What is 2.5D Packaging? A Complete Guide to This Key Semiconductor Innovation

2.5D packaging revolutionizes chip design by integrating multiple dies on a silicon interposer with TSV and RDL technology. From AMD MI300 to NVIDIA A100, it’s the key to unlocking performance in the AI era. This guide breaks it all down clearly!

What is 2.5D Packaging Technology?

2.5D packaging sits between traditional 2D and cutting-edge 3D semiconductor packaging technologies. In 2D, a single die is mounted on a substrate with interconnects running through the PCB—simple, but limited in bandwidth. In 3D, multiple dies are vertically stacked to shorten communication distance and boost performance, but heat and yield challenges follow.

Comparison illustration of 2D vs 3D IC packaging. 2D shows chips side-by-side on a PCB; 3D stacks them vertically with TSV links.

2.5D offers a hybrid approach. It uses a silicon interposer to place multiple dies side by side, then connects them via Through-Silicon Vias (TSVs) or Redistribution Layers (RDLs). This architecture retains modularity while delivering high bandwidth and thermal manageability—crucial for heterogeneous integration (HI) in modern chip design.

A realistic rendering of a 2.5D package with multiple chiplets and HBM stacks mounted on a silicon interposer—common in AI processors.

This technique is ideal for applications that demand high memory bandwidth between processors and memory, such as AI training and HPC. It also lays the foundation for chiplet-based design, increasing packaging density and enabling scalable system-in-package (SiP) solutions.

Why Is It Called "2.5D"?

"2.5D" isn't a formal term from a standards body—it’s an industry-coined label for an architecture that bridges 2D and 3D. In traditional 2D, dies are wired together via the PCB. In 3D, they’re stacked and interconnected internally via TSVs.

2.5D instead arranges dies horizontally on a silicon interposer, which itself contains embedded TSVs and high-density metal routing. It delivers nearly 3D-level performance with fewer thermal or cost issues. Designers benefit from modular flexibility without complex 3D stack constraints.

2.5D packaging enables the integration of heterogeneous dies—built on different process nodes, serving different functions—on one platform. That’s a game changer for flexible, high-performance semiconductor systems.

Architecture and Materials of 2.5D Packaging

The core of 2.5D packaging includes:

• Silicon Interposer: Offers matching thermal expansion with silicon dies and supports dense metal layers.

• TSV (Through-Silicon Vias): Provides vertical connectivity between layers.

• RDL (Redistribution Layers): Redistributes I/O pads for efficient die-to-die routing.

• High-Density Substrate: Made from BT or ABF laminate, supports system-level connections.

• Thermal Management: Copper heat spreaders, TIM, heat pipes, or even liquid cooling solutions are used.

These components form a modular system with high-speed die-to-die communication and effective heat dissipation—crucial for AI and HPC chips.

Real-World Applications: From AI Accelerators to Data Centers

• AMD Instinct MI300: Combines CPU, GPU, and HBM in a single APU module using 2.5D and 3D technologies. AMD Press Release

• NVIDIA A100: Uses TSMC’s CoWoS to integrate HBM2 and GPU on a silicon interposer, enabling over 1 TB/s bandwidth. Yole A100 Report

• Intel EMIB: Enables die-to-die links via embedded bridges within the substrate—no full interposer required.

Future applications will expand to SoCs in autonomous vehicles, 5G base stations, aerospace electronics, and edge AI processors—all leveraging 2.5D for compact, high-performance integration.

Strengths and Challenges

Strengths:

• High bandwidth, low latency

• Modular design flexibility

• Better thermal profile than 3D IC

• Higher yield than full 3D stacks

Challenges:

• Cost of interposers and TSV manufacturing

• Complex testing: one faulty die can compromise the whole package

• Incomplete EDA toolchains for co-design

• Standardization gaps in die interfaces

But with growing UCIe standardization and platform maturity (TSMC 3DFabric, Intel Foveros/EMIB), these hurdles are being overcome.

Market Trends: AI Chips Fueling 2.5D Packaging Growth

According to Yole Group’s 2023 report, the 2.5D packaging market is projected to grow from $2.2B in 2023 to $5.7B in 2029, a 17.5% CAGR. Drivers include:

1. Explosive AI/HPC demand for high memory bandwidth

2. Chiplet design adoption across AMD, Intel, NVIDIA

3. UCIe standard rollout (v1.1 launched Oct 2023) unifying interconnect protocols

   
   

UCIe.org now lists over 100 member companies building interoperable ecosystems for chiplets. 2.5D is evolving from an elite AI tool into a scalable packaging strategy for broad markets.

Conclusion: The First Puzzle Piece in the Chiplet Era

In the post-Moore’s Law era, 2.5D packaging is no longer just a stepping stone—it’s the enabler of modular, multi-vendor, high-performance system design.

It breaks down monolithic SoC constraints, empowers cross-node integration, and supports faster innovation across AI, HPC, 5G, automotive, and defense sectors. As UCIe matures, 2.5D becomes the vital bridge between design freedom and production feasibility.

It's quiet but crucial—supporting the AI age from the inside out.