加速浸润方法在塑封可靠性分析中的应用

在对塑封集成电路进行封装可靠性评估中,预处理过程(precondition)是必经的步骤。其中的浸润测试(soak)通常在非加速条件下进行,其耗时较长。在市场竞争日趋激烈的环境下,企业迫切需要缩短新产品的可靠性验证时间。文章针对JEDEC(电子器件工程联合委员会)和JEITA(日本电子信息技术协会)标准中涉及到的三种加速浸润条件,以组件在非加速条件下(JEDEC Level 3和JEITA Rank E)潮气的穿透力、吸收量及由此产生的失效为参照,确定在加速条件下,组件达到同样的潮气吸收量并产生相类似的失效所需的时间。同时应用有限元分析的方法进行建模和计算,并与实际的测量结果比较验证。     

液晶显示器件电极腐蚀失效可靠性研究

利用Arrhenius模型和Eyring模型分析了温度应力和湿度应力对LCD电极腐蚀可靠性的加速影响特性,并根据加速特性推导出典型的可靠性加速试验可验证的产品寿命.结果表明,温度应力和湿度应力对LCD腐蚀的加速作用都呈指数关系,典型的腐蚀可靠性验证试验条件(55℃×95%RH×24 h)所对应的LCD产品在常温常湿条件下的理论寿命约为3年.同时,试验统计了40℃×70%RH和常温常湿条件下产品发生腐蚀失效比例随时间的趋势.结果表明,40℃×70%RH×48 h的条件可筛选出95%以上的潜在腐蚀失效产品.     

TR组件焊接可靠性工艺研究与应用

对毫米波TR(transmitter and receiver)组件焊接过程中线膨胀系数(CTE)失配机理和由于CTE失配导致的热机械应力对组件可靠性的影响进行了分析。根据阶梯焊接温度精确控制和无铅焊料可靠浸润的要求,从实践中总结出了一种真空预镀涂焊接新工艺。实践表明,该新工艺可以精确地进行阶梯焊接温度控制,使无铅焊料有很好的浸润效果,焊透率由70%以下提高到98.3%,延长了CTE不匹配造成的疲劳失效发生时间,提高了TR组件使用可靠性。     

SMT互连组件在热循环中的可靠性预计模型

电子设备中表面安装器件和电路基板以及焊接材料的热膨胀系数差异,使得SMT互连组件在热循环条件下产生热膨胀失配,在焊接处产生热应力,在长时间的交变应力的作用下,焊接处遭到疲劳破坏而使设备工作失效,这就是SMT互连组件在热循环条件下的基本失效机理。文中还介绍了美国MIL—HDBK—217F NOTICE Ⅱ公布的表面安装连接组件可靠性预测lSMT模型。给出一系列具有实用价值的参数。     

基于加速退化的电子设备可靠性分析

提出了电子设备在退化状态下的可靠性分析问题,通过建立电子设备退化失效模型与失效阈值,解决了有正常退化数据的电子设备可靠性问题。在此基础上,研究了加速退化时的电子设备退化问题,利用加速试验来分析电子设备在非加速状态下的退化失效,从而解决了非加速状态时退化数据不足以进行可靠性分析的问题。最后,给出了计算实例。     

相变存储器失效时间分析

从保持力失效时间的角度出发,对相变存储器实施了保持力加速寿命实验。实验过程中发现,在比较高的温度下,随着测试时间的增长,存储器单元的RESET阻值会逐渐变小。这个现象符合Arrhenius模型。而且,温度越高,失效时间越短。不同初始RESET阻值条件下的阻值分布曲线也验证了通过增加非晶区域的有效体积可以改善保持力可靠性。不同存储器单元的失效时间分布也验证了一个假设:若在非晶区域中本来就存在晶粒,则晶粒生长重组会缩短失效时间;若是晶化过程发生在非晶区域和结晶区域的边界处,失效时间会明显增长。     

DC/DC模块中功率器件的寿命预计方法

模拟开关电源DC/DC模块内部电路为开关电源中的功率器件—垂直导电双扩散MOS(VDMOS)和肖特基二极管(SBD)—提供恒定电应力,并对其施加温度应力进行加速寿命试验。采用恒定电应力温度斜坡法(CETRM),对开关电源中功率器件VDMOS和SBD的可靠性进行评价;对其失效机理一致性进行分析,计算其失效激活能;并在失效机理一致的范围内外推正常使用条件下的寿命,为开关电源整体可靠性评价提供依据。     

国外红外焦平面探测器组件可靠性研究综述

介绍了国外焦平面探测器组件可靠性研究的主要特点和内容。焦平面探测器组件的主要制造商,建立了较完善的可靠性保证体系,可靠性研究融入设计与制造全过程,是基于过程的可靠性研究。在研制阶段进行失效模式的充分暴露与加速试验研究;批生产阶段进行工艺优化,并降低系统成本;建立数据库,进行可靠性评估方法研究。     

