Electroless Copper Plating Process Research Articles

Ultrasound-assisted fabrication of dispersed two-dimensional copper/reduced graphene oxide nanosheets nanocomposites

Graphene oxide nanosheets (GOS) were employed as template and hydrazine hydrate was used as reductant for GOS and cupric ion. Highly dispersed two-dimensional (2D) copper/reduced graphene oxide nanosheets (Cu/RGOS) nanocomposites were effectively fabricated by ultrasound-assisted electroless copper plating process. Sandwich-like 2D Cu/RGOS nanocomposites consist of uniform Cu layer on the both side of centric RGOS. The Cu layer with thickness of about 60nm exhibits almost single-crystalline with (111) preferred crystalline direction and have tight binding with RGOS. The effect of ultrasound on electroless Cu plating includes: accelerating deposition rate, enhancing interfacial bonding and preventing 2D Cu/RGOS nanocomposites from aggregating.

Electromagnetic-shielding, Wood-based Material Created Using a Novel Electroless Copper Plating Process

A copper coating was deposited on Fraxinus mandshurica veneers to create an EMI-shielding, wood-based material via a simple electroless copper plating process. The wood veneers were pretreated in a NaBH4 solution. The wood veneers treated with NaBH4 were immersed in a plating bath in which copper coating was successfully initiated. The coatings were characterized by SEM-EDS, XPS, and XRD. The metal deposition, surface resistivity, and the effectiveness of electromagnetic shielding were measured. The morphology of the coating was uniform, compact, and continuous. The grain of the wood was preserved on the plated wood veneer, which had a copper-like color. But the samples were less glossy compared to those from Pd activation. EDS, XPS, and XRD results indicated that the coating consisted of Cu0 with a crystalline structure. The surface resistivity and copper deposition were 0.399 Ω/cm2 and 31.98 g/m2 when the veneer was pretreated with a 3 g/L NaBH4 solution for 10 min and plated for 25 min at 60 °C. The plated veneers exhibited good electromagnetic shielding effectiveness of over 40 dB in frequencies ranging from 10 MHz to 1.5 GHz.

Influence of polyethylene glycol 6000 and potassium ferrocyanide on electroless copper plating at the nickel-modified surface of para-aramid fibers

Influence of polyethylene glycol 6000 (PEG6000) and potassium ferrocyanide (K4Fe(CN)6) on electroless copper plating at the nickel-modified surface of para-aramid fibers was investigated in the present work. The surface of para-aramid fibers was roughened using sodium hydride/dimethyl sulfoxide (NaH/DMSO) to guarantee successful electroless plating. Then, electroless copper plating at the nickel-modified surface of para-aramid fibers was adopted because nickel had catalytic activity during the electroless copper-plating process. Meanwhile, PEG6000 can regulate the growth rate of the crystalline grain to produce a morphology-controlled deposit and K4Fe(CN)6 is a brightener and leveling agent for deposit during electroless-plating process. Hence, both PEG6000 and K4Fe(CN)6 were selected as the additives together. On adding PEG6000 to the plating solution, the copper grains turned fine and sleek. Copper deposits became homogeneous, smooth, and compact, and the appearance of deposits changed from dark-brown to red-brown. On adding K4Fe(CN)6 into the plating solution with 4 mg/L PEG6000, the copper deposits became more compact and smoother, and the color of deposits changed from red-brown to bright copper. Correspondingly, the conductivity of deposits increased. In addition, the breaking strength of metal-deposited para-aramid fibers still remained at values up to 45 N.

Treatment of wastewater containing EDTA-Cu(II) using the combined process of interior microelectrolysis and Fenton oxidation–coagulation

Wastewater containing EDTA-Cu(II) originating from the electroless copper-plating process was treated in a combined system of interior microelectrolysis (IM) and Fenton oxidation and coagulation (FOC). The intermittent operation of an IM reactor showed that the treatment efficiencies and Fe(II) yields were much higher under lower initial pH of the wastewater, and when the raw wastewater was treated by IM for 20min, the Fe(II) yields and pH of the IM effluent were 336.1mg/L and 4.6, respectively. The proper reaction conditions for the treatment of IM effluent by the FOC process were a [H2O2]/[COD] ratio of 2.0, [Fe(II)]/[H2O2] ratio of 0.2–0.3, initial pH of 2.0–5.0, and reaction time of 60–80min; thus, the Fe(II)-rich effluent of IM was suitable for treatment during a subsequent Fenton oxidation (FO) process without Fe(II) addition or pH adjustment. Under the optimal operating parameters, 100% Cu(II) and 87.0% COD were removed by the IM–FOC process. The contributions of IM, FO and coagulation to Cu(II) removal were 97.5%, 0%, and 2.5%, respectively, and those to COD removal were 22.3%, 47.8%, and 10.9%, respectively. After treatment, the BOD5/COD ratio of wastewater was enhanced from 0 to 0.42, indicating that EDTA was effectively oxidized in the combined system.

Microwave absorption properties of fabric coated absorbing material using modified carbonyl iron power

The modified absorbing agent was prepared by depositing copper particles on carbonyl iron power (CIP) using a ultrasonic electroless copper plating method. Subsequently, a fabric coated absorbing material was fabricated on non-woven fabric coated absorbing dope containing 85 wt% modified CIP. Scanning electron microscope (SEM) and energy dispersion spectrum (EDS) were used to analyze the microstructure and components of modified CIP. Electromagnetic parameters of modified CIP and reflectivity losses of multi-layer fabric coated absorbing material were measured by a 3 cm waveguide system. The results showed that copper particles were successfully deposited on the surface of CIP. Compared with initial CIP, the values of the complex permeability and permittivity of modified CIP increased after CIP was disposed by ultrasonic electroless plating process, which resulted in a minimum reflection loss −8.43 dB with the thickness of about 2 mm in the frequency range of 8–12 GHz. Furthermore, non-woven fabric absorbing material has a reflection loss −26 dB with the matching thickness of 2.08 mm at 9.35 GHz. It was concluded that ultrasonic electroless copper plating process had great effects on increasing microwave absorption properties of CIP. Moreover, structure of non-woven fabric had a contribution to improve absorbing performance. In addition, because fabric used was light enough, monolayer non-woven fabric coated absorbing material (FCAM) had a low planar density about 0.2 kg/m 2.

Investigation of the Arc Erosion Behaviour of W-Cu Composites

In practical applications, silver-based composite materials have been used for high load bearing or high class contact materials. However, composites such as CdO-Ag and silver-based SnO2, TiO2 and ZnO are not economically feasible due to toxicity concerns and cost effectiveness. On the other hand, copper matrices are widely used for electrical contact applications in a diverse range of fields. In particular, W-Cu alloys are considered as an alternative for contact materials and arcing resistance electrodes due to the high thermal and electrical conductivity of copper and the high arc erosion resistance and low thermal expansion coefficient of tungsten. However, the contacts are vulnerable to thermal damage due to the high temperature and mass flow on the local surfaces of the contacts during the make-and-break of the contacts. In this study, particle-reinforced copper (W-Cu and TiC-Cu) composite powders were fabricated using a novel electroless copper plating process. Electrical contacts made of pure Cu and the Cu matrix powders were employed for dynamic electrode tests. The specimens were subjected to 1,000 and 10,000 arc breakings to study the effects of arc erosion on the contacts as well as their make-and-break life. Results show that the contacts made of pure Cu had the greatest loss of mass and the shortest life while the W-Cu composites preserved most of their mass; in addition, the W-Cu composites with finer W particles (1 μm) outperformed the rest of the composites.RésuméDans les applications pratiques, on a utilisé les matériaux composites à base d'argent dans les matériaux porteurs de charge élevée ou dans les matériaux de contact de qualité supérieure. Cependant, les composites tels que CdO-Ag ou SnO2, TiO2 et ZnO à base d'argent ne sont pas économiquement réalisables à cause de problèmes de toxicité et de souci d'économie. D'un autre côté, les matrices de cuivre sont largement utilisées dans les contacts électriques dans une grande gamme de champs d'application. En particulier, les alliages de W-Cu sont considérés comme solution de rechange pour les matériaux de contact et pour les électrodes de résistance à la formation d'arc grâce à la conductivité thermique et électrique élevée du cuivre et grâce à la résistance élevée à l'érosion de l'arc et au faible coefficient d'expansion thermique du tungstène. Cependant, les contacts sont vulnérables à l'endommagement thermique à cause de la température élevée et du haut débit sur les surfaces locales des contacts lors de l'enclenchementdéclenchement des contacts. Au cours de cette étude, on a fabriqué des poudres composites de cuivre renforcées de particules (W-Cu et TiC-Cu) en utilisant un nouveau procédé de placage chimique du cuivre. On a utilisé des contacts électriques faits de cuivre pur ou de poudres à matrice de cuivre pour des essais dynamiques d'électrode. On a soumis les échantillons à 1,000 et 10,000 ruptures d'arc pour étudier l'effet d'érosion de l'arc sur les contacts ainsi que leur durée de vie d'enclenchement-déclenchement. Les résultats montrent que les contacts faits de cuivre pur avaient la plus grande perte de masse et la plus courte durée de vie alors que les composites de W-Cu préservaient presque toute leur masse; de plus, les composites de W-Cu avec les particules de W les plus fines (1 μm) surpassaient le reste des composites.

