15.2 Polluting Agents 612 15.3 Recycling of Water 613 15.4 Recovery Techniques 613
15.4.1 Filtration 614
15.4.2 Water Use Reduction Technique 614 15.4.3 Ion Exchange System 615
15.4.4 Reverse Osmosis 617 15.4.5 Evaporative Recovery 618
15.4.6 Precipitation of Heavy Metals 619 15.4.7 Electrolytic Recovery 619
15.5 Air Pollution 620 15.5.1 Dust 621 15.5.2 Fumes 621
15.5.3 Clean Environment in Assembly Rooms 622 15.6 Recycling of Printed Circuit Boards 623
15.6.1 Present Approach to PCB Scrap Disposal 623 15.6.2 Characteristics of PCB Scrap 625
15.6.3 Dis-assembly of Equipment 625 15.6.4 Technologies of Recycling of PCBs 626 15.7 Environmental Standards 628
15.8 Safety Precautions for the Personnel 629 15.9 Toxic Chemicals in PCB Fabrication 629 15.10 Lead-free Soldering 630
15.10.1 Substitutes for Tin/Lead Solders 632 15.11 Useful Standards 633
Glossary 635 References667 Index 678
1 Preface
density of modern electronic and mechanical components. They now include finer conductor tracks and thinner laminates, present in an ever-increasing number of layers. Integrated circuits have become dramatically sophisticated especially in the last decade. This has in turn created new design requirements for mounting them on the boards. While insertion was common with DIP (dual in- line-package) technology in the 1970s, surface mount technology in now being increasingly employed.
holes is increasing; and hole diameters are rapidly decreasing. These requirements have lead to a rising trend in the implementation of microvias as blind-vias or through-holes. In the future, PCBs will have higher functionality/density, improved reliability and lower cost through better and more tightly controlled/cost-effective processing. The industry will also move towards more environmental friendly PCBs. Furthermore, the advantages in contract manufacturing at the global level will effectively ensure that the design and manufacture of PCBs are of internationally accepted quality.
Most of the books currently available on this subject, do not address several of the above mentioned (important) aspects. This book is a single-source reference covering these vital areas of PCB technology. This includes design, fabrication, assembly and testing, including their reliability and quality aspects. The book therefore, addresses not only the design considerations but also provides a general understanding on all the processes needed in the physical construction and testing of the printed circuit boards. Despite the several highly specialized disciplines in this field, such as, electronics, mechanical engineering, fluid dynamics, thermodynamics, chemistry, physics, metallurgy and optics, the attempt in this book has been to keep the text lucid and to explain the salient aspects of PCBs without indulging in an exhaustive theoretical approach. Extensive bibliographical references are provided to represent such specialized extensions of the subject which lie outside the domain of this book.
In addition, line and space dimensions are diminishing; the number of conductors between through- electronic products. PCB requirements today have developed with the increase in the packaging Printed circuit boards arethe most frequently used interconnection technology for components in
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The book is divided into fifteen chapters. Each chapter is comprehensive in its coverage and can be read and well understood as an independent chapter. However, the chapters are so arranged that they represent the processes as they progress in actual practice. The book has been written keeping in mind professionals in the field for whom there is much practical information, coupled with information from manufacturers of various machines and materials.
Chapter 1 is an introduction to the field of printed circuit boards. From their historical developments, it progresses to the description of the types of PCBs and the sequence of their manufacture from design to assembly. The major drivers for modern PCB technology, particularly high density interconnects, are also illustrated. The field of printed circuits is now largely governed by a high degree of standardization, with IPC (Institute of Electronics Circuit Packaging) taking the central role, and accordingly, a brief about this aspect is also given in the first chapter.
In many design offices, the persons responsible for layout design and artwork generation are draughts-men trained in mechanical engineering who need to understand the basics of all electronic components including integrated circuits (ICs) and surface mount devices (SMDs). To fulfill this requirement, Chapter 2 is devoted to the fundamentals and characteristics of a wide variety of electronic components.
Chapter 3 deals with the layout planning and general design considerations for PCBs; and Chapter 4 details design guidelines for specialized circuits such as high frequency circuits and high density interconnects. Special considerations for analog circuits and high power dissipating circuits are also included in this chapter.
Until about a decade ago, artwork generation was carried out manually. The CAD systems available today, with software packages available from a number of vendors, have not only simplified this work, but have also made the artwork design of high density board more convenient. CAD has made it possible to integrate the artwork generation with CAM (Computer-aided manufacturing). The design data transfer mechanism is assuming great importance due to theincreasing role of distributed manufacturing facilities. Artwork generation techniques, both manual as well as CAD/CAM based, are covered in Chapter 5.
Chapter 6 deals with the base materials or the laminates, which form the core of the printed circuits.
The chapter discusses not only the constructional aspects of PCBs, it also details the usual defects present in them, along with the testing methodology from the point of view of quality assurance.
Image transfer techniques (of the artwork on to the laminate) have undergone tremendous developments, particularly because of the stringent requirements of the fine line printed circuits.
Thelaser direct image transfer method is becoming increasingly popular. Chapter 7 covers the conventional as well as the modern techniques of image transfer.
The next logical step in the manufacture of PCBs is etching. Various techniques of etching, both wet and dry, are explained in Chapter 8, while Chapter 9 details the plating techniques. In addition, Chapter 9 also covers various methods for providing proper surface finish to the conducting pathways, including application of solder mask and conformal coatings.
Precision mechanical operations form an important step in the quality manufacture of PCBs. It is reported that about 85% of all the defects which are discovered in PCBs, are directly or indirectly associated with drilling. In addition, the ever-decreasing size of the holes has made mechanical drilling methods inadequate. Chapter 10 discusses the use of lasers which are now popular in overcoming this limitation.
Multi-layer boards, which have enabled high-density boards, are based on special design and fabrication techniques. These are covered in Chapter 11. Chapter 12 includes special features of flexible PCBs, their design and fabrication techniques, and applications.
Chapter 13 is devoted to soldering and assembly techniques, both manual as well as machine- based automatic systems. It includes rework procedures, especially for boards with surface mount devices and mixed assemblies.
Chapter 14 explains quality and reliability aspects of PCBs and sets out criteria for their acceptability. Various tests on bare boards and assembled boards are detailed along with their limitations and areas of applications. Issues on pollution, associated with thePCB industry, along with their treatment methods, are covered in the last chapter. A brief reference to the end-of-life disposal of PCBs and the concept of Design for Environment is also illustrated. The chapter also addresses the vital issue of lead free soldering and the present status of its adoption.
The book provides an exhaustive glossary of commonly used terms. The extensive bibliography will be useful to readers who need specialized information in greater detail. The internet has become an invaluable resource for a wide range of general and technical information, especially from the manufacturers of PCBs and related technologies. References are provided in the text for any material which has been included from the internet.
In conclusion, I would like to thank my wife Mrs. Ramesh Khandpur who has been a source of great inspiration in helping me attain my goals in life. Her wholehearted support never let me slacken in my professional endeavors. Thanks are due to my children and grandchildren who are looking forward to this new publication.
My thanks are also due to Tata McGraw-Hill, New Delhi, for permitting me to use some illustrations from the book Printed Circuit Boards by Mr. W C Bosshart and for bringing out this high quality book.
R S KHANDPUR
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