Introduction

A circuit board, also known as a printed circuit board (PCB), is an essential component of most modern electronic devices. It provides the physical structure and electrical connections between the various components that make up an electronic circuit. Circuit boards allow for the efficient and compact arrangement of complex circuits in a small space. They are found in almost every electronic device, including computers, smartphones, home appliances, automobiles, and industrial equipment. But what exactly are the functions of a circuit board and why are they so ubiquitous in electronics? This article will examine the key roles circuit boards play in electronic devices.

Key Functions of a Circuit Board

Physical Support and Organization

One of the most basic yet critical functions of a circuit board is to physically support and organize the components of an electronic circuit. The rigid structure of the board, usually made of insulating materials like fiberglass or plastic, provides a solid foundation to mount components like integrated circuits (ICs), resistors, capacitors, diodes, and other parts. The board’s flat surface and defined areas allow for the orderly and optimized placement of these components. Without the organizing template of a circuit board, building circuits would be far more challenging.

Electrical Connections

In addition to physical support, circuit boards provide the electrical connections between components in an electronic circuit. The boards contain thin copper sheets laminated onto the substrate, which are etched into conductive paths or traces. The traces interconnect to form the wires that carry electrical signals between components mounted on the board. Printed circuit boards enable the compact routing of these connections, as traces can be etched in densely packed patterns and on both sides of the board. This allows complex circuit designs to be miniaturized and fit into very small spaces. The board’s conductive layers and traces replace messy hand-wired connections with an organized printed wiring layout.

Mounting Locations

Circuit boards include pre-defined locations for mounting and securing electrical components in their designed positions. These mounting locations often have holes, pads, or sockets to facilitate the attachment of parts. For example, boards usually have evenly spaced holes drilled in an alignment pattern to accept the leads of integrated circuits and other through-hole components. For surface-mount components, there are solder pads to affix the part. These mounting features ensure components are reliably secured and properly oriented on the board.

Interconnectivity

In conjunction with the conductive traces, the mounting locations provide electrical connectivity between attached components. The pads and holes are electrically connected to the network of traces on the board, enabling components to be powered and share signals. Standardized hole spacing allows integrated circuits to plug into interchangeable compatible boards. The mounting locations essentially act as connection points to integrate components into the overall functioning circuit. This interconnectivity is key to assembling multiple parts into a complex circuit system.

Efficient Manufacturing

Circuit boards allow for the mass production of electronic products through efficient, automated manufacturing and assembly processes. Printed circuit boards started replacing hand wiring specifically to streamline electronics manufacturing. Printed wiring layouts enable the high-volume fabrication of identical boards. Component mounting locations support quick precision assembly by automated pick-and-place machines. And solder pads/holes facilitate the bulk wave soldering of components onto boards. These PCB design and manufacturing capabilities drive the cost-effective production critical for consumer electronics.

Repairability and Usability

In many designs, circuit boards can be detached and replaced, supporting repair and maintenance. Built-in testability features help technicians diagnose faults and issues. The organization of the board allows manual probing of test points. Modular boards that plug into a backplane simplify system configuration changes. Together, these usability-related aspects maximize field serviceability and system reconfiguration with printed circuit boards.

Heat Dissipation

Circuit boards are designed to dissipate heat efficiently to prevent overheating of components. Copper inner layers conduct heat laterally to limit local hot spots. Thermal vias help transfer heat to lower layers and the board backside. Pads and traces are sized to carry expected load currents without overheating. High-power areas have larger copper fill to spread heat. Boards may have cutouts, drilling, and shaping to enhance airflow. These thermal management design elements are critical as circuits operate at ever-higher frequencies.

Interfacing and Connecting Externally

Importantly, circuit boards interface electronic devices and subsystems with external components, peripherals, and systems. Edge connectors and brackets along the board perimeter provide connections for plugging into a larger system. Internal headers/connectors allow linking to other PCBs or wires. Boards may have ports for device cables and memory cards. Multilayer boards incorporate networks for data buses and high-frequency signals. In essence, printed circuit boards enable internal device circuitry to connect together and communicate with outside components.

