What exactly is possible to UL certify?

by Aaron Dai, Logistics Manager

The no 4 issue of the NCAB Group newsletter In Focus was all about the importance of UL Approval. Why you need it, what does the approval process involve and other important things. In this blog post, guest blogger Emma Hudson, Lead PCB Engineer for Europe and Latin America at UL, present a list of UL´s Recognition Programs related to the PCB industry.
Security is key in the electronics industry. It is vital that users can rely on the finished products when considering factors such as fire and electrical safety. To ensure that the boards do conform, it has become common practice to UL certify the constituent materials or the PCB itself. To read the whole article about UL, download our newsletter (ENGLISH).

What exactly is possible to UL certify?

This is a list of what kind of Recognition Programs UL have, related to the PCB industry.

MATERIALS Dialectric materials
(UL Category Code QMTS)

• Includes laminates, prepregs, resin coated copper, metal base (IMS) material, vulcanised fibre, mass-lam materials – uses UL 746E for evaluation
• Includes flex films, cover films, bonding films – uses UL 746F for evaluation
Coating materials
(UL category code QMJU)

• Includes solder resists, conformal coatings, and permanent coatings – uses UL 746E for evaluation
• Note: Marking Inks do not need to be UL Recognized unless they will be used for purposes other than letters, numbers, or symbols applied to the board to aid the OEM
(UL Category Code ZPMV, may also be ZPXK for some flexible / flex-rigid boards)

• Includes single layer (no internal Cu layers), multilayer, HDI, metal base and embedded component – uses UL 796 for evaluation – all of these board types will use ZPMV
• Includes flexible and flex-rigid – uses UL 796F for evaluation
• Flex / flex-rigid boards can be assessed under ZPMV or ZPXK – if a board was evaluated as ZPMV then it will have been a comprehensive evaluation including any stiffener and stiffener adhesive that may or may not be used. If a board was evaluated under ZPXK we will not have evaluated any stiffener or stiffener adhesive that may be applied to the board and this would have to be evaluated under the end product certification; the rest of the evaluation would be the same.
(UL category code ZPVI)
• Traceability programme only used to make sure the board is being populated with the correct components and any soldering processes are not exceeding the solder limits recognized for the PCB.
(UL category code TEOU)
• Used by companies that receive bulk lots of material and then split them into smaller lots before shipping, for example laminate distributors.
• Exists because materials such as laminates and coatings are not directly marked with the UL markings for the material and therefore when the materials are repackaged these original markings are lost and new marks applied – use this to insure the PCB manufacturer is receiving the material they think it is.
• Not used for companies distributing PCBs as the boards are directly marked with the UL markings.
• Traceability programme only.
  • For all of these Recognition Programs all manufacturing locations are controlled within the companies UL file and inspected four times a year.
  • When a critical PCB manufacturing process step is subcontracted we also control these facilities and inspect them four times a year.
  • When a non-critical PCB manufacturing process step is subcontracted we do not inspect these facilities but the PCB manufacturer has a responsibility to demonstrate traceability of each board leaving and coming back to the factory and this information is inspected by our UL inspectors.
  • For all of the UL category codes detailed you will typically see a “2” or an “8” detailed at the end of them. The “2” stands for US Recognition and the “8” stands for Canadian Recognition.
  • Any company that has a Recognition in one of the categories above will be found on the publically available UL Listing Cards for you to see.