Mechanical Design of Electronic Systems

MECHANICAL DESIGN OF
ELECTRONIC SYSTEMS

JAMES W. DALLY, University of Maryland

PRADEEP LALL, Auburn University

JEFFREY C. SUHLING, Auburn University

mech_d2

PREFACE

This book has been written for engineers to serve as a first text on the packaging of electronic systems. The material has been written for an engineering student or for a practicing professional working as a mechanical or electrical engineer with a company producing electronic products or systems. The engineering student should have completed fundamental courses in the engineering sciences, thermal sciences and materials as prerequisites. The practicing professional will probably be at the early stages of his or her career and be more concerned with the technical details of the design rather than the business strategy of a product line.

This book is an introduction to the design of electronic systems from a mechanical engineering perspective, although attention is given to circuit analysis that may be of more interest to the electrical engineer. As such it covers a very broad range of topics from the physics of semiconductors to the design of advanced high performance heat exchangers. To accommodate this breadth, we have divided the text into four independent parts. In Part 1, which includes three chapters, deals with foundations for design. Chapter 1 provides an overview of the entire field, covering in some detail the mechanical design issues that arise in developing an electronic system. Also covered are business aspects of this industry, particularly as they are related to a rapidly changing technology, which leads to early obsolescence of an existing product line, and exacting requirements for investing in new product development. Chapter 2 describes electronic components with emphasis on semiconductor devices. Importance is placed on silicon technology and the new developments in logic and memory circuits with higher levels of integration. We try to show in this chapter the dynamics of the technology and the emerging design problems associated with the ever increasing scale of integration. The most important problems are handling high I/O counts and dissipating very large heat flux with exceedingly small temperature differences. Chapter 3 covers circuit analysis. The conventional methods of analysis of ordinary ac and dc circuits are briefly reviewed. However, the emphasis is placed on transmission lines where inductance, resistance and capacitance is distributed along the length of the line. This development is new to most mechanical engineers and it is critical to their understanding of propagation delay, line charging and pulse reflections that must be taken into account in the design electronic systems with even moderate performance specifications.

Part 2 deals with the different levels of packaging electronic components and the methods commonly used in manufacturing and assembly. The chip carrier, the first level package is treated in detail in Chapter 4. Through-hole packages, surface-mounted chip carriers, chip scale packages, flip-chip and ball-grid-arrays are described in some detail. The printed circuit board, the second level package, is described in Chapter 5. The treatment is often descriptive and provides the opportunity to introduce the terminology used in the industry to depict circuit board features. Some of the very difficult problems associated with component placement and trace routing are introduced in this chapter with simple examples. The manufacturing processes associated with production of circuit boards is are described in Chapter 6. These processes must be well understood if one is to design circuit boards suitable for a quality product. The production methods employed in assembling electronic products are described in Chapter 7. These methods include the technologies associate with surface mounting components. It also includes descriptions of solder processes and materials. The chapter concludes with a discussion of quality assurance programs and reworking processes. Chapter 8, the final chapter in Part 2, deals with third level packaging. Third level packaging is a loose term that describes the many components encountered when enclosing a number of printed circuit boards in instrument cases or cabinets. We treat connectors, back panels, cabling, power supplies, cooling hardware and for both commercial, and military enclosures, and consumer electronics in some detail.

Analysis methods commonly employed to predict performance of systems are covered in the six chapters included in Part 3. While much of the analysis in industry is performed using specialized software programs, we have emphasized a more theoretical approach that leads to closed form solutions for simple problems. Chapter 9 deals with heat transfer by conduction. Basic conduction equations are reviewed and applications to problems arising in conducting the heat generated on a chip to the heat sink are given. Heat transfer by radiation and convection are treated in Chapter 10. We have only limited coverage of heat transfer by boiling, because its use in the industry to date has been limited. Chapter 11 presents the basic methods for calculating stresses and predicting failure by yielding or fatigue. This chapter also presents methods for the analysis of fasteners. Methods for determining stresses imposed by temperature changes are described in Chapter 13. These methods include closed form solutions for solder joints and die stresses in molded packages. Bi-material stresses and PCB warpage are also covered. The chapter includes descriptions of finite element solutions that illustrate the approach often used in industry to study stresses in solder joints and in molded chip carriers. Results from a recent study that enable a prediction of the thermo-reliability of BGAs has have been included. The final chapter in Part 3 covers vibration of components and circuit boards. Here the emphasis is on simple analytical procedures, which give insight on methods to reduce transmissibility coefficients and, if possible, to avoid resonance conditions. We recognize that failure by fatigue is a major problem in systems exposed to vibration, and methods for treating of failure by fatigue are covered. Advanced methods for dealing with shock and vibration of fine pitch BGAs are presented. Examples of finite element analysis are presented together with results from an extensive test program involving drop testing.

