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Nolan’s Notes: UHDI—Raising Awareness and Interesting Questions

It was over lunch on the second day of the recent IPC Symposium on Advanced Packaging when I asked a question that triggered an interesting discussion about advanced packaging and ultra high density interconnect (UHDI). While these two technologies are distinct, they are also symbiotic; it takes both to make either one successful. As the symposium delivered on its agenda, the inter-relationship between these two technologies became crystal clear.

UHDI is the fabrication technology necessary if you want to manufacture the interposer subcomponents so critical to connecting the semiconductor chips to the enveloping package. For the history of semiconductors, each component package contained one and only one chip. Advanced packaging uses sophisticated techniques to include and connect multiple chips inside one package. This allows for a more modular approach to building up the finished product.

But how do the chips get connected inside? Interposers—super small fanout or interconnect features. Interposers provide the interim fanout steps from nanometer-scale IC pads to the ultimate goal of BGA solder balls leading to the outside world. Interposers work a lot like a PCB, but their feature sizes are in the micron range—much smaller than most PCB shops can fabricate, and much larger than current semiconductor facilities can build. Ironically, the advanced packaging component that fills the gap needs to be built with a technology that is right in the middle of the fabrication gap. It is within this fabrication gap that UHDI resides: To make the interposers necessary to deploy advanced packaging, UHDI fabrication is necessary; advanced packaging is the “killer application” that makes UHDI a financially feasible investment for a fabricator. There, in a nutshell, is the symbiosis.

Our technical editor, Happy Holden, “father of HDI,” is well-quoted saying that HDI took a long time to be adopted, in part because it took a long time for the cost vs. capability evaluation to flip. Until cellphones, there just hadn’t been a “killer application” for HDI that pushed it out of its niche status. It seems safe to say that UHDI will grow out of its niche status and into a major technology supporting the semiconductor industry’s appetite for advanced packaging.

Ah, but there’s a piece missing from this puzzle, upon which my lunchtime question centered. I asked, “Which mid-career engineer is more likely to pivot their career into UHDI for substrates—PCB fabricators or IC manufacturers?” Our conversation kicked this conundrum around for much longer than I expected. So, what was the outcome?

On the one hand, PCB fabs seem the most likely to understand the interposer game, but they will need a facility that resembles the semiconductor fabs of 25 or 30 years ago. That’s a big step up for most of them. Will they be able to pick up the necessary expertise?

That’s precisely the challenge for the semiconductor engineer. Moving to UHDI feature sizes is a big step backward from current semiconductor feature sizes. While the semiconductor engineers would have the experience, would they also find it lacking in challenge? The upshot: Even when we build out packaging capabilities, where will the skilled staffing come from? Suddenly, and once again, the industry’s gaze turns to the academic community to educate talent, and to employers to remain competitive with hiring packages. But that’s an entirely different conversation.

In this issue of PCB007 Magazine, we pull out the microscope and peer down into the UHDI niche in the marketplace. Calumet’s Todd Brassard and Meredith LaBeau discuss UHDI and the give-and-take that comes with helping define a new market niche in their interview, while Sunny Patel at Candor Industries sheds light on the operational side of ramping up UHDI skill sets and facilities. Jan Pederson shares his industry-wide perspective on supply and demand for UHDI as well. As features get smaller, drilling and cutting capabilities must also become more precise; in a group discussion with the MKS/ESI team, they share their work to deliver laser systems for UHDI applications. Of course, we bring you columns from IPC’s Dr. John Mitchell, Gardien's Todd Kolmodin, Chemcut’s Christopher Bonsell, Paige Fiet in her IPCEF role, Travis Kelly representing PCBAA, and our very own Happy Holden.

There is still a lot to work through in UDHI; there are many more questions than answers at this moment. But what is clear is that we will be embracing this technology, adding these capabilities, whether we want to or not. Semiconductor advancements will require it.

As always, our mission is to help move the conversation forward in the industry. To that end, we appreciate your feedback and suggestions identifying the most important topics. To be honest, yours are among our favorite emails to receive. Please keep in touch.

This column originally appears in the November 2022 issue of PCB007 Magazine.