Numerical Study Of Hotspots And Structure Optimization In Microchannel Heat Sink

With advantages of large specific surface area and high heat dissipation efficie nc y,microchannel heat sink has been widely used in chip cooling.But with rapid development of microelectronics technology,not only the total power and heat flux of chips are significa nt ly increased,but also hotspots are locally generated with large heat flux,which has an extremely side effect on thermal performance.Therefore,how to effectively remove the heat on hotspot,while ensuring the total heat transfer performance becomes an urgent problem to solve in chip thermal management.In this paper,a package model containing hotspots and microchanne l heat sink is established based on electronic packing.The total performance is evaluated from two aspects of flow heat transfer and thermal stress,and the geometric structure is optimized.Firstly,a microchannel heat sink with a single hotspot is established,and the effect of the hotspot on cooling performance of heat sink was numerically investigated.The results show that the hotspot partly change the distribution of temperature and thermal stress and increases the corresponding gradient.Meanwhile,the deterioration gradually increases as the thermal load at the hotspot increases,which deteriorates thermal performance.Based on these results,combining the characteristics of MCM and BGA packaging technology,an MCM-BGA 3D package model containing multi-chip(hot-spot)and micro-channel heatsinks was established.Through the thermal-fluid-solid coupling calculations,the total and local flow heat transfer performance and thermal stress characteristics were analyzed separately,and comprehensive ly evaluate the thermal management of the package system.The results show that temperature and thermal stress are kept in a reasonable range and distribute quite uniform in most area,but it has huge gradient partly.The temperature concentrates on chips and chips solder balls near the outlet and the maximum thermal stress appears near the spot welds.The thermal interface resistance has negative effect on both heat transfer and thermal stress performance.Based on the results of the characteristic analysis,the maximum temperature,the maximum temperature difference of the single chip,and the maximum thermal stress are selected as optimiza t io n objective,and the flow and structural parameters are optimized.Studies have shown that the relative flow direction of two areas,the thermal conductivity and thickness of the thermal medium material,the thickness of the thermal expansion surface and the thickness of the substrate all alter the heat transfer and thermal stress properties.Based on the single parameter optimization results,the Nelder-mead method was used to optimize the MCM-BGA 3D package model.Finally,the model of non-uniform distribution of hotspot was established from the aspects of heat flux density and geometric arrangement based on uniform hotspot model,and the internal arrangement under optimal performance was explored.The results show that the model has the best performance when the power of a chip near the entrance of a row is 50W.Both translation and rotation of the chips can improve the flow characteristics,optimize the heat transfer and thermal stress performance.The overall performance gets best when the translation distance is about 0.75mm or the rotation angle is about 10~°.The results and conclusion in this paper could improve cooling efficiency of hotspots on chips and provide important insights to design high thermal characteristic packing model.