苛刻环境下多芯片FC-PBGA器件板级温循可靠性研究

研究了宇航用多芯片扁出型倒装芯片球栅（FC-PBGA）器件在温度循环下的板级可靠性。通过宏观形貌观察、微观结构演变等手段对温循后的器件进行了分析,并利用有限元仿真对器件的疲劳寿命进行了评估。研究结果表明,经温度循环后FC-PBGA器件表面三防漆出现起皮现象,但封装组件未出现失效故障。器件中倒装芯片的布局对温度循环后危险焊点的位置具有显著的影响。危险焊点在温度循环后产生了明显的塑性变形,在靠近芯片端的界面处形成了显微裂纹。通过有限元仿真结合修正的Coffin-Manson方程计算得到了组件的温度循环疲劳寿命约为1 002次,具有较好的可靠性,为塑封器件的高可靠性应用提供了参考。     

湿热环境下吸潮对QFN器件可靠性的影响研究

由吸潮引起的微电子塑封器件失效已经越来越多地引起人们的关注.选用QFN器件作为研究对象,首先进行QFN器件在高温高湿环境下吸潮17 h、50 h、96 h试验;然后利用有限元软件分析和模拟潮湿在QFN器件中的扩散行为,并建立湿气预处理阶段应力计算模型;最后,通过试验与仿真相结合,分析潮湿对封装可靠性的影响.研究表明:微电子塑封器件的潮湿扩散速度与位置有着重要的关系;在高温高湿环境下,微电子器件吸潮产生的湿热应力在模塑封装材料(EMC)、硅芯片(DIE)和芯下材料(DA)的交界处最大;QFN器件在高温高湿环境下吸潮产生的裂纹主要出现在硅芯片与DA材料交界面的边界.     

PBGA封装的耐湿热可靠性试验研究

塑封电子器件作为一种微电子封装结构形式得到了广泛的应用,因此湿热环境下塑封电子器件的界面可靠性也越来越受到人们的关注.为了研究塑封器件及其所用材料在高湿和炎热(典型的热带环境)条件下的可靠性,采用耐湿温度循环的试验方法,以塑封球栅平面阵列封装(PBGA)器件为例进行测试.试验结果表明,芯片是最容易产生裂纹的地方,试验后期器件产生的裂纹主要出现在芯片和DA材料界面处及芯片、DA材料和EMC材料三种材料的交界处.空洞缺陷是使界面层间开裂的主要原因,在高温产生的蒸汽压力和热机械应力的作用下,界面上的微孔洞扩张并结合起来,导致器件最后失效.     

基于埋置式基板的3D-MCM封装结构的研制

研制一种用于无线传感网的多芯片组件（3D-MCM) . 采用层压、开槽等工艺获得埋置式高密度多层有机（FR-4）基板,通过板上芯片（COB) 、板上倒装芯片（FCOB) 、球栅阵列（BGA）等技术,并通过引线键合、倒装焊等多种互连方式将不同类型的半导体芯片三维封装于一种由叠层模块所形成的立体封装结构中;通过封装表层的植球工艺形成与表面组装技术（SMT）兼容的BGA器件输出端子;利用不同熔点焊球实现了工艺兼容的封装体内各级BGA的垂直互连,形成了融合多种互连方式3D-MCM封装结构. 埋置式基板的应用解决了BGA与引线键合芯片同面组装情况下芯片封装面高出焊球高度的关键问题. 对封装结构的散热特性进行了数值模拟和测试,结果表明组件具有高的热机械可靠性. 电学测试结果表明组件实现了电功能,从而满足了无线传感网小型化、高可靠性和低成本的设计要求.     

