This article will introduce the commonly used thickness of FR4 sheet and parameter classification like dielectric constant parameter, dielectric loss parameter and TG value parameter.
Commonly used thickness of FR4 sheet are: 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.8mm, 1.0mm, 1.2mm, 1.5mm, 1.6mm, 1.8mm, 2.0mm. Thickness error of FR4 sheet depends on the production capacity of the factory.
Classification: dielectric constant parameter, dielectric loss parameter, TG value parameter. The dielectric constant (Dk,ε, Er) determines the speed at which an electrical signal travels through the medium. The speed of an electrical signal is inversely proportional to the square root of the dielectric constant. The lower the dielectric constant, the faster the signal is transmitted. Let's say you're running on the beach, and the water is up to your ankles, and the viscosity of the water is the permittivity. The more viscous the water, the higher the permittivity.
Permittivity is not very easy to measure or define. It is related not only to the properties of the medium itself, but also to the test method, test frequency, the state of the material before and during testing. The permittivity also varies with temperature, which is taken into account in the development of some special materials. Humidity is also an important factor affecting the permittivity, because the permittivity of water is 70, very little water will cause significant changes.
Dielectric loss of FR4 sheet: Due to the hysteresis effect of dielectric conductance and dielectric polarization, the internal energy loss of insulating material under the action of electric field is also known as medium loss. Under the effect of alternating electric field, the complement δ of of the angle (power factor Angle Φ) between the voltage phasor and current phasor in the dielectric is called dielectric loss angle. The dielectric loss of FR4 sheet is generally 0.02, and the dielectric loss will increase with the increase of frequency.
TG value of FR4 sheet: also known as glass conversion temperature, generally 130℃, 140℃, 150℃, 170℃.