Surface plasma functionalization of polycarbonate: Application to electroless nickel and copper plating

Electroless metallization of polymers requires different steps including (i) the preconditioning of the surface to render it chemically reactive, (ii) the chemisorption of a catalyst (Pd) to activate the so-modified surface towards subsequent metallization, and (iii) the metallization itself. In the present work, electroless metallization was carried out on poly(carbonate) substrates, and step (i) was performed using plasma treatments in various gaseous atmospheres (NH₃, N₂, O₂). When a sufficiently high surface concentration of nitrogenated groups is grafted it is shown from X-ray photoelectron (XPS) analyses that the so-functionalized surfaces can chemisorb Pd²⁺ ions directly from a simple PdCl₂ solution. Thus, step (i) allows simplification of the conventional electroless processes commonly used up to now. Moreover, XPS analyses indicate chemical reduction of Pd²⁺ ions to Pd(0) during the more or less long initiation time before the start of metallization. This reduction is easily performed in nickel plating baths thanks to the hypophosphite reducer. On the other hand, this reduction is possible with formaldehyde, the reducer of copper plating baths, only if Sn²⁺ ions (brought by the conventional processes using SnCl₂ and PdCl₂ solutions) are present.     

高分子表面金属化技术

高分子表面金属化是对高分子材料表面进行改性处理使其具有良好物理性能、力学性能及金属光泽的表面技术,广泛应用于高分子导电、薄膜修饰、电磁屏蔽等领域。本文综述了高分子表面金属化的两大类技术方法,即干法镀膜和湿法镀膜。介绍了几种典型的表面处理技术,如真空镀膜、喷涂金属转移法、化学镀、化学还原金属化以及电镀,并总结了它们的技术特点以及在科学研究和工业生产应用中的难点。阐明了从传统电镀技术发展而来的高分子表面直接电镀工艺的优势,直接电镀工艺省去了电镀前的活化工序,缩短了工艺时间,避免了电镀前工艺对环境造成的污染,成为高分子表面金属化技术发展的新方向。     

塑料表面直接电镀

综述了在塑料基体上直接电镀的三种主要形式：导电性高分子直接电镀;Pd／Sn活化直接电镀;碳粒子悬浮液直接电镀。这几种方法虽然都是直接电镀,但其原理各不相同,导电性高分子直接电镀是使用导电性的高分子材料为基础;Pd／Sn活化是形成一金属Pd层直接电镀或Pd层催化铜置换锡;碳粒子悬浮液体系使用石墨作为导电基体附着于塑料表面而进行直接电镀。     

A new electroless Ni plating procedure of iodine-treated aramid fiber

A new, durable, etchant- and tin-free catalyzation process was studied for electroless nickel metallization of aramid fiber via iodine pretreatment. Firstly, iodine components were selectively doped onto the inner part of the fiber using vapor iodine exposure followed by treatment with a tin-free acidic palladium chloride solution to form palladium iodide (PdI₂) on the fiber surface. After subsequent reduction of PdI₂ into metal palladium (Pd), electroless plating was carried out. A uniform Ni plating layer was formed on the fiber surface, which exhibited high durability against resistance tests of ultrasonic exposure, tape peel-off, and corrosion in NaCl solution. Here, Pd particles that formed at the inner part near the fiber surface functioned as an anchor of the plated layer as well as a catalyst of electroless plating. Investigation of the plate bath composition shows that the use of anionic surfactant enhances the adhesion of the plated layer with fiber matrix, while a reducing agent in the plate bath reduces the smoothness of the plated surface. Also, the plate bath pH and the temperature of the plating solution control the layer deposition rate noticeably more than does the plating time. The proposed method retained good tensile strength in the plated fiber. Ni-plated aramid fiber exhibited durable electrical conductivity and magnetic properties.     

