Electroless Plating Bath Research Articles

Effect of surfactants on performance of electroless plating baths for nickel–ceramic composite membrane fabrication

Nickel–ceramic microfiltration membranes were prepared by electroless deposition of nickel on the activated ceramic membrane substrates having a nominal pore size of 275 nm. Two different surfactants, namely sodium dodecyl sulphate (SDS) and cetyltrimethyl ammonium bromide (CTAB), were studied for their ability to alter the performance characteristics of plating baths as well as composite membranes. Parameters evaluated include the bath conversion, plating efficiency, metal film thickness, average pore size of the composite membranes and per cent pore densification. The overall plating rate was found to increase up to 32% with the addition of SDS and 45% with the addition of CTAB. Addition of surfactants not only resulted in increased film thickness (4–5 μm) but also accounted for considerable reduction in average pore size of the composite membrane. CTAB was found to be more effective and efficient than SDS for nickel membrane fabrication.

Combining X-Ray Diffraction and Substrate Deflection Analysis to Understand Internal Stress in Electroless Copper Films

ABSTRACTElectroless copper films are usually the first conducting layer on the insulating substrates of printed circuit boards. For this and other emerging applications, the internal stress of the copper layer is an important consideration both for film adhesion and film-substrate interaction. We have combined stress/strain analysis based on X-ray diffraction, which is sensitive to the strain of the copper crystallites, with a conventionally used technique that analyses the bending of the substrate (Deposit Stress Analyzer). Both techniques were implemented in such a way that the stress could be monitored continuously during the deposition of the films from the electroless plating bath as well as afterwards. These tests were carried out for three chemical formulations and the results from both techniques agree qualitatively. For one bath, the substrate bending method detects a 60 nm region of local stress at the film-surface interface.

Evaluation of crystal structure of porous Si nanowires prepared by metal assisted etching

ABSTRACTThe macro and micro morphology of the Si surface, depending on noble metal ion concentration in etching solution, prepared by metal assisted etching were investigated. We defined the morphology of etched Si in four types, and developed the phase diagram of Si morphology. Mixture of silver nitrate (AgNO3) and hydrofluoric acid (HF) was used as an electroless-plating bath of Ag, as well as etching solution of Si. The morphology of the etched Si surface as function of concentration of AgNO3 in etching solution was observed by SEM. With increasing concentration of the AgNO3 in the etching solution, the surface of etched Si tended to be porous structure with very fine pores of a few nm (porous Si). When concentration of AgNO3is low, single crystal Si nanowires with a smooth surface without pores were observed.

Performance characteristics of hydrothermal and sonication assisted electroless plating baths for nickel–ceramic composite membrane fabrication

This paper addresses the performance characteristics of nickel–ceramic composite membranes fabricated with hydrothermal mass transfer coupled electroless plating baths. Deposition of nickel on a ceramic membrane support with an average pore size of 275 nm was considered to study the effect of autogenous pressure under hydrothermal conditions and sonication coupled hydrothermal conditions on the process as well as membrane characteristics. Bath conversion, plating efficiency, average film thickness and percent pore densification (PPD) were studied. Parametric investigations were carried out for wide range of initial nickel sulfate concentration (0.04–0.16 mol/L) in the solution at a higher loading ratio (393 cm 2/L). An interesting observation from this study was that the autogenous pressure together with ultrasound provided the best performance characteristics of electroless plating. The optimal performance characteristics refer to 81.87% conversion, 84.19% plating efficiency, 99.92% PPD for a nickel composite membrane with film thickness of 37 μm prepared using 0.16 mol/L of nickel solution metal concentration. The microfiltration study on oil-in-water emulsions inferred that the membrane fabricated with HTSO coupling and C i = 0.04 mol/L gave a rejection of 90.13% and membrane permeability of 0.11 × 10 − 10 m 3.m − 2 .s − 1 .Pa − 1 .

