FR4 PCB: Why FR4 is Used for Most PCBs [2022 Updated]

This blog will tell you what FR4 is, and in the process of making the FR4 PCB boards, what aspects should be considered when choosing FR4, and why this PCB material is so widely used.

To find out more please see below:

Part 1: What is FR4 PCB?

To put it first, FR4 PCBs are printed circuit boards using FR4 laminates. Most PCBs are made of FR4 (Flame Retardant level 4).

FR4 is not the certain name of the material. It is rather the grade of the material. It refers to the fourth grade of retardant material. The composition of the material constitutes fibers of glass in the epoxy resin. This material has anti-flame properties. The composition of the material is according to the standard UL94V-0.

This grade of laminate material has high strength and performance. Moreover, it has a good ratio between strength and weight. As this material does not have any capability for absorption of water, it has good electrical insulating properties.

Below is the reason why the FR4 own great demand in the market:

First, we use this material as an insulating material for PCB, then by adding copper to it, we made it to use as a conducting sheet. It has a greater strength for resisting and the ability to absorb the moisture on the PCB sheet. Its maximum ambient temperature is 248°F to 266°F depending on its brand and its filler.

FR4 makes the PCB a small cost and good quality. The FR4 PCB material is basically the backbone of PCB devices.

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

Depending upon the design of PCBs copper forms on the circuits on both sides.

Now we are going to discuss different types of FR4 PCB.

Part 2: Types of FR4 PCB:

• Single-sided FR4 PCB
• Double-sided FR4 PCB
• Multilayer FR4 PCB
• Rigid FR4 PCB
• Flex-rigid FR4 PCB

Single-sided FR4 PCB:

The FR4 single-sided printed circuit boards are made of epoxy resin, having copper foil on one side, and its components are pasted on one side.

Talking to their size we generally have a length of 100mm, a width of 70mm, and a height of 1.5mm.

With time and the development of new technologies which include the hard process of production with new machinery, the product becomes more expensive, but single-sided PCBs are very advanced and affordable.

Double-sided FR4 PCB:

The FR4 single-side printed circuit boards also are made of epoxy resin PCB having copper foil on one side, but its components are pasted on two sides which gives the path of traces to cross each other.

These boards contain copper for conduction.

In double side FR4, PCB components are pasted on both sides of PCBs which gives the path of traces to cross each other.

Multilayer FR4 PCB

Multilayer PCBs have more than two layers. It contains three layers of material for conduction.

That is pasted in the center of the materials. The core material is laminated together under high pressure and high temperature to produce multilayer PCBs. Components are pasted on both sides of PCBs.

Rigid FR4 PCB

In this type of FR4 PCB, the core materials used are only Fr, so that is why this is called a rigid FR4 printed circuit board.

There are no other materials or impurities added to it it’s a pure circuit, which is why it is rigid for the whole PCB.

Rigid-flex FR4 PCB

In rigid-flex PCBs, the core material of the flex layers is polyimide, and that of the external rigid layers is FR4.

We used rigid-flex FR4 boards because they are more flexible and can fit in extremely small spaces.

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Part 3: Factors to Consider When Choosing FR4 PCB:

1. Thickness of Sheet:

Basically, the thickness depends on your project and what you want to make; the thinnest boards are widely used for printed circuit boards designed.

Thin PCBs reduce stress. Ideally, we require FR4 thickness almost from 1 to 3 inches.

2. Impedance matching

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

Paying more attention to those points would help the boards to derive and run safely.

It also can tell us about the capacitance in multi-sided boards.

3. Spacing

During the designing of FR4 printed circuit boards, space-saving is a very important factor.

For USB connectors and Bluetooth accessories, spacing is very important.

Mostly we used the thinnest boards for designing.

4. Flexibility

The thinner board is more flexible than the thicker one. Most manufacturers used thin boards as compared to thick ones due to their flexibility.

While using FR4, if the substrate used is very thin and the area or dimensions of FR4 PCB is more it would be a great risk.

In electrical and electronic devices thin FR4 PCBs have the ability to reduce stress.

Thin boards are more flexible and more vulnerable to heat.

During soldering, it can be bent to make a desirable angle.

5. Weight

Mostly FR4 PCB thickness decides its weight, for small or lighter products it would be lightweight and vice versa.

6. Thermal conduction:

Thermal conduction is a very important term to know when choosing FR4 PCB.

What’s more, it depends on the temperature.

For the temperature identification we should have to look at the thermal coefficient of the dielectric medium or dielectric constant, FR4 has excellent heat resistance, which is why it is very popular.

7. Compatibility with the Components:

FR4 is useful to produce different kinds of printed circuit boards and its thickness and spacing tell us about the devices or components to be used in FR4 PCB.

Like using THT types devices are different from other devices and thus this device requires a thinner PCB design.

We are going to discuss the properties of FR4 PCB and the material used in it.

Part4: Properties and Materials of FR4:

In the abbreviation of FR4, the FR stands for "flame retardant", which shows that the material used with the UL94-0 standard on plastic materials inflammability. The code 94-0 would be written on all the fr-4 PCBs, which shows the guarantee to protect the device from fire propagation during the burning of the material.

A good FR4 PCB has multiple layers of FR4 pasted between the two thin layers of the laminate copper plate because bromine is used for its manufacturing so it is also called a halogen element.

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

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

It is ideal for insulation as well as for board supports with no laminated copper, and it has a higher TG of around 180°c.