水汽或结构对塑封电子器件可靠性的影响研究

传塑封装微电子器件在回流焊时的可靠性是微电子行业内最关心的问题之一。当一个具有不良可靠性的微电子器件通过红外回流焊接炉最终被焊接在印刷线路板上时,就会发生诸如裂纹、脱层、鼓胀等致命的缺陷。长期以来,＂水汽作用＂理论认为造成回流焊失效的原因是：处于潮湿环境中的封装材料-模制化合物从空气中吸收水汽,并且水汽沿着塑封体以及塑封体与引脚的界面向内扩散;当回流焊时在快速加热引起的热应力的作用下导致水汽膨胀而引起器件失效。于是回流焊前的预烘干就成为防止失效的重要手段。在多年的工作经历中遇到了＂预烘干＂也不能避免回流焊失效的一些生产案例,但是用＂结构强度＂的观点去改进结构的方法却十分有效。因此,认为＂水汽理论＂可能是人类认识上的一个＂误区＂,而决定传塑封装微电子器件回流焊可靠性的首要因素应是＂结构强度＂。     

“水汽”或“结构”对塑封微电子器件可靠性的影响研究

传塑封装微电子器件在回流焊时的可靠性是微电子行业内最关心的问题之一。当一个具有不良可靠性的微电子器件通过红外回流焊接炉最终被焊接在印刷线路板上时,就会发生诸如裂纹、脱层、鼓胀等致命缺陷。长期以来“水汽作用”理论认为造成回流焊失效的原因是：处于潮湿环境中的封装材料一模制化合物从空气中吸收水汽并且水汽沿着塑封体以及塑封体与引脚的界面向内扩散;当回流焊时在快速加热引起的热应力的作用下水汽膨胀而引起器件的失效。于是回流焊前的预烘干成为防止失效的重要手段。本文的作者是一位传塑封装工程师,在多年的工作经历中遇到了“预烘干”也不能避免回流焊失效的一些生产案例,但是用“结构强度”的观点去改进结构的方法却十分有效。因此,作者认为“水汽理论”可能是人类认识上的一个“误区”,而决定传塑封装微电子器件回流焊可靠性的真正首要因素是“结构强度”。     

倒装芯片中铝腐蚀的红外显微镜观测研究

倒装芯片（ｆｌｉｐｃｈｉｐ）是当前电子封装领域中的研究热点之一．本文利用新型的红外显微镜,在不破坏焊点的情况下,首次观测到一种倒装芯片封装器件经过稳态湿热试验后的铝腐蚀模式,并用一种有损失效分析的方法验证了红外显微镜的观测结果．实验发现,该倒装芯片在含有与不含有下部填充料的情况下具有完全不同的铝腐蚀模式和腐蚀机理     

倒装芯片焊点可靠性的有限元模拟法综述

随着集成电路封装技术的发展,倒装芯片技术得到广泛的应用。由于材料的热膨胀失配,使倒装焊点成为芯片封装中失效率最高的部位,而利用快捷又极具参考价值的有限元模拟法是研究焊点可靠性的重要手段之一。介绍了集成电路芯片焊点可靠性分析的有限元模拟法,概括了利用该方法对芯片焊点进行可靠性评价常见的材料性质和疲劳寿命预测模型。     

第四十届国际微电子学术会议论文摘要选编（续一）

电子封装的预先可靠性评估和建立失效率模型;高端倒装芯片系统级封装（SiP）的第二级和第三级焊点可靠性;3-DVLSI芯片堆叠所用的组装技术;半导体封装中水汽所致失效的数值分析;高温和元素合金影响Al芯片金属化层上Au球焊互连中的Kirkendall空隙生成;高密度电场中功率晶体管管芯表面上的铝迁移.     

塑封器件无损开封技术介绍

随着现代微电子行业的发展,对产品质量和结构安全性、使用可靠性提出了越来越高的要求。由于无损检测（NTD）技术具有不破坏试件、检测灵敏度高等优点,其应用日益广泛。塑封材料又以其低成本、生产工艺简单、适合大规模生产等特点,占据了整个微电子封装材料97％以上的市场。文章对塑封器件的开封技术及需要注意的事项进行了较详细的介绍和说明,列出了针对各种封装形式的无损开封方案,为无损开封的实际应用提供了便利。通过对塑封器件开封办法的研究,确保塑封器件的开封质量,为进一步对塑封器件进行DPA和失效分析建立了基础。     

湿热环境下倒装焊无铅焊点的可靠性

对板上倒装芯片底充胶进行吸湿实验,并结合有限元分析软件研究了底充胶在湿敏感元件实验标准MSL—1条件下吸湿和热循环阶段的解吸附过程,测定了湿热环境对Sn3.8Ag0.7Cu焊料焊点可靠性的影响,并用蠕变变形预测了无铅焊点的疲劳寿命。结果表明:在湿热环境下,底充胶材料内部残留的湿气提高了焊点的应力水平。当分别采用累积蠕变应变和累积蠕变应变能量密度寿命预测模型时,无铅焊点的寿命只有1740和1866次循环周期。     

