The most commonly available and cost-effective PCB material available in the electronic industry is FR4. It has the biggest market share among all the PCB substrate materials in industry use due to its widely acceptable performance, both electrically and physically in many applications. FR4 PCB is in great demand because of its properties of good material strength and flame resistance properties, among others.
FC - FR4 PCB board
FC- FR4 board
FC - FR4 circuit board

What is FR4 in PCB?

Fiberglass material layers are infused with epoxy resin to make FR4 material. Different fiberglass sheets are joined layer by layer with epoxy resin and covered with an outer copper layer, hence given the grade of glass-reinforced epoxy laminate PCB material. Epoxy resin applied along with bromine gives it fire-resistant properties. Bromine is good for its flame-resistant properties and is quite better in performance than other PCB materials.
Then these sheet layers are pressed in a controlled way to bind them into one sheet. ‘FR-4’ is named due to its fire retardant properties that the fire doesn’t spread if the material catches fire. This property of PCB materials is particularly valuable in electronic systems where safety standards like UL94V-0 are required. That is why it is a suitable material for applications, where fire vulnerability is a concern.

FR4 vs. Other PCB Materials

If we compare FR-4 with other commonly used PCB substrate materials in the industry like CEM-1 and CEM-3, all of these materials are cost-effective and find their application in consumer electronics. But cost is not the only measure of success. The main difference lies in their usability, durability, and performance.
    • CEM-1 is considered the cheapest due to its poor quality, and reliability and is only suitable for very low-cost circuit applications. It has low heat resistance, dimensional stability, humidity control, electrical insulation, and material strength. They found their application only in low voltage, low power DC, or very low-frequency electronic circuits.
    • CEM-3, on the other hand, is better than CEM-1 due to its better insulation, dimensional stability, strength, thermal endurance, and reliability.
    • FR-4 stands out among its low-cost competitors due to its high dimensional stability, dielectric strength, lower coefficient of thermal expansion, fire resistance, lower moisture absorption, and reliable performance. Due to its reliability and stability, FR-4 PCB has found its use in industrial applications such as automotive, health care, high-end consumer electronics, processing, and control circuits.
fr4 material

Characteristics of FR4 PCB Material

If we look at the generic datasheet of FR-4 substrate material, we find that many characteristics that are there which are desirable for many industrial and consumer applications.
Following are the general characteristics of FR4 material used in PCB substrates.
Electrical Insulation
FR4 has got high surface (2x10(5 ) Mega Ohm) and volume resistivity (8x10(5) Mega Ohm), making it a very good electrical insulator. Hence the leakage currents are extremely low.
Dielectric Break Down
FR4 has a high breakdown voltage of 55KV (min.), making it suitable for high-voltage applications as well.
Dielectric Physical Strength & Mechanical Stability
FR4 has good physical strength. It is semi-rigid, but not brittle. FR-4 has got high flexural strength of more than 60,000 psi (longitudinal and crosswire). It is a lightweight material.
Coefficient of Thermal Expansion
The coefficient of thermal expansion (CTE) describes the change in dimension of a material with temperature change. In general, FR-4 has got reasonably good CTE of less than 15 ppm/(◦)C in the lateral dimension and around 70 ppm/(◦)C in the vertical direction.
This parameter depicts the expansion and contraction of material with changing temperature which is essential for the integrity of tracks, especially plated through hole vias. If CTE for PCB material is much different than CTE of metal used for via, there could be mechanical stresses that need to be managed.
Fire Retardancy
Fire resistance is a very important and desirable property of FR4 PCBs.
Moisture Absorption
Having a very low moisture absorption level of <0.25%, FR-4 is suitable for many electronic applications.
Dielectric Permittivity
FR4 has a dielectric constant or dielectric permittivity of 4.6. It is a measure of substrate polarization due to the applied electric field. It is a measure generally useful for high-frequency applications.
Dielectric Loss Tangent
It is a measure of energy dissipated in the substrate due to an alternating electric field. So, this measure should be low for high-frequency PCB. FR-4 has a general dielectric loss tangent of around 0.02.
Glass Transition Temperature
It is an important aspect of materials. It defines the temperature at which a material changes from a solid state to a soft and flexible state. FR-4 has got glass transition temperature of 135 (◦)C, which makes it quite resistant to heat/temperature.
fr-4 pcb

FR4 Grades and Specifications

  1. Standard FR4
Standard FR-4, the most widely manufactured and used, has the same electrical and physical properties as mentioned in the previous section.
  1. High-frequency FR4
For high-frequency applications in RF & microwave circuits, researchers have worked out to design an FR-4 grade suitable for these applications. As mentioned in the previous section, loss tangent is a measure of signal loss in high-frequency signals. Scientists have worked out to reduce dielectric loss tangent in this FR-4 grade along with stable dielectric permittivity, which is crucial for high-frequency circuit design.
  1. High Tg FR4
Although standard FR4 has a high glass transition temperature (Tg) of 135(◦)C. Advances in this material have revealed methods to improve ‘Tg’ to 175. This has also improved its temperature-oriented performance, like further lowering the CTE and more temperature stability.
  1. High CTI FR4
The Comparative Tracking Index (CTI) describes the extent to which the electrical breakdown of dielectric material on a surface (called tracking) can occur. It is not the same as dielectric breakdown. The dielectric material can withstand unwanted current flow between conductive tracks on the PCB, especially under conditions of dirt, humidity, and high voltage.
The standard CTI of FR-4 is around 200V. However, high CTI FR-4 has an improved value of around 600V, improving reliability for high-voltage applications.
  1. FR4 without Copper Laminate
Without copper, this is not a printed circuit board application but is used as a spacer or physical/mechanical support.
  1. FR4 G10
G10 FR-4 is the predecessor to modern-day FR-4 materials. They have similar properties to standard FR-4 material. FR-4 materials have bromine in epoxy resin which makes it better in fire resistance.

