气孔缺陷位置对SMT焊点热疲劳寿命影响的数值分析

通过用统一的粘塑性本构方程描述SMT焊点的力学行为，对气孔缺陷在SMT焊点中不同位置的情况建立二维有限元分析模型，并采用有限元方法分析了气孔位置对SMT焊点疲劳寿命的影响。分析发现，与无缺陷焊点相比，气孔使焊点中应力应变分布发生了改变，使焊点疲劳寿命缩短；焊角、焊趾和焊点中部位置的气孔对焊点中的应力应变和焊点的疲劳寿命影响较小，而焊点根部气孔的影响则显著。     

基于反求修正模型技术的装载机板焊桥壳疲劳寿命分析

以装载机板焊驱动桥壳为研究对象,首先利用反求技术对所建有限元模型的关键部位进行修正,然后运用有限元分析软件ANSYS对其进行强度分析,并将强度分析的结果导入根据名义应力法和局部应力-应变法所编制的疲劳寿命计算软件中,对装载机板焊桥壳的疲劳寿命进行求解,所得结果与桥壳疲劳寿命台架试验数据较为接近,表明通过基于反求修正模型技术的装载机板焊桥壳疲劳寿命分析方法提高了有限元分析模型的精度,增加了分析数据的可靠性。     

基于多因素修正的超越离合器保持架疲劳寿命分析

以超越离合器保持架为研究对象,针对其交变载荷作用下易发生疲劳断裂的现状,首先利用有限元分析手段获得其模拟载荷谱,然后建立残余应力修正载荷谱的数学模型并在此基础上完成模拟载荷谱的修正,最后将修正后的分析载荷谱及材料的疲劳性能参数导入多因素修正后的名义应力法疲劳寿命计算软件中,对保持架的疲劳寿命进行求解,并通过台架试验加以验证。通过对比数值分析与试验可以发现结果基本吻合,基于多因素复合修正的疲劳寿命分析方法不仅增加了分析数据的可靠性,而且为零件疲劳寿命预估提供了新的技术路径。     

考虑修正平均等效应力强度因子的焊点缺陷疲劳寿命研究

提出了一种基于超声回波的焊点缺陷疲劳寿命预测评价方法。该方法采用模糊数学理论，基于超声回波特征获得损伤系数，然后综合考虑法向应力、剪切应力和初始缺陷的影响，将焊点缺陷在裂纹扩展路径上的修正平均等效应力强度因子作为疲劳评价的参量。通过对DP600GI材料的合格焊点、焊核过小焊点和烧穿焊点的接头进行疲劳试验，比较不同缺陷对焊接疲劳寿命的影响，得到一条修正平均等效应力强度因子与疲劳寿命的拟合曲线作为含初始缺陷的焊点疲劳寿命预测曲线，研究结果表明，该曲线能有效预测含初始缺陷的点焊接头的疲劳寿命。该方法有助于合理设计电阻点焊的缺陷容限。     

基于残余应力修正疲劳强度原理的桥壳疲劳寿命分析

以装载机板焊驱动桥壳为研究对象,首先建立桥壳的有限元分析模型,然后运用有限元分析软件ANSYS对其进行强度分析,建立残余应力-疲劳强度修正数学模型,并将运用X射线残余应力测试技术测量所得的桥壳残余应力通过修正数学模型进行强度分析的结果修正,最后将强度修正结果导入根据基于残余应力修正的应力-寿命数学模型编制的名义应力法和局部应力应变法疲劳寿命计算软件中,对桥壳的疲劳寿命进行求解,所得结果与桥壳疲劳寿命台架试验数据较为接近,表明通过基于残余应力修正疲劳强度原理的装载机板焊桥壳疲劳寿命分析方法增加了分析数据的可靠性。     

基于某电动汽车电池箱焊点的疲劳寿命预测与优化

基于焊点疲劳寿命预估理论,联合HyperMesh和Abaqus软件对某电池箱进行定频振动分析,得到响应的应力结果;在nCode软件中关联有限元载荷工况与时间历程,结合焊点材料的疲劳特性和Miner线性累积损伤法则计算得出焊点的疲劳寿命,并与试验破坏情况进行对比,验证了电池箱焊点疲劳寿命分析方法的有效性。同时对电池箱的焊接薄弱区域进行焊点优化布置,提高了焊点整体的疲劳寿命。     

某型飞机单机寿命监控技术研究

用一类疲劳危险部位的寿命代替全机疲劳寿命的方法,对某型飞机的寿命做了定量分析,并基于考虑材料记忆特性的局部应力应变法,对某型飞机的疲劳危险部位进行了标准谱下的寿命计算,计算结果与试验结果较吻合。最后采用局部应力应变法及修正的Manson-Coffin公式,得到了基于飞参数据载荷谱的某型飞机危险部位的实际寿命,并与基于标准谱的疲劳寿命做了对比,为某型飞机的单机寿命监控奠定了基础。     