Simulation and measurement of the flip chip solder bumps with a Cu-plated plastic core

With the aim to miniaturize and to reduce the cost, the increasing demand, regarding to advanced 3D-packages as well as high performance applications, accelerates the development of 3D-silicon integrated circuits. The trend to smaller and lighter electronics has highlighted many efforts towards size reduction and increased performance in electronic products. The radio frequency (RF) performances are limited by parasitic effects due to the resistor–inductor–capacitor (RLC) network, between the wire bond connections from the dies to the lead frame. The use of flip-chip bonding technology for very fine pitch packaging allows high integration and limits parasitic inductances. Electromigration (EM) and thermomigration (TM) may have serious reliability issues for fine-pitch Pb-free solder bumps in the flip-chip technology used in consumer electronic products. A possibility to extend the reliability is the use of plastic ball in the solder bumps. Bumps containing a plastic solder balls have an excellent reliability. Using a plastic ball with a low Young modulus, the solder hardness is moderated and the stress on a ball is relaxed. Due to this, the stress does not concentrate on the solder joint which prolongs the lifetime. In this investigation, the thermal–electrical–mechanical coupling of electromigration on bumps containing a plastic solder is studied.     

Field reworkable underfill materials for flip chip on boardassemblies

Studies have shown that underfill encapsulation dramatically improves the solder joint fatigue reliability of flip chip on board (FCOB) assemblies. The lack of reworkability of the underfill after the product is in the field has limited the integration of FCOB into cost sensitive electronic products and the continued proliferation of the FCOB technology will depend on the development of reworkable underfill materials systems. This paper presents data that correlates reliability performance to mechanical properties for twelve field reworkable underfill materials from three different suppliers. Their respective properties, processing parameters, and reliability performances are compared to the qualified, commercially available high performance underfills. Techniques were developed to redress the printed wiring board (PWB) site to enhance the reworked FCOB assembly yield. In addition, reliability performance results and failure analysis observations were compared to the first time nonreworked assemblies     

WLCSP中微焊球结构尺寸对其热应力的影响

晶圆级芯片尺寸封装(WLCSP)微焊球结构尺寸对其热机械可靠性有重要的影响。通过二维有限元模拟筛选出对WLCSP微焊球及其凸点下金属层(UBM)中热应力影响显著的参数,采用完全因子实验和多因子方差统计分析定量评估各种因子影响的显著性,最后建立三维模型,用子模型技术研究关键尺寸因子对热应力变化的影响。研究发现,焊球半径是影响焊球热应力的最关键尺寸因子,电镀铜开口和铜焊盘厚度对焊球热应力的影响也较显著;钝化层开口和焊球半径是影响UBM热应力的最关键尺寸因子。随着焊球半径增大,焊球热应力减小。     

Thermal cycling analysis of flip-chip solder joint reliability

The reliability concern in flip-chip-on-board (FCOB) technology is the high thermal mismatch deformation between the silicon die and the printed circuit board that results in large solder joint stresses and strains causing fatigue failure. Accelerated thermal cycling (ATC) test is one of the reliability tests performed to evaluate the fatigue strength of the solder interconnects. Finite element analysis (FEA) was employed to simulate thermal cycling loading for solder joint reliability in electronic assemblies. This study investigates different methods of implementing thermal cycling analysis, namely using the "dwell creep" and "full creep" methods based on a phenomenological approach to modeling time independent plastic and time dependent creep deformations. There are significant differences between the "dwell creep" and "full creep" analysis results for the flip chip solder joint strain responses and the predicted fatigue life. Comparison was made with a rate dependent viscoplastic analysis approach. Investigations on thermal cycling analysis of the temperature range, (ΔT) effects on the predicted fatigue lives of solder joints are reported     

无铅电子封装材料及其焊点可靠性研究进展

随着2006年7月1日RoHS法令实施的最后期限的来临,无铅焊料的研究与应用又掀起了新一轮的热潮。由于封装材料与封装工艺的改变,给焊点可靠性带来了一系列相关问题。笔者就近年来国内外开发的无铅焊料、焊点的失效模式、焊点可靠性评价方法和焊点的主要缺陷进行了综述;对今后该领域的研究前景及方向进行了展望。     

