what is FR4 PCB?

The structural stability of fiberglass makes it an ideal material for printed circuit boards. Its flame-resistant epoxy resin layer provides the necessary strength and durability to endure the elements. These boards are commonly used by electronic contract manufacturers.

The term flame retardant, FR4, refers to a type of fiberglass-reinforced material that is commonly used in various applications. This type of material looks like a woven cloth sheet, but it has a different grade.

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Why you need the FR4 PCB?

The FR4 material is a light green color that can be used for various applications. It doesn’t absorb water, which makes it ideal for marine applications. It also has good electric loss properties and is moisture-resistant.

The high strength-to-weight ratio and lightweight nature of FR4 make it ideal for various applications. Its electrical insulation properties are also attributed to its high dielectric strength.

FR4s are a common choice for the fabrication of small batches of PCBs or for electrical prototyping due to their low cost.

How arrange the fr4 material in the PCB fabrication?

Any PCB’s foundation is made of FR4. Copper foil layers are bonded onto the material. Both heat and glue are used in this lamination. The material may be laminated from one or both sides using the copper foil.

What condition you shouldn’t use FR4 in PCB?

1.When environment with hi-frequency signal, you shouldn’t use FR4 pcb. FR4 boards are unable to keep their impedance constant when subjected to high-frequency signals. As a result, variations take place, which may compromise the signal integrity.

2. when PCB manufacturing use lead-free soldering, you shouldn’t use fr4 in PCB. Lead-free soldering is required if your client requests a RoHS-compliant PCB. Due to its low-temperature resistance, FR4 material cannot endure lead-free soldering’s peak reflow temperatures, which can reach up to 250 degrees Celsius.

3. High temperature working environment. If the circuit board is intended to be utilized in high-temperature conditions, it is not advised to use FR4 material. For example, PCBs used in aircraft applications shouldn’t be made of FR4 material.

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What thickness of the FR4 material you should use in your PCB?

The designer or electrical engineer must specify the FR4 thickness when placing an order for a laminate board for a PCB project. Depending on whatever is most suitable for the environment, this is measured in inch-based units, such as the thousandth of an inch, thou, or millimeters. FR4 sheets can be any thickness, however they often range from ten thou to three inches depending on the project’s requirements.

Although board thickness might not appear to be a crucial element in a PCB’s design, it actually is. In order to determine the thickness of a board for design, numerous criteria are taken into account because board thickness impacts a number of the board’s functional characteristics. The following are some of them.

  • Light weight: The final PCB’s weight will naturally depend on the FR4 thickness. Although it may not be a concern in all applications, weight is frequently taken into account in consumer electronics. Lighter PCBs result in lighter goods, which can sometimes be more appealing to customers and cost less to transport.
  • Thinner better for compatibility.: The compatibility of components with a board can also be impacted by the thickness of the board. Many components only function with a narrow range of board thicknesses, much as edge connections. For some through-hole components, for instance, this is particularly true.
  • According design: Because of the restrictions thin boards have on PCB layouts, thin boards are not always ideal. Grooves and excessive size are not practically possible on thin FR4 boards without running the danger of breakage. However, thicker boards can do both. When comparing FR4 thickness alternatives, take this into consideration at all times.
  • The application: Boards that are thinner can flex to some extent. Flexibility is a unique quality that, depending on the situation, may be advantageous or disadvantageous. In various situations where the product is often pressured or bent, boards with greater flexibility are frequently preferred. Due to the continual stress and stretching that PCBs used in medical and automotive applications are frequently subjected to, users frequently choose flexible boards in these applications.
  • PCB Board Function: Each multi-layered board serves as a capacitor for the layers below it. Because the thickness of the PCB FR4 material impacts the thickness of the dielectric, which in turn affects the capacitance value, the thickness of this board is crucial. This is a particularly important consideration for some high-frequency PCB designs, such as RF and microwave ones. Getting the proper capacitance for each layer is vital in high-frequency designs because impedance matching is a crucial element for maintaining good board performance.
  • Connection design: An edge connection is necessary to link the two sides of a two-sided PCB design. Since PCB edge connections can only fit a specific range of PCB thicknesses, this might be a significant limiting factor for the PCB’s final size. To avoid slippage or PCB damage, a connector’s mating component must fit tightly against the side of the PCB. This is one of the main explanations for why selecting the materials for the circuit comes before designing the circuit.
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FR4 VS high-frequency laminates

