钎料稀土相表面Sn晶须生长的研究

为了解对钎料可靠性影响极大的Sn晶须的生长机理,系统研究了钎料稀土相CeSn3、LaSn3及ErSn3表面Sn晶须生长的影响因素.结果表明:稀土相的氧化倾向与时效温度共同影响其表面Sn晶须的生长.室温时效条件下,在稀土相CeSn3与LaSn3表面易出现小尺寸的线状Sn晶须,直径为0.1～0.2 μ.m,而在稀土相ErS...     

SnAgCuLa钎料合金表面Sn晶须的生长研究

在钎料中添加微量稀土可以显著改善钎料合金的综合性能。但添加过量的稀土时,将会出现Sn晶须的快速生长。研究发现,如果将Sn3.8Ag0.7Cu1.0La钎料内部的稀土相暴露于空气中,稀土相将发生氧化而产生体积膨胀,钎料基体对体积膨胀的抑制作用将使稀土相内部产生巨大的压应力从而加速Sn晶须的生长。晶须直径约1μm,长度可达300μm。     

Statistical analysis of tin whisker growth

As the result of the global movement to lead-free electronics, companies which assemble semiconductor devices are switching from finishes incorporating lead to pure tin or high tin lead-free alloys. This transition has resulted in a reliability issue, concerning the formation of conductive tin whiskers which can grow across leads of a package and cause current leakage or short circuits. This paper presents the results of an experimental tin whisker growth study of bright tin on brass substrates. A probabilistic model is applied to describe the phenomenon of whisker growth in terms of whisker density, length and growth rate.     

The effect of tin grain structure on whisker growth

Tin whisker growth has become a major concern in the electronics industry as banning Lead application. In order to further understanding whisker growth with varied grain structures, three different grain structures (columnar, semi-columnar, and horizontal) and three mixed type deposits were prepared by changing the deposition conditions. The grain structure of deposited layer and intermetallics (IMC) were examined by focused ion beam (FIB) and chemical etching. After 4000 h of testing in 55 °C with 85% RH, whisker growth on the columnar sample was easily observed, and caused by the wedge type IMC. The semi-columnar tin grains formed small amounts of long straight whiskers accompanied with hillocks, and also seeing uneven IMC. The horizontal type tin grains formed only hillocks, accordingly finding the IMC more uniform than the others. Mixed grain structures were prepared, and consisted of different structures on the top and bottom layers. The top layer dominates the forms of whiskers or hillocks, owing to the grain boundary guiding the diffusion of tin atoms, and the bottom layer affects the density of whiskers or hillocks due to local stress building up from the formation of intermetallic phase.     

Suppression of tin whisker formation on fine pitch connectors by surface roughening

In the electronics industry, lead-free solder processes such as the terminal plating of electronic components, fine pitch connectors, and flexible printed circuits (FPCs) are invariably hampered by the serious problem of tin whisker formation. Here, a new and simple method, the JVC Micro Island (JMI) process, is proposed for the prevention of tin whisker formation in fine pitch connectors. Briefly, the base copper terminal was acid etched to afford a roughened surface, which was then tin plated. The contact test with Knoop indentation proved the effectiveness of the present process. The maximum length of the as-formed tin whiskers was less than 50 μm. The solderability of the JMI FPCs was not influenced by the present process. Thus, the new JMI process is shown to have a great advantage for the prevention of tin whisker formation in fine pitch connectors.     

Effects of continuously applied stress on tin whisker growth

A simple four-point bending technique in conjunction with scanning electron microscopy (SEM) was employed to investigate the relationship between continuously applied mechanical stress and tin whisker growth on bright tin-plated copper specimens at room temperature. Measurements of whisker length and density were periodically taken for each specimen during a 7-month exposure to applied stress. Tin whiskers were found on the tin-plated specimens with or without the presence of mechanically applied stresses. A continuously applied compressive stress resulted in formation of longer and more dense tin whiskers, in comparison with the cases of no applied stress and applied tensile stress. However, an increase in the applied compressive stress level caused an increase in the whisker density but a decrease in the whisker length. On the other hand, a continuously applied tensile stress was found to reduce both the whisker density and length, compared to the case of no applied stress. Apparently, application of a continuous tensile stress could provide an effective means in retarding tin whisker growth.     

