Back in 2020 I built two modules using mostly SMD components — one was problematic and I needed outside help with it, the other went OK. Then I got into Kosmo, and there aren’t many SMD Kosmo modules out there and I was designing my on PCBs through hole for the most part. I did build a VCO using the MFOS PCB with one SMD part, and my output module used an SMD amplifier you can’t get as through hole, but that was it.

I’ve been intending to do more SMD work all along, though. I’d bought an SMD Eurorack version of the MFOS VC LFO and considered using it behind a Kosmo panel, but I didn’t — and recently I dug it up and put it up for sale . I bought a hot air station thinking I’d use it for assembly — but I haven’t, it’s been handy for unsoldering though.

There’s a circuit I’ve been considering building which calls for some SMD-only transistors. I’d want to breadboard it, though, which means getting those transistors onto breakout boards. Last spring I had some boards fabricated, and I bought a hot plate soldering station from a Tindie seller. If you’re interested, it’s unfortunately no longer in production. But it’s open source so you could make one. But that requires SMD soldering. Chicken, egg.

I also bought an electronic microscope, useful for SMD assembly and other purposes.

And then I was busy with other things, but recently I finally got around to it. I used the hot plate to attempt several breakout boards. The first ones partly suffered from my use of some quite old solder paste; then I bought some new and used that. I was having trouble dispensing it, though, getting too much solder on the pads and ending up with enormous blobs:

Two SOT-23 breakout boards with transistors soldered. The joints are very big solder blobs.

Blobby breakouts

The paste I’d gotten comes in a syringe. The supplied “needle” is more like a hose — the diameter is such that the paste comes out wider than many SMD pads. I tried instead applying the paste with a tool of some kind such as a toothpick, but that didn’t work too well.

The hot plate did, though. The temperature display is way off, reading around 25–30°C below what my infrared thermometer says it is, so I set it at 160°C and that seems to work.

I ended up following the example of one of the Amazon commenters and got some 10 ml syringes and 22 Ga blunt needles. Using those I was finally able to start to get controlled paste application. It’s still tricky and requires more practice but I’m getting there. I assembled 0805 resistors and caps on an NLC Bong0 PCB. The hot plate is small enough that even this rather dimimutive board can’t be heated all at once; I started at one end and shifted it to the other. A more typical Kosmo size board full of SMD would be hopeless. The results looked better, though some pads evidently didn’t get enough paste and had to be touched up with the iron.

Section of an NLC Bong0 PCB with SMD parts assembled. Joints are not so blobby.

Non blobby Bong0

The rest of the parts on this PCB are through hole. I assembled them and tested, and it worked right away.

I need to think more about how I feel about SMD. I feel like I can fairly confidently take on at least simpler SMD board assembly. But do I want to design SMD boards? Some parts are available SMD only (LM13700 for instance, though I still have a good stash of DIP ones) or are cheaper as surface mount ( AD633: $13 vs $18 ). However, I like to try to sell my extra boards to offset the fabrication cost, but SMD boards might be harder to sell. Besides, with Kosmo there’s usually enough PCB space that the smaller component size isn’t really needed.

With an SMD design you can get it assembled from the fabrication company. For a price, of course. Pre-assembled extra boards might be easier to sell… or might not, given the higher cost.

I’m inclined to think it’d generally not be worth it. Single SMD parts on otherwise SMD boards is another matter; I can be less hesitant about that now. But mainly I’m thinking SMD would be something I’d do only if there were a commercially available board I wanted to use. Maybe. We’ll see.

As for hot plate vs. hot air vs. hot iron, I think for 0805 components I’m not conviced the iron isn’t just as good and just as easy as the hot plate. For stuff like SOT-363 it’s probably another story, but I need more experience. The hot plate I have is great for little breakouts but not so much for whole circuit PCBs. I could see if I can find an electric skillet I can adapt. Or I have an old toaster oven I could try to convert to a reflow station. But only if I end up doing much more of this.