Electromigration in eutectic SnAg solder reaction couples with various ambient temperatures and current densities

The electromigration behavior of eutectic SnAg solder reaction couples was studied at various temperature （25 and 120℃ when the current density was held constant at 104 A/cm^2 or 5×10^3 A/cm^2. Under the current density of 104 A/cm^2, scallop type Cu6Sn5 spalls and migrates towards the direction of electron flow at room ambient temperature （25℃）, but transforms to layer type Cu3Sn and leaves Kirkendall voids in it at high ambient temperature （120℃）. Under the current density of 5×10^3 A/cm^2 plus room ambient temperature, no obvious directional migration of metal atoms/ions is found. Instead, the thermal stress induced by mismatch of dissimilar materials causes the formation of superficial valley at both interfaces. However, when the ambient temperature increases to 120℃, the mobility of metal atoms/ions is enhanced, and then the grains rotate due to the anisotropic property of β-Sn.

Solder joint geometry of tin-lead alloy and its application in electronic packaging

By employing the minimum energy theorem, the Potential energy controlling equation, which consists of surface energy and gravitational energy for molten meniscus, was investigated. The soder joint geometry of molten tin-lead soder alloy for chip component and thin quad flat package were simulated with finite element method. The simulation results 0f solder joint geometry are coincident well with the experimental results. The solder joint geometry was applied to study the solder joint reliability for chip component RC3216.The thermal cycling tests revealed that the solder joint geometry plays an important ro1e in solder joint reliability.

车用垂直腔面发射激光器模组整板金锡共晶焊接工艺

激光雷达及飞行时间(ToF)传感器中垂直腔面发射激光器(VCSEL)模组使用的银胶固晶工艺存在银迁移及硫化问题,亟需开发一种可靠性高并可量产的整板金锡共晶焊接工艺。以单颗焊接模式下单因素实验及正交实验为基础,借助Ansys热仿真工具,探究整板焊接中基板与压头之间合适的匹配温度。单因素控制变量实验发现,固晶芯片推力随共晶温度、压头行程、共晶时间的增加先增大后减小,正交实验得到最佳工艺参数为共晶温度320℃、压头行程500μm、共晶时间4 s。采用优选工艺参数500μm、4 s、270~350℃进行整板焊接,平均固晶芯片推力为821 N,相较银胶固晶工艺提高了139%。

共蒸发法制备金锡共晶焊料环及其性能研究

采用电子束共蒸发法制备了金锡共晶(Au80Sn20)焊料环,与非制冷红外探测器芯片进行气密性封装。通过SEM、AFM、X-ray、振荡测试以及测漏氦等方式验证了封装后芯片的气密性和可靠性。结果表明:键合后焊料环无明显缺陷,仅存在轻微溢料现象;经过振荡测试,溢料无脱落、无位移,且芯片密封性能可达到1×10^(-3) Pa/(cm^(3)·s),符合探测器的气密性要求。

Effects of cooling rates on microstructure and microhardness of lead-free Sn-3.5%Ag solders

The microstructure and microhardness of Sn-3.5%Ag solders were explored in the cooling rate ranging from 0.08 to 104 K/s. Under rapid cooling condition, the strong kinetic undercooling effect leads to the actual solidification process starting at the temperature lower than the equilibrium eutectic point, and the actual metastable eutectic point shifts to the higher Ag concentration. Hence, the higher the applied cooling rate is, the more the volume fraction of primary β-Sn crystal forms. At the same time, the separation of primary β-Sn crystal favors restraining the formation of bulk Ag3Sn intermetallic compounds (IMCs) in solder due to the mismatch crystalline orientation relationship, those Ag3Sn phase separating through the eutectic reaction could hardly cling to the primary β-Sn crystal and grow up. Additionally, the Vickers hardness test shows that fine β-Sn and spherical Ag3Sn phase in the rapidly solidified alloy strongly improves the microhardness of the Sn-3.5%Ag solder.

