Everything You Need to Know about FR4 PCBs
Printed circuit boards use a variety of different materials for the substrate; metal cores, ceramic, PTFE, FR4, and polyimide are the most well known, reliable, and effective materials. However, when it comes to FR4, the circuit stands out because it has many advantages. FR4 is a unique material that consists of woven fiberglass mixed with an epoxy resin which acts like a binder and is a flame retardant (hence the name FR).
FR4 is a self-extinguishing material and was invented in 1968. Since then it has gained tremendous popularity for being a plastic laminate grade; it makes use of Bromine to activate the fire resistant properties. Nowadays, it is used to produce rigid and high density printed circuit boards.
FR4 PCB incorporates a thin sheet of copper, often laminated to an epoxy glass panel. The lamination is applied either on a single side or both sides of the panel. Hence, these panels are also known as ‘copper-clad laminates’. To manufacture a PCB, the copper-clad sheets are made with various circuit interconnections, which have been embedded into the copper layers. More advanced and sophisticated versions of Multilayered PCBs are also produced. This is called a ‘multilayer circuitry’.
Their Specifications
FR4 PCBs come in different sizes; hence, it is very important to specify the thickness of the copper foil and the FR4. The thickness is usually measured in inches or thou, with the most commonly used thicknesses ranging from 10 thou (254 micrometers, 0.010 in) to 3000 thou (3 inches, 76 mm).
The thickness of the copper foil is specified in ounces per square foot and the general thicknesses are 1, 2, and 3 ounce per square foot, which correspond to thicknesses of 1.34 thou, 2.68 thou, and 4.02 thou. A few manufacturers claim that their 1 ounce per square foot thickness of copper foil is equal to about 35 micrometers.
- 1/0: 1 ounce per square foot contains copper on only a single side
- 1/1: It means that 1 ounce per square foot consists of copper on both the sides
- H/H or H/0: 0.5 ounce per square foot of copper on either a single side or on both sides
- 2/2 or 2.0: 2 ounce per square foot of copper on either a single side or on both sides
Benefits
FR4 is the most preferred material when it comes to PCB fabrication. This is because it has many advantages:
- An FR4 PCB has a low cost as compared to other types of substrates.
- FR4 laminates can allow you to achieve data rates of up to 6 Gbps; it depends on the routing dimensions and the width of the trace.
- FR4 is lead free, which proves useful in high speed applications and in reduction of power costs.
- FR4 PCBs have good thermal-mechanical properties which are further being enhanced by layering the board with a hybrid and non-critical stack-up.
- The dissipation factor of an FR4 laminate is much better than its counterparts.
- Overall, FR4 PCBs have a high dielectric strength, they are lightweight, and they possess an excellent strength to weight ratio.
- It has a very low moisture absorption rate and a good mechanical strength. Hence, it has the ability to retain its insulating properties in humid weather.