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[on:]

I'm a novice in electronics and I don't know much about tools for PCB production and soldering. I was surfing around on eBay today and came acros this:

http://cgi.ebay.com/Infrared-SMD-IC-Automatic-Desktop-Reflow-Oven-2-heater_W0QQitemZ200296916863QQcmdZViewItemQQptZBI_Soldering?hash=item200296916863&_trksid=p3286.c0.m14&_trkparms=72%3A1205%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318%7C301%3A1%7C293%3A1%7C294%3A50

"Infrared SMD IC Automatic Desktop Reflow Oven"

What is this? Can you place the components on a PCB, put it into the oven and then the components is automaticly soldered on?

[Reply #1 on:]

http://en.wikipedia.org/wiki/Reflow_soldering

You have to apply solder paste and position your components, and then the oven will melt the solder and leave them attached.

[Reply #2 on:]

Thank you for the reply, now I learned something new today as well.

So a reflow oven is mostly used when soldering SMD component I guess? How do you place the components on the PCB and how do you apply the soldering paste? I guess there is some kind of special tool for this? I'm not thinking in big production lines, but in manual production in small quantities.

[Reply #3 on:]

I've never done it but I think for small quantities, it's just like spackling your basement wall, with smaller tools.  A little dab'll do ya.  Some people use a pancake griddle instead of a full oven, but you have to vent some vapors.

The bigger production places use "pick and place" robots to select parts from a series of tapes or tubes, and stick the parts where they need to go on the board.  Then they go through a wave solder tray, or a reflow oven, to finish the soldering process.

[Reply #4 on:]

you can apply solder paste either "very carefully", using a syringe, or by using a stencil and a process not too difficult from screen printing.  I think Sparkfun has a tutorial with pictures.

Placement is either "very carefully" using tweezers or vacuum tweezers, or by robot.

[Reply #5 on:]

You can use the same solder paste syringe/tweezer placement techniques with a hot air rework station (not a hot hair gun for shrinking heat shrink or stripping paint) instead of a reflow oven.  I finally got one on ebay and have been pleased with the results.

I'll also echo the suggestion of reading SparkFun's tutorials - good info there.

-j

[Reply #6 on:]

I often wonder why the solder isn't applied to SMD pads when the board is manufactured. The pads already have a thin layer of solder covering the surface of the pad. Why not add enough so SMD can simply be applied and then heated?

[Reply #7 on:]

Because the metal is only part of the process.  Flux is a vital component in a good solder joint, and it is a chemical that can at the very least dry out.  Bad flux = bad solder joint.

Solder paste for SMT work is roughly half solder, half flux.

-j

[Reply #8 on:]

For the DIY guys: http://www.rcgroups.com/forums/showthread.php?t=911539

[Reply #9 on:]

Why not add enough so SMD can simply be applied and then heated

Because the part would then sit on top of the solder. With paste the solder surrounds the part and flows round it when melted. Also the surface tension of the paste holds the component in place while the other parts are placed. If the solder was solid they would just slide off the pad of solder with the vibration.

And then as mentioned is the flux.

[Reply #10 on:]

Also the surface tension of the paste holds the component in place while the other parts are placed. If the solder was solid they would just slide off the pad of solder with the vibration.

Well flux can always be added, but this reason makes more sense.