While researching various types of PCBs (Printed Circuit Boards), you may have frequently encountered Halogen-free PCBs. This may raise several questions, such as what defines a Halogen-free PCB and why manufacturers prefer them.
Halogen-free PCBs are increasingly discussed in modern PCB construction. Essentially, a Halogen-free PCB refers to a printed circuit board that excludes halogen elements like chlorine, bromine, fluorine, iodine, and astatine, which are known to be harmful to living organisms. To be classified as “Halogen-free,” the board must contain less than 900 parts per million of chlorine or bromine and a total of less than 1500 parts per million of all halogen elements.
According to the JPCA-ES-01-2003 standard, a Halogen-free lamination of copper-clad must contain less than 0.09% weight ratio of bromine (Br) and chlorine (Cl), with a total combined amount not exceeding 0.15% (1500 ppm). This standard ensures that the PCB is manufactured using Halogen-free laminated copper-clad materials.
To delve deeper into Halogen-free PCBs and find answers to all your queries on this topic, continue reading this article.
Halogen elements include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). They are known for their flame retardant properties, particularly chlorine and bromine, which are commonly used in electronics.
Many widely used PCBs, such as FR4 and CEM3, traditionally incorporate halogen-containing flame retardants. Research has shown that these flame retardants emit highly toxic gases with a strong odor when burned, posing significant hazards to both human health and the environment. Exposure to chlorine or bromine can cause symptoms ranging from respiratory issues and skin irritation to more serious conditions like dioxin formation, a potent carcinogen.
In response to these concerns, regulations like RoHS (Restriction of Hazardous Substances) have been implemented to prohibit the use of certain halogenated flame retardants in electronic products since July 1, 2006. Initially, this included Polybrominated Biphenyls (PBB) and Polybrominated Diphenyl Ethers (PBDE), with Tetrabromobisphenol A (TBBPA) and Hexabromocyclododecane (HBCD or HBCDD) added later in 2008. The European Union and China have since banned PBB and PBDE from all electronic equipment to promote safer practices and environmental protection.
In pursuit of sustainable advancements, the electronics industry has shifted towards developing PCBs without halogenated chemicals. Nowadays, phosphorus-nitrogen compounds are preferred over halogens in PCB production. These compounds undergo thermal decomposition during resin burning, producing polyphosphoric acid and forming a carbonized layer on the polymer resin’s surface. This process enhances flame retardancy by releasing non-combustible gases that suppress fire propagation.
Replacing halogens with phosphorus and nitrogen reduces the molecular polarity of epoxy resins, thereby improving insulation resistance and breakdown voltage. Halogen-free PCBs exhibit higher nitrogen and phosphorus content compared to traditional boards, resulting in enhanced monomer molecular weight and glass transition temperature (Tg). Moreover, they demonstrate a lower coefficient of thermal expansion (CTE) due to reduced molecular mobility during heating.
Unlike halogen-containing PCBs, which form hydrogen bonds with water molecules, halogen-free variants exhibit reduced water absorption, thereby potentially enhancing reliability.
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