Most electrical engineers and those involved in printed circuit boards are familiar with FR4 materials. FR4 is the basic material for
most rigid circuit boards. However, many people don’t know what FR4 is,
let alone why it is the most popular PCB foundation.
FR4, also known as FR-4, is both a name and a grade. The name is applicable to glass fiber reinforced epoxy laminates used in printed
circuit board manufacturing. “Fr” means the material is flame retardant,
“4” means glass fiber reinforced epoxy resin. However, the name is also
used as a rating for epoxy laminates. The name essentially indicates
the basic quality of the laminate, indicating that all kinds of plates
and designs are lower than FR4 grade. “Fr” in the name stands for flame
retardant, while 4 is different from similar materials.
The material widely known as FR4 is a composite structure. The most basic layer of the material is glass fiber woven into a thin cloth.
Glass fiber endows FR4 with necessary structural stability. Then, the
innermost glass fiber layer is surrounded by flame retardant epoxy resin
and bonded. In addition to other physical properties, the resin gives
the material rigidity.
