微尺度热传导理论及金属薄膜的短脉冲激光加热

概述了微尺度热传导理论的几种模型及其求解方法。以金属薄膜的短脉冲激光加热为例,分析了固体材料在微尺度条件下的热响应特征,主要包括短脉冲激光加热条件下金属薄膜中的热平衡时间、薄膜中热传递的波动性特征和微尺度条件下热传递的尺寸效应;同时讨论了对流热损失对金属薄膜热行为的影响。     

浅谈PCB图形转移中的短路现象

研究了一种少见的PCB短路现象,及解决问题的全过程.     

厚膜片状电阻器开路失效分析

分析了厚膜片状电阻器波峰焊时开路失效的原因 ,并提出了相应的解决方法。     

电子元器件中热传递功能的声学评价

半导体电子元器件的内部缺陷会影响其散热效率从而导致元器件失效。为了检测元器件的内部缺陷,采用声学显微镜来检测塑料封装集成电路器件的芯片胶接层和倒装芯片散热片与芯片间的热界面材料,结果显示,前者的胶接层的孔隙率达46.22%。而后者的热界面材料中发现有孔隙。对热界面材料的厚度通过参考回声的方法进行了测量,结果显示其厚度为30~75μm,均在要求范围之内。     

Examination of natural convection plumes from partially heated PCB plates and estimation of the heat transfer coefficients

Accurate values of convection heat transfer coefficients are required for the simulation of the thermal characteristics of printed circuit boards. This paper presents the results of experiments carried out using a Schlieren apparatus to examine the natural convection plumes from a horizontally positioned partially heated printed circuit board plate. It has been demonstrated that for a board with a centrally positioned resistor, the convection coefficients may be approximated to two values, one over the heated resistor area and another over the rest of the plate. These observations were then used in an optimization process to estimate the convection coefficients from such surfaces. Values of 4 W/m²K and 13.5 W/m²K were obtained for the resistor and the adjoining unheated sections, respectively. It is concluded that it is not generally satisfactory to assume a uniform value for convection coefficients during thermal simulation of electronic structures. However, a simplifying assumption of two values for convection coefficient appears to be acceptable; the lower value applying in the region of convection plumes and the higher value elsewhere.     

微通道的流动阻力分析

针对在恶劣温度条件下工作的芯片热控制问题,提出由微泵、微通道、热电模块、智能控制单元、散热片以及液体管道等构成的微通道对流换热设计思想。数值仿真分析了换热微通道结构的速度和压力分布,计算了管道、微通道等部件的阻力损失和换热系统的流动阻力曲线,确定了系统必需的微泵工作性能参数,求解了微泵的最佳工况点。最后,制作了微通道对流换热装置,测得了系统流量和流动阻力,证实了可用经典流体理论来分析该系统的流动阻力。     

电子产品散热器的设计

对电子产品使用的散热器的散热原理、主要影响因素进行了分析,建立了数理模型,并对如何选择散热器提供了一些可行的依据.     

Bounding relations for natural convection heat transfer from vertical printed circuit boards

The simplicity and convenience of direct cooling with freely circulating air, as well as the ubiquity of such systems in the marketplace, make this the technique of choice for many thermal packaging tasks. While standard heat transfer correlations are generally unsuitable for determining the detailed thermal behavior of individual components, the maximum surface temperature of integrated circuit packages mounted on PCBs can often be shown to lie between two analytical bounds: an upper, "asymmetric isoflux," bound based on heat transfer from just one side of the PCB and a lower, "symmetric isoflux," bound based on identical thermal transport from both sides of each PCB. Following a brief review of the development and validation of the theoretical symmetric and asymmetric isoflux relations for smooth-plate channels, this study focuses on the application of the proposed bounding relations to widely and closely spaced component-carrying PCBs. Successful comparison with much of the available data demonstrates the acceptable accuracy of these analytical expressions, for all except the narrowest spacings, and their utility to the thermal designer of air-cooled PCBs.     

Convection heat transfer in electrostatic actuated liquid droplets for electronics cooling

In this paper, the internal flow and heat transfer inside the electrostatic actuated droplets are studied for different droplet velocities by means of detailed flow computations. It is shown that the internal droplet flow exhibits a parabolic characteristic at one hand and that the presence of two convection cells decreases the heat transfer to the lower part of the droplet, thereby limiting the overall heat transfer through the droplet. A typical enhancement of the heat transfer with a factor 2 is achieved with respect to the minimal value that would be obtained assuming heat conduction as the only means of heat transfer in the liquid. Further an analytic lumped model is presented to estimate the transient average droplet temperature with an accuracy of 5% compared to the full transient computational fluid dynamics modelling.     

Impact of radiative‐heat transfer on photovoltaic module temperature

The prediction and the optimization of the energy production of a photovoltaic (PV) module require a good knowledge of its optical, electrical, and thermal behavior. We build a complete multi‐physics model able to describe the behaviors of a PV module depending on the environmental conditions (ambient temperature, wind speed, total irradiance, and installation conditions). The model treats radiation heat transfer in participating media. This feature reveals the limits of the commonly used modeling. It also opens new possibilities on improvement of the PV module yield and may influence the design strategy. Copyright © 2015 John Wiley & Sons, Ltd.     

