Typically fluoropolymer laminates have a main reinforcement of glass fibre, but this is normally random matte rather than woven fabric, in order to improve the consistency of dielectric performance. Most also contain ceramic fillers to modify the permittivity. Note that the permittivity of the base resin is low (of the order of 2.0), and the higher dielectric constant of the laminate is due to the combined effect of the reinforcement and fillers.
Compared with epoxy-glass laminates, fluoropolymers have:
By contrast, epoxy-glass thermoset systems have dielectric constants that vary with frequency, with a higher loss tangent, and tend to flow on pressing, leading to variations in dielectric thickness.
The reported severity of processing problems with fluoropolymer laminates depends on who is reporting! Certainly care has to be taken to avoid both mechanical scrubbing when cleaning and smearing during drilling (use sharp drills!), because the resin is comparatively soft. Also, hole walls have to be treated within a short interval before plating either using a plasma or special chemical process (such as a sodium naphthenate etch). Higher temperature processing is also required for pure PTFE laminates.
Fluoropolymer laminates are considerably more expensive than FR-4, typically 5-9 times more expensive. As regards quality and reliability issues:
On the positive side, fluoropolymer laminates have excellent resistance both to high temperature and to humidity.
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