Metallic micro heat pipe heat spreader fabrication

Micro heat pipe heat spreaders (MHPHS) with three copper foil layers were designed to allow liquid and vapor flow separation to reduce viscous shear force. Two wick designs, one using 200 μm wide etched radial grooves and the other with 100-mesh copper screens were investigated. The foils were vacuum diffusion bonded to form 31 mm × 31 mm × 2.7 mm heat spreader. Thermal performance of the MHPHS was evaluated experimentally in a fan-heat sink CPU test apparatus with a heating area of 13.97 mm × 13.97 mm. The clamping pressure between the spreader and the heat sink was maintained at 13 kgf during the test. After evaluation, the MHPHS with 82% methanol fill rate, radial groove wicking structure showed the best performance compared to the other samples. The superior MHPHS had lower evaporator temperature with a 17 °C value, corresponding to a 30% decrease in thermal resistance at an actual input power of 35 W, compared to the system without MHPHS.