Solder paste and application methods

We are just getting into SMD. Curious which pastes to use and which to not use for hot air methods? Can anyone offer ideas to apply the solder paste to the board? trying to build a screed system for low production assembly. We have CNC machine ability so we can build something if needed. Was thinking about using thin Al sheet and drilling holes where we need paste. Put over PCB and push solder paste over that to push paste on board.

Thoughts?

Normally, a stencil made of stainless steel sheet is used to accurately apply the solder paste to the bare PCB. These are usually laser cut or chemically milled to produce the apertures and are usually relatively expensive.

I have also seen low-cost stencils made from laser-cut kapton and mylar film sheets. I can't vouch for the quality of any of these, but they don't seem to be too expensive. A Google search for "smd stencil designs" should give you a good place to start.

You need some amount of thickness to solder screen. A mounted 10 to 20 mil brass sheet with milled openings will work. The thickness of the brass should be based on minimum pin pitch part.

You should have a ridge frame, mill anchoring holes around perimeter then stretch and epoxy the brass solder screen to frame.