Chemical “kick start” for the autocatalytic formaldehyde‐free electroless copper plating process

PurposeThe purpose of this paper is to examine the use of additives in formaldehyde‐free copper‐plating solutions with low reducing agent (RA) concentration to improve the start reaction of electroless copper deposition and to enable a copper‐plating process which is more environmentally friendly.Design/methodology/approachDifferent additives were investigated and their influence on the plating reaction and deposition rate was elucidated using several deposition trials.FindingsOn palladium‐activated base material, the additives reacted with the palladium and generated additional electrons in the initial phase of the deposition. Thus, the adequate supply of electrons from two sources (RA and additive) permits the deposition of a homogeneous and compact copper layer.Research limitations/implicationsAt the present time, formaldehyde is the established RA in the electroless copper metallization process used with plated through‐holes. Because of its environmental impact, there is a need to replace formaldehyde. In this investigation, the more environmentally friendly glyoxylic acid is used as an autocatalytic RA. However, glyoxylic acid is more expensive and causes undesirable side reactions. In order to keep process costs under control, the concentration of glyoxylic acid in the copper bath should be reduced without affecting the quality of the copper deposits.Originality/valueAdditives can compensate for the lower RA concentration, and thus the lack of essential electrons for the copper deposition.

Electroless copper plating and surface characterization of thermoplastic PPO based printed circuit boards

PurposeThe adhesion between electroless copper and a substrate is one of the most important factors in the reliability of thermoplastic printed circuit boards. The purpose of this paper is to investigate the effects of mechanical grinding and acid etching of thermoplastic substrate materials on the adhesion of copper deposited by an electroless copper plating process. The base material of the test substrates was a new high temperature thermoplastic polyphenylene oxide (PPO) compound.Design/methodology/approachThe effects of pre‐treatment on plastic surfaces are analyzed by the following methods: Fourier transform infrared (FTIR), SEM, the Dyne surface energy test and the surface roughness test. The adhesion between electroless copper and thermoplastic substrate is measured with a peel strength test.FindingsThe results showed that mechanical grinding of the substrates significantly increased adhesion but the highest adhesion is gained by using an acid etch treatment before electroless plating. These results indicated that adhesion between copper and the substrates was not directly proportional to the roughness and surface energy values.Originality/valueThe conventional sweller/desmear treatment used in a printed circuit board factory for pre‐treating epoxy based laminates prior to electroless plating is not suitable for these PPO compound boards. The copper adhesion is adequate when the substrates are etched with sulphuric acid/chromate solution. In that case the bonding between the metal layer and the plastic surface is stronger than the bondings between the polymer chains of the thermoplastic material. The adhesion mechanism of electroless copper in these mechanically abraded samples is mechanical interlocking of metal particles.

Surface Morphology of Electroless Copper Deposits Using Different Reducing Agents

Electroless copper plating has been used in the printed circuit industry for plating from bare laminate and plating through hole. Common commercial plating solutions consist of formaldehyde as the reducing agent. However, due to its hazardous nature, many alternatives were brought out to reduce the potential risk in electroless copper plating process, among which glyoxylic acid is highly competitive. The aim of this research is to examine the surface evolution process and the surface morphology of the electroless copper deposits plated under different conditions with either formaldehyde or glyoxylic acid as the reducing agent. Electroless copper deposits were plated on the epoxy board in solutions with either formaldehyde or glyoxylic acid as the reducing agent with different chemical concentrations at 60°C or 45°C. Four substrates were used for each plating, each of which was taken out of the plating solution after being plated for 5, 15, 60 and 120 minutes, respectively. The surface morphology of all the samples was characterized using scanning electron microscopy (SEM). The SEM image of the epoxy substrate before plating shows an eroded‐like rough surface where many dimples can be observed. The images of the plating sequence indicate that copper was plated almost evenly on both inside and outside of the dimples in the formaldehyde solutions and the final surface tended to be still rough or even hollow, while in the glyoxylic acid solutions, copper was plated more on the inside of the dimples and the final surface tended to be smoother. Lowering temperature resulted in much smoother surfaces from both formaldehyde and glyoxylic acid solutions. The research reveals that glyoxylic acid has promising prospect as an alternative to formaldehyde in electroless copper plating. Under certain conditions, glyoxylic acid can be very effective for smooth plating on rough surfaces.

