Ni-B Deposits Research Articles

Replacement of Lead stabilizer in electroless Nickel-Boron baths: Synthesis and characterization of coatings from bismuth stabilized bath

Only a few compounds have been completely characterized as stabilizers in alkaline electroless nickel‑boron plating and most of them have serious impact on health or the environment. In this paper, the effects of bismuth salts on the bath stability and characteristics of electroless NiB deposits obtained from an alkaline electroless nickel bath reduced by borohydride are presented. The objective of this paper is to propose a healthy and environmental friendly electroless NiB coating. The process of production was maintained the same as traditional NiB to facilitate the industrial adaptation. Bismuth accelerates the rate of deposition up to 10−5 mol/L and inhibits plating from a concentration of 0.01 mol/L. The bismuth ions in the NiB bath act as stabilizer but some bismuth also co-deposits with the nickel‑boron coating, leading to a coating with 3 wt% bismuth. The coating presents a homogeneous surface morphology with a 15.11 μm/h plating rate in agitated and non-replenished bath. The X-ray diffraction patterns of electroless NiB coatings stabilized by Bi3+ exhibit a single broad peak, indicating a strong tendency to form amorphous structure. The coatings present the typical high hardness of NiB coatings (830 hv50), with a relatively smooth surface. The wear behavior was characterized by ball-on-disc tests and a friction coefficient of 0.45 is obtained after 100 m of test with 5 N charge and an alumina ball. Scratch test results show the first damage after 16 N. NiB-Bi coatings have impressive properties and can replace lead stabilized electroless NiB in different fields.

Effect of Heat Treatment on the Characteristics of Electroless Ni-B, Ni-B-W and Ni-B-Mo Coatings

In the present work, electroless Ni-B, Ni-B-W and Ni-B-Mo coatings are deposited on AISI 1040 medium carbon steel specimens. Deposit characterization is done using scanning electron microscope, energy dispersive X-ray analysis and X-ray diffraction techniques. The as-deposited coatings present a dense nodular surface morphology in case of Ni-B and Ni-B-W coatings whereas Ni-B-Mo coatings reveal a cauliflower like morphology with aggregated clusters of nickel nodules and visible surface cracks. Heat treatment results in grain growth and visible grain boundaries in case of all the three electroless deposits. Energy dispersive X-ray analysis reveals that the Ni-B deposits are boron rich. The boron content decreases with the co-deposition of W in the EN matrix. From X-ray diffraction analysis it is concluded that the coatings are primarily amorphous in their as-deposited condition and turns crystalline on heat treatment. The microhardness of Ni-B-W coatings is the highest amongst the three in as-deposited condition and up to a heat treatment temperature of 400°C. While Ni-B-Mo coatings show higher thermal stability.

Production of hard hydrophilic Ni-B coatings on hydrophobic Ni-Ti and Ti-6Al-4V alloys by electroless deposition

Abstract This paper is mainly focused on the wetting state of liquid droplets on Ni-Ti and Ti-6Al-4V hierarchical structured hydrophobic surfaces in micro/nanoscale. Electroless Ni-B deposition as a surface coating treatment has recently drawn considerable attention of researchers owing to remarkable advantages when compared with other techniques such as low price, conformal ability to coat substrates, good bath stability and relatively easier plating process control. The Ni-Ti and Ti-6Al-4V substrates were plated by electroless Ni-B plating process. The coated films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), hardness testing and static contact angle measurement. Results obtained from the analyses show that electroless Ni-B deposition may improve the hardness and wettability of the Ni-Ti and Ti-6Al-4V alloy surfaces.

Formation and characterization of multilayers borohydride and hypophosphite reduced electroless nickel deposits

Electroless nickel coatings are popular surface treatments for industrial application because they can provide either excellent corrosion protection (in the case of nickel-phosphorus − Ni-P − coatings) or excellent wear resistance and superficial hardness (in the case of nickel-boron − Ni-B − coatings). The properties provided by both types of coatings are thus complementary and recent work has focused on combining electroless Ni-P and Ni-B in the form of duplex coatings. This work goes further on this research by studying multilayer electroless Ni-P/Ni-B coatings. The Ni–P/Ni–B multilayer coatings were prepared using a commercial bath for the Ni-P coatings and a lab-developed alkaline bath based on sodium borohydride for the Ni-B deposits. Single layers of Ni-P and Ni-B as well as multilayers constituted of 10 layers, alternating between Ni-P and Ni-B electroless bath, were prepared. Scanning electron microscopy (SEM) observations of the cross-sections of the nickel duplex coatings reveal that coatings are uniform with proper compatibility between layers. When compared with the single layers of NiB and NiP the multilayer coatings have better wear and abrasion properties. Scratch test was used to qualify the adherence between the layers. Hardness and adhesion properties are closer to NiP.

