T字型硅通孔不同位置界面裂纹扩展研究

硅通孔(TSV)技术是实现三维封装的关键技术.随着技术发展,TSV被设计成多种不同结构.以T字型TSV为研究对象,仿真分析了两种温度载荷下T字型TSV中产生的热应力及其分布情况.以此为基础,通过计算裂纹尖端能量释放率,研究了T字型TSV中3个不同位置的界面裂纹失效扩展.结果 表明,T字型TSV中钉头的存在改变了铜/硅/钉头三重连接处和硅材料顶部钉头外周边界条件,在这两处易产生应力集中现象.与完全填充TSV结构相同位置的垂直裂纹相比,T字型TSV中垂直裂纹能量释放率明显下降.另外,T字型TSV中水平向外开裂的界面裂纹扩展时裂纹尖端能量释放率最小,水平向里开裂的界面裂纹扩展时裂纹尖端能量释放率最大,更易发生失稳扩展.     

激光熔覆过程中裂纹在线研究

激光熔覆层中的裂纹一直是一个限制其工业应用的难题。本文首次提出利用声发射技术在线检测熔覆及冷却过程中裂纹的发生和扩展,对三种熔覆粉末的裂纹信号进行分析比较,得出随熔覆层面积厚度及冷却速度的增加,裂纹数增大。多数裂纹产生于熔覆过程,个别在冷却过程。裂纹走向以垂直于激光扫描方向为主,裂纹起源为熔覆层和基体结合带,多数贯穿整个熔覆表面。如能结合热检测,可通过对熔覆材料特定温度下性能改进控制熔覆层裂纹。     

变参数激光冲击TC17钛合金疲劳裂纹扩展特性

研究采用两种不同变能量参数激光冲击TC17钛合金,通过疲劳试验分析变能量参数激光冲击对其疲劳裂纹扩展寿命和扩展速率的影响规律,通过X射线残余应力测试仪分析激光冲击后试件表面残余应力分布状态。结果表明:相比于未强化试件,在高数值残余压应力作用下的强化后试件疲劳寿命分别提高了2.14倍和1.74倍,稳定扩展初期疲劳裂纹扩展速率分别降低了21%和16%;在裂纹稳定扩展前期区域,LP-1试件扩展速率发生明显减小的现象,C′值最大,m值为最小,减为负数;LP-2试件C′值增大,m值减小。残余应力场分布是疲劳裂纹扩展的主要影响因素,两种强化方案对TC17钛合金疲劳裂纹扩展均产生抑制作用,激光能量越大,产生残余压应力值越大,激光冲击对裂纹扩展前期区域的强化作用大于对裂纹扩展中后期区域的强化作用。     

激光冲击处理金属板材后的裂纹扩展速率

采用1.5mm厚高强钢以及1.7mm厚高温合金薄板制作成紧凑拉伸试件,对预制裂纹延长线进行3次叠加(光斑直径6mm)激光冲击处理,进行裂纹扩展速率试验并与未处理的试件进行对比,由于激光冲击处理产生的强化效应在裂纹扩展路径上存在区域差别,所以裂纹扩展速率无法进行公式拟合,但在整体上能大大降低裂纹扩展速率。     

基于红外热像法的金属裂纹扩展研究北大核心CSCD

疲劳裂纹是金属结构件在工程实际中常见的失效形式之一,裂纹的扩展则会导致大部分塑性功以热量的形式耗散,因此基于红外热像法的金属结构温度监测是实现裂纹扩展评估的有效方法之一。本文分析了金属裂纹扩展过程中材料的热耦合方程,使用ABAQUS软件进行直接热力耦合数值模拟,揭示了塑性功转化系数、拉伸速度对单轴拉伸载荷下含裂纹的Q235试件表面温度变化的影响规律,并基于红外热像仪测量试验得到了同数值模拟吻合度较高的结果,以此验证了此规律的正确性。结果显示,拉伸过程中试件表面温度经过平稳阶段、稳步上升阶段。裂纹扩展过程中,试件表面温度最高点位于裂纹尖端前方。同时拉伸速度越大,试件断裂时间短,裂纹扩展过程中热损失越小,试件表面温升越大。该结果对金属结构的裂纹监测和预警具有重要意义。     

