Development of liquid cooling techniques for flip chip ball grid array packages with High Heat flux dissipations

In this paper, development of single-phase liquid cooling techniques for flip chip ball grid array packages (FBGAs) with high flux heat dissipations is reported. Two thermal test chips with different footprints, 12 mm× 12 mm and 10 mm ×10 mm, respectively, were used for high heat flux characterizations. A liquid-cooled aluminum heat sink with an area of 15 mm (L) ×12.2 mm (W) populated by microchannels was designed and fabricated. The microchannel heat sink was assembled onto the chip, using a thermal interface material to reduce the contact thermal resistance at the interface. A variable speed pump was used to provide the pressure head for the liquid cooling loop. The measured thermal resistance results ranged from 0.44 to 0.32°C/W for the 12-mm chip case and from 0.59 to 0.44°C/W for the 10-mm chip case, both under flowrates ranging from 1.67×10^-6 m³/s to 1.67×10^-5 m³/s. An analytical model of the flow and heat transfer in microchannel heat sinks is also presented. Computational predictions agree with the measurements for pressure drop within 15% and thermal resistances within 6%. The analytical results indicate that thermal interface resistance becomes a key limitation to maximizing heat removal rate from electronic packages.