Sn0.7Cu无铅焊点的电迁移失效模拟及优化分析

基于ANSYS有限元软件,综合考虑电子风力、温度梯度、应力梯度和原子密度梯度四种电迁移驱动机制,采用原子密度积分法(ADI)对倒装芯片球栅阵列封装(FCBGA)的Sn0.7Cu无铅焊点进行电迁移失效模拟。针对焊点直径、焊点高度、焊点下金属层(UBM)厚度三个关键参数进行电迁移失效的正交试验优化,探究焊点尺寸对电迁移失效的影响。研究表明:焊点直径和高度的增加会缩短焊点的电迁移失效寿命(TTF),而UBM层厚度对焊点失效寿命的影响相对较小;焊点局部拉应力对焊点的失效寿命影响较大,通常会加剧焊点的空洞失效。     

关于Sn—Ag系无铅焊膏的低熔点化的分析

在对无铅回流焊炉技术进行了充分研究的基础上，认识到市场对无铅焊膏技术的迫切需求，本文针对这种技术要求，对目前国内外无铅焊膏技术作了一些了解和分析。为国内焊膏生产厂家及使用厂家提供一些参考和指导。     

PBGA无铅焊点热可靠性优化研究

在田口实验法的基础上,采用非线性有限元建模,对温度循环载荷作用下的PBGA无铅焊点进行可靠性优化研究。L18(21×37)田口正交表被选用来分析PBGA封装体的8个控制因子,包括PCB的尺寸和厚度、基板的尺寸和厚度、焊点的直径和高度、芯片以及塑封的厚度。通过田口实验法,得出了关于PBGA最佳的结构参数组合,其中最重要的控制因子为基板厚度和焊点高度,最佳参数分别为0.66mm和0.60mm。     

电迁移对Sn3.0Ag0.5Cu无铅焊点剪切强度的影响

通过热风回流焊制备了Cu/Sn3.0Ag0.5Cu/Cu对接互连焊点,测试了未通电及6.5 A直流电下通电36 h和48 h后焊点的剪切强度.结果表明,电迁移显著地降低了焊点的剪切强度,电迁移36 h使剪切抗力降低约30%,电迁移48 h降低约50%.SEM观察断口和界面形貌表明,界面金属间化合物增厚使断裂由韧性向脆性...     

42Sn58Bi—96.5Sn3.5Ag系焊点疲劳性能的研究

本文研究了热处理时间对不同组分的４２Ｓｎ５８Ｂｉ－９６．５Ｓｎ３．５Ａｇ焊料疲劳性能的影响,研究发现适当的热处理时间能提高焊点的机械强度,延长焊点的疲劳寿命。     

Sn3.8Ag0.7Cu和Sn37Pb焊点界面显微结构研究

利用扫描电子显微镜（SEM）和透射电子显微镜（TEM）研究了Sn3.8Ag0.7Cu（Sn37Pb）/Cu焊点在时效过程中的界面金属间化合物（IMC）形貌和成份。结果表明：150℃高温时效50、100、200、500h后,Sn3.8Ag0.7Cu（Sn37Pb）/Cu焊点界面IMC尺寸和厚度增加明显,IMC颗粒间的沟槽越来越小。50h时效后界面出现双层IMC结构,靠近焊料的上层为Cu6Sn5,邻近基板的下层为Cu3Sn。之后利用透射电镜观察了Sn37Pb/Ni和Sn3.8Ag0.7Cu/Ni样品焊点界面,结果显示,焊点界面清晰,IMC晶粒明显。     

无铅焊点在电迁移与高低温冲击下的失效机理

研究了Cu/Sn-3.0Ag-0.5Cu/Cu焊点接头在电迁移与高低温冲击双重耦合作用下的失效机理。结果表明,在高低温冲击条件下,由于铜柱、钎料合金及镶样用环氧树脂的热膨胀系数不匹配,因此,焊点接头在高低温冲击过程中无法自由伸缩,在热疲劳的作用下,焊接接头易于在界面处形成裂纹,且随着时间的延长裂纹会发生扩展,造成焊点接头的有效横截面积减小,使得焊点接头的电阻增大、焦耳热增加,进而导致焊点接头发生熔化而失效。     

