Evaluations of the BGA Solder Ball Shape by Using Energy Method

Presented herein are the evaluation results of the BGA solder ball shape using energy method, two types of solder, viz. Sn37Pb and Sn80Pb, are selected .The geometry of the solder bump is firstly estimated using free computer software, the Surface Evolver, an interactive program which is an energy-based approach for the study of liquid droplet surfaces shaped by surface tension and other energies. The solder bump is then numerically constructed in a finite element model that simulates a BGA package. The influences of both upper and bottom solder pad radii, the surface tension on the balls, and the external load axially applied to the reflow solders on the stand-off height and the contact angle for both solder materials are investigated. The results show that for both solder materials, the stand-off height remains at a height under some pad radius. The height decreases as both upper and bottom pad radii increase. On the other hand, the contact angle presents a nearly inverse trend with respect to the pad radii. The study of the effect of surface tension reveals that at a constant pad radius, the solder ball stand-off height increases with surface tension; however, the trend becomes saturated eventually. The contact angle decreases as the surface tension becomes large. The trend also tends to be saturated. The results of the effects of axially applied load on the stand-off height and the contact angle show that as the applied load is increased so is the contact angle; nevertheless, the stand-off height becomes shorter.     

Conformal ZnO nanocomposite coatings on micro-patterned surfaces for superhydrophobicity

A conformal coating process is presented to transform surfaces with inherent micro-morphology into superhydrophobic surfaces with hierarchical surface structure using wet chemical spray casting. Nanocomposite coatings composed of zinc oxide nanoparticles and organosilane quaternary nitrogen compound are dispersed in solution for application. The coating is applied to a micro-patterned polydimethylsiloxane substrate with a regular array of cylindrical microposts as well as a surface with random micro-structure for the purpose of demonstrating improved non-wettability and a superhydrophobic state for water droplets. Coating surface morphology is investigated with an environmental scanning electron microscope and surface wettability performance is characterized by static and dynamic contact angle measurements.     

Reduction of liquid pumping power by nanoscale surface coating

The objective of the present study is to reduce the liquid pumping power by controlling the contact angle of the riser surface with the nanoscale surface treatment. The efficiency of a bubble pump is examined depending on the size of the riser, submersion ratio, gas inlet flow rate, and contact angle variations by nanoscale surface coating between 23.7° and 153.8°. By the nanoscale surface coating, the efficiency is improved by 22.5%, 25%, and 18%, respectively, for the 11 mm, 8 mm, and 5 mm risers compared to the uncoated surface. However, the superhydrophobic surface with a contact angle of 153.8° shows a lower efficiency compared to other surfaces due to the reversed liquid vibration flow. The highest efficiency of the liquid pumping power is obtained at the contact angle of 90.3°. An experimental correlation for the dimensionless volumetric liquid flow rate is developed with an error band of ±20%.     

Influence of fluorinated self-assembled monolayer on wetting dynamics during evaporation of refrigerant–oil mixture on metal surface

Reducing wettability of a metal surface is a promising method for enhancing boiling heat transfer of refrigerant–oil mixture on the metal. As fluorinated self-assembled monolayer (F-SAM) coating is effective for wettability reduction, its influence on wetting dynamics including meniscus shape, contact angle, contact line velocity and rising liquid height during evaporation of refrigerant–oil mixture on metal surface were experimentally investigated. The refrigerant–oil mixture was prepared by R141b and NM56, the oil mass fraction ranged from 0 to 10 wt%, and the surface roughness ranged from 0.028 to 1.166 µm. The results show that during evaporation of refrigerant–oil mixture, the presence of F-SAM changes the evaporation mode to be constant contact line velocity followed by both constant contact angle and contact line velocity, while decreases the rising liquid height. The results suggest that larger surface roughness and higher oil mass fraction are preferred when using F-SAM to reduce surface wettability.     

