Deformation and bonding processes in aluminum ultrasonic wire wedge bonding

The ultrasonic wire bonding (UWB) process has been examined using transmission electron microscopy (TEM) and standard wire pull testing techniques. Al-0.5 wt.% Mg wires 75 μm in diameter were bonded to pure and alloyed Al substrates. The bonding parameters, surface roughness, and surface contamination levels were variables in the experiments. Cross-section TEM specimens were made from these samples. TEM analysis was conducted on the wire, wire/substrate interface and substrate. Pull tests showed that for the Al substrates the surface roughness or the presence of contamination did not effect the bond strength, whereas for contaminated stainless steel substrates, a three μm surface finish resulted in the highest bond pull strength. The TEM observations revealed features such as low-angle grain boundaries, dislocation loops and the absence of a high dislocation density, indicating that the wire and substrate were dynamically annealed during bonding. Based on the width of a zone near a grain boundary in the wire which was depleted of dislocation loops, it was estimated that local heating equivalent to a temperature of 250° C for 90 msec was achieved in the wire during bonding. No evidence was found for melting along the bond interface, indicating that UWB is a solid-state process. Based on the TEM observationsof the bond interface and the pull tests, it is concluded that the ultrasonic vibrations clean the surfaces to be joined to the extent that a good bond can be obtained by intimate metal-metal contact in the clean areas.     

IC键合铜线材料的显微力学性能研究

用于IC(集成电路)的键合铜线材料具有低成本、优良的导电和导热性等优点,但其高硬度容易对铝垫和芯片造成损伤,因此对其硬度的测量是一项关键技术。纳米压痕测量技术可以方便、准确地测量铜线材料的显微硬度值和其他力学性能参数。描述了纳米压痕测量技术的原理以及对铜线材料样品进行纳米压痕测量的参数选择,进行了测量试验。结果表明,原始铜线、FAB(金属熔球)、焊点的平均硬度分别为1.46,1.51和1.65GPa,为键合铜线材料的选择和键合工艺参数的优化提供了依据。     

铜线键合技术的发展与挑战

铜线键合技术近年来发展迅速,超细间距引线键合是目前铜线键合的主要发展趋势.介绍了铜线键合的防氧化措施以及键合参数的优化,并从IMC生长及焊盘铝挤出方面阐述了铜线键合的可靠性机理.针对铜线在超细间距引线键合中面临的问题,介绍了可解决这些问题的镀钯铜线的性能,并阐述了铜线的成弧能力及面临的挑战.     

孔口铜丝问题的原因分析与改善

电镀工艺能够增加面铜厚度并实现不同层次的导电连接而被广泛的应用于PCB行业。然而,针对该工艺的品质保证绝非易事。电镀工艺受钻孔效果、沉铜前处理、电镀参数等因素的影响,在品质上容易出现铜丝铜粒等不良问题。本文从电镀基本原理出发,初步分析了电镀工艺铜丝的产生原因,并通过试验验证了铜丝产生的原因,得出了有效的改善措施。     

Comparison of the copper and gold wire bonding processes for LED packaging

Wire bonding is one of the main processes of the LED packaging which provides electrical interconnection between the LED chip and lead frame. The gold wire bonding process has been widely used in LED packaging industry currently. However, due to the high cost of gold wire, copper wire bonding is a good substitute for the gold wire bonding which can lead to significant cost saving. In this paper, the copper and gold wire bonding processes on the high power LED chip are compared and analyzed with finite element simulation. This modeling work may provide guidelines for the parameter optimization of copper wire bonding process on the high power LED packaging.     

Comparison of the copper and gold wire bonding processes for LED packaging

Wire bonding is one of the main processes of the LED packaging which provides electrical interconnection between the LED chip and lead frame.The gold wire bonding process has been widely used in LED packaging industry currently.However,due to the high cost of gold wire,copper wire bonding is a good substitute for the gold wire bonding which can lead to significant cost saving.In this paper,the copper and gold wire bonding processes on the high power LED chip are compared and analyzed with finite element simulation.This modeling work may provide guidelines for the parameter optimization of copper wire bonding process on the high power LED packaging.     

铝基板表面氧化铝层分子自组装活化法镀铜

采用分子自组装活化法在铝基板表面氧化铝上实施化学镀铜,镀层有很好的剥离强度,通过SEM、EDS和离子色谱对其进行了表征。研究了硅烷化时间与基体表面硅烷修饰量的关系,浸钯时间对基体表面钯含量的影响,硅烷化时间对镀层剥离强度的影响。通过正交试验得到最佳工艺条件:硅烷化处理用3-氨基丙基三乙氧基硅烷,质量分数为0.4%,硅烷化时间12h、温度50℃、浸钯溶液活化时间30min、30℃;得到的镀铜层剥离强度为1.00。     

Thermosonic bonding of gold wire onto a copper pad with titanium thin-film deposition

