4 Main Difference Between HDI PCB and Ordinary PCB

Introduction

Editor's Note (February 2026): This article has been updated with the latest industry data regarding Ultra-HDI trends, AI hardware requirements, and manufacturing standards for the 2026-2027 production cycle.

HDI (High-Density Interconnect Board) is a compact board designed for small-volume users. Compared to ordinary PCB, the most significant feature of HDI is the high density of wiring.

In the context of 2026 electronics manufacturing, HDI has become the backbone of "Edge AI" devices and foldable smartphones. As chips move toward 3nm and 2nm architectures, the demand for HDI boards that can support extreme miniaturization has surged.

The difference between HDI and standard PCBs is mainly reflected in the following 4 aspects:

1. Table of Contents
2. 1. HDI PCB - Smaller and Lighter
3. 2. High HDI Wiring Density (2026 Standards)
4. 3. HDI PCB with Better Electrical Properties
5. 4. HDI PCB Requirements for Buried and Plug Hole
6. 5. Comparing HDI PCBs and Traditional PCBs
7. 6. Stack-up of HDI PCB
8. 7. Manufacturing Process of HDI PCBs
9. 8. HDI PCB Main Application Areas
10. 9. FAQ: 4 Main Differences Between HDI and Ordinary PCB
11. Conclusion

1. HDI PCB - Smaller and Lighter

HDI board uses the traditional double-sided board as the core board, formed through the continuous accumulation of laminated layers. This method of continuous layer accumulation is also known as the Build-up Multilayer (BUM) process. Compared to conventional boards, HDI boards have the distinct advantages of being "light, thin, short, and small".

The electrical interconnection between the layers of the HDI board is achieved through conductive through-hole, buried via, and blind via connections. Unlike ordinary multilayer PCBs, HDI boards are designed with a large number of micro-buried blind vias.

Ordinary PCBs are usually drilled using mechanical methods, whereas HDI PCBs are drilled using laser technology. Consequently, the number of layers and the aspect ratio of HDI PCBs are often increased to accommodate complex designs.

2. High HDI Wiring Density

The high density of HDI boards is mainly reflected in the hole, line, pad density, and interlayer thickness. As of 2026, the industry is shifting from standard HDI to Ultra-HDI (UHDI) to meet the needs of high-performance computing.

• Micro-Through Via: HDI circuit boards contain blind holes and other micro-conductor hole designs.
  Standard HDI: Micro-hole diameters less than 150μm.
  2026 Trend: Advanced applications are now pushing for laser vias under 75μm to match fine-pitch BGA components used in AI processors.
• Refinement of Line Width and Spacing: Requirements for wire defects and wire surface roughness are increasingly strict.
  Standard: General line width and spacing of no more than 76.2μm (3 mil).
  2026 Update: For flagship consumer electronics, Modified Semi-Additive Processes (mSAP) are enabling line widths/spacing down to 30μm/30μm.
• High Density of Pads: The density of welded joints is greater than 50 per square centimeter.
• Thinning of Dielectric Material: This is manifested in the trend of interlayer medium thickness reducing to 80μm or below. The requirement for thickness uniformity is stricter than ever, especially for high-density plates and packaging substrates requiring precise impedance control for 5G/6G signals.

3. HDI PCB with Better Electrical Properties

HDI PCBs not only facilitate miniaturized product designs but also meet higher standards of electronic performance and efficiency.

The increased interconnect density of HDI PCBs allows for enhanced signal strength and improved reliability. Furthermore, HDI boards offer better shielding against Radio Frequency Interference (RFI), Electromagnetic Interference (EMI), static discharge, and improve thermal conduction.

2026 Performance Note: With the adoption of PCIe 6.0 and early 6G prototyping, the signal integrity provided by HDI's shorter transmission paths (via micro-vias) is crucial for reducing signal loss and latency.

4. HDI PCB Requirements for Buried and Plug Hole

While HDI offers superior volume and electrical performance compared to ordinary PCBs, the manufacturing threshold and process difficulties are significantly higher. A critical area of focus is the buried plug holes.

The core pain point of HDI manufacturing is the buried plugging hole process. If not executed correctly, major quality issues arise, such as:

• Uneven Surfaces: If the board surface is not flat, lines may become distorted in depressions, causing "beach phenomena," leading to line gaps or broken lines.
• Impedance Fluctuations: Uneven dielectric thickness causes characteristic impedance to fluctuate, resulting in signal instability—a critical failure in high-speed 2026 data transmission.
• Packaging Failures: Uneven pads lead to poor quality in subsequent component packaging and potential loss of expensive components.