共价功能化石墨烯超疏水防腐复合涂层材料的制备

石墨烯/有机聚合物复合涂层材料较纯聚合物材料具有更优越的阻隔性能,然而由于石墨烯之间高表面能和分子间作用力,使石墨烯在防腐等领域的应用潜力无法充分发挥。本文首先以传统自由基共聚方法合成一种含氟丙烯酸酯共聚物,并采用丙炔胺对氧化石墨烯改性合成炔基化氧化石墨烯,然后利用含氟丙烯酸酯共聚物末端氰基通过点击化学反应以共价键形式接枝在炔基化氧化石墨烯表面。疏水性分析表明,含氟共聚物功能化石墨烯的水接触角达到153°,将制备的功能化石墨烯涂敷于钢板基体时,水接触角提高到171.3°。扫描电镜显示,在炔基化石墨烯表面生长有大量300~600 nm的半球形接枝物。同时,将含氟共聚物功能化石墨烯/环氧树脂复合材料应用于碳素结构钢中,通过Tafel曲线和电化学阻抗谱对其耐蚀性能进行表征。结果显示,氟化石墨烯含量为0.5wt%的复合涂层的电流密度I_corr最低(8.872×10?9 A/cm2),比其他涂层样品低1~2个数量级。综上所述,本实验所制备的涂层材料具有良好的防腐性能,这一研究为开发石墨烯防腐蚀涂层材料提供了一种新的策略。      

Adhesion enhancement of sol-gel coating on polycarbonate by heated impregnation treatment

The main limitation in using coated plastics for optical components, electronic applications and display systems is the softness of the substrate surfaces, which is responsible for the low impact and abrasion resistance and weak adhesion between the coating and the substrate. In this paper, we report a new strategy for surface pre-treatment of plastics using heated vacuum equipment and sol-gel materials to provide both chemical bonds and penetrated hard layer into the plastic surface to increase the overall performance of the coated plastic components. The heated vacuum treatment process involves: (1) surface cleaning and pore opening by heating and vacuum conditions, (2) impregnation of hydrolyzed hybrid precursor into polymer substrate under pressure and elevated temperature, (3) aminolysis of diffused precursor with surface to form chemical bonds and hardened surface layer, (4) formation of chemical bonds at treated surface with sol-gel hard coating. An impregnation depth of 1.5 µm was detected. Water contact angle dropped to below 40° and roughness increased after treatment. These provided better adhesion by increased wettability and contact area. Much increased nanoindentation hardness and Young's modulus after impregnation provided a gradient in mechanical properties between soft substrate and hard sol-gel coating. The hardened substrate delays the plastic deformation in substrate during pencil scratch test, thereby preventing early gouge failure. Both the better adhesion and the delayed gouge failure contributed to the increased scratch resistance from 6B to 8H after sol-gel coating.     

Spreading Characteristics of liquids

We encounter the spreading phenomenon in the fusing of powder images in Electrophotographic Imaging.

This paper presents a model for droplet spread on a substrate based on Frenkel’s theory. The model yields a set of master curves for spreading characteristics of the droplet. The curves describe the contact angle θ between the boundaries of droplet and the substrate as a function of the normalized time. This normalized time is a function of surface tension and viscosity of the liquid and the size of the droplet.

The other variable is the equilibrium contact angle between the liquid and substrate.

Experiments were carried out to check the validity of this model for a spreading droplet. Both experimental observations and the model verify the functional relationship, θ = f (normalized time, equilibrium contact angle).     

纳米SiO2@超支化PDMS复合超疏水涂层的制备与性能调控

超疏水涂层在实际应用中受化学腐蚀、刮擦磨损等外界环境的影响,易造成涂层老化、开裂甚至脱落,造成涂层失效。因此,针对这一问题,设计出具备耐候性的自修复超疏水表面：以超支化聚二甲基硅氧烷为柔性基底和低表面能物质,引入纳米二氧化硅构筑表面粗糙结构,制备超疏水涂层。当SiO₂粒径为50 nm、固含量为30wt%时,得到了接触角为154.87°的超疏水涂层。经过5次胶带剥离试验,涂层表现出良好的机械稳定性。经历10次温差循环试验和24 h紫外光照射后,涂层表面接触角仍大于150°,表明涂层具有良好的耐候性。涂层经过80℃、2 h的热处理可修复划痕,表明该涂层具有一定的自修复功能。同时,Tafel及Nyquist测试结果表明,对基底进行超疏水处理可显著提高防腐性能,并且该涂层具有明显的自清洁效果。综上所述,本文所制备的纳米SiO₂@超支化聚二甲基硅氧烷(PDMS)复合超疏水涂层具有自修复功能,为自修复超疏水涂层的开发提供了新的研究策略。     

