组件温度筛选应力的确定方法

分析了目前国内在组件温度筛选方面的一般做法，吸收国外加速试验的经验，并借鉴定量筛选中根据成效率确定无故随检验时间的方法，提出了组件温度筛选中各参数(如温度范围、温度变化速率、高低温保持时间和循环数)的确定方法，并以一种税控加油机主板的温度筛选为例，介绍了组件温度筛选方法研究中所总结的一些经验。     

焊点的失效模式与分析

焊点疲劳寿命通常是通过电子组件进行温度循环加速试验来确定.针对典型元器件进行温度循环试验,在不同的循环周期检查焊点的开裂情况,并采用金相分析观察焊点的显微组织,分析焊点在温度循环条件下的失效模式,为改进工艺参数提供依据.     

矿用仪器老化试验方法探讨

本文从矿用仪器的特殊性出发，探讨了矿用本质安全型仪器的元器件和整机老化试验方法。确定了温度老化试验参数，即试验温度、温变速率和温度时间与循环次数。文章介绍了温度老化装备的技术指标，给出了矿用仪器温度试验流程。采用文中的方法和流程，能够提高矿用仪器的可靠性，使仪器的故障率降至随机故障水平。     

组件类产品环境应力筛选试验研究与应用

基于目前国内电子产品ESS(环境应力筛选)依据《GJB1032—90电子产品环境应力筛选方法》中有关温度循环和随机振动试验的普遍做法,介绍了在研制和生产阶段开展ESS的目的和基础,讨论了ESS试验和环境试验的不同目的,以及ESS试验对组件类产品的影响。还介绍了各种环境应力适用性,明确了温度循环和随机振动是最有效的应力筛选。结合《GJB360A—96电子及电气元件试验方法》,通过对实际应用中的三种组件类产品原ESS条件、补充ESS条件和最终ESS条件的确定过程的对比分析,给出了三种组件类产品在补充ESS试验过程中的失效原因及解决措施,为同类型产品制定ESS试验条件提供参考依据。     

非密封性分系统热循环试验中的防结露问题

电工和电子分系统在热循环试验中没有采取防结露措施或措施不当 ,导致温度循环过程中空气中的水汽凝结在分系统内部加电工作的组件上 ,使组件的漏电增加、性能变坏 ,从而导致分系统出现故障。通过对某分系统在热循环试验中失效组件的分析 ,发现导致组件失效的原因是试验中防结露措施不当造成的 ,从而对热循环试验中的防结露保护措施提出了改进方法。     

某空间反射镜支撑装调技术

为了降低反射镜支撑装调对反射镜面形精度的影响,文中针对某空间相机的反射镜组件,设计了一种带有柔性环节的反射镜支撑方式,制定了反射镜组件的装调方法及路线。通过计算给出了反射镜粘结胶层厚度、粘结区域、柔性铰链等参数,并对反射镜组件进行了重力和5 ℃温变共同作用下的有限元分析。最后,根据装调工艺对反射镜组件进行粘胶、固化处理,并通过反射镜组件力学试验和热真空试验对装调方法进行验证。试验结果表明:力学和热真空环境下反射镜粘胶没有破坏,该反射镜组件的面形精度优于1/50 。验证了反射镜支撑方案以及装调方法的有效性。     

基于正交试验方法的Si基碲镉汞工艺优化

采用正交试验方法优化了Si基碲镉汞分子束外延工艺参数,以缺陷密度和缺陷尺度为评判标准。采用三因素三水平正交试验方法,分别使用生长温度、Hg/Te比、生长速率三个因素作为变化的参数。结果表明生长温度对HgCdTe缺陷影响最大,生长速率次之,Hg/Te比最小。使用正交试验获得的生长参数进行试验即生长温度212℃,Hg流量61 sccm,生长速率为1.5 μm/h,获得的HgCdTe材料缺陷密度控制在500 cm-2以内,平均缺陷直径小于3.5 μm。     

