You should look for halogen-free printed circuit boards when purchasing them. What is PCB, halogen free? Why do PCB producers produce it? This article will clear up any doubts you may have.
Halogen Free PCB
From the literal meaning, it is easy to understand that halogen free printed circuit boards are circuit boards which do not contain any halogen material or have a negligible halogen content.
Standard for halogen free printed circuit boards states that the chlorine or bromine content must be lower than 900 parts/million, while the halogen content must be below 1500 parts/million. The halogen used in halogen free circuit boards is not an actual material, but a gas. Not only is it harmful to the human body, but it also pollutes the environment. We should therefore choose materials that are halogen free when manufacturing PCBs. This is beneficial to the environment as well as human health.
What Are the Halogen Substances?
In middle school, we all learned that halogens are a broad category. It is composed of fluorine and other elements. In the electronic industry, bromine is used to make PCB laminates, prepreg layers, and other materials. Bromine is a good flame retardant and used in FR4 substrates. This property is critical in many PCB application.
Why Is the 'Halogen' Banned?
Research has shown that halogen flame retardant materials release toxic gases, including hydrogen halides and PBDE. They also emit an unpleasant odor when they are burned. Acid rain occurs when hydrogen halides react with the water vapor present in the air. Acid rain contains sulfur dioxide, which is corrosive to the environment. PBDE, PBDF and other carcinogens are harmful to people's health. EU RoHS regulations clearly state that PBDE and PBB are restricted.
Halogen Substitutes
By replacing flame retardant compounds and resins with halogen-free materials, halogen-free circuits eliminate the need for halogens.
Many PCB manufacturers replace halogen PBBs and PBDEs with phosphorus or phosphorus-nitrogen.
When phosphorus is burned, it decomposes to polyphosphoric acid. The polyphosphoric acid then dries on the surface and forms a carbonized layer that prevents the insulating resin from coming into contact with air. This creates a flame retardant effect. The entire process is free of harmful or combustible gasses, and can help extinguish a fire source by preventing oxygen.
Disadvantages of Halogen-Free PCB
Expensive:
PBB and PBDE are easy to manufacture, but chemical resins that eliminate halogens from printed circuit boards need special formulations. Companies that offer coatings charge more.
Few Manufacturers:
There are more manufacturers that offer traditional printed circuit boards, than there are halogen free printed circuits. This means the number of halogen free circuits you can purchase will be limited.
The Manufacturing Process can Be More Difficult:
The PCB can become more fragile and susceptible to white spots without halogens, which makes the manufacture of halogen free printed circuit boards harder, especially when it comes to manufacturing processes like solder mask production or appearance processing.
Advantages of Halogen Free PCB
Halogen-free PCBs are made from environmentally friendly materials, which are not harmful to health or the environment. Halogen-free circuit boards also offer the following advantages:
Environmentally Friendly
Halogen-free printed boards will reduce environmental pollution, and they will comply with the EU's halogen ban.
Protecting the Health and Safety at Work:
Halogen compounds release toxic gasses that can be harmful to humans at high temperatures. Using halogen-free material can reduce harmful gases produced during welding and heat treatments, protecting the health of workers and improving the safety of their working environment.
Insulate Circuit Boards:
The insulation materials that are free of halogens can be used for electronic disposables at a low cost. The polarity is reduced in epoxy resins when halogens have been replaced with phosphorus or Nitrogen. This improves the circuit insulation resistance and reduces the breakdown force.
Reduced Water Absorption
Low water absorption can improve the durability and reliability of boards. The phosphorus nitrogen molecule has fewer electrons compared to halogens. The molecules of halogens are difficult to combine with those of water, so halogen-free printed circuit boards resist water better. The halogen-free printed boards are smaller in size than PCBs but they can cope better with humid environments.
High Thermal Stability
The monomer molecular mass and Tg of halogen-free boards are higher because they contain more nitrogen and phosphorus. The molecular movement of halogen free materials is less than traditional epoxy resin circuit boards under heating conditions. Halogen-free boards are able to resist higher temperatures because they have lower thermal expansion coefficient. A halogen-free circuit board can withstand higher temperatures and is therefore more suitable for the design of high-power products.
Recyclable:
By recycling halogen-free boards, you can make the most of all metals in circuit boards such as copper, gold, and silver. These metal materials, when recycled, can help reduce the need for scarce resources and drive growth in related businesses, as well as provide employment for social talent.
