Solder Reflow Oven (for Less Than $100)

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About: I am an incoming freshman at ASU studying robotics. I love to make things and perform music. I am always working on several projects at a given time.

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.

Step 1: !!!Safety!!!

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!!!

Step 2: Materials and Tools

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

Step 3: Assemble the Control Board

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.

Step 4: Program the Arduino

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.

Step 5: Printing the Shell

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.

Step 6: Final Assembly

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.

Step 7: Using the Oven

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.

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    15 Discussions

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    cnludwig

    3 months ago

    Zachary,
    Thanks for documenting this project. I have a medical oven (the size of a large dorm fridge) that I plan to do something similar with for powdercoating. Where I live, the Goodwill/Thrift type stores absolutely have toaster ovens. I bought one which appeared unused for $9. Perhaps you could find a convection one if you feel you need it. If not, hey, your setup seems to work great for your needs already!

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    PhilTilson

    3 months ago

    A couple of things spring to mind.

    First, I'm not sure that a thermistor is the best thing to use here. Although they are probably OK up to around 300°C, putting it directly in the path of infra-red radiation from the elements may well be too much for it. I used a thermocouple for my version of this project - safe up to 1000°C!

    Second, the wire connecting the thermistor to the unit will need to be capable of withstanding that temperature as well - this is another advantage of using a thermocouple as they are usually connected via glass-fibre covered wire.

    Third, it seems a terrible waste to use an Arduino to control this and yet not to use it to follow a typical recommended profile for SMD components. Just heating from cold to melting temperature may well work in many cases, but it is trivially simple to program the Arduino so that it heats fairly rapidly to 120°C, pre-heats for 60 seconds, allowing the solvent to evaporate, heats slowly to 180°C, to allow for flux activation, then heats to quickly to (say) 220°C for 10 - 30 seconds before switching off.

    For my unit, I then open the door about 2cm at the top which allows a cool-down rate of around 3 - 5 °C per second, as recommended to control the grain size. I think leaving the door shut might keep the devices at too high a temperature for too long which could adversely affect the joint reliability.

    Just some thoughts!

    3 replies
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    Zachary GoodePhilTilson

    Reply 3 months ago

    I agree with you that a thermocouple is probably a much better option. I only chose a thermistor because it was what I had on hand at the time. Given that the particular ones I chose were used for 3D printers, I think that they should be adequate (just not ideal) for this.
    Using an Arduino for this is not such a huge waste (in my opinion) since if you look around clones can be had for as cheap as $1-2.

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    PhilTilsonZachary Goode

    Reply 3 months ago

    I think you have misunderstood me! The use of an Arduino is a very good idea. What I was saying was that you could have got so much more out of it than you have. Rather than just switching on, heating up and cooling down, it would be very easy to program the Arduino to follow the correct heating and cooling profile recommended by the manufacturers for surface mount components.

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    Zachary GoodePhilTilson

    Reply 3 months ago

    You are right that I should have made a better heating curve. I was looking through the code for marlin 3d printers to try and figure something like that out and wasnt able to get my head around it. Maybe something to do with pwm? There are definitely a lot of improvements that I need to make to this and will hopefully get around to doing eventually.

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    SilverL2

    3 months ago

    According to the IEC "high voltage" is above 1,000 volts AC or 1,500 volts DC so your mains supply at 120 volts AC is far from "high voltage". In fact it is classed as low voltage though I accept that it can give you a nasty jolt. Even our more shocking 240 volts is now perversely rated as "low".

    2 replies
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    Zachary GoodeSilverL2

    Reply 3 months ago

    Even though 120V AV is not officially considered "high voltage" it is still dangerous and can be lethal. It still requires caution when working with. When I was referring to IEC I was not referring to a standard, but in fact the type of plug that was used (the kind on the back of a PC power supply).

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    SilverL2Zachary Goode

    Reply 3 months ago

    All understood and accepted. My comment was more to highlight the oddness of the IEC classification than to be critical of your post, my apologies if that was your impression.

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    ZukeMan1

    Tip 3 months ago on Introduction

    A great place to get all sorts of things cheap, like a toaster oven and help the environment by repurposing items is Goodwill!

    1 reply
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    Zachary GoodeZukeMan1

    Reply 3 months ago

    As a toaster oven can already be had for as cheap as $20 I don't think there is any point in getting one used and nasty. I don't believe any thrift stores or goodwill would actually take one as a donation. While I am all for helping the environment I don't think that a used toaster oven would be a good idea for this project.

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    starphire

    3 months ago

    This takes me back to 2003, when I first tried this using plans from the internet that have long since gone away. But lots of people were experimenting with the idea and sharing their results. A common complaint was that the radiant temperature in a basic toaster oven is uneven, so your boards needed to occupy only the center of the oven - meaning small and few in number. Boards near the edges of the rack won't reflow as quickly, and by then boards in the middle were overdone. Also, components with more thermal mass, such as heat sink tabs, required extra time - meanwhile etched parts of the boards in the center tended to get scorched!

    What the Sparkfun article gets right is what I also found to be *critical* to getting results approaching a commercial reflow oven - a convection-style toaster oven with a fan in the back! The results with these ovens are FAR superior, especially with improved cooldown times that nearly match the recommended reflow temperature profile (just crack open the door when the element goes off). They also used a thermocouple, which can take the radiant heat in the center of the oven where most thermistor assemblies would quickly melt into goo.

    For those thinking of trying this, the modest extra investment in a tabletop convection oven and a thermocouple probe & amplifier will really help ensure you end up with a tool that you'll want to use again and again. And if you want to reflow larger boards, or run batches of smaller boards at once, it's almost an essential upgrade.

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    Zachary Goodestarphire

    Reply 3 months ago

    I must have missed the importance of a convection oven. That is an upgrade I may consider making myself instead of buying a new oven. As for why I chose a thermistor, it is just because that is what I happened to have on hand. I whole-heartedly agree with you that a thermocouple would probably be much better, as I had ordered a few thermocouples a couple weeks back I will be making an ammendment to my instructable if I get that to work.

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    kiwironnie

    3 months ago

    Key is to use a toaster oven that can achieve at least 1 degree C rise in temperature per second to achieve a correct reflow temperature curve. I discovered the hard way that ovens with the typical solid heating elements are too slow (even convection types) unless they are augmented with additional elements to output a huge wattage. The oven type that eventually worked best for me, has been operating successfully for years and that was cheap and easy to adapt, is a type with quartz glass elements (one top and one bottom) that heat up fast and glow very brightly. The toaster oven will also need to be prepared with additional insulation beneath its outer metal shell (e.g. rock wool). Thermal insulation on the outside also helps. This does mean that to cool down fast enough the door needs to be progressively opened after the oven has reached reflow temperature, which can be done manually or automatically using a servo motor.

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    KISELIN

    3 months ago

    Gee...Sorrry..I didn''t read the whole instrct. of yours. Still, You make a wery importatnt warning in the wery beginning of your instr. about the leathabilelty of the main's power!!
    To knowledge to anyone: a "LEATHAL = DEADLY" through a human with 230VAC/50Hz
    body is appr. 50mAmps, (Yes, 50milliAmps = 0,05Amps), yes, thank you and good bye.
    Sure there are these "safety- circuitbrakers" but often they jump in when 50mA is past long ago.
    These "current-circuit-brakers" are just a mechanical things. That is; say it takes for the "circuit.braker" 20mSek. to brake, hmm... now you get the whole 16Amps in a fraction of a second, can you take thar?