Executing Complex PCBs 2nd Edition Scott Miller Freedom CAD Services The Printed Circuit Designer's Guide to...™ Executing Complex PCBs 2nd Edition Scott Miller FREEDOM CAD SERVICES INC. © 2019 BR Publishing Inc. All rights reserved. BR Publishing Inc. dba: I-Connect007 942 Windemere Dr. NW Salem, OR 97304 U.S.A. ISBN: 978-0-9980402-4-0 Visit I-007eBooks.com for more books in this series. I-Connect007.com Peer Reviewers John R. Watson, CID Building Control Division Legrand, North America John R. Watson, CID, has worked in the PCB design field for nearly 20 years. In that time, he has held almost every position available. As the senior PCB engineer, John leads a team of 50+ designers in multiple divisions spanning the world in the Building Control Division of Legrand North America. Although he is a highly sought out speaker and writer, John’s passion still lies with mentoring and teaching, espe- cially young people. Stephen V. Chavez, CID/CID+ IPC Designers Council Executive Board Stephen V. Chavez, CID/CID+, is a member of the IPC Designers Council Executive Board and a lead electrical designer at a large, globally recognized aerospace company. He is an IPC CID+ certified designer and has been involved with the PCB design industry, both domestically and internationally, for over 28 years. Further, Stephen is an IPC CID designer certification instructor (CIT) with EPTAC Corporation and VP of the Phoenix chapter of the IPC Designers Council. He has also been a keynote speaker at several design forums at IPC APEX EXPO and other industry confer- ences and seminars and has published several industry articles to date. About the Author Scott Miller Chief Operating Officer Freedom CAD Services Inc. Scott has spent over 40 years in the electronics industry. His early career focused on the interconnect field of high-performance connectors and printed circuit boards. Scott joined Freedom CAD Services in 2004 after a 20-year career with Teradyne Connec- tion Systems (now Amphenol TCS) in sales and marketing. Drawing on his experiences from the high-speed connector and PCB industries, Scott has helped Freedom CAD to develop its services beyond printed circuit board layout to include electrical, mechanical, and signal and power integrity engineering services as well as prototype PCB fulfillment. Contents Chapter 1 1 Communication Chapter 2 7 Plan It Before You Design It Chapter 3 15 More Planning: The Layout Chapter 4 21 The Design Kickoff Chapter 5 27 Design Rules, Simulations, and Analyses Chapter 6 33 Quality Assurance and Manufacturability Chapter 7 41 Post-layout Processes 45 About Freedom CAD Services 8 Chapter 1 Communication The single biggest problem in communication is the illusion that it has taken place. —George Bernard Shaw Introduction When has a meaningful electronics career challenge ever not been complex? There is probably no better example to illustrate the definition of complexity than a printed circuit board (PCB). Open up your computer or cellphone. At first glance, the PCB stands out as a major part of the inner workings of the device. Now, look closer. The PCB is full of smaller devices; they’re like build- ings, each interconnected with roads of copper. Yes, a PCB has been described metaphorically as a small city. The metaphor runs deep because along with the “buildings,” the design industry now refers to “floor planning” a layout. This book will provide a set of guidelines for designing complex PCBs, with real-world examples as well as handy tips, tricks, and techniques by some of the veteran technologists at Freedom CAD Services. The Challenge: Getting Complex Designs to Market Complex printed circuit design is not easy. Data indicates that only 25% of projects are released on time without any resource surges, and 17% of all projects are canceled. The rest suffer from either project delays or they need addi- tional resources such as an increase in personnel (Figure 1.1). Life- cycle Insights also reports that the typical board project goes through 2.9 re-spins with an average cost of $44,000 per re-spin. Figure 1.1: The fate of complex printed circuit design projects. (Source: Lifecycle Insights) 1 Attempting to Define Complexity The complexity of printed circuits can be elusive. This industry continues to evolve at an ever-increasing rate, and the definition of “complex” is constantly changing. For this book, we will use several characteristics listed here, but realize that the list is not complete. A printed circuit is complex if it has one or more of these characteristics: • The density of component pins exceeds 110 pins per square inch (17 pins per square cm) • The density of component parts exceeds an average of 5 pins per part • The density of component parts exceeds 10 parts per square inch (1.55 per square cm) • The number of pins of any BGA exceeds 800 • The pitch of the pins of any BGA is less than 0.8 mm • The thickness of the finished board exceeds 3.0 mm or is less than 0.5 mm • The rise time of any complex component is less than one picosecond • The circuit requires mixed technology of digital, radio frequency (RF), or analog • The board will require mixed materials for construction • The finished board needs to be cost sensitive for high-volume production • The board needs to be finished in less than the standard process time • The board has a lot of electrical constraints Using these criteria, Freedom CAD has selected three past projects to help characterize our topic (Table 1.1). 