Unforseen issue with hot-plate reflow

Doesn't an electric toaster oven work pretty well for this also? Then you could put a "NO FOOD" sign on it...

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Den onsdag den 11. marts 2015 kl. 03.11.34 UTC+1 skrev bitrex:

yep, you can even get controllers for it so you can do something that resembles the recommended temperature profile

I've used one of those magnetic stirrer hotplates normally used in the lab

just don't forget to remove the magnet

-Lasse

A convection oven would have better temperature uniformity.

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John Larkin         Highland Technology, Inc 
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Would it get hot enough?

Mine goes to 450F, 232C.

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John Larkin         Highland Technology, Inc 
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I've always used a small heat gun. Warm the bottom, warm the top, warm the bottom, wait for flux to stabilize, then full heat to the bottom.

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There's a bazzillion different recommendations. Goodwill didn't have any toaster ovens. The skillet was $5.

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I considered a convection oven, but I've heard a lot of good things about hot-plate reflow, and the skillet was only $5.

The biggest thing that makes me look askance at a convection oven (aside from price) is the fact that "real" reflow ovens use IR, not convection. I don't know why this is, so I don't know if it matters or not.

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Idea: Before assembly, give the heatsinks for a product a light coating of $FOOD grease, let them soak for a while, and then wipe it off again. Put it in the manual: "If your Niftytron 100 starts to smell like bacon, please reduce output power, or turn it off for at least 10 minutes."

Matt Roberds

If you use a convection oven, you'll likely blow parts off the board.

It is an IR based source, but the chamber gas has convective impingement as well. The ramp up makes the transition to actual reflow small. The final zone at reflow is in the heart of the chamber, so there is a convective "ambient" and IR heaters take it to the reflow zone temp within that area of the chamber.

The skillet thing... should be cast iron. It holds the heat and transitions less when 'loaded'.

An Aluminum skillet transitions temp almost instantly. I preheat my eggs in the morning, and they fry up a lot better than cracking a cold egg onto lame AL thin skillets. There is a shock to it.

Cast iron does not do that as it is thicker and conducts slower. But it sticks to food.

Makes a great reflow heat source for small SMD PCBs though.

Use IR to get to and monitor reflow temps, and use a chamber (toaster oven) to pre-heat it before you set it onto the skillet.

On the other hand, that might give too much incentive to run it beyond ratings... :-p

On a related note, bacon grease, cut halfsies with a thin oil like kerosene or mineral spirits or WD40 (stoddard solvent), is superb for cutting steel and heavy things like that. (WD40 alone works great on aluminum.)

Tim

-- Seven Transistor Labs Electrical Eng>> Don't gleefully stuff your board right before dinner time and cook it

Den torsdag den 12. marts 2015 kl. 01.35.06 UTC+1 skrev Tim Williams:

I found the best for aluminum is ethanol, cuts like butter and doesn't leave a mess

-Lasse

Den torsdag den 12. marts 2015 kl. 01.51.23 UTC+1 skrev Tom Miller:

I usually use the denatured kind for cutting, you don't want to drink that ;)

-Lasse

Do you drink it first?

One more recommendation can't hurt.

I use a Black and Decker Toaster Oven purchased at Kmart for $25 new. I bought it new because I don't like PCB's with a residual pizza smell. The boards in the photos are various HP LaserJet PCB's that are notorious for horrible BGA soldering. Batting average so far is

25 successful reflows out of 29 boards. Note the various temperature monitoring aids.

I use the above arrangement more for repair than for the initial PCB soldering. I've only done one prototype PCB using this oven, which mostly worked as expected on the 3rd try. It was single sided, fairly large parts, and a fairly spacious layout.

One advantage of this oven is also a big disadvantage. The small size and small physical mass means that it heats up and cools down fairly quickly. That produces dramatic changes in temperature when the door is opened. I didn't try to find a fix and simply tweaked the reflow soldering temperature profile to something that I thought was tolerable. Without the thermocouple thermometer, I wouldn't have had a chance. A more massive oven would have worked better, but at the price, it's good enough.

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Can't say I've seen yellow coolants in use before, although the most common water-base ones have a milky appearance to them. Um, I'll let you judge what bodily function corresponds... :-)

Tim

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By "skillet" do you mean some kind of non-stick or stainless or aluminum? I would expect metal to solder itself to the board.

It's a used, scratched, teflon-coated electric skillet.

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Tim Wescott 
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