铜线性能及键合参数对键合质量的影响

为了提高铜线性能及其键合质量,采用拉力-剪切力测试仪、扫描电镜等研究了不同力学性能铜线及相应的键合参数对其键合质量的影响,分析了不同伸长率和拉断力、铜线表面缺陷、超声功率和键合压力对铜线键合质量的作用机制.结果表明:伸长率过小和拉断力过大会造成焊点颈部产生微裂纹,从而导致焊点的拉力和球剪切力偏低;表面存在缺陷的铜线其颈部经过反复塑性大变形会造成铜线表面晶粒和污染物脱落而出现短路和球颈部断裂;键合过程中键合压力过大能够引起的焊盘变形,同时较大的接触应力引起铝层溢出;过大的超声功率使键合区域变形严重产生明显的裂纹和引起键合附近区域严重的应力集中,致使器件使用过程中产生微裂纹而降低器件的使用寿命.     

键合Cu线无卤直接镀Pd工艺及性能研究

利用扫描电镜、聚焦离子束、强度测试仪研究了键合铜线无卤直接镀钯工艺及不同模具孔径对镀钯键合铜线表面质量、镀层厚度的影响规律,分析了钯层均匀性对键合性能的影响机理.研究结果表明:无卤直接镀钯工艺可获得镀层均匀的镀钯键合铜线;直接镀模具孔径大于被镀铜线直径3~4μm时,镀钯铜线镀层均匀且表面光洁;镀钯铜线钯层不均匀会造成Electronic-Flame-Off(EFO)过程中的Free Air Ball(FAB)偏球缺陷,进而降低焊点力学性能;直接镀钯键合铜线镀层均匀,避免了Free Air Ball(FAB)偏球缺陷,焊点球剪切力≥15 g、球拉力≥8 g,呈非离散分布,满足工业化要求.     

镀Au键合Ag线性能对键合质量的影响研究

利用扫描电镜、能谱仪、拉力-剪切力测试仪等研究了不同镀Au厚度的镀Au键合Ag线Free Air Ball(FAB)特性和不同力学性能的镀Au键合Ag线对键合强度及其可靠性的影响规律，研究结果表明：镀Au键合Ag线镀层厚度过小会造成Electronic-Flame-Off(EFO)过程中的FAB偏球及球焊点形状不稳定，镀层厚度过大会导致FAB变尖；高强度、低伸长率会造成焊点颈部产生裂纹而造成焊点的拉力偏低并在颈部断裂，低强度、高伸长率引起颈部晶粒粗大进而降低颈部连接强度；镀Au键合Ag线颈部应力集中或内部组织结构不均匀，在冷热冲击周期性形变作用下，球焊点颈部产生裂纹并引起电阻增加，进而导致器件失效.     

IC封装中镀钯铜线与裸铜线键合比较研究

镀钯铜线（PdCu）是半导体封装中传统金线键合向铜线键合发展过程中出现的产物,与裸铜线（Bare Cu）键合相比,有着其特有的优劣势。本文通过分析研究发现两种铜线工艺参数有比较大的差别,第一焊点的可靠性测试结果基本相同,而第二焊点结果有一定的区别。本文主要实验数据研究分析镀钯铜线与裸铜线键合的区别,包括第一焊点空气球的可重复性、电火花（EFO）电流大小对焊接结果的影响、铝层挤出的比较。第二焊点的焊接表现,参数范围的变化。可靠性测试结果等。     

超细节距线键合的镀钯铜线和裸铜线的研究

由于铜线较之金线明显节约成本,所以对铜(Cu)线键合的关注日益增长。但是,对铜线易腐蚀及封装可靠性的考虑推动产业开发替代材料。当前,敷钯铜(PdCu)线由于其改善了可靠性而已广泛使用。本文中,我们用0.6密耳PdCu线和裸铜线做实验。研究了PdCu烧球(FAB)的钯分布和晶粒结构。观测到电子灭火(EFO)电流和覆盖气体类型对钯分布有重大影响。测量了烧球(FAB)的硬度及与钯分布和晶粒结构的关系。对首次键合工艺响应作了定性研究。用高温存储测试研究了钯对线键合能力和线金属间键合的影响。PdCu线的这些结果与裸铜线进行了比较。     

Au含量对Ag基键合合金线键合强度及可靠性影响研究

利用扫描电镜、强度测试仪研究了?0.025 mm的不同Au含量对银基键合合金线键合强度及可靠性的影响,研究结果表明,对于Ag-Au键合合金线,随着Au含量增加,其无空气焊球成球性较好,球拉力和球剪切力均增加,热影响区长度降低,Ag-5Au键合合金线球拉力和球剪切力比Ag-1Au球拉力和球剪切力高出28.4%和28.6%; Ag-5Au键合合金线热影响区长度比Ag-1Au键合合金线短42.8%;Ag-5Au键合合金线拉力测试过程中中间位置断裂比例为96%,Ag-1Au键合合金线中间位置断裂比例为21%;含Au银基键合合金线冷热冲击后失效模式为颈部断裂,Ag-5Au键合合金线可靠性高于Ag-1Au键合合金线。     

