Substrate Permittivity Shifts during Lead-Free Reflow Soldering
Lead-free reflow shifts substrate permittivity by altering free volume and desorbing moisture, changing line impedance by up to 2.5 ohms on high-speed traces.
PTFE Glass Weave
Composite Laminate
Dielectric materials designed for high frequency radio frequency applications often combine the low-loss properties of fluoropolymers with the mechanical strength of fiberglass. The compound structure of ptfe glass weave relies on a woven fiberglass fabric saturated with polytetrafluoroethylene resin to create a dimensionally stable substrate. This combination offsets the high cold flow and poor dimensional stability of pure fluoropolymer, allowing for precise conductor layout and circuit fabrication.
It is used as a laminate for microwave boards and antennas that operate at millimeter-wave frequencies.
Signal Performance
Electrical performance in high frequency circuits is sensitive to the uniformity of the dielectric constant across the board. The presence of the ptfe glass weave keeps the dissipation factor extremely low, which minimizes signal loss in transmission lines. However, the difference in dielectric constant between the glass bundles and the surrounding resin can cause phase skew in high speed signals, meaning that critical lines must be routed carefully to avoid this effect.
Machining Challenge
Fabricating boards with these materials requires specialized drills and chemical treatments to ensure reliable plated through-holes. The softness of the resin combined with the hardness of the glass fibers makes it difficult to drill holes without causing fiber protrusion or smear. For this reason, special etchback steps are required before the copper plating process.