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Jarnistech > HDI PCB > 1+N+1 HDI PCB

The growth of technological advancements in various industries has led to increased demand for compact, high-performance electronic devices. In response to this demand, the development of advanced printed circuit board (PCB) technologies has been crucial. One such technology is 1N1 HDI (High-Density Interconnect) PCB.

In this article, we delve into the design considerations, manufacturing processes, and design guidelines specific to 1N1 HDI PCBs. We explore the challenges associated with these PCBs, including complexity, manufacturing costs, and Important.

What Is 1+N+1HDI PCB?

1N1 HDI PCBs are designed to address the need for miniaturization while maintaining high functionality in electronic devices. They are characterized by their intricate layer stackup and interconnection density. The term “1N1” refers to a single lamination with a single layer of buried vias and a single layer of through-hole vias. This configuration allows for a higher density of circuitry and component placement, resulting in compact and powerful electronic devices.

1+N+1 HDI (High-Density Interconnect) PCB refers to a type of printed circuit board with a specific layer configuration and interconnect density. The “1+N+1” notation describes the layer stackup of the PCB.

In 1+N+1 HDI PCBs:

The “1” represents a single lamination layer. It consists of a solid inner copper layer.

The “N” signifies the number of additional core layers or laminations, which can vary depending on the specific design requirements. These additional core layers provide the necessary routing channels and help increase the interconnect density.

The final “+1” denotes another single lamination layer, similar to the first layer. This outermost layer usually serves as a power or ground plane.

The purpose of utilizing the 1+N+1 configuration in HDI PCBs is to achieve higher circuit density and miniaturization. This layer stackup allows for an optimal balance between functionality, signal routing, and component placement within a limited board area. By employing microvias (smaller, miniaturized vias) and intricate interconnect patterns, 1+N+1 HDI PCBs enable the design of compact electronic devices with enhanced performance and functionality.

1+N+1 HDI PCBs find applications in various industries, particularly where size, weight, and performance are critical factors. They are commonly used in the production of smartphones, tablets, wearable devices, medical equipment, and other electronic devices that require high-density packaging and advanced functionality.

High-Density Interconnect Printed Circuit Board Structures

For optimal performance, HDI Printed Circuit Boards (PCBs) employ various layering methods based on design requirements. To ensure successful manufacturing of your desired HDI board design, We strongly advises submitting the Board Stackup to our email at [email protected].

HDI PCB (1+N+1), the simplest HDI configuration, features one “build-up” of high-density interconnection layers. This structure is particularly suitable for BGA packages with lower I/O counts. It incorporates advanced technologies like fine lines, microvias, and precise registration capabilities, enabling compatibility with a 0.4 mm ball pitch. This design exhibits excellent mounting stability, reliability, and may involve copper filled vias for improved performance.

1+N+1 HDI PCB Stack-up

Typical applications benefiting from this HDI PCB design include cell phones, MP3 players, GPS systems, and memory cards.

Please feel free to send us your Board Stackup to [email protected] so we can validate the manufacturability of your desired HDI board design. As PCB manufacturer, we are committed to delivering exceptional quality and meeting your specific requirements.

Common Types of High Density Interconnector (HDI) 1+N+1 PCB Stackup

The HDI 1+N+1 structure represents the fundamental configuration for HDI (High-Density Interconnect) PCBs. In this structure, both the first and last layers require blind hole drilling, typically accomplished through laser drilling techniques. These holes are primarily targeted in the area occupied by BGA (Ball Grid Array) components, while leaving sufficient space in other regions.

For a four-layer board, the layer arrangement follows a 1-2 layer and 3-4 layer configuration. Similarly, in the case of a six-layer board, the layers are organized as 1-2 layers and 5-6 layers. Buried holes, as the term suggests, are not visible from the outer layers and remain concealed within the board.

 HDI 1+4+1(6 layers) typical Stackup, without buried vias

The six-layer HDI (High-Density Interconnect) PCB with a first-order design follows a 1+4+1 stackup configuration, where the layers are organized as one core layer, four signal layers, and one additional core layer. Unlike through-hole boards, this design solely utilizes through holes and blind vias without any buried vias.

