FR-4 PCB Fabrication | NextPCB 2022

What is FR4?

FR4 is a common material used in the printed circuit board. FR stands for Fire Retardant, which means fire resistance.

Thus, FR material is a material with good fire resistance. After being combined with thin copper layers on the surface of the FR layer of fireproof material, experts produce the material to use in the printed circuit for a wide range of applications.

What are FR4 Properties and Materials?

Physical properties:

• Base and foil thickness
• Material density
• Surface quality
• combustibility
• Water absorption, etc.

Electrical properties:

• Relative permittivity
• Loss tangent
• Specific surface resistance
• Specific volume resistance
• Breakdown voltage, etc.

Mechanical properties:

• Elasticity
• Bending strength
• Peel strength of foil, etc.

Thermomechanical properties:

• Glass transition temperature, Tg
• Thermal expansion coefficient, KTP
• Destruction or decomposition temperature, Td, etc.

What is FR4 material structure?

Materials that fall under the NEMA FR-4 specification are most often used for the production of double-sided and multilayer printed circuit boards.

Standard FR-4 is a composite material based on glass fiber. Standard FR-4 1.6 mm thick consists of eight layers (“prepregs”) of fiberglass. The manufacturer's logo is usually located on the central layer; its color reflects the flammability class of this material: red - UL94-V0, blue - UL94-HB.

Usually, FR-4 is transparent; the standard green color is determined by the color of the solder mask applied to the finished PCB.

Thus, FR-4 is the most common base material worldwide for the production of double-sided and multilayer printed circuit boards, as well as for the production of single-sided printed circuit boards with increased requirements for mechanical strength.

Material G10

It is a predecessor of FR4, they have all the features, but it has been replaced by FR4 with a safer level.

Electro-Static Dissipation This groundbreaking material provides users with several important advantages over other ESD products. ESD materials are an integral part of G10/FR4 epoxy glass bases. Surface resistors can be supplied to the specification for use. It helps improve machinability and tighter tolerances.

Fiberglass FR-4

Foiled fiberglass with a nominal thickness of 0.1 to 3 mm, lined with copper foil with a thickness of 18 to 105 microns on one or both sides. The manufacturer's logo is usually located on the central layer; its color reflects the flammability class of this material (red - UL94-VO, blue - UL94-HB).

Usually, FR-4 is transparent; the standard green color is determined by the color of the solder mask applied to the finished PCB.

Fiberglass FR-4 Tg 180

Foil dielectric with low Z-axis thermal expansion and high glass transition temperature Tg for lead-free soldering, with a nominal thickness of 0.1 to 2 mm, lined with copper foil with a thickness of 18 to 70 microns on one or two sides.

FR4 PCB Thickness Fabrication

1. For a common circuit board, the core can combine with the stiffness and make the base for the circuit with the copper layer on it.

2. For 2-layer printed circuit boards, the FR4 type is separated between the top and bottom copper layers, for multi-layer printed circuit boards it is common to add FR4 PrePreg layers between the inner and outer copper layers.

3. The inner core of the FR4 material, in addition to the task of making a rigid object and a foundation for the circuit, also has another factor to help prevent the two layers of copper, to help create an insulating dielectric layer.

4. For creating a required thickness of the PCB is done by adding or removing laminates so that different thicknesses can be made.

- For example, the FR4 circuit with a thickness of 1.6 mm is normally made up of 8 layers of fiberglass. Want FR4 printed circuit board thickness from 0.8 mm, users can reduce from 8 layers to 4 layers.

What Advantage of FR4 Materials PCB?

Foiled fiberglass FR 4 is a laminate (layered plate) for the production of printed circuit boards, pressed from several layers of fiberglass with epoxy impregnation. The material is produced with one- and two-sided copper foiling, of different thicknesses and sizes.

• FR4 is a low-cost material.
• It has a high dielectric strength which contributes to its electrical insulation properties.
• The material has a high strength-to-weight ratio and is lightweight.
• It is moisture-resistant and has relative temperature resistance as well.
• The material has good electric loss properties.
• FR4 doesn’t absorb water, which makes it suited for various marine PCB applications, too.
• The material is yellow to light green in color, which perfectly goes with any application.

Below is the reason why the FR4 is in high demand in the market:

● Compact and easy to design
● Strongest plastic fastening materials
● Low cost but with many functions
● Moisture resistance provides high mechanical strength
● Good insulation in a dry or humid environment

We first use this material as insulation material for PCB, then by adding copper to it; we used it as a conductive sheet. It has greater strength in resistance and moisture absorption ability on the PCB sheet. Its maximum ambient temperature is 248 ° F to 266 ° F depending on the brand and filler.

