Assembly lines for electronics products are complicated beasts, often composed of many custom tools and fixtures. Typically a microcontroller must be programmed with firmware, and the circuit board tested before assembly into the enclosure, followed by functional testing afterwards before putting it in a box. These test platforms can be very expensive, easily into the tens of thousands of dollars. Instead, this project uses a set of 12 Raspberry Pi Zero Ws in parallel to program, test, and configure up to 12 units at once before moving on to the next stage in assembly.
Through-hole assembly means bending leads on components and putting the leads through holes in the circuit board, then soldering them in place, and trimming the wires. That took up too much space and assembly time and labor, so the next step was surface mount, in which components are placed on top of the circuit board and then solder paste melts and solders the parts together. This made assembly much faster and cheaper and smaller.
Now we have embedded components, where in order to save even more, the components are embedded inside the circuit board itself. While this is not yet a technology that is available (or probably even desirable) for the Hackaday community, reading about it made my “holy cow!” hairs tingle, so here’s more on a new technology that has recently reached an availability level that more and more companies are finding acceptable, and a bit on some usable design techniques for saving space and components.
You’ve spent months developing your product, your Kickstarter just finished successfully, and now you’re ready to order all the parts. Unfortunately, your main component, an ATmega328P, is out of stock everywhere with a manufacturer lead time of 16 weeks. Now what?
When manufacturing things in large volumes, acquiring enough stock at the right time can be tricky. There can be seasonal shortages with companies trying to get products manufactured and available for Christmas. There can be natural disasters like floods of hard drive factories, or politically-related availability problems like tantalum for capacitors, or maybe new markets open up that increase demand or a new product sucks up all the available supply. The result is all the same; you have a harder time getting what you need. Fortunately, there are some ways to avoid this problem, or at least mitigate it.
Those of us who have our PCBs manufactured by Chinese PCB fab houses will be used to seeing tempting offers to also assemble our completed boards. Send the Gerbers as normal, but also send a BoM, and for an extra slice of cash you can receive fully assembled PCBs instead of just bare boards. It sounds alluring, but leaves a few questions for those without the experience. How much will it cost, what will the quality be like, and will my boards work? [Alexander Lang] had a limited run of ten small pressure sensor boards to make, and since his board house had started an assembly service, decided to take the plunge and opt for full assembly.
His first step was to assemble his BoM and send it with the Gerbers. He is at pains to stress that the BoM is key to the whole project, and getting it right with the correct packages and more than one source for each component is critical. The board house first charged him £32.05 ($41.76) to make his PCBs and stencil, and assess his BoM for a build quote. A few days passed, and then he had a quote for assembly, £61.41 ($80). He placed the order, the board house processed it and made the boards, and in due course his working PCB modules arrived.
This might sound at this point like an unexciting saga, but its very smoothness is the key to what makes it interesting. Those of us who have wondered about the risks involved in taking up such a service need to hear stories like this one as surely as we do stories of failure, because without them we’re flying blind. Whether £93.46 ($121.76) for ten small boards represents good enough value is another matter, but if surface-mount soldering is not your thing you might be interested to follow [Alexander]’s example. After all, it wasn’t so long ago that getting a cheap PCB made in China was a similar leap of faith.
Hackaday is all about the neat hacks and the repurposing of old components into new projects, but many people then try to take those projects and turn them into businesses. We’ve seen lots of people offer their stuff as kits and sell them on Tindie, with the rare few going on to develop a consumer electronic product at scale.
The Hackaday Prize 2017 Best Product highlights this journey. “Scale” itself is a vague term, but essentially it means to be able to produce enough to meet market demand. We hope that market demand is roughly 7 billion units, purchasing yearly, but the reality is that it is somewhere between 1 and a few hundred thousand, with very big differences in manufacturing at each order of magnitude. So how do you start with a proof of concept and design your product from the very beginning to be optimized to scale to meet whatever demand you can handle?
Designing pcbs for assembly is easy, right? We just squirt all the footprints onto a board layout, connect all the traces, send out the gerbers and position files, and we’re done–right?
Whoa, hold the phone, there, young rogue! Just like we can hack together some working source code with variables named after our best friends, we can also design our PCBs in ways that make it fairly difficult to assemble.
However, by following the agreed-upon design specs, we’ll put ourselves on track for success with automated assembly. If we want another party to put components on our boards, we need to clearly communicate the needed steps to get there. The best way to do so is by following the standards.
Proper Footprint Orientation
Now, for a moment, let’s imagine ourselves as the tip of a vacuum pickup tool on a pick-and-place machine. These tools are designed to pick up components on the reel from their centroid and plunk them on their corresponding land pattern. Seems pretty straightforward, right? It is, provided that we design our footprints knowing that they’ll one day come face-to-face with the pick-and-place machine.
To get from the reel to the board, we, the designers, need two bits of information from out part’s datasheet: the part centroid and the reel orientation.
The part centroid is an X-Y location that calls out the center-of-mass of the part. It basically tells the machine: “pick me up from here!” As designers, it’s our responsibility to design all of our footprints such that the footprint origin is set at the part’s centroid. If we forget to do so, the pick-and-place will try to suck up our parts from a location that may not stick very well to the package, such as: the corner.
In our final installment of Tools of the Trade (with respect to circuit board assembly), we’ll look at how the circuit board is tested and programmed. At this point in the process, the board has been fully assembled with both through hole and surface mount components, and it needs to be verified before shipping or putting it inside an enclosure. We may have already handled some of the verification step in an earlier episode on inspection of the board, but this step is testing the final PCB. Depending on scale, budget, and complexity, there are all kinds of ways to skin this cat.