The production of HDI PCBs necessitates specific processes, including press fitting, plating of blind vias, and through-hole formation. Compared to traditional multi-layer boards, HDI PCBs require additional manufacturing steps such as laser drilling for blind vias.

1+N+1 HDI PCB 6-Layer Stack-up

In the case of the 1+4+1 stackup configuration, where buried holes are absent, the 1st and 3rd layers can be utilized as a core board, while the 4th and 5th layers can serve as another core board. The outer layers are supplemented with a dielectric PP layer and copper foil. These layers are laminated together, with the addition of the dielectric PP layer in the middle. This manufacturing approach simplifies the PCB structure, reduces production costs, and shortens the overall production cycle.

HDI 1+4+1 typical Stackup, without through vias

To manufacture the 6-layer first-order blind buried via HDI PCB, a two-step lamination process is employed. In the first lamination, the core layers are fused together, and the buried vias are plated. Then, in the second lamination, resin is used to fill the blind vias. Finally, the blind vias are plated to establish electrical connections.

This HDI structure offers several benefits, including reduced costs and shorter delivery times. By eliminating the through-hole structure and employing blind and buried vias, the complexity of the PCB is minimized, resulting in more efficient production and cost savings.

Standard 6 layer HDI 1+4+1 Stackup

The standard 6-layer HDI 1+ PCB board follows a stackup format of 1+N+1, where N is an even number greater than or equal to 2. This stackup configuration, consisting of 1 signal layer sandwiched between 4 internal signal layers and 1 final signal layer, is widely utilized in the industry as the mainstream design for 6-layer HDI PCBs.

This particular board design incorporates various advanced features such as through holes, buried vias, and blind vias. The manufacturing process for this 6-layer HDI 1+ PCB is highly intricate and involves multiple steps. It requires two pressings, wherein the layers are pressed together, followed by plating to establish the buried vias. Subsequently, a resin plug is utilized to fill the holes, and plating is applied to create the blind vias and through holes.

Design Guidelines for 1+N+1 HDI PCBs

Designing 1+N+1 HDI (High-Density Interconnect) PCBs requires careful consideration of various factors to ensure successful implementation. Here are some important design guidelines to follow:

Layer Stackup:

Optimize the layer stackup to accommodate the required signal, power, and ground planes while considering the space constraints. Utilize microvia technology, such as blind and buried vias, to achieve higher interconnect density.

Component Placement:

Plan component placement strategically to minimize signal path lengths, reduce crosstalk, and optimize thermal management. Consider the specific requirements of high-speed signals to maintain signal integrity, including signal vias and differential routing.

Routing Guidelines:

Follow proper routing guidelines to maintain signal integrity and minimize signal losses. Use controlled impedance routing for high-speed signals and differential pairs. Maintain appropriate spacing and clearance between different signal traces and critical components.

Power Integrity:

Ensure a well-designed power distribution network (PDN) to maintain power integrity. Use dedicated power and ground planes to minimize noise and achieve low impedance paths. Strategically place decoupling capacitors near critical components to suppress voltage fluctuations.

Thermal Management:

Consider thermal management techniques to dissipate heat effectively. Ensure an efficient thermal pathway by connecting thermal vias to heat sinks or ground planes. Distribute heat-generating components evenly to prevent localized hotspots.

Design for Manufacturing (DFM):

Collaborate with PCB fabricators and assembly houses to understand their manufacturing capabilities and limitations. Follow DFM guidelines to optimize the design for manufacturability, including proper clearances, minimum via sizes, and panelization requirements.

EMI/EMC Considerations:

Pay attention to electromagnetic interference (EMI) and electromagnetic compatibility (EMC) issues. Minimize emissions by using proper grounding techniques, shielding, and signal routing practices. Implement signal integrity measures to reduce susceptibility to external interference.

Design for Testability (DFT):

Incorporate features that facilitate testing and diagnostics, such as test points, access to critical signals, and built-in self-test (BIST) capabilities. Design the board in a way that allows for efficient debugging and troubleshooting during the manufacturing and assembly stages.

