PCB News - Why does PCB have halogen free PCB requirements?

According to jpca-es-01-2003 standard, copper clad laminates with chlorine (C1) and bromine (BR) contents less than 0.09% wt (weight ratio) are defined as halogen-free copper clad laminates. (meanwhile, the total amount of CI + br ≤ 0.15% [1500ppm]) halogen-free materials include tu883 of TUC, DE156 of Isola and greenspeed? Series, Shengyi s1165 / s1165m, S0165, etc. Second, why should halogen be prohibited

Halogen:

Refers to halogen elements in the periodic table of chemical elements, including fluorine (f), chlorine (CL), bromine (BR) and iodine (I). At present, the flame retardant base materials, such as FR4 and CEM-3, are mostly brominated epoxy resin.

Studies by relevant institutions have shown that halogen containing flame retardant materials (polybrominated biphenyls PBB: polybrominated diphenyl ether PBDE) will release dioxin (TCDD) and benzofuran (benzfuran) when they are abandoned and burned. They have large smoke volume, bad smell, high toxic gases and cause cancer. They can not be discharged after human intake, which seriously affects health.

Therefore, the EU law prohibits the use of six substances such as PBB and PBDE. China's Ministry of information industry also requires that electronic information products put into the market shall not contain substances such as lead, mercury, hexavalent chromium, polybrominated biphenyls or polybrominated diphenyl ether.

It is understood that PBB and PBDE are basically not used in the copper clad laminate industry. Bromine flame retardant materials other than PBB and PBDE are mostly used, such as tetrabromobisphenol A and dibromophenol. Their chemical molecular formula is cishizobr4. Although this kind of copper clad laminate containing bromine as flame retardant is not regulated by any laws and regulations, this kind of bromine containing copper clad laminate will release a large amount of toxic gas (brominated type) and produce a large amount of smoke in case of combustion or electrical fire; When PCB is used for hot air leveling and component welding, the plate will also release a small amount of hydrogen bromide under the influence of high temperature (> 200); Whether it will also produce toxic gases is still under evaluation.

To sum up. Halogen as a raw material has a great negative impact, so it is necessary to ban halogen.

Principle of halogen free PCB

At present, most halogen-free materials are mainly phosphorus system and phosphorus nitrogen system. When the phosphorus containing resin is burned, it is heated and decomposed to produce metaphosphoric acid, which is highly dehydrated, forming a carbonized film on the surface of the polymer resin, isolating the resin combustion surface from contact with the air, extinguishing the fire and achieving the flame retardant effect. The polymer resin containing phosphorus and nitrogen compounds produces non combustible gas during combustion to assist the flame retardant of the resin system.

Characteristics of halogen-free PCB

1 insulation of materials

Because P or n is used to replace halogen atoms, the polarity of molecular bond segment of epoxy resin is reduced to a certain extent, so as to improve the insulation resistance and puncture resistance of epoxy resin.

2 water absorption of materials

Because the electrons of N and P in the nitrogen phosphorus system oxygen reducing resin are less than that of halogen, the probability of forming hydrogen bond with hydrogen atoms in water is lower than that of halogen materials, so the water absorption of halogen-free materials is lower than that of conventional halogen-based flame retardant materials. For plates, low water absorption has a certain impact on improving the reliability and stability of materials.

3 thermal stability of materials

The content of nitrogen and phosphorus in Halogen-free plate is greater than that of ordinary halogen materials, so its monomer molecular weight and TG value are increased. When heated, its molecular motion ability will be lower than that of conventional epoxy resin, so the coefficient of thermal expansion of halogen-free materials is relatively small.

Compared with halogen-containing plates, halogen-free plates have more advantages. It is also a general trend for halogen-free plates to replace halogen-containing plates.

Experience in producing halogen-free PCB

1 lamination

Lamination parameters may vary from company to company. Take the above-mentioned Shengyi substrate and PP as multilayer board. In order to ensure the full flow of resin and good adhesion, it requires low sheet temperature rise rate (1.0-1.5 degree Celsius / min) and multi-stage pressure matching. In addition, it requires a long time in the high-temperature stage, which is maintained at 180 degree Celsius for more than 50 minutes. The following is a set of recommended platen program settings and actual sheet temperature rise. The bonding force between the copper foil and the substrate was 1.on/mm. After six times of thermal shock, there was no delamination and bubble.

2 drilling workability

Drilling condition is an important parameter, which directly affects the hole wall quality of PCB in the processing process. Halogen free copper clad laminates use P and N series functional groups to increase the molecular weight and enhance the rigidity of molecular bonds, so they also enhance the rigidity of materials. At the same time, the TG point of halogen-free materials is generally higher than that of ordinary copper clad laminates. Therefore, the effect of drilling with ordinary FR-4 drilling parameters is generally not very ideal. When drilling halogen-free plate, some adjustments shall be made under normal drilling conditions.

3 alkali resistance

Generally, the alkali resistance of halogen-free plates is worse than that of ordinary FR-4. Therefore, in the etching process and rework process after resistance welding, special attention should be paid to that the soaking time in alkaline film stripping solution should not be too long to prevent white spots on the substrate.

4. Fabrication of halogen-free resistance welding

At present, there are many kinds of halogen-free solder resist inks launched in the world. Their performance is not different from that of ordinary liquid photosensitive inks, and their specific operation is basically similar to that of ordinary inks.

Because halogen-free PCB has low water absorption and meets the requirements of environmental protection, it can also meet the quality requirements of PCB in other properties. Therefore, the demand for halogen-free PCB has become larger and larger.