This is a guide for those involved in the procurement, design, or fabrication of high-speed impedance or insertion loss-controlled PCBs and complex HDI PCBs requiring detailed documentation. While a follow-up to The Printed Circuit Designer’s Guide to Secrets of High-speed PCBs, Part 1 and Part 2, this book stands on its own.
This book is designed to help you bridge the gap between the idealized environment of your CAD or CAM system, the specifications for PCB procurement, and the complex realities of manufacturing processes. It provides a deeper understanding of how production materials, processes, and testing methods can differ from the multi-digit precision you may be tempted to specify, often leading to unrealistic expectations.
This book is for PCB designers, engineers, and procurement teams, or anyone who wants to learn more about what can and can’t be achieved when a suite of CAD layout data and its associated stackup are submitted to the fabrication process.
This book emphasizes the most effective methods for transitioning quality designs from prototype to production with a focus on signal integrity. In the realm of signal integrity, the most skilled designers and fabricators consistently measure, model, and then measure again to guarantee the highest quality and predictable signal integrity in their designs and products.
ISBN: 978-1-959894-20-9
Martyn Gaudion is the managing director of Polar Instruments Ltd. He began his career in the early 1980s at Tektronix, where he was responsible for test engineering on high-bandwidth portable oscilloscopes. During his time at Tektronix, he gained widespread experience in PCB assembly and was extensively involved with the introduction of surface mount technology.
In 1990, Gaudion joined Polar, where he was responsible for the design and development of the Toneohm 950, Polar’s multilayer PCB short circuit locator. He became marketing manager at Polar during 1997 as the market for controlled impedance test became a major section of Polar’s product range. He was appointed sales and marketing director in 2001 and CEO in 2010. Gaudion also writes occasional articles for a number of PCB industry publications, and regularly contributes to IPC’s High-Speed High-Frequency standards development activities.
Gaudion is a chartered company director and a fellow of the London-based IoD (Institute of Directors). In 2016, he was appointed vice chairman of the European Institute of Printed Circuits (EIPC).
Polar Instruments specializes in designing EDA and measurement tools which simplify the design, fabrication, testing and specification of high-speed printed circuit boards (PCBs). Polar’s innovative product line includes the industry standard Controlled Impedance Test System (CITS), which provides the global PCB industry with an easy-to- use test system for high-speed digital and RF boards, as well as class-leading tools for fast and accurate design and testing of impedance and insertion loss controlled PCBs. Polar Speedstack is the layer stack-up design and documentation tool of choice for many designers, fabricators and PCB technologists. Established in 1976, Polar Instruments now has operations and long term channel partners in the US, UK, Europe and Asia Pacific.
Rick Hartley Principal, RHartley Enterprises
Rick Hartley is the principal of RHartley Enterprises, through which he consults and teaches internationally. Hartley’s focus is on the correct design of circuits and PC boards to prevent and/or resolve EMI, noise, and signal integrity problems. His career has focused on telecommunications, [...]
Eric Bogatin Dean, Signal Integrity Academy
Professor Bogatin has a BS in physics from MIT and an MS and PhD in physics from the University of Arizona. He has worked in various industry roles, including senior engineering and management positions at Bell Labs, Raychem, Sun Microsystems, Ansoft, and Interconnect Devices.
Chapter Summaries
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Chapter 0
Chapter 0
This chapter addresses the complexities of remote communication, especially in signal integrity measurements. A case is discussed where a fabricator's choice led to measurement issues, resolved only after an in-person inspection emphasizing the importance of clear communication and understanding in technical fields. -
Chapter 1
Chapter 1
Highlighting the importance of understanding material properties, consulting supply specialists, and balancing specifications to optimize performance and cost, this chapter covers the complexities of selecting materials for PCB fabrication. Speed, thermal challenges, layer stackups, and environmental conditions are also discussed.
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Chapter 2
Chapter 2
In this chapter, the reader will learn strategies for optimizing PCB design to balance costs and performance. Clear supply chain communication is critical, and simulation tools can be leveraged to avoid over-constraining designs. The chapter concludes by stressing the need for effective communication across disciplines to ensure materials are correctly specified and manageable production variations.
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Chapter 3
Chapter 3
Chapter 3 covers the challenges of correlation in PCB manufacturing, highlighting the complexity of tracking errors despite advanced modeling tools. Comprehensive checklists for impedance modeling and measurement are provided to ensure accuracy.
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Chapter 4
Chapter 4
The importance of preprocessing data for field solvers in PCB transmission line modeling is discussed. The key to precise results lies in feeding field solvers accurate, real-world data, especially considering the complexities of copper surface roughness and PCB substrate variations. The chapter emphasizes the need for quality input dimensions, validated measurement data, and effective use of stackup tools to simulate pressed thickness.