Functionalization of Polymer Surfaces Using Excimer VUV Systems and Silent Discharges. Application to Electroless Metallization

New approaches for electroless plating of nonconductive polymers or polymer-based materials are described. In this work, polyimide substrates were surface-functionalized (i) in nitrogenated (ammonia at reduced pressure) and oxygenated (air at atmospheric pressure) atmospheres under assistance of vacuum-ultraviolet (VUV) irradiation (use of a xenon silent discharge excimer source) or (ii) directly in air at atmospheric pressure using a dielectric-barrier discharge (DBD) device. After functionalization, the substrates were “activated” by dipping in a dilute acidic PdCl₂ solution or by spin-coating of a thin metal-organic film (from a solution of palladium acetate (PdAc) in chloroform). The catalytic activity of the so-deposited palladium species toward the electroless deposition of nickel was studied before and after a VUV post-irradiation (in air at atmospheric or reduced pressure) with a view to understanding better the role of the reducer (sodium hypophosphite) within the electroless bath.

This work confirms the specific interest of grafting nitrogenated functionalities onto polymer surfaces for attaching covalently the palladium-based catalyst (in particular in the case of the PdCl₂ route), forming thus strong Pd - N - C bonds at the metal/polymer interface. This results from the strong chemical affinity of palladium toward nitrogen. On the other hand, when oxygenated functionalities are surface-grafted, the conventional two-step procedure using SnCl₂ and PdCl₂ solutions can be proposed due to the strong chemical affinity of tin toward oxygen. The Ni deposits obtained under these different conditions pass the standard Scotch^®-tape test and, therefore, exhibit a good practical adhesion. For this same purpose, it is interesting to note that the DBD treatment operating in air at atmospheric pressure causes an increase of the surface roughness and, therefore, an improvement in adhesion of metallic films when their initiation is catalyzed through the PdAc route. In addition, this work demonstrates that extensive research still has to be performed to understand and improve the Ni/polymer adhesion when the PdAc route associated with a VUV irradiation is considered.     

Plasma Chemical Modification of Polycarbonate Surfaces for Electroless Plating

The preliminary steps of the “electroless” metallization of polycarbonate are investigated by XPS. They consist of the chemisorption of a catalyst (Pd) on the surface to be metallized. The corresponding surface can be activated either by chemical etching or by reactive or non-reactive gas plasma treatment. Therefore, the surface treatment of polycarbonate determines the palladium adsorption. It is shown here that a surface carrying oxygenated functions adsorbs palladium through Sn²⁺ ions which are themselves bonded to oxygen atoms. On the other hand, a surface on which nitrogenated groups have been grafted (by NH₃ or N₂ plasma treatment) chemisorbs palladium directly on these nitrogen atoms. Reaction mechanisms are proposed in both cases and a new and simplified process for making the surfaces catalytic is proposed.     

A generalized sample preparation method by incorporation of metal–organic compounds into polymers for electroless metallization

Polymer metallization is important for several applications but triggering of electroless deposition is problematic. A simple and inexpensive method to prepare the polymers for initiating the electroless copper deposition is successfully applied to Liquid Crystal Polymer and Polyethylene Terephthalate. The samples are prepared by incorporation of a small amount (<0.5 wt%) of metal–organic compounds (palladium, nickel, or copper acetates) in the molten polymers. During blending, the polymers are held at sufficiently high temperatures to thermally decompose the acetates, yielding the metallic particles (Pd, Ni, or Cu) which are used as the activators. After surface preparation, copper is deposited on polymers in an electroless bath including formaldehyde as reducer. The influence of bath parameters (temperature, composition) and the nature of activators is investigated. This method can be extended to other polymers by finding an appropriate polymer/metal–organic couple. It is also demonstrated that cheaper Ni or Cu can substitute expensive Pd.     

Copper nanowires within the central channel of tobacco mosaic virus particles

Simple electrochemical deposition techniques can produce highly defined metal nanostructures in templates. Electroless deposition (ELD) can be effectively used for depositing metals on insulators such as biological or plastic surfaces. With biomolecular templates, metallization methods are often restricted to mild reductions, and the deposition of copper at pH values above 12 is usually not applicable. We produced copper nanowires of 3 nm in diameter and up to 150 nm in length by electroless deposition within the 4 nm wide channel of tobacco mosaic virus (TMV) particles. We employed a low pH (7.5) copper electroless deposition solution that is compatible with biomolecules. The fabrication process of the nanowires is based on sensitization of tobacco mosaic virus with Pd(II) prior to the electroless deposition. We analyzed the chemical composition of the nanowires by energy-filtering transmission electron microscopy, and used the method also for nickel and cobalt nanowires deposited within the viral channel.     

