HDI stands for High-Density Interconnect, and these PCBs are revolutionizing the trends of electronic devices. Such circuit boards are crucial in the development of slim, lightweight, and strong gadgets and appliances, inclusive of telecommunications gadgets such as cell phones and medical instruments.

High-Density Interconnect Printed Circuit Boards have a higher wiring density per unit area compared to normal PCBs. This density is achieved by thinner lines and spaces, with all the vias and capture pads also being smaller, and an increased connection pad density. In other words, the concept of HDI PCBs demands circuits with greater densities with more specific functions.

FC HDI PCB Display

Understanding the Types of HDI PCBs

Several types of HDI PCBs are classified by structures and the intensity degree of interconnections. It is important to comprehend those types to choose the proper PCB for the needed application. Here, we’ll delve into the three primary types of HDI PCBs: basic categories namely the Type I, Type II, and Type III with variations in functionality as well as usability.

Understanding the Types of HDI PCBs

 Type I HDI PCB:

The basic and most common type of HDI PCB is Type I HDI PCB. They have one layer of microvias on either the top or bottom side of a core layer, but do not have any microvias through the thickness. These microvias link the outer layer to the next layer below and can accommodate more components than newer PCBs.

Type I HDI PCBs are ideal for use in moderate complexity circuits that perform at high levels of efficiency. It is used primarily in products such as smartphones and tablets where the size and reliability of certain components are important.


Type II is a more advanced version of Type I where in addition to a thin core layer; one or more microvias planes are added to each side of the core plane through holes that connect the outer planes with the inner planes. In this configuration more interconnections are possible, and the densities of components on the substrate are also higher.

These PCBs are useful where the application requires greater functionality such as in medical equipment, automobile technology, and high-end computing. They cause additional layers and vias and improve connectivity and performance.


Type III is considered the most innovative and developed type of HDI PCB. They involve a high density of microvias layers one above the other, and the buried and through-hole via arranged Section 2. This structure makes it possible to have several interconnections of high density and miniaturization to the maximum level.

Such PCBs are used where performance is critical and available space is a measure; in aircraft, military equipment, and specific consumer goods. Because chipsets of this type can accommodate a large number of interconnections, they are paramount for devices that need to offer the utmost performance coupled with miniaturization.

Understanding the Types of Vias Used in HDI PCB

In HDI PCB routing, you’ll find several types of vias:

  • Through-Hole Vias:  These run from the top to the bottom, and tie all the layers of the board together.
  • Blind Vias: These join an external layer to one or more internal layers but do not pass through the entire board. They are compact and good for complicated path determination.
  • Buried Vias:  These remain strictly within the inner layers and link the layers without going to the outer layers.
  • Microvias: Microvias are commonly used in HDI design and are mainly developed by laser drilling. A specific type of component is compatible with the high-density routing and it can be arranged vertically or horizontally where needed.
  • Stacked Vias: These are the micro vias that have been placed one above the other in different layers to give vertical interconnections.
  • Staggered Vias: These are micro vias that are distributed in an alternating manner through various layers to avoid direct vertical connections.

What Is the Difference Between Stacked Microvias and Staggered Microvias?

What Is the Difference Between Stacked Microvias and Staggered Microvias

Stacked Vias:

These microvias are positioned plain one over the other through several layers of the PCB. This configuration offers a cortege right and vertical and therefore ensures easy passage of electrical connections. Thus, stacked vias can be useful in applications that imply the need for densely populated connections in a relatively small area. However, they can be slightly more sensitive to stress and failure in reliability on temperature-sensitive or mechanically demanding applications.

Staggered Vias:

These microvias are put in different layers and not aligned horizontally but offset from the plane of the other microvias. Such a pattern improves mechanical loading and it has the effect of lowering the probability of adjacent-via failure and subsequently improves the reliability of the board. Staggered vias are usually employed in designs for which durability is considered the highest priority as such vias perform better in terms of thermal and mechanical stress. Thus, the application of one vias above the other saves space and ease of routing while the application of the vias offset from each other offers the durability and reliability of the board in the worst conditions

What Are HDI Pcb Stackups?

