- Fine-Tuning Your Component Placement
- Placing Your Power, Ground & Signal Traces
- Keeping Things Separate
- Combating Heating Issues
- Checking Your Layout Against Your PCB Design Rules
What’s the key to designing a board that’s realistic on paper and in physical form? Let’s explore the top 5 design guidelines that you need to know to design your next manufacturable, functional and reliable PCB.
Top 5 PCB Design Guidelines for Engineers
When starting a new design, it’s easy to leave the PCB design guidelines as an afterthought as you spend most of your time focusing on your circuit design and component selection. But at the end of the day, not providing ample time and focused effort on the PCB layout basics can lead to a design that translates poorly from the digital domain to physical reality, and could ultimately become troublesome for your manufacturer to fabricate. So what’s the key for designing a board that’s realistic on paper and in physical form? Let’s explore the top 5 PCB design guidelines that you need to know to design your next manufacturable, functional and reliable PCB.
#1 - Fine-Tuning Your Component Placement
The component placement stage of your PCB layout process is both an art and a science, requiring a strategic consideration about the prime real estate available on your board. While this process can be challenging, how you place your electronic components will determine how easy your board is to manufacture, as well as how well it meets your original PCB design requirements.
There are many PCB layout rules to consider during component placement. While general board layout guidelines tell you to place components in order of connectors, power circuits, precision circuits, critical circuits, etc…, there are also several specific board layout guidelines to keep in mind.
Orientation. Be sure to orient similar components in the same direction as this will help with effective routing in PCB design. It also helps ensure an efficient and error-free soldering process during assembly.
Placement. Avoid placing components on the solder side of a board that would rest behind plated through-hole components.
Organization. It’s recommended to place all your surface mount devices (SMD) components on the same side of your board according to SMD PCB design rules. All through-hole (TH) components should be placed on the top side of your board to minimize the number of assembly steps.
One final PCB design guideline to keep in mind - when using mixed-technology components (through-hole and surface mount components), manufacturers might require an extra process to assemble your board, which will add to your overall costs.
Good Chip Components Orientation (left) and Poor Chip Components Orientation (right)
Good Components Placement (left) and Poor Components Placement (right)
#2 - Placing Your Power, Ground & Signal Traces
With your components placed, it’s now time to route your power, ground and signal traces to ensure your signals have a clean and trouble-free path of travel. Here’s some guidelines to keep in mind for this stage of your layout process:
Orienting Power and Ground Planes
It’s always recommended to have your power and ground planes internal to your board, while also being symmetrical and centered. This will help to prevent your board from bending, which will also affect whether your components are properly positioned. Note that this is not possible on a two-layer board as you will not have any room for components. To power your ICs, it’s recommended to use common rails for each supply, ensure you have solid and wide traces, and also avoid daisy-chaining power lines from part to part.
Routing Guidelines for PCB Layouts
Next up, connecting your signal traces to match your schematic guidelines. PCB layout best practices recommend that you always place traces as shortly and directly as possible between components. If your component placement forces horizontal trace routing on one side of the board, then always route traces vertically on the opposite side. This is one of many important 2 layer PCB design rules.
Printed circuit board design rules and PCB layout guidelines become more complex as the number of layers in your stackup increases. Your routing strategy will require alternating horizontal and vertical traces in alternating layers, unless you separate each signal layer with a reference plane. In very complex boards for specialized applications, many of the commonly-touted PCB best practices may no longer apply, and you'll need to follow PCB design guidelines that are particular to your application.
Defining Net Widths
Your design will likely require different nets that will carry a wide range of currents, which will dictate the required net width. With this basic requirement in mind, it’s recommended to provide a 0.010” width for low current analog and digital signals. Traces that carry more than 0.3 A should be wider. Here’s a free Trace Width Calculator that makes this process easy. You can also use this calculation (based on IPC-2152) to determine your PCB trace width.
#3 - Keeping Things Separate
You’ve likely experienced how the large voltage in power circuits and current spikes can interfere with your low voltage and current control circuits. To minimize this interference issue, PCB design guidelines for power electronics tend to recommend the following:
Separation. Be sure to keep the power ground and control ground separate for each power supply stage. If you do have to tie them together in your PCBs, make sure it’s toward the end of your supply path.
Placement. If you have placed your ground plane in the middle layer be sure to place a small impedance path to reduce the risk of any power circuit interference and to help protect your control signals. The same guideline can be followed to keep your digital and analog ground separate.