Evaluation of Friction Behavior of Electroless Ni-B Coating and its Optimization under Engine Oil Lubricated Condition

The present study deals with the deposition of electroless Ni-B coating on mild steel substrate. The friction behavior under lubricated condition is analyzed on a pin – on – disc type tribo – tester. The applied normal load, sliding speed and sliding time are varied at three different levels. Their effect on coefficient of friction (COF) of the deposits is analyzed. Experiments are carried out following the combinations in Taguchi’s L27 orthogonal array. Finally, an attempt is made to optimize the tribo – testing parameters for minimum COF of the deposits.

Preparation of High-Speed Signal Transmission Line on Thin Polyimide Layer By All-Wet Process

Polyimide materials are widely used for printed circuit board as substrate/insulation layer because of its high mechanical stability, high electrical insulation properties, high heat resistance, etc. Low dielectric constant and superior flat surface are requested for applying to high speed signal circuit. Applying the polyimide film to high-speed circuit board, high adhesion length and superior flat interface between metal wiring and polyimide is needed. Our group proposed an all-wet process to fabricate the diffusion barrier layer and Cu wiring by using an organosilane layer as an adhesive/catalyst layer [1, 2]. Additionally, wet processes offer relatively simple procedures and tools, and usually are cost effective. In previous study, an immobilized aminosilane film on polyimide works as an adhesion layer and a catalyst supporting layer for electroless deposition of NiB. This process showed superior smooth surface of catalyzed polyimide because of without etching processes. Adhesion of electroless-deposited NiB film on superior smooth polyimide is a particular need for realizing a high-density printed circuit board [3,4]. In this investigation, this technique was applied for preparation of the silicone chip substrate called interposer. The high-speed signal transmission line for interposer was developed by our proposed method. Soluble block copolymerization polyimide (Q-VR-X1014, PI R&D CO.,LTD) was used for polyimide film source, and thin polyimide layer with and superior flat surface was prepared on glass substrate by spin-coating. After drying, hydrophilic surface of polyimide was developed by UV-irradiation in 10 min. Aminosilane layer in the polyimide was formed in toluene solution containing aminocilane molecule at 60 oC, 10 min. Then, modified surface was catalyzed by palladium, and thin metal layer as seedlayer/adhesion layer and conductive layer were formed by electroless NiB deposition and Cu electrodeposition, respectively. Cu electrodeposition was carried out using alkaline electrolytes bath (Meltex Inc). First, Cu electrodeposition on polyimide was investigated. Figure 1 shows schematic illustration of electrodeposited Cu film on aminocilane-modified polyimide film. To form Cu conductive layer using electrodeposition with conventional acidic bath, film peeling between Pd/aminosilane interfaces was observed. Acid condition was affected for Pd catalyst layer, and Pd was dissolved from the aminocilane supporting layer. We therefore used the alkaline electrolytes bath for Cu electrodeposiotion. We optimized operating condition of electrodeposition and thermal annealing to decrease electronic conductivity, adhesion strength. Using this optimized condition, Cu film with 2 μΩcm could be obtained. Second, roughness of the surface and its interface was measured. Figure 2 shows cross sectional TEM image of electrodeposited Cu film on aminosilane-modified polyimide film after annealing. Roughness of interface between polyimide and NiB was not observed and superior smooth interface was obtained using this technique. Moreover, surface roughness of deposited Cu film was very smooth of Rq = 14 nm. Final, a coplanar waveguide as high-speed signal transmission line was fabricated by this technique. Cu wiring was prepared by semi-additive method. Line width was 100 μm, and film thickness and space between grand and signal line was varied. The characteristic impedance of the fabricated coplanar waveguide showed almost the same value of the theoretical designed one that was 50 Ω.