BGA结构无铅微焊点的低周疲劳行为研究

基于塑性应变能密度概念提出微焊点低周疲劳裂纹萌生、扩展和寿命预测模型,阐明其与连续介质损伤力学的联系,评估应力三轴度对预测模型的影响,并通过试验和数值计算相结合的方法确定出微米尺度球栅阵列(Ball grid array,BGA)结构单颗Sn3.0Ag0.5Cu无铅焊点(高度为500～100 μm,焊盘直径为480 μm)疲劳裂纹萌生和扩展模型中的相关常数。研究结果表明,疲劳裂纹萌生和扩展循环数与每个循环所产生的塑性应变能密度均呈幂函数关系;应力三轴度会影响疲劳裂纹扩展速率,并最终影响焊点的疲劳寿命;应力三轴度与加载方式有关,拉伸载荷下焊点的应力应变行为受异种材料界面和封装结构力学约束作用的影响,应力三轴度随焊点高度降低而明显升高;而剪切载荷作用下焊点中的力学约束十分有限,焊点高度变化对应力三轴度的影响非常小;测得的高度为100 μm焊点的疲劳裂纹扩展相关常数可以很好地用于预测其他不同高度焊点的疲劳寿命,表明所提出的预测模型可以有效地减小由几何结构和体积变化造成的塑性应变能集中现象对焊点疲劳寿命的影响。     

7075/2A12异种铝合金搅拌摩擦焊搭接接头疲劳寿命预测研究

对7075/2A12异种铝合金搅拌摩擦焊搭接接头进行了疲劳加载测试,并观察了疲劳断口特征。根据实际试件结构建立局部应力应变法和缺口应力法有限元模型,对焊缝区域进行应力应变分析;结合Soderberg修正方程对Manson-Coffin(MC)模型中应力部分进行修正,再根据有限元分析结果,使用局部应力应变法和缺口应力法对异种铝合金搅拌摩擦焊搭接接头进行疲劳寿命预测。试验结果表明,有效搭接厚度严重影响试件的疲劳寿命;位于受载7075前进侧的钩状缺陷比7075后退侧钩状缺陷对疲劳寿命的影响大。与试验结果相比,局部应力应变法中,2组试件最小板厚处疲劳寿命的预测结果都要比钩状缺陷根部处疲劳寿命的预测精度高。部分试件结合Soderberg方程修正的MC模型预测误差大部分都在2个因子之内,而Smith-Watson-Topper(SWT)模型和其他MC修正模型预测结果均在3个因子之内,Sachs修正的MC模型和Morrow修正的MC模型的预测结果相近;缺口应力法中,部分试件预测结果较好,误差在2个因子之内。     

PCB组装板多器件焊点疲劳寿命跨尺度有限元计算

随着电子设备向着小型化、多功能化方向发展,互连的可靠性越来越受到人们的重视。现有研究的分析对象大多为单个器件,而实际服役过程中,印制电路板(Printed circuit board,PCB)的形变、传热、受力情况都将对焊点可靠性产生影响。传统焊点可靠性有限元分析以单一器件为基础,而将仿真对象扩展为整个PCB板,对于提升焊点可靠性评估的准确性和有效性具有重要的意义。利用ANSYS有限元软件,对处于不同尺度的焊点、器件以及PCB板进行建模,分析再流焊载荷下各器件焊点的残余应力应变分布,讨论热循环后各器件焊点的危险位置,并根据修正的Coffin-Manson模型,给出各封装类型焊点的热循环寿命。通过与器件级焊点可靠性模拟结果的对比,说明板级有限元分析的必要性和不可替代性,进一步完善焊点可靠性有限元分析理论。     

