UL 94V Certification vs. UL 94 VTM Certification

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.

Certification Classification

ulvtm_coneFor 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

Ver­ti­cal Rat­ing
for Thin
Mate­ri­als
Require­ments
VTM-0
  • Spec­i­mens must not burn with flam­ing com­bus­tion for more than 10 sec­onds after either test flame appli­ca­tion.
  • Total flam­ing com­bus­tion time must not exceed 50 sec­onds for each set of 5 spec­i­mens.
  • Spec­i­mens must not burn with flam­ing or glow­ing com­bus­tion up to the spec­i­men hold­ing clamp.
  • Spec­i­mens must not drip flam­ing par­ti­cles that ignite the cot­ton.
  • No spec­i­men can have glow­ing com­bus­tion remain for longer than 30 sec­onds after removal of the test flame.
  • No spec­i­men shall have flam­ing or glow­ing com­bus­tion up to a mark 5 inch­es from the bot­tom of the spec­i­men.
VTM-1
  • Spec­i­mens must not burn with flam­ing com­bus­tion for more than 30 sec­onds after either test flame appli­ca­tion.
  • Total flam­ing com­bus­tion time must not exceed 250 sec­onds for each set of 5 spec­i­mens.
  • Spec­i­mens must not burn with flam­ing or glow­ing com­bus­tion up to the spec­i­men hold­ing clamp.
  • Spec­i­mens must not drip flam­ing par­ti­cles that ignite the cot­ton.
  • No spec­i­men can have glow­ing com­bus­tion remain for longer than 60 sec­onds after removal of the test flame.
  • No spec­i­men shall have flam­ing or glow­ing com­bus­tion up to a mark 5 inch­es from the bot­tom of the spec­i­men.
VTM-2
  • Spec­i­mens must not burn with flam­ing com­bus­tion for more than 30 sec­onds after either test flame appli­ca­tion.
  • Total flam­ing com­bus­tion time must not exceed 250 sec­onds for each set of 5 spec­i­mens.
  • Spec­i­mens must not burn with flam­ing or glow­ing com­bus­tion up to the spec­i­men hold­ing clamp.
  • Spec­i­mens can drip flam­ing par­ti­cles that ignite the cot­ton.
  • No spec­i­men can have glow­ing com­bus­tion remain for longer than 60 sec­onds after removal of the test flame.
  • No spec­i­men shall have flam­ing or glow­ing com­bus­tion up to a mark 5 inch­es from the bot­tom of the spec­i­men.

For more infor­ma­tion of UL clas­si­fi­ca­tion or poly­imide tapes, vis­it us or con­tact us for more details.

About Chris Perabo

Chris is an energetic and enthusiastic engineer and entrepreneur. He is always interested in taking highly technical subjects and distilling these to their essence so that even the layman can understand. He loves to get into the technical details of an issue and then understand how it can be useful for specific customers and applications. Chris is currently the Director of Business Development at CAPLINQ.

4 thoughts on “UL 94V Certification vs. UL 94 VTM Certification

  1. 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?

  2. 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?

  3. 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.

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