FR4 is a printed circuit board based on glass-reinforced epoxy laminate material. It is one of the most used material because it is low-cost in comparison with other materials and it can be utilized in many applications.
FR4 Types
You can discover different FR4 boards:
Single layer boards, with only copper in the top of the substrate or double layer, with 2 copper layers, one on each side.
With different substrate density. It can be discovered thickness from 0.1 mm approximately 3.2 mm. The required density will depend on the application it will be used. Typical thinner densities are used in multilayer boards in which the FR4 board is utilized to disperse signals to other boards, in order to not increase the thickness of the PCB. Higher thicknesses are utilized when high robustness of the PCB is needed due to the fact that a large PCB is developed.
With different copper layer density. Typical copper densities are 17, 35 or 70 um.
Various panel sizes can be bought, the usage of one or another will depend upon the equipment the maker has and depending on the final size of the asked for PCBs. Typical panel sizes are 12x18 inches, 18x24 inches, and 21x29 inches. When you are developing a panel, you need to consider that not all the panel can be utilized to draw your PCBs. Around 2 inches length and 2 inches width will be used for other functions, like fiducial holes and other manufacturer tasks and likewise avoid the panel can bend if work is carried out near to the borders.
FR4 Properties
It has a dielectric loss tangent of around 0.017 to 0.025 while, for example, Rogers laminates have normal worths of 0.002 and alumina PCBs have worths of around 0.0002. The dielectric loss tangent indicates the insertion losses of the material with the frequency. As can be seen, FR4 has greater values and this is the factor it can be used only for low-frequency applications. Due to the fact that at high frequencies, the insertion losses of the lines are higher, in comparison with other, more costly, choices.
Another important parameter is the dielectric constant. The normal worth is around 4.6. This value is somewhat based on the maker and also the density of the substrate, but it is a worth that typically supplies excellent results when calculations are carried out from it. From this criterion, the relation impedance/thickness of the line can be gotten. This is extremely helpful when designing RF and digital circuits.
It is flame resistant.
It has hardly absolutely no water absorption
It has a very high dielectric breakdown, higher than 60KV. This suggests a very high voltage is required to alter the properties of the material
It preserves its mechanical and electrical properties in different ecological conditions as dry or wet.
Common temperature read more levels in which FR4 can work is from -55 to +125 ºC.
There are improved FR4 variations that supply other characteristics such as lower dielectric values or greater temperature level ranges. These boards are not requirements and not all the suppliers will offer them.
FR4 Uses
FR4 is utilized around the world for various applications, commercial, civil, automotive or even military applications.
It is used for DC, digital and low-frequency RF applications.
Practically the total of DC boards are finished with FR4 considering that it is the cheapest material, with really excellent performance and since it is the material all the manufacturers have the possibility to utilize.
FR4 is a very good alternative for digital applications, in which, FPGA, microcontrollers, ADCs, DCAs, buses, etc are used.
FR4 boards can be utilized for low-frequency applications. As much as 1-2 GHz the homes of this material can be compared with other more costly alternatives like Rogers laminates or alumina. From MHz approximately 1 GHz the outcomes will be slightly worse but the difference in rate can assist to decide for the FR4 choice. From 2 GHz the distinctions are greater and typically other materials are chosen. With FR4 and the matching parts, a wide catalog of RF circuits can be correctly created and produced as amplifiers, switches, attenuators, and so on.
The FR4 option on the PCB order page is the grade classification for the epoxy fiberglass that often forms the PCB core and prepreg layers. In a common PCB, the core supplies the rigidity and the structure on which the PCB traces can be 'printed' onto. For double layer boards, an FR4 core separates the top and bottom copper layers whereas, in multilayer PCBs, extra layers of FR4 prepreg are sandwiched between the inner core and the external copper layers. Common thinner densities are utilized in multilayer boards in which the FR4 board is used to disperse signals to other boards, in order to not increase the thickness of the PCB. Greater densities are used when high effectiveness of the PCB is required because a large PCB is developed.