Don't engineering yourself into a corner with your PCB design - here's how to avoid it!
Designing printed circuit boards can be tricky work - and the bigger your project gets, the more complicated things can get! To help you avoid some of the pitfalls that many engineers fall into, here are three ways to prevent designing yourself into a corner with your PCB design. As an added bonus, this also gives you ideas on how to make your designs stronger and smarter as well!
Make sure you have space
A poorly designed PCB can end up costing you thousands of dollars in materials and hours wasted. If you're designing a PCB, these are some steps that will keep the process on track:
- Draw the basic schematic first, including all electronic components and external devices such as sensors or motors. It is important to identify what each component needs so that it can be connected correctly. Some components need more pins than others; therefore when connecting two components, make sure they use the same number of pins.
- Consider if there are any ways to eliminate parts from the original design by using off-the-shelf modules instead of custom hardware or software. Doing this may reduce hardware size and cost as well as development time since modules are typically pre-tested and come fully assembled. For example, it would take me 3 days to build an 8x8 LED matrix controller module for the Chibitronics Circuit Scribe Kit. The same project would take an hour and a half to program using their module. For complex circuits where I want fine control over parameters like display brightness, I recommend purchasing modules that include variable resistors or potentiometers instead of resistors fixed at certain values. If none exist, consider making them yourself by hand soldering small strips of metal wire together in varying lengths to create variable resistor chains like I did for my Open Hardware Graphics Card project. - Ensure all components have space around them to fit within the layout of the PCB, but also check that it does not exceed circuit board dimensions. When laying out a PCB, try to leave as much room between components as possible. Leave enough space between input and output ports (ie connectors) so wires do not short circuit. Make sure no solder joints fall outside of the solder mask area defined on the board outline layer. Solder joints are fragile structures which require support structures in order to remain intact during the production process. Solder masks provide that support structure, so if your solder joint falls outside of the mask area then it will likely break during assembly and you'll have to repair it by reheating and pressing it back down into place. In addition, be aware of differential pairs used for signals carrying high speed data; these should always be symmetrical about a center line on the PCB. Typically one side of the pair has a copper plane and shield cover which is covered with insulation material (solder mask), while the other side does not. To maintain symmetry, mirror both sides before sending to manufacture. This will ensure that the conductor traces are routed the same on both halves of the PCB. These traces must be symmetrical in order to cancel out electromagnetic interference and ensure proper data transmission.
- Include notes for manual assembly. This can save you a lot of headaches later on. Here are some things to note in your documentation: - Any components that must be manually installed or wired together, and the length of wiring required to connect them with each other or externally.
Avoid obstructions
Obstructions can lead to really bad outcomes, like a board that doesn't have enough clearance for mounting or an inability to make small adjustments. The two key ways to prevent obstructions are physical and programmatic.
● Physically ensure there is plenty of room by laying out the whole project on the table in front of you and test fit everything so you know where the pieces should go before making any changes. If there isn't enough space, consider adding spacers or shrinking down parts. If nothing else works, try redesigning the layout completely! ● Programmatically define the size of each component and spacing between components so that you won't have trouble at assembly time. If you've already committed to this layout but realize too late that there's not enough space between some components because they're intersecting one another, use Kicad cutouts (which require a grid) rather than regular polygons as these give more flexibility when placing them. You can also resize objects or move them around to free up some space if you want to be less drastic about changing the overall design. It might take a little bit of trial and error, but with careful planning you'll end up with a circuit board that has no obstructions from start to finish. That way, you'll be able to manufacture it quickly and easily without errors! Good luck with your next PCB design! Hopefully this post helped save you some headaches. Now go back to designing circuits instead of reading blogs ;-)
Include buffer zones around edge-traces
Buffer zones are the distance left between traces on the same plane and edges of PCB board. There is no set standard for the width of these zones, but generally they should be at least 20% of the trace width or 25 mils. The most important thing is to never let any pads touch other pads or traces. When pads do touch, this can cause solder bridges that don't connect any component pins and create shorts between traces in different layers. So, always leave buffer zones around edge-traces.
A good way to ensure you have enough buffer space is by specifying the net width (after adding all necessary spacing) when designing the board layout in EAGLE CAD software. You can then use autorouter tools like SmartRouters and Design Rules Checker (DRC) to help guide your path while routing individual nets. But there's another option: change the shape of your boards. If you're using 5mm (1/4) square copper boards, for example, and need more room around an edge-trace, try using 3mm x 2mm rectangle copper boards instead.