Effect of Bismuth Addition on Structure and Mechanical Properties of Tin-9Zinc Soldering Alloy

Sn-Zn based solder is a possible replacement of Pb solder because of its better mechanical properties. The alloys need to be studied and explored to get a usable solder alloy having better properties. In this work eutectic Sn-9Zn and three Tin-Zinc-Bismuth ternary alloys were prepared and investigated their microhardness and mechanical properties. Microhardness, tensile strength and elastic modulus increase with Bi addition while ductility decreases with Bi addition.

Sn60Pb40 solder powders produced by the planar flow casting atomization process

Conventional planar flow casting(PFC) is one of rapid solidification processes for the fabrication of microcrystalline or amorphous ribbons.Based on the conventional PFC process,the planar flow casting atomization(PFCA) process has been developed,which is a new rapid solidification process for the production of metal powder directly from alloy melts.A prototype experimental apparatus was designed and manufactured.With the apparatus,Sn60Pb40 alloy solder powders were prepared,and the effects of the main technological parameters on the powder size distribution and morphology were experimentally studied.The experimental investigations indicate that the metal powders produced by the PFCA process can be classified by velocity;and fine spherical tin-lead alloy solder powders can be fabricated by adjusting the technical parameters.The new PFCA process has such features as high productivity and efficiency,low energy consumption,simple operation,short technological process,and large gross yield.

Study on laser and hot air reflow soldering of PBGA solder ball

Laser and hot air reflow soldering of PBGA solder ball was investigated. Experimental results showed that surface quality and shear strength of solder bump reflowed by laser was superior than the solder bump by hot air, and the microstructure within the solder bump reflowed by laser was much finer. Analysis on interfacial reaction showed that eutectic solder reacted with Au/Ni/Cu pad shortly after the solder was melted. Interface of solder bump reflowed by laser consists of a continuous AuSn 4 layer and remnant Au element. Needle like AuSn 4 grew sidewise from interface, and then spread out to the entire interface region. A thin layer of Ni 3Sn 4 intermetallic compound was found at the interface of solder bump reflowed by hot air, and AuSn 4 particles distributed within the whole solder bump randomly. The combination effect of the continuous AuSn 4 layer and finer eutectic microstructure contributes to the higher shear strength of solder bump reflowed by laser.

Thermal and Electrical Properties of Sn-Zn-Bi Ternary Soldering Alloys

Sn-Zn based solder is a possible replacement of Pb solder because of its better mechanical properties. The alloys need to be studied and explored to get a usable solder alloy having better properties. In this work, eutectic Sn-9Zn and three Tin-Zinc-Bismuth ternary alloys were prepared and investigated their thermal and electrical properties. Thermo-mechanical Analysis and Differential Thermal Analysis were used to investigate thermal properties. Microstructural study is carried out with Scanning Electron Microscope. The alloys have single melting point. The co-efficient of thermal expansion and co-efficient of thermal contraction varies with alloy composition and temperature range. Electrical conductivity changes with Bi addition.

基于新工艺技术的高功率裸芯片模块微流体系统的散热技术

为解决高功率裸芯片的散热问题,本文在功率模块腔体上设计了一种自循环一体化微流道散热系统,并对有无微流道、平直流道以及交联流道的散热特性进行对比。研究表明:有微流道的裸芯片散热特性优于无微流道,有交联流道的裸芯片散热特性优于具有平直流道;将裸芯片共晶焊接到金刚石热沉,再将热沉共晶焊接到功率模块腔体,裸芯片到功率模块腔体之间的传导热阻降至传统工艺热阻的1/360~1/280;仿真与实验能够相互验证,最大偏差仅为7.16%。该微流道系统具有较强的散热能力,可解决环境温度为70℃,热流密度为320 W/cm^(2)时的裸芯片散热问题。

