When you hear an expert explain the idea to change the body of modern computer chips from plastic to glass, the logic is persuasive. This body, called the substrate, connects and protects the silicon brains inside, and compared to current organic substrates, glass does everything better. It’s flatter (important for connecting flat silicon die to a very flat motherboard), it’s harder (better able to hold an increasing number of smaller and smaller wires) and it’s stronger.
As compelling as moving from plastic to glass substrates sounds, however, it’s not a straightforward switch.
“The whole substrate industry has to remap to be able to handle the glass,” says Srini Pietambaram, who’s played a big role on the Intel team in Assembly Test Technology Development driving that “remap.”
Nothing Simple about Glass Chips
Pietambaram and team have labored through the past few years on an unusual combination of pioneering technology and materials inventions alongside, basically, saving glass from itself.
More chips in a package with more wires connecting them puts more pressure on today’s organic plastic package, now in its third decade of reliable service. Glass substrates not only promise to do the basic jobs better but also the potential for a 10x increase in interconnect density and integration of optical interconnects.
In other words, future chips could shuttle through a lot more data a lot faster. Imagine, for instance, AI accelerators that are orders of magnitude more capable than today’s.
“It is no simple technology,” Pietambaram says. Getting everything to work took “a lot of tailoring.” As revealed in September, Intel has it figured out and has a plan to deliver complete glass substrate solutions to the market in the second half of this decade.
For his contributions to the hundreds of unknowns and problems the teams solved in bringing about glass substrates — in addition to ongoing work to extend the capabilities of organic substrates — Pietambaram earned Intel’s 2023 Inventor of the Year award. The inventor honor is an award employees can earn only once, as measured by inventions recorded (some of which may become patents or company trade secrets).
‘When It’s Chaos … I Jump in’
“A brand-new technology especially has so many unknowns that we anticipate over time,” he says. “No technology comes easy.”
This is Pietambaram’s happy place.
“My strength is dealing with ambiguity,” he says. “When it’s chaos or something’s not working or not there, I jump in.”
His team saw the potential in glass early. As far as substrates go, “It’s very well behaved,” he explains. “How do we take advantage of this? I spent a lot of time looking at all the key attributes of glass and building a value proposition. And that’s what I loved in this job.”
Part of Pietambaram’s day job is figuring out where to steer his and his colleagues’ inventive efforts. As a pathfinding lead in module engineering within Intel’s center of packaging and substrate innovation, he says, “I scope the various technologies that this organization should focus on.” The aim is to “drive the roadmap based on anticipating the needs of the various products,” spanning Intel’s portfolio. And now through Intel Foundry Services, he also takes orders from “everybody in the industry.”
What’s the Big Deal with Glass?
Occasionally a developing chipmaking solution is dubbed “the new lithography” to signify its import to the continuation of Moore’s Law. Advanced packaging technologies fall (carefully) into this bucket.
The reason: Demand for more capable and more powerful processing has led to the creation of multi-chip amalgamations, changing packaging from basic utility to critical ingredient in a processor’s complete design.
“Substrate is basically a space transformer,” Pietambaram explains. A silicon die connects its nanometer-scale brains to the substrate via micron-scale bond pads on its back, and the substrate “transforms” those pads to millimeter-scale connections on the motherboard. To do so, it needs to be flat, stay flat and handle power input and fast signals with high precision.
Challenges on the technical side of making glass work included figuring out what kind of glass works best; how to layer metal and devices, add microscopic holes and runs wires in it; and how to make it better handle heat and mechanical forces through its life inside a computer.
On the more pragmatic side: How to make the edges less prone to cracking; how to cut or “singulate” a sheet full of substrates; and, simply, how to protect and move them around a factory without bouncing glass off a conveyor belt or roller or it taking any form of flight.
‘Our Backs up to the Wall — That’s Where the Best Ideas come from’
“When there is a problem or a bottleneck for a particular technology we need, that brings out the best in me,” Pietambaram says. “I spend days and nights reading, trying to understand and come up with something. That’s what inspires me.”
But the breakthroughs are achieved in ways that mirror today’s multi-chip processors, a team of brains coming together. “Ideation is a collaborative effort,” he says.
It’s not a shower or jog or commute that spurs his thinking, but, maybe surprisingly, a meeting. “We are sitting in a task force. We have our backs up to the wall and we have to come up with a solution. That’s where the best ideas come from.”
Though he might’ve been predestined for his job — Pietambaram didn’t want to follow in his dad’s footsteps as a professor of physics and instead earned a Ph.D. in materials science — he credits good mentors with keeping his craft sharp. He keeps a running list of ideas and questions for experts and engineers around Intel, including more recent college grads with unique specialties like electrochemistry or polymers.
The idea of glass substrates has been widely known, he points out. “A lot of people have worked on it, but Intel, with its scale and the kind of people we have here, we are able to take it to the next level and make it a reality.”
As Pietambaram and team continue to refine the recipe, Intel is working internally and with foundry customers to plan the first products built with a body of glass.