One of the reasons I picked the Breadboard PSU as the first project to attempt to ship and sell was its simple. At the same time, its representative of what would be required for any design to be seen though to actually being in people’s hands – other designs just have more parts.
Unexpectedly this week a bunch of the PSUs sold, and more needed to be built in a (relatively) short time. This is quite different as an experience to the prototyping phase, where every build is unique and new, and the timeline is as long or short as you feel like. I’m glad that I chose something simple to start with, because I’ve very quickly found the things I need to think about for larger and more complex designs going into production.
Inventory management is important
During the prototyping phase on all of the projects I have underway at the moment, I’ve built up quite a stack of parts. Some of these parts overlap with other designs, but most are design-specific. For example, every design will probably involve a ton of 100nF power supply decoupling caps scattered all around various ICs. But this is the exception, not the rule.
For a while, “inventory management” was a pile of parts in bags. It started out in small bins, when it was mostly PTH parts which really were easier to store in little bins, but as the number of parts escalated it fell off a little. I only knew if I could build one by actually finding all the parts at the time.
Inventory management is really critical if you need to know quickly how many you can build beyond just one. One is easy. Five or ten imposes more need to know how many you have of all your components. At least twice now I’ve been caught out by problems in inventory – one part important part wasn’t tracked at all, and a second wasn’t updated properly to reflect builds completed.
Some of this comes from the fact upstream part suppliers probably won’t sell you one of a part, but often if you want good prices you’ll need to buy 10, or 50, or 150 at a time anyway. And they’ll get used at different rates, so you need to track the build usage carefully as well.
Plastic stencils last; stencilling jig needs work
I’ve only ever used plastic stencils for assembling my mostly-SMD boards, and had some concerns about how long they would last. It turns out more than long enough, and now I have a cheap source to make them (Ponoko) I’m less worried about exactly how long they’ll last. Still, I’ve gotten sixteen builds out of the first stencil and they’ve effectively cost a buck for each stencil, so it’s a good run.
The more significant problem with the stenciling approach is the jig I use is .. primitive. I’ve just used spare boards I had from prior prototypes to form something to wedge the target board in place, and it does the job, but only just. It would be easier with something more purpose cut to surround the board as much as possible. One option is to get something laser cut by Ponoko but I’ll need to figure out how close their material thicknesses will get to a PCB thickness.
Frypan works, reflow oven nicer
Despite how primitive the frypan cooking method for board soldering is, it actually does work, and I can manage to get a few boards at a time being soldered up. The reliability has been reasonable so far, although we’ll see how these turn out in the field. The main problem is actually the need to watch it. A controlled oven I could put a set of boards on a tray, stick them in, and just run the cook profile.
This will mean I might have to step up efforts to work on building a reflow oven myself. A full commercial one is both far too large, too expensive, and probably not a lot better than a hacked up toaster oven, but something with control is better than none.
SMD parts are great for production
It feels very strange to be so in favour of surface mount parts, but they are so much easier to solder together a bunch of components than PTH by hand with a soldering iron. I had already come to the conclusion SMD parts made things easier in general, but it wasn’t until I realised I was spending 33% of the build time on just a single PTH component that it really hit home how much easier.
There are still some challenges, getting tiny parts orientated out of the tape they often come in is a pain, and tweezers are a bit prone to too much force causing the part to fly off and disappear to never be seen again .. but those are mostly going to come down to practice. I’ve also ordered a cheap vacuum pencil to see how that works for part pick-up and placement, as a sort of poor human pick-and-place machine.
Production is confidence-building
Lastly, production builds confidence in two ways. Being able to reproduce a build and have them pass basic QA tests first time, every time, gives you a lot more certainty about the way something has been designed. It works, so your understanding of how it works looks a bit better each time.
Having other people using your builds is also helps out a bit with motivation to build other things. It’s fun, no doubt about it I have enjoyed all the things I’ve built whether they worked or not, but it’s a very nice feeling having new devices you made, put for the first time into an anti-static bag, all clean and ready to be used by someone else.