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Reflowing after applying paste


#1

What are you guys using for reflowing after applying the solder paste? I see lots of info out there about using toaster ovens or hot plates, but then I read lots of issues with those as well-- not getting hot enough, burning boards, melting parts, needing to monitor board temp with a thermocouple. Seems like a bit of a dicey proposal.

Is there any reason not to just use a hot air SMT soldering station and reflow each part one at a time? It may be a little slower than a hot pad, but with paste applied through a stencil will the results be any worse/better? I’m not concerned about the time- I’m doing small boards and just a few prototypes.

Thanks,
Eric


#2

Hi, Eric.

We have some relatively nice reflow ovens here at Pololu, so I don’t have much practical experience using a hot-air gun for anything other than rework. I expect you could use it for reflowing solder paste, but I can’t offer much insight into how well it would work or how it would compare to using a hot plate.

Sparkfun has a tutorial on soldering SMD parts that you might find helpful:

sparkfun.com/tutorials/59

(They also have one on using mylar stencils for printing.)

- Ben


#3

I’ve used a hot plate in conjunction with hot air for SMD reflow work. I started off using just a hot plate for, but found that occasionally I would overheat the bottom of my boards prior to solder past achieving liquidus even when trying to closely monitor the temperature and ramp. To avoid this problem, my technique now is to use a hot plate providing heat from below to the pcb until the solder paste is near liquidus and then hit the board with hot air from above; as the boards and components are already pre-heated to a significant extent, the reflow usually occurs within seconds of air being applied. Using this combination, I can keep the hot plate temp low enough so that I’m not on the edge of scorching the boards and still get the requisite heat to the paste and components - a quick pass with the hot air over each component typically suffices.

Eric


#4

Thanks useful information… I am impressing thanks…