HDI PCB stackups are the structured layers applied in a High-Density Interconnect (HDI) printed circuit board. All these layers are specially fabricated to accommodate more components and/or complex wiring in confined area. Here’s what makes them special:

  • Multiple Layers: The mounting of components is on the outer layers of the HDI boards while wiring and connections are on the inner layers of the boards. Since the signal and power are separate, the board design can be extremely intricate without monopolizing the real estate.
  • Microvias: These are small holes made through a laser that interconnects one layer to the other. They are essential as they can define very specific inputs and outputs for signaling and power between layers, which is important for high-end electronics.
  • Sequential Lamination: This is the technique used in making the HDI boards where they are constructed in layers. It is a progressive process and is initiated from the basic layers and as we proceed more layers and connections are brought into the picture. It allows all the elements to align smoothly and be functional, this creates more reliability in the operations.
  • Thin Dielectrics: Between these two layers the material is very thin, yet it acts as insulation and defends the contacts. This thinning is beneficial inasmuch that it contributes to a compact design of the board and good electrical characteristics at the same time.
  • Via-in-Pad: This technique positions vias on the component side and places them directly under the pads of the components that they serve. It is as if miniature shortcuts for signals are provided right at those points and this manner enables the board to dissipate heat efficiently.

What Is the Most Common Type of PCB Stackups in HDI PCB?

2+N+2 Stackups:

The actual stacking of substrate layers in the form of 2+N+2 in the High-Density Interconnection PCB technology is defined as two layers of metallic layers on each side of the PCB with NH core layers sandwiched in the middle. This configuration is generally applied in cases where there is a requirement for moderate to high levels of component packaging and intricate routes to be drawn with. Here’s why it’s effective:

What Is the Most Common Type of PCB Stackups in HDI PCB

  • Outer Layers: These outer layers can accommodate components on their surface, and have microvias to connect inner layers. They enable high-density routing particularly when it comes to signals which need to be routed in the most efficient pathways possible.
  • Core Layers: The core layers also perform a global mechanical function in that they accommodate conventional THVholes and play an extra routing role. These shed power and ground planes as well as assist in the stability of the PCB or the printed circuit board.
  • Microvias: Also known as hidden micro vias, common microvias relate the outer layer to the inner core layers to achieve more accurate and dense routing of signals across the board. This feature is used to ensure that the signals on the PCB do not interfere with each other, or with other accessories nearby.

As for other configurations:

  • 1+N+1: This stack-up is relatively easier with only one core layer sandwiched between two other layers, for simple high-density applications.
  • 3+N+3: It is more complicated than 2+N+2 because it includes yet an extra level on both occasions where multiple components’ placement and interconnection requirements are significantly greater.
  • Any-layer HDI: Here in this configuration, microvias go through all the layers of the PCB to provide the maximum freedom to design complicated geometrical patterns and extremely high component packing density.

These different stack-up configurations serve different levels of integration and performance application in electronic devices ranging from simple smartphones phone, tablets to advanced applications in aerodynamics and healthcare industries. Thus, each of the configurations addresses such issues as space requirements, signal quality, and the manufacturability of the configuration according to the application requirements.

Advantages of HDI PCBs

let us explore the major benefits of using HDI PCBs and why their use is growing in the electronics market.

Improved Performance

HDI PCBs have thinner lines and spaces, smaller vias, and a greater number of connection pads on PCBs. The unique design enhances the quality of signals as it cuts short the transmission loss and crosstalk; hence, making the signals to have shorter transmission time and higher efficiency.

Space-Saving Design

Space-Saving Design

For the current generation of gadgets, combined with the ever-evolving miniaturization of electronic devices, the possibilities of HDI PCBs are phenomenal. It is crucial to discuss that the classic printed circuit boards might occupy considerable space and hinder the enhancement of the miniaturization of electronics. HDI PCBs do this but have intricacies of micro vias, blind vias, and buried vies that make the circuits more complicated and dense.

Enhanced Reliability

HDI PCBs tend to be manufactured with high laminates and substrates so that thermal stability and mechanical strength are feasible. Also, its fabrication features including laser drilling of microvias and the sequential lamination are enhanced to provide accurate and exact circuit board construction.


HDI PCBs are essential components in contemporary electronics since they provide performance, minimized space, and reliability. Comprising microvias and/or sequential lamination, the HDI PCBs provide high levels of miniaturization and integration as are needed in smartphone and healthcare instruments as well as aerospace applications. HDI PCBs will play a significant role in the future growth and development of numerous industries because of the increasing demand for electronics that are small and perform efficiently.