Beyond Design: High-speed Rules of Thumb
Global PCB Connections: A Technical Overview of Long-flex Printed Circuit Boards
The Shaughnessy Report: A Handy Look at Rules of Thumb
Mark Thompson's Biggest Problems With PCB Designs
July 6, 2023 | Mark Thompson, Out of the Box ManufacturingEstimated reading time: 1 minute
What are the top problems I see with PCB design? From where I sit now on the assembly side, one of my biggest concerns related to PCB design is the lack of uniform part markings on the Gerber or ODB++ data, specifically the way customers reference diodes. We would prefer either an “A” depicting the anode side or a “C” or “K” for the cathode side. Many customers simply use either a line or a dot, which requires us to contact them to clarify which side is the cathode and which side is the anode.
If a line is used to denote the cathode side, many times the silkscreen clip using the mask clearance by the fabricator wipes out most of the line, making it difficult or impossible to determine the location of the cathode side. Using a dot doesn’t really help; does a dot depict an anode or cathode? Besides, dots are typically used to denote Pin 1 designators. Please use an “A” for the anode side and a “C” or “K” for the cathode side.
Controlling Controlled Impedances
Another area that concerns me is controlled impedances. Don’t make assumptions about controlled impedances. Your goal as a PCB designer is to simulate impedance to within 10% of your goal. The fabricator should be able to take it the rest of the way since the fabricator knows its press parameters, press values, and effective Dk. Trust your chosen fabricator and use the numbers they provide you.
If you simply go online and check material PDFs for the purpose of establishing impedances yourself be aware that many of the generic spec sheets are for very thick dielectrics (.014" core and sometimes even .028" core) the Dk associated with the thicker dielectrics are higher which, if used for trace widths .005" and below will create a mismatch and the fabricator will come back with a line size that your space may not support.
Also, consider the speed. If the literature is showing 4.5 Dk at 1 Mhz, and you know this product will be running at higher speeds, such as 5,10 or even 20 Ghz, understand the Dk will be driven way down. You may be looking at something closer to 3.8 Dk at 5 Ghz and the mismatch will affect the impedance.
Mark Thompson is an engineering manager with Out of the Box Manufacturing and a longtime CAM expert.
This article appeared in the June 2023 issue of Design007 Magazine.
Share on:
Suggested Items
Happy’s Tech Talk #34: Producibility and Other Pseudo-metrics
11/12/2024 | Happy Holden -- Column: Happy’s Tech TalkAs an engineer, I thrive on data, and one of my favorite forms is metrics. However, the one metric that has always challenged me is producibility. I define this as more than just passing a DRC in CAM, but the entire envelope of “simplicity of design,” “suitability for test,” and many more. Yet, producibility seemed to be different for different engineers and we had no clear way to establish and define producibility other than opinion. When I worked at HP, the company invested in a methodology called design for manufacturing and assembly using the GE/Hitachi Methodology and Dewhurst-Boothroyd software. Finally, I had a methodology that created a producibility score.
Flexible Thinking: Musings on High Density Interconnections
10/30/2024 | Joe Fjelstad -- Column: Flexible ThinkingPeople have been using high density interconnection (HDI) technology since the early 1980s, although it was not called HDI until the late 1990s. In the 1970s, ’80s, and early ’90s, engineers used HDI methods to develop hybrid circuits, which were later referred to as multichip modules (MCMs). These were arguably the first instantiation of heterogeneous interconnection technology, which has been the industry buzzword for almost a decade. These devices are a way of integrating multiple chips—both integrated circuits and discrete devices (resistors, capacitors, and inductors)—into a single package, typically using ceramic substrates with layers of insulation and metallic inks (often gold) and firing them at high temperatures.
It’s Only Common Sense: Want to Succeed? Stay in Your Lane
10/28/2024 | Dan Beaulieu -- Column: It's Only Common SenseIn today’s busy world, there are so many things going on, that it’s easy to get distracted. We live in an era of constant comparison and nonstop disruption. Everyone’s talking about the latest technology, the economy’s twists and turns, globalization, or how Company X is doing something you’re not. But here’s the thing: None of that matters if you’re not focused on your path. I’m going to say it straight: Stay in your lane. It’s the only way you’ll ever find success in business and life.
Book Excerpt: The Printed Circuit Designer’s Guide to... DFM Essentials, Ch. 1
10/25/2024 | I-Connect007The guidelines offered in this book are based on both ASC recommendations and IPC standards with the understanding that some may require adjustment based on the material set, fabricator processes, and other design constraints. This chapter details high-frequency materials, copper foil types, metal core PCBs, and the benefits of embedded capacitance and resistor materials in multilayer PCBs.
The Cost-Benefit Analysis of Direct Metallization
10/21/2024 | Carmichael Gugliotti, MacDermid AlphaCarmichael Gugliotti of MacDermid Alpha discusses the innovative realm of direct metallization technology, its numerous applications, and significant advantages over traditional processes. Carmichael offers an in-depth look at how direct metallization, through developments such as Blackhole and Shadow, is revolutionizing PCB manufacturing by enhancing efficiency, sustainability, and cost-effectiveness. From its origins in the 1980s to its application in cutting-edge, high-density interconnects and its pivotal role in sustainability, this discussion sheds light on how direct metallization shapes the future of PCB manufacturing across various industries, including automotive, consumer electronics, and beyond.