BGA Pick and Place to Oven

I have a general question about how BGAs are worked with in industry.

As far as I know a pick and place machine aligns the BGA with the pads on PCB and places other components.
Then the PCB goes to soldering oven.

My Question is how these components are kept in place when moving from pick and place to oven ??

BGAs have no solder paste under them so why are they not misalligned while moving
?

Small components are secured to PCB board by Solder paste or glue and hence do not get displaced while moving.

I am going to make a small pick and place machine for hobby projects.

Soldering is the root cause of 99% of all defects in Electronics contract manufacturing. Murphy's Law prevails. If anything can go wrong, it will. Flux drying, surface tension, solder balls, coplanarity issues, blind solder joints requiring Xray Inspection tests, almost opens and almost shorts, fragile joints, insufficient/excess solder, paste shelf life, inconsistency, reflow thermal shadows, etc etc etc...

Step 1 design boards, solder stencils, test fixtures, solder reflow profiles and verification process

Step 2 prove in the design with prototypes and perform root cause on all the failures

Step 3 redesign boards, stencils, assembly process until yields are cost effective for 100pcs, 1k, 10k and verify reliability with HASS.

Making 1-10 of one type may be easy if youare lucky.

Repeats are frequently necessary unless you have 10yrs DFT, DFM, DFX SMT reflow experience in this busness.

I unserstand many issues involved in the process.
But I am still curious how are BGAs secured on PCB before being soldered ??