South Korean Firm Unveils Bottom-Up Copper Filling Method for AI Chip Glass Substrates

South Korean semiconductor packaging company Kools has unveiled a new metallization technology aimed at one of the toughest manufacturing problems in next-generation chip packaging: reliably filling microscopic holes in glass substrates with copper. The company announced its Self-Propagating Electrode Architecture (SPEA) on August 21, 2026, according to TheElec, and plans to present it at an advanced packaging seminar in Suwon, South Korea.

Glass substrates are thin panels increasingly used as the base for advanced chip packages, offering greater flatness, lower electrical signal loss and more precisely tunable thermal expansion than traditional organic substrates. As AI accelerator chips grow larger and more complex, glass is being explored as the material for the core substrate and the interposer that links multiple chiplets together -- Intel has already demonstrated glass core substrates, and Samsung Electronics and SK Absolics are developing their own versions.

Connecting the top and bottom of a glass substrate requires through-glass vias (TGVs), tiny holes filled with metal. In high-aspect-ratio vias, where the hole is narrow relative to the glass's thickness, existing methods struggle: sputtering deposits metal in relatively straight paths and cannot reach the bottom of deep vias evenly, while wet electroless plating can form its catalyst layer unevenly, weakening adhesion and risking defects.

Kools' SPEA instead first creates a uniform interface layer across the via's inner wall, then forms an initial electrode at the via's bottom; as metal grows from that point, the newly filled regions become electrodes themselves, filling the via sequentially from bottom to top. The company says this reduces blockage at the via entrance and internal voids, and is compatible with panel-level packaging for large-area manufacturing. "Glass core substrates and glass interposers differ in via size and wiring density, but their manufacturing principles are the same," said Kools CEO Cho Jin-hyun.