PCB Design Basics

Printed Circuit Board (PCB) Design is the process of laying out the electrical and mechanical connections for electronic circuits. A PCB provides physical support and a platform to interconnect components like resistors, capacitors, ICs, and connectors. Below are the key concepts and steps involved in PCB design.

Key PCB Design Terms

  • Trace: Conductive pathways on the PCB that connect components, the “wires”.
  • Pad: Metalized areas on the surface of the board for soldering components.
  • Via: Conductive holes that allow connections between different layers of the PCB.
  • Ground Plane: A large area of copper connected to the ground to reduce noise and improve stability.
  • Silkscreen: Text and symbols printed on the PCB to label components and provide information.
  • Solder Mask: A protective layer applied to the PCB to prevent short circuits and corrosion.

PCB Design Process

Schematic Design:

  • The circuit diagram is created to define the electrical connections between components.
  • This should be the first step in the design process

PCB Layout:

  • This is the process of placing components on a board.
  • Allows designer to place components where they make sense relative to other components.
  • Gives an early idea of where traces will be routed and how large the board will be

Design Rule Check (DRC):

  • Verify the design adheres to manufacturing constraints, such as minimum trace width, clearance, and via sizes.
  • These can be set based on the JLCPCB’s constraints

Gerber File Generation:

  • Export the design into Gerber files, these are used to actually produce the board
  • JLCPCB has a guide that explains what files they need for manufacturing

Fabrication:

  • The boards are produced and arrive blank
  • It is a good idea to do some basic tests with a multimeter to check for short circuits.

Design Guidelines

Component Placement:

  • Position components logically, with related components placed close together.
  • Keep high-speed signal traces as short as possible.
  • Place decoupling capacitors near power pins of ICs.
  • Place things in order of importance
    • High speed signals and decoupling capacitors first with things like power last
  • Add test points for easier debugging in signal traces

Trace Routing:

  • Use wider traces for higher current-carrying capacity.
  • Avoid sharp angles in traces to reduce impedance changes.
    • Use 45 degree corners
  • Separate analog and digital signal paths to reduce interference.
  • Make sure that sensitive signals have a ground plane under it

Layer Management:

  • For two-layer PCBs, one layer is often used for signal routing and the other for ground.
    • Top signal layer can have a power polygon as well to make power routing simpler.
  • For multi-layer PCBs, dedicate inner layers to ground planes.
    • Having two internal ground planes allows for better signal integrity.

Thermal Considerations:

  • Use copper pours for better heat spreading for high heat components
  • Add thermal relief connects on ground vias to help with manufacturability.

Electromagnetic Compatibility (EMC):

  • Minimize loop areas in critical signal paths.
  • Use proper grounding and shielding techniques.
    • Add stitching and shielding vias when required

Common Pitfalls

  • Incorrect footprint selection for components.
  • Overlapping traces or insufficient clearance.
  • Not considering manufacturing tolerances.
  • Missing test points for debugging.

External Resources