Cratering on thermosonic copper wire ball bonding

Copper wire bonding offers several mechanical and electrical advantages as well as cost saving compared to its gold wire predecessor. Despite these benefits, silicon cratering, which completes the fracture and removal of bond pad underlayers, has been a major hurdle to overcome in copper wire bonding. Copper wire is harder than gold, and thus needs greater ultrasonic power and bond force to bond it onto metal pads such as aluminum. This paper reports a study on the influence of wire materials, bond pad hardness, and bonding-machine parameters (i.e., ultrasonic power and bond force) on silicon cratering phenomenon. Ultrasonic power and z-axis bond force were identified as the most critical bonding machine parameters in silicon cratering defects. A combination of greater bond force and lower ultrasonic power avoids silicon cratering and gives the desired effects. Results also show that a harder bond pad provides relatively good protection from silicon cratering.     

键合时间对粗铝丝超声引线键合强度的影响

试验研究了不同超声功率条件下,键合时间对粗铝丝引线键合强度的影响规律.试验中记录了每种键合试验的键合时间,采集了每一个键合点的剪切测试力作为键合点抗剪强度的表征,记录了每个键合点的状态.结果表明:(1)在小超声功率条件下,键合强度对键合时间敏感;在大超声功率条件下,敏感性下降;(2)短键合时间条件下主要键合失败形式为剥离和无粘接,表明键合界面的原子扩散不够;(3)大超声功率长键合时间条件下的键合失败形式多为根切,表明键合界面的原子扩散虽然足够,但长时间的超声振动也会使粗铝丝产生疲劳断裂,形成过键合.     

Effect of ultrasonic power on wedge bonding strength and interface microstructure

During the aluminum wire wedge bonding, the ultrasonic power and bonding strength were obtained. Based on those data, the relationship between ultrasonic power and bonding strength was studied. The results show that： 1） ultrasonic power is affected by ultrasonic power ratio and other uncontrolled factors such as asymmetric substrate quality, unstable restriction on the interface between wedge tool and aluminum wire; 2） when ultrasonic power is less than 1.0 W, increasing ultrasonic power leads to increasing bonding strength and decreasing failure bonding; on the contrary, when ultrasonic power is greater than 1.6 W, increasing power leads to decreasing bonding strength and increasing failure bonding; 3） only when ultrasonic power is between 1.0 W and 1.6 W, can stable and high yield bonding be reached. Finally, the microstructure of bonding interface was observed, and a ring-shaped bond pattern is founded in the center and friction scrape besides the ring area.     

Temperature effect in thermosonic wire bonding

1 Introduction Currently, thermosonic wire bonding and flip chip bonding are the main electrical packaging types in first level IC chip manufacture domain. Wire bonding is simple and somewhat mature, and nowadays it holds 75% in all electrical packaging …     

Bonding mechanism of ultrasonic wedge bonding of copper wire on Au/Ni/Cu substrate

The ultrasonic wedge bonding with d 25 μm copper wire was achieved on Au/Ni plated Cu substrate at ambient temperature. Ultrasonic wedge bonding mechanism was investigated by using SEM/EDX, pull test, shear test and microhardness test. The results show that the thinning of the Au layer occurs directly below the center of the bonding tool with the bonding power increasing. The interdiffusion between copper wire and Au metallization during the wedge bonding is assumed negligible, and the wedge bonding is achieved by wear action induced by ultrasonic vibration. The ultrasonic power contributes to enhance the deformation of copper wire due to ultrasonic softening effect which is then followed by the strain hardening of the copper wedge bonding.     

银丝键合烧球参数对键合质量的影响

经键合试验,测试焊线挑断力和焊球推力,观察焊球和电极界面形貌,研究了烧球电流和时间对银键合丝键合质量的影响。结果表明,随烧球电流增大、时间延长,键合无空气焊球(FAB)直径增大;FAB球颈晶粒尺寸是电流和时间共同作用的结果,晶粒尺寸越大、挑断力越小,18 mA-1.0ms烧球所得挑断力最小;在FAB尺寸相近的前提下随烧球电流减小,焊球推力降低,键合过程中电极易受损导致电极材料挤出率增大;高电流-短时间(23 mA-0.6 ms)烧球有利于银丝获得较好的键合质量。     

金丝的力学特征对球键合的微观组织和性能的影响

用电子背散射衍射仪对具有不同力学特征金丝的微区组织进行表征,采用扫描电镜和光学显微镜观察线弧轮廓、热影响区和焊点形貌,并通过推拉力测试仪测量线弧拉力和焊球剪切力,分析金丝力学特征对球键合质量的影响。结果表明：半硬态1和半硬态2的金丝芯部保持纤维状组织,边缘晶粒为细小的等轴晶,沿径向微区组织形貌有明显差异。打火烧球后形成的热影响区长度短,球颈部的组织有明显的梯度性,键合后弧高较小。软态金丝的组织为粗大的等轴晶,沿径向分布均匀,键合拉力低,易发生滑球现象。半硬态2金丝与焊盘的结合力强,引线键合拉力高,综合键合质量优,是最适合球键合工艺的金丝。     

