Halogen elements, including chlorine (Cl), bromine (Br), and fluorine (F), are members of the 17th group of the chemical periodic table. These elements are commonly used to manufacture flame retardant materials, aiming to enhance the fire resistance of electronic products. However, in certain situations, especially during the disposal of electronic products, halogen elements may be released into the environment, posing potential threats to ecosystems. Moreover, when electronic products burn, substances like polybrominated diphenyl ethers (PBDE) and polybrominated biphenyls (PBB) can release toxic compounds, including polycyclic aromatic hydrocarbons and dioxins, in the emitted black smoke, which can endanger human health. Due to these harmful emissions, the European Union and China have banned the use of PBDE and PBB in electronic products.

In an effort to reduce the use of halogen elements and mitigate the environmental pollution risks, people have started to adopt halogen-free PCB. Halogen-free PCB do not contain halogen elements. According to IEC standards, the chlorine and bromine content in halogen-free copper-clad laminates must not exceed 900 ppm individually, with a total content not exceeding 1500 ppm. These circuit boards typically employ alternative flame retardant materials such as phosphorus and nitrogen to ensure an adequate level of fire resistance. This means that halogen-free PCB not only meet the performance requirements of electronic products but also reduce the adverse impact of halogen elements on the environment and human health.