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I'm new to SMD soldering, and tried to assemble a couple of boards, using a reflow oven. I 'm using a stencil (Kapton - mylar) and so far it worked fine except for the LQFP48 devices (pitch 0.5mm). In this case, the pins are bridged (too much paste creating short circuits between the pins). I guess the problem is too much paste in the pads, but I'm using just one pass over the stencil.

Is there any way to do this and avoid this problem? Should I reduce the IC pads area in the solder paste layer?

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    \$\begingroup\$ Some fine braid and an iron will let you clean up individual shorts. For that matter, unless you are making several I would just solder these with an iron. It's actually fairly quick and easy once you get the hang of using surface tension to control where the solder goes while using a tip much much larger than the pads. \$\endgroup\$ – Chris Stratton Oct 19 '12 at 15:54
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    \$\begingroup\$ Your stencil is probably too thick. I use a 0.004" thick stainless steel stencil and the results have been great. I've soldered 0.5mm pitch TQFP-100 parts successfully with this approach. You should apply even pressure using your squeegee and gently pass it over just once. Place the parts using a vacuum pickup tool. If you can't align it well, use a microscope to aid you. \$\endgroup\$ – Saad Oct 19 '12 at 16:19
  • \$\begingroup\$ The stencil I'm using is 0.0035" so I don't think this is the problem. However, I since my stencil is flexible, I guess this makes a difference if it's somewhat lifted over the PCB... \$\endgroup\$ – Gus Sabina Oct 19 '12 at 17:43
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I have been building boards for a long time and can tell you that the best approach here is usually to use solder wick and a soldering iron to suck up the excess solder. Then if needed, retouch the component by heating it up with a soldering iron and gently move it. It will self align and will look great.

Also, just taking the soldering iron and moving it against the solder towards you does it as well.

I have also found that using a hot air gun, heat up the place where there's excess solder paste and using tweezers just move them between the pins. Because solder paste has metallic balls, it tends to ball up and you can pick it up.

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  • \$\begingroup\$ don't forget the flux! \$\endgroup\$ – markrages Feb 22 '13 at 21:04

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