Wire Span Research Articles

Effect of liquid bridge on the thickness deviation between wafers sawn by diamond wire

Diamond wire web will be rearranged due to the reduction of structural stiffness and the enhancement of capillary force in the system for sawing ultra-thin wafers with fine-diameter diamond wire, which can cause uneven thickness between the as-cut wafers and affect the subsequent processing. A model for analyzing the transverse sawing behavior of the diamond wire caused by the liquid bridge after sawing into a workpiece was developed in this study by extending the dynamical model for a double-wire system with liquid bridge action to a multi-wire system. The stable transverse sawing state of the wire was obtained by analyzing the variation of the transverse sawing force with the as-cut wafer thickness thinning. Accordingly, the wafers thickness deviation rate affected by the wire groove wear and the liquid bridge action was calculated. The effects of the wire groove wear, the initial wire web gap, and the wire length between the guide wheel and the workpiece on the thickness deviation between the wafers sawn by the diamond wire were explored. The results show that the wafers thickness deviation increases with the increased wear of the wire grooves when the initial wire web gap is smaller than the minimum gap at which spontaneous wires adhesion can occur. The increase of wire groove wear makes the double-wire sawing more likely to occur. In addition, the wafers thickness deviation increases with decreases in the initial wire web gap and increases in the wire length between the guide wheel and the workpiece. Reducing the ratio of the initial wire span to the workpiece width helps to suppress the liquid bridge action during slicing and avoid the double-wire sawing. Since the minimum gap at which spontaneous wires adhesion can occur is large for the thick-diameter diamond wire, the fine-diameter diamond wire can be a better option for sawing the ultra-thin wafer to avoid the effect of liquid bridge on the wafers thickness deviation to the greatest extent.

Effect of the diamond saw wires capillary adhesion on the thickness variation of ultra-thin photovoltaic silicon wafers during slicing

In order to improve the performance of solar cells and reduce their manufacturing costs, monocrystalline silicon wafers used for manufacturing solar cells are developing towards larger sizes and ultra-thin thickness, and the diameter of diamond saw wires used to cut silicon wafers is also continuously decreasing. These aspects cause uneven thickness and lager thickness variation (TV) of the as-cut wafer during slicing process. The reason of uneven thickness was analyzed from the point of liquid bridge with capillary force between the saw wires in this paper. The mechanical equilibrium equation between the liquid bridge and the saw wires was established based on the Young-Laplace equation, and the theoretical model of the as-cut wafer thickness was derived during the sawing process. The effect of the saw wire tensioning force, span, the diameter of the core wire and the wetting angle of coolant on the as-cut wafer thickness variation was analyzed based on the model. The results show that the increase in the saw wire tensioning force, the core wire diameter and the wetting angle of coolant improved the thickness accuracy and reduced the thickness variation of the as-cut wafer. And the increase in the saw wire span reduced the thickness accuracy and increased the thickness variation. The research results of this paper provide the mechanism analysis for the thickness variation of the ultra-thin wafer during the slicing process. It is of great significance to produce the ultra-thin photovoltaic silicon wafers with the fine saw wire in the future.

Effect of a liquid bridge on the dynamic behavior of diamond wires during slicing

Diamond wire sawing with narrower kerf losses and thinner as-cut wafers is a critical technology to further reduce wafering costs in the semiconductor industry. Nevertheless, as the scale of the wire web decreases, the effect of the liquid bridge formed by the capillary condensation of the cutting fluid between the diamond wires becomes significant. Moreover, the transverse wire vibration reduces the wire web gap at certain moments, which makes it easier for the wires to adhere to each other after wetting, thus hindering the slicing process. Therefore, a dynamical model for a double-wire system with liquid bridge action was developed in this study based on the transverse vibration theory of a diamond wire under support excitations to reveal the action mechanism of the liquid bridge between diamond wires. The dynamic adhesion process between the diamond wires moving with the supports is discussed. The effects of the guide wheel manufacturing error and the sawing parameters on the critical gap for spontaneous adhesion between the diamond wires are analyzed. The results show that the static double-wire system does not generate spontaneous adhesion when the surface gap of the wires is between the critical gap for spontaneous adhesion and the maximum adhesion gap. The support excitation causes the transverse wire displacement, which increases the critical gap for spontaneous adhesion to increase the risk of wires adhesion. The critical gap for spontaneous adhesion increases with increases in the guide wheel manufacturing error and the wire span as well as the wire speed and decreases with increases in the wire groove diameter and the wire tension. When the manufacturing error is doubled, the critical gap for spontaneous adhesion will increase more than twice this error increment. Strict control of the guide wheel manufacturing error is the most effective way of reducing the risk of wires adhesion during processing. Increases in the guide wheel diameter and decreases in the wire span and the wire speed within a reasonable range, or enhancing the mechanical properties of the wire to improve its breaking force, also help to reduce the critical gap for spontaneous adhesion.

