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SMD at home
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mayor:
Quick question for you guys. Every time I populate a board for SMD using solder paste, I end up having to do a fair bit of manual clean up with a soldering iron. I get solder bridges, parts in the wrong orientation, and general untidiness. I sometimes use ChipQuick low temp paste, and I've tried paste bought off eBay from China. My technique these days is to heat the board from underneath with hot air (doing from above makes it worse, with parts flying off, even at super low air flow!).

Is it technique? Solder paste I use?

Attached pic is with eBay paste, and I even used a stencil here. Notice solder bridges, misplaced parts, and like I said, general ugliness!

jbb:
I get this problem a bit too.

It looks like you've got too much paste.  Have you looked at your stencil thickness and aperture sizing?  (I'm no expert, so I can't offer much advice.)  The other thing that can get you is if the stencil bows up a little and the paste oozes out between the PCB and stencil.  Have you checked for that?

In terms of not blowing the components around, I find that the best results come from using a preheater to warm the board up from the underside.  This melts the flux which tends to hold the components down.  Then you can come down on top with the hot air tool to finish soldering.
james_s:
I usually end up with a bridge or two on larger ICs but it's very rare that I have any trouble with other parts. Usually it's a matter of having too much paste, it really takes very little. You could *almost* just skip the paste and just add some flux, using the tinning already on the board in a lot of cases.
wraper:
How do you apply the paste? You won't get away with simply applying paste from syringe to QFN pads.
mayor:

--- Quote from: wraper on April 15, 2019, 12:50:47 am ---How do you apply the paste? You won't get away with simply applying paste from syringe to QFN pads.

--- End quote ---

Stencil!
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