I went to target and bought a very similar skillet to the one in the sparkfun tutorial. Has anyone used one before? It seems to have worked fine, the connections look solid (I haven’t tested yet) but maybe I overheated it because the PCB looks nasty… it turned from its original yellow to a darker burnt looking version. The traces and everything are intact, is there any reason why it shouldn’t work?
Also, this is what I did:
Put PCB on hot plate and heated to max temperature (about 400 F = 204 C). Then when the light went off indicating the temperature got to 400 F I took out the PCB.
Also, I didn’t reflow solder paste, I put solder on each pad on the PCB and then solder flux.
204C is a decent temp for lead solder (btw, lead free is around 260 iirc). How were you measuring the temp? If it was a setting on the skillet, then that’s about as accurate as flipping a coin… I’d use a real thermometer. baring that, I’d put a small pcb scrap with a little solder on it, keep upping the temerature until it melts and that’s the right settling.
So, you toasted the board. big deal. try it. if it doesn’t work, put the board in your IFU collection and try again. Ugly and functional beats pretty and busted any day.
Instead of waiting for the light to go out, watch the paste (or solder). As things heat up you will see the paste liquefy and turn shiny. Once things are shiny you are done, kill the heat and let 'er cool down.
In your case the solder should liquefy in a similar fashion. You really should not have to go much longer than that liquid state change. Generally the party is over in 3 to 6 minutes after cranking the knob up to 425F. Any longer than that and white silkscreens turn yellow, boards brown or blacken, and things get really nasty. But I agree Philba, I’ll settle for ugly and funtional when I get lucky.
A little hotplate update and maybe some insight into your problem.
We bought a small (5" diameter) hot plate, $20 from Target. It’s got a solid plate instead of the standard black ‘wire’ type element commonly found on stove tops. This solid plate makes it ideal for reflowing.
What we’ve found over a couple days of use is that it gets REALLY hot. Like 500+ F hot. Our infrared temp guns crap out so I can’t really say, but it’s hot enough to melt the solder mask off and the PCB laminate starts to bulb. I actually heard PCBs sizzling and popping - a VERY bad sign. So now I know we can do lead free paste but this hot plate on ‘High’ is pretty dangerous. On low or medium, it works great.
So it sounds like you are cooking for too long, too hot. Get a temp gun, or just watch the boards to see when the paste goes from grey to shiny (molten) and then shut the plate off. Don’t move the boards until they’ve cool for 1-2 minutes or else you’ll run the risk of bumping components around.
sparky:
A little hotplate update and maybe some insight into your problem.
We bought a small (5" diameter) hot plate, $20 from Target. It’s got a solid plate instead of the standard black ‘wire’ type element commonly found on stove tops. This solid plate makes it ideal for reflowing.
What we’ve found over a couple days of use is that it gets REALLY hot. Like 500+ F hot. Our infrared temp guns crap out so I can’t really say, but it’s hot enough to melt the solder mask off and the PCB laminate starts to bulb. I actually heard PCBs sizzling and popping - a VERY bad sign. So now I know we can do lead free paste but this hot plate on ‘High’ is pretty dangerous. On low or medium, it works great.
So it sounds like you are cooking for too long, too hot. Get a temp gun, or just watch the boards to see when the paste goes from grey to shiny (molten) and then shut the plate off. Don’t move the boards until they’ve cool for 1-2 minutes or else you’ll run the risk of bumping components around.
Have fun reflowing!
-Nathan
I bought a small hotplate from Target, but the surface was rough with fine concentric rings (for traction?), and the center 1 1/2" or so was slightly depressed. It’s about 6.5" in diameter, with a solid surface.Is this the one? If so, I’ll get a 3/16" piece of aluminum to cover it.
Yes - the sounds like the evil one, exactly. I fried many a PCB with that one.
On another note - we managed to reflow some lead-free RoHS designs using the regular hot-plate. The $30 plate has a thermostat dial built into the plug on that inserts into the side of the plate. 5 minutes to pull the screws out of the plug, we disabled the mechanical stops at 450F and screwed the thing back together. Now we can cook the lead-free paste at 500F Works well.
but this hot plate on ‘High’ is pretty dangerous. On low or medium, it works great.