Could you attach the schematic as well :)?

Question: Why do your IC pins sometimes have multiple tracks going into them? For example, why is C2 not connected to the other tracks on the net? Some very strange things going on with some of your IC tracking

@MCG Hello, it's just multiple VCC via for same IC, I saw somewhere that they say it's good practice to have multiple VCC or GND via if we have place. Maybe it's not necessary.

@Sorenp thanks for reply, honestly I didn't draw schematics, I just implemented it on breadboard and than layout. I know, I should do schematics first as a good practice, but I just felt lazy about it. :)

The vias without traces on the other side look weird...

Is this a four-layer board?

@Hearth it's just simple 2 layer board. Both bottom and top plane has ground pour.

@bobflux they're just via for VCC, connected at both bottom and at top layer.

You have a lot of vias that are doing nothing but taking up space then. The point of a via is to connect a trace on one layer to another layer, either to a trace or a ground/power plane. You seem to have read something about ground/power vias (i.e. vias that connect through to a ground or power plane) and taken it to mean that you should just put vias on every ground and power pin--but that's not the case.

Can you show a different view that overlays the top and bottom traces, so that they're easier to follow?

Why is it that only one of your bolt mounting pads has thermals to the ground pour?

@Reinderien thanks for reply, I just uploaded layout images

@Reinderien actually I was planning to connect earth ground to PCB ground.

Are you planning to assemble this by-hand??? (With a soldering gun). That TPS3430 has a thermal pad underneath that is gonna be (nearly) impossible to solder manually. These devices are meant to pass through a mass soldering (reflow) process. I know you don't want to hear that because it's the center IC of your design, but if you could, I'd strongly suggest you find something with a different package. Your 555 timer will be an easy thing to solder --- Seek those kinds of packages.

@KyleB thank you for reply, actually , I already soldered it to an adapter to test it on breadboard, so I believe it'll be okay to solder it, but you're definitely right about it, it took me a while to solder. :))

^^^ Good to know. Still I'll point out that the center pad is a "thermal" pad -- It serves to remove heat from the device. You can't really know if you did it right unless you powered it up. If I were doing this by hand, I'd put a small blob of solder on the pad, then use HOT AIR to reflow the solder. Barring that, you can make the job maybe a little easier by extending the soldermask past the chip boundary --- In other words so you can heat the copper underneath ... As is, your solder mask will prevent your tip from being able to contact it.

You can solder packages with a ground pad using a small heat gun. I usually make a mask by drilling a hole (about the size of the part) in a piece of scrap sheet metal. The mask allows you to heat the one part without blowing on the rest of the board. First put down solder paste for the pad and all the part leads. Place the part, and then place the mask over the part. Then blow hot air on the part until the solder melts.

You can solder this with a soldering iron, but you need to extend the thermal pad outside of the chip footprint (up and down on the schematic) so there is enough exposed copper to put the soldering iron there and, heat the pad, and apply solder which will then wick under the chip. But this absolutely needs a powerful iron.

However this chip has a supply current of 19µA so I guess the thermal pad is only there if you have a large output current. If you don't, perhaps you can get away with not soldering it.

So when the Pi halts, the relays power it down permanently? Crashing the SSD card? Are you aware the Pi has a reset pin, which is labelled as 'RUN' on the PCB ? This means you can reset it with the watchdog. So don't need the relays nor 555 chip.