Improve Market Competitiveness:
Halogen-free products can help enterprises improve their market competitiveness by attracting more customers. Halogen-free circuits can help enterprises show their commitment to the environment, and also their concern about the health and quality of their products. This can improve their brand reputation and their long-term growth.
Halogen-Free Materials
Halogen is used primarily in the production of laminates or prepreg layers. These substances are sometimes used in the solder paste that is used to assemble PCBs. In halogen-free systems, the compounds used to make halogen are replaced by safer materials.
• Halogen-Free Laminate
The substrate is laminate in halogen-free FR4 PCB. It is usually halogen-free, FR4 (FR = flame retardant). Here are some alternatives to both resin and flame retardant.
• Flame Retardants
In traditional PCBs are several brominated compounds, including PBB, PBDE TBBPA and HBCD. These compounds are substituted by the following flame retardant additives in halogen free printed circuit boards.
• Aluminum (aluminum hydroxide, aluminum diethyl phosphinate)
• Phosphorus
• Magnesium Hydroxide
• Ceramics
• Melamine derivatives
• Epoxy Resin
Epoxy resin is used to make FR4 laminates that are halogen free. This thermosetting polymer provides insulation and mechanical stability. This resin has traditionally contained halogens. The resins that are used in halogen-free board production are typically:
• Benzoxazine resin
• Bismaleimide triazine
• Trifunctional epoxy resin
• Bisphenol Epoxy Vinyl Ester
• Cyanate
• Polyimide
• Halogen-Free Flux
Circuit boards are assembled using halogenated flux or solder paste. Solder paste with bromine activater helps to remove oxidation from the soldering and also provides sanding qualities. Flux has been replaced with safer alternatives in the halogen free solder.
Halogen-Free PCB Manufacturing
The manufacturing process for halogen free boards is very similar to the conventional PCB production, with one exception: halogen material has been replaced by halogen free materials. Here are a few steps that you should know.
• Material Preparation
All materials used for the substrate, copper foil and solder mask, including epoxy resin, polyimide, etc., should be halogen free.
• Laminated
Lamination involves bonding the layers of the circuit together using the adhesiveness in the PP sheet. Copper foil, bonding sheets (prepreg sheets), and other materials can be overlapped to meet the requirements of the process.
• Drilling
The drilling conditions are crucial to the quality and thickness of PCB holes. Due to the higher rigidity of the material, drilling parameters are required for halogen-free copper clad laminates.
• Alkali Resistance
In general, the alkali resistance is lower for halogen-free sheets than it is for ordinary glass fibers. Therefore, extra care should be taken during the etching and rework processes after solder masking. To avoid white spots, the soaking time of the alkaline solution must not be excessive. When reworking halogen free solder mask boards it is recommended to first make the board, then find the parameters that work best, and then rework the boards in batches.
• Solder Mask
On the market, there are several halogen-free inks for solder masks. They perform similarly to liquid photosensitive inks and operate using the same methods as traditional PCBs.
Halogen Test Methods
You can use several different analytical techniques to determine the halogen level:
Combustion Ion Chromatography (CIC): Burning the sample releases halogen to be detected
X-ray fluorescence spectroscopy: Using X rays to stimulate halogen emission
Headspace analysis: Detection and measurement of halogen gas released during heating
Wet Chemistry: Solution-Based titration methods
Total Halogen Analysis: Measuring total Halogens bound to organic matter
Halogen Test Standards
This standard tests the finished PCB and substrate. Industry testing standards relevant to the industry include:
• IPC-4101 - Testing for Halogen in laminate base
• IEC 61249-2-21 - Testing PCB laminates for halogen after manufacture
• UL 746A: Determination by flammability of halogens in laminated panel
• IEC 61249-2-41 - Testing of total halogen in laminating Resins
Use of Halogen Free Circuit Boards
PCBs have been used in many different fields due to the popularity of electronics. In recent years, halogen-free printed boards have also become more popular. Common uses include:
• High-end computers and robots as well as large server farms
• Cellular phones and other wireless devices
• Transportation and signaling equipment
• Consumer electronics, such as televisions and gaming consoles
• Applications for traffic such as GPS and onboard computer equipment
• Substations and power stations
• Laboratory
• Sorting and distribution rooms
Halogen-Free Technology: The Future of Development
Halogen-free printed boards are safer, more environmentally friendly and more reliable than conventional circuit boards. The industry standard will become the new development trend for various manufacturers. More and more companies are investing heavily in research to create safer and cheaper halogen free sheets. In the future, we can expect to see more halogen-free sheets at lower prices.
