The semiconductor industry is at a pivotal moment as the limits of Moore’s Law motivate a transition to three-dimensional integrated circuit (3D IC) technology. By vertically integrating multiple chiplets, 3D ICs enable advances in performance, functionality, and power efficiency. However, stacking dies introduces layers of complexity driven by multi-physics interactions—thermal, mechanical, and electrical—which must be addressed at the start of design.
This shift from two-dimensional (2D) system-on-chips (SoC) to stacked 3D ICs fundamentally alters the design environment. 2D SoCs benefit from well-established process design kits (PDKs) and predictable workflows.
Figure 1 The 3D IC technology takes IC design to another dimension. Source: Siemens EDA
In contrast, 3D integration often means combining heterogeneous dies that use different process nodes and new interconnection technologies, presenting additional variables throughout the design and verification flow. Multi-physics phenomena are no longer isolated concerns—they are integral to the design’s overall success.
Multi-physics: a new design imperative
The vertical structure of 3D ICs—interconnected by through-silicon vias and micro-bumps and enclosed in advanced packaging materials—creates a tightly coupled environment where heat dissipation, mechanical integrity, and electrical behavior interact in complex ways.
For 2D chips, thermal and mechanical checks were often deferred until late in the cycle, with manageable impact. For 3D ICs, postponing these analyses risks costly redesigns or performance and reliability failures.
Traditional SoC design often relies on high-level RTL descriptions, where many physical optimizations are fixed early and are hard to change later. On the other hand, 3D IC’s complexity and physical coupling require earlier feedback from physics-driven analysis during RTL and floorplanning, enabling designers to make informed choices before costly constraints are locked in.
A chiplet may operate within specifications in isolation, yet face degraded reliability and performance once subjected to the real-world conditions of a 3D stack. Only early, predictive, multi-physics analysis can reveal—and enable cost-effective mitigation of—these risks.
Continuous multi-physics evaluation must begin at floorplanning and continue through every design iteration. Each change to layout, interfaces, or materials can introduce new thermal or mechanical stress concerns, which must be re-evaluated to maintain system reliability and yield.
Moving IC design to the system-level
3D ICs require close coordination among specialized teams: die designers, interposer experts, packaging engineers, and, increasingly, electronic system architects and RTL developers. Each group has its own toolchains and data standards, often with differing net naming conventions, component orientations, and functional definitions, leading to communication and integration challenges.
Adding to the internal challenges, 3D IC design often involves chiplets from multiple vendors, foundries and OSAT providers, each with different methodologies and data formats. While using off-the-shelf chiplets offers flexibility and accelerates development, integration can expose previously hidden multi-physics issues. A chiplet that works in isolation may fail specification after stacking, emphasizing the need for tighter industry collaboration.
Addressing these disparities requires a system-level owner, supported by comprehensive EDA platforms that unify methodologies and aggregate data across domains. This ensures consistency and reduces errors inherent to siloed workflows. For EDA vendors, developing inclusive environments and tools that enable such collaboration is essential.
Inter-company collaboration now also depends on more robust data exchange tools and methodologies. Here, EDA vendors play a central role by providing platforms and standards for seamless communication and data aggregation between fabless houses, foundries, and OSATs.
At the industry level, new standards and 3D IC design kits—such as those developed by the CDX working group and industry partners—are emerging to address these challenges, forging a common language for describing 3D IC components, interfaces, and package architectures. These standards are vital for enabling reliable data exchanges and integration across diverse teams and supply chain partners.
Figure 2 Here is a view of a chiplet design kit (CDK) as per JEDEC JEP30 part model. Source: Siemens EDA
Programs such as TSMC’s 3Dblox initiative provide upfront placement and interconnection definitions, reducing ambiguity and fostering tool interoperability.
Digital twin and predictive multi-physics
The digital twin concept extends multi-physics analysis throughout the entire product lifecycle. Maintaining an accurate digital representation—from transistor-level detail up to full system integration—enables predictive simulation and optimization, accounting for interactions down to the package, board, or even system level. By transferring multi-physics results between levels of abstraction, teams can verify that chiplet behavior under thermal and mechanical loads accurately predicts final product reliability.
Figure 3 A digital twin extends multi-physics analysis throughout the entire product lifecycle. Source: Siemens EDA
For 3D ICs, chiplet electrical models must be augmented by multi-physics data captured from stack-level simulations. Back-annotating temperature and stress outcomes from package-level analysis into chiplet netlists provides the foundation for more accurate system-level electrical simulations. This feedback loop is becoming a critical part of sign-off, ensuring that each chiplet performs within its operational window in the assembled system.
Keeping it cool
Thermal management is the single most important consideration for die-to-die interfaces in 3D ICs. The vertical proximity of active dies can lead to rapid heat accumulation and risks, such as thermal runaway, where ongoing heat generation further degrades electrical performance and creates mechanical stress from varying thermal expansion rates in different materials. Differential expansion between materials can even warp dies and threaten the reliability of interconnects.
To enable predictive design, the industry needs standardized “multi-physics Liberty files” that define temperature and stress dependencies of chiplet blocks, akin to the Liberty files used for place-and-route in 2D design. These files will allow designers to evaluate whether a chiplet within the stack stays within its safe operating range under expected thermal conditions.
Multi-physics analysis must also support back-annotation of temperature and stress information to individual chiplets, ensuring electrical models reflect real operating environments. While toolchains for this process are evolving, the trajectory is clear: comprehensive, physics-aware simulation and data exchange will be integral to sign-off for 3D IC design, ensuring reliable operation and optimal system performance.
Shaping the future of 3D IC design
The journey into 3D IC technology marks a transformative period for the semiconductor industry, fundamentally reshaping how complex systems are designed, verified, and manufactured. 3D IC technology marks a leap forward for semiconductor innovation.
Its success hinges on predictive, early multi-physics analysis and collaboration across the supply chain. Establishing common standards, enabling system-level optimization, and adopting the digital twin concept will drive superior performance, reliability, and time-to-market.
Pioneers in 3D IC design—across EDA, semiconductor and system developers—are moving toward unified, system-level platforms that allow designers to iterate and optimize multi-physics analyses within a “single cockpit” environment that allows designers to optimize and iterate across different types of multi-physics analyses.
Figure 4 The Innovator3D IC solution provides the single, integrated cockpit 3D IC designers need. Source: Siemens EDA
With continued advances in EDA tools, methodologies and collaboration, the semiconductor industry can unlock the full promise of 3D integration, delivering the next generation of electronic systems that push the boundaries of capability, efficiency, and innovation.
Todd Burkholder is a senior editor at Siemens DISW. For over 30 years, he has worked as editor, author, and ghost writer with internal and external customers to create print and digital content across a broad range of high-tech and EDA technologies. Todd began his career in marketing for high-technology and other industries in 1992 after earning a Bachelor of Science at Portland State University and a Master of Science degree from the University of Arizona.
Tarek Ramadan is applications engineering manager for the 3D-IC Technical Solutions Sales (TSS) organization at Siemens EDA. He drives EDA solutions for 2.5D-IC, 3D-IC, and wafer level packaging applications. Prior to that, Tarek was a technical product manager in the Siemens Calibre design solutions organization. Ramadan holds BS and MS degrees in electrical engineering from Ain Shams University, Cairo, Egypt.
John Ferguson brings over 25 years of experience at Siemens EDA to his role as senior director of product management for Caliber 3D IC solutions. With a background in physics and deep expertise in design rule checking (DRC), John has been at the forefront of 3D IC technology development for more than 15 years, witnessing its evolution from early experimental approaches to today’s production-ready solutions.
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