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For our multi-board design issue, I interviewed Dave Wiens, product marketing manager for Mentor, a Siemens business. We discussed how the multi-board design technique differs from laying out single boards, along with the planning, simulation and analysis processes required to design multi-board systems.
Andy Shaughnessy: Dave, what are some of the typical end products that might use multiple PCBs?
Dave Wiens: The easy answer is almost every end product that includes electronics is a multi-board system. It's things down to your cell phone. If you look up your cell phone on iFixit, you'll see a tear down that's got multiple boards in there. At a minimum, there'll be, let's say a separate board for the camera or for the audio or for the external connections. Those are all separate functions and, in some cases, when somebody's designing they won't necessarily design all of those pieces. They might, for instance, be acquiring the camera from somebody else, and so that basically represents a component. It is a complete PCB, but to them it's a component because they didn't design it. We're not necessarily talking big back planes, with tons and tons of data cards on them. Certainly, that's a multi-board system, but pretty much everything you see today is multi-board.
I don't know about you, but when something in my house stops working, I tend to tear it apart. Sometimes I'm trying to figure out if I can fix it, but often I just want to see how they designed it. Really, when you're designing something and making decisions to make it into multiple boards, you start thinking about things like size and space. Should I put this all on one board? Should I break it up into multiple boards for space reasons? Should I do it because of reliability reasons? If this data board fails, it's easier to plug and play it with something else versus throwing away the whole system. Should I do it for cost reasons? Performance reasons? And then there's the make versus buy decision, right? For this particular function of my system, should I just buy a board and connect it to my system? Or should I design it into the system?
You see that with like your home PC. It's got dedicated graphics built into it now, but you still may want to put an add-on graphics card, but those used to be things that weren't necessarily integrated into one system. They've done that over time.
Shaughnessy: It sounds like some of the biggest challenges are the trade-offs you have to decide. Like, should you add another board? What are some of those challenges?
Wiens: Yes, the trade-offs are a huge one and, frankly, because of that a lot of people kind of avoid it. I mean, they make decisions very early on to segment something. They take their high-level requirements, and then they start building an architecture from that. They decide what's going to be hardware, what's going to software, and how that's going to interplay with mechanical structures, cabling structures, all of that is decided way up front, and then the question is: Do they ever revisit that? If they don't revisit it, then they were either really good and they got it right up front, or as the design progressively refines itself, as the engineers refine it from that high-level architecture down into the physical implementations, they may find things.
To read this entire interview, which appeared in the June 2018 issue of Design007 Magazine, click here.