Pad Surface Research Articles

QUAD FLAT NO-LEAD PACKAGE WITH DIFFERENT THERMAL PROFILES AND SOLDER PAD FINISHING FOR VOID MINIMIZATION

Voiding in solder joints is a common problem that occur in electronic packaging, specifically for bottom terminated component (BTC). Quad Flat No-Lead (QFN) is a good example of BTC component that susceptible to void. Thus, QFN component thermal pads were used as the test vehicle in this voiding assessment. The objectives of this study are to analyze the influence of the variables from every parameter evaluated in the experiment on voiding area in QFN thermal pad solder joint and obtain the best combination of variables that can minimize the total void area percentage inside QFN thermal pad solder joint down to below 5%. In this study, several variables and their impacts on voiding based on the literature review were studied. No clean lead-free solder paste of SAC305 composition was employed in this experiment. Various stencil patterns were tested, including Window-Pane, Round, and Triangle/Polygon. The influence of pad surface finishing of the test board on the voiding reduction was analyzed in this study. The effects of convection reflow of various profiles and atmospheres were also considered. All the variables were setup for the experiment execution which begins by solder paste printing, solder paste inspection, component pick & place, convection reflow soldering, Xray inspection, void data extraction & analysis, and finally void results compilation. The results shown that reflow profile Ramp-To-Spike (RTS) Long Reflow Time High Peak Temperature gave lesser void area % than Ramp-Soak-Spike (RSS) Long Soak and RTS Normal profiles.

Plasma-activated polypropylene coated with alginate-phosphorous triazatetrabenzocorrole for diesel photodegradation

The leakage of heavy metals, dependence on H2O2, and difficulty of loading restrict the application of nano-oxide photocatalyst in the treatment of marine petroleum pollution. In this study, a photocatalytic absorbent pad was prepared on a plasma-activated polypropylene substrate using phosphorous triazatetrabenzocorrole as the photocatalyst and sodium alginate as the catalyst carrier. In seawater, sodium alginate can form a gel layer (calcium or magnesium alginate) on the polypropylene pad surface to achieve efficient photocatalysis. The prepared photocatalytic pad can overcome the physical adsorption limit of commercial polypropylene and continuously degrade diesel in seawater under visible-light irradiation. Moreover, the prepared polypropylene pad did not contain heavy metals and showed an advantage of pH independence.

Transfer of Frictional Contact Derived Phthalates from Pad Surface Enhances Dermal Exposure.

Dermal exposure to chemicals derived from object surface contact is an important contributor to increased health risk. However, chemical transfer induced by mechanical friction between dermal and object surface has yet to be adequately addressed. To fill this knowledge gap, rubbing fabrics were used as surrogate skins to stimulate dermal mechanical friction with pad products with phthalates as target analytes. The results showed that the amounts of phthalates transferred increased linearly with contact burden (50-1000 g), contact duration (1-10 min), and sliding speed (3.0-9.0 cm s-1). The surface texture of surrogate skins dictated the accumulation of phthalates. Net/pocket micro-surface structures of rubbing fabrics induced a higher accumulation of phthalates than U-shape structures of fabrics with a similar surface roughness. Covering of the pad surface by a layer of textile was effective in minimizing the transfer of phthalates induced by mechanical motion. The estimated transfer efficiency of bis(2-ethylhexyl) ester (DEHP) derived from rubbing friction (0.005-0.05%) upon the pad surface over 8 h was greater than those for gas-phase emission (0.00002-0.0005% over 24 h) and sweat transfer (0.008-0.012% over 24 h). These results indicated that dermal frictional contact with the surface of pad products was an important exposure pathway.

Standing Balance Measures In Collegiate Cheerleaders Between New And Old Cheer Specific Footwear

