Electroless Plating Bath Research Articles

Effects of Bath Composition on the Adhesion Characteristics of Electroless Cu Layers on Epoxy-Based Polymer Substrates

We investigated the effects of bath composition on the adhesion characteristics of electroless Cu on epoxy-based polymer substrates. The Cu layer was electroless-plated on the epoxy-based polymer substrate via four electroless-plating baths. A Cu layer was electroplated, which was then cured at 150°C for 1 h. The adhesion was evaluated using a 90° peel test. The size of the nodules and grains found in the electroless Cu layers decreased with increasing electrolyte concentration in the plating bath, resulting in increased hardness. At the highest electrolyte concentration, the electroless Cu layer exhibited high porosity in conjunction with the least coverage. The porosity of the electroless Cu layer decreased and the coverage improved with decreasing electrolyte concentration; however, a non-uniform layer formed at the lowest electrolyte concentration. The peel strength increased initially with the bath concentration, and then decreased upon further increase in bath concentration. The variation of the peel strength was related to the coverage and the hardness of the electroless Cu layer. We utilized a two-step electroless-plating method (the first layer with better coverage and second layer with larger ductility). The peel strength of the optimized double-layered electroless Cu layer was higher than that of the single-layered electroless Cu layer.

Highly Adhesive Displacement Plated Cu Seed on Cowb Barrier for All-Wet TSV Fill Process

Fabrication of TSV is one of key technology for 3D-ICs. For realizing conformal barrier layers against Cu diffusion with a low temperature process is important to achieve highly reliable TSVs. Electroless plated metals such as Co-alloy and Ni-alloy are considered to have a high potential as a barrier layer. We succeeded in conformal electroless plating of CoWB on SiO2, using DMAB as a reducing agent after forming self-assembled monolayer (SAM) of silane coupling agent (APTES) on SiO2 [1-2], assisted with Pd nanoparticle catalyst. The adhesion strength of CoWB decreased with an increase in film thickness [1], which might be due to an increase in film intrinsic stress. Electroless Cu plated film using reducing agent on the CoWB layer showed a very poor adhesion property. In this study, we studied to form electroless Cu seed layer with a high adhesion strength by displacement reaction without reducing agent, and furthermore examined the barrier and seed formation into a high aspect ratio TSVs. The electroless CoWB plating bath composed of cobalt sulfate and tungstic acid as a metal salt, citric acid as a complex agent, DMAB as a reduction agent. The Cu displacement plating bath composed of sulfuric acid and copper sulfate, and its pH was 3.5. The adhesion strength was evaluated by the stud-pull test. Table 1 shows the adhesion strengths of various films such as CoWB (70nm) only, displacement plated Cu on CoWB, electroless Cu plated with reducing agent (glyoxylic acid) on CoWB. The adhesion strength of the 70 nm CoWB film was 20MPa. That of displacement plated Cu/CoWB was 50 MPa. The adhesion strength of electroless plated Cu with reducing agent was very poor. We succeeded in obtaining a high adhesion strength by Cu displacement plating. Figure 1 shows the displacement plated Cu seed layer on 80 nm electroless CoWB layer in TSV. The diameter is 3 μm and aspect ratio is 10. Displacement plated Cu film was formed almost uniformly from top to bottom of TSV. The sidewall and bottom coverages of Cu/CoWB bilayer in TSV was 70 to 80 % against that of the flat area. At the bottom of TSV, Cu(40nm)/CoWB(40nm) bilayer was formed succesfully without delamination. We succeeded in the formation of highly adhesive electroless plated Cu seed layer on CoWB layer. Further study of complete fill of TSV with ECP Cu is in progress.

