Detection of micro solder balls using active thermography and probabilistic neural network

Micro solder ball/bump has been widely used in electronic packaging. It has been challenging to inspect these structures as the solder balls/bumps are often embedded between the component and substrates, especially in flip-chip packaging. In this paper, a detection method for micro solder ball/bump based on the active thermography and the probabilistic neural network is investigated. A VH680 infrared imager is used to capture the thermal image of the test vehicle, SFA10 packages. The temperature curves are processed using moving average technique to remove the peak noise. And the principal component analysis (PCA) is adopted to reconstruct the thermal images. The missed solder balls can be recognized explicitly in the second principal component image. Probabilistic neural network (PNN) is then established to identify the defective bump intelligently. The hot spots corresponding to the solder balls are segmented from the PCA reconstructed image, and statistic parameters are calculated. To characterize the thermal properties of solder bump quantitatively, three representative features are selected and used as the input vector in PNN clustering. The results show that the actual outputs and the expected outputs are consistent in identification of the missed solder balls, and all the bumps were recognized accurately, which demonstrates the viability of the PNN in effective defect inspection in high-density microelectronic packaging.     

Measuring Light Field of Light Source with High Directional Resolution Using Mirrored Ball and Pinhole Camera

This paper presents a method of measuring a light field of a light source with high directional resolution using a mirrored ball and a pinhole camera. The light field describes a spatial and directional distribution of radiances from the light source. The directional distribution is expanded by a reflection on the mirrored ball, and the radiances are measured by a charge-coupled device (CCD) camera with a pinhole lens. The light source is laterally moved by a robot arm to measure the directionally expanded light field, and each pixel on a CCD can obtain the radiances from the light source through the pinhole lens with high directional resolution. The light field is estimated from the pixel value and the position of each pixel using a ray tracing technique. The light field of a krypton lamp was experimentally measured by the proposed method, and the accuracy of the measurement was evaluated against the irradiances measured by a spectro-radiometer at sample points.     

风沙运动的DPM数值模拟

采用离散颗粒模型对风沙气固两相流动进行了数值计算．在该模型中,采用体平均的Navier-Stokes方程来描述气相的运动,对离散颗粒采用拉格朗日方法模拟,求解颗粒运动方程．采用硬球模型描述颗粒问碰撞作用．计算结果表明,沙粒平均水平速度廓线在0．02 m以上高度可以表示为按对数函数或幂函数规律增加,在0．02 m以下则发生偏离;在大于0．02 m的高度,输沙通量随高度按指数规律衰减,而在地面附近由于颗粒蠕移的影响发生偏离,这与已有文献结果一致。本文的模拟有助于风沙运动规律的研究与掌握。     

Disordered Magnetic Phase in Partially Oxidized Bulk Nanocrystalline Iron

Magnetically frozen partially disordered state was observed in nanocrystalline bulk iron prepared by ball-milling of microcrystalline Fe. Role of nanostructure and oxidized fraction is pointed out. Altough we have found a small constituent which is proportional to 1/T in the ZFC curve, the magnetization scaling with T ^3/2 at high fields and the hysteretic behavior in FC-ZFC curves signalizes the presence of frozen ferromagnet at low temperatures.     

匀速直线运动的实验演示

介绍了用落球法演示匀速直线运动的方法、原理。     

第14届亚洲物理奥林匹克竞赛实验试题与中国队学生实验能力分析

介绍了第14届亚洲物理奥林匹克竞赛实验试题,并针对参赛学生在竞赛中的失分情况分析了竞赛评分规则,指出了实验数据处理方法中的重点和存在的问题。     

激光诱骗干扰装备实弹对抗训练方法研究

随着训练需求的不断变化和深入,激光诱骗干扰装备训练迫切需要探索新的更加符合实战要求的训练方法。在分析激光诱骗干扰装备干扰原理和激光半主动制导武器作战过程的基础上,以制式激光末制导炮弹为对抗目标,设计了激光诱骗干扰装备实弹对抗训练方法,为激光诱骗干扰装备的干扰性能检验和战法运用的完善提供了新的训练思路,对进一步开展类似训练提供了参考。     

Microstructural characterisation of nanoparticles using, XRD line profiles analysis, FE-SEM and FT-IR

In this investigation, the structural characteristics of α- Fe₂O₃ nanoparticles synthesised by a mechanical milling have been explored. The structure and morphology of samples were characterized by X-ray powder diffraction, field-emission scanning electron microscope (FE-SEM) and FT-IR measurements. The crystallite size and internal strain were evaluated by XRD patterns using Williamson-Hall and Scherrer methods. The results did not reveal any phase change during the milling. The average particle size decreases with a prolongation of milling times, while the lattice parameters and internal strain increase. It was found that using this method allowed the formation of hematite nanoparticles.     

Formation of long range ordered arrangement of quantum dots with the help of lateral centripetal flow

A simple “chimney” method was used to eliminate the voids in an arrangement of quantum dots sized 2 nm on a solid substrate, which resulted in a large well ordered superlattice of area in the order more than 1 μm². Based on the principle of speeding up the interparticle interaction of nanoparticles to overcome the particle-substrate one, a lateral centripetal force originated from a glass tube acting as a chimney in a simple evaporation device is imposed. This method allows the packing process to be controlled in a mechanical force field, that is, with the same nanogold dispersion different patterns on a substrate—from separate dots to an ordered compact monolayer or even a multilayer structure—could be easily obtained.     

图像稳定技术中的像运动描述及其处理分析

随着图像系统的广泛应用,对图像的稳定要求也越来越高。图像的运动和不稳定是常见的,往往是由于载体的运动引起的,为了达到图像稳定的目的,就需要对其运动进行描述,然后采用相应的算法进行补偿。给出了运动对图像清晰度的影响及像偏移的估算,并对数字电子图像稳定系统进行了简单阐述。