Introduction to Printed Circuit Boards (PCB) Design and Manufacturing

Posted on Jun 18, 2024 in Technology

UNIT 1. CAD/CAE/CAM

CAD (Computer Aided Design)

Technique of designing a computer-based product and capturing its schematic diagrams using software.

Components of CAD:

  • Editor: Schematic editor with a library of components.
  • Processor (Database Connectivity): Renders the circuit design and connects to simulation programs or PCB layout tools.

CAE (Computer Aided Engineering)

Electronic CAE involves verifying the functionality of the designed product through computer simulations.

CAM (Computer Aided Manufacturing)

Electronic CAM focuses on controlling the manufacturing process using computers and software. This includes PCB design software, generating documentation, and providing information for practical product implementation.

Basis for Choosing CAD/CAE/CAM Software

Consider these characteristics when selecting a suitable package:

1. Design Power (Potential of the Design Package)

  • a) Capture Schemes: Library size (larger libraries offer more components) and the ability to generate database connectivity in various formats.
  • b) Simulation: The simulation tools should integrate seamlessly with the schematic capture and PCB layout tools, ideally using the same database schema.
  • c) PCB Design: This aspect significantly determines the overall power of the design package. Autorouters, essential for PCB design, aim to achieve the following:
    • Route 100% of the board connections.
    • Complete the routing in the shortest time possible.
    • Ensure high-quality routing with optimal interconnections.

2. Computer Hardware (Requirements for Proper Functioning)

  • a) Technological Development:
    • Adequate computing power for installation, automatic drawing, and simulations.
    • Powerful graphics capabilities for rendering complex designs.
    • Local Area Network (LAN) for sharing programs, libraries, and components among design teams.
  • b) Applications: While personal computers were initially not as powerful as workstations for PCB design, their evolution has transformed them into capable machines for running demanding design software.

UNIT 2. Laminates

Functions of a Printed Circuit Board (PCB)

A PCB serves two primary functions:

  • Provides mechanical support for components.
  • Establishes electrical interconnections between components.

Advantages of PCBs over Traditional Wiring

  • Space saving.
  • Ease of component assembly.
  • Elimination of broken wires or cuts.
  • High repeatability and uniformity in electrical characteristics.
  • Improved reliability.
  • Simplified identification of circuit parts.
  • Suitable for mass production and automation.
  • Reduced reliance on highly skilled labor.
  • Easier inspection and troubleshooting (fewer errors).

Limitations of PCBs

  • Design complexity and limitations.
  • Longer design cycles.
  • Difficult to repair.
  • Higher production costs in small quantities.

Building Blocks of a PCB

  • Insulating base material (substrate).
  • Mounting holes for components.
  • Conductive pathways (traces).
  • Connectors.
  • Interconnect plates.
  • Input/Output (E/S) terminals.
  • Soldering mask.
  • Silkscreen printing.

Classification of Printed Circuit Boards

  • Based on Support:
    • Rigid.
    • Flexible.
  • Number of Conductive Layers:
    • Single-Sided (SC).
    • Double-Sided (DC).
    • Multilayer (MC).

Factors Affecting PCB Density

  • Size and shape of components.
  • Number of conductors and components.
  • Complexity of interconnections.

Density Measurement: Number of holes per unit area.

PCB Classification System

  • First Digit: Type of board (SC, DC, MC) and interconnection method.
  • Second Digit: Maximum conductor density, which depends on:
    • Nominal width of components.
    • Nominal separation between conductors.
    • Differences in diameters between component leads and holes.

Materials Used in PCB Manufacturing

Characteristics of PCB Materials:

  • Physical: Robustness, stability, and flexibility (for flexible PCBs).
  • Thermal: Compatibility with fabrication processes, coefficient of thermal expansion (CTE), and thermal conductivity.
  • Electrical: Dielectric strength, insulation resistance, and permittivity.

Common PCB Materials:

  • Phenolic paper (Bakelite) – impregnated with phenolic resins (typically with metallic holes).
  • FR-4 (Flame Retardant 4) – epoxy resin-impregnated glass fiber cloth.
  • Epoxy resin-impregnated paper.
  • Polyimide – high-temperature resistant material.
  • Mylar and Teflon – flexible substrates.

Limitations on PCB Size and Shape

  • Size of manufacturing equipment.
  • Availability of tools and materials.
  • Manufacturing facility constraints.

Factors Affecting PCB Costs

  • Number of layers (conducting planes).
  • Customer specifications and design complexity.
  • Selection of base material.
  • Base material thickness (rigid boards typically range from 0.6mm to 1.6-2mm, with varying tolerances).
  • Conductive layer thickness.
  • Size of component pads and holes.
  • Interconnect design complexity.
  • Maintenance costs of manufacturing equipment.
  • Order size and production volume.
  • Overall board size.

Deformation and Warping in PCBs

Factors Influencing Deformation:

  • Temperature: Phenolic paper materials tend to deform more at higher temperatures, while epoxy resins with fiberglass exhibit less distortion.
  • Layer Structure: Board type (SC or DC), board size, and the distribution and balance of metal content within the layers can contribute to warping.

Minimizing Deformation:

  • Using thicker substrates.
  • Incorporating stiffeners or ribs for structural support.
  • Strategically placing connectors to minimize stress on the board.