长条形空间反射镜轻量化及其支撑结构设计

为保证空间反射镜在空间应用环境中保持高位置精度和面形精度,实现良好成像,从结构材料的选择、反射镜轻量化设计及支撑结构设计三个方面对某长条形空间反射镜进行了详细的结构设计。提出了一种底面局部开口、三角形加强筋的轻量化形式,反射镜采用背部三点支撑方案,通过合理设计柔性支撑结构参数,使反射镜保证了高刚度和热尺寸稳定性要求。采用有限元法对反射镜系统进行了静、动态特性和热特性分析。分析结果表明:自重及5 ℃均匀温变载荷工况下,反射镜面形精度达到λ/10 PV,λ/50 RMS（λ=632.8 nm）;反射镜组件一阶固有频率230 Hz,具有足够高的动静态刚度和热尺寸稳定性,满足空间应用要求。     

一种小型化激光陀螺SINS的温度补偿初步研究

针对小型化激光陀螺捷联惯导系统(SINS),建立了四种不同的温补模型,分析和对比了包含高温、低温和变温三种不同温度模式下的温补效果.试验结果表明:温度变化率是影响惯性器件误差的重要因素,考虑温度和温变率模型的动态模型温补效果明显优于单纯考虑温度的静态模型.另外,为了检验小型化SINS的稳定性以及温补模型与时间的关系,5个月后再一次对其温度特性进行研究,结果表明:SINS稳定性良好,温补模型基本不受时间影响,满足工程应用的需求.     

电子设备组件级的可靠性

在电子系统可靠性评价中,目前缺乏的是电子系统电路卡等级以上各级的计算机模型和模拟.CALCEEPRC的PWB级软件已投入使用5年多,而新的组件级软件(微电子封装的计算机辅助设计)正在政府和工业的50多个部门进行β试验.为了预先在组件级评价电子系统的可靠性,由美国国防部模型和模拟办公室投资的一项新的补充软件工具研究项目正在进行中.这一项目由美国陆军、CALCE EPRC和艾奥华大学模拟与设计优化中心(SDO)合作进行。新项目的模型与模拟目标分为三部分的工作:计算电子组件位置上的动态负载;计算通过组件传送到PWB的负载.电子组件本身的可靠性评价.艾奥华大学将负责计算电子组件周围的动态负载与运行记录,CALCE EPRC则负责传送到PWB级的负载信息,并研制评价组件可靠性的新型分析手段.作为这一项目的抽样试验,艾奥华SDO还对高移动性的多功能轮式机车(Vehicle)进行了动态模拟分析。两个选定电子组件周围的动态负载和运行数据要转换到新的组件级可靠性评价软件中.其他环境负载,如温度、湿度、化学杂质和辐射等,则由使用者指定。     

Thermal Cycling Reliability of Sn-Ag-Cu Solder Interconnections. Part 1: Effects of Test Parameters

The work presented in part 1 of this study focuses on identifying the effects of thermal cycling test parameters on the lifetime of ball grid array (BGA) component boards. Detailed understanding about the effects of the thermal cycling parameters is essential because it provides means to develop more efficient and meaningful methods of reliability assessment for electronic products. The study was carried out with a single package type (BGA with 144 solder balls), printed wiring board (eight-layer build-up FR4 structure), and solder interconnection composition (Sn-3.1Ag-0.5Cu) to ensure that individual test results would be comparable with each other. The effects of (i) temperature difference (ΔT), (ii) lower dwell temperature and lower dwell time, (iii) mean temperature, (iv) dwell time, and (v) ramp rate were evaluated. Based on the characteristic lifetimes, the thermal cycling profiles were categorized into three lifetime groups: (i) highly accelerated conditions, (ii) moderately accelerated conditions, and (iii) mildly/nonaccelerated conditions. Thus, one might be tempted to use the highly accelerated conditions to produce lifetime statistics as quickly as possible. However, to do this one needs to know that the failure mechanisms do not change from one lifetime group to another and that the failure mechanisms correlate with real-use failures. Therefore, in part 2 the observed differences in component board lifetimes will be explained by studying the failure mechanisms that take place in the three lifetime groups.     

