New Routing Possibilities with Ultra HDI

PCB designers are constantly facing the challenge of packing more functionality into smaller spaces while ensuring high performance. What was once used only for IC substrate and package fabrication, today Ultra HDI (Ultra High-Density Interconnect) technology is being brought to the PCB level to allow very high density routing capabilities. But what exactly makes Ultra HDI so powerful, and how does it elevate routing efficiency?

More Connections, Less Space

Newer components push routing density to higher levels, and the traditional simple stackups struggle to keep up. Ultra HDI fabrication capabilities allow PCB designers to place smaller features, with trace widths and spacing as small as 25/25 μm. This means you can fit more routing within the same board area, making it ideal for space-constrained applications like mobile devices and wearables.

There is a famous picture from Signal Integrity Journal (see below), where multiple traces are being routed out from a high-density BGA. This illustrates the sizes of traces and trace densities that can be achieved with Ultra-HDI PCB fabrication. In the traditional approach, a PCB designer would use dogbone fanout or via-in-pad to route traces from the BGA to other components.

If you’ve ever wished for just a little more room to work with, Ultra HDI gives you that extra breathing space. Even using 50/50 um trace and space is a significant improvement over traditional subtractive etch capabilities.

This increase in routing density is particularly beneficial in applications where miniaturization is key. For example, in advanced medical devices such as implantable sensors or hearing aids, every millimeter of board space counts. Ultra HDI ensures that complex circuits can fit into these tiny footprints without compromising performance. For consumer electronics where aesthetics and portability drive design decisions, thinner and more compact PCBs enabled by Ultra HDI can lead to sleeker, lower-profile products.

A Breakthrough for BGA Routing

High pin-count BGAs (Ball Grid Arrays) can be difficult to route, especially when dealing with pitches as small as 0.4 mm. Traditional methods often require additional PCB layers just to design escape routes from BGAs. Ultra HDI changes the game by leveraging microvias and ultra-fine traces to break out more connections without increasing layer count.

While enabling routing for high-density BGAs, Ultra HDI assembly comes with dangers of BGA assembly defects like head-in-pillow, non-planarity, and solder bridging or misalignment. To overcome this and ensure higher manufacturing yields and fewer design iterations, engineers require thinner Ultra-HDI specific materials which exhibit lower CTE values than standard FR4 grade materials. For designers working with fine-pitch components in applications like smartphones or high-performance computing, these materials are still being developed and brought to market at scale.

Fewer Layers, Lower Costs

More layers often bring more complexity and increased fabrication costs, which are not ideal for modern electronics. Because Ultra HDI allows higher routing density with smaller trace width, designers can consolidate traces from multiple layers into a single layer, resulting in fewer overall layers in the PCB stackup. Fewer layers translate into lower fabrication costs at high volume.

Reducing the layer count doesn’t just cut costs—it also improves manufacturability. Fewer layers mean less drilling, fewer lamination cycles, and lower chances of defects such as delamination or misregistration. This ultimately results in higher reliability and consistency in production. Plus, by optimizing the layer structure, Ultra HDI helps improve thermal management, which is particularly useful in high-power applications such as automotive electronics or data centers, where excess heat can degrade performance.

Challenges and Considerations

While Ultra HDI offers many benefits for advanced miniaturized products, implementing it requires careful planning and expertise. Manufacturing processes need to be optimized to handle ultra-fine features, and designers must work closely with fabricators to ensure manufacturability. Additionally, ensuring proper material selection is critical—dielectric materials with low loss and high reliability must be chosen to support Ultra HDI’s fine-pitch fabrication capabilities.

Another consideration is cost trade-offs. While Ultra HDI can reduce layer count and improve efficiency, the initial investment in advanced fabrication techniques and materials may be higher. However, as the technology becomes more widely adopted, economies of scale will drive costs down, making it more accessible for a broader range of applications.

The Future of PCB Routing Is Here

Ultra HDI isn’t just an incremental improvement. It’s a revolutionary shift in PCB design. By enhancing routing density, optimizing BGA breakouts, reducing layer count, and improving high-speed performance, Ultra HDI empowers designers to push boundaries like never before. Whether you're working on next-gen mobile devices or cutting-edge automotive tech, Ultra HDI gives you the tools to create smaller, smarter, and more efficient PCBs.