FR4 PCB connections

• These things make FR4 perfect for PCB manufacturing.
• These features make PCBs affordable and of good quality.
• FR4 PC material is the base of PCB devices.

During the FR4 PCB manufacturing process, the FR4 boards are laminated with copper layers at a specific temperature.

Depending on the design of the printed circuit boards, copper forms on the circuits on both sides. Speaking of complexity, printed circuit boards use more than one layer to make complete circuits.

We will discuss the different types of FR4 PCB

Single-sided FR4 PCB:

Single-sided FR4 printed circuit boards are made of epoxy PCB resin having copper foil on one side, and its components glued on one side.

Speaking of their size, we usually have a length of 100mm, a width of 70mm, and a height of 1.5mm.

With the development of new technologies, including the difficult production process on new machines, the product becomes more expensive, but single-sided printed circuit boards are very advanced and affordable.

Double-sided FR4 plate:

Single-sided FR4 printed circuit boards are also made of epoxy PCB with copper foil on one side, but its components are glued on two sides, which give a path of crossing paths.

These plates contain copper for conductive purposes.

In the double-sided FR4, the PCB components are pasted on both sides of the PCBs, which give a crossing path.

Multilayer FR4 PCB

The multilayer FR4 PC board has more than two layers. It contains three layers of conductive material.

It is glued to the center of the materials. The core material is laminated under high pressure and high temperature to produce multilayer printed circuit boards. The components are glued on both sides of the PCB.

Rigid PCB FR4

In this type of FR4 PCB, the materials used are only FR, which is why it is called a Rigid FR 4 PCB.

No other materials or impurities are added to it. It's a clean circuit; therefore it's rigid for the entire board.

Rigid flexible PCB FR4

In this type of printed circuit board, the core material is rigid and flexible; therefore they are called rigid-flexible F R 4 PCBs. 

Flexibility comes from the flexibility of the perimeter. We used thin boards because they are more flexible and more susceptible to heat.

It may bend during soldering to obtain the desired angle.

Properties and materials of FR4:

The FR4 material is used under the UL94-0 standard for the flammability of plastics. The code 94-0 would be written on all FR-4 plates, which proves that the device is guaranteed to be protected against the spread of fire when burning the material.

Good PCB FR4 with multiple layers of FR4 glued between two thin layers of the laminated copper plate because bromine is used in its production, which is why it is also called a halogen element.

The standard FR4 PCB has a heat resistance of almost 248 ° F to 266 ° F.

Application of FR4 PCBs

Foiled fiberglass FR 4 is used to produce printed circuit boards for a wide range of military pcb, telecommunications, industrial, and instrumentation equipment. The material is the base for printed circuit boards used in consumer electronics and computer equipment.

The Difference between FR-4 Material and High-Frequency Laminate

The reliability of an electronic device is primarily influenced by the quality and type of components used during its production. Undoubtedly, printed circuits fall into this category. They enable the proper functioning of the electronic system. The selection of the base laminate on which the circuit will be produced is therefore crucial.  

Currently, PCB production uses laminates on the following substrates:

• glass-epoxy,
• marked with the symbol FR4
• aluminum MCPCB (Metal Core PCB)
• Similarly, Teflon and ceramic

 The choice of the type of laminate depends on the intended use of the device and its operating conditions.

What is PCB Laminate?

Laminate is defined as a glass-epoxy, aluminum, Teflon, or ceramic substrate covered on one or both sides with a copper foil, having such technical parameters that enable its use in specific devices. We divide laminate parameters into basic,

5. Temperature
5. moisture absorption
5. Electrical Parameters                                                                                                                                              

Typical PCB designs are based on the use of a standard FR4 glass-epoxy laminate, with an operating temperature of typically -50 to +110 ° C, with a glass transition temperature Tg of about 135 ° C. The dielectric constant Dk can range from 3.8 to 4.6 depending on the supplier and the type of material. 

With increased requirements for heat resistance high-temperature, FR4 High Tg or FR5 is used. Polyimide is used with the requirements for constant operation at high temperatures or with sudden temperature drops. 

In addition, polyimide is used in the production of tiles with increased reliability, for military applications, and when increased electrical strength is needed. For PCBs with very high frequency (bwcz) circuits - above 2 GHz, individual layers of bwcz material are used or the tile is entirely made of bwcz material. 