STM互连组件在热循环中的可靠性预计模型

电子设备中表面安装器件和电路基板以及爆接材料的热膨胀系数差异，使得STM互连组件在热循环条件下产生热膨胀失配，在焊接处产生热应力，在长时间的交变应力的作用下，焊接处遭到疲劳破坏而使设备工作失效，这就是STM互连相件在热循环条件下的基本失效机理。文中还介绍了美国MIL－HDBK－217F NOTICE Ⅱ公布的表面安装连接组件可靠性预测λSMT模型，给出一系列具有实用价值的参数。     

失效机理鉴别在加速试验中的作用

就正常使用条件下出现的某些主要失效机理而论，加速寿命试验技术提供了一种研究电子元器件可靠性的简便方法，然而，加速试验经常是在不知道失效机理，以及不保证被试验所加速的失效机理与正常使用条件下所观察到的失效机理相同的情况下，本文总结了电子元器件和封壳的普通失效机理，并研究了在加速试验过程中可能出现的失效机理转变。     

Effects of different test profiles of temperature cycling tests on the reliability of RFID tags

Passive UHF radio-frequency identification (RFID) tags are used for object identification in various environmental conditions, which may affect the reliability of these tags. The effects of different environmental stresses can be studied with accelerated life tests (ALT). Choosing the most suitable test may be challenging: The results are needed as fast as possible, but the failure mechanisms must replicate those occurring in the real operating environment. Here the effects of different temperature cycling profiles were studied by altering temperature ranges, extreme temperatures, soak times to extreme temperatures and transition times between extreme temperatures. Failure times clearly differed between the tests. The test with the fastest transition time and the shortest soak time seemed to have the most acceleration. It was also observed that the different temperature cycling profiles affected the failure mechanisms detected. Cracking of the antenna was observed with lower temperature extremes or shorter soak and transition times. However, with longer soak and transition times, cracks were seen in the RFID interconnections. Both cases led to changes in the impedance matching and consequently to failures. The totally different failure mechanisms clearly demonstrate the importance of carefully determining the test parameters in order to achieve the correct failure mechanism.     

Evaluation of damp‐heat testing of photovoltaic modules

Temperature, temperature cycling, moisture, ultraviolet radiation, and negative bias voltage are considered as main degradation factors for photovoltaic modules by causing hydrolysis and photo‐degradation of polymeric components, corrosion of glass, and of metallic components like grids and interconnectors. Commercially produced photovoltaic modules with crystalline silicon cells were exposed to accelerated damp‐heat testing in the lab. Test temperatures were 75, 85, and 90 °C. The tests were continued until a final degradation state was reached (3500–7000 h). The degradation function could be modeled by a Boltzmann function allowing the determination of the time to failure (20% power loss). The time to failure as function of the test temperature follows Arrhenius relations allowing the evaluation of the activation energy of the dominating degradation process. These time‐transformation functions could be used for service life estimation. Electroluminescence pictures illustrate the degradation behavior and the differences of the modules, indicating no changes in the degradation mechanisms for the different temperatures. A procedure for the evaluation of outdoor operation conditions towards accelerated service life testing with respect to moisture impact is proposed. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of High-Humidity Testing on Material Parameters of Flexible Printed Circuit Board Materials

The tendency of polymers to absorb moisture impairs especially their electrical and mechanical properties. These are important characteristics for printed circuit board (PCB) materials, which should provide mechanical support as well as electrical insulation in many different environments in order to guarantee safe operation for electrical devices. Moreover, the effects of moisture are accelerated at increased temperatures. In this study, three flexible PCB dielectric materials, namely polyimide (PI), fluorinated ethylene-propylene (FEP), and polyethylene terephthalate (PET), were aged over different periods of time in a high-humidity test, in which the temperature was 85°C and relative humidity 85%. After aging, the changes in the structure of the polymers were studied by determining different material parameters such as modulus of elasticity, glass-transition temperature, melting point, coefficient of thermal expansion, water absorption, and crystallinity, and changes in the chemical structure with several techniques including thermomechanical analysis, differential scanning calorimetry, Fourier-transform infrared spectroscopy, moisture analysis, and a precision scale. The results showed that PI was extremely stable under the aging conditions and therefore an excellent choice for electrical applications under harsh conditions. Similarly, FEP proved to be relatively stable under the applied aging conditions. However, its crystallinity increased markedly during aging, and after 6000 h of aging the results indicated oxidation. PET suffered from hydrolysis during the test, leading to its embrittlement after 2000 h of aging.     

塑封器件的贮存环境与使用可靠性

介绍了用潮热环境试验模拟塑封器件在长期贮存时对水汽的吸附以及用潮热试验和焊接热的综合影响来评价塑封器件耐潮湿性能的方法.     

