Amateur reflow soldering with halogen oven

[mariush]

I bought this oven that's advertised on tv a lot here, and it's actually pretty good at cooking:

(see pictures,just realized i have a digital working camera... just cooked in the oven so it's dirty..)

I've opened it up, it's basically two semi-circles of 500w-ish halogen lights and a large fan behind them moving the air inside.  The lights are basically turned off by a mechanical relay as the temperature inside reaches the set value ... basically there's a metal pin expanding as the heat goes up and at some point it snaps off the other contact, turning off the lights... when it cools down a bit, the contact is made again.

I've been thinking.. wouldn't it be good to do some reflow soldering, as long as one's sure to adjust the target temperature and follow the curve? I mean, it wouldn't be hard to pre-heat for about 3-5 minutes the oven to 100c or whatever's lowest, then set the timer to about 15 minutes and adjust temperature gradually following the curve.

Surely, it would be also possible to replace the mechanical relay with a digitally controlled  one and have a temperature probe inserted near the pcb and have a more accurate reading.

If you guys say it may work, then my only concern is the fan.. which may have a high speed, and it's basically an AC motor running at 230v and using about 15-20 watts.

[nanofrog]

It's been done with toaster ovens, and IIRC, even convection models. Sparkfun even sells a controller kit last I saw.

[JuKu]

I'd guess it would work. There are various hobby projects and even some commercial products for the temperature controller (in my bookmarks I have http://www.reflow-kit.com). You do want monitor the temperature and control the profile, either manually or automatically. The fan would be very good in getting even temperature in all parts of the PCB, but it needs to be rather gentle in order not to blow components out of alignment. Remember, at the reflow phase, the components are floating on top of melted solder. Also, since you have the oven, you might want to check the maximum temperature and the heating/cooling speed before dedicating a unit for soldering work. Let us know how it turned out!

[mariush]

Well, I kinda like the food it makes, so I'm not planning to modify this one.

But it's on my todo list, definitely. I'll get a second one - they're not very expensive - and mod this old one when I get a bit of experience with pic - just got a pickit 3 and some pic16f chips to play with.

The even temperature is precisely why I thought it would be a good choice to reflow - the pcb would sit in the center and the fan would move the hot air all around so it won't be just the top side heated, which I heared is a problem with some of those electric ovens.

The fan speed might be a bit of a problem to change as it's an ac powered fan, not sure if some pwm tricks would work on it or... i don't know yet. But who knows, the surface tension might just be enough to not have the parts blown away.

[metalphreak]

Once you use it to reflow boards, you should never again use it for cooking food especially if used with lead-based solders!

[mariush]

Agreed. Didnt use this one to reflow boards and I'm not planning to use one for both cooking and soldering.
Once it's committed to a job, it stays on that only.

I wouldn't worry too much about the lead in the solder pastes but rather about the flux in them.

 

[itdontgo]

I bought a cheap Chinese reflow oven on eBay.  It's not perfect but it does work.

One thing you need to do is give it a full cycle to warm up before putting any boards in it.  Shows how accurate the measurement process is I suppose!

It cost about £150 delivered and was here within a week.

I do fear I can see asbestos through the window but it could be a modern material.  I dont plan on smashing it up any time soon though!