无铅PBGA用Sn—Pb焊膏焊接焊点失效分析

某典型航天电子产品印制板采用共晶Sn-Pb埠膏,无铅PBGA焊接,以此为研究对象,主要采用X射线检测、金相切片分析、扫描电子显微镜等一系列试验手段,研究分析PBGA焊点失效的机理与成因,检测结果表明,用共晶Sn-Pb焊膏焊接无铅BGA(球栅阵列封装)的可靠性和Sn-Pb BGA的可靠性相当,试验用PCBA失效原因是PBGA焊球上焊膏与PCBA焊盘润湿性较差,焊膏与焊盘之间未形成良好的金属间合金层,其主要原因是PCB焊盘焊接性较差.     

HXD2机车转向架拉杆座角焊缝疲劳失效机理

针对HXD2型电力机车在某穿越秦岭山脉线路服役中多台次拉杆座角焊缝出现裂纹的问题,进行了试验与仿真分析。发现裂纹表面有明显疲劳辉纹,表明角焊缝服役中发生疲劳失效;焊缝根部是疲劳起裂位置,有多源起裂形貌特征;起裂后裂纹从中心向两侧扩展、从根部向焊缝表面扩展,在接头横截面上裂纹路径与水平方向夹角近似为45°;统计分析和仿真计算表明,角焊缝裂纹的发生与拉杆座/基板之间的间隙值有关联性,根部间隙越大,则角焊缝抗疲劳性能越差;分析其主要机理是间隙较小时,焊缝受压后拉杆座底面与构架基板表面更容易发生接触,接触后基板表面分担部分载荷。因此,间隙较小时,焊缝应力幅较小;而间隙较大时,不仅应力幅较大,而且在焊根处易出现末端尖劈形貌。 创新点： 分析了某穿越秦岭山脉线路HXD2电力机车拉杆座角焊缝疲劳失效行为,揭示了电力机车车架角焊缝疲劳裂纹与角焊缝根部间隙的相关性,阐明了根部间隙影响拉杆座角焊缝抗疲劳性能的机理。     

基于晶粒取向的无铅互连焊点可靠性研究

对球栅阵列封装(ball grid array,BGA)组件进行热循环实验,通过EBSD对焊点取向进行表征,观察不同取向焊点内晶粒取向演化情况.同时采用Surface Evolver软件对BGA焊点进行三维形态模拟,并基于实际焊点内的晶粒构成,对热加载条件下BGA组件热应力应变分布进行计算.实验和模拟结果表明,晶粒取向对焊点可靠性和失效模式产生非常显著的影响.对于单个晶粒构成的焊点,应力应变主要集中在靠近界面的钎料内部,该处发生明显的再结晶并伴随着裂纹的萌生和扩展;而对于多个晶粒构成的焊点,应力应变分布则依赖于晶粒取向,再结晶和裂纹倾向于偏离界面沿原有晶界向钎料内部扩展.部分特殊取向焊点,当原有晶界与焊盘界面垂直时,不利于形变,表现出较高的可靠性.当晶界与焊盘夹角为45°时,在剪切应力和焊点各向异性的双重作用下,原有晶界处产生较大的应力应变集中,加速了裂纹的萌生和扩展,导致焊点最终沿着原有晶界发生再结晶和断裂,焊点发生早期失效的可能性增加.     

FCBGA封装器件的失效分析与对策

FCBGA(Flip-chip ball grid array)封装形式器件是近年来集成电路封装的最佳选择,其可靠性日益引起重视.本文简要介绍了FCBGA封装形式器件的结构特点以及相关的可靠性问题,通过两个FCBGA封装器件失效的案例,分析了两只FCBGA器件失效的原因,一个是由于芯片上的焊球间存在铅锡焊料而导致焊球短路,另一个则是因封装内填料膨胀分层而导致的焊球开路.本文提出了针对这种形式封装的器件在使用过程中的注意事项及预防措施,以减少该类失效情况的发生.     

