To The Moon

Although TSMC continues to aggressively expand its CoWoS capacity, supply still falls short of demand. As a result, excess demand is spilling over to other OSAT players—this has become one of the key narratives in the market recently. Chip-on-Wafer (CoW), being the most technically challenging step, is handled directly by TSMC, while Wafer-on-Substrate (WoS) is partially outsourced. WoS players are responsible for attaching the CoW to the substrate.

$Amkor Technology(AMKR)$   is the largest OSAT company headquartered in the U.S., with manufacturing sites across Taiwan, South Korea, Japan, Vietnam, and Malaysia, which helps diversify geopolitical risk (many OSAT peers are heavily concentrated in Taiwan and China). Amkor also operates a facility in Arizona, making it the largest advanced packaging provider on U.S. soil, well positioned to support the backend needs of TSMC’s Arizona fab.

Amkor’s Turnkey Services include:

Design Innovation: Assisting customers in designing advanced packaging architectures.

Materials Management: Procuring substrates, leadframes, and other key materials.

Wafer Bumping, Probing, and Dicing: Performing wafer-level testing and singulation after receiving wafers.

Package Assembly: Assembling the chips into finished packages.

Final Test, Burn-in, and SLT: Conducting final product testing, burn-in, and system-level testing (SLT) to ensure reliability.

Drop Ship: Shipping finished products directly to end customers on behalf of clients.

Amkor’s Advanced Packaging Offerings:

S-Swift: Combines traditional silicon interposer (TSV) technology with Amkor’s proprietary S-SWIFT (HDFO-on-Substrate). It primarily targets the same market as TSMC’s CoWoS-S, using silicon-based processes for high-density interconnects. This is currently the most mature solution for AI/HPC chips and Amkor’s most stable revenue contributor.

S-Connect: Positioned against CoWoS-L. The core concept is to replace large, expensive silicon interposers with silicon bridges, enabling larger package sizes to support more HBM. It is currently in development and early-stage mass production.

SWIFT / HDFO: High-density fan-out packaging mainly used for smartphone processors and wearables. Capacity is currently ramping up.

While Amkor’s revenue mix is still dominated by communications, indicating continued reliance on consumer electronics, advanced packaging has become the fastest-growing segment, with a CAGR of around 12%, starting from roughly a 20% revenue contribution.

Peers comparable to CoWoS-L include:

Intel EMIB: Based on a similar concept of embedding silicon bridges in the substrate. Intel actually introduced this earlier, but it saw limited adoption until recently, with reports of bookings from large CSPs.

Amkor S-Connect: Aligned with U.S. onshoring policies and significantly reduces geopolitical risk, allowing Amkor to capture nearby spillover demand. However, it remains in the development phase.

ASE FOCoS-Bridge: Technologically more advanced than Amkor’s solution and closely integrated with AMD, positioned as a high-end offering within ASE’s VIPack platform.

Samsung I-Cube E: Yield and customer trust are still not fully proven.

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