PURPOSE: Cheerleading requires athletes to perform movements with a focus on balance maintenance. Footwear affects human balance, and older footwear may cause balance decrements. However, balance has not been examined in cheerleader-specific footwear. Thus, the purpose of this study was to examine balance in collegiate cheerleaders while wearing “old” and “new” cheer shoes. METHODS: Twenty-five healthy male and female collegiate cheerleaders with no history of neuro-musculoskeletal disorders completed this study. Participants completed balance testing on separate days while wearing either a “new” or “old” pair of cheerleading shoes. Participants self-reported the number of training hours that the shoes have been worn to calculate shoe age. Balance testing consisted of three 20-second trials for each condition. Balance conditions were randomized for each participant and included bilateral stance on the force plate and foam pad. Unilateral stance on the dominant, and non-dominant limb on the force plate, and foam pad. The average sway velocity (VEL) and root-mean-square (RMS) of the center of pressure was used to quantify balance in the anterior-posterior (AP) and medial-lateral (ML) directions. Paired samples t-tests were used to analyze the results, with an alpha level of 0.05, and cohen’s d was reported as a measure of effect size. RESULTS: Analyses revealed no statistically significant differences for balance measures between footwear (all p > 0.05). However, results suggest moderate effect sizes in the non-dominant foam pad condition for APRMS (d = 0.58) and MLRMS (d = 0.48) suggesting balance decrements in the new shoes. CONCLUSIONS: While not statistically significant, findings may suggest balance decrements in the new cheer shoes. These findings may be due to the novel aspect of the new shoes compared to the older shoes the participants may be more familiar with. Because of the novelty of the new shoes participants may have attempted to rely more on proprioceptive input during balance compared to the old shoes. If participants relied more on proprioceptive information on the unstable foam pad surface that may partially explain the increased postural sway. Future research should examine varying ages of shoes to potentially identify when cheer footwear begins to break down and cause balance decrements.

Modeling the microscale contact status in chemical mechanical polishing process

The micro-scale contact status between pad and workpiece surface plays one of the most significant roles in determining the material removal rate (MRR) during the chemical mechanical polishing (CMP) process. To evaluate the contribution of random contact status to the material removal process, the paper proposed a novel concept of “effective contact spots”. It represents the probability of randomly distributed pad asperities sliding across a given coordinate point on the workpiece surface. Furthermore, mechanical removal capacity parameter γ and chemical reaction capacity parameter β were defined to mathematically model the material removal process from a micro-scale chemical-mechanical synergistic perspective. To validate the model, a series of CMP tests (with in-situ conditioning) were conducted on three types of materials (BK7 glass, fused silica, and Si). The real contact status was also measured and analyzed statistically after being conditioned with two types of conditioners. Experimental observations and theoretical analysis results indicated that the chemical-mechanical synergism was the fundamental mechanism for the contribution of the micro-scale contact status to the material removal process. Resulting in the fact that the real contact ratio, radius, and spacing of the real contact spots play different dominant roles on MRR for different materials. Moreover, solution strategies in this study can provide the knowledge needed for improving the material removal stability, and further enable predictive control on the polishing or conditioning recipe before a non-ideal contact status result in an unexpected material removal rate.

Regional Characteristics and Control Method of the Mixing Flow Pattern for Water-Lubricated Tilting Pad Thrust Bearings

The water-lubricated tilting pad thrust bearings (WTTBs) of the reactor coolant main pump and high-power RDT operate at a large linear velocity, heavy load, and low viscosity. On the basis of the performance prediction of WTTBs in the mixing flow pattern, a hypothesis of the regional flow pattern is proposed. To compare the lubrication performance under four kinds of flow pattern modes, a thermo-elasto-hydrodynamic lubrication model of the WTTB considering the flow pattern is established, and a partition iteration algorithm for the mixing flow pattern is provided. Moreover, a method for controlling the flow pattern by changing the pad surface morphology is proposed. A simulation is used to indicate that the bearing performance under the mixing flow pattern calculated by the regional flow pattern mode is between that of the laminar and turbulent flows. The regional mixing flow pattern mode can automatically retrogress to the single flow pattern mode by changing the operation conditions. Both the circumferential bulge and radial concave pad surfaces are beneficial for increasing the turbulent area and thereby improving the load-carrying capacity of the WTTB.

Effect of thermoplastic polymer in brake pads on particulate matter emission: A case study with polyethylene

The reduction of brake emissions was attempted by adding a small amount of polyethylene (PE) in a low-steel brake friction material. The results indicated that the particle concentration and pad wear were considerably reduced. PE facilitates the formation of friction films on the pad surface, indicating that molten PE promotes wear particle agglomeration at the sliding interface. The friction films on the pad with PE prevent the metallic adhesion of the steel fibres on the pad to the iron disc and decrease the particle concentration and wear of the friction couple, which was confirmed via the analysis of airborne and settled wear particles.

Simulation and Experimental Investigation of the Radial Groove Effect on Slurry Flow in Oxide Chemical Mechanical Polishing

Slurry flow on the pad surface and its effects on oxide chemical mechanical polishing (CMP) performance were investigated in simulations and experiments. A concentric groove pad and the same pad with radial grooves were used to quantitatively compare the slurry saturation time (SST), material removal rate (MRR), and non-uniformity (NU) in polishing. The monitored coefficient of friction (COF) and its slope were analyzed and used to determine SSTs of 25.52 s for the concentric groove pad and 16.06 s for a certain radial groove pad. These values were well correlated with the simulation prediction, with around 5% error. Both the laminar flow and turbulent flow were included in the sliding mesh model. The back mixing effect, which delays fresh slurry supply, was found in the pressure distribution of the wafer–pad interface.

Planar polishing process method based on real-time dressing of a polishing pad surface.

Planar polishing is an important manufacturing process for high-precision planar components. In this study, a real-time dresser and a planar polishing process based on real-time dressing for large-aperture optical plane components were developed. Efficient dressing of a polishing pad surface can be achieved with the real-time dresser. Compared with the conventional method, real-time correction for the surface shape of the polishing pad was realized via the temperature parameter t in the real-time dresser, and this parameter can be optimized through optimization experiments. Finally, a series of experiments was carried out to verify the effectiveness of the real-time dresser on surface dressing. Through the real-time dressing of the polishing pad surface, the flatness peak-valley deviation and the root-mean-square deviation of the flat optical element surface (430×430mm) can reach 3λ and 0.9λ, which is improved by 25% and 33%, respectively.

Influence of Process Parameters on Surface Activated Aluminum-to-Aluminum Wafer Bonding

Aluminum-to-aluminum wafer bonding is a promising technique for future wafer-level packaging and heterogeneous integration. The main challenge for a successful Al-to-Al thermocompression bonding is the fast oxidation of the aluminum surface. In this article, a surface-activated Al-to-Al wafer bonding process for patterned 200-mm wafers is presented, which removes the oxide in an argon plasma and enables a high bond quality with an accurate alignment. The influence of the bonding parameters’ temperature (200 °C–300 °C), force (20–40 kN), and activation time (2.5–5 min) on the contact resistances and bonding yield is analyzed. Additionally, we modified an etch mask during wafer fabrication and thereby improved the condition of the Al pad surface, which resulted in a higher bonding quality. Based on this optimized wafer fabrication process, we achieved a high bonding yield of >85% and contact resistances in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}\Omega $ </tex-math></inline-formula> range for bonding temperatures as low as 250 °C. This demonstrates the potential of Al-to-Al wafer bonding to create reliable interconnects for 3-D wafer-level integration.

Atomic-level smoothing of glass and silicon surfaces by water polishing with an acrylic polymer plate

Polishing techniques have been used since antiquity but remain important in high-value manufacturing processes in optics and semiconductor fields. State-of-the-art polishing enables the production of atomically flat surfaces of even advanced materials, such as diamond, SiC, and GaN, by exploiting the exceptional chemical characteristics of particle surfaces, fluid solutions, and pad surfaces. Although various effective chemical reactions are employed, chemical reactivities of organic polymer surfaces have not been thoroughly explored. We demonstrate a water-only and slurry-less polishing technique using an acrylic polymer plate. We investigated the possibility of glass processing with several polymer materials and found that normal acrylic polymers have remarkable properties for polishing. Glass and silicon surfaces with atomic-level flatness can be produced using only an acrylic polymer plate and water. We believe that the developed polishing methods will become popular in the future because they are simple and cost-effective processes.

Influence of Brake Pad Properties to Braking Characteristics

In this research, field and laboratory testing of three commercially available brake pads with the lowest, mid-dle, and highest price were performed. Complex field testing, where brake pads were tested in real extreme conditions on a loaded van vehicle and laboratory tests were performed. The field testing intended to investigate the temperatures that occur during the braking process and to determine the stopping distance, deceleration, and stopping time separately on the type of brake pads. Labo-ratory tests included the determination of the friction co-efficient according to ASTM G77, the structure of brake pad surfaces before and after the testing, and quantitative chemical analysis of brake pads. The aim of this study was to determine the influence of brake pad temperature on braking time depending on their purchase prices. The obtained results show a significant difference between the temperature, friction coefficient, chemical composi-tion, and braking time of the brake pads and their price.

A real-time dressing method for metal lapping pads based on the thermal deformation effect

Surface shape and accuracy of the metal lapping pad have a significant impact on the performance of the lapping process for flat optical components, which are usually improved by the dressing process. A real-time dressing system for metal lapping pad surface shape (RDLS system) based on the bimetal thermal deformation effect is proposed. Unlike traditional dressing methods (e.g., turning dressing with a diamond tool), the real-time dressing based on the RDLS system is a material-loss-free and in-process dressing method. A full-aperture lapping turntable based on the RDLS system was designed, in which the working heat was analyzed. The displacement models of the lapping pad surface were established by regression analysis. Finally, several experiments were conducted to verify the functionality of the RDLS system. During turning dressing (turntable rotational speed n = 100 rpm), the displacement error was compensated by the RDLS system, which was caused by the working heat of the turntable shaft system. During the lapping processing for optical elements (n ≤ 20 rpm), the correction displacement was controlled by the RDLS system, which realized the real-time dressing of the lapping pad surface. The process performance of the plane optical component was optimized with the RDLS system (process parameter: the coolant temperature t). The effectiveness and practicality of the RDLS system were demonstrated experimentally.

Theoretical Model Study on Chemical Compositions Affecting the Space Launch Vehicles

In this paper we clearly discussed about composition of chemical substances that affects the launch vehicle in ground station as well as atmospheric conditions. During the rocket-launching the large amount of inhalation of an exhaust gas released and it majorly affects the surface of the launch pad as well as the atmosphere. In rocket, the combustion produces huge number of hot gases with high temperature and pressure. This hot gas passes into the nozzle and accelerates, that time hot cloud is formed in the ground station which composed of (CO2) Carbon dioxide, (HCl) Hydrogen chloride, and carbon monoxide (CO). These hot gases not only affect the ground surface but also the atmospheric layers, will see how it’s affecting the launch vehicle as well as to protect the environment from air pollution affected by emission of gases from different types of rockets and spacecrafts

Polishing Characteristics and Mechanism of Polishing Glass Substrate Using Suede Pad with Fine Micrometer-Sized Pores

Chemical mechanical polishing (CMP) using a suede polishing pad is an essential fabrication process for glass substrates that require ultra-high planarization. However, the effect of surface asperities of the suede pad on its polishing characteristics is not completely understood because the structure of the suede pad in the thickness direction is not constant, and its surface asperities can easily change during the pad conditioning or marathon polishing processes. In addition, many previous studies have discussed the polishing mechanism using a suede pad; however, these studies used suede pads with a pore size of approximately 100 μm. This paper discusses the polishing characteristics of a suede pad with fine micrometer-sized pores by clarifying the relationships between the removal rate, friction coefficient, pore parameters, and roughness as the pad surface asperities. In this study, a series of marathon polishing tests were performed with and without conditioning. It was discovered that the removal rate was affected not only by the pore parameters but also by the surface roughness of the suede pad with fine pores. The relationship between the removal rate and the friction coefficient changed owing to the influence of pad conditioning, and this change is significant when the break-in conditioning time is short.

Investigation of braking performance and thermal effect of sintering of brake pads with Al2O3 additive

Nowadays the improvement researches of pad materials, which are widely used in braking mechanisms of land vehicles, still maintain their popularity. In general, it has been proven by the studies that the material characteristics of the brake pads in composite structure vary greatly depending on the manufacturing parameters. In this study, the effects of sintering of Al2O3 added composite pads on braking performance via surface temperature were investigated. In this context, 50, 75, and 125 mm Al2O3 particles were added to the lining composition and the results were evaluated comparatively. The braking performances of the tested samples were evaluated in terms of pad wear, pad surface temperature and friction coefficient. As a result, it was observed that the braking performance of sintered Al2O3 additives in all three dimensions was better.

Lab-in-a-Cup (LiC): An autonomous fluidic device for daily urinalysis using smartphone

Since urine can be collected noninvasively, a wide range of biomarkers found in urine makes urinalysis well suited for continuous routine health screening. Although there has been amazing progress in automated urine analyzers, they are laboratory-centered and still suffer from labor-involved sample processing and analysis being infeasible for routine healthcare. To facilitate routine healthcare, this work presents a cost-effectively implemented lab-in-a-Cup (LiC) hybrid urinalyzer developed using a disposable plastic cup in association with conventional paper-based urine sensors. Since the sensor pad is precisely fixed with the bottom of the cup, the small gap between the sensor pad and cup surface leads to the limited diffusion of urine which results in the stable, reproducible, repeatable data and sample volume-irrelevant measurement. To characterize the urine sample in the cup, a smartphone application with an image recognition algorithm has been developed and applied that automatizes the entire analysis procedures enabling it for routine healthcare without relying on the manual color scheme. The device was successfully applied for investigating a number of urinary biomarkers such as glucose, pH, protein, and red blood cell (RBC) to a wider concentration covering their clinical ranges. While quantified, the proposed analyzer was found to significantly improve the reaction time and sample volume-dependent irregularities enhancing the colorimetric assessment of urine sensors as a major concern for biological samples. As a result, the user-friendly LiC device may suitably be applied as a near-patient urinalyzer.

Single crystal silicon wafer polishing by pretreating pad adsorbing SiO2 grains and abrasive-free slurries

Single crystal silicon wafers are widely applied in the field of Integrated Circuits (ICs). However, in order to pursue high surface quality and efficient material removal rate (MRR) on polishing single crystal silicon, a large amount of abrasives is consumed, which increases the processing cost and burdens the environment on discharge. A novel abrasive-free method of polishing single crystal silicon wafers was proposed and explored to solve the above problems. A polishing pad pretreated by colloidal silica was employed. The MRRs of the polished silicon wafers with potassium carbonate, potassium silicate and potassium hydroxide slurries before and after pretreating pads were measured and compared. The polishing pad pretreated by colloidal silica can improve the processing efficiency, stability and quality of single crystal silicon wafers in the abrasive-free slurries containing potassium carbonate, potassium hydroxide or potassium silicate. The outstanding MRR of silicon wafer was obtained using abrasive-free slurries containing potassium carbonate and potassium silicate. The material removal mechanisms of polishing single crystal silicon wafers with pretreating pad adsorbing SiO2 grains and abrasive-free slurries were investigated by XPS analysis of silicon wafer surfaces and EDS and SEM analysis of the pad surfaces.

Synergistic effects of iron and hexagonal-Boron Nitride additions in copper-based composites for braking application

This paper explores the addition of h-BN and iron to Cu-based brake pads on the performance benefits. It also investigates the effect of graded layering by synthesizing three and four-layer brake pads by powder compaction and sintering route. The top one or two layers are made of Cu-based composite containing Fe, h-BN, and W, while the middle layer is pure Cu and, bottom steel plate. Two different compositions were explored for the composites by varying Fe content. From the two composite compositions, brake pads with single-layer composite or two-layer composite were synthesized. Characterization of brake pad specimens was carried out using density measurements, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy. The brake pads were subjected to simulated braking tests at braking energy/cycle of 60, 96, and 136 K Joules. Wear rate, coefficient of friction, stopping distance, stopping time, and hardness were measured and compared among other brake pads. The brake pad containing single-layer Fe rich Cu composite showed the best performance in the simulated braking tests. EDS analysis of wear debris shows the formation of iron (boride, nitride, oxide) complex which is indicative of a surface with superior dry lubricating properties. This surface is a result of synergetic interaction between h-BN and Fe particles. The iron particles which are scattered in the Cu matrix composite act as low friction regions on the brake pad surface that interrupt the high friction regions on the Cu matrix, thus reducing the local and bulk temperature rise. The two-layer composite brake-pad showed performance intermediate to the two single-layer brake pads. No advantage due to higher thermal conductivities in Fe deficient composite was observed as the two composite layers, showed similar Fe contents in their matrix phases.

Influence of Flux and Related Factors on Intermetallic Layer Growth within SAC305 Solder Joints.

Flux contained in solder paste significantly affects the process of solder joint creation during reflow soldering, including the creation of an intermetallic layer (IML). This work investigates the dependence of intermetallic layer thickness on ROL0/ROL1 flux classification, glossy or matt solder mask, and OSP/HASL/ENIG soldering pad surface finish. Two original SAC305 solder pastes differing only in the used flux were chosen for the experiment. The influence of multiple reflows was also observed. The intermetallic layer thicknesses were obtained by the image analysis of micro-section images. The flux type proved to have a significant impact on the intermetallic layer thickness. The solder paste with ROL1 caused an increase in IML thickness by up to 40% in comparison to an identical paste with ROL0 flux. Furthermore, doubling the roughness of the solder mask has increased the resulting IML thickness by 37% at HASL surface finish and by an average of 22%.