Determination of Water-Proof Coal (Rock) Pillar Height in Mining Coal Seam Group under Water-Bearing Rock Stratum

In order to determine the reasonable height of water-proof coal (rock) pillar when mining multiple coal seams under aquifer, this paper analyzes the expansion height of water-conducting fracture zone when coal seams mining. Considering the expansion law of water-conducting fracture zone in coal seams mining, two schemes of coal seams mining in upper and lower groups and one-time mining of all coal seams are designed for comparative analysis, and the height of water-proof coal (rock) pillar is determined based on the expansion height of water-conducting fracture zone. The results show that the height of water-proof coal (rock) pillar is calculated as 91.08 m when mining upper and lower groups and 105.46 m when mining all coal seams at the same time. According to UDEC numerical simulation results, the height of water-proof coal (rock) pillar is 56.08 m when mining upper and lower groups and 86.36 m when mining all coal seams at the same time. Comparing the results of theoretical calculation and numerical analysis, the maximum value is selected as the final result, and the reasonable water-proof coal (rock) pillar height is determined to be 105.46 m.

Optimization of High-Speed Electrolytic Plating of Copper Pillar to Achieve a Flat Top Morphology and Height Uniformity

Cu plating bath for high-speed electrodeposition of Cu pillar was designed in consideration of a flat top morphology of pillar and a pillar height uniformity. An ideal polarization curve was assumed for the flat top morphology. To obtain the ideal polarization curve, an effect of organic additive concentration and solution agitation on the polarization curve were investigated. The basic bath components were optimized considering a Wagner number to improve the pillar height uniformity. To confirm the pillar top morphology and the pillar height uniformity, a 300-mm diameter wafer was plated with Cu at 20 A/dm2. As a result, improved pillar top morphology and pillar height uniformity were obtained. The optimized plating bath was applied to the plating of a large-size panel of 415 × 510 mm.

Optimization of High-Speed Electrolytic Plating of Copper Pillar to Achieve a Flat Top Morphology and Height Uniformity

Cu plating bath for high-speed electrodeposition of Cu pillar was designed in consideration of a flat top morphology of pillar and a pillar height uniformity. An ideal polarization curve was assumed for the flat top morphology. To obtain the ideal polarization curve, an effect of organic additive concentration and solution agitation on the polarization curve were investigated. The basic bath components were optimized considering a Wagner number to improve pillar height uniformity. To confirm the pillar top morphology and the pillar height uniformity, a 300 mm diameter wafer was plated with Cu at 20 A/dm2. As a result, improved pillar top morphology and pillar height uniformity were obtained. The optimized plating bath was applied to the plating of large-size panel of 415 × 510 mm.

Controlling wetting properties on nanostructure surfaces by the coupled effect of the structural parameter and roughness factor

Aims: The wetting properties of the nanostructure surface can be controlled by the structural parameter associate with roughness surface. Background: Increasing the roughness of hydrophobic surface can enhance the hydrophobicity of the surface. Objective: We chose copper material modified by fluorosilane as the substrate, and used Lammps software to establish four different shapes nanostructures, square pillar, cylinder, frustum and cone nanostructure respectively with pillar height and theoretical gap changing to study the influence of structural parameter and roughness factor on wetting properties of surfaces. Method: Molercular dynamic simulation Result: The structural parameter h/b can determine the wetting transition of the droplet on surfaces. With the same height and theoretical gap, the contact angle of the frustum and the cone surfaces is larger than that of the square pillar surfaces and cylinder surfaces due to the effect of wedge surface. Conclusion: (1)The values of the contact angle exhibit a strong dependence on roughness factor. The roughness factor will increase by this way of increasing height and decreasing gap, and the contact angle of droplet increase with the roughness factor increasing on the four surfaces. There exists the critical structural parameter h/b to determine the Cassie and Wenzel state transition of the droplet on various nanostructure surfaces.And the critical structural parameter values are 1.5, 1.5, 2.08 and 2.24 for the square pillar, cylinder, frustum and cone nanostructures respectively. Other: The wetting properties can be controlled by the structural parameter associate with the roughness factor. Increasing the pillar height and decreasing the gap of the nanostructure surfaces will make the structural parameters reach the standard of transition value h/b of the droplet state, and the droplet will change from Wenzel state to Cassie state.

Electroplating Fundamentals for Coplanarity Improvement

As the definition of 3D packaging softens to include an exhaustive array of inexpensive alternatives to TSV and interposers, adjustments to processes and materials are being made to enable more and more complex 3D integration schemes. For chip stacking in SIP integration, there are at least two planarity concerns. Overall die parallelism issues lead to uneven stacks, and plated bump to bump variability across the die creates standoff issues that could result in open circuit (a short pillar) or shorting across multiple pillars in the case that solder volume or pillar height is abnormally large. Both issues can be strongly influenced by electroplating uniformity. Both potentially also create stresses in the bonded dies that drive warp and reliability failures. This fact is creating a general demand for better coplanarity for stacked dies. Measuring uniformity of plated films has a long history starting with mechanical stylus profilometers. Normal specifications for within wafer (WIW) and within die (WID) uniformity have been refined as metrology systems stepped up to full wafer measurement (all bumps) and to allow statistical calculations using huge data sets. A plated wafer may have up to 20 million pillars. As solder bumps transitioned to copper pillars, and pitches and solder volumes decreased, the possibility of pillar height variation causing failures at assembly also increased. Devices were seldom laid out with plating uniformity in mind and as issues arose, dummy features were sometimes added to aid uniform plating. While WiW and WiD uniformity are global and local versions of the same measurement respectively, the length scale difference creates dramatically different influences on each response. At the global (wafer) scale, relatively coarse (millimeter to tens of millimeter) scale uniformity of electric field drives plating rate. Note here that plating rate variations exactly correlate to uniformity variations. Plating rate is driven by current, generally governed definitively by Faraday's Law: the amount of a substance deposited on each electrode of an electrolytic cell is directly proportional to the amount of electricity passed through the cell. The goal of chamber design in electroplating involves delivery of current in as precise a manner as necessary to create uniform deposition across the wafer. Design elements include various current distribution techniques, mass transfer, RPM, electrolyte flow control, etc. Ideally these devices allow uniform plating such that the average thickness of each die is the same, or that a similarly arranged feature on each die is the same height. If these factors are well controlled, they have little effect on the final WiD uniformity (where length scales vary across tens to hundreds of microns), and all dies across the wafer will have a similar plated thickness variation. This “residual” or intrinsic WID uniformity is governed by a variety of factors including current density, pattern geometry, bath conductivity, bath temperature, and functionality of bath additives. Ultimately, these factors govern where metal ions at the plating interface relinquish their autonomy to become part of a stable plated metal film. The combination of these factors determines the Wagner number, a quantity that describes the local current distribution uniformity. Like the term “throwing power” used in parts plating applications, a higher Wagner number indicates better plated thickness uniformity. Predicting, validating, and improving the intrinsic WID uniformity requires attention to the relationship between the plating chamber, the chemistry, and the pattern being plated. Die specific modelling of the plating system, including calculation of the Wagner number, allows prediction of the WID coplanarity. This information can be used as feedback to refine die layout or to optimize chemistry functionality to plating tool parameters to drive WID uniformity to the lowest possible value.

DEM-CFD Modeling of Proppant Pillar Deformation and Stability during the Fracturing Fluid Flowback

In this study, proppant pillar deformation and stability during the fracturing fluid flowback of channel fracturing was simulated with DEM-CFD- (discrete element method-computational fluid dynamics-) coupling method. Fibers were modeled by implementing the bonded particle model for contacts between particles. In the hydraulic fracture-closing period, the height of the proppant pillar decreases gradually and the diameter increases as the closing stress increases. In the fracturing fluid flowback period, proppant particles could be driven away from the pillar by the fluid flow and cause the instability of the proppant pillar. The proppant flowback could occur easily with large proppant pillar height or a large fluid pressure gradient. Both the pillar height and the pillar diameter to spacing ratio are key parameters for the design of channel fracturing. Increasing the fiber-bonding strength could enhance the stability of the proppant pillar.

Ice nucleation on nanotextured surfaces: the influence of surface fraction, pillar height and wetting states

Ice nucleation and growth on nanostructured surfaces.