封闭加固型计算机冷板/卡槽界面热阻分析与优化

Analysis and optimization on the thermal contact resistance at the cooling board/chassis rail interface in an enclosed rugged computer

温度过高是导致电子产品可靠性降低的重要原因,而大量军用机载计算机因防护要求需采用封闭加固设计,芯片产生的热量只能通过冷板和机箱卡槽的接触面传输到箱体再散播到周围环境中,因此,锁紧界面间存在的接触热阻成为影响机载计算机芯片散热效率的重要因素。首先通过实验分析了接触压力和表面粗糙度对6061-T6铝合金接触热阻的影响,然后针对某型机载加固型计算机板卡装配结构进行了有限元分析,最后以减小接触热阻为目的进行了优化设计。结果表明,接触压力的增加和表面粗糙度的减小都可以使铝合金接触热阻显著减小,但通过加大载荷或减小表面粗糙度来减小实际装配结构的热阻效果却十分有限,最多只能降低约10.5%。压力云图和热阻云图分析发现,引起上述现象的原因在于装配结构自身特点导致界面上存在严重的非均匀接触,良好接触区只占总界面的很少部分。通过优化原有机箱卡槽镂空部分的尺寸,可以有效改善接触区的压力分布,最终可以使热阻降低约24%,同时还使界面最大接触压力降低约37%。

High temperature is one of the most important factors which can significantly reduce the reliability of electronics.In most military airborne computers,however,an enclosed reinforced design is necessary to cope with serious battlefield environments.In such design,the heat produced by the integrated circuit can only diffuse into the environment from the interface between the cooling board and the chassis rail.Unfortunately,the thermal contact resistance(TCR)at the interface can considerably reduce the heat transfer efficiency.Therefore,it is important to find feasible methods to reduce the TCR.In the present work,effects of contact pressure and surface roughness on the TCR between 60601-T6 aluminum surfaces are experimentally studied,and then the mechanical behavior and TCR problems involved in a certain type of enclosed rugged computer are numerically analyzed.Finally,a parameter optimization design is carried out to reduce the TCR of the structure mentioned above.Experimental results show that TCR can be considerably decreased by an increasing contact pressure,or a decreasing surface roughness.However,numerical results show that the contact pressure and surface roughness just have a little effect on the TCR of the cooling board/chassis rail interface.The average TCR can only be reduced by no more than about 10.5%through increasing the contact pressure or decreasing the surface roughness.Further examination on the contact pressure distribution and TCR distribution reveals that such a phenomenon is due to the fact that serious inhomogeneous contacts occur at the cooling board/chassis rail interface.In other words,well contacts only take place at very small fractions of the total interface.Based on these findings,the present work proposes a method to improve the contacts by optimizing the size of the groove in the chassis rail.FEM simulation shows that the TCR can be effectively reduced by 24%.At the same time,the highest contact pressure is also reduced by about 37%compared with that in the original design.