Placement strategy: connectors first

Placement, more than routing, decides 80% of PCB quality. Place in the order: mechanical constraints, power flow, then separating fast and analog sections.

Placement order

Placement starts with what cannot move.

Mechanical constraints: board outline, mounting holes, height limits
Connectors, switches, LEDs: parts that must line up with openings in the case
Power section: one direction of flow, input connector → protection → converter → output
MCU and crystal
Fast / high-current parts: motor driver, MOSFETs
Analog parts: current sensing and ADC inputs, far from noise sources
Passives: decoupling right next to the chip pins

Dividing into areas

Divide the board by character. Keep large currents from passing under the analog area.

Area	Principle
High-current power	Short, wide traces, at one end of the board
Digital	Centred on the MCU
Analog	Opposite the power section, so ground return does not cut across it
RF / antenna	At the board edge, with ground removed underneath

Practical tips

Aligning polarised parts (diodes, electrolytic capacitors) in the same direction reduces assembly mistakes and inspection effort.
Place test points and the debug connector from the start. There is no room to add them later.
Check part clearances and connector heights in the 3D view.