Solder Paste with a hot-air gun
TLDR – get a stencil!
Assembling prototypes with solder paste can be quite a bit faster than hand soldering every joint. The first time we tried this, we just used a syringe to put down a bead of paste on the pads like the YouTube videos show. We did get some bridging under the chips as we probably put down too much paste, or perhaps did not heat the board hot enough:
(sorry about the poor focus)
For the next prototypes, we ordered a stencil and applied the paste with a plastic card. This worked much better:
Below are some images of the applied paste:
Alignment was not perfect, but the result was much better – only one bridge on the entire board with some fairly fine-pitch parts.
We are using an ATTEN ST-862D Hot-air rework station with a large nozzle to reflow the paste. It only takes a couple of minutes with a small board and works pretty well, so it seems a reflow oven is probably overkill for now until we get to BGA components.
Not perfect, but much better than hand soldering each joint:
