Influences of fine pitch solder joint shape parameters on fatigue life under thermal cycle

The solder joint reliability of a 0.5mm lead pitch, 240-pin quad flat package(QFP) was studied by nonlinear finite element analysis(FEA). The stress/strain distributions within the solder joints and the maximum plastic strain range of the solder joints were determined. Based on the calculated maximum plastic strain range the thermal fatigue life of the solder joints was calculated using Coffin-Manson equation. The influences of shape parameters including volume of solder joint, pad size and stand-off on the thermal fatigue life of the solder joints were also studied. The results show that the stress and strain distribution in the solder joint are not uniform; the interface between the lead and the solder joint is the high stress and strain region; the maximum stress and stain occur at the topmost point where the solder joint intersects with the inner side of the lead. The solder joint cracks should occur firstly at this point and propagate along the interface between the solder and the lead. The solder joint with the pad size of 1.25mm×0.35mm, the stand-off of 0.02mm and the solder volume of 0.026mm^3 has longer fatigue life than that of any others. These optimal parameters have been applied in practice to assemble the 240-pin, 0.5mm pitch QFP.

QUICK ASSESSMENT METHODOLOGY FOR RELIABILITY OF SOLDER JOINTS IN BALL GRID ARRAY (BGA) ASSEMBLY——PART Ⅰ: CREEP CONSTITUTIVE RELATION AND FATIGUE MODEL

In this study, a new unified creep constitutive relation and a mod- ified energy-based fatigue model have been established respectively to describe the creep flow and predict the fatigue life of Sn-Pb solders. It is found that the relation successfully elucidates the creep mechanism related to current constitutive relations. The model can be used to describe the temperature and frequency dependent low cycle fatigue behavior of the solder. The relation and the model are further employed in part Ⅱ to develop the numerical simulation approach for the long-term reliability assessment of the plastic ball grid array (BGA) assembly.

Solder joint geometry of tin-lead alloy and its application in electronic packaging

By employing the minimum energy theorem, the Potential energy controlling equation, which consists of surface energy and gravitational energy for molten meniscus, was investigated. The soder joint geometry of molten tin-lead soder alloy for chip component and thin quad flat package were simulated with finite element method. The simulation results 0f solder joint geometry are coincident well with the experimental results. The solder joint geometry was applied to study the solder joint reliability for chip component RC3216.The thermal cycling tests revealed that the solder joint geometry plays an important ro1e in solder joint reliability.

Fatigue damage behavior of a surface-mount electronic package under different cyclic applied loads

This paper studies and compares the effects of pull-pull and 3-point bending cyclic loadings on the mechanical fa- tigue damage behaviors of a solder joint in a surface-mount electronic package. The comparisons are based on experimental investigations using scanning electron microscopy （SEM） in-situ technology and nonlinear finite element modeling, respec- tively. The compared results indicate that there are different threshold levels of plastic strain for the initial damage of solder joints under two cyclic applied loads; meanwhile, fatigue crack initiation occurs at different locations, and the accumulation of equivalent plastic strain determines the trend and direction of fatigue crack propagation. In addition, simulation results of the fatigue damage process of solder joints considering a constitutive model of damage initiation criteria for ductile materials and damage evolution based on accumulating inelastic hysteresis energy are identical to the experimental results. The actual fatigue life of the solder joint is almost the same and demonstrates that the FE modeling used in this study can provide an accurate prediction of solder joint fatigue failure.

Study on Higher Efficiency Thermal Cycling Profile for HALT

HALT(highly accelerated life test) is a new reliability test technique.This paper uses nonlinear finite element method to analyze the stress strain characteristic of solder joints of PQFP(plastic quad flat packaging) and BGA(ball grid array) under thermal cycle test,and studies influences of profile parameters of the thermal cycle,such as hot and cold soak temperature,hot and cold soak time and temperature change rate,on elastic strain range,accumulated plastic strain,fatigue life and test efficiency of two types of solder joints.Based on the above research and experimental verification,this paper presents the method to build an optimal thermal cycling profile for HALT of electronic components.

Study on Integrated Thermal Cycle and Vibration Profile for HALT

Focusing on electronic products,this paper establishes a finite element model for printed circuit board(PCB)assembling with enhanced ball grid array(EBGA)component under vibration environment.Based on this model,it studies relations between fatigue rate of solder joint and temperature,vibration frequency.Moreover,it analyzes propagation of micro-crack produced by thermal cycle under vibration stress.The results offer a method to optimize the thermal cycle and vibration integrated profile and to combine vibration test and thermal cycling for highly accelerated life test(HALT).

陶瓷封装球栅阵列焊点失效机理研究

研究了陶瓷封装球栅阵列(CBGA)的焊点在长期使用后开裂的失效机理,提出了改善此类元器件焊点可靠性的有效措施。通过X-ray分析、显微剖切、扫描电镜和能谱分析(SEM&EDS)等手段,研究分析了CBGA封装器件焊点失效的机理与成因;基于失效机理,提出了针对性的改善措施,并验证了相关措施的有效性。研究结果表明,由于CBGA器件本体与印制板之间存在较大的热膨胀系数差异,导致焊点在长期使用后出现了热疲劳开裂失效,通过更换焊球类型以增加焊点高度可以显著地改善焊点的可靠性。

温度循环和随机振动载荷下堆叠封装焊点可靠性模拟研究

采用有限元模拟研究了堆叠封装(Package on package, PoP)在温度循环和随机振动载荷下的焊点可靠性,包括封装内部的基板堆叠焊点和封装外部的板级互连焊点。通过应力分析定位危险焊点并计算焊点在温度循环下的疲劳寿命。模拟结果表明:在温度循环载荷下,应力主要集中于基板边角处焊点,基板堆叠焊点的疲劳寿命为3 002周次,板级互连焊点的疲劳寿命为1 552周次;在随机振动载荷下,两层焊点的应力值均较低,在50~2 000 Hz的随机振动频率范围内具有较高的可靠性。

PBGA焊点形态对疲劳寿命的影响

通过Surface Evolver软件预测了塑料球栅阵列(PBGA)焊点形态,将焊点形态结果导入Ansys软件中进行-55~125℃热循环仿真实验,通过Coffin-Masson模型预测焊点寿命。选取焊点钎料量、焊点高度、下焊盘直径作为影响焊点寿命的主要因素进行了3因素3水平正交实验,通过均值响应分析得到了影响凸点寿命的最敏感因素及最优形态尺寸组合。结果表明对焊点寿命影响最大的因素为下焊盘半径,其次是钎料量,最后是焊点高度,且上下等大的焊盘具有较好的可靠性。

基于Anand模型的BGA封装热冲击循环分析及焊点疲劳寿命预测

BGA封装在电子元器件中的互连、信息传输等方面起着重要作用,研究封装元件的可靠性以及内部焊点在高温、高湿、高压等极限条件下的稳定性显得尤为重要。基于Anand模型分析了封装元件在热冲击下的塑性变形和应力分布,同时对不同空间位置焊点的最大应力与主要失效位置进行了对比,并运用Darveaux模型计算出焊点最危险单元的裂纹萌生、裂纹扩展速率和疲劳寿命。结果表明,在热冲击极限载荷下,封装元件的温度呈现对称分布,表面温度与内部温度差较大,约为15℃;最大变形为0.038 mm,最大变形位置为外侧镀膜处;最大应力为222.18 MPa,内部其余部分的应力值为20 MPa左右。对于内部焊点,最大应力为19.02 MPa (250 s),应力最大位置在锡球下方边缘,预估其疲劳寿命为6.29天。

PCB各向异性行为对焊点疲劳寿命的影响研究

当前微系统不断向着小型化、高密度和高可靠性方向发展,印制电路板(PCB)为微系统器件提供电气连接和机械支撑,对系统的服役可靠性起着至关重要的作用。根据PCB在不同方向上热膨胀系数(CTE)的差异,通过数值模拟研究了3种PCB模型在温度循环载荷下焊点的寿命和应力应变响应情况,并对比了3种模型得到的计算结果,发现3种模型得到的结果存在较大差别。通过试验结果验证了仿真的准确性,表明在进行板级有限元分析时,关注焊球寿命时应充分考虑PCB复合材料的各向异性行为。同时,定量分析了由不同类别PCB模型获得的焊点寿命,为建立板级高保真数值模型和调控焊点寿命提供依据。

电热固耦合作用下车载功率模块引脚焊点振动疲劳寿命研究

本文对车载功率模块引脚焊点在器件功率损耗产生的热量和路面颠簸引起的随机振动共同影响下的可靠性进行了研究.建立多物理场有限元分析模型对引脚焊点进行电热固耦合疲劳寿命仿真,得到发热状态和常温状态下的焊点随机振动响应应力分布和振动疲劳损伤值.利用基于经验的Dirlik疲劳损伤模型和Miner线性损伤累积法则对两种状态的疲劳寿命进行了估算和对比分析.结果表明:在考虑电热固耦合作用下,局部约束刚度降低和焊点振动响应应力增大导致焊点振动疲劳寿命明显降低,但仍然满足规定的振动可靠性要求.结合满功率负载发热状态下的振动失效试验结果,验证了分析结果的准确性和装置设计的可靠性.

环境应力影响下球栅阵列封装焊球仿真分析与力学性能研究

高密度、高性能集成电路主要封装技术采用球栅阵列封装(ball grid array,BGA),其高密度Sn-Pb焊球在极端高、低温及湿热环境的影响下可靠性无法保证。为解决温度变化产生的热膨胀问题,笔者通过有限元仿真计算BGA电路中焊球在高、低温交替循环应力下瞬态黏塑性应变范围,并采用改进的Coffin-Manson经验方程计算器件在温度循环试验下的热疲劳寿命;此外,进一步采用准静态剪切和拉脱试验分析分别经过温度循环及高压蒸煮环境试验后焊球的力学性能,同时采用扫描电子显微镜(scanning electron microscopy,SEM)和能谱分析仪(energy dispersive spectroscopy,EDS)对焊球切面进行分析。研究表明:焊球在温度循环试验下具有较长的疲劳寿命,在不考虑焊球导电与连接性能的前提下,适当环境应力的影响可促使焊球与焊盘界面区域金属间化合物的生成,有效增强了焊球的剪切力学性能。

法兰端面防松片焊点疲劳寿命及分布优化研究

关于法兰端面防松片焊点疲劳寿命与焊点布置问题,如果根据焊接标准对工件焊点布置方案进行设计,可能会导致工件材料的性能得不到完全发挥,若在一些危险区域的焊点过少,则会导致焊接失败,焊点过多则会导致材料性能的破坏,焊接成本增加。因此,根据防松片焊点疲劳寿命与个数之间的关系,对防松片焊点布置方案进行了优化设计,提高法兰端面防松片焊点疲劳寿命性能。首先,对法兰端面防松片焊点布置方案进行了设计;其次,基于ANSYS建立了防松片焊接有限元模型,通过对焊接过程中热流密度分布的分析,采用高斯热源模型作为防松片焊接模型热源;通过对防松片焊点模型分析求解出了法兰端面防松片不同焊点布置方案的最大应变;最后,建立了焊点疲劳寿命预测模型,根据应变进行疲劳寿命预测并进行求解,求解出不同分布方案下焊点的疲劳寿命,并对数据进行高斯曲线拟合建立优化函数关系,通过拟合优化结果表明当防松片内圈焊点24个、外圈焊点30个同时作用在防松片上时,其焊点疲劳寿命能够得到较好的保持。

Pb_(90)Sn_(10)焊点硅基器件与PCB板组装的温循可靠性研究

采用有限元仿真和实验两者相结合的方法,对-40~70℃使用环境下的Pb_(90)Sn_(10)焊点硅基器件与PCB板组装的组件,选择-55~85℃温度循环条件进行可靠性分析和研究。Anand模型仿真分析焊点在温循下应力应变行为,提取模型焊点在最后一个温度循环结束时的等效塑性应变分布并进行分析,确定最易发生热疲劳失效的关键焊点和关键位置。基于Coffin-Manson方程对热循环条件下焊点的服役寿命和失效模式进行预测。仿真结果表明焊点失效机理为热疲劳失效,失效模式为焊点开裂,失效循环周期为3984 cycles。实验表明:温度循环500次,未出现焊点裂纹、空洞等缺陷;温度循环2000次后焊点形貌由球形变为椭球形,焊点未出现明显缺陷。

