基于交互作用的无铅波峰焊接正交试验分析

通过开展无铅波峰焊正交试验,以大量的试验数据为依据确定了无铅电子组装工艺参数,建立了无铅波峰焊工艺参数间的关系模型,考察了不同试验因素的组合对焊点缺陷率的影响,对工艺参数进行了优化,并得到了各因素对实验结果重要性的影响顺序及优化的参数结果。     

线性自旋阀读磁头的材料性能及结构参数优化（一）

优化材料性能参数和自旋阀巨磁电阻磁头的结构参数是微磁器件实用化的关键。基于建立的物理计算模型,首先利用传输线方法和微磁学理论对铁磁自由层中信号场和磁化强度分布进行了计算,优化了材料性能参数。     

小波神经网络预测变电站VRLA电池工作寿命

研究预测变电站阀控式密封铅酸(VRLA)电池工作寿命的方法。引入小波神经网络(WNN),建立电池工作寿命的WNN模型,再通过实验数据对WNN模型进行训练,得到用于电池运行寿命预测的WNN模型,最后将WNN模型的预测结果与实际结果进行对比。预测的平均相对误差为1.49%,最大相对误差为2.35%。WNN模型可以快速、准确地得到电池的工作寿命,可用于变电站电池工作寿命的预测。     

软驱磁头的清洗方法

软盘驱动器在整个微机系统中使用最频繁,长期下去软盘驱动器的磁头会被污染,严重时会导致驱动器出现读写错误。下面介绍两种清洗磁头的方法: 1.使用磁头清洗盘在使用微机时,应定期用磁头清洗盘清洗软驱磁头。磁头清洗盘是一种特制的盘片,其外形与一般软磁盘相似。它是利用盘片表面纤维在磁头表面摩擦而清除磁头污物。磁头清洗盘有两种:湿洗盘和干洗盘。湿洗盘在使用时需在读写孔滴少量磁头清洗液,但不可     

锂离子动力电池寿命预测技术综述

锂离子动力电池的寿命预测已经成为近几年研究的热点问题。总结了国内外近几年的电池寿命预测方法:基于模型的方法、基于数据驱动的方法和基于融合模型的方法,并分析了各种方法的优缺点,给出了未来锂离子动力电池寿命预测的研究方向。     

金属化膜电容器寿命预测方法

为了提高金属化膜电容器寿命预测精度,保证脉冲功率系统安全稳定的运行,提出一种新的基于粒子滤波算法的电容器寿命预测方法。该方法不需要大量寿命数据,能通过历史数据不断更新模型参数,准确地预测单个电容器寿命。对54个金属化膜电容器进行3种工况下的寿命退化实验,可以得到,相比于传统Weibull分布模型方法和Birnbaum-Saunders分布模型方法,所提方法的预测精度更高,3种工况下的平均预测偏差都100次,验证了所提出方法的有效性。     

Wiener过程性能退化电子产品的剩余寿命预测方法

针对Wiener过程性能退化电子产品剩余寿命预测中存在先验信息获取困难、预测不能有效体现个体差异性的问题,研究一种基于自助法的电子产品剩余寿命预测方法。首先,基于Wiener过程建立性能退化模型;其次,利用自助法获取先验数据,并以此数据确定退化模型参数的先验分布;最后,由贝叶斯方法融合退化数据确定退化模型参数的后验估计,进而由剩余寿命分布确定产品的剩余寿命。该方法能够得到具有个体差异性的预测结果,适合于单个电子产品的在线剩余寿命预测,并通过对GaAs激光器的实例分析验证了该方法的有效性。     

灰色双重残差修正的多芯片组件寿命预测

针对利用传统灰色模型进行多芯片组件寿命预测时存在的精度不足,以及预测精度随时间跨度增加而显著降低的问题,提出马尔科夫-尾段双重残差修正的多芯片组件寿命灰色预测方法。将在灰色GM(1,1)模型预测值基础上经马尔科夫法优化后的残差作为尾段灰色残差模型的输入值,实现双重残差修正。以对热循环加速试验条件下得到少量试验数据的影响多芯片组件寿命的电阻值进行寿命预测为例,试验结果表明,相较于传统灰色模型和神经网络预测方法,所提出方法在小样本条件下平均残差分别减小了80.469%和68.53%,预测精度得以提高,结果更加可靠,能够更准确地预测多芯片组件的寿命。     

基于电池寿命模型的微网控制方法

微网储能系统可有效平抑风力发电和光伏发电输出功率的波动,增大微网系统惯性,保障供电可靠性,改善电能质量。在分析电池寿命模型和微电源控制理论的基础上,提出一种基于电池寿命模型的控制方法。电池寿命受到电池充放电电流、荷电状态和温度等因素的影响,当电池的实际运行参数低于寿命保护限值时,可延长电池寿命。最后通过一个实例验证了所提控制方法。     