Coupling. To reduce capacitive coupling due to the placement of a large ground plane and the lines routed above and under it, try to have your analog ground crossed only by analog lines.
#4 - Combating Heating Issues
Ever have your circuit performance degraded or even your board damaged because of heat issues? This problem afflicts many designers when heat dissipation isn’t taken into consideration. Here’s some guidelines to keep in mind to help combat heating issues:
Identifying Troublesome Components
The first step is to start considering which components will dissipate the most heat on your board. This can be accomplished by first finding the “Thermal Resistance” ratings in your component’s datasheet, and then following the recommended guidelines to divert the heat being produced. Of course, heatsinks and cooling fans can be added to keep component temperatures down, and also remember to keep critical components away from any high heat sources.
If you have more than one component that generates a large amount of heat, it may be best to distribute these components throughout the board, rather than clustering them in one location. This prevents hot spots from forming in the board. You may have to carefully balance placement of these components against keeping trace lengths short as you devise a routing strategy, which can be challenging.
Adding Thermal Reliefs
Adding thermal reliefs can be incredibly useful to produce a manufacturable board and they are critical for wave soldering application on assemblies and multilayer boards with high copper content. Because it can be difficult to maintain process temperatures, it’s always recommended to utilize thermal reliefs on through-hole components to make the soldering process as easy as possible by slowing the rate of heat sinking through the component plates.
Some designers will tell you to use a thermal relief pattern for any via or hole that is connected to a ground or power plane. This is not always the best advice. Note that a power/ground via can appear near an IC with fast switching speed, which generates a lot of heat. Moving heat away from the IC helps regulate the temperature of the IC.
The ground plane can act as a large heat sink that then transports heat evenly throughout the board. Therefore, if a particular via is connected to a ground plane, omitting the thermal relief pads on that via will allow heat to conduct to the ground plane. This is preferable to keeping heat trapped near the surface. However, this can create a problem if your board is assembled using wave soldering, as you need to keep heat trapped near the surface.
In addition to thermal reliefs, you can also add teardrops where traces join pads to provide additional copper foil /metal support. This will help to reduce mechanical stress and thermal stress.
#5 - Checking Your Layout Against Your PCB Design Rules
It’s easy to get overwhelmed toward the end of your design project as you scramble to fit your remaining pieces together for manufacturing. Double and triple-checking your work for any errors at this stage can mean the difference between a manufacturing success or failure.
To help with this quality control process, it’s always recommended to start with your Electrical Rules Check (ERC) and Design Rules Check (DRC) to verify you’ve met all of your established constraints. With these two systems, you can easily define gap widths, trace widths, common manufacturing requirements, high-speed electrical requirements, and other physical requirements for your particular application. This automates PCB layout review guidelines for validating your layout.
Note that many design processes state that you should run design rule checks at the end of the design phase while preparing for manufacturing. If you use the right design software, you can run checks throughout the design process, which allows you to identify design potential problems early and correct them quickly.
When your final ERC and DRC have produced error-free results, it’s then recommended to check the routing of every signal and confirm that you haven’t missed anything by running through your schematic one wire at a time. And of course, ensure that your PCB layout matches your schematic with the use of your design tool’s probing and masking feature.
Rounding It Up
There you have it - our top 5 PCB design guidelines that every PCBs designer needs to know. By following this small list of recommendations, you’ll be well on your way towards designing a functional and manufacturable board in no time, and a truly quality printed circuit board at that.
Good PCB design practices are crucial for success. These PCB design guidelines only scratch the surface, but they form a foundation for building upon and solidifying a practice of continual improvement in all your design practices.
Want some more best practices on how to design a board that gets manufactured right the first time? Check out our Design for Manufacturing webinar - Maximizing Your PCB Production Yield or start trying these PCBs design guidelines now with our flagship software.
Check out Altium Designer® in action...
Modern Interface Experience
“I had not been exposed to much 3D PCB design capability in the past. As a relatively new ALTIUM user I have to say that designing flexible and rigid PCBs in 3D using Altium is a lot easier than I thought it would be. Trading 3D PCB layout files with my mechanical cohorts for review has never been easier!”
Kelly Dack, CID+ CIT
PCB Designer / IPC Instructor
Sign up and try Altium 19 today.
About the AuthorMore Content by David Marrakchi