Solder reflow toaster oven

[Sebastian] needed a small solder oven so he bought himself a small toaster oven (Spanish, Google Translate). It’s not the kind of thing we’d make our breakfast in now, but for soldering it’s a very nice oven.

After a little bit of research on Google, [Sebastian] discovered that the best technique when dealing with reflow ovens and solder paste is following a specific temperature curve. Ideally, Tin/Lead solder needs to preheat from room temperature to 150 degrees C, then level off so the flux can activate. After that, a quick jaunt above 183 degrees C makes the solder flow. To get his toaster working optimally, [Sebastian] stuck a thermistor in the toaster and measured the temperature profiles of different ‘modes.’

The correct temperature curve was calculated using different heater elements and [Sebastian] was off to the races. He did have a few problems on his first few boards – solder bridging, mostly – but that’s not the fault of the oven. An LCD display (translate) was added recently so accurate real-time temperature monitoring is available.

20 thoughts on “Solder reflow toaster oven

  1. Would a small convection fan help keep the temperature from stratifying and constant? A digital PID and thermocouple would be nice to dial in the perfect temperature.

  2. ummm I don’t think this is a good “Kitchen Hack”. I am not talking about the hack itself, but the category it is in. After reflowing solder the oven should never be used for preparing food again.

    1. The AD595 have a could junction compezation, is not easy make this circuit whit a lm358, you need a extra temperatura sensor, the best choise for this chip is a MAX31855KASA+

      1. that maxim part is no better :(
        my problem with them is they are for industrial/Automobile markets and are priced accordingly, namely ~$10
        while lm358 + lm50 will be <$1

  3. I decided to do pretty much the same thing when I found I needed a “reflow oven” for the small boards I need to make.

    I went to a local “big” store, bought a cheap, small toaster oven capable of hitting 480 F ($20!) and used the temperature reading on my multimeter to mark the dial for 125 C and 218 C.

    Although it’s pretty manual (I’ve elected to not automate anything) it’s very easy to turn the dial and click a stopwatch. For the peak, I tend to turn the temp up a little higher, then watch for when the solder begins to flow as my signal to turn the temp dial down to shut off the heater elements. Cooldown is actually as easy as simply opening the door and waiting for the boards to cool off naturally. (Turns out both the heat up and cooldown C/sec stay within the reflow soldering profile very nicely with no additional help.)

    And yes, I got the idea from reading… HackADay!

    (Now if I could only find a cheap way to make a solder paste stencil…)

    1. (Now if I could only find a cheap way to make a solder paste stencil…)

      The cheapest way is to not make a stencil at all. Solder paste is available in syringes, so print the solder paste on using a modified Reprap or Makerbot.

  4. Unless your toaster oven is overflowing with solder and paste that spilled off your boards (This should never happen), it will still be OK to toast in. Our parents drank out of soldered copper pipes and they’re not that brain damaged, are they? All this “OMG, it was near lead!” stuff is ridiculous.

  5. I mean, it’s not like the oven gets hot enough to vapourize the lead and have it stick to all surfaces then flash back onto your food. Suck it up, princesses.

  6. @jasong:
    i admit i’m a princess – but with that comes incredible beauty :)
    it’s not just the lead: rosin is a known allergen. boards and parts contain all kinds of plasticizers, that might be hormone disrupters
    my rule of thumb: if it smells like molten plastic, like overheated circuit boards, or just like a room i wouldn’t want to sleep in, i also don’t use it to bake the food for my precious body in it. – your body might be less precious, so what do i know.

  7. A simple PT1000 voltage divider with AREF at 1.667V could give enough precision without a opamp (about +/-2C).

    I currently use a simple on/off mechanical relay in a 1S loop, so it gives a few clicks while running, but nothing too annoying, since it is only off for a bit during flux activation, the other stages requires full power.

    For cooling the human can open the door a bit to start the cooling, and full when about 150C, board can be removed at 100C or so.

  8. Reflow solder I have used contains methyl pyrolidone which is a bit nasty and vaporizes at 200c = 396f. Lead is not the only thing to think about. Wash your hands kids and have adequate ventilation.

    The skillet reflow jig previously listed gives a good jedec heating curve too.

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