Composite Ratio
The percentage of the total laminate volume occupied by glass fibers determines the mechanical strength and thermal expansion characteristics of a printed circuit substrate. Glass volume fraction controls the balance between the resin properties and the reinforcement properties within the cured dielectric. A higher ratio typically leads to a lower coefficient of thermal expansion and higher stiffness.
Structural Property
Designers select specific weave styles like 1080 or 7628 to achieve the target glass volume fraction for a given layer thickness. Because glass is much more dimensionally stable than epoxy, it restricts the movement of the resin during heating. Inconsistent distribution of these fibers can lead to localized warping or drill deflection.
The dielectric constant of the finished board depends on the relative amounts of glass and resin present in the stackup. Since glass has a higher dielectric constant than most resins, the glass volume fraction directly influences the signal propagation speed. Fabricators monitor this ratio to ensure that impedance-controlled traces meet the signal integrity requirements of high-speed designs.
Electrical Performance
Accurate control of the material composition is necessary for high-frequency circuit performance. If the glass volume fraction deviates from the specification, the impedance of the signal lines will shift. This parameter is a fundamental property of the base laminate material.
