Re: gEDA-user: OT: soldering QFN packages with exposed bottom pad?

[joe tarantino <joeft@xxxxxxxxxxxxx>]

   I've done this, but not always with success.
   First, get some fine solder paste and a flux pen.
   When you do the layout, put a pad on the other side of the board,
   connect with a few vias to the part's bottom pad.  Be sure to have a
   solder resist opening on the back side pad.
   Apply flux to the large pad only, on both sides of the board.  Then
   paste the pad, both sides.  Then place the part.  When you heat the
   back with the iron, the part may want to move.  It often helps to
   tack-solder a couple of the other pads on the QFN (farthest away from
   the large pad) to keep it from moving.  Solder the remaining small
   pins last.
   Good luck -
   Joe T

   On Mon, Apr 27, 2009 at 8:59 PM, DJ Delorie <[1]dj@xxxxxxxxxxx> wrote:

   > Got any recommendations for how to hand-solder a QFN package that
   > has an exposed bottom pad?  At the moment, all I have is a soldering
   > iron.

     Spend $20 and buy a cheap hotplate :-)
     Not sure what you'd do about solder paste; perhaps put solder dots
     on
     the pcb with your iron, add flux, and reflow it.

   > Do you think I could just put a plated-through via underneath the
   > pad, and then flow solder through that from the back side?

     I've done that as well, but beware you need a pretty hefty iron to
     generate enough heat to melt the solder.

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References

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