PCB Designing Overview

PCB Designing

• Printed Circuit Board (PCB): A non-conductive substrate mechanically supporting and electrically connecting electronic components. Components are connected using etched tracks, pads, and other features on a laminated copper sheet.
• Printed Circuit Board Assembly (PCBA): A PCB populated with electronic components.
• History: First developed by Australian engineer Paul Eisler. Earlier point-to-point wiring and later wire wrapping preceded PCBs.
• Types of PCBs:
  • Single-sided
  • Double-sided
  • Multilayer
• PCB Materials:
  • Copper-clad fiberglass (or thin copper sheets)
  • Copper foil
  • Copper plating
  • Solder flow
  • Solder mask
  • Traces
  • Slots and cutouts
• Through-Hole Technology: Early PCBs used this method to install components. Leads pass through holes in one side of the board and are soldered to traces on the other side. Boards can be single- or double-sided.
• Surface Mount Technology (SMT): Emerged in the 1960s. Components with small metal tabs or end caps are directly soldered to the PCB surface.
• PCB Base Material: Fiberglass, specifically FR-4. FR-4 is a flame-retardant composite material.
• PCB Design Equipment (Early Days): Design and layout was done manually using tape placed on translucent film, then photographically reduced for manufacturing.
• Modern PCB Design Equipment: Computerized design, PCB CAM (Computer-Aided Manufacturing) systems, and software packages for improved efficiency and more features (like simulations and complex routing).
• PCB CAM Functions:
  • Input of fabrication data.
  • Data verification (and potentially Design for Manufacturing (DFM).
  • Compensation for manufacturing process deviations (e.g., scaling).
  • Panelization: Grouping multiple PCBs for manufacturing onto a larger panel. Can use single design or mix several designs on a single panel.
  • Output of digital tools (copper patterns, solder mask, legend, drill files, and other data needed for production).
• Depaneling: Breaking the panel into individual PCBs. The process is often assisted with lines or cuts in the panel, and now often done by lasers for better results.
• Copper Patterning: Reproducing the copper pattern using either silk screen printing, photoengraving (using UV-sensitive resists), or other direct imaging techniques, to create the desired copper layout, removing unwanted copper.
• PCB Milling: A mechanical method to remove copper.
• Laser Resist Ablation: A process for removing unwanted copper using a laser and a coating for resistance in certain areas.
• Subtractive, Additive, and Semi-Additive Processes:
  • Subtractive method: Removing copper from an entire copper-coated board.
  • Additive method: Adding the desired copper pattern on a plain substrate.
  • Semi-additive: The board starts with a thin copper layer and a reverse mask to deposit more copper to the desired areas.
• Chemical Etching: Using chemical solutions (like ammonium persulfate or ferric chloride) to remove copper from a PCB. Crucial for Plated-Through-Holes (PTH).
• Drilling: Using small drill bits (often made of tungsten carbide) to create holes in the PCB.
• Vias: Small holes for connecting board layers, or for passing components and signals between layers. Can also have micro vias.
• Blind Vias: Connecting an internal layer to an outer layer without passing through the entire board.
• Buried Vias: Connecting layers on a PCB but do not pass through the outer layers.
• Plating and Coating: Applying solder, tin, gold, or nickel to the copper to act as a physical and/or chemical coating/resistance to allow copper etch/removal.
• Legend Printing: Using screen printing, liquid photo imaging, or ink-jet printing to print labels and other information onto the board.
• Final Steps: Testing, soldering, packaging, and protection after the PCB assembly is completed.
• Advantages of PCBs: Fixed components, minimal short circuit/wiring concerns, inexpensive for mass production, perfect for reproduction.
• Disadvantages of PCBs: Not easily repairable once damaged, potential environmental impact, difficult to update designs, and limited to specific circuits.