回路热管换热性能的实验研究

为研究回路热管(LHP)的换热性能,制作了简单的回路热管换热性能测试装置。采用不锈钢为回路热管的材料,500目铜丝网为吸液芯,实验研究了回路热管不同功率下对启动时间和热管热阻的影响。研究结果表明,回路热管的功率增大,启动时间越短,热阻也相应的减小;同时,回路热管冷凝器入口和储液室入口的温度在LHP启动后,会呈现相反的温度波动。研究结果为回路热管散热器的应用提供了理论依据和方便的测试手段。     

风对二维平面物体传热的影响

为了研究风对二维平面物体传热的影响,分析了此过程的传热机理并建立了理论模型;在不同风速情况下,用铁板和混凝土块进行了实验,验证了理论分析;最后对风这一因素的影响进行了总结,对研究意义作了展望.     

热流传感器信号采集系统硬件设计

为了解热流传感器的自身温度与输出的具体数量关系,设计一种基于C8051单片机的热流传感器信号采集系统。该系统增加专用的温度信号采集模块。使系统结构更小,功能更多,且数据采集更精确,从而为后续数据处理奠定基础。     

Theory of CCD transfer noise from a circuit model

The transfer function and noise of a CCD can be accounted for by a simple block model of the elementary cell. From the analysis of ann-cell device, the noise properties of the output signal are derived in both the frequency and the time domain. The approach requires no approximations to calculate the power spectral density and amplitude variance so that the validity of asymptotic expressions can be evaluated. The model lends itself easily to include noise sources other than the transfer noise.     

焊锡中气泡对电子元件热传导的影响

采用有限元软件ANSYS建立了空调中一种电子元件的三维模型,利用有限元"生死单元"技术,模拟电子元件焊锡层中存在不同大小和位置的气泡时的情形,分别对模型的热传导进行模拟计算,并对分析结果进行比较,以研究焊锡中气泡对电子元件热传导的影响。结果表明,气泡大小占焊锡体积比达4/49时,气泡对热传导影响开始明显化。气泡位于边缘位置对热传导影响更大,与中间位置相比,温度约低3K。     

SMT激光再流焊传热中几种效应的研究

简介热风再流焊弊端,研究激光数控再流焊传热中的效应,推动SMT表面贴装技术的发展,并应用于PCB的制作。     

激光辐照温度场计算中的"像热源"研究

激光热作用研究中 ,通常只能采用纯数值计算方法研究异形工件激光热处理温度场 ,本文介绍轴对称像热源处理边界问题的半解析计算方法并给出实验证明。该方法适用于任意分布光束的热作用计算 ,当工件的局部边界由非正交平面构成时 ,可以获得满意的计算结果     

CO2激光热处理光热转换层的应用分析

介绍了CO_2激光热处理光热转换层技术,分析了磷化法和喷涂法工艺生成的光热转换层在激光热处理中的特点。针对磷化法光热转换层的热稳定性差、温度升高吸收率下降、磷酸盐溶液的污染等缺陷,探讨了喷涂法光热转换层作为激光热处理预处理层的应用,可显著地提高激光热处理的效率。     

Flow and heat transfer in porous micro heat sink for thermal management of high power LEDs

A novel porous micro heat sink system is presented for thermal management of high power LEDs, which has high heat transport capability. The operational principle and heat transfer characteristics of porous micro heat sink are analyzed. Numerical model for the micro heat sink is developed to describe liquid flow and heat transfer based on the local thermal equilibrium of porous media, and it is solved with SIMPLE algorithm. The numerical results show that the heated surface temperature of porous micro heat sink is low at high heat fluxes and is much less than the bearable temperature level of LED chips. The heat transfer coefficient of heat sink is very high, and increasing the liquid velocity can enhance the average heat transfer coefficient. The overall pressure loss of heat sink system increases with the increasing the inlet velocity, but the overall pressure drop is much less than the pumping pressure provided by micro pump. The micro heat sink has good performance for thermal management of high power LEDs, and it can improve the reliability and life of LEDs.     

翅片散热板大空间自然对流散热数值方法探讨

LED灯具散热板的翅片与散热空间在尺度上存在很大的差距。在数值模拟中,空间边界条件的设置、翅片壁面附近湍流模式的处理及压力差值格式的选用对于计算结果会产生很大的影响。结合某型LED灯具的翅片散热板在大空间中自然对流散热的数值模拟,将压力入口和压力出口两种边界条件、壁面函数法和低Re数k-ε模型两种壁面处理方式以及SIMPLE算法中的标准和PRESTO两种压力差值格式的组合进行了模拟计算对比,并将模拟结果用实验进行了检验。实验表明,模拟结果可与实验结果很好匹配,其误差可在2%以内。