The first thing that we teach young children who are learning to read and write is their ABCs. For most of us, these lessons occurred so long ago that we’ve forgotten the majority, but there is a lot more to the ABCs than you might remember. Teachers are specially trained to help children learn how to correctly pronounce and use their ABCs to build a strong foundation of English language skills that will serve them throughout their lives.
Just as the ABCs are the basics of English language skills, other skills also rely on basic principles or ABCs. One of these is circuit board design and layout. Although PCB design encompasses various board types and design technologies, some basic ABCs still apply. Here is a list of the ABCs of PCB design basics that can help engineers avoid problems and create successful designs.
What are the Basics of PCB Layout that Designers Need to Know?
First, let’s ask ourselves what basics we need to know to design a circuit board? Circuit design itself requires an understanding of and training in electrical design. We won’t cover electrical theory or how to design different types of circuits here. And likewise, we won’t cover the operational details of the various CAD tools used in the PCB design process. Those systems range from schematic capture and circuit simulators to PCB layout, auto-routers, CAM systems, and analysis tools.
Instead, we will look at the key points of the overall PCB design process. If any of these points are missed or executed incorrectly, it can result in problems later during manufacturing, testing, debugging, or throughout the product’s lifetime. So, let’s start our ABCs at the beginning of the design process by gathering the necessary design information and then go on from there.
PCB Design Basics from A to N
A) Collect as much information upfront as possible
The more data you collect upfront, the less you will have to change later in the design. This data includes mechanical specifications, library parts, critical placement, sensitive nets, and more. You probably won’t get it all, but the more you start with, the better.
B) Verify the bill of materials (BOM)
Are the components in your design available and at a competitive price point? Are your library parts current, and has your CAD database been updated with these parts?
C) Work from a clean schematic
Even with a completed schematic, you should expect changes along the way. However, you can ensure that there aren’t missing sections of circuitry or duplicated areas that need to be deleted, run the DRCs and clean up any problems reported. Start with a well-developed set of design rules and constraints within the schematic and synchronize the schematic and layout databases.
D) Verify the board’s mechanical data
Confirm with your mechanical design team that you are working with their most current data. This data includes dimensions, layer stackups, and fixed locations for components such as connectors, switches, and brackets.
E) Use the schematic when laying out the board
Most PCB design systems support cross-probing from the schematic to the layout. This feature is invaluable for floor-planning the component placement in layout and organizing components by their sensitive signals, voltages, and high-speed signal paths.
F) Follow design for manufacturing (DFM) rules
Using good DFM rules and guidelines for component placement will make the difference when designing a manufacturable circuit board. It is essential to work ahead with your manufacturer to establish these rules before starting the PCB layout.
G) Keep thermal cooling in mind with component placement
As signal speeds increase and PCB form factors shrink in size, the circuitry on small high-speed designs can run very hot, necessitating effective thermal management. It is imperative to follow good thermal layout guidelines, such as locating processors and other hot parts in the center of the design for heat dispersion. You will also want to separate different power supplies from each other and avoid blocking airflow with tall components.
H) Place your parts with routing in mind
Avoid the temptation to crowd components, and leave yourself room for escape vias, bus routing, and power and ground connections.
I) PDN development is just as important as signal routing
The power delivery network is essential to the successful operation of your circuit board. Avoid using separate or split ground planes as unobstructed ground or reference planes are critical for clear signal return paths on high-speed and mixed-signal designs. A well-designed PDN also delivers clean power to all voltages, and the ground plane helps absorb power spikes and noise.
J) Be careful routing sensitive traces
Don’t ever route high-speed nets over splits or breaks in the reference plane. This mistake will block the signal’s return path, causing it to create a lot of noise as it tries to find its way home.
K) High-speed lines should be as direct as possible
Keep high-speed traces as short as possible to reduce the chance of reflection and noise. The exception to this rule is for measured lines that have to match a certain length for signal timing.
L) Keep power supply connections short and wide
Power traces should be short in length and as wide as possible. This configuration will reduce the inductance and noise in the power circuitry and help dissipate the heat of high-current connections.
M) The design doesn’t stop when the routing is complete
It is not uncommon for designers to let their guard down after component placement and trace routing is completed on their designs. This neglect is a classic mistake and could cost you time and money in redesigns and corrections. Solder mask, solder paste, and silkscreen design need the same level of care in their design as the rest of the circuit board.
N) Design reviews are essential
The more eyes you have on the design, the more likely you will spot problems that could cost you time and money.
Work Together with Your Contract Manufacturer
Yes, the last point on our list of ABCs is “N,” so you might be wondering what the rest of the alphabetic points are in this list? The answer is that they all have the same point: “Make sure to work together with your PCB contract manufacturer before you submit the design to be built.”
A PCB contract manufacturer has the design capabilities to help you with component-related questions, DFM rules, and guidelines, or how to engineer the best circuitry performance. At VSE, we have been working with customers like you for over 35 years, answering these questions and helping them to realize success with their electronic designs.
