I’m a software guy, but have tinkered with electronics since I was a kid. Haven’t done it in years though, until a couple months ago I came up with an idea for a little project. Its amazing what a small-time tinkerer can do now compared with just a few years ago. Anyway, I’m so tickled with how this is turning out I thought I’d share it. No reason really haha, but its: my first PCB ever, my first SMT, my first reflow soldering. So I wasn’t sure if I could pull it off. I’ve also never used Eagle, so I had lots of learning to do. But I’ve used PIC microcontrollers in the past and I had my breadboard prototype up and running surprisingly quick considering I haven’t touched a PIC in about 15 years. So I decided to get half serious and make a small batch of prototypes. I used BatchPCB - AMAZING! Well- after submitting my files 5 times until I finally passed the DRC it was amazing. The quality to cost ratio is ridiculously awesome, what a great service. They even threw in a bunch of extra boards - I guess just in case some were bad or something. This was helpful because i used some of them to put together a frame for the solder paste template. I got the templates made at pololu, but when I go for a larger batch I think I’ll use a metal template. For the enclosure, I’m using laser-cut acrylic. Its amazing what you can do now. I could have invested a bunch of money into tools and could never come close to the precision or flexibility that I get from the laser cut acrylic. I was going to use pololu for the laser cutting as well but found a local shop that would do it for about the same price.
Well, I ordered parts for 6 units and waited for the boards to come. Everything was all ready to go. I wasn’t sure if I could pull it off. Well I did- all 6 boards came out perfect. Not a single short, missing connection or any other significant production issue. I attached a photo of my boards and also the little jig I made for a stencil frame.
I made some silly noob mistakes, but nothing fatal:
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The worst was that I wired the 12v barrel connector backwards. Not a big deal these are prototypes so I’ll just cut the wires on the wall warts and switch the polarity. But I double checked that a bunch of times. Doh.
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Maybe worse than that is that I didn’t leave room for the screw heads around my screw holes. Well I thought I left room but when a 1"x1.75" board is blown up onto your computer screen, everything looks nice and big. Only 2 of my holes will be able to hold screws. 2 is enough for the prototype haha.
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When I started I had never heard of 0603 or 0805 or anything like that. I didn’t know what they meant and what the decision criteria was. I guess I could have googled that. But to keep things easy I went with things that I could find in the Eagle library (and some useful libraries from sparkfun). So when the default package for capacitors was 0402, I figured that must be the one everyone uses. At least I was sure to order the parts that matched the footprint I selected in Eagle. You can imagine my surprise when I opened the box from DigiKey and discovered how tiny 0402 capacitors are haha. Actually it wasn’t that hard to place them anyway. But just to avoid problems I’ll probably stick to slightly larger parts in the future.
-I ordered a tub of solder paste well before the boards arrived. I also had a small syringe of solder paste I experimented with. Well when I got things ready I realized my solder paste was actually “solder paste flux”. Doh. So all I had was this small syringe that had been sitting un-refrigerated for over a month. I wasn’t sure if there was enough to spread on 6 boards but I was bound and determined to get this done before the weekend was over. I got the idea to mix some of the flux into the solder paste- increasing the volume about 20%. I don’t know if this is advisable, but it didn’t seem to hurt anything on this project.
-I explored lots of options for reflowing the boards at home. Based on the recommendations here on sparkfun I went with a skillet- well actually a $15 hot plate from amazon with a 6x6 aluminum plate on top of the burner. I went a little crazy here- I wanted to have a super awesome precision temp control that could match the reflow curves exactly. I invested a huge amount of effort into researching and acquiring a PID ramp/soak controller, software to program it, and thermocouples to use with my hot plate. Well this was a waste. The hot plate couldn’t heat fast enough to match the profile - so I quickly plugged the hot plate directly into the wall and tried timing with a stopwatch like everyone else does. Even that turned out unnecessary- again it just wasn’t heating fast enough for that to matter. I ended up just turning on the hot plate and watching for the solder pads to reflow, let it stay on the burner a few extra seconds, then removed it. It worked perfect every time. Actually this PID controller is very cool and it very well could be a part of a precise closed loop setup in the future. But not with a $15 hot plate.
Well these certainly aren’t the most complex boards you’ll see anywhere. But I’m pretty stoked that I was able to pull this off. Now that I know what capabilities are at my fingertips, I will definitely have to build out some other ideas. The sky is the limit. Well, that and 0402 capacitors.
