Effects of K<Subscript>4</Subscript>Fe(CN)<Subscript>6</Subscript> on electroless copper plating using hypophosphite as reducing agent

K₄Fe(CN)₆ was used to improve the microstructure and properties of copper deposits obtained from hypophosphite baths. In electroless copper plating solutions using hypophosphite as the reducing agent, nickel ions (0.0038 M with Ni²⁺/Cu²⁺ mole ratio 0.12) was used to catalyze hypophosphite oxidation. However, the color of the copper deposits was dark or brown and its resistivity was much higher than that obtained in formaldehyde baths. The effects of K₄Fe(CN)₆ on the deposit composition, resistivity, structure, morphology and the electrochemical reactions of hypophosphite (oxidation) and cupric ion (reduction) have been investigated. The deposition rate and the resistivity of the copper deposits decreased significantly with the addition of K₄Fe(CN)₆ to the plating solution and the color of the deposits changed from dark-brown to copper-bright with improved uniformity. The nickel and phosphorus content in the deposits also decreased slightly with the use of K₄Fe(CN)₆. Smaller crystallite size and higher (111) plane orientation were obtained by addition of K₄Fe(CN)₆. The electrochemical current–voltage results show that K₄Fe(CN)₆ inhibited the catalytic oxidation of hypophosphite at active nickel sites and reduced the reduction reaction of cupric ions on the deposit surface by adsorption on the electrode. This results in lower deposition rate and a decrease in the mole ratio of NaH₂PO₂/CuSO₄ consumed during plating.     

复合添加剂对次磷酸钠化学镀铜的影响

在以次磷酸钠为还原剂的化学镀铜体系中,考察了2,2'-联吡啶/亚铁氰化钾复合添加剂对化学镀铜的影响。采用电化学方法分析了无添加剂、单一添加剂和复合添加剂对次磷酸钠氧化电势和电流的影响,结果表明,2,2'-联吡啶、亚铁氰化钾和2,2'-联吡啶/亚铁氰化钾复合添加剂均使次磷酸钠氧化电势增加,氧化电流减小。扫描电子显微镜(SEM)、能量色散谱(EDS)、X射线衍射(XRD)、四探针测试法(SZT-90)检测结果显示:较之单一添加剂,10 mg/L 2,2'-联吡啶/4 mg/L亚铁氰化钾复合添加剂所得铜镀层纯度更高〔w(Cu)=96.27%〕,外观更加光亮、致密和均匀,铜层表面平均电阻率也降低至0.022 9μΩ.m。     

Electroless copper plating using Fe as a reducing agent

Although the electroless plating method is known to be an effective method for obtaining fine wiring in particular, 1 mol hydrogen gas is generated during 1 mol Cu deposition, and voids are generated in the wiring when electroless Cu plating is applied to fine wiring. To avoid the hydrogen evolution, the possibility of performing electroless Cu plating was confirmed using an inexpensive Fe^II compound as a reducing agent. The bath contains CuSO₄, FeSO₄, NaCl, ethylenediamine, sodium citrate, polyethylene glycol (PEG), and 2,2′-bipyridine. Under optimal conditions, over 1.7 μm of copper deposit with a smooth surface was obtained after 3 h of plating, which did not contain iron as an impurity. The electrical resistivity of the copper film is about 3-4 μΩ cm corresponding to that of electroplated copper films.     

次磷酸钠化学镀铜镍合金的研究

研究了以次磷酸钠为还原剂的化学镀铜过程。分析了温度、pH、硫酸镍含量对化学镀铜沉积速率的影响及镀层的表面形貌和结构。结果表明,沉积速率随着镀液温度、pH和N i离子浓度的提高而增大。镀层组分含量和XRD实验结果表明镀层为铜镍合金,呈面心立方结构,晶面间距d与晶胞参数a与标准Cu-N i的相比略大。SEM实验表明,镀层表面形貌为团粒状,颗粒大小较不均匀。     

Electrochemical impedance studies of modified Ni-P and Ni-Cu-P deposits in alkaline medium

Ni-P and Ni-Cu-P deposits were supported over the commercial carbon using the electroless plating technique. The formed samples were characterized by applying SEM, XRD and EDX analyses. An amorphous Ni-P surface was obtained with 73.70 wt% Ni and 11.45 wt% P. The addition of copper to the plating bath reduces the deposited amount of nickel and phosphorus. The electrochemical performance of these deposits has been investigated in 0.1 M KOH solution using electrochemical impedance spectroscopy (EIS) measurements. The effect of pH, deposition time and temperature of the plating bath on the impedance characteristics of the two deposits was studied. It was found that the resistance (R_T) and relative thickness (1/C_T) of the two coatings in 0.1 M KOH solution increase with increasing either pH or deposition time or temperature of the plating bath. Our results indicate that Ni-Cu-P deposit has more corrosion resistance and lower corrosion current density (i_corr) value than Ni-P deposit under different conditions. EIS results were well confirmed by potentiodynamic polarization and cyclic voltammetry techniques.     

