A lot of old thinking still floats around about advanced manufacturing, especially high-density interconnects (HDIs). People’s ideas are stuck in the past, while the reality of modern electronics in automotive, aerospace, and data comms has completely changed. Lumentum’s work in this area, for example, is often misunderstood, which means engineers are working with outdated ideas about what’s actually possible in terms of size and performance.
Key Takeaways
- Lumentum’s advanced HDI fabrication can regularly hit trace widths and spaces below 25 microns, which makes the old 75-micron ‘limit’ look ancient.
- Integrating HDI with optics is happening now. Lumentum has working, scalable modules that push data past 400 Gbps in a tiny package.
- Dense HDI designs don’t have to cook themselves. Smart substrate materials and built-in cooling solutions keep performance high even under extreme heat.
- HDI isn’t just for high-end budgets anymore. Manufacturing has gotten so much more efficient, and the demand for small, powerful electronics is making it a mainstream choice.
- Lumentum’s approach is all about co-design. Electrical, optical, and mechanical teams work together from day one to avoid problems down the line and get the best system performance.
Myth 1: High-Density Interconnects are only for niche, high-cost applications.
This idea is a hangover from the early days of HDI, when costs were sky-high. Sure, at first HDI was mostly for military and medical gear that needed the performance at any cost, but that world is long gone. Today, HDI is the backbone of tons of consumer electronics, car systems, and computing platforms. A Grand View Research report projects the global HDI market will top $18 billion by 2028, mostly thanks to demand from smartphones, wearables, and ADAS. With that kind of adoption, you can’t call it a niche technology anymore. Lumentum’s work on making manufacturing scalable and finding better materials has been a big part of this, making these advanced interconnects cheap enough for mass production.
The cost for each connection point has dropped for a decade, driven by big steps forward in laser drilling, forming micro-vias, and plating. For instance, switching from mechanical to laser drilling for micro-vias cut process time, boosted precision, and directly lowered the final cost, a huge deal. We’ve seen this happen in the car industry, where HDIs aren’t just for fancy infotainment systems anymore. Now they’re essential for safety hardware like radar modules and LiDAR sensors. The better performance you get, like less signal loss and better electromagnetic compatibility (EMC), is often worth the slightly higher cost over a traditional PCB, especially when you think about the smaller total system size and better reliability.
Myth 2: Achieving sub-50 micron trace widths and spaces reliably is still a major manufacturing hurdle.
A lot of engineers, especially if they’re used to standard PCB fab, think that getting reliable traces and spaces below 50 microns (µm) is still some kind of black art with terrible yields. That’s just not the case anymore, at least not for the top-tier manufacturers. Lumentum, for one, has its processes so dialed in that they’re routinely hitting trace widths and spaces of 25 µm and even lower in a production setting. You need this capability for their advanced optical components and integrated circuits, where signal integrity and tiny footprints are everything. The secret sauce is a combination of advanced lithography, better photoresists, and extremely precise etching processes. You literally couldn’t build the current generation of small, high-performance optical transceivers without this.
Just look at the needs of an 800G optical transceiver, which are becoming the new standard in data centers. These tiny modules demand incredibly dense routing, where the electrical traces carrying signals at hundreds of gigabits per second must maintain precise impedance control and minimal crosstalk to avoid turning into a noisy mess. Getting this right means you need more than just narrow traces. You need incredibly uniform dielectric layers and perfect layer-to-layer registration. A technical paper from the IPC Association Connecting Electronics Industries points out how modified semi-additive processes (MSAP) and better subtractive etching have made these fine features more repeatable than ever. It’s a standard manufacturing capability now for companies leading the pack in HDI. If you’re still designing around a 75 µm practical limit, your information is a decade out of date. The industry has already lapped that.
Myth 3: Optical and electrical interconnects cannot be smoothly integrated at the HDI level.
For years, everyone assumed you had to keep optical and electrical paths separate until you got way up the system chain, with the connection point being a discrete, often clunky, interface. But Lumentum’s designs prove that you can get true optoelectronic co-integration at the HDI level, and it makes financial sense to do so. They’re actively building waveguides and optical parts right onto substrates next to the electrical traces. Doing it this way slashes latency, cleans up signal integrity, and lets you build things smaller than ever before.
A great example of this is how they integrate silicon photonics with high-density electrical routing. By building optical waveguides right on the same substrate (or very close to) the electrical ICs, Lumentum gets rid of the bulky fiber optic connectors you’d normally need at the component level. This matters a lot for things like co-packaged optics (CPO) in next-gen data center switches, where the optical engine has to sit right beside the main switch ASIC. A recent presentation at the Optical Fiber Communication Conference (OFC) showed off modules where 400 Gbps and even 800 Gbps optical links are tightly woven in with the host electronics. This is about designing the two to work as a single, optimized unit from the start, which cuts conversion losses and crams in as much bandwidth density as possible.
Myth 4: Thermal management becomes insurmountable with increasing HDI density.
