晶体类型对无铅BGA焊点疲劳断裂失效影响的研究

借助ANSYS有限元分析软件,使用子模型分析技术对单晶结构和多晶结构两种不同晶体类型的无铅BGA焊点做了应力应变计算,并结合通过扫描电镜(SEM)获取的断裂焊点截面照片,对比分析了不同晶体类型对BGA焊点疲劳断裂失效的影响。得出结论:焊点晶体类型也是影响无铅BGA焊点疲劳断裂失效的重要因素。     

热循环条件下空洞对PBGA焊点热疲劳寿命的影响

球栅阵列(ball grid array, BGA)封装器件的广泛应用使空洞对焊点可靠性的影响成为业界关注的焦点之一.采用非线性有限元分析方法和统一型粘塑性本构方程,以PBGA组装焊点为对象,建立了互连焊点热应变损伤的三维有限元模型,并基于修正的Coffin-Manson方程,分析了在热循环加裁条件下不同位置和大小的空洞对焊点疲劳寿命的影响.研究结果显示,位于原应力集中区的空洞将降低焊点疲劳寿命,基于应变失效机理,焊点裂纹易在该类空洞周围萌生和扩展;位于焊球中心和远离原应力集中区的空洞,在一定程度上可提高焊点的疲劳寿命.     

QFP焊点塑性应变的数值模拟

元素铅既对人体存在神经毒性也对环境产生重金属污染,因此,无铅焊料的研究倍受封装业的重视。文章采用温度循环下有限元数值模拟方法,针对4种焊料5种配比包括SnPb（60／40,10／90）、SnPbAg（5／92．5／2．5）、SnAg（96．5／3．5）和SnAgCu（95．5／3．8／0．7）,定量评估QFP焊点的塑性应变。给出焊料各参数对于焊点塑性应变的影响程度,第一主元分析显式为△Ps≈-2．56△（Q／R）,相应的Y向塑性应变均值降低为优化前的11％。所得的结果可为QFP封装时的焊料选择提供新的设计参考。     

Assessment of Solder Joint Fatigue Life Under Realistic Service Conditions

The behavior of lead-free solder alloys under complex loading scenarios is still not well understood. Common damage accumulation rules fail to account for strong effects of variations in cycling amplitude, and random vibration test results cannot be interpreted in terms of performance under realistic service conditions. This is a result of the effects of cycling parameters on materials properties. These effects are not yet fully understood or quantitatively predictable, preventing modeling based on parameters such as strain, work, or entropy. Depending on the actual spectrum of amplitudes, Miner’s rule of linear damage accumulation has been shown to overestimate life by more than an order of magnitude, and greater errors are predicted for other combinations. Consequences may be particularly critical for so-called environmental stress screening. Damage accumulation has, however, been shown to scale with the inelastic work done, even if amplitudes vary. This and the observation of effects of loading history on subsequent work per cycle provide for a modified damage accumulation rule which allows for the prediction of life. Individual joints of four different Sn-Ag-Cu-based solder alloys (SAC305, SAC105, SAC-Ni, and SACXplus) were cycled in shear at room temperature, alternating between two different amplitudes while monitoring the evolution of the effective stiffness and work per cycle. This helped elucidate general trends and behaviors that are expected to occur in vibrations of microelectronics assemblies. Deviations from Miner’s rule varied systematically with the combination of amplitudes, the sequences of cycles, and the strain rates in each. The severity of deviations also varied systematically with Ag content in the solder, but major effects were observed for all the alloys. A systematic analysis was conducted to assess whether scenarios might exist in which the more fatigue-resistant high-Ag alloys would fail sooner than the lower-Ag ones.     

板级跌落碰撞下无铅焊点的可靠性研究

文中引入一块不同于JEDEC标准测试板的圆形测试板,探究板级跌落碰撞下无铅焊点的可靠性.首先做模态试验了解测试板的动力学特性,接着做跌落测试,同时测量板的应变和加速度历程.并用ABAQUS软件进行模拟,模拟焊点在跌落碰撞条件下焊点的应力应变等.结果表明有限元模拟得到的应变、板中心的加速度响应和试验吻合,而且用模拟预测的失效焊点的位置与试验一致.失效模式是靠近封装一侧的金属间化合物(IMC)界面的脆性断裂.     

