Adv Packaging SiP l

2.5D packaging uses a silicon or organic interposer to integrate multiple dies side-by-side with fine-pitch interconnects. Unlike full 3D stacking, 2.5D allows chips to be placed laterally while still benefiting from high-bandwidth, low-latency connections through the interposer’s redistribution wiring. It has become the workhorse for high-performance GPUs, AI accelerators, and networking ASICs, particularly when paired with High Bandwidth Memory (HBM).

Process Overview

• Step 1: Fabricate a large silicon or organic interposer with fine-pitch wiring and TSVs (for silicon-based versions).
• Step 2: Mount logic dies (GPU, CPU, ASIC) and memory stacks (HBM) onto the interposer using microbumps.
• Step 3: Attach the interposer assembly to an organic package substrate.
• Step 4: Encapsulation, lid attach, and thermal solutions are added for mechanical protection and heat dissipation.
• Step 5: Final electrical testing ensures high-bandwidth operation and reliability.

Key Features

• High Bandwidth: Thousands of fine-pitch interconnects allow terabits per second of die-to-die communication.
• Flexibility: Supports integration of dies from different process nodes and foundries.
• Yield Efficiency: Uses known-good dies (KGD) to improve yield for large multi-die systems.
• Scalability: Interposer sizes can reach reticle limits; organic interposers offer a cost-reduced alternative.

Applications

• AI Accelerators: NVIDIA H100, AMD MI300 GPUs integrate multiple HBMs with logic dies on silicon interposers.
• HPC & Supercomputing: CPUs and accelerators in exascale systems rely on 2.5D packaging for bandwidth scaling.
• Networking: High-end ASICs use interposers to connect switch logic with memory.

Representative Products

Advantages & Constraints

• Advantages: Proven high-bandwidth packaging; scalable for large AI/HPC devices; compatible with heterogeneous dies; enables HBM integration at scale.
• Constraints: Large silicon interposers are expensive and have yield risks; warpage and thermal management are challenging; organic interposers reduce cost but with lower density.

Cleanroom & Environment

• Assembly performed in Class 1000–10,000 packaging facilities.
• Silicon interposer fabrication requires FEOL-like cleanroom standards.
• Thermal management strategies include lids, heat spreaders, and liquid cooling for large AI/HPC modules.

Market Outlook

2.5D interposer technology will remain critical for AI and HPC packaging through 2030. Silicon interposers (CoWoS, I-Cube) dominate high-end applications, while organic interposers are gaining traction in networking and mid-range markets as a cost alternative. Hybrid bonding and 3D ICs may eventually supplement 2.5D, but interposers will continue to provide the bandwidth needed for AI accelerators and exascale compute.