Speaking of PCB materials, we have to explain the most important one material in PCB- glass fiber. Glass fiber has some special properties, such as:

High Strength: compared with other textile fibers, the glass has a very high strength. In some applications, the strength / weight ratio even exceeds the iron wire.
Heat resistance and fire: glass fiber is inorganic, it will not burn.
Chemical resistance: can resistant most chemicals, can not be penetrated by the mold、bacteria，and insects’attack.
Moisture resistance: glass does not absorb water, even in very humid environment, still maintain its mechanical strength.
Thermal properties: glass fiber has a very low boil linear expansion coefficient, and high thermal conductivity, so it has excellent performance in high temperature environment.
Electrical Performance: Because non-conductive of glass fiber, it is a good choice of insulating material.

The E-grade glass that PCB substrate used , the most important is its very good water resistance. So in a very humid, harsh environment, still maintain a very good electrical and physical properties, such as dimensional stability.

The FR-4 is defined by the NEMA specification: LI1-1983, which refers to a burned sample of fiberglass epoxy, the size is 5 inches long and 0.5 inches wide, informal thickness non-copper substrate is determined by a specific Bunsen burner, the samples were ignited with an incline of 45 degrees, and the plates were then extinguished with the addition of a flame retardant (such as 20% bromine),and use code table to write down the number of seconds from the fire after the “burn” . After ten times burned, the total burned seconds is less than 50 seconds called V-0, less than 250 seconds who called V-1. Where in line with V-1 of glass fiber epoxy sheet, all called as FR-4.

In addition to the commonly used FR-4 material, there are other high-function high-Tg resins, such as BT, Polymide, Cyanate Ester and PTFE, etc. However, FR-4 has the advantages of low cost, good adhesion, low hygroscopicity is not other resin can match, so most of the PCB are made of FR-4 copper foil substrate (Copper-clad Laminate), referred to as CCL, is PC board’s important body components. It consists of copper foil(skin), resin (meat), reinforcing material (bone), and other functional reinforcement additives (tissue).