Optimization of process conditions for electroless copper plating on polyester fabric

Dimethylamine borane (DMAB) was used in electroless copper plating on liquid crystal polymer (LCP) films. An orthogonal test was applied to optimize the plating condition. With Cu film resistivity as the evaluation index, the optimum plating condition is: 10 g/L of CuSO4 ⋅ 5H2O, 14 g/L of EDTA‐2Na, 6 g/L of DMAB, 9.5 of pH value and 50 °C. As pH value increases, the Cu film resistivity decreases and the depo‐ sition rate increases. As temperature increases, the Cu film resistivity decreases first and then increases with a minimum at 50 °C while the deposition rate increases first and then decreases with a maximum at 50 °C. The decreased Cu film resistivity can be attributed to the occurrence of CuO. The adhesive strength of copper layer to LCP film is constant at pH values lower than 8.5 and decreases slightly with the increase in pH value. As temperature increases, the adhesive strength decreases slightly. The decreased adhesive strength with both pH and temperature may be a result of an increased corrosion attack from the bath to the surface of LCP films. Low Cu film resistivity and high deposition rate as well as high adhesive strength can be obtained using DMAB reducing agent.

An impedance study of the electrochemical double layer of copper in an electroless copper plating bath was performed. Of the bath components (formaldehyde, ethylenediamine‐tetraacetic acid (EDTA), CuEDTA2−, NaOH, Na2SO4, and NaHCOO) only the influence of hydroxide on the double layer is visible from capacitance data. The estimated surface coverage of hydroxide at the mixed potential of the electroless plating process is about 10%. On copper single crystal surfaces the OH−‐adsorption shows specific characteristics. Due to a surface reconstruction these characteristics, however, disappear with time after the immersion of the electrode. During the deposition process high electrode capacitances are measured (200–500 μF/cm2). They are mainly caused by a surface roughness on the microscopic scale. When the deposition process is terminated, the surface relaxes within about 10 minutes. The addition of cyanide or Gafac (a mixture of organic esters of phosphoric acid) to the electroless plating bath markedly influences the capacitance data. However, always a correlation between the deposition rate and the electrode capacitance is observed. If, on the other hand, at potentiostatic cupric ion reduction formaldehyde in the plating bath is substituted by ethylenediamine, which also catalyzes the CuEDTA2−‐reduction, the capacitance values decrease with increasing deposition current. Presumably, in the first case the nucleation rate dominates the deposit growth, while in the second case the opposite is true.

Area-selective copper deposition on screen printed Ag pattern/anodized Al/Al substrate was attempted using a neutral electroless plating processes for printed circuit boards (PCBs), according to a range of variation of pH 6.5-pH 8 at 70 °C. The utilized basic electroless solution consisted of copper(II) sulfate pentahydrate, sodium phosphinate monohydrate, sodium citrate tribasic dihydrate, ammonium chloride, and nickel(II) sulfate hexahydrate. The pH of the copper plating solutions was adjusted from pH 6.5 to pH 8 using NH4OH. Using electroless plating in pH 6.5 and pH 7 baths, surface damage to the anodized Al layer hardly occurred; the structure of the plated Cu-rich films was a typical fcc-Cu, but a small Ni component was co-deposited. In electroless plating at pH 8, the surface of the anodized Al layer was damaged and the Cu film was composed of a lot of Ni and P which were co-deposited with Cu. Finally, in a pH 7 bath, we can make a selectively electroless plated Cu film on a PCB without any lithography and without surface damage to the anodized Al layer.

A new activation process for electroless copper plating has been developed, which does not require the use of a palladium-based activation bath as typically employed in the plating industry. The activation bath of the new process described herein is entirely free of palladium and is based on colloidal metallic copper particles, which are nanoscopic in size. This bath can also be readily analysed and controlled. The new copper-based activation bath can be operated in such a way that colloid agglomeration and colloid oxidation are efficiently and effectively suppressed, while electroless copper plating quality and electroless copper bath stability is maintained. In addition, the new activation bath can be operated for several weeks without any detectable deterioration in electroless copper plating performance. Furthermore, acrylonitrile butadiene styrene (ABS) and FR4 coupons treated with the new copper-based colloidal activation bath can be vigorously rinsed with water for several minutes prior to immersion in the electroless copper bath without loss of plating quality. The new activation process performs comparably to an established palladium-based process operated at typical vertical equipment immersion times. Even though the electroless copper plating initiation is somewhat delayed for the new copper-based activation process, the final electroless copper deposit thicknesses are the same for both the new process and the palladium-based reference process. The adhesion of the electroless copper deposit obtained with the copper-based activation process is also similar to that obtained with the palladium-based reference activation system. Moreover, the electroless copper coverage performance of the new copper-based activation process, as determined by the backlight test, is comparable to that of the palladium-based reference process.

