Au丝键合改为Cu丝键合技术

现阶段Au丝作为内引线一直占着键合的主导地位,由于Cu丝具有优良的电性能和价格优势,随着键合技术的发展,以Cu丝代替Au丝作为键合用内引线已经成为必然,封装行业许多厂家正热衷于将原有的Au丝键合设备进行改造,但还存在这样那样的问题。以Au丝键合改为Cu丝键合的技术研究为出发点,首先介绍了键合技术的发展,然后通过工艺调整和设备改造,使得Cu丝作为内引线能够代替Au丝在该设备上使用,同时达到了节约生产成本,节约资金的目的。对改造过程中的气体流量、压力、功率、焊接时间等参数问题进行了详细地阐述,同时对芯片、键合劈刀等也做了相应调整,使得改造后的检测结果完全满足产品要求。大力推进以Cu丝替代Au丝键合技术,可节约生产成本,提高键合强度,增强导电率、导热率等,具有重要的经济技术效益,必将迎来封装业的又一次大变革。     

混合集成电路的外引线键合技术

混合集成电路外引线键合的方式很多。与混合集成电路的内引线键合不同，外引线键合时，键合丝的1端在管壳的引线柱上。因此，管壳外引线金属镀层的结构、镀层材料、键合丝的性能和键合工艺因素都将影响混合电路外引线键合的质量。本文主要对Au丝球焊、Au丝点焊、SiAl丝超声焊等不同的键合工艺及其对应的金属学系统进行研究，并对其结果进行比较。采用Au丝点焊工艺键合混合电路外引线的效果最佳。     

镀Pd Cu线键合工艺中Pd行为研究

由于Cu线热导率高、电性能好、成本低,将逐渐代替传统Au线应用于IC封装.但Cu线键合也存在Cu材料本身固有特性上的局限:易氧化、硬度高及应变强度等.表面镀Pd Cu线材料的应用则提供了一种防止Cu氧化的解决方案.然而,Cu线表面的Pd层很可能会参与到键合界面形成的行为中,带来新的问题,影响到Cu线键合的强度和可靠性.对镀Pd Cu线键合工艺中Pd的行为进行了系统的研究,使用了SEM,EDS等分析手段对cu线、烧结Cu球(FAB)、键合界面等处Pd的分布状况进行了检测,结果证明Pd的空间分布随着键合工艺的进行发生了很大的变化,同时还对产生Pd分布变化的原因进行了分析和讨论.     

引线带键合技术在混合集成电路中的应用

在混合集成电路的引线带键合中,由于与圆形键合丝在键合引线形状上的不同,导致其键合方式和键合参数有所不同。本文以金带键合为例,就混合集成电路中金带键合点的失效模式、键合引线的评价等问题进行了讨论,通过采用正交试验法对键合参数进行优化试验,提高键合的可靠性,达到引线带在混合集成电路中实际应用的要求。     

半导体器件组装技术的突破——Cu丝球焊将替代Au丝球焊

评述了A1、A1合金、Ag和Cu四种引线材料在半导体器件组装技术中作为球焊键合引线的前途.Cu的情况最喜人,Cu丝焊技术将应用到年导体器件的大批量生产中去.     

超声楔键合Al/Ni系统高温存储过程界面扩散行为(英文)

应用电子扫描电镜(SEM)及X射线能谱(EDX)分析了直径为25μm的Al+1％Si引线与 Au／Ni／Cu焊盘键合后以及老化过程中界面间的冶金行为,结果表明:接头形成于键合点塑性流动 最大的周边区域;超声引线键合的连接本质是压力使引线发生塑性流动导致Al元素与Ni元素之 间的扩散,而超声一方面使金属引线软化增强了塑性流动的程度,另一方面超声使引线内部产生大 量的缺陷,成为扩散的通道,大大加速了扩散的进行;短路扩散是键合点形成的主要机制。在170℃ 时,键合点空气中高温存储后X射线能谱线扫描分析结果表明:老化10 d时,有明显的Ni向Al引 线内扩散现象;老化30 d时,引线内部出现孔洞以及裂纹,界面出现云状组织,成份分析为15．55％ Ni和78．82％Al;老化40 d时,引线内部出现大量的孔洞并存在方块岛状的Al-Ni组织,其尺寸和 形状显示与Kirkendall孔洞不同。     