TiCl_3/PdCl_2法活化多孔陶瓷基体制备透氢Pd膜

以TiCl3取代SnCl2作为敏化剂,考察TiCl3/PdCl2活化法对Pd膜制备及性能的影响。所制备Pd膜的表面与断面形貌采用SEM与金相显微镜表征,测试膜的透氢性、选择性以及高温稳定性,比较了TiCl3/PdCl2与SnCl2/PdCl22种活化方法对Pd沉积速率的影响。结果表明:TiCl3/PdCl2活化法同样能够在多孔陶瓷基体表面形成活性催化层,并最终成功获得高性能的Pd膜。相对而言,TiCl3/PdCl2活化法更有利于Pd膜的快速形成,而且彻底避免了Sn对Pd膜的污染,有望成为SnCl2/PdCl2活化法的一种理想替代方法。     

Electrically conductive coatings of nickel and polypyrrole/poly(2-methoxyaniline-5-sulfonic acid) on nylon Lycra textiles

Woven nylon Lycra^® has been coated with finely-divided electroless nickel-phosphorus, polypyrrole and electroless nickel/polypyrrole to produce flexible and electrically conductive textiles. The coated textiles were tested for their electrochemical activity, electrical resistivity and resistivity in response to mechanical strain. Pre-dyeing the textile with poly(2-methoxyaniline-5-sulfonic acid) (PMAS) prior to electroless metallization by electroless nickel and via chemical polymerization of polypyrrole was found to be beneficial in enhancing the resultant coating as well as stabilizing surface resistance responses when exposed to a wide range of strain. The mass gain due to the nickel coating was found to increase linearly with deposition time. The surface resistivity of the coated textile was found to decrease at longer nickel deposition times.     

Functionalization of Polymer Surfaces Using Excimer VUV Systems and Silent Discharges. Application to Electroless Metallization

New approaches for electroless plating of nonconductive polymers or polymer-based materials are described. In this work, polyimide substrates were surface-functionalized (i) in nitrogenated (ammonia at reduced pressure) and oxygenated (air at atmospheric pressure) atmospheres under assistance of vacuum-ultraviolet (VUV) irradiation (use of a xenon silent discharge excimer source) or (ii) directly in air at atmospheric pressure using a dielectric-barrier discharge (DBD) device. After functionalization, the substrates were “activated” by dipping in a dilute acidic PdCl₂ solution or by spin-coating of a thin metal-organic film (from a solution of palladium acetate (PdAc) in chloroform). The catalytic activity of the so-deposited palladium species toward the electroless deposition of nickel was studied before and after a VUV post-irradiation (in air at atmospheric or reduced pressure) with a view to understanding better the role of the reducer (sodium hypophosphite) within the electroless bath.

This work confirms the specific interest of grafting nitrogenated functionalities onto polymer surfaces for attaching covalently the palladium-based catalyst (in particular in the case of the PdCl₂ route), forming thus strong Pd - N - C bonds at the metal/polymer interface. This results from the strong chemical affinity of palladium toward nitrogen. On the other hand, when oxygenated functionalities are surface-grafted, the conventional two-step procedure using SnCl₂ and PdCl₂ solutions can be proposed due to the strong chemical affinity of tin toward oxygen. The Ni deposits obtained under these different conditions pass the standard Scotch^®-tape test and, therefore, exhibit a good practical adhesion. For this same purpose, it is interesting to note that the DBD treatment operating in air at atmospheric pressure causes an increase of the surface roughness and, therefore, an improvement in adhesion of metallic films when their initiation is catalyzed through the PdAc route. In addition, this work demonstrates that extensive research still has to be performed to understand and improve the Ni/polymer adhesion when the PdAc route associated with a VUV irradiation is considered.     

Towards the selective fixation of palladium on composite oxide carriers

The selective metallization of a semiconducting oxide (ceria) supported on an insulating oxide (silica) is investigated through new methods involving optical and electronic properties of the components of the composite. Supported ceria particles in the nanometer range are studied. Two methods of Pd deposition are applied: (i) electroless deposition via laser activation of the composite suspension in the Pd precursor solution; (ii) UV photoreduction of Pd on the composite. Electroless deposition results in a wide distribution of metal particle size, from 2–3 run to 600 nm, while some ceria particles are not metallized at all. On the contrary, photoreduction fixes the Pd on ceria selectively, yielding Pd particles with sizes comparable to that of the ceria. The influence of various parameters governing the metal deposition is discussed.     

