TSMC Achieves 98% Yield on Advanced CoWoS Packaging, Shifting the AI Chip Bottleneck

At the OCP APAC Summit in Taiwan on August 11, Jun He—the TSMC vice president affectionately known in the semiconductor industry as "Mr. CoWoS"—delivered a single statistic that redefines the global AI hardware supply chain: 98 percent.[1][6]

That number represents the manufacturing yield TSMC is currently achieving on its massive 5.5x reticle-size CoWoS (Chip-on-Wafer-on-Substrate) packaging. Across multiple high-volume AI products, the process is consistently clearing the 98 percent threshold, with some specific designs reaching as high as 99 percent.[1][3]

To understand why a packaging yield is industry-shaking news, one must look at how modern AI accelerators are built. The era of monolithic silicon—printing one giant chip—is dead. Instead, companies like Nvidia and AMD design "chiplets," separating the compute logic from the memory to maximize performance and reduce waste.[4][5]

CoWoS is the mechanism that stitches these disparate pieces back together. It is not simply placing a chip in a plastic shell; it is a microscopic construction project. In the CoWoS-L variant, TSMC embeds local silicon interconnects within a redistribution layer, creating a high-speed data highway between the central compute dies and the surrounding High Bandwidth Memory (HBM) stacks.[2][5]

The scale of this assembly is staggering. A standard "reticle limit" is the maximum area a lithography machine can expose in a single flash of light—roughly 858 square millimeters. A 5.5x reticle package is five and a half times that size, covering over 4,500 square millimeters of delicate, interconnected silicon.[2][3]

At that size, the physics of manufacturing become hostile. Common defects include microscopic air bubbles trapped in the underfill resin, or bump misalignment where the thousands of microscopic copper pillars connecting the chips fail to line up perfectly.[3]

Furthermore, combining different materials—silicon dies, organic substrates, and metal interconnects—introduces severe thermal warpage. As the massive package heats and cools during the manufacturing process, the materials expand at different rates, causing the entire assembly to bend.[2][4]

Achieving a 98 percent yield means that out of every 100 of these massive, fragile assemblies attempted, 98 survive the gauntlet without a fatal defect. It is a testament to TSMC's mastery of the physical variables, proving that extreme advanced packaging is now a stable, mature manufacturing process rather than an experimental art.[1][3]

For the past two years, CoWoS has been the absolute binding constraint on the AI revolution. Global demand for CoWoS is projected to double from roughly 1.3 million wafers in 2026 to 2.6 million in 2027, gating shipments for every major AI hardware developer.[4]

TSMC has been aggressively expanding its physical footprint to meet this demand. The foundry has nearly doubled its CoWoS capacity annually for three consecutive years, aiming to reach between 120,000 and 140,000 wafers per month by the end of 2026.[4][6]

However, high yield in the CoWoS process does not instantly translate to an infinite supply of AI accelerators. As TSMC clears the packaging bottleneck, the constraints are shifting outward to the materials that feed into the process.[2]

The first new bottleneck is the ABF (Ajinomoto Build-up Film) substrate. This specialized organic board sits beneath the silicon interposer, translating the microscopic wiring of the chip to the larger scale of the server motherboard. As packages grow to 5.5x reticle size and beyond, manufacturing perfectly flat, defect-free ABF substrates becomes increasingly difficult, and supply is tightening.[2]

The second constraint is the memory itself. CoWoS assembly cannot begin without the required High Bandwidth Memory stacks on hand. With memory manufacturers projecting tight supply-demand conditions for HBM through 2027, the packaging lines can only run as fast as the memory arrives.[2][4]

Despite these shifting constraints, TSMC is already mapping the next leap in scale. The foundry's roadmap projects that by 2028, it will produce 14x reticle-size interposers capable of carrying 20 3D-stacked compute chiplets and 20 HBM modules.[1][5]

By 2029, the company plans to push beyond 14x, alongside advancements in SoIC (System on Integrated Chips) true 3D stacking, shrinking the hybrid bonding pitch down to 4.5 microns.[1][6]

The 98 percent yield milestone at the 5.5x scale proves that this aggressive roadmap is physically viable. Advanced packaging is no longer just a way to connect chips; it has become the primary engine driving the next decade of computing power.[5]