Surface functionalization of silk fabric by PTFE sputter coating

This paper describes the surface functionalization of woven silk fabric by magnetron sputter coating of PTFE (polytetrafluoroethylene). The PTFE sputter coating was applied to improve the hydrophobic property of silk fabric. The effects of PTFE sputter coating on surface morphology and surface chemical properties were characterized using atomic force microscopy (AFM) and ATR-FTIR (attenuated total reflection-Fourier transform infrared spectroscopy). The wettability of the fabric was characterized through measuring the surface contact angle by a dynamic sessile analysis (DSA) technique. The contact angle of the PTFE coated fabric showed a significant increase from 68° to about 138°. The experimental results also revealed that larger sputtering pressures brought less contact angle hysteresis.     

Superstrong,Chemically Stable,Superamphiphobic Fabrics from Particle‐Free Polymer Coatings

Superamphiphobic fabrics with a robust, chemically stable, highly liquid‐repellent surface have been prepared by one‐step coating treatment of fabric substrate using a coating solution comprising poly(vinylidene fluoride‐co‐hexafluoropropylene), fluoroalkyl silane, and a volatile solvent (e.g., acetone). The coated fabric has a contact angle of 162°, 156°, and 150° to water, olive oil, and silicone oil, respectively. The highly volatile solvent in the coating solution plays an important role in forming highly liquid repellent surface on the fabric. The coating is highly stable, and can withstand 98% concentrated sulfuric acid and strong alkaline solution (e.g., 40% KOH). It is also durable enough against at least 800 cycles of machine wash, and 10 000 cycles of abrasion. Physical damages such as abrasion with a fabric, rubbing with sandpaper, or scratching with a sharp blade can even increase the liquid repellency to a certain extent. In addition, the coating has a self‐healing property against UV damages. Such a superstrong, superamphiphobic fabric coating may find applications in development of innovative textiles and functional clothing for various applications.     

The effect of electron beam sterilization on the physical properties of the bioresorbable polymer coatings on the titanium 6-aluminum 4-vanadium substrate

The aim of the work is to determine the physical properties of titanium 6-aluminum 4-vanadium alloy with poly (glycolide-ϵ-caprolactone) coating after electron beam sterilization. First, the metal substrate is machined with grade 120 and 320 grinding papers. Some of the samples are subjected to anodic oxidation. Then, the samples are coated with a biodegradable polymer layer of poly (glycolide-ϵ-caprolactone). Samples with polymer coatings are subjected to electron beam sterilization. To evaluate the effect of sterilization on physical properties of modified titanium alloy the scanning electron microscopy and atomic force microscopy, adhesion studies of the polymer coating to the metal substrate and wettability tests are applied. On the basis of the obtained results, an increase of the contact angle value is found both after applying the polymer coating to the surface of the tested titanium 6-aluminium 4-vanadium alloy as well as after electron beam sterilization. In addition, a slight increase of the adhesion in sterilized samples comparted to non-sterilized is observed. In scanning electron microscopic observations, traces of machining on the surface of the metal substrate and the continuity of the polymer coatings before and after sterilization are found. In the atomic force microscopic studies in relation to the initial state, a very good mapping of the surface topography of the samples with a homogeneous coating is found.     

轮胎模具DLC涂层的制备及性能

为探究高性能轮胎模具类金刚石(DLC)涂层的应用前景,提高模具花纹块内表面的疏水性及耐磨减摩性,采用等离子体增强化学气相沉积法在35钢基体上制备DLC涂层,并对所制备的DLC涂层的表面形貌、粗糙度、疏水性、表面元素组成、纳米硬度、摩擦系数等关键指标进行了测定.结果表明:DLC涂层具有优良的表面完整性,水接触角可达19.62°,乙醇接触角达20.37°,纳米硬度可达19.62 GPa,摩擦系数低至0.405 8,DLC涂层有望替代Teflon涂层,用于高性能轮胎模具.     

