Halogen Free PCB – All You Need To Know

What is a halogen free PCB and why do you need it for your project. This guide explains all that there is to know about this type of printed circuit board. Among the items discussed are: the meaning of halogen free circuit board, its benefits, the types of halogen free materials used, and its example uses.

What is a Halogen Free PCB?

The halogen free PCB means a printed circuit board that’s been made using materials that do not contain halogens (or contain them in negligible amounts). Generally, a PCB with less than 900 ppm for either halogen (bromine and chlorine) is considered halogen free.

But what are halogens? You may ask. Halogens are a group of nonmetals that include bromine, chlorine, fluorine, iodine, and a few others. In the electronics world, two of these halogens, bromine and chorine, often form part of PCB materials such as laminates and the pre-preg layer.

Bromine, in particular, has been used to produce flame retardants for FR4 substrates, a property that’s crucial in many PCB applications. A halogen free PCB eliminates the need for halogenated materials by providing alternative flame retardant compounds and resins.

Halogen free PCB material
Resource: https://www.designworldonline.com

Why Halogen Free PCB?

There are several reasons for the adoption of halogen-free electronics. Halogenated materials are toxic when released into the air, such as when a PCB is burned down. They’re also corrosive, in addition to making circuit boards less recyclable. Usually, it’s also a requirement that manufacturers produce safe PCBs. This is explained below.

Halogen Free PCB Legislation

RoHS regulations restrict the use of dangerous substances in electronics, and these include halogen free PCB requirements. Additionally, several organizations define industry standards for PCB material compositions, offering certifications to companies or businesses that adhere to them. These standards include the following:

  • UL 746E
  • IPC 4101
  • JEDEC JS709
  • IEC 61249-2-21
  • IEC 61249-2-41

Each of the mentioned standards recommends a maximum of 900 ppm (parts per million) halogens for either chlorine or bromine, and up to 1500 ppm for both halogens.

Halogen vs. Halogen Free PCB

The traditional circuit board relied on halogenated laminates and other parts. Comparing a halogen vs. halogen free PCB, we can see a number of benefits that the non-halogen board has to offer:

  • Without harmful substances, the non-halogen circuit board is a safer option for humans and the environment in general, providing for a sustainable alternative to the traditional board.
  • Halogen free materials offer good electrical insulation, which is necessary when designing high power boards.
  • Non halogen materials also absorb less moisture when compared to halogenated types.
  • Halogen free PCBs offer greater thermal stability, and will not expand by much when subjected to heat or higher temperatures.
  • PCB materials that are laden with bromine can be a challenge to recycle when compared to those without the halogen.
  • As we have seen, regulations across the globe prohibit the use of flame retardants that contain harmful substances—and halogens in particular.

On the down side, a halogen free FR4 or other material is generally more expensive, usually by up to 30%. Overall though, these boards offer benefits on many fronts, including compliance with regional and international standards or regulations.

PCB solder paste application
PCB solder paste application
Resource: https://hackaday.com

Halogen Free PCB Material

Halogens have mostly been used in the material that makes the laminate or the pre-preg layers. Sometimes, these substances are used in the solder paste that manufacturers use to assemble PCBs. In a non-halogen circuit board, the dangerous compounds are replaced by safer materials as explained below.

Halogen Free Laminate

Here, the laminate is used in reference to the substrate. This is often a halogen free FR4 core where FR indicates the flame retardant material and 4 the epoxy resins that hold everything together. Possible alternatives for these two materials—the flame retardants and resins—are provided below.

Flame Retardants: in a halogen printed circuit board, several brominated compounds were traditionally used. These are PBB, PBDE, TBBPA, and HBCD. In the safer version of the board, the compounds are replaced by the following halogen free, flame retardant additives.

  • Aluminum (aluminum hydroxide, aluminum diethylphosphinate)
  • Phosphorus (phosphorus based FR4 materials, phosphorus based flame retardants)
  • Magnesium hydroxide
  • Ceramics
  • Melamine derivatives

Epoxy Resins: epoxy resin is used in FR4 laminates. It’s usually a thermosetting polymer that provides mechanical stability and insulation, among other functions. Traditionally, this resin contained halogens. In a non-halogen board, the resins used are.

  • Benzoxazine resins
  • Bismaleimide triazine
  • Tetrafunctional epoxy resins
  • Bisphenol epoxy vinyl esters
  • Cyanate esters
  • Polyimide

Halogen Free Flux

Halogenated solder paste or solder flux has been used to assemble circuit boards. This paste contains bromine activators that serve to help remove oxidation during soldering, while also offering whetting properties. In the era of halogen free solder or solder paste, the flux is replaced by safer options.

Other measures for ensuring bromine or chlorine free circuit boards include using solder mask or coatings that do not contain the offending substances. Cleaning chemicals too, and printing inks. In other words, the overall presence of halogens is reduced to less than 900 ppm.

Halogen free PCB board for photographic equipment application
Halogen free PCB board for photographic equipment application
Resource: https://www.researchgate.net

Halogen Free PCB Applications

Non-halogen printed circuit boards, given their safety and other benefits, find useful applications in many different industries and electrical or electronic products. Some of the most common applications for these PCBs are listed below.

  • Lighting products
  • Consumer electronics
  • Automotive systems
  • Power generation plants
  • Electric motor circuits
  • Medical equipment and devices
  • Telecommunication systems and devices
  • Military electronics
  • Railway electrical systems
  • Laboratory equipment
  • Manufacturing equipment
  • Aviation industry systems and products and systems

Conclusion

The halogen free PCB uses materials that are safe to both humans and the environment. Despite being a more expensive option, this type of board also allows manufacturers to comply with set rules and PCB manufacturing standards from across the world. The non halogen PCB is also used in many different applications, from commercial to industrial systems and equipment or products.

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