Solder Reflow Oven (for Less Than $100)

A solder reflow oven is a very useful piece of equipment for boards with a large quantity of surface mount components or making batches of surface mount boards. The reason that I made this was because I had to make several boards containing around twenty parts each. It was too much of a pain to try and solder them by hand, considering all I own is a convention soldering iron. Looking around I saw that actual solder ovens were out of my budget, so I ended up modifying a twenty dollar toaster oven from Amazon. All in all this cost me about $50 to make, and I was able to use parts that I already had sitting around. It made my life much easier to be able to use the oven to do the soldering instead of a traditional iron. Work that would have probably taken me around 3-4 hours was able to be done in only around 20-30 minutes. I got the idea from an old Sparkfun post that was trying to do something similar, but ended up being abandoned in 2006 and becoming nothing more than a concept. If anyone is interested in that post here it is. I used this in my Faux-Nixie clock since the boards were such a massive pain in the butt to do by hand.

Before starting on this project make sure that you take the proper precautions to safely work with mains AC voltage. It is very dangerous and unforgiving. Make sure that the wire used is suitable for 120V AC 10A and that every joint is either electrical taped or heat shrinked. When turning things on to test I recommend using a power strip so that you can immediately flip the off switch on it to cut power if anything goes wrong.

In the design I have include an emergency stop button, indicator light, and used a fused outlet. When working with high current and voltage there can never be too many precautions. While these are not necessary to make it work I would still recommend including them for safety reasons.

!!!Never, Never, Never leave this machine running unattended due to the serious fire hazard it presents!!!

Materials:

Electronics:

• Arduino Nano
• 10K Resistors
• 4.7K Resistors
• Tactile Push Button
• 1602 LCD Display
• 100K Thermistor
• Male Pin Headers
• PCB-Mount Screw Terminals
• Panel Mount Emergency Stop Button
• Panel Mount Indicator Light
• Panel Mount Two Position Rotary Switch
• Wall Outlet w/ Cove
• Toaster Oven
• 12 AWG Wire
• Fused IEC connector w/ switch

Other:

• PLA Filament
• M4 Screws and Nuts
• 3mm Heatshrink Tubing
• Kapton Tape

Tools:

• 3D Printer (Not necessary but very useful)
• soldering iron and 60/40 solder
• Heat gun or lighter
• Screwdrivers
• Wire Cutters
• Pliers
• Utility Knife
• Super Glue

You can either order the board from a fab-house like JLCPCB or manufacture the board yourself. I designed the board in Autodesk Eagle and have provided both the original CAD files I made and the Gerber files that I sent to JLCPCB. When assembling the board start with the smaller parts first; the buttons and resistors. The resistors and female header need to go on the back side of the board to leave clearance for the screen and buttons. Then put on the pin headers and female headers. Last solder in the screw terminals and the 1602 LCD Display. Once all of the parts are on the board insert the Arduino Nano into the slot on the back of the board.

Connect the Arduino Nano to your computer and open the Arduino environment. Make sure to select Arduino Nano and the right bootloader version before uploading. Compile and upload the code to the Arduino.

For the case print out the provided files. Print out one of each the body and cover and then five of the button pieces. Use .2 mm or lower layer height and with 100% infill. For the larger parts print them at a slower speed since they are very tall and have thin walls of 1mm. For the body use supports.

While my print isn't the best quality, as seen in the pictures, that doesn't matter as long as it is functional. I have plans to redo the case using laser cut wood instead of printed plastic to make it both quicker and easier to assemble. I wasn't able to get around to that since the laser I use is temporarily out of commission.

Before assembling the last few components and putting everything in the case there are a few final safety precautions that need to happen. Wrap the power supply and SSR in electrical tape, making sure to leave any holes and other necessary section uncovered. This is so that none of the wires or metal can make contact once sealed in the case. Even though I didn't do this, it might also be a good idea to isolate the arduino board.

Connect all wires as shown in the fritzing diagram. Make sure that any of the wires that carry 120V for the outlet and oven are using heavy duty wire so as to handle the high current load of the oven. The outlet is installed in the larger side of the case and the IEC jack is installed on the cover of the box. To secure the Arduino and board insert the printed buttons into place, and then hot glue the board inside of the case on top. Make sure that the hot glue does not interfere with the buttons. Close the box by screwing the side panel on and then super gluing the cover's pegs into place.

To attach the thermistor to the oven insert it through the side of the door. With the particular oven I used there is about 3mm of clearance between the door and the main body, which was more than enough to insert the thermistor through. Wrap the end of the thermistor with kapton tape so that the metal of the oven will not interfere with the wiring and the readings. Attach it to the side of the oven using kapton tape. Use plenty to ensure that the thermistor will not fall off.

To use the oven, plug everything in and then turn it on. It will display a splash screen to let you know that the Arduino is turned on and working. To switch between always on mode and timed mode use the rotary switch. When the switch is in its on position it will be in Always On mode, and when off it will be in timed mode. When in timed mode, to start heating press the select button (the middle one) to go to the temperature selection menu. Using the up and down buttons change the temperature values and the left and right buttons switch the cursor between the hundreds, tens, and one value. Once you have selected your desired temperature press the select button to start heating the oven. It will take some trial and error to find the exact temperature that your particular solder melts at, also accounting for any error in the thermistor's calibration. For me my sweet spot temperature is around 215-220 C (measured with the Arduino). Once it hits the set temperature it shuts the oven off and starts the cool down procedure. The cool down procedure is letting the oven cool down to 50 degrees C so that when you take the boards out of the oven the solder isn't still hot and liquid with parts shifting around. When letting the oven cool down, leave the door shut as you don't want to damage the boards with any sudden changes in temperature. You need to let them cool off gradually. Once the oven has reached around 50 C it is safe to remove the boards and finish work on them.

If there is a problem during use shut the box and oven off immediately by hitting the emergency stop and pulling the plug. I have included both the indicator light and emergency stop as a safety precaution since the amount of power going through the relay to power the toaster oven is significantly more than I normally work with. Never leave this unattended when plugged in and running as it has serious potential to start a fire. When using it for the first few times I would keep a close eye on it to make sure that everything is working properly.