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。     

回流时间对焊点质量的影响

讨论TSnAgCu305焊料和cu焊盘在不同回流时间下形成的金属间化合物的厚度和形貌,以及焊点内部的组织结构.通过剪切试验测得不同回流时间下得到的焊点强度.试验结果表明:回流时间较短时,IMC层的厚度随着时间的增大快速增长,随着时间推移最后IMC的厚度在5 μm左右趋于稳定.焊点内部的组织形貌随着时间变化由等轴晶到枝状...     

冷却速率对无铅钎料和焊点质量影响

阐述了再流焊冷却速率对无铅钎料和焊点质量的影响的研究现状.已有的研究结果表明:冷却速率对于无铅钎料的微观组织、拉伸性能、金属间化合物的形态和尺寸以及焊点中的凝固缺陷等都有显著的影响.选择合适的冷却速率可以提高焊点质量.     

焊盘尺寸对FC—PBGA焊点可靠性的影响

影响封装可靠性的因素很多,其中对封装及供货厂商相关的封装设计方面的各种变量应该给予足够的重视。焊盘尺寸是影响焊点可靠性的关键因素之一,不同供货厂商的各种工艺造成焊盘尺寸方面的差异,对可靠性造成了极大的影响。有限元应力分析、波纹干涉测量试验及可靠性试验表明,基板厚度影响封装可靠性。文章采用有限元模拟来定量分析焊盘尺寸对PBGA封装可靠性的影响,把空气对空气热循环试验结果与FEM预测进行比较,讨论最佳焊盘尺寸,并预测对焊点可靠性的影响。     

电路板焊点在工程环境条件下寿命分析

在电子设备寿命周期中．要经历各种环境载荷。我们需要综合号虑载荷对电子设备可靠性和寿命的影响。在该文中．以一块电路板为案例。建立整板模型．然后设定边界、分别加载温度和随机振动载荷。并利用有限元分析工具ANSYS计算,得出应力应变云值。最后基于Coffin—Manson疲劳寿命模型和线性叠加模型,分析和预测热循环和随机振动条件下．器件焊点疲劳寿命,为整板器件可靠性设计提供参考,     

BGA焊点空洞对信号传输性能的影响

焊点空洞问题是影响BGA焊点质量和可靠性的重要因素之一.基于三维电磁场仿真软件HFSS对单个焊点空洞建模,分别研究了BGA焊点中不同位置、大小和数目的空洞对焊点传输性能的影响.研究结果表明,焊点内部空洞比表面处空洞对信号传输性能的影响更大;在焊点表面上的空洞,位于焊点中部的空洞比接近上下焊盘的空洞对信号传输性能的影响大;随着焊点中空洞体积增大或空洞数目的增加,焊点的回波损耗增大.     

SMT焊点形态成形和焊点可靠性CAD

以PBGA焊点形态成形CAD和焊点热疲劳寿命可靠性CAD研究为例,提出SMT焊点形态成形和可靠性一体化设计思想,并对其实现方法进行了分析研究,给出了具体实现步骤和研究结果.     

SMT焊点形态成形和焊点可靠性CAD

以ＰＢＧＡ焊点形态成形ＣＡＤ和焊点热疲劳寿命可靠性ＣＡＤ研究为例,提出ＳＭＴ焊点形态成形和可靠性一体化设计思想,并对其实现方法进行了分析研究,给出了具体实现步骤和研究结果．     

振动载荷下电路板级焊点失效信号表征及分析

针对板级焊点在振动载荷下的失效问题,搭建了具有焊点电信号监测功能的振动加速失效实验平台,在定频定幅简谐振动实验的基础上,对表征信号进行分析,通过电阻信号峰值标定焊点的失效程度.实验结果表明,焊点失效初期呈现为3个阶段,每个阶段包含电阻变化的平缓区间和陡变区间.随着3个阶段的改变,焊点低阻值区间振动循环数递减,焊点高阻值区间振动循环数递增.在此基础上,以电阻均值表征焊点平均失效程度,建立了表征焊点振动疲劳寿命的多项式模型,可以描述不同阶段焊点阻值和振动循环数的关系.     