5. Comparing HDI PCBs and Traditional PCBs

6. Stack-up of HDI PCB

The stack-up of an HDI PCB is a critical blueprint that defines the arrangement and composition of its various layers. Here is a breakdown of the key components:

• Core: Similar to traditional PCBs, often utilizing rigid dielectric material like FR-4. However, high-performance applications in 2026 increasingly use Low-Loss materials to support higher frequencies.
• Signal Layers: HDI PCBs boast a significantly higher layer count, often ranging from 6 to 12+, enabling dense routing in limited space.
• Dielectric Layers: Ultra-thin insulating layers separate signal layers. In HDI, these must be thinner to accommodate high layer counts while maintaining a compact Z-axis profile.
• Via Layers:

1. - Blind Vias: Connect internal layers to the surface without extending through the entire board.
2. - Buried Vias: Completely encased within the core material.

• Via Size: HDI employs significantly smaller vias requiring high-precision laser drilling.

Surface Layers: Top and bottom layers provide connection points. In 2026 designs, "Pad-in-Via" technology is standard to maximize component density.

7. Manufacturing Process of HDI PCBs

The fabrication of HDI PCBs is a complex process. Key differences include:

• Lamination: Requires precise alignment of blind/buried vias (Sequential Lamination).
• Drilling: High-precision laser drilling replaces mechanical drilling for microvias.
• Plating: Specialized plating is required for high aspect ratios and to fill stacked vias (Copper Filled Vias).
• Patterning: Requires higher resolution photoresists (LDI - Laser Direct Imaging) for fine line widths.

8. HDI PCB Main application areas (2026 Update)

HDI PCBs are the backbone of modern electronics. Key application areas in the 2026 landscape include:

• Consumer Electronics: Foldable smartphones, ultra-thin laptops, and wearables.
• Spatial Computing: AR/VR Headsets (e.g., Vision Pro ecosystem) requiring extreme density.
• Automotive: EV ADAS systems, LiDAR modules, and in-cabin AI controllers.
• Telecommunications: 5G Advanced and 6G prototype base stations.
• Medical: Miniaturized diagnostic devices and smart implants.

9. FAQ: 4 Main Differences Between HDI and Ordinary PCB

Q1: How do wiring density and trace dimensions differ?

A: HDI PCBs offer significantly higher wiring density than ordinary PCBs. While standard boards have larger limits, HDI processes can currently produce fine traces with a width of 0.025 mm and spacing of 0.05 mm. Some advanced processes can even achieve trace widths as narrow as 12 μm.

Q2: What is the difference in via technology?

A: Ordinary PCBs primarily use Plated Through-Holes (PTH). In contrast, HDI PCBs utilize microvias (blind and buried vias) with diameters smaller than 0.25 mm. These microvias allow for a "small, thin, dense, and flat" design, which is essential for modern compact electronics.

Q3: How do the stackup structures and manufacturing processes vary?

A: Standard PCBs are typically pressed once, whereas HDI PCBs use a sequential build-up (SBU) method.

• Order of HDI: Adding one layer of microvias to a core is called 1st-order (1+N+1), while adding two layers is 2nd-order (2+N+2), and so on.
• Advanced Techniques: HDI manufacturing involves specialized processes like laser drilling for smaller apertures, Resin Coated Copper (RCC), and conductive ink or plated hole plugging.

Q4: What are the differences in physical characteristics and applications?

A:

• Physical Characteristics: HDI boards are designed to be "small, thin, dense, and flat". Specific types, such as Type 4 HDI, incorporate a metal core to aid in heat dissipation, allowing for even higher assembly density.
• Applications: Ordinary PCBs are used for general electronics. HDI PCBs are predominantly used in high-end communication products like mobile phones (2G through 5G/6G and beyond) to meet the demand for miniaturization.

Conclusion

Not all board factories have the capability to manufacture high-reliability HDI boards. NextPCB has been refining this technology for over 15 years.

Today, NextPCB's HDI manufacturing utilizes a complete, in-house system with no outsourcing. We have invested heavily in advanced 2026-era equipment (such as Laser Direct Imaging and automated optical inspection). All quality acceptance standards strictly adhere to IPC-2/IPC-6012 Class 2 and Class 3 standards—ensuring hole copper thickness ≥ 20μm—to guarantee the high reliability required for modern high-tech applications.

About the Author

Lolly Zheng- Sales Account Manager at NextPCB.com

Four years of proven sales experience across electronic components and PCBA industries, with strong expertise in key account acquisition, customer relationship management, and contract negotiations. Focused on driving revenue growth through strategic client development and solution-based selling. Experienced in expanding high-value accounts, securing long-term partnerships, and consistently exceeding sales targets in competitive markets.

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