Additional Functions

• Serve as platform for mounting other components like batteries or displays
• Shield sensitive circuits from electrical interference
• Contain built-in test points, fuses, filters, and voltage regulators
• Allow coding with silkscreened markings, labels, and board revision numbers
• Accommodate high-density component packaging with multilayer boards
• Support cost-effective automated assembly and testing

Circuit Board Materials and Construction

To fulfill their many functions, circuit boards are constructed using specialized materials and fabrication techniques. Here is an overview of the common materials and construction methods.

Substrate Materials

The substrate forms the base of the circuit board onto which traces and components are attached. The most prevalent substrate material today is FR-4 fiberglass, composed of woven fiberglass cloth with an epoxy resin binder that is rigid and fire retardant. Other common substrate materials include:

• Phenolic paper resin – Cheaper option suitable for low-frequency consumer products
• CEM-1/CEM-3 – Woven cotton paper base, good thermal resistance and stability
• Rogers – Circuit boards with high frequency requirements above 3GHz like 5G, WiFi, and radar systems
• Polyimide – Flexible boards that can bend and fold without breaking traces
• Aluminum or steel – Metal core boards for high thermal conductivity applications

Laminated Copper Traces

The conductive traces on circuit boards are made from thin copper foil laminated onto the substrate. Standard thicknesses range from 1 to 2 ounces (35 to 70 μm) per square foot. The foil is attached using high heat and pressure in a process called lamination. Photoimaging and chemical etching techniques are then used to etch the desired trace patterns into the copper foil. The resulting copper traces conduct electricity between mounted components.

Protective Solder Mask

After etching to form the conductive traces, a thin layer of epoxy-based solder mask is selectively coated over the entire board surface except at points requiring soldering. The solder mask protects copper traces from oxidation and short circuits. It also forms the background color of finished circuit boards. Common solder mask colors are green, blue, red, yellow, black, and white.

Silkscreen Legends

Printed markings on the solder mask layer provide component labels, logos, board name, test points, and other annotations. White is a typical legend color. These silkscreen markings identify components, connections, and help with debugging or servicing the board.

Mounting Holes and Pads

Circuit boards have pre-drilled holes and pads for attaching and soldering components. Plated through holes (PTHs) allow leads or pins to pass through and connect on both sides. Non-plated mounting holes simply provide a screw anchor point. Solder pads on the surface mount provide attachment points for surface mount devices (SMDs).

Multilayer Boards

Complex high-density boards are constructed using multiple substrate and copper foil core layers laminated together into a multilayer board. This allows conductive traces to cross over each other on different layers isolated by dielectric substrate layers. High-end boards may contain 10 or more layers. Blind and buried vias electrically connect traces between layers.

Common Finishes

Special finishes are applied to protect circuit boards and facilitate soldering:

• Hasl – A solder coating over pads and holes for oxidation resistance and solderability
• ENIG – Electroless nickel immersion gold provides a wire bondable corrosion resistant finish
• Immersion silver – Silvery finish offers excellent solderability and shelf life
• OSP – Organic solderability preservative leaves a clear finish that promotes soldering

Major Types of Circuit Boards

There are several major classifications of circuit boards designed for different electronic products and mounting requirements:

PCB Classifications by Structure:

• Single-sided – Conductive traces on one side of a single substrate layer
• Double-sided – Traces on both sides of a single core substrate layer
• Multilayer – Multiple substrate and trace layers laminated together
• High-density interconnect (HDI) – Densely spaced traces and microvias

PCB Classifications by Function:

• System/Motherboard – The main board with microprocessor in a computer or embedded system
• Daughterboard – Plug-in boards that interface to a motherboard in large systems
• Backplane – Passive interconnecting board that daughterboards plug into
• Shield/Riser – Boards providing structure, orientation, and shielding to daughterboards plugged into a backplane

Classifications by Supported Components:

• Through-hole technology (THT) – For leaded components that pass through holes in the board
• Surface-mount technology (SMT) – For surface mount devices (SMDs) soldered directly to pads on the surface
• Mixed technology – Boards supporting both through-hole and surface mount components

Key Steps in PCB Design and Fabrication

Taking a circuit board from initial concept through fabrication involves several important stages and steps:

Schematic Capture

A schematic diagram is drawn containing logical connections between electrical components and functions. This schematic capture is usually done using CAD software tools like Eagle, OrCAD, or Altium Designer.

