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HDI Multilayer PCB

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HDI Multilayer PCB

In recent years, the implementation of HDI (High-Density Interconnect) multilayer PCBs has brought about significant advancements in the technical industry. These specialized printed circuit boards offer distinctive features that set them apart from typical multilayer boards, including a higher number of interconnections and improved performance.

HDI multilayer PCBs comprise multiple inner and outer layers, providing enhanced circuit density, smaller dimensions, and superior functionality when compared to traditional single-layer or double-layer PCBs. These advancements allow for higher signal transmission speeds, reduced power consumption, and enhanced thermal performance.

A notable characteristic of HDI multilayer PCBs is their capacity to accommodate a higher number of interconnections, with approximately 120 to 160 pins per square inch of surface area. These boards consist of various layers, optimizing their capabilities and making them highly suitable for efficient and compact electronic designs. The primary focus of this discussion revolves around the significant contributions of HDI multilayer PCBs.

What is HDI Multilayer PCB?

The HDI multilayer PCB, characterized by its numerous interconnections, is a multilayer circuit board that offers a compact design. This board finds application in diverse technological fields such as automotive and military, where its utilization brings about improvements in signal integrity and overall performance.

The development of HDI multilayer PCBs was primarily driven by the need for smaller and more powerful devices, particularly in industries such as telecommunications. This demand led to the creation of these boards, which deliver enhanced performance and computational power within a reduced space. Nonetheless, other significant factors contributed to the evolution of HDI PCBs, including the trends observed in IC (Integrated Circuit) technology.

These trends prompted a reevaluation of PCB interconnects and layouts by manufacturers. Furthermore, HDI multilayer PCBs possess the ability to accommodate increased power within a smaller footprint. This capability is realized through the integration of advanced interconnect techniques such as vias in pad and micro vias. These innovative approaches to interconnections contribute to the HDI multilayer PCB’s ability to package higher power densities while maintaining compact dimensions.

What Material Is Appropriate For Manufacturing HDI Multilayer PCB Stackup?

The selection of appropriate materials for manufacturing an HDI (High-Density Interconnect) multilayer PCB stackup depends on various factors, including the specific requirements of the application and the desired performance characteristics. Typically, the materials for the HDI multilayer PCB stackup include:

Substrate materials:

The core layer and prepreg materials form the core of the PCB and provide structural support. Common substrate materials used in HDI multilayer PCBs include FR-4 (Flame Retardant-4), FR-4 High Tg (high glass transition temperature), and various high-performance laminates such as polyimide (PI) or liquid crystal polymer (LCP). The choice of substrate material depends on factors like thermal stability, electrical properties, and cost considerations.

Copper foils: Copper foils are used for conductive layers in the PCB stackup. They provide the necessary electrical conductivity and serve as the foundation for interconnections. High-quality copper foils with good thermal and electrical conductivity, along with appropriate thickness, are preferred for HDI multilayer PCBs.

Build-up materials:

HDI multilayer PCBs typically involve stacked microvia layers to achieve high-density interconnections. Build-up materials, including thin dielectric layers and conductive materials, are used to create these microvias. Materials such as resin-coated copper (RCC), thin core materials, and specialized build-up laminates are employed for creating the stacked microvia layers.

Solder mask and surface finish:

Solder mask materials are applied to protect the exposed copper traces and prevent solder bridging during assembly. Materials such as epoxy-based liquid photoimageable solder mask (LPI) are commonly used. The surface finish, which provides a protective layer and improves solderability, can include materials like ENIG (Electroless Nickel Immersion Gold), HASL (Hot Air Solder Leveling), or OSP (Organic Solderability Preservative).

Advantages of HDI Multilayer PCB

HDI multilayer PCBs offer several key advantages that contribute to their growing importance in the industry:

Enhanced circuit density:

HDI multilayer PCBs excel in achieving high circuit density, enabling greater connectivity and functionality. This empowers designers to integrate more circuit functions onto a single board, resulting in reduced product size and cost.


With their high circuit density, HDI multilayer PCBs can accommodate a larger number of components within the same physical space. This facilitates product miniaturization, improving portability and reliability.

Superior performance:

HDI multilayer PCBs deliver notable performance benefits, including faster data transmission speeds, lower power consumption, and improved heat dissipation. These advantages make them well-suited for diverse applications in high-speed communication, high-performance computing, and other demanding fields.