Automatic characterisation method for statistical evaluation of tin whisker growth

In this paper, an automatic method was developed to characterise whisker growth quantitatively in SEM images. The key step of the automatic methods in this case is the determination of the optimal threshold value for image segmentation, i.e. separation of the objects (whiskers) from the background (substrate). A thresholding method was developed for this purpose and was compared to manual and to general purpose automatic methods as references. As it was proven in previous studies the vacuum deposited tin layers on copper substrates can produce numerous tin whiskers in various shapes and lengths in a short time. This layer deposition technology was therefore chosen for the comparison of the thresholding methods. Images of the produced whiskers were captured by a FEI Inspect S50 Scanning Electron Microscope. By executing the automatic methods in the captured images, the area density of the whiskers, and the maximum and the mean length of the whiskers were measured. Based on the results of area density, the automatic methods were compared to manual counting and the Mean Absolute Percentage Error (MAPE) was determined. Finally, the reference automatic methods were compared to the self-developed method from the maximum and mean length of whiskers point of view.     

Whisker growth on surface treatment in the pure tin plating

Whisker behavior at various surface treatment conditions of pure Sn plating are presented. The temperature cycling test for 600 cycles and the ambient storage for 1 year was performed, respectively. From the temperature cycling test, bent-shaped whiskers were observed on matte and semibright Sn plating, and flower-shaped whisker on bright Sn plating. The bright Sn plating has smaller whiskers than the other types of Sn plating, and the whisker growth density per unit area is also lower than the others. After 1 year under ambient storage, nodule growth of FeNi42 lead frame (LF) was observed in some parts. The Cu LF showed about a 9.0 μm hillock-shaped whisker. This result demonstrated that the main determinant of whisker growth was the number of temperature cycling (TC) in the FeNi42 LF, whereas it was the time and temperature in the Cu LF. Also, whisker growth and shape varied with the type of surface treatment and grain size of plating.     

Indium and tin oxide nanowires by vapor-liquid-solid growth technique

Regular three-dimensional (3-D) arrays of crystalline SnO₂-In₂O₃ nanowires were produced on m-sapphire using a gold catalyst-assisted vapor-liquid-solid growth process. The growth characteristics at multiple growth conditions were analyzed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), x-ray photoemission spectroscopy (XPS), and Rutherford backscattering spectroscopy (RBS) to evaluate the functional dependence of nanowire structure and composition on growth parameters such as temperature and source composition. The results indicate that nanowires of mixed composition are not possible from the catalytic clusters; rather, a mixture of indium and tin oxide wires are formed in the range of conditions investigated here.     

高能球磨法制备纳米氧化锡粉体工艺研究

通过调整高能球磨工艺参数,于不同工艺条件下制备了氧化锡粉体,分别测试了对应粉体的比表面积,并利用扫描电镜观察粉体的微观形貌。结果显示:对于80 mL的球磨罐体,球料质量比为20∶1,填充率为40%,直径分别为8,6,4 mm的钢球质量比为1∶5∶3时,制得氧化锡粉体比表面积最大,为28.415 2 m2·g–1;且颗粒分布均匀,粒径为50~100 nm。     

稀土相表面Sn晶须生长的研究

研究了Sn-3.8Ag-0.7Cu-RE(RE为Ce、Er或Y)焊料在空气中室温与高温时效过程中稀土相CeSn3、ErSn3与YSn3表面Sn晶须的生长情况。结果表明,Sn晶须的开始生长时间、形态及数量与稀土相的种类及时效条件有密切关系。稀土相因氧化产生的体积膨胀提供了Sn晶须生长的驱动力。稀土与氧的化学亲和力参数及时效温度共同影响稀土相表面Sn晶须的生长。室温实效条件下,三种稀土相表面Sn晶须的直径为0.1~2.0μm,长度可达几百微米;150℃时效条件下,Sn晶须的直径为0.1~0.2μm,长度也可达上百微米。     

The impact of electrical current, mechanical bending, and thermal annealing on tin whisker growth

This paper presents the results of an eight-month design-of-experiment assessment of whisker growth on bright and matte tin-plated copper, mechanically deformed and unformed coupons, subject to a continuous 50 °C/50%RH environment, with and without the presence of a constant electrical current density magnitude of 0.48 × 10² A/cm². Whiskers were observed to grow both at the anode and cathode end. The distribution-based data showed a reduction in whisker density due to annealing and/or the application of electrical current for both bright and matte tin. However, the application of electrical current was observed to increase the standard deviation of the length distribution, and to generate longer whiskers.     