PCB Layout Routing

The physical layout of traces, vias, and component footprints is routed based on the schematic diagram. Engineers use PCB layout software to design the multilayer board stackup and route traces following layout constraints.

Component Libraries

PCB layout tools rely on component libraries containing the footprints and 3D models of parts to be placed on the board. Libraries are provided by manufacturers or generated based on datasheets.

Design Rule Checking

Software design rule checking verifies the PCB layout adheres to specified clearance, spacing, and other design constraints. Electrical rules checking (ERC) confirms correctness of connections.

Prototyping and Testing

Prototype PCB manufacturing allows testing and verification of the board design. Engineers examine layout issues, signal integrity, thermal performance, and functionality on prototype boards.

Fabrication Data Generation

Completed board layout data undergoes processing to generate manufacturing files like Gerber files, drill data, and assembly drawings needed to fabricate boards.

Board Fabrication

The PCB manufacturing process transforms fabrication data into physical circuit boards using processes like lamination, drilling, imaging, plating, and milling.

Assembly

In assembly, components are soldered onto fabricated bare boards using either automated surface mount pick-and-place or manual attachment of through-hole parts.

Key Circuit Board Manufacturers

Some of the leading global manufacturers producing bare printed circuit boards and performing PCB assembly include:

• Shenzhen Fastprint – One of the largest PCB manufacturers in China
• TTM Technologies – Leading US-based PCB manufacturer
• AT&S – Major European PCB maker headquartered in Austria
• Unimicron – Taiwanese PCB manufacturer with advanced HDI and packaging capabilities
• Zhen Ding Tech – Major PCB supplier to Taiwanese electronics firms
• Tripod Technology – Taiwanese manufacturer specializing in high-end PCBs
• Ibiden – Japanese PCB company that is a key supplier for automotive electronics
• Samsung Electro-Mechanics – Major Korean PCB fab for consumer electronics
• ISU Petasys – Leading high-density PCB maker in Japan
• Würth Elektronik – German PCB producer focused on circuit carriers

These and many other manufacturers around the world mass produce a huge variety of printed circuit boards for all types of electronics applications. Global PCB sales exceeded an estimated $72 billion in 2021.

Example Applications Showcasing Circuit Board Functions

To demonstrate how circuit boards fulfill key roles in real-world products, here are some example applications:

Smartphones

Modern smartphones incorporate multilayer boards that:

• Provide rigid foundation to mount display, processors, wireless chips, camera modules, connectors, and other components
• Interconnect components with high-density traces and vias
• Manage heat dissipation from high-power processors
• Interface internal circuits with external displays, antennas, battery, and peripherals
• Allow compact, optimized component layout and miniaturization
• Facilitate assembly, automated testing, and repairability of modules

Automotive Electronics

Vehicles utilize printed circuit boards to:

• Connect engine control unit (ECU) processors, sensors, actuators, and networks
• Link cameras, radars, media, and other systems through high-speed buses
• Withstand vibration, shock, and temperature extremes in harsh environments
• Support fault diagnosis and field replacement of controllers and modules
• Enable dense packaging of circuits in tight spaces like dashboards and doors

Data Centers

Server racks in data centers rely on boards that:

• Provide backplanes, motherboards, and daughtercards to interconnect high-power processors, memory, storage, and network interfaces
• Allow hot-swapping of replaceable cards during operation for maximum uptime
• Facilitate technical servicing and upgrades by mounting components in accessible locations
• Optimize airflow and cooling of densely packed hardware
• Carry high-speed buses between rack-mounted servers and network switches

Industrial Robotics

Industrial robots use circuit boards to:

