模板参数对倒装焊焊点形态的影响

模板开口的尺寸和厚度决定应用于PCB板上焊膏的量，从而决定了回流焊后生成的焊点形态。本文根据IPC-7525模板设计理论，拟定多组开口方案，设计了16组模板结构参数，并通过软件Surface Evolver输入数据文件，得到16组倒装焊焊点形态，用有限元软件进行焊点寿命分析，得到了模板结构参数与热疲劳寿命的关系，探讨不同的开口尺寸和厚度对焊点形态的影响。     

LGA焊点形态对焊点寿命影响的有限元分析

通过Surface Evolver软件对LGA焊点进行了三维形态预测,利用有限元数值模拟对LGA焊点在热循环条件下寿命进行了分析。研究了热循环条件下LGA焊点的应力应变分布规律,随着焊点远离元件的中心位置焊点所受到的等效应力、等效应变和塑性应变能密度逐渐增大,从而得出处于外面拐角的焊点最先发生失效的结论。基于塑性应变范围和Coffin-Manson公式计算了焊点热疲劳寿命;找出了LGA焊点形态对焊点寿命的影响规律,模板厚度一定时PCB焊盘尺寸小于上焊盘时LGA焊点的热疲劳寿命与PCB焊盘尺寸成正比,大于上焊盘时成反比,大约相等时焊点寿命最大。当PCB焊盘和模板开孔尺寸固定时,通过增大模板厚度来增加焊料体积在一定程度上可提高LGA焊点的热疲劳寿命,但是模板厚度增大到一定值时LGA焊点寿命会逐渐降低。     

振动载荷下特种设备中电路板级焊点疲劳寿命预测

基于内聚力模型,提出一种用于振动载荷下特种设备中电路板级焊点疲劳寿命预测的介观尺度模型。将单调载荷与振动周期载荷相结合,建立焊点累积损伤参数来表征焊点的剩余疲劳寿命,利用焊点损伤累积率来表征焊点损伤演化规律。以Sn3.0Ag0.5Cu(SAC305)细间距无铅焊点为例分析了模型参数确定方法,并通过振幅为5 mm与10 mm的定频振动试验对模型的预测精度进行了验证,寿命预测结果误差小于10%。由于模型参数为焊点钎料累积塑性应变的固有函数,与焊点尺寸与几何形态无关,通过小样本试验,数据一经确定即可应用于同种钎料不同尺寸焊点在不同振动等级下的疲劳寿命预测,节约了时间与试验成本,该模型能为特种设备中的电子组件提供一种评估板级焊点疲劳寿命的简洁、实用方法。     

CSP封装Sn-3.5Ag焊点的热疲劳寿命预测

对芯片尺寸封装(CSP)中Sn-3.5Ag无铅焊点在热循环加速载荷下的热疲劳寿命进行了预测.首先利用ANSYS软件建立CSP封装的三维有限元对称模型,运用Anand本构模型描述Sn-3.5Ag无铅焊点的粘塑性材料特性;通过有限元模拟的方法分析了封装结构在热循环载荷下的变形及焊点的应力应变行为,并结合Darveaux疲劳寿命模型预测了无铅焊点的热疲劳寿命.     

CSP封装Sn-3.5Ag焊点的热疲劳寿命预测

对芯片尺寸封装(CSP)中Sn-3.5Ag无铅焊点在热循环加速载荷下的热疲劳寿命进行了预测.首先利用ANSYS软件建立CSP封装的三维有限元对称模型,运用Anand本构模型描述Sn-3.5Ag无铅焊点的粘塑性材料特性;通过有限元模拟的方法分析了封装结构在热循环载荷下的变形及焊点的应力应变行为,并结合Darveaux疲劳寿命模型预测了无铅焊点的热疲劳寿命.     