Ultrasonic evaluation of the bonding strength of dissimilar metal bonds

Diffusion bonding of steel plates to titanium plates was carried out, and shear testing and ultrasonic measurement of bonds were performed to obtain the relationships between bonding strength, state of bonding interface and ultrasonic parameters. Fourier spectra of the ultrasonic wave reflected from the bonding interface were dependent on the state of the bonding interface; when an interlayer did not melt the spectrum showed a simple profile with one peak, and when the interlayer melted, the spectrum showed a profile with large irregularity. Transfer functions obtained from the spectrum were analysed with the subspace method (a kind of principal component analysis) and were represented by two major components. The bonding strength was quantitatively evaluated by two major components and a diameter estimated from the ultrasonic measurement.     

Ni-Al超声楔焊键合分离界面的结构特性及演变规律

设计了一系列的粗铝线楔焊键合试验，用扫描电镜测试分离的楔焊界面，通过采集驱动电信号分析了压电陶瓷输入功率特性。结果表明，Ni—Al超声键合的界面模式形如脊皱圆环，中心和外边是未结合的摩擦痕，脊皱构成强度，相同参数条件下，一焊脊皱峰和转化的超声能大于二焊；其它参数不变的条件下，随压力的增加，键合面尺寸增大，圆环的短轴延伸为长轴，随时间的增加，脊皱扩展为完整的圆环，脊皱尺寸向中央扩大，随功率的增加，摩擦痕和脊皱加剧，且这些参数存在一个最佳范围。     

Development of a bonding interface between steel/steel and steel/Ni by ultrasonic welding

Ultrasonic welding is a solid-state welding technique that can bond materials at a relatively low temperature and pressure. In this study, steel/steel and steel/Ni combinations were successfully bonded by ultrasonic welding, and the development of the bonding interface was examined. The bonding strength was obtained by a lap shear test and increased with welding time, as did the fraction of bonded area observed by SEM. The bonding process sequence was investigated by SEM and electron backscatter diffraction (EBSD) analysis of a cross-section at the bonding interface. It was revealed that abrasion is caused by oscillation to form small particles consisting of steel and Ni and that the particles are grown and subsequently flattened with welding time. Bonding is achieved by the flattened particles spreading along the bonding interface without any voids.     

TiAl/40Cr扩散焊接头强度评价与预测

为了解决界面回波幅度均值无法评价异种材料扩散焊接头强度的问题,文中提出一种接头强度评价与预测方法.该方法基于二叉树支持向量机构建界面缺陷的识别模型,根据识别结果计算界面的焊合率,建立焊合率与抗剪强度的关系.采用线性拟合的方法获得抗剪强度的经验公式,用于预测接头强度.结果表明,构建的缺陷识别模型可以有效地识别出扩散焊界面未焊合、弱接合和微孔缺陷,焊合率与接头抗剪强度具有相关性,抗剪强度随着焊合率的增加而增加.实现了接头强度的预测,预测强度与实测值吻合较好.     

304不锈钢扩散焊界面的超声非线性成像

运用信号处理技术对扩散焊界面的超声非线性行为进行了研究.首先通过控制焊前表面处理和焊接工艺制备了具有典型缺陷的扩散焊接头,并对其进行超声检测,获得了反映界面状态的超声信号数据.在固相连接接头超声非线性的理论分析、界面超声非线性图像、界面显微特征和接头抗剪强度的基础上,研究了不锈钢扩散焊接头不同界面状态的超声非线性效应.结果表明,非线性超声检测对弱结合缺陷比较敏感,可在一定程度上将超声C扫描成像和超声非线性成像结合起来实现扩散焊接头的无损检测.     

连接条件对00Cr25Ni7Mo3N双相不锈钢扩散连接的影响

利用热模拟试验机并结合扫描电镜(SEM)对00Cr25Ni7Mo3N超级双相不锈钢的超塑扩散连接进行实验研究,对不同连接条件下的孔洞形貌、界面组织进行相应的分析。研究结果表明,超塑性扩散连接试样的界面结合强度随扩散连接压力的增大、表面质量的提高及连接时间的延长而增大。扩散连接在连接温度1100℃时,连接压力为10MPa～20MPa;待连接表面经精磨处理后,连接时间10min～20min的条件下,可实现焊合率为96%～98%的扩散连接,且连接试样的初始连接界面消失,界面孔洞基本闭合,界面剪切结合强度达到407MPa～413MPa。     

