Bottom-up manufacturing

Size of product parts – starting very small – upward size limit

This term generally refers to assembling an in relation big assembly from its small constituent pieces.

It is usually used for processes that make assembled products in the nano to low micro size-range. The upper limit for artificial structures is basically the limit of what is achievable today (2021-03). But that may change with the emergence of true advanced gem-gum-tec APM. As of today there are still only natural macroscopic bottom up structures around. Namely: All life on Earth.
It is usual not used for processes that already start at the mesoscopic or macroscopic size-scale like like e.g. FDM 3D printing.

It is used in the context of self assembly like self folding and self finding.
It is also used in the context of building stuff up via (macroscopic) scanning probe microscopes

So this is independent of the size of the manufacturing device.

It seems to make sense to also apply the term to future positional synthesis and assembly at the nanoscale like e.g. in mechanosynthesis and following convergent assembly.
It also seems usable for exponential assembly.

Gasseous deposition processes can be an edge case.

If deposition is sticking to by SPM premade patterns only then it could be considered bottom up I guess.
If it is a hole surface cover in the context of chip production then it's most definitely top down.

Nanoscale non atomically precise resin hardening 3D printers may blur the line a bit.