采用锡铅焊膏粘接的Sn—Ag—Cu BGA元件的焊点可靠性

在转向无铅电子产品过程中，元件供应商可能需要支持无铅和合铅元件的双线生产。而这可能合在生产制造中引起广泛的后勤问题。全部使用无铅元件是这个问题的一个解决方法。因此，用锡铅共晶焊膏粘接的Sn-Ag—Cu BGA元件的焊点可靠性需加讨论。在这篇论文中介绍了对两种无铅封装：超细间距BGA(VFBGA)和层叠式CSP(SCSP)的焊点可靠性评估结果，它们是应用锡铅共晶焊膏贴在PCB板上。而这些封装都是采用不同的回流曲线在标准的锡铅组装条件下组装的。采用合保温区或斜升区的热度曲线。回流峰值温度为208℃和222℃。组装后PCB(称为板级)进行温度循环(-40℃—125℃，每个循环30分钟)和落体实验。下面将会详细叙述失效分析。     

回流次数对Sn3.8Ag0.7Cu-xNi/Ni焊点的影响

研究了复合无铅焊料Sn3.8Ag0.7Cu-xNi(x=0.5,1.0,2.0)与Au/Ni/Cu焊盘在不同回流次数下形成的焊点的性能.结果表明,Ni颗粒增强的复合焊料具有良好的润湿性能,熔点小于222℃;X为0.5的焊料界面IMC由针状(CuNi)6Sn5演化为双层IMC,即多面体状化合物(CuNi)6Sn5和回飞棒...     

Sn基无铅钎料与Cu基板间化合物Cu_6Sn_5的研究进展

主要介绍了Sn基无铅钎料和Cu基板在界面处反应生成的金属间化合物Cu6Sn5与焊接点可靠性的关系。综述了近年来Cu6Sn5的研究进展,内容包括:Sn基无铅钎料在Cu基板上形成的Cu6Sn5的生长形态、晶体取向、生长动力学以及纳米颗粒对界面Cu6Sn5尺寸及形貌的影响。     

热处理对96.5Sn3.5Ag焊点中Cu-Sn合金层的影响

在焊点与铜基之间形成的Ｃｕ－Ｓｎ合金成分对表面安装器件的疲劳寿命起着关键性的作用。本文着重研究了９３．５Ｓｎ３．５Ａｇ（简写为Ｓｎ－Ａｇ）焊料与Ｃｕ基界面间形成的合金层,通过电子扫描显微镜（ＳＥＭ）,Ｘ衍射（ＸＤＡ）及能谱Ｘ射线（ＥＤＸ）等分析发现,在Ｓｎ－Ａｇ与Ｃｕ基界面上存在Ｃｕ６Ｓｎ５及Ｃｕ３Ｓｎ两种合金成分,且随着热处理时间增加,Ｃｕ６Ｓｎ５合金层增厚,并在该处容易出现裂纹而导致焊点强度减弱,从而使焊点产生疲劳失效。     

Intermetallics Evolution in Sn-3.5Ag Based Lead-Free Solder Matrix on an OSP Cu Finish

The 0.2Co + 0.1Ni dual additives were used to dope a Sn-3.5Ag solder matrix to modify the alloy microstructure and the solder joint on an organic solderability preservative (OSP) Cu pad. The refined microstructure of the Sn-3.5Ag-0.2Co-0.1Ni solder alloy or the reduced β-Sn size was attributed to the depressed undercooling achieved by the Co-Ni addition. After soldering on the OSP Cu pad, a large Ag₃Sn plate was formed at the Sn-3.5Ag/OSP solder joint, whereas it was absent at the Sn-3.5Ag-0.2Co-0.1Ni/OSP solder joints. With isothermal aging at 150°C, large Ag₃Sn plates formed at the Sn-3.5Ag/OSP solder joint were still observed. A coarsened and dispersed Ag₃Sn phase was found in the solder joints with Co-Ni additions as well. Compared to Cu₆Sn₅, the (Co,Ni)Sn₂ intermetallic compound showed much lower microhardness values. However, (Co,Ni)Sn₂ hardness was comparable to that of the Ag₃Sn phase. Pull strength testing of Sn-3.5Ag-0.2Co-0.1Ni/OSP revealed slightly lower values than for Sn-3.5Ag/OSP during aging. Such results are thought be due to the phase transformation of (Co,Ni)Sn₂ to (Cu,Co,Ni)₆Sn₅.     

Constraining Effects of Lead-Free Solder Joints During Stress Relaxation

Reliability and quality control of microelectronics depend on a detailed understanding of the complex thermomechanical properties of miniaturized lead-free solder joints. With the continuous reduction in size of modern electronic devices, including also the size of the solder joints themselves, mechanical constraint effects may become of importance for the reliability of the joints. In the present study stress relaxation tests in tensile mode were performed on model solder joints consisting of eutectic Sn-3.5Ag solder between Cu substrates. The gap size of the joints was varied between 750 μm and 150 μm in order to investigate the variation of the mechanical properties as a function of the gap size. As it turned out, stress relaxation was dramatically reduced when the solder gaps became smaller due to constraint effects already well known from earlier measurements of the tensile strength. By employing a traditional creep model, the stress exponents and the activation energies were derived and compared with available data in the literature. The consequences of these constraint effects for the case of thermomechanical fatigue are discussed.     

