Defining Constraints for a PCB Layout

Define Constraints

1. Define board dimensions.
2. Define top and bottom board clearance.
3. Note dimensions of cutouts slots and unusable areas.
4. Define the board thickness.
5. Define edge clearance areas.
6. Define all slots and cutouts.
7. Define assembly requirement such as keying information.
8. Mark predefined component locations, including hardware, connectors, lights/LEDs, and switches.
9. Place polygon on mask layer for area that requires no mask.
10. Place keep-out (all layers or per layer) on area that require clearance from/for traces, vias, pads, and hardware clearance (by hardware-to-hole tolerance, hardware movement area, or hole tolerance).
11. Define requirements: IPC, Mil-spec, etc.
12. Determine assembly type for production, such as manual, automatic, or manual prototype-to-automatic. 
13. Determine servicing type:

•   No service/troubleshooting (throw away board) 
•   Low service (inexpensive components on the board, or easily swappable application, low serviceable location)
•   Highly serviceable (expensive components on the board or difficult to swap application, highly serviceable location)
•   Determine technology limitations and target technology.