人工神经网络在激光涂层多冲碰撞疲劳寿命预测中的应用

运用人工神经网络技术,采用激光涂层多冲碰撞寿命试验数据和专家数据相结合,以涂层材料、基体材料、涂层厚度和应力水平为输入因子建立疲劳寿命的预测模型,该模型精度较高,可为今后激光涂层多冲碰撞疲劳试验结果的预测提供理论根据。     

多冲碰撞载荷下激光涂层的接触损伤分析

进行了激光熔覆试件的多冲碰撞试验,并对多冲碰撞接触疲劳损伤的表象和机理进行 了微观分析。观察到多冲碰撞载荷下试件表面的微观点蚀较为普遍;接触疲劳点蚀深度大约为0. 05～0. 1mm或更浅,比一般滚动或滚滑接触疲劳的点蚀坑浅得多。激光涂层多冲碰撞表面点蚀剥落一般在较小的应力下发生,裂纹萌生周期较长;而表面剥层一般在较大应力下发生,裂纹萌生周期较短。     

多冲载荷下激光熔覆涂层裂纹机理分析

为了研究激光熔覆涂层在小能量多冲载荷下抗裂性能,进行了激光熔覆涂层在小能量多冲载荷下作用的多冲试验,结果显示激光熔覆涂层出现裂纹损伤失效现象,裂纹形式的特征有明显差异,表现为横断裂纹和边缘裂纹.根据裂纹的不同特征,进行了裂纹形成的理论分析,其结论在实验中得到了验证.     

多冲载荷下表面涂层覆盖形式与基体开裂

对在多冲碰撞载荷下的激光厚涂层试件进行试验，发现涂层在基体上的全覆盖形式比部分覆盖形式的极限应力要低，但在相同多冲应力作用下寿命长。后者的基体在涂层覆盖区边缘下部会出现强烈的形变硬化与材料流动现象，同时此处容易产生裂纹并扩展，造成涂层脱落。     

多冲循环下激光涂覆件的形变硬化与软化

在多冲碰撞峰值应力仅为激光涂覆件涂层与基体材料静屈服强度的1 /10～1 /6和1 /2～3 /4的试验条件, Co基、Ni基涂层及碳钢、不锈钢基体均产生了多冲累积宏观形变硬化或软化,其变形率最大达到9. 4% ,形变硬化程度由表及里呈衰减趋势,且仅在一定深度上发生。涂层硬度在500HV以下时多冲后以硬化为主; 550HV左右时随硬度高低变化对应出现软化或硬化,随冲击次数增加可能出现循环软化或硬化。低应力多冲宏观硬化软化是材料在多冲碰撞载荷下的一种特有性能。     

基于虚拟样机技术的货车车架疲劳寿命预估

汽车车架是汽车底盘中主要的受力部件,承受着各种方向和形式的载荷,其主要的损伤形式是在交变载荷作用下发生的疲劳失效。为了准确预测车架结构的疲劳寿命,将有限元分析与多体动力学仿真结合,建立了整车多体动力学模型,并根据中国路况进行仿真,得到相应的载荷谱;建立了车架的有限元模型并进行强度分析,在此基础上根据车架材料的疲劳性能数据和以上载荷历程利用有限元分析软件进行了车架的疲劳寿命分析,得到了车架的疲劳寿命分布情况以及容易发生疲劳失效的位置,结果表明,车架的强度和疲劳寿命均设计要求。     

激光点状合金化对42CrMo钢疲劳裂纹扩展速率的影响

裂纹倾向严重和搭接区软化是激光表面强化技术面临的两大难题,为此,提出了一种激光点状合金化方法:使预涂在基体表面的合金涂层或由喷嘴送入的合金粉,在激光小孔效应作用下,与基体形成混合熔池,得到合金化点。研究表明,大量规则分布、互不重叠的合金化区及其周围的相变硬化区从总体上降低了疲劳裂纹扩展速率,提高了材料的疲劳寿命。对疲劳裂纹断口的初步分析显示,相变硬化区对阻滞裂纹扩展其到了重要作用。     

