Reverse Plating Research Articles

Preparation of gradually componential metal electrode on solution-casted Nafion™ membrane

A typical ionic polymer–metal composite consists of a thin perfluorinated ionomer membrane and noble metal electrodes plated on both surfaces. It undergoes a large bending motion when an electric field is applied hence exhibits deformation by a certain amount of cation. With proper arrangement and package, a great number of “smart devices” are anticipated. In this study, a solution-cast route was used to prepare the electro-active polymer membrane and platinum electrodes were fabricated onto the membrane through electro-less plating. The ionic polymer used is the commercial Nafion™, the perfluoro-sulfonated ionomer membrane, developed by DuPont Co. Nafion™ membrane was cast by the solution-casting route and then loaded with different weights simultaneously. The optimized processing conditions, membrane properties and electrodes behaviors were investigated. The results of shift in WAXD peaks showed that weights delineated the crystallinity of the solution-cast membranes. The number and size of the crystalline domains of solution-cast membrane decrease as studied by SAXS. The Young's modulus of solution-cast membrane decreases as increasing weight because of the loss of crystallinity (180–140 MPa). A finely dispersed platinum particle deeper and gradient penetrating within the near-boundary region with a smaller average particle size and more uniform distribution could be obtained through a reverse electro-less plating. Its surface roughness is 3 nm comparing to 52 nm of a typical process. But its surface resistance is too high (3.5 Ω) to activate the bending motion. To solve this problem, we coated the second Pt electrodes by a typical electro-less plating, and the resistance decreased to 0.7 Ω. The results depicted that the fabricated IPMC shows longer bending lifetime than typical IPMC. In a 0.09% NaCl solution, the device was able to vibrate for 8 h under a 5 V, 0.1 Hz actuation.

Multicriteria optimization of mechanical and morphological properties of chromium electrodeposits under reverse pulse plating

In this work, a central composite design experiment was performed to estimate the effect of the electroplating parameters (temperature of electrolyte, cathodic and anodic pulse current densities, and cathodic and anodic pulse lengths,) on four properties of hard chromium electrodeposits. The studied responses were the hardness (Hv), the roughness quantified by the two criteria Ra (nm) and R (μm)), and the specific abrasive energy, Es (μJ μm−3). Analysis of the responses using optimal path technique did not lead to a common set of experimental conditions which fulfilled the required properties. Thus, the desirability function approach has been employed in order to find the best compromise between the different experimental responses. The optimal conditions are: electrolyte temperature: 49.9 °C; cathodic pulse current density: 42.0 A dm−2; anodic pulse current density: 51.5 A dm−2, cathodic pulse length: 6.23 s and anodic pulse length: 28.5 ms. Under these conditions, the estimated response values are 738 Hv, 262 nm, 2.61 μm and 0.027 μJ μm−3 for hardness, Ra, R and specific abrasive energy respectively, validated experimentally. The resultant coating, examined by AFM, exhibits a nodular fine-grained morphology.

From Copper Nanocrystalline to CuO Nanoneedle Array: Synthesis, Growth Mechanism, and Properties

In the present work, a novel method for synthesizing a one-dimensional CuO nanoneedle array was introduced; that is, first, a pure copper nanocrystalline layer was plated by using a periodic reverse pulse plating process, and then the CuO nanoneedle array grew upon the layer through thermal oxidation in the air. The nanocrystalline layer and nanoneedles were characterized by using scanning electron microscopy, regular and high-resolution transmission electron microscopies, X-ray diffraction, X-ray photoelectron spectroscopy, and a thermal analysis system (thermogravimetry and differential scanning calorimetry). The results showed that the oxidation temperature and the Cu2O intermediate phase played key roles for growing CuO nanoneedles. A self-catalyzed based-up diffusion model was proposed for interpreting the nanoneedles' growth mechanism. The field emission property of the nanoneedles showed that the electron emission turn-on field is about 0.5 V μm-1 at current density 10 μA cm-2, and the maximum current density is 2.5 mA cm-2 with a linear F−N relationship. The full Sun efficiency (η) of the CuO nanoneedle used as a cathode in dye-sensitized solar cells is 1.12%, which shows it to be a potential material in solar cells.

Pulse reverse electrodeposition from a Kyoto perspective

Using the Kyoto Protocol as a driver to find ways of reducing energy usage, a Life Cycle Analysis of producing copper, as an example of an energy intensive cycle, shows that if direct current plating of copper in rack plating of complex geometry parts is substituted by pulse reverse plating, not only is less copper deposited, and therefore consumed, but the energy efficiency of the process is also improved. In addition CO2 emission reduction throughout the product chain is likely to be significant, as are improvements in waste reduction and pollution prevention.

