A finished chip, built on a two-nanometer process, tested and working, gets thrown in the bin. Not because the silicon failed. Because the packaging around it did.
That is the reality silicon photonics is walking into. What decides whether a photonic chip becomes a product is no longer the device. It is the package.
That shift is happening fast, and it is happening because of AI. Data centers are pushing bandwidth, latency and power past what current interconnects can handle, and silicon photonics is one of the few credible answers. But moving from a working device to millions of reliable units depends on assembly, alignment and bonding, not on lithography. The industry spent years perfecting the front end. The constraint has moved to the back.
This is where high-precision die bonding decides whether a design ever reaches production. Optical performance, electrical signal integrity, thermal behavior and mechanical stability all come down to how accurately the package is assembled and how well that process holds up at volume. Finetech builds the bonding systems that sit at exactly this point, and the company has spent years working with the developers pushing silicon photonics toward scale. This is where the real challenges sit, and what it takes to get past them.
The Package Became the Product
In conventional electronics, packaging came last. It protected the device, connected it to the outside world and was treated as a cost-sensitive assembly step.
Silicon photonics breaks that model. The package now has to do four things at once:
- Guide light
- Preserve high-speed electrical signals
- Manage heat
- Hold different materials in precise positions over years of operation
Small deviations degrade coupling efficiency, signal quality and long-term reliability. This is why packaging can account for a major share of the final product value, in some cases approaching the cost of the chip itself. It forces companies to rethink process development, equipment and supply-chain readiness.
Die-to-wafer bonding, chiplet integration, interposers, hybrid bonding and heterogeneous integration are pulling packaging closer to wafer-level manufacturing. These are not backend assembly tasks. They demand cleanroom-compatible processes, accurate placement and stable, repeatable bonding.
“If the packaging is compromised, the entire product is lost,” says Sylvain Dulphy, Sales Manager at Finetech. “Regardless of the quality of the 2-nanometer chip inside, if the packaging is not executed perfectly, the unit is discarded.”
Pluggables Hit a Wall at the Switch
Pluggable optical modules have served the industry well, but as data centers get faster and denser, power consumption, signal integrity and physical distance become harder to control. The copper and fiber worlds are merging, and that is why co-packaged optics are gaining ground. Bringing optical engines closer to the switch ASIC or processor shortens the electrical path before the signal converts to light. At very high speeds, that distance directly affects system performance. The catch is that shorter, denser connections are exactly the ones hardest to place accurately at volume.
“If the electrical signal path is too long, it effectively becomes a filter,” Dulphy explains. “You might have speed, but if the connection length reduces signal strength, overall performance is capped.”
Connections have to get shorter, denser and more direct. That pushes designs toward bumps, interposers, metal-to-metal contacts, chiplets and 3D architectures.
The difficulty compounds:
- Optical and electrical functions share one package
- Materials with different thermal expansion have to coexist
- Mechanical tolerances tighten
- Alignment has to hold during assembly and across the full operating life of the product
Aligning Every Unit by Hand Does Not Scale
Optical alignment is one of the hardest parts of silicon photonics packaging.
In many applications it is still done actively. The cycle runs like this: a fiber, lens or optical element is moved into position, the laser is switched on, the signal is measured, the position is adjusted, and the sequence repeats until coupling is good enough.
The method is accurate and well established. It is also slow and expensive at volume.
For higher volumes, the industry is shifting toward passive alignment. Mechanical references, intermediate optical structures and repeatable placement accuracy reduce the need to power up and optimize every unit.
Passive alignment does not remove the difficulty. It moves it into the process chain. Substrates, optical elements, bonding accuracy, thermal behavior and inspection all have to line up. A concept that works in development still has to prove it survives the move to production without losing its performance window.
SiN photonic wafer populated with VCSELs, photodiode arrays and thermistors. It takes precise assembly of the active components to turn the wafer into a working product. (© PHIX B.V.)
No Standards, No Tools, No Shortcut
The scaling problem is structural. Silicon photonics packaging still lacks broadly accepted standards. Companies build their own architectures, interfaces and process flows, which is understandable in a fast-moving field but slows learning across the industry.
Equipment is the other constraint. Conventional assembly equipment was never built for this. The systems needed here have to combine several capabilities in one platform:
- High placement accuracy
- Mixed-material handling
- Optical and electrical interfaces
- 3D alignment
- Process traceability
- Manufacturing repeatability
Waiting for an application to mature and adapting production systems afterward is a bad bet. Equipment and process development have to move together.
This is already reshaping how companies work. Foundries are extending their advanced integration capabilities, front-end players are moving deeper into packaging, and equipment suppliers are being brought into application development earlier. Research institutes, system integrators and packaging specialists now sit at the same table.
Die Bonding Is the Transition Point
Most silicon photonics processes fail not in the lab but in the handoff to production. A bonding recipe that works on a development platform has to survive the move to a line where speed, yield and traceability decide whether the product is viable. That handoff is where Finetech works.
High-precision die bonding is the step that makes or breaks it. Placement accuracy, controlled bonding force and temperature, and the ability to handle different materials in one process are what separate a promising demonstrator from a manufacturable product. A research group at TU Wien, for instance, used a Finetech bonder to flip-chip III-V terahertz quantum cascade lasers directly onto silicon, which made the electrical contacting possible and improved the lasers’ thermal performance (see the customer story). Finetech builds systems for exactly these requirements, and works with customers from first feasibility tests through to repeatable production, so the process developed early does not have to be reinvented later.
The same demands show up beyond photonics, in quantum technology, MEMS, implantable medical electronics and advanced sensors. The common thread is assembling high-value components with tight tolerances and almost no margin for error. In each case, the bonding process is tied directly to performance, yield and scalability, which is why it belongs in the conversation from the start and not at the end.
From Working Device to Shipping Product
Silicon photonics has a clear place in the next generation of AI infrastructure, high-speed networking and advanced sensing. Getting there will take more than good device design.
The industry needs several things to line up at once:
- Mature packaging standards
- Scalable alignment strategies
- Production-capable bonding
- Equipment developed alongside the application
- Closer cooperation between foundries, tool makers, research institutes, system integrators and packaging specialists
The demand is already forming around AI data centers, co-packaged optics, high-performance computing and tightly integrated photonic-electronic systems. What happens next depends on how fast the supply chain can turn promising devices into products that can be built at scale.
The two-nanometer chip in the bin is the warning. Every one of those is a working device lost to a process that did not hold. Getting silicon photonics to volume means making sure that stops happening.
Adapted from Sylvain Dulphy’s feature in Silicon Semiconductor, Issue V 2026.