The observation of the nucleation and growth of electrolessly plated nickel deposited from different bath pH by TEM and QCM method

The important factors for fabricating thinner and more uniform films by electroless plating were discussed. Two kinds of Ni-P films were electrolessly plated from hypophosphite baths. The number density of the grains was low in the Ni-5.3 wt%P deposits which were plated from the pH 9 bath. As deposition proceeded, the grains grew and merged to form a continuous structure. In case of the Ni-12.6 wt%P deposits, which were plated from the pH 6 bath, the number density of the grains was more than twice that of the Ni-5.3 wt%P deposits. The grains formed a continuous structure, with nucleation governed by the initial deposition. Thus, the transition thickness, i.e., the thickness at which the deposits assumed a continuous structure, was lower in the case of pH 6. The difference was caused by the different autocatalytic activity of the deposits due to the difference in phosphorus content. It was found that the thinner and more uniform nickel films could be electrolessly plated under lower autocatalytic activity.     

次磷酸钠和甲醛为还原剂的化学镀铜工艺对比

比较并评价了以甲醛和以次磷酸钠为还原剂的化学镀铜工艺。结果表明,次磷酸钠镀铜液的稳定性高于甲醛镀铜液,次磷酸钠镀液的沉积速率高于甲醛镀液。以甲醛为还原剂的镀层晶粒细小,而以次磷酸钠为还原剂的镀层呈团粒状。甲醛镀铜层铜的质量分数接近100%,次磷酸钠镀铜层中铜的质量分数为93.9%,镍的质量分数为6.1%,镀层为铜-镍合金。以甲醛为还原剂的化学镀铜层的电导率、抗拉强度、延伸率等物理性能均优于次磷酸钠化学镀铜层。     

添加聚四氟乙烯对化学沉积复使度层性能的影响

在化学镀Ｃｕ（Ｎｉ）－Ｐ合金镀液中添加碳化硅和聚国烯制得Ｃｕ（Ｎｉ）－Ｐ－ＳｉＣ－ＰＴＥＥ复合镀层。研究了碳化硅、聚四氟乙烯的添加量对镀层沉积速度、硬度、磨损及减摩性能的影响。结果表明：碳化硅和聚四氟乙烯的加入能提高Ｃｕ（Ｎｉ）－Ｐ合金镀层的沉积速度、硬度、耐磨及减摩性。     

Obtaining of high surface roughness copper deposits by electroless plating technique

The use of pyridine-2,6-dicarboxylic and 4-hydroxypyridine-2,6-dicarboxylic acids as copper(II) ligands in formaldehyde-containing alkaline electroless copper plating solutions allowed to obtain copper layers with extremely high surface roughness factor reaching approximately 120. The Cu deposits of higher surface area were formed at highly negative open-circuit (mixed) potentials; the correlation between copper electrode overpotential and roughness of the deposit was found and discussed. The copper films obtained demonstrate a high electrocatalytic activity in anodic formaldehyde oxidation process, the oxidation rate reaches 40 mA cm⁻² and exceeds considerably that for other copper surfaces.     

化学镀镍-铜-磷三元合金工艺的研究

为提高化学镀镍－磷合金镀层的性能及获得多种性能的合金镀层以拓宽其应用范围。在化学镀镍－磷合金液中加入硫酸铜制得镍－铜－磷三元合金。研究了镀液中硫酸镍、次磷酸钠、柠檬酸钠、硫酸铜、稳定剂、光亮剂的含量以及pH值和温度等因素对合金镀层的外观、沉积速度及铜含量的影响。通过5％氯化钠溶液和10％硫酸溶液浸泡试验比较了所得镍－铜－磷合金镀层与镍－磷合金镀层以及前人制得的镍－磷合金镀层的耐蚀性，同时比较了上述镀层的其它性能。结果表明，所得镍－铜－磷合金镀层的耐蚀性、外观、结合力、孔隙率、沉积速度、硬度和耐磨性等性能优于镍－磷合金及前人制得的镍－铜－磷合金镀层。     