Effect of deposition methods on the magnetic properties of nanocrystalline permalloy

In this study, methods for developing high permeability in nanocrystalline permalloy by electrodeposition and magnetron sputtering as well as the relationship between the grain size and the magnetic properties of the nanocrystalline permalloy are investigated. Using DC plating with and without saccharin as grain refining agent, pulsed plating with saccharin added, pulsed reverse plating with saccharin added and magnetron sputtering, permalloy specimens of grain sizes ranging from 5 to 52 nm are obtained. The coercivity values of the specimens are characterized. The results show that the coercivity decreases drastically as the crystallite size was decreased from 52 to 7 nm. However, the variation range of coercivity magnitude against the crystallite size varies significantly for specimens by different deposition methods due to other factors such as uniformity and residual stresses of the specimens.

High conductivity silver nanocoatings on aluminium obtained from pulse plating techniques

The present work is part of an industrial project involving the electrodeposition of conductive silver coatings with the help of pulse plating techniques. Silver shows an excellent reflectivity for electromagnetic waves and is commonly used as a coating in parts for the telecommunication and aerospace sectors. Nanocrystalline silver layers were deposited on pretreated aluminium samples from a standard cyanide plating bath using reverse pulse plating. A qualitative overview is given as to how the pulse parameters affect the throwing power of the process and smoothness of the layers. Special attention was paid to compactness and low porosity in order to improve the corrosion resistance and good adherence to the substrate.

Recent progress in pulse reversal plating of copper for electronics applications

Based on demands for modern printed circuit board (pcb) manufacturing, the copper electroplating process is discussed. Electroplating from an additive free solution using low frequency pulse reversal plating with superimposed cathodic pulsation is suggested, which meets the demands for precise dimensions, high ductility and conductivity, low costs and environmental friendliness.

Pulse reversal plating of nickel alloys

Pulse plating has previously been reported to improve the properties of nickel and nickel alloy deposits. Typically, focus has been on properties such as grain size, hardness and smoothness. When pulse plating is to be utilised for microtechnologies such as microelectromechanical systems (MEMS), internal stress and material distribution are even more important. With baths based upon nickel chloride, and nickel and cobalt chlorides, pulse reversal plating of both pure nickel and nickel–cobalt alloys has been used to fabricate tools for microinjection moulding. Pulse reversal plating of ternary soft magnetic alloys, comprising 45–65%Co, 15–35%Fe and 15–35%Ni, is also reported.

Pulse reverse plating for uniform nickel height in zone plates

Nickel soft x-ray zone plates are fabricated by through-mask electroplating. The authors report on how a uniform nickel thickness can be obtained over the entire zone plate using pulse and pulse reverse plating. If the plating is carried out at a constant current the nickel thickness has been observed to decrease with radius. This results in lower outer zones and reduced diffraction efficiency in the outer parts of the zone plates. Here they show that the height profile can be controlled by adjusting the current density of the pulses. A high current density is found to primarily affect the edges while a low current density was observed to affect the central parts of the structures. This is true for both cathodic and anodic currents, which means that local plating and dissolution rates can be adjusted to obtain a uniform mass distribution.

Nickel pulse reversal plating for image reversal of ultrathin electron beam resist

The effects of various pulse reversal plating parameters on the grain size and smoothness of Ni film on silver seed layers has been studied. The duty cycle, frequency, bath temperature and agitation methods have been tested. The objective was to form a thin continuous hard etch mask (20–30 nm of thickness) of Ni films for image reversal of thin film resist using electroplating. While nickel sulfamate solution without additives or brighteners has been used to plate Ni films, reactive ion etching (RIE) has been used to test the durability of the plated Ni films in fluorine plasma. It was found that pulse reversal plating with current intensity of 12 mA/cm 2, duty cycle of 90%, bath temperature of 45 °C, ultrasonic agitation of power 80 W, and 400 kHz wave frequency resulted in a plating rate as low as 0.2 nm/s. This plating rate made the control of the film thickness an easy task to achieve. This yielded to a smooth plated surface free from defects or voids, with 25 nm film thickness. Combining electron beam lithography with pulse reversal plating for image reversal and RIE offers the prospect of patterning patterns with the desired aspect ratio. Holes of 100 nm diameter, 250 nm period, and 300 nm depth are achieved using this process.