MECHANICAL PROPERTIES OF FINE PITCH DEVICES SOLDERED JOINTS BASED ON CREEP MODEL

Nonlinear analyses of quad flat package （QFP） on printed circuit board （PCB） assemblies subjected to thermal cycling conditions are presented. Two different solders are considered, namely, Sn37Pb and Sn3.5Ag. The stress and strain response of fine pitch devices soldered joints was investigated by using finite element method based on Garofalo-Arrheninus model. The simulated results indicate creep distribution of soldered joints is not uniform, the heel and toe of soldered joints, the area between soldered joints and leads are the creep concentrated sites. The similar phenomena of stress curves simulated based on Garofalo-Arrheninus model and Anand equations is confirmed, and the creep strain value of Sn3.5Ag soldered joints is lower than that of Sn37Pb soldered joints. Thermal cycling results show that Sn3.5Ag strongly outperforms Sn37Pb for QFP devices under the studied test condition. This is well matched with the experimental outcome analyzed. In addition, the soldered devices were tested by micro-joints tester, the tensile strength of Sn3.5Ag soldered joints is found to be higher than that of Sn37Pb soldered joints. By analyzing the fracture microstructure of soldered joints, it is found that fracture mechanism of Sn3.5Ag soldered joints is toughness fracture, while fracture mechanism of Sn37Pb soldered joints includes brittle fracture and toughness fracture. The results of this study provide an important basis of understanding the mechanical properties of fine pitch devices with traditional Sn37Pb and Sn3.5Ag lead-free soldered joints.     

SMT软钎焊接头热循环力学行为研究

应用粘背景性理论分析研究了SMT软钎焊接头热循环力学行为,并用热膨胀模拟加载试样进行了试验验证。研究结果表明：SMT软钎焊接头在热循环过程中的应力由全部热循环的温度历史决定,时间效应（变温速率、保温时间等）对软钎焊接头在热循环中的力学行为具有显著影响。随热循环温度升高和保温时间延长,钎焊接头内将发生显著的应力松弛。     

EFFECTS OF LEAD WIDTHS AND PITCHES ON RELIABILITY OF QUAD FLAT PACKAGE （QFP）SOLDERED JOINTS

The finite element method(FEM)is used to analyze the effects of lead widths and pitches on reliability of soldered joints.The optimum simulation for QFP devices is also researched.The results indicate that when the lead pitches are the same,the maximum equivalent stress of the soldered joints increases with the increasing of lead widths,while the reliability of the soldered joints reduces. When the lead widths are the same,the maximum equivalent stress of the soldered joints doesn't decrease completely with the increasing of lead pitches,a minimum value of the maximum equivalent stress values exists in all the curves.Under this condition the maximum equivalent stress of the sol- dered joints is relatively the least,the reliability of soldered joints is high and the assembly is excel- lent.The simulating results indicate the best parameter:The lead width is 0.2 mm and lead pitch is 0.3 mm(the distance between two leads is 0.1 mm),which are benefited for the micromation of QFP devices now.The minimum value of the maximum equivalent stress of soldered joints exists while lead width is 0.25 mm and lead pitch is 0.35 mm(the distance between two leads is 0.1mm),the devices can serve for a long time and the reliability is the highest,the assembly is excellent.The simulating results also indicate the fact that the lead width is 0.15 mm and lead pitch is 0.2 mm maybe the limit of QFP,which is significant for the high lead count and micromation of assembly.     

Anand Parameters Determination for SnAgCu Solder Bearing Micro-amounts Rare Earth Ce

SnAgCu solder system with the addition of rare earth Ce,which has better thermo-mechanical properties compared to those of SnPb solder,is regarded as one of the promising candidates for electronic assembly.Moreover,the SnAgCuCe solder alloys can provide good quality joints with Cu substrates.However,there is few report of the constitutive model for SnAgCu solder beating micro-amounts rare earth Ce.In this paper,the unified viscoplastic constitutive model,Anand equations,is used to represent the inelastic deformation behavior for SnAgCu and SnAgCuCe solders.In order to obtain the acquired data for the fitting of the material parameters of this unified model,a series of experiments of constant strain rate test were conducted under isothermal conditions at different temperatures.The Anand parameters of the constitutive equations for SnAgCu and SnAgCuCe solder were determined from separated constitutive relations and experimental results.Nonlinear least-square fitting was selected to determine the model constants.And the simulated results were then compared with experimental measurements of the stress-inelastic strain curves:excellent agreement was found.The model accurately predicted the overall trend of steady-state stress-strain behavior of SnAgCu and SnAgCuCe solders for the temperature ranges from 25℃ to 150℃,and the strain rate ranges from 0.01 s-1 to 0.001 s-1.It is concluded that the Anand model can be applied for representing the inelastic deformation behavior of solders at high homologous temperature and can be recommended for finite element simulation of the stress-strain response of lead free soldered joints.Based on the Anand model,the investigations of thermo-mechanical of SnAgCu and SnAgCuCe soldered joints in fine pitch quad flat package by finite element code were done under thermal cyclic loading,it is found that the reliability of SnAgCu soldered joints can be improved remarkably with addition of rare earth Ce.The results may provide a theory guide for developing constitutive model for lead-free solders.     

The development of the physical fundamentals of contact soldering as a factor for reducing the number of defects in electronic devices

Automated control systems employ electronic components that are connected with a printed circuit board (PCB) by soldered joints. At elevated temperatures and with high vibration levels, soldering defects may occur that are characterized by the deterioration or complete loss of contact with the PCB, which can lead to the failure of the system. In this work, an approach is proposed to considerably improve the reliability of soldered joints.     

