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PCBs are sometimes seen as an over-glorified way to wire up electronic components. However, once you understand the complexity of advanced PCBs and the importance of enforcing some order to your components on a single board, you’ll realize the importance of creating a PCB for your new device. If you’re a new designer, it can be difficult to find a good set of guidelines for getting started designing your first PCB.
We want to give new designers some important PCB design guidelines to follow when building a new board. The guidelines below are not strict PCB design rules, but are suggestions that might help save you a lot of rework. You might not need to follow all of these guidelines for every design. At the end of the day, you are the master of your design, and with some practice, you will know what works best for your project.
Top PCB Design Guidelines for Beginners
Once you have validated your design idea with a breadboard, individual components, and what seems like a couple hundred wires, it is time to move start designing your own PCB. The most important considerations for a successful PCB design are that it should be manufacturable, functional, and reliable. The design tool you use can help ensure manufacturability by allowing you to checkyour layout against standard design rules and constraints.
The first step is to start designing a schematic for your board in the tool of your choice. This process is rather easy as you are placing connections between the components. The design tool you use should include a schematic capture tool as this allows you to generate an initial layout from your schematic. It’s good to have a detailed schematic that gives you access to different component specifications, such as pin-out, names, and ratings. Once you finish your schematic, your schematic capture tool will create the initial layout, and you can then start making real connections on a PCB.
A PCB is like a piece of real estate; some areas carry higher value than others. Placement of each component depends on its individual importance. Precision; sensitive analog parts must not go to the edges and they should be kept away from any areas on the board with fast digital components (i.e., TTL components). Similar parts should also have similar orientation on the board as this aids routing between components. All surface-mounted components must be on the same side of the board, and all through-hole components must be on the top layer of the board.
Power, Signal, and Ground Routing
Once you have tentatively placed your components (this might change as layout is a dynamic process!) it’s time to start connecting them together with copper traces. If you have a multilayer PCB, make sure to keep power and ground planes symmetric and overlapping. This helps prevent any bending or stress development on the board. If you have only two layers, then you will need to have thick power and ground lines able to withstand the heat generated by the total current flowing through your board.
The two methods for connecting functional blocks of electronic components are star configuration and daisy chaining. It is highly recommended that you not daisy chain the power lines to different functional blocks in a PCB. Instead, use a star configuration to connect power rails to different portions of the board. This is a basic requirement for ensuring ICs receive consistent voltage during operation.
Daisy chaining should be avoided
Signals on the top and bottom layers of a two-layer PCB should run orthogonal to each other to avoid inductive coupling between them. For a multi-layer board, the same strategy should be followed for signal lines on adjacent layers. You should only break this guideline if there is a copper plane between the signal layers.
Orthogonal routing of traces on a two-layer PCB
Each PCB that contains digital components will have some areas with high switching activity and greater current consumption. Voltage and current spikes will occur when these digital components switch. These voltage and current spikes occur due to a large rush of current into a circuit during digital switching, sometimes called ground bounce. These voltage/current spikes can couple between different traces, known as crosstalk.
This problem can be solved using capacitors between the power and ground pins on a digital component. If you look at manufacturer’s guidelines for different components, they will often recommend a certain capacitor size which you can use to compensate for ground bounce.
It is also important to prevent coupling between digital and analog traces during switching using isolation. With mixed signal PCBs, it is important to keep analog and digital grounds separate in order to keep digital signals from interfering with sensitive analog components. This does not literally mean using two different ground planes; this can mean placing digital and analog components over different areas of the same ground plane. The DC bias signals should also be shielded from any coupling with digital signals. A good way to do this is to run two ground lines run on both sides of a trace carrying an analog signal or DC voltage. This simple design choice is known as shielding.
Signal or bias shielding
While designing a PCB, you should also consider heat management. First, you should look through your component datasheets for thermal resistance and power consumption values to determine which components will likely be producing the most heat and reach the highest temperature. In addition to heatsinks or cooling fans on hot components, there are some simply layout choices that help keep temperature low.
If more than one component will produce a large amount of heat, then it is best not to place these components in one location, otherwise hot spots might form. Circuits that are very sensitive to temperature changes should be placed farther away from these blocks. There should be at least 2-4 vias for each layer transition near high current paths. This helps conduct heat away from the surface layer and helps reduce inductive and resistive losses.
This is a huge area of PCB design, however there are some simple ways to ensure signals in your board do not get distorted during operation. Signals should be routed directly between components over the shortest possible path to reduce loop inductance. You should also avoid running parallel tracks over long distances as this increases capacitive coupling. If tracks need to cross, this must be done at a right angle to reduce coupling capacitance. These guidelines will help suppress crosstalk and reduce susceptibility to electromagnetic interference (EMI).
To ensure your PCB meets functionality and reliability criteria, it is important to check the design for any rule violations. Electrical rule checks (ERCs), and design rule checks (DRCs), are two very important tools that should be performed once you have laid out your board. The right design software can run these checks dynamically (i.e., as you place components and route traces). This helps you identify design errors that may not be obvious from a visual inspection. Once you have verified your schematic is correct and your layout complies with all design rules, you are ready to think about producing your board.
Choosing the Right PCB Design Tools
There are many PCB design tools in the market. A good tool is the one that provides easy integration between schematic and layout, a vast library with reliable components, and provides easy platform for collaboration and sharing. You should also be able to generate documentation for a manufacturer. This includes Gerber files, assembly drawings, and a bill of materials for your components.
Upverter® provides schematic design and PCB layout capabilities for designing boards from start to finish. Its browser-based platform gives you access to your work from anywhere and makes it easy to collaborate. Upverter’s cloud-based platform verifies part designs, removing the risk of symbol and footprint errors so that you can manufacture your designs with confidence.