激光涂层零件的多冲碰撞形变效应与分析

报道了多冲碰撞载荷下激光涂层零件塑性变形现象。利用坐标网格法、显微分析法等分析了激光涂层零件的多碰累积变形现象和规律。这种塑性变形在常温即可发生,且具有低应力和累积特性。变形发生在涂层表面及以下一段区域内,并由大到小呈梯度变化。碰撞能量驱动、冲击温升效应、晶界滑动与迁移、亚结构的形成与孪晶等,是引起多碰累积变形的可能原因。     

激光熔覆Ni-2涂层在冲击载荷下失效机理研究

采用冲击碰撞载荷,对奥氏体不锈钢表面激光熔覆镍基合金涂层进行冲击试验,涂层与基体都产生了微塑性变形,反复作用可产生累积宏观塑性变形,从涂层到基体都出现了均匀的形变硬化现象。在涂层覆盖区边缘下部会出现强烈的形变硬化与材料流动现象,同时此处容易产生裂纹并扩展。     

半导体器件金铝键合的寿命研究

金铝键合失效是MOSFET器件常见的失效模式之一,主要是由于金属间化合物的生成,影响了金铝键合的接触电性能,从而导致键合强度下降,接触电阻升高。针对这种失效模式,进行了三种不同高温条件下的加速寿命试验,并对这三种试验的器件进行金铝键合现象观察,对目前工艺水平下的金铝键合寿命进行了评估。     

Board level reliability of PBGA using flex substrate

Assurance of board level reliability is necessary and required for adopting any new packages into products. This paper presents board level reliability test results of a flex substrate BGA under thermal and bend cyclic tests. It is well known that solder joint reliability is affected by many factors, such as the size of chip, joint stand-off height, pad design, test board surface finish, substrate gold plating thickness and the utilization of underfill material, etc. However, most of the works have been conducted are BGA on rigid substrates. In this work, thermal cyclic test is performed to re-examine these factors using package housed on a flex substrate. Bending test with two deflections is also performed to investigate solder joint fatigue life and failure modes under mechanically repetitive loading.Two-parameter Weibull model is used to analyze joint fatigue life. Failure analysis is conducted and discussed for each case. Under temperature cycling test, chip size, polyimide thickness and underfill material utilization were found to have significant impacts on joint fatigue life, especially the effect of applying underfill material to the joint. Epoxy thickness was found to have little effect on the joint fatigue life for this case.The effects of test board surface finish and substrate gold plating thickness on the joint fatigue life were found coupled. The term “substrate” here refers to the chip carrier, while the “board” here refers to motherboard, which is the board to assemble test vehicles on. The gold thickness here all refers to the electrolytic gold plating on the substrate. Using organic solderability preservative boards, substrate gold plating thickness affects joint fatigue life slightly, but with Au–Ni test boards, the effect is tremendous. The difference is due to different intermetallic compounds (IMC) formed. In other words, different IMC systems are formed due to different combination of test board surface finish and substrate gold plating thickness. As a result, different IMC induces different failure modes. The joint fatigue life under cyclic bend test with different deflections is also probed and shown. The corresponding failure modes are also discussed.     

通信用光纤可靠性影响因素分析

光纤的可靠性是保证光网络寿命的关键,可靠性由光纤的强度分布和疲劳行为共同决定.应用光纤的强度分布数据和蒙特卡洛方法,分析了筛选强度、应力腐蚀敏感性参数和载荷水平等因素对光纤可靠性的影响.分析结果表明,筛选强度的提高可改善筛选后光纤的强度分布,但同时会导致部分筛选后光纤的强度明显降低;按照基于幂定律理论的光纤疲劳行为模型...     

激光熔覆对铝合金疲劳性能的影响

对模拟腐蚀损伤的铝合金试样表面进行了激光熔覆填充处理,分析了激光熔覆层的显微组织,并对熔覆试样和基材试样进行了疲劳寿命对比实验。结果表明,表面激光熔覆会显著降低材料的疲劳性能,在99%可靠度的前提下,熔覆试样的安全寿命比基材试样有所降低。其主要影响因素有熔覆层底部的枝晶、重熔区内的缺陷和熔覆层内的拉应力。经过表面机械冲击后,疲劳性能得到显著提高,提高幅度为244%,疲劳断口形貌表明,熔覆层有明显的疲劳特征。     

CSP封装Sn-3.5Ag焊点的热疲劳寿命预测

对芯片尺寸封装(CSP)中Sn-3.5Ag无铅焊点在热循环加速载荷下的热疲劳寿命进行了预测.首先利用ANSYS软件建立CSP封装的三维有限元对称模型,运用Anand本构模型描述Sn-3.5Ag无铅焊点的粘塑性材料特性;通过有限元模拟的方法分析了封装结构在热循环载荷下的变形及焊点的应力应变行为,并结合Darveaux疲劳寿命模型预测了无铅焊点的热疲劳寿命.     

