What Is The Difference between Halogen And Halogen-free PCBs? Why Do PCBs Need To Be Halogen-free ?

PCB, or printed circuit board, is one of the basic components commonly used in electronic products. When it comes to the choice of PCB materials, there are two options: halogen and halogen-free.

What are Halogens?

In the periodic table of chemical elements, the elements of Group VIIA of the periodic system refer to the 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) contents less than 0.09% Wt (weight ratio) (at the same time, the total amount of Cl+Br ≤ 0.15% [1500PPM]) are defined as halogen-free copper clad laminates. Halogen-free materials include: TUC's TU883, Isola's DE156, GreenSpeed® series, Shengyi's S1165/S1165M, S0165, etc.

In simple terms, halogen-containing panels are not environmentally friendly, while halogen-free panels are relatively environmentally friendly. This is especially true for some environmentally friendly technology companies, which have strict requirements on the green and environmental protection of panel making due to the particularity of their industry.

What is the difference between halogen-free circuit boards and the boards we usually make?

At present, the flame retardant substrates used in the circuit board market are FR4, CEM-1, CEM-3, etc., and the flame retardants are mostly brominated epoxy resins. Relevant institutions have conducted research on epoxy resin substrates: when halogen-containing flame retardant substrates are discarded and burned, they will release harmful substances such as dioxins. These substances have a bad smell, are highly toxic, and can cause cancer. Once inhaled, they cannot be excreted by the human body, which is extremely harmful to the human body.

Halogen-free boards achieve environmental protection and non-toxicity of PCBs by replacing or substituting these harmful elements. At present, most halogen-free materials are mainly based on phosphorus and phosphorus-nitrogen. Interestingly, polymer resins containing phosphorus-nitrogen compounds will produce non-flammable gases when burned. This gas can isolate the burning surface of the resin from the air and achieve the purpose of flame retardancy.

The differences between halogen PCB boards and halogen-free PCB boards from several main aspects :

1. Material composition:

- Halogen PCBs: Halogen PCBs are made of materials containing halogen elements (such as chlorine and bromine), the most common of which are brominated flame retardants.

- Halogen-free PCB boards: Halogen-free PCB boards are made of materials that do not contain halogen elements. Common alternative materials include ammonium phosphate, nano-graphite, nano-magnesium hydroxide, etc.

2. Environmental impact:

- Halogen PCB boards: During the manufacturing and processing of PCB boards, halogen elements may release harmful substances, such as halogen compounds and dioxins. These substances have certain potential risks to the environment and health.

- Halogen-free PCB boards: The materials used in halogen-free PCB boards do not contain halogen elements, so fewer harmful substances are produced during manufacturing and processing, and the impact on the environment is relatively small.

3. Fire safety:

- Halogen PCB board: Halogenated flame retardants will release a large amount of toxic gases when the PCB board is exposed to flame, and these gases may cause harm to personnel and equipment.

- Halogen-free PCB boards: The materials used in halogen-free PCB boards have good flame retardant properties, which can reduce harmful gases generated in fires and improve safety.

The principle of halogen-free substrate

At present, most halogen-free materials are mainly phosphorus-based and phosphorus-nitrogen-based. When phosphorus-containing resins are burned, they are decomposed by heat to form partial phosphoric acid, which has strong dehydration properties, forming a carbonized film on the surface of the polymer resin, isolating the burning surface of the resin from contact with air, extinguishing the fire and achieving a flame retardant effect. Polymer resins containing phosphorus-nitrogen compounds produce non-flammable gases when burned, which help the resin system to be flame retardant.

In addition to being environmentally friendly, halogen-free PCBs also have good heat dissipation reliability and are more suitable for the high-temperature process required by lead-free circuits. Since halogen-free PCBs use P or N to replace 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-puncture capability of the material.

The advantages of halogen-free boards come at the cost of increased complexity not only in the manufacturing process but also in the design. There are differences between halogen-free PCB and conventional PCB, such as drilling. The P and N series functional groups used in halogen-free boards increase the molecular weight and enhance the rigidity of the molecular bonds, resulting in enhanced rigidity of the material. At the same time, the TG point of halogen-free materials is generally high, so the drilling parameters of ordinary FR-4 are not ideal. When drilling halogen-free boards, it is necessary to make some appropriate adjustments under normal drilling conditions.

