What aspect of halogen-free PCBs are you most interested in—regulations, materials, or environmental impact?
This article discusses the processing characteristics of halogen-free printed circuit boards and offers some insights from the processing experience.
1.3 Principle of Halogen-Free Substrate
Currently, most halogen-free materials are primarily phosphorus-based or phosphorus-nitrogen-based. When phosphorus resin is burned, it decomposes under heat to form meta-polyphosphoric acid, which has strong dehydrating properties. This results in the formation of a carbonized film on the resin’s surface, insulating it from air and extinguishing the fire, thereby achieving a flame-retardant effect. Additionally, phosphorus and nitrogen compounds in the polymer resin generate incombustible gases when burned, further enhancing the flame-retardant properties of the resin system.
2. Features of Halogen-Free Sheet
2.1 Insulation of Materials
By replacing halogen atoms with phosphorus or nitrogen, the polarity of the molecular bonds in the epoxy resin is reduced, improving the material’s insulation resistance and breakdown resistance.
2.2 Water Absorption of Materials
Halogen-free sheet materials, which use nitrogen-phosphorus-based oxygen reduction resins, contain fewer electrons compared to halogen-based materials. Consequently, the likelihood of forming hydrogen bonds with water is lower, resulting in reduced water absorption compared to conventional halogen-based flame retardant materials. For the board, lower water absorption positively impacts the material’s reliability and stability.
2.3 Thermal Stability of Materials
The nitrogen and phosphorus content in halogen-free sheet materials is higher than the halogen content in traditional halogen-based materials. This increases the monomer molecular weight and Tg value. As a result, when heated, the molecular mobility of halogen-free materials is lower than that of conventional epoxy resins, leading to a smaller coefficient of thermal expansion.
3. Experience in Producing Halogen-Free PCBs
Halogen-Free Sheet Suppliers
Currently, numerous suppliers have developed or are developing halogen-free copper-clad laminates and corresponding prepregs. Examples include Polyclad’s PCL-FR-226/240, Isola’s DEl04TS, Shengyi S1155/S0455, Nanya, Hongren GA-HF, and Matsushita Electric Works GX series.
3.1 Laminating
Lamination parameters may vary between companies. For example, using Shengyi substrates and prepregs for a multi-layer board, to ensure proper resin flow and strong bonding, a lower heating rate (1.0-1.5°C/min) is required, along with multi-stage pressure fitting. The high-temperature stage should be maintained at 180°C for more than 50 minutes. Below is a recommended platen program and actual temperature rise. The bonding force between the copper foil and the extruded board substrate was 1.0 N/mm, and after six thermal shocks, the board showed no delamination or air bubbles.
3.2 Drilling Processability
Drilling conditions are crucial as they directly affect the quality of the hole walls in the PCB. Halogen-free copper-clad laminates use phosphorus and nitrogen-based functional groups, which increase molecular weight and bond rigidity, thereby enhancing material rigidity. The Tg point of halogen-free materials is generally higher than that of standard copper-clad laminates, so conventional drilling parameters for FR-4 may not yield satisfactory results. When drilling halogen-free boards, adjustments should be made. For example, for a four-layer board made from Shengyi S1155/S0455 core board and prepreg, the drilling speed should be increased by 5-10% compared to normal parameters, while feed and retract speeds should be reduced by 10-15%. This approach minimizes hole roughness.
3.3 Alkali Resistance
Typically, the alkali resistance of halogen-free plates is lower than that of standard FR-4. Therefore, during the etching and rework processes after the solder mask, it is crucial to monitor the immersion time in alkaline stripping solutions to avoid white spots on the substrate. In practice, if a halogen-free board that has been cured and soldered requires rework after the solder mask, the standard FR-4 method may be inadequate. For example, after immersing in 10% NaOH at 75°C for 40 minutes, white spots were removed, but reducing the soaking time to 15-20 minutes resolved the issue. It is advisable to first optimize the rework parameters for halogen-free boards before proceeding with batch production.
3.4 Production of Halogen-Free Solder Mask
Many types of halogen-free solder mask inks are available globally, and their performance is comparable to that of ordinary liquid photosensitive inks. The application procedures for these inks are essentially the same as those for conventional inks.
4. Conclusion
Halogen-free PCBs exhibit low water absorption and meet environmental protection standards while maintaining other quality requirements. Consequently, the demand for halogen-free PCBs is rising, prompting major PCB suppliers to invest significantly in the research and development of halogen-free substrates and materials. It is anticipated that affordable halogen-free circuit board options will soon become available. Therefore, PCB manufacturers should prioritize the trial and adoption of halogen-free PCBs, develop detailed plans, and progressively increase their use to stay ahead of market demands.
WellCircuits is a leading manufacturer of halogen-free PCBs. For information about products manufactured by WellCircuits, click: Halogen-free PCB.