Friction and wear reduction with tribological coatings

The basic requirements for a good tribological surface are (1) low sliding friction, (2) good resistance to scuffing, wear and abrasion, (3) long contact fatigue life and (4) adequate subsurface strength to provide dimensional stability. Coatings have inherent deficiencies. The major problem is failure at the interface between the coating and the substrate, which results in flaking, peeling or spalling of the coating under the repetitively applied contact stresses.Three types of coatings which employ different mechanisms to improve the tribological properties and to maintain coating integrity are described in this paper. Nitrocarburizing represents a class of coatings in which the elements are allowed to diffuse into the surface of the structural material to form an alloy with the substrate. Diffusion provides compositional gradients which result in hard wear-resistant surface and which at low shear strengths avoid the interfaces that frequently exist between coatings and substrates. Chemically vapor-deposited chromium and titanium carbides represent a class of coatings in which a chemically distinct layer is grown on top of the substrate and is bonded to the substrate by diffusion. In the third type of coating, hard particles are suspended in a soft matrix. The hard particles provide the wear and abrasion resistance and the soft matrix both bonds the particles together and provides the low friction. Although the bond strength of this coating to the substrate is lower than that provided by diffusion in the other coatings, the soft matrix will yield without flaking under the shear stresses which are developed at the interface.     

Fabrication of superhydrophobic and oleophobic zinc coating on steel surface

In this work, a simple method, including electrodeposition and chemical modification, for fabrication of a superhydrophobic and oleophobic coating on steel substrate is reported. The surface morphology of this coating showed concave structure, and the contact angles of water and glycerol on this coating surface were about 153.57° and 149.32°, respectively. In addition, the water droplet was easy to roll on this coating surface, and the sliding angle was smaller than 10°. The contact angle of the water/ethanol droplet with different surface tension, from 56 to 36?mN?m^?1, was also >130° on this coating surface, indicating this as superhydrophobic and oleophobic coating surface with good lyophobicity. Moreover, this coating surface had excellent non-sticking property for the water droplet under a certain external pressure, self-cleaning property and long-term stability.     

Failure assessment of a hard brittle coating on a ductile substrate subjected to cyclic contact loading

Hard brittle films and coatings are often employed as a protective coating for metallic ductile substrates. In use, such coatings are generally subjected to cyclic/repeated contact loading and sliding over long periods of time. This study investigated the monotonic and cyclic contact fracture mechanism of hard coatings on ductile substrates (an electroplated Ni–P coating on a stainless steel substrate, SUS304) in order to evaluate their mechanical durability. In the experiment, both monotonic and cyclic indentation tests using a ball indenter with large contact force were performed. The fracture nucleation process was identified using the acoustic emission method. For monotonic contact loading (single indentation), coating cracks are produced by the excessive plastic deformation of the substrate, itself caused by contact loading, which makes the bending curvature of a coating a critical moment. Subsequently, cyclic contact loading (cyclic indentation) was applied to the coating in order to investigate the cycle number of film cracking. It was found that the critical contact force for coating fracture decreases, compared with that of monotonic loading. This critical force is dependent on the number of loading cycles. This may be due to the fact that cyclic contact loading encourages large plastic deformation of the SUS304 substrate owing to cyclic plasticity. Therefore, the cyclic plastic deformation behavior of the substrate was investigated using cyclic microindentation tests and the finite element method. In the computation, the Chaboche model was employed to compute the cyclic plastic deformation of the substrate, since it simulates cyclic plasticity. We clarified the cyclic contact fracture mechanism of electroplated Ni–P coating on an SUS304 substrate. Based on this, we finally predicted the coating lifetime (i.e., mechanical durability) under cyclic contact loading. Therefore, the present study is useful for obtaining information about film/coating fracture properties under both monotonic and cyclic contact loadings.     

Tailoring surface properties of paper using nanosized precipitated calcium carbonate particles

Pigment particles used in paper coatings are typically of micrometer size and consequently the thickness of the coatings is, even at its lowest, in micrometer scale. Progress in nanotechnology has given way to the development of nanosized materials to be used in coatings, yet their exploitation has not been studied to a great extent. This study examines utilization of nanosized precipitated calcium carbonate (nanoPCC) particles in nanoscale thin coating layers. In contrast to commonly used coatings, a thin nanoparticle-based coating was targeted to change the substrate surface characteristics via controlled surface structure rather than via high coat weight. A novel approach for stabilizing and modifying the nanoPCC particles with pectin and alkenyl succinic anhydride (ASA) was utilized and a nanoparticle coating with uniform particle distribution was created. The coating applied on paper substrate was hydrophobic, having a water contact angle of 125°. Particle surface modification provided dispersion stability, enabling control of the coating layer structure. The introduced concept provides a new approach to paper coatings utilizing controlled deposition of nanoparticles with extremely low coat weight, yet having high impact on substrate surface properties. Additionally, as paper is an environmentally sound product, the approach to form a controllable nanostructure on a green substrate has potential in applications outside the traditional paper products.     