A novel surface activation method for Ni/Au electroless plating of acrylonitrile–butadiene–styrene

Direct electroless metallization on acrylonitrile–butadiene–styrene (ABS) plastic with Pd-free activation method could reduce the cost of production. A novel surface activation method with the immobilization of Ni(0) nanoparticles by chitosan (CTS) film on ABS and then the deposition of Ni and Au on ABS were investigated in this paper. X-ray photoelectron spectroscopy (XPS), fourier transform infrared (FTIR) spectra and scanning electron microscopy (SEM) data revealed the related interfacial reaction mechanism in activation process. The Ni(0) nanoparticles immobilized by the CTS films were effective auto-catalysts in the nickel electroless plating process. The formations of Ni plating layers at different deposition time were observed by SEM. The x-ray diffraction (XRD) patterns revealed the Ni layer at 30 min was in an amorphous phase. Au was successfully plated on the Ni layers in a new, stable non-cyanide Au electroless plating bath with different reducing agents. The chemical compositions of Ni/Au layers were analyzed by inductive couple plasmas (ICP) and ion chromatography (IC) measurements. Inorganic element (P or S) from reducing agents made the surface morphology of Au layers different in SEM images. However, they did not change the Au crystallization phase at all based on XRD patterns.

Effect of Ultrasound on the Performance of Nickel Hydrazine Electroless Plating Baths

This article addresses the relationship between morphology of metallic skin layer and process parameters of hydrazine-based electroless plating baths during the fabrication of nickel-ceramic microfiltration membranes. While process performance was evaluated in terms of overall conversion and metal plating efficiency, the film morphology was characterized in terms of average metal film thickness, pore size, and percent pore densification. Sonication was considered as an additional degree of freedom to the conventional electroless plating process. Process parameters varied include initial nickel solution concentration (0.04–0.16 mol/L), loading ratio (196 and 393 cm2/L), and relevant mass transfer coupling (sonication). It was observed that sonication assisted electroless plating provided the best combination of both process as well as performance characteristics in comparison with the base case and membrane stirred cases. Ultrasound was found to enhance the selective conversion by more than 50% compared to the other cases. About 50–100% excess nickel plating rate was evaluated for the sonication assisted case due to which the membranes with pore size as low as 11 nm were achieved.

Manufacture of Nickel-Ceramic Composite Membranes in Agitated Electroless Plating Baths

Nickel hydrazine electroless plating baths with membrane stirring as a mass transfer enhancement is considered to evaluate the membrane morphological dependence on metal solution concentration, loading ratio (membrane area per unit volume of plating solution), and stirrer speed. Inexpensive sintered ceramic supports with an average pore size of 275 nm were used for all experimental investigations. Other parametric investigations include conversion and plating efficiency. It was observed that the loading ratio significantly influenced metal film thickness but not the nominal pore size of the membranes. On the other hand, effect of stirrer speed is significant for solutions with 0.04 mol/L metal solution concentrations, moderate for solutions with 0.08 mol/L solution concentration, and insignificant for 0.16 mol/L concentration. Based on several experimental investigations, it is inferred that the optimal choice of the agitated plating process are 0.08 mol/L initial nickel solution concentration, 393 cm2/L of loading ratio, and 100 rpm stirrer speed.

Electroless Deposition of Ru Films Via an Oxidative-Reductive Mechanism

An electroless Ru plating bath is prepared by mixing Ru precursor (K2RuCl5·xH2O), oxidizer (NaClO), stabilizer (NaOH), and reducing agent (NaNO2) simultaneously in deionized water at a molar ratio of 1:1:20:10. Instead of conventional direct reduction route, the RuCl52− experiences an oxidative-reductive sequence to form metallic Ru on an activated Si substrate. Spectra from ultraviolet-visible and X-ray absorption spectroscopy indicate that the RuCl52− is oxidized to form RuO4 initially, followed by a slight reduction becoming RuO42−. The RuO42− solution is relatively stable and is able to undergo further reduction to render metallic Ru via heterogeneous nucleation and growth. Images from scanning electron microscope demonstrate a solid film of 100 nm with scattered protrusions and cavities after 120 min plating time. Analysis from atomic force microscope determines its surface roughness of 7.8 nm. From X-ray diffraction patterns, the as-deposited film reveals an amorphous structure but turns crystalline after Ar annealing at 400°C for 2 h. Curve-fitting of Ru 3p3/2 signal from X-ray photoelectron spectroscopy suggests a film composition of 92.49 atom % Ru and 7.51 atom % RuO2. The electroless Ru plating bath exhibits impressive life time (137 h) and negligible homogeneous precipitation without involving surfactants and unnecessary chemical additives.

