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2.5D vs. 3D Packaging

Key Takeaways

  • 2.5D and 3D semiconductor packaging technologies are crucial for electronic device performance. Both solutions offer enhanced performance, size reduction, and improved power efficiency to different extents.

  • 2.5D packaging is advantageous for combining various components and reducing footprints. It suits applications in high-performance computing and AI accelerators.

  • 3D packaging provides unparalleled integration, efficient heat dissipation, and reduced interconnect lengths, making it ideal for high-performance applications.

Array of microchips being packaged

2.5D and 3D packaging technologies both have their unique advantages and uses.

In the fast-paced world of semiconductor technology, packaging plays a crucial role in determining electronic device performance, size, and power efficiency. Two prominent packaging technologies, 2.5D and 3D packaging, have emerged as prominent solutions. Each offers unique advantages and challenges, making them essential considerations for semiconductor manufacturers and designers.

We will explore the differences and applications of 2.5D and 3D packaging and how they have revolutionized the semiconductor landscape.

2.5D vs. 3D Packaging

Understanding 2.5D Packaging

2.5D packaging, also known as 2.5D interposer technology, is an intermediate step between traditional 2D packaging and full-fledged 3D packaging. In 2.5D packaging, multiple semiconductor dies, typically from different process technologies, are placed side by side on a silicon interposer. 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 on a single package.

The most prevalent 2.5D integration technology involves combining a silicon interposer with TSVs. 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. The surface of the silicon substrate is interconnected using Redistribution Layer (RDL) wiring, while the TSVs act as conduits for electrical connections between the upper and lower surfaces of the silicon substrate. 

This form of 2.5D integration is well-suited for scenarios where the chip's size is relatively large, and there is a high pin density requirement. Typically, the chip is mounted on the silicon substrate in a FlipChip configuration.

Advantages of 2.5D Packaging

  1. Enhanced Performance: 2.5D packaging enables the integration of diverse components, such as processors, memory, and sensors, on a single package. This proximity results in reduced interconnect lengths, leading to improved signal integrity and lower latency.

  2. Size Reduction: By stacking dies on an interposer, 2.5D packaging reduces the overall footprint of the package (compared to 2D), making it ideal for smaller and thinner devices.

  3. Improved Power Efficiency: Shorter interconnects and optimized chip placement in 2.5D packaging lead to reduced power consumption, making it suitable for battery-powered devices.

Applications of 2.5D Packaging

2.5D packaging has found applications in various industries, including high-performance computing, data centers, and networking equipment. It is particularly well-suited for artificial intelligence (AI) accelerators, where multiple types of chips need to work together efficiently.

Understanding 3D Packaging

3D packaging takes integration to the next level by stacking multiple semiconductor dies on top of each other, creating a three-dimensional structure. This approach enhances the overall performance and functionality of the package. This results in even shorter interconnects and smaller package footprints. However, as chips delve deeper into the domain of true 3D-ICs, where logic or memory chips are stacked atop one another, the design, manufacturing, and ultimately the yield and testing processes become considerably more complex and challenging.

The world of 3D packaging offers various approaches to cater to different requirements. There is "True 3D" packaging, where wafers are intricately stacked on top of each other for maximal integration. There is also another category of "3D system-on-chip (SoC) integration," which may involve features like a backside power distribution layer or the stacking of memory wafers on top of one another. Finally, "3D system-in-package (SiP)" involves contact pitches of around 700 microns and incorporates fan-out wafer-level packaging. 

Each of these approaches addresses specific technological needs and challenges within the domain of 3D packaging.

Advantages of 3D Packaging

  1. Unparalleled Integration: 3D packaging allows for the most compact integration of a wide range of components and functionalities, making it possible to create highly complex systems in a compact form factor.

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

  3. Reduced Interconnect Lengths: 3D packaging further reduces interconnect lengths (over 2.5D), minimizing signal delays and power consumption.

A very notable advantage of 3D packaging technology is this reduction in distances. In a stacked 3D structure, the distances between various components become approximately 0.7 of what they would have been in a 2D counterpart. This distance reduction directly impacts power consumption within the wiring part of the system, as it leads to a decrease in capacitance. Consequently, the power consumption is now roughly 0.7 times what it was in the 2D configuration.

3D Packaging Applications

3D packaging is gaining traction in applications where extreme performance and miniaturization are critical. It is commonly used in advanced memory technologies like High Bandwidth Memory (HBM) and advanced processors for high-end smartphones, gaming consoles, and specialized computing.

Comparing 2.5D and 3D Packaging

2.5D IC vs. 3D IC Packaging: A Comparison Table


2.5D IC Packaging

3D IC Packaging

Technology Level

Intermediate between 2D and 3D

Most advanced and compact 

Die Arrangement

Side by side on silicon interposer

Stacked on top of each other

Interconnect Lengths

Reduced compared to 2D

Even shorter than 2.5D

Footprint Reduction

Smaller than 2D

Smallest footprint

Power Efficiency

Improved over 2D

Most efficient 


Less complex than 3D

More complex design, requires manufacturing and testing

Heat Dissipation

More efficient heat dissipation compared to 2D

Best heat dissipation

Future Prospects

Type of transitional technology with continued relevance

Growing prevalence and coexistence with 2.5D

Heterogeneous Integration Capabilties


Potential for significant benefits in specialized applications

While both 2.5D and 3D packaging offer significant advantages, they are not mutually exclusive, and their suitability depends on the application's specific requirements. 2.5D packaging is a stepping stone toward 3D packaging, balancing performance and complexity. It is often chosen when a moderate level of integration is needed or when transitioning from traditional 2D packaging to more advanced technologies.

On the other hand, 3D packaging is ideal for applications that demand cutting-edge performance, compactness, and power efficiency. 3D integration, if possible, will always be more efficient in all of the ways discussed compared to 2.5D, just with added complexity. As the technology matures, we can expect to see 3D packaging becoming more prevalent in various domains. 3D packaging won't replace 2.5D packaging but rather complement it. In the future, we'll likely see an ecosystem where chiplets can be mixed and matched within a 2.5D package alongside true 3D configurations for various applications.

Furthermore, heterogeneity holds the potential for significant benefits in 3D integration. Heterogeneous technology architectures, such as combining a photonic integrated circuit (IC) with an electronic IC, can greatly benefit from 3D integration. In such integrations, achieving the numerous die-to-die interconnections required without substantial sacrifices in power or performance may be unattainable through any other means.

Harness the Power of 2.5D and 3D Packaging With Cadence

Ready to harness the power of 2.5D and 3D packaging for your semiconductor designs? Take the next step with Allegro X Advanced Package Designer and turn your vision into reality. Learn more in our article and explore how Allegro X can revolutionize your semiconductor projects. 

Leading electronics providers rely on Cadence products to optimize power, space, and energy needs for a wide variety of market applications. To learn more about our innovative solutions, talk to our team of experts.