Rapid method for testing efficacy of nano-engineered coatings for mitigating tin whisker growth

The risk of failure of electronic components due to tin (Sn) whiskers growth has become an issue with the current regulations limiting the use of lead in Sn solders. New strategies using engineered coatings for mitigating Sn whiskers are being developed. Typically, these coatings are evaluated by an aging process where whiskers are allowed to grow naturally. Unfortunately, this process can produce unreliable growth results and can take several years. Thus, faster, more reliable methods are needed. In this study, a simple, rapid (3–10 days), and cost-effective method was developed for testing the efficacy of nano-engineered coatings for mitigating the growth of Sn whiskers. This method consisted of a micro-indentation process using a ball-bearing adhered to a few hundred gram weight, which are placed in a stabilizing printed holder. For uncoated samples, Sn whiskers and hillocks were abundant near the indentation area, while only hillocks were found further outside the area (i.e., >0.2 mm). For samples coated with nano-engineered ceramic or polymeric coatings, the indentation method was observed to damage coatings only at the point of contact (e.g., no delamination), while still allowing Sn whiskers and hillocks to grow outside the indentation area.     

The effect of electroplating parameters and substrate material on tin whisker formation

Electroplated tin finishes are widely used in the electronics industry due to their excellent solderability, electrical conductivity and corrosion resistance. However, the spontaneous growth of tin whiskers during service can result in localised electrical shorting or other harmful effects. Until recently, the growth of tin whiskers was successfully mitigated by alloying the tin with lead. However, restriction in the use of lead in electronics as a result of EU legislation (RoHS) has led to renewed interest in finding a successful alternative mitigation strategy.Whisker formation has been investigated for a bright tin electrodeposit to determine whether whisker growth can, at least partially, be mitigated by control of electroplating parameters such as deposition current density and deposit thickness. The influence of substrate material and storage at 55 °C/85% humidity on whisker growth have also been investigated.Whisker growth studies indicate that deposition parameters have a significant effect on both whisker density and whisker morphology. As deposition current density is increased there is a reduction in whisker density and a transition towards the formation of large eruptions rather than potentially more harmful filament whiskers. Increasing the tin coating thickness also results in a reduction in whisker density. Results demonstrate that whisker growth is most prolific from tin deposits on brass, whilst that from tin deposits on rolled silver is greater than that observed for tin deposits on copper.     

The configurable-biomolecular nano pattern controlled by surface potential

Biomolecular patterning on surfaces plays a critical role in the field of biochip developments. Therefore, we designed and fabricated a device to realize the programmable biomolecular patterning technique driven by electrical surface potentials. In this work, the electrical surface potential was used to control the hydrophobicity of surfaces. Utilizing hydrophobicity interactions, the adhesion affinity between biomolecules and chip surfaces can be modulated by the applied electrical field. By activating the electrical potential of specific electrodes, biomolecules can attach to specific regions as designed or programmed. Based on this technique, in addition, we demonstrated the 250 nm width bovine serum albumin (BSA) pattern with a 5-min operation. This work shows the potential for various biomolecular applications and research fields.     