Optimization of Wear Performance of Electroless Ni-B Coating under Lubrication

This paper presents an experimental study on tribological behavior of electroless Ni-B coating under lubricated condition based on Taguchi’s method. Mild steel specimens are used as the substrate material for the deposition of Ni-B coating and the thickness of the deposits is found to be around 35 μm. Based on Taguchi’s L27 orthogonal array of experiments, the wear tests are done on a pin-on-disc type tribotester This experiment is carried out by utilizing the combination of process parameters of the tribotester like normal load, sliding speed and duration of sliding. The analysis of the experimental data is carried out with the help of MINITAB® software package. It is seen that the normal load is the most significant factor followed by sliding time at 99% confidence level. The surface morphology, composition and compound analysis of the coatings are done by means of scanning electron microscope, energy dispersed X-ray micro-analyzer and X-ray diffraction analyzer respectively. Finally, a confirmation test is carried out to validate the analysis.

Optimization of Wear Performance of Electroless Ni-B Coating under Lubrication

This paper presents an experimental study on tribological behavior of electroless Ni-B coating under lubricated condition based on Taguchi’s method. Mild steel specimens are used as the substrate material for the deposition of Ni-B coating and the thickness of the deposits is found to be around 35 μm. Based on Taguchi’s L27 orthogonal array of experiments, the wear tests are done on a pin-on-disc type tribotester This experiment is carried out by utilizing the combination of process parameters of the tribotester like normal load, sliding speed and duration of sliding. The analysis of the experimental data is carried out with the help of MINITAB® software package. It is seen that the normal load is the most significant factor followed by sliding time at 99% confidence level. The surface morphology, composition and compound analysis of the coatings are done by means of scanning electron microscope, energy dispersed X-ray micro-analyzer and X-ray diffraction analyzer respectively. Finally, a confirmation test is carried out to validate the analysis.

(Invited) Electrochemical Synthesis of High Strength Regular Metal Foams and 3D Micro-Lattices

Three-dimensional metal micro- and nanostructures offer opportunities to develop multifunctional materials with unique combinations of material properties. Traditional strategies to improve the mechanical properties of materials consist of altering either the microstructure or the composition. Both strategies, albeit successful, tend to be rather incremental. The third approach is that of controlling not only the microstructure but also the architecture1. By combining the effect of the architecture with the effect of the microstructure, architectured cellular materials with enhanced mechanical properties are achieved. Modern templating techniques, including colloidal crystal lithography2 and 3D laser lithography3, enable the creation of structures with well-defined sub-micron features. Used in combination with electrochemical routes, the deposition of nickel or copper micro-architectures is achieved with fine control of the microstructure and dimensions. Although electrodeposition is a well-established technique, metal electroforming of cellular micro-materials is demanding. Specific challenges include the electrodeposition onto non-conductive surfaces, adequate surface preparation, appropriate throwing power for electrolyte infiltration into submicron features or proper process optimization. The present talk will cover our recent research activities on the fabrication of nickel and copper regular foams and micro-lattices synthesized by electrochemical processes aiming at achieving high strength and low density materials. Regular porous metal structures are produced by colloidal crystal templating of polystyrene (PS) microspheres. The PS templates are formed by sedimentation of PS microspheres. Under gravity and drying, the PS microspheres form a self-assembled multilayer with a face-centered cubic structure. The templating step is followed by either metal electrodeposition to obtain a metal inverse opal (Figure 1.a) or by electroless deposition of NiB to form a hollow-shell opal (Figure 1.b). The metallic micro-lattices (Figure 1.c) were fabricated by electroless deposition of NiB onto a surface-modified polymer template produced by 3D laser lithography. In situ micromechanical testing of these micro-architectures showed enhanced mechanical properties despite being low density. Increasing the metal coating in micro-lattices from 10 nm to 100 nm improve the mechanical performances by a factor of 3.5 while the density is only multiplied by 2.3.

