FR-4, is a widely acceptable international grade desination for fiberglass reinforced epoxy laminated that are flame retardant (self extinguishing). After add copper layer on one or each side FR4, it become to Copper Clad Laminate (CCL), and this is the non-conductive core materail for normal printed cricuit board (PCB). Printed circuit board using FR4 as core material will be named as "FR4 PCB".

PCB is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper clad laminate substrate. Sometimes, PCB also named Printed Wiring Board (PWB) or etching wiring board if no extra electronic components was added on.

FR4 copper clad is short for fiberglass epoxy resin copper clad, it’s divided into the following levels：

FR-4 A1 level CCL: This level of CCL is mainly used in military, communications, computers, digital circuits, industrial instrumentation, automotive circuits and other electronic products.

This level of CCL widely used, the technical performance indicators to meet the needs of all the electronic products.

This level of product quality and fully meet world-class level, the highest level, the best performance of the product.

FR-4 A2 level CCL: This level of CCL is mainly used ordinary computer, instrumentation, advanced home appliances and electronic products in general. This grade series CCL widely used, the performance index can meet the general needs of industrial electronic products. A very good price-performance ratio, enabling customers to effectively improve their competitiveness.

FR-4 A3 level CCL: This level CCL is mainly used household appliances, computer peripheral products and general electronic products (such as toys, calculators, games, etc.) development and production of FR-4 product. It is characterized by its performance to meet the requirements of the premise, highly competitive prices.

FR-4 (or FR4) is a grade designation assigned to glass-reinforced epoxy laminate sheets, tubes, rods and printed circuit boards (PCB). FR-4 is a composite material composed of woven fiberglass cloth with an epoxy resin binder that is flame resistant (self-extinguishing).

"FR" stands for flame retardant, and denotes that safety of flammability of FR-4 is in compliance with the standard UL94V-0. FR-4 was created from the constituent materials (epoxy resin, woven glass fabric reinforcement, brominated flame retardant, etc.) by NEMA in 1968.

FR-4 glass epoxy is a popular and versatile high-pressure thermoset plastic laminate grade 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 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.