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Jarnistech > HDI PCB > 4+N+4 HDI PCB

The 4+N+4 HDI PCB (High-Density Interconnect Printed Circuit Board) represents a significant technological advancement in the field of PCB design and fabrication. This sophisticated circuit board offers enhanced capabilities for complex electronic applications, providing improved signal integrity, reduced power consumption, and increased miniaturization.

In this article, we will delve into the features, benefits, Challenges ,Limitations, applications, design, stack-up and manufacturing of the 4+N+4 HDI PCB, exploring its role in advancing various industries and driving innovation in electronic devices.

Overview of 4+N+4 HDI PCB

A 4+N+4 HDI PCB refers to a high-density interconnect (HDI) printed circuit board with a specific layer configuration. HDI technology is used to create PCBs with high-density and fine-pitch components, allowing for smaller and more complex electronic devices.

The “4+N+4” notation in 4+N+4 HDI PCB refers to the layer stackup of the board. Let’s break it down:

The first “4” represents the four conventional layers in the PCB. These are typically made of a core material like FR-4 and contain the basic circuitry and power/ground planes.

The “N” represents the number of additional layers, which are often referred to as “microvia” layers. Microvias are small, laser-drilled holes used to create electrical connections between the layers. The number of microvia layers can vary depending on the specific design requirements but is typically higher in HDI boards to accommodate the high-density components.

The second “4” represents the final four conventional layers, similar to the first four layers. These layers provide additional routing space and power/ground planes.

In total, the 4+N+4 configuration consists of four conventional layers, a variable number of microvia layers (N), and another four conventional layers. This stackup allows for increased routing density, finer traces, and smaller via sizes, enabling complex and compact electronic designs.

4+N+4 HDI PCB Stack-up

The stack-up for a 4+N+4 HDI PCB (High-Density Interconnect Printed Circuit Board) typically consists of four outer signal layers, N number of microvia (build-up) layers, and four inner signal layers. Here is a general example of a stack-up for a 4+N+4 HDI PCB:

4+N+4 HDI PCB Stack-up

1. Top Signal Layer: This is the topmost layer of the PCB, where high-speed signal traces and components are placed. It may also include top-side solder mask and silkscreen.

2. Inner Signal Layers (1-4): These are the four inner layers of the PCB, sandwiched between the outer signal layers. They typically consist of signal traces, power planes, and ground planes, depending on the specific design requirements.

3. Microvia (Build-up) Layers (1-N): These are the intermediate layers in the stack-up. The number of microvia layers, denoted by N, can vary depending on the design complexity and density requirements. Microvias are used to connect the inner signal layers and enable high-density interconnections.

4. Core Layer: This is the central layer of the PCB that provides mechanical strength and stability. It may consist of a solid core material or a combination of multiple laminated core materials.

5. Prepreg Layers: Prepreg layers are resin-impregnated fiberglass layers used to bond the core layer and the inner signal layers together. They provide insulation and help in maintaining the structural integrity of the PCB.

6. Inner Signal Layers (5-8): Similar to the inner signal layers (1-4), these layers consist of signal traces, power planes, and ground planes. They are positioned below the microvia layers and above the bottom signal layer.

7. Bottom Signal Layer: This is the bottom most layer of the PCB, where additional signal traces and components can be placed. It may also include bottom-side solder mask and silkscreen.

It’s important to note that the specific stack-up configuration may vary depending on the design requirements, such as impedance control, signal integrity, thermal considerations, and manufacturing constraints. Consulting with a PCB designer and manufacturer is recommended to determine the optimal stack-up for your specific 4+N+4 HDI PCB design.

Importance and Applications of 4+N+4 HDI PCB

The 4+N+4 HDI PCB offers significant advantages over traditional PCBs, making it crucial in various industries where high-density and compact electronic designs are required. Here are the importance and applications of 4+N+4 HDI PCBs:


The primary importance of 4+N+4 HDI PCBs lies in their ability to enable miniaturization of electronic devices. With their high-density interconnect technology, these PCBs allow for smaller and more compact designs, which is particularly valuable in portable consumer electronics like smartphones, tablets, wearables, and IoT devices. The reduced size and weight of devices enhance their portability and usability.

High-density component integration:

The HDI technology used in 4+N+4 PCBs allows for the placement of high-density and fine-pitch components. This enables the integration of more functionality within a limited board space. The increased routing density and smaller via sizes facilitate the incorporation of advanced features, such as advanced sensors, high-speed connectors, processors, and memory modules. Consequently, HDI PCBs are vital for applications requiring complex electronic systems, including telecommunications, automotive electronics, medical devices, and aerospace systems.

Improved signal integrity:

The high-density interconnects and reduced trace lengths in 4+N+4 HDI PCBs contribute to improved signal integrity. This means that high-frequency signals can be transmitted with minimal loss or distortion, ensuring reliable performance of the electronic device. This feature is particularly crucial in applications such as high-speed data communication, wireless devices, and high-frequency RF applications.