2 Table 1.1: Characteristics of three complex PCBs. 3 PCB Design Process Flow Because of the number of projects going at any one time, Freedom CAD uses a standard PCB design process flow (Figure 1.2). This process flow is simplified for this book with all the checkpoints and customer approval steps omitted. For the remainder of the book, this process flow will be followed. Figure 1.2: The Freedom CAD PCB design layout flow. Communication Challenges in the PCB Industry To an electrical engineer (EE) facing the pressures of looming deadlines, communicating with your fabricator should be a primary focus. Hopefully, an EE adheres to the vast amount of electronic standards available from IPC, IEEE, UL, and others during the schematic capture design process. There are also manufacturing standards to consider when selecting parts. Odd PCB outlines and thicknesses? Through-hole, surface mount, or pin-in- paste? Many design options must be clarified to be considered on the front end. There are times when the EE is faced with a design challenge that is so advanced and cutting edge that there are no standards to follow. During a complex PCB design challenge, creative forms of communication must take place to achieve a successful design. 4 5 6 Chapter 2 Plan it Before You Design It complex /kɑmˈplɛks/ Brit /ˈkɒmˌplɛks/ aadjective complex highwayDefinition system. 1 [more complex; most complex]: Having parts that connect or go together in complicated ways: Verbal, Written, Graphic, and Electronic Communication For the finer points of complex PCB design, communication standardization is required more than ever. IPC has done a good job helping the PCB industry in both verbal and written forms of communication with IPC-T-50 (Terms and Definitions for Interconnecting and Packaging Electronic Circuits). A successful design process cannot tolerate terms that can have entirely different mean- ings to various stakeholders. Non-standard terms can become a major source of confusion. A member of the operations team* emphasized that designers need to be aware of all the possible communication options available: “We find that more and more layout designers are working remotely from their engineer. Freedom CAD performs 99% of our layout support remotely from our customers’ engineers. We, like many organizations, utilize web conferencing tools such as WebEx, GoToMeeting, or Google Hangout, to name a few. These tools enable screen sharing and drawing, which greatly reduce the obstacles of working remotely. Web conferences can be set up in seconds by either party for real-time collaboration to view and discuss issues without resorting to lengthy emails that can cause delays while waiting for answers. When we are not local to the engineer, we use these web conferences to hold a kick-off meeting between the layout engineer, electrical engineer, and others related to the design to walk through the design details. This provides the opportunity to visually share information and ask questions to learn what’s critical and what’s not from the customer to facilitate a smooth launch of the design process.” *Editor’s Note: All quoted sources are Freedom CAD employees. 7 The Logic Diagram and Schematic Ready for another metaphor? The preliminary preparation for a PCB project is like planning for an expedition. Can you imagine any successful adventurer undertaking an expedition to a challenging destination without proper plan- ning? Maps with direct and alternate travel routes must be charted. Transpor- tation hubs and timing schedules must be researched and recorded. Expense and supply estimations must be secured. Often, the expedition is underwritten and funded by sponsors who must approve all of its major aspects. This is similar to a complex PCB design. Before any electronic copper trails are trod, all of the pieces of a complex PCB design—the parts and their value, source, cost, connectivity, and performance requirements—need to be captured within a schematic capture design database. The schematic capture database, also known as the front end, serves as the repository for the entire virtual design. A tremendous amount of data is hier- archically organized and stored here in the front end of the design by the EE.