纳米压痕法分析Sn-9Zn/Cu焊点力学性能

通过对Sn-9Zn/Cu焊点进行纳米压痕实验发现:在保载阶段,体钎料产生了明显的蠕变特征,蠕变深度随着加载速率的增加而增加.基于压痕做功概念确定了Sn-9Zn/Cu焊点中体钎料的蠕变应力指数n约为5.128.硬度和弹性模量测试结果表明:金属间化合物Cu5Zn8的压痕硬度(5.152±0.224) GPa约是体钎料压痕硬...     

基于纳米压痕法的SnBi-xNi钎料的塑性比较

借助纳米压痕的方法,采用压痕形成过程中塑性应变与总应变的比值来表征钎料塑性。对Sn Bi-x Ni(x=0,0.05,0.1,0.15和0.2)成分钎料的硬度、弹性模量及塑性进行了对比。结果表明:Sn58Bi钎料合金加入Ni元素后,钎料硬度和弹性模量升高。当Sn58Bi-x Ni钎料中Ni含量的质量分数为0.1%时,其硬度及弹性模量最大。当Ni质量分数超过0.1%时,钎料的硬度与弹性模量有所下降。当添加Ni元素质量分数为0.05%~0.1%时,钎料合金的组织得到了细化,钎料合金的塑性提高;当Ni质量分数大于0.15%时,钎料的塑性降低。     

无铅BGA焊点局部再结晶与损伤模式的研究

小型化、高性能的BGA无铅器件已成为现代高集成度电子产品的组装必需器件,在其服役过程中,会经历热循环,出现失效。使用扫描电镜(SEM)、电子背散射衍射分析(EBSD)和显微硬度,对经历热循环BGA器件损伤模式进行了研究。得出结论:材料的热膨胀系数失配为裂纹萌生和扩展提供了驱动力,裂纹沿着钎料球内部弱化的局部再结晶晶界扩展,最终导致焊点断裂失效。     

电子封装与组装焊点界面反应及微观组织研究进展

软钎焊焊点界面反应是连接金属的最古老的冶金工艺过程。随着倒装芯片(FC)、球栅阵列(BGA)和芯片级封装(CSP)等面封装技术的兴起,近年来Sn基钎料被广泛应用于微电子制造,包括芯片和基板之间的封装互连以及基板与印制电路板之间的组装互连。这就需要系统地研究Sn基钎料焊点界面反应及微观组织。从形态学、热力学和动力学的角度回顾总结了SnPb共晶钎料、高Pb钎料和无Pb钎料与Cu、Ni、Au/Ni/Cu、PdAg焊盘之间的界面反应。     

SAC105焊锡膏的开发与评价

采用低银化焊料合金是无铅化电子组装提高性价比的发展趋势。开发了采用SAC105低银焊料合金的SUPER105系列焊锡膏,抗氧化、表面绝缘电阻、印刷性能、BGA空洞率、焊点推力等测试结果表明,SUPER105焊锡膏完全适用于消费类电子产品组装。     

BGA封装器件焊点缺陷X-射线检测法

讨论了BGA器件焊接的特点,并对BGA器件焊接过程中产生的缺陷进行了阐述,采用X-射线检测仪检测了BGA封装器件安装焊点的几种常见缺陷,分析、阐述了其图像与相应缺陷的关系,结果表明X-射线检测方法能够准确地检测出BGA封装器件安装中的各种焊点缺陷,并能够自动计算BGA封装器件安装焊点的空洞率,对空洞缺陷的快速检测和预防具有实际意义.     

回流焊峰值温度对混装BGA焊点的影响研究

针对当前大量使用有铅焊料焊接无铅BGA的实际现状,通过调控有铅制程回流曲线的峰值温度,研究其对混装BGA焊点坍塌高度、空洞率及微观组织的影响。结果表明,峰值温度从210℃提升至225℃,无铅BGA焊球能够全部充分坍塌且高度保持一致;峰值温度为210℃时,混合焊点内的空洞率最低,随着峰值温度的升高,空洞尺寸和空洞率均有所增加;峰值温度为215℃时的微观组织最细小且尺寸分布最均匀,继续提升峰值温度,微观组织尺寸会随之增大。因此使用有铅焊料焊接无铅BGA的最佳峰值温度为215℃,与有铅制程保持一致。     

IC键合铜线材料的显微力学性能研究

用于IC(集成电路)的键合铜线材料具有低成本、优良的导电和导热性等优点,但其高硬度容易对铝垫和芯片造成损伤,因此对其硬度的测量是一项关键技术。纳米压痕测量技术可以方便、准确地测量铜线材料的显微硬度值和其他力学性能参数。描述了纳米压痕测量技术的原理以及对铜线材料样品进行纳米压痕测量的参数选择,进行了测量试验。结果表明,原始铜线、FAB(金属熔球)、焊点的平均硬度分别为1.46,1.51和1.65GPa,为键合铜线材料的选择和键合工艺参数的优化提供了依据。     

