From process development to high-volume manufacturing

ASMPT is experiencing strong demand for ultra-precision die-bonding systems – from manufacturers of AI infrastructure and optical interconnects to aerospace applications. As data rates continue to increase, scalable manufacturing of photonic devices is becoming a key enabler for the next generation of computing.

An Interview with Sebastian Rappl, Technical Sales Manager at ASMPT AMICRA GmbH

AI clusters, high-performance computing, and hyperscale data centres require faster, denser, and more energy-efficient data movement. Co-Packaged Optics integrates optical engines closely with ASICs or other high-performance processors in a single package, shortening electrical paths to reduce signal loss, power consumption, and latency. As data rates increase, manufacturers face demanding CPO assembly challenges: sub-micron optical alignment, reliable bonding, thermal management in compact packages, heterogeneous integration of optics and electronics, metrology, process control, and scalable production with consistent yield and reliability. ASMPT addresses these needs with high-precision placement systems, proprietary vision alignment, in-line metrology, and automation capabilities for scalable CPO assembly. As optical interconnects increasingly replace copper connections in AI-enabled data centres, scalable optoelectronic manufacturing is becoming a key element of ASMPT’s strategy to empower the Intelligence Revolution.

What are the key considerations in the volume production of co-packaged optics? We interviewed Sebastian Rappl, Technical Sales Manager at ASMPT AMICRA GmbH.

Q: Which CPO applications are driving current manufacturing requirements?

Sebastian Rappl: What we see today is that the discussion around co-packaged optics has become much more application driven. Customers are no longer asking about CPO as a system architecture. Instead, they are now developing concrete assembly processes for glass dies, micro-lenses, lens arrays, photonic integrated circuits and optical sub-assemblies integrated alongside ASICs, drivers and TIAs, e.g. processes for CoC-embedded CPO architectures or CPO systems supplied by external laser sources in an ELSFP form factor. Following alignment, these optical components are typically fixed using UV-curable adhesives. What makes these assemblies particularly demanding is the direct relationship between mechanical precision and optical performance. Parameters such as x/y position, z-height, tilt, bond-line thickness and post-bond shift directly influence optical coupling efficiency. A mechanically acceptable assembly can therefore still fail to meet optical specifications if curing shrinkage, adhesive flow or substrate movement changes the optical path. Many engineers initially focus on placement accuracy. In practice, however, placement accuracy alone is no longer sufficient to ensure optical performance. In many photonics applications, the challenge is not only placing components accurately, but ensuring that this alignment is maintained throughout bonding, curing and subsequent handling. Manufacturing success depends on controlling the complete process rather than individual steps. Component handling, adhesive dispensing, alignment, placement, UV curing, post-bond inspection and metrology all must work together as one integrated process. Only then can highly sensitive optoelectronic assemblies be manufactured with the repeatability and scalability required for volume production.

The source stage of the MEGA multi-chip bonding platform is part of a flexible system that is able to provide different components in one single production step. Image credits: ASMPT

Q: At what stage should customers start thinking about manufacturability in CPO?

Sebastian Rappl: One of the most important lessons we’ve learned is that manufacturability has to be addressed very early – ideally before the package architecture is frozen. Many later assembly limitations like component layout, optical access, fiducial strategy, substrate material, surface planarity, adhesive keep-out zones, thermal budget and the available space for tooling, dispensing, curing and inspection are already defined by design decisions. A good example is alignment access. If the design does not provide suitable optical or visual access, process control becomes much more difficult. The same applies to substrate warpage, adhesive flow paths or material combinations with different coefficients of thermal expansion. These factors can influence the final position of a glass die or lens after curing or during thermal cycling. One of the first tasks in CPO development is translating optical performance requirements into mechanical and process tolerances right from the start. It must be determined during the development phase how much placement deviation, bond-line variation, post-cure shift or angular error the design can tolerate. Otherwise, the assembly process is forced to compensate for constraints that should have been considered during package design. This is why CPO requires close interaction between design, process engineering and equipment capability. Manufacturability is not a correction step at the end; it becomes part of the design strategy.

Q: Where does the main technical bottleneck occur when CPO moves from concept to manufacturable assembly?

Sebastian Rappl: In our experience, the bottleneck is rarely a single parameter. It is usually the accumulation of tolerances across the process chain. Placement accuracy, die geometry, substrate flatness, adhesive distribution, bond-line thickness, curing behaviour, thermal expansion and inspection limits all interact. A robust process window does not happen by accident – it has to be engineered deliberately. Only a sufficiently robust process window can absorb normal process variation without compromising optical performance or yield. Each step should be characterized based on how much variation it contributes to the final optical result. For example, if post-bond shift is the dominant factor, improving nominal placement accuracy alone will not solve the issue. If substrate planarity is unstable, better curing control may not be sufficient. A manufacturable CPO process only emerges when placement, bonding, adhesive behaviour, metrology and automation are treated as one connected system.

The AMICRA NOVA’s four-arm flip unit supports the combination of high throughput and precision required for volume production of silicon photonics and optical interconnect modules. Image credits: ASMPT

Q: Why are glass dies, lenses and UV-curable adhesives particularly challenging in CPO assembly?

