PCB FR Level

UL certification is the certification of FR level. At the beginning, the flammability standard was established by Underwriters Laboratories Inc. (UL) of the USA. UL 94 is the Standard for Safety of Flammability established by the UL according to the burning condition, burning duration, and burning stop time of the lighted DUT.
The classification of flammability from the lowest to the highest is as follows:

• HB：Slow burning on a horizontal specimen; burning rate < 75mm/min for thickness <3mm.
• V2：Burning stops within 30 seconds on a vertical specimen; drips of flaming particles are allowed.
• V1：Burning stops within 30 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed.
• V0：Burning stops within 10 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed.
• 5VB：Burning stops within 60 seconds on a vertical specimen; no drips allowed; plaque specimens may develop a hole.
• 5VA：Burning stops within 60 seconds on a vertical specimen; no drips allowed and plaque specimens also may not develop a hole.

Currently, FR4 is the most common FR level of PCB base materials. Referring to UL certification, FR4 must comply with V0 of UL94.