Simplified design and manufacturing:

HDI multilayer PCBs employ standardized design and manufacturing processes, simplifying the tasks for both designers and manufacturers. Additionally, by leveraging existing technologies and tools for rapid prototyping, HDI multilayer PCBs contribute to shorter product development cycles.

Design Considerations for HDI Multilayer PCBs

The production processes involved in manufacturing HDI multilayer PCBs significantly differ from those used for standard multilayer PCBs. The production of HDI multilayer boards begins with a complex design process that requires careful consideration of various physical, thermal, and electromagnetic factors. Several design considerations must be taken into account during the production process:

Via fill types: The specific application and PCB requirements determine the appropriate via fill types to be used. It is crucial to match the via fill type with the intended application of the PCB. Options for via fills include conductive epoxy, electrochemical plating, and non-conductive epoxy, among others. Non-conductive epoxy is the most commonly used via fill type.

Sequential lamination: During lamination, the PCB designer combines the PCB cores with copper by applying pressure and heat. The number of layers in the board determines the required amount of pressure and heat. After the lamination stage is completed, the PCB designer drills vias. HDI multilayer boards often require multiple vias drilling operations. Sequential lamination helps prevent breakage and shifting during the drilling process.

Laser drill technology: Multilayer HDI designs often necessitate the use of laser microvias. These microvias are created using laser drills capable of generating around 20-micron laser diameter. These laser drills can cut through materials like glass and metal, ensuring the creation of clean and tiny holes.

Impedance control: Designers must maintain tolerances within +- 10% on trace widths and dielectric layer thicknesses when designing HDI multilayer PCBs. This is essential to ensure that impedance does not adversely affect signal integrity.

These considerations highlight the complexity and intricacy involved in the production of HDI multilayer PCBs. Attention to detail during the design and manufacturing processes is paramount to achieve the desired performance and functionality of these advanced circuit boards.

What’s the Principle of HDI Multilayer PCB?

The principle of HDI (High-Density Interconnect) multilayer PCB revolves around maximizing circuit density and functionality within a compact form factor. This is achieved through the implementation of advanced design and manufacturing techniques.

The key principles of HDI multilayer PCB can be summarized as follows:

High circuit density: HDI multilayer PCBs are designed to accommodate a large number of interconnections and components within a limited space. This is achieved by utilizing multiple layers, incorporating microvias (smaller holes) for interconnections, and reducing the size of components.

Microvias and stacked vias: HDI multilayer PCBs utilize microvias, which are much smaller in diameter compared to traditional vias, to establish connections between different layers. These microvias allow for more interconnections in a smaller area. Additionally, stacked vias, which connect multiple layers in a vertical manner, further enhance the circuit density.

High-speed signal integrity: HDI multilayer PCBs are designed to optimize signal integrity, particularly in high-speed communication systems. By minimizing signal loss, reflections, and crosstalk, these PCBs enable faster data transmission and improved performance.

Advanced manufacturing techniques: HDI multilayer PCBs require specialized manufacturing techniques to achieve the desired level of circuit density and interconnection complexity. These techniques include laser drilling for microvias, precise alignment during lamination, and advanced plating methods to ensure reliable and efficient connections.

By adhering to these principles, HDI multilayer PCBs enable the integration of more functions, higher performance, and smaller form factors in electronic devices, thereby driving advancements in various industries that rely on compact and high-performance systems.

Applications of HDI Multilayer PCBs

HDI (High-Density Interconnect) technology plays a crucial role in a wide range of advanced technologies. The miniaturization of electronic components has enabled manufacturers to design smaller devices without compromising reliability and performance. HDI multilayer PCBs find extensive application in various fields, including:


HDI multilayer PCBs are commonly used in communication equipment such as modules, routers, semiconductors, and switches. They are also integrated into digital audio and video devices and personal communication devices, enabling improved functionality.

Medical devices:

HDI PCBs are well-suited for advanced electronic medical devices, including monitoring, imaging, and laboratory analysis equipment. By incorporating HDI multilayer boards, the performance and precision of medical testing and monitoring devices can be significantly enhanced.

Automotive and aerospace:

The automotive and aerospace industries benefit from the use of HDI multilayer PCBs due to their ability to provide increased capabilities within limited space and reduce weight. These boards are extensively utilized in modern cars, which rely on microprocessors for safety, control, and diagnostic features. HDI multilayer PCBs also enable various features such as rearview cameras, GPS, and WiFi in automobiles. Similarly, the aerospace industry leverages HDI technology to enhance electronic systems in aircraft.

