Reliability of a flip-chip package thermally loaded between −55°C and 125°C

Low-temperature reliability of flip-chip plastic ball-grid array packages is a concern for manufacturers. Packages that perform well when thermally cycled from 20 to 120°C fail at an unacceptable rate when the temperature is extended down to −55°C. Electron-beam moiré was used to study local deformations in a flip-chip package and the interactions among the various materials found within the package. The specimen was subjected to a total of ten complete thermal cycles from −55 to 125°C over several nonconsecutive days. Debonding initiated between the solderball and the solder mask where that interface meets the printed circuit board. Deformation was also induced within the solderball, becoming more pronounced with more thermal cycles. Out-of-plane strains appear to be the dominant mechanism for deformation at this location.     

红外热像仪在被动式超低能耗建筑性能检测中的应用

概述了红外热成像技术探测外墙热工缺陷的原理及应用现状,结合工程实例对红外热像仪的应用进行了分析,分别采用定性和定量两种方式判定热工缺陷严重等级。结果表明,利用红外热像仪可以快速得到建筑围护的温度场分布,从而判断是否存在热工缺陷,更是为建筑节能效果的评价提供了高效、准确的检测手段。     

电路板嵌入元器件有机模块技术的开发

为了提高电子组装密度,基板嵌入元器件的三维安装模式受到人们更多的关注.介绍了一种以铜芯为基板核心材料的元器件嵌入技术(EOMIN),详细叙述了其外形结构和制造工艺,并通过实验与FR-4基板嵌入元器件和低温共烧陶瓷基板(LTCC)安装元器件进行比较,通过实验数据对比得出EOMIN元器件嵌入技术具有导热性能好,抗疲劳性强,承受热冲击时铜的塑性变形量小,连接可靠性高等优良特性的结论.     

激光3D成像系统主被动探测技术的研究进展

随着探测器件技术的进步,新概念的主/被动3D成像技术将主被动探测技术优势有机结合起来,能同时获得目标更加丰富的图像信息(如距离像、强度像、距离-角度像等),从而为正确识别和跟踪目标提供更多的决策信息,大大提高了目标识别概率和可靠性.本文首先介绍了激光3D成像系统的发展现状,重点介绍了林肯实验室研制的Gen-Ⅲ系统和美国航空航天局的自主精确着陆和危险的检测避免技术项目的3D闪光激光雷达系统,接着结合HgCdTe雪崩光电二极管(APD)器件的特点介绍了下一代激光3D成像系统主被动探测技术的发展.最后对激光3D成像系统主被动探测技术的未来应用前景进行了展望.     

光波强衰场悬浮颗粒检测中的显微摄像术

被烟尘、粉末、水雾等充斥的空间对光波有极强的衰减作用,统称为强衰场。普通的摄像技术不可能从此类强衰场中获取清晰的图像。融合了显微光学原理和CCD摄像技术的显微摄像术与相应的技术手段配合,可以摄取强衰场中悬浮颗粒的放大图像,并实现远距离传输和多用户监测,从而为强衰场悬浮颗粒检测实践了一条新思路。     

半导体薄片激光器窗口散热模式的热效应

基于垂直外腔面发射半导体激光器窗口散热模式的传热模型,用有限元法计算了不同条件下量子阱有源区的温度变化,建立了量子阱最高温度的等效热阻模型和计算公式,并通过拟合确定了热阻模型的相关参数.计算表明量子阱最高温度与抽运功率存在线性关系,与光斑面积近反比关系,窗口散热片可显著降低量子阱有源区温度和温度的不均匀度.等效热阻模型表明由于半导体晶片内热流在径向难以扩散,热传导中存在较大串联热阻,使得散热片热扩散能力趋于饱和,其中碳化硅的散热性能约为金刚石的75%.     

红外成像制导中的气动热辐射效应机理

高速导弹光学窗口外存在激波层,为高度不均匀的高温气体介质。其热辐射效应使红外探测设备获得的红外遥感图像存在退化和畸变。通过对分子热运动的计算,分析高温气体分子、原子辐射吸收系数,将流场数据有限元处理,实现灰气体总体模型与逐线计算方法的改进结合;通过对气体介质求解辐射传递方程,基于离散传递法的思想,推衍出激波层的热辐射强度计算模型;结合光线传输模型寻找导引头探测口径内的视线路径,解析大气热辐射机理,发展激波层热辐射数值计算方法,两种定量计算模型互为比较验证。研究得出激波层热辐射噪声与来流参数之间的关系,并给出了经验公式。     

基于GaAs基大功率激光器的热分析

The thermal characteristics of 808 nm Al Ga As/Ga As laser diodes(LDs) are analyzed via electrical transient measurements and infrared thermography. The temperature rise and thermal resistance are measured at various input currents and powers. From the electrical transient measurements, it is found that there is a significant reduction in thermal resistance with increasing power because of the device power conversion efficiency. The component thermal resistance that was obtained from the structure function showed that the total thermal resistance is mainly composed of the thermal resistance of the sub-mount rather than that of the LD chip, and the thermal resistance of the sub-mount decreases with increasing current. The temperature rise values are also measured by infrared thermography and are calibrated based on a reference image, with results that are lower than those determined by electrical transient measurements. The difference in the results is caused by the limited spatial resolution of the measurements and by the signal being captured from the facet rather than from the junction of the laser diode.     

Charging effects in CdSe nanocrystals embedded in SiO2 matrix produced by rf magnetron sputtering

Charging effects in CdSe nanocrystals embedded in SiO₂ matrix fabricated by rf magnetron co-sputtering technique were electrically characterized by means of capacitance-voltage (C-V) combined with current-voltage (I-V). The presence of CdSe nanocrystals was demonstrated by X-ray diffraction technique. The average size of nanocrystals was found to be approximately 3 nm. The carriers transport in the CdSe/SiO₂ structure was shown to be a combination of Fowler-Nordheim tunnelling and Poole-Frenkel mechanisms. A memory effect was demonstrated and a retention time was measured.     

Transient thermal loading induced optical effects in single-coated optical fibers with interlayer thermal resistance

The transient microbending loss and refractive index changes in a single-coated optical fiber subjected to thermal loading with stress-dependent interlayer thermal resistance are investigated. The effects of interlayer thermal resistance on the transient microbending loss and refractive index changes of the optical fiber are analyzed and discussed. Results show that the interlayer thermal resistance will increase the transient thermal loading induced lateral pressure in the single-coated optical fiber and, thus, the microbending loss. To the contrary, the interlayer thermal resistance will decrease the transient thermal loading induced refractive index changes.     

Self-heating effects in organic semiconductor crossbar structures with small active area

We studied the influence of heating effects in an organic device containing a layer sequence of n-doped/intrinsic/n-doped C₆₀ between crossbar metal electrodes. These devices give a perfect setting for studying the heat transport at high power densities because C₆₀ can withstand temperatures above 200 °C. Infrared images of the device and detailed numerical simulations of the heat transport suggest that the electrical circuit produces a combination of homogeneous power dissipation in the active volume and strong heat sources localized at the contact edges. Hence, close to the contact edges, the current density is significantly enhanced with respect to the central region of the device, demonstrating that three-dimensional effects have a strong impact on a device with seemingly one-dimensional current transport.