Chip-level thermal analysis solves a main barrier to 3DICs

As the semiconductor industry adds more functionality into smaller footprints, we are pushing the boundaries of traditional two-dimensional integrated circuit (2DIC) designs. The next phase in the growth of performance and functionality is building three-dimensional integrated circuits (3DICs). However, this new dimension introduces a host of challenges, the most significant of which is managing heat dissipation.

The allure and pitfalls of 3DICs

The advantages of stacked dies interconnected using vertical interconnect accesses (vias), to create a single, compact package include:

1. Increased performance: By reducing the distance between components, signal propagation delays are minimized, leading to faster processing speeds.
2. Enhanced functionality: Multiple functions can be integrated into a single package, enabling more complex and capable devices.
3. Reduced power consumption: Shorter interconnects can result in lower power consumption compared to traditional 2D ICs.

To realize these benefits, designers first need to clear some key hurdles, including the significant challenge of managing heat dissipation (figure 1). Because 3DIC architectures are so compact, heat generated by the densely packed components can cause hot spots that affect performance and reliability.

Figure 1. Illustration of a 3DIC with heat dissipation.

So, robust thermal management is essential as the designers continue to develop 3DICs devices. Traditionally, thermal analysis has been performed at the package and system levels, often as a separate process from IC design. However, this approach is no longer sufficient for 3DICs. Designers need to perform thermal analysis at the die level, starting at the early chip/package design phase in order to identify and mitigate potential thermal issues before they become critical problems. Early-stage thermal analysis helps to:

1. Find hotspots: Detecting areas of high thermal activity early in the design process allows for design adjustments to spread heat more evenly.
2. Optimize die and package design: Iterative thermal analysis during die and package design helps in optimizing thermal performance, ensuring that heat is effectively managed.
3. Improve reliability: By addressing thermal issues early, the overall reliability of the final product is enhanced, reducing the risk of thermal-induced failures.

Solutions for die-level thermal analysis

Solutions for accurate thermal analysis in the 3D assembly (die-to-die and die-to-package) required design automation software to create new tools and flows. The new flows enable comprehensive thermal analysis from the early stages of design through to final signoff, allowing for continuous thermal management and optimization.

Some key features of a thermal analysis solution for 3DICs include:

1. Integration with IC design flow: Seamless integration with existing IC design tools ensures that thermal analysis is an integral part of the design process, rather than an afterthought.
2. High accuracy and resolution: Advanced thermal solvers provide accurate and detailed analysis, capturing fine-grained thermal behaviors and interactions within the 3DIC assembly.
3. Automated thermal simulation: Automation simplifies the thermal analysis process, enabling designers without thermal expertise to perform accurate simulations and analyses.
4. Iterative analysis capability: The ability to perform iterative thermal analysis allows designers to continuously refine and optimize their designs based on thermal performance feedback.

Example of an integrated thermal analysis solution

One new tool in the market embeds a customized 3D solver from a popular package-level thermal tool within a proven IC design platform. This combination lets designers perform accurate chip and package-level static or dynamic thermal analysis of the full 3DIC assembly. It also allows for early and continuous thermal assessment from initial feasibility analysis to design signoff and is integrated with other 3D design tools and flows from IC to package to system levels. It supports all 3D integration technologies, including chiplets on package, interposers with through-silicon vias (TSVs) and direct bonding techniques.

Thermal analysis, debug and verification throughout the design flow

Designers need to track, fix, and verify thermal issues throughout the design flow, including:

1. Early design planning: During the conceptual stage, designers can apply high-level power estimates to explore the thermal impact of different design options like 3D partitioning schemes, die assembly, block and TSV floorplan, interface layer design, and package selection. Finding potential thermal issues early lets designers make informed decisions that avoid costly redesign later.
2. Detailed design and implementation: As designs become more detailed, thermal analysis runs verify that the design stays within its thermal budget. This involves analyzing the maturing package and die layout representations to account for their impact on thermally-sensitive electrical circuits. Fine-grained power maps are crucial at this stage to capture hotspot effects accurately.
3. Design signoff: Before finalizing the design, 3DICs need comprehensive thermal verification to ensure that the design meets all thermal constraints and reliability requirements. Automated constraints checking and detailed reporting can expedite this process, providing designers with clear insights into any remaining thermal issues.
4. Connection to package–system analysis: Models from IC-level thermal analysis can be used in thermal analysis of the package and system. The integration lets designers build a streamlined flow through the entire development process of a 3D electronic product.

Usability

Many 3DIC designers will not have the experience of a thermal engineer, so thermal analysis at the die level must be user-friendly. Examples of advanced automation to help 3DIC designers include:

1. Gridding optimization: The tool would automatically apply finer grids in critical areas of the model to get high resolution where needed, while using coarser grids elsewhere for efficiency.
2. Automated time steps: Smaller time steps in transient analysis would be automatically generated during power transitions to capture key impacts.
3. Reduction of model complexity: Applying equivalent thermal properties would reduce model while maintaining accuracy by using higher fidelity at targeted hotspots.
4. Power map compression: Using adaptive bin sizes to compress fine-grained power maps and precisely capture non-uniform power distribution across the design.
5. Automated reporting: Designers need summary reports that highlight key results for easy review and decision-making.

Examples of 3DIC thermal analysis

Some real-world applications demonstrate the practical benefits of integrated thermal analysis solutions. The research organization, CEA, used the 3D thermal analysis tool from Siemens EDA to study the thermal performance of their 3DNoC demonstrator. The thermal model they developed showed excellent correlation between simulation and measured data with a worst-case difference of just 3.75% and average difference within 2% (figure 2).

Figure 2. Correlation of simulation versus measured results.

CEA also use the Calibre 3DThermal tool to perform chip-package thermal co-design on a complex design composed of 16 chiplets on an active interposer. During early design exploration, they performed thermal-aware 3D partitioning and optimized the TIM layers, copper lid, and heatsink design. For design tapeout, they performed thermal-aware signoff analysis, which accounted for the 150K fine-grained 3D structures, such as TSVs and µ-bumps, revealing important anisotropic thermal properties of the die-to-die layers. Detailed and accurate power maps captured the thermal impact of heterogeneous hotspots in multiple power application scenarios.

Conclusion

3DICs are a significant leap forward for creating devices with unprecedented levels of performance and functionality. For 3DICs to become a commercial success, the thermal challenges associated with these designs need robust, integrated thermal analysis and management solutions. Designers now have the tools to perform accurate and fast thermal analysis throughout the design flow from early analysis through to design tapeout.

We will see rapid adoption of these advanced thermal analysis tools that will help realize the full potential of 3DIC technology. 3D thermal tools not only help designers push the boundaries of what is possible but also ensure that these cutting-edge technologies are reliable, efficient, and ready for the challenges of tomorrow.

Category: Siemens

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