(Invited) A Wet Process of Copper Wiring on Surface Modified Polyimide Film By Aminosilanes

Polyimide (PI) film is widely used in several applications especially in the electronics industry, e.g., as a base material for flexible printed wiring assembly, because of its excellent mechanical and thermal stability and a low dielectric constant. Our group proposed an all-wet process to fabricate the diffusion barrier layer and Cu wiring by using an organosilane layer as an adhesive/catalyst layer as shown in fig. 1 [1, 2]. Additionally, wet processes offer relatively simple procedures and tools, and usually are cost effective. In previous study, an immobilized aminosilane film on polyimide works as an adhesion layer and a catalyst supporting layer for electroless deposition (ELD) of NiB. Adhesion of NiB-ELD film on ultra-smooth polyimide is a particular need for realizing a high-density printed circuit board [3]. We have reported that an induction time of NiB-ELD was changed by the number of amino groups in aminosilane, and a shorter induction time was found in the aminosilane having two or three amino groups as compared with that having single. Our recent critical problem is in the step of Cu deposition onto NiB-ELD: a low reduction rate of cupric ion in sulfuric acid, or if the reduction proceeded, the film peeling was observed. We therefore used the alkaline electrolytes developed by Japanese company or it’s improved to fabricate Cu wiring, and examined thermal annealing effect on the electronic conductivity, crystallinity.

Investigation of the Electroless Deposition Process of Magnetic Nanostructures

We have studied electroless deposition of Ni-B within a template structure as a model process to optimize the deposition of nanostructures. Our results show that depending on the deposition rate and deposition time employed end-opened or end-closed nanotubes connected at both ends by a thin film can be prepared. We have found that if the deposition rate is large, then deposition within the nanotubes is mass transport limited. By reducing the deposition rate the reaction becomes kinetically controlled and continuous uniform nanotubes are formed. The deposition rate was controlled by varying the temperature, pH or concentrations of the reactants. Optimal parameters of 20 ºC, a pH of 10 and a concentration of 0.12 M diammonium citrate have been found for the deposition of magnetic nanostructures. Employing the optimised deposition process we have prepared uniform end open nanotubes and characterized their associated magnetic properties.

Investigation of the Electroless Deposition Process of Magnetic Nanostructures

Magnetic nanostructures can be formed via a variety of preparation methods. The most common of these is electrochemical deposition. However, recently there has been an increased interest in electroless deposition of magnetic nanostructures. Electroless deposition of nanotubes or nanowires requires a template, commonly a porous polycarbonate (PPC) or aluminium oxide membrane. Usually dimethylamine borane or hypophosphite is used to reduce ions such as Ni+2, Co+2, Fe+2 and Cu+2to metals. The use of these reducing agents results in the simultaneous deposition of B or P in the magnetic nanostructures. Although magnetic structures have been deposited previously via electroless deposition a detailed investigation of the deposition process is lacking.Previously we have prepared CoNiFe-B [1] and NiCu-B [2] nanostructures via electroless deposition and investigated their associated magnetic properties. In this work, we use electroless deposition of Ni-B as a model process to study the preparation of nanostructures on a PPC membrane. We obtained Ni-B nanostructures consisting of nanotubes with outer diameter 400 nm and length of 20 μm, connected together by a Ni-B film at both top and base. We have analysed the electroless deposition process using scanning electron microscopy (SEM) imaging at different stages of deposition as shown in insets (i) and (ii) in Fig. 1. The magnetic properties of these nanostructures have also been investigated as shown in Fig. 1.Prior to electroless deposition the membrane is activated by deposition of catalytic palladium nuclei throughout the pores and surface. Initial electroless deposition of Ni-B occurs at these catalytic palladium sites. This results in the formation of Ni-B islands on the membrane surface and along the pore surface as shown in Fig. 1(i). Once initiated the deposition becomes self-sustaining. As deposition continues the islands coalesce together forming a continuous film on the membrane surface and nanotubes within the membrane pores. The membrane is then dissolved with only the Ni-B nanostructure remaining as shown in Fig. 1(ii).We have observed that deposition on the membrane surface occurs at a faster rate than inside the membrane pores. We believe that the lower deposition rate inside the pores is associated with local changes of Ni concentration and pH. The midpoint of the tube axis has the lowest deposition rate and thus here, the tube wall is thinnest. Due to the higher deposition rate on the membrane surface, the nanotubes become closed at both ends before continuous nanowires are formed. If the rate of deposition on the surface is very large the nanotubes can become end-closed before the tube is fully formed.In this study the nanostructure growth is analysed at different deposition rates by varying the concentration, temperature and pH of the deposition bath. By controlling each of these parameters the deposition rate at the surface and the within the pores can be controlled. Modelling of the deposition rate as a function of position along the tube axis is also carried out.The authors would like to acknowledge funding provided by the Irish Research Council (RS/2011/270), New Foundations 2014 and Science Foundation Ireland (12/IP/1692).[1] J.F. Rohan, D.P. Casey, B.M. Ahern, F.M.F Rhen, S. Roy, D. Fleming, S.E. Lawrence, Electrochem. Commun. 10,1419 (2008)[2] D. Richardson, F.M.F. Rhen, IEEE Trans. Magn. Submitted (2014)Figure. 1. Magnetic measurements carried out perpendicular and parallel to the tube axis, of end-closed Ni-B nanotubes after 15 minute electroless deposition at 65 °C at a pH of 9. Inset (i) SEM image of initial Ni-B island deposition at Pd nucleation sites and (ii) Ni-B nanotubes connected with a Ni-B thin film.