FR4 is a material that is extensively applicable and well-liked for its affordability and relative mechanical and electrical stability. Although FR4 material has many advantages and is offered in a range of thicknesses and sizes, it isn’t always the greatest option, particularly for high-frequency applications like RF and microwave designs. A high-frequency laminate is preferable in these later situations. However, it’s simple to understand why FR4 is still so widely used today. We compare FR4 and high frequency material and list their feature as below:

Application Environment

Another consideration when deciding between a FR4 and a high-frequency laminate board is the operating environment for the circuit. This covers things like humidity and temperature in the environment. In both situations, high-frequency laminates are more heat- and moisture-resistant than FR4, which means the operational environment will have a far smaller influence on the circuit’s performance. If the PCB will function in harsh industrial or outdoor conditions, this is an important factor to take into account.

In summary, high-frequency laminates have a variety of physical properties, many of which are better than those of FR4. The relative greater cost of high-frequency laminates over FR4 is their main disadvantage, which is a big deal for cost-conscious designers. Therefore, the key consideration is whether the benefits of high-frequency laminates outweigh their costs.


Another aspect to take into account when deciding between a FR4 board and a high-frequency laminate for a PCB foundation is temperature performance. The thermal coefficient of dielectric constant is a reliable indicator of temperature performance. This figure represents the degree to which the dielectric constant of a substance varies with temperature:

Despite the fact that both appear to be tiny numbers, the outcomes they produce are very different. Due to the high coefficient of FR4, the Dk of a FR4 board may differ significantly throughout its surface. High-frequency laminates’ smaller coefficient, in contrast, denotes less temperature variance throughout the board’s surface. When developing boards for warmer conditions, it is crucial to keep this in mind.

Dk Stability

Another crucial consideration for many designs is stable impedance, which frequently translates into more predictable performance, particularly for bigger circuits or high-frequency designs. Again, FR4 and high-frequency laminates provide distinct outcomes in this region. A material must maintain a consistent Dk, or dielectric constant, throughout the material as its temperature varies in order to maintain stable impedance.

Due to its Dk value’s significant variation both within a single board and when the board’s temperature changes, FR4 is not a material that is suited for maintaining stable impedance in this respect. The Dk values of high-frequency laminates don’t vary as much and stay largely consistent throughout the course of a board as temperature changes.

DK value

The dielectric constant of a circuit board may occasionally be just as significant as any other property. Particularly in high-frequency circuits like RF or microwave designs, a circuit board’s dielectric constant affects the size of a circuit’s transmission lines. The circuit itself may be made smaller by using smaller transmission cables.

Therefore, a board material with a greater Dk value is the ideal option if a smaller circuit board size is desired. The dielectric constant (Dk) of FR4 is around 4.5, which is lower than the Dk of high-frequency materials, which typically ranges from 6.15 to 11. The size of the finished circuit board may be reduced by at least 25% by utilizing these high-value Dk materials.

Signal Loss

In many circumstances, signal loss is a crucial component of a PCB design, particularly in high-frequency settings where signal loss is a bigger issue. Since FR4 has a larger Df, or dissipation factor, than high-frequency laminates, it is not the best material for these designs. Accordingly, FR4 circuits will experience greater signal loss than a comparable circuit built on a high-frequency laminate.

While most high-frequency laminates have a Df of roughly 0.004, or one-fourth of FR4’s, FR4 has a Df of around 0.020. There is less total signal loss the lower the Df. The second problem is that when a signal’s frequency rises, greater signal loss is experienced since the Df of FR4 increases. High-frequency laminates have less loss at higher frequencies because they have more consistent Df properties.


Because of its comparatively inexpensive cost, FR4 material is a highly popular PCB basis. On the other hand, high-frequency laminates are significantly more expensive, which is a big disadvantage for designers and manufacturers that are worried about costs. This is the main criterion that businesses use to decide between high-frequency and FR4 laminates.

So how can an electrical engineer or PCB designer pick between FR4 and a high-frequency laminate in light of the facts provided above? The final PCB’s electrical and mechanical requirements must first be listed and compared, utilizing the most precise characteristics feasible. The designer must next compare FR4’s performance with a laminate made to handle high-frequency signals to see how well it will match these specifications. Industry data sheets make it simple to find more exact information for each of the aforementioned aspects.

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