A dynamic model for solder and the problem of accelerated life testing

Solder joint reliability under thermal cycling is a key problem in electronic packaging. Accelerated life testing (few cycles, larger temperature excursions) is often a practical necessity in predicting fatigue life in field environments (many cycles, smaller temperature excursions). Complex solder behavior with marked temperature dwell and cycle time influence at slower frequencies makes this a difficult problem. A dynamic model is presented which couples the effect of instability of coarsened grain shear band evolution in microstructure with the change in macroscopic constitutive behavior. Key features of the model include effects of shear band thickness compared with total solder joint thickness, pertinent to small scale design, and frictional resistance at slow deformation rates. Model correlation with test data is discussed and applied to the accelerated life test design.     

热循环参数及基板尺寸对焊点可靠性的影响

采用Ansys软件建立BGA倒装芯片模型考察焊点的热应力。通过改变热循环保温时间、温度范围和最高温度,研究各参数对焊点热疲劳寿命的影响,同时也考察了基板的长度和厚度的影响。采用Coffin-Manson方程计算并比较热循环寿命。结果表明:随着热循环高低温停留时间、温度范围以及最高热循环温度的增大,热循环寿命减小,最小寿命为879周;同时热循环寿命也随着基板长度和厚度的增大而减小。     

A dislocation model of shear fatigue damage and life prediction of SMT solder joints under thermal cycles

In this paper, a damage model of low-cycle shear fatigue has been developed in the dislocation theory. On the basis of this model, a formula including the factors of thermal cycle temperature, dwell time and atmospheric oxidation has been established to predict the life of SMT solder joints under thermal cycles, and this has been verified by experiments on the specimens of true SMT assemblies. The results show that the life formula established in this paper coincides with the experimental results.     

The effect of power cycling on the reliability of lead-free surfacemount assemblies

A power cycling in-test monitoring system has been constructed to test the reliability of eight different lead-free surface mount assemblies. The assemblies included SnAg3.8Cu0.7 and SnAg3.8Cu0.7X solder joints on OSP-Cu (organic solderability preservative on Cu), electroless NiAu, immersion Ag and immersion Sn board metallizations. One Pb containing assembly, Sn62PbAg2 on OSP-Cu board metallization, was included for comparison. The components on the assemblies were 1206 resistors (Sn100 metallization on the end terminals) and 100 lead QFP with gullwing leads (SnPb15 metallization). All assemblies experienced up to 5000 power cycles of ambient to 100°C with a 15 min dwell at each temperature. Solder joint reliability was evaluated by monitoring electrical resistance after each power cycle and examining mechanical strength and microstructure with number of power cycles. The 1206 resistors on four of the assemblies (one of which was the Pb containing assembly) exhibited electrical resistance increases after 4000 power cycles. All resistor samples decreased in strength by more than 70% at 5000 cycles and cracks appeared after 1000 power cycles. All gullwing lead solder joints exhibited good reliability over 5000 power cycles, with no resistance increase and no strength reduction. Small cracks appeared after 3000 power cycles     

环境温度对气流式角速度传感器灵敏度的影响

采用有限元方法,计算了不同温度下敏感元件内的温度场和流场。结果表明:在输入恒定角速度时,敏感元件内的温度场和流场随环境温度发生变化,温度增加,在两个检测热电阻丝处的气流速度之差减小,检测电桥输出电压减小,传感器灵敏度降低;温度下降,在两个检测热电阻丝处的气流速度之差增加,检测电桥输出电压增加,传感器灵敏度增加。当输入角速度为20°/s时,传感器的灵敏度随温度平均变化率为0.0336mV/(°)·s–1·℃–1。     