Part 4 of this text deals with reliability, with the theory of reliability supporting this important topic presented in Chapter 15. In addition to the basic coverage of the various measures of reliability, the chapter includes a description of reliability models. Also included is a discussion of statistical methods for predicting failure including both the normal distribution function and the Weibull distribution function. Chapter 16, the final chapter discusses design methods to improve reliability. Failure mechanisms are described to provide a better understanding of why failures occur after some period of time in operation. Reliability improvement is achieved by preferred part selection, derating and stress management, screening and accelerated testing.

The book does differ to some degree from the conventional design textbook commonly found in engineering colleges. We have attempted to introduce some business aspects of design. Of particular importance here is the fact that the market price of a product drives the design. We have also tried to cover some of the thought process associated with design by describing both design and manufacturing aspects (good and bad) in the narrative parts of the text. The exercises that are given at the end of each chapter are markedly different from those found in the usual engineering textbook. They often require the student to do much more than plug and chug. The students are required to sketch, to prepare graphs describing solution space, to conceive new designs better than existing designs, to write engineering briefs, to interpret solutions and draw conclusions related to design merits and to make judgments based on business aspects. These exercises will stretch the experience base of most students and, indeed, they may stretch the experience base of some instructors. Care should be taken in assigning the exercises because they range in difficulty from trivial to impossible. Hopefully, the more difficult problems can be used to stimulate classroom discussion and the easier ones will not lull the student into a false sense of security.

CONTENTS

PART 1 MECHANICAL DESIGN OF ELECTRONIC SYSTEMS

CHAPTER 1 INTRODUCTION

1.1 Overview and Objectives
1.2 Functions Involved in Mechanical Design of Electronic Systems
1.3 Mechanical Development of Electronic Systems
1.4 Mechanical Design Aspects of Packaging
1.5 Range of Products
1.6 Business Aspects

CHAPTER 2 ELECTRONIC COMPONENTS AND SEMICONDUCTOR DEVICES

2.1 Introduction
2.2 Conductors, Insulators and Semiconductors
2.3 Extrinsic Semiconductors
2.4 The P-N Junction
2.5 Semiconductor Diodes and Resistors
2.6 Transistors
2.7 Comparison of Transistor Types
2.8 Logic Gates
2.9 Gate Technologies
2.10 Chip and Wafer Fabrication
2.11 Scale of Integration
2.12 I/O Count and Rent’s Rule
2.13 Memory Devices

CHAPTER 3 CIRCUIT ANALYSIS

3.1 Introduction
3.2 The Analog Method of Analysis
3.3 Electrical Properties of Wires
3.4 Wires as Transmission Lines
3.5 Sinusoidal Signal Propagation along a Transmission Line
3.6 Termination of Transmission Lines
3.7 Pulse Propagation along a Low Los Line
3.8 Effect of Termination on Pulse Propagation
3.9 Reflections from Discontinuities
3.10 Characteristic Impedance of Conductors
3.11 Transmission Lines on Circuit Boards
3.12 Resistance of Printed Circuit Lines

PART 2 PACKAGING

CHAPTER 4 FIRST LEVEL PACKAGING — THE CHIP CARRIER

4.1 Introduction
4.2 Types of Chip Carriers
4.3 Chip Carrier Manufacturing
4.4 First Level Packaging for Discrete Components

CHAPTER 5 SECOND LEVEL PACKAGING: SUBSTRATES AND PRINTED CIRCUIT BOARDS

5.1 Introduction
5.2 Types of Printed Circuit Boards (PCB)
5.3 Circuit Board Materials
5.4 Footprint Design
5.5 Layer Count
5.6 Placement for Enhanced Wirability
5.7 Routing Methods

CHAPTER 6 PRODUCTION OF PRINTED CIRCUIT BOARDS

6.1 Introduction
6.2 Overview of the Production Process
6.3 Preparation of Master Circuit Layouts
6.4 Lithography
6.5 Drilling and Punching
6.6 Lamination
6.7 Plating
6.8 Solder Masks
6.9 Production of Flexible Substrates
6.10 Ceramic Circuit Boards