以次磷酸钠为还原剂的化学镀铜

研究了以次磷酸钠为还原剂、硫酸镍为再活化剂的化学镀铜工艺和镀层结构,指出工艺的基本特性。结果表明,在含有次磷酸钠和硫酸镍的镀液中,化学镀铜过程可以持续进行并呈现自催化特性;只有在合适的镀液pH范围内才可获得铜镀层;铜镀层为面心立方结构,没有明显的晶面择优取向现象,镀层结构的晶面间距d和晶胞参数a与标准Cu粉末的相比均较大,说明铜镀层仍存在应力和缺陷。     

Studies of stoichiometry of electrochemically grown CdSe deposits

The proper deposition bath composition for electrochemical synthesis of the CdSe deposit in the hexagonal structure of the right elemental stoichiometry, and photoreacting as an n-type semiconductor which can be used as a stable photoanode is investigated. The deposits were prepared by a cyclic potentiodynamic technique and the concentration of Cd²⁺ and SeO₃²⁻ in the deposition baths varied from 10⁻⁴ M to 0.1 M, and from 10⁻⁵ M to 10⁻³ M, respectively. The electrochemical, the X-ray diffraction (EDS and XRD), and the photoactivity studies of a number of deposits have shown that application of the solution composition following Cd:Se = 5:1 results in deposition of the stoichiometric CdSe. The detected ratio of reagents is explained on the base of reaction mechanism and necessary excess of cadmium ions preventing CdSe deposit dissolution. The procedure of CdSe electrosynthesis was developed to yield of a direct semiconductor in the hexagonal structure. The necessity for cadmium cations excess is explained on the basis of the mixed electrochemical/chemical deposition mechanism.     

Electrochemical studies on electroless ternary and quaternary Ni-P based alloys

The autocatalytic (electroless) deposition of Ni-P based alloys is a well-known commercial process that has found numerous applications because of their excellent anticorrosive, wear, magnetic, solderable properties, etc. It is a barrier coating, protecting the substrate by sealing it off from the corrosive environments, rather than by sacrificial action. The corrosion resistance varies with the phosphorus content of the deposit: relatively high for a high-phosphorus electroless nickel deposit but low for a low-phosphorus electroless nickel deposit. In the present investigation ternary Ni-W-P alloy films were prepared using alkaline citrate-based bath. Quaternary Ni-W-Cu-P films were deposited by the addition of 3 mM copper ions in ternary Ni-W-P bath. X-ray diffraction (XRD) studies indicated that all the deposits were nanocrystalline, i.e. 1.2, 2.1 and 6.0 nm, respectively, for binary, ternary and quaternary alloys. Corrosion resistance of the films was evaluated in 3.5% sodium chloride solution in non-deaerated and deaerated conditions by potentiodynamic polarization and electrochemical impedance (EIS) methods. Lower corrosion current density values were obtained for the coatings tested in deaerated condition. EIS studies showed that higher charge transfer resistance values were obtained for binary Ni-P coatings compared to ternary or quaternary coatings. For all the coatings a gradual increase in the anodic current density had been observed beyond 740 mV. In deaerated condition all the reported coatings exhibited a narrow passive region and all the values of E_p, E_tp and i_pass were very close showing no major changes in the electrochemical behavior. In the non-deaerated conditions no passivation behavior had been observed for all these coatings.     

化学镀镍铜磷三元合金沉积工艺的研究

为提高化学镀镍的硬度、耐磨及耐蚀性,以拓宽在电子工业中应用,采用在化学镀镍磷合金液中添加适量的铜离子制得镍铜磷三元合金。研究了镍离子与铜离子浓度比、次磷酸钠含量、沉积温度对合金镀层沉积速率的影响,利用Ｓ－５７０扫描电镜和Ｈ－８００透电镀观察了镀层表面形貌和显微组织,通过硝酸腐蚀试验比较了镍磷合金与镍铜镀层的耐蚀性。结果表明,铜的共沉积能明显提高镍磷合金的耐蚀性。     

Co-deposition mechanism of nanodiamond with electrolessly plated nickel films

The co-deposition behavior and mechanism of nanodiamond with electrolessly plated nickel films was investigated. Due to the variation of complexing agents, various composite films with 0.9-8.0% nanodiamond were plated from electroless nickel plating baths which contained the same amount of nanodiamond (5.0 g dm⁻³) and sodium hypophosphite. In addition, composite films with 0-14% nanodiamond, semi-brilliant, were successfully fabricated from the bath which contained only citrate as a complexing agent. The plating bath was very simple and was sufficiently stable without any decomposition until termination of the plating reaