Ultrarapid formation of homogeneous Cu6Sn5 and Cu3Sn intermetallic compound joints at room temperature using ultrasonic waves

Homogeneous intermetallic compound joints are demanded by the semiconductor industry because of their high melting point. In the present work, ultrasonic vibration was applied to Cu/Sn foil/Cu interconnection system at room temperature to form homogeneous Cu₆Sn₅ and Cu₃Sn joints. Compared with other studies based on transient-liquid-phase soldering, the processing time of our method was dramatically reduced from several hours to several seconds. This ultrarapid intermetallic phase formation process resulted from accelerated interdiffusion kinetics, which can be attributed to the sonochemical effects of acoustic cavitation at the interface between the liquid Sn and the solid Cu during the ultrasonic bonding process.     

The effect of ultrasonic waves on the nucleation of pure water and degassed water

In order to clarify the mechanism of nucleation of ice induced by ultrasound, ultrasonic waves have been applied to supercooled pure water and degassed water, respectively. For each experiment, water sample is cooled at a constant cooling rate of 0.15 °C/min and the ultrasonic waves are applied from the water temperature of 0 °C until the water in a sample vessel nucleates. This nucleation temperature is measured. The use of ultrasound increased the nucleation temperature of both degassed water and pure water. However, the undercooling temperature for pure water to nucleate is less than that of degassed water. It is concluded that cavitation and fluctuations of density, energy and temperature induced by ultrasound are factors that affect the nucleation of water. Cavitation is a major factor for sonocrystallisation of ice.     

New insights into the mechanisms of ultrasonic emulsification in the oil–water system and the role of gas bubbles

Ultrasonic emulsification (USE) assisted by cavitation is an effective method to produce emulsion droplets. However, the role of gas bubbles in the USE process still remains unclear. Hence, in the present paper, high-speed camera observations of bubble evolution and emulsion droplets formation in oil and water were used to capture in real-time the emulsification process, while experiments with different gas concentrations were carried out to investigate the effect of gas bubbles on droplet size. The results show that at the interface of oil and water, gas bubbles with a radius larger than the resonance radius collapse and sink into the water phase, inducing (oil–water) blended liquid jets across bubbles to generate oil-in-water-in-oil (O/W/O) and water-in-oil (W/O) droplets in the oil phase and oil-in-water (O/W) droplets in the water phase, respectively. Gas bubbles with a radius smaller than the resonance radius at the interface always move towards the oil phase, accompanied with the generation of water droplets in the oil phase. In the oil phase, gas bubbles, which can attract bubbles nearby the interface, migrate to the interface of oil and water due to acoustic streaming, and generate numerous droplets. As for the gas bubbles in the water phase, those can break neighboring droplets into numerous finer ones during bubble oscillation. With the increase in gas content, more bubbles undergo chaotic oscillation, leading to smaller and more stable emulsion droplets, which explains the beneficial role of gas bubbles in USE. Violently oscillating microbubbles are, therefore, found to be the governing cavitation regime for emulsification process. These results provide new insights to the mechanisms of gas bubbles in oil–water emulsions, which may be useful towards the optimization of USE process in industry.     

Cavitation intensity of water under practical ultrasonic cleaning conditions

When measuring cavitation during cooling of thermally degassed water cavitation maxima are frequently observed at various temperatures. Relations between this phenomenon and frequency and power of ultrasounds as well as air content in water have been examined. It was found out that the secondary water regassing with air is the reason.     

Chemical activation of ultrasonic cavitation

A method for intensifying ultrasonic cavitation in water and aqueous solutions has been proposed, which consists of a chemical fixation of dissolved oxygen. The influence of selected reducing agents on the intensity of cavitation in water and alkaline solutions has been investigated.     

An investigation of generalized lamb waves using ultrasonic reflectivity measurements

Ultrasonic critical angle reflectivity method is used to measure the phase velocity of generalized Lamb waves in cadmium and zinc platings. In addition to the free propagating modes, leaky-wave modes are also observed. Leaky waves are considered using principles familiar from the discussion of surface waves in anisotropic media and a relatively good agreement is obtained between the theoretical computations and measured data.     

