SparkFun Forums

[designer]

Does the use of a fan in a convection toaster oven increase the rate of temperature rise of the PCB?

The claim for these convection ovens is that they speed up the cooking time. But is that the same as saying the rate of temperature rise is faster?

[MGP]

I didn't see an increase in rate of temperature rise in my convection oven with the fan on. It did seem to even out the temperature in the oven chamber though, which makes sense since it forces air circulation around the oven. I measured the temperature with a thermocouple probe at different points in the oven to look at temperature rise and temperature at different points in the oven space.

[designer]

Thanks for replying.

As a follow-up, do you know what the temperature rise was? I do know you previously posted a little over a year ago, and talked about the DeLonghi toaster - I forget the model, but it was a digital convection oven.

I am thinking of using a temperature controller from Omega along with a thermocouple in an attempt to get as good a profile as I can. I am stymied by choosing the oven. There are those who seem to get into the heater elements themselves, and others control the AC mains via the line cord. For the digital models, this presents a problem, unless you power the digital circuits separately. This entails reverse engineering since I can't find a schematic for any of the ovens.

Anyway, if you do recall the approximate rate of increase that would help me. Also, do you think the results are good enough if you are running maybe 30 boards a month?

[MGP]

Funny you mention the Omega temperature controller. I was looking into putting one (or one from Automation Direct, they're cheaper) in my oven and just programming the profile into it. I'm always pressed for time and it's a quick way to get an excellent temperature controller for not too much money.

I'm planning on controlling the heating elements and fan directly since my oven has a digital controller and it's not easy to have it "always ON".

I don't recall the rate of rise I measured but it was in line with what the Sparkfun guys measured. I do remember it was slightly faster than the value they measured on their toaster oven page. Mine has four heating elements (two top, two bottom) and heats pretty evenly throughout the oven. When I reflow the boards I leave the rack in the center position so the boards are about equally spaced between the upper and lower heating elements.

If you do get a reliable temperature controller I can't see why you'd have any trouble making boards in 30 piece batches. One thing you'll definitely want to do is use a solder paste stencil. I've found that the better the paste job the better the reflow results. I'm not sure how many components your typical board has but anything more than a handful of components gets really tedious to paste by hand.