大尺寸仿生微结构表面防污涂层制备及性能研究

鲨鱼、海豚等海洋生物的表皮结构具有防污功能,猪笼草的口缘区具有液膜单向传递特征,这些表面结构形貌可为船舶涂层的防污和减阻设计提供重要依据.根据鲨鱼皮表面肋条状结构、猪笼草口缘区单向沟槽和弧形结构,设计简化单向V型沟槽微结构形貌,并结合CFD模拟计算分析V型沟槽减阻性能,确定了仿生微结构的形貌及尺寸.利用皮秒激光刻蚀技术...     

激光原位合成Al_2O_3-TiO_2复合陶瓷涂层组织结构与性能

先利用火焰喷涂技术在中国低活化马氏体钢表面制备了CrFeAlTi涂层,然后通过激光原位反应技术在火焰喷涂涂层表面原位合成了Al_2O_3-TiO_2复合陶瓷涂层。分别采用体视显微镜、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射仪(XRD)、显微硬度计、立式万能摩擦磨损试验机以及静态铅铋腐蚀实验装置等分析测试手段对涂层的形貌、微观组织结构、物相组成、显微硬度、干滑动摩擦磨损性能以及耐液态铅铋合金腐蚀性能等进行了研究。实验结果表明:激光原位合成的Al_2O_3-TiO_2复合陶瓷涂层表面整体平整、光滑、致密,基本没有凹坑、裂纹和孔隙等缺陷,与基体之间形成了良好的冶金结合。涂层内部存在完全结晶区和非结晶区,且界面明显。涂层表面主要物相为Al_2O_3,TiO_2,(Al.948Cr.052)_2O_3,Fe_2TiO_5和FeCr等。涂层截面平均显微硬度约为1864.2HV0.2,比基体CLAM钢提高了约3倍,且沿横截面方向呈平稳过渡的阶梯状分布。与基体CLAM钢相比,涂层具有良好的耐磨性能,其磨损量仅为基体的1/6,并且涂层在液态铅铋中表现出良好的耐腐蚀性能。     

液态树脂基材料与铜基材料的界面润湿现象分析

采用静滴法观察了液态树脂基材料与铜基材料的界面润湿现象,测定了298～363 K温度范围内的接触角,计算了附着功.结果表明:接触角随时间呈下降趋势,基板表面粗糙度对接触角的影响较大,在表面粗糙度较小时,接触角随时间下降较快,平衡接触角较小;初始接触角和平衡接触角均随树脂基材料中环氧树脂含量的增加而降低;升高温度使接触角的变化速率加快,加入树脂后的液体的平衡接触角对温度更加敏感;附着功随着时间的延长逐渐增加,但随着温度的上升而减小.     

阳极氧化法制备铝基超疏水涂层及其稳定性和耐蚀性的研究

铝由于在潮湿的环境中很容易受到污染和损坏,从而严重影响了其美观性和用途。为了改善铝基材料的耐腐蚀性能,采用电化学阳极氧化法与十四酸修饰相结合的方式在铝基底上制备了超疏水涂层。通过场发射扫描电镜(FESEM)和X射线能量色散光谱(EDS)对涂层表面形貌和化学组成进行了表征。同时利用接触角测量仪、喷砂实验和电化学测试分别对涂层表面的润湿性、机械稳定性以及耐腐蚀性能进行了研究。结果表明:当阳极氧化电压为20V时,所制备的涂层为最佳铝基超疏水涂层,此时涂层的接触角为(155.2±0.5)°,滚动角为(3.5±1.3)°。其对应的腐蚀电流密度较铝基底降低了2个数量级,腐蚀电位从-0.629V正移到-0.570V,呈现出优异的耐腐蚀性能。此外,该涂层还具有良好的机械稳定性。