Documentation and Communication:

Maintain clear and comprehensive design documentation, including a detailed bill of materials (BOM) and assembly drawings. Communicate effectively with the manufacturer and assembly house to ensure a smooth transition from design to production.

Simulation and Validation:

Utilize simulation tools to analyze and validate the design, including signal integrity, power integrity, thermal performance, and EMI/EMC characteristics. Iterate and optimize the design based on simulation results to achieve desired performance.

These guidelines will help ensure the success of your 1+N+1 HDI PCB design, taking into account factors such as signal integrity, power integrity, thermal management, manufacturing considerations, and compliance with industry standards.

Manufacturing Process 1+N+1 HDI PCBs

The manufacturing process for 1+N+1 HDI (High-Density Interconnect) PCBs involves several specialized steps to achieve the desired level of miniaturization and interconnection density. Here is an overview of the manufacturing process for 1+N+1 HDI PCBs:

Design and Layout:

The design phase involves creating a detailed layout considering the specific requirements of the circuit, component placement, and signal routing.

High-density designs require careful consideration of trace widths, spacing, and via sizes to ensure signal integrity and manufacturability.

Substrate Preparation:

The manufacturing process begins with preparing the substrate material. Typically, high-performance materials like FR-4, FR-4 with high Tg (glass transition temperature), or specialized materials such as polyimide (PI) are used.
The substrate is cut into appropriate size panels according to the design requirements.

Inner Layer Processing:

The inner layers of the HDI PCB are processed separately and then laminated together to form the multilayer structure.

A thin layer of copper is applied to both sides of the inner layer panels through a process called copper cladding.

The inner layers undergo a series of processes, including photoresist application, exposure, and development to create the desired copper traces and circuit patterns.

Laser Drilling:

Laser drilling is a critical step in the manufacturing of 1+N+1 HDI PCBs. High-precision lasers are used to drill microvias and blind vias in the inner layers.
The drilled holes provide interconnection between the different layers and allow for the routing of traces in smaller areas.

Dielectric Layer Buildup:

The dielectric layers, typically made of epoxy resin and glass fiber, are built up on the inner layer panels. This buildup can be achieved using multiple lamination cycles or semi-additive processes, depending on the specific design requirements.

Plating and Copper Deposition:

After forming the dielectric layers, the panels go through a process called electroless copper plating. This involves the deposition of a thin layer of copper onto the inner walls of the drilled microvias and blind vias.

Next, an additional layer of copper is electroplated onto the exposed copper surfaces to increase the thickness and enhance conductivity.

Outer Layer Processing:

The outer layer of the PCB is processed similarly to traditional PCBs. This involves applying a photoresist layer, patterning the circuitry using photolithography techniques, and etching away the unwanted copper.

Surface Finish and Solder Mask Application:

A surface finish is applied to protect the exposed copper surfaces and facilitate component soldering. Common surface finishes include HASL (Hot Air Solder Leveling), ENIG (Electroless Nickel Immersion Gold), and OSP (Organic Solderability Preservative).

Finally, a solder mask is applied to cover the entire PCB surface, leaving openings for pad areas where components will be soldered.

Final Inspection and Testing:

The finished PCBs undergo a thorough inspection and testing process to ensure quality and reliability. This includes checks for dimensional accuracy, circuit continuity, solderability, and electrical performance.

Importance of 1+N+1 HDI PCBs

The importance of 1+N+1 HDI (High-Density Interconnect) PCBs lies in their ability to meet the ever-increasing demand for smaller, lighter, and more complex electronic devices. Here are some key reasons why 1+N+1 HDI PCBs are important:


1+N+1 HDI PCBs allow for the miniaturization of electronic devices by enabling higher circuit density and reducing the overall size of the PCB. This is crucial for applications where space is limited, such as mobile devices, wearables, and IoT devices.

Increased functionality:

With their high-density interconnects, 1+N+1 HDI PCBs enable more complex and advanced electronic designs. They provide the necessary routing capabilities to accommodate a larger number of components, allowing for increased functionality and features in electronic devices.