Transverse forced vibration of a diamond wire under support excitations

Diamond wire sawing is a key technology for wafer processing in the semiconductor industry. Transverse wire vibration decreases the wire web gap to below the critical adhesion spacing between the wires, which is an important factor that limits the development of diamond wire slicing technology toward narrower kerf losses and thinner as-cut wafers. In fact, the external excitation source that causes the diamond wire vibration comes primarily from the supports at both ends of the wire. Therefore, an analytic model for transverse forced vibration of a diamond wire under support excitations was developed in this study based on the transverse vibration theory of an axially-moving string fixed at both ends. This partial differential equation with non-homogeneous boundary conditions was solved using the superposition principle and the finite element method. To verify the theoretical model, experimental equipment to text the transverse vibration of a diamond wire with support excitations was developed. The support excitation signal and the wire vibration response were obtained using accelerometer measurements and machine vision detection, respectively. The theoretical results agree well with the experimental results, indicating the correctness of this proposed model. The effects of the vibration source and the installation parameters on the transverse vibration displacement of a diamond wire are discussed. The results show that hysteresis in the movement of the center of the wire causes a certain additional high-frequency vibration, which can make this maximum transverse displacement to be greater than the excitation amplitude, thus making the wire transverse vibration change non-linearly with some parameters. The maximum transverse vibration displacement at the center of the diamond wire increases with increases in the guide wheel machining error amplitude and the wire diameter as well as the wire span, while it decreases with increases in the wire groove diameter and the wire tension. This maximum transverse vibration displacement decreases by approximately 100.22 % and 6.17 % when the guide wheel manufacturing error amplitude and the wire groove diameter are reduced by half and doubled, respectively. Improving the manufacturing accuracy of the guide wheel is still the most effective way of reducing the transverse vibration displacement of the wire. In addition, appropriate increases in the groove diameter and the wire tension and decreases in the wire span are also beneficial for suppressing the wire vibration.

Examination of Machining Parameters and Prediction of Cutting Velocity and Surface Roughness Using RSM and ANN Using WEDM of Altemp HX

The Altemp HX is a nickel-based superalloy having many applications in chemical, nuclear, aerospace, and marine industries. Machining such superalloys is challenging as it may cause both tool and surface damage. WEDM, a non-contact machining technique, can be employed in the machining of such alloys. In the present study, different input parameters which include pulse on time, wire span, and servo gap voltage were investigated. The cutting velocity, surface roughness, recast layer, and microhardness variations were examined on the WEDMed surface. The genetic algorithm was used to optimize the cutting velocity and surface roughness, thereby improving the overall quality of the product. The highest recast layer values were recorded as 25.8 µm, and the lowest microhardness was 170 HV. Response surface methodology and artificial neural network were employed for the prediction of cutting velocity and surface roughness. Artificial neural network prediction technique was the most efficient method for the prediction of response parameters as it predicted an error percentage lesser than 6%.

Action mechanism of liquid bridge between electroplated diamond wires for ultrathin wafer slicing

Ultrathin wafer slicing with low kerf loss for electroplated diamond wire sawing is the primary means to improve the productivity in wafering and reduce the manufacturing costs in the photovoltaic industry. Nevertheless, the reduction of the diameter and spacing of the diamond wires makes the liquid bridge action between them significant, which will affect the slicing process. Therefore, based on the principle of minimum potential energy, an analytic model of adhesion caused by the liquid bridge between the diamond wires with protruding abrasives is established in this paper. The variation of the adhesion length with initial wire web gap, wire span, and wire tension as well as wire diameter is analyzed. The results show that the adhesion length was increased with the increase of the wire diameter. The reduction of the initial wire web gap would increase the adhesion length, that was, the limitation of the liquid bridge on the thinner wafers sawing was more obvious. The adhesion length was decreased with the decrease of the wire span or the increase of the wire tension. So it is effective to weaken the limitation of the liquid bridge on the wafers slicing by reducing the wire span or enhancing the wire strength. Then, an experiment on the action of the liquid bridge between the diamond wires was carried out. The theoretical results were in accord with the experimental ones well, and the maximum error was 8.27%. The research work is of great significance to further reduce kerf loss and wafer slicing thickness.

