Types of PCB by Layers

One of the main ways to categorize PCBs is by the number of conductive layers they contain. PCB layer count can range from one to over 40 layers for the most complex boards. More layers allow for higher component density and more complex circuits but also increase manufacturing cost. The main types of PCB by layer count are:

Single Layer PCB

Single layer PCBs have one conductive layer made of a thin copper foil laminated on a non-conductive substrate, typically FR-4 glass epoxy. Components are mounted on one side of the board and the copper layer on the other side provides the interconnections.

Advantages of single layer PCBs include:

• Low cost – Simplest and cheapest PCB to manufacture
• Smaller form factor – Thinnest PCB type
• Easier inspection and repair – Components and traces are easily accessible

Disadvantages include:

• Low component density – Limited space for components and traces
• Unsuitable for complex circuits – Single layer limits routing options
• Higher chance of electromagnetic interference (EMI) – Components and traces are close together

Single layer PCBs are commonly used in simple, low-cost consumer electronics such as calculators, radio, LEDs, printers, and power supplies.

Double Layer PCB

Double layer PCBs have two conductive layers with a substrate in between. Components are mounted on both sides of the board. Through-hole vias are used to connect traces on the top and bottom layers.

Advantages of double layer PCBs include:

• Higher component density than single layer – Components can be mounted on both sides
• Suitable for more complex circuits – Two layers provide more routing options and space for traces
• Lower EMI than single layer – Ground plane can be added between layers to reduce interference

Disadvantages include:

• Higher cost than single layer – Additional manufacturing steps required
• Thicker than single layer – Two layers plus substrate increase thickness
• More difficult inspection and repair – Components and traces on both sides can be hard to access

Double layer PCBs are widely used in a variety of electronic devices such as amplifiers, automotive electronics, instrumentations, power monitoring, and switching circuits.

Multi-Layer PCB

Multi-layer PCBs have three or more conductive layers alternating with insulating substrate layers. Adjacent layers are connected with vias. More layers allow for higher component density, more complex interconnections, and better EMI performance.

Multi-layer PCBs are further categorized by layer count:

• 4-layer PCB – Typically has two inner signal layers and two outer layers for components and planes. Commonly used in industrial controls, medical equipment, robotics, and telecom hardware.

• 6-layer PCB – Has four signal layers and two plane layers for power and ground. Used in more complex devices such as servers, GPS technology, and satellite systems.

• 8-layer PCB – Has six signal layers and two plane layers. Used in high-speed networking, radar systems, and advanced telecom equipment.

• 10+ layer PCB – With 10 or more layers, these are used for the most complex, high-performance applications such as supercomputers, advanced military and aerospace systems, and medical imaging equipment.

Advantages of multi-layer PCBs include:

• Very high component density – More layers provide more space for components and traces
• Suitable for highly complex circuits – Many layers allow for intricate routing and interconnections
• Excellent EMI performance – Dedicated ground and power planes and shorter traces minimize interference

Disadvantages include:

• High cost – More layers require more material and manufacturing steps which increases cost significantly
• Thick form factor – Multiple layers result in a thicker board
• Difficult inspection and repair – Inner layers are not accessible for testing and rework

Types of PCB by Rigidity

Another way to categorize PCBs is by the rigidity of the substrate material. The main types are:

Rigid PCB

Rigid PCBs use a solid, inflexible substrate material, typically FR-4 fiberglass. This provides mechanical strength and stability to support components and maintains the shape of the board.

Advantages of rigid PCBs include:

• Strong and durable – Suitable for applications with high mechanical stress
• Stable dimensions – Maintains shape and size over wide temperature range
• Better heat dissipation – Rigid substrate helps transfer heat away from components

Disadvantages include:

• Not flexible – Cannot conform to curved surfaces or flex during use
• Heavy and thick – Rigid material adds significant weight and thickness
• Difficult to install in tight spaces – Rigid shape may not fit in confined areas

Rigid PCBs are used in a wide range of applications where durability and stability are important such as consumer electronics, industrial controls, medical devices, and military equipment.

Flex PCB

Flex or flexible PCBs use a thin, flexible plastic film as the substrate, typically polyimide. This allows the PCB to bend and flex during use without damaging the circuits.