Including buffer zones will give you peace of mind as a designer and make your product function properly without risking costly mistakes in manufacturing. And remember, the world of electronics design is constantly changing and developing; new technologies come out every day which can sometimes make older methods obsolete. What works today may not work tomorrow so don't risk leaving yourself behind with old techniques. Get ahead of the curve and start making smarter decisions now! And finally, NEVER forget to verify your PCB designs with a final review and inspection before sending them off for production. Any issues found at this stage will be easier and cheaper to fix than if you wait until after fabrication begins! Your board vendor will send you detailed schematics of what was fabricated and tell you about any defects that were detected during manufacture. Double check the schematic against your original circuit diagram and find any errors, or differences from what was expected to be produced. If anything looks amiss, report it back to your supplier right away and discuss what needs to happen next. It could turn out that they forgot something crucial, such as a missing cutout hole or some additional circuitry needed to finish off the project.
Route high-speed signals away from each other
Do not route high-speed signals on the same trace. This is one of the most important things to remember when routing traces on your PCB. If you don't do this, and fast signals run on the same line as slower ones, the slow signals will corrupt the faster signal in what is called crosstalk. Avoid running high-speed circuits close together in order to prevent crosstalk. Keep all traces near each other at roughly the same length as well in order to prevent variations in impedance (slow signal), which can also lead to crosstalk. Also remember that crosstalk worsens when high frequency signals are transferred over long distances so keep all routing as short as possible. It is good practice to make sure high-speed signals do not cross any other signals or power planes.
What if I have some devices with strict timing requirements? You may need to have different layers for different types of devices in order to meet their requirements while still avoiding cross talk. Designers use a technique called clock stretching or skewing where they move timing critical components like CPUs and memory away from routing critical components like digital logic gates. The CPU and memory are placed on a layer that has less electrical noise so they function correctly while digital logic gates stay on a layer with more noise because they function just fine there due to their lower speed requirements. Remember that the metal ground plane should be connected to every component on the board to provide an earth ground connection. Make sure these connections are made before applying power, especially during initial testing. A last note: always save early and often! Save your files frequently so you never lose work and always backup your board files separately from your CAD program file in case something happens. Once you're done designing, double check everything by measuring currents between ground and power pins on ICs and resistors to ensure no unintended voltage sources exist.
Add decoupling capacitors to power/ground pins and sensitive nodes
This is an important step in the layout of any IC on a PCB. Generally, decoupling capacitors are needed for power and ground pins and for any sensitive nodes. Capacitors are able to hold onto a charge much longer than resistors so they should be used when anticipating frequent changes in voltage on a node or fluctuating current demands. This can prevent situations where noise is generated due to voltage fluctuations at input pins, such as clock frequencies running faster or slower than expected. The greater the range of operation, the more critical it becomes to use these components.
High-speed interfaces (USB 3.0) require careful attention to impedance matching: Impedance matching is essential for high-speed signals because mismatches create reflections that can cause significant signal degradation or even interfere with normal operation. The source impedance should match the load impedance in order to minimize reflections from interfering with normal operation. To achieve this, termination resistors are often required. In the case of differential signaling pairs, one resistor neneedsu to be placed in series with each line. If a cable has unbalanced lines, then two resistors must be used. A single resistor is not sufficient to cancel out all reflections since both lines are terminated by different impedances. When terminating differential data lines on the board, an additional capacitor may also need to be added near each terminator in order to further reduce reflections between traces.
Place power nets close to ICs, split power nets for greater distances
There are two important things to keep in mind when designing power nets. First, you want to place power nets close to the ICs. You don't want the net drawing a lot of current because those parts tend to go over the recommended current limit and can create excessive heat. Second, if your ground plane has slots that are too big, you can split them up for greater distances and make your connections more efficient. It’s a good idea to have one or two lines in parallel per slot as well. Placing these at different depths makes your board layout more effective and less expensive. For example, placing an HDMI connector on the surface while hiding SATA connectors deeper is a cost-effective way to use space. The same is true for using copper planes instead of copper fill layers; some topologies require copper fill layers but most do not. Using copper planes also prevents issues with differential pairs and can be used to create impedance changes, reduce EMI and increase bandwidth between boards (on multilayer boards). Differential pairs use twice as much copper but they have an advantage: they produce no crosstalk which eliminates noise and they provide twice the bandwidth of single wire transmission. However, you should know their disadvantages: increased dielectric losses and decreased efficiency due to inductance. In general, using differential pairs is beneficial for high speed signals like PCIe or Ethernet. Single wires are better for low frequency analog or digital signals. One drawback to using differential pairs is that they typically need twice as much copper which means higher costs and takes up more space on the board. Another disadvantage is that they produce no crosstalk which eliminates noise and provides twice the bandwidth of single wire transmission. However, there are disadvantages to this as well: increased dielectric losses and decreased efficiency due to inductance. So it really depends on what type of signal you're trying to transmit. Overall, I would say it's best to have both types of wiring in order to take full advantage of your board space so the decision really comes down to what type of signal will be transmitted across these cables.
