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Learning With Leo: UHDI—The Next Leap in PCB Manufacturing

High density interconnect (HDI) technology has been a cornerstone of miniaturized electronics since Hewlett-Packard introduced the first chip-scale implementation in 1982. Over time, HDI processes became central to organic flip-chip packaging in the semiconductor industry. Today, the convergence of IC substrates and system-level PCBs has accelerated the adoption of UHDI.

A Fundamental Shift in Manufacturing Methodology

As electronic devices become smaller, more powerful, and data-intensive, the demand for advanced interconnect technology is rapidly increasing. UHDI technology represents a significant leap forward from traditional high density interconnect (HDI) systems. By enabling trace widths and spacing below 25 micrometers and utilizing microvias as small as 5 micrometers, UHDI opens the door to unprecedented levels of miniaturization, performance, and system integration in PCB design and manufacturing.

The evolution from HDI to UHDI reflects a fundamental shift in manufacturing methodology. HDI technology, which introduced blind vias and 75/75 µm geometries, has served as a key enabler of compact electronics for decades. However, UHDI builds on that foundation by moving from subtractive etching processes to semi-additive (mSAP) and fully additive (SAP) approaches. These newer methods allow for finer feature sizes, tighter design tolerances, and enhanced electrical performance, making UHDI an essential technology for high-performance applications.

Key Features and Benefits

UHDI technology introduces several critical features that distinguish it from its predecessors. It supports much finer trace widths and spacing, which significantly reduce the PCB footprint while enabling more complex and powerful electronic assemblies. Microvias improve signal integrity by reducing resistance and shortening interconnect paths. Thinner traces and dielectrics allow for higher routing density, which is crucial for high-speed and high-frequency designs. Collectively, these attributes make UHDI an ideal solution for advanced networking, telecommunications, and mission-critical electronic systems.

The benefits of UHDI extend well beyond miniaturization. With UHDI, designers can achieve higher component density without increasing board size, allowing for more compact and feature-rich products. Signal integrity is enhanced due to optimized routing paths that minimize crosstalk and electrical interference. While UHDI requires investment in advanced manufacturing equipment, the overall cost can be offset by the reduction in PCB layers and improved material efficiency. Additionally, UHDI is uniquely suited for high-speed applications such as 5G networks, autonomous vehicles, aerospace systems, and high-performance computing platforms.

Applications and Manufacturing Considerations

UHDI is already being adopted across multiple industries where compactness, speed, and reliability are critical. In consumer electronics, it enables the development of thinner smartphones, wearables, and tablets that support faster data transmission and richer functionality. In the automotive sector, UHDI supports advanced driver-assistance systems, infotainment platforms, and autonomous driving technologies that require high-density and high-speed data processing.

Aerospace and defense applications benefit from UHDI’s compact, reliable, and high-frequency interconnects in systems such as avionics and secure communications. Medical devices such as pacemakers, implants, and diagnostic imaging tools leverage UHDI to improve functionality and reliability while reducing size. In telecommunications and IoT infrastructure, UHDI supports the development of smaller, faster, and more efficient devices with reduced latency and higher bandwidth.

The shift to UHDI also demands significant changes in PCB manufacturing methodologies. Unlike subtractive techniques that remove copper to form traces, UHDI relies on additive methods that build up conductive paths with high precision. Semi-additive and fully additive processes are central to this approach, enabling controlled geometries and finer copper features.

The use of microvias, combined with high-performance laminates and build-up films, allows for complex multilayer routing in minimal space. Ultra-thin dielectric layers are essential for high-frequency performance, as they reduce parasitic effects and improve signal propagation. In addition, GHz-range performance requirements drive the need for materials with superior electrical properties and thermal stability.

Assembly, Inspection, and Industry Outlook

Assembly and soldering processes must also evolve to accommodate UHDI’s fine features and tight tolerances. Solder paste selection becomes critical, with Type 6 and Type 7 solder powders—ranging from 5 to 15 micrometers—required for ultra-fine pitch components. Stencil printing must achieve sub-micron alignment precision, and step-stencil designs are often necessary to prevent defects like tombstoning and bridging. Reflow soldering profiles must be carefully controlled, often using nitrogen environments, to minimize oxidation and thermal stress. Common UHDI assembly challenges such as pad misalignment, voiding, and component shifting require advanced process controls and continuous monitoring to maintain yield and reliability.

Inspection and quality assurance become even more crucial in UHDI manufacturing. Traditional visual inspection is no longer sufficient at these scales. Advanced lithography and laser drilling systems replace mechanical drilling to accommodate UHDI’s micro-scale features. Automated optical inspection (AOI) systems are used to detect fine-line defects and ensure pattern accuracy. Solder paste inspection (SPI) is critical for confirming precise volume and placement of solder materials. X-ray inspection is required to identify hidden soldering issues, such as voids and insufficient solder joints, that would otherwise go unnoticed. These inspection techniques are essential for maintaining quality, reducing rework, and ensuring long-term reliability.

Despite its advantages, UHDI adoption presents a balancing act between cost and performance. The equipment, training, and process development required to manufacture UHDI boards involve significant upfront investment. However, the ability to build smaller, faster, and more capable products can provide a competitive advantage in markets that demand high performance and compact form factors. Industries that prioritize innovation—such as telecommunications, aerospace, and advanced computing—are already moving in this direction.

Conclusion

UHDI technology is redefining the future of PCB manufacturing and assembly. It enables a new level of miniaturization and performance that supports the increasing complexity of modern electronic systems. While UHDI demands a rethinking of manufacturing, soldering, and inspection practices, the benefits it delivers, especially in terms of signal integrity, reliability, and space efficiency, are compelling. As industries push the boundaries of what electronics can do, UHDI will be at the forefront of enabling the next generation of connected, intelligent, and compact systems. It is not just the next step in HDI’s evolution; it is the new frontier in electronic interconnect technology.

Resources

1. “The Way to UHDI: From Subtractive Through mSAP to SAP,” by N. Shpaisman, Ultra High Density Interconnect Symposium, KLA Corporation. 2023.
2.  “Understanding Solder Paste Powder Sizes,” AIM Solder.
3.  Printed Circuit Handbook (6th ed.), by Clyde Coombs, 2007.

Upcoming Webinar

Join us for EPTAC/I-Connect007’s UHDI: Q&A Manufacturing and Inspection Insights with Leo Lambert webinar.

Discover how UHDI is transforming design, materials, and inspection across advanced electronics manufacturing — and get your questions answered live during our open Q&A session with Leo Lambert.

Date: Wednesday, November 19, 2025

Time: 12noon – 12:45pm

Register at EPTAC: webinar-leo-lambert-uhdi

Leo Lambert is the Technical Director at EPTAC Corporation