Reliability assessment of hydrofoil-shaped micro-pin fins

As the need for high performance and extreme power-dissipation microelectronic devices continues to rise, innovative thermal management solutions are being developed to efficiently remove the high heat fluxes dissipated in these applications. At heat flux rates surpassing the 1000 W/cm2 level in some localized hot spot cases, conductive spreading to an external heat sink is no longer a viable thermal management option. On-chip, enhanced microfluidic cooling with pin fins offers new opportunities to deliver coolant in close proximity to power dissipation zones and hot spots. In state-of-the-art designs a two-phase refrigerant is pumped through a microfluidic channel within an active device absorbing heat at high velocity. Hydrofoil-shaped, silicon micro-pin fins populate the flow space to increase surface area available for heat removal and for liquid films to coalesce. The proposed thermal-management system has been fabricated by etching the microchannel with hydrofoil pin fins into the backside of the silicon device and then bonding it to a capping layer. While the hydrofoil shape is designed to benefit thermal-fluid performance properties, reliability consideration must also be given to the geometry. Phase change of the liquid facilitates optimal heat removal rates but also requires high-pressure conditions for operation. At these high-pressure conditions, the pin fins will be subjected to stress due to fluid pressure. Because of the unique geometry of the hydrofoil pin fins, special consideration must be given to the interaction of stress concentrations due to fluidic pressure loading and the small radius of curvature of the hydrofoil tail. The objective of this paper is to examine the various sources of stress in this high-performance, micro-pin fin channel and explore the reliability of this hydrofoil pin fin design under high-pressure conditions.