Include LEDs, displays and buttons on an area by themselves
When you're creating a project from scratch, you're going to want to use different kinds of components. LEDs, displays and buttons are some of the most common components for beginners, so let's take a look at how you can design them.
First off, we'll need some basic concepts for understanding the way that these devices work. They will be powered either by batteries or through an external power supply like an Arduino board. Since they need power, they also have to have something called a ground. The ground is used as one side of the circuit where electricity flows in and out. It also helps with reducing electromagnetic interference (EMI) which makes it harder for other electronics nearby to function properly.
The size of an LED is measured in millimeters (mm). A red LED is usually around 5mm across, while a blue LED might be closer to 10mm. You can control their brightness by adjusting the voltage applied between ground and the positive lead on the LED. If you apply more voltage than necessary, then you will get too much light coming out from them which could damage your eyesight over time. Conversely, if you lower the voltage too much then they won't give off enough light to be useful. Buttons are typically found on projects that have a user interface since they make it easier for someone using the device to interact with it. Unlike LEDs and displays, buttons don't come in varying sizes but instead vary depending on what kind of button was chosen. For example, a push button would go back up when pressed while a toggle button would stay pushed down until pulled up again.
There are many ways to go about designing PCBs and none of them is wrong! Just remember that there may be tradeoffs involved when choosing any given route such as cost or production time.
Ensure all of your ground connections are joined together.
You may have made the mistake of not joining all of your ground connections together and now you're wondering why there are stray, unconnected, electrical components in the circuit. With individual ground connections, voltage differences will inevitably form which cause cross-talk, an undesirable occurrence that can lead to poor circuit performance. Some people might say: doesn't 'ground' mean that they all meet anyway? Yes and no. When you go out and actually test all of these components on an electrical ground (that is established by screwing something metallic into the earth), they will in fact touch, but this is not what we want in our project because doing so will create yet another difference in potential between each component. The whole point of grounding one thing or another is to minimize potential differences from forming in the first place; so remember this when laying out your PCB. Lastly, don't forget to use ferrite beads to suppress unwanted high frequency noise.: A ferrite bead is a type of magnetic filter that has two major properties: 1) it has a large inductance and 2) it suppresses high frequency noise. Ferrite beads are used for all sorts of applications, but specifically for electronics, they serve as filters for unwanted noise generated by both digital circuits as well as power supply lines. Remember this also when designing your PCB! If you know that a specific component of your design produces lots of noise, try using a ferrite bead to reduce its effects. It could save you from some serious headaches down the line if done correctly! For example, many times when a chip starts producing erratic behavior, it's due to insufficient decoupling capacitors. To solve this problem, simply add more capacitors next to the chip. But again, remember to make sure that the capacitor’s polarity matches up. Sometimes this information can be found on a datasheet or sometimes you’ll need to consult an engineer who knows their stuff. Good luck out there! Always keep in mind those tips above and you'll be able to successfully get through any potential problems that arise while designing your PCB. And lastly, always take pictures of your work in progress. They can come in handy if you ever need to refer back to them later on. Happy wiring!
At first glance, someone might ask what’s wrong with having extra ground wires? They look like they do connect...look here, here and even over there. Seems fine to me... On second thought though, it does seem strange for a group of conductors all going towards one spot to not end up at the same place. Maybe these wires aren’t connected after all... Why do I need extra wires anyways? We already have separate grounds.... So let me explain where I am coming from by breaking down all these extra ‘unnecessary’ wires. Here's a scenario to illustrate my point. Say you have five components and three ground wires. Well, with only three wires there are six different possible ways to wire the components and their respective grounds. That’s not so bad, right? All six combinations would be equivalent in terms of potential differences and they would all work just as well as the other. Now imagine that instead of five components, you have 50 components and 20 ground wires.
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