PBGA封装回流焊翘曲变形仿真与验证

回流焊温变过程中,由于不同材料热膨胀系数（Coefficient of Thermal Expansion,CTE）的不匹配,塑料焊球阵列（plastic ball grid array,PBGA）封装会发生翘曲变形现象。本文采用有限元法对PBGA封装的翘曲变形及应力应变进行仿真分析,并用阴影云纹法对翘曲变形的模拟分析结果进行测试验证。结果表明：PBGA封装翘曲值的模拟值与实测值非常接近,分别为35.9 μm和36 μm;模拟回流焊过程中,翘曲值的模拟值与实测值的变化趋势具有一致性。回流焊过程中,PBGA封装的热应力应变最大值都在基板靠近粘接层的位置,该位置是PBGA封装出现热可靠性问题的最大风险点。PBGA封装边角处的翘曲量最大,因而边角处的焊点也最容易出现开路、虚焊等装联缺陷。     

基于多元线性回归的PBGA可靠性灵敏度分析

基于全局灵敏度分析方法,研究了塑封球栅阵列(PBGA)的热机械疲劳可靠性,得出对PBGA热机械疲勇寿命影响较大的设计参数.利用正交试验法,建立BT基板弹性模量、PCB弹性模量和焊球半径不同水平组合下的PBAG有限元模型,并对其进行热应力分析,利用修正后的Coffin-Manson方程对其进行寿命预测.基于多元线性回归法,建立PBGA寿命与关键设计参数的函数关系,并对该方程的预测效果进行验证.结果表明预测结果可信.     

CCGA焊点热循环加载条件下应力应变有限元分析

SMT焊点在热循环加载条件下的应力应变过程分析是 SMT焊点可靠性研究的重要内容。SMT焊点的可靠性问题主要是焊点在热循环过程中 ,由于陶瓷芯片载体与基板材料之间的热膨胀失配而导致焊点的蠕变疲劳失效。以 CCGA焊点为例 ,利用 CCGA三维焊点形态预测表面节点输出结果 ,将焊点形态分析三维表面模型转换为焊点应力应变有限元分析三维实体模型 ,从而建立了 CCGA焊点可靠性分析模型 ,采用三维有限元方法分析了 CCGA焊点在热循环条件下的应力应变过程。在此基础上 ,对 CCGA焊点疲劳寿命进行了计算     

基于Taguchi实验设计方法优化PoP的翘曲

通过对PoP的翘曲进行优化分析,采用有限元分析方法分析了PoP中FBGA和PBGA的翘曲形变,并利用Taguchi设计和有限元模拟相结合的方法进行优化设计.分析结果表明:PBGA具有较大的翘曲,增加基板厚度和塑封料热膨胀系数,减小芯片大小和厚度可以改善PBGA的翘曲.对比优化前后的翘曲,在25 ℃时翘曲值从53.3 μm降到39.1 μm,260 ℃时翘曲值从-112 μm降到了-67.7 μm.塑封料热膨胀系数和芯片尺寸在优化翘曲中起着重要作用.     

无铅封装中镀覆层对PBGA耐湿热可靠性的影响

随着电子产业中无铅替代有铅的迫切要求,无铅产品的应用越来越广泛,多种材料在无铅电子封装中的应用,使得界面反应与含铅产品相比更为复杂.通过对PBGA器件与不同表面镀层(OSP,ENIG)的PCB板互连形成的SnAgCu焊点,在高湿和炎热条件下的可靠性进行研究.试验结果表明:焊点的寿命在使用ENIG镀层时比使用OSP镀层时更长,说明焊点的可靠性与界面金属间化合物类型密切相关;试验后期还发现器件本身最易产生裂纹的地方位于芯片(DIE)、粘接层材料(DA)和塑封材料(EMC)交界处的芯片以及芯片和DA材料交界处的芯片上,主要是因为芯片与聚合物材料间不能形成过渡层,芯片应力无法得到松弛.     

CCGA焊点热疲劳寿命统计分析与评价优化

通过对 CCGA焊点形态参数与热疲劳寿命进行正交回归分析 ,得出了 CCGA焊点形态主要参数与热疲劳寿命之间的关系表达式。利用得到的焊点形态参数与热疲劳寿命的关系表达式 ,采用优化程序对基于焊点热可靠性的焊点形态进行了评价优化 ,得到了优化后的焊点形态参数。     

Electrical conductivity changes of bulk tin and Sn-3.0Ag-0.5Cu in bulk and in joints during isothermal aging

The changes of electrical conductivity(resistance) between Sn-3.0Ag-0.5Cu solder joints and printed circuit board(PCB) assembly during aging at 125℃were investigated by the four-point probe technique.The microstructural characterizations of interfacial layers between the solder matrix and the substrate were examined by optical microscopy and scanning electronic microscopy.Different types of specimens were designed to consider several factors.The experimental results indicate that electrical conductivitie...     

