SMT Oven Reflow: A DIY Solution using Raspberry Pi and Halogen Oven
In the world of electronics, surface mount PCBs (Printed Circuit Boards) are widely used for their smaller size and higher component density. Soldering surface mount components can be challenging, especially when it comes to reflow soldering. Reflow soldering is a process of melting solder paste to create a mechanical and electrical connection between the components and PCB. This process requires precise temperature control and consistency to produce high-quality and reliable results.
Commercially available convection reflow ovens are expensive and may not always be accessible to hobbyists, makers, or small businesses. Therefore, a DIY solution can be a cost-effective and rewarding alternative. In this article, we present a DIY solution for a solder reflow oven using a halogen oven and Raspberry Pi Zero W.
Halogen ovens are cheap and easy to obtain appliances that use halogen lamps to heat food. These ovens have various temperature control settings and can be modified to fit the requirements of a reflow oven. Andy Brown’s awreflow project is an excellent reference for the halogen oven modification, where he removes the fat spatter shield, modifies the fan, and installs a thermocouple for temperature sensing.
Temperature sensing is a critical aspect of reflow soldering. MAX6675 is a thermocouple to digital converter that can communicate with the Raspberry Pi and provide accurate temperature readings. PicoReflow is an open-source software for PID control that uses the MAX6675 readings to maintain precise temperature control.
We made some improvements to the picoReflow software to improve its performance. Trimmed mean averaging is used to allow the use of noisy thermocouples, and retries are implemented for failed MAX6675 connections to ensure proper functioning upon power-on reset. A temperature compensation offset is added to adjust for variations between different temperature sensors. The sudden temperature increase check is removed, which allows PID step and bump tests. The PID control uses 2Hz PWM, following Andy Brown’s code.
The power/control system is housed in an old desktop PC PSU case, with the unnecessary components removed. The SSR relay and heatsink, Raspberry Pi Zero W, and MAX6675 are placed inside the case, with connections kept straightforward. The relay and the fan are connected to 240V, while the MAX6675 is connected to the Raspberry Pi, which controls the relay. A push-button is added, connected to a Raspberry Pi GPIO, to shut down the system cleanly.
Finally, we tested the reflow oven using lead-based solder and followed a reflow profile. The results were promising, with reliable connections on the PCB.
In conclusion, a DIY reflow oven using a halogen oven and Raspberry Pi Zero W is a low-cost and effective solution for reflow soldering. With some modifications and improvements, high-quality and reliable results can be achieved.