Podcast Ep. 13: Automated Optical Inspection (AOI) for PCB Assembly
In this episode we delve into the process of Automated Optical Inspection (AOI).
A big thanks to Angus Thomson at CircuitBuilder for authoring this guest post. CircuitBuilder provides an easy way to create custom electronics, no matter what step in the process you’re at. Simply upload your requirements, see a detailed breakdown of costs and watch in real-time as your project progresses to completion.
Turning an idea for an electronic product into something ready to sit on a store shelf isn’t particularly easy. Thomas Edison’s classic quote about success being 1% inspiration and 99% perspiration isn’t far off when applied to taking a product to market.
One of the issues is that many of the tricky bits of the process aren’t at all obvious at the outset. Very few inventors would consider how to achieve FCC certification before actually testing their invention worked! This guide is a very brief overview of the whole process, taking a product idea from a sketch on the back of an envelope all the way to something ready to be stocked in a store or the usual online retailers (including some of the bits often forgotten about).
A design will often start with a high-level block diagram showing the main functional elements and how they all fit together. I usually use this as the first stage in designing as it is an opportunity to break the design down into functional blocks, which makes it much easier to work out how everything will fit together.
Note that if you’re starting with a full list of requirements this is fairly straightforward, but often real projects start with a lot less in the way of specifications.
Another thing to note at this stage is that it has never been easier to build quick hardware prototypes! There are countless development boards (Arduino, Raspberry Pi, Teensy etc.) which are an incredibly quick way to test things out without breaking out the soldering iron. I highly recommend building what you can at this stage, especially given how easy and inexpensive it is.
Once you know roughly what parts you need, the next stage is to identify the exact components that will be used in your design. This is often quite time-consuming, though there are a few tools and websites to help you out.
One site I use frequently at this stage is Octopart; it allows you to select a few key attributes of almost any component and it will list all suitable parts as well as showing you current prices and stock levels.
There are also some very useful tools provided by a lot of component manufacturers, although of course they will only show you parts produced by them! One example I use a lot is WEBBENCH by Texas Instruments; by entering a few known parameters it will suggest a suitable power supply IC (integrated circuit) and even produce a schematic, bill-of-materials and thermal model.
Once you know which parts you’ll be using, you’ll be able to start putting together your schematic. The schematic is a logical representation of the design - it shows you how everything connects together electrically but doesn’t bear much resemblance to the physical circuit board.
The subject of schematic design is huge and there is enough material on the subject to write a whole book about. I have a few ‘golden rules’ here which are useful to keep in the back of your head at this stage:
Just as with the schematic design, whole books could be (and have been) written about circuit layout. So without trying to cram everything into a single paragraph, a few bullet points I often refer to at this stage:
Once the layout is complete you can look at actually building and assembling your design. The traditional route here is to generate Gerbers, pick & place data, assembly drawings and your BOM and spend a long time emailing your assembler. An alternative is to use CircuitHub (I don’t work for them, but I do think the service is excellent!) which can take in the original design file and will take care of the rest!
Whatever route you choose, it’s a very good idea to make sure your bill-of-materials contains enough information to reliably order every component in your design. At the very least, make sure every single component includes the manufacturer and the manufacturer’s part number. I also find adding a recommended supplier’s order code too, which helps when buying the parts.
Once your boards are built and tested, you are ready to go through the laborious process of certification. This is an area which is often overlooked, but is very important as selling your device without considering what regulations apply is not a good idea.
The exact testing you will need to do on a product depends on where you will be selling it. Since each country has its own set of rules and regulations, you’ll need to get advice on your specific product, especially if it includes any sort of radio interface.
For devices sold in the EU, it will need to be CE marked - to do this you’ll need to check exactly which requirements apply but it’s likely the device will need to be tested to ensure EMC compliance - essentially this ensures that it won’t interfere with, or be affected by, any existing equipment. There is also ESD (electrostatic discharge) to think about - this is when your product is zapped with a few thousand volts and tested to make sure it recovers by itself.
For the US, the FCC mandates certain tests, and again it’s best to get professional advice to ensure you know exactly which tests to carry out.
Assuming your layout is good and you’ve added plenty of filtering on any signals entering or leaving your product your design should get through EMC testing without too much stress!
I should mention here that if at all possible, using pre-certified modules (such as Espressif’s WROOM or Rigado’s BMD-350) reduces the risk of any issues at this stage. It also slightly reduces the cost of testing slightly.
The above is a very rough summary of the work that goes into taking an electronic design to market. Although every step is fairly straightforward, the whole process can be daunting!
Full disclosure: I run a company called CircuitBuilder, and we can help at any (or all) of the stages above! If you do have an idea of a product or would just like some feedback on your design, feel free to get in touch at firstname.lastname@example.org or create an account at circuit-builder.com to get started!