The semiconductor industry enters the era of integration. Various foundries are focusing on advanced packaging technologies, but the terminology surrounding advanced packaging can be daunting. This article aims to explain these terms in the simplest way possible.

According to a report from TechNews, currently, there are two main trends in advanced packaging: heterogeneous integration and chiplets.

In fact, the concept of “heterogeneous integration” has been developing for many years and is not exclusive to advanced packaging. It is not only used for the integration of heterogeneous chiplets but also for integrating other non-chip active/passive components into a single package, which is the technology commonly used in traditional Outsourced Semiconductor Assembly and Test Services(OSATs).

• Heterogeneous Integration = Big Building Blocks? Advanced Packaging = Small Building Blocks? 

In the simplest terms, “heterogeneous integration” can be likened to building with large building blocks, while “advanced packaging” is akin to assembling with small building blocks. Some manufacturers, like traditional Outsourced Semiconductor Assembly and Test Services(OSATs), excel in stacking large blocks, such as logic circuits, radio frequency circuits, MEMS (Micro-Electro-Mechanical Systems), or sensors, onto a IC substrate. The stacking of these different large blocks represents the concept of heterogeneous integration.

On the other hand, some blocks are too small to stack effectively, requiring assistance from advanced packaging, typically provided by semiconductor foundries.

Advanced packaging also encompasses 2.5D packaging and 3D packaging. Using the metaphor of building blocks, the former involves horizontally stacking small building blocks on a interposer, while the latter involves vertically stacking small building blocks with interconnection facilitated through Through-Silicon Vias (TSVs), which are ultra-small building blocks.

It’s important to emphasize that stacking blocks is a conceptual representation, and the distinction between large and small blocks is relative. The analogy above refers to heterogeneous integration in traditional packaging, and heterogeneous integration in advanced packaging follows a similar concept, but with even smaller building blocks.

• SoC / SiP / Heterogeneous Integration / Chiplet

With this concept in mind, let’s discuss the applications of heterogeneous integration in advanced packaging:

Among the various packaging types, SoC (System On Chip) involves integrating different chips such as processors and memory, with different functions, redesigned and fabricated using the “same process,” integrated onto a single chip, resulting in a final product with only one chip.

On the other hand, SiP (System in Package) involves connecting multiple chips with “different processes” through “heterogeneous integration” technology, integrated within the same packaging module. Therefore, the final product will be a system with many chips on it, resembling the stacking of different-sized building blocks mentioned earlier.

Therefore, heterogeneous integration refers to integrating different and separately manufactured components (heterogeneous) into higher-level assemblies. These components include blocks of different sizes, such as MEMS devices, passive components, logic chips, and more.

However, at a certain point, for the sake of process development, researchers found that separating components at the right time might facilitate miniaturization. Hence, chiplet was born.

• Is Chiplet the Fusion of Heterogeneous Integration and Advanced Processes?

As demands for ICs become increasingly complex, the size of SoC chips continues to grow. However, cramming too many components onto a limited substrate poses significant challenges, including heightened process complexity and reduced yield.

Hence, the concept of chiplets emerged, advocating for the segmentation of SoC functionalities, such as data storage, computation, signal processing, and data flow management, into smaller individual chips. These chiplets are then integrated through packaging to form a interconnected network.

It’s worth noting that Chiplets are essentially chips, whereas SiP refers to the packaging format. Chiplet architecture enable the reduction of individual chip sizes, simplify circuit design, overcome manufacturing difficulties and yield issues, and offer greater design flexibility.

• Advanced Packaging Technologies in Foundries

Currently, advanced packaging can be broadly categorized into three main types: Wafer-Level Packaging (WLP), 2.5D Packaging, and 3D Packaging. Traditional packaging involves cutting wafers into chips before packaging, while advanced packaging entails packaging the silicon wafer before cutting, requiring subsequent stacking processes in fabs. Therefore, the technology is primarily the responsibility of fabs.

Traditional packaging involves cutting wafers into chips before packaging. Advanced packaging, starting from wafer-level packaging, involves packaging silicon wafers before cutting, and subsequent stacking requires wafer fabrication processes.

Therefore, this article will delve into advanced packaging technologies offered by the three major foundries, with a focus on 2.5D and 3D packaging.

• 2.5DIC / 3DIC Packaging

To further explain using building blocks, the difference between 2.5D and 3DIC packaging lies in the “stacking method.”

In 2.5D packaging, processors, memory, or other chips are stacked horizontally on a silicon interposer using a flip-chip method, with micro bumps connecting different chip’s electronic signals. Through silicon vias (TSVs) in the interposer link to the metal bumps below, then packaged onto the IC substrate, creating tighter interconnections between the chips and the substrate.

In a side view, although the chips are stacked, the essence remains horizontal packaging, with the chips positioned closer together and allowing for smaller chip sizes. Additionally, this is a form of “heterogeneous integration” technology.

3D packaging involves stacking multiple chips (face down) together, directly using through-silicon vias to stack them vertically, linking the electronic signals of different chips above and below, achieving true vertical packaging. Currently, more and more CPUs, GPUs, and memories are starting to adopt 3D packaging technology.

• Hybrid Bonding

Hybrid bonding is one of the die bonding techniques used in advanced chip packaging processes. One of the commercially available technologies in this domain is the “Cu-Cu hybrid bonding.”

In traditional wafer bonding processes, there are interfaces between copper and dielectric materials. With “Cu-Cu hybrid bonding,” metal contacts are embedded within the dielectric material. Through a thermal treatment process, these two materials are bonded together, utilizing the atomic diffusion of copper metal in its solid-state to achieve the bond. This approach addresses challenges encountered in previous flip-chip bonding process.

Compared to flip-chip bonding, hybrid bonding offers several advantages. It allows for achieving ultra-high I/O counts and longer interconnect lengths. By using dielectric material for bonding instead of bottom fillers, the cost of filling is eliminated.

Additionally, hybrid bonding results in minimal thickness compared to chip-on-wafer bonding. This is particularly beneficial for future developments in 3D packaging, where stacking multiple layers of chips is required, as hybrid bonding can significantly reduce the overall thickness.

• Advanced Packaging Moves Towards the Era of Heterogeneous Integration

As the semiconductor industry enters the “post-Moore’s Law era,” the development focus of advanced packaging is gradually shifting from 2D planar structures to 3D stacking and from single-chip designs to multi-chip configurations. Therefore, “heterogeneous integration” will play a crucial role in future advanced packaging.

Currently, prominent companies such as TSMC, Samsung, and Intel are intensifying their research and development efforts and capacity expansions in this field, introducing their innovative packaging solutions.

With ongoing technological advancements and innovations, advanced packaging and heterogeneous integration will play increasingly vital roles in propelling the semiconductor industry towards greater heights, meeting the complex and diverse demands of future electronic devices.

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(Photo credit: Intel)