What is fr4 and what electrical characteristics does it have

FR4 material FR4 is a type of printed circuit board substrate made of flame retardant epoxy resin and glass cloth. FR stands for flame retardant and meets the requirements of UL94V-0. FR4 has good adhesion to copper foil and very low water absorption, making it ideal for standard applications. FR4 can be used both as copper plating material for 1- and 2-layer PCBs and as prepreg and core material for multi-layer PCBs.

 

The electrical properties of PCB materials are critical to signal integrity and impedance considerations. They specify how fast an electrical signal can propagate through the material and how much charge it can hold in a given volume. The following table lists some important electrical

gas characteristics and their typical values.

Insulation stability

While FR4 is a good insulator, it has its limitations when it comes to withstanding high power, voltage, or heat. If certain limits are exceeded, the materials' insulating properties become worse and they will begin to conduct electricity. This can cause circuit board failure

barrier.

Controllable impedance

FR4 does not provide uniform electrical constants like high-read plate materials. As frequency increases. DK will change. High-speed materials have a dielectric constant of less than 2%, while FR4 has a dielectric constant of up to 10%. Dk changes in FR4 present challenges while maintaining impedance values. Therefore, this material is not a first choice for controlled impedance panels

signal loss

Signal loss is an important aspect of PCB design, especially in high-frequency applications. FR4 is not the best material for these applications because it has a larger Df (dissipation factor) than high frequency materials.

The Df of FR4 is about 0.020, while the Df of most high-frequency laminates is about 0.004, which is one-quarter of the Df of FR4. The smaller the Df, the smaller the overall signal loss. Another disadvantage is that the Df of FR4 increases as the signal frequency increases

And increase. As a result, these PCBs suffer from higher signal losses than boards built using high frequency laminates, the graph above plots frequency versus loss per inch (dB) for FR4 and Rogers RO4350B (high speed material)

Relationship. It clearly depicts that FR4 materials suffer greater losses at high frequencies.

 

temperature stability

FR4 materials are not recommended for use in devices exposed to high temperatures. Additionally, these materials do not support lead-free hard joints. This is because the reflow temperature of shipless PB assemblies can reach as high as 250°C, which is significantly higher than many FR4 versions.

Ben’s Tg.