A Flame retardant (Fr) is a type of PCB made using a specific material which, like the name suggests, is a material that is resistant to hot temperatures and flames. One of the many components that go into making a PCB is FR material or flame-resistant material. They offer up to four variations, from FR1 PCB to FR4, which is interesting. However, understanding the distinctions between these options and figuring out which ones will benefit you the most can take time and effort. Fortunately, this article will explain the variations between different FR materials and their applications for them.

A Brief Introduction To PCB

A PCB is an integral part of microelectronics. It is the base used in electronic circuits to support wires and other components. A printed circuit board (PCB) is a copper-laminated, non-conductive board on which all electrical and electronic parts are attached, and the board’s base physically supports it. We cannot build a big circuit like a motherboard using this method because, without a PCB, all of the components are connected by wire, which adds complexity and lowers circuit stability. It will reduce the complexity of the overall circuit design because all components on a PCB are internally connected and connected without wires. Electricity and connectivity between the components are provided by PCB, allowing it to operate as intended. PCBs can be customized to meet any user requirements or specs. With regards to applications, you can find them in various electronics, including TVs, smartphones, digital cameras, and computer components like graphics cards and motherboards. Several other industries also use it, including lighting, industrial machinery, automotive, and medical devices.

What are Fr1, Fr2, Fr3 and Fr4 PCBs?

Most manufacturers employ FR1 PCB layers for single-sided boards, which are paper substrates. It is an eco-friendly substrate that complies with the requirements of the ROHS legislation. Additionally, it has an excellent flame retardant rating. Many manufacturers create films suitable for PC boards, power supplies, insulating industrial equipment, and buttons using FR1 PCB substrates. Additionally, it is simple to process, mold, fold, and bend. Similar to FR1 PCB, FR2 almost shares the same characteristics. However, its TG is lower at 105°C than the FR1’s, which is 130°C. FR1 PCB laminate producers typically do not produce FR2 laminates. Why? since the prices and uses of both materials are comparable. There is no need for both, therefore.

On the other hand, FR3 is comparable to FR2. But instead of the phenolic resin used in FR2, it employs epoxy resin. FR1, FR2, and FR3 materials work best in single-layered setups. Applying epoxy glue to the PCB is simpler using FR3, and the paper substrate is advantageous. Although one can employ these materials to create multi layer boards, we don’t suggest them.

On the other hand, FR3 is comparable to FR2. But instead of the phenolic resin used in FR2, it employs epoxy resin. FR1, FR2, and FR3 materials work best in single-layered setups. Applying epoxy glue to the PCB is simpler using FR3, and the paper substrate is advantageous. And while all FR materials have characteristics that set them apart. The commonalities between FR1-3 substrates are more significant, whereas FR4 is entirely distinct.

Let’s analyze these variations in the various categories in more detail:

1. The most used PCB material

FR4 is the most widely used PCB material among manufacturers and designers. Additionally, it is the ideal material for making PCBs. Plus, using through holes on FR4 is simpler than difficult-to-drill FR1, FR2, and FR3. The manufacturers can use FR4 to design any PCB layer. Further, FR4 is used by many manufacturers because it can handle applications requiring continual or constant flexing. Various gadgets like USB ports and Bluetooth accessories rely on the FR4 substance.

• Resistance to elevated temperatures

Another characteristic that sets FR1 PCB, FR2, FR3, and FR4 PCB materials apart is their heat resistance. Comparing FR4 to other FR materials, it is the most heat resistant. Extreme temperature operation, the development of applications requiring high thermal loads, or the use of components producing heat exceeding 130 degrees Celsius are all possible with FR4 PCBs.

• Composition of materials

As we just discussed, there are several similarities between FR3 and FR2. However, what distinguishes them is the types of materials they employ. Additionally, FR1 PCB and FR2 share the same raw ingredients. However, FR4 is distinct and uses a glass fiber epoxy laminate.

Let’s deeply examine these resources.

• Phenolic resin (Fr2)

For your FR2 PCB, you can choose between the novalocs and resoles phenolic resin kinds. These kinds are suitable for various uses, such as coating, circuit boards, and adhesives. Additionally, it is reasonably priced and moisture resistant, making it appropriate for locations that need frequent cleaning.

