Halogen-free, in materials science and electronics manufacturing, refers to a material that does not contain halogen elements (fluorine, chlorine, bromine, iodine, and astatine), especially chlorine and bromine, as these two elements are commonly used in flame retardants. When materials such as plastics, circuit boards, or cable insulation do not use flame retardants containing chlorine and bromine during production, these materials can be called halogen-free. Although halogen flame retardants can improve product safety in the event of a fire, they may release toxic gases at high temperatures, posing risks to the environment and human health. Therefore, increased environmental awareness has prompted many manufacturers and industry standards to adopt halogen-free materials to reduce these potential risks. Halogen-free products are crucial for enhancing consumer safety, protecting the environment, and complying with environmental regulations in certain countries and regions (such as the EU's RoHS directive). Halogen-free standards typically require the total halogen content in materials to be below a certain proportion, for example, the halogen-free circuit board standard defined by IEC 61249-2-21 requires the content of chlorine and bromine to be below 0.09%, and the total halogen content must be below 0.15%.