PCB Designing - Introduction and Overview

PCB Designing - Introduction

• Printed Circuit Boards (PCBs) are non-conductive substrates that mechanically support and electrically connect electronic components.
• Components are connected using etched tracks, pads, and other features on a laminated copper sheet.
• PCBs populated with electronic components are called Printed Circuit Board Assemblies (PCBA).

PCB Designing - History

• First developed by Australian engineer Paul Eisler.
• Earlier technologies included point-to-point wiring and wire wrapping.
• PCBs provide a structured way to connect various points together.

PCB Designing - Types

• Primarily three types: single-sided, double-sided, and multilayer PCBs.

PCB Designing - Components

• Basic PCBs consist of copper foil, copper plating, solder flow, solder mask, traces, and slots/cut-outs.
• The copper-clad fiberglass material or thin copper sheets are attached to each side of the board.

PCB Designing - Through-Hole Technology

• Initial PCBs used this technology.
• Components' leads passed through holes in the board and soldered to traces on the other side.
• Variations include single-sided (one side plated), and double-sided (both sides plated) boards.

PCB Designing - Surface Mount Technology

• Emerged in the 1960s.
• Components were redesigned with small metal tabs or end caps for direct soldering onto the PCB surface, instead of passing through holes.

PCB Designing - PCB Base

• The base material of the substrate is fiberglass.
• FR-4 is commonly used due to its high-temperature characteristics.
• A solid core gives PCBs rigidity and thickness.
• Flexible PCBs use high-temperature plastics like Kapton.

PCB Designing - FR-4

• A composite material combining woven fiberglass cloth and an epoxy resin binder.
• It is flame-resistant, thus "Flame retardant".
• Created from epoxy, glass fabric reinforcement, brominated flame retardant, etc. in 1968.
• Uses bromine to enhance flame resistance.

PCB Designing - PCB Design Equipment

• Early PCBs were manually designed using tape on translucent film.
• These designs were typically larger and reduced photo-graphically to 1:1 scale.
• Modern PCB design relies on computerized PCB CAM systems and software for more efficient layout and design.

PCB Designing - PCB CAM

• PCB Computer-Aided Manufacturing (CAM) performs key functions:
• Input of fabrication data.
• Data verification, potentially including Design for Manufacturing (DFM) checks.
• Compensation for manufacturing process variations (e.g., scaling).
• Generatting output files for copper patterns, solder resist, layout, drill files.

PCB Designing - Panelization

• A procedure grouping multiple PCBs for efficient manufacturing onto a larger panel board.
• Typically a panelized board has one primary design, though multiple designs can be combined.
• Two primary panel types: assembly (often called Arrays) and bare-board panels.
• Manufacturing panels are often preferred due to production efficiency and plating process requirements.

PCB Designing - Depaneling

• Once manufacturing is complete, the panel is separated into individual PCBs.
• Techniques often include drilling/routing perforations along the board's boundaries.
• V-shaped grooves are also used as a line of weakness for breaking apart PCBs.

PCB Designing - Copper Patterning

• Replicating the PCB design on a protective mask placed on the copper foil layers is the initial step in PCB production.
• Unwanted copper is removed through various etching processes.
• Techniques include silk screen printing, Photoengraving (using UV-sensitive photoresist masks) and direct imaging techniques, along with thermal resistant procedures.

PCB Designing - PCB Milling

• Uses a mechanical milling system to remove copper foil from the substrate in non-plated sections.
• Laser-based techniques also exist for removing excess copper or material where no resist is needed.

PCB Designing - Subtractive, Additive, and Semi-Additive Processes

• Subtractive: Removes copper from completely copper-coated PCBs, leaving desired patterns.
• Additive: Electroplates the pattern onto a bare substrate through a more complex process. This approach often has lower material waste.
• Semi-Additive: Starts with a thin copper layer on the board. A reverse mask pattern is then applied. Copper is plated only on the exposed areas. This is often used in multilayer boards.

PCB Designing - Chemical Etching

• Uses ammonium persulfate or ferric chloride to dissolve unwanted copper.
• Frequently used for creating Plated-Through Holes (PTHs), a critical manufacturing process to create connectivity between opposite sides, which often involve electroless copper plating.

PCB Designing - Drilling

• Holes are drilled with small diameter drill bits, often solid tungsten carbide-based, which are more durable and efficient than steel or other less durable solutions.
• Drill requirements often involve factors such as high RPM, and high feed-rate.

PCB Designing - Holes (Conductive)

• Holes may be made conductive through electroplating or inserting metal eyelets (hollow), for electrical and thermal connectivity.
• Specialized holes called 'vias' connect different layers within the board.
• 'Blind vias' connect an internal layer to an outer layer.
• 'Buried vias' interconnect two or more internal layers without reaching any external layer.

PCB Designing - Plating and Coating

• PCBs have solder, tin, or gold plating over nickel as a resist for etching away the unnecessary underlying copper.
• After etching, a solder mask is applied, then the exposed copper is coated with compounds to prevent corrosion.
• The coating might include various materials like nickel/gold, or other anti-corrosion substance. A matte solder is frequently used for better bonding surfaces or for stripping to bare copper.

PCB Designing - Legend Printing

• Silk screen printing, liquid photo images and ink jet printing are techniques employed to print identification information on PCBs.

PCB Designing - Final Steps

• Testing (ensuring proper functionality.)
• Soldering.
• Packaging (encasing the board for protection.)
• Protection

PCB Designing - Advantages

• Fixed components, reduced short circuit and wrong wiring risk, economical mass production, high reproducibility.

PCB Designing - Disadvantages

• Difficult repair after damage, harmful effects on environment from etching process, difficulties with updating existing designs, unsuitable for some non-specific circuit applications.

PCB Designing - Component Library

• Component information is stored in a library in the design software for retrieval and placement. This includes design information that is needed for component identification and positioning information.