SMD solder now or later

reflowsolder-pastesolderingsurface-mount

I'm soldering up some boards with smd parts, using a hot plate to reflow, and I'm (inevitably) realizing that I got some of the wrong parts. Now, is it better to leave the boards with smd components stuck on them (sitting in wet solder paste) until I can get the other parts, and then do the reflow all at once, or to reflow now, and then paste and heatgun (or just solder iron) the other parts in later?

I only have a few parts for which I need to do this, and I can stick the boards in a quiet refrigerator until I get the parts. I might not have ready access to a heat gun later, which is why this isn't a no-brainer (I'm imagining soldering iron+paste isn't the best way to do things, since I can't get to pads under the parts). Personally, I think the real question is whether reflowing twice negatively affects smd components, but context might prove it otherwise.

Best Answer

I've left wet paste on a board overnight in cool weather without problems, but I'd be worried it would dry out over a few days - especially if left uncovered in a refrigerator (although I'm not sure if this would adversely effect the reflowing).

If there are pads under the parts, then soldering with an iron is out of the question, but a hot air rework gun should work fine. Depending on the complexity and the number of missing parts, I would either:

  • Flow now and solder the additional parts later (you can place a cube of metal under specific parts of the board to reflow individual parts on the hotplate).
  • Clean the board and restart when you've got the new parts