激光冲击处理金属板材后的裂纹扩展速率

采用2.5 mm厚的铝合金LYl2(2024)T62、1.5 mm厚高强钢以及1.7 mm厚高温合金薄板制作成紧凑拉伸试件,对预制裂纹延长线进行三次搭接(光斑直径6 mm)激光冲击处理,进行裂纹扩展速率试验并与未处理的试件进行对比,由于激光冲击处理产生的强化效应在裂纹扩展路径上存在区域差别,所以裂纹扩展速率无法进行Paris公式拟合,但在整体上能大大降低裂纹扩展速率.     

激光喷丸强化CT试样疲劳裂纹扩展的数值研究

为了研究激光喷丸强化对疲劳裂纹扩展的影响,采用有限元分析软件ABAQUS和MSC.Fatigue相结合,以6061-T6铝合金CT件即紧凑拉伸试样为研究对象,数值模拟其经1次～3次激光双面喷丸处理后的残余应力大小、疲劳寿命、裂纹扩展速率及最终裂纹尺寸。在理论分析的基础上,建立面向抗疲劳制造的激光喷丸工艺有限元分析模型,首先在ABAQUS中模拟出激光喷丸诱导的残余应力场,再将其导入疲劳分析软件MSC.Fatigue进行激光喷丸后疲劳裂纹扩展及其性能的数值模拟分析。结果表明,激光喷丸处理可以有效抑制疲劳裂纹的扩展,降低裂纹扩展速率和增大最终断裂尺寸长度,从而达到延长疲劳寿命的目的,喷丸次数的增加在一定程度上增大了激光喷丸强化的效果,但增益的效果会减弱。这为激光喷丸强化抗疲劳制造的理论分析和后续试验提供了必要的依据。     

密质骨双裂纹反平面模型问题复变方法研究

文章构建密质骨双裂纹反平面模型,通过复变方法求解了该模型问题,并给出了裂纹尖端处应力及应力强度因子的解析表达式。数值算例分析了骨单元与基质的剪切模量比、裂纹尖端处与骨单元中心的距离和裂纹长度对裂纹尖端应力强度因子的影响。     

垂直于双压电材料界面裂纹的反平面问题研究

研究了双压电材料中垂直于界面裂纹的反平面问题。在裂纹面为可通导的边界条件下,通过对控制方程进行傅里叶(Fourier)变换,并利用边界条件将问题转化为奇异积分方程进行求解,得到了裂纹面的位移函数、裂纹尖端的应力强度因子、电位移强度因子和裂纹尖端能量释放率的表达式。数值分析了双压电材料的材料属性对裂纹尖端能量释放率的影响。     

涡流脉冲热像检测中金属疲劳裂纹的生热分析

涡流脉冲热像技术是一种将电磁生热和红外热成像相结合的新型无损检测技术.针对金属疲劳裂纹生热研究不深入的问题,本文以含有贯穿的疲劳裂纹金属平板试件为研究对象,搭建了涡流脉冲热像检测实验系统,并建立了涡流脉冲热像有限元模型,分析了涡流脉冲热像检测中裂纹生热的规律.研究结果表明:在红外热像中,同一时刻越靠近裂纹根部的位置,温升的最大值越大;在激励过程中,裂纹区域的温升逐渐升高,当激励结束时,裂纹区域的温升则具有逐渐下降趋势,并且呈现先迅速后缓慢的下降速度.进一步揭示了裂纹尺寸对裂纹区域温升的影响.     