基于门控循环单元神经网络的LED寿命预测方法

LED寿命预测仍存在预测结果准确性不高、预测速度不足等问题。本文提出了一种基于门控循环单元神经网络的LED寿命预测方法,提出利用门控循环单元简化神经网络预测模型,并将模型输入数据的长度设置为变量,使预测过程能够考虑更多的LED历史退化信息;再采集LED流明维持数据作为训练样本,训练寿命预测模型;最后利用训练好的模型对LED进行寿命预测实验,并与其他三种方法进行对比。实验结果表明,本文方法具有更高的预测准确度和更快的预测速度,且具有良好的鲁棒性。     

Reliability and failure analysis of Sn-Ag-Cu solder interconnections for PSGA packages on Ni/Au surface finish

The reliability and failure modes of eutectic Sn-Ag-Cu solder joints were studied and compared to eutectic Sn-Pb-Ag ones. Two different failure modes occur: brittle fracture and fatigue. The results show that with a Ni/Au surface finish the reliability of Sn-Ag-Cu solder is much better than that of Sn-Pb-Ag solder. First, when the joint is deformed at high thermomechanical strain, the chance of brittle fracture at the Ni-Au interface is significantly reduced when using Sn-Ag-Cu solder. The reason is a reduced formation of the brittle (Au, Ni)Sn/sub 4/ intermetallic at the UBM interface, responsible for the brittle fracture mode. Second, after deformation at low thermomechanical strain, both solders fail due to solder fatigue, but the Sn-Ag-Cu shows a better lifetime. This better reliability of the Sn-Ag-Cu solder is attributed to a new solder fatigue mechanism: the crack propagates through the bulk of the solder in a web-fashion way, linking the Au-containing particles formed in the volume. This is beneficial for the joint reliability as it hinders the crack propagation.     

基于2-D彩色图像模型的PCB焊点检测方法研究

提出了一种基于2-D彩色图像模型的PCB焊点检测方法.首先,基于3色LED环形结构光源和彩色数字相机的图像采集子系统获取的彩色PCB图像,分析了片式晶片元器件焊点表面信息与其焊点图像色彩分布规律,建立了片式晶片良品焊点类型的焊点检测模型,其次,给出了反映可接受焊点图像中心感兴趣区域(ROI)色彩分布规律的灰度曲线图.在...     

Reliability of power cycling for IGBT power semiconductor modules

Power cycling capability is one of the most important reliability items in the application of power semiconductor modules. This paper describes the failure mechanism of power cycling by analysis of the structure of lead-based solder and joint failure due to solder fatigue. By the application of some additional elements, it has been found that a newly developed tin-silver-based solder shows both excellent mechanical properties and wettability. Further, we have established, both by experiment and computer calculation, that the dependence of the failure mechanism on /spl Delta/Tj is completely different between the new tin-silver-based solder and conventional lead-based solder. According to these evaluations, it has become clear that the power cycling lifetime of the new tin-silver-based solder depends on the solder joint at higher than around 110 K, while it depends on the aluminum wire bonds at lower than around 50 K. As a result, higher power cycling capability can be successfully achieved by using this newly developed solder instead of conventional lead-based solder.     

计及焊层疲劳影响的风电变流器IGBT模块热分析及改进热网络模型

针对不同疲劳寿命时期对风电变流器绝缘栅双极型晶闸管(IGBT)模块结温的影响,分析焊层在不同脱落度下的IGBT模块热阻变化规律,并建立考虑热阻变化的改进热网络模型。首先,依据风电机组变流器IGBT模块的结构和材料属性,建立三维有限元热-结构耦合分析模型,对基板焊层和芯片焊层在不同脱落度下IGBT模块结温和热应力的分布规律进行仿真分析。其次,确定不同焊层脱落度下其热阻增量值,并建立IGBT模块改进热网络模型。最后,将三维有限元模型和改进热网络模型的结温计算结果进行对比分析,验证了所提的改进热网络模型的有效性。     

Reliability Estimation for Large-Area Solder Joints Using Explicit Modeling of Damage

The issues of available cyclic fatigue models in life prediction of large-area solder joints using finite-element analysis (FEA) are discussed. In this paper, a new FEA approach called successive initiation (SI) is modified and introduced in conjunction with energy partitioning (E-P) damage model to resolve some of the issues with available damage models such as geometry and scale dependency and provide a solution to large-area solder joints. This new technique models damage explicitly, meaning that it separates initiation from propagation by monitoring the plastic and creep damage at the tip of the crack successively. The SI technique could be easily used with continuous loadings of different types and frequencies. The modeling approach is then implemented on a power device with large-area solder. Sensitivity study is conducted with the help of the experiment to determine the right initiation threshold for smooth crack initiation and propagation. The results of modeling are then compared with available experimental data for the same power device. The comparison shows that using the damage model constants generated for small solder joints such as ball-grid array or chip-scale package could significantly overpredict the life of larger area solders. New E-P damage model constants for large-area solder joints are obtained and presented by calibrating the modeling to the experiment.     

