2.5D and 3D Integration

Technology Integration for Unparalleled Peformance

2.5D and 3D integration are advanced packaging technologies that combine diverse components such as processors, memory, and sensors on a single chip. In a 2.5D design, two or more chips are placed side-by-side on a silicon interposer, which acts as a bridge to connect them with fine pitch wire, to achieve extremely high-density die-to-die interconnect. 2.5D packaging is advantageous for combining various components and reducing footprints. It suits applications in high-performance computing and AI accelerators. In a 3D design, multiple chips are stacked on top of one another for unparalleled integration, efficient heat dissipation, and reduced interconnect lengths, making it ideal for high-performance applications, with the smallest package footprint.

What is 2.5D Integration?

Performance with Efficiency and Reliability

Key Features of 2.5D

2.5D is the mid-point technology between traditional 2D packaging and 3D integration, also known as 2D interposer technology. It is an advanced semiconductor packaging design that places multiple individual chips, or chiplets, side-by-side on a shared intermediary substrate called an interposer, with the interposer typically made of organic, silicon, and glass, allowing close proximity between chips without stacking them vertically. The interposer acts as a bridge, connecting the individual dies and providing a high-speed communication interface. This arrangement allows for greater flexibility in combining different functionalities in a single package.

The most common 2.5D integration involves combining a silicon interposer with Through-Silicon-Vias (TSV). In this configuration, the chip is typically connected to the interposer using MicroBump technology. The silicon substrate, serving as the interposer, is connected to the substrate through Bump connections. This design is beneficial where the chip's size is relatively large, and there is a high pin density requirement, mounted on a silicon substrate in a Flip-Chip configuration.

Benefits of 2.5D

Applications of 2.5D

High-Performance Computing (HPC): Used in supercomputers and AI accelerators.

AI Processors: Major components like high-end GPUs from AMD and Nvidia use this technology to integrate large amounts of HBM (High Bandwidth Memory) with the main processor on an interposer.

FPGAs (Field-Programmable Gate Arrays): Intel and Xilinx use 2.5D integration in their high-capacity FPGAs.

Networking Gear: Employed in network switches and routers for data centers and 5G infrastructure to enable faster data processing.

Interposer: A silicon, glass, or organic substrate that acts as the base for the chips.

Side-by-side placement:

Chips are arranged on the interposer in a two-dimensional plane, differing from the stacked "3D" approach.

High-density interconnects:

The interposer provides a dense network of connections between the chips, which can minimize the distance between them and improve performance.

Through-Silicon Vias (TSVs):

Vertical connections that pass through the interposer to connect the chips to the package substrate below.

Thermal profile: Easier to cool due to planar layout

Heterogeneous integration: It allows for the combination of diverse types of chips, such as processors, memory, and sensors on a single package, even if they were built with different manufacturing processes.

Performance: By shortening the distances between chips, 2.5D integration can lead to higher signal speeds and better performance compared to traditional 2D integration.

Cost and risk reduction: Companies can reuse existing chip designs, such as chiplets, and combine them, which reduces the need for a full redesign of a monolithic chip.

Flexibility: It is possible to adjust or replace individual components without redesigning the entire system, making it easier to upgrade or repair.

Size Reduction: By stacking dies on an interposer, 2.5D packaging reduces the overall footprint of the package, making it ideal for smaller and thinner devices.

What is 3D Integration?

Taking Advanced Packaging to New Heights

3D integration is the semiconductor technology that takes integration to new heights. It involves stacking multiple dies on top of each other, to create a 3-dimensional structure. This design is achieved through advanced interconnects, like through-silicon vias (TSVs) or micro-bumps, which allow for shorter distances between components. The process results in higher performance, greater functionality, and a smaller physical footprint compared to traditional 2D chips. Although 3D integration no doubt offers higher density interconnect compared to 2.5D integration, manufacturing, yield, and testing become considerably more complex and challenging with 3D integration.

