PDA

View Full Version : Interesting Article: Toaster Oven Programmed Heat Cycle



Paul Alciatore
06-03-2008, 11:30 PM
I got a new issue of Nuts and Volts magazine today and found a very interesting article in it on using a toaster oven for making circuit boards with reflow solder.

http://www.nutsvolts.com/

I know many of those here do some electronic work so I think it would be of interest. The author also says the program is capable of other heating cycles up to several hours in length so it could be used for other purposes as well. You are limited only by the temperature capability and heating and cooling speeds of the oven. One of the internal mods was bending the cutoff switch just a bit to allow 425 to 450 degree F temperatures.

The conversion consisted of a circuit board (available ready made) and a relay for controlling the current to the oven. Some minor changes were made inside the oven to allow the temperature to go a bit higher. It used a PIC style chip as it's basis and has a LCD display. The program for it can be downloaded from a couple of sites. You would need a PROM burner to load the program. You can get the source code if you want to modify it. For reflow solder work it produces a heating/cooling cycle that is several minutes long and closely follows the temperature curve recommended by the solder/component manufacturers. It has a temperature sensor and the author clains temperature accuracy to within a few degrees. The temperature is displayed on the LCD.

I am sure it can have many shop uses. I think I will build one for the reflow solder capability alone. I would think the board and program could be modified for use in higher temperature ovens for heat treating work. Probably need a higher temperature sensor. You could have a precisely controlled heating cycle with highly accurate temperatures. And a controlled cool-down.

Anyway, It sounds like a most useful project and I just thought I would share.

lazlo
06-03-2008, 11:59 PM
Yeah, I'm reading that article right now -- it's a pretty straightforward mod, especially if you use the pre-assembled SparkFun controller board.

Sure would save a lot of time on hand soldering little SMT parts!

lwalker
06-04-2008, 06:00 AM
Going by the experiences of the guys who own SparkFun, I skipped the toaster oven method (even though I had set aside an old toaster oven for that purpose) and went straight to the skillet: works like a charm.

Briefly, the SparkFun fellows tried both a toaster oven and a small industrial SMT reflow oven that cost about $3,000. Then they discovered that a $20 electric skillet did a better job.

Not having a skillet on hand, I used a 1/4" thick aluminum sheet (for even conduction & thermal mass) sitting on an electric stovetop with an SMT board on top of that. In 3 minutes I had a perfectly reflowed board like magic. The entire process was faster than hand soldering and will scale to multiple boards easilyl

lazlo
06-04-2008, 11:39 AM
Going by the experiences of the guys who own SparkFun, I skipped the toaster oven method (even though I had set aside an old toaster oven for that purpose) and went straight to the skillet: works like a charm.

Wow, that's cool! I have an industrial hot-plate that I use in my shop heating bearings and such -- it sounds like I can just lay a plate of aluminum on it, and set the PCB board on top? What temperature did you set the plate?

I'm looking on the SparkFun web site, but can't find a reference to the skillet -- is there an article somewhere?

Edit: found it - 450 F:

http://www.sparkfun.com/commerce/present.php?p=Reflow%20Skillet

The one issue they had was non-uniform heating, but a large plate of aluminum would be a lot better than a cheap pot-metal skillet from Target...

Dawai
06-04-2008, 12:04 PM
Metal casting, Wax burnout----- the flask with investment must be heated in stages to the point of gas-ifying the wax from the mold.

With the old pc program I had written in the early 80s.. I could sit and drink beer and the burnout and metal melt would complete at the same time and tell me to get up and pour white hot metal drunk.. Yeah, I know it's a wonder I lived this long..

I no longer drink, I see the folly of my youth. I am the luckiest man alive..

snowman
06-04-2008, 12:09 PM
Do a lot of you guys do reflow work? I've got a tube of kester that's been in the fridge for a year or two....so it's obviously out of it's prime, but I don't see myself ever using it.

lazlo
06-04-2008, 12:15 PM
Snowman -- yes! Just sent you a PM...