Industrial applications:

Modern industrial equipment is increasingly computerized, with a growing integration of IoT (Internet of Things) devices in warehousing, manufacturing, and other industrial settings. HDI technology is widely integrated into advanced industrial equipment, enabling efficient data collection, control, and monitoring. Businesses utilize electronic tools for inventory management, equipment performance monitoring, and the integration of smart sensors for data collection in machinery.

What Factor Effect for HDI Multi-layer PCB Cost?

Several factors can influence the cost of HDI (High-Density Interconnect) multilayer PCBs. The key factors that affect the cost include:

Complexity of the design:

The complexity of the HDI multilayer PCB design significantly impacts the cost. Designs with intricate features, numerous layers, and intricate trace routing require more sophisticated manufacturing processes, specialized equipment, and longer production times, which can increase the overall cost.

Number of layers:

The number of layers in the HDI multilayer PCB affects the cost. As the number of layers increases, the complexity of the manufacturing process and the materials required also increase, resulting in higher costs.

Via types and densities:

HDI multilayer PCBs often incorporate various via types, such as microvias and stacked vias, to achieve high circuit density. The complexity, size, density, and type of vias used impact the cost, as they require specific equipment and processes for drilling, plating, and filling.

Materials used:

The choice of materials for HDI multilayer PCBs influences the cost. High-performance materials such as specialized laminates, high TG (glass transition temperature) substrates, and advanced build-up materials can be more expensive than conventional materials like FR-4. The selection of materials depends on the desired electrical, thermal, and mechanical properties of the PCB.

Manufacturing process and technology:

HDI multilayer PCBs typically require advanced manufacturing processes, such as laser drilling, sequential lamination, and precise alignment techniques. These processes involve specialized equipment and skilled labor, which can contribute to higher manufacturing costs.

Surface finish and additional features:

The choice of surface finish and any additional features, such as impedance control, blind vias, or buried vias, can impact the cost. Certain surface finishes (e.g., gold) and additional features require additional processing steps or specialized materials, which can increase the overall cost.

Quantity and lead time:

The quantity of HDI multilayer PCBs ordered and the required lead time can affect the cost. Bulk orders or longer lead times may result in volume discounts or better utilization of manufacturing resources, potentially reducing the per-unit cost.

The Future Development Trend of HDI Multilayer PCB

The ongoing technological advancements are driving the continuous development of HDI (High-Density Interconnect) multilayer PCBs towards higher performance and lower power consumption. This progress is being achieved through the utilization of new materials and processes, enabling the realization of circuit boards with smaller dimensions and higher densities.
Moreover, the introduction of new design concepts and technical methods is enhancing the reliability and stability of these circuit boards.

In line with the growing emphasis on environmental protection and sustainable practices, the HDI multilayer PCB industry is also shifting towards eco-friendly approaches. Manufacturers are increasingly incorporating environmentally conscious considerations into the development and production of these PCBs. This includes the use of materials and manufacturing techniques that minimize the environmental impact, such as reducing hazardous substances and adopting energy-efficient processes.

Furthermore, the industry is actively exploring innovations to improve the overall performance and functionality of HDI multilayer PCBs. These advancements involve the integration of advanced technologies, such as miniaturization, high-density interconnections, and optimized signal integrity. By continuously pushing the boundaries of performance, HDI multilayer PCBs are facilitating advancements in various fields, including consumer electronics, telecommunications, medical devices, automotive, and aerospace applications.

As the demands for smaller and more powerful electronic devices continue to rise, the HDI multilayer PCB industry remains committed to meeting these evolving requirements. By embracing new materials, processes, design concepts, and environmental standards, the industry is poised to contribute to sustainable development while delivering higher performance and enhanced reliability in future PCB designs.


HDI Multilayer PCBs have become indispensable in the technological landscape, enabling the development of smaller, more powerful, and highly reliable electronic devices. From smartphones and tablets to automotive systems and medical devices, HDI multilayer PCBs have proven critical in achieving compact form factors, high circuit density, and optimal signal integrity.

As technology continues to advance, the demand for even more compact and powerful devices will persist. In response, the HDI multilayer PCB industry will undoubtedly continue to push the boundaries of innovation, leveraging new materials, advanced manufacturing techniques, and eco-friendly practices. With these advancements, we can look forward to a future of ever-smaller, yet more powerful and efficient electronics, made possible by the remarkable capabilities of HDI multilayer PCBs.

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