Study on Influence of Zwitterionic Surfactant on the Surface Finish and Surface Morphology of Electroless Ni-B Coatings on Al 7075-T6 Alloy

The influence of Zwitterionic - propanesulfonate surfactant on the surface properties such as surface roughness, surface morphology and microhardness of Ni-B coatings using electroless alkaline bath was reported in this paper. Ni-B deposits obtained from nickel chloride as the source of nickel and borohydride as the reducing agent at a pH of 11 and 12 and temperature 85 ± 2 OC. This study reveals that the Ni – B coatings were clearly influenced by the addition of surfactant propanesulfonate on surface roughness and surface morphology. Electroless nickel (EN) - B coatings with addition of surfactant has changed the surface morphology from non-smooth nodular appearance to a smooth surface with average roughness value 1.4μm, which is less than the Ra value of without surfactant 1.98μm. The hardness of the deposit increased with lesser concentration of the surfactant when compared to without surfactant addition. Surface morphology and composition of the Ni–B coatings was analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD).

Anisotropic Deposition of Localized Electroless Nickel for Preferential Bridge Connection

Preferential bridge connection by localized electroless NiB deposition was investigated. The phenomenon of “bridge” formation by so-called extraneous deposition was utilized as a technique to perform the selective deposition of NiB on organic surfaces. The films used for bridging were preferentially deposited in the area between facing pads. The deposition proceeded in the direction perpendicular to the surfaces of the facing pads. The occurrence of this anisotropic deposition strongly depends on solution diffusion, and the fabrication of a connection could be controlled by changing the pattern and pad dimensions. This method does not use a resist pattern for selective deposition; thus, it is a high throughput maskless fabrication process for the connection between separated pads. Using this technology, a preferential bridge connection for a pad array with a pad width, a pad height, a distance of between the facing pads, and a pitch was fabricated. Moreover, the combined use of localized electroless deposition and conventional electroless deposition on the bridging film is expected to realize for pad-to-pad connections with low electric resistance.

Maskless Fabrication for Micropad Interconnection using Electroless NiB Deposition and Application to "Chemical" Flip-Chip Bonding

Deposition behavior of localized electroless NiB deposition for pad-to-pad connection was investigated. Localized deposition occurred mainly on the area between facing pads, and anisotropic deposition toward each facing pad was obtained. Thus, this connection, "preferential bridge connection", is no need of photolithographic technique. These results indicated that this process is one of the maskless fabrication processes. Moreover, chemical flip-chip bonding containing preferential bridge interconnection was demonstrated. The chip-to-substrate interconnection with 30 micrometer pitch was successfully achieved.

