What is a halogen-free circuit board?

What is a halogen-free circuit board? What is the difference between halogen-free PCB and usual made PCB?

Are there environment-friendly circuit boards? What is going on with the halogen-free PCB, which is widely used abroad? How is the halogen-free board different from the board we usually make?

What is halogen?
In the periodic table of chemical elements, the elements of group ⅦA of the periodic system refer to halogen elements, including fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).

What is a halogen-free circuit board?
According to the JPCA-ES-01-2003 standard, copper clad laminates with chlorine (Cl) and bromine (Br) elements less than 0.09% Wt (weight ratio) are defined as halogen-free copper clad laminates. (JPCA is the abbreviation of Japan Electronic Circuit Industries Association.)

What is the difference between the halogen-free circuit board and the board we usually make?
At present, the flame retardant CCL substrates FR4, CEM-1, CEM-3, etc. used in the circuit board market are mostly brominated epoxy resins.

Relevant institutions have done research on epoxy resin substrates: when halogen-containing flame-retardant substrates are discarded and burned, they will release harmful substances such as dioxins. This substance has an unpleasant smell, is highly toxic, and can cause cancer. Once inhaled, it cannot be discharged, which will cause huge harm to the human body.

The halogen-free board realizes the environmental protection and non-toxicity of the PCB by replacing or reducing these harmful elements.

At present, most of the halogen-free materials are mainly phosphorus-based and phosphorus-nitrogen-based. What's interesting is that high polymer resins containing phosphorus and nitrogen compounds will produce non-combustible gas when burned. This gas can isolate the burning surface of the resin from the air and achieve the purpose of flame retarding.

What are the advantages of halogen-free PCB?
In addition to being environmental-friendly, halogen-free PCB also has good heat dissipation reliability and are more suitable for the high-temperature processes required by lead-free circuits.

Since the halogen-free PCB uses P or N to replace the halogen atoms, the polarity of the molecular bond segment of the epoxy resin is reduced to a certain extent, thereby improving the insulation resistance and anti-breakdown ability.

Things often have two sides. The advantages of halogen-free boards are at the cost of increasing complexity, not only in the PCB manufacturing process but also in the PCB design. There are differences between halogen-free PCB and conventional PCB, such as drilling. 
The P and N series functional groups used in the halogen-free board increase the molecular weight and enhance the rigidity of the molecular bond, resulting in increased rigidity of the material. At the same time, the TG point of the halogen-free material is generally higher, so the effect of using the ordinary FR-4 drilling parameters to drill is not satisfactory. When drilling halogen-free boards, some adjustments should be made under normal drilling conditions.