PCB substrate flame resistance is classified into multiple ratings. The primary common grades from highest to lowest performance are V‑0, V‑1, V‑2 and HB. Additional classifications include 5VA / 5VB for demanding high‑end applications, as well as the VTM series designated for flexible circuit boards.

1. UL94 V‑0: The Widely Adopted Top Flame Retardant Standard for Industry

V‑0 is the most extensively used and recognized flame rating within the electronics industry, and it sets the minimum compliance threshold for most certified formal electronic products.

Its key safety advantage is no flaming molten drips. When the board catches fire, no burning fragments are released, and drips cannot ignite cotton material underneath. This effectively stops flame propagation and prevents secondary fire hazards.

Common mainstream substrates including FR‑4, FR‑5 fiberglass epoxy laminates, alongside CEM‑1 and CEM‑3 composite materials, achieve V‑0 rating by default. Thanks to outstanding heat resistance, flame retardancy and insulation, V‑0 PCBs are widely deployed in safety‑critical applications: switching power supplies, industrial controllers, lithium battery equipment, medical instruments, automotive electronics and new energy charging piles. This rating is also a mandatory requirement for China 3C certification and export certifications for European and American markets.

All PCBs manufactured by Jiangsu Zhongxinhua Electronics Co., Ltd. use grade‑A substrate materials that fully meet UL94 V‑0 flame resistance requirements.

2. UL94 V‑1: Mid‑Range Cost‑Effective Flame Retardant Grade

V‑1 is also a vertical flame classification. Molten drips are permitted during combustion, yet these drips carry insufficient heat and flame energy to ignite underlying cotton material, preventing fire spread.

Typical substrates for V‑1 rated PCBs are flame‑retardant phenolic paper laminates FR‑1 and FR‑2. These materials are low‑cost and easy to process, yet inferior to FR‑4 in thermal endurance, mechanical strength and insulation performance.

V‑1 boards are limited to low‑power, low‑heat, low‑voltage simple electronics such as basic calculators, small toys and entry‑level home appliances. They must not be used in high‑voltage, high‑power or continuously operated electronic devices.

3. UL94 V‑2: Basic Flame Retardant Grade (Use with Extreme Caution)

V‑2 shares identical burn duration parameters with V‑1. The critical safety drawback: flaming molten drips are allowed, and these drips can ignite nearby combustible materials.

This grade only meets minimum self‑extinguishing criteria and fails safety requirements for mainstream electronic products. It is only adopted for ultra‑low power circuits with no heat generation and no high voltage. Industrial and commercial products generally prohibit V‑2 substrates, and most safety standards do not accept materials of this rating.

4. UL94 HB: Lowest Flame Classification (Non‑Self‑Extinguishing Grade)

HB is the sole horizontal burning rating and the lowest flame resistance class for PCBs. It possesses no vertical self‑extinguishing capability and is not formally categorized as a flame‑retardant material.

It is only suitable for low‑end disposable electronics without safety specifications. HB substrates are banned for products requiring China 3C certification, powered heat‑generating equipment and commercial export goods.

5. Special High‑Performance Flame Retardant Ratings

Beyond the four standard grades, two special classifications exist in the industry:

5VA / 5VB: Ultra‑stringent flame ratings for high‑power high‑voltage hardware such as photovoltaic inverters and industrial UPS systems. 5VA does not allow substrate penetration during combustion, delivering maximum flame resistance; 5VB permits limited minor burn‑through.

VTM‑0 / VTM‑1 / VTM‑2: Formulated exclusively for flexible FPC circuits. Designed around the combustion characteristics of ultra‑thin flexible substrates, these grades are widely applied in foldable displays, wearables and other flexible electronics.