Early Stage Design Considerations of Starting a PCB Project from Scratch
There’s nothing quite like the smell of hot solder on a Sunday afternoon, tinkering in your basement as you bring a new electronic concept to life. PCBs are the foundation of modern electronics. Thanks to improvements in manufacturing processes and lower production costs, the DIY community around electronic projects is thriving, and you can easily find instructions for everything from hacking your espresso machine to punch-activated arm flamethrowers.
Love technology, but not sure where to get started with your first PCB project? This article is for you. In this post, we’ll do a step-by-step walkthrough of the early stage design considerations of starting a PCB project from scratch.
What are you trying to build?
If you’re a professional electrical engineer, chances are you’ll already be familiar with the requirements gathering that generally takes place at the start of any product development project. But for the uninitiated, here’s a quick list of questions you can ask yourself:
What are you making? Project requirements will vary depending on what you’re building and if there’s a specific problem you’re trying to solve. Specs for an autonomous robot will differ from the requirements for building a wearable fitness watch.
What sensors do you need? From thermistors, to microphones, to buttons, to remote control, and cameras—there are many ways for your PCB to interact with the environment, it’s just a matter of finding the right sensor to do it.
What’s your budget? Knowing your budget can help you make design decisions such as choice of materials and components, and number of layers you can have in your board.
Who’s going to use it? Do you need to meet certain standards? If your business is building a board for NASA, you’ll need space rated parts. If this is a maritime applications, resistance to salt fog is desirable. There are also “mil-specs,” ISO documents, and other standards you may have to adhere to depending on your industry. More generally you might want to choose parts based on the target market for your business. Things like preferred connectors (e.g. Amphenol for aerospace) or affordability.
How many products do you plan to build? Is this a personal project, a limited small batch release, or something that will eventually be mass produced? Your layout, choice of interconnects, choice of materials, and number of layers are all influenced by the manufacturability of the end design.
The more detailed you are in your answers up front, the easier the rest of the development process will be. Other common considerations include familiarity with certain PCB design software and existing relationships with part vendors you can tap.
Create a Schematic
Once you have a clearer picture of what your project is going to be about, it’s time to sketch it out on paper or with your favorite PCB design software. What you’re looking for at this stage is a simple circuit diagram (a.k.a wiring diagram), which is a basic layout of components and electrical connections.
For example if you were seeking to build your own headphone amplifier circuit, you might list out the parts such as the subwoofer or speaker, an audio jack, and the audio amplifier circuit (e.g. LM386 IC). You’ll then apply electrical engineering 101 concepts such as Kirchoff’s Voltage Law to put together a functioning circuit, adding all the resistors and capacitors required to make it work.
Even if you prefer to use design software, it can be useful to sketch things out with pen and paper first or play around with a breadboard and jumper cables while you’re designing your board.
Ease of Manufacture
Manufacturability is something that’s tempting to put off towards later in the design process. In reality, this is something that should factor into your requirements gathering process before you start picking components and materials for your board.
Cost optimizations such as using copper instead of higher conductivity silver, or opting for pins instead of high speed interconnects, should be decided up front.
Panelization, which involves building multiple boards as an array, can streamline product testing, and make your boards easier to mass produce. Before you invest hours laying out your board, it’s a good idea to factor in the standardized PCB panel sizes of your local manufacturing house.
Understanding your manufacturing needs can help you with material selection and where to locate components, traces, and vias.
Physical PCB Layout
Once you know what you want to do electrically, it’s time to consider how that circuit should be laid out in a 3-dimensional space. How big or small do you want your PCB to be? Where do you want to situate the audiojack on that retro handheld gaming console you’ve working on for winter break?
Here are some of the common features you’ll want to consider as you design your board layout:
Routing features, such as connectors, vias, and traces.
Physical layout of components on a board. Be especially mindful of EMI/EMC and thermal considerations.
There are two things you have to be mindful of as you layout your board:
EMI/EMC noise can mess with the performance of your circuit and cause problems to nearby electronic devices. Multi-layer boards can help you distribute current and prevent the formation of accidental antennas and noise boxes. You can also employ shielding around ICs that generate a lot of noise.
Thermal heat generation is a problem that arises in high signal circuits like your laptop’s GPU. If your PCB will be in a small enclosure and its components are prone to generating heat, you may also want to consider adding heat mitigation features such as cooling lines, fans, and heat sinks. It’s common to use the case or chassis as a thermally conducting medium for heat dissipation.
Everything in PCB design is interconnected, which is why PCB design software is a must for modern board designs. As the market demands ever smaller, faster, circuits, software becomes an integral part of the PCB designer’s toolkit.