Introduction
Nowadays many of the most âexitingâ chips come only in leadless packages, such as BGA and QFN which are hard or impossible to solder just by soldering iron, because leads are under the chip where they canât be reached. These kinds of chips are usually soldered using reflow soldering. In reflow process solder paste is used instead of solder wire. It contains very small balls of solder in flux, diameter of the balls is just few micrometers. First this paste is put on the contact pads, then components are placed on the pads and whole board is heated in reflow oven where solder balls in the paste melt and attaches the components firmly in place.
For the solder paste to work correctly temperature of the oven must follow correct temperature profile accurately. If the temperature rises too quickly it can damage the components and if the temperature rises too slowly, too much flux can evaporate and the components arenât soldered reliably.
Real reflow ovens are usually expensive, like many other manufacturing tools, but ordinary toaster ovens can be used in reflow soldering with few modifications. They are much cheaper than real reflow ovens, but temperature cannot be set programmatically or accurately. External controller board can be used to control these ovens.
Reflow oven controller
Toaster oven reflow controllers have been done before many times (for example 1 and 2). I wanted to make a simple and cheap controller that wouldnât use outdated parts. Instead of buttons and dedicated display, it should use USB port for setting the temperature profile and monitoring the temperature if needed. This would be cheaper to make and easy to use. If the computer isnât connected, it should be able to be switched on by just connecting the power supply, load the temperature profile from non-volatile memory and run without user intervention.
Because the oven gets very hot, itâs not possible to add any electronics inside it. Controlling is done by switching the power on and off rapidly with solid state relay that is connected on extension cord. Temperature is measured using thermocouple inside the oven. Microcontroller will read the temperature and output PWM signal for the solid state relay which can be used to accurately control the temperature of the oven.
For more detail: Toaster oven reflow controller