The effect of model building on the accuracy of fatigue life predictions in electronic packages

Empirical fatigue life models such as the Coffin–Manson rule and its variants are commonly used at the present time to predict the reliability of microelectronic packages. While there have been reports of substantial error in empirical correlations relative to the experiments, this has not been accompanied by a rigorous understanding of the sources of the error. In this paper we systematically explore the various modeling errors in the fatigue life prediction. These errors include those in geometry representation, material behavior, load history and boundary condition application, and in the numerical solution procedure. As part of the study, experimentally validated correlations between temperature cycling and power cycling are developed for a TI 144 chip-scale package. The accuracy of the predicted life under power cycling conditions compared to the experimentally determined life is used as the basis for judging the model accuracy. The criticality of spatial refinement, temporal refinement, and accurate boundary conditions, including the often ignored natural convection boundary conditions, and their effect on predicted life is described in detail. It is shown that model errors can be a significant part of both the constitutive life models and the application models that use the constitutive life models to predict the fatigue life under a given environmental condition. It is also shown that with careful model building, solutions accurate to within 3% can be obtained.     

Reliability model for Al wire bonds subjected to heel crack failures

In power electronic packages wire bonding is used for the electrical contact of the chips and for interconnections on the module substrate. Limiting factors for the reliability are solder fatigue and wire bond failures. In this work we investigate the material fatigue of aluminum bonding wires stressed by cyclic lateral bonding area displacement. Bond wire heel crack failures observed by experiments are found to be strongly dependent on the loop geometry. Based on a finite element model that accounts for elastic-plastic material properties, a life-time model for the Al wire (Coffin-Manson representation) is derived from the experiments.     

层间粘接剂对刚挠板通孔可靠性的影响分析

在刚挠结合印制板中,层间不同粘接材料的热性能与镀层差异较大时,在热循环的条件下孔内镀层会发生疲劳断裂从而导致电性能缺陷。以两种典型的层间材料(不流动半固化片和纯胶片)为例,对影响PTH孔铜可靠性的材料特性因素方面进行探讨,首先采用一定的通孔应力应变模型理论分析通孔的应力分布,进而结合通孔的失效评估模型理论计算了不同材料下不同孔径的通孔的疲劳寿命,确定了不同介质材料下通孔的耐热循环性能;最后,通过冷热循环试验进行验证,对比出两种层间材料的差异,同时,通过对失效板件进行切片及SEM形貌分析,提出了PTH在热冲击下的失效原因和机理,获得了材料选择和性能对比的依据。     

An optimal structural design to improve the reliability of Al2O3–DBC substrates under thermal cycling

An optimal structural design of direct bonding copper (DBC) substrate with ladder shaped copper layers was proposed through numerical optimization approach in this paper. In order to study the fatigue mechanism and life, thermal–mechanical stress and strain distributions of DBC substrates under thermal cycling ranged from − 55 °C to 150 °C were simulated and analyzed by finite element (FE) method. Improved Coffin–Mason law was applied to calculate the fatigue life under thermal cycling, Chaboche constitutive model with non-linear kinematic hardening was used to describe the elastic–plastic behavior of ductile copper. Design of experiment method was applied to investigate the sensitivity of geometric parameters on the thermal–mechanical performance. The ladder shaped DBC substrate design with specific designed copper ladder thickness was demonstrated to be robust. The fatigue life of proposed design was about three times longer than the traditional one under thermal cycling test. Moreover, the length of edge tail of the second copper ladder played an important role on the fatigue life. The lifetime of the substrate can be improved by the increase of edge tail length. The simulated results of the DBC substrate fatigue life were verified by experimental results.