Implementation of Pads Re-layout for QFN Multi-row Breakthrough

An alternative design of Quad-Flat No-lead (QFN) leadframe capable with three or more arrays of lead is discussed and presented on this paper. The leadframe design is integrated with connecting bars that can be routed and bonded with wires to decrease the wire span and create a more manufacturable wirebonding structure in densified design of QFN. In addition, the connecting bars produced an inter-connection link between relocated pads and extended input/output (I/O) leads for the 3rd array electrical connections. The implementation of the proposed augmented design would improve the manufacturability of multiple arrays of I/O in QFN, enabling cost-saving initiative and manufacturing solution to devices with multiple arrays requirement.

PSO/GA Combined with Charge Simulation Method for the Electric Field Under Transmission Lines in 3D Calculation Model

The accurate calculation of electric field intensity under transmission lines is more and more important with the expansion of high voltage engineering, which largely determines the site selection and design of transmission projects. In order to get more accurate results, a methodology of a charge simulation method (CSM) combined with an intelligent optimization algorithm for a 3D calculation model is proposed in this paper. Three key points are emphasized for special mention in this optimized charge simulation method (OCSM). First, the number of sub-segments on the finite length conductor, the position and number of the simulating charge set on a sub-segment are taken as the optimization parameters for unified calculation. Secondly, the fitness function of optimization algorithm is constructed by two values, voltage relative error and electric field intensity relative error. Thirdly, a finite element method (FEM) was used to obtain the electric field intensities, which are compared with the results of the proposed algorithm. A simulation case is carried out on a 3D calculation model of 220 kV transmission lines, which verify the effectiveness of the optimization algorithm. The proposed OCSM solves the parameter optimization problem of CSM in the 3D computational model, which considers physical shape of wire span, and has the advantages of strong global search ability and higher calculation accuracy.

Rotor Walks on Transient Graphs and the Wired Spanning Forest

We study rotor walks on transient graphs with initial rotor configuration sampled from the oriented wired uniform spanning forest (OWUSF) measure. We show that the expected number of visits to any vertex by the rotor walk is at most equal to the expected number of visits by the simple random walk. In particular, this implies that this walk is transient. When these two numbers coincide, we show that the rotor configuration at the end of the process also has the law of OWUSF. Furthermore, if the graph is vertex-transitive, we show that the average number of visits by $n$ consecutive rotor walks converges to the Green's function of the simple random walk as $n$ tends to infinity. This answers a question posed by Florescu et al. (2014).

Novel Three-Dimensional Embedded FPGA Technology and Achitecture

In this paper we present a high density three-dimensional (3D) interconnect network implementation based on a modified Mesh-of-Trees (MoT) topology for an embedded FPGA architecture design targeted for high performance 3D integration. To obtain the optimal MoT-based interconnect structure, the routing architecture of the 2D MoT-based FPGA is modified to include long routing segments that span multiple switch blocks in every row and column. By adjusting the percentage of long wire and span, a 2.5D or 3D high density MoT-based embedded FPGAs can be designed. For the 3D multi-stacked MoT-based FPGAs, the 2D MoTbased FPGA is sliced into two or more equal sections by adjusting the length of the long wire span. The long wire segments are realized using 3D through silicon via (TSVs) and 2.5D interposer-based multi-FPGAs, we increase the number of cuts and apply appropriate optimization models to scale down the number of long wires and horizontal inter-FPGA interposer wires. Using our 2.5/3D CAD models, we demonstrate the speed and area of 3D MoT-based FPGA architecture improved by 54% and 41% respectively in comparison to 3D Mesh-based FPGAs.

New Methodology of On-Line Monitoring for Transmission Line Galloping

When the overhead transmission line is galloping, a variety of natural disasters occur on the role of the natural conditions, the vibration of conductor is one of the more serious harm to the power system. Over the past decade, as the construction of EHV and UHV, wire cross-section, tension, suspension height and span of overhead transmission lines are increasing, and hence the number of conductor vibration is significantly increased. Vibration in a large scale will led to frequent tripping or even broken line or tower collapses, which cause large area power failures and impact security and stability operation. Online monitoring method for overhead transmission line dancing is mostly needed to add additional equipment, however, once situated on the route environment overlying ice or high winds and other inclement weather, online monitoring is difficult to achieve. This paper presents a method, which is made correlation analysis based on the voltage and current acquired from both ends of the transmission lines, online monitoring of line galloping can be achieved.

Harmonic models and spanning forests of residually finite groups

We prove a number of identities relating the sofic entropy of a certain class of non-expansive algebraic dynamical systems, the sofic entropy of the Wired Spanning Forest and the tree entropy of Cayley graphs of residually finite groups. We also show that homoclinic points and periodic points in harmonic models are dense under general conditions.