Reliability Evaluation of QFN Devices Soldered Joints with Creep Model

The solder joint reliability of quad flat non-lead (QFN) package,which has become very popular over the past few years,has received intense interest.The finite element method (FEM) is essential to evaluate the reliability of QFN device.In this paper,Garofalo-Arrheninus model was implemented to simulate the deformation of QFN soldered joints.Equivalent creep strain of the soldered joints was calculated by means of finite element analyses,and was used to evaluate the reliability of QFN packages.It is found that the critical soldered joint of QFN is located the package corner while the maximum creep strain is obtained at the top interface of peripheral soldered joint.The creep strain is provided with periodicity and additivity as the thermal cycling.Nonlinear analysis of QFN package with different lead counts was presented as well,in which the phenomenon that the value of induced creep strain arise as the package size decreasing is noted.Moreover,SnPb and two lead-free solders,namely,Sn3.5Ag/Sn3.8Ag0.7Cu,were both taken into consideration.Simulated results indicate that the creep strain value of lead-free soldered joints is lower than that of SnPb soldered joints,which can be attributed to the difference of stiffness and coefficient of thermal expansion among three solders.Garofalo-Arrheninus model is used to calculate the creep strain of the QFN device for the first time in this study.The results provide an important basis for evaluating the reliability of QFN package.     

The reliability of soldered joints produced at a low temperature

Under severe service conditions of electronic instruments (at elevated temperatures and vibrations in electronic systems), failures in their operation frequently occur. Severe intrinsic thermal conditions of operating instruments may cause such failures. However, malfunctions in electronic devices may often be due to defects in soldered joints that were made at lowered temperatures. An approach is proposed that makes it possible to considerably improve the reliability of soldered joints.     

Eddy-current quality control of soldering of current-carrying joints in electrical machines. I. General principles

The possibility of testing the electrical conductivity of soldered joints using and eddy-current transducer has been studied. The simplest model calculations allowing evaluation of the relative value of a signal from an inhomogeneity depending on its location inside a specimen are presented. It is shown that signals yielded by an eddy-current transducer are quite informative for determining the quality of soldering of current-carrying joints.     

Improving the Reliability of Eddy-Current Quality Control of Soldering in Current-Carrying Copper Joints and Expanding the Nomenclature of Inspected Joints in Energy Equipment

The possibilities of increasing the reliability of eddy-current quality control of soldering in current-carrying copper joints of the stator windings of electrical machines and expanding the nomenclature of inspected joints by using an improved eddy current transducer with a U-shaped core are investigated. To achieve this goal, rectangular cutouts were made in the poles of the U-shaped core, made of transformer steel plates, to allow the transducer to be mounted on a tested solder joint in two mutually perpendicular directions. Using such a transducer for testing allows one to induce closedloop eddy currents in the solder joint along these two directions, thus significantly improving the reliability of testing by virtue of all soldered surfaces in the joint contributing to the eddy-current transducer signal. The use of such a transducer also significantly expands the range of tested joints due to the possibility of exciting closed-loop eddy currents perpendicular to the direction of such joints (testing the side walls of the joints). It is shown that despite local changes in the distribution of electromagnetic field in the interpole space as compared to the case of no cuts, the presence of rectangular cuts in the poles of the U-shaped core of the eddy current transducer practically does not affect the accuracy of determining the degree of soldering of tested joints along and perpendicular to their direction.

     

Mechanical Properties of QFP Joints Soldered with SnAgCu and SnPb Solders

With the development of lead-free solder alloys, the investiagtion focusing on the relibility of lead-free solders are essential. Since the reliability database of lead-free solder joints needs to be further supplied, the creep behavior of SnAgCu soldered joints on Quad Flat Package (QFP) devices under thermo cycling load are studied in this paper, compared to conventional SnPb solder, by finite element simulation based on Garofalo-Arrhenius creep model. Meanwhile, the mechanical properties of SnAgCu and SnPb soldered joints in the pitches of QFP devices are also carried out by means of tensile test. The results indicate that the values of strain and stress of SnAgCu soldered joints were all smaller than those of SnPb under thermal cycling, and the tensile strength of the joints soldered with SnAgCu solder was higher than that of SnPb, which means the reliability of the joints soldered with SnAgCu solder is better than SnPb soldered joints. As the fracture surface morphology of the soldered joints compared, SnAgCu soldered joint presented ductile fracture, while the fracture mechanism of SnPb solder joints displayed both brittle and ductile fracture. Above all, the experimental results is in accord with that of simulation, which will provide guidance for reliability study and application of lead-free solders.