Thermal Cycling Reliability of Sn-Ag-Cu Solder Interconnections—Part 2: Failure Mechanisms

Part 1 of this study focused on identifying the effects of (i) temperature difference (ΔT), (ii) lower dwell temperature and shorter dwell time, (iii) mean temperature, (iv) dwell time, and (v) ramp rate on the lifetime of ball grid array (with 144 solder balls) component boards. Based on the characteristic lifetime, the studied thermal cycling profiles were categorized into three groups: (i) highly accelerated conditions, (ii) moderately accelerated conditions, and (iii) mildly/nonaccelerated conditions. In this work, the observed differences in component board lifetime are explained by studying the failure mechanisms and microstructural changes that take place in the three groups of loading conditions. It was observed that, under the standardized thermal cycling conditions (highly accelerated conditions), the networks of grain boundaries formed by recrystallization provided favorable paths for cracks to propagate intergranularly. It is noteworthy that the coarsening of intermetallic particles was strong in the recrystallized regions (the cellular structure had disappeared completely in the crack region). However, under real-use conditions (mildly/nonaccelerated conditions), recrystallization was not observed in the solder interconnections and cracks had propagated transgranularly in the bulk solder or between the intermetallic compound (IMC) layer and the bulk solder. The real-use conditions showed slight coarsening of the microstructure close to the crack region, but the solder bulk still included finer IMC particles and β-Sn cells characteristic of the as-solidified microstructures. These findings suggest that standardized thermal cycling tests used to assess the solder interconnection reliability of BGA144 component boards create failure mechanisms that differ from those seen in conditions representing real-use operation.     

Experimental Determination of a More Powerful Burn-In

This paper describes an experiment in which it was determined that burn-in could be made more powerful (i.e., capable of precipitating more failures in a given burn-in period) by reducing the time spent at the high temperature extreme. The number of failures precipitated in burn-in using a cycle consisting of a 2-hour non-operating cold soak and a 2-hour operating heat soak were compared to those precipitated using a 2-hour non-operating cold soak and a 4-hour operating heat soak. The shorter cycles precipitated as many failures as the longer, for an equal number of cycles. The fact that the shorter cycle required two-thirds the chamber time of the longer cycle equates to more cycles, and hence more failures removed, in a given burn-in period.     

Effect of Non-Uniform Moisture Distribution on the Hygroscopic Swelling Coefficient

The coefficient of hygroscopic swelling is a material property used to measure the volumetric change with moisture absorption under given humidity and temperature conditions. Current hygroscopic swelling characterization techniques use an averaged approach based on the averaged moisture content. However, the moisture distribution is not uniform across the test specimen during measurement. This introduces analysis errors in determining the material property. In this paper, an exact analytical solution was derived to obtain the accurate coefficient of hygroscopic swelling, with the consideration of 3-D moisture diffusion across the specimen. The correlation between the locally defined and the averaged coefficient of hygroscopic swelling was obtained analytically. The results showed that the coefficient of hygroscopic swelling obtained based on the previous method using the averaged approach may overestimate the property up to 250%. The methodology and formulation developed in this paper was then applied to analyze a set of existing experimental data, and results were compared to the current approach. This paper also investigated the reliability of a flip chip ball grid array package under high accelerated stress test condition (120degC/100%RH). Finite element analysis simulation results revealed the significance of contribution of hygroscopic swelling induced tensile stresses under bump region. The finite element results gave an insight of the failure mechanism associated with moisture absorption.     

Accelerated popcorn testing of high solder-reflow crack resistant molding compounds

In testing the resistance of a molding compound to popcorn failures after solder reflow, there are two basic options for shortening the moisture absorption phase: varying the severity of moisture exposure by varying the temperature and percent relative humidity or maintaining a constant humidity/temperature profile and varying the length of time the compounds are exposed. In addition, the total testing time can be accelerated by the choice of test method. There are three major measurement techniques for evaluating the extent of popcorn cracking: SAM testing; bubble chamber testing; and visual crack inspection. In this paper we will explore the effects of differing lengths of exposure time and the merits of different measurement techniques.A variety of epoxy resins, filler mixtures and adhesion additives were examined in semiconductor molding compounds for solder-reflow crack resistance (popcorn crack resistance). A limited comparison of molding compound high-temperature strength properties and extent of popcorn cracking suggests no strong positive correlation. On the other hand, factors that might have an impact on adhesion properties of the molding compound, such as low melt viscosity resins and putative adhesion additives, appear to have the greatest impact. A molding compound developed with these factors showed no internal or external cracks on 84 lead QFPs (29.2 × 29.2 × 3.68 mm) after 72 h of 85°C/85% R.H. and one 10 s solder dip at 260°C. Nor were any external cracks observed after 168 h of 85°C/85% R.H. and one solder dip. However, minor internal cracks were observed.The most data can be obtained by using bubble chamber testing for large numbers of parts and evaluating a smaller sample of the best of those compounds via SAM testing with crack extension analysis. The length of exposure time affected the parts as expected, with longer times being more severe. There did not appear to be a gradient effect or a threshold level. In general, 72 h allowed the greatest differentiation among the compounds tested for internal defects; external defects were not fully developed until 168 h of moisture exposure.