A PCB That Reflow Solders Itself and Then Self Propagates!
Carl Bugeja combines clever trace design along with low-temp solder paste.
Carl Bugeja's latest PCB project combines some of his findings over the past few years. Previously we have seen Bugeja create absolutely crazy yet astounding concepts using innovative PCB design and manufacturing techniques. This project is a PCB that reflow solders itself and THEN can self-propagate RepRap style.
The self-soldering PCB is a multi-layer design. One of the layers is a serpentine trace that acts as a resistor/heating element. Applying power to this trace and monitoring the PCB's self-rise temperature can generate enough heat to cause the solder paste to reflow.
Bugeja is using ChipQuik's TS391LT50 low-temp solder paste. This temperature-stable paste is a Bismuth, Tin, and Silver alloy with a melting point of 138 degrees Celcius. (For more information on low-temp paste, check out this video.) The SnBiAg's low melting point works well with Bugeja's design since he could safely achieve temperates around 165 degrees Celcius.
One trade-off with this design is that the heater element is no longer functional after the PCB reflows. So one idea Bugeja has is to short the trace to ground to get some of the benefits of a partial ground layer.
The results are awe-inspiring. But what does THIS circuit do? When would a self-soldering board be practical? Turns out, the first board Bugeja reflowed was a heating controller! Like the RepRap 3d printer that can print itself, this self-soldering board can solder other boards! The idea is that you manually control the heat for the first one, and then it can create a proper reflow profile for future boards.
It turns out this circuit needed a few changes. However, it worked out nicely that when Bugeja received the corrected PCB, it was easy to reflow several of them. He even demonstrated the process using a test board with an LED ring light!
His entire video takes you through his journey with this design. There's even a short segment explaining the layers of a PCB by comparing it to a pizza. (An delicious analogy, for sure.) If you'd like to download the design files, they are available in this GitHub repo.
If you are not familiar with Bugeja's other work, you should check out two of his previous projects: flexible-PCB actuators and a flexible heating panel — that eventually became a self-heating sweater.