金属外壳引线键合可靠性研究

引线键合以工艺简单、成本低廉、适合多种封装形式的优势,在连接方式中占主导地位。其中把内部电路与金属外壳内引线柱之间的连接称为引线键合,目前90%以上的封装管脚采用引线键合连接。引线键合强度和可靠性不仅与键合工艺有关（比如键合工艺参数、键合设备、操作技能等因素）,而且与外壳引线的镀覆结构、镀层厚度、内引线柱高度等因素密切相关。文章简要介绍了引线键合工艺的基本原理,通过试验分析并比较了金属外壳镀覆结构、镀层厚度、内引线柱高度对键合可靠性的影响,提出了优化键合可靠性的外壳设计原则。     

超声楔键合Au/Al和Al/Au界面IMC演化

基于固体相变理论,研究Au丝、Al丝超声楔-楔键合接头的温度长期可靠性.200℃下,存储时间＜48 h时,Au/Al接头界面并未发生明显变化;随着接头存储时间增加,界面金属间化合物(IMC)开始由焊盘向引线方向生长(垂直生长);240 h时,Al焊盘完全被消耗,接头连接界面部位生成Au5Al2,周边为Au2Al;继续增加存储时间,IMC向接头水平方向生长(水平生长),Au5Al2向更稳定的Au2Al转变,IMC与引线之间形成严重的Kirkendall孔洞.Al/Au系统相对稳定得多,界面IMC生长缓慢,然而,界面化合物AuAl2导致接头裂纹,而引线内部出现严重的空洞.对比并分析了两种楔焊系统界面演变特点和产生机制.     

SiP模块键合线疲劳寿命预测及可靠性分析北大核心

针对SiP中键合线易疲劳失效问题,为提高键合线模块可靠性,展开疲劳寿命预测研究。梳理了键合线的常见失效机理和温循实验中瞬态热力耦合原理;对整体模块进行对称简化建立有限元模型,并对单根键合线进行参数化建模,在相同的温度循环载荷下,对比研究了键合线的直径、拱高、一二焊点的水平和垂直间距四种结构参数的等效应力、塑性应变幅值;建立了键合线模块的疲劳寿命模型,揭示了键合线结构参数对可靠性的影响。结果表明,键合线易失效点集中在焊点颈部和足底部分;在一定范围内,减小键合线的直径、减小一二焊点间水平和垂直间距、增加键合线的拱高,可提高键合线结构的可靠性,延长疲劳寿命。     

引线带楔焊键合技术

引线带楔焊键合和引线(圆形)楔焊键合是不同的。对于高频器件应用来说,引线带键合较之于圆形引线键合更为有利。为了让更多的人了解该项技术,文章对部分相关技术,其中包括键合工艺过程、键合引线的断丝方式、键合引线带规格以及键合劈刀的选择作了介绍。     

The development of Cu bonding wire with oxidation-resistant metal coating

Although Cu bonding wire excels over Au bonding wire in some respects such as production costs, it has not been widely used because of its poor bondability at second bonds due to surface oxidation. We conceived an idea of electroplating oxidation-resistant metal on the Cu bonding wire to prevent the surface oxidation. The electroplating of Au, Ag, Pd, and Ni over Cu bonding wire all increased bond strengths as expected, but it caused problematic ball shapes except Pd-plated Cu bonding wire. The wire could produce the same ball shape as that of Au bonding wire. It was also proved to have excellent bondability sufficient to replace Au bonding wire. That is, it excelled in bond strengths, defective bonding ratio, and wideness of "Parameter Windows". It also showed the same stability as Au bonding wire in reliability tests, while bonds of Cu bonding wire were deteriorated in a few of the tests. In short, the Pd-plated Cu bonding wire can realize excellent bonding similar to Au bonding wire, while having much lower production costs.     

Effects of Cu and Pd addition on Au bonding wire/Al pad interfacial reactions and bond reliability

Finer pitch wire bonding technology has been needed since chips have more and finer pitch I/Os. However, finer Au wires are more prone to Au-Al bond reliability and wire sweeping problems when molded with epoxy molding compound. One of the solutions for solving these problems is to add special alloying elements to Au bonding wires. In this study, Cu and Pd were added to Au bonding wire as alloying elements. These alloyed Au bonding wires—Au-1 wt.% Cu wire and Au-1 wt.% Pd wire—were bonded on Al pads and then subsequently aged at 175°C and 200°C. Cu and Pd additions to Au bonding wire slowed down interfacial reactions and crack formation due to the formation of a Cu-rich layer and a Pd-rich layer at the interface. Wire pull testing (WPT) after thermal aging showed that Cu and Pd addition enhanced bond reliability, and Cu was more effective for improving bond reliability than Pd. In addition, comparison between the results of observation of interfacial reactions and WPT proved that crack formation was an important factor to evaluate bond reliability.     

