FR-4 is a NEMA grade designation for woven fiberglass cloth in a flame-retardant epoxy resin, the workhorse material of the PCB industry. Standard FR-4 has a glass transition temperature around 130 to 140 degrees C and a dielectric constant of roughly 3.8 to 4.6 at 1 GHz, depending on resin content, while high-Tg grades reach 170 degrees C or more for lead-free reflow and thick multilayers. Its losses climb at multi-gigahertz frequencies, which is the point where designers move to low-loss or PTFE laminates.
It's a four-layer, 1.6 mm, plain FR-4, nothing exotic, quote it on your cheapest standard stackup.
High-Tg FR-4 on a fab note usually means a Tg of 170 degrees C or more, chosen so thick boards survive lead-free reflow.
Also heard as
- FR4
- glass-epoxy
Related terms
Laminate
Sheet of reinforced resin, usually clad with copper foil, that rigid printed circuit boards are built from.
Tg
Glass transition temperature: the point where a board's resin turns from rigid to rubbery and expands much faster.
Dk
Dielectric constant: how much a board material slows signals and sets trace impedance, relative to vacuum.
Rogers
Shop shorthand for high-frequency PTFE or ceramic-filled laminate, from the name of a major RF materials maker.