高钢级管道环焊缝裂纹失效分析

含裂纹缺陷的环焊缝失效分析,是解决X70及以上高钢级管道环焊缝质量风险的必要环节。文中对现阶段含裂纹缺陷的环焊缝排查和失效分析进行了梳理和成果总结分析,及时发现问题和规律,为后续安全管控和裂纹机理研究提供参考。已有失效分析规律总结如下：X70及X80管道环焊缝裂纹以根焊开裂形式为主;变壁厚、管道顶部和底部等位置容易发生环焊缝裂纹缺陷,焊接施工和缺陷无损检测及评判时应重点关注,尽量避免漏评误判;焊瘤、错边、余高等外观检测指标超标,导致环焊缝成形较差,影响裂纹缺陷的检出并加重根焊位置的应力集中。基于上述规律,建议对新建管道需加强针对管道环焊缝外观检测、根焊裂纹检测工艺。而对于在役管道,重点防范弯曲等附加载荷影响,依托环焊缝裂纹失效分析,进一步研究环焊缝裂纹形成的微观机理和控制参数。     

新型手机用PCB板焊点的失效分析

采用多种宏微观分析手段,对新型手机用PCB板的失效焊点(BGA)与散落焊珠的组分进行了系统的表征分析.结果表明,表面贴装技术(SMT)回流焊工艺参数控制不当是主要的失效起因;焊膏质量不佳及回流焊工艺与其不匹配是导致焊点焊块失效的另一重要原因.针对上述问题,就回流焊工艺参数的调整以及焊膏质量的改善提出了具体建议,以确保该PCB板的结构完整性和安全可靠性.     

热循环对CBGA封装焊点组织和抗剪强度的影响

陶瓷球栅封装阵列(CBGA)器件的陶瓷基器件与印刷电路板之间膨胀系数的差异是导致焊点失效的主要因素,其可靠性一直是CBGA封装器件制造时需重点考虑的问题.研究了在-55～125℃热循环试验条件下,热循环对CBGA封装焊点的组织变化及对抗剪强度的影响.结果表明,随着热循环次数的增加,焊点的抗剪强度不断下降;随着热循环次数的增加,CBGA封装焊点在焊球边缘处开始萌生裂纹,然后裂纹沿着晶界扩展,最终导致完全失效.与此同时,焊点的组织变化的微观机制表现为焊点晶粒不断地长大,组织粗化,金属间化合物层逐渐增厚.     

透平压缩机叶片失效分析及再制造技术

针对某透平压缩机叶片进气口端产生断口和裂纹等失效问题,通过断口宏观和显微形貌分析、失效叶片化学成分和力学性能分析及有限元分析,对叶片裂纹形成和扩展机理进行研究。结果表明,叶片进气口端断口是由于杂质冲击导致,而叶片根部的裂纹是由于腐蚀引起材料表面产生微观缺陷,最终叶片在反复扭转力的作用下产生疲劳断裂。     

BGA焊球表面状态与微观结构关系的研究

焊球是球栅阵列封装(BGA)的主要连接部件,电子产品自动化生产要求焊球具有良好的表面光亮度.用均匀射流断裂方法生产BGA焊球,研究焊球内部显微结构,从焊球的微观结构推测钎料液滴的凝固行为.通过对小球光滑和粗糙部位微观结构分析,总结小球表面粗糙部位显微组织的特征.最后研究少量稀土元素对小球表面状态的影响.     

国产TIG焊导电辊接头失效机理分析

通过对国产TIG焊失效导电辊哈氏合金C-22断口进行XRD、EDAX成分分析、失效区金相组织及断口形貌观察、极化曲线测定等手段分析了国产TIG焊导电辊的失效原因及其失效机理.金相观察表明哈氏合金筒体焊后未经过固溶处理,会导致焊缝金属和母材之间存在组织差异;腐蚀裂纹宏观形貌观察表明导电辊断裂失效的裂纹源主要萌生于筒体表面的焊缝区域,并逐渐向焊缝内部扩展并最终进入母材;极化曲线测试表明填丝TIG焊焊缝的腐蚀电位要低于母材的腐蚀电位,腐蚀电位差异是导致导电辊焊缝区域发生严重腐蚀的主要原因.这项研究成果可为进一步开展哈氏合金导电辊的制造提供理论依据和技术指导.     

