Toaster oven reflow controller

liyf · 发表于 2017-2-19 16:42:33

Toaster oven reflow controllerDate 2013-09-08

Almost finished controller board. This one was soldered by hand.

IntroductionNowadays many of the most "exiting" 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 can't 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 componentsare placed on the pads and whole board is heated in reflow oven where solder ballsin the paste melt and attaches the components firmly in place.

Temperature profile in reflow soldering. Source: Wikipedia

For the solder paste to work correctly temperature of the oven mustfollow correct temperature profile accurately. If the temperature risestoo quickly it can damage the components andif the temperature rises too slowly, too much flux can evaporate and thecomponents aren't 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 programmaticallyor accurately. External controller board can be used to control these ovens.
Reflow oven controllerToaster oven reflow controllers have been done before many times (for example 1 and 2).I wanted to make a simple and cheap controller that wouldn't use outdated parts.Instead of buttons and dedicated display, it should use USB portfor setting the temperature profile and monitoring the temperature if needed.This would be cheaper to make and easy to use.If the computer isn't 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, it's not possible to add any electronics inside it.Controlling is done by switching the power on and off rapidly with solid state relaythat is connected on extension cord. Temperature is measured using thermocouple insidethe oven. Microcontroller will read the temperature and output PWM signal forthe solid state relay which can be used to accurately control the temperature of the oven.

1380W Toaster oven with convection. Bought second hand for 20