Solder balling of lead-free solder pastes

Solder balling in Sn/Ag/Cu solder pastes was studied in this work. Three different solder pastes, several different reflow profiles and conditions, and two stencil thicknesses were used in the investigation. During the first phase, called the verification phase, the solder pastes were checked to ensure they met the minimum requirements. In the process-screening phase, the reflow profile was varied. Results show that besides flux chemistry, reflow atmosphere plays the major role in solder balling. The average number of solder balls with the best paste was one fifth of that with the worst paste. Furthermore, with all the pastes, the number of solder balls dropped close to zero when nitrogen atmosphere was used. Another finding during the reflow process screening was the influence of the stencil thickness on the solder-balling result. With a thinner stencil, two of the pastes exhibited significant solder balling. This is assumed to be caused by the different ability of fluxes to withstand oxidation during the preheating in the reflow process. In the last phase, the effect of the solder-paste particle size on solder balling was studied more closely. The flux chemistry was kept unchanged, and the solder particle size was varied between type 3 and type 4. The results show that, with type 4 paste, significantly more solder balls are formed compared to type 3 paste. It was also confirmed that, regarding the reflow profile, the ramp-up rate from 150°C to 217°C and the reflow atmosphere were the most significant factors that determine the solder-ball formation for both types of paste.     

Experimental Wettability Study of Lead-Free Solder on Cu Substrates Using Varying Flux and Temperature

The selection of soldering flux plays a critical role in promoting wetting and product reliability of printed circuit board assemblies. In this study, the effects of fluxes on the wetting characteristics of the Sn-3.0Ag-0.5Cu solder alloy on Cu substrates was researched by using various flux systems at different soldering temperatures. Because of the distinct characteristic of the lead-free solder—poor wettability—three kinds of fluxes [no-clean flux with high solid content (NCF), rosin mildly activated flux (RMA) and water-soluble flux (WSF)] were chosen for the wetting experiments. The wetting time and force were the evaluating indicators. The experimental observations indicated that the wettability clearly depended on the soldering temperature and flux system when using the same solder. Furthermore, the corrosion potential of flux residues was measured by surface insulation resistance (SIR) testing. Scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used to determine the contents of the flux residues and corrosion products.     

Maximum entropy fracture model and its use for predicting cyclic hysteresis in Sn3.8Ag0.7Cu and Sn3.0Ag0.5 solder alloys

Appropriate constitutive, damage accumulation and fracture models are critical to accurate life predictions. In this study, we utilize the maximum entropy fracture model (MEFM) to predict and validate cyclic hysteresis in Sn3.8Ag0.7Cu and Sn3.0Ag0.5 solder alloys through a damage enhanced Anand viscoplasticity model. MEFM is a single-parameter, information theory inspired model that aims to provide the best estimate for accumulated damage at a material point in ductile solids in the absence of detailed microstructural information. Using the developed model, we predict the load drop during cyclic fatigue testing of the two chosen alloys. A custom-built microscale mechanical tester was utilized to carryout isothermal cyclic fatigue tests on specially designed assemblies. The resultant relationship between load drop and accumulated inelastic dissipation was used to extract the geometry and temperature-independent damage accumulation parameter of the maximum entropy fracture model for each alloy. The damage accumulation relationship is input into the Anand viscoplastic constitutive model, allowing prediction of the stress–strain hysteresis and cyclic load drop. The damage accumulation model is validated by comparing predicted and measured load drops after 55 and 85 cycles respectively for Sn3.8Ag0.7Cu and Sn3.0Ag0.5 solder alloys. The predictions agreed to within 10% and 20% of the experimental observations respectively for the two alloys. The damage enhanced Anand model developed in this study will enable the tracking of crack fronts during finite element simulations of fatigue crack initiation and propagation in complex solder joint geometries.     

铜铟铋硫对Sn-Ag基无铅焊料性能的影响

研究了Cu、In、Bi、S元素对Sn-Ag基无铅焊料熔点和铺展性的影响。结果表明:Sn-Ag-Cu三元合金成分为95.5%Sn3.5%Ag1%Cu时具有较低熔点(215℃)和好的铺展性;加入适量的In可降低Sn-Ag合金的熔点和改善铺展性能;随w(Bi)的增加Sn-Ag-Bi三元合金的熔点降低、铺展性变好;Sn-Ag合金的熔点随w(S)的增加而升高,加入少量S能改善Sn-Ag合金的铺展性。