Less-often encountered materials:
FR-1, like FR-2, typically specified to 105 °C, some grades rated to 130 °C. Room-temperature punchable. Similar to cardboard. Poor moisture resistance. Low arc resistance.
FR-3, cotton paper impregnated with epoxy. Typically rated to 105 °C.
FR-5, woven fiberglass and epoxy, high strength at higher temperatures, typically specified to 170 °C.
FR-6, matte glass and polyester
G-10, woven glass and epoxy - high insulation resistance, low moisture absorption, very high bond strength. Typically rated to 130 °C.
G-11, woven glass and epoxy - high resistance to solvents, high flexural strength retention at high temperatures. Typically rated to 170 °C.
CEM-1, cotton paper and epoxy
CEM-2, cotton paper and epoxy
CEM-3, non-woven glass and epoxy
CEM-4, woven glass and epoxy
CEM-5, woven glass and polyester
PTFE, ("Teflon") - expensive, low dielectric loss, for high frequency applications, very low moisture absorption (0.01%), mechanically soft. Difficult to laminate, rarely used in multilayer applications.
PTFE, ceramic filled - expensive, low dielectric loss, for high frequency applications. Varying ceramics/PTFE ratio allows adjusting dielectric constant and thermal expansion.
Alumina, a ceramic. Hard, brittle, very expensive, very high performance, good thermal conductivity.
Polyimide, a high-temperature polymer. Expensive, high-performance. Higher water absorption (0.4%). Can be used from cryogenic temperatures to over 260 °C.
Copper thickness of PCBs can be specified directly or as the weight of copper per area (in ounce per square foot) which is easier to measure. One ounce per square foot is 1.344 mils or 34 micrometers thickness. Heavy copper is a layer exceeding three ounces of copper per ft2, or approximately 0.0042 inches (4.2 mils, 105 μm) thick. Heavy copper layers are used for high current or to help dissipate heat.
On the common FR-4 substrates, 1 oz copper per ft2 (35 µm) is the most common thickness; 2 oz (70 µm) and 0.5 oz (18 µm) thickness is often an option. Less common are 12 and 105 µm, 9 µm is sometimes available on some substrates. Flexible substrates typically have thinner metalization. Metal-core boards for high power devices commonly use thicker copper; 35 µm is usual but also 140 and 400 µm can be encountered.