? I thought the #1 thing PCB layout software did for the user was look at the connection needs and tell me how many layers I need to make all the connections as traces, and then lay the traces out for me. Surely it doesn't just show me how to arrange my components in a compact way—presumably minimizing the induction on the board—and create a Gerber file for me..?
Would be great indeed. Hasn't happened, and won't happen in the near future. Not even in the most expensive, most advanced EDA tools.
This is actually similar to expecting that a compiler would write the software for you, given a top-level specification.
Laying out a PCB is surprisingly complex and requires a lot of knowledge. Board parasitics are almost always in important role, so it's not just about finding shortest connections.
Modern AI is still at a toddler level, yet designing a complex PCB requires over-average IQ and years if not decades of experience. Seeing the rate AI and modern algorithms develop, maybe this is possible in 2050? And I think this is optimistic.
There are autorouters to do the most boring part of the job, but these require a lot of configuration to guide the process. This configuration step is where the designer inputs said "knowledge" into the system, and this requires a lot of work. The problem is, inputting "knowledge" into an algorithm means it needs to be formally defined, so inputting it does take more work than just applying the knowledge within your brain while drawing the layout, some of which happens subconsciously after seeing "good design practices" elsewhere. Some of this "good practice" is actually wrong, but it tends to average out quite well.
A concrete example? Even the most basic beginner would understand how to place the 0.1uF power decoupling capacitor right next to the IC power pin, and use a thicker track for power. For auto placer and auto router, this already requires multiple formal definitions, or quite a lot of artificial intelligence to figure out common names for power pins, deducing that capacitors on the same nets need to be close, and so on. And this is the simple case!
Many ICs have specific requirements on layout and placement. So the AI should be able to read the PDF and understand the text and figures that even many experienced designers struggle to understand. Then, often these datasheets give wrong advice. An expert designer knows this situation and use their experience to bypass the bad advice.
Autorouters are only relevant when designing computer motherboards or things of similar complexity. You don't want to manually route a length-matched, impedance controlled 128-bit wide bus, or break out 1000 pins from a massive BGA manually, but you need to know how to setup characteristic impedances, EMI shielding, board stackup and so on. These are complex
concepts with no single easy answer or universal formula, and require a lot of input parameters, so automation is difficult. Instead, EDA software vendors have noticed that it pays back to make the actual
drawing as easy and fast as possible, by designing neat shove, push, walk-around drawing modes, matched pair routing, bus mass routing, etc.
Note that component placement is often constrained by connectors, switches, buttons, LEDs etc.