Effect of Thermal Aging on the Microstructure Evolution and Solder Joint Reliability in Hard Disk Drive Under Mechanical Shock

The effect of thermal aging on the microstructure evolution and solder joint reliability in hard disk drive (HDD) under mechanical shock was investigated. Significant coarsening of ${hbox {Ag}}_{3} {hbox {Sn}}$ particles was found in SnAgCu solder, and ${rm AuSn}_{4}$ intermetallic compound (IMC) changed from needle-type to layer-type during aging. For as-soldered SnAgCu solder joints after mechanical shock, the cracks were initiated in ${hbox {AuSn}}_{4}$ at the corner of the solder joints, and mainly propagated along the thin ${hbox {Ni}}_{3} {hbox {Sn}}_{4}$ IMC layer. After aging at 150 $^circ$C for 21 days, the cracks were mainly propagated along the solder, ${hbox {Ni}}_{3} {hbox {Sn}}_{4}$, Au–Sn–Ni–Cu, and Au–Cu–Sn. The significant coarsening of microstructure was found in SnPb solder joints, and only microcracks were found on the surfaces of as-soldered and aged solder joints after mechanical shock.      

Modeling Fracture of Sn-Rich (Pb-Free) Solder Joints Under Mechanical Shock Conditions

With the increasing focus on developing environmentally benign electronic packages, lead-free solder alloys have received a great deal of attention. Mishandling of packages during manufacture, assembly, or by the user may cause solder joint failure. In this work, we conducted finite-element analysis to model solder joint fracture under dynamic loading conditions. The solder is modeled as a porous plastic material, and the intermetallic compound (IMC) material is characterized as an elastic material. The fracture of the solder is governed by void nucleation, and the IMC fracture is brittle in nature. The randomness of the void volume fraction in the solder and the defects in the IMC are considered and implemented in the finite-element package ABAQUS. The finite-element results show that the fracture mechanisms of the solder joints depend on the strain rate and IMC thickness. High strain rate and larger IMC thickness favor IMC-controlled fracture, which is brittle in nature. Low strain rate and smaller IMC thickness lead to solder-controlled fracture, which is governed by void growth and nucleation. Based on this finding, a mechanistic explanation for solder joint fracture is suggested.     

氮气保护对无铅再流焊焊点外观质量的影响

由于无铅钎料润湿性较差,在实际生产中普遍采用氮气保护。通过新制定的氮气保护无铅再流焊工艺,对焊点外观质量进行了统计分析。其结果显示氮气保护可以减少元件偏移和桥连等缺陷,对竖碑、焊球和锡珠等缺陷也有一定影响。     

热循环加载条件下SMT焊点应力应变过程的有限元分析

ＳＭＴ焊 热循环条件下的应力应变过程分析是ＳＭＴ焊点可靠性的重要方向。本文采用粘弹塑性材料模式描述ＳｎＰｂ钎料的力学本构响应，对非城堡型ＬＣＣＣ焊蹼结构进行三维有限元分析，考察焊点在热循环加载过程中的应力应变等力学行为。研究结果表明，焊点钎料内的高应力发生在热循环的低温阶段，升降温过程中的蠕变和非弹性应变的累积显著，蠕变应变在非弹性应变中占主导地位，应力应变滞后环在热循环的最初几个周期内就能很快稳     

稀土含量对Sn—Pb—Re钎料SMT焊点热循环性能的影响

本文对不同稀土含量Ｓｎ－Ｐｂ－Ｒｅ钎料系焊点的热循环寿命进行了实验研究，结果表明，钎料中稀土含量为０．０５％－０．５％时，可使焊点的热循环寿命提高到普通Ｓｎ６０Ｐｂ４０钎料的２－３倍以上；