FR4 Material Sub-Types

FR-4 materials are the most common for the production of single-sided, double-sided, and multilayer printed circuits with increased requirements in terms of mechanical strength. 

 Depending on the properties and application, FR-4 is divided into the following subclasses:

• Standard, with glass transition temperature Tg ~ 130 ° C, with or without ultraviolet blocking. The most widespread and widely used type, and at the same time the cheapest of the FR-4;
• with high glass transition temperature, Tg ~ 170 ° C- 180 ° C, suitable for lead-free tinning and soldering technology;
• halogen-free, suitable for lead-free tinning and soldering technology;
• with the normalized index of CTI ≥ 400, ≥ 600;

High-Frequency Laminate

The durability and reliability of electronic devices depend on the quality and type of components used, including printed circuits, which form the basis of a properly functioning electronic system. For this reason, the appropriate selection of the parameters of the base laminate, ensuring the long and reliable operation of the finished product, is very important.

Laminate parameters

1. Basic parameters of laminates:

• The thickness of the dielectric and copper foil - determines the mechanical resistance, fit with the housing, current carrying capacity, etc.
• CTI class - responsible for resistance to punctures between paths in a humid environment;
• Non-flammability class (UL) - determines the degree of flammability of a given material.

2.  Temperature parameters of laminates:

• glass transition temperature (limit): Tg - yield point;
• the temperature of chemical decomposition of laminate: Td - temperature causing a 5% loss in weight of the laminate;
• time to delamination: T260 / 288 - time after which delamination appears in the material (for temperatures 260 and 288 ° C);
• the thermal expansion coefficient of the laminate in the XY plane and the direction of the Z axis: CTEZ, XY;
• Maximum operating temperature MOT - safe temperature for continuous operation.

3. Absorption of moisture by laminates:

• maximum moisture content in the laminate;
• Resistance to the CAF phenomenon.

4. Electrical parameters of laminates:

• dielectric constant Dk;
• loss Df;
• Dielectric breakdown resistance.

PCB Boards with an Aluminum Core

The complexity of systems and the degree of packing of their elements on printed circuits is more and more problematic due to the need to ensure proper heat dissipation, generated in high-power semiconductor elements. 

The use of a standard, glass-epoxy FR4 laminate in such devices, high-power components adapted to THT assembly, and typical heat sinks, increases the production costs of these devices, their size, and their weight. 

Therefore, PCB manufacturers and designers use laminates on an insulated metal substrate IMS (Insulated Metal Substrate), in the form of an aluminum core, referred to as MCPCB (Metal Core Printed Circuit Board).

Aluminum Core Laminates

Laminates with an aluminum core are characterized by high thermal conductivity, described by the TC value (Thermal Conductivity). In the case of a standard IMS laminate, it is at the level of 2 W / mK. There are also materials with a TC of 2-5 W / mK available on the market. 

For comparison, the TC coefficient of a typical FR4 laminate is by an order lower - 0.3 W / mK. In addition, laminates with aluminum core have higher mechanical strength (stiffness) with the same material thickness and lower thermal expansion than FR4.

The use of FR4 and MCPCB laminates

Ordinary FR4 laminate is intended for the assembly of systems operating with frequencies up to 0.5 GHz. However, there are special varieties of FR4 laminate with better frequency parameters.

 Laminates designed to work in the microwave range are based on ceramic (eg Rogers RO4003) or Teflon (eg Rogers RO3003) dielectrics. Another advantage of these laminates is the high Tg temperature of 280 ° C compared to the FR4 laminate.

MCPCB circuits are commonly used in high-power devices, such as switching power supplies (converters) and lighting lamps, where the light sources are matrices of high-power LEDs in SMD casings. 

LED lamps of this type are commonly used, among others, in lighting, in the automotive industry as external lights for vehicles, and in street light signals. Laminates for these applications are usually covered with a white solder mask, which increases the reflection of light.

The choice of specific production material is dictated by the assumed working conditions and the type of the designed device. There is also an economic factor in the decision-making process. However, it is worth bearing in mind that the use of high-quality materials has a key impact on the reliability and lifetime of the device.

Unusual applications of laminates

The laminate typically used in the production of PCBs is also used in non-standard applications, including:

Front plates

An example is measuring systems worn on the head. They are used, among others in medicine, aviation, and various types of simulators; as well as electric instruments, in toys, e.g. electronic dice or educational robots. 

Integrated surface-mounted modules directly to another printed circuit; Examples include commonly used Wi-Fi, Bluetooth or GSM, and GPS modems.