Chip Scale Package (CSP) solder joint reliability and modeling

A viscoplastic constitutive model was used to analyze the thermally induced plastic and creep deformation and low cycle fatigue behavior of the solder joints in Chip Scale Packages (CSP) mounted on Printed Circuit Boards (PCB). The time-dependent and time-independent viscoplastic strain rate and plastic hardening work factors of solder material were used in 2-D plane strain finite element models. The viscoplastic strain rate data was fitted to the viscoplastic flow equation. The plastic hardening factors were considered in the evolution equation. A viscoelastic constitutive model was used for molding compound. Finite element models, incorporating the viscoplastic flow and evolution equations for solder and the viscoelastic equations for molding compound, were verified by temperature cycling tests on assembled CSPs. The effect of the cyclic frequency, dwell time, and temperature ramp rate on the response of the viscoplastic deformation was studied for a tapeless Lead-on-Chip (LOC) CSP and a flexible substrate CSP. The ramp rate significantly affects the equivalent stress range in solder joints while a dwell time in excess of 10 min per half cycle does not result in increased strain range. The failure data from the experiments was fitted to the Weibull failure distribution and the Weibull parameters were extracted. After satisfactory correlation between the experiment and the model was observed, the effect of material properties and package design variables on the fatigue life of solder joints in CSPs was investigated and the primary factors affecting solder fatique life were subsequently presented. Furthermore, a simplified model was proposed to predict the solder fatigue life in CSPs.     

Characterization on acceleration-factor equation for packaging-solder joint reliability

The well-known Norris-Landzberg acceleration factor (N-L AF) empirical equation was developed based on the accelerated thermal cycling (ATC) test. It has been widely used for many years to predict product lifetimes. However, some recent test results have shown the insufficiency of this equation when the ramp rates change. The AF equation predicts a longer lifetime when the ramp rate is higher, which contradicts the experimental test data. The reason for this discrepancy is that the N-L AF equation combines both ramp rate and dwell time factors in one frequency term. Thus, modifying the current AF equation to more precisely predict product lifetimes has become an important topic.This study proposes a new AF equation to decouple the effects of the ramp rate and dwell time during an ATC test, replacing the frequency term used in the N-L equation with two new terms. One is related to the ramp rate for the strain rate effect, and the other is related to the dwell time for the creep effect of the packaging solder joint material. The new AF equation produces a good correlation between the simulation and test results for different package types discussed in the literature with various ramp rates and dwell times.     

Reliability of lead-free interconnections under consecutive thermal and mechanical loadings

To simulate more realistically the effects of strains and stresses on the reliability of portable electronic products, lead-free test assemblies were thermally cycled (−45°C/+125°C, 15-min. dwell time, 750 cycles) or isothermally annealed (125°C, 500 h) before the standard drop test. The average number of drops to failure increased when the thermal cycling was performed before the drop test (1,500 G deceleration, 0.5 ms half-sine pulse). However, the difference was not statistically significant due to the large dispersion in the number of drops to failure of the assemblies drop tested after the thermal cycling. On the other hand, the average number of drops to failure decreased significantly when the isothermal annealing was carried out before the drop test. The failure analysis revealed four different failure modes: (1) cracking of the reaction layers on either side of the interconnections, (2) cracking of the bulk solder, (3) mixed mode of component-side intermetallic and bulk solder cracking, and (4) voidassisted cracking of the component-side Cu₃Sn layer. The assemblies that were not thermally cycled or annealed exhibited only type (1) failure mode. The interconnections that were thermally cycled before the drop test failed by mode (2) or mode (3). The drop test reliability of the thermally cycled interconnections was found to depend on the extent of recrystallization generated during the thermal cycling. This also explains the observed wide dispersion in the number of drops to failure. On the other hand, the test boards that were isothermally annealed before the drop testing failed by mode (4).