• Mount powerful motor drivers, controllers, sensors, and embedded processors
• Connect to external control systems, actuators, and peripherals
• Withstand vibrations from high-torque motors and heavy payloads
• Support simple replacement of controllers or interface cards in the field
• Allow compact, optimized layout of complex motion control circuits

Advantages and Disadvantages of Printed Circuit Boards

Here is a summary of key benefits provided by printed circuit boards, along with a few disadvantages to consider:

Advantages

• Compact, high component density and optimized layouts
• Reliable electrical connectivity between components
• Simplified manufacturing with automation-friendly design
• Speeds up assembly process and reduces human errors
• Allows minimization and portability of complex electronic circuits
• Facilitates testing, diagnostics, and repair procedures
• Cost-effective for high-volume manufacturing

Disadvantages

• Initial design requires expensive software tools and prototyping
• Complex multilayer boards can be costly to fabricate
• Density makes troubleshooting faults more difficult
• Repairs often need complete board replacement
• Lead times of weeks to produce complex designs
• Cannot modify traces post-production like wires

The Future of Printed Circuit Boards

As electronics become smaller, faster, and more complex, circuit board technology continues advancing in some key directions:

• More layers – Up to 30+ layers to interconnect high pin count chips
• Miniaturization – Thinner boards with tighter trace spacings and microvias
• Higher frequencies – Above 50 GHz for upcoming wireless standards
• Advanced materials – Low-loss substrates for antennas, radars, and high-speed digital
• Embedded components – Capacitors, resistors, and actives integrated into the board
• Flexible circuits – Bendable boards for wearables and consumer devices
• Stretchable circuits – Boards that can deform for flexible electronics
• 3D multilayer – Multilayer boards folded over each other into compact modules
• Smart boards – Integrated monitoring for temperature, vibration, and power
• Green technology – Lead-free, halogen-free, and recyclable materials

Continued innovations in printed circuit board materials, design, and fabrication will push the performance limits while supporting emerging applications like autonomous vehicles, IoT devices, high-speed communications, and more.

Conclusion

In summary, printed circuit boards are integral core components that enable and enhance virtually every modern electronic system. The many functions of circuit boards include providing:

• Physical structure to mount and arrange components
• Electrical connectivity through traces and vias
• Standardized mounting points for components
• Efficient manufacturing and assembly processes
• Repairability and servicing access to components
• Thermal management of heat dissipation
• Interfaces to connect subcircuits to larger systems

Underlying the tremendous growth of electronics, printed circuit boards will continue improving to deliver smarter, faster, smaller, and more reliable electronic circuit implementations well into the future through ongoing innovation and discoveries.

Frequently Asked Questions

What are the main functions of a printed circuit board?

The key functions of printed circuit boards are:

• Provide physical structure and organization for components
• Create electrical connections between components with traces
• Define mounting locations for attaching components
• Enable manufacturing automation and assembly
• Facilitate testing, diagnostics, repair and upgrades
• Allow interconnection of subcircuits to larger systems
• Help dissipate heat from high power components

What are the essential parts of a circuit board?

Essential parts of a circuit board include:

• Substrate – Forms the base, usually fiberglass or plastic
• Copper traces – Etched conductive wiring paths
• Pads/holes – For mounting and connecting components
• Silkscreen – Printed markings and component labels
• Vias – Vertical interconnects between copper layers
• Edge connectors – For connecting to external systems

What are the main materials used in PCB construction?

Common PCB substrate materials are fiberglass, plastic, ceramic, copper, and aluminum. Copper forms the conductive traces and pads. Solder mask coats the board to insulate copper traces. Components are attached with solder alloys or conductive adhesives.

What are the advantages of using a circuit board over wiring?

Key advantages of printed circuit boards versus wiring are:

• More compact and organized layouts
• Simplified manufacturing and assembly
• Eliminates hand wiring errors
• Faster design changes by altering printed traces
• Allow high-volume automated component mounting
• Facilitates field replacements and repairs

What are some key innovations happening with circuit boards?

Notable PCB innovations include: