Pad Pattern Research Articles

Enhancing CMP Performance of Micro-Structured Pad Patterns: CFD Simulations and Experimental Evaluations

Enhancing CMP Performance of Micro-Structured Pad Patterns: CFD Simulations and Experimental Evaluations

Research on composite pattern design and lapping performance of fixed abrasive pads controlled by multi-physical fields

The present work provides an innovative method of composite pattern design for fixed abrasive pads, addressing issues such as machining non-uniformity and passivation blockage arising from uneven lapping flow, pressure, and velocity fields in lapping. First, a multi-physical field modeling method is provided, a material removal distribution model and evaluation criteria for the performance of the abrasive pad are established, and the reliability of this model is validated. Second, based on the model, a composite pattern abrasive pad coupled with a spiral groove and concentric micro groove is designed. Comparative experiments are conducted with the grid abrasive pad. The results show that the clogging and passivation performance of the composite pattern abrasive pad is improved, and the pressure distribution is optimized. Compared with the grid abrasive pad, in the pressure range of 20 N–70 N, the surface roughness Ra of sapphire is reduced by 6.4 %–25.42 %, defects such as brittle fracture pits and scratches on the workpiece surface are reduced, and the surface quality of the workpiece is significantly improved. The material removal rate is between 0.23 μm/min to 0.34 μm/min. This confirms the effectiveness of optimizing abrasive pad pattern design based on multi-physics fields. The research results provide a novel approach for abrasive pad pattern design with engineering application value.

Effect of Conformal Coating on Electrochemical Migration Behavior of Multi-Layer Ceramic Capacitor for Automotives Based on Water Drop Test

A large amount of multi-layer ceramic capacitor (MLCC) is mounted inside a printed circuit board (PCB) constituting electronic components. The use of MLCC in electric vehicles and the latest mobile phones is rapidly increasing with the latest technology. Environments in which electronic components are used are becoming more diverse and conformal coatings are being applied to protect mounted components from these environments. In particular, MLCCs in electronic components mainly have voltage applied. They might be used in environments where humidity exists for various reasons. In a humid environment, electrochemical migration (ECM) will occur, with the cathode and anode on the surface of the MLCC encountering each other. This can result in product damage due to a short circuit. In this study, the effects of voltage, NaCl concentration, and distance between electrodes on a non-mount MLCC, surface mount MLCC, and solder pad pattern were evaluated using a water drop test (WDT). Based on the analysis of the effects of the presence of conformal coating, applied voltage, concentration of NaCl, and the distance between electrodes, a mechanism model for ECM behavior in MLCCs was proposed.

Experimentation of a device collecting at source airborne particles issued from rolling stocks brakes systems

A specific air quality exists in underground railway stations, influenced by railways operations as infrastructure wears, mechanical braking or station design and ventilation. Among solutions existing to improve the air quality (air treatment in the station; use of less emissive brake shoes and pads, increase of electrical braking), the study focuses on a device collecting at source airborne particles issued from trains brake systems. A groove pattern of braking pads has been designed with finite element distortion analysis, air flow circuit optimisation and tested on a braking bench equipped with sensors to characterise the particles emitted and the braking performances under standardised conditions. Above 70% reduction of emissions has been noted. A suburban train bogie has then been equipped to evaluate the reliability and maintainability of the device on commercial service conditions.

The Effect of the Number of Cooling Pads on the Output Air Condition and Effectiveness of Air Cooler

To get comfortable air, it can be done by using an air conditioner or air cooler. The electrical power used for the air cooler is relatively lower. This research aims to see the effect of the number of cooling pads on the output air condition and on the effectiveness of the air cooler. The research was conducted experimentally. The research was conducted by varying the number of cooling pads used, thick. The distance between the cooling pads is 1.5 cm. The air temperature inlet of the air cooler has a dry bulb air temperature of 30𝑜𝐶 with an air humidity (RH) of 60%. The lowest dry bulb air temperature achieved was 24,04𝑜𝐶 when the number of cooling pads was 6 pieces. The highest air cooler effectiveness achieved was 0.99. Research has given satisfactory results. However, research can be developed by varying the cooling pad material or cooling pad pattern in order to obtain a small number of cooling pads.

Gene expression of secretory proteins in the nuptial pads of three Lithobates species (Anura: Ranidae)

Abstract Many amphibian species possess male-specific secretory breeding glands. In anurans, such specialized glands are often present as nuptial pads at the first digit of the hand, which are pressed against the female during amplexus. However, the role of nuptial pad secretions remains largely unknown. Here, we investigate the inner morphology as well as the RNA expression patterns of the nuptial pads of several Central American Lithobates species (Ranidae). As shown for the breeding glands of other amphibian species, the Lithobates nuptial pads are composed of large specialized mucus glands, excreting proteinaceous content to the surface. Whole-transcriptome sequencing revealed that for one of the species the most highly expressed transcripts encoding secretory proteins in the nuptial pads are sodefrin precursor-like factor (SPF) proteins, known to have a pheromone function in multiple amphibian species. The other two species, however, lack high expression of SPF transcripts but express other secretory proteins, whose roles in amphibian breeding glands remain unknown. Several of these proteins are highly expressed in all samples, suggesting a direct role during courtship or for the maintenance/development of the glands.

An Experimental Investigation of a Rubber Sponge Padded Motorcycle Helmet Subjected to Impact

This research has aimed to improve the impact absorption capacity of motorcycle helmet by installing rubber sponge pads underneath its comfort foam. Three types of Thai commercial helmets have been used in this study, namely the Shorty, Open-face and Full-face. A number of off-the-shelf helmets and padded-helmets have been us as experimental specimens. The thicknesses of the rubber sponge pads have been 1.0 cm and 1.6 cm and they have been installed to the helmets with two different patterns, i.e. Full Area (FA) and Oregon Aero (OA). Two series of test, the impact and the drop test, have been carried out. Time-histories of the transmitted load and of acceleration have been considered. The peak load, the peak acceleration, and the HIC have been investigated and discussed. The experimental results have indicated that the padding technique could significantly improve the impact absorption capacity of the helmet. The maximum peak load reduction has been 55.21% in the case of the padded-helmet at the at impact height of 1.2 m. However, the peak load reduction has decreased with an increase in the impact height. The values of the peak acceleration and the HIC of commercial helmets have been found to exceed the standard value of ECE22.05, particularly for the Shorty helmet. By padding the helmet with a rubber sponge, the peak acceleration and the HIC have been also significantly decreased. The highest reduction of peak acceleration and the HIC were approximately 70% for the Shorty with 1.6 cm pad. In the case of the Open-face and the Full-face, the reductions have ranged in between approximately 12-35%. In addition, this study has revealed that the influence of rubber sponge thickness has been more prominent than the one of the pad patterns. Therefore, the OA pattern may be preferable since it is lighter and uses less material.

Stability of Polythiophene-Based Transistors upon Bending for Gas Sensing Applications

It is presented herein a fabrication procedure for organic thin film transistors over flexible substrates, as well as an evaluation of the electrical performance upon bending stresses. Top gate/bottom contact flexible transistors of poly(3-hexylthiophene) (P3HT) were successfully fabricated, by carefully tuning organic films drying temperatures, photolithography solvents and the pattern of electrode pads. The transistors were processed over both rigid and flexible substrates for comparison purposes. A P3HT hole mobility approaching 0.01 cm2/Vs was observed for all devices and even on different substrates. In spite of a current modulation of ca. 10, P3HT over poly(ethylene terephthalate) (PET) featured transistor behavior upon bending down to a curvature radius of 8 mm. Bending direction, however, produced different effects on the transistor characteristics, especially on gold electrodes.

Dye-soaked cotton pads for latent blood fingerprint development

Visualization of latent blood fingerprints (LBFPs) at violent crime scenes is very important for identifying criminals, while current reagents/methods for developing LBFPs still have more or less limitations. Here, we advance a new strategy for LBFP development based on the dye-soaked cotton pads as “ensemble” materials. The cotton pad was first soaked in the dye solution and then placed on the substrate with deposited blood fingerprint for development. After peeling off the pad, uniform and legible fingerprint patterns were obtained in all cases where different dyes and substrates were employed. The dye-soaked pads displayed superior developing effect compared with those using conventional methods (immersing, smearing and spraying). The pad-based method exhibited many other merits, such as little damage to the fingerprint patterns and less dye stains left on fingerprint and substrate, as well as the reusability. This pad-based method was also applicable for developing sebaceous latent fingerprints by replacing the small molecular dyes with fluorescent conjugated polymer nanoparticles. In all, the dye-soaked cotton pad developing protocol is feasible, cost-effective and universally applicable for developing different types of latent fingerprints on various substrates.

Patterned anodes with sub-millimeter spatial resolution for large-area MCP-based photodetector systems

Micro-channel-plate-based photo-detectors are unique in being capable of covering very large areas such as those required in elementary particle and nuclear physics, while providing sub-millimeter space resolution, time resolutions of less than 10 picoseconds for charged particles, and time resolutions of 30psec–50psec for single photons. In such systems the electronic channel count is a major cost driver. Incorporating a capacitively-coupled anode allows the use of external pickup electrodes with patterns of individual channels optimized for occupancy, rate, and time/space resolution. The signal pickup antenna can be economically implemented as a printed circuit card with a 2-dimensional array of pads for high-occupancy/high-rate applications such as in particle colliders and medical imaging, or a 1-dimensional array of strips for a lower channel count in low-occupancy/low-rate applications such as large neutrino detectors. Here we present pad patterns that enhance signal-sharing between pads to lower the channel count per unit area in large-area systems by factors up to 4, while maintaining spatial resolutions of approximately 100 to 200μm for charged particles and 400 to 1000μm for single photons. Patterns that use multiple signal layers in the signal-pickup board can lower the channel count even further, moving the scaling behavior in the number of pads versus total area from quadratic to linear.

Temperature Analysis of Wet Clutch Surfaces During Clutch Engagement Processes Based on Friction Pad Patterns

Temperature distributions of wet clutch contact during engagement and disengagement processes are investigated considering lubricant flow behaviors in the gap between the friction pad and steel separator. Frictional heat generated by wet clutch contact in repeated operational modes that simulates high thermal endurance performance of a wet clutch system is modeled. This study applies CFD analysis to the lubricant convective flows that remove most of the frictional heat with respect to groove patterns on the frictional pad surface. Based on fluid flow analysis between the friction pad gap and the steel separator that includes the effects of pattern shapes on the friction pad, frictional heat, convective cooling behaviors and temperature distributions are computed with the repeated modes of varying sliding velocities and applied loads. The cooled frictional heat is investigated considering the convective flows in the gap of friction pad and separator. Frictional temperature variations on a wet clutch surface are computed for the effects of groove pattern shapes on the friction pad, waffle, and radial-arc types for better cooling effects. It is expected that the computational results will provide design methods for higher heat resistance durability and stable frictional torque transfer and effective cooling performance in wet clutch systems.

Influence of pellet shape and size on the pattern performance of textured fixed-abrasive pads in single-sided lapping

ABSTRACTLapping with fixed-abrasive pads is regarded as a potentially efficient machining technology due to the precise controllability of abrasive trajectory. For trajectories can be changed by pellet patterns of textured fixed-abrasive pads (T-FAPs), it is essential to studythe influence of pellet shape and size on the pattern performance of T-FAPs. In this paper, different pellet shapes and sizes were studied based on a T-FAP design algorithm in a single-sided lapping, and the pattern performance of T-FAPs was evaluated by the non-uniformity of trajectory (NUT). Based on the results, it is found that pellet shapes and sizes have an obvious influence on the performance of T-FAPs. When circular pellet shape with its size of 4, 8, or 14 mm, NUT value can be lower than 0.08. Therefore, much lower NUT values can be obtained when matching selection of pellet shape and size in pad pattern design.

Thermal Cycle Tests of CLCC Solder Joints: Influence of Substrate, Solder, and Pad Patterns

Thermal Cycle Tests of CLCC Solder Joints: Influence of Substrate, Solder, and Pad Patterns

A Global Correction Process for Flat Optics With Patterned Polishing Pad

To improve the efficiency of flat optics fabrication, a global correction method with the patterned polishing pad is developed in this paper. Through creating grooves on a polishing pad, the contact pressure distribution on the optics surface can be adjusted to change the material removal rate (MRR) distribution during polishing. Using the patterned pad, the selective removal ability of the polishing process is greatly enhanced. The predictability and stability of the MRR distribution are the preconditions to efficiently implement the proposed global correction method. Relying on the MRR distribution prediction method proposed and validated in this paper, the pad pattern can be designed based on the original surface figure of the workpieces. The designed groove pattern is created on the polishing pad using the custom-developed equipment. Then, the optical glass is polished on the designed pad with the optimized polishing time. A flat optical glass sample (Φ 100 mm) is polished with the global correction method to show its feasibility and advantage. The correction instance shows that the peak-to-valley (PV) value of the surface profile (with 3 mm edge exclusion) dropped from 1.17 µm to 0.2 µm in 14 min using a polyurethane pad with two ring grooves. Comparing with the conventional polishing process, which usually takes hours or days, the global correction method proposed in this paper can improve the efficiency of the optics manufacturing significantly.

Centrifugal and hydroplaning phenomena in high-speed polishing

Super fine polishing with compliant tools can achieve nanoscale roughness, but has limited productivity due to low material removal rate (MRR). Increased spindle speed in high-speed polishing (HSP) might increase MRR, but significant challenges appear above 10,000 rpm because of centrifugal deformation of the tool and pad lifting due to hydroplaning phenomenon. Here, a tool offset compensation strategy is proposed for centrifugal deformation and novel pad patterning design that mitigates hydroplaning. Through this new approach, linear increase in MRR for spindle speed up to 24,000 rpm is demonstrated. This work lays the foundation for future developments of HSP in fabrication of ultraprecision optics.

AlCu Pitting Prevention in Post Etch Cleaning

Three different cases of wet polymer removal in presence of AlCu are described: namely a) oxide passivation opening, b) vias etch and c) pad patterning. The occurrence of pitting at such levels is analyzed and linked to halogens presence. Moving from these results, a proposal to limit such kind of defects is given, focusing on a trimmed DIW rinsing step and on a possible AlCu passivation through a plasma ashing process.

Study on geometrical patterns of textured fixed-abrasive pads in sapphire lapping based on trajectory analysis

Geometrical patterns of textured fixed-abrasive pads (T-FAPs) play a key role during the lapping or polishing process, which not only affect the fluid liquidity but also affect the global distribution of fixed abrasives located at the pad surface. However, the T-FAP performance caused by the changed abrasive distribution was seldom revealed and evaluated. As the trajectory distribution on the workpiece surface is mainly determined by the abrasive distribution and machining parameters, the present work intended to evaluate trajectories induced by the different geometrical patterns of T-FAPs and their influences on the lapping process. For this purpose, a test method consisting of T-FAP digital modelling and kinematic analysis was demonstrated. A digital modelling method of T-FAPs was proposed to build T-FAPs containing information of testing abrasives distributed on the pad geometrical surface, and the kinematic analysis was used to obtain trajectories on the workpiece surface. Based on the method, the trajectory profiles and their non-uniformity induced by the specific T-FAP and the non-textured fixed-abrasive pad (NT-TAP) were studied. Validation experiments were carried out in lapping of sapphire slices, using 90 min of lapping time and the distilled water as lubricant. The surface profile, total thickness variation, surface roughness and material removal due to the lapping were measured. The results show that better lapping performance can be reflected by the lower non-uniformity of trajectory (NUT) induced by the geometrical patterns of T-FAPs. The values of NUT influenced by the different T-FAPs were found to be either minimized or maximized according to the specific geometrical patterns on the T-FAP surface, and the maximum value could be up to 0.3 while the minimum value is less than 0.1.

Enhanced piezoelectric properties of aluminium doped zinc oxide thin film for surface acoustic wave resonators on a CMOS platform

The increase in frequency spectrum for wireless communication system has led to the growing interest in thin film electroacoustic technology that scales favorably upon miniaturization. Non-ferroelectric piezoelectric thin films such as Zinc Oxide is one of the most promising material for Complementary Metal Oxide Semiconductor-Microelectromechanical system (CMOS-MEMS) integration due to its silicon compatibility and good piezoelectric properties. This paper compares ZnO and Al doped ZnO (AZO) thin films performance characteristics when applied as CMOS-based surface acoustic wave (SAW) resonators. The interdigitated electrodes were fabricated using 0.35 μm CMOS technology followed by piezoelectric thin film deposition and probe pad patterning. Pure ZnO and AZO with 2 wt% Al2O3 have been prepared by pulse laser deposition and RF magnetron sputtering respectively. Both deposited ZnO and AZO thin films exhibited preferential crystalline growth in 002 direction. EDS analysis confirmed the incorporation of aluminium in zinc oxide thin films. High frequency electrical measurement results revealed that the devices with AZO thin film have enhanced performances as compared to devices based on ZnO thin film. It is shown that the insertion loss for AZO thin film was reduced from −65.1 to −53.5 dB and the quality factor was enhanced from 11.33 to 25.81. More significantly, the electromechanical coupling coefficient and piezoelectric coefficient were enhanced from κ = 0.044–0.069% and d31 = 5.00 to 5.41 pm/V for AZO devices compared to those based on ZnO devices, respectively. One possible explanation of these enhanced piezoelectric properties comes from the almost ideal c-axis orientation of AZO thin film as compared to pure ZnO thin films. Our results suggest that the AZO thin film can be a better candidate for surface acoustic wave resonator using the CMOS-MEMS platform.

3D chip stacking with through silicon-vias (TSVs) for vertical interconnect and underfill dispensing

3D chip stacking with through silicon vias (TSVs) has been identified as one of the major technologies for achieving higher silicon packaging density and shorter interconnect. The test vehicle presented in this paper is a 3D chip stack package. Each layer of the test vehicle has two silicon flip chips mounted at the bottom of a silicon interposer with solder bumps. The flip chip has the equivalent dimensions and pad patterns as commercial memory chips. The interposer, with multiple interconnect TSVs for electrical connection and a central TSV for underfill dispensing, can function as a logic chip or as a redistribution chip in a real application. The assembly steps of the test vehicle include conductive adhesive filling for the interconnect TSVs, bonding two bumped flip chips on an interposer (to form a single layer), vertical stacking of the single layers and underfill dispensing. For the filling of the interconnect TSVs, an auger-dispensing method is first adopted to overfill the interconnect TSVs, followed by removing the excessive adhesive beyond the interconnect TSVs by squeegeeing. A jet valve continuously dispenses free dots of an underfill encapsulant into the central TSVs. The central TSVs function as an entrance for underfill dispensing and an uninterrupted point-source to provide fluid for each layer. The free dots form a capillary flow to fill the under-chip spaces of the test vehicle. The usage of TSVs rather than chip edges eliminates the presence of a wide edge reservoir, resulting in smaller ‘keep-out’ area occupation on the substrate.

Pattern Optimization for Phyllotactic Fixed Abrasive Pads Based on the Trajectory Method

Fixed abrasive pads patterned with phyllotaxis theory of biology have been developed to be novel lapping and polishing pads. However, the influences of phyllotactic parameters on pad patterns were not deeply indicated. To design optimal pad patterns with fixed abrasives, the trajectory analysis method is adopted. As the uniformity of the abrasive trajectory has a significant influence on workpiece surface quality, the coefficient of trajectory distribution (CTD) is put forward in order to quantitatively evaluate the uniformity of trajectory distribution, and has been validated by simulation with three different pad patterns. Based on the method, the influences of phyllotactic parameters on the uniformity of trajectory distributions under different pad patterns are further studied. It is found that the phyllotactic angle parameter, which determines the pad pattern types, has a heavy influence on the trajectory distribution, but the phyllotactic density parameter has a little influence on trajectory distribution. Through analyzing the influences of phyllotacitc parameters on the values of CTD under a wide range, the periodic effects caused by the phyllotactic angle parameter are pointed out. Through appropriate combination of phyllotactic parameters, more optimal pad patterns can be obtained besides optimal machining parameters based on the proposed method.