PCB Design

PCB design relies on CAD (Computer-Aided Design) software. Tools vary widely in features and complexity:

• Professional (Paid) Tools
  • Altium Designer, PADS, Allegro, OrCAD
  • Used for advanced, high-speed, multilayer designs.
  • Support complex routing rules, signal integrity analysis, and simulation.
• Free / Entry-Level Tools
  • KiCad, ExpressPCB
  • Good for students, hobbyists, or simple designs.
  • Limited features compared to professional software.

• First step after the product design specification.
• Engineers draw the circuit schematic using CAD software.
• Each component has:
  • Schematic symbol (logic representation).
  • PCB footprint (physical layout: dimensions, pads, holes, SMT vs thru-hole).
• Output: Netlist file that defines electrical connections.

• Transition from 2D schematic to 3D board layout.
• Consider board shape, size, mechanical constraints, and drill info.
• Place related components in logical groups.
• Steps:
  • Rough placement (fit check + grouping).
  • Critical component placement (high-speed signals, sensitive parts).
  • General placement, finalized before routing begins.

• Connects components with copper traces according to the schematic.
• Types:
  • Critical routes first → high-speed signals, differential pairs, timing-sensitive nets.
  • General routing → remaining connections.
• Traces may cross layers using vias.
• CAD software enforces Design Rule Checks (DRC) to prevent violations.
• Output: A complete and reviewed layout ready for manufacturing.

Once the PCB design is finalized:

• For Fabrication
  • Gerber files → layer images (copper, solder mask, silkscreen).
  • NC Drill file → hole information.
• For Assembly
  • BOM (Bill of Materials) → parts list for sourcing.
  • Pick-and-place file → coordinates for assembly machines.
  • Netlist → ensures proper testing and inspection.