Are toaster oven mod's any good ?

[MathWizard]

Once again I moved into a spot with an old dirty toaster oven. What's the real deal on using these for soldering? What has to be done, added insulation? How good does the temperature control have to be ? Can it be done for $10 ? Or should I just toss it, it's a pipe dream of newbs ? And not even worth the hassle ? I'd use it once and a while on computer hardware. It would be cool to have 1.

[Whales]

Experiences with various reflow methods at small scale -> https://www.sparkfun.com/tutorials/59

Really interesting.  I've been looking for a 2nd hand electric skillet ever since.  Once tried keeping an old electric oven, but it took up too much space.

[alanb]

This by Ian Scott Johnston is worth watching

https://youtu.be/Dube38fpLtc

[rstofer]

I modified a Black & Decker Infra-Wave Toaster Oven (out of production?) and it works really well.  I used this Arduino Shield for the controller:
https://www.rocketscream.com/blog/docs-item/reflow-controller-shield/

I buried the SSR in the side wall cavity so the installation looks fairly clean.  The controller is in a little metal box bolted to the top of the oven.

The big issue with all of these conversions is the heat up rate.  I stuffed the cavity between the inner and outer walls with thermal matting that I bought from McMaster-Carr.  I have no idea which material I used:

https://www.mcmaster.com/thermal-insulation-sheets


For small boards, a hot plate works just as well.  If the top has a void at the center, you can use an old sawblade to spread the heat.  This process is simple:  Turn the plate on full, watch for the solder to flow, remove the board (carefully) and turn off the heat.  There is nothing about this process that resembles the factory heating curves but it seems to work fine.

[fourfathom]

I recently got a small toaster oven and am using it with no oven modifications.  I built a simple power controller for it that monitors the internal temperature (using a thermocouple) and switches the power (using a solid-state relay), and have been able to get a quite reasonable temperature/time profile from this.  There's more info in this thread:
https://www.eevblog.com/forum/manufacture/reflow-solder-station-recommendations/msg2943048/#msg2943048

I honestly don't know how uniform the heating is across the entire oven tray, since the boards I build are fairly small.  Perhaps insulating the oven helps there, but what I have works very well for me.
Here's a plot of my typical reflow cycle (I'm using lead/tin solder paste, so I'm shooting for a 230 deg C max temp) X-axis is seconds, Y axis is degrees C: [corrected: degrees C, not F]

[jmelson]

I got a Philips CSM84 pick & place machine in 2007.  I bought the biggest toaster oven Walmart had, it was a GE brand.  It has two straight elements below, and two above the board.  These run left to right, two near the back, two near the front.  I got a ramp and soak thermocouple
controller on eBay.  The ramp and soak feature allows you to program temperature ramp rates and holds at particular temperatures.

One of the tricks I found was to poke the thermocouple into a plated through hole on one of the boards, to sense actual temperature.
The boards absorb WAY more heat than the air, so a thermocouple hanging in the air gets a much lower reading and hence the boards get
fried!

Since 2007, I have manufactured over 2000 boards in this oven, usually doing 6 small boards at a time.  I have some larger boards that I can only fit one or two at a time.  I have a slight variation in temperature from one area to another, but raising the peak temp by a few degrees C allows all the boards to reflow properly.

Jon

[jmelson]

Here's a plot of my typical reflow cycle (I'm using lead/tin solder paste, so I'm shooting for a 230 deg F max temp) X-axis is seconds, Y axis is degrees F:

Are you SURE this is Fahrenheit?  230 F is about 110 C, not nearly enough to melt SnPb solder.  Unless the board is getting much hotter than the thermocouple (the boards absorb IR much better than air, don't ask how I know this!)  I usually heat to 220 C for SnPb and 234 C for lead-free solder.  But, that is actual board temp with the thermocouple poked into the board.

Jon

[doobedoobedo]

I converted a cheap Aldi oven a few years ago. Wrote my own controller. It works really well.

[fourfathom]

Here's a plot of my typical reflow cycle (I'm using lead/tin solder paste, so I'm shooting for a 230 deg F max temp) X-axis is seconds, Y axis is degrees F:

Are you SURE this is Fahrenheit?  230 F is about 110 C, not nearly enough to melt SnPb solder.  Unless the board is getting much hotter than the thermocouple (the boards absorb IR much better than air, don't ask how I know this!)  I usually heat to 220 C for SnPb and 234 C for lead-free solder.  But, that is actual board temp with the thermocouple poked into the board.

Jon

Oops!  Thanks, you are correct, it's all in deg C.  I corrected my post.  My thermocouple is wire-tied onto a small unpopulated PCB so the probe is in tight contact with a plated-through-hole.  I put that PCB next to the boards I am reflowing, so the temp I measure should be fairly close to what the board being soldered sees.

[fourfathom]

I modified a Black & Decker Infra-Wave Toaster Oven (out of production?) and it works really well.  I used this Arduino Shield for the controller:
https://www.rocketscream.com/blog/docs-item/reflow-controller-shield/

That's a nice looking little controller!  Those guys have a newer, smaller one (Tiny Controller V2) that is also attractive -- a simplified design, and it only costs $30.  You need to add the thermocouple and the SSR.

No doubt a well-insulated oven behaves differently, but my un-modified one only ramps up at 1.5 deg C / second max, heating elements on 100% (ceramic, one top, 1 bottom).  Cool-down with the door open is about 0.75 deg/sec (no fans).  When I turn off the heaters, the temperature continues to ramp up significantly for many seconds.  Given this behavior I decided to not bother with a PID control loop, but instead designed the program to learn when to shut off the heat (and for how long) in order to obtain the desired soak and reflow profiles.  I also collected data for various duty-cycle modulations of the heaters, but there being no need for slower temperature ramps, that lead me to use the full-on / full-off control.