Advantages of flex PCBs include:

• Flexible and conformable – Can bend and twist to fit in tight spaces and conform to curved surfaces
• Lightweight and thin – Minimal weight and thickness added to the device
• Resistant to vibration and shock – Flexibility helps absorb mechanical stress
• Reduced assembly cost – Can replace multiple rigid boards and connectors

Disadvantages include:

• Higher cost than rigid PCB – Flexible materials and specialized manufacturing processes increase cost
• Limited component options – Not all components are suitable for use on flex circuits
• Vulnerable to tearing and delamination – Thin, flexible material can be easily damaged

Flex PCBs are commonly used in applications that require flexibility or must fit in confined spaces such as cameras, printers, smartphones, wearable electronics, aerospace and medical devices.

Rigid-Flex PCB

Rigid-flex PCBs combine rigid and flexible substrates in a single board. Rigid sections are used for mounting components while flexible sections act as interconnects between rigid areas.

Advantages of rigid-flex PCBs include:

• Combines benefits of rigid and flex – Rigid areas for components and stability, flex areas for interconnects and tight spaces
• Eliminates connectors – Flex sections replace wires and connectors between rigid boards
• Reduces size and weight – Eliminates need for multiple boards and connectors
• Improved reliability – Fewer interconnects means fewer potential failure points

Disadvantages include:

• High cost – Combining rigid and flex materials and processes significantly increases complexity and cost
• Complex design – Requires careful planning of rigid and flex areas and interconnects
• Difficult assembly – Specialized equipment and techniques needed to assemble rigid and flex sections

Rigid-flex PCBs are used in applications that require high reliability, small size and tight packaging such as aerospace and military systems, medical implants, and robotics.

Types of PCB by Material

PCBs can also be categorized by the type of substrate material used. The choice of material depends on the electrical, mechanical, and environmental requirements of the application. Common PCB substrate materials include:

FR-4

FR-4 (Flame Retardant 4) is the most widely used PCB substrate material. It is a composite material made of woven fiberglass cloth with an epoxy resin binder. The “4” refers to the woven glass reinforcement used.

Advantages of FR-4 include:

• Low cost – Widely available and inexpensive material
• Good mechanical strength – Fiberglass reinforcement provides rigidity and stability
• Good dielectric properties – Suitable for most applications with frequencies below 1 GHz
• Flame retardant – Self-extinguishing and resistant to burning

Disadvantages include:

• Limited high frequency performance – Dielectric losses increase above a few GHz
• Moisture absorption – Can absorb moisture which affects dielectric properties
• Not suitable for high-temperature applications – Glass transition temperature around 135°C

FR-4 is used in a wide variety of consumer, industrial, and commercial electronics.

Polyimide

Polyimide is a high-performance polymer material that offers superior thermal, mechanical, and chemical resistance compared to FR-4. It is commonly used as a substrate for flex PCBs.

Advantages of polyimide include:

• Excellent thermal stability – Glass transition temperature around 360°C
• High mechanical strength and flexibility – Tensile strength and elongation superior to FR-4
• Low dielectric constant and dissipation factor – Suitable for high-frequency applications up to a few GHz
• Resistant to chemicals and solvents – Ideal for harsh environments

Disadvantages include:

• High cost – Significantly more expensive than FR-4
• Difficult to process – Requires specialized equipment and techniques for drilling, plating, and soldering
• Moisture absorption – Can absorb moisture which affects dimensional stability and dielectric properties

Polyimide is used in high-reliability applications such as aerospace, military, and medical devices that require operation in harsh environments and wide temperature ranges.

PTFE

Polytetrafluoroethylene (PTFE) is a fluoropolymer material known for its excellent dielectric properties, low dissipation factor, and high thermal stability. It is commonly used as a substrate for high-frequency PCBs.

Advantages of PTFE include:

• Excellent high-frequency performance – Low dielectric constant and dissipation factor up to millimeter-wave frequencies
• Wide operating temperature range – Usable from cryogenic temperatures to over 200°C
• Low moisture absorption – Hydrophobic material resists moisture uptake
• Non-stick surface – Resists adhesion of contaminants and Solder Flux

Disadvantages include:

• Very high cost – One of the most expensive PCB substrate materials
• Difficult to process – Requires specialized equipment and techniques for drilling, plating, and bonding
• Poor mechanical strength – Soft and easily deformed material requires careful handling

PTFE is used in high-frequency applications such as radar, satellite communications, and microwave circuits that require ultra-low loss and stable dielectric properties.

Rogers

Rogers Corporation produces a variety of specialty PCB substrate materials for high-frequency, high-speed, and high-reliability applications. These include PTFE-based materials such as RT/duroid and ceramic-filled hydrocarbon materials such as RO4000 series.

