What is halogen-free PCB

1.1. What is Halogen-free Substrate

According to JPCA-ES-01-2003 standard, copper clad laminates with chlorine (C1) and bromine (Br) content less than 0.09% Wt (weight ratio) are defined as halogen-free copper clad laminates. (Meanwhile, the total amount of CI+Br is less than 0.15%[1500PPM])

1.2. Why should halogen be banned?

Halogen refers to halogen group elements in the periodic table of chemical elements, including fluorine (F), chlorine (CL), bromine (Br), and iodine.

At present, the flame retardants of FR4, CEM-3 and so on are brominated epoxy resin. Among brominated epoxy resins, tetrabromobisphenol A, polybrominated biphenyl, polybrominated diphenyl ether and polybrominated diphenyl ether are the main barrier fuels for copper clad laminates. They are low cost and compatible with epoxy resins.

However, studies by relevant institutions have shown that halogen-containing flame retardants (polybrominated biphenyl PBB: polybrominated biphenyl ether PBDE) emit dioxin dioxin dioxin dioxin TCDD and benzfuran when they are discarded and burned. They have large smoke volume, bad odor, high toxic gases, carcinogenic, unable to be discharged after intake, and are not environmentally friendly. Influencing human health.

Therefore, the EU initiated a ban on the use of PBB and PBDE as flame retardants in electronic information products. The Ministry of Information Industry of China also requested that electronic information products put on the market should not contain lead, mercury, hexavalent chromium, polybrominated biphenyls or polybrominated diphenyl ethers as of July 1, 2006.

Six substances, such as PBB and PBDE, are prohibited by EU law.

It is understood that PBB and PBDE are no longer used in the copper clad laminate industry. The brominated flame retardants, such as tetrabromobisphenol A and dibromophenol, are mostly used except PBB and PBDE. The chemical formula of PBB and PBDE is CISHIZOBr4.

This kind of copper clad laminate containing bromine as flame retardant has not been stipulated by any laws and regulations, but this kind of copper clad laminate containing bromine will release a large amount of toxic gases (brominated type) and smoke when burning or electrical fires; when PCB is used for hot air leveling and component welding, the plate will be affected by high temperature (>200), and will also release trace hydrogen bromide. Whether dioxins can also be produced is still under evaluation. Therefore, FR4 sheet containing tetrabromobisphenol A flame retardant is not prohibited by law and can be used, but it can not be called halogen-free sheet.

This paper discusses the processing characteristics and some experiences of halogen-free PCB.

1.3. Principle of Halogen-free Substrate

At present, most halogen-free materials are mainly phosphorus and phosphorus-nitrogen systems. When phosphorus-containing resin is burned, it is decomposed by heat to form polyphosphoric acid, which has strong dehydration. It forms carbonization film on the surface of polymer resin, insulates the burning surface of resin from contacting with air, extinguishes the flame and achieves flame retardant effect. Polymer resins containing phosphorus and nitrogen compounds produce non-flammable gases during combustion to assist in flame retardant resin systems.

2. Characteristics of halogen-free sheets

2.1. Insulation of materials

The use of P or N to replace halogen atoms reduces the polarity of the molecular bonds of epoxy resin to a certain extent, thus improving the insulation resistance and breakdown resistance of the epoxy resin.

2.2. Water Absorption of Materials

Halogen-free sheets are less absorbent than conventional halogen-based flame retardants because the foxes of N and P in nitrogen-phosphorus-based oxygenation resins have fewer electrons than halogens, and their hydrogen bonding probability with hydrogen atoms in water is lower than halogen-based materials. For sheet metal, low water absorption has a certain effect on improving the reliability and stability of the material.

2.3. Thermal stability of materials

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

3. Experience in Halogen-free PCB Production

Halogen-free sheet supplier

At present, many plate suppliers have developed or are developing halogen-free copper clad laminates and corresponding semi-curing sheets. As far as we know, there are Polyclad PCL-FR-226/240, Isola Del04TS, Shengyi S1155/S0455, South Asia, Hongren GA-HF and Panasonic Electrical GX series.

In 2002, our company began to use PCL-FR-226/240 of Polyclad in batches to produce cell phone batteries. This year, we have developed the production of Shenyi S1155 substrate and multi-layer panel. In addition, halogen-free panel in South Asia is also being tested. At present, the use of halogen-free sheets has accounted for 20% of our total sheet consumption.

3.1. lamination:

Lamination parameters may vary from company to company. Take the above-mentioned beneficiary substrates and PP as multi-layer boards. In order to ensure the full flow of resin and good bonding force, it requires lower heating rate (1.0-1.5 C/min) and multi-stage pressure coordination. In addition, it requires a longer time at high temperature stage, 180 C for more than 50 minutes. Following is a recommended set of pressure plate program settings and the actual temperature rise of sheet metal. The bonding force between the copper foil and the base plate was 1.ON/mm. No stratification and bubbles were observed after six thermal shocks.

3.2. Drilling machinability:

Drilling condition is an important parameter, which directly affects the quality of PCB hole wall in the process of processing. Halogen-free copper clad laminates have increased the molecular weight and increased the rigidity of molecular bonds by using P and N functional groups. At the same time, the Tg point of halogen-free materials is generally higher than that of common copper clad laminates. Therefore, the drilling parameters of common FR-4 are generally not ideal for drilling. When drilling halogen-free plates, some adjustments should be made under normal drilling conditions.

For example, the drilling parameters of Shengyi S1155/S0455 core plate and PP four-layer plate are not the same as the normal drilling parameters. When drilling halogen-free plate, its rotational speed is 5-10% faster than the normal parameters, while the feed and withdrawal speed is 10-15% lower than the normal parameters, so that the roughness of the drilled hole is small.

3.3. alkali resistance

The alkali resistance of halogen-free sheets is generally worse than that of FR-4. Therefore, special attention should be paid to the etching process and the rework process after welding resistance. The soaking time in alkaline defilm solution should not be too long in order to prevent the occurrence of white spots on the substrate. In actual production, our company has suffered a loss: after welding and solidified halogen-free plate, some problems need to be washed back, but when washed back, it still soaks 40 minutes in the normal FR-4 backwash mode at 75 C and 10% NaoH concentration. As a result, all the white spots of the base material are washed out, and then the soaking time is shortened to 15-20 minutes. This problem no longer exists. Therefore, for halogen-free plate rework resistance welding, it is best to do the first plate, in order to get the best parameters, and then batch rework.

3.4. Halogen-Free Welding Resistance Manufacturing

At present, there are many kinds of halogen-free solder-proof inks on the world. Their performance is not much different from that of ordinary liquid photosensitive inks, and their specific operation is almost the same as that of ordinary inks.

4. Concluding remarks

Halogen-free PCB boards can also meet the quality requirements of PCB boards because of their low water absorption and environmental protection requirements. Therefore, the demand for halogen-free PCB boards has increased. In addition, major vendors have invested more funds in the research and development of halogen-free PCB boards and halogen-free PP boards. I believe that in the near future, the demand for halogen-free PCB boards will be low. Halogen-free plate structure of price will be put into the market immediately. Therefore, each PCB manufacturer should put the trial and use of halogen-free sheet on the agenda, formulate a detailed plan, gradually expand the halogen-free sheet occupancy in the factory, so that they can take the lead in market demand.