QFP焊点可靠性研究

随着人们对健康和环境的要求越来越高,无铅焊料的研究倍受封装业的重视。塑性应变是影响电子封装焊点可靠性的主要因素,文章采用在多次温度循环条件下进行有限元数值模拟的方法,针对由不同元素(Sn,Pb,Ag,Cu)及配比构成的焊料,计算QFP焊点的塑性应变,定量评估其可靠性。给出焊料各参数对焊点可靠性的影响程度,仿真表明焊料激活能与气体常数的比值的变化对焊点可靠性影响最大,相应的焊点Y向塑性应变均值仅为优化前的11%。所得的结果可为今后QFP封装时的焊料选择提供新的理论依据。     

Effect of substrate flexibility on solder joint reliability. Part II: finite element modeling

Solder joint fatigue failure is a serious reliability concern in area array technologies, such as flip chip and ball grid array packages of integrated-circuit chips. The selection of different substrate materials could affect solder joint thermal fatigue life significantly. The mechanism of substrate flexibility on improving solder joint thermal fatigue was investigated by thermal mechanical analysis (TMA) technique and finite element modeling. The reliability of solder joints in real flip chip assembly with both rigid and compliant substrates was evaluated by accelerated temperature cycling test. Finite element simulations were conducted to study the reliability of solder joints in flip chip on flex assembly (FCOF) and flip chip on rigid board assembly (FCOB) applying Anand model. Based on the finite element analysis results, the fatigue lives of solder joints were obtained by Darveaux’s crack initiation and growth model. The thermal strain/stress in solder joints of flip chip assemblies with different substrates were compared. The results of finite element analysis showed a good agreement with the experimental results. It was found that the thermal fatigue lifetime of FCOF solder joints was much longer than that of FCOB solder joints. The thermal strain/stress in solder joints could be reduced by flex buckling or bending and flex substrates could dissipate energy that otherwise would be absorbed by solder joints. It was concluded that substrate flexibility has a great effect on solder joint reliability and the reliability improvement was attributed to flex buckling or bending during temperature cycling.     

LCCC封装器件热疲劳失效分析及结构优化研究

针对LCCC封装器件在温度循环载荷下焊点开裂的问题,首先分析其失效现象和机理,并建立有限元模型,进行失效应力仿真模拟。为降低焊点由封装材料CTE不匹配引起的热应力,提出了两种印制板应力释放方案,并分析研究单孔方案中不同孔径和阵列孔方案中不同孔数量对热疲劳寿命的影响。之后,为降低对PCB布局密度的影响,提出一种新型的叠层焊柱应力缓冲方案,进行了不同叠层板厚度和焊柱间距的敏感度分析。结果表明,更大的开孔面积、更小的叠层板厚度、更密的焊柱可有效降低焊点应力,提高焊点热疲劳寿命,使得LCCC封装器件焊点热疲劳可靠性得到有效提高。     

Application assessment of high throughput flip chip assembly for ahigh lead-eutectic solder cap interconnect system using no-flowunderfill materials

Flip chip on board (FCOB) is one of the most quickly growing segments in advanced electronic packaging. In many cases, assembly processes are not capable of providing the high throughputs needed for integrated surface mount technology (SMT) processing (Tummala et al, 1997). A new high throughput process using no-flow underfill materials has been developed that has the potential to significantly increase flip chip assembly throughput. Previous research has demonstrated the feasibility and reliability of the high throughput process required for FCOB assemblies. The goal of this research was to integrate the high throughput flip chip process on commercial flip chip packages that consisted of high lead solder balls on a polyimide passivated silicon die bonded with eutectic solder bumped pads on the laminate substrate interface (Qi, 1999). This involved extensive parametric experimentation that focused on the following elements: no-flow process evaluation and implementation on the commercial packages, reflow profile parameter effects on eutectic solder wetting of high lead solder bumps, interactions between the no-flow underfill materials and the package solder interconnect and tented via features, void capture and void formation during processing, and material set compatibility and the effects on long term reliability performance