Advantages of Rogers materials include:

• Excellent high-frequency performance – Low dielectric constant and dissipation factor up to millimeter-wave frequencies
• Low moisture absorption – Resistant to moisture uptake and stable dielectric properties
• Controlled dielectric constant – Materials with tightly controlled dielectric constant available
• Good thermal conductivity – Some materials offer high thermal conductivity for heat dissipation

Disadvantages include:

• High cost – Specialty materials with premium prices
• Limited availability – Not as widely available as FR-4 or polyimide
• Difficult to process – May require specialized equipment and techniques for fabrication

Rogers materials are used in demanding high-frequency applications such as 5G wireless, automotive radar, aerospace and defense systems, and high-speed digital circuits.

Types of PCB by Application

PCBs can also be categorized by their intended application or industry. Some common types include:

Consumer Electronics PCB

PCBs used in consumer electronics such as smartphones, laptops, televisions, and home appliances. These boards prioritize low cost, small size, and high volume production.

Industrial PCB

PCBs used in industrial control systems, automation equipment, power electronics, and transportation systems. These boards prioritize reliability, ruggedness, and long-term stability.

Medical PCB

PCBs used in medical devices such as imaging systems, patient monitors, and implantable devices. These boards prioritize reliability, biocompatibility, and compliance with strict regulatory standards.

Automotive PCB

PCBs used in automotive electronics such as engine control units, infotainment systems, and advanced driver assistance systems (ADAS). These boards prioritize reliability, temperature resistance, and vibration resistance.

Aerospace and Defense PCB

PCBs used in aircraft, spacecraft, satellites, and military systems. These boards prioritize reliability, ruggedness, and ability to withstand extreme environments such as vacuum, radiation, and wide temperature swings.

PCB Types Comparison Table

PCB Type	Layers	Rigidity	Common Materials	Typical Applications
Single Layer	1	Rigid	FR-4, Polyimide	Simple, low-cost consumer electronics
Double Layer	2	Rigid	FR-4, Polyimide	Power supplies, automotive, instrumentation
Multi-Layer	4+	Rigid	FR-4, Polyimide	Complex devices, high-speed digital, RF
Rigid	1+	Rigid	FR-4, Polyimide	Consumer, industrial, medical, aerospace
Flex	1+	Flexible	Polyimide	Wearables, portables, medical implants
Rigid-Flex	1+	Rigid and Flexible	FR-4, Polyimide	Aerospace, military, robotics
High-Frequency	1+	Rigid or Flexible	PTFE, Rogers	Radar, satellite, 5G, microwave

PCB Types FAQ

Q: What is the most common type of PCB?

A: The most common type of PCB is the FR-4 rigid PCB. FR-4 is a widely available and inexpensive material that offers good mechanical and dielectric properties for most applications. Rigid PCBs are used in a wide variety of consumer, industrial, and commercial electronics.

Q: What type of PCB is used in smartphones?

A: Smartphones typically use a combination of rigid and flex PCBs to fit all the necessary components in a compact and lightweight package. Rigid PCBs are used for mounting larger components such as the processor, memory, and modem, while flex PCBs are used for interconnects and smaller components such as cameras and sensors.

Q: What is the cheapest type of PCB?

A: The cheapest type of PCB is the single layer rigid FR-4 board. Single layer boards require the fewest manufacturing steps and materials which minimizes cost. FR-4 is also one of the least expensive substrate materials. However, single layer boards are limited in terms of circuit complexity and component density.

Q: What are the advantages of using a flex PCB?

A: The main advantages of using a flex PCB are:
1. Flexibility and conformability – Flex PCBs can bend and twist to fit in tight spaces and conform to curved surfaces.
2. Light weight and thin profile – The thin and flexible substrate adds minimal weight and thickness.
3. Vibration and shock resistance – The flexibility helps absorb mechanical stress and vibration.
4. Reduced assembly cost – Flex circuits can replace multiple rigid boards and connectors reducing assembly complexity.

Q: What are the disadvantages of using a multi-layer PCB?

A: The main disadvantages of using a multi-layer PCB are:
1. High cost – Each additional layer requires more material and manufacturing steps which rapidly increases cost.
2. Thick profile – Multiple substrate layers result in a thicker board which may not fit in space-constrained devices.
3. Difficult inspection and repair – Inner layers are not accessible for testing and rework making faults hard to diagnose and fix.