Electroless copper plating applicable for bulk-silicon micromachined radio frequency inductor

An electroless copper plating process has been developed for bulk-silicon micromachined radio frequency (RF) inductor. In the process, isotropic oxygen plasma bombardment is used for silicon surface pretreatment and activation time is optimized. High quality copper film with thickness up to 890 nm is plated on single-crystal silicon surface, resulting in low sheet resistivity of 0.04 Ω/□. The electroless copper plating technology is combined with bulk-silicon micromachining to fabricate a new kind of RF inductor consisting of suspended single-crystal silicon spiral with copper coated as conducting surface. A highly conformal copper coating layer is formed on every side of the suspended silicon spiral inductor using the plating process. Quality factor over 30 at 11 GHz and self-resonant frequency higher than 15 GHz are achieved for an inductance of 4 nH. Further inductor RF performance improvement by means of thicker copper coating is conceivable.

Electroless copper plating process of N, N, N′, N′-tetrakis (2-hydroxypropyl) ethylenediamine system with high plating rate

Electroless copper plating process of N, N, N′, N′-tetrakis (2-hydroxypropyl) ethylenediamine (THPED) chelating agent was researched comprehensively. The results indicate that plating rate decreases with the increase of concentration for THPED, CuSO4 · 5H2O and HCHO, pH value and bath temperature. The additive of K4[Fe(CN)6] · 3H2O, 2, 2′-dipyridyl and polyethylene glycol(PEG) decrease plating rate and K4[Fe(CN)6] · 3H2O has a bad effect on deposits quality, but 2, 2′-dipyridyl and PEG make deposits quality improve greatly. Low concentration of 2-mercaptobenzothiozole (2-MBT) increases plating rate and improves deposits quality, but decreases plating rate and worsens deposits quality when 2-MBT reaches 5 mg/L. The optimal conditions of this electroless copper plating process are that the concentration of THPED, HCHO, CuSO4 · 5H2O, PEG, 2, 2′-dipyridyl and 2-MBT are 16.8 g/L, 16.0 mL/L, 13.3 g/L, 0.5 g/L, 5.0 mg/L and 2.0 mg/L, respectively, pH value is 12.75, bath temperature is 30 °C. Plating rate reaches 9.54 µm/h plating for 30 min in the bath. The SEM images demonstrate that the surface of copper film is smooth and the crystal is fine.

The Deposition Characteristics of Accelerated Nonformaldehyde Electroless Copper Plating

The deposition process of an electroless copper plating solution using sodium citrate as the main complexing agent and sodium hypophosphite as the reducing agent has been investigated. The deposit composition, structure, and catalytic activity for the oxidation of hypophosphite during the process have been investigated. Formamidine disulfide (fd) has been shown to accelerate the deposition rate of the electroless plating just as it does with electroless plating solutions using N-(2-hydroxyethyl)ethylenediaminetriacetic acid trisodium salt hydrate (HEDTA) as the complexing agent. For solutions with the mole ratio of 42, the deposition rate decreased with time and terminated after 90 min plating because the surface catalytic activity of the deposit had decreased with thickness. A copper deposit with total thickness of 6.48-6.59 μm was obtained after 90 min plating. The decrease in the deposition rate with time was mitigated by decreasing the mole ratio, holding the concentration of copper ions constant. An optimized electroless copper plating process with sustained deposition rate with time and high metal conductivity was developed. The bath was used in a fully additive high density wiring process. © 2003 The Electrochemical Society. All rights reserved.

Electroless plating of palladium and copper on polypyrrole films

A novel process for the metallization of polypyrrole (PPY) film surface through consecutive electroless plating of palladium and copper in the complete absence of the SnCl2 sensitization step was demonstrated. X-ray photoelectron spectroscopy (XPS) technique was used to characterize the polymer surface at each stage of the metallization process. It was found that only the fully reduced PPY film could reduce palladium ions to palladium metal (Pd(0)) in substantial amounts from either the Pd(NO3)2 or PdCl2 acid solution. The palladium metal was necessary for catalyzing the subsequent electroless plating of copper. The reduction of Pd(II) ions in acid solution to Pd(0) on the film surface was accompanied by a simultaneous increase in intrinsic oxidation state and doping level of the film. The copper plating process after the palladium uptake step was highly dependent on the [Pd]/[N] ratio on the film. Through XPS and Auger photoeletron spectroscopy measurements, it was postulated that during the electroless copper plating process, the Cu(II) ions were first reduced to Cu(I) on the PPY film surface before complete reduction to copper metal.

