What is an HDI PCB? How Does It Differ from a Standard PCB?

September 15, 2025

1. What is an HDI PCB?

An HDI PCB refers to a circuit board produced using high-density micro-wiring and micro-via technology. HDI stands for High-Density Interconnector. It is a circuit board with a relatively high line distribution density that employs micro-blind and buried via technology. HDI boards have inner and outer layer circuits, and the connection between these layers is achieved through processes like drilling and metallization of the holes.

HDI boards are generally manufactured using the build-up method. The more build-up layers, the higher the technical grade of the board. Basic HDI boards are typically 1-step build-up, while advanced HDI uses 2 or more build-up layers, alongside advanced PCB techniques such as stacked vias, plated via filling, and direct laser drilling.

As electronic products continuously evolve towards higher density and precision, the goal is not only to improve performance but also to reduce size. HDI technology allows for more miniaturized end-product designs while meeting higher standards for electronic performance and efficiency. Many popular electronic products, such as mobile phones, digital cameras, laptops, and automotive electronics, utilize HDI boards. With the iteration of electronic products and market demand, the development of HDI boards is very rapid.

Traditional PCB drilling is limited by drill bits; when the drill hole diameter reaches 0.15mm, the cost becomes very high and is difficult to improve further. In contrast, HDI board drilling no longer relies on traditional mechanical drilling but uses laser drilling technology (hence it's sometimes called a laser board).

The drill diameter of an HDI board is generally 3-6 mils (0.076-0.152 mm), and the line width is generally 3-4 mils (0.076-0.10 mm). The size of the pads can be significantly reduced, allowing for more lines to be distributed per unit area, which is the origin of the term "high-density interconnect."

The emergence of HDI technology has adapted to and promoted the development of the PCB industry. It allows for the placement of denser BGAs, QFPs, and other components on HDI boards.

2.Advantages of HDI Boards

(1).Increased Line Density: Micro-via technology allows the necessary interconnects to be routed to the next layer, connected directly by blind vias within the pads, eliminating the need for fan-in/fan-out routing. This frees up outer layer space for more components, increasing board density.

(2).Lighter, Thinner, Shorter, Smaller: Increased wiring density allows PCBs to achieve required functionality in a smaller area and with fewer layers, making the board smaller and thinner overall.

(3).Supports Advanced Packaging: The advancements in micro-via processes allow designers to incorporate the latest high-density IC packaging technologies.

(4).Better Electrical Performance and Signal Integrity: Micro-vias can reduce signal reflection, crosstalk, and switching noise due to their small and short physical structure, which reduces inductance and capacitance effects.

(5).Higher Reliability: Micro-vias, with their thinner thickness and 1:1 aspect ratio, offer higher reliability in signal transmission compared to standard through-holes.

(6).Improved Thermal Properties: The insulating dielectric materials used in HDI boards often have a higher glass transition temperature (Tg), leading to better thermal performance.

(7).Improved RFI/EMI/ESD: Micro-via technology allows designers to shorten the distance between ground and signal layers, reducing interference, and to increase ground lines for better ESD protection.

(8).Increased Design Efficiency: The ability to route lines on inner layers gives designers more flexibility, increasing design efficiency.

3.HDI Board Design Considerations

Laser via diameter: 0.076-0.15mm (3-6 mils); annular ring width ≥ 3 mils.
Laser vias cannot be through-holes; the dielectric thickness between layers must be ≤ 0.1mm.
Copper thickness for layers processed by laser drilling must be ≤ 1 oz.
Stack-up design should be symmetrical, with an even number of layers, and copper/dielectric thicknesses should be as symmetrical as possible.

Answering Two Common Questions:

1).Are all PCBs with blind/buried vias considered HDI?

Not necessarily. HDI boards involve blind vias that are plated and then subjected to secondary lamination. Boards with only buried vias may not be HDI.

2).How to distinguish between 1st, 2nd, and 3rd order HDI?

This depends on the complexity of the blind hole stacking. The first stage is the simplest. Designs of the second stage and above are more complex, involving advanced techniques such as hole alignment and overlapping (stacked holes). The higher the stage, the greater the technical difficulty.

4.The Difference Between HDI Boards and Standard PCBs

Standard PCB: A printed circuit board, the support for electronic components. It uses traditional mechanical drilling and through-hole technology. The standard material is FR-4 (epoxy resin + electronic grade glass fabric).

Key Differences:
Drilling Technology: Standard PCBs use mechanical drills; HDI uses lasers.
Via Types: Standard PCBs primarily use through-holes; HDI uses micro-blind/buried vias.
Density: HDI offers much higher wiring density.
Materials: Early HDI required special materials like resin-coated copper (RCC) without glass fiber for laser drilling. However, modern high-power lasers can drill through standard glass fabric, blurring the material distinction.