塑封球栅阵列焊点在温度循环下可靠性数值模拟

根据实际封装器件建立了三维有限元分析模型,模拟了PBGA焊点在温度循环载荷下的蠕变应变,比较了95.5Sn-3.8Ag-0.7Cu和63Sn-37Pb两种焊料形成的焊点在温度循环下的蠕变情况,预测了焊点在温度循环下的疲劳寿命,评价了两种焊点在温度循环条件下的可靠性.结果表明,两种焊点相比较,63Sn-37Pb焊点在循环中的蠕变现象更为显著,95.5Sn-3.8Ag- 0.7Cu焊点的疲劳寿命更长,可靠性更高.     

基于AutoCAD的SMT焊点三维形态数据处理技术

针对SMT焊点形态预测模型和焊点力学性能与可靠性分析模型不统一的现象,在利用VBA技术对AutoCAD进行二次开发和对SurfaceEvolver软件预测的焊点三维形态有限元数据进行分析的基础上,对SurfaceEvolver软件预测的焊点三维形态模型到ANSYS实体模型的转换方法进行了研究。编制了模型转换程序,并以218节点PBGA焊点三维形态预测模型为例,进行了应用实例转换,得到了较为满意的转换结果。模型的成功转换,实现了焊点形态预测模型和焊点力学性能与可靠性分析模型的统一,推进了SMT焊点形态预测的实用化进程。     

基于X射线的焊点图像预处理方法及应用

为解决焊点隐藏在芯片底部的BGA封装元件的焊点检测问题,研究了基于X射线的焊点质量检测的基本原理,阐述了图像预处理方法的设计与实现.为了提高效率,引入了基于迭代方式的阈值产生技术,实现了焊点的区域分割.最后,讨论了焊点质量判别规则并给出了实验结果,结果表明所设计的图像预处理方法能够很好地满足实际生产中的应用要求.     

CSP焊点焊后残余应力分析与预测

该文建立了芯片尺寸封装(CSP)焊点有限元分析模型并对其进行了再流焊焊后残余应力应变分析。以焊点直径、焊点高度、焊盘直径和焊点间距为输入参数,焊后残余应力为输出参数进行了灵敏度分析。选取灵敏度分析结果中对残余应力影响显著的因子作为输入,建立了带动量项神经网络预测模型,对CSP焊点焊后残余应力进行了预测。结果表明,置信度为95%时,焊点直径、焊盘直径和焊点间距对CSP焊点残余应力影响显著,灵敏度从大到小的排序为:焊点直径>焊盘直径>焊点间距。所建立的带动量项神经网络预测模型对CSP焊点焊后残余应力预测最大相对误差为7.93%,平均误差为3.19%,实现了对CSP焊点焊后残余应力准确预测。     

PBGA器件焊点成形建模与三维形态预测

应用最小能量原理和有限元方法，建立塑料球栅阵开（ＰＢＧＡ：Ｐｌａｓｔｉｃ Ｂａｌｌ ＧｒｉｄＡｒｒａｙ）器件焊点三维形态预测模型，对ＰＢＧＡ焊点三维形态时间预测和分析，并将预测结果与试验结果以及国外学者用数学分析模型所得到的预测结果进行了对比验证，具有很好的一致性。     

改进PSO-BPNN的电力变压器故障诊断与模式识别

为了优化反向传播网络相关学习参数,提出一种粒子群优化辅助BP神经网络(BPNN)的新方法.以变压器油中气体体积分数百分比构造故障特征,将BP网络的初始权值和阈值进行实数编码,以对应PSO中的粒子,实现BP网络的离线训练与在线分析,对变压器故障模式做出判断.结果表明,该算法更合理地更新了粒子的位置和速度,最优地设置了全局极值,有效克服了粒子的早熟收敛,获得的故障诊断准确率高达91%,并大大提升了BP网络的收敛速度.该算法为此类设计提供了有效的模型参考.     

混合集成电路用Pb-Sn-Sb-Ag钎料的热疲劳

为了解决混合集成电路中环境温度变化引发的焊点可靠性问题,开发了具有高可靠性的新型钎料来满足微型化和高密度化的混合集成电路的焊接需要。对新研发的Pb-Sn-Sb-Ag四元合金钎料进行了DSC熔点测试,热电偶测试了回流焊的温度曲线,对焊点显微组织进行了相分析,并参照IPC-9701A测试方法进行了热循环实验,结果发现热循环前后钎料的显微组织和力学性能发生了明显的变化。研究表明：钎料合金液相点在245益;回流焊峰值温度为267益;显微组织中主要有Pb、Sb2 Sn3和Ag3 Sn三种相;热失配产生的剪切应力导致了微裂纹产生,温度交变使裂纹持续扩展,最终导致焊点出现了整体剥离的断裂失效模式;金属间化合物厚度和剪切强度呈现逐渐递减的近似线性关系;对比已应用的钎料,新研制的Pb-Sn-Sb-Ag钎料显微组织均匀,在-40~150益热循环条件下表现出高的可靠性。     