微流体系统在高功率裸芯片模块上的散热研究

为解决高热流密度功率裸芯片的散热问题,在功率模块腔体上设置了一种自闭环一体化微流道散热系统。将裸芯片共晶焊接到金刚石,再将金刚石共晶焊接到功率模块腔体,有效降低了裸芯片到功率模块腔体之间的传导热阻。通过实验和仿真探究了微流道形式和流道宽度对散热能力的影响。结果表明:相同条件下交联微流道散热性能较好,同时减小流道宽度,提高芯片温度性能。仿真结果与实验结果具有良好的一致性,最大误差为7.16%。提出的微系统具备较好的散热能力,在环境温度70℃下,可处理的芯片热流密度为320 W/cm^(2)。

芯片共晶模块高钎透率真空回流焊接工艺

芯片共晶模块是微波组件的重要组成部分,芯片共晶模块到壳体封装质量直接影响微波组件的电学性能和可靠性。采用真空回流焊接技术对芯片共晶模块进行低温焊接,通过优化压块材质、温度曲线和真空制程参数等方式,实现芯片共晶模块焊接钎透率达90%以上、单个空洞率低于5%的标准要求。

金锡镀层在CSP气密封装中的应用及其可靠性

芯片级尺寸封装的气密性被越来越广泛的关注,为了实现CSP器件的可伐管帽与陶瓷基板之间的气密性互连,采用分层电镀沉积的方法在高温共烧陶瓷(HTCC)基板表面制备了金/锡/金镀层,利用金与锡间的共晶反应以实现管帽和基板的气密性可靠封接.文中分析了金/锡/金镀层质量、焊接工艺对Au80Sn20共晶焊料封接结果的影响.结果表明,金/锡/金镀层厚度和层间的结合力决定了Au-Sn共晶焊料的封接质量.在焊接升温过程中,锡镀层首先熔化形成“熔池”,溶解上下侧与之接触的金镀层,直至完成共晶反应;采用较短的焊接时间能够实现更好的金锡共晶封接;焊接温度为330℃、保温时间为30 s时,Au-Sn镀层共晶反应形成δ/(Au,Ni)Sn—ζ相—δ/(Au,Ni)Sn的分层共晶组织,实现了可伐管帽与HTCC基板的气密性封接.

Soldering of Zr-based bulk metallic glass and copper by Au-12Ge eutectic alloy

Zr-based bulk metallic glass and copper with different surface roughness were soldered using low temperature eutectic Au-12 Ge(wt%) solder on a thermomechanical simulator. The cross-sectional microstructures of the brazed joints were analyzed by scanning electron microscopy(SEM) and transmission electron microscope(TEM) in detail, and the compositional distribution along the interface was analyzed by energy-dispersive spectrometer(EDS). Results show that the surface roughness of base metals plays an important role in the quality of the brazed joint because the surface roughness can enlarge the effective contact area, which can improve the brazing surface quality between two materials. A moderate roughness of treated Zr-based metallic glass of 18 μm is shown to be the best for the soldering, while the surface roughness has a weak effect on the soldering behavior of Au-12 Ge solder on copper. After soldering, long-range diffusion of atoms occurs between the base metal and solder, and five distinct regions are formed at the joint region.

基于国产金锡焊料的功率芯片焊接工艺及可靠性研究

金锡焊料具有强度高、抗氧化性好、抗疲劳、蠕变性能优良等优点,在混合集成电路中得到越来越多的应用,尤其是在大功率高可靠集成电路中通过共晶焊接来降低封装热阻和提高芯片焊接可靠性。本文分析了国产金锡焊料的基础特性,基于国产金锡焊料采用手动方式进行功率芯片摩擦共晶焊接关键控制参数焊接工艺研究;对功率芯片金锡焊接宇航应用可靠性进行验证。结果表明,经历系列严苛的宇航环境热力学试验,剪切强度满足相关标准要求并保持强度稳定,显示了焊接的高可靠性。

Dendritic Growth, Eutectic Features and Their Effects on Hardness of a Ternary Sn–Zn–Cu Solder Alloy

