Pick and place has always needed to rotate because the odds of the PCB part being in the same orientation as the supplied tape is extremely low especially for analog parts or RF parts. Even for "purely digital designs" (LOL, all circuits are analog) you never had tapes of 0.1 uF decoupling capacitors in vertical vs horizontal orientation, or four tapes of LEDs in various orientations (LEDs have polarity).

> Or are we used to "perpendicular" layouts simply because assembly machines weren't able to rotate components like that?

I used a small pick and place machine 15 years ago (Europlacer something or other). It was able to place components at any angle. You'd have an X,Y package centre, and then a theta rotation angle.

Programming it would not have been fun, but the placing is controlled by the programming and machine vision and fiducial markings.

I don't know, but if I were responsible for layout, that's the kind of thing I'd do. I think it looks great. I wonder if this design makes PNP more expensive.

I worked on a pick and place SMT line for a few years- part rotation is pretty basic so it shouldn't affect cost.

It might increase the cost of the one-off programming.

Which gets exported from the PCB CAD package anyway as a pick & place file, with correct orientations.

Typically designers would turn a part to better align interfaces. e.g. if you have to chips which need to be connected you might rotate one to get the 'straighter' traces.

This looks like it might be to align the DDR better to the main processor but who knows.

This one looks like it was designed by a genetic algorithm or someone who just slapped the chips down randomly and wired them up. Either one.

I'm no expert, but it also depends on how you solder them. That ethernet chip is at 45 degrees to allow better soldering (is it wave soldering?).

The big chips have melting balls underneath to make the connections, I guess here you are more free on the rotation.

EDIT: This is wrong! See Kliment's post below.

Wave soldering is used for through hole, not surface mount, components.

With wave soldering you have a bucket of molten solder that is pushed over the lip of one edge of the bucket. This is the wave. The circuit board is transported over the wave, just touching it. Solder flows to the exposed copper, but not anything else (which is referred to as solder resist in this context - that blue colour is solder resist).

Surface mount would tend to use screen printed solder paste and then a hot oven to melt the paste.

The Slow mo guys have a video about how expensive cameras are made which covers some of the process: https://www.youtube.com/watch?v=LaqeLrLxYOg

Just a clarification here: you can in fact wave solder surface mount parts, and it's often done. It doesn't work for leadless parts or parts with pins under the package such as BGA and LGA but it can be used, with proper board design, for most other parts, even surprisingly fine-pitch ICs. The parts are glued to the PCB and then passed through the wave. The most common use is for passives, such as decoupling caps, on the bottom of a PCB.