People are right to worry about heat in super-dense HDI designs, but thinking the problem is unsolvable is just wrong. While packing more stuff into a smaller space definitely raises the thermal density, Lumentum and other industry leaders have developed sophisticated ways to deal with it. They tackle this with a mix of strategies, using advanced substrate materials, integrated heat spreaders, and clever cooling techniques. Just slapping a fan on the outside doesn’t cut it anymore with these power densities.
Modern HDI substrates often use materials with much better thermal conductivity than old-school FR-4, like certain ceramic-filled laminates or advanced polymer composites in hot spots. On top of that, Lumentum’s designs regularly use embedded thermal vias and copper planes specifically laid out to pull heat away from active components. For the really tough jobs, they can even build microfluidic cooling channels right into the substrate layers to circulate dielectric coolants and keep everything at the right temperature. A white paper on thermal solutions from Electronic Design noted that these built-in cooling methods can drop junction temperatures by 15-20°C compared to just using air cooling. That directly improves reliability and makes components last longer. Thermal management is now a core part of the initial HDI design, not an afterthought where you just hope the heat finds its way out.
Myth 5: HDI design tools are too complex and require specialized, proprietary software.
There’s a perception that to design HDIs, especially with integrated optics, you have to buy some weird, specialized, and probably proprietary EDA (Electronic Design Automation) software. And while there are some niche tools for specific optical simulations, the main HDI design work happens on the same mainstream EDA platforms everyone already uses. The big EDA companies have been updating their software for years to handle micro-vias, fine traces, and complex layer stack-ups. What’s really happened is a big push to bring the electrical and optical design worlds together.
Lumentum, like a lot of other advanced component makers, typically uses industry-standard tools for its electrical layout, adding specialized modules for optical simulation. Platforms from companies like Cadence Design Systems and Synopsys now provide integrated workflows that let an engineer design the electrical schematic, lay out the high-density board, and simulate optical waveguide performance all in one environment. This integration cuts down on data translation mistakes and speeds up the whole design cycle. The hard part isn’t learning the software. It’s having the deep knowledge of physics, materials science, and manufacturing that lets you actually push the limits of what’s possible. The tools enable the design. They don’t gatekeep it.
Myth 6: HDI manufacturing yields are inherently low due to the extreme precision required.
Because HDI requires such extreme precision, think 25 µm traces and stacked micro-vias, many assume the manufacturing yields must be terrible. That was definitely a concern back in the day, but big improvements in process control, automation, and inspection have made it a non-issue for a modern fab. Lumentum’s plants, for example, use strict statistical process control (SPC) and advanced automated optical inspection (AOI) systems that can spot microscopic defects at every stage. You have to have these systems to get high yields on these complex designs.
The constant progress in materials science is a huge help, too. Better photoresists, more uniform copper foils, and more stable dielectrics all lead to a wider process window and fewer defects. On top of that, fabs are now using predictive analytics and machine learning to make real-time adjustments to process parameters, preventing defects from happening in the first place. According to a recent presentation by SEMI (Semiconductor Equipment and Materials International), top factories are getting first-pass yields on complex HDI boards that are as good as, or even better than, what they got on traditional multi-layer PCBs a decade ago. It’s proof of a relentless focus on manufacturing quality. So the old ‘yield nightmare’ reputation of HDI is completely outdated. Modern plants prove that every single day.
Getting past these old myths shows you a field that’s moving incredibly fast, where Lumentum’s design innovations are constantly setting new performance targets. When you understand what’s actually possible today, you can make better design choices and unlock the potential for the next wave of electronic systems in all sorts of industries.
What is the primary advantage of high-density interconnects (HDI) over traditional PCBs?
HDI lets you pack way more function into a much smaller space. You get that by using finer traces and spaces, tiny vias (called micro-vias), and more layers, which leads to smaller products with better electrical performance and shorter signal delays compared to a traditional circuit board.
How are micro-vias created in HDI manufacturing?
Mostly with lasers. Laser drilling technology ablates (or vaporizes) tiny holes, typically 150 microns or less in diameter, through one dielectric layer at a time. Those holes are then metallized and the layers are laminated together to build up the final HDI board, allowing for complex via structures like stacked or staggered vias.
Can HDI technology be used for flexible circuits?
Yes, HDI tech is being used in flexible circuits all the time now, creating high-density flexible printed circuits (HD-FPCs). It’s perfect for wearables, medical implants, and aerospace parts where you need things to be both compact and able to bend.
What role do advanced materials play in Lumentum’s HDI innovations?
Materials are everything for Lumentum’s HDI work. They depend on things like low-loss dielectric materials for clean high-frequency signals, high-thermal-conductivity substrates to pull heat away, and specialized photoresists to create those super-fine trace geometries. The material choices make or break the performance and reliability of their high-speed components.
Is HDI design more susceptible to electromagnetic interference (EMI)?
You’d think more density means more EMI, but good HDI design practices, like tight impedance control, smart ground plane layout, and careful component placement, are all about managing it. In many situations, the shorter signal paths you get with HDI can actually *reduce* EMI compared to a bigger, less optimized board.
