I've printed, populated and baked a test PCB with most components that I needed. I left off a GPS chip and associated passives because the GPS chip itself costs more than the rest of the board, and I'm testing unrelated functionality at the moment (and I thought there would be a good chance that I'd have to change something). That said, the stencil was made with the GPS components in mind, and those pads are now covered with solder.
Would simply covering all the pads with flux, populating the components and reflowing again work?
I'm doing all of this by hand, and would prefer to avoid having populate another 100+ BOM lineitem board. The IC itself is an LGA 69 package, and the passives are mostly 0402.
Best Answer
If you are only doing a few for your development then I would suggest you manually solder the missing parts on, using an iron or a hot air tool. Put on the flux as you said and then reflow just the added components.
Modules sometimes try to use a slightly higher temperature solder so the standard reflow profile will not remelt them, however as mentioned in the comments components will not just drop off unless they are heavy and on the bottom of a hot board.
When wave soldering surface mount components it is usual to use a glue dot to hold the parts in place but with IR reflow this is usually not done as it would need a dot dispenser in addition to the solder stencil process.
Multiple reflow cycles are not recommended but I would certainly think that taking the occasional risk may be worth it on a development board, worst case is it does not work.