Dielectric Constant:
The relative dielectric constant of FR-4 material typically ranges from 4.2 to 4.7, with specific values varying with temperature and signal frequency.
Within a temperature range of 0 to 70°C, the maximum variation in dielectric constant can reach 20%, leading to a 10% change in line delay. The higher the temperature, the greater the delay.
The dielectric constant also decreases as the signal frequency increases. A classic value of 4.4 is commonly used for design purposes.
The dielectric constant determines the speed at which electrical signals propagate through the medium. The propagation speed of electrical signals is inversely proportional to the square root of the dielectric constant, meaning that the lower the dielectric constant, the faster the signal transmission.

Dielectric Loss:
The dielectric loss (also known as loss tangent or dissipation factor) of FR-4 material is typically around 0.02, with this value increasing with frequency.
The dielectric loss angle (the complementary angle of the phase angle between the current phasor and voltage phasor flowing within the dielectric) is also an important parameter for measuring dielectric loss.

Glass Transition Temperature (Tg Value):
The glass transition temperature (Tg value) of FR-4 material is typically 130°C, 140°C, 150°C, or 170°C, depending on the manufacturing process and material formulation.
The Tg value is an important indicator of a material's heat resistance, determining its stability and service life at high temperatures.

Board Thickness:
FR-4 material is available in a wide range of thicknesses, including 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.8mm, 1.0mm, 1.2mm, 1.5mm, 1.6mm, 1.8mm, 2.0mm, and other specifications both thicker and thinner.
The thickness tolerance of the board may vary depending on the manufacturing capabilities of the board factory.

Other Parameters:
FR-4 material also exhibits excellent flexural strength, peel strength, thermal shock resistance, flame retardancy, volume resistivity, surface resistivity, and other performance indicators.
The dimensional stability, maximum operating temperature, and warpage of FR-4 material are also important parameters for assessing its quality.