Pulse reverse plating of Ni–Co alloys: Deposition kinetics of Watts, sulfamate and chloride electrolytes

Fundamental electrochemical properties of electrolyte systems are the prerequisite for the development of a successful pulse deposition process. Three different electrolyte systems for the galvanic deposition of nickel cobalt alloys (chloride, Watts and sulfamate type) were investigated in order to reveal underlying deposition mechanisms and rate determining factors. The electrochemical experiments were supported by X-ray fluorescence analyses of the alloy composition in dependence on the current density and the type of bath. A special focus was set on the investigation of the passive (oxide) layer formation by the anodic pulses. The choice of electrolyte system strongly influences the reaction mechanism and thus the alloy deposition. Also the cobalt content within the deposited layer varied strongly in dependence on the electrolyte system used. While sulfamate and Watts baths show an ability for passive layer formation, the chloride bath exhibits a lower proneness to passivation, accompanied by pit formation

Copper electroplating to fill blind vias for three-dimensional integration

The continued demand for electronic products with decreased size, higher performance, and increased functionality requires improvements in the system level integration of logic, memory, and other functional integrated circuits. The formation of vertical interconnects in silicon may be one approach to provide this integration. This method involves stacking of individual die to form a highly interconnected three-dimensional structure by placing electrically conductive vias through the body of the silicon to bring the connections from top to bottom. Copper is the metal used to fill the through silicon via structure because of its high conductivity and common use in multilevel wiring. A process will be described in this article to electroplate copper into small diameter (5–10μm) vias of aspect ratio >3. The objective of this project is to develop an electroplating process to obtain a void-free copper filled blind via; a via that does not go through the silicon substrate but terminates inside the silicon. Prior to plating, vias are formed by both reactive ion etch (RIE) and deep RIE processes and are then lined with insulation, barrier, and seed films. The insulation layer, SiO2, is deposited by plasma enhanced chemical vapor deposition while the barrier (TaN) and Cu seed layers are deposited by sputtering. A combination of three electroplating techniques is used in this study to fill the vias. They consist of optimized bath composition (additive control), fountain plating, and reverse pulse plating. The goal during electroplating is to achieve a bottom-up fill, also referred to as “a superfill.” This article describes the process that results in void-free electroplating to fill an array of blind vias as well as the related processing issues.

Use of the reverse pulse plating method to improve the properties of cobalt–molybdenum electrodeposits

Conditions leading to cobalt–molybdenum (Co–Mo) electrodeposits with high Mo percentages were studied. Deposits prepared by means of direct current electroplating showed a large amount of cracks. Maximum amount of Mo in the films was attained by applying deposition potentials in the −1200mV to −1300mV range. Reverse pulse plating mode has been proved useful for obtaining nanocrystalline, low stressed Co–Mo deposits with similar Mo percentages as in direct current conditions (35–40wt.%). The coatings were exposed to a static microindentation test, which highlighted that the pulse plated samples were more compact and less fragile than the direct current plated ones.

Copper-Platinum Deposition by Pulse Plating

In order to improve the mechanical properties of copper, pulse plating techniques were investigated for deposition of alloys employing a pyrophosphate bath containing chloroplatinic acid as a source of platinum. Cyclic voltammetry experiments showed that the copper reduction is a two-step process and that platinum reduction occurs at potentials close to that observed for copper deposition. Forward peak current densities ranging from 2.5 to were employed for the bulk electrodeposition experiments. Bright, shiny, and crack-free deposits were obtained at low current densities. The amount of platinum observed in the deposits was found to increase with the current impressed for both forward pulse and pulse reverse techniques. The Knoop hardness was found to increase with the platinum content of the deposits. The corrosion rate of the deposits measured in a solution of was found to decrease with platinum content. The data show that deposits containing up to 5.6 and of platinum can be obtained by forward pulse (only) and pulse reverse plating, respectively. As compared to a copper sample, the deposits obtained by forward pulse and reverse pulse techniques exhibited a 31 and 55.4% increase in Knoop hardness, respectively. As compared to copper, up to a 45.4% increase in corrosion resistance was observed for deposits produced by the application of a forward pulse. The deposits obtained by pulse reverse exhibited a 35.6% improvement in corrosion resistance over those obtained by the forward pulse technique under identical forward peak current density.

Materials Aspects to Consider in the Fabrication of Through-Silicon Vias

ABSTRACTThe formation of vertical interconnects to create three-dimensional (3D) interconnects enables integration of dissimilar electronic material technologies. These vertical interconnects are metal filled blind vias etched in silicon and are formed by a series of processing steps that include: silicon etch; insulation/barrier/seed layer deposition; electroplating of Cu to fill the via; wafer grinding and thinning; and back side processing to form contacts. Deep reactive ion etching (DRIE) is used to etch silicon vias with attention given to process parameters that affect sidewall angle, sidewall roughness, and lateral etch growth at the top of the via. After etching, vias are insulated by depositing 0.5 μm of silicon dioxide by plasma enhanced chemical vapor deposition (PECVD) at 325°C. A barrier film of TaN is reactively sputtered after insulation deposition followed by a Cu sputtered seed film allowing electroplated Cu to fill the blind via. Reverse pulse plating is used to achieve bottom-up filling of the via. Once void-free electroplated vias are prepared, the process wafer is attached to a carrier wafer for silicon back grinding. Vias on the process wafer are “exposed” from the back side of the wafer with a combination of processes that include mechanical grinding, polishing, and reactive ion etching (RIE). Contact pads are then formed by conventional IC processes. Cu posts are used to connect the electronic devices and to address thermal management issues as well. This paper presents materials aspects to consider when fabricating through silicon vias (TSVs). Modeling of the Cu-filled vias to investigate thermal management schemes and Cu posts to investigate mechanical reliability is also presented.

Copper electrodeposition in sulphate solutions in the presence of benzotriazole

DC and pulse plating of copper in acidic sulphate solutions containing benzotriazole (BTA) has been studied. When BTA is the only additive present, it generally has a stronger effect than the plating mode and significantly enhances deposit morphology and surface brightness over that produced in additive-free solutions. XPS and voltammetry analyses indicate that BTA is present at the surface of the deposit, but not through the entire coating, and does not become depleted within the solution over the course of plating. This may help explain why the initial surface smoothness and brightness is maintained as the coating grows beyond 5 lm thick. Plating mode does have a strong effect on deposit morphology under specific conditions. Pulse current plating at low frequency (50 Hz) and low duty cycle (20%) produces deposits with poorer quality than that obtained by DC plating. Pulse reverse plating yields very coarse and dull coatings when the frequency is low enough for metal dissolution to occur during the reverse time. Regardless of the plating mode, the addition of Cl ) eliminates most of the beneficial effects of BTA and leads to very rough and dull deposits. The observed effects are discussed in light of previous research on the electrodeposition and corrosion of the Cu–BTA and Cu–BTA–Cl systems.

Modelling of Faradaic current profiles during pulse reverse plating

A study has been made, using computer integration techniques, of the influence of the double layer capacitance on the Faradaic current profile during pulse reverse plating (PRP) from acid copper electrolytes containing organic additives. It was found that using typical reverse pulse times, the double layer capacitance had a strong influence on the actual current available for metal dissolution during the reverse pulse.

Effect of Pulse Plating Parameters on the Composition of Alumina/Nickel Composite

Nickel/aluminum oxide composite was electroformed in a sulfamate bath with of aluminum oxide powder. Different plating methods, including direct current plating, periodic pulse plating, and periodic reverse pulse plating, were used. With conventional direct current plating, the maximum particle inclusion in the nickel matrix remains about 2 wt %. However, much higher percentile particle inclusions were achieved when a specific pulse reversal plating technique was applied. The particle incorporation approaches the theoretical maximum when the deposit thickness per cycle approaches the particle diameter size at lower duty cycle. The highest particle incorporation achieved is 23% (by weight). Conceptual models interpreting the dramatic differences in the results of these plating methods are proposed.

Importance of pulse reversal effect of CdSe thin films for optoelectronic devices

Systematic studies of cadmium selenide thin films were prepared by without and with pulse reversal plating technique. In the present work, preparation of CdSe thin films was reported with lower duty cycle and pulse reversal effect. Due to these effects electrical and opto-electronic property of the material were changed. The thin film of CdSe was deposited on cleaned conducting substrates like titanium, SnO 2, nickel and stainless steel, respectively. The pulse plated CdSe films without and with pulse reversal films were heat treated and characterized by XRD, optical studies, scanning electron microscopy and photo electrochemical properties. Semiconductor parameters were estimated for without and with pulse plating technique. The barrier height Φ b was calculated for CdSe deposited on different conducting substrates.

Electrochemical deposition and characterization of zinc-nickel alloys deposited by direct and reverse current

Zn-Ni alloys electrochemically deposited on steel under various deposition conditions were investigated. The alloys were deposited on a rotating disc electrode and on a steel panel from chloride solutions by direct and reverse current. The influence of reverse plating variables (cathodic and anodic current densities and their time duration) on the composition, phase structure and corrosion properties were investigated. The chemical content and phase composition affect the anticorrosive properties of Zn-Ni alloys during exposure to a corrosive agent (3%NaCl solution). It was shown that the Zn-Ni alloy electrodeposited by reverse current with a full period T = 1 s and r=0.2 exhibits the best corrosion properties of all the investigated alloys deposited by reverse current.