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．     

焊盘尺寸对PBGA组装板可靠性的影响

研究了焊盘尺寸对氮气再流焊ＰＢＧＡ组装板可靠性的影响。氮气保护再流焊炉内的氧含量可低至５×１０－５。对ＰＢＧＡ组装板的焊点进行了拉伸试验、弯曲疲劳试验以及热冲击疲劳试验。结果表明：经氮气保护再流焊组装的ＰＢＧＡ板其焊点的各项性能均比无保护的ＰＢＧＡ组装板好。当ＰＣＢ板焊盘直径等于ＰＢＧＡ基底焊盘直径时,其焊点有最好的性能。     

球栅阵列(BGA)器件焊点形态成形建模与预测

本文基于最小能量原理建立了塑料球栅阵列（ＰＢＧＡ）焊点形态成形模型,运用有限元方法预测ＰＢＧＡ焊点形态,并对预测结果与其它不同模型的预测结果和实验结果进行了对比．结果表明,有限元方法预测结果与其它模型结果和实验结果吻合良好．     

塑料球栅阵列（PBGA）焊点三维形态预测与分析

本文应用最小能量原理和有限元方法，建立塑料球栅阵列（ＰＢＧＡ）器件焊点三维形态预测模型。对ＰＢＧＡ焊点三维形态进行预测和分析。并将预测结果与试验结果以及国外学者用数学分析模型所得的预测结果进行了对比验证。     

模板对倒装焊焊点形态的影响及其可靠性研究

本文通过用于焊点形态预测软件SURFACE EVOLVER的输入数据文件,得到倒装焊焊点形态.参考模板开口指导说明(IPC-7525),拟定模板开口方案,得到相应的焊点形态.通过建立有限元模型,运用ANSYS软件对含铅焊点在热循环加载条件下的应力应变和疲劳寿命进行分析.根据预测得到的热疲劳寿命,找出了适合本文模型的模板结构参数,同时分析了其它设计与工艺参数和焊点可靠性之间的关系.     

PCBA结构参数与振动谱型对BGA焊点疲劳寿命的影响

为获得印制电路板组件(PCBA)的板厚、芯片布局等结构参数和随机振动谱型(功率谱密度,PSD)变化对球栅阵列(BGA)封装芯片焊点振动疲劳寿命的影响,利用HYPERMESH软件建立了带BGA封装芯片的PCBA三维有限元网格模型,并采用ANSYS软件对PCBA有限元模型进行了随机振动响应分析。结果表明,随着PCB厚度增加,BGA焊点振动疲劳寿命呈现明显提升的趋势,当PCB厚度由1.2 mm增加到2.2 mm时,BGA焊点振动疲劳寿命N由45363大幅增加到557386;合理的芯片安装间距能够明显增加焊点振动疲劳寿命,特别是当芯片安装在靠近固定约束并处于两个约束对称中间位置时;当PCBA的第一阶固有频率位于随机振动谱最大幅值对应的频率区间时,BGA焊点的振动疲劳寿命会明显降低。     

叠层芯片封装元件热应力分析及焊点寿命预测

研究了温度循环载荷下叠层芯片封装元件(SCSP)的热应力分布情况,建立了SCSP的有限元模型。采用修正后的Coffin-Masson公式,计算了SCSP焊点的热疲劳寿命。结果表明:多层芯片间存在热应力差异。其中顶部与底部芯片的热应力高于中间的隔离芯片。并且由于环氧模塑封材料、芯片之间的热膨胀系数失配,芯片热应力集中区域有发生脱层开裂的可能性。SCSP的焊点热疲劳寿命模拟值为1 052个循环周,低于单芯片封装元件的焊点热疲劳寿命(2 656个循环周)。     

基于最小能量原理的SMT焊点三维形态预测

本文应用最小能量原理和有限元方法建立表面组装技术（ＳＭＴ：Ｓｕｒｆａｃｅ Ｍｏｕｎｔ Ｔｅｃｈｎｏｌｏｇｙ）形成的焊点三维形态预测模型,并运用该模型对塑料球栅阵列（ＰＢＧＡ：Ｐｌａｓｔｉｃ Ｂａｌｌ Ｇｒｉｄ Ａｒｒａｙ）器件焊点三维形态问题进行了预测和分析。最后将预测结果与试验结果以及国外学者用数学分析模型所得的预测结果进行了对比验证。     

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。     

焊点疲劳寿命的量化评价方法及其影响因素

焊点蠕变疲劳是电子产品破坏中一种最主要的形式,对焊点疲劳寿命的量化评价是电子产品可靠性分析中的关键环节。总结了IPC标准中的焊点蠕变疲劳模型,然后利用实例说明了如何在实际使用中对焊点寿命进行分析和预计,最后重点讨论了模型中的6个相关参数对焊点疲劳寿命及参数设计优化所带来的影响。分析表明,当有、无引脚器件的焊点间距分别大于1.143 0与0.063 5 cm时,器件的疲劳寿命均随引脚间距变大而急剧减小;此外,热失配仍然是影响焊点疲劳寿命的主要因素。     

A Probabilistic Approach to Predict Thermal Fatigue Life for Ball Grid Array Solder Joints

