They say that time flies when you’re having fun. Maybe that’s why I feel like time slows to a crawl when I’m constructing a multi-board PCB device. Designing even one board can be an agonizing task, what with trying to avoid EMI, ground everything properly, mitigate static discharge, and optimize your routing. Creating a system of PCBs that all fit together physically and electrically sometimes tests the limits of tedium. Lucky for us there are tools that are just on the horizon that will make creating multi-board schemes more of a pleasantry than a punishment. There are three kinds of features that help with PCB design in general, but are particularly useful when it comes to multi-board PCBs: board to board connectivity, MCAD integration, and modular organization. Interboard rule checking can be a nightmare, and can even lead to scrapped boards. This tool makes tracing connections throughout the various boards simple and can help you when last minute changes come up. Interactive models can ease the hassle of clearance checking and making sure that everything fits together and into the enclosure. Lastly, modular organization assist you when you’re creating new circuits that could use boards or connectors that you designed in the past.
Having a 3D modeling tool incorporated into your program may not seem like a big deal, but it can make a huge difference in your PCB design process. Using MCAD to model your PCBs can stop you from making expensive mistakes. It can also put your mind at ease when you’re sending off a board for prototyping or production. When that same kind of tool is at your fingertips, instead of those of a mechanical engineer somewhere else, it will totally revolutionize the way you PCB circuit design boards. Let’s look at how it does this:
3D Clearance Checking
Have you ever designed a board and found out the expensive prototype, or maybe even a production run, didn’t fit inside the enclosure? That happened to me once, after I’d added an electrolytic capacitor to a design at the last second before sending it off to be prototyped. It turned out my clearance calculations had been a tiny bit off. So I had to send the designs off the mechanical guys to model and check it, then back again for mock-up. Imagine making that kind of mistake on a production run - good luck explaining that to your boss. The stakes are high when it comes to clearance checking, especially when you’re working with multiple PCBs. Each one has to fit together, like a very expensive 3D puzzle. All of that then has to fit into a custom enclosure, which may or may not have been designed by people at your company. I consider myself a good designer, but even I make mistakes that are difficult to catch without a 3D model of my system.
Modeling at Your Fingertips
By now most of us use computer models of our boards, but we’re often not the ones making them. That’s generally the domain of the mechanical engineers. What if, though, you could be the one making models and doing clearance checking yourself, without having to send off changes over and over to someone else? I’m not talking about you learning a standalone MCAD program and literally doing the work yourself. I’m talking about your circuit board software doing the work for you. That’s what a great, well integrated, MCAD tool will do. There are tools available now that can generate 3D models of individual components and create models of your board with everything on it. The best ones will also allow you to import a 3D model of your enclosure and do clearance checking with that as well. This kind of feature allows you to cut out the middleman when it comes to MCAD. Need to see if an electrolytic capacitor fits? A few button clicks and you’ll see.
Interboard Electrical Rule Checking
Checking electrical rules isn’t usually a big hassle because your software will do it for you at a board level. However, It can be nearly impossible to keep track of connections when they cross from board to board. There are very few programs that can check an entire system as a whole to ensure that everything fits together electrically and mechanically. This kind of tool will help you keep all your ducks in a row during design by allowing you to do rule checking between various boards. It can also help you a great deal during re-design, when an enclosure change or other external factor forces you to make significant connection alterations on your PCBs.
Error Checking During Development
There’s nothing more tedious than tracing a net through your system, board by board, to ensure that it makes all the right connections. It makes me feel like a dog chasing its own tail. I go along until I find an error, fix it, then start tracing everything back from the beginning. A good multi-board PCB systems design program will not only help you trace connections through your system, but automatically notify you when things aren’t quite right. You need to know at the beginning if one of your routes has a dead end, not just when you’re reviewing everything near the end of design.
Your software should also allow you to highlight your nets so you can see where they all go. That kind of feature is especially helpful when dealing with EMI. FCC certification can be a hassle, and you don’t want to have to go through radiated or conducted emissions testing twice. There are so many interference concerns that come with routing signals across boards. You need to be careful with high speed traces, differential pairs, and the analog and digital portions of your PCBs. Proper grounding is also essential as you’re probably not going to be able to use a star ground, and will have to watch out for current return paths through your entire system. Keeping track of all of these nuances is nearly impossible without a tool that can show you exactly where all your connections are routed.
Redesign Made Easy
Highlighting nets isn’t just useful for EMI reduction, it can also end up saving your design. I’ve been on projects where one PCB had to be re-worked or scrapped entirely due to late game system level changes. Sometimes you can’t control when a mechanical engineer will need to tweak the enclosure, and that adjustment may mean you need to move several pins or maybe a bus connection. Doing so without a tool that can highlight your nets can be an exercise in futility. However, if you have software that can show you where every trace is going, what was impossible now becomes simple.
At first glance this feature may not excite you as much as MCAD integration or system level electrical rule checking. You’ll see, however, that it is quite useful and can help you reuse old designs. No more wasting time re-designing the same old PCB that you’ve made 1,000 times. This kind of tool will allow you to significantly reduce time wastage in your design process and help you focus on new and exciting work.
King Solomon once said that there’s nothing new under the sun, and that’s starting to apply to PCBs. If you’re designing for areas like the Internet of Things (IoT) you already know many of the different components you’re going to need. Of course you’ll need a module for WiFi, Bluetooth, or soon maybe even 5G to allow the device to communicate. If you’re making a wearable and you want it to be convenient for the user you’ll hopefully utilize a micro USB connector instead of devising your own proprietary kind. There’s no reason you should have to build the PCBs that these modules sit on and connect to over and over. Great multi-board software will allow you to make you entire system modular, so that you don’t have to reinvent the wheel each time you design a new product.
Save Time During Design
There’s a lot of work to be done in PCB design, what with the IoT blowing up and connected cars revving their engines. We don’t have time to waste in re-hashing the same old designs. PCB design software that allows you to modularize your designs will help you save time that you can use to focus on making new, cutting edge devices. Of course, true modular design and integration isn’t really possible without the first two features mentioned. If you import an old design and have to send it off for multiple rounds of modeling and clearance checking you might as well build it from the ground up. Multi-board PCB electrical rule checking will let you import a sub-system and instantly check its connections. It’s really the combination of all three of these tools that can revolutionize your design process.
Currently there’s only one program out there that’s looking to add all of these features together on top of what is already great PCB design software. Altium Designer has a host of great features that will enable you to create exciting new PCBs. Its tools include those listed here, as Altium is expanding their scope to include multi-board PCB systems design. Individual PCB design has already been re-vamped by Altium, with elements like a PDN analysis tool and increasingly important rigid-flex support.
Have more questions about multi-board design? Call an expert at Altium.
About the Author
PCB Design Tools for Electronics Design and DFM. Information for EDA Leaders.More Content by Altium Designer