铝锌硅镀层的冲压性能

铝锌硅镀层(Galvalume)作为钢铁基体的热浸镀材料,具有良好的耐腐蚀能力,但是Galvalume镀层在受力变形时容易出现裂纹。针对热浸镀Galvalume镀层成形开裂问题,通过对不同镀层厚度(重量)镀铝锌板进行冲压试验和180°弯曲试验,观察裂纹源的产生。采用扫描电镜(SEM)和能谱(EDS)对镀层及中间过渡层进行研究,分析影响镀层冲压开裂的原因。结果显示:镀层的重量(厚度)是影响其冲压开裂的主要原因,随着镀层厚度的下降,镀层外侧受拉应力作用开裂趋势变小;开裂位置显示主要元素为Fe、Al、Si元素,变形过程中Galvalume合金过渡层相对于镀层更容易开裂;Galvalume合金过渡层的厚度是影响Galvalume冲压开裂的主要原因,随着合金过渡层厚度的降低,过渡层开裂趋势变小。     

金丝在镀银铜支架上的键合性能研究

键合金丝是电子封装过程中的关键材料,其键合可靠性对电子元器件的性能稳定性与寿命具有重要的影响。使用自制的Au丝将2835 LED芯片与镀Ag支架键合,并采用破坏性键合强度测试和加速寿命试验,测试并研究了Au丝的键合强度及Au-Ag键合界面的可靠性,通过扫描电镜(SEM)、电子探针(EPMA)等手段,对比分析了高温及电流加载对Au丝及Au-Ag键合界面组织演变及元素扩散行为的影响。研究结果表明,高温偏压寿命试验(TBOL)后,Au与Ag的相互扩散加剧,Au-Ag键合点残金面积增大,Au焊点中Ag含量从0.195%提高至1.584%(质量分数),使焊点固溶强化效应增强,焊点平均推力值增大约10%,进一步提高了焊点的键合可靠性。     

金-硅共晶键合技术及其应用

采用金属过渡层来实现硅-硅低温键合,首先介绍了选择钛金作为金属过渡层的原因和金硅共晶键合的基本原理,然后探索了不同键合面积和不同金层厚度对金硅共晶键合质量的影响规律,开展了图形化的硅晶圆和硅盖板之间的低温共晶键合实验研究,获取了最优键合面积的阈值和最优金层厚度.最后将该低温金硅共晶键合技术应用到MEMS器件圆片级封装实验中,实验结果表明较好地实现了MEMS惯性器件的封装强度,但是还存在密封性差的缺陷,需进一步进行实验改进.     

Cu/Sn等温凝固芯片键合工艺研究

研究了Cu/Sn等温凝固芯片键合工艺,对等离子体处理、键合气氛、压力以及Sn层厚度等因素对焊层的键合强度的影响进行了分析和优化。实验表明,等离子体处理过程的引入是保证键合质量的重要因素,在功率500W、时间200s的处理条件下,得到了最大的键合强度;而键合气氛对键合质量有显著的影响,在真空环境下,能得到最佳的键合质量;压力对键合质量的影响较小,施加较小的压力(0.05MPa)即能得到较大的剪切强度;而Sn层厚度对键合质量的影响极小,而较薄的厚度能够缩短键合时间。在最优化条件下,得到的键合强度值全部达到了美军标规定的6.25MPa的强度要求(对于2mm×2mm芯片)。     

Study on cold metal transfer welding–brazing of titanium to copper

3 mm Pure titanium TA2 was joined to 3 mm pure copper T2 by Cold Metal Transfer (CMT) welding–brazing process in the form of butt joint with a 1.2 mm diameter ERCuNiAl copper wire. The welding–brazing joint between Ti and Cu base metals is composed of Cu–Cu welding joint and Cu–Ti brazing joint. Cu–Cu welding joint can be formed between the Cu weld metal and the Cu groove surface, and the Cu–Ti brazing interface can be formed between Cu weld metal and Ti groove surface. The microstructure and the intermetallic compounds distribution were observed and analyzed in details. Interfacial reaction layers of brazing joint were composed of Ti₂Cu, TiCu and AlCu₂Ti. Furthermore, crystallization behavior of welding joint and bonding mechanism of brazing interfacial reaction were also discussed. The effects of wire feed speed and groove angle on the joint features and mechanical properties of the joints were investigated. Three different fracture modes were observed: at the Cu interface, the Ti interface, and the Cu heat affected zone (HAZ). The joints fractured at the Cu HAZ had higher tensile load than the others. The lower tensile load fractured at the Cu interface or Ti interface was attributed to the weaker bonding degree at the Cu interface or Ti interface.     