Numerous studies of the reliability of solder joints have been performed. Most life prediction models are limited to a deterministic approach. However, manufacturing induces uncertainty in the geometry parameters of solder joints, and the environmental temperature varies widely due to end-user diversity, creating uncertainties in the reliability of solder joints. In this study, a methodology for accounting for variation in the lifetime prediction for lead-free solder joints of ball grid array packages (PBGA) is demonstrated. The key aspects of the solder joint parameters and the cyclic temperature range related to reliability are involved. Probabilistic solutions of the inelastic strain range and thermal fatigue life based on the Engelmaier model are developed to determine the probability of solder joint failure. The results indicate that the standard deviation increases significantly when more random variations are involved. Using the probabilistic method, the influence of each variable on the thermal fatigue life is quantified. This information can be used to optimize product design and process validation acceptance criteria. The probabilistic approach creates the opportunity to identify the root causes of failed samples from product fatigue tests and field returns. The method can be applied to better understand how variation affects parameters of interest in an electronic package design with area array interconnections.     

Experimental Approach and Evaluation on Dynamic Reliability of PBGA Assembly

The aim of this paper is to provide a systematic method to perform experimental test and theoretical evaluation on fatigue characteristics of plastic-ball-grid-array (PBGA) assembly under random vibration. A specified PBGA assembly which contains different structural and material parameters was manufactured. The fatigue characteristics of PBGA assembly under random vibration were tested. Manson-Coffin empirically derived formula and rain-flow algorithm were used to achieve the fatigue life of solder joints. In the meantime, the failure curve (reliability-cycle number curve) can be obtained by using Weibull distribution method when PBGA assembly is on different working situation. Finally, life prediction of corner solder balls was deduced based on three-band technology and cumulative damage index. Test results lay a basis for high-reliability design of PBGA assembly for engineering application.     

Vibration fatigue experiments of SMT solder joint

The low-cycle fatigue induced by thermal cycling is the major concern in the reliability of SMT for electronic packaging; however, dynamic loading effects on solder joint fatigue life have not been thoroughly investigated. In fact, the high-cycling fatigue induced by vibration can also contribute a significant effect. In certain circumstances it can become a dominant failure case when semiconductor devices are used in vibration environment. In this paper, a series of vibration fatigue experimental vehicles including PBGA256 assembly and FCBGA1521 assembly were conducted. After these experiments, a new phenomenon of cracks of solder joints have been detected and given a reasonable reason, which could lead to a new concept of solder joints' fatigue.     

Thermal cycling aging effects on microstructural and mechanicalproperties of a single PBGA solder joint specimen

This paper reports on an experimental study on how thermal cycling aging exposure changes the solder joint microstructure, intermetallic layer thickness and the residual shear strength and fatigue life in a single plastic ball grid array (PBGA) solder joint specimen. The single BGA solder joint specimen was specially designed to evaluate the microstructure and mechanical properties of three different batches of solder joint after subjected to 0, 500, 1000, and 2000 cycles of thermal cycling aging (-40°C to 125°C). It is important to relate the effects of thermal cycling aging on the changes of the microstructural and intermetallic layer thickness to the residual shear strength and fatigue life of solder joints subjected to thermal cycling aging exposure. The results of this study shows that the microstructural and intermetallic development due to thermal cycling aging has a major impact on the residual mechanical and fatigue strength of the solder joint. It was noted that the solder joint shear strength and residual fatigue life degrades with exposure to thermal cycling aging     

基于稳健设计的PBGA器件焊点热机械疲劳可靠性的优化设计

基于稳健设计与有限元法,研究了加速热循环测试条件下塑封球栅阵列(PBGA)焊点的热机械疲劳可靠性.考虑PCB大小(A)、基板厚度(D)、硅片热膨胀系数(G)、焊点热膨胀系数(H)等八个控制因素,使用L₁₈(2¹×3⁷)混合正交表,以对焊点热机械疲劳寿命的考核为目标,对PBGA焊点进行了优化设计.结果表明,影响焊点可靠性的显著性因素依次是基板热膨胀系数、焊点的热膨胀系数、基板厚度、芯片的热膨胀系数;最优方案组合为A1B2C3D1E2F1G3H1.进一步的验证试验结果表明,与原始方案相比,该优化方案的最大等效应变降低了66%,信噪比提高了22.4％.     

Mechanical, thermal, and electrical analysis of a compliant interconnect

Ball grid array (BGA) package styles use solder balls as electrical interconnects between packages and application boards. Solder balls are rigid and tend to fracture under thermal fatigue and/or shock loading. Metalized polymer spheres (MPS) offer a more compliant interconnect, compared to solder balls, thereby increasing the thermal cycling fatigue life. A reduction in thermal and electrical performance may be expected for MPS interconnects as a result of its higher thermal and electrical resistances. A 5% and an 8% increase in MPS thermal resistance was measured for a carrier array ball grid array (CABGA) package and a plastic ball grid array (PBGA) package, respectively, compared to eutectic solder balls. However, this small reduction was offset by large gains in the solder joint life. A 1.6 times increase in the mean thermal fatigue life was measured for a CABGA using MPS interconnects compared to eutectic solder balls. A first-order model showed that eutectic solder balls provide greater process margins, compared to MPS interconnects, due to the ball collapse during reflow.     

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。