Self-Soldering Circuits [video]
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I really love his flexible PCB experiments too, he’s made a lot of awesome things from them.
A self-heating board is more efficient than heating an entire enclosure. A sensitive circuit or part could use this trick to efficiently keep key componants warm on demand without an entire external heating system. And dont let Louis Rossmann about this. Inbuilt desoldering circuits underneath key componants might make at-home board repair too easy even for his tastes.
One of the components of a voltage controlled oscillator (VCO) is a linear to exponential converter, that converts the 1V per octave control voltage to a per-hertz reset pulse for the sawtooth waveform.
Such components can be done in various ways, but one of the most traditional is to use the exponential part of a transistor's voltage-to-current transfer function (not sure what the actual term is here). The issue is that this function is very sensitive to temperature, and so fluctuation in temperature on this part can easily detune the VCO by a very audible amount. Fluctuation is less of an issue at higher temperatures (around 70-80°C), so the solution was: heat!
The trick we implemented in the synth was to use a transistor array in a chip: use two transistors for the Lin/Exp converter, another as a heat source (we nicknamed it "the oven"), and another as a heat measurement device, to get some sort of PID feedback loop. I believe there were five transistors in the chip, so there was a leftover that got used for another purpose.
Surprisingly efficient, though we could still hear some pitch drop when blowing on the transistor array chip. Once in the enclosure, we figured only applying some ice on the front panel would have an effect.
This "heating trace" in the PCB would have been a good alternative, as some of those transistors arrays were particularly hard to source (we needed a particular transistor type, can't remember which).
It turns out that no matter how carefully you stabilize a circuit for temperature changes, it gets much more stable when held at a controlled temperature.
Arrangements for this go from simple (gluing the component to a PTC thermistor driven at constant voltage) to elaborate (thermocouple-controlled PID heater in multiple styrofoam insulating enclosures). There are some pictures at https://en.wikipedia.org/wiki/Crystal_oven
I've never seen PCB traces used for this, but I've always wanted to try making a clock from a piece of LCD color-change material laminated to a PCB with traces in seven-segment patterns.
Could make for a nice transition effect though.
On top of that he’s probably figured out a bunch of interesting things that he can apply to his next project and other things and so on. this is good stuff.
If we start thinking about it in practical terms it stops making any sense. Specifically, a standard 2 layer board costs few $ to make. Here we're paying a huge premium for extra internal layers. You may as well take that money and put it towards a hob with an scr and a cheap controller to solder them on it.
It does not have to be a good idea to get traction.
Nice to see hobbyists in the field coming up with the same concepts.
Where this is great is that you can finely control the temperature of the board since you're in control of the current you pump into it.
Where it's not great is that it uses a full layer and could cause issues if any of your PCB needs special considerations, when using high frequency clocks or RF (say implementing a switch mode power supply can be quite sensitive to how your layers are composed). You also end-up with either a floating layer or a ground layer that has a long path instead of a real ground plane. That could also create noise issues.
If you assemble a few PCB a year, a PCB oven is fairly cheap. You can make one with a regular US$50 oven and a PID control kit or just buy a dedicated one like the T-962 (that can be further hacked and improved) for about US$250 from Aliexpress.
But that hack is still cool and Carl Bugeja's channel[1] has lots of fun projects that push PCB to new limits for hobbyists, showing what you can achieve with flex PCB in particular and using them as mechanical interfaces for creating motors, actuators, etc. It's a great channel!
The trouble with the T-962 is that the stock units heat so unevenly that you can scorch the center of the board while getting cold solder joints near the edges.
I have one of those with the mods for improved firmware and better thermocouple references. It's OK. The firmware runs the fan all the time, even during heating, which improves the heat distribution. There's a better mod which adds a second fan.
A number of companies in China made clones of those things, but none of them seem to have done a redesign to make a better one at roughly the same price. Now there seems to be a new generation of these things, with more fan power. That's a step forward. No idea if they're any good. (There are reflow oven review sites, as bogus as mattress review sites.) There ought to be a good $200 reflow oven by now.
You can buy good small reflow ovens from the US and Germany, but prices are upwards of US$3000.
You don't even need that; you can solder PCBs in a frying pan. It works very well. I never even tried an oven to be honest because a frying pan worked so well and Adafruit or someone like that said it was better than a toaster oven.
Although I do have induction hobs now. Not sure if a PCB would be too happy about that. But if not you can buy a portable mini hob for like £15.
It's a really cool tech demo though.
Track lighting circuitry is one example. LED lighting is another.
I achieved much better results with just a (convection) toaster oven and multimeter thermocouple- I only added PID controller because I started using the oven for drying something as well.
Doing a row of vias on both sides then paralleling the top/bottom traces to make some big T shaped terminals might make it easier to get uniform current distribution.
For an atmega that's clocked at 16MHz?
I guess I'm curious how much worse the heater-shorted-into-grounding-plane performs as compared to a classic full grounding plane.
If anyone is curious about the cool-looking pcb holder used in the early shots, that's the Omnifixo [1]. It's been on my wanted list for a while but it's not cheap and often sold out (I think it's basically a one-man company).
Oops I guess that proves that I'm the cheap one. :)
"This device will self-desolder in 5 seconds"
[0] https://www.oshstencils.com/ (one of many hobbyist level examples)
It’s also worth looking at the costs for SMT assembly. Companies like JLC are amazingly cheap for fully assembled boards (provided you stick to their standard parts catalog).
But yeah, even for something like 10 boards the prices for assembly has become pretty reasonable, especially if you design for the parts they have in stock.