Self-assembling PCB - something for electronics enthusiasts (film, 8 minutes)
In his latest video, Carl Bugeja explores the fascinating concept of self-soldering PCB circuits. He draws a parallel between the reflow soldering process and making a pizza, where the PCB acts as the dough, solder paste as the sauce, and electronic components as the toppings. To create a circuit that can solder itself by simply attaching two wires, the design consists of copper layers. Carl discusses how introducing a heater in the form of a long resistive track on the PCB can help melt the solder paste and bond the components together. However, a challenge arises with the one-time use of the ground plane layer, and Carl plans to short the newly constructed PCB to ground, serving as both a grounding plate and aiding in the soldering process.
The next step involves testing the circuit using the PCB design software Altium Designer, which features an automatic length tuning function to avoid obstacles during thermal track design. The author is enthusiastic as he powers on the circuit, successfully soldering the first PCB. The video continues with Carl aiming to automate the process using a PID controller that utilizes a temperature sensor to achieve an ideal reflow soldering profile.
Carl points out that the PCB design contains minor flaws encountered during his initial attempts with the ATMEGA32 microcontroller. After a somewhat complicated bootloader uploading procedure, he makes small adjustments, such as replacing capacitors and re-routing LEDs and switches for better connectivity. This technology enables a “mother” PCB capable of soldering “daughter” PCBs, all using the previously mentioned components to facilitate reflow soldering.
Through testing, Carl's new daughter board is successfully soldered and fully operational, demonstrating that the new motherboard can execute soldering at a more advanced level. Further tests confirm that this technology may lead to systems capable of soldering additional circuits on their own, signaling an innovative leap in electronic solutions.
All of this takes place as the video garners 1,211,773 views and 32,266 likes at the time of writing this article. In other words, Carl Bugeja is garnering a wider audience intrigued by the possibilities of self-soldering circuits. Indeed, the future of soldering might well lie in our own projects. If you’re interested in this project, all source files are available on GitHub. Remember to always use low-temperature solder paste and be cautious about the power supplied to the thermal track.
Toggle timeline summary
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Introduction to creating a self-soldering circuit.
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Comparison of reflow soldering to pizza making.
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Explaining components of the PCB and soldering process.
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Description of PCB layers and ground plane use.
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Shorting the PCB to ground after soldering for dual use.
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Initial circuit layout and challenges with thermal track.
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Upcoming explanation of the circuit's operation.
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Discussion on achieving optimal resistance for soldering.
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Temperature requirements for melting low-temperature solder.
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Testing the soldering setup with gradual voltage increase.
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Successful completion of the first soldering test.
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Improvements planned for temperature control.
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Integration of a PID controller for better solder reflow.
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Admitting flaws in the motherboard design.
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Solving issues with programming the ATMEGA32 chip.
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Modifications made to the board for successful operations.
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Thanking PCBWay for manufacturing the new board.
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Assembly of components and preparation for soldering.
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Succession of soldering the daughter PCB.
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Highlighting the potential of mother PCB to solder other circuits.
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Identifying a soldering error with a zero-ohm resistor.
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Encouragement to check out open-source project files.
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Safety tips for working with low-temperature solder.
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Closing remarks and invitation to explore more videos.
