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What is halogen-free PCB

Oct 19, 2018

I. what is a halogen free base material

According to the standards of jpca-es-01-2003, the content of chlorine (C1) and bromine (Br) is less than 0.09% Wt(weight ratio) respectively, which is defined as halogen free copper clad sheet.

(meanwhile, the total amount of CI+Br is no more than 0.15% [1500PPM])

Two, why to want to ban halogen

Halogen refers to halogen elements in the periodic table of chemical elements, including fluorine (F), chlorine (CL), bromine (Br), and iodine (1).

At present, flame retardant base material, FR4, CEM-3, etc., flame retardant is mostly brominated epoxy resin.

In brominated epoxy resin, tetrabromobisphenol A, polymerization polybrominated biphenyl, polymerization polybrominated biphenyl ether and polybrominated diphenyl ether are the main resistance fuels for copper clad laminates.

But research shows that institutional containing halogen flame retardant materials (polymerization polybrominated biphenyl PBB: polymerization polybrominated diphenyl ether PBDE), waste burning, emit two well English (dioxin dioxin TCDD), benzene furan (Benzfuran), such as large amount of smoke, smelled, highly toxic gas, carcinogenic, unable to discharge after intake, not environmental protection, affect human body health.

Therefore, the eu initiated a ban on the use of PBB and PBDE as flame retardants in electronic information products.

China's ministry of information industry also requested that, as of July 1, 2006, electronic information products put on the market should not contain lead, mercury, hexavalent chromium, polybrominated biphenyls or polybrominated biphenyl ether.

Six substances such as PBB and PBDE are prohibited by eu laws. It is understood that PBB and PBDE are basically no longer used in the copper clad plate industry, and brominated flame retardant materials other than PBB and PBDE are mostly used, such as tetrabromobisphenol A and dibromophenol. The chemical formula is CISHIZOBr4.

There is no law or regulation on this type of copper clad with brominated flame retardant. However, when this type of copper clad with brominated flame retardant is burned or electrical fire, a large amount of poisonous gas (brominated type) will be released and the amount of smoke will be large.

When the PCB is welded with hot air rectification and components, the plate is affected by high temperature (>200), and the trace amount of hydrogen bromide is also released.

Whether dioxins can also be produced is still being assessed.

Therefore, FR4 plates containing tetrabromobisphenol A flame retardant are not legally prohibited and can be used, but cannot be called halogen free plates.

Iii. Principle of halogen free base plate

At present, most of the halogen-free materials are mainly phosphorous system and phosphorous nitrogen system.

When the phosphorous resin is burned, it is decomposed by heat to form poly-polyphosphate, which is very strong to be dehydrated, so that carbonized film is formed on the surface of the polymer resin, and the flame is extinguished when the burning surface of the resin is in contact with air.

High polymer resin containing phosphorus and nitrogen compounds produces non-combustible gas during combustion to assist the flame retardant of the resin system.

Features of halogen free plate

1

Insulation of materials

The use of P or N to replace halogen atoms reduces the polarity of the molecular bond segment of the epoxy resin to some extent, thus improving the insulation resistance and resistance to penetration.

2

The material is absorbent

Because the N and P fox in N and P reoxygenated resins have fewer electron pairs than halogen ones, their probability of forming hydrogen bond with hydrogen atoms in water is lower than that of halogen materials, so their absorbency is lower than that of conventional halogen flame-retardant materials.

For the plate, low water absorption has a certain impact on the reliability and stability of the material.

3

Thermal stability of material

The content of n and p in halogen free plate is higher than that of halogen in common halogen materials, so the monomer molecular weight and Tg value are increased.

Under the condition of being heated, the motion capacity of the molecules will be lower than that of conventional epoxy resin, so the heat expansion coefficient of halogen free material is relatively small.

Experience in producing halogen free PCB

At present, there are many plate suppliers who have developed or are developing halogen free copper clad sheets and corresponding semi-cured sheets. As far as we know, Polyclad pcl-fr-226/240, Isola DEl04TS, shengyi S1155 / S0455, South Asia, hongren ga-hf and panasonic electric GX series, etc.

In 2002, our company began to use Polyclad pcl-fr-226/240 plates in batches for the production of mobile phone panels. This year, we have developed shengyi S1155 base plates and multi-layer plates, and the halogen free plates of South Asia are also in trial.

At present, the use of halogen - free plate has accounted for 20% of our total plate usage.

1

laminated

The lamination parameters may vary from company to company.

Take what is said above raw profit base board and PP laminated, its in order to guarantee the full flow of the resin, the binding force is good, less demanding of sheet metal heating rate (1.0 to 1.5 ℃ / min) and the pressure of the multistage coordination, the other insist on for a long time at high temperature stage, 180 ℃ lasts more than 50 minutes.

The following is a recommended set of pressure plate program setting and the actual plate material heating situation.

The binding force of the copper foil and the substrate was 1.ON/mm, and no stratification or bubble occurred in the plate after six thermal shocks.

2

drillability

The drilling condition is an important parameter which directly affects the quality of the hole wall during PCB processing.

Since the adoption of P and N series functional groups increases the molecular weight and strengthens the rigidity of molecular bonds, the materials are also strengthened. Meanwhile, the Tg spot of the non-halogen material is generally higher than that of common copper clad plate. Therefore, the drilling parameters of common fr-4 are generally used for drilling, and the effect is not very ideal.

When drilling halogen free plate, some adjustment should be made under normal drilling conditions.


3

Alkali resistance

Generally, the alkali resistance of halogen free plate is worse than that of normal fr-4. Therefore, special attention should be paid to the etching process and the rework process after resistance welding. The soaking time in the alkaline solution should not be too long to prevent the appearance of the substrate white spots.

4

Production of halogen free resistance welding

There are many kinds of halogen resistance soldering ink which are introduced in the world at present.

conclusion

Due to low water absorption and environmental protection requirements, halogen free PCB board can meet the quality requirements of PCB board in other performances. Therefore, the demand for halogen free PCB board has been increasing.


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