Liquid encapsulated MCM package-thermal demonstration

This experimental study was undertaken to demonstrate the capability of liquid-encapsulated system in its simplest form of implementation to cool an MCM package. The MCM package was made of kovar (dimension: 58×35×11 mm). Two silicon thermal test chips were bonded to an FR-4 board and housed inside the metal package. Tests were performed on both dry (no liquid-filled) and liquid-filled packages. In the liquid-filled situation, either a pure dielectric liquid or a dielectric liquid mixture was employed. The MCM package was externally cooled by either free-air or forced-air (1.0 to 2.54 m/s of air flow). Heat transfer history from single-phase, through nucleate boiling, to film boiling was documented. The overall improvement for the liquid-filled package was 2-4 times compared to the dry package, due to the superior thermal properties of dielectric liquids compared to air. The maximum power dissipation in the liquid-filled package at 2.54 m/s external air flow was 18 W (based on junction temperature maximum of 125°C). In the liquid-filled package, both the single-phase and boiling heat transfer were enhanced by varying the external boundary conditions from free-air to forced-air. The total power dissipation limit in the liquid-filled package is strongly influenced by the ability to condense the vapor in the package. By changing the boundary conditions from free-air to forced-air (2.54 m/s), the condenser (top lid) efficiency is raised, thus raising the maximum power dissipation by 2.5 times