埋入式基板微尺度球栅阵列焊点三点弯曲应力应变分析

建立了埋入式基板微尺度球栅阵列焊点三点弯曲应力应变有限元分析模型,分析了焊点材料、焊点间距、PCB支撑跨度及焊点阵列对焊点弯曲应力应变的影响,结果表明,三点弯曲加载条件下,埋入式基板微尺度BGA焊点阵列的最大弯曲应力应变均出现在最外围拐角处焊点上.当三点弯曲加载到相同位移载荷下,SAC387材料焊点的弯曲应力最大,62Sn36Pb2Ag材料焊点的弯曲应力最小;随着支撑跨度的增大,焊点内最大弯曲应力应变均随之减小;随着BGA焊点间距的增大,焊点内部最大弯曲应力应变值均增大;随着BGA焊点阵列数的增大,焊点内部最大应力应变值均增大.     

The effects of additives to SnAgCu alloys on microstructure and drop impact reliability of solder joints

The impact reliability of solder joints in electronic packages is critical to the lifetime of electronic products, especially those portable devices using area array packages such as ball-grid array (BGA) and chip-scale packages (CSP). Currently, SnAgCu (SAC) solders are most widely used for lead-free applications. However, BGA and CSP solder joints using SAC alloys are fragile and prone to premature interfacial failure, especially under shock loading. To further enhance impact reliability, a family of SAC alloys doped with a small amount of additives such as Mn, Ce, Ti, Bi, and Y was developed. The effects of doping elements on drop test performance, creep resistance, and microstructure of the solder joints were investigated, and the solder joints made with the modified alloys exhibited significantly higher impact reliability.     

Solder joint reliability in flip chip package with surface treatment of ENIG under thermal shock test

This study investigated the microstructural evolution and evaluated the thermo-mechanical reliability of a Sn-3.0Ag-0.5Cu (in wt.%) flip chip package during a thermal shock test. The reliability of the flip chip bonded packages was evaluated by means of the thermal shock in the temperature range of 233 K to 398 K. After 250 thermal shock cycles, cracks finally occurred at the corner solder bump joint on the chip side interfacial regions. In that, the crack initiated at the solder region near the intermetallic compound (IMC) layers. For the interpretation of the failure mechanism of the package, finite element analyses were conducted. From the finite element analysis or computational simulation result, the distribution of the plastic work in the corner solder bump was found to be most considerable. This means that the corner solder bump has the highest potential for first crack initiation and growth, because the thermo-mechanical failure of the solder joints is mainly caused by the accumulation of the plastic work. This matched well with the experimental results.     

Role of grain orientation in the failure of Sn-based solder joints under thermomechanical fatigue

A small Pb-free solder joint exhibits an extremely strong anisotropy due to the bodycentered tetragonal (BCT) lattice structure of β-Sn. Grain orientations can significantly influence the failure mode of Pb-free solder joints under thermomechanical fatigue (TMF) due to the coeffcient of thermal expansion (CTE) mismatch of β-Sn grains. The research work in this paper focused on the microstructure and damage evolution of Sn3.0Ag0.5Cu BGA packages as well as individual Sn3.5Ag solder joints without constraints introduced by the package structure under TMF tests. The microstructure and damage evolution in cross-sections of solder joints under thermomechanical shock tests were characterized using optical microscopy with cross-polarized light and scanning electron microscopy (SEM), and orientations of Sn grains were determined by orientation imaging microscopy (OIM). During TMF, obvious recrystallization regions were observed with different thermomechanical responses depending on Sn grain orientations. It indicates that substantial stresses can build up at grain boundaries, leading to significant grain boundary sliding. The results show that recrystallized grains prefer to nucleate along pre-existing high-angle grain boundaries and fatigue cracks tend to propagate intergranularly in recrystallized regions, leading to an accelerated damage after recrystallization.     

The embrittlement mechanism and improvement of impact strength for lead-free solder joints in BGA packaging using electrolytic Ni/Au plating

Impact strength evaluation and fracture mechanism analysis in board level of Sn–3mass%Ag–0.5mass%Cu solder joints of ball grid arrays (BGA) using electrolytic Ni/Au plating were performed. The cause of impact strength degradation of BGA solder ball joints is the existence of low density defects, which contain organic materials, in the (Cu,Ni)₆Sn₅ intermetallic compound grain boundary formed in the solder joints. These organic materials are taken in by the nickel plating film at the time of nickel plating. To improve the impact strength of the Sn–3mass%Ag–0.5mass%Cu solder joint of the BGA, it is necessary to lower the concentration of these organic materials. The contamination prevention and nickel plating bath sanitization, solder mask material selection (to minimize nickel plating bath contamination) and higher current density of nickel plating are effective to keep a lower concentration of organic materials in nickel plating film.     