3D integration is further broken down into 3 categories of design. There is True 3D packaging, which involves stacking dies on top of each other for maximum density interconnect. Another design is 3D System-on-Chip (Soc) integration that vertically stacks multiple chips, or "chiplets," on top of each other to create a single, compact component. This approach is used to build high-performance, power-efficient chips by connecting them with through-silicon vias (TSVs), which allows for shorter, faster, and more efficient data pathways than traditional 2D chips. The final variation of 3D integration is System-in-Package (SiP). This approach integrates multiple semiconductor dies and components vertically within a single package to create a more compact and high-performance electronic system. By stacking components in the third dimension, it reduces the distance signals must travel, leading to higher performance and lower power consumption compared to traditional 2D approaches.

Key Features of 3D

Vertical Stacking: Instead of placing all components side-by-side on a flat surface (2D), dies are placed one atop another.

Through-Silicon Vias (TSVs): These are tiny, vertical electrical connections that pass through the silicon layers, enabling high-speed, low-power communication between the stacked dies.

Advanced Bonding: Techniques like micro-bumps and hybrid bonding are used to meticulously align and physically connect the layers.

Thermal profile: Complex, often requiring advanced cooling solutions

Benefits of 3D IC

Improved Performance: Shorter interconnect lengths between components reduce signal delays, allowing data to transfer faster and improving overall system speed.

Lower Power Consumption: The reduced distance for electrical signals to travel translates directly to lower energy use, which extends battery life in mobile devices and reduces power consumption in data centers.

Smaller Form Factor: By using vertical space, more functionality can be packed into a smaller physical footprint, ideal for compact devices like smartphones and wearables.

Heterogeneous Integration: Different types of components (e.g., logic processors, memory, sensors, analog circuits) can be manufactured using their optimal process technologies and then combined into a single, highly optimized package.

Improved Heat Dissipation: The vertical arrangement of dies in 3D packaging enables efficient heat dissipation, addressing thermal challenges associated with high-performance computing.

Applications of 3D

Artificial Intelligence (AI) & High-Performance Computing (HPC): Used to integrate High Bandwidth Memory (HBM) directly with processors, accelerating parallel processing for large-scale AI models and scientific simulations.

Consumer Electronics: Enables powerful, yet compact, processors in smartphones, tablets, and AR/VR devices.

Automotive Systems: Supports safety-critical applications like Advanced Driver-Assistance Systems (ADAS) by processing data from multiple sensors in real-time.

Cloud Computing and Data Centers: Improves performance-per-watt in servers, which is crucial for managing overall energy consumption in large-scale data infrastructures.

2.5D Integration

VS

3D Integration

2.5D Integration	Key Characteristics	3D Integration
Limited	Heterogeneous Integration Capabilities	Potential for significant benefits in specialized applications
Type of transitional technology with continued relevance	Future Prospects	Growing prevalence and coexistence with 2.5D
Uses redistribution layers (RDLs) on the interposer and through-silicon vias (TSVs) to connect to the package substrate.	Interconnect	Uses direct TSVs or hybrid bonding for extremely short vertical links between dies.
High and better than 2D	Power Efficiency	Ultra-high due to dramatically shorter signal paths.
Lower Design risk and complexity	Design Risk	Higher risk and complexity due to through-silicon-vias and the stacking processes
Easier to manage heat as dies are adjacent, allowing for more direct cooling.	Thermal Management	More difficult due to heat from lower dies becoming trapped by those stacked above.
Lower Fabrication Cost and Higher Yield	Cost Sensitivity	Higher complexity and cost due to TSV and stacking processes, greater manufacturing risk.
Smaller than 2D, but larger than 3D due to horizontal layout.	Footprint	Smallest, offering maximum integration density.
High bandwidth (e.g., HBM-class memory), but lower than 3D due to slightly longer interconnects.	Performance Needs	Highest performance and minimal latency due to shortest interconnects.
Side-by-Side on Passive Interposer	Die Arrangement	Vertically Stacked on Top of Each Other