This DIY Hotplate Delivers Surface-Mount Reflow with a "True" USB Power Delivery Input

Pseudonymous maker "Markus24152," hereafter simply "Markus," has released a PCB-based hot-plate for surface-mount soldering projects — powered by USB Power Delivery (PD) and capable of negotiating up to 100W of power.

"If you have ever tried soldering tiny SMD [Surface-Mount Device] components with a handheld iron, you know the struggle," Markus writes of the project's inspiration. "It's tedious, shaky, and often frustrating. Commercial reflow ovens are bulky, and professional hotplates can be prohibitively expensive for a hobbyist workbench. I wanted a better solution: compact, smart, and powerful. So, I designed and built my own Mini Reflow Hotplate. But I didn't want another device with a clunky 12V power brick. My goal was modern portability. This hotplate is powered entirely by USB-C Power Delivery (PD). This means you can run it off the same high-power charger you use for your laptop, negotiating up to 20V for rapid heating."

Inside the custom 3D-printed housing is an STMicroelectronics STM32 microcontroller driving a compact OLED as the user interface and a proportional-integral-derivative (PID) feedback loop from an Analog Devices MAX6675 thermocouple digital temperature sensor with K-type probe. It's this that reads the temperature of the hotplate itself, built from an aluminum-core PCB covered in a long winding copper trace. "This trace acts as a giant resistor," Markus explains. "When we push current through it, that electrical energy is converted directly into heat."

The power is supplied via a USB Type-C connection, feeding into an STMicro STUSB4500QTR USB Power Delivery controller — designed to negotiate higher voltages from compatible power supplies in order to reduce the current required for a given power. In this case, it negotiates up to 20V at 5A for a 100W supply to the hot-plate PCB.

"Realistically, this specific design struggles to reach temperatures above 300°C [572°F]," Markus admits. "The surface area simply dissipates heat faster than the 100W input can supply it at those high ranges. There is [also] one factor I underestimated during the design phase: the positive temperature coefficient. As the copper traces inside the PCB get hot, their electrical resistance increases. Since we are working with a fixed voltage (20V), an increase in resistance means a decrease in current and therefore a drop in power. Basically: The hotter the plate gets, the less power it draws. This makes the last few degrees the hardest to reach."

The project is documented in full on Instructables, with hardware and firmware available on GitHub under an unspecified open source license.