Electronic – How to clean solder paste needles

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

For laser-cutting, it seems like a few mils is enough precision to ensure you create the necessary "mask wire" for the paste. As long as your stencil is framed well and you are gentle with it, I doubt the application of paste would stress the stencil much...