An intelligent method for contact fatigue reliability analysis of spur gear under EHL

To complete the contact fatigue reliability analysis of spur gear under elastohydrodynamic lubrication(EHL) efficiently and accurately, an intelligent method is proposed. Oil film pressure is approximated using quadratic polynomial with intercrossing term and then mapped into the Hertz contact zone. Considering the randomness of the EHL, material properties and fatigue strength correction factors, the probabilistic reliability analysis model is established using artificial neural network(ANN). Genetic algorithm(GA) is employed to search the minimum reliability index and the design point by introducing an adjusting factor in penalty function. Reliability sensitivity analysis is completed based on the advanced first order second moment(AFOSM). Numerical example shows that the established probabilistic reliability analysis model could correctly reflect the effect of EHL on contact fatigue of spur gear, and the proposed intelligent method has an excellent global search capability as well as a highly efficient computing performance compared with the traditional Monte Carlo method(MCM).     

Reliability-based design optimization for flexible mechanism with particle swarm optimization and advanced extremum response surface method

To improve the computational efficiency of the reliability-based design optimization(RBDO) of flexible mechanism, particle swarm optimization-advanced extremum response surface method(PSO-AERSM) was proposed by integrating particle swarm optimization(PSO) algorithm and advanced extremum response surface method(AERSM). Firstly, the AERSM was developed and its mathematical model was established based on artificial neural network, and the PSO algorithm was investigated. And then the RBDO model of flexible mechanism was presented based on AERSM and PSO. Finally, regarding cross-sectional area as design variable, the reliability optimization of flexible mechanism was implemented subject to reliability degree and uncertainties based on the proposed approach. The optimization results show that the cross-section sizes obviously reduce by 22.96 mm~2 while keeping reliability degree. Through the comparison of methods, it is demonstrated that the AERSM holds high computational efficiency while keeping computational precision for the RBDO of flexible mechanism, and PSO algorithm minimizes the response of the objective function. The efforts of this work provide a useful sight for the reliability optimization of flexible mechanism, and enrich and develop the reliability theory as well.     

Sn-Ag-xCu-Bi-Ni/Cu焊点界面IMC演变

为了研究低银无铅焊点界面金属间化合物(IMC)的形成与演变,以低银无铅焊点Sn-Ag-xCu-Bi-Ni/Cu为研究对象,研究了钎料中Cu质量分数对界面IMC厚度、形貌和成分的影响.实验结果表明,随着钎料中Cu质量分数的增加,回流焊后焊点IMC层厚度变薄,IMC晶粒尺寸增大,IMC晶粒形貌由颗粒状转变为棱柱状以及鹅卵石状,同时界面IMC成分发生由(Cu,Ni)6Sn5向Cu6Sn5的转变.高温时效后,界面IMC层厚度增长.当钎料中Cu质量分数超过1%时,时效后生成较厚的Cu3Sn化合物层,对焊点可靠性不利.钎料中Cu质量分数应控制在1%以下.     

基于正交设计的QFN焊点三维形态建模与预测

采用基于最小能量原理和有限元数值分析方法的Surface Evolver软件,建立了四方扁平无引脚器件(QFN)焊点三维形态预测模型;选取焊盘长度、焊盘宽度、焊料体积、间隙高度作为4个关键因素,采用水平正交表设计了9种不同的QFN焊点工艺参数水平组合,建立了这9种焊点的三维形态预测模型,得到了不同工艺参数水平组合下的QFN焊点形态;焊盘长度、焊盘宽度、焊料体积、间隙高度等工艺参数的改变对QFN焊点的三维形态均有影响.     

A PSO-SVM Model for Short-Term Travel Time Prediction Based on Bluetooth Technology

The accurate prediction of travel time along roadway provides valuable traffic information for travelers and traffic managers. Aiming at short?term travel time forecasting on urban arterials, a predict...     

Preliminary Investigation of Copper Joints Soldered with Sn58Bi

In recent years, intensive studies have been carried out to find an alternative for Tin (Sn)-Lead (Pb) solder alloys with increasing demand over lower temperature solder alloys in current electronic packaging industry. High temperature operational solder alloys seem to produce drawback to other components on the printed circuit board (PCB). Low melting temperature Sn58Bi substrate as a potential replacement was investigated in this paper based on the melting properties, wettability, and shear strength. The Sn58Bi was soldered at a temperature below 200 ℃ on the Cu substrate, and the shear strength and contact angle were calculated. A peak temperature (melting temperature, TM) of 144.83 ℃ was identified. Single lap joint method was performed at a strain rate of 0.1 mm/min and an average shear strength of 23.4 MPa was found from three samples. The contact angle (wettability) was calculated to study the solder joint behaviour at reflow temperature of 170 ℃. The contact angle of the Sn58Bi was found to be 32.4 ° and considered to be desired value since the angle is less than 50 °. The low temperature soldering provides a preliminary result to allow further application on the real PCB.