Semiconductor packaging company Kools has developed bonding technology that suppresses warpage in ultra-large artificial intelligence (AI) semiconductor packages. The technology uses a high-stiffness lid to control package warpage and a Thermal Clutch to shorten heating and cooling times. It is designed to prevent bonding defects in ultra-large packages such as Nvidia's next-generation AI accelerator Rubin Ultra.
Kools said on Sept. 16 that it developed the ultra-large semiconductor package bonding technology by combining a high-stiffness lid with its proprietary Thermal Clutch. Instead of attaching the lid for heat dissipation at the final packaging stage after bonding chips and interposers, the lid is attached before bonding. Pressure is applied to the top of the lid to keep the package flat and maintained until the solder solidifies, suppressing warpage during bonding.
The Thermal Clutch addresses the productivity issue. High-stiffness lids are thick and have high heat capacity, increasing heating and cooling times during thermocompression bonding (TCB). The Thermal Clutch blocks heat from escaping to the cooling section during heating. During cooling, it connects the heat-transfer path to rapidly dissipate heat from the bonded area.
The technology reduced the heating and cooling time for an ultra-large 180×70mm package from more than one minute to less than 10 seconds. Warpage after bonding is less than 0.1mm.
As semiconductor packages grow larger, TCB is increasingly replacing oven reflow in bonding processes. Larger packages are more susceptible to deformation caused by differences in the coefficient of thermal expansion (CTE) between silicon chips and organic materials, which can result in warpage and bonding defects. Oven reflow melts solder with heat, while TCB applies heat and pressure simultaneously to maintain package flatness during bonding.
TCB, however, becomes less productive as the bonding area increases because more time is required for heating and cooling. High thermal output and warpage control are key challenges in large-area TCB processes. Kools proposes addressing these issues by restraining the package with a high-stiffness lid and shortening heating and cooling times with its Thermal Clutch.
"Conventional TCB requires more than one minute to heat and cool an ultra-large 180×70mm package, but the Thermal Clutch can reduce that to less than 10 seconds," Kools CEO Cho Jin-hyun said. "By maintaining the package shape with a high-stiffness lid while shortening bonding time, we can secure productivity for ultra-large four-graphics-processing-unit (GPU) packages."
Ultra-large packages such as Nvidia's next-generation AI accelerator Rubin Ultra are among the target applications. Nvidia originally envisioned Rubin Ultra with four GPU dies and 16 seventh-generation high-bandwidth memory (HBM4E) devices integrated into a single package. Semiconductor market research firm SemiAnalysis reported in June that Nvidia had scrapped the four-GPU design over manufacturing concerns and switched to a two-GPU structure.
"Nvidia's original Rubin Ultra design placed four GPUs in a row within a single package so they could operate in parallel like a single chip," Cho said. "Applying Kools' technology can suppress warpage and shorten bonding time even in elongated ultra-large packages, improving the manufacturability of a four-GPU structure."
Kools said it has secured prior patents for the technology. Its total intellectual property (IP) portfolio comprises 277 assets. The company plans to expand the technology's application to next-generation advanced packaging that integrates multiple semiconductor chips, including GPUs and HBM.