Characteristics of halogen-free sheets

1. Insulation of materials

Since P or N is used 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-puncture ability of the material.

2. Water absorption of materials

Halogen-free boards have fewer electron pairs in N and P in nitrogen-phosphorus-based flame retardant resins than halogens, so the probability of forming hydrogen bonds with hydrogen atoms in water is lower than that of halogen materials. Therefore, the water absorption of halogen-free boards is lower than that of conventional halogen-based flame retardant materials. For boards, low water absorption has a certain impact on improving the reliability and stability of materials.

3. Thermal stability of materials

The nitrogen and phosphorus content in halogen-free PCB boards is greater than that of ordinary halogen materials, so the monomer molecular weight and Tg value are increased. When heated, the molecular mobility is lower than that of conventional epoxy resins, so the thermal expansion coefficient of halogen-free materials is relatively small.

Compared with halogen-containing panels, halogen-free panels have more advantages, and it is also a general trend for halogen-free panels to replace halogen-containing panels.

Why do PCB exports use halogen-free materials?

Halogen refers to the halogen group elements in the periodic table of chemical elements, including fluorine (F), chlorine (Cl), bromine (Br), iodine (I). At present, flame retardant substrates, FR4, CEM-3, etc., flame retardants are mostly brominated epoxy resins.

Relevant institutions have shown that halogen-containing flame retardant materials (polymerized polybrominated biphenyls PBB: polymerized polybrominated biphenyls ether PBDE), waste fire burning, will release di- uming (dioxin Daiohsing TCDD), benzofuran (Benzfuran), etc., the amount of fumes is large, the smell is unpleasant, with a high degree of toxicity of the gas, cancer, the human body can not be discharged after ingestion, a serious impact on health.

Therefore, the EU law prohibits the use of six substances such as PBB and PBDE. China's Ministry of Information Industry, the same document requires that electronic information products put on the market can not contain lead, mercury, hexavalent chromium, polymerized polybrominated biphenyls or polymerized polybrominated biphenyl ethyl ether and other substances.

It is understood that PBB and PBDE in the copper-clad laminate industry is basically not in use, more often used in addition to PBB and PBDE bromine flame-retardant materials, such as tetrabromobisphenol A, dibromophenol, etc., whose chemical molecular formula is CISHIZOBr4. This kind of bromine-containing as a flame retardant for the copper-clad laminate, although there are no laws and regulations to be stipulated, but this kind of bromine-containing type of copper-clad laminate, combustion or electrical appliances, fire, will release a large amount of toxic gases (e.g., chlorine, chlorine, chlorine). Release a large number of toxic gases (brominated), the amount of smoke; in the PCB for hot air leveling and component welding, the plate by the high temperature (>200), will also release a trace of hydrogen bromide; whether it will also produce toxic gases, but also in the assessment.

Summarizing: Halogen as a raw material used to bring about the negative consequences of a huge impact, banning halogen is necessary.

Halogen ban is mainly reflected in the following reasons:

1. International environmental regulations: Many countries and regions have issued environmental regulations to limit the content of halogen, requiring PCB boards used in electronic products should minimize or do not contain halogen elements. In order to meet the requirements of the export market, PCB exports usually choose to manufacture halogen-free materials.

2. Health and Safety Considerations: The use of halogen-free PCB boards reduces the release of hazardous substances and potential health risks to operators and end users. This is important for compliance and sustainability of exported products.

3. International Competitiveness: Halogen-free PCB boards have become a trend in the international market. While meeting environmental and health and safety requirements, choosing PCBs made from halogen-free materials can increase product competitiveness and gain more market share.

Halogen PCBs and halogen-free PCBs differ in terms of material composition, environmental impact and fire safety. In order to comply with environmental regulations, safeguard health and safety, and increase international competitiveness, PCB exports are often manufactured with halogen-free materials.