Bond reliability under humid environment for coated copper wire and bare copper wire

There is growing interest in Cu wire bonding for LSI interconnection due to cost savings and better electrical and mechanical properties. Conventional bare Cu bonding wires, in general, are severely limited in their use compared to Au wires. A coated Cu bonding wire (EX1) has been developed for LSI application. EX1 is a Pd-coated Cu wire to enhance the bondability.Bond reliability at a Cu wire bond under a humid environment is a major concern in replacing Au wires. The bond reliability of EX1 and bare Cu was compared in the reliability testing of PCT and UHAST (Unbiased HAST). The lifetimes for EX1 and the bare Cu in PCT testing were over 800 h and 250 h, respectively. Humidity reliability was significantly greater for EX1. Continuous cracking was formed at the bond interface for the bare Cu wire. Corrosion-induced deterioration would be the root cause of failure for bare Cu wires. The corrosion was a chemical reaction of Cu-Al IMC (InterMetallic Compound) and halogens (Cl, Br) from molding resins. EX1 improves the bond reliability by controlling diffusion and IMC formation at the bond interface. The excellent humidity reliability of the coated Cu wire, EX1 is suitable for LSI application.     

Investigation on copper diffusion depth in copper wire bonding

Due to the dramatic price increase of precious metals, the replacement of Au with Cu in wire bonding has become an emerging trend for IC packaging nowadays. Similar to the Pb-free soldering transition, such a replacement is not just a simple drop-in material change. Comprehensive processing and reliability investigations are required before a mass production of electronic devices with Cu wire bonding can be implemented. However, among the existing studies on Cu wire bonding, it appears that most researchers just focused on issues above the wire bond pads. In fact, the Cu in the wire bonds may diffuse into the Si chip and impose reliability threats to the electronic devices. So far there was no research on the Cu-to-Si diffusion issue in Cu wire bonding. In this paper, an experimental study on the Cu-to-Si diffusion in Cu wire bond is reported. The Cu diffusion depth was characterized with the secondary ion mass spectrometry (SIMS) technique. Specimens with various configurations were designed and fabricated to investigate the effects of several parameters on the Cu-to-Si diffusion depth. The issues of concern include the amount of Cu supply, the bond pad deformation, and the barrier layer under the bond pad. In addition, some samples with conventional Au wire bonding were fabricated and tested in parallel for comparison.     

Influence of bonding process parameters on chip cratering and phase formation of Cu ball bonds on AlSiCu during storage at 200 °C

Wire bonding remains the predominant interconnection technology in microelectronic packaging. Over the last 3 years a significant trend away from Au and towards Cu wire bonding has become apparent. This has been due to general efforts to lower manufacturing costs and price increases for raw materials like Au. Although much research has been carried out into wire bonding over recent decades, most has focused on Au ball/wedge bonding. The results of this research have shown that bonding parameters, bonding quality and reliability are closely interconnected. However, the different material properties of Cu compared to Au, such as affinity to oxidation and hardness, mean that these insights cannot be directly transferred to Cu bonding processes. Thus, further research is necessary. This paper discusses a study of bonding interface formation under various bonding parameters. Cu wire was bonded on AlSiCu0.5 metallization and a bonding parameter optimization was carried out to identify useful parameter combinations. On the basis of this optimization, different samples were assembled using parameter combinations of low, medium and high US-power and bonding force. An interface analysis was subsequently carried out using shear testing and HNO₃ etching. Intermetallic phase growth was analyzed on cross sections of devices annealed at 200 °C for 168 h and 1000 h. Contacts bonded with low bonding force and high US-power tended towards cratering during shear testing. Bonding force proved to have a significant effect on intermetallic phase formation whereas US-power was found to exert only a minor influence. The intermetallic phase formation of annealed samples was analyzed using EDX and interpreted on the basis of phase formation kinetics. Three main intermetallic phases were identified.     

Development of a thermosonic wire-bonding process for gold wire bonding to copper pads using argon shielding

To improve the bondability and ensure the reliability of Au/Cu ball bonds of the thermosonic (TS) wire-bonding process, an argon-shielding atmosphere was applied to prevent the copper pad from oxidizing. With argon shielding in the TS wire-bonding process, 100% gold wire attached on a copper pad can be achieved at the bonding temperature of 180°C and above. The ball-shear and wire-pull forces far exceed the minimum requirements specified in the related industrial codes. In a suitable range of bonding parameters, increasing bonding parameters resulted in greater bonding strength. However, if bonding parameters exceed the suitable range, the bonding strength is deteriorated. The reliability of the high-temperature storage (HTS) test for Au/Cu ball bonds was verified in this study. The bonding strength of Au/Cu ball bonds increases slightly with prolonged storage duration because of diffusion between the gold ball and copper pad during the HTS test. As a whole, argon shielding is a successful way to ensure the Au/Cu ball bond in the TS wire-bonding process applied for packaging of chips with copper interconnects.     

