What is Halogen Free PCB?
When talking about Halogen Free PCB, PCB manufacturing in recent years is often mentioned. According to jpca-es-01-2003 standard, copper clad laminates with chlorine (CL) and bromine (BR) content less than 0.09% wt (weight ratio) are defined as halogen-free laminates (at the same time, CI + br content ≤ 0.15% [1500ppm]). Halogen free PCB is made of halogen-free copper-clad laminate.
The common compounds used in PCB development belong to halogen family. Although the compositions themselves provide some benefits for the development of electronics, they are harmful to human life in one way or another.
These elements are:
Although there are still arguments about halogen toxicity in PCB development, there are two main factors that constitute the general consensus of halogen free PCB. These two are chlorine and bromine. Each of them brings special benefits to the overall security and functionality of electronic products, but poses a threat to the continuity of human and natural life.
At present, the EU and China have banned the use of PBBs and PBDEs in electronic materials. In order to achieve sustainable development, it is necessary to ban halogen.
What is a substitute for halogen?
At present, most halogen free PCB mainly use phosphorus and phosphorus nitrogen instead.
When the phosphorus containing resin burns, it is decomposed by thermal decomposition to form polyphosphoric acid, which is highly dehydrated and forms a carbonized film on the surface of the polymer resin. The insulating surface of insulating resin contacts with air to extinguish the flame and achieve flame retardant effect. The polymer resin containing phosphorus nitrogen compounds produces nonflammable gas during combustion to help the flame retardant resin system.
Performance of halogen free PCB
- Insulation: because halogen is replaced by P or N, the polarity of molecular bond of epoxy resin is reduced, which improves the insulation resistance and breakdown voltage.
- Water absorption: because the electrons of N and P in nitrogen phosphorus reducing resin are relatively low, the possibility of hydrogen bonding in water is lower than that of halogen. The water absorption of halogen-free PCB is lower than that of conventional PCB, which affects the reliability to a certain extent.
- Thermal stability: the content of nitrogen and phosphorus in Halogen-free PCB is higher than that of ordinary PCB, so the molecular weight and TG value of monomer increase.
When heated, the molecular mobility of halogen-free PCB is lower than that of conventional epoxy resin board, so the coefficient of thermal expansion (CTE) of halogen-free PCB is relatively low.