• Epoxy resin (Fr3)

Reactive epoxides like epoxy resins fall into two categories: pre-polymers and polymers. They can produce crosslinks through interactions with co-reactants such as alcohols, thiols, phenols, acids, and amines. These co-reactants are referred to as cures or hardeners. In addition, various compounds, such as imidazoles and anhydrides, can be used to cure epoxy resins. Additionally, the epoxy resin needs to heal to have excellent chemical, mechanical, and thermal resistance. It is also an exothermic reaction that needs careful management. The resin’s thermal characteristics will be compromised otherwise.

• (Fr4) Glass Fiber Epoxy Resin

Glass epoxy, a laminate-grade material with good strength-to-weight ratios, is used in FR4. It can maintain its strong mechanical and electrical insulating characteristics in humid and dry situations. Bromine is a component in glass epoxy resins that helps to produce flame-resistant features. These qualities make this material ideal for various mechanical and electrical applications, along with an excellent fabrication characteristic. The resistance, thermal characteristics, and electrical strength of a material depend on its composition.

• Cost

The price of PCB materials might range from 10% to 100%. It is a component that has an impact on PCB production. Since they use similar materials and have comparable pricing, FR1 PCB and FR2 materials are identical, as we previously indicated. Due to the usage of epoxy resin, FR3 PCBs are more expensive than FR2 PCBs. Additionally, it offers excellent heat resistance and durability and is better suited for heavy-duty applications. FR4 materials cost a little more than FR3 and FR2 equivalents. However, manufacturers can only employ FR4 to create several PCB kinds, which also helps to lower costs over time.

• Mounting technology

Surface Mount Technology (SMT) and Through Hole Mounting are the two mounting methods used to add electrical components on FR1, FR2, FR3, and FR4 PCBs (THM). Through-hole technology is usable on FR1, FR2, and FR3 boards, but the results will not be optimal. Why? These PCBs performed better when surface mounted. Contrarily, drilling through FR4 PCBs to add components is safe because through-hole will not degrade their performance.

• Choosing between single and multilayer boards

For multilayer boards, some materials are ideal, while others are not. Note that PCBs with three or more layers are multilayer PCBs and these Printed circuit boards can even contain 32 layers. While multilayer PCBs have been produced using all FR1 PCB, FR2, and FR3 materials, FR4 is among the most popular. Since FR4 material is excellent for creating several PCBs, many designers like it. Some materials (like FR2 and FR3) could be less expensive than FR4 materials, but many designers still prefer FR4. Sifted through, FR1, FR2, and FR3 multilayer PCBs lack stability and dependability. For this reason, choosing FR4 materials is an excellent idea. Overall, another aspect that distinguishes FR1, FR2, FR3, and FR4 materials frequently used in PCB production is their suitability for multilayer PCBs.

• Suitable material for through-hole technology

Many electrical components use the through-hole mounting technique, often known as thru-hole technology. Leads must be inserted into the holes drilled in the printed circuit board when employing through-hole technology. After that, the components must be soldered to pads on the other side. It can be done manually or with the use of specialized tools. Most designers have attempted to pass FR1, FR2, and FR3 through thru-holes, but the outcomes have yet to be outstanding. It makes PCBs made of FR4 perfect for having through-holes put into them. Again, FR1, FR2, FR3, and FR4 materials differ in that they are suited for through-hole technology.

• Compatibility to high voltage

Due to their single-layer construction, FR1, FR2, and FR3 PCBs are vulnerable to harm from high-voltage components. Additionally, they may quickly burn single-layered PCBs and produce much power. It would help if you always used FR4 when working with such components. Better insulating qualities make FR4 ideal for multilayered PCBs.

Conclusion

Depending on your use, you can choose the finest fire-resistant material for your board. FR4 is, without a doubt, the best material for handling anything you throw at it. However, some applications can call for the more fundamental FR1 PCB, FR2, or FR3. They will need to deliver consistent and dependable results. They are ideal for introductory single-layered courses, nevertheless. For more complex circuits that call for high-temperature or voltage components, FR4 is your best bet. Would you like to construct an FR material PCB? If so, then you already know at your disposal. So let’s get started.