Transcription
I want to make a circuit that can solder itself by just connecting two wires to it, and I want to use the same circuit to solder other PCBs like it in mid-air, the revrap way. I really like to compare reflow soldering with pizza making. The PCB is like the dough, the solder paste is the sauce and the toppings are the electronics. The oven's heat is what bonds these individual items together, so using the same analogy, making a self-soldering circuit is going to be like putting the oven in the dough and make it edible. PCBs are made from multiple layers of copper stacked together. One of those layers is usually a solid ground plane, and if we chop this up into a one long trick, it can also be used as a small resistor that heats up and melts the solder. The bummer is that this layer will only be used one time, so it will kind of be stuck in the FR4 forever. So what I'm thinking is that after the PCB gets soldered, I short it to ground, so this can also be used as a ground plane. And I think that makes sense, right? This is the circuit that I chose to do the first test with. But as you can see, there are vials and holes that makes laying out the thermal track a little bit harder. But luckily Altium Designer has this interactive length tuning feature that automatically avoids the obstacles for you. And as you can see, the track is passing underneath all the components. I connected the track to these two pads over here, which are surrounded with mouse-bite vials, so that I can remove this part when it's soldered. The track will also get directly soldered to ground once this zero-ohm resistor gets soldered. I will explain how this circuit works later on in the video. And if you'd like to get a free trial of Altium Designer, check out the link in the description. There you can also get 25% off any purchased license. So somewhere in there should be a secret heater. The goal was to keep the resistance as small as possible, so that it wouldn't need a high voltage to reflow. In fact, it reached 165 degrees at around 9 volts. This is the maximum temperature that the PCB has to reach in order to melt this low-temperature solder paste. This may seem a little bit high considering that the temperature has to come from in between the layers. But the PCB has a TG value of 170 degrees Celsius, which is a little bit more pricey. Besides this, the board only has to reflow one time for less than 5 minutes, so it will kind of be like putting it on a hot plate. As you can see, every single component that's going to be soldered is surface-mounted, so that I avoid hand soldering. Everything looks ok, time to power it on. I'm going to slowly increase the voltage. Yep, it's happening. We have officially cooked our first PCB. There are some soldering blobs, but nothing that can't be fixed. Damn, that looks so good. Ok, so the board has cooled off and there's zero sign of delamination. Now here's when the fun really starts. So far I have been manually increasing the board's temperature by hand, which did an ok job, but a computer can definitely do it better by reflowing the solder paste with its exact temperature profile. And that's what this circuit is going to do. As you can see, the PCB thus not only has a thermal input, but also a thermal output. These pins are connected to a MOSFET transistor, which can be turned on and off using this ATMEGA3204 microcontroller. And the software will read the temperature from the thermocouple sensor. And when the user presses the start button, it will implement a PID controller to match the reflow temperature profile. So we can kind of say that this board is like a mother that can reflow other daughter PCBs. The only problem is that our motherboard has flaws. This was my first time using the ATMEGA32 on a custom PCB, and for some reason I thought that its serial-to-ASB module would come with a preflash bootloader. So I had to flash the Arduino bootloader by soldering some wires to the chip. Once the bootloader was uploaded, I removed these wires and uploaded my software sketch directly through the USB, which led to the discovery of more issues. The reading from the temperature sensor was glitching. This was fixed by replacing the 22uF ceramic capacitor with a larger electrolytic one. I also had to rewire the LEDs and one of the switches because they were sharing the same pins as the ISP programming pins. So to make this work, the board ended up with a couple of modifications, but the cool thing is that we can still use it to reflow a new daughter PCB that doesn't contain its mother flaws. Let's all say a big thank you to PCBWay for manufacturing this lovely new board again. I kind of made the mistake not taking the inch finish for this one, so I guess we can take this opportunity to test the Hazel surface finish. Okay, so all the components are assembled and ready to be soldered. This is a mother to daughter test. Testing in 3, 2, 1, let's go. Okay, so the temperature is slowly climbing. Now it has reached 90 degrees and is going up with a slower gradient. Now it's climbing much faster to reach 165 degrees Celsius. So it should happen in a second now. The board is cooling off. Yep, it's done. I think we have a new daughter PCB. I fletched the bootloader from the new programming pins and then I uploaded the same firmware. This is now officially the new mother. I assembled then their daughter board to test the new mother and it soldered it pretty well. Now the coolest thing about this is that all these mothers can solder other new circuits. Which means that we're kind of building circuits that can solder other circuits, which can solder other circuits. And the loop continues, which means that we're kind of doing like soldering re-prep, which is like so freaking cool. I can definitely see this technology gets combined with like a pick and place. Obviously, this design is not the only one that can use the thermal grounded heater. It can actually be combined with any PCB. I made this small daughter test board that has an LED ring light and all the servo LEDs managed to get soldered. The only thing that didn't was the zero ohm resistor. But this was definitely my fault because I didn't cover the thermal track underneath this component. Anyway, if you'd like to get into self-reflowing PCBs, this project is open source and all its files are available on GitHub. If you're making a custom PCB, always remember to use low temperature solder paste and not to overpower the track, because it can get delaminated or catch on fire. That was way too many smoke. If you'd like to learn more about thermal circuits, check out some of my other videos. But before going there, just remember to like this video, subscribe and consider becoming a Patreon. There it is, our thermal track.