Heat Stick Is Carl Bugeja's Flexible PCB Heater with a Sticky Back
Continuing his experiments with flexible printed circuit boards (PCBs), Carl Bugeja's latest video introduces the idea of a flexible heating element with a sticker backing. He calls this concept the incredibly clever yet descriptive name: Heat Stick.
Initially, Bugeja attempted to develop a printed circuit board-based heater for reflow soldering. However, several issues kept the "hot plates" from functioning well at the extreme temperatures needed when soldering. So, Bugeja turned his experimental attention towards using the PCB heater concept for warming instead of baking.
Heat Stick is a flexible printed circuit board measuring 10 by 10 millimeters. This square puts it slightly taller than a coffee mug and wide enough to cover almost half of its circumference. The plastic material is polyimide, also known by its trade name of Kapton. Traces embedded in the bendable plastic act as resistive heating elements. In this case, the sheet's resistance is less than one ohm!
The flexible PCB covers the "heat" part of the Heat Stick. The "stick" part is a double-sided translucent adhesive acrylic sheet that attaches to the flexible PCB while leaving an exposed tacky surface. Its manufacturer says the materials are heat resistant up to 260 Celcius — making it an ideal companion for the flexible polyimide. Bugeja, of course, decided to test the performance.
A straightforward first attempt demonstrated an issue with a serpentine PCB heat trace. The entire structure folded onto itself along the lengthy traces. Over the successive attempts, Bugeja modified the design so that the heating elements caused less self-damage with the generated heat. After running multiple long-term tests, it appears Heat Stick has two potential application uses.
Bugeja found Heat Stick works well in long-term low-temperature and short-term high-temperate situations. For example, the long-term low-temperature application is a warming device like a wearable sweater. In contrast, a short-term high-temperature application could be a one-time use solder reflow "plate."
Like many of his flexible PCB experiments, Bugeja provides the design files for Heat Stick on GitHub. There, you can find the Gerber files for PCB production and Altium design if you want to tweak the design for your application.