In situ ultrasonic force signals during low-temperature thermosonic copper wire bonding

Ultrasonic in situ force signals from integrated piezo-resistive microsensors were used previously to describe the interfacial stick-slip motion as the most important mechanism in thermosonic Au wire ball bonding to Al pads. The same experimental method is applied here with a hard and a soft Cu wire type. The signals are compared with those obtained from ball bonds with standard Au wire. Prior to carrying out the microsensor measurements, the bonding processes are optimized to obtain consistent bonded ball diameters of 60 μm yielding average shear strengths of at least 110 MPa at a process temperature of 110 °C. The results of the process optimization show that the shear strength c_pk values of Cu ball bonds are almost twice as large as that of the Au ball bonds. The in situ ultrasonic force during Cu ball bonding process is found to be about 30% higher than that measured during the Au ball bonding process. The analysis of the microsensor signal harmonics leads to the conclusion that the stick-slip frictional behavior is significantly less pronounced in the Cu ball bonding process. The bond growth with Cu is approximately 2.5 times faster than with Au. Ball bonds made with the softer Cu wire show higher shear strengths while experiencing about 5% lower ultrasonic force than those made with the harder Cu wire.     

基于田口方法的微波组件金丝键合工艺优化

为了提高微波组件金丝键合的可靠性,采用楔形金丝键合工艺进行了金丝互连,通过田口试验方法设计 和试验验证,确定了金丝键合最优化的工艺参数组合。研究结果表明：键合金丝质量的影响因素依次是超声功率、键 合压力和键合时间,优化的工艺参数组合依次为超声功率、键合压力、键合时间,优化的工艺参数组合为超声功率 15、键合压力16、键合时间50;采用优化后的工艺参数进行金丝键合操作,获得了稳定性良好的互连金丝,完全满 足混合集成微波电路金丝键合互连应用的需求。     

Development and Status of Cu Ball/Wedge Bonding in 2012

Starting in the 1980s and continuing right into the last decade, a great deal of research has been published on Cu ball/wedge (Cu B/W) wire bonding. Despite this, the technology has not been established in industrial manufacturing to any meaningful extent. Only spikes in the price of Au, improvements in equipment and techniques, and better understanding of the Cu wire-bonding process have seen Cu B/W bonding become more widespread—initially primarily for consumer goods manufacturing. Cu wire bonding is now expected to soon be used for at least 20% of all ball/wedge-bonded components, and its utilization in more sophisticated applications is around the corner. In light of this progress, the present paper comprehensively reviews the existing literature on this topic and discusses wire-bonding materials, equipment, and tools in the ongoing development of Cu B/W bonding technology. Key bonding techniques, such as flame-off, how to prevent damage to the chip (cratering), and bond formation on various common chip and substrate finishes are also described. Furthermore, apart from discussing quality assessment of Cu wire bonds in the initial state, the paper also provides an overview of Cu bonding reliability, in particular regarding Cu balls on Al metalization at high temperatures and in humidity (including under the influence of halide ions).     

Enhancing bondability with coated copper bonding wire

There is growing interest in Cu wire bonding for LSI interconnection due to the cost savings and better electrical and mechanical properties. However, the scope of use for Cu bonding wires is generally severely limited compared to Au wires; e.g. for wire oxidation, lower bondability, forming gas of N₂ + 5%H₂, and lower reliability. It is difficult for conventional bare Cu wires to achieve the target of LSI application.A coated Cu wire (EX1) has thus been developed. It is a Pd-coated Cu wire and has many advantages compared to bare Cu wires. Its stitch strength was far superior under fresh conditions and remained constant without any deterioration after being stored in air for a prolonged period. EX1 had a lifetime of over 90 days in air, as compared to just 7 days for bare Cu wire. Spherical balls were formed with pure N₂ (hydrogen-free), whereas the bare Cu produced off-center balls. Finally, the cost-effective and secure gas, pure N₂ was only available for EX1. The excellent performance of the EX1 coated Cu wire is comparable to that of Au wires, making it suitable for LSI packaging.