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。     

国外工艺文献导读

20 0 30 4 0 1　在线BGA焊点开路检测—GlenLeinbach .CircuitsAssembly,2 0 0 3 ,1 4 (3) :36～ 40 (英文)随着BGA器件的广泛应用 ,并逐步替代传统的封装形式如QFP、SOIC、TSOP、SSOP和PLCC等。然而所有的面阵列封装都存在一个普遍的问题 ,焊点不在封装的边缘 ,而隐藏在器件体的下面 ,这就给PCB质量检验和缺陷检测带来许多困难。本文从AXI与BGA、BGA焊点、BGA焊点开路、翘曲等方面介绍了一种探测BGA焊点开路的新方法 ,该方法采用AXI,对再流焊后的BGA焊球尺寸进行比较 ,从而探测出BGA开路缺陷。2 0 0 30 4 0 2　无铅…     

Local and Global Properties of a Lead-Free Solder

Elastic and viscous properties including Young’s modulus, hardness, creep rate sensitivity, and fatigue resistance of Sn-1.2Ag-0.5Cu-0.05Ni lead-free solder have been investigated. The properties of bulk specimens and in situ solder balls are compared. Experiments show good correlations of Young’s modulus and creep rate sensitivity between conventional measurements and nanoindentation results on bulk specimens. Further mechanical properties of the beach-ball microstructure in solder balls are characterized by nanoindentation. The load–partial unload technique has been used to determine the variation in mechanical properties with increasing depth of penetration into the intermetallic inclusions in the in situ solder. The fatigue resistances of the bulk specimens and solder balls are compared by using the novel nanoimpact method. In comparison with bulk specimens, it is found that in situ solder has higher Young’s modulus, lower creep strain rate sensitivity, and better fatigue resistance. The effects of soldering and the scale differences strongly affect the mechanical and fatigue properties of in situ solder.     

Nanoindentation on SnAgCu lead-free solder joints and analysis

The lead-free SnAgCu (SAC) solder joint on copper pad with organic solderability preservative (Cu-OSP) and electroless nickel and immersion gold (ENIG) subjected to thermal testing leads to intermetallic growth. It causes corresponding reliability concerns at the interface. Nanoindentation characterization on SnAgCu solder alloy, intermetallic compounds (IMCs), and the substrates subjected to thermal aging is reported. The modulus and hardness of thin IMC layers were measured by nanoindentation continuous stiffness measurement (CSM) from planar IMC surface. When SAC/Ni(Au) solder joints were subject to thermal aging, the Young’s modulus of the NiCuSn IMC at the SAC/ENIG specimen changed from 207 GPa to 146 GPa with different aging times up to 500 h. The hardness decreased from 10.0 GPa to 7.3 GPa. For the SAC/Cu-OSP reaction couple, the Young’s modulus of Cu₆Sn₅ stayed constant at 97.0 GPa and hardness about 5.7 GPa. Electron-probe microanalysis (EPMA) was used to thermal aging. The creep effect on the measured result was analyzed when measuring SnAgCu solder; it was found that the indentation penetration, and thus the hardness, is loading rate dependent. With the proposed constant P/P experiment, a constant indentation strain rate h/h and hardness could be achieved. The log-log plot of indentation strain rate versus hardness for the data from the constant P/P experiments yields a slope of 7.52. With the optimized test method and CSM Technique, the Modulus of SAC387 solder alloy and all the layers in a solder joint were investigated.     

Superplastic creep of eutectic tinlead solder joints

This paper presents experimental evidence that as-solidified eutectic Pb-Sn solder joints can exhibit superplastic behavior in shear creep loading. Stepped load creep tests of as-solidified joints show a change in the stress exponent from a high value typical of con-ventional creep at high stress and strain rate to a superplastic value near 2 at lower stress and strain rates. In addition, the change in stress exponent is accompanied by a change in the activation energy for creep from a value near that for bulk self-diffusion (20 kcal/mol) to a value near that for grain boundary diffusion (12 kcal/mol). The total shear deformation of joints in stress-rupture tests performed at 65° C are found to ex-ceed 150%. The concomitant observation that quenched solder joints creep faster than air-cooled ones is attributed to a grain, or phase, size dependence of the strain rate. The source of superplastic behavior is a fine, equiaxed microstructure. It is not yet clear whether the superplastic microstructure is present in the as-solidified joint, or develops during the early stages of plastic deformation.     

Impact of temperature cycle profile on fatigue life of solder joints

In this paper the influence of the temperature cycle time history profile on the fatigue life of ball grid array (BGA) solder joints is studied. Temperature time history in a Pentium processor laptop computer was measured for a three-month period by means of thermocouples placed inside the computer. In addition, Pentium BGA packages were subjected to industry standard temperature cycles and also to in-situ measured temperature cycle profiles. Inelastic strain accumulation in each solder joint during thermal cycling was measured by high sensitivity Moire interferometry technique. Results indicate that fatigue life of the solder joint is not independent of the temperature cycle profile used. Industry standard temperature cycle profile leads to conservative fatigue life observations by underestimating the actual number of cycles to failure.     