Adapters for integrated circuits

They allow you to mount elements with a different pin layout or housing on the PCB, without the need to design a newer version of the circuit.

Planar transformers

Unlike a typical transformer, the windings are made on a copper layer in the form of flat coils. Inside them, holes are made through which the halves of the ferrite core pass. 

These types of structures are characterized by: compact structure, small dimensions, no need to use a separate transformer outside the printed circuit (lower cost), low leakage induction, and higher energy efficiency compared to a standard transformer in the form of a separate element.

Why should pcb manufacturers have adequate knowledge of laminates?

Knowledge of the most important parameters of laminates will allow pcb manufacturers to choose the most optimal laminate tailored to the requirements and operating conditions of a given device. 

To ensure a long and trouble-free operation of devices, it is essential to use high-quality laminates. This is often associated with the necessity to incur higher costs. In the long run, however, it is more cost-effective than servicing and repairing devices damaged due to the use of an unsuitable laminate.

What are FR4 Alternative PCB Materials?

Paper Phenol Substrate (FR-1, 2)

Mainly used for single-sided substrates. Among the materials, it has been used for a wide range of purposes such as white goods, pre-high-definition TVs, stationary VTRs, stereos, radio cassette recorders, home phones, game consoles, keyboards, and electronic components. ..

Normally, through-holes cannot be formed by plating, but they are used for silver through-hole substrates that form through-holes by filling holes with silver paste and are used for remote controls for game consoles, TVs, and air conditioners, and audio.

Paper Epoxy Substrate (FR-3)

Used for single-sided boards like paper phenolic boards, but because of their excellent arc resistance, tracking resistance, and moisture resistance, it is used for high-voltage circuits and circuits that require moisture resistance. It seems that there are many cases.

Glass composite substrate (CEM-3)

Epoxy resin is impregnated into a mat-like material made by cutting and aligning glass fibers. In particular, it has excellent tracking resistance and is cheaper than glass epoxy.

Therefore, it is used in a wide range of double-sided plates, from home appliances and AV equipment related to amusement to some industrial equipment, which cannot be handled by single-sided plates.

ITEQ IT-180A

Fiberglass IT-180A has a high glass transition temperature Tg (175°C), high thermal stability, low Z-axis CTE, and high reliability. It is compatible with lead-free soldering.

MI 1222

MI 1222 is a layered pressed material based on fiberglass impregnated with an epoxy binder, lined on one or both sides with electrolytic copper foil.

• surface electrical resistance (Ohm): 7 x 1011;
• specific volume electrical resistance (Ohm m): 1 x 1012;
• dielectric constant: 4.8;
• foil peel strength (N): 1.8.

FAF-4D

Fiberglass-reinforced PTFE is lined on both sides with copper foil. It is used as the basis of printed circuit boards operating in the microwave range, and as electrical insulation for printed elements of receiving and transmitting equipment. It can work for a long time in the temperature range from -60 to +250 ° C.

• The adhesion strength of the foil to the base per strip is 10 mm, N (kgf), not less than 17.6(1.8);
• Tangent of the dielectric loss angle at a frequency of 106 Hz, no more than 7 x 10 ^-4 ;
• Dielectric constant at a frequency of 1 MHz: 2.5 ± 0.1;
• Let out sizes of sheets (maximum deviation on width and length of a sheet of 10 mm.) 500 x 500 mm.

Tips to Select the Right FR4 Material for Your FR4 PCB

Choosing a printed circuit board material is an important part of the printed circuit board manufacturing process. When designing a printed circuit board, if you know the discrimination of materials, you can choose the printed circuit board suitable for the product, which is useful.

• The material of the general printed circuit board was a combination of resin, reinforcing material (almost glass fiber), and metal copper foil.
• The material properties of the printed circuit board were influenced by the resin content and type. Therefore, it is necessary to select the appropriate printed circuit board material according to various printed circuit board designs.
• Currently, the printed circuit board material often used in the printed circuit board industry is glass epoxy board (FR-4), which is one of the flame-retardant materials.

Know Your Requirements to Use FR4 Material

First, you need to find out where to use the materials you need and what properties you want the board to have so that you can choose the materials you need.

FR4 chips are typically used for common electronic products. It is the grade of the material, not the name of the material. This means that the resin material must be able to burn itself.

Currently, there are many fr-4 materials used in ordinary circuit boards, but most of them are made of terra-functional epoxy resin, fillers, and heat-resistant fiberglass composites.