Printed circuit board inspection using image analysis

Computer vision has been widely used in the online inspection of electronic components. In this paper, the authors present a computer vision system using structured lighting, which provides them with an efficient solution for solder joint inspection. Their system uses a novel structured-lighting inspection technology to overcome some difficulties that traditional computer vision systems often experience. They developed a slant map surface shape estimation technique for the solder joint. From this technique, a solder joint can be determined to be a good (concave), bad (convex), bridged solder joint, or solder joint with surplus solder, or lacking solder     

Board level solder reliability versus ramp rate and dwell time during temperature cycling

Effects of ramp rate and dwell time are studied through laboratory results and a nts (DOE) using finite element analysis (FEA) incorporating stress/strain and plastic work history. Results demonstrate that solder joint fatigue life is more sensitive to dwell time than ramp rate during thermal cycling. A nonlinear relationship exists between solder fatigue life (mean time to failure, MTTF) and dwell time. Increasing dwell time past 20 min has a minimal effect on the acceleration factor or lifetime. Modeling shows that the acceleration factor increases by a factor of 1.23 for a specific ball grid array (BGA) assembly when the test condition changes from a slow ramp/long dwell (single chamber) to a fast ramp/short dwell (dual chamber). Experiments were performed to validate the FEA modeling. Different ramp time/dwell times were achieved by modulating the temperature profile in a single chamber oven. If dwell time changes from 5 to 10 min with an invariant ramp time of 5 min, apparent MTTF decreases by 55%. However, if the invariant dwell time is 10 min, MTTF remains practically the same as the ramp time increases from 5 to 10 min. These test results are consistent with modeling predictions. The focus of temperature cycling tests should not be on number of chambers, nor upon ramp rate, but upon dwell time. We recommend 8 to 10 min dwell at a high temperature of 125/spl deg/C.     

基于维纳过程的光伏逆变器寿命评估方法

针对传统高可靠电子产品寿命评估方法难以有效获取充足的失效数据等难题,本文提出一种基于随机过程理论的光伏逆变器可靠性评估与寿命预计方法。首先,通过加速退化实验获取光伏逆变器性能退化数据,并选取输出功率作为表征其健康状态的性能参数;其次,采用典型一元维纳过程建立其性能退化模型,并利用最大似然法与贝叶斯理论更新退化模型参数;最后,依据光伏逆变器失效阈值实现其寿命估计,并预测逆变器在不同退化程度下的剩余使用寿命及其置信区间。实验结果验证了所提方法的有效性和准确性。     

基于 GBDT 算法的锂电池剩余使用寿命预测

针对现有方法对锂电池剩余使用寿命(RUL)预测精度不高,模型训练时间较长的问题,提出一种基于梯度提升决策树 算法(GBDT)结合网格搜索法(GS)的预测模型。 首先,分析锂电池的充放电循环过程,确定电压、电流、温度为可用健康因子 (HI);其次,处理历史数据中的异常值,并均值化可用健康因子数据为特征输入;最后,通过 GBDT 算法建立锂电池剩余使用寿 命预测模型,并采用 GS 优化模型参数。 基于 NASA 锂电池容量衰减数据,实验结果表明,模型在 RMSE、MAE、MAPE 评价指标 上相对其他方法均提升了约 10 倍,并且可将锂电池剩余使用寿命预测误差率控制在 0. 05 以内,训练时间缩减至 4. 5 s。     

Interaction Effect of Voids and Standoff Height on Thermomechanical Durability of BGA Solder Joints

This paper documents simulation studies on the interactive effect of standoff height and void volume on the thermomechanical durability of ball-grid-array solder joints using a 3-D viscoplastic finite element analysis. Surface Evolver software was used to find the optimized shape of the solder joints and standoff height by minimizing the surface energy as voids with different sizes were placed in solder balls. A global–local modeling approach was then utilized to model the thermomechanical durability of voided solder joints. Void-area-fraction ranges of 14%–40% were analyzed. A nonmonotonic behavior of durability versus void area fraction was observed. The results showed that, if the void is completely inside the solder ball and has no interface with the boundaries of the joint, it does not have a detrimental effect and even improves the durability as the void size increases. However, voids located at the interface of the solder joint and copper pads were found very detrimental to durability. Factors such as load bearing area, stress concentration factor, and overall compliance of the structure were found responsible for the nonmonotonic behavior of the joints. An analytical micromechanics approach was used to calculate the compliance of the structure, and a nonmonotonic trend in phase with the durability trend was observed. The stress concentration factor also showed the same nonmonotonic trend. The rise of these two factors for the void interfacing with copper pads in addition to the decreased-load-bearing-area effect resulted in a drastic decrease in durability.