Why is FR4 more suitable for manufacturing PCB?

FR4 is a kind of epoxy fiberglass laminate. Its corresponding name under the IEC standard is EPGC202 (i.e., epoxy glass fiber cloth 202), which is made of electronic grade alkali-free glass fiber cloth impregnated with flame retardant epoxy and phenolic resin by hot pressing technology. The only difference between FR4 (EPGC202) and EPGC201 (the corresponding GB/T standard is 3240) is the flame retardancy. It can be simply considered that FR4, enhanced with flame retardancy, is an improved product for 3240. FR means flame retardant and 4 represents a category of reinforcing sheet added flame retardant. In short, FR4 is the grade code of flame retardant material. Besides FR4, flame retardant materials also include FR1, FR2, FR3 and FR5, with FR grade ranging from low to high.

The combustibility of materials (aka flame retardancy) refers to the properties of significantly retarding the spread of flame and it is used to classify the flame retardancy grade of materials. UL94 standard is the U.S. test method on the combustibility of materials, which means the specimen should be lighted by the flame required for a given time, then the flame is removed. On an ascending scale, the specimen falls into four categories in accordance with its burning degree, i.e., HB, V-2, V-1 to V-0. The flame retardant grade of FR-4 is V-0, the highest grade. Other types of epoxy laminates, including 3240 (EPGC201), G10 (EPGC203), and G11 (EPGC306), are classified as HB. The basal materials used for PCB must be flame retardant, which relates to the size stability of the PCB. FR4 PCB board is popular among the manufacturers is precisely because of its excellent comprehensive performance: high flame retardant grade, good dielectric properties, high mechanical strength, suitable strength-to-weight ratio, non-absorbent, low cost, many colors (yellow, green, black, and white, etc.). The characteristics mentioned above make it suitable for various environments.

PCB can be divided into the single-sided, double-sided, and multi-layered. HB sheet with low flame retardancy is mostly used for single-sided PCB boards of the simple electronic products, while V-0 sheet with high flame retardancy is mostly used for more complicated double-sided PCB boards and multi-layered ones.

FR4 is the most widely used basal sheet for manufacturing PCB, followed by FR1 and FR2. FR1 and FR2 are both phenolic paper based with temperature resistance levels of grade B (130℃) and grade A(105℃)respectively. However, FR1 and FR2 are not conducive to punching and are usually used for single-layer PCB. FR3 is epoxy paper based, generally not used for multi-layered PCBs. FR5 has better heat resistance than FR4, but much more expensive and less cost-effective than FR4. FR4 can be used to produce highly reliable PCBs ranging from the single-sided, double-sided to the multi-layered, which makes it easier for manufacturers’ cost management and quality control.