HDI PCB: Improving Circuit Utilization with High-Density Interconnect Technology

Electronic engineers worldwide are diligently engaged in the pursuit of advancing technology to minimize electronic footprint while maximizing functionality. HDI PCB technology represents a significant breakthrough in this endeavor, aiming to deliver remarkable circuit layouts and performance within confined spaces. In this article, FS Technology will immerse you in the realm of HDI, unveiling the exciting prospects it holds for the future of electronic manufacturing. Are you prepared? Let us embark upon this exhilarating voyage of exploration!

What is HDI PCB

HDI PCB Definition

The full form of HDI in PCB is High Density Interconnect, which refers to a specialized circuit board type designed to achieve a higher wiring density per unit area compared to standard PCBs. It incorporates advanced features such as smaller vias, increased pad density, and optimized routing channels to enhance electrical performance and minimize the overall size and weight of both the board and the devices utilizing it.

The primary objective of HDI PCB boards is to maximize space utilization by reducing the board size while accommodating a greater number of components. This is made possible through the utilization of microvias, blind vias, and buried vias, which enable the incorporation of additional routing layers within a smaller footprint. Moreover, the reduced diameter and pitch of these vias allow for more efficient routing channels, further optimizing the board’s functionality and performance.

Importance of High Density Interconnect PCB in Electronics

The increasing demand for compact and efficient electronic products necessitates the use of high density circuit boards, enabling the integration of more complex circuits within a smaller area. Let’s explore the applications of HDI technology in various fields:

  • Artificial Intelligence (AI): The advancement of AI technology requires equipment with exceptional computing power and rapid data processing. HDI technology in PCB finds significant relevance in this domain, as higher circuit density plays a pivotal role in handling extensive AI data and intricate algorithms.
  • Internet of Things (IoT): Refers to the interconnection of physical devices, sensors, and objects through Internet connectivity. The integration of multiple components and sensors within limited space, along with the need for functional integration and complex circuit connections, highlights the importance of the HDI PCB board in IoT applications.
  • High-Frequency Applications: Although high-frequency PCB is commonly associated with high-frequency applications, HDI PCB also play a crucial role in this domain. High-frequency PCBs operate in the GHz frequency range, transmitting electromagnetic waves between 500MHz and 2GHz. They are preferred for high-speed signal processing with minimal distortion and signal loss, while also reducing Electromagnetic Interference (EMI) and Radio Frequency Interference (RFI). HDI PCB enhances these advantages through technologies such as microvias, blind vias, and buried vias. In wireless communication devices, a combination of high-frequency and High Density Interconnection is often employed.
  • Consumer Electronics: Although high density PCB may not be cost-effective for projects with low-profit margins in the consumer electronics sector, they are essential for devices like laptops, tablets, and smartphones. The popularity of these products lies in their compactness and lightweight design, both of which necessitate high-density interconnection through PCB.
  • Medical Devices and Aerospace Defense: HDI printed circuit boards find favorable applications in these industries due to their reliability and durability. Medical equipment, such as MRI and ultrasound scanners, as well as aerospace defense systems and missile technology, benefit from the robustness and high-performance capabilities offered by HDI PCB.

Benefits of HDI Printed Circuit Boards

  • Increased Component Density: Leverage advanced technologies like microvias, blind vias, and buried vias to enable higher component density on the board’s surface.
  • Enhanced Signal Integrity: The implementation of microvias allows for shorter signal paths, minimizing signal interference, crosstalk, and ensuring superior signal integrity and overall board performance.
  • Improved Reliability: With fewer vias reduce the risk of via failure and enhance thermal management. Controlled impedance helps mitigate signal distortion and electromagnetic interference, resulting in heightened circuit reliability.

HDI PCB vs.Traditional PCB

Layer countFewer More
Routing densityLowerHigher
Component densityLowerHigher
Signal integrityLowerHigher
Thermal managementLessMore
Manufacturing timeShorterLonger

Types of HDI PCB


1+N+1HDI PCB structure

The 1+N+1 HDI PCB configuration is a highly advanced multi-layer structure designed to optimize component placement and enhance signal integrity in a cost-effective manner. While offering numerous advantages, it requires a more comprehensive manufacturing process compared to traditional PCBs, resulting in increased production time and expenses.

The “1” represents a standard PCB layer, while “N” denotes additional HDI layers. This configuration involves combining a conventional PCB layer with an extra HDI layer on the top surface. This integration significantly improves routing density and minimizes signal loss, making it an ideal solution for high-speed and high-frequency applications.

