According to the JPCA-ES-01-2003 standard, copper-clad laminates with chlorine (Cl) and bromine (Br) content each less than 0.09% by weight are defined as halogen-free copper-clad laminates. Additionally, the total amount of Cl and Br combined must not exceed 0.15% (1500 PPM).

Why Ban Halogens?

Halogens refer to elements in the halogen group of the periodic table, including fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). Currently, flame-retardant materials such as FR4 and CEM-3 often use brominated epoxy resins as flame retardants.

Studies by relevant organizations have shown that halogen-containing flame retardant materials (polybrominated biphenyls PBB and polybrominated diphenyl ethers PBDE) release toxic and harmful substances, such as dioxins and furans, when burned. They produce a large amount of smoke, have an unpleasant odor, are carcinogenic, and cannot be expelled from the human body once ingested, severely affecting health and posing serious hazards to the environment and ecosystem.

Therefore, EU laws prohibit the use of six substances, including PBB and PBDE. The Chinese Ministry of Information Industry also requires that electronic information products marketed must not contain lead, mercury, hexavalent chromium, polybrominated biphenyls (PBB), or polybrominated diphenyl ethers (PBDE).

It is understood that PBB and PBDE are no longer commonly used in the copper-clad laminate industry. Currently, other brominated flame retardants, such as tetrabromobisphenol A and dibromophenol, with the chemical formula C15H12O2Br4, are more frequently used. Although these brominated flame retardants are not explicitly regulated by laws and regulations, they can release a large amount of toxic gas and produce substantial smoke when burned or during electrical fires. Additionally, during the hot air leveling of PCBs and component soldering processes, when the material is exposed to high temperatures (exceeding 200°C), trace amounts of hydrogen bromide may be released. Whether these produce toxic gases is still under evaluation.

In conclusion, the negative impacts of using halogens as raw materials are significant, making it necessary to ban halogens.

Flame Retardant Principle of Halogen-Free Copper-Clad Laminate

Currently, most halogen-free materials primarily use phosphorus-based and phosphorus-nitrogen-based systems.

Phosphorus-containing resins decompose upon heating during combustion, producing polyphosphoric acid, which has strong dehydration properties. This causes a carbonized film to form on the surface of the polymer resin, isolating it from air and extinguishing the fire, thereby achieving a flame retardant effect.

Phosphorus-nitrogen compound polymer resins produce non-combustible gases when burned, assisting the resin system in flame retardancy.

Characteristics of Halogen-Free Materials

   1. Insulation
   By using phosphorus or nitrogen to replace halogen atoms, the polarity of the epoxy resin molecular chain segments is reduced to a certain extent, thereby increasing the material's insulation resistance and breakdown strength.

   2. Water Absorption
   The nitrogen and phosphorus in halogen-free epoxy resins have a weaker electron attraction compared to halogen materials, which results in a lower probability of forming hydrogen bonds with hydrogen atoms in water. Therefore, the water absorption is lower than that of conventional halogenated flame retardant materials. For the material, lower water absorption helps improve its reliability and stability.

   3. Thermal Stability
   The nitrogen and phosphorus content in halogen-free materials is higher than the halogen content in conventional halogenated materials. As a result, the monomer molecular weight and glass transition temperature (Tg value) both increase. When heated, the molecular mobility is lower than that of conventional epoxy resins, resulting in a relatively smaller thermal expansion coefficient for halogen-free materials.

Compared to halogenated materials, halogen-free materials have more advantages, making the replacement of halogenated materials a growing trend.