A halogen-free PCB is a circuit board fabricated using halogen-free raw materials and is classified as an environmentally friendly material. According to the JPCA - ES - 01 - 2003 standard, a copper-clad laminate is defined as halogen-free when the chlorine (Cl) and bromine (Br) contents are each less than 0.09% Wt (weight ratio), and the total amount of Cl + Br is ≤ 0.15% (1500 PPM).
There is a wide range of common halogen-free materials. For example, TUC's TU883 exhibits stable performance and excels in high-frequency and high-speed signal transmission scenarios. Isola's DE156 offers excellent heat resistance and electrical properties. The GreenSpeed series is renowned for its environmental friendliness and high efficiency. Shengyi's S1165/S1165M and S0165 are widely used in the domestic market and can meet the diverse needs of different customers.
The flame-retardant mechanism of halogen-free materials mainly involves two aspects. On one hand, phosphorus-containing resins decompose during combustion to generate metaphosphoric acid. This metaphosphoric acid has strong dehydrating properties, enabling the formation of a carbonized film on the surface of the polymer resin. This film isolates the burning resin surface from air contact, thereby achieving a flame-retardant effect. On the other hand, phosphorus-nitrogen compounds produce non-combustible gases, such as nitrogen, during combustion. These gases can dilute the oxygen concentration and assist the resin system in flame retardancy.
Halogen-free laminates use P or N to replace halogen atoms, which to a certain extent reduces the polarity of the molecular bond segments in the epoxy resin. Tests have shown that their insulation resistance can be increased by 10% - 20% compared with conventional halogen-containing laminates, and their breakdown voltage resistance is also significantly enhanced, effectively ensuring the safe and stable operation of circuits.
Since the nitrogen-phosphorus-based epoxy resins in halogen-free laminates have relatively fewer lone pair electrons on N and P compared with halogen materials, the probability of forming hydrogen bonds with hydrogen atoms in water is lower than that of halogen materials. Experiments indicate that under the same environmental conditions, the water absorption rate of halogen-free laminates is 30% - 50% lower than that of conventional halogen-based flame-retardant materials. This helps improve the reliability and stability of the materials and reduces performance changes caused by water absorption.
The nitrogen and phosphorus contents in halogen-free laminates are higher than the halogen contents in ordinary halogen-based materials, resulting in an increase in their monomer molecular weights and glass transition temperatures (Tg values). Generally, the Tg value of halogen-free laminates is 10 - 20 degrees Celsius higher than that of ordinary halogen-based laminates. When heated, the molecular mobility of halogen-free laminates is lower than that of conventional epoxy resins, and their coefficients of thermal expansion are relatively smaller, effectively reducing board deformation and dimensional changes caused by temperature variations.
Halogen-containing flame-retardant materials, such as PBB and PBDE, produce toxic substances like dioxins and benzofurans during combustion. Studies have shown that for every kilogram of halogen-containing flame-retardant material burned, several milligrams to tens of milligrams of toxic substances such as dioxins may be generated. These substances pose a serious threat to human health and release a large amount of toxic gases and dense smoke during combustion, causing environmental pollution. In contrast, halogen-free PCBs generate fewer harmful substances during production and use, comply with environmental requirements, and do not produce toxic gases during combustion, which is beneficial for environmental protection and human health.
During the production of halogen-free PCBs, precise adjustments to the heating rate and pressure are required in the lamination process. A too-fast heating rate may lead to uneven resin flow, while insufficient pressure can affect the resin's adhesion. Generally, the heating rate should be controlled at 2 - 5 degrees Celsius per minute, and the pressure should be adjusted according to the board thickness and specifications to ensure that the resin is fully filled and forms a good bond.
In the drilling process, the rigidity and Tg value of the materials need to be considered. Due to the high rigidity of halogen-free laminates, burrs and cracks are prone to occur during drilling. At the same time, parameters such as drill bit speed and feed rate should be adjusted according to alkaline conditions to prevent damage to the substrate. For example, the drill bit speed can be controlled at 8000 - 12000 revolutions per minute, and the feed rate can be adjusted between 0.1 - 0.3 meters per minute depending on the board thickness.
The operation of halogen-free solder mask inks is similar to that of ordinary inks, but special attention should be paid to the curing conditions of the inks. The curing temperature and time of halogen-free solder mask inks differ from those of ordinary inks. Generally, the curing temperature is 150 - 160 degrees Celsius, and the curing time is 30 - 60 minutes to ensure complete curing of the inks and achieve good insulation and protection effects.
Halogen-free PCBs are widely used in fields such as telecommunications, computing, and aviation. In the telecommunications field, with the rapid development of 5G technology, the performance requirements for PCBs are becoming increasingly high. Halogen-free PCBs, with their excellent electrical properties and environmental characteristics, have become key components in 5G base stations and other equipment. According to statistics, the proportion of halogen-free PCBs used in 5G base station construction has exceeded 60%. In the computing field, halogen-free PCBs are suitable for high-performance servers, laptops, and other devices, meeting their requirements for high-speed signal transmission and heat dissipation. In the aviation field, due to its extremely high requirements for material reliability and safety, halogen-free PCBs are gradually becoming the mainstream choice due to their outstanding thermal stability and environmental advantages. In addition, as market demands for environmental protection and performance continue to rise, halogen-free PCBs are particularly suitable for high-temperature processes required by lead-free circuits, and their market demand is increasing. It is expected that the market demand will grow at an annual rate of 10% - 15% in the coming years.
FR4PCB.TECH, Specialized Production: FP4, High TG, halogen-free, aluminum/copper/ceramic-based, and Rogers material printed circuit boards (PCBs).
Offerings: Double-sided boards, multilayer boards, HDI (High-Density Interconnect) boards, rigid-flex boards, high-frequency boards, etc., to cater to diverse requirements.
Surface Finish Processes: OSP (Organic Solderability Preservative), HASL (Hot Air Solder Leveling), ENIG (Electroless Nickel/Immersion Gold), immersion silver, immersion tin, electroplated nickel-gold, and electroless palladium, etc.
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