Pulse Current Plating Research Articles

Coated Conductor Processing: Copper Stabilizer

Abstract We present here a report about a copper stabilizer processing unit and the function on IBAD – HPLD coated conductor properties. A continuous reel - to- reel Cu plating stabilizer manufacturing technology was developed and will be transferred to Bruker HTS. The quality and performance of one- side and double- side 20 μm Cu layers are evaluated with respect to critical current behavior and conductor joint fabrication. By current pulse plating technology in copper sulphate CuSO4 we have gained to optimize the plating speed to more than 30 m/h by variation the electrical, electrode and solution parameters. With the new 6 m long Cu reel plating unit improved production yield and reproducible Cu stabilizer performance is demonstrated. The non-vacuum deposition unit has a high flexibility in processing a homogeneous Cu stabilizer of thickness of 5 – 50 μm. Using the Cu layer face -to -face joints with resistances of 10 -7 Ωcm 2 level by standard soldering are becoming routine. We will provide an overall analysis of our construction and results in the PLD Cu – HTS hybrid conductor engineering and processing.

Formation of Co–Ni alloy coatings under direct current, pulse current and pulse-reverse plating conditions

Co–Ni coatings have been deposited by galvanostatic direct current, unipolar pulse plating and bipolar pulse reverse plating in buffered additive-free sulfate solutions at pH 3 and analyzed for their alloy composition, deposition current efficiency and surface morphology. A main objective is to determine whether the use of pulse or pulse reverse plating can overcome the anomalous behavior of this system whereby cobalt preferentially deposits over nickel even from solutions containing more NiSO 4 than CoSO 4. This study focuses on the use of a plating solution having a NiSO 4:CoSO 4 molar ratio of 2:1 and another bath containing a large excess of NiSO 4 over CoSO 4. Experiments reveal that both pulse plating and pulse reverse plating are unable to significantly alleviate the anomalous behavior in either solution over the range of pulse frequencies, duty cycles and current amplitudes considered in this study, unlike that observed in previous studies when deposition is carried out in chloride-based solutions. On the other hand, significant improvement and better control of coating morphology over that achievable by direct current plating is possible using unipolar pulse plating in particular. Smoother and brighter deposits with finer-grained structures are obtained by increasing pulse duty cycle and frequency and decreasing cathodic pulse amplitude.

Pulse current electrodeposition of Al from an AlCl 3-EMIC ionic liquid

Electrodeposition of aluminum from an AlCl 3-EMIC ionic liquid with or without the addition of saturated LaCl 3 was carried out by both direct- and pulse-current plating methods. The effects of various parameters, including current density, pulse frequency, current on/off duration ( t on and t off), and temperature, on deposit morphology and crystal size were investigated. Deposits prepared by pulse-current plating gave a brighter and flatter surface than those prepared by direct-current plating at appropriate pulse current parameters. Temperature and pulse–current frequency ( t off) were shown to significantly affect deposit morphology. Coalescence of grains during t off periods in the pulse current plating was observed, especially at temperatures above 60 °C. Increasing the temperature from 25 to 90 °C caused an increase in deposit grain size and resulted in a change of grain shapes from a small sphere-like form to a feather-like form. As a result, the adhesion of the deposited aluminum to the substrate was lowered. Smaller grain sizes and well-adhered deposits were achieved at lower temperatures. For example, deposition at 25 °C resulted in the smallest crystal size of about 0.3 μm under the conditions of t on = 80 ms, t off = 20 ms, and i = 8 mA/cm 2. Furthermore, the addition of LaCl 3 to the melt at 60 °C effectively reduced the porosity and improved compactness of deposits.

Properties of Al 2O 3 nano-particle reinforced copper matrix composite coatings prepared by pulse and direct current electroplating

Cu–Al 2O 3 nano-composite coatings have high potential for use in applications in which high mechanical properties together with high corrosion resistance are required. In the present study it is intended to produce copper nano-alumina composite coatings with various nano-alumina contents in order to investigate the effect of alumina reinforcement particles on corrosion resistance and mechanical properties such as hardness and wear resistance. The composite coatings were deposited using direct current (DC) and pulse current (PC) plating. The microstructures of the coatings produced from both methods were examined via scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The wear behaviors, micro hardness, coating thickness, corrosion rate and coating porosity were examined using appropriate methods. Compared to DC deposition, PC plating facilitated higher amounts of particle incorporation with more uniform distribution. The results indicated that the mechanical properties of the applied coatings with incorporated nano-alumina reinforcement were far more superior as compared to its own matrix as well as non-composite copper coatings. It was also found out that increasing the amount of nano-alumina content in the coating, led to enhanced general properties of the coatings.

Pulse Current Electrodeposition of Al from an AlCl3-EMIC Ionic Liquid Containing NdCl3

Electrodeposition of aluminum from the AlCl3-EMIC ionic liquid containing saturated NdCl3 has been carried out by direct and pulse current plating. The effects of some parameters such as current density, pulse frequency, and on/off time ratio (ton/toff) on deposit morphology and crystal size have been investigated. The results showed that the microdeposits changed from polygon crystals to smaller-size spherical crystals as the direct current density increased. The deposits prepared by the pulse current plating gave brighter and flatter surface compared with those by the direct current plating at the same average current density. The deposits displayed dense and smooth surface with about 0.5 µm crystal size under the conditions of ton/toff=8:2, f=100 Hz, im=15 mA/cm2 at 25°C.

Mass transfer considerations during pulse plating

A conceptual description of material transport through a liquid phase diffusion layer during pulse and reverse pulse current plating is provided. The formation of a dual diffusion layer, with an inner pulsating diffusion layer and an outer, unaffected diffusion layer is described. The quantification of these two layers using limiting current experiments and theoretical analysis is discussed. Based on these material transfer phenomena, the basis of selection of pulse parameters is shown. The step by step approach to use these mass transfer equations as a set of design rules, and their subsequent use in a graph to select pulse and reverse pulse parameters is described.

Effect of α-picoline and quinoline on dc and pulse plating of nickel directly on aluminium

Nickel electrodeposits were formed directly on to AA 1100 aluminium alloy using a simple chemical pretreatment both by direct current plating (DCP) and pulsed current deposition (PCD) methods in the absence and presence of α-picoline and quinoline. In dc plating the current density was varied between 1 and 4 A dm−2. In pulse plating, the current density was varied between 1 and 4 A dm−2 and the duty cycle was varied between 10 and 80% at the frequency of 100 Hz. The throwing power and current efficiency of the bath were determined. The influence of current density, duty cycle, α-picoline and quinoline on throwing power and current efficiency of the bath during direct and pulse current plating have also been studied.

Study of electrodeposition of bismuth telluride by voltammetric methods and in-situ electrochemical quartz crystal microbalance method

The authors examine Bi 2Te 3 deposition and stripping mechanisms by means of cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). Accumulated charges and related mass changes for Bi 2Te 3 deposition on working electrodes are measured in-situ. Linear scanning voltammetry and EQCM results are then used to propose a two-stage deposition process. During the initial stage, a thin layer of Bi-rich Bi 2Te 3 forms on the surface of the Au electrode, followed by a bulk deposition of Te-rich Bi 2Te 3. The composition variation is minor. During anodic linear stripping of a thin deposit, Bi 2Te 3 oxidation with a single peak was observed. Two oxidation peaks were detected during anodic stripping of a thick deposit-one corresponding to Bi 2Te 3 oxidation and the other to a combination of Bi 2Te 3 and Te oxidation. The Bi 2Te 3 deposit was synthesized via pulsed plating in order to study the effects of pulse parameters on deposit composition. Results indicate that Bi 2Te 3 film composition is affected by changes in pulse potential from potential pulse plating or by changes in current pulse plating relaxation time.

Characterization of Cr-Ni Multilayers from Chromium(III)-Nickel(II) Baths Using Pulse-Current Plating

The effects of plating conditions were investigated on the composition of Cr-Ni alloys electrodeposited on brass substrates from a chromium(III)-nickel(II) bath at 30oC. At 10 A/dm2, Ni-rich deposits were obtained, whereas and at 40 A/dm2, Cr-rich deposits were formed. Hence, pulsed-current electroplating was used to develop Cr- and Ni-rich multi- layers with a thickness modulation of tens of nanometers. Microstructures of Cr-Ni multilayers were investigated by transmission electron microscopy (TEM) and electron diffraction.

Preparation of highly preferred orientation TiB 2 coatings

This paper focuses on the preparation of titanium diboride (TiB 2) coatings on the graphite substrate by continuous current plating (CCP) and pulse current plating (PIC) electrochemical techniques in fluoride electrolytes (LiF-NaF-KF) containing K 2TiF 6 and KBF 4 as the electrochemically-active components at 700°C. Thick leveled and uniform coatings were obtained and were composed of relatively pure TiB 2. The effect of the experimental parameters on the microstructure of the coatings was studied. The results showed the electrodeposition with PIC produced coatings with better quality, when compared with those obtained by CCP, under the conditions of the current density i = 0.6 A/cm 2, frequency = 100 Hz, and t on/ t off = 4/1. XRD analysis indicated that the preferred orientation of coatings is (110) plane, which is in accordance with the prediction of the two-dimensional crystal nuclei theory. The effect of a ratio of t on/ t off and frequency on the crystal size, texture coefficient and microstress was also investigated.

Texture and morphology of pulse plated zinc electrodeposits

Zinc coatings were deposited under pulse-current plating conditions from an acidic sulphate bath on low-carbon steel cathodes. The effect of the (peak) deposition current density, duty cycle and pulse frequency on the microstructural texture and morphology of the deposits was studied by X-ray diffractometry and scanning electron microscopy. The zinc films consisted of crystallites having an average size controlled by deposition current density, and oriented mostly with basal (00.2) and high index (10.3), (10.4), (10.5) pyramidal planes parallel to the surface. Pulse plating resulted in coatings which were microstructurally different to those prepared under similar conditions by direct current deposition. Texture and grain size modification is illustrated. The effect of pulse current is explained in terms of enhanced nucleation and inhibited growth.

Characterization of Cr-Ni Multilayers Obtained from the Trivalent Chromium-nickel Bath by using Pulse-current Plating

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Ni–P–SiC composite produced by pulse and direct current plating

This study attempted to incorporate 300 nm SiC particles into a Ni–P alloy matrix by pulse current (PC) and direct current (dc) plating. The effects of bath composition and operating conditions of electrodeposited Ni–P–SiC composite coatings were studied, and the micro-hardness of the deposits was determined. Both plating methods showed that the phosphorus content in the deposit falls with increasing SiC content in the bath, and that the SiC content in the composite coating rises with rising SiC content in the bath. The pulse plating deposit with SiC particles 0.2–1.5 wt.% was higher than direct current plating with SiC particles 0.2–0.5 wt.% in deposits. The wear-proof shows that the tribological behavior of Ni–P–SiC of the PC plating is better than that of the dc plating deposit, due to the higher ultra-fine SiC particles.

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.

Electrodeposition and properties of NiW films for MEMS application

The study reports basic investigations on the electroplating and properties of movable NiW microstructures with potential application in MEMS as temporary contacts for IC integration. The NiW layers have been deposited from nickel sulphamate electrolyte (MICROFAB NI-110, Enthone GmbH, Germany) with addition of citric acid stabilized tungsten complex at operating temperature of 50 °C and pH of about 3.0 using direct und pulse current plating regimes. The influence of the electroplating parameters, such as the tungsten concentration in the electrolyte and the current density on the tungsten content in the electroplated alloy, the surface structure and morphology of the deposits, as well as the mechanical properties of the alloy have been thoroughly investigated. The process allows deposition of 12 μm thick homogeneous NiW layers. An essential improvement of the mechanical properties such as micro hardness, elasticity and internal stress compared to that of the pure nickel has been achieved at comparatively low tungsten content of 3.2 wt.%.

Pulse and direct current plating of Ni–W alloys from ammonia–citrate electrolyte

The effect of the potential of deposition and electrode rotation rate on current efficiency and partial current density of nickel deposition from ammonia–citrate electrolyte with and without tungstate ions was investigated. In addition, the effect of pulse deposition parameters, such as frequency and ratio between pause and deposition time, tp/tc, on current efficiency and composition of Ni–W alloys was investigated. Partial current densities of tungsten and nickel deposition were calculated from experimental results and compared with those in direct current (dc) deposition at the same average current density, as well as with those calculated using theoretical equations for the pulse current (pc) deposition process controlled by mass transport. Obtained partial current densities of tungsten are in fair agreement with those predicted by theory in both cases, as a function of dimensionless pulse period and as a function of the tp/tc ratio. That confirms that the tungsten deposition process is controlled by mass transport. Dependences of the partial current densities of nickel deposition on the rotation rate as well as on the pc variables (frequency and pause to pulse ratio) were attributed to changes in surface concentration of ammonia and the pH.

The effects of electroplating parameters on the composition and morphology of Sn-Ag solder

The Sn-Ag solder was electrodeposited from a bath that basically is composed of tin sulfate (SnSO4), silver nitrate (AgNO3), and thiourea (CH4N2S), acting as a complexing agent to silver. The composition and morphology of electrodeposited Sn-Ag solder were studied in terms of silver concentration in bath current density, duty cycle, and additives. It was possible to control silver content in the electrodeposit by means of varying silver concentration in bath and current density. The microstructure and surface morphology of the electrodeposit become finer and smoother with increasing current density. The pulse-current (PC) plating method was applied to compare to the conventional direct-current (DC) plating. Varying duty cycle in PC plating did not change the microstructure in general, but some improvement in surface roughness was observed compared to DC plating. However, the silver composition in the electrodeposit increased with decreasing the duty cycle at a constant current density. An addition of a surface-active agent helped to reduce the surface roughness and the variation of silver content in the electrodeposit. In an optimum condition, eutectic Sn-Ag solder bumps with a fine pitch of 30 µm and height of 15 µm were successfully electroplated. The composition of Sn-Ag bumps was analyzed by energy dispersive x-ray spectrometry (EDS) and wavelength dispersive x-ray spectrometry (WDS) methods, and the surface morphology was characterized by scanning electron microscopy (SEM) and a three-dimensional surface analyzer.

Effect of plating mode, thiourea and chloride on the morphology of copper deposits produced in acidic sulphate solutions

The influence of plating mode, chloride and thiourea (TU) on morphology of copper deposits has been studied. All experiments were conducted on disc electrodes rotating at 500 rpm and an average current density of 4 A dm −2 to produce 10 μm thick deposits. In additive-free solutions, the use of pulsed current (PC) improved deposit morphology and brightness over DC plating. In the presence of thiourea (no Cl −), the deposits obtained by DC and PC plating were similar under most plating conditions. The presence of thiourea generally improved deposit quality over that obtained in additive-free solutions, but caused the formation of microscopic nodules and the deposits to appear slightly cloudy, resulting in lower reflectances than that of a polished uncoated copper surface. The addition of Cl − to thiourea-containing solutions strongly influenced deposit morphology at both microscopic and macroscopic scales depending on chloride concentration and pulse conditions. It prevented nodule formation and created microscopically bright and reflective deposits, but caused extreme macroscopic roughness. Nevertheless, PC plating at 50 Hz in solutions containing appropriate amounts of thiourea and Cl − was found to yield macroscopically and microscopically smooth deposits with reflectance similar to that of a polished uncoated copper substrate.

Effect of pulse plating on composition of Sn–Pb coatings deposited in fluoroborate solutions

Galvanostatic pulsed current (PC) and pulse reverse (PR) plating of Sn–Pb coatings onto copper rotating disks from fluoroborate solutions has been conducted to obtain alloy compositions otherwise not achievable by DC plating. PC plating investigated over a wide range of pulse frequencies (20 Hz–200 kHz) and duty cycles produces coatings with compositions that differ only slightly from those obtained by DC plating at the same current density. On the other hand, the use of PR plating can be dramatic, producing Pb contents both well above and below that achievable by DC plating. Varying the frequency from 20 Hz to 200 kHz with the duty cycle and average current density fixed at 80% and 3.78 A dm−2 yields compositions between 2.5 and 28 wt.% Pb. The Pb:Sn ratio in the deposit is always lower than that in the plating bath when a PR frequency of 20 Hz is imposed, but generally exceeds it at a frequency of 20 kHz. Alloy composition appears to be closely related to the working electrode potential reached during the anodic pulse. A higher frequency leads to less positive potentials during the anodic pulse and shorter anodic pulse times, which may enhance Sn dissolution and enrich the coating in Pb.

Electrochemical deposition and structural characterization of Au-Sn alloys

In the present work the electrochemical deposition of Au-Sn alloys is addressed and a cyanide-free process is presented. The electrolyte is an acidic thiourea solution containing gold as a Au[CS(NH2)2]+ complex and tin as stannous ions. Results concerning the plating process development and deposit characterization are reported. Au-Sn alloy films with a Sn content up to 50 at% and a single-phase structure can be obtained from the acidic thiourea–Au(I) solution under pulsed current plating conditions. Alloy deposits show three main crystal structures: a face centred cubic (fcc) Au(Sn) solid solution, extending up to 7 at% Sn; a hexagonal close-packed structure, of the same type as the metallurgical ζ phase, up to about 18 at% Sn; and a NiAs-type structure, corresponding to the δ phase of the equilibrium diagram, with an enlarged homogeneity range. Mechanical properties of thin layers of Au-Sn alloys derived from micro-indentation measurements follow the structural modification with the alloy composition. The ordered intermetallic phases occurring in the equilibrium binary system, in particular the β and ζ′ phases at 8 at% and 16 at% Sn, respectively, are not detected in the electrodeposited alloys. The main factors controlling electrochemical phase formation are pointed out, considering the differences between the phase structure of the electrodeposited alloys and the equilibrium phase diagram.