A colloidal hydroxide solution consisted of nickel sulfate, copper sulfate, and tartaric acid was prepared as a substitute for a palladium catalyst in nickel-phosphorus electroless plating. The colloids were adsorbed on an ABS resin substrate and then reduced chemically to produce activated sites for electroless plating. After nickel-phosphorus electroless plating, the articles were used for the evaluation of the 90°peeling strength and of the initial covering velocity with the nickel-phosphorus film during the electroless plating. Results indicated the following.(1) An ABS resin substrate treated with the colloidal solution yielded an adhesion strength for the plating film as strong as one activated by a conventional coupling of tin (2+) ions as sensitizer and palladium (2+) ions as activator for the electroless plating. The ABS resin substrate, in particulars activated using a colloidal solution of pH 7.8 consisting of 0.08mol/dm3 nickel sulfate, 0.01mol/dm3 copper sulfate and 0.04mol/dm3 tartaric acid, caused cohesive-destruction with the plated nickel-phosphorus film during the 90°peeling strength test.(2) Both copper ions and copper hydroxide in the colloidal solutions served to reduce the time for the ABS resin substrate to be covered uniformly by the nickel-phosphorus film during electroless plating. However, they tended to enhance the surface roughness.

A facile process to fabricate metal coating on PET sheet: Preparation of highly active polymer brush/Ag particle and its application in electroless copper plating

We investigated the characteristics of electroless plated Cu films on screen printed Ag/Anodized Al substrate. Cu plating was attempted using neutral electroless plating processes to minimize damage of the anodized Al substrate; this method used sodium hypophosphite instead of formaldehyde as a reducing agent. The basic electroless solution consisted of <TEX>$CuSO_4{\cdot}5H_2O$</TEX> as the main metal source, <TEX>$NaH_2PO_2{\cdot}H_2O$</TEX> as the reducing agent, <TEX>$C_6H_5Na_3O_7{\cdot}2H_2O$</TEX> and <TEX>$NH_4Cl$</TEX> as the complex agents, and <TEX>$NiSO_4{\cdot}6H_2O$</TEX> as the catalyser for the oxidation of the reducing agent, dissolved in deionized water. The pH of the Cu plating solutions was adjusted using <TEX>$NH_4OH$</TEX>. According to the variation of pH in the range of 6.5~8, the electroless plated Cu films were coated on screen printed Ag pattern/anodized Al/Al at <TEX>$70^{\circ}C$</TEX>. We investigated the surface morphology change of the Cu films using FE-SEM (Field Emission Scanning Electron Microscopy). The chemical composition of the Cu film was determined using XPS (X-ray Photoelectron Spectroscopy). The crystal structures of the Cu films were investigated using XRD (X-ray Diffraction). Using electroless plating at pH 7, the structures of the plated Cu-rich films were typical fcc-Cu; however, a slight Ni component was co-deposited. Finally, we found that the formation of Cu film plated selectively on PCB without any lithography is possible using a neutral electroless plating process.

Electroless copper plating is a vital technique for depositing uniform and conductive copper layers, particularly for fabricating copper-coated polymer microspheres used in anisotropic conductive adhesives. However, achieving high-quality coatings on polymer microspheres remains challenging due to their inherent catalytic inertness and the lack of reliable evaluation metrics. Herein, copper nanoparticles are utilized as catalytic seeds for electroless copper plating on styrene-divinylbenzene (PSDVB) microspheres via a prereduction step using ammonia borane. After tailoring the bath composition and processing conditions, the optimized PSDVB@Cu microspheres with a dense 0.047 μm thick copper layer, 50.60 wt % copper content, and a low resistivity of 6.04 × 10-6 Ω·m can be obtained. Crucially, two novel quantitative indicators, named oxidation degree and densification degree, are introduced to comprehensively assess coating quality. A clear correlation is established among the densification degree, oxidation degree, and electrical performance. Specifically, the microspheres become conductive only when the densification degree exceeds 0.2 and the oxidation degree falls below 3.0. With a densification degree above 0.4 and an oxidation degree below 1.4, the resistivity stabilizes near 10-6 Ω·m. Beyond elucidating a tunable electroless copper plating process, this work provides a quantitative framework for coating assessment, paving the way for the standardized fabrication of high-performance copper-coated microspheres in advanced electronics.