通孔元件焊点的抗热疲劳性能预测Ⅰ.焊点抗热疲劳能力的实验研究

针对通孔焊点进行了热冲击的可靠性测试，以非破坏性和破坏性的实验方法，对比分析了波峰焊点和再流焊点的抗热疲劳能力．结果表明，CTE(热膨胀系数)失配是焊点产生裂纹的主要原因，而焊点形态的差异又使得再流焊点内部断裂程度不同于波峰焊点．再流焊点裂纹产生在钎料内部；而波峰焊点由于具有饱满的圆角过渡形态，裂纹产生在镀铜孔与线路板的连接拐角处．裂纹的产生导致了两种焊点强度的降低，对其电性能的影响却甚微。     

钛合金自冲铆接头微动磨损机理及疲劳性能

对钛合金同种TA1-TA1（TT）及异种TA1-Al5052（TA）,TA1-H62（TH）自冲铆接头进行疲劳试验,用扫描电子显微镜对断口及微动区进行观测研究其微动磨损机理,并研究下板强度对接头疲劳寿命和失效形式的影响.结果表明,断口裂纹萌生区即为微动磨损区.微动磨损导致微动区亚表面产生微裂纹并逐步扩展为宏观疲劳裂纹导致接头最终失效;微动磨屑在微动磨损过程中主要起减轻磨损作用.总体上TT接头具有最优疲劳性能,疲劳载荷较高时TA接头疲劳性能优异,疲劳载荷较低时TH接头疲劳性能优异.两板强度相当且疲劳载荷较高时失效形式主要为铆钉断裂,疲劳载荷较低时失效形式主要为下板断裂;而下板强度与上板强度相差较大时,疲劳失效形式为下板断裂.     

航天电子产品CCGA加固工艺可靠性分析

航天电子产品大量应用陶瓷柱栅阵列封装(ceramic column grid array, CCGA)器件,其装焊质量与器件本体尺寸和加固工艺息息相关.文中通过试验和数值仿真方法,研究印制电路板(primted circurt board, PCB)约束、器件加固工艺对大尺寸CCGA焊点可靠性的影响. 仿真与试验结果表明,优化CCGA周围印制电路板约束方式、使用EC-2216环氧胶加固CCGA均可大幅降低随机振动过程中焊点受力. 使用少量环氧胶加固CCGA提高焊点抗振性能的同时,对焊点抗热疲劳性能影响较小,满足QJ 3086A—2016高可靠装焊要求;随着环氧胶点胶量的增多,焊点抗热疲劳性能显著下降,焊点在温差变化较大的服役环境下存在失效风险;在充分优化PCB约束以降低板级振动响应的情况下,使用GD414硅橡胶加固器件也满足航天电子产品高可靠装配要求.     

复杂背景下X射线BGA焊点气泡检测

基于全局阈值分割的焊点气泡提取不准确,且当焊点被遮挡造成的气泡提取困难时,导致球栅阵列(ball grid array,BGA)焊点气泡检测困难. 针对这些复杂背景下BGA焊点气泡的X射线缺陷检测问题,采用阈值分割、焊点圆度、焊点面积等标准提取未被遮挡的焊点,并提出了一种交互式射线轮廓提取方法完成被遮挡焊点轮廓的提取. 针对焊点气泡的特点,提出基于灰度形态学、直方图拉伸、模糊增强、BLOB分析综合处理的焊点气泡检测方法. 对比试验研究结果表明,该算法对复杂背景下BGA焊点气泡检测有较高准确率.     

BGA封装器件焊点抗剪强度的试验

采用微焊点强度测试仪研究了Sn-Pb共晶钎料BGA（球栅阵列封装技术）封装器件焊点的抗剪强度，并对不同直径的BGA球焊点的抗剪强度进行了比较。研究结果表明，在相同条件下，BGA球直径越大，抗剪强度越小，共晶钎料BGA球焊点的抗剪强度比锡铅合金钎糕点自身的抗剪强度大。