CHAPTER 7 ELECTRONICS MANUFACTURING: CHIP CARRIER TO SUBSTRATE

7.1 Introduction
7.2 Mounting Technologies
7.3 Solder Processes
7.4 Post Soldering Operations
7.5 Solder Materials
7.6 Quality Assurance
7.7 Rework and Repair

CHAPTER 8 THIRD LEVEL PACKAGING: CONNECTORS, CABLES, MODULES, CARD CAGES AND CABINETS

8.1 Introduction
8.2 Circuit Card Connectors
8.3 Back Panels, Wire Wrap Board and Cable Connectors
8.4 Power Supplies and Buss Bars
8.5 Card Racks
8.6 Electronic Enclosures
8.7 Wires and Cabling
8.8 Fans
8.9 Cold Plates and Cold Rails

PART 3 ANALYSIS METHODS

CHAPTER 9 THERMAL ANALYSIS METHODS: CONDUCTION

9.1 Introduction
9.2 Steady State Heat Transfer by Conduction
9.3 Overall Coefficient of Heat Transfer
9.4 Contact Resistance
9.5 Conduction from Discrete Heat Sources
9.6 Transient Conduction
9.7 Heat Transfer in Chip Carriers
9.8 Conduction in Circuit Cards
9.9 Cold Plates and Cold Rails
9.10 Advanced Cooling Methods

CHAPTER 10 THERMAL ANALYSIS METHODS: RADIATION AND CONVECTION

10.1 Introduction to Radiation Heat Transfer
10.2 Laws Governing Heat Transfer by Radiation
10.3 Introduction to Convective Heat Transfer
10.4 Convection Heat Transfer
10.5 Natural Convection
10.6 Forced Air Convection Coefficients
10.7 Forced Convection with Flow in Ducts
10.8 Heat Transfer and Friction Coefficients for Air Flow in Ducts
10.9 Air Flow in Electronic Enclosures
10.10 Introduction to Heat Transfer by Evaporation, Boiling and Condensation

CHAPTER 11 STRESS AND FAILURE ANALYSIS OF MECHANICAL COMPONENTS

11.1 Introduction
11.2 Stress, Strain and Deformation in Axial Members
11.3 Stress Concentrations
11.4 Bending of Thin Rectangular Plates
11.5 Stresses in Thin Walled Pressure Vessels
11.6 Failure Theories
11.7 Fatigue Failure
11.8 Fasteners
11.9 Fastened Joints Loaded in Tension
11.10 Fastened Joints Loaded in Shear

CHAPTER 12 THERMO-MECHANICAL ANALYSIS

12.1 Introduction
12.2 The DNP Relation
12.3 Chip Stresses in Plastic Packages
12.4 Thin Film Stresses on Rigid Substrates
12.5 Stresses in Bi-material Laminates Due to D T
12.6 Warpage of Chip Carriers and PCBs
12.7 Finite Element Solutions
12.8 Cyclic Thermal Fatigue Test Results
12.9 Statistical Prediction of Thermo-Mechanical Reliability
12.10 Summary

CHAPTER 13 ANALYSIS OF VIBRATION OF ELECTRONIC EQUIPMENT

13.1 Introduction
13.2 Vibrating Systems with One Degree of Freedom
13.3 Isolation of Systems from Exciting Forces
13.4 Vibration of Circuit Boards
13.5 Lead Wire Failures on Vibrating Printed Circuit Boards
13.6 Shock Isolation
13.7 Modeling Shock with Finite Elements
13.8 Experimental Study of Failures under Shock Loading

PART 4 RELIABILITY

CHAPTER 14 THEORY OF RELIABILITY

14.1 Introduction
14.2 Reliability Theory
14.3 Accelerated Testing
14.4 Reliability Models
14.5 Statistical Methods
14.6 Characterizing Statistical Distributions
14.7 Statistical Distribution Functions

CHAPTER 15 DESIGN TO IMPROVE RELIABILITY

15.1 Introduction
15.2 Failure Mechanisms
15.3 Preferred Part Selection
15.4 Derating and Stress Management
15.5 Screening Components and Assemblies
15.6 Accelerated Testing
15.7 Reliability Improvement

APPENDIX A
Acronyms

INDEX

Mechanical Design of Electronic Systems

Pricing

Title ISBN # Price
Mechanical Design of Electronic Systems

Hard cover

Copyright 2008,  664 Pages

 

978-0-9762413-3-1

 

$90.00

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