Ball-grid-array solder joint model for assembly-level impact reliability prediction

It has been well established that lead-free solder underperforms conventional leaded solder in reliability under dynamic impact. Common failures observed on ball-grid-array (BGA) solder balls on chip under board level impact include bulk solder ductile failure, intermetallic (IMC) layer crack and pad-lift. In this work, a finite element modeling approach was proposed to model bulk solder ductile failure and intermetallic layer crack. The use of beam elements and connector elements to represent the bulk solders and board/component side intermetallic layers, respectively, offers the advantage of simplicity over the use of continuum elements and cohesive elements for solder joints. This approach enables the modeling of assembly level impact with significantly less computational resources. The model was verified by comparing its prediction of BGA solder reliability against actual test results in a dynamic four-point bend test. The physical tests consist of ball impact at varying heights on a board with a mounted chip, and the subsequent analysis of the failure modes of the BGA solder joints. Simulation results were in good agreement with test results. The study shows that it is feasible to model BGA solder joint ductile failure and intermetallic layer crack under impact with simple elements with reasonable accuracy.     

Reliability model for bridging failure of Pb-free ball grid array solder joints under compressive load

The ever increasing power density in high performance microelectronic devices for applications such as large business computing and telecommunication infrastructure has led to several new reliability challenges for solder interconnects. One of them is the creep collapse and bridging of ball grid array (BGA) solder joints under heatsink compressive loads. For characterizing the solder joint response to compressive load and model the corresponding reliability failure, the compressive creep behavior of Sn3.8Ag0.7Cu solder was first investigated. A viscoplastic constitutive model developed from the creep characterization was then incorporated into numerical finite element (FE) analysis to predict solder joint creep collapse and bridging under heatsink compressive load. The numerical analysis results were validated by experimental studies of solder joint collapse under compressive load and isothermal aging condition. A simplified power-law formula is also provided for modeling the creep collapse of Sn3.8Ag0.7Cu solder joint. The model may be applied for predicting solder joint compressive reliability under a prescribed heatsink compression, or to determine the maximum allowable heatsink load for a given life expectancy.     

Investigation of mechanical shock testing of lead-free SAC solder joints in fine pitch BGA package

The lead-free Sn-Ag-Cu (SAC 305/405) solder that replaced the tin-lead eutectic solder tends to be more brittle in nature due to high stiffness and excessive solder interfacial reactions. This leads to higher occurrences of solder joints failure during surface mount assembly and handling operations as a result of PCB bending, shock impact and drop. In this work, mechanical tests simulating the shock impact were conducted on lead-free SAC of different weight percentages. These SAC materials were prepared for use in the solder joints of fine pitch ball grid array (BGA) components which were mounted onto the motherboard. After the mechanical shock tests, strain measurements were performed on the BGA components to gauge the solder joint integrity, which was shown to be related with the formation of intermetallics in the bulk and at the interface of the SAC solder. The ball pull tests were conducted to determine both the bulk and interfacial strength and the solder joint fracture, which was classified as either mode 1, 2 or 3. A correlation was made between the silver (Ag) and copper (Cu) weight percentages with the metallurgical reactions.     

剪切蠕变下无铅焊点厚度的尺寸效应

利用自制的电子测试系统,测量分析了试样焊点厚度(0.05～0.50mm)对电阻应变的影响。结果表明:在剪切蠕变条件下,焊点厚度为0.25mm时,电阻应变最小,蠕变寿命最长。利用有限元软件ANSYS对焊点的蠕变应变进行仿真分析。结果显示:随着焊点厚度变化,焊点蠕变应变的变化趋势与实验结果一致。将相同厚度下的电阻应变与蠕变应变进行拟合,得到了电阻应变与蠕变应变之间的定量关系式。     

Constitutive modeling on creep deformation for a SnPb-based composite solder reinforced with microsized Cu particles

In the present work, the creep strain of solder joints is measured using a stepped load creep test on a single specimen. Based on the creep strain tests, the constitutive modeling on the steady-state creep rate is determined for the Cu particle-reinforced Sn37Pb-based composite solder joint and the Sn37Pb solder joint, respectively. It is indicated that the activation energy of the Cu particle-reinforced Sn37Pb-based composite solder joint is higher than that of Sn37Pb solder joint. In addition, the stress exponent of the Cu particle-reinforced Sn37Pb-based composite solder joint is higher than that of the Sn37Pb solder joint. It is expected that the creep resistance of the Cu particle-reinforced Sn37Pb-based composite solder joint is superior to that of the Sn37Pb solder. Finally, the creep deformation mechanisms of the solder joint are discussed.