液体薄层中的超声空化*

液体薄层中的超声空化,因其边界及所处空间的特殊性,而呈现出非常独特的空化结构和演化行为,在超声清洗、超声钎焊、表面处理、近场声悬浮、超声化学等领域都有所应用。该文梳理了近几年该课题组在液体薄层中的超声空化研究中的一些成果,力图揭示液体薄层内空泡、空化云、空化场的运动和分布规律,及其产生、发展和演化过程,以期对液体薄层中的超声空化行为有一个相对清晰和完整的认识。     

超声滚压中的空化现象*

在超声滚压加工中引入切削液后可能会产生空化现象,由此产生的微射流和冲击波对超声表面强化将有积极作用。为研究超声滚压加工中空化现象是否存在及空化效应在超声滚压中的作用,本文首先分析了超声滚压中的空化阈值,然后进行了染色法试验和超声滚压后试样氧元素能谱分析,最后通过超声滚压加工对比试验研究了空化效应对加工后材料表面粗糙度和显微硬度的影响。研究发现,超声滚压加工中的声压幅值远大于空化阈值,满足空化存在的必要条件;超声滚压中发生了明显的卡纸染色现象,引入切削液后工件超声滚压加工表面氧元素含量显著提高,表明超声滚压中发生了空化现象。超声滚压加工中的空化效应能进一步降低工件表面粗糙度和提高表面显微硬度,有利于提高工件表面强化质量。本研究为空化效应在超声滚压中的积极利用提供了依据。     

Cavitation dose in an ultrasonic cleaner and its dependence on experimental parameters

The aluminum foil erosion method is widely used in cavitation activity studies of ultrasonic cleaners. However, owing to its limited sensitivity, it is difficult to observe the effects of various experimental parameters on the cavitation activity using this method. In the present work, a higher-sensitivity method for quantifying cavitation activity as a cavitation dose based on passive cavitation detection was presented. The influences of various factors (e.g., insonation duration, driving power, gas content, temperature and cleaning agents) were studied for this system. The results showed that the cavitation dose became unstable over long insonation times, and that the instability was more significant at high power. Generally, the cavitation activity could be enhanced by increasing the power, gas content, and the concentration of a cleaning agent. However, due to the exhaustion of the cavitation gas nuclei, the cavitation activity might tune to saturate of even decrease slightly when some impact parameters (e.g., acoustic driving power, gas content and the concentration of the cleaning agent) are above a certain level of each of these parameters.     

空化泡液体外围压强的分布

本文从空化泡动力学理论出发,分别讨论了空化泡在压缩和膨胀时液体中的压强分布情况,并作了数值模拟。研究结果表明,空化泡在膨胀和压缩时其外围压强分布明显不同,不能将其一并而论。发现当空化泡的半径增大时液体的压强在不断变化,压强是先变小后变大。而且这个压强的变化还与待测点距空化泡的距离有关。当空化泡的半径在不断变小时外界的压强在不断增大,当空化泡刚开始压缩时液体中的压强变化情况不是很明显,但当空化泡的半径变到1μm时,空化泡外界压强出现明显变化。当空化泡压缩到较小时,此时再增加外界压强空化泡的半径也不会在有很大的变化。     

The structures and evolution of Smoker in an ultrasonic field

The structures and evolution of Smoker in a 20 kHz ultrasonic field were investigated experimentally with high-speed photography. The spine-plume structure of Smoker was discovered. A few large bubbles align themselves along the central line and form the spine of Smoker. Numerous small bubbles move towards the spine and form the plume structures. The size of large bubbles differs almost by an order of magnitude from that of small bubbles. The evolution of cavitation structure from Flare to Smoker was found. When a Flare appears near a Smoker, the Flare may merge into the plume structures of the Smoker, or form a double-tipped Smoker. A double-tipped Smoker seldom splits into two Smokers, while two separate Smokers tend to merge as one. The large bubbles (or dense plume structures) in the middle part of the two separate Smokers attract each other, driving the two Smokers to bend towards each other and merge.     

Measurement of viscosity of highly viscous non-Newtonian fluids by means of ultrasonic guided waves

In order to perform monitoring of the polymerisation process, it is necessary to measure viscosity. However, in the case of non-Newtonian highly viscous fluids, viscosity starts to be dependent on the vibration or rotation frequency of the sensing element. Also, the sensing element must possess a sufficient mechanical strength. Some of these problems may be solved applying ultrasonic measurement methods, however until now most of the known investigations were devoted to measurements of relatively low viscosities (up to a few Pa s) of Newtonian liquids.