Electrical Treeing Breakdown Properties for Polyimide Nanocomposite Film in Inverter-Fed Motors

The failure of magnet wires used in inter-turn insulation of inverter-fed motor winding is the main cause which leads to the motor insulation breakdown. This paper conducted electrical tree breakdown experiments on magnet wire insulating film (FCR 100) used in the inter-turn insulation of JD117 inverter-fed motor and meanwhile combining with energy spectrum analysis and scanning electrical microscope (SEM), by which type and content of elements, breakdown main body and electrical tree channel could be clearly observed, the corresponding failure mechanisms were analyzed. The experiment results reveal that all the breakdown main bodies are located at the pointedness and insulation joint of magnet wires, of which dielectric strength is relatively lower; they are the insulation “weak point”, which should be paid enough attention and strengthened at the manufacturing period. The electrical tree breakdown time is quite long and the life span of magnet wire is 11 hours. The electrical breakdown strength of envelope is very low when containing metal impurity. It is also found that the aluminum occupies the highest content tested by energy spectrum analysis.

Activating a 2 x 4 appliance.

When the long span of wire in a 2 x 4 orthodontic appliance enters a bracket in a nonparallel manner, it develops a couple and tendency for rotation called a moment. The moment of a couple creates inherent equal and opposite Newtonian equilibrium forces not readily sensed clinically. Moments at successive brackets, producing rotations in opposite directions, create equilibrium forces also in opposite directions which are subtractive from each other. When these equilibrium forces are equal and opposite, they cancel each other out. If the moments produce rotations in the same direction, the equilibrium forces are also in the same direction and are additive. The apparent simplicity of the 2 x 4 appliance conceals the fact that it is a powerful orthodontic tool that uses engineering mechanics in a way not possible with fully bracketed appliances. Clearly the application of engineering mechanics is a distinguishing characteristics of modern orthodontics.

Bond failure rates for V-loop vs straight wire lingual retainers

The V-loop bonded lingual retainer is an innovative design that allows the patient to floss with ease, a significant advantage over the conventional straight wire design for interproximal plaque control. The aim of this retrospective study was to compare the efficacy of straight wire and V-loop fixed retainers with respect to detachment rate when used to stabilize maxillary or mandibular anterior teeth after orthodontic treatment. Fixed, customized retainers were placed in 300 patients and followed for 6 months. The conventional retainer system was a .0175-in stainless steel multi-stranded wire placed as a straight, bonded lingual retainer. The newer system was a .016-in stainless steel black Australian wire placed in a V-loop design. The detachment rates were 14.3% for the V-loop design and 12.4% for the straight wire retainer. The difference was not statistically significant. The V-loop retainer system addresses cleanability and physiologic adaptability, both critical for the clinical success of bonded lingual retainers used for long-term retention. The interdental wire span of the V-loop design allows easier access for flossing and sufficient flexibility for independent tooth movement in the periodontal space. Patient acceptance of the V-loop bonded lingual retainer was excellent, and most patients in this study found the retainer comfortable and easy to floss.

New encapsulation development for fine pitch IC devices

The continuous reduction of chip size driven by the market demand has a significant impact on circuit design and assembly process of IC packages. Shrinking chip size and increasing I/O counts require finer bond pad pitch and bond pad size for circuitry layout. As a result, serious wire deflection during transfer molding process could make adjacent wires short, and this issue becomes more critical as a smaller wire diameter has to be applied for the finer pitch wire bonded IC devices. This paper presents a new encapsulation process development for 50 μm fine pitch plastic ball grid array package. Since reduced wire diameter decreases the bending strength of bonded wires significantly, wire deflection during molding process becomes quite serious and critical. Experiments on conventional transfer molding were conducted to evaluate wire span threshold with 23.0 μm diameter gold wire. The results show that the wire span threshold is about 4.1 mm, which is much shorter than the wire span threshold of over 5.0 mm for wire with 25.4 μm diameter. Finite element analysis shows there is a significant difference in the wire deflection between 23.0 μm gold wire and 25.4 μm gold wire diameter under the same action of mold flow. A novel encapsulation method is introduced using non-sweep solution. The wire span could be extended to over 5.0 mm with wire sweep less than 1%. Reliability tests conducted showed that all the units passed 1000 temperature cycles (−55 to 125 °C) with JEDEC moisture sensitivity level 2a (60 °C/60% relative humidity for 120 h) and 3 times reflow (peak temperature at 220–225 °C). It is believed that this solution could efficiently overcome the risk of wire short issues and improve the yield of ultra fine pitch wire bonds in high-volume production.