Effects of simplified pretreatment process on the morphology of W–Cu composite powder prepared by electroless plating and its sintering characterization

Selective electroless copper plating micro-coil assisted by 248 nm excimer laser

The addition of bis(3-sulphopropyl) disulphide in Cu electroless plating results in Cu superfilling. However, the deposition rate of superfilling copper plating is decreased, which hinders its application for filling Cu into via holes of ultralarge scale integrations. In the present study, the effect of triethanolamine (TEA) on the deposition rate of electroless copper plating was investigated. The deposition rates of electroless plated copper both in traditional and superfilling copper plating were accelerated with an addition of TEA, which was attributed to a decrease in reaction activation energy of a dominant reduction reaction. X-ray diffractometry and atomic force microscopy measurements indicated that with an addition of TEA, the peak intensity ratio /(111)//(200) of electroless plated Cu film was increased and the average surface roughness was decreased.

A new electroless copper plating process was studied to improve throwing power (ratio of thickness of deposited films at the center of through-hole to that of the films at the surface of the board) of high-aspect-ratio through-holes in multilayer printed circuit boards. An alternating one-side air stirring method was devised to supply adequate plating solution into through-holes. In this method, a board was put between peripheral plates via spacers. Plating solution was stirred through supplying air to one side of a narrow flow channel composed of the board and the plate by air-supplying pipes arranged at the bottom of the flow channel, while the solution in the other channel was kept static. Air was alternately supplied for each channel. This operation was expected to generate differential-pressure between the front and the back of a board, leading to supplying the solution into through-holes. Plating tests were conducted to verify the effect of this method on throwing power of the high-aspect through-holes. A plating test by applying a conventional method (both-side air stirring) was also conducted as a reference. Electroless copper plating solution was used that contained copper sulfate, formaldehyde, sodium hydroxide, ethylenediaminetetraacetic acid, dipyridyl and surfactant. Sodium sulfate, sodium formate, and sodium carbonate were also added into the solution as salts accumulated as plating time increased. The plating rate of the solution was approximately 2 to 3 μm/h. Copper sulfate, formaldehyde, and sodium hydroxide were periodically supplied by using the concentrated solution. Temperature and pH were 73 °C and 12.4. Six-mm-thick printed circuit boards with through-holes of 0.25-, 0.20-, and 0.15-mm diameter (aspect ratio: 24, 30 and 40, respectively) were used as substrates. Flow velocity of the solution was controlled by adjusting the flow rate of supplied air. Studied flow velocity was preliminary calculated by applying the Bernoulli and Hagen-Poiseuille equations on the basis of consideration that the supplying rate of reactants, particularly copper ion, needed to be higher than the consumption rate of the ion in a through-hole to improve throwing power. Plating tests revealed that throwing power indicated approximately 0.4 for the through-holes of a 24 aspect ratio in the conventional method. On the other hand, throwing power indicated nearly 1 even for through-holes of a 40 aspect ratio under the conditions in which flow velocity of the solution was more than 7 cm/s by applying our alternating one-side air stirring method. Throwing power was also found to increase as flow velocity of the solution increased at one side for any through-hole (24, 30, or 40 aspect ratio). Throwing power decreased remarkably as flow velocity of the solution decreased, implying that flow velocity of the solution significantly affected throwing power as the aspect ratio of through-hole increased. Moreover, flow velocity theoretically estimated by fluid equation reflected behavior of throwing power measured in the plating tests. Therefore, it is concluded that the alternating one-side air stirring method efficiently improves throwing power of high-aspect-ratio through-holes.