玻璃纤维化学镀银的工艺研究

采用AgNO3活化剂代替传统的PdCl2,进行化学镀银包覆玻璃纤维降低了工艺成本;通过超声波粗化、敏化、活化等工艺对玻璃纤维进行了前处理,讨论了主盐、还原剂、pH等因素对化学镀银沉积速度、电阻率及镀层含量的影响,从而确定了最佳的工艺配方。使低密度的银包玻璃纤维作为导电高分子材料用于电磁屏蔽中。     

化学镀法制备钯膜工艺

以多孔Al2O3陶瓷管为载体,采用化学镀法制备了钯膜。考察了化学镀温度及载体孔径对制备钯膜的影响,并利用扫描电镜对钯膜形貌结构进行了表征。研究表明,化学镀15min,钯沉积速率较快;反应时间延长至120min,钯沉积量增加,但是沉积速率降低。随着化学镀温度的升高,钯沉积量增加;但是温度过高,会导致钯利用率降低;温度为318K,化学镀钯膜较适宜。在孔径为0.2μm的Al2O3陶瓷管表面制备的钯膜平整、致密,其二次镀钯膜N2渗透速率为1.7×10-9mol/(m2·s·Pa)。     

Long-term stability of Cu/Pd nanoparticles and their feasibility for electroless copper deposition

Poly-vinylpyrrodione (PVP) protected Cu/Pd nanoparticles synthesized with citric complexing agent were developed as activator for electroless copper deposition in printed-circuit boards (PCBs) industry. Cu/Pd nanoparticles in different molar ratio were employed in electroless copper deposition and found that the catalytic activity was influenced not only by the amount of Pd content or particle size but also by the surface protected PVP layer. From the time-resolved electroless copper deposition, we suggested that the catalytic efficiency should be evaluated by both initial activity and the structure of deposited copper film. As a result, the Cu/Pd nanoparticles of molar ratio = 1/2 was found to have best catalytic activity which was comparable to traditional Pd/Sn or pure Pd activator. In regard to the most concerned stability issue of Cu-content system, a surprising slow galvanic corrosion of Cu was found when Cu/Pd nanoparticles were exposed to the open air. Besides, slightly oxidation of Pd was found after air-exposure. Surprisingly, these Cu/Pd colloids maintain part of activity and well suspension even after 6-month exposure, suggesting well long-term stability as activator. In short, Cu/Pd nanoparticles synthesized with citric complexing agent with high catalytic activity and long-term stability was a promising activator for electroless copper deposition.     

Plasma Chemical Modification of Polycarbonate Surfaces for Electroless Plating

The preliminary steps of the “electroless” metallization of polycarbonate are investigated by XPS. They consist of the chemisorption of a catalyst (Pd) on the surface to be metallized. The corresponding surface can be activated either by chemical etching or by reactive or non-reactive gas plasma treatment. Therefore, the surface treatment of polycarbonate determines the palladium adsorption. It is shown here that a surface carrying oxygenated functions adsorbs palladium through Sn²⁺ ions which are themselves bonded to oxygen atoms. On the other hand, a surface on which nitrogenated groups have been grafted (by NH₃ or N₂ plasma treatment) chemisorbs palladium directly on these nitrogen atoms. Reaction mechanisms are proposed in both cases and a new and simplified process for making the surfaces catalytic is proposed.     

Selective Metal Pattern Fabrication Through Micro-Contact or Ink-Jet Printing and Electroless Plating onto Polymer Surfaces Chemically Modified by Plasma Treatments

Simple versatile processes combining plasma treatments, micro-contact printing (µCP) or ink-jet printing (IJP), and electroless deposition (ELD) have been developed to produce micrometer and sub-micrometer scale metal (Ni, Ag) patterns at the surface of polymer substrates. Plasma treatments were mainly used to graft the substrate surfaces with either nitrogen-containing functionalities on which a palladium-based catalyst can be subsequently chemisorbed (case of Ni deposition through a tin-free process in solution) or oxygen-containing functionalities on which a tin-based sensitization agent can be subsequently chemisorbed (case of Ag deposition through a redox reaction). µCP of the catalyst or of self-assembled monolayers (SAMs) as well as ink printing were used to obtain locally active or non-active areas at the polymer surfaces. The metal micro-patterns were characterized using optical microscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). Surface chemical characterization was carried out by X-ray photoelectron spectroscopy (XPS).     