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Chapter 5
Chapter 5
This chapter discusses the critical role of simulation and modeling in engineering. It emphasizes understanding the materials used in PCBs and their impact on the final design. Also covered is the importance of accurate input data for simulations, underscoring the need for engineers to comprehend both material properties and production variations to improve product design and yield.
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Chapter 6
Chapter 6
Chapter 6 explores the complexities of PCB fabrication and regional differences in material properties, focusing on the varying electrical characteristics of glass cloth used for reinforcement. It delves into issues like bulk and local Er, the evolution of glass fabrics, and the significance of materials' composite structure in high-speed PCB performance. The chapter emphasizes the importance of collaboration between designers and fabricators to navigate these variations and achieve optimal results, highlighting that PCBs are products of multifaceted processes rather than single machines.
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Chapter 7
Chapter 7
Here the author discusses the compromises involved in using crosshatched ground planes in PCB designs, especially in flex and flex-rigid circuits. It explores the balance between mechanical flexibility and signal integrity, highlighting the broader tolerances required compared to solid planes. Potential issues of crosstalk and EMC at higher frequencies due to crosshatching are also discussed.
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Chapter 8
Chapter 8
Chapter 8 explores the impact of loss tangent values on dielectric loss in PCB design. It highlights the importance of precise numerical representation, demonstrating how even small rounding errors can significantly affect performance.
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Chapter 9
Chapter 9
This chapter emphasizes the importance of understanding the vocabulary of signal integrity, introducing three key terms: S-parameters, surface roughness, and skin effect. S-parameters measure transmission line performance across frequencies, surface roughness impacts signal losses, and skin effect describes current flow near conductors' surfaces at high frequencies.
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Chapter 10
Chapter 10
This chapter discusses the role of copper roughness in bonding laminates and its impact on PCB high-speed performance. It covers various modeling methods for predicting signal losses due to roughness and emphasizes the complexity of different roughness metrics and the importance of using the correct model based on specific roughness data.
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Chapter 11
Chapter 11
Chapter 11 addresses the complexities of measuring differential insertion loss in high-speed PCBs, focusing on methods like S21 and SDD21 parameters. Unlike straightforward impedance measurements, insertion loss requires meticulous approaches such as SPP, SET2DIL, and Delta-L methodologies. The chapter emphasizes collaboration between PCB designers and fabricators to decide on the appropriate measurement technique, highlighting the significance of test coupons and the role of VNAs for accurate results.
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Chapter 12
Chapter 12
Chapter 12 covers the complexities of measuring PCB insertion loss and the importance of using Touchstone files to build measurement confidence. The author discusses the steps involved in modeling and measuring insertion loss, the differences between impedance and insertion loss measurements, and the potential errors that can arise.
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Chapter 13
Chapter 13
Here, readers will learn practical advice on managing via stubs, ensuring proper return paths, and leveraging differential pairs for better signal integrity. The author advocates for thoughtful design and modeling to confirm rather than rectify designs. Also introduced are upcoming discussions on back-drilling and advancements in modeling techniques.
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Chapter 14
Chapter 14
This chapter emphasizes the crucial role of accurate drill documentation in high-density interconnect (HDI) PCB builds. It discusses various drill styles and fills, including the benefits of precision-controlled-depth drilling for signal integrity and the different applications of via fills.
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Chapter 15
Chapter 15
Chapter 15, authored by guest contributor Bert Simonovich, provides a practical approach to modeling differential vias for high-speed backplane designs. It introduces a 'Poor Man’s PCB via modeling methodology,' utilizing simple circuit models and equations to estimate key parameters like odd-mode impedance and effective dielectric constant without relying on expensive 3D electromagnetic field solvers.
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Chapter 16
Chapter 16
This chapter explores the complexities of making accurate high-frequency measurements in PCB fabrication, starting from DC and moving through higher frequency bands. Highlighted are the importance of distinguishing precision from accuracy and a discussion of the escalating costs of measurement equipment and interconnects as frequency increases.
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Chapter 17
Chapter 17
This chapter discusses how to approach discrepancies between measured and calculated trace impedance in PCBs by not jumping to conclusions and considering alternative factors.
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Chapter 18
Chapter 18
The chapter examines the causes of discrepancies in predicted versus measured impedance in PCB traces, especially in ultra HDI designs. It explains how DC resistance becomes significant in finer line designs and discusses the use of Launch Point Extrapolation (LPE) to measure instantaneous impedance. The importance of checking TDR waveforms for slopes due to resistive effects and considering multiple measurement points to ensure accurate impedance evaluation is highlighted.
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Chapter 19
Chapter 19
Chapter 19 addresses the common misconception about the frequency of measuring PCB track impedance, explaining that characteristic impedance remains constant across various frequencies. Whether using a TDR or VNA, the characteristic impedance measurement does not significantly vary with frequency. The chapter debunks myths associated with faster rise times and offers solutions for de-embedding DC resistance from measurements.