Enhanced reliability:

The use of microvias in 4+N+4 HDI PCBs provides several reliability benefits. Microvias enable more direct signal routing, reducing the length of signal paths and minimizing the risk of signal degradation. Additionally, the smaller via sizes reduce the possibility of solder joint failures and improve thermal management. These factors collectively enhance the overall reliability and longevity of the electronic devices.

Cost optimization:

While HDI PCBs may be more expensive than traditional PCBs due to their specialized manufacturing processes, they can lead to cost savings in other areas. The miniaturization and increased functionality enabled by HDI PCBs can reduce the need for additional components, connectors, and cables, resulting in cost savings in assembly, material, and overall system costs.

In summary, the importance of 4+N+4 HDI PCBs lies in their ability to enable miniaturization, high-density integration, improved signal integrity, enhanced reliability, and overall cost optimization. These features make them essential components in a wide range of applications, including consumer electronics, telecommunications, automotive, medical devices, and aerospace systems.

Design Considerations for 4+N+4 HDI PCB

Designing a 4+N+4 HDI (High-Density Interconnect) PCB requires careful consideration of various factors to ensure optimal performance and reliability. Here are some key design considerations to keep in mind:

Signal Integrity and Impedance Control:

Maintain signal integrity by properly controlling impedance throughout the PCB design.

Use controlled impedance traces and ensure consistent trace widths, spacing, and dielectric materials to achieve desired impedance values.

Employ impedance matching techniques for high-speed signal paths to minimize signal reflections and maintain signal integrity.

Thermal Management:

Effective heat dissipation is crucial for the reliability and performance of electronic components.

Incorporate thermal vias and thermal pads to facilitate heat transfer from hot components to the PCB’s copper planes or heat sinks.

Ensure proper component placement and thermal relief to minimize heat buildup and temperature differentials.

Component Placement and Routing:

Optimize component placement to minimize signal crosstalk, reduce electromagnetic interference (EMI), and ensure efficient signal flow.

Group components based on their functional requirements and signal characteristics to minimize signal interference.

Utilize advanced design tools and techniques, such as blind and buried vias, to optimize the layout and routing of the PCB.

Power and Ground Plane Distribution:

Distribute power and ground planes strategically to provide low-impedance paths for power distribution and effective noise shielding.

Use multiple power and ground planes to minimize voltage drops, reduce noise, and provide stable power supply to sensitive components.

Ensure proper decoupling capacitor placement near high-speed components to suppress power supply noise and maintain signal integrity.

EMI/EMC Considerations:

Implement proper grounding techniques, such as star grounding, to minimize ground loops and reduce EMI.

Use shielding techniques, such as ground planes and signal isolation, to prevent electromagnetic interference between different circuit sections.

Follow EMC (Electromagnetic Compatibility) guidelines and standards to ensure compliance with electromagnetic emission and immunity requirements.

Design for Manufacturability (DFM):

Consider manufacturing constraints and capabilities during the design phase to ensure ease of fabrication and assembly.

Use design rules and guidelines provided by the PCB manufacturer to avoid issues related to minimum trace widths, spacing, and manufacturing tolerances.

Collaborate closely with the PCB manufacturer to optimize the design for manufacturability and achieve desired performance within manufacturing constraints.

Reliability and Testing:

Consider reliability aspects, such as thermal stress, vibration, and mechanical stability, during the design phase.

Perform thorough design verification and testing, including signal integrity analysis, thermal analysis, and functional testing, to ensure the reliability and performance of the PCB.

By taking these design considerations into account, you can optimize the performance, reliability, and manufacturability of 4+N+4 HDI PCBs for your specific application requirements.

Manufacturing Process of 4+N+4 HDI PCB

The manufacturing process of 4+N+4 HDI (High-Density Interconnect) PCB involves several steps to create the desired layer structure and interconnections. Here is an overview of the typical manufacturing process for 4+N+4 HDI PCBs:

1.Layer Stackup and Material Selection:

Determine the layer stackup configuration based on the design requirements, including the number of signal layers, power and ground planes, and additional signal layers.

Select high-quality materials with excellent electrical properties, such as high Tg (glass transition temperature) laminates, to ensure optimal performance.

2.Inner Layer Processing:

Start with a copper-clad laminate sheet, which acts as the base material for the inner layers.

Clean the laminate surface and apply a photosensitive dry film or liquid photoresist to create a protective layer.

Use a photomask to expose the desired circuit patterns on the photoresist and develop it to remove the unexposed areas.

Etch the exposed copper to create the circuit traces and remove the remaining photoresist.

3.Microvia Fabrication:

Microvias are small drilled holes used to establish connections between different layers in HDI PCBs.

Utilize laser drilling or mechanical drilling techniques to create microvias in the appropriate locations.

Copper is then plated inside the microvias to create reliable interconnections.

4.Build-Up Process:

The build-up process involves laminating multiple thin layers of dielectric material and copper foils to create the desired layer structure.

Each layer is carefully aligned and bonded together using heat and pressure.

Excess material is removed through chemical or mechanical processes, leaving behind the desired circuit patterns.