Sebastian Rappl: Glass dies and optical components combine mechanical, optical and material-related requirements within a single assembly process. Unlike conventional die attach, the final optical performance depends not only on placement accuracy but also on maintaining that alignment throughout adhesive curing and subsequent handling. UV-curable adhesives enable rapid fixation after alignment, but they also introduce critical process variables, including dispense volume, wetting behaviour, bond-line thickness, curing sequence and material shrinkage. Even very small movements during curing can alter the optical path and reduce coupling efficiency. This is why we always recommend looking beyond the alignment step itself. Alignment cannot be evaluated only before bonding. Manufacturers must verify whether the component remains within specification after curing and under realistic production conditions. A process that delivers good engineering samples but cannot maintain repeatability across substrates, material lots and thermal cycles is not scalable. Consequently, UV adhesive processing should be treated as an integral part of the optical alignment strategy rather than as a separate fixation step.

Q: How can process capability and yield be measured and optimized?

Sebastian Rappl: Customers often start by asking about placement accuracy. But nominal placement accuracy alone is not enough. For photonics assembly, the distribution of results is often more meaningful than a single best-case value. Useful indicators include placement repeatability, post-bond shift, bond-line variation, angular deviation, curing-related displacement and correlation with optical test data. This is why metrology plays such a central role. While visual inspection can confirm mechanical assembly quality, only the combination of machine data, in-line inspection and optical measurements provides a reliable assessment of process capability. This integrated data allows engineers to distinguish whether yield losses originate from placement variation, adhesive behaviour, substrate effects or thermal stress. As CPO modules become increasingly complex, yield management extends beyond individual process steps. Every transfer, handling operation and interface introduces additional sources of variation. Reducing these transitions while maintaining complete process traceability is essential for stable, high-volume manufacturing. Ultimately, process capability depends on the ability to measure, understand and continuously control process variation rather than achieving a single best-case accuracy value.

Q: How do AMICRA NANO, AMICRA NOVA and MEGA support the transition to volume production?

Sebastian Rappl: As we work with customers moving from feasibility studies into production, we see that the requirements for manufacturing technology change significantly. For many customers, AMICRA NANO is the starting point during early process development. The platform provides the sub-micron placement accuracy and process stability required to evaluate alignment and bonding strategies as well as material interactions. AMICRA NANO features ±0.2 μm @ 3σ placement accuracy, flip-chip bonding capabilities for advanced semiconductor packaging, a granite-based platform with high-resolution motion control for stable alignment, high-resolution imaging systems that enable dynamic alignment for precise bonding and a laser-based heating system that ensures controlled, localized bonding processes. Its controlled environment enables engineers to identify which process variables truly limit optical performance before scaling begins.

Once the process window has been established, AMICRA NOVA supports the transition to volume production with more than 1,000 UPH by combining high precision with higher throughput, dynamic alignment and robust process control. It features ±1 µm placement accuracy for precise photonic and electronic component integration and dynamic alignment and high-resolution imaging for controlled positioning during bonding. It is designed for demanding photonics applications such as silicon photonics, optical transceivers and optical interconnect modules for AI data centres, where consistent optical performance must be maintained at production scale.

For increasingly complex multi-chip architectures, MEGA extends this capability by integrating multiple bonding, inspection and adhesive-related process steps into a single flexible manufacturing platform. MEGA is a multi-chip bonding platform for advanced semiconductor packages that integrate multiple dies in compact, high-performance architectures. Its look-through pattern recognition supports accurate die placement for complex assemblies. The photonics version MEGA-P achieves a throughput of up to 8,000 UPH and offers unparalleled precision of ± 2 μm @ 3σ and ± 0.1° @ 3σ in terms of rotation. The MEGA platform offers various epoxy dispensers and stamp options, the ability to use multiple adhesives in parallel, and automatic switching between application variants. Since adhesive control is a critical factor in CPO manufacturing, MEGA also incorporates dedicated 3D inspection of epoxy dispensing. One of MEGA’s key strengths is its ability to consolidate critical process steps into a single manufacturing platform, reducing handling, improving process visibility and minimizing cumulative process variation.

Together, these three platforms support the complete manufacturing journey – from process development and validation to scalable, high-yield production.

A look inside the AMICRA NANO: Source stage, flip unit and bond head support the sub-micron precision required to evaluate optical alignment strategies and process windows during early CPO development. Image credits: ASMPT

Q: What ultimately defines a production-ready CPO process?

Sebastian Rappl: Ultimately, a production-ready process is one where the critical variables are understood and kept under control. For glass die and lens attach, this includes alignment accuracy, bond-line thickness, adhesive volume, curing behaviour, post-bond shift, component stability and inspection capability. For us, repeatability – not peak performance – is what defines a CPO process ready for high-volume manufacturing. Every critical parameter must remain measurable, reproducible and consistently controlled under real production conditions. The objective is not simply to build functional prototypes. It is to establish an integrated manufacturing process that consistently delivers predictable optical performance, stable yield and scalable production without relying on manual intervention or process-specific adjustments.

The industry is no longer asking whether co-packaged optics can be manufactured – it is asking how these highly sensitive assemblies can be produced at scale while maintaining optical performance, yield and long-term process stability.

Thank you very much for sharing your expertise and providing such valuable insights into the key manufacturing challenges and opportunities shaping the future of co-packaged optics.

Visitors to ECOC Exhibition 2026, Europe’s largest exhibition and one of the world’s leading meeting places for optical communications and photonics, taking place 21–23 September at FYCMA in Málaga, Spain, will have the opportunity to continue the conversation with Sebastian Rappl at the ASMPT booth 2158. Alongside the topics discussed in this interview, ASMPT will showcase the AMICRA NANO, AMICRA NOVA and MEGA platforms, giving visitors the opportunity to explore solutions for sub-micron alignment, advanced bonding, adhesive processing, integrated inspection and process control. Whether discussing early process development, production scalability or the industrialization of next-generation photonic devices, ASMPT’s experts will be available to discuss specific manufacturing challenges and application requirements.