Introduction to UL Certification

UL (Underwriters Laboratories) is a global safety certification company that tests and certifies products to ensure they meet rigorous safety standards. UL certification is a widely recognized mark of safety compliance for electrical and electronic products, including printed circuit boards (PCBs).

Obtaining UL certification for your PCBs demonstrates that they have been thoroughly tested and meet the applicable safety requirements. This can provide assurance to your customers and end-users that your products are safe and reliable. In some cases, UL certification may be required by law or by specific industries.

Key Benefits of UL Certification for PCBs

• Ensures PCBs meet safety standards and regulations
• Provides credibility and trust in your products
• May be required for certain industries or applications
• Can facilitate market access and sales
• Reduces liability risks

UL Safety Standards for PCBs

There are several UL safety standards that apply specifically to printed circuit boards:

UL 796 – Printed Wiring Boards

UL 796 is the primary safety standard for rigid and flexible printed wiring boards. It covers requirements for materials, construction, and performance testing. Key aspects include:

• Flammability ratings of PCB base materials
• Minimum conductor spacing (clearance and creepage)
• Current carrying capacity
• Thermal cycling and shock
• Dielectric strength

UL 746E – Polymeric Materials for Electrical Equipment

UL 746E covers requirements for polymeric materials used in printed wiring boards and other electrical equipment. It includes tests for:

• Flammability
• Electrical properties
• Thermal rating
• UV and chemical resistance
• Mechanical strength

UL 94 – Tests for Flammability of Plastic Materials

UL 94 is the standard for testing the flammability of plastic materials used in devices and appliances. It defines several flammability ratings based on material performance in vertical and horizontal burn tests:

UL 94 Rating	Burning stops within	Burning drips allowed	Application
5VA, 5VB	60 seconds	No	Highest fire safety
V-0	10 seconds	No	High fire safety
V-1	30 seconds	No	Moderate fire safety
V-2	30 seconds	Yes	Low fire safety
HB	Slow burning rate	Yes	Minimum fire safety

Choosing PCB materials with the appropriate UL 94 flammability rating is important for meeting the overall UL 796 requirements for the finished board.

How to Obtain UL Certification for PCBs

The process of obtaining UL certification for printed circuit boards typically involves the following steps:

1. Determine applicable UL safety standards based on the type of PCB and end application
2. Select UL recognized materials (e.g. laminates, solder mask) and components
3. Design the PCB in accordance with the UL safety requirements
4. Have product samples built by a UL authorized PCB manufacturer
5. Submit product samples and documentation to UL for testing and evaluation
6. Address any issues or non-conformances identified by UL
7. Receive UL certification and authorization to mark products

Working closely with your PCB manufacturer and performing a pre-certification review of your design can help streamline the UL evaluation process.

Timeline and Costs

The time and cost to obtain UL certification can vary depending on the complexity of the product and scope of testing required. Typically, the process takes about 6-12 weeks. Costs include UL project fees, testing charges, and annual maintenance fees, which can range from a few thousand to tens of thousands of dollars.

However, the long-term benefits and risk reduction of UL certification often make it a smart investment, especially for products aimed at industries that mandate compliance with safety standards.

Marking UL Certification on PCBs

Once a printed circuit board has been certified by UL, it must be properly labeled to indicate compliance with the relevant safety standards. The UL mark on a PCB provides traceability and shows that the product continues to meet requirements throughout ongoing production.

UL Recognized Components Mark

PCBs are considered “recognized components” by UL, which means they are intended to be part of a complete product or system. Therefore, bare PCBs are labeled with the UL Recognized Component mark, which consists of a backward UR inside a circle:

This mark indicates that the PCB itself meets the applicable UL safety standards, but the end product may require further evaluation.

UL Listing Mark

If the complete end product, including the PCB and all other components, has been evaluated and certified by UL, it can bear the UL Listing mark:

The UL Listing mark signifies that the product as a whole meets the applicable safety requirements.

Placing the UL Mark

The UL mark should be permanently applied to the PCB in a visible location, typically using one of the following methods:

• Silkscreen or legend printing
• Etching or engraving
• Labels or stickers (must use UL approved label materials)

The exact size, color, and placement of the mark can vary as long as it remains legible and follows UL’s guidelines. The PCB manufacturer is responsible for properly applying the UL mark to each production board.

In addition to the UL logo, the marking should include:

• The manufacturer’s name or trademark
• The factory location or identification
• The electrical ratings (voltage, current, wattage)
• The UL file number

Example UL mark on a PCB:

[UL Logo]
XYZ Co. 
E123456
Anytown, CN
48V 10A 500W

Proper and consistent UL marking on PCBs ensures traceability and ongoing compliance with safety standards.

Working with a UL Authorized PCB Manufacturer

To simplify the UL certification process and ensure ongoing compliance, it’s recommended to partner with a PCB manufacturer that is authorized by UL. UL authorized facilities have demonstrated the ability to consistently produce boards that meet the applicable safety standards.

Benefits of Using a UL Authorized Manufacturer

• Familiarity with UL requirements and processes
• Ability to source UL recognized materials and components
• In-house UL certified inspectors and testing equipment
• Authorization to apply UL marks to qualified products
• Streamlined certification process and reduced time to market

When selecting a PCB manufacturer, look for the UL Registered Firm mark or check UL’s online database of authorized facilities.

UL Follow-Up Services

To maintain UL certification over time, authorized manufacturers are subject to periodic unannounced audits and inspections by UL. These Follow-Up Services verify the continued compliance of production boards with the original safety requirements.

UL inspectors will review the PCB manufacturing process, materials, and testing records to ensure there have been no unauthorized changes. They will also pull sample boards for testing and verification.

Manufacturers must address any issues found during the audit in order to maintain their UL authorization. This ongoing oversight helps ensure the integrity and consistency of UL certified PCBs in the market.

Conclusion

UL certification is an important consideration for anyone designing, manufacturing, or selling printed circuit boards. By meeting the rigorous safety standards set forth by UL, you can provide assurance to your customers and end-users that your products are safe and reliable.

The key steps to UL certification for PCBs include:

1. Identifying applicable safety standards
2. Designing with compliance in mind
3. Selecting recognized components and materials
4. Manufacturing boards through an authorized facility
5. Submitting products for UL testing and evaluation
6. Properly marking certified products

By partnering with a UL authorized PCB manufacturer and maintaining ongoing compliance through Follow-Up Services, you can streamline the certification process and ensure the long-term safety and success of your products in the market.

FAQ

What is the difference between UL Listed and UL Recognized?

UL Listed products are complete end-products that have been fully evaluated and certified by UL. UL Recognized components, such as PCBs, are intended to be used as part of a complete product and have been evaluated for specific safety requirements. The end-product may still require further UL evaluation.

Can I self-certify my PCBs to UL standards?

No, UL certification requires an independent evaluation and testing by UL. Manufacturers cannot apply UL marks to their own products without authorization from UL.

How long does UL certification take for PCBs?

The UL certification process typically takes 6-12 weeks, depending on the complexity of the product and the scope of testing required. Working with a UL authorized manufacturer and performing a pre-certification design review can help expedite the process.

What happens if a UL certified PCB is modified?

Any changes to a UL certified PCB Design or manufacturing process must be evaluated and approved by UL. Unauthorized modifications can void the certification and authorization to use the UL mark.

How can I verify that a PCB is UL certified?

Look for the appropriate UL mark on the PCB itself, which should include the manufacturer’s name, factory location, and UL file number. You can also search for the manufacturer or product in UL’s online certifications directory.