Ni–P electroless deposition directly induced by sodium borohydride at interconnected pores of poly (ether ether ketone)/multiwalled carbon nanotubes composites surface

In this study, an interpenetrated anchorage connection between Ni–P coating and poly (ether ether ketone)/multiwalled carbon nanotubes (PEEK/MWCNT) composites was realized by electroless deposition process. The absorbed NaBH4 reduced the Ni2+ ions in electroless plating bath to Ni0 species and simultaneously the Ni0 acted as catalyst initiating the electroless deposition. SEM, EDS, XPS, and XRD were used to characterize each step of the process. The thickness and weight of the coating both increased over time linearly. The coating rate was 4.68μmh−1 and there was no induction period in the electroless process. After electroless deposition for 20min, the sheet resistance of the samples dropped to 0.78Ω/square. And the volume resistivity in the direction of thickness dropped sharply from 1.0×105Ωm to 1.0Ωm after N-P deposition for 10min. An interpenetrating anchorage effect was formed between the Ni–P coating and the PEEK/MWCNT composite surface, which contributed to a good adhesion (the highest 5 B scale according to ASTM D3359 and 5.7MPa by pull off test).

Effect of Pd concentration on electroless dense Pd-PSS membrane fabrication

This work addresses the effect of palladium solution concentration on combinatorial plating characteristics of surfactant and sonication coupled electroless plating baths for the fabrication of dense palladium films on porous stainless steel substrates. All plating experiments were carried out using palladium solution concentration of 0·005 and 0·01M plating baths with cetyltrimethylammonium bromide surfactant at four critical micelle concentrations and loading ratio of 203 cm2 L−1. The evaluated combinatorial plating characteristics include selective conversion, plating efficiency, plating rate, Pd film thickness and per cent pore densification. The enhancement in palladium solution concentration was found to be insignificant to provide better combinatorial plating characteristics, and the plating bath consisting of 0·005M Pd solution concentration has provided 99·98% per cent pore densification with a Pd film thickness of 8·81 μm and plating efficiency of 80·69%.

Rate enhanced electroless fabrication of nickel ceramic composite membranes

Elaborating upon the role of surfactant and sonication, this work addresses the combinatorial plating characteristics for the fabrication of nickel ceramic composite membranes. Specific novelty corresponds to controlled addition of hydrazine hydrate as a reducing agent to nickel electroless plating bath. The experimental investigations evaluated the optimality of solution concentrations of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulphate surfactants during coupled sonication and surfactant based electroless plating. Among both surfactants, CTAB surfactant with a solution concentration of 4 CMC provided maximum combinations of pore densification (73·4%), metal film thickness (8·4 μm) and plating efficiency (89·9%). In all, it was observed that with CTAB surfactant the pore densification and plating efficiencies increased with increasing surfactant solution concentration from 1–4 CMC and were maximum at 4 CMC which drastically decreased at 6 CMC respectively probably due to surfactant adsorption on the substrate surface.

Effects of bath composition on the morphology of electroless-plated Cu electrodes for hetero-junctions with intrinsic thin layer solar cell

The morphology of an electroless-plated Cu electrode was investigated as a function of bath composition. To enhance the selectivity of Cu electrode deposition on the surface of an indium tin oxide layer, a Ti/Cu multi-layer was deposited as a Cu electrode seed layer by physical vapor deposition, and then electroless plating was performed using various complexing agents and a surfactant. The degree of selectivity was effectively influenced by the type of complexing agent. The electroless plating solution containing N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine (THPED) as complexing agent showed excellent selective growth of the Cu electrode as compared to the solution containing ethylenediaminetetraacetic acid. Even though THPED led to better selective growth of the electroless-plated Cu electrode, the aspect ratio of electrode lateral growth was about 2.7 times that of vertical growth. By adding a nonionic surfactant, the ratio between vertical growth rate and lateral growth rate was improved about 4.6 times. The Cu–THPED electroless plating with nonionic surfactant provided a drastic decrease in lateral growth rate, compared with the Cu–THPED electroless plating bath excluding nonionic surfactant. The Cu–THPED solution including nonionic surfactant is a promising composition of electroless plating solution for the clear selective plating of Cu electrodes on hetero-junctions with intrinsic thin layer solar cells.

Autocatalytic deposition of copper coating on poly (ether ether ketone)/multiwalled carbon nanotubes composites via a palladium-free and simplified electroless process

Poly (ether ether ketone)/multiwalled carbon nanotubes composites were metallized by electroless copper plating. The process was based on NaBH4 reducing the Cu2+ ions in electroless plating bath to Cu0 species on the wall of micropores of the swelled composites and simultaneously the Cu0 acted as catalyst initiating the autocatalytic deposition of copper. A dense copper coating was formed. The sheet resistance decreased with increasing the electroless plating time. The adhesion of the copper coating reached the highest 5 B scale according to ASTM D3359. And the electroless process avoided using noble metal Pd as catalyst.

Stabilization of an Electroless Platinum Plating Bath Using S-Bearing Additives

Moderation of an electroless platinum plating bath by thiol, thioether, disulfide, thiocarbonyl, thiosulfate and sulfide compounds was investigated. The inhibitory effect of stabilizers on catalyzed anodic oxidation of the reducing agent used, sodium borohydride, on platinum surfaces was electrochemically characterized by linear sweep voltammetry. Catalytic oxidation inhibition was found to correlate with chemisorption dynamics to catalytic sites on the platinum surface and the steric structure of the sulfur in the compound. Evaluation of the compounds as moderators in electroless plating revealed that the deposition rate and bath stability correlated with the sodium borohydride oxidation inhibition character. Tiopronin had a moderate inhibitory effect on catalytic sodium borohydride oxidation and functioned as an effective stabilizer in the electroless platinum plating bath. Based on the correlation, an inhibitor concentration optimization method using anodic polarization curves was established. The dynamics of the electroless plating reaction concurred with electrochemical analysis and was comprehensively described by the mixed potential theory. Using cyclic voltammetry, the deposits had similar electrochemical characteristic to that of pure polycrystalline platinum, although less than 0.5 wt% sulfur inclusion was confirmed by elemental analysis.

A study on the uniformity of silver coatings on nanometer SnO<SUB align="right">2 particles through chemical plating

The dispersion of AgSnO2 contact materials could be improved by using silver coated SnO2 particles as the starting powders in the powder metallurgy (P/M) process. For that purpose, nanosized SnO2 particles covered with silver coatings were prepared through chemical plating in this study, and the stability of the chemical plating solution and the uniformity of silver coatings were studied. The results showed that by dropping reduction fluids into ammoniacal silver solution, the self-decomposition of the electroless plating bath were completely inhibited, and by adjusting the dropping speed, the uniformity of silver coatings on SnO2 particles could be improved relatively.

2-Mercaptobenzimidazole, 2-Mercaptobenzothiazole, and Thioglycolic Acid in an Electroless Nickel-Plating Bath

The use of three different materials, 2-mercaptobenzimidazole, 2-mercaptobenzothiazole, and thioglycolic acid, was investigated to improve the performance of electroless nickel-plating baths. By changing the concentrations of these materials, sample plates were coated. Optical microscope images were obtained by selecting representative coated plates. From the results of the investigations, the effects of these materials on electroless nickel plating were observed, and the most appropriate amounts of these materials for nickel plating were determined. Moreover, the nickel plating speed observed with the bath solution containing 2-mercaptobenzimidazole, 2-mercaptobenzothiazole, and thioglycolic acid is higher than that in the case of traditional electroless plating baths, but the nickel consumption amount in the former case is lower. In order to minimize the waste water generated from electroless nickel-plating baths, we determined the lowest amounts of the chemicals that can be used for the concentrations reported in the literature.

A novel method of reducing agent contacting pattern for metal ceramic composite membrane fabrication

Deliberating upon process modifications for surfactant induced electroless plating (SIEP), this article highlights the plating bath performance characteristics for two distinct reducing agent contacting modes (bulk and drop wise). Eventually, the effect of reducing agent concentration (50, 100, 200% excess) suitable for electroless plating bath for a nickel concentration of 0.08mol/L was investigated. Finally, the compatibility of variation in nickel concentration (0.08–0.24mol/L) with respect to variation in reducing agent concentration (50, 100, 200% excess) was investigated. LPSA, BET, FTIR, XRD, FESEM and nitrogen permeation experiments were used for surface and physical characterization. It was observed that for the bulk addition of reducing agent, the PPD values were 84.5% which increased to 89.3% for dropwise addition case. Thus the optimal combinations of SIEP process parameters were identified as 0.08mol/L of nickel metal solution concentration with 100% excess drop-wise reducing agent. These conditions provided a plating rate of 5.5×10−5mol/m2s, PPD of 89.3% and a metal film thickness of 15.7μm respectively after 12h of sequential plating.

Combinatorial Electroless Plating Characteristics for Dense Pd–PSS Composite Membrane Fabrication

Emphasizing upon a process–product combinatorial perspective, this article addresses the role of rate enhanced electroless plating baths for the fabrication of dense Pd/porous stainless steel composite membranes. Adopting phasewise contacting pattern of the reducing agent, plating experiments have been carried out with variegated Pd electroless plating baths at a palladium solution concentration of 0.005 M with a loading ratio of 203 cm2/L for the plating time of 2–6 h. Amongst all processes, surfactant and sonication coupled electroless plating baths provided optimal combinations of combinatorial plating process characteristics for dense Pd composite membrane fabrication.

Effect of novel ternary ligand system on acidic electroless Ni-P plating on AZ91D magnesium alloy

The electroless Ni-P coatings on AZ91D magnesium alloy substrate were prepared using the acidic hypophosphite-reduced electroless nickel bath containing the novel ternary ligand system. The results indicate that the deposition rate varies with the ternary ligand concentration in plating solution. The structural and morphological characteristics of the coatings were analyzed by XRD and SEM. The anticorrosion properties of the Ni-P coatings were evaluated in 3.5% NaCl solution by electrochemical impedance and potentiodynamic polarization methods. The amount of ternary ligands in electroless plating bath has an significant effect on the surface morphology and structure of Ni-P coatings. The decrease of crystallization temperature and increase of crystallization heat of all the deposits with an increase in ternary ligand concentration are found by DSC measurements. The coating obtained with 0.035 mol/L ternary ligand additive in plating bath can offer a better surface homogeneity and improve corrosion resistance.

Electrospun sulfur fibers as a template for micrometer-sized copper sulfide tubes

Micrometer-sized copper sulfide (CuS) tubes have been prepared by combining melt-electrospinning method using elemental sulfur and electroless copper plating technique. Melt-electrospinning of elemental sulfur provided a yellow non-woven sheet with micrometer-sized sulfur fibers. The color of the sheet changed to black by immersing the sheet into an electroless copper plating bath. SEM observation and XRD measurement of the blackened sheet indicated that the deposition layer on the sulfur fibers is CuS. Removing of the template fibers by dipping into a carbon disulfide bath provided the micrometer-sized CuS tubes.

Formation and Structural Characterization of Electroless Ni-B-P Ternary Alloy Coatings

The aim of the present investigation is to study the formation of electroless Ni-B-P alloy coatings and structural and morphological characterization of various coatings with different boron and phosphorous content. An alkaline plating bath with nickel chloride hexahydrate as the source of nickel ions and sodium borohydride and sodium hypophosphite as reducing agents were used for the formation of electroless Ni-B-P alloy coatings. The influence of changes in the concentrations of the reducing agents in the electroless plating bath on the chemical composition, structural and morphological characteristics of the coatings were studied. Scanning electron microscopic studies revealed that the surface morphology of Ni-B-P alloy coatings changed from corn cob-like structure to cauliflower-like structure with increasing borohydride concentration in electroless plating bath, whereas increase in hypophosphite concentration favoured sideway growth, thereby decreased the surface roughness of the Ni-B-P alloy coatings. The peak broadening in the X-Ray Diffraction profiles indicates the large reduction in the crystallite size of the electroless Ni-B-P alloy coatings with increasing boron content in the coating (i.e. for higher borohydride concentration in the plating bath).

Nickel and copper conductive patterns fabricated by reactive inkjet printing combined with electroless plating

A simple, low-cost and easy scale-up technique for fabrication of conductive interconnects for flexible electronic devices is presented. A thin seed layer of nickel or copper was formed on the surface of PEN substrate via reactive inkjet printing of metal salt and reducing agent instead of traditional seed layers such as palladium nanoparticles and palladium or silver salts. For deposition of a uniform metal coating a polymer substrate patterned with the seed layer was immersed in an electroless plating bath. The electrical resistivity of deposited nickel–phosphorus and copper layers was 3.8±0.2mΩ·cm and 29±2µΩ·cm, respectively. The obtained structures possess excellent adhesion to polymeric substrates and reveal only slight decrease of conductivity after 20,000 bending cycles.

Fe-based surface activator for electroless nickel deposition on polyester: Application to electromagnetic shielding

The activation of the polyester (PET) by the solution of ferrous compound was examined as a palladium-free activation process. The principle of the process is based on the adsorption of Fe2+ on the substrate surface, reduction of Fe2+ into elementary substance Fe0, which is served as the catalyst for electroless plating. The Ni/PET composite can be obtained in three steps, namely: (i) the grafting of amino groups onto PET surface, (ii) the iron Fe0 seeding of the PET surface, and (iii) the nickel metallization using electroless plating bath. XPS, XRD, and AFM were used to characterize each step of the process. Adhesion of the nickel coating on PET was evaluated by a Scotch® tape test. Corrosive resistance of the Ni/PET composite was examined by a salty solution. The electromagnetic shielding effectiveness of the Ni/PET composite was more than 50dB at frequency ranging from 100 to 1000MHz. Comparing Fe2+ with Ni2+ as the metallic resource of the catalyst for electroless plating via the same process: the former resulting in a quicker nickel deposition rate and better nickel adhesion performance.

Role of electroless nickel diffusion barrier on the combinatorial plating characteristics of dense Pd/Ni/PSS composite membranes

Abstract This work addresses the combinatorial plating characteristics of dense Pd/Ni/porous stainless steel (PSS) composite membranes in comparison with Pd/PSS membranes. While Pd/PSS membranes were fabricated using 0.1 μm nominal pore size PSS supports, Pd/Ni/PSS membranes were fabricated using 0.5 and 0.1 μm nominal pore size PSS supports. Both Ni and Pd films were deposited using an identified novel electroless plating process that characterizes the optimal utilization of surfactant, sonication and reducing agent contacting pattern in Pd electroless plating baths. It was observed that the combinatorial plating characteristics for Pd/Ni/PSS membranes were significantly different and poorer in comparison with those obtained for the Pd/PSS membranes. In summary, it has been inferred that the introduction of nickel interdiffusion barrier was not fruitful to reduce the critical thickness of dense Pd film without jeopardizing upon the pore densification.

Factors Affecting the Morphology of Pb-Based Glass Frit Coated with Ag Material Prepared by Electroless Silver Plating

Pb-based glass frit coated with nanosilver material for Si solar cell applications has been directly prepared by electroless silver plating. Activation of the glass frit was accomplished by using glycol, with the aim of reducing the silver ions to elemental silver on the surface of the glass frit. Electroless silver plating onto the glass frit was successfully realized using two kinds of electroless plating bath. However, the morphology of the composite powder greatly affected the modality, sheet resistance, series resistance, and photoelectric conversion efficiency of the conducting silver films. We found that the activation temperature affected the number and distribution of silver nanoparticles. Meanwhile, the average grain size of the silver particles and the silver content in the Pb-based glass frit coated with Ag material could be controlled by adjusting the pH value and loading capacity, respectively, during plating.

Effect of Surfactant Concentration and Loading Ratio on the Electroless Plating Characteristics of Dense Pd Composite Membranes

This article presents the effects of the concentration and loading ratios of a cationic surfactant (CTAB) on the performance characteristics of sonication-induced electroless plating baths for the fabrication of dense palladium composite membranes. The plating experiments were conducted with dropwise addition of reducing agent at loading ratios of 203 and 407 cm2/L, a palladium solution concentration of 0.005 M, and surfactant solution concentrations of 1–4 CMC. A plating bath consisting of 0.005 M Pd with a surfactant concentration of 2 CMC at a loading ratio of 203 cm2/L provided a 100% dense palladium composite membrane after 8 h of sequential plating with a Pd film thickness of 11.16 μm and a plating efficiency of 96%. The identified process can provide dense Pd/PSS composite membranes at a fabrication cost of 13.27 $/cm2, which is 60% more cost-effective than the best-known SIEP process.