PCB Design Basics for New Designers
Let’s set the scene: you’ve just installed your new PCB design program and you’re ready to jump into your first PCB layout. What should you do to get started? Most engineers are excellent at working with schematics and selecting their core components, but someone who is new to PCB layout might find the process overwhelming. PCB design software contains a lot of tools and follows a specific workflow, but it’s possible for a beginner to move through the design process with knowledge of some PCB design basics.
In this article, I’ll present some design basics that every new designer should follow to help ensure their design process is successful. Some of these points may challenge the conventional view of how circuit boards are constructed, but they are intended to help balance low noise signaling, manufacturability, and ease of solving a layout.
The Basics of Starting a New PCB Design
The PCB design process follows a standard workflow, and it’s important for any ew designer to understand how this workflow unfolds. The standard workflow in PCB design focuses on taking an engineered design, finishing a physical PCB layout, and preparing the finalized design for manufacturing.
Understand the PCB Design Workflow
It’s best to take some time to briefly acquaint yourself with the standard workflow before proceeding further, so read the above link. The design workflow proceeds through the following list of steps:
- Select core components that are in-stock and sourceable from major distributors
- Create and review schematics based on engineering requirements
- Create a blank PCB, build the stackup, and create design rules
- Import component data from the schematics into the new PCB layout
- Place components and review placement to ensure engineering requirements are met
- Route traces and connections between components
- Clean up the PCB layout and perform a final design review
- Prepare design outputs and send these in for manufacturing
Once you’ve got a high-level view of the design process, read the link below to see how the PCB design workflow unfolds and the standard set of tasks every designer must perform to finish a new circuit board.
Schematics and Layout Must Be Synchronized
If you’re just starting your journey as a PCB designer, you’ll probably create your own schematics for your device. Whenever you make a change to the design, you have to synchronize those changes between the schematics in the layout. In particular, this includes any of the following design changes:
- Adding, removing, or swapping components
- Adding, removing, or changing nets
- Grouping nets into Net Class objects
- Changing component parameter information (part number, supplier information, etc.)
- Any other electrical rules or directives applied to objects in your schematics
After any changes are made, they have to be applied over to the PCB layout. This is done with an import feature in your PCB design software. This ensures everything in your design is synchronized and the design rules engine in your software will read your design data correctly.
Learn About the PCB Manufacturing Process
Any design that you intend to produce as a physical product should be manufacturable at scale. ECAD software will allow you to implement any design feature you can imagine into your PCB layout. However, your design decisions need to be manufacturable in standard processes, so a designer needs to be familiar with the limits of what can be fabricated in a PCB.
This means that every PCB designer should take time to learn the basics of PCB manufacturing so that they can ensure their designs are fully manufacturable. This relates to an important set of practices that should be built into your design process, known as design for manufacturing (DFM). Take some time to learn about some basic design mistakes that can derail manufacturing and cause your board to be sent back to you for redesigns before production.
Design Rules Are Key to Success
After you’ve learned about the manufacturing process, as well as some of the standard capabilities found from PCB fabricators, it will be much easier to understand some of the limits imposed in design rules. Most DFM problems relate to the size of copper features in the PCB, or the clearance between different features. The default design rules programmed into PCB design software are usually a bit conservative, and you should know the limits to which you can violate those design rules.
As an example, consider the footprint below. This footprint has pad-to-pad spacing of about 9 mils, but it triggers a design rule error (seen in green) once the component is transferred to the PCB layout. You can comfortably violate this design rule and set your limit lower as most fabricators will require minimum spacing of approximately 5 mils. Make sure to check clearances on your fabricator’s capabilities sheet before you start messing with design rules.
Use a Ground Plane
Every PCB will need to have a clear ground connection so that all components in the design will form complete circuits and so that electrical power will be supplied throughout the design. The ground connection can be to a battery on the board or to an external power supply. No matter how that connection is made, that ground connection then needs to be supplied to all other components in the PCB. By far, the easiest way to do this is with a ground plane, where one of the layers in the PCB is used for ground with a large sheet of copper covering the entire layer.
To this day, I’m still surprised at the number of new designers that hesitate to place a ground plane in their PCB stackup. Many basic noise problems that affect digital and analog signals can be traced back to the absence of a ground plane in the device. In modern PCBs, it is a standard guideline to use a solid ground plane throughout your device. There are some exceptions where split planes or a star ground on a PCB are appropriate, but those approaches are not appropriate for the vast majority of digital and analog designs.
Complete Placement Before Routing
As soon as you transfer your schematic data into a new PCB layout, you’ll have to place components around the board. At this point in the design, your goal is to place components to ensure that the design is solvable, meaning it can be routed easily. Therefore, it’s best to avoid doing any routing until after the components are placed and placement is approved. If you route before all the components are placed, it’s inevitable that you’ll have to change the routing. Before routing anything, try to get the layout to the point where all net crossings are minimized.
After everything is placed and finalized, it’s time to start routing the PCB. If you took the advice above and reviewed your design rules before you started working on your PCB layout, then you’re more likely to route a design successfully. When we use the word “success” to describe routing, we’re generally referring to three areas:
- Minimize the need for new signal layers to route all your signals
- Minimize transitions between layers when possible
- Minimize noise, which is aided by the use of a ground plane in the PCB stackup
- Try to keep as many routes as possible short and direct
This list of guidelines is not exhaustive, but they are applicable to traces carrying most of the signals you’ll route throughout your PCB. High speed, low speed, low frequency analog, and RF designs all make use of these PCB routing tips, so get used to implementing these same practices in your PCB layout.
Don’t Forget: Your Goal is to Manufacture!
Once everything in the layout is routed and finalized, your job still isn’t finished. As a designer, it’s your job to create manufacturing files from the PCB layout. PCB design software includes tools to create these output files automatically. Even after you prepare outputs, you should still review these files to ensure you did not mis-apply any of the settings in the output file exporter, so take some time to review everything before sending it in to your manufacturer.
What Happens Next?
Congratulations! You’ve reached the end of the design phase and it’s on to manufacturing. Next, your manufacturer will review the design to ensure it conforms to their processing capabilities. If everything passes a final DFM review, your board will go into production and assembly.
Once you’ve learned the PCB design basics, try using the complete set of PCB design and layout features in Altium Designer®. When you’ve finished your design, and you’re ready to release files to your manufacturer, the Altium 365™ platform makes it easy to collaborate and share your projects. You can also complete a comprehensive design review to help ensure your new board can be produced with high yield and high quality.
We have only scratched the surface of what’s possible with Altium Designer on Altium 365. Start your free trial of Altium Designer + Altium 365 today.
Checkout this related video on Selecting PCB objects and more tips and guides on Altium Academy Youtube Channel