Advantages of FR4 PCBs

Cost-effectiveness
Cost-effective among the other alternatives to PCB substrate as per the reliability and performance it provides.
Mechanical Strength
Rigid and reliable material having good mechanical strength to endure physical and environmental stresses.
Thermal Stability
Reliable and stable electrical and mechanical performance for a wide temperature range, making it suitable for a wide range of applications.
Flame Retardancy
One of the most desirable features for almost every electronic circuit application.
Wide Usage
Low cost, reliability, and good performance characteristics make it well-suited for most of the applications.
Easy Manufacturing
Easy to fabricate using conventional chemical etching, laser etching, or machine milling and drilling processes.

Disadvantages of FR4 PCBs

Thermal Conductivity
FR4 material has relatively poor thermal conductivity (0.3 W/m·K), which can be a limitation in applications where high power is dissipated in the form of heat, which can be accumulated in PCB due to poor heat conduction.
CTE Mismatch
CTE mismatch between the PCB material and other components like via, cladding, solder connection, etc. can lead to mechanical stress and eventually physical cracking or open circuit during thermal cycling. This can cause potential failure in some harsh thermal conditions.
High-Temperature Limitations
Although good thermal and performance stability for a defined temperature range, the properties can degrade sharply after the temperature threshold is exceeded.
Performance at High Frequency
The dielectric constant of high-frequency FR-4 is not frequency-independent. Moreover, its tolerance level is less than 10%, making it less reliable, especially for wideband applications.
Environmental Concerns
FR4 PCB board uses bromine as a flame retardant, which can be a health hazard if E-waste is not properly managed.

How to Make FR4 PCB?

The manufacturing process of FR-4 PCBs involves several key steps to produce high-quality and reliable boards:
  1. Design and Layout: The first step is to design the schematic design of the PCB. The PCB layout is designed using circuit design software. This includes placing PCB components as per their dimensions and routing traces on the PCB.
  1. PCB board: Now choose an FR4 PCB board with the desired thickness. Place reference markers for proper placement of PCB layout.
  1. Drilling and electroplating vias: Holes are drilled into the PCB for through-hole components and vias (to make electrical connections between layers). Then a thin layer of copper is electroplated onto the entire surface of the PCB, including the walls of the drilled holes.
  1. Etching: In this process, the unwanted copper is removed using a chemical etching process; leaving behind only the desired circuit traces, vias, and pattern.
  1. Solder Mask Application: A solder mask is used as an insulative protection layer to the PCB to prevent solder bridges from forming between closely spaced tracks and protect the tracks against oxidation.
  1. Silkscreen Printing: The Silkscreen layer is printed where labels and component outlines are printed on the PCB to guide circuit assembly.
  1. Assembly: Components are placed and soldered onto the PCB. At this stage, the circuit board FR4 is ready for inspection and testing.
fr4 pcb board

Wide Range Applications of FR4 PCBs

FR4 and its grades have got applications in almost every industry, where FR4 PCB boards are utilized. This includes but is not limited to the following applications.
  1. Consumer Electronics: Common products in consumer electronics include household appliances like TVs, refrigerators, washing machines, dryers, electric ovens, security systems, LED bulbs, etc along with other products of personal use including watches, smartphones, desktop computers, and laptops.
  1. Automotive Industry: The rugged nature of FR4 and High ‘Tg’ FR-4 PCB enables its use in the high-temperature conditions of automotive environments. The application includes utilization in control and sensing circuits for engines, airbags, and satellite navigation systems.
  1. Aerospace and Defense Industry: The characteristic property of flame retardant of FR4 PCB is very crucial in aerospace, avionics, and defense applications to reduce the risk of fire spread in electronic circuit boards. Its thermal stability and reliability are the features along with other electrical and physical properties that make it suitable for use in avionics, communication, and flight control systems.
  1. Industrial Equipment: FR4 is also used as a PCB substrate in applications that involve industrial equipment, such as power supplies, electronic sensors, motor drives, test & measurement devices, and control systems. Its reliable performance and mechanical strength ensure the safe operation of these devices to endure the challenging conditions of industrial environments.
  1. Medical Devices: FR4 PCB is also used in medical equipment for patient monitoring systems, diagnostic equipment, and medical implants. Its reliability, mechanical stability, and flame retardant make it fit for these critical applications.
FC - FR4 PCB

Top FR4 PCB Manufacturer in China - FC PCBA

FR4 PCB has improved the electronic manufacturing process reliability and cost-effectiveness due to its stable and suitable characteristics for most electronic/electrical circuit applications. This has made electronic manufacturing cheap, and safe, and products reach the general population. Its compatibility with standard PCB fabrication processes like drilling, etching, and soldering has simplified manufacturing and reduced production costs.
FC PCBA is the leading FR4 PCB manufacturer in China, if you want to know more about our FR4 PCB board, please feel free to contact us.