P.K. Chan

Thermal management of hotspots using upstream laminar micro-jet impinging array

The problem of heat removal is likely to become more severe due to the presence of hotspots in the integrated circuit chip. The heat dissipation capability of the upstream laminar micro-jet impinging array is investigated for hotspot cooling. Micro-jet impingement array cooling is an effective method of using liquids to cool electronics where high convective heat transfer rates are required. Several simulations have been implemented on the thermal structure of 4 tiny inline-aligned hotspots to evaluate the heat dissipation capability of the laminar micro-jet impinging array. The effects of the jet diameter, jet pitch and jet-to-wall distance on the Nusselt number, heat convection coefficient, Reynolds number and thermal resistance are studied. The limit of the dissipated heat fluxes of the considered thermal structure are evaluated for the hotspots of different sizes.

GaN-on-Si hotspot thermal management using direct-die-attached microchannel heat sink

GaN-on-Si device posts new challenge to thermal management with its highly concentrated heat flux dissipation from HEMT. In order to characterize GaN-on-Si hotspot and to develop an effective cooling solution, a customized thermal test chip is built with highly doped resistors to produce tiny (150 × 350 μm2) hotspots. Direct-die-attached copper microchannel heat sink is used instead of the conventional slap on heat sink to significantly improve the heat removal rate from the device. By using Infra-red (IR) thermography, the current experimental work demonstrated the cooling capability of microchannel heat sink up to 11.9 kW/cm2 hotspot heat flux with a maximum hotspot temperature of 175 °C.

Development of package level hybrid silicon heat sink for hotspots cooling

In this paper, the fabrication of package level silicon microchannel heat sink for hotspot thermal management is presented. These include the design, micro fabrication process and chip level integration of a hybrid silicon heat sink, which integrates jet impingement, microchannel cooling technologies. The fabrication of hybrid heat sink is proposed by bonding two Si chips which patterned with nozzle and microchannel structures separately. The nozzle array is fabricated using though silicon vias (TSV) process. This nozzle plate is used to generate jet impingement effect into the microchannel heat sink. On the other hand, the microchannel heat sink consists of micro fins and channels which are fabricated using deep reactive ion etch (DRIE) process. The micro fins increase the area for convective heat transfer while the micro channels serve as the liquid conduit to carry the intense heat away from the heat source. Two silicon chips are bonded using thermal compression bonding (TCB) process. For the packaging, the integration of thermal chip and diamond heat spreader onto silicon heat sink is performed using gold-tin eutectic bonding through TCB process. In this paper, the major fabrication steps and critical process parameters will be discussed in details along with the hydraulic test and thermal analysis.

Large area spray cooling by inclined nozzles for electronic board

To cool a 1 kW 6U electronic card, an innovative inclined spray chamber with multiple nozzles has been developed and investigated with a closed-loop refrigeration system. A large heated surface (12.3 × 15.5 cm2) was sprayed by four gas-assisted nozzles with an inclined angle of 39° relative to the normal direction. A reasonable spray coverage area can be obtained by the inclined spray chamber while enabling a relatively lower spray chamber height than that required by a normal spray chamber. R134a was implemented as the working fluid in this study. The mass flow rate, pressure drop across the nozzles, and the spray chamber pressure were varied experimentally, and the results suggest that the increases of the mass flow rate, the pressure drop across the nozzles, and the spray chamber pressure can improve the thermal performance of the inclined spray. The average heated surface temperature can be maintained within 20.0°C, and the maximum heat transfer coefficient of 4742.2 W/m2·K can be achieved at a suitable working condition.

Heat transfer characteristics of impingement spray cooling system for electronic test cards

A closed-loop impingement spray cooling system which is capable of cooling a 1kW 6U electronic test card has been developed. The heated surface area is 13.5 × 15.1 cm2. R134a was used as working fluid in a modified refrigeration closed-loop cycle. Four vapor assisted nozzles are implemented to generate spray to cover a large ratio of the heated area of the card. The effects of mass flow rate and spray saturation temperature on thermal performance are investigated experimentally in this study. Experimental results are promising with a stable average temperature of around 25 C being maintained on the heated surface with small temperature variation on the heated surface at suitable operating conditions. It is found that cooling performance has been improved with increasing of mass flow rate and spray saturation temperature.