In an earlier blog concerning CAPLINQ’s UL Certification policy, it was outlined how CAPLINQ supports its customers with the UL certification of polyimide and other tapes. This time, the differences between UL94 V‑0 and UL94 VTM‑0 will be described.
For tapes and other thin materials, the certification classification typically used is UL94 VTM‑0. The UL94 V‑0 code is used for a self supporting material. The problem that arises with a very thin material is that it may not burn but it will shrink or distort as the flame is directed to the sample and if it cannot withstand a ten second application before in shrinks to the holding clamp, so it will not be classified as a 94V material. Cases like this are what UL 94VTM is used for. You take a sheet 200mm X 50m and form a cone with it to perform the flame test as shown in the figure. Many thin materials that will not burn but will shrink to the clamp and need VTM testing.
Vertical Testing of Thin Materials (VTM‑0, VTM‑1, VTM‑2)
This test is used for materials that are thin, or are too flexible or may distort, shrink or flex during ordinary vertical testing. Procedure: An 8x2 in specimen is rolled longitudinally around a 1/2 in diameter mandrel and taped on one end. When the mandrel is removed the specimen forms a cone. The cone is supported in a vertical position and a flame is applied to the bottom of the specimen. The flame is applied for three seconds and then removed until flaming stops at which time the flame is reapplied for another three seconds and then removed. Two sets of five specimens are tested. The two sets are conditioned under different conditions.
Vertical Flame Test for Thin Materials
For more information of UL classification or polyimide tapes, visit us or contact us for more details.
4 thoughts on “UL 94V Certification vs. UL 94 VTM Certification”
Outstanding post but I was wondering if you could write a litte more on this topic?
I’d be very grateful if you could elaborate a little bit more.
Since most solder resists only have a V‑0 rating because they have been tested ona FR4.0 carrier I was wondering if a solder rests for flex that passed VTM‑0 on polyimide would be considered more flame resistant than a regular Soldermask on FR4.0?
May I know the differences between V‑0 and HF‑1 rating when we tested to UL 94 for thermal insulation made from NBR (Nitrile Rubber)?
Because I checked on UL listed directory with the same material (NBR) but you have 2 results V‑0 and HF‑1 also.
Do you have any comparison which is better?
When we have to use V‑0 rated and when HF‑1 rated?
UL94 is the standard for safety of flammability of plastic materials for parts in electrical equipment and accessories. There are different versions of this standard for different type of materials whereof UL94 V is the most common, however this test is not suitable for all types of plastic materials. For some specific cases a separate method and set of classifications has been created. For example, the UL94 HBF standard is specifically for foams and the UL94 VTM standard is for thin materials. HF‑1 is one of the possible classifications from the UL94 HBF standard.