The “N” layer in the 1+N+1 HDI board incorporates buried vias and microvias, enabling the routing of multiple layers within a limited area. These additional routing channels facilitate higher component density and reduce the overall size of the board.


2+N+2 HDI PCB structure

Similar to the 1+N+1 structure, the “2” in 2+N+2 refers to two conventional board layers, while N represents the number of additional HDI layers. In this configuration, two regular board layers are combined with an extra HDI layer on the upper surface. This arrangement enhances component density and improves signal integrity, resulting in increased routing density and reduced signal loss. Consequently, the 2+N+2 configuration is particularly well-suited for intricate design projects requiring optimal performance.

Any Layer

Any Layer HDI PCB structure

Any Layer, also referred to as “Every Layer Interconnect” (ELIC) or Any Layer Interstitial Via Hole, is a design concept widely used in HDI technology. It is specifically designed to achieve the maximum component density and enhance signal integrity compared to other types of HDI boards. By enabling the utilization of more routing layers within a limited space, it offers engineers greater flexibility in component placement and routing. In the realm of HDI multilayer PCB, Any Layer technology allows for the placement of vias on any layer of the circuit board, be it an internal layer or a surface layer.

HDI PCB Design Guidelines

  • Component Placement: On the HDI board surface, precise component placement is crucial for achieving a compact and efficient design. Designers meticulously evaluate the size and positioning of components to optimize board space utilization and functionality.
  • Layer Stackup: It require a sophisticated layer stackup with multiple layers incorporating various via types. The layer stackup is carefully optimized to meet the specific requirements of the application.
  • Routing Density: The routing density of HDI circuit is significantly higher than that of conventional boards. Designers must skillfully plan and implement the routing, aiming to minimize signal paths and reduce signal loss.
  • Thermal Management: Due to the high component density, HDI PCBs generate more heat compared to conventional PCBs. Therefore, thermal management considerations play a crucial role in ensuring the board operates within the appropriate temperature range.
  • Material Selection: Necessitate the use of high-quality materials capable of withstanding the demands of production and challenging operating conditions. Commonly employed materials for HDI PCB include high-Tg FR4, polyimide, and liquid crystal polymer (LCP).
  • Manufacturing Technology: The production of HDI PCB requires advanced manufacturing techniques such as laser drilling and sequential lamination. These processes enable the creation of the necessary layer stackup and routing density, ensuring the successful realization of the desired design.

HDI PCB Manufacturing Process

  • Laser Drilling: It is employed to create microvias, which enable interconnection between different layers of the HDI PCB board. This precise technique uses lasers to form small holes in the board.
  • Electroless Copper Deposition: After the microvias are drilled, electroless copper deposition is utilized to coat the walls of the vias with a thin layer of copper.
  • Imaging and Plating: In this step, a photolithography technique is employed to apply a photosensitive layer to the surface of the printed circuit board. The desired circuit pattern is created by exposing the layer to UV light through a mask. Once the pattern is formed, the board undergoes copper plating.
  • Lamination and Pressing: The layers of the PCB are laminated and tightly pressed together using high temperature and pressure. This process ensures a solid bond between the layers.
  • Surface Finishing: The final stage of the HDI manufacturing process involves applying a surface finish to the board. This coating serves multiple purposes, including facilitating soldering processes, protecting the board from oxidation, and improving its overall durability.

The Future of High Density Circuit Board

As technology continues to advance, there is a growing demand for electronic devices that are both compact and efficient. HDI PCBs, with their ability to accommodate complex circuitry in a smaller form factor, are poised to play a significant role in meeting this demand. The future of these PCB boards holds promising opportunities across various industries, including automotive, robotics, and telecommunications. However this can come with some challenges:

  • Manufacturing Complexity: Inherently more complex than conventional PCBs, which can result in higher manufacturing costs and longer lead times. PCB manufacturers will need to streamline their production processes and invest in advanced manufacturing technologies to improve efficiency.
  • Component Availability: Use smaller components during assembly, which can pose challenges in terms of availability and management. Component suppliers will need to keep pace with the demand for miniaturized components suitable for HDI circuit.
  • Design Constraints: The high component density will impose design constraints that limit the flexibility of the overall design. Designers will need to carefully consider these constraints and find innovative solutions to optimize the layout and routing of the board, striking a balance between functionality, performance, and manufacturability.

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