Computer simulation and characteristic analysis of electrode fluctuation in wire electric discharge machining

In wire electric discharge machining, the vibration of the wire electrode has a significant influence on the performance and stability of the machining process. A method of computer simulation has been adopted in this paper to study the vibration of the wire electrode under the action of successive discharges, by which the effect of wire fluctuation on the distribution of the discharge points is also analysed. The result shows that the discharge points can be distributed much more evenly along the span of the wire when an optimum condition is reached between discharge energy, discharge frequency, wire tension and wire span. Under such a condition, it is possible that the hazard of wire breaking can be avoided.

The components of the Wired Spanning Forest are recurrent

We show that a.s. all of the connected components of the Wired Spanning Forest are recurrent, proving a conjecture of Benjamini, Lyons, Peres and Schramm. Our analysis relies on a simple martingale involving the effective conductance between the endpoints of an edge in a uniform spanning tree. We believe that this martingale is of independent interest and will find further applications in the study of uniform spanning trees and forests.

A polymer sensitive to humidity and its electrical properties analysis

A humidity sensor is a device which can covert the ambient moisture variation into an electrical signal (resistance or capacitance) variation, so it can be easily installed in electronic equipment to detect or control the ambient humidity. The humidity sensors based on polymers can be classified as resistive-type and capacitivetype. Because it has a simple fabrication technique and small hysteresis, is easily decorated and does not need heat cleaning, the former type is more interesting. But for all humidity sensors based on polymers, a problem still remains that they cannot be used in high humidity or at a place where dew (condensation water) may occur. Otherwise, the sensitive film will gradually change due to a very slow irreversible reaction with water vapor in atmosphere. The investigation for the problem is focused on improving water-resistive properties of the material. The main methods to solve the problem are interpenetrated polymer network (INP), graft polymerization and modification of substrate and/or surface [1, 2]. In general, the molecular structure of polymers sensitive to moisture has either hydrophilic group or hydrophobic group. We made hydrophilic monomer graft polymerized with hydrophobic monomer and obtained copolymer. The ratio of the two monomers in the reaction is an important parameter to effect the characteristics of the humidity sensor. The humidity sensor based on the polymer is water-resistive, even when put in water atmosphere for 48 min, its characteristic has no change. We utilize the hydrophilic monomer graft polymerization reaction with hydrophobic monomer. The hydrophilic monomer is hydroxyethylate methylacrylate trimethyl ammonium chloride (Qb), the hydrophobic monomer is butyl methylacrylate (Bu). Fig. 1 gives the structures of the two monomers. From many experiments, we found the proportion of two monomers, reaction path and reaction time is important to material properties. The best result shows that Bu : Qb= 7 : 3 is a suitable ratio. The reaction path is better, when Qb is dipped into the reaction container after Bu has been heated for a period of time under 351 K (absolute temperature). The infrared spectrograph (IR) gives main absorption peaks as shown in Fig. 2. The N–C bond vibration peaks appear at 3087.48 cm−1 and 952.06 cm−1. We believe polymerization really took place because homo-copolymer of Bu and Bu itself are both dissolvable in water, and the special peaks still exist after the material obtained dissolves in water. The substrate is a ceramic plate with gold interdigital electrodes made by screen-printing. The ceramic plate scale is 10 mm× 5 mm, electrode dimension is 4 mm× 4 mm, and the wire width and span of electrode are both 0.5 mm, as shown in Fig. 3. The spin-coating technique is employed to fabricate the sensitive film. In order to improve water-resistive properties of the sensor further, another polymer (cellulose) film is coated on the surface of the sensing film. We called the film “protecting film”, which can allow water molecules to

Predicted Stresses in Wire Bonds of Plastic Packages During Transfer Molding

An analytical stress model is developed for the evaluation of flow induced stresses in wire bonds of plastic packages during molding. We limit our analysis to the stresses acting in the plane of a wire bond. These stresses can possibly result in liftoff of the ball bond from the bonding pad of the integrated circuit. The main purpose of the analysis is to evaluate the effect of the wire bond configuration. It is shown that the stresses in wire bonds are proportional to the square of the ratio of the wire-bond span to the diameter of the wire. This explains the difficulty in molding assemblies with long wire bond spans. We also showed that wire configurations, characterized by nonzero slope angles at the ends, result in lower stresses than conventional wire shapes, where the wedge bond to the electric lead forms a zero angle. The obtained results are useful when designing plastic package assemblies and/or choosing the appropriate wire bond loop height and span.