Bridge Connection for Facing Pads Arrays with Pad-position Shifts Using Controlled Extraneous Deposition of Electroless NiB

Bridge Connection for Facing Pads Arrays with Pad-position Shifts Using Controlled Extraneous Deposition of Electroless NiB

Interconnection of Multi-Pad Electrodes by "Controlled Anisotropic Extraneous (CAEx) Deposition" of Electroless NiB Film

Interconnection of multi-pad array was developed by using the electroless CAEx deposition of NiB for application to the new flip-chip bonding technology. Behavior of CAEx deposition of Electroless NiB films was depended on pad width and distance between facing pads, and pad with nearer distance and wider pad size was achieved. Practical feasibility of this technique was demonstrated by forming interconnection between pads separated by 5 micrometer and measuring 5 micrometer in both height and width. This method was applied successfully to interconnecting the pads forming an array with a pitch of 20 micrometer.

Effect of Heat Treatment of the Diffusion Barrier for Bus Electrode of Plasma Display by Electroless Ni-B Deposition

Thin Ni-B films, 1 <TEX>${\mu}m$</TEX> thick, were electrolessly deposited on Cu bus electrode fabricated by electro deposition. The purpose of these films is to encapsulate Cu electrodes for preventing Cu oxidation and to serve as a diffusion barrier against copper contamination of dielectric layer in AC-plasma display panel. The layers were heat treated at <TEX>$580^{\circ}C$</TEX>(baking temperature of dielectric layer) with and without pre-annealing at <TEX>$300^{\circ}C$</TEX>(<TEX>$Ni_{3}B$</TEX> formation temperature) for 30 minutes. In the layer with pre-annealing, amount of Cu diffusion was lower about 5 times than that in the layer without pre-annealing. The difference of Cu concentration could be attributed to Cu diffusion before <TEX>$Ni_{3}B$</TEX> formation at grain boundaries. However, the diffusion behavior of the layer with pre-annealing was similar to that of the layer without pre-annealing after <TEX>$Ni_{3}B$</TEX> formation. With increasing annealing time, Cu concentration of both layers increased due to grain growth.

Surface strengthening pure copper by Ni-B coating

An electroless deposition technique is used in strengthening the surface of pure copper. The microstructure, the effect of chemical composition of the coating bath on Ni-B deposition rate and some properties of Ni-B coating are studied. It is practicable to coat a uniform and continuous Ni-B hardening layer on copper surface by this technique. The coating rate is controlled mainly by the concentration of NiCl 2, KBH 4, NaOH, Pb(NO 3) 2 and H 2NCH 2CH 2NH 2. The phase structure of Ni-B coating is a nickel—supersaturated solid solution, and Ni 2B and Ni 3B are formed in the Ni-B coated layer during heat treatment where the microhardness of the coating is improved. The Ni-B coating has a little effect on the specific resistance of the pure copper.

Formation and characterization of borohydride reduced electroless nickel deposits

The present work aims to study the formation of electroless Ni-B deposits and evaluation of their characteristic properties. An alkaline bath having nickel chloride as the source of nickel and borohydride as the reducing agent was used to prepare the electroless Ni-B deposits. The influence of variation in bath constituents as well as operating conditions on the plating rate, and, the nickel and boron content, of the resultant Ni-B deposits were studied. Selected deposits were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), evolved gas analysis (EGA), vibrating sample magnetometer (VSM) and transmission electron microscope (TEM), respectively, for assessing the phase content, phase transformation behaviour, liberation of hydrogen during crystallization, saturation magnetic moment and micro-structural features. The corrosion resistance of Ni-B deposits, in 3.5% sodium chloride solution, both in as-plated and heat-treated (450 °C/1 h) conditions, was also evaluated by potentiostatic polarization and electrochemical impedance studies. XRD patterns reveal that Ni-B deposits of the present study are amorphous in as-plated condition and undergo phase transformation to crystalline nickel and nickel borides upon heat-treatment. DSC traces exhibit two exothermic peaks at 306 and 427 °C, corresponding to the phase transformation of amorphous Ni-B to crystalline nickel and Ni 3B phases and the transformation of a higher phase compound to Ni 3B and Ni 2B, respectively. TEM microstructures and EGA strongly support the occurrence of phase transitions at 306 and 427 °C. Electroless Ni-B deposits demonstrate a moderate corrosion resistance in 3.5% sodium chloride solution. The extent of corrosion resistance offered by electroless Ni-B deposits is relatively less compared to electroless Ni-9 wt.% P deposit.