This article discusses the processing characteristics of halogen-free printed circuit boards and offers some insights from the processing experience.
1.3 Principle of Halogen-Free Substrate
Currently, most halogen-free materials are primarily phosphorus-based or phosphorus-nitrogen-based. When phosphorus resin is burned, it decomposes under heat to form meta-polyphosphoric acid, which has strong dehydrating properties. This results in the formation of a carbonized film on the resin’s surface, insulating it from air and extinguishing the fire, thereby achieving a flame-retardant effect. Additionally, phosphorus and nitrogen compounds in the polymer resin generate incombustible gases when burned, further enhancing the flame-retardant properties of the resin system.
2. Features of Halogen-Free Sheet
2.1 Insulation of Materials
By replacing halogen atoms with phosphorus or nitrogen, the polarity of the molecular bonds in the epoxy resin is reduced, improving the material’s insulation resistance and breakdown resistance.
2.2 Water Absorption of Materials
Halogen-free sheet materials, which use nitrogen-phosphorus-based oxygen reduction resins, contain fewer electrons compared to halogen-based materials. Consequently, the likelihood of forming hydrogen bonds with water is lower, resulting in reduced water absorption compared to conventional halogen-based flame retardant materials. For the board, lower water absorption positively impacts the material’s reliability and stability.
2.3 Thermal Stability of Materials
The nitrogen and phosphorus content in halogen-free sheet materials is higher than the halogen content in traditional halogen-based materials. This increases the monomer molecular weight and Tg value. As a result, when heated, the molecular mobility of halogen-free materials is lower than that of conventional epoxy resins, leading to a smaller coefficient of thermal expansion.
3. Experience in Producing Halogen-Free PCBs
Halogen-Free Sheet Suppliers
Currently, numerous suppliers have developed or are developing halogen-free copper-clad laminates and corresponding prepregs. Examples include Polyclad’s PCL-FR-226/240, Isola’s DEl04TS, Shengyi S1155/S0455, Nanya, Hongren GA-HF, and Matsushita Electric Works GX series.
3.1 Laminating
Lamination parameters may vary between companies. For example, using Shengyi substrates and prepregs for a multi-layer board, to ensure proper resin flow and strong bonding, a lower heating rate (1.0-1.5°C/min) is required, along with multi-stage pressure fitting. The high-temperature stage should be maintained at 180°C for more than 50 minutes. Below is a recommended platen program and actual temperature rise. The bonding force between the copper foil and the extruded board substrate was 1.0 N/mm, and after six thermal shocks, the board showed no delamination or air bubbles.
3.2 Drilling Processability
Drilling conditions are crucial as they directly affect the quality of the hole walls in the PCB. Halogen-free copper-clad laminates use phosphorus and nitrogen-based functional groups, which increase molecular weight and bond rigidity, thereby enhancing material rigidity. The Tg point of halogen-free materials is generally higher than that of standard copper-clad laminates, so conventional drilling parameters for FR-4 may not yield satisfactory results. When drilling halogen-free boards, adjustments should be made. For example, for a four-layer board made from Shengyi S1155/S0455 core board and prepreg, the drilling speed should be increased by 5-10% compared to normal parameters, while feed and retract speeds should be reduced by 10-15%. This approach minimizes hole roughness.
3.3 Alkali Resistance
Typically, the alkali resistance of halogen-free plates is lower than that of standard FR-4. Therefore, during the etching and rework processes after the solder mask, it is crucial to monitor the immersion time in alkaline stripping solutions to avoid white spots on the substrate. In practice, if a halogen-free board that has been cured and soldered requires rework after the solder mask, the standard FR-4 method may be inadequate. For example, after immersing in 10% NaOH at 75°C for 40 minutes, white spots were removed, but reducing the soaking time to 15-20 minutes resolved the issue. It is advisable to first optimize the rework parameters for halogen-free boards before proceeding with batch production.
3.4 Production of Halogen-Free Solder Mask
Many types of halogen-free solder mask inks are available globally, and their performance is comparable to that of ordinary liquid photosensitive inks. The application procedures for these inks are essentially the same as those for conventional inks.
4. Conclusion
Halogen-free PCBs exhibit low water absorption and meet environmental protection standards while maintaining other quality requirements. Consequently, the demand for halogen-free PCBs is rising, prompting major PCB suppliers to invest significantly in the research and development of halogen-free substrates and materials. It is anticipated that affordable halogen-free circuit board options will soon become available. Therefore, PCB manufacturers should prioritize the trial and adoption of halogen-free PCBs, develop detailed plans, and progressively increase their use to stay ahead of market demands.
WellCircuits is a leading manufacturer of halogen-free PCBs. For information about products manufactured by WellCircuits, click: Halogen-free PCB.