A novel thermosonic (TS) bonding process for gold wire bonded onto chips with copper interconnects was successfully developed by depositing a thin, titanium passivation layer on a copper pad. The copper pad oxidizes easily at elevated temperature during TS wire bonding. The bondability and bonding strength of the Au ball onto copper pads are significantly deteriorated if a copper-oxide film exists. To overcome this intrinsic drawback of the copper pad, a titanium thin film was deposited onto the copper pad to improve the bondability and bonding strength. The thickness of the titanium passivation layer is crucial to bondability and bonding strength. An appropriate, titanium film thickness of 3.7 nm is proposed in this work. One hundred percent bondability and high bonding strength was achieved. A thicker titanium film results in poor bond-ability and lower bonding strength, because the thicker titanium film cannot be removed by an appropriate range of ultrasonic power during TS bonding. The protective mechanism of the titanium passivation layer was interpreted by the results of field-emission Auger electron spectroscopy (FEAES) and electron spectroscopy for chemical analysis (ESCA). Titanium dioxide (TiO₂), formed during the die-saw and die-mount processes, plays an important role in preventing the copper pad from oxidizing. Reliability of the high-temperature storage (HTS) test for a gold ball bonded on the copper pad with a 3.7-nm titanium passivation layer was verified. The bonding strength did not degrade after prolonged storage at elevated temperature. This novel process could be applied to chips with copper interconnect packaging in the TS wire-bonding process.     

Sn基钎料与Cu和Al基板的润湿性比较研究

采用润湿平衡法测量了四种Sn基钎料(Sn-37Pb、Sn-3.OAg-0.5Cu、Sn-0.7Cu与Sn-9Zn)分别在250,260和270℃与Cu、Al两种基板的润湿性能.结果表明:钎料与Al基板的润湿时间均比Cu基板长,除Sn-9Zn外,其他三种钎料与Cu基板的润湿力比Al基板大,并且随着温度升高,润湿性能提高,...     

低压铝箔交流腐蚀工艺中的超声波辅助应用

采用国产铝箔,在超声波辅助条件下,对铝箔进行交流腐蚀,研究了超声波辅助腐蚀对腐蚀箔比容和力学性能的影响。结果发现:当腐蚀箔保持率为1.63g/dm2,采用磁力搅拌的腐蚀箔比容只有71.8×10–6F/cm2,而采用超声波辅助腐蚀的腐蚀箔比容为79.4×10–6F/cm2,提高了10.6%,且抗拉强度提高约20%。     

Ultra-fine pitch palladium-coated copper wire bonding: Effect of bonding parameters

Copper (Cu) wire bonding has become a mainstream IC assembly solution due to its significant cost savings over gold wire. However, concerns on corrosion susceptibility and package reliability have driven the industry to develop alternative materials. In recent years, palladium-coated copper (PdCu) wire has become widely used as it is believed to improve reliability. In this paper, we experimented with 0.6 ml PdCu and bare Cu wires. Palladium distribution and grain structure of the PdCu Free Air Ball (FAB) were investigated. It was observed that Electronic Flame Off (EFO) current and the cover gas type have a significant effect on palladium distribution in the FAB. The FAB hardness was measured and correlated to palladium distribution and grain structure. First bond process responses were characterized. The impact of palladium on wire bondability and wire bond intermetallic using a high temperature storage test was studied.     

不锈钢表面镀铜对铝/钢YAG激光焊接的影响

对0.3 mm厚的316L不锈钢/6061铝合金进行了脉冲激光(YAG)封边焊接试验。为了改善铝钢的冶金结合,对不锈钢表面进行了镀Cu处理,对比了镀铜前后的焊接情况;利用光学显微镜、扫描电镜及能谱分析等方法研究了接头界面区显微组织特征、熔合情况、元素分布和断口形貌。结果表明:对于铝/钢直接焊接,焊接电流I=130 A,激光脉宽D=4 ms,激光频率f=13 Hz,焊接速度V=150 mm/min,气体流量25 L/min,零离焦时,焊缝平整、成型美观。镀铜层形成了铝钢焊接的过渡层,减缓了界面处液态金属传递,抑制了铁铝之间的熔合,铝钢熔合线向钢一侧偏移。不锈钢未镀铜情况下,焊接接头组织主要由靠近铝一侧的针状或粗大板条状Fe2Al5及靠近钢一侧的FeAl 组成;镀铜后Cu主要固溶到Fe中,接头界面组织主要由(Fe,Cu)2Al5、(Fe,Cu)3Al组成。镀铜前后接头拉伸断口形貌未发生明显变化,然而,接头强度明显提高,提高约40.32%,达到15.63 N/mm。     

Thermosonic bonding of gold wire onto silver bonding layer on the bond pads of chips with copper interconnects

