FR4 is a printed circuit board based upon glass-reinforced epoxy laminate material. It is one of the most used material because it is cheap in contrast with other materials and it can be used in lots of applications.
FR4 Types
You can discover various FR4 boards:
Single layer boards, with just copper in the top of the substrate or double layer, with 2 copper layers, one on each side.
With different substrate thickness. It can be found thickness from 0.1 mm up to 3.2 mm. The required thickness will depend on the application it will be used. Common thinner thicknesses are used in multilayer boards in which the FR4 board is used to distribute signals to other boards, in order to not increase the thickness of the PCB. Greater densities are utilized when high toughness of the PCB is needed since a big PCB is developed.
With various copper layer density. Normal copper densities are 17, 35 or 70 um.
Various panel sizes can be purchased, the usage of one or another will depend upon the devices the maker has and depending upon the last size of the asked for PCBs. Normal panel sizes are 12x18 inches, 18x24 inches, and 21x29 inches. When you are creating a panel, you need to think about that not all the panel can be utilized to draw your PCBs. Around 2 inches length and 2 inches width will be utilized for other functions, like fiducial holes and other maker jobs and likewise prevent the panel can flex 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 common values of 0.002 and alumina PCBs have values of around 0.0002. The dielectric loss tangent suggests the insertion losses of the material with the frequency. As can be seen, FR4 has higher values and this is the reason it can be used only for low-frequency applications. Because at high frequencies, the insertion losses of the lines are greater, in contrast with other, more pricey, alternatives.
Another crucial parameter is the dielectric constant. The common value is around 4.6. This value is slightly reliant on the maker and likewise the thickness of the substrate, but it is a worth that typically offers excellent results when computations are carried out from it. From this parameter, the relation impedance/thickness of the line can be obtained. When designing RF and digital circuits, this is extremely helpful.
It is flame resistant.
It has hardly no water absorption
It has an extremely high dielectric breakdown, higher than 60KV. This implies a very high voltage is required to change the residential or commercial properties of the material
It keeps its mechanical and electrical properties in different environmental conditions as dry or wet.
Normal temperature levels in which FR4 can work is from -55 to +125 ºC.
There are improved FR4 versions that provide other characteristics such as lower dielectric values or higher temperature level varieties. These boards are not requirements and not all the vendors will provide them.
FR4 Uses
FR4 is used worldwide for different applications, industrial, civil, automobile or even military applications.
It is used for DC, low-frequency and digital RF applications.
Almost the overall of DC boards are done with FR4 since it is the cheapest material, with great efficiency and since it is the material all the manufacturers have the possibility to use.
FR4 is an excellent choice for digital applications, in which, FPGA, microcontrollers, ADCs, DCAs, buses, etc are used.
FR4 boards can be used for low-frequency applications. Up to 1-2 GHz the homes of this material can be compared to other more pricey alternatives like Rogers laminates or alumina. From MHz approximately 1 GHz the outcomes will be somewhat worse but the distinction in rate can assist to choose for the FR4 choice. From 2 GHz the differences are higher and normally other materials are picked. With FR4 and the matching elements, a wide brochure of RF circuits can be properly designed and fabricated as amplifiers, switches, attenuators, etc.
The FR4 option on the PCB order page is the grade classification for the epoxy fiberglass that frequently forms the PCB core and prepreg layers. In a normal PCB, the core provides the rigidity and the foundation on which the PCB traces can be 'printed' onto. For double layer boards, an FR4 core separates the bottom and leading copper layers whereas, in multilayer PCBs, extra layers of FR4 prepreg are sandwiched between the outer copper and the inner core layers. Typical thinner thicknesses are used 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. Higher densities are utilized when high effectiveness of the PCB is needed due to the fact that get more info a large PCB is designed.