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Halogen Free Circuit Board Stackups

Jarnistech > Halogen Free PCB > Halogen Free Circuit Board Stackups
Purple Soldermask Halogen Free PCB

In today’s environmentally conscious landscape, there is a growing demand for halogen-free printed circuit boards (PCBs) due to their superior environmental friendliness and reduced health risks compared to traditional halogenated PCBs. However, designing halogen-free PCBs comes with various challenges, including material availability, cost implications, and considerations for performance and reliability.

This comprehensive guide aims to equip you with the necessary knowledge to successfully design halogen-free circuit board stackups. We will delve into the complexities and limitations associated with halogen-free materials while outlining the essential steps involved in creating a high-performance and reliable halogen-free PCB stackup.

Design Considerations for Halogen-Free Stackups

When embarking on the design of halogen-free PCB stackups, it is imperative to consider several key factors to guarantee optimal performance and unwavering reliability. These crucial considerations encompass:

Material Selection:

The meticulous selection of base materials, prepregs, and laminates assumes paramount importance in halogen-free stackup design. Every layer of the stackup, including the core, prepregs, and surface finishes, must be composed of halogen-free materials.

Stackup Architecture:

The layer count, thickness, and sequencing of the stackup layers necessitate meticulous deliberation to attain the desired electrical and mechanical properties. Given that halogen-free materials often exhibit dissimilar dielectric constants and thermal expansion coefficients compared to halogenated materials, these factors must be accounted for during stackup design.

Via Selection and Placement:

Optimal selection of via barrel material and via fill material is crucial to ensure adherence to halogen-free standards. Viable options for halogen-free via barrel materials encompass copper, nickel, and tungsten, while epoxy and conductive paste are among the suitable choices for halogen-free via fill materials.

Fabrication and Assembly:

The fabrication and assembly processes for halogen-free PCBs demand particular attention. It is imperative to employ halogen-free materials and processes for laminate processing, drilling and routing, plating and etching, as well as soldering and assembly.

By diligently considering these design factors, engineers can successfully craft halogen-free PCB stackups that exhibit exceptional performance and reliability, aligning harmoniously with the specific requirements of their applications.

Additional Tips for Halogen-Free Stackup Design:

1. Utilize a design for manufacturability (DFM) tool to proactively identify potential fabrication issues and rectify them at the design stage.

2. Collaborate closely with your chosen PCB fabricator to ensure that they possess the requisite experience and capabilities to effectively manufacture halogen-free PCBs.

3. Subject your halogen-free PCB stackups to rigorous testing to validate their adherence to the desired electrical and mechanical performance requirements, ensuring their compliance with industry standards and regulations.

By adhering to these guidelines and leveraging the expertise of experienced professionals, PCB designers can confidently navigate the intricacies of halogen-free stackup design, yielding superior results and enhancing the overall quality of their PCB designs.

How to Design Halogen Free Circuit Board Stackups?

Designing halogen-free circuit board stackups involves several steps to ensure compliance with halogen-free standards and regulations. Here’s a guide from a designer’s perspective on how to design halogen-free circuit board stackups:

1. Understand Halogen-Free Requirements: Familiarize yourself with the specific halogen-free requirements and standards applicable to your project. Common standards include IEC 61249-2-21 and IPC-4101C.

2. Select Halogen-Free Materials: Choose circuit board materials that are specifically labeled as halogen-free. These materials typically consist of halogen-free laminates and prepregs that do not contain bromine or chlorine compounds. Look for materials that meet the desired electrical, thermal, and mechanical properties for your application.

3. Determine Layer Count: Determine the required number of layers for your circuit board based on the complexity of the design and functionality requirements. Consider factors like signal integrity, power distribution, and component density.

4. Define Layer Stacking Sequence: Decide on the layer stacking sequence, which determines the arrangement of signal, power, and ground planes within the stackup. A typical stackup for a halogen-free design may include signal layers, power planes, and ground planes in alternating layers.

5. Plan Power and Ground Plane Distribution: Distribute power and ground planes strategically throughout the stackup to minimize noise, provide solid return paths, and ensure proper power distribution. It’s advisable to have dedicated power and ground planes adjacent to signal layers to reduce electromagnetic interference (EMI) and maintain signal integrity.

6. Consider Impedance Control: If your design requires controlled impedance traces, incorporate appropriate dielectric materials and trace geometries to achieve the desired impedance values. This is particularly important for high-speed designs. Consult with your PCB manufacturer for specific impedance control guidelines.

7. Define Copper Weight and Thickness: Specify the desired copper weight and thickness for each layer. The copper weight determines the amount of current the traces can carry, while the copper thickness affects the overall thickness and flexibility of the board.

8. Incorporate Solder Mask and Silkscreen Layers: Include solder mask layers to protect copper traces and pads from oxidation and facilitate soldering. Add silkscreen layers for component identification and assembly reference markings.

