3 Top PCB Design Guidelines
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 selections. But at the end of the day, not providing ample time and focused effort on your PCB design 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 3 top PCB design guidelines that you need to know to design your next functional and reliable PCB.
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, follow these guidelines:
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 PCB, 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.
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’re 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.
Adding thermal reliefs -- It can be incredibly useful to produce a manufacturable board and they are critical for the wave soldering application on high copper content assemblies and multilayer boards. 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. As a general guideline, always use a thermal relief pattern for any via or hole that is connected to a ground or power plane. In addition to thermal reliefs, you can also add teardrops where traces join pads to provide additional copper/metal support. This will help to reduce mechanical stress and thermal stress.
Checking Your Work
It’s easy to get overwhelmed toward the end of your design project as you scramble to fit your remaining pieces together for manufacturing. But double and triple-checking your work for any errors at this stage can really mean the difference.
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 enforce gap widths, trace widths, common manufacturing setups, high-speed requirements, and short circuits.
When your 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.
There you have it - our top 3 PCB design guidelines that every PCB designer needs to know. By following this small list of recommendations, you’ll be well on your way towards designing a functional board in no time, and a truly quality printed circuit board at that.
Good PCB design practices are crucial for success, these design rules form a foundation for building upon and solidifying a practice of continual improvement in all your design practices.