IBM has pioneered the use of large-area alumina multilayer ceramic substrates using state-of-the-art greensheet, molybdenum paste, and tooling technologies for its mainframe computers since 1980. During this time, a new generation of substrate materials have been developed based on copper metallization and a unique glass that crystallizes to cordierite (2Al2O3 · 2MgO · 5SiO2), which has a very low dielectric constant (5.0 compared to 9.4 in previous IBM systems). The glass-ceramic/copper system provides a factor of 3 improvement in electrical conductivity over alumina/molybdenum in previous IBM systems, and the number of metallized substrate layers has been increased from 45 to 63. The thermal expansion of the new substrate (30 ×10−7°C−1) is matched with that of the silicon chips, thereby enhancing the reliability of the 78,500 solder-bonded chip-to-substrate connections in the System/390®-Enterprise System/9000™ computers. Each substrate is 127.5 mm square and can support up to 121 complex logic and memory chips. The IBM advanced multichip module dissipates more than twice the heat flux of previous alumina/multichip modules-to 17 W/cm2 at the package level and 50 W/cm2 at the chip level.
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IBM Journal of Research and Development
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06 April 2010
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