9. Define Board Thickness: Determine the overall board thickness based on mechanical requirements, such as fitting within enclosures or meeting specific dimensional constraints. Ensure the chosen thickness is within the capabilities of your PCB manufacturer.

10. Verify Compliance: Double-check that your chosen materials and stackup design meet the halogen-free requirements and standards mentioned in the first step. Consult with your PCB manufacturer or a compliance expert if needed.

11. Document the Stackup: Create a comprehensive stackup documentation that includes layer order, material types, thicknesses, copper weights, and any additional considerations. This documentation helps ensure consistency during fabrication and assembly.

Remember to collaborate closely with your PCB manufacturer and follow their guidelines to ensure a successful and compliant halogen-free circuit board stackup design.

Challenge and Limitations of Designing Halogen Free PCB Stack-up

Designing halogen-free PCB stackups entails a set of challenges and limitations that necessitate careful consideration from engineers. These challenges encompass:

Material Availability: The availability of halogen-free materials for PCB fabrication is comparatively limited in comparison to their halogenated counterparts. This can pose difficulties in finding materials that precisely meet the requirements of a specific application.

Cost: Halogen-free materials often come with a higher price tag than halogenated materials. This can escalate the manufacturing cost of halogen-free PCBs.

Performance: Halogen-free materials may exhibit distinct electrical and mechanical properties when compared to halogenated materials. As a result, the performance of the PCB can be affected.


Halogen-free PCBs may exhibit lower reliability than their halogenated counterparts. This is because halogenated materials have a protective effect against environmental factors such as moisture and heat.

Overcoming the Challenges:

Despite these challenges, it is possible to design halogen-free PCB stackups that deliver high performance and reliability. By conducting meticulous material selection and optimizing the stackup design, engineers can overcome the limitations associated with halogen-free materials.


However, it is important to acknowledge that certain limitations in designing halogen-free PCB stackups cannot be entirely overcome. For instance, halogen-free materials may not provide the same level of protection against moisture and heat as halogenated materials. Consequently, halogen-free PCBs may not be suitable for applications that demand exceptional reliability or that will be subjected to harsh environmental conditions.

By exercising prudence, leveraging available resources, and making informed decisions, PCB designers can navigate these challenges and limitations associated with halogen-free PCB stackup design, ensuring the development of robust and effective solutions aligned with the specific requirements of their applications.

Which Types PCBs Board will need Halogen Free Stack-ups?

Halogen-free PCB stackups are typically required for a wide range of printed circuit boards (PCBs) used in various industries. Here are some examples of PCB types that commonly require halogen-free stackups:

1. Single-Sided PCBs: Even though single-sided PCBs are relatively simple in design, they may still require halogen-free stackups if they are used in applications that need to comply with environmental regulations or industry standards.

2. Double-Sided PCBs: Double-sided PCBs, with copper traces and components on both sides of the board, often require halogen-free stackups. These PCBs are commonly used in consumer electronics, automotive applications, and other industries where environmental compliance is necessary.

3. Multilayer PCBs: Multilayer PCBs, which consist of three or more layers of conductive material separated by insulating layers, frequently require halogen-free stackups. These PCBs are used in a wide range of applications, including telecommunications, industrial equipment, medical devices, and more.

4. High-Speed PCBs: PCBs used in high-speed applications, such as data communication systems, network equipment, and high-frequency devices, often need to be halogen-free. These PCBs require careful design considerations for impedance control, signal integrity, and EMI/RFI (electromagnetic interference/radio frequency interference) mitigation.

5. RF/Microwave PCBs: PCBs used in radio frequency (RF) and microwave applications, such as wireless communication systems, radar systems, and satellite equipment, may require halogen-free stackups. These PCBs need to meet stringent requirements for signal integrity, impedance control, and low loss.

6. Flexible PCBs: Flexible PCBs, also known as flex PCBs, are used in applications that require the board to be bent, twisted, or folded. Halogen-free stackups are often necessary for flexible PCBs used in industries such as consumer electronics, automotive, and medical devices.

7. High-Density Interconnect (HDI) PCBs: HDI PCBs are designed to accommodate a high density of components and interconnections in a compact form factor. These PCBs, commonly used in smartphones, tablets, and other miniaturized devices, often require halogen-free stackups to meet environmental regulations and industry standards.

It’s important to note that the specific requirement for a halogen-free stackup may vary based on the industry, application, and regional regulations.


Designing halogen-free circuit board stackups is an essential aspect of modern PCB design, aligning with the growing emphasis on environmental sustainability. By carefully selecting halogen-free materials, optimizing the stackup architecture, and considering fabrication and assembly processes, engineers can create PCBs that are both high-performing and environmentally friendly. Embracing halogen-free design practices not only reduces the potential risks associated with halogens but also contributes to a greener and more sustainable future. Let us strive for halogen-free circuit board stackups, paving the way for a cleaner and safer electronics industry.

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