超声固结钛/铝箔材界面剥离强度与结合机理分析

以1100铝箔和TA1钛箔为基体材料进行异种金属材料超声固结试验研究,制备了Ti/Al箔材金属层状复合材料试样,应用剥离试验研究了振幅、静压力对Ti/Al箔材界面结合强度的影响规律,利用扫描电镜研究了剥离界面的微观组织形貌,采用EDS对剥离界面进行能谱分析,通过透射电镜对Ti/Al箔材界面微观组织进行观察。结果表明,超声固结可以实现Ti/Al箔材良好的结合界面,界面结合强度随着静压力的增大先增大后减小,随着振幅的增大单调递增;在振幅35μm,静压力1.5kN条件下,获得最佳的超声固结界面,其剥离强度为11.325N/mm;Ti箔材的剥离界面中Al元素均匀分布,并存在明显的韧窝组织;Ti/Al界面存在元素过度区,界面处晶粒细化明显;铝箔表面氧化膜破碎,且钛元素以弥散的形式嵌入到铝晶粒内部。     

引线键合中多向超声波能量传输特性研究

引线键合主要是采用超声波热键合技术，而超声波振动传播和能量传递是超声波键合设备中一个非常关键和复杂的问题。利用波在弹性体中传播的机理，给出超声波聚能杆和劈刀的振动传递特性，利用多普勒振动计PSV-300-F(1．5MHz)测量了振动位移和速度，证实了理论分析结果，并对双向垂直传输超声波能焊具的性能进行了研究，阐明垂直双向加载是一种高效的传能模型。     

用200nm铜颗粒在空气中快速压力辅助烧结及连续无压退火提高结合强度

为了设计一种有效且适用于功率器件的烧结结合工艺,提出一种两步工艺,使用约200 nm的铜颗粒基浆料形成具有高温可持续性和优越导热性的粘结层.该工艺涉及在空气中快速压力辅助烧结和在氮气气氛中连续无压退火.当使用20％(质量分数)的羟基丁二酸和80％(质量分数)的乙二醇混合物浆料时,在300℃、5 MPa烧结30 s后的剪...     

黄铜/钢扩散复合双金属界面组织与性能

用扫描电镜、能谱分析和压剪试验等方法,研究了扩散退火温度与时间对黄铜/钢扩散复合双金属界面附近组织、成分和界面结合强度的影响.结果表明,通过扩散复合可使黄铜/钢界面实现良好的冶金结合;在一定温度和时间范围内,随扩散温度和时间的增加界面结合面积增大,结合强度增加,可达220MPa;界面附近发生了原子的互扩散,界面上无有害相生成.     

Influences of diffusion bonding process parameters on bond characteristics of Mg-Cu dissimilar joints

In many circumstances,dissimilar metals have to be bonded together and the resulting joint interfaces must typically sustain mechanical and/or electrical forces without failure,which is not possible by fusion welding processes.The melting points of magnesium(Mg)and copper(Cu)have a significant difference(nearly 400℃)and this may lead to a large difference in the microstructure and joint performance of Mg-Cu joints.However,diffusion bonding can be used to join these alloys without much difficulty.This work analyses the effect of parameters on diffusion layer thickness,hardness and strength of magnesium-copper dissimilar joints.The experiments were conducted using three-factor,five-level,central composite rotatable design matrix.Empirical relationships were developed to predict diffusion layer thickness,hardness and strength using response surface methodology.It is found that bonding temperature has predominant effect on bond characteristics.Joints fabricated at a bonding temperature of 450℃, bonding pressure of 12 MPa and bonding time of 30 min exhibited maximum shear strength and bonding strength of 66 and 81 MPa, respectively.     

Perspectives offered by combining a laser beam with arc welding procedures

Summary

With regard to the fact that, during Cu wire stitch bonding of copper lead frames, the wire deformation strongly affects the bondability and strength of the bonds obtained, this paper describes an investigation of the wire deformation being varied through variation in the initial capillary tip load and capillary tip load during application of ultrasonic vibration as well as the bondability and bond strength then obtained. When stitch bonding with soft copper wire is performed by the two‐step load control method, which has a higher initial capillary tip load and a lower capillary tip load during the second stage, the range of action of the material being worked under ultrasonic vibration can be widened, the deformation during the working time of ultrasonic vibration can be suppressed, the ultrasonic energy can make a greater contribution to bonding, and a higher bond strength can be obtained. The results obtained in this study suggest that, during wire bonding by the two‐step load control method, the optimum capillary tip load is obtained. Within the presently adopted experimental range, the optimum values are a capillary tip load of 1.4 N before the application of ultrasonic vibration and a capillary tip load of 0.4 N during ultrasonic vibration.     

Initial bond formation in thermosonic gold ball bonding on aluminium metallization pads

The morphological features of lift-off footprints on the aluminium metallization pads were investigated to gain an understanding of the effects of bonding parameters on formation of initial bonds during thermosonic gold ball bonding. The obtained results showed that metallurgical bonding initiated at the peripheral areas of the contact area situated along the direction of ultrasonic vibration. Those areas extended inwards with an increase in ultrasonic power. Both the external bonded area and central non-bonded area increased with increasing bonding force. Based on the evolution of footprints, the bonding models were proposed, and the effects of the bonding parameters on the formation of initial bonds were discussed.