A copper pad oxidizes easily at elevated temperatures during thermosonic wire bonding for chips with copper interconnects. The bondability and bonding strength of a gold wire onto a bare copper pad are seriously degraded by the formation of a copper oxide film. A new bonding approach is proposed to overcome this intrinsic drawback of the copper pad. A silver layer is deposited as a bonding layer on the surface of copper pads. Both the ball-shear force and the wire-pull force of a gold wire bonded onto copper pads with silver bonding layers far exceed the minimum values stated in the JEDEC standard and MIL specifications. The silver bonding layer improves bonding between the gold ball and copper pads. The reliability of gold ball bonds on a bond pad is verified in a high-temperature storage (HTS) test. The bonding strength increases with the storage time and far exceeds that required by the relevant industrial codes. The superior bondability and high strength after the HTS test were interpreted with reference to the results of electron probe x-ray microanalyzer (EPMA) analysis. This use of a silver bonding layer may make the fabrication of copper chips simpler than by other protective schemes.     

Microstructural study of copper free air balls in thermosonic wire bonding

Copper wires are increasingly used in place of gold wires for making bonded interconnections in microelectronics. In this paper, a microstructural study is reported of cross-sectioned free air balls (FABs) made with 23 μm diameter copper bonding wire. It was found that the FAB is comprised of a few columnar grains and a large number of fine subgrains formed within the columnar grains around the periphery of the FAB. It was determined that conduction through the wire was the dominant heat loss mechanism during cooling, and the solidification process started from the wire-ball interface and proceeded across the diameter then outward towards the ball periphery.The microstructure of the Cu ball bond after thermosonic bonding was investigated. The result showed that the subgrain orientations were changed in the bonding process. It is evident that metal flow along the bonding interface was from the central area to the bond periphery during thermosonic bonding.     

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.     

平整度对细Al丝超声引线键合强度的影响

为避免双键合点破坏性拉力实验不易准确的缺陷和剪切力测试不能评价键合点整体特性的缺陷,采用了破坏性单键合点的测试方法.在尽量排除其他干扰因素的情况下,通过实验比较了10种不同平整度条件下细Al丝超声引线键合的结果.结果表明,平整度对超声引线键合的强度有影响,随着平整度的提高,键合强度和稳定度也随之提高.实际测试键合拉力时发现,键合良好断裂点均在跟键(heel)处,采取补强的方式使1.25 mil(3.125×10-3 cm)细Al丝超声键合后的键合强度均值可以达到0.156 8 N.分析了以上实验现象产生的原因,探讨了键合强度形成的机理.     

铝材管道管壁厚度对激光超声信号影响的探究

为了探究管壁厚度对超声信号的产生与探测的影响,采用有限元法建立了理想化的管道模型,分别探究均匀管壁厚度变化和激发源处、接收端处及传播路径上等畸变管壁厚度的变化对超声信号产生的影响。结果表明,当接收端处管壁厚度较薄时,无法探测到可分辨的瑞利波信号;传播路径上管壁厚度变小到一定程度后,高频成分会出现明显的衰减,但随着厚度的增大又会在一定程度内恢复。这一结果对激光超声在柱状、管状材料的无损检测中的进一步应用提供了有益的补充。     

AA7075铝合金表面激光熔覆Zr基复合涂层的组织与磨损行为

为了提高铝合金的磨损性能,采用激光熔覆技术在AA7075铝合金表面熔覆了Zr-Cu-Ni-Al-TiC复合粉末,制备出Zr基复合涂层。采用SEM和XRD技术研究了熔覆层的组织；采用干滑动磨损方法评价了涂层的耐磨性。研究结果表明：熔覆层组织主要由非晶和金属间化合物组成。在非晶相和金属间化合物复合作用下,熔覆层表现出优异的耐磨性,尤其是随着熔覆层中TiC含量的增加,耐磨性得到显著的提高。     

激光熔覆层摩擦学特性的研究

为研究激光熔覆层的磨损性能，采用激光熔覆技术，在球墨铸铁材料表面制备原位析出颗粒增强金属基复合材料表层。以激光强化的球墨铸铁为上试样、灰铸铁为下试样，进行标准的SRV快速磨损试验。利用表面形貌仪测量配副双方的磨损深度，扫描电子显微镜（SEM）观察磨痕形貌。结果表明；激光熔覆强化层与灰铸铁配副，磨损深度分别为1．78μm、0．87μm，摩擦系数在0．067～0．085内变化，摩擦系数随摩擦时间的增加呈逐渐降低的趋势；磨损机制为微切削。     

功率器件封装中铝引线焊点剥离失效机制研究

比较回流焊前后两组器件样品的电学测量结果,并结合样品的失效分析,发现引线框架氧化也是导致焊点剥离失效的一个重要因素,而且回流焊工艺下的热机械效应,会加速原先潜在的焊点剥离失效的发生.样品的连接性测试发现,在低峰值交流测试电压下显示开路,而高峰值测试电压下显示正常,可以将其归结为典型的焊点剥离失效的测试现象.发现引线键合前的等离子清洗可以减少焊点剥离失效,并可使焊点的剪切强度提高25%.