PCBs are not a foreign concept to the hackaday crowd; pads, traces, vias, solder mask and silkscreen are part of the lingua franca. But if you're anything like me you really don't know how PCBs are made. Sure, I've etched my own boards and have had them manufactured at our friendly neighborhood purple PCB house but the process was just shy of ✨magic✨. So I went down a rabbit hole, trying to learn everything I can about the process.
Before getting ahead of ourselves, we need to level-set on terms. A PCB serves many roles but the main ones I think about are:
- Electrically connecting components that should be connected
- Electrically isolating things that shouldn't be connected, aka preventing shorts
- Assisting in soldering
- Documenting assembly and debug
- Providing mechanical structure
- Looking pretty*
The process of making PCBs enable these role. Pads and traces of a thin conductor are removed from a non-conductive material through a subtractive process while vias are formed with an additive process. The soldermask and silkscreen are squirted on the board in turn. Of course that's a wildly simplified generalization of the actual process and varies depending on the constraints of the board being made. 2-layer vs 2n, low-cost, fast-turn, large-volumes and flexibility are just some of the attributes that impact the processes implemented.
I could go into each process and their variations but then this wouldn't be a TL;DR post. Instead I'm going to rely on the wealth of knowledge found on YouTube. I've watched just about every video I could find on the subject and have saved the ones that cover the most ground so you don't have to sift through the cruft like I did. Feel free to bookmark the playlist here. I’ve called out the highlights below and broken them into Professional and DIY buckets.
Dave Jones over at the EEVBlog has a fairly complete overview covering the highlights of making a standard 2-layer board for his µCurrent product. What I like most about Dave’s video is that he calls out the differences between lower-cost, small-volume and legacy processes. When I first watched the video I gained an appreciation of just how important the order of things matter. If you’ve always wondered how through-holes and vias are made - take note; electroplating is the key.
Eurovision produced an educational video of their multi-layer process targeting students and is the complement to Dave’s video (in fact, Dave borrowed a clip or two.) You’ll notice that the process is very similar to the one used for 2-layer - expose copper, etch and repeat. Instead of a thick fiberglass with copper, multi-layer boards use thinner sheets and stacks of thin insulators pre-treated with resin (the “prepreg.”) Then the whole stackup is baked and it is pretty much like a stiff 2-layer board at this point.
The last professional video is from Robert Feranec of FEDEVEL Academy. He’s actually narrating a silent video series and accompanying website from SQP International. I definitely recommend checking out the whole site since it is a wealth of knowledge. I’ve also compiled all the videos found on the site into a playlist, if silent movies are your thing.
There are many video’s from hobbyists on YouTube, often demonstrating one part of the PCB fabbing process (and sometimes providing wrong information.) upgrdman two-part video is a good representation of the complete process - and it includes reflowing to boot. He’s since done updated videos using a slightly different process.
This video is pretty epic - both how perfectly-aligned the creator gets his double-sided stencils as well as the awesome soundtrack. You’ll notice that most DIYers don’t bother with silkscreen. I wonder if they just don’t know how easy and similar it is to the other steps. 🤔
channelengineer has several videos on PCBs but 2 stand out as unique - he goes through different techniques for making vias and through-holes, including a lab-grade electroplating rig.
I threw in this last video because it shows the actual process of using a silkscreen for PCBs - a process that is no longer popular but the progenitor of the process which keeps its name.
I hope this provides a good foundation for future discussions about PCB manufacturing. Did I miss anything? Found mistakes? Let me know if the comments.
* Some might argue this is optional. Those people don't frequent hackaday.io.