Copper hydride formation in the electroless copper plating process: in situ X-ray diffraction evidence and electrochemical study

Copper hydride, CuH, has been shown by in situ X-ray diffraction method to form in the process of electroless copper deposition in alkaline solutions containing Cu II complexes with tartrate and ammonia and borohydride, BH 4 −, as a reducing agent. The rate of possible chemical and electrochemical steps was measured and compared with the rate of autocatalytic Cu II reduction process. Results indicate the existence of two process routes: (1) coupling of simultaneous electrochemical reactions of BH 4 − oxidation and Cu II reduction with the enhancement of cathodic reaction due to H 2 evolution in anodic reaction, (2) electrochemical steps of Cu II reduction to Cu I and consecutive chemical steps of CuH formation and decomposition. The route including CuH intermediate gives a lower Cu deposition rate.

Monolayer Molecular Adsorption Model for Electroless Copper Plating Process

Monte Carlo simulation has been applied to the adsorption process on liquid‐solid interface. A simple monolayer molecular adsorption model was proposed to analyze the electroless copper plating process and adsorption characteristics was discussed. The adsorption constant estimate based on the theoretically calculated desorption constants well reproduced the experimental values.

Differential electrochemical mass spectrometry study of the electroless copper plating process using a thin-layer flow-through cell

Differential electrochemical mass spectrometry (DEMS) using a thin-layer flow-through electrochemical interface was used for simultaneous on-line studies of the dependence of mass spectra and Faradaic current on the electrode potential during electrocatalytic reduction of copper(II) ions by formaldehyde. The feasibility of the thin-layer flow-through DEMS cell for investigating electrode processes involving metal phase formation was demonstrated. The method permits to obtain the instantaneous values of partial reactions of the catalytic process.

小特集／無電解めっきの現状と将来 無電解銅めっきの廃液処理

小特集／無電解めっきの現状と将来 無電解銅めっきの廃液処理

The surface layer pH in the electroless copper plating process

The pH at the surface of the coating (pH s) was measured using an ordinary glass electrode, the surface of which was in the zone of the reaction during the autocatalytic reduction of copper(II) ions by formaldehyde. The pH s value is significantly lower (by up to 1.3 units) than the pH bulk value in most tartrate and ethylenediamine tetraacetate (EDTA) solutions. The pH s value changes the dependence of the electroless copper plating rate on the alkalinity of the solution (the rate maximum shifts from 12.6 - 12.7 to 11.7 - 12.0). The pH changes at the surface depend mainly on the catalytic process rate and the buffering capacity of the solution; the evolution of H 2 also has a great influence at the medium rate of copper plating (1 - 3 μm h -1).

On the Anodic Oxidation of Formaldehyde during the Electroless Copper Plating Process

The electro‐oxidation of formaldehyde at copper is examined in relation to the process of electroless plating (EP) of copper. RBS and AES analyses show that Pd catalyst migration from the deposit‐substrate to the deposit‐solution interface during the EP process is negligible. This is the case for either Cu or Ni EP deposits, and when either wet or evaporated Pd catalyst is employed. The catalytic electro‐oxidation of thus proceeds during the EP process at a copper surface with no significant coverage by any other metal atoms. It is shown that the mechanism and measured rates of electro‐oxidation at copper can be understood on the basis of recent data for relevant copper/gas systems, and some special characteristics of the copper/alkaline solution system. Detailed calculations show that , rather than , is expected to be the final product of electro‐oxidation at copper at potentials as high as +0.4V vs. RHE, provided the activation energy for recombinative hydrogen desorption from the copper surface is less than 10 kcal/mole.

Electrochemical study of the electroless copper plating process

An electrochemical investigation of the autocatalytic reduction of copper(II) by formaldehyde has been carried out employing the concepts of “mixed potential” theory. The anode process associated with electroless copper plating in an alkali-ethylenediaminetetraacetic acid solution was studied by potentiometric and potentiostatic methods. A cell design was proposed which allows measurements to be conducted on the electrode under examination when it is in contact with a solution of the reducing agent under both open-circuit and potentiostatic conditions. It was shown that when a copper electrode is in contact with a solution containing formaldehyde at a constant potential close to the mixed potential a transient current appears whose density exceeds the rate of reduction of the copper, expressed in current-density units.