Improved signal integrity:

HDI technology reduces the signal path length, thereby minimizing signal losses, crosstalk, and electromagnetic interference (EMI). This results in improved signal integrity and higher performance in high-speed digital and RF applications.

Enhanced reliability:

The use of 1+N+1 HDI PCBs can improve reliability in electronic devices. The reduced size and increased density minimize the number of interconnections, decreasing the probability of failure points. It also enables better thermal management and can help optimize the overall system reliability.

Cost optimization:

While 1+N+1 HDI PCBs may have a higher initial cost compared to traditional PCBs, their ability to reduce the overall size and weight of electronic devices can lead to cost savings in areas such as materials, manufacturing, assembly, and transportation.

Limitations and Challenges of 1+N+1 HDI PCBs

When it comes to 1+N+1 HDI (High-Density Interconnect) PCBs, there are certain limitations and challenges that need to be considered. Here are some common ones:

Complexity and Design Constraints:

The design of 1+N+1 HDI PCBs can be more complex compared to traditional PCBs. The increased density and miniaturization require careful consideration of routing, layer stackup, and component placement. Designers need to deal with tight design constraints, such as trace widths, spacing, and pad sizes, which can be challenging.

Manufacturing Processes:

1+N+1 HDI PCBs often require advanced manufacturing processes, such as laser drilling, sequential buildup, and multiple lamination steps. These processes can be more expensive and time-consuming compared to standard PCB manufacturing, adding to the overall production cost and lead time.


Implementing 1+N+1 HDI PCBs can be costlier compared to traditional PCBs due to the intricacies of design and manufacturing. The higher complexity and specialized processes involved can increase material costs, fabrication costs, and assembly costs.

Signal Integrity and Electromagnetic Interference (EMI):

As the density of components and interconnections increase in 1+N+1 HDI PCBs, signal integrity and EMI become more significant concerns. Careful layout and routing techniques need to be employed to mitigate signal integrity issues such as impedance mismatches, signal reflections, and noise coupling.

Thermal Management:

Higher circuit density in 1+N+1 HDI PCBs can lead to increased heat dissipation challenges. Efficient thermal management becomes critical to prevent overheating and ensure the long-term reliability of the electronic components.

Reliability and Repairability:

The miniaturization and complexity of 1+N+1 HDI PCBs can make them more challenging to repair and troubleshoot in case of failure. Accessibility to individual components and repair points may be limited, requiring specialized equipment and expertise.

Testing and Inspection:

The dense layout and multiple layers of 1+N+1 HDI PCBs can make testing and inspection processes more challenging. Extra care and sophisticated testing methods may be necessary to ensure thorough functionality testing and quality control.

Despite these limitations and challenges, the benefits, such as miniaturization, increased functionality, and improved signal integrity, make 1+N+1 HDI PCBs indispensable for many advanced electronic applications. As technology advances and the industry continues to innovate, efforts are being made to address and overcome these challenges in 1+N+1 HDI PCB design and manufacturing.


HDI PCB technology plays a pivotal role in enabling the design of miniaturized electronics by incorporating high density interconnects, fine features, and thin materials. With the increasing demand for thinner and lighter products, HDI offers a solution to accommodate a greater amount of functionality and components in compact spaces.

1+N+1 HDI boards are widely employed in the production of printed circuit boards (PCBs), particularly when dealing with a BGA (Ball Grid Array) pitch of 0.5. These boards are specifically utilized when the thickness of the HDI circuit board FR4 sheet is equal to or less than 4 mil. In the case of utilizing PP (Prepreg) material, it is generally recommended to use 1080, while avoiding the usage of 2116 PP whenever possible.

When customers do not provide specific requirements, it is preferable to use 1OZ copper foil on the inner layer of traditional PCBs. However, for HDI boards, it is preferable to use HOZ copper foil, while 1/3OZ copper foil is preferred for the internal and external plating layers. These guidelines are aimed at ensuring optimal performance and compatibility with the given specifications. As a professional PCB manufacturer, we prioritize the use of appropriate materials and techniques to meet the highest industry standards.

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