Pololu's stencils leave much to be desired. They do work but I feel like https://www.oshstencils.com/ makes a higher quality stencil instead at similar prices.

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Note that BGA chips mostly come pre-soldered / solder balls. You also design PCBs so that there is a "well" for the balls to melt into and settle into place, and molten-solder has a significant amount of surface tension, so you can magically watch the solder "pull" your designs into place. Of course, the OP is likely talking about QFN not BGA, but... just in case people are worried about BGAs its not terrible... (its just impossible to inspect a BGA XRays).

The surface-tension can be harmful in the case of tombstoning (ex: a resistor or capacitor with two leads, especially a "sideways" low-inductance capacitor, will get "pulled up" by one side, lifting off the 2nd pad).

If you have a solder-plate + hot-gun, you can "feel" the surface tension by just grabbing a toothpick and pushing on these components as they're still hot. You'll find the pressure to be far higher than you expect.

Funny, I had the exact opposite experience. For OSH Stencils, they had a scaling issue with their setup that I pointed out to them, and they just shrugged and said that was the nature of the beast essentially and they couldn't do anything about it. They might have said something about Kapton shrinkage or some such. (I don't currently have the exact numbers, but it was off a couple of percent linearly, which doesn't matter for a tiny board, but for a 4" board, the difference adds up, so that if you align the apertures on one end of the board, they don't on the other side of the board. Like the aperture was off by a whole 0603 pad or more). I went back to Pololu for that same board, and everything was spot on. And I have had zero complaints with them since. If I had to complain about something, I might slightly ding them slightly on the super-tiny aperture shapes and the kerf width of their laser. But everything has always worked. Apparently YMMV.

Hmmm, maybe my designs have been small enough that it hasn't been an issue.

I'll keep your experience in mind then. Thanks for sharing your experience.

Who knows, it may be fixed by now.

JLC's polished stencils will happily work at 0.2mm pitch for ~$10.