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Halogen Free PCBs - A Useful Guide

Halogen Free PCBs

Halogen Free PCBs are printed circuit board without halogens in their construction. Halogens include Chlorine, Bromine, Fluorine, Iodine, and Astatine, which have health & safety concerns. For a PCB to be considered “Halogen-Free,” there must either be less than 900 parts per million of chlorine or bromine, or fewer than 1500 parts per million of any halogens.

Chlorine (CL) and bromine (Br) had been used as constituents for flame retardancy in electronics. Halogen-containing flame retardants can be harmful when combusted generating toxic gas effecting the environment and carcinogenic to humans.

Beginning back in 2006, when RoHS (Restrictions on Hazardous Substances) regulations were first released, two halogenated flame retardants were initially banned from PCB laminates such as FR4 or CEM 3.

  • Polybrominated biphenyls (PBB)
  • Polybrominated diphenyl ethers (PBDE).

In 2008, the legislation became more restrictive when two more chemicals were included.

  • Tetrabromobisphenol A (TBBPA)
  • Hexabromocyclododecane (HBCD or HBCDD)

Which were also common PCB flame retardants?

In response laminate manufacturers have developed, products which are halogen free.

Commonly phosphorus & phosphorus-nitrogen have replaced the above four banned substances. When combusted, phosphorus containing resins decompose to polyphosphoric acid (anhydrous) and produces a carbonized film which is self-extinguishing.

Replacement of halogens with phosphorus or phosphorus-nitrogen results in a reduction of the molecular bonds in the epoxy resin, enhancing insulation resistance and dielectric break-down voltage of the laminate.

Phosphorus and nitrogen increase the monomer molecular weight and Tg (Glass transition temperature) as compared to the older halogen containing materials. The halogen-free materials have a relatively low coefficient of thermal expansion (CTE).

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