I am designing a Raspberry Pi hat PCB for a home automation control project. It contains many SMD resistors and capacitors.
I was just wondering if aligned components have any benefit over not-aligned components for real PCBA processes in the factory. Is alignment only for visual beauty?
It depends: Wave soldering requires strict adherence to rules about component position and orientation because of potential problems with solder flow. Reflow soldering can do pretty much anything.
Given that most SMD PCBs are manufactured using reflow soldering these days, you can just go wild. The pick-and-place machine will place your components however you like, even rotated, and the reflow oven doesn't care about component orientation / alignment at all.
If you're actually going to let someone manufacture your PCBs for you, make sure that all of your components can be picked and placed by a machine (and soldered in a reflow oven). Otherwise they'll have to place and/or solder some of the components manually and that'll cost you extra. Things like heavy capacitors, sockets, and connectors (and any through-hole parts in general) will often require manual steps.
I agree with @Jonathan S., reflow soldering is way more permissive than other techniques. But the fact that the pick and place can do almost anything you may think of doesn't mean than you should.
Of course, it always depends on the number of board you plan to produce. For hobby. small batch, do whatever you want.
But, it's when you are targeting more volume or better yield that things starts to become interesting. Aligning the component doesn't have a real impact on anything. But the orientation does.
Imagine that you have a row of 10 diodes on your board. Some of them are put at 0° rotation, some at 90°, others at 180° and at 270��. The pick and place machine is likely to pick several component at a time. And when it has to put them on the board, the head will have to spend some time to rotate between all the diodes. This will increase the pick and place time significantly if the board contains 1000's of components. And machine time is money.
It's even weirder with resistors or unpolarized components. Usually the pick and place is dumb and doesn't know that a 0° rotation resistor is the same than a 180° resistor. Thus even if all your resistors are in "portrait" orientation, the pick and place head will do a lot of rotations to match exactly the angle you specified in your CAD software.
I remember one project where the manufacturing engineer came to me and asked edit my PCB to fix all my unpolarized component orientation on my board...
The second thing that may be related to aligning the component is "thermal masking". A reflow soldering stations uses hot air and IR radiation to heat up the board. Thus if you put components next to another, big, fatty component with a big thermal mass, the big one will mask the others by blocking somehow the hot air flow and it will also suck all the heat next to it. It's therefore likely that all the components next to the big one won't be correctly soldered.