Contact resistance between pentacene and indium–tin oxide (ITO) electrode with surface treatment

Contact resistance between indium–tin oxide (ITO) electrode and pentacene was studied by transmission line method (TLM). Organic solvent cleaned, inorganic alkali cleaned, and self-assembled monolayer (with OTS: octadecyltrichlorosilane) modified ITO electrode structures were compared. Pentacene layer of 300 Å thickness was vacuum deposited on patterned ITO layer at 70 °C with a deposition rate of 0.3 Å/s. Alkali cleaned and SAM modified ITO gave a lower contact resistance of about 6.34 × 10⁴ Ω cm² and 1.88 × 10³ Ω cm², respectively than organic solvent cleaned ITO of about 6.58 × 10⁵ Ω cm². Especially with the SAM treatment, the work function of ITO increased closer to the highest occupied molecular orbital (HOMO) level of pentacene, which lowers the injection barrier between ITO and pentacene. It was also believed that pentacene morphology was improved on SAM modified ITO surface due to the lowering of the surface energy. We could obtain the low contact resistance with SAM treatment which is comparable to the measured value of gold–pentacene contact, 1.86 × 10³ Ω cm². This specific contact resistance is still much higher than that of amorphous silicon thin film transistor (0.1–30 Ω cm²).     

纳米级颗粒系对激光的多次散射特性

激光在具有一定浓度的离散随机介质中传输时,将会经历多次散射.为了研究纳米级颗粒系对激光的多次散射特性,建立了一种考虑颗粒多次散射的累加模型.利用此模型研究了纳米级颗粒系对激光的多次散射特性,得到了反射和透射光强随着散射角以及光学厚度的变化关系.粒子的单次散射相函数采用瑞利相函数,并与根据Mie计算的相函数进行了比较.结...     

时效温度下钎料的稀土相CeSn3表面Sn晶须生长

于Sn3.8Ag0.7Cu钎料中添加过量的稀土Ce会在其内部形成大尺寸的稀土相CeSn3,将稀土相CeSn3暴露于空气中,研究在时效处理过程中时效温度对其表面Sn晶须生长的影响规律.结果表明:时效温度对稀土相CeSn3表面Sn晶须的生长产生显著影响.室温时效20 min后,其表面会形成少量的白色Sn颗粒:75℃时效20...     

Investigation of relation between intermetallic and tin whisker growths under ambient condition

The relation between the whisker growth and intermetallic on various lead-free finish materials that have been stored at ambient condition for 2 yrs (6.3 × 10⁷ s) is investigated. The matte Sn plated leadframe (LF) had the needle-shaped whisker and the nodule-shaped whisker was observed on the semi-bright Sn plated LF. Both the Sn plated LFs had a same columnar grain structure and both whiskers were grown in connection with the scalloped intermetallic compound (IMC) layer. The morphology of the IMC layer is similar, regardless of the area which has whisker or not. On the Sn–Bi finish and bright Sn plated LF, hillock-shaped and sparsely grown branch-shaped whiskers were observed, respectively. The IMC grew irregularly under both the areas with or without whisker. The IMC growth along the Sn grain boundaries generated inner compressive stress at the plating layer. Atomic force microscopy (AFM) profiling analysis is useful for characterization the IMC growth on the Sn and Cu interface. The measured root mean square (RMS) values IMC roughness on semi-bright Sn, matte Sn, and bright Sn plated LF were 1.82 μm, 1.46 μm, and 0.63 μm, respectively. However, there is no direct relation between whisker growth and the RMS value. Two layers of η′-Cu₆Sn₅ were observed using field emission transmission electron microscopy (FE-TEM): fine grains and coarse grains existed over the fine grains.     

焦耳热效应引发的晶须生长机理研究

研究了Cu/Sn3.8Ag0.7Cu/Cu一维焊点在电流密度为5×103 A/cm2、环境温度为100℃作用下晶须的生长机理。研究结果表明,通电300 h后,在Cu/Sn3.8Ag0.7Cu/Cu焊点的阳极界面出现了一些小丘,而在焊点的阴极出现了一些裂纹;通电500 h后,焊点阴极界面的裂纹进一步扩展,而且在裂纹处发现了大量纤维状Sn晶须,其长度超过10μm;继续通电达到700 h后,Sn晶须的数量没有增加,同时停止生长。由于电迁移的作用,金属原子在电子风力的作用下由焊点的阴极向阳极进行了扩散迁移,进而在阴极处形成裂纹。随着裂纹逐渐扩展,导致该区域处的电流密度急剧增大,焦耳热聚集效应明显,为了释放应力,形成了纤维状的晶须。