An In-Depth Explanation of Advanced Packaging Technology: CoWoS

Over the past few decades, semiconductor manufacturing technology has evolved from the 10,000nm process in 1971 to the 3nm process in 2022, driven by the need to increase the number of transistors on chips for enhanced computational performance. However, as applications like artificial intelligence (AI) and AIGC rapidly advance, demand for higher core chip performance at the device level is growing.

While process technology improvements may encounter bottlenecks, the need for computing resources continues to rise. This underscores the importance of advanced packaging techniques to boost the number of transistors on chips.

In recent years, “advanced packaging” has gained significant attention. Think of “packaging” as a protective shell for electronic chips, safeguarding them from adverse environmental effects. Chip packaging involves fixation, enhanced heat dissipation, electrical connections, and signal interconnections with the outside world. The term “advanced packaging” primarily focuses on packaging techniques for chips with process nodes below 7nm.

Amid the AI boom, which has driven demand for AI servers and NVIDIA GPU graphics chips, CoWoS (Chip-on-Wafer-on-Substrate) packaging has faced a supply shortage.

But what exactly is CoWoS?

CoWoS is a 2.5D and 3D packaging technology, composed of “CoW” (Chip-on-Wafer) and “WoS” (Wafer-on-Substrate). CoWoS involves stacking chips and then packaging them onto a substrate, creating a 2.5D or 3D configuration. This approach reduces chip space, while also lowering power consumption and costs. The concept is illustrated in the diagram below, where logic chips and High-Bandwidth Memory (HBM) are interconnected on an interposer through tiny metal wires. “Through-Silicon Vias (TSV)” technology links the assembly to the substrate beneath, ultimately connecting to external circuits via solder balls.

The difference between 2.5D and 3D packaging lies in their stacking methods. 2.5D packaging involves horizontal chip stacking on an interposer or through silicon bridges, mainly for combining logic and high-bandwidth memory chips. 3D packaging vertically stacks chips, primarily targeting high-performance logic chips and System-on-Chip (SoC) designs.

When discussing advanced packaging, it’s worth noting that Taiwan Semiconductor Manufacturing Company (TSMC), rather than traditional packaging and testing facilities, is at the forefront. CoW, being a precise part of CoWoS, is predominantly produced by TSMC. This situation has paved the way for TSMC’s comprehensive service offerings, which maintain high yields in both fabrication and packaging processes. Such a setup ensures an unparalleled approach to serving high-end clients in the future.

Applications of CoWoS

The shift towards multiple small chips and memory stacking is becoming an inevitable trend for high-end chips. CoWoS packaging finds application in a wide range of fields, including High-Performance Computing (HPC), AI, data centers, 5G, Internet of Things (IoT), automotive electronics, and more. In various major trends, CoWoS packaging is set to play a vital role.

In the past, chip performance was primarily reliant on semiconductor process improvements. However, with devices approaching physical limits and chip miniaturization becoming increasingly challenging, maintaining small form factors and high chip performance has required improvements not only in advanced processes but also in chip architecture. This has led to a transition from single-layer chips to multi-layer stacking. As a result, advanced packaging has become a key driver in extending Moore’s Law and is leading the charge in the semiconductor industry.

(Photo credit: TSMC)