UL certification plays a vital role in ensuring the safety, reliability, and market acceptance of printed circuit boards (PCBs), particularly in North America and other regulated markets.
As a globally recognized safety science organization, UL establishes strict standards.
These standards cover flammability, electrical insulation, mechanical strength, and the long-term performance of PCB materials and constructions.
For PCB manufacturers and OEMs alike, understanding UL standards, recognition types, and marking requirements is essential to achieving compliance, avoiding certification risks, and supporting downstream product approvals.
What Is UL?
UL (Underwriters Laboratories) is one of the most authoritative safety certification organizations in the United States and has evolved into a global safety science company.
UL certification indicates that UL has tested the product and confirmed that it meets specific safety standards.
For PCBs, UL certification mainly focuses on flammability rating of base materials, electrical insulation performance, mechanical strength, and long-term reliability.
Why Do PCBs Need UL Certification?
In many target markets—especially North America—end products such as power supplies, home appliances, and IT equipment must obtain UL certification.
To achieve this, manufacturers must produce the PCBs used inside these products using UL-recognized materials and processes.
In addition, major OEMs such as Apple, Dell, and HP often treat UL certification as a mandatory supplier qualification requirement.
UL certification helps ensure that PCBs will not cause safety hazards such as overheating, fire, or electric shock during operation, which could lead to system failure or accidents.
The UL mark is also an internationally recognized symbol of product safety, significantly enhancing customer confidence.
Key UL Concepts Related to PCBs
The core UL standards for PCBs are UL 94 (Flammability of Plastic Materials) and UL 796 (Printed-Wiring Boards).
UL 94 defines common flammability ratings such as V-0, V-1, V-2, and HB, where V-0 offers the highest flame resistance and HB the lowest.
The copper-clad laminate (CCL) supplier’s certification determines these ratings, not the PCB manufacturer itself.
UL 796 covers comprehensive requirements including PCB structure, materials, minimum spacing, dielectric strength, thermal shock resistance, and mechanical strength.
PCB manufacturers obtain certification primarily based on this standard.
Each UL-certified entity (factory or product line) is assigned a unique UL file number, such as E123456, which serves as the core identifier in UL’s traceability system.
UL also assigns a Category Control Number (CCN) to define product categories.
For rigid PCBs, the most common CCN is DQMF2, while flexible PCBs or metal-core PCBs use different CCNs.
Listed vs. Recognized PCBs
Listed PCBs are sold as independent end products, such as general-purpose prototyping boards. This category is relatively rare today.
UL treats recognized PCBs as components installed inside other end products.
The vast majority of PCB manufacturers obtain UL Recognized Component status.
This status means manufacturers may produce the PCB only under specific approved conditions—including materials, processes, and specifications—and may use it only as part of a larger certified product.
Copper-clad laminate suppliers provide UL Yellow Cards, which detail the material’s UL file number, flame rating (e.g., FR-4, V-0), and thermal properties such as Tg.
PCB manufacturers must use materials with valid and current Yellow Cards.
Compliance Requirements for Adding the UL Mark on PCBs
Adding the UL logo to a PCB is one of the most error-prone and high-risk compliance areas and must strictly follow UL rules.
A manufacturer may add a UL mark only when UL explicitly recognizes the specific PCB model or series.
The manufacturer may also add the mark only when the production batch uses materials and processes that fully comply with the approved conditions.
The UL mark on a PCB is not just a logo but a complete traceable information set, which must include:
UL Symbol
The official “UL” mark must match the exact format shown in the UL report and must not be redesigned.
UL File Number
For example, E123456, identifying the certified manufacturer.
UL Type / Control Number
This is the internal identification number assigned by UL to a specific recognized PCB construction.
It is not the customer’s product model number. The marking format must be clearly defined in the UL report.
Typical marking examples include:
① Company trademark + UL Type + 94V-0
② UL file number + UL Type + 94V-0
Recommendations to Ensure UL Compliance
To maintain compliance, PCB manufacturers should:
Assign a dedicated UL coordinator responsible for communication with UL, internal training, and audit preparation.
Purchase and use only UL-recognized materials with valid approval status, including laminates, solder mask, and legend inks.
During order review, verify that design parameters (minimum spacing, board thickness, layer count, material type, etc.) fall within the existing UL approval scope. Any deviation requires a formal UL extension.
Treat UL marking information as customer-specified legend data, implementing double verification during engineering and silkscreen preparation.
Keep production sites and documentation well organized, actively cooperate with routine UL inspections, and promptly correct any nonconformities.
Conclusion
UL certification is a critical foundation for PCB safety, market access, and customer trust—especially in North American and global high-end markets.
Understanding UL standards, recognition scope, and marking requirements is essential for PCB manufacturers to ensure compliance, avoid risks, and support customers in obtaining end-product certification.