Also, when heated, the board bends, the expansion and contraction of the board affect the parts, the electrodes come off, and reliability decreases.

Therefore, it is necessary to select a steel plate with a small curvature, and the FR4 substrate is suitable.

The following factors should be considered when choosing a PCB board material:

(1) Select an appropriate board with a glass transition temperature (Tg) that is higher than the operating temperature of the circuit.

(2) High heat resistance generally required 50 seconds, 250 ° C / heat resistance.

(3) Good flatness. SMT requires the use of boards with the smallest possible curvature and warpage of less than 0.0075 mm / mm.

(4) The coefficient of thermal expansion is low. Since the coefficients of thermal expansion of X and Y do not match the thickness direction, the PCB is prone to deformation. In severe cases, the metalized holes will break and cause component damage.

(5) Electrical performance. For high-frequency circuits, it is necessary to select a material with a high dielectric constant and low dielectric loss. Insulation resistance, voltage strength, and arc resistance must meet product requirements. Knowing some of the board selection factors above, the author believes that choosing a board material can save a lot of effort

Factors to Consider When Choosing the Thickness

1. Sheet thickness:

The thickness depends on the project you want to build. The thinnest boards are widely used for the printed circuit boards they're designed for.

Thin PCBs reduce stress. Ideally, you'd need an FR4 thickness of nearly 1-3 inches.

2. Impedance Matching

In electrical and electronic equipment, impedance or frequency matching is very important for low or high-frequency printed circuit boards.

Paying more attention to these points will help your board get up and running safely. It can also tell you about the capacitance of a multifaceted board.

3. Flexibility

Thin boards are more flexible than thick boards. Most manufacturers use thin boards compared to thick boards because of their flexibility.

While using FR4, if the board you are using is very thin and your FR4 PCB has more area or dimensions, you will be at great risk.

• Thin FR4 PCB with the ability to reduce stress in electrical and electronic devices.
• Thin boards are more flexible and more susceptible to heat.
• It can be bent to any desired angle while soldering.

4 Compatibility with components

FR4 is useful for producing various kinds of printed circuit boards; thickness and spacing are used for devices or components FR4 PCB.

Similar to using the THT method, a thinner PCB design is required because the device is different from other devices.

How Is FR-4 Used in PCBs?

FR4 is the fundamental part of the printed circuit board which has a comprehensive lamination of the copper foil layers. FR4 pcb board manufacturers apply this lamination with the help of heat and adhesives.

During the FR4 PCB manufacturing process, the FR4 boards are laminated with copper layers at a specific temperature.

It is ideal for insulation as well as board supports without laminated copper and has a higher TG of around 180 ° C.

When to Avoid FR4 Material?

FR4 material is not the best thing if you want to build a product under the following requirement:

• Excellent temperature resistance. FR4 materials are not recommended for highly extreme temperatures.
• High-frequency signals. FR4 material cannot maintain accurate high-frequency signals.
• Lead-free soldering. During reflow soldering, the temperature can catch its peak which can be dangerous for the fr4 material.

Nextpcb's Standard FR-4 Material Properties

• Real Value according to the Nextpcb:
• High Glass Transition Temperature (Tg) (150Tg or 170Tg)
• High Decomposition Temperature (Td) (> 345º C)
• Low Coefficient of Thermal Expansion (CTE) ((2.5%-3.8%)
• Dielectric Constant (@1 GHz): 4.25-4.55
• Dissipation Factor (@ 1 GHz): 0.016
• UL rated (94V-0, CTI = 3 minimum)
• Compatible with standard and lead-free assembly.
• Laminate thickness available from 0.005” to 0.125”

Conclusion

Thin FR4 material is widely used in applications where space is always limited. These materials are known to provide better flexibility, so they are used to build complex and thin PCBs used in the medical and automotive industries.

 Choose a material that has a uniform dielectric constant at different frequencies, FR4 is suitable for this. Avoid using other thin PCB materials with grooves as this may result in a high risk of breaking or damaging the board.

With the same needs, FR4 is manufactured and available in a variety of sizes and configurations. Their favorable physical and chemical properties have contributed to their popularity.

If you plan to consider FR4 in your upcoming electronics application, it is always a good practice to consult with industry players who may provide technical assistance including material selection.

Why NextPCb for your future FR4 PCB order?

NextPCB delivers full turnkey service and on-time delivery with free shipping globally. Our PCB manufacturing capabilities can accelerate contemporary printed circuit board requirements that include major industries like military, medical, security, automotive, and power.