Untersuchungen zu den Mechanismen des Ultraschall-Drahtbondens

Ultrasonic (US) wire bonding is a predominating interconnection technique in the microelectronic packaging industry. Despite its long-term usage and wide applications, the mechanisms, especially those of the friction and softening phases, are still unclear more than half a century after its invention. Targeting on reducing the big gap to a good understanding of the mechanisms, this dissertation focuses on the relative motions at the wire/substrate and wire/tool interfaces, and the oxide removal process. In addition, an energy flow model from the electrical input energy to the different energies involved in the mechanisms is developed and quantified. The relative motions at the two interfaces were investigated by a real-time observation system with which the micrometer-motions of the tool and the wire were captured. The motions were then tracked and quantified. In addition, the influences of the process parameters including the normal force, US power and process time were analyzed and the combined effect of the normal force and US power was emphasized. By a further investigation on the changes of the surface topography and elements distribution, it was proved that the relative displacement amplitudes at different locations of the wire/tool interface differ. With the substitution of the metal substrate by a transparent glass, the bonding process was visualized and different areas including the contact, friction, stick, microwelds and oxides areas were detected. The oxide removal process was studied with artificial coatings on either the wire or the substrate. A complete removal process including cracks, detachment, milling and transportation was studied. The transportation further includes penetration, oxide flow, pushing and metal splash. The quantification of energy flows shows that most US energy flows to the vibration induced friction at the two interfaces and the vibration induced formation, deformation and breakage of microwelds. Based on the energy flow to the wire/substrate interface and to the formation of microwelds, the optimal combination of the normal force and the ultrasonic power is determined

Characterizing and Optimizing the Molten Salt Cleaning

Molten salt cleaning is an important cleaning approach in remanufacturing which can remove a variety of contaminants from metal substrates with high efficiency. Facing the very limited research of this approach in literature, this thesis intends to characterize molten salt cleaning process and optimize its parameters when big parts with complicated shapes are cleaned. Based on the development of molten salt cleaning and studies on contaminations, two experiments are conducted. The first one investigates the influences of the hot salts on three metal substrates and shows the applicable of cleaning carbon steel and grey iron parts with molten salt. The other one which applies a central composite design demonstrates that the cleaning efficiency tends to be better with the increase of temperature and decrease of quantities of sodium nitrate. Furthermore, digital models are established and recommendations are given based on the analysis of the results

Analysis of the Interactive Strategy of Microblog for Snack Food Enterprises

With the development of economic conditions and consumption patterns, snack foods have become the first choice in people\u27s daily diet and consumption, while the market scale is rising, snack foods have also gained high public opinion attention. The existing research results show that the micro-blog interaction effect will positively affect the sales performance, but there are few characterization studies on the effective micro-blog interaction strategy of the snack food enterprises. In this paper, the typical snack food enterprises as an example, mainly through the network crawler to collect micro-blog interactive contents, text analysis, and finally through ANOVA analysis to study the effect of different interaction strategies. The research finds that the strategy of micro-blog interaction of snack food enterprises is better. The characteristic research results of this paper possibly provide reference and enlightenment for the future research of micro-blog interaction strategy of snack food enterprises

Study on the Reasonable Smoke Exhaust Rate of the Crossrange Exhaust Duct in Double-layer Shield Tunnel

AbstractThe research on the concentrated smoke extraction system of crossrange exhaust duct in double-layer shield tunnel is still very lack in the world. This paper is on the smoke extraction system of double-layer shield tunnel. It will provide the supports and references for the smoke control of tunnel fire and the determination of related technical parameters in the design of tunnel fire ventilation and smoke extraction, so it has important scientific value, practical significance and application prospects. This paper bases on the tunnel project of Slender West Lake in Yangzhou. By using the method of combining theory and numerical simulation, a conclusion can be drawn that the reasonable smoke exhaust rate of the upper tunnel is 140 m3/s

Impact of surface texture on ultrasonic wire bonding process

Due to the complex mechanisms, the ultrasonic (US) wire bonding process is usually optimized in the way of varying the processing parameters including normal force, US power, and processing time. In this study, a new way by creating different surface textures on substrates was used to alter the bonding process and improvements of the bonding process were detected. Three different surface textures including deposited strips, straight ditches at different angles, and elliptic ditches were designed and created on glass substrates. The results showed that the elliptic ditches hardly influence the bonding process while the deposited strips and straight ditches significantly alter the bonding process. The deposited strips help break the oxide scale and facilitate the transportation of oxides to the outside of contact. With the straight ditches, the oxide removal efficiency was significantly enhanced. Especially when the driving current exceeded 0.45 A, long chips from the ditches were clearly observed during the bonding process. The chips were aluminum and aluminum oxide which were continuously cut from the wire, accumulated in the ditches, pressed and squeezed to the outside of the contact. With a different angle of the straight ditches, the shape of the bonding footprint can be changed correspondingly. Compared to the bonding on smooth surfaces, the bonding strength on substrates with deposited strips and straight ditches was a few times higher and had a smaller deviation. The bonding process window was significantly enlarged

Investigations on the mechanism of microweld changes during ultrasonic wire bonding by molecular dynamics simulation

Despite the wide and long-term applications of ultrasonic (US) wire bonding and other US metal joining technologies, the mechanism of microweld changes during the bonding process, including formation, deformation and breakage, is rarely known as it is very difficult to be investigated by experiments. In this work, this mechanism under different surface topographies and displacement patterns is studied by molecular dynamics simulation. It is found that microwelds can be formed or broken instantly. Due to the relative motion between the local wire part and the local substrate part, microwelds can be largely deformed or even broken. The impacts of material, surface topography, approaching distance and vibration amplitude on the microweld changes are investigated via the quantification of the shear stress and the equivalent bonded area. It is shown that these four factors significantly influence the final connection and the interface structure. The analysis of the scale influence on the microweld changes shows that the simulation results at a small-scale are able to represent those at a large-scale which is close to the range of the commonly used surface roughness. This deeper understanding on the microweld changes leads to a better control strategy and an enhancement of the bonding process

Cooling and Crack Suppression of Bone Material Drilling Based on Microtextured Bit Modeled on Dung Beetle

In recent years, the number of patients with orthopedic diseases such as cervical spondylosis has increased, resulting in an increase in the demand for orthopedic surgery. However, thermal necrosis and bone cracks caused by surgery severely restrict the development and progression of orthopedic surgery. For the material of cutting tool processing bone in bone surgery of drilling high temperature lead to cell death, easy to produce the problem such as crack cause secondary damage effects to restore, in this paper, a bionic drill was designed based on the micro-structure of the dung beetle’s head and back. The microstructure configuration parameters were optimized by numerical analysis, and making use of the optical fiber laser marking machine preparation of bionic bit; through drilling test, the mathematical model of drilling temperature and crack generation based on micro-structure characteristic parameters was established by infrared thermal imaging technology and acoustic emission signal technology, and the cooling mechanism and crack suppression strategy were studied. The experimental results show that when the speed is 60 m/min, the cooling effects of the bionic bit T1 and T2 are 15.31% and 19.78%, respectively, and both kinds of bits show obvious crack suppression effect. The research in this paper provides a new idea for precision and efficient machining of bone materials, and the research results will help to improve the design and manufacturing technology and theoretical research level in the field of bone drilling tools