The flame retardant of the early halogen-free CCL is mainly achieved by the addition of flame-retardants. Common flame-retardants are phosphorus and nitrogen-containing additive flame-retardants such as phosphate ester, poly-phosphoric acid, melamine, aluminum hydroxide, magnesium hydroxide, and so on. Due to the large amount, glass transition temperature (Tg), heat resistance, processability and other performances of plates are decreased. If we use the added phosphorus-containing flame-retardants, it will increase the water absorption and decrease moisture resistance, plates are easy to delaminate and foam in the high temperature shock of the hot air leveling or component assembly, and the electrical performance of plates in the wet conditions will also decline. For cost, performance and application, the current halogen-free paper-based CCL and halogen-free composite CCL is still mainly adopt the additive flame-retardants. However, halogen-free glass fiber cloth CCL mainly adopt the reaction-type flame retardants.
In recent years, phosphorus-containing epoxy resins synthesized with DOPO or ODOPB and other phenanthrene-containing phosphorus compounds have been extensively used in the production of halogen-free FR-4 CCL. Because of the different epoxy resins and synthesis processes, the performances of the phosphorus-containing epoxy resins produced by different factories have large differences. With phosphorus-containing epoxy resins from different manufacturers, the production of halogen-free CCL needs to adjust the formulation and production process. Generally, phosphorus-containing epoxy resinω(phosphorus) is 2%-3.2%, and when ω is 2.6%, the burning behavior of the plate can attain to UL94 V-0. Phosphorus-containing epoxy resin is a reactive flame-retardant, which can produce halogen-free copper clad laminate with good comprehensive performance. At present, the price of phosphorus-containing epoxy resin is several times of common brominated epoxy resin, resulting in high prices of halogen-free CCL.
Nitrogen-containing phenolic resin is another material of halogen-free CCL. Phosphorus and nitrogen have a good flame-retardant synergistic effect. The halogen-free copper clad laminate using nitrogen-containing phenolic resin as a curing agent has better comprehensive performance. A number of Japanese manufacturers are currently supplying nitrogen-containing phenolic resins. It has also begun to be paid attention that using phosphorus-containing phenolic resin as curing agent for the development of halogen-free copper clad laminate in recent years. A ODOPM-MPN type epoxy resin curing agent containing phosphorus and nitrogen was introduced, which can reduce phosphorus content of phosphorus-containing epoxy resin and improve the moisture resistance of the plates by using the synergistic effect of nitrogen and phosphorus. Nippon Mitsubishi Gas Co., Ltd. uses Polyhydroxy styrene (PHS) that produced by Nippon Maruzen Petrochemical Co., Ltd. and (c6h5o) 2PCl that produced by Japan’s largest Chemical Co., Ltd. The synthesized DPC-PHS phosphorus-containing phenolic resin has 3% phosphorus. The phosphorus-containing phenolic resin is not only a curing agent is also a flame retardant. What’s more, with the common phenolic epoxy resin and phenolic resin, it can be made of halogen-free glass fiber cloth CCL with V-0 grade flame-retardant and Tg165℃.