Fatigue crack growth behavior in 63Sn-37Pb and 95Pb-5Sn solder materials

Fatigue crack growth behavior of two typical solders 63Sn-37Pb and 95Pb-5Sn has been investigated under room temperature (20°C) and frequency of 10 Hz. Fatigue crack growth behavior of the 63Sn-37Pb specimen tested at stress ratios up to 0.5 and the 95Pb-5Sn specimen tested at stress ratios up to 0.7 were dominantly cyclic dependent. Intergranular crack growth was observed for the 63Sn-37Pb specimen tested at stress ratio of 0.7, which indicates that a crack grows under influence of creep. The difference of effect of stress ratio on crack growth behavior between two solders may results from the difference of homologous temperature. Fatigue crack growth mechanisms for solder materials are summarized as follows: A crack propagates in a transgranular manner at low homologous temperature and low stress ratio, while it propagates along eutectic grain boundaries at high homologous temperature and high stress ratio under influence of creep. At the intermediate homologous temperatures, a crack propagates in a transgranular manner with some region of intergranular fracture.     

直接金属选区激光烧结热应力场有限元模拟

在考虑随温度变化而变化的热传导、比热容等热物性参数的作用下,建立了直接金属多道烧结的三维有限元分析模型。采用先进行温度场分析、再进行应力场分析的间接热力耦合策略。模拟结果显示,随着烧结过程的进行,由于已烧结部分的影响,最大热应力有减小的趋势;在扫描烧结道的前方有比后方更大的应力分布,这与实验结果相吻合。     

超声红外热像技术中金属平板裂纹的生热特性

超声红外热像技术是一种新型无损检测技术,缺陷区域生热特性的研究有利于最优化检测方案的制定。实验分析表明:超声激励作用于含贯穿裂纹的金属平板时,与激励同侧的裂纹区域温度升高比异侧更明显,但裂纹面总体的生热效率稳定。针对上述实验现象,采用显式有限元方法建立了与实验系统对应的仿真模型,进行了机热耦合分析。在仿真模型中,采用压电-力类比方法模拟超声换能器的逆压电效应,并引入动态松弛模拟预紧力对被测平板初始状态的影响。仿真与实验结果得到了一致的裂纹区域温度分布和裂纹面生热规律,建立了裂纹面生热效率与裂纹面摩擦力及相对运动速度之间的联系,揭示了工具杆和被测平板之间的预紧力使裂纹面接触状态改变是裂纹生热向激励同侧偏移的直接原因。     

填充不流动胶的倒装焊封装中芯片的断裂问题

用断裂力学方法和有限元模拟分析了填充不流动胶芯片断裂问题 .模拟时在芯片上表面中心预置一裂缝 ,计算芯片的应力强度因子和能量释放率 .模拟表明 ,由固化温度冷却到室温时 ,所研究的倒装焊封装在填充不流动胶时芯片断裂临界裂纹长度为 12 μm,而填充传统底充胶时为 2 0 μm.模拟结果显示芯片断裂与胶的杨氏模量和热膨胀系数相关 ,与胶的铺展关系不大 .焊点阵列排布以及焊点位置也会影响封装整体翘曲和芯片断裂 .     

Analysis of Cu-wire pull and shear test failure modes under ageing cycles and finite element modelling of Si-crack propagation

In microelectronic packaging, wire bonding is the predominant method for making electrical connections. Copper is increasingly substituting gold as interconnection material since it is a much cheaper alternative and it also offers several physical advantages.Adequate and reliable mechanical integrity of the connection is usually checked by process controls based onto “wire pull” and “ball bond shear” tests. In this paper the two methods are compared in terms of sensitiveness in detecting a latent weakness of the bond-pad structure, either induced by inappropriate wire bonding process or cumulated during reliability ageing. The failure modes (in terms of frequency and maximum test load) observed at the ball bond interface have been investigated on two different batches of a same chip, obtained from different wire-bonding recipes and including both unstressed and aged units. Cross-sections of the samples, submitted to pull and shear both in destructive and non-destructive tests, have allowed us to investigate the relationship between the bond morphological characteristics (metal deformation and potential micro-damages induced by copper bonding) and the weak points for fracture propagation inside the bond-pad inner layers and the silicon substrate.Besides the experimental activities, fracture mechanics and the finite element method have been employed to model the pull and shear tests. The aims of the finite element modelling have been to predict the reduction of test maximum load in defective ball bonds and the crack growth angle adopting a mixed-mode criterion. Good results have been obtained by the numerical fracture analysis, which can then support the reliability characterization and mechanical improvement of the bond.     