倒装焊焊点形态及其可靠性研究

本文采用Surface Evolver软件对倒装焊复合焊点的几何形态进行了模拟。通过非线性有限元方法研究有铅和无铅两种焊点在热循环作用下的应力应变关系，基于疲劳寿命C—M预测公式对焊点的热疲劳寿命进行预测与比较。     

PBGA焊点热疲劳寿命的正交试验及回归分析

通过对ＰＢＧＡ焊点形态参数与焊点热疲劳寿命的正交试验,利用大型统计分析软件进行多元线性回归分析,建立起ＰＢＧＡ焊点高度固定,芯片在上焊点高度不固定及芯片在下焊 度不固定三种不同工作条件下形态参数与热疲劳寿命之间的回归多项表式,即ＰＢＧＡ焊点形参数与热疲劳寿命的关系表达式。     

气孔缺陷对同轴电缆焊点热疲劳寿命影响

利用ANSYS软件建立了热循环条件下同轴电缆焊点的三维有限元模型,分析了气孔的大小及位置对焊点在热循环过程中的应力应变分布特征的影响,结合Manson-Coffin方程预测了不同气孔大小及位置对焊点的热疲劳寿命的影响.结果表明:气孔的存在使焊点的热疲劳寿命急剧缩短;相同尺寸的气孔存在于焊点内部时位置的改变对热疲劳寿命影响很小;处于焊点内部的气孔对焊点的疲劳寿命影响要小于靠近表面的气孔;处于焊点根部的气孔对焊点疲劳寿命的影响要远大于其它位置的气孔;气孔越大,对焊点的疲劳寿命影响越大.     

BGA焊点的形态预测及可靠性优化设计

制定了BGA(球栅阵列)焊点的形态预测以及可靠性分析优化设计方案，对完全分布和四边分布的两种BGA元件，通过改变下焊盘的尺寸得到不同钎料量的焊点，并对其形态进行了预测，建立了可靠性分析的三维力学模型。采用有限元方法分析了元件和焊点在热循环条件下的应力应变分布特征，预测了不同种类和不同形态的BGA焊点的热疲劳寿命，由此给出了最佳的上下焊盘比例范围。     

承载式车身焊点疲劳寿命分析研究

文中针对某承载式车身焊点结合疲劳寿命虚拟分析技术与强化耐久试验进行了比较研究。根据疲劳寿命分析理论,采用经模态试验验证了其精度及有效性的模型,结合多体动力学分析得到的载荷谱,对车身焊点的疲劳寿命进行预测分析;并与强化疲劳耐久试验结果进行了比较,分析了造成车身焊点低寿命区域的原因并提出了改进方案,从而有效解决了该车车身焊点疲劳寿命设计中存在的缺陷,为后续设计与优化提供了参照。     

焊膏厚度对CBGA组装板可靠性的影响

为了研究焊膏厚度对氮气保护再流焊CBGA组装板可靠性的影响 ,设计采用 0 .10mm、0 .15mm、0 .2 0mm三种厚度的焊膏和压缩空气与氮气保护再流焊来准备CBGA组装板可靠性试样。通过对组装板试样进行剪切强度、弯曲疲劳、热冲击和振动疲劳等可靠性试验来优化组装工艺过程。试验结果显示出 0 .15mm厚度的焊膏具有最佳的机械性能 ,氮气保护对改进组装板的性能起明显的作用。理论模型也定量给出了焊膏厚度与焊点性能之间的关系。     

Board level solder joint reliability modeling and testing of TFBGA packages for telecommunication applications

For thin-profile fine-pitch BGA (TFBGA) packages, board level solder joint reliability during the thermal cycling test is a critical issue. In this paper, both global and local parametric 3D FEA fatigue models are established for TFBGA on board with considerations of detailed pad design, realistic shape of solder joint, and nonlinear material properties. They have the capability to predict the fatigue life of solder joint during the thermal cycling test within ±13% error. The fatigue model applied is based on a modified Darveaux’s approach with nonlinear viscoplastic analysis of solder joints. A solder joint damage model is used to establish a connection between the strain energy density (SED) per cycle obtained from the FEA model and the actual characteristic life during the thermal cycling test. For the test vehicles studied, the maximum SED is observed at the top corner of outermost diagonal solder ball. The modeling predicted fatigue life is first correlated to the thermal cycling test results using modified correlation constants, curve-fitted from in-house BGA thermal cycling test data. Subsequently, design analysis is performed to study the effects of 14 key package dimensions, material properties, and thermal cycling test condition. In general, smaller die size, higher solder ball standoff, smaller maximum solder ball diameter, bigger solder mask opening, thinner board, higher mold compound CTE, smaller thermal cycling temperature range, and depopulated array type of ball layout pattern contribute to longer fatigue life.     

