Laminates --- FR-4 brief
FR-4 (or FR4) is a kind of material grade designation, which means that the resin material is flame resistant (self-extinguishing). FR-4 is a kind of material specifications, not a material name, but a material grade. "FR" stands for flame retardant, and denotes that safety of flammability of FR-4 is in compliance with the standard UL94V-0.

FR-4 glass epoxy is a popular and versatile high-pressure thermoset plastic laminate with good strength to weight ratios. With near zero water absorption, FR-4 is most commonly used as an electrical insulator possessing considerable mechanical strength. The material is also known to retain its high mechanical values and electrical insulating qualities in both dry and humid conditions. These attributes, along with good fabrication characteristics, lend utility to this grade for a wide variety of electrical and mechanical applications.

Laminates --- FR-4 Applied on printed circuit boards (PCBs)
FR-4 grade materials are generally used on the circuit board has many types, but most are based on the so-called four function (Tera-Function) composite material which is composed of woven fiberglass cloth with an epoxy resin binder that is flame resistant.

FR-4 is the primary insulating backbone upon which the vast majority of rigid printed circuit boards (PCBs) are produced. A thin layer of copper foil is laminated to one or both sides of an FR-4 glass epoxy panel. These are commonly referred to as copper clad laminates (CCL).

FR-4 copper-clad sheets are fabricated with circuitry interconnections etched into copper layers to produce printed circuit boards (PCBs). More sophisticated and complex FR-4 printed circuit boards (PCBs) are produced in multiple layers, also known as "multilayer circuitry".

Specifications of Laminates FR-4
When ordering a copper clad laminate board, the FR-4 thickness and the copper foil thickness must be specified separately.
FR-4 thickness is specified in thou or inches, and common thicknesses range from 10 thou (0.010 in, 254 μm) to 3 inches (76 mm).
Copper foil thickness is specified in units of ounces per square foot (oz/ft2), commonly referred to simply as ounce. Common thicknesses are 1 oz/ft2 (300 g/m2), 2 oz/ft2 (600 g/m2), and 3 oz/ft2 (900 g/m2). These work out to thicknesses of 34.1 μm (1.34 thou), 68.2 μm (2.68 thou), and 102.3 μm (4.02 thou), respectively. Some PCB manufacturers refer to 1 oz/ft2 copper foil as having a thickness of 35 μm (may also be referred to as 35 μ, 35 micron, or 35 mic).

1/0 - denotes 1 oz/ft2 copper one side, with no copper on the other side.
1/1 - denotes 1 oz/ft2 copper on both sides.
H/0 or H/H - denotes 0.5 oz/ft2 copper on one or both sides, respectively.
2/0 or 2/2 - denotes 2 oz/ft2 copper on one or both sides, respectively.

Due to the development needs of electronic product installation technology and PCB technology, the high Tg (Glass temperature) FR-4 products was born.