5.Outer Layer Processing:

Similar to the inner layer processing, the outer layer processing involves applying a photosensitive dry film or liquid photoresist on the outer copper layers.

The desired circuit patterns are exposed and developed, and the exposed copper is etched to create the outer layer circuitry.

6.Surface Finish and Solder Mask Application:

Apply a surface finish to protect the exposed copper and provide a solderable surface. Common surface finishes include HASL (Hot Air Solder Leveling), ENIG (Electroless Nickel Immersion Gold), and OSP (Organic Solderability Preservative).

Apply a solder mask over the entire PCB surface, leaving openings for component pads and vias.

The solder mask protects the copper traces and prevents solder bridges during assembly.

7.Silkscreen Printing and Legend Marking:

Silkscreen printing is used to apply component designators, logos, and other markings on the PCB surface.

Legend marking is performed to provide additional information, such as component values, reference designators, and assembly instructions.

8.Electrical Testing and Inspection:

Conduct electrical testing, such as continuity testing and impedance measurement, to ensure the integrity of the circuitry.

Perform visual inspection and automated optical inspection (AOI) to detect any manufacturing defects or soldering issues.

9.PCB Panelization and Separation:

Multiple PCBs are often fabricated on a single larger panel to optimize manufacturing efficiency.

After testing and inspection, the panel is separated into individual PCBs using methods like routing, scoring, or laser cutting.

10.Final Inspection and Packaging:

Conduct a final inspection to verify the quality and functionality of the finished PCBs.

Clean the PCBs to remove any residues or contaminants.

Package the PCBs according to the specific requirements, ensuring protection during transportation and storage.

Throughout the manufacturing process, close collaboration between the PCB designer and the manufacturer is crucial to address any design-related issues, ensure manufacturability, and achieve the desired performance and reliability of the 4+N+4 HDI PCBs.

Challenges and Limitations of 4+N+4 HDI PCB

While 4+N+4 HDI (High-Density Interconnect) PCBs offer numerous benefits, they also present some challenges and limitations that designers and manufacturers need to consider. Here are some of the key challenges and limitations associated with 4+N+4 HDI PCBs:

Complexity of Design:

Designing 4+N+4 HDI PCBs can be complex due to the high density of components and interconnections. Careful consideration is required for signal integrity, power distribution, thermal management, and routing constraints.

Manufacturing Complexity:

The manufacturing process for 4+N+4 HDI PCBs is more complex compared to traditional PCBs. It involves additional steps such as microvia drilling, sequential lamination, and multiple build-up cycles, which can increase production time and cost.


The complexity and additional manufacturing steps involved in producing 4+N+4 HDI PCBs can result in higher manufacturing costs compared to standard PCBs. The use of specialized materials and advanced manufacturing techniques can further contribute to the overall cost.

Manufacturing Yield:

The high density and complexity of 4+N+4 HDI PCBs can increase the risk of manufacturing defects. Achieving high manufacturing yield and ensuring consistent quality can be challenging, especially for intricate designs and fine-pitch components.

Signal Integrity and Crosstalk:

With the increasing density of components and interconnections, maintaining signal integrity and minimizing crosstalk become critical. Proper impedance control, controlled routing, and careful placement of components are essential to mitigate signal integrity issues.

Thermal Management:

The high component density in 4+N+4 HDI PCBs can lead to thermal challenges. Effective heat dissipation becomes crucial to prevent overheating and ensure the reliability of components. Designers need to consider proper thermal management techniques, such as thermal vias and heat sinks.

Design for Manufacturability (DFM):

The complex nature of 4+N+4 HDI PCBs requires close collaboration between designers and manufacturers. Ensuring that the design is manufacturable and meets the capabilities and constraints of the manufacturing process is essential to avoid costly rework or manufacturing issues.

Testing and Debugging:

The increased complexity and density of 4+N+4 HDI PCBs can pose challenges during testing and debugging. Accessing and probing individual components or signals can be difficult, requiring specialized testing techniques and equipment.

Component Availability and Size Limitations:

The miniaturization and high-density requirements of 4+N+4 HDI PCBs may limit the availability of certain components, especially for fine-pitch and high-pin-count devices. Designers need to carefully select components that meet the size and performance requirements.

Despite these challenges and limitations, 4+N+4 HDI PCBs are widely used in applications that demand high-density interconnections, such as mobile devices, telecommunications equipment, medical devices, and high-speed data communication systems. With careful planning, collaboration, and optimization, these challenges can be overcome to achieve the desired performance and functionality in 4+N+4 HDI PCB designs.

In Conclusion

the 4+N+4 HDI PCB stands as a remarkable achievement in PCB technology, revolutionizing the electronic industry’s landscape. With its high-density interconnects, multiple layers, and advanced fabrication techniques, this PCB offers unparalleled performance, reliability, and miniaturization. It has become a crucial component in a wide range of applications, from smartphones and tablets to medical devices and automotive systems. As technology continues to advance rapidly, the 4+N+4 HDI PCB will undoubtedly play a vital role in enabling the development of cutting-edge electronic devices, pushing the boundaries of what is possible in the world of innovation.

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