Comprehensive board-level solder joint reliability modeling and testing of QFN and PowerQFN packages

For quad flat non-lead (QFN) packages, board-level solder joint reliability during thermal cycling test is a critical issue. In this paper, a parametric 3D FEA sliced model is established for QFN on board with considerations of detailed pad design, realistic shape of solder joint and solder fillet, and non-linear material properties. It has the capability to predict the fatigue life of solder joint during thermal cycling test within ±34% error. The fatigue model applied is based on a modified Darveaux’s approach with non-linear viscoplastic analysis of solder joints. A solder joint damage model is used to establish a connection between the strain energy density (SED) per cycle obtained from the FEA model and the actual characteristic life during thermal cycling test. For the test vehicles studied, the maximum SED is observed mostly at the top corner of peripheral solder joint. The modeling predicted fatigue life is first correlated to thermal cycling test results using modified correlation constants, curve-fitted from in-house QFN thermal cycling test data. Subsequently, design analysis is performed to study the effects of 17 key package dimensions, material properties, and thermal cycling test condition. Generally, smaller package size, smaller die size, bigger pad size, thinner PCB, higher mold compound CTE, higher solder standoff, and extra soldering at the center pad help to enhance the fatigue life. Comparisons are made with thermal cycling test results to confirm the relative trends of certain effects. Another enhanced QFN design with better solder joint reliability, PowerQFN, is also studied and compared with QFN of the same package size.     

片式元件与基板间隙对无铅焊点可靠性的影响

采用非线性有限元方法,讨论了片式元件与基板的间隙对Sn-2.5Ag-0.7Cu无铅钎料焊点的应力分布和热疲劳寿命的影响。结果表明,当间隙高度为0.1~0.2mm时,焊点薄弱处——元件底部拐角处、焊根的顶部和底部以及焊趾顶部具有较低的应力,此时预测得到焊点的热疲劳寿命也最长。这一结果对于焊点几何形态的设计及优化具有指导意义。     

Reliability Analysis of Lead-Free Solder Castellations

In this paper, the reliability of lead-free solder castellations is considered. The newly developed stress-dependent Engelmaier's solder fatigue model is utilized in this task. Based on this model, it is possible to interpret the thermal cycling test results. A very good agreement between the test results and the lifetime predictions is obtained. Using the lifetime prediction model, optimal solder castellation shape is investigated. Based on the findings, the fatigue life can be improved by up to 30% simply by solder pad length optimization. Further increment in lifetime length can be expected if the solder joint shape is optimized with the help of modeling tools presented here. Understanding how the crack propagates in solder material is vital if optimal lifetime behavior is expected.     

CQFP器件板级温循可靠性的设计与仿真

温度循环是考核封装产品板级可靠性的重要试验之一。陶瓷四边引脚扁平封装(CQFP)适用于表面贴装,由于陶瓷材料与PCB热膨胀系数的差异,温循过程中引线互联部分产生周期性的应力应变,当陶瓷壳体面积较大时,焊点易出现疲劳失效现象。CQFP引线成形方式分顶部成形和底部成形两类。针对CQFP引线底部成形产品在板级温循中出现的焊接层开裂现象,采用有限元方法对焊接层的疲劳寿命进行了预测分析。采用二次成形方法对引线进行再次成形以缓解和释放热失配产生的应力。仿真和试验结果显示,引线二次成形有利于提高焊接层的温循疲劳寿命。与引线底部成形相比,当引线采用顶部成形时,焊接层的温循疲劳寿命显著提高。     

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。     

Computational parametric analyzes on the solder joint reliability of bottom leaded plastic (BLP) package

The bottom-leaded plastic (BLP) package is a lead-on-chip type of chip scale package (CSP) developed mainly for memory devices. Because the BLP package is one of the smallest plastic packages available, solder joint reliability becomes a critical issue. In this study, a 28-pin BLP package is modeled to investigate the effects of molding compound and leadframe material properties, the thickness of printed circuit board (PCB), the shape of solder joint and the solder pad size on the board level solder joint reliability. A viscoplastic constitutive relation is adopted for the modeling of solder in order to account for its time and temperature dependence on thermal cycling. A three-dimensional nonlinear finite element analysis based on the above constitutive relation is conducted to model the response of a BLP assembly subjected to thermal cycling. The fatigue life of the solder joint is estimated by the modified Coffin-Manson equation. The two coefficients in the modified Coffin-Manson equation are also determined. Parametric studies are performed to investigate the dependence of solder joint fatigue life on various design factors.