UL Splits FR-4 Standards Into Two Categories

Estimated reading time: 3 minutes

For the past year, it seemed likely that designers and users of new FR-4 laminate and prepreg materials would have to run new materials through complete testing to be certified by Underwriters Laboratories Inc. (UL). That 2012 requirement disappeared when UL’s Standards Technical Panel (STP) split what was a single category of FR-4 into two categories in the UL 746E Polymeric Materials Safety Standard.

One category, now designated as FR-4.0, contains FR-4 that utilizes halogenated flame retardants while the second category, designated as FR-4.1, is an FR-4 formulation with non-halogenated flame retardants. FR-4 laminates that belong in either of these two flame retardant categories and have at least 50% epoxy plus no more than 45% inorganic filler in the resin portion of the laminate make-up, can now be certified using metal clad industrial laminate (MCIL) abbreviated test procedures.

This change comes after a decade of effort by UL in conjunction with IPC to accommodate new and innovative laminate formulations plus certifications of printed boards produced per the UL 796 printed board safety standard with both “halogen-free” flame retardants (originally established by European regulators) as well as brominated flame retardants.

IPC, through its Chair of the 3-11 Laminate/Prepreg Materials Subcommittee, Antonio (Tony) Senese and Subcommittee Vice Chair, Doug Sober, came up with a compromise approach that ultimately won the approval of the UL STP.

That approach handily passed the STP’s approval process with more than 80% approval, surprising many industry observers. The actual STP Ballot and required recirculation occurred over a brief six-week time period which also was unexpected, given the controversial nature of the topic.

“IPC was proud to support this modification to UL 746E. This redefinition of FR-4 and splitting this material category into the two categories of FR-4.0 and FR-4.1 will definitely help the global printed board industry as it removes a tremendous amount of uncertainty. It makes the new material certification process defined within the UL 746E much simpler, quicker and more cost effective,” said Tom Newton, IPC’s director of PCB programs, standards and technology.

The dual-classification approach follows two unsuccessful alternatives that were rejected by STP voters. The recent approval of IPC’s sponsored proposal ends what has been a period of great consternation and uncertainty within the printed board industry. If the UL’s requirements had been left to stand, nearly every new formulation of FR-4 laminates would have required complete testing that routinely takes six months to one year to complete.

In 2001, UL established 14 infrared scans of representative epoxy functionalities that were purported to make it easier for companies to prove that newly-conceived, flame-retarded, epoxy resin-based, woven fiberglass reinforced laminates were indeed “FR-4. These 14 reference scans were inserted into the UL 746E standard. Laminate resins that didn’t conform to one of the 14 IR scans would then have to be considered “non-ANSI” materials which, in turn, had to be run through the full blown, six-to-12-month testing process.

“However, with some creative interpretations of newer epoxy formulations in the subsequent decade, especially those that had other, newer polymer systems added, UL and industry were able to limp along and maintain the status quo with an abbreviated testing program for the 746E/796 standards until 2011,” Newton said.

That’s when UL’s PDE, Standards, Engineering and Commercial teams agreed that the requirements already written into UL 746E and 796 standards had to be strictly enforced, because of market integrity and accreditation requirements. This included requiring that those newer epoxy/epoxy blends and co-polymers no longer matching the 14 reference IR scans be put through complete, lengthy and costly testing. Only through rewriting the standard could suppliers and users certify their new, innovative formulations for FR-4 laminate materials and the consequent printed boards made from these new resins.

Now that UL 746E has been approved with a dual FR-4 category system, companies will have more freedom to develop and utilize FR-4 laminate materials that suit their specific requirements at significantly lower costs, both in monetary as well as timing terms.