Surface modification is an effective method to improve the electrochemical property of hydrogen storage alloy. In order to investigate the influence of process factors of electroless copper (Cu) plating for AB5-type hydrogen storage alloy on Cu coating mass, a novel modeling approach, support vector regression (SVR) combined with particle swarm optimization (PSO), was proposed to construct a mathematical model for prediction of the mass changes of Cu coating over the AB5 hydrogen storage alloy surface based on three factors, including temperature, pH value and Ni2+ concentration. The modeling accuracy and reliability of the created SVR model are validated through leave-one-out cross validation (LOOCV), and compared with those of a second-order polynomial model. The results show that the predicted errors by SVR-LOOCV models are all smaller than those achieved by the second-order polynomial model. The SVR model is further applied to predict the process parameters for the maximum Cu coating mass. These studies suggest that SVR can be used as an effective methodology to assist the design of experiment, and is helpful to precisely control the coating mass via fine adjustment of the process parameters. Key words: Surface modification, electroless copper plating, hydrogen storage alloy, support vector regression, modeling and prediction.

The electroless copper plating of textiles, which have been previously printed with a catalyst, is a promising method to selectively metallise them to produce high-reliability e-textiles, sensors and wearable electronics with wide-ranging applications in high-value sectors such as healthcare, sport, and the military. In this study, polyester textiles were ink-jet printed using differing numbers of printing cycles and printing directions with a functionalised copper–silver nanoparticle catalyst, followed by electroless copper plating. The catalyst was characterised using Transmission Electron Microscopy (TEM) and Ultraviolet/Visible (UV/Vis) spectroscopy. The electroless copper coatings were characterised by copper mass gain, visual appearance and electrical resistance in addition to their morphology and the plating coverage of the fibres using Scanning Electron Microscopy (SEM). Stiffness, laundering durability and colour fastness of the textiles were also analysed using a stiffness tester and Launder Ometer, respectively. The results indicated that in order to provide a metallised pattern with the desired conductivity, stiffness and laundering durability for e-textiles, the printing design, printing direction and the number of printing cycles of the catalyst should be carefully optimised considering the textile’s structure. Achieving a highly conductive complete copper coating, together with an almost identical and sufficiently low stiffness on both sides of the textile can be considered as useful indicators to judge the suitability of the process.

The work is devoted to the study of the effect of various compounds on the stability of electroless copper plating solution containing Trilon B. as a chelating agent. The stability of electroless copper plating solutions was estimated by the accelerated method as the time before the start of intensive decomposition of the solution after the introduction of 0.15 ml of colloidal palladium activator solution heated to 75 °C in 250 ml. As stabilizers, both known, currently used, and newly selected compounds were investigated. Sulfur- and/or nitrogen-containing organic and inorganic compounds such as: sodium diethyldithiocarbamate, 2,2’–dipyridyl, thiosemicarbazide, potassium hexacyanoferrate (III), potassium hexacyanoferrate (II), thiourea, thioglycolic acid, dimethylglyoxime, potassium rhodanide in concentrations in the range of 1 - 50 μmol/l were among the first studied. It is shown that when the stabilizers are contained in the solution at the optimal concentrations set (for each compound), solutions containing sodium diethyldithiocarbamate, thioglycolic acid, thiosemicarbazide, thiourea (in descending order of stabilizing action), i.e. compounds containing a sulfur-carbon bond, have the greatest stability. With this in mind, other sulfur-containing compounds, including heterocyclic ones, were selected and studied as stabilizers: α-lipoic acid, thiamine chloride, methyl orange, nitroso-p-salt, methylene blue and SPADNS (sodium salt of 2-(psulfophenylazo)-1,8- dihydroxynaphthalene-3,6- disulfonic acids). In addition, nitrogen-containing compounds that were not previously used in electroless copper plating solutions as stabilizers were also studied: nicotine, pyridoxine, Janus Green B (8-(4-dimethylaminophenyl) diazenyl-N, N-diethyl-10-phenylphenazine-10-ium-2-amine chloride), nigrosine, however. Solutions of electroless copper plating in the presence of these compounds did not show high stability. It has been established that the most effective, comparable in effect to the stabilizers currently used, are α-lipoic acid and thiamine chloride. The advantages of the latter are their availability and low toxicity. For citation: Solopchuk M.S., Grigoryan N.S., Asnis N.A., Vagramyan T.A., Shmelkova P.O., Bardina O.I. Stabilizers of solutions of chemical copper plating. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 3. P. 100-107. DOI: 10.6060/ivkkt.20236603.6708.