How to Build a Solder Reflow Oven

2023-10-03 | By Zach Hipps

License: See Original Project Solder

If you want to solder surface mount components to a PCB, you've got a few options. ‎You can use a regular old soldering iron with magnification and do it by hand, or you ‎can use a hot air workstation and heat the board and the solder until everything flows. ‎But if you've got a lot of components, or you have a whole batch of PCBs, this is going ‎to get really tedious. In this article, I'll show you how to convert a toaster oven into a ‎solder reflow oven. Obviously, there are industrial ovens designed to do this, but if ‎you're a hobbyist like me and you want to reflow your components at home, this is a ‎really great option. I'm not doing anything novel here. There are a whole bunch of ‎people out there who have already taken regular toaster ovens and turned them into ‎reflow ovens. But I want to do this in a way that requires as few modifications to the ‎toaster oven as possible.‎

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Just a quick disclaimer: If you're going to do this, don't use the toaster oven for food ‎after you've used it to reflow solder. There are a lot of extra chemicals and fumes that ‎result from reflowing solder, and you don't want that mixing in with your food.‎

Solder reflow ovens need to be able to follow a solder reflow profile, which means they ‎need to be able to adjust their temperature over time according to certain specifications. ‎To accomplish this, I'm going to use a few components. I've got a thermocouple that I ‎will connect to a microcontroller. This is going to give me a precise reading of the ‎temperature of the board inside the oven. I'm going to use a PID control loop inside the ‎microcontroller to signal a solid-state relay to turn on and off the oven. Most DIY reflow ‎ovens that I've seen require you to disassemble the toaster oven and cut wires to attach ‎them to your relay. I want to avoid that. I'm going to have a separate external enclosure ‎that houses the relay and the thermocouple, and I'll plug the toaster oven into that ‎external box. I also want to have a user interface for this reflow oven, so I've got a TFT ‎touchscreen display.‎

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To start things off, I found a little knob on the back of the oven and I'm not sure what it ‎does. Maybe it has a purpose and I'm not supposed to mess with it, but I want to ‎remove the little rivet and drill the perfect-sized hole to stick the thermocouple through. ‎With that done, I can write some code on the Arduino board and start measuring the ‎temperature inside the toaster oven. There’s an integrated circuit on a breakout board ‎that can read the thermocouple. It communicates with the microcontroller using the SPI ‎interface. I've got the thermocouple wire run through the hole in the back of the toaster ‎oven, and I've got it wrapped around the rack. This will give me temperature readings ‎inside the toaster oven, but if I want to control the heat of the toaster oven, I need to be ‎able to turn on and off the power source. So, I need to connect the solid-state relay to ‎the plug of the oven.‎

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Like I said earlier, I'll be using a PID control loop to control the temperature inside the ‎oven. The input is the temperature sensor, and my output is the relay. I can turn on and ‎off the toaster oven to maintain the heat. When I start the controller, you can see a ‎basic solder reflow profile. It's got three segments: a preheat stage, a soak stage, and a ‎reflow stage. I have different temperatures and durations set for each of those stages. ‎With the basic functionality of this working, I need to put all the components into an ‎enclosure and write some firmware for the user interface on the TFT display.‎

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The user interface for the solder reflow oven is pretty straightforward. It has a few ‎buttons to edit the preheat, the soak, and the reflow stages so the user can set the ‎temperature and the duration for each stage. I've used a different color to designate the ‎different stages. Red is for preheating, orange is for soaking, yellow is for reflowing, ‎and blue is for cooling down. Once I confirm those settings, the controller will plot the ‎reflow profile. This gives me a quick little visualization of what the reflow profile looks ‎like before hitting the start button. To test the reflow oven, I'm going to put a couple of ‎switches on a PCB that I designed. If I was going to populate this whole board, I would ‎use the stencil that I ordered for this PCB. But since this is just a demonstration and it's ‎just a couple of components, I'm going to apply that solder paste using a syringe. If you ‎want to learn more about prototyping with solder stencils, check out the blog and video ‎on Prototyping with Solder Stencils.‎

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This is a project that has been on my list for a really long time, and I'm really excited to ‎have it now and actually be able to use it. If this is something you want to build for ‎yourself, you can find all the design documents and bill of materials on the GitHub ‎page for this project. Right now, the firmware is super basic. There are a lot of cool ‎features that I would love to add. If you end up downloading this code and making ‎modifications, please make a pull request on GitHub. That way everybody can benefit ‎from your hard work.