基于Darveaux模型的BGA焊点寿命预测影响因素研究

以微系统封装结构中球栅阵列封装(BGA)焊点为研究对象,对热循环载荷下Darveaux模型疲劳寿命预测方法的影响因素进行了探讨.结合有限元仿真分析,分别讨论了裂纹扩展相关系数、粘塑性应变能密度增量和断裂特征长度对Darveaux模型寿命预测结果的影响,揭示了目前焊点可靠性研究中对Darveaux寿命模型在使用时影响因素考虑不充分的现状,并给出了如何考虑上述影响因素的相关建议.进一步,基于蒙特卡洛抽样的全局敏感度分析方法,研究了不同断裂特征长度下,疲劳寿命对Darveaux模型中材料参数的敏感性.研究结果为热循环载荷下正确使用Darveaux模型来预测微系统封装结构的热疲劳寿命提供了有益的参考,为这些关键因素的确定提供了合理性建议与参考依据.

BGA几何建模对仿真分析结果的影响研究

有限元分析是研究BGA封装焊点可靠性以及疲劳寿命的主要手段,由于焊点密集,通常需要通过简化模型进行计算。本文分别以球形、柱状及混合型三种焊点形状建立了含有BGA封装的电路板有限元模型,对比分析了三种焊点模型下含BGA封装的电路板的模态特性、随机振动响应、疲劳寿命计算结果,结果表明柱状焊点可有效提高计算效率,球状焊点最接近真实情况,混合型焊点具有代替球形焊点的可行性。

QFP焊点形态模拟及随机振动疲劳寿命预测

针对电子设备中翼型焊点的振动可靠性问题,介绍了电子设备元器件焊点在随机振动载荷下的仿真分析的通用方法。通过Surface Evolver软件得到了某机载电子设备元器件焊点的形态预测模型,然后结合Hypermesh将模型导入到ABAQUS有限元软件中完成有限元模型搭建;在有限元软件中,对模型加载随机振动载荷,采用Steinberg模型,结合Manson高周疲劳经验公式及Palmgren-Miner线性疲劳损伤累计准则;得到了焊点随机振动载荷下的可靠性寿命,研究成果对电子设备元器件焊点的失效分析具有实用价值。

无引线陶瓷芯片载体器件焊点开裂分析及焊接可靠性提升

由于封装体、焊料和基板的热膨胀系数存在差异,无引线陶瓷芯片载体(LCCC)器件的焊料在温度循环测试条件下会反复发生剪切变形,进而引起疲劳失效、焊点可靠性下降。通过热疲劳寿命预测模型对LCCC封装焊点热疲劳寿命进行理论分析;通过增加焊点高度提升焊接可靠性,并通过试验加以验证;研究了增加焊点高度的不同方式对提升LCCC器件焊接可靠性的影响。分析结果和实施方案对确立LCCC器件的焊接指导原则及扩展LCCC器件的应用范围具有参考价值。

QFP组件的优化模拟及焊点热疲劳寿命的预测

采用有限元方法研究了方形扁平式封装QFP(quadflatpackage)组件的优化模拟及引线宽度与间距对焊点疲劳寿命的影响规律。结果表明,在QFP64组件的所有焊点中,最外侧焊点的正前面存在最大应变值,易产生裂纹,发生疲劳破坏,为组件的最脆弱部位。QFP引线间距固定时,随着引线宽度的增加,焊点等效应变值逐渐增加,焊点可靠性降低,热疲劳寿命降低;QFP引线宽度固定时,随着引线间距的增加,存在一个焊点热疲劳寿命最大值;所选取的计算模型中,当引线宽度为0.15mm,引线间距为0.45mm时,焊点可靠性最高,组件具有最长的疲劳寿命。