高重复率下硅酸镓镧电光晶体压电特性有限元分析

介绍了在高重复率高电压的载荷下,以硅酸镓镧为例的电光晶体的压电特性。建立了电光晶体的有限元模型,并基于有限元数值方法,模拟分析了在固定和自由边界条件下硅酸镓镧晶体由逆压电效应产生的应变及应力。结果表明:自由边界条件下的晶体形变是呈线性变化的;固定边界条件下晶体有明显的位移变化,且其形变相对于晶体中心处呈对称分布,由于加在晶体的电压数值分布不同,晶体周围区域比中心区域的形变更为严重。晶体在自由边界条件下产生的应力远远小于固定边界条件下产生的应力。     

Phase coarsening and crack growth rate during thermo-mechanical cycling of 63Sn37Pb solder joints

The effects of phase coarsening in 63Sn37Pb solder joints produced by isothermal annealing and during thermo-mechanical cycling (TMC) on the fatigue cracked area growth rate dA_c/dN were investigated. The phase coarsening by isothermal annealing was in accord with the mechanism of interphase boundary diffusion; that during TMC was significantly greater than by isothermal annealing. The phase coarsening in the range considered (D=1–5 μm, N<150 cycles) had only little, if any, influence on dA_c/dN, which occurred mainly in Stage I of the fatigue crack growth rate regime. Results obtained previously, however, indicate that for N>150 cycles dA_c/dN is significantly decreased by a reduction in the as-reflowed phase size. Reasonable agreement occurred between the calculated fatigue lifetime vs initial as-reflowed phase size and that measured.     

微尺度BGA焊点拉伸过程有限元仿真分析

建立了微尺度 BGA焊点拉伸有限元分析模型,研究了拉伸加载条件下焊点高度、直径和焊盘直径对焊点拉伸应力应变的影响。结果表明：拉伸条件下,微尺度 BGA焊点顶端和底端的应力应变要大于焊点中间部分,焊点顶部和底部位置为高应力应变区域;在只单一改变焊点高度、直径和焊盘直径其中之一的前提下,随着焊点高度、直径和焊盘直径的增加,微尺度BGA焊点内的最大应力应变均相应减小;在置信度为90%的情况下,焊点直径对拉伸应力影响最大,其次是焊盘直径,最后是焊点高度;焊点直径对焊点拉伸应力具有显著影响,焊盘直径和焊点高度对焊点拉伸应力影响不显著。     

Finite element analysis of the cogging force in the linear synchronous motor array for the Thirty Meter Telescope

In this paper, a finite element analysis of the cogging force generated by an array of linear synchronous motors (LSM) moving on a curvilinear track is presented. This system is under consideration as the driving system for the two main axes of the proposed Thirty Meter Telescope that will be built in Mauna Kea, Hawaii. The main objective of this work is the quantification of the effects of the curvilinear track of LSM arrays on the cogging force. The finite element analysis is carried out using planar cross sections, and the results found are used to find an approximate solution for the three-dimensional model. The results show that the presence of the curvilinear-configured track increases the cogging force of a single LSM significantly, while the presence of the array of LSMs interacts in limiting the increase in the cogging force. A geometric optimization in regards to the relative positions of the LSMs along the curvilinear tracks is subsequently carried out in order to reduce the total cogging force.