Grains,deformation substructures,and slip bands observed in thermosonic copper ball bonding

In integrated circuit manufacturing, bonding a copper wire of diameter 25–75 μm (1–3 mil) on an aluminum-metallized silicon substrate has been accomplished by the application of ultrasonic energy along with compressive force at 200 °C. Prior to the bonding, the wire tip was melted by electric sparking to form a spherical ball, which, when analyzed, displayed columnar grain growth. Microstructural study of the final bonding showed that the application of ultrasonic energy resulted in the subdivision of the grains of a few micrometers in size, giving rise to deformation substructures (or cells). In addition, slip bands were observed inside the cells. Microhardness studies showed that the ball bonds had a higher hardness (112 VHN) than that of the unannealed bare copper wire (102 VHN), suggesting that the applied ultrasonic energy strain hardened the copper ball by creating the deformation substructures and slip bands. Furthermore, the heat-affected zone above the copper ball clearly contained recrystallized grains along with deformation markings.     

铜包钢线材室温拉变形后的显微组织和力学性能

研究了经室温拉变形后的纯铜包覆Q195钢的不同线径的线材的显微组织及力学性能.结果表明,显微组织自原始的等轴晶变为细长条纤维状,纤维长度与形变量的平方近似地成正比,纤维直径与形变量近似地成反比.经室温拉变形的包覆线材的抗拉强度,随形变量增大而增大,与形变量平方根呈直线关系;但延伸率降低,延伸率波动偏高与晶界融合及Q195钢的渗碳体球化现象吻合.根据原始纯铜和Q195钢的抗拉强度值,可以用复合材料强度的混合法则来近似地预测不同线径的包覆线材的抗拉强度.     

铜箔抗拉强度及延伸率的尺寸效应研究

为了研究尺寸参数对金属箔材的抗拉强度和延伸率的影响规律,采用不同厚度和晶粒尺寸的铜箔进行室温单向拉伸试验.试验结果表明:铜箔的抗拉强度和延伸率同时受厚度和晶粒尺寸的影响,这种尺寸效应的描述必须引入无量纲的厚度晶粒尺寸比(T/D)作为比较参数.抗拉强度在不同厚度晶粒尺寸比区间内的变化规律不同;而延伸率在厚度晶粒尺寸比相同时都随厚度的减小而降低.拉伸断口的扫描电镜分析显示箔材的延伸率随着厚度的减小出现的突降和断裂机制的变化有关.     

Recrystallization and fracture characteristics of thin copper wire

In this study, the annealed effect (at 150 °C ∼ 250 °C for 1 h) on the tensile mechanical properties of thin copper wires with φ = 25 μm (1 mil) was investigated. The microstructural characteristics and the mechanical properties before and after an electric flame-off (EFO) were also studied. Results indicate that with annealing temperatures of more than 200 °C, the wires possessed a fully annealed structure, the tensile strength and the hardness decreased, and the elongation was raised significantly. Through recrystallization, equiaxed grains and a few annealed twins formed in the matrix structure. The microstructures of the free air ball (FAB) of the various wires after EFO contained column-like grains. The column-like grains grew from the heat-affected zone (HAZ) to the Cu ball, and the preferred orientation was <100>. According to Weibull’s reliability analysis, the failure rates of all the specimens were the modus of wear-failure. The tensile strength and the reliability of both the 200 °C and 250 °C annealed wires in the HAZs showed the highest values of all.     

Fundamentals of thermo-sonic copper wire bonding in microelectronics packaging

Fine copper wire bonding is capable of making reliable electrical interconnections in microelectronic packages. Copper wires of 0.8–6 mil diameter have been successfully bonded to different bond pad metallized and plated substrate materials such as Al, Cu, Ag, Au and Pd. The three metallurgical related factors; solid-solubility and diffusion of dissimilar contact metals, oxide film breakage and plastic deformation of asperities play a critical role in the bonding. Plastic deformation of an asperity is the most significant factor one has to consider to attain good bonding. Soft aluminum metal (30–40 VHN), with a lower % asperity threshold deformation is easier to wire bond than harder metallic surfaces (Ni, W, Mo, Cr, Co, Ta) of 150–500 VHN. Good adhesion of wire bonding is achieved for the surface roughness (Ra) of 0.01–0.15 μm and 0.02–0.6 μm of bare and plated surfaces respectively. It is rationalized that the application of ultrasonic energy principally breaks the oxide film and deform the asperities, while a compressive force increases the proximity of asperities. Hence wire welds to bond pad surface by molecular attraction and inter diffusion. Storage of copper ball bonds at 175 °C for 100–1,000 h forms copper aluminide at the interface. EDAX and Auger analysis reveal 22 at% Al + 78 at% Cu composition of the aluminides and Cu₃Al₂ empirical formula is calculated, which, does not match with any of the reported copper aluminides. Hardness of the copper ball bonds and stitch bonds are higher than wire exhibiting work hardening of the bonds on processing.     

Gas tungsten-arc filler welding of AZ31 magnesium alloy

Optical microscopy and scanning electron microscopy (SEM) were used to examine the microstructure and fracture of AZ31 magnesium alloy joint welded by automatic gas tungsten-arc filler (GTAF) welding process with AZ61 wire. More endeavors have been put on investigating the effect of filler wire on microstructure and performance of welded joint. The result showed that the grain size in heat-affected zone (HAZ) of GTAF welded joint holds significant variety compared with that of GTA welded joint (without filler wire). The modification of microstructure in HAZ has changed the fracture location as well as the ultimate tensile strength (UTS) of joint in tensile test.