Electroless plating of rhenium–nickel alloys

In this study, rhenium–nickel (Re–Ni) films were formed by electroless deposition on conductive (Cu) and non-conductive (SiO 2) substrates. Different bath compositions were evaluated, aiming to achieve high Re-content. Both sodium hypophosphite and dimethylamine-borane were used as reducing agents. Films containing up to 75 at% Re were obtained. The influence of nickel concentration in the solution on alloy composition, deposition rate and surface morphology were determined. It is shown that Ni 2+ acts as a catalyst for the in situ reduction of the perrhenate ion, in a manner similar to what was proposed for electroplating of the same alloy. The rate of electroless plating is similar to that found in electroplating at an applied current density of 50 mA cm −2. While pure Re cannot be deposited from our electroless plating baths, the addition of even a very small amount of Ni 2+ ions (0.25 mM) is enough to start the induced codeposition of Re. Proper selection of the bath composition can lead to fine control of the alloy thickness and its Re-content, thus making it potentially attractive for thin barrier layers.

Effect of surface roughness and mass transfer enhancement on the performance characteristics of nickel-hypophosphite electroless plating baths for metal–ceramic composite membrane fabrication

Mass transfer enhanced electroless plating is a relatively new concept in the field of metal–ceramic composite membrane fabrication. In this article, we present the effect of substrate surface roughness along with various mass transfer enhancement techniques such as solution stirring, membrane stirring and sonication on metal conversion, plating efficiency, thickness, and percent pore densification using electroless plating of nickel on a porous disk shaped ceramic support with a nominal pore size of 700 nm. The plating characteristics were investigated for three different roughness values, stirrer speeds (0–300 rpm) and a loading ratio (defined as membrane area per unit volume of plating solution) value of 196 cm 2/L. It was evaluated that stirring as well as sonication had a profound effect on sodium hypophosphite based electroless nickel baths. This led to a reduction in average membrane pore size by 100 nm for stirring and 130 nm for sonication when compared to the base case. Surface roughness was observed to influence the metal deposition characteristics for base case without mass transfer enhancement. Sonication, irrespective of surface roughness, provided the maximum values of selective conversion, densification and membrane thickness along with acceptable values of plating efficiency.

Combinatorial performance characteristics of agitated nickel hypophosphite electroless plating baths

In this article, we present the combinatorial performance characteristics of agitated sodium hypophosphite electroless plating baths. Various performance characteristics assessed include bath conversion, plating efficiency, selective conversion, metal film thickness, average pore size, effective porosity and percent pore densification (PPD). Bath agitation was brought forward by rotating a symmetric disk shaped porous ceramic substrate with a nominal pore size of 275 nm. The plating characteristics were investigated for wide range of nickel solution concentrations (0.04–0.16 mol/L), stirrer speed (0–200 rpm) and for two different loading ratios (defined as substrate surface area per unit volume of plating solution) values (196 and 393 cm 2/L). It was evaluated that stirring had a profound effect on sodium hypophosphite based electroless nickel baths, which are characterized with lower conversions (10–39%) and higher plating efficiencies (62–99%) without stirring phenomena. The stirred plating baths provided about 20–56% excess nickel plating rate when compared to the baths without stirring. This lead to a reduction in average membrane pore size by 20–42 nm and an enhancement in percent pore densification values by about 2–7%. Further, higher concentrations as high as 0.16 mol/L have been found to be detrimental to reduce the metal plating efficiency to lower values (42%). Observed data trends confirm upon the urgent need to identify suitable mass transfer enhancement techniques that target enhancement in selective conversion while providing good values of plating efficiency and PPD.

Nickel-ceramic composite membranes: Optimization of hydrazine based electroless plating process parameters

Based on the experimental investigation, this article addresses optimization of nickel hydrazine electroless plating process parameters for the fabrication of mesoporous nickel-ceramic composite membranes. An inexpensive sintered ceramic support with an average pore size of 275nm was used for all the experiments. Parametric optimization was experimentally investigated for a wide range of nickel solution concentrations (0.04–0.16mol/L) and loading ratios (196–393cm2/L). Process parameters such as conversion, plating efficiency and membrane morphological parameters such as average thickness, pore size and effective porosity were evaluated. Based on these evaluated parameters, the optimal process parameters have been evaluated as 0.12mol/L and 393cm2/L respectively. In general, it was also observed that hydrazine electroless plating baths are efficient from both processes as well as membrane perspective as they have been observed to provide a maximum selective conversion and PPD of 38% and 98.8% respectively.

Comparison of Bottom‐up Filling in Electroless Plating with an Addition of PEG, PPG and EPE

AbstractThe bottom‐up filling capabilities of electroless copper plating bath with an addition of additives, such as polyethylene glycol (PEG), polypropylene glycol (PPG) and triblock copolymers of PEG and PPG with ethylene oxide terminal blocks termed EPE, were investigated by the cross‐sectional scanning electron microscopy (SEM) observation of sub‐micrometer trenches. Though three additives had inhibition for electroless copper deposition, the suppression degrees of three additives were different. EPE‐2000 had the strongest suppression for electroless copper deposition, and the suppression of PEG‐2000 was the weakest. The bottom‐up filling capability of electroless copper was investigated in a plating bath containing different additives with the concentration of 2.0 mg/L. The cross‐sectional SEM observation indicated the trenches with the width of 280 nm and the depth of 475 nm were all completely filled by the plating bath with an addition of EPE‐2000, but the trenches were not completely filled by the plating bath with an addition of PEG‐2000 or PPG‐2000, and some voids appeared. Linear sweep voltammetry measurement indicated that three additives all inhibited the cathodic reduction reaction and the anodic oxidation reaction, and the inhibition of EPE‐2000 was the strongest among three additives, which agreed with that of the deposition rate of electroless copper. Significant differences in surface roughness of deposited copper film were observed by UV‐visible near‐infrared for different suppressors, and the bright and smooth of deposited copper film were in accordance with the inhibition of three additives.

A study of chromium-free pickling process before electroless Ni–P plating on magnesium alloys

A chromium-free pickling process of magnesium alloys in H 3PO 4 + Na 2MoO 4 solution for electroless Ni–P plating was described. The dosage of Na 2MoO 4 was established by detecting adhesion and corrosion resistance of chemical nickel coatings. Electrochemical behaviors of pickling solution of H 3PO 4 + Na 2MoO 4 and NH 4HF 2 activation solution were investigated with the open circuit potential curves and the polarization curves. The results show that the Na 2MoO 4 has strong inhibition ability. Na 2MoO 4 in H 3PO 4 solution can reduce active sites of microcathodic and microanodic zones in the corrosion cells of the substrate surface of magnesium alloys and plays an inhibition role. The activation film with some oxides and fluorides can prevent the substrate magnesium from the fierce displacement and corrosion reaction of electroless plating bath. The chemical Ni–P coating with good adhesion and corrosion resistance was obtained by the pretreatment of 200 cm 3 dm −3 85% H 3PO 4 + 5 g dm −3 Na 2MoO 4 pickling bath and activation in 200 g dm −3 NH 4HF 2 solution. This procedure of surface pretreatment before electroless nickel plating can replace the existing acid pickling containing chromium and HF activation.

Preparation and Kinetics of Wood-Based Ni-P Coating Electromagnetic Shielding Material by Ytterbium-Improved Electroless Plating

A wood-based Ni-P coating electromagnetic shielding material was prepared in an ytterbium oxide-added electroless plating bath. The kinetic model was established and confirmed to be in accord with the experiment and can be used to predict the deposition rate within a certain range. The experimental results showed that the Ni-P coating prepared with the addition of Yb2O3 were smoother, denser and brighter than that prepared without addition of Yb2O3. The deposition rate and electromagnetic shielding effectiveness of the former were 2.662mol×10-4/(cm2h) and 56.48 dB which is about 13% and 9% higher than those of the latter under the same bath compositions and operation conditions.

Effect of alumina nanoparticles as nanocomposites on morphology and corrosion resistance of electroless Ni–P coatings

Electroless Ni–P–Al2O3 nanocomposite coating was obtained by adding alumina nanoparticles to the nickel electroless plating bath. Particles of ∼74 nm in size were selected in order to study the influence of the particle incorporation to the coating properties. The composite coatings were heat treated at 200, 400 and 600°C for 1 h (60 min) and structural changes were evaluated by X‐ray diffraction (XRD) analysis. Surface morphology of composite deposits has been investigated by scanning electron microscopy (SEM). Electrochemical impedance spectroscopy and potentiodynamic polarisation method have been used to evaluate the coating performance before and after heat treatment. The Ni–P electroless coating contains 9·18 wt‐%P while the alumina composite coating contains 8·30 wt‐%P. The composite coatings, which contains alumina nanoparticles, exhibit better properties of hardness and corrosion resistance.

Copper Electroless Bonding of Dome-Shaped Pillars for Chip-to-Package Interconnect

Electroless plating was used to achieve compliant bonding between two components with electroplated copper pillars for chip-to-package interconnects. The geometry of the pillars was modified from flat-topped to round, dome-shaped structures by addition of a leveler to the electroplating bath used to form the pillars. The effect of the dome-shaped structure on the electroless joining process was studied using different electroless plating baths. The baths contained a surfactant and used forced convection during electroplating. Void trapping was observed in the electroless region between the domed, electroplated pillars, however, the size of the voids is smaller than previously reported with flat-topped pillars. The surfactant, Triton X-100 was found to decrease void formation at the electroless joint.

Direct Formation of Patterned Nickel Film on Polymer Using Selective Electroless Deposition and Electroless Anisotropic Growth Plating

Plating on plastic technology is widely applied in electronics-related fields. Conventionally, good adhesion strength between metal and resin has been obtained from the anchoring effect of a roughened surface. However, as the frequency increases, detrimental influences arise from the skin effect in the high-speed transmission. Therefore, the interface of the conductor and substrate should be as smooth as possible. A metal film with high adhesion strength and surface smoothness can be formed by surface modification with UV irradiation. This led us to the examination of selective deposition with the UV irradiation technique. In addition, anisotropic growth has been obtained by the addition of inhibitors to the electroless plating bath where pattern formation was possible without using resist by controlling the horizontal growth during plating. Anisotropic growth on selectively UV-irradiated regions has been obtained by the addition of inhibitors to the electroless nickel-plating solution and in this study, direct nickel-pattern formation was accomplished without using resist by controlling the plating growth in the horizontal direction in a technique combining selective deposition and anisotropic growth.

Fabrication of various electroless Ni–P alloy/multiwalled carbon nanotube composite films on an acrylonitrile butadiene styrene resin

Ni–P alloy/multiwalled carbon nanotube (MWCNT) composite films were fabricated on acrylonitrile butadiene styrene (ABS) resin by electroless plating and their microstructures, adhesion strengths, and friction properties were investigated. Various types of MWCNTs were used. In addition, various electroless plating baths were prepared to form Ni–P alloy matrices with various phosphorus contents. To enhance the adhesion strength, the ABS resin substrate was subjected to roughening treatment. The microstructures of the composite films were examined by scanning electron microscopy and X-ray diffraction. Their adhesion strengths were measured by tensile tests. The friction properties of the composite films were investigated using the ball-on-plate method. Ni–P alloy/MWCNT composite films containing various types of MWCNTs and with Ni–P alloy matrices having various phosphorus contents were fabricated on the ABS resin substrates by electroless deposition. The adhesion strength between the Ni–P alloy/MWCNT composite films and the ABS resin substrate was more than 1300 N cm − 2 . The Ni–P alloy/MWCNT composite films had considerably lower friction coefficients than the Ni–P alloy films. The friction coefficients of the composite films were significantly affected by the type of MWCNTs used.

Site-Selective Electroless Nickel Plating on Patterned Thin Films of Macromolecular Metal Complexes

We demonstrate a simple route to depositing nickel layer patterns using photocross-linked polymer thin films containing palladium catalysts, which can be used as adhesive interlayers for fabrication of nickel patterns on glass and plastic substrates. Electroless nickel patterns can be obtained in three steps: (i) the pattern formation of partially quaterized poly(vinyl pyridine) by UV irradiation, (ii) the formation of macromolecular metal complex with palladium, and (iii) the nickel metallization using electroless plating bath. Metallization is site-selective and allows for a high resolution. And the resulting nickel layered structure shows good adhesion with glass and plastic substrates. The direct patterning of metallic layers onto insulating substrates indicates a great potential for fabricating micro/nano devices.