The present investigation is based on the results of a directionally solidified （DS） Sn-9 wt%Zn-2 wt%Cu alloy, including primary/secondary/tertiary dendrite arm spacings of the Sn-rich matrix, the morphologies of the eutectic mixture and the corresponding interphase spacing, the nature and proportion of the Cu-Zn intermetallic compound （IMC）. The main purpose is to establish interrelations of these microstructure features with experimental solidification thermal parameters, such as cooling rates and growth rates （v）, macrosegregation and hardness. Such interrelations are interesting for both industry and academy since they represent a tool permitting the preprogramming of final properties based on the design of the microstructure. In the case of Sn-Zn-Cu alloys, hardly anything is known about the combined effects of the length scale of the microstructure and fraction and distribution of the primary IMC on hardness. The alloy microstructure is composed of a β-Sn dendritic region, surrounded by a eutectic mixture of α-Zn and β-Sn phases and the γ-Cu5Zn8 IMC. The eutectic interphase spacing varies in the range 1.2-3.6 μm, with the α-Zn phase having a globular morphology for ν 〉 0.5 mm/s and a needle-like morphology for ν 〈 0.3 mm/s. A modified Hall-Petch-type experimental expression relating hardness to the interphase spacing is proposed.

共晶焊后热敏电阻的应力分析及优化

为了研究与解决热敏电阻在共晶焊后阻值变大的问题,采用扫描电子显微镜(SEM)观测失效的热敏电阻,发现其内部有裂纹。采用有限元分析法分析热敏电阻经过共晶焊后产生的应力,结果表明,最大应力的位置与裂纹位置基本一致,最大应力的方向与裂纹方向正交,这说明裂纹是由应力引起的。分析了热敏电阻上最大应力与焊料厚度的关系,结果表明,焊料越厚,则热敏电阻在共晶焊时产生的应力越小。通过验证试验可知,采用适当加厚的焊料对热敏电阻进行共晶焊,共晶焊后热敏电阻的外观良好,没有裂纹发生,且阻值没有增大。因此,可采用加厚焊料的方法防止热敏电阻开裂。

无铅焊料研究现状与发展展望

随着电子工业飞速发展以及人们环保意识的提高,以"绿色焊接"为主题的电子装配技术对无铅焊料的需求也尤为迫切。本文从焊料可焊性和焊接结构的可靠性等方面介绍了近年来国内外无铅焊料研究方面的最新成果;着重概括了为提高焊接性能而在配料组分、金属间化合物析出与组织控制等工作,重点阐明了稀土元素在焊料组织控制中的关键作用;针对我国稀土资源蕴藏丰富的特点,指出了无铅焊料进一步发展的方向。

共晶SnBi/Cu焊点界面处Bi的偏析

利用SEM,TEM,XRD分析了共晶SnBi/Cu焊点经120℃时效7 d后界面组织结构的变化.焊点界面处金属间化合物厚度由原来初始态的约2 μm增至时效态的10 μm,并且化合物也由原来单一的Cu6Sn5转变为Cu6Sn5和Cu3Sn 相.进一步研究表明,在Cu3Sn与Cu之间界面处偏析了大量尺寸约100 nm的Bi颗粒.双缺口试样的断裂韧性实验表明, 热时效促使焊点断裂韧性快速下降,同时该焊点的断口也由原来初始态的韧性断裂转变为时效后Cu3Sn与Cu界面处的脆性断裂,脆性断裂后一侧断口为鲜亮的Cu表面.在TEM下,通过与220℃/5 d时效态纯Sn/Cu焊点相同界面的比较,可以断定引起该焊点失效的原因是Bi颗粒在此界面处的偏析.含Bi无Pb焊料由于Bi在界面析出而引发的脆断将会是微电子器件长期使用中的一个潜在危害.

金锡合金自动共晶焊接工艺参数优化研究

为了更好地控制共晶焊接空洞率和剪切力,提出了一种采用正交试验法优化自动共晶焊接参数的方法。对焊接温度、焊接时间、焊接压力三个关键参数采用正交法进行三因子两水平极差分析,得到了影响芯片金锡共晶焊接质量的主次因子及共晶焊接参数的最优组合。试验结果证明,使用优化的工艺参数,芯片焊接质量得到明显提升,共晶焊接区空洞率均值及芯片剪切力Cpk值均完全满足GJB548B的要求。