations include extracting more light emitted from the chip for increasing the lumen efficacy and achieving a uniform color distribution, etc. Nevertheless, different applications may require different light output patterns. For example, a rectangular light pattern is preferred to a circular one for street lighting. In such cases, the regular LED packaging process may not be able to cater for the specific requirements of each case. Secondary optics components (e.g. lenses) may be required to adjust the light pattern accordingly. This chapter covers the basic concepts of optical simulation, which is a powerful tool in optimizing the design of secondary optics components.

2.2 Overall Packaging Process and LED Package Types

Similar to traditional IC packaging, there are basically three types of packages in LED packaging, namely plated through hole (PTH), surface mount devices (SMD