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Designs on Flex: Underwriters Laboratory and Flexible Printed Circuits
November 12, 2015 | Mike Morando, PFC Flexible CircuitsEstimated reading time: 1 minute
Underwriters Laboratory is a worldwide safety consulting and certification company headquartered in Northbrook, Illinois. UL certifies, validates, tests, inspects, audits, and advises on safety of electrical and electronic products.
I am sure you have seen the UL logo on many of your electrical and electronic products at home. Electronic equipment, in many cases, requires a UL certification. In turn, the components that make up the electronic or electrical system must be certified.
What Does UL test?
The test process for UL varies based on what is being certified, but in essence, the tests consist of determining how flammable a product is and the functionality of the circuit. In most cases, UL will perform flammability on the consumer product to insure its safety.
For UL 796F standard,
There are two categories of the safety test: flammability and function.
- Adhesion
- Bending / fatigue
- Current / voltage limit
UL 94 Standard
These requirements cover tests for flammability of plastic materials used for parts in devices and appliances. There are three grades of flammability rating:
1)Vertical Burning Test: V-0, V-1, or V-2
2) Thin Material Vertical Burning Test: VTM-0, VTM-1, or VTM-2
3) Horizontal Burning Test: HB
UL Testing of Flex Materials
To obtain UL certification for a flex circuit is a little different. UL does not require each flex circuit to be tested and certified, but, rather the materials that make the circuit- (specific stack up of polyimide, copper, FR-4 and adhesive).
To get approval from UL, a flex circuit manufacturer provides samples of a specific construction for flammability and flexibility testing. UL will test and approve that specific construction. Once the construction is approved, the flex manufacturer can use that specific construction on other circuits as a UL-approved construction.
Process
From a high level, here are the procedures to get specific flex materials certified for flammability from UL.
- Flex vendor submits request to UL have a flammability test
- UL evaluates and creates a test plan,, procedures and processes. Test plan includes flammability test
- Flex vendor manufactures test samples (coupons) and provides all required paperwork
Testing and certification takes 8-10 weeks.
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07/30/2025 | I-Connect007 Editorial TeamThe Global Electronics Association is alerting industry members that a potential 50% tariff on copper could hit U.S. electronics manufacturers where it hurts.
Connect the Dots: Sequential Lamination in HDI PCB Manufacturing
07/31/2025 | Matt Stevenson -- Column: Connect the DotsAs HDI technology becomes mainstream in high-speed and miniaturized electronics, understanding the PCB manufacturing process can help PCB design engineers create successful, cost-effective designs using advanced technologies. Designs that incorporate blind and buried vias, boards with space constraints, sensitive signal integrity requirements, or internal heat dissipation concerns are often candidates for HDI technology and usually require sequential lamination to satisfy the requirements.
OKI Launches Rigid-Flex PCBs with Embedded Copper Coins Featuring Improved Heat Dissipation for Space Equipment Applications
07/29/2025 | BUSINESS WIREOKI Circuit Technology, the OKI Group’s printed circuit board (PCB) business company, has developed rigid-flex PCBs with embedded copper coins that offer improved heat dissipation for use in rockets and satellite-mounted equipment operating in vacuum environments.
Designers Notebook: Basic PCB Planning Criteria—Establishing Design Constraints
07/22/2025 | Vern Solberg -- Column: Designer's NotebookPrinted circuit board development flows more smoothly when all critical issues are predefined and understood from the start. As a basic planning strategy, the designer must first consider the product performance criteria, then determine the specific industry standards or specifications that the product must meet. Planning also includes a review of all significant issues that may affect the product’s manufacture, performance, reliability, overall quality, and safety.
I-Connect007 Editor’s Choice: Five Must-Reads for the Week
07/18/2025 | Nolan Johnson, I-Connect007It may be the middle of the summer, but the news doesn’t quit, and there’s plenty to talk about this week, whether you’re talking technical or on a global scale. When I have to choose six items instead of my regular five, you know it’s good. I start by highlighting my interview with Martyn Gaudion on his latest book, share some concerning tariff news, follow that up with some promising (and not-so-promising) investments, and feature a paper from last January’s inaugural Pan-European Design Conference.