Preparation and characterization of silica-supported, group IB–Pd bimetallic catalysts prepared by electroless deposition methods

Electroless deposition has been used to synthesize a series of Au–, Ag–, and Cu–Pd/SiO₂ bimetallic catalysts having incremental surface coverages and compositions of each group IB metal. Thermodynamically unstable, yet kinetically stable, electroless bath(s) were developed using metal bis-cyano salts of the group 1B metal and N₂H₄ (for Au and Ag) or DMAB (for Cu) as reducing agents. The times (1–2 h) and profiles (1st order in group 1B metal concentration) observed for complete deposition indicate good kinetic control of the electroless deposition process. The bimetallic catalysts have been characterized using selective chemisorption, atomic absorption spectroscopy (AAS), Fourier transform infrared spectroscopy (FTIR) of adsorbed CO, and X-ray photoelectron spectroscopy (XPS) techniques. Decreases in Pd surface sites with addition of IB metals confirm deposition onto the supported Pd nanoparticle surfaces. FTIR studies suggest that deposition of Cu and Ag are selective towards Pd(1 1 1) sites, while Au deposits non-discriminately on all Pd sites. Finally, XPS measurements for each family of bimetallic catalysts suggest a net electron transfer from the Pd to the deposited metal.     

Synthesis of monodisperse nickel‐coated polymer particles by electroless plating method utilizing functional polymeric ligands

In the electroless plating process, to omit a sensitizing process with SnCl₂, we utilized amino‐functional groups on polymer particles. At first, highly monodisperse functional polymer particles could be prepared by a two‐step seeded polymerization of styrene, divinylbenzene, and glycidyl methacrylate. Then, surface epoxy‐functional groups were converted to amino‐functional groups by treating the particles with a diamine. By using these surface amino functionalities, we tried to prepare uniformly metal‐coated monodisperse polymer particles by electroless plating method. The constituents of an electroless nickel solution bath are nickel salt, a reducing agent, suitable complexing agents, and stabilizers. And the metal thickness was simply controlled by changing the loading amount of substrate polymer particles. Morphological observation of nickel‐plated polymer particles was conducted by using optical microscopy, scanning electron microscopy, and transmission electron microscopy. The structural composition of plated nickel was also investigated. Most of all, the function and the efficiency of the amino‐functional group of polymer particles as a polymeric ligand for metal binding was elucidated. From all observations, it was evident that in the electroless metal plating process without any sensitization step, the deposition of metal clusters on substrate particles is largely dependent upon the particle surface functionality. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3801–3808, 2006     

Atmospheric-Pressure Plasma Amination of Polymer Surfaces

Using dielectric barrier discharges (DBDs) in suitable gas atmospheres, appreciable densities of amino groups can be generated on polymer surfaces. After the introduction and a few remarks on analytical methods for the determination of functional groups densities, this paper presents a short summary of recent studies on the mechanism of the polymer surface amination from nitrogen and nitrogen/hydrogen mixtures, and possible relevant precursor species. Combination of chemical derivatization with quantitative FT-IR spectroscopy was employed for the determination of primary amino groups densities introduced on polyolefin surfaces in DBD afterglows in N₂ and N₂ + H₂ mixtures. Owing to the possibility to generate atmospheric-pressure plasmas in sub-mm³ volumes, DBD plasmas can be used to modify polymer surfaces area selectively: a new process termed 'plasma printing' can be applied for the achievement of micropatterned surface modifications, such as hydrophilization/hydrophobization or chemical functionalization. Direct-patterning polymer surface modification processes are of interest for biochemical/biomedical applications as well as for polymer electronics. Two examples are presented in more detail: ? the area-selective plasma amination of carbon-filled polypropylene minidiscs to manufacture microarrays with peptide libraries utilizing parallel combinatorial chemical synthesis, and ?the continuous treatment of polymer foils by means of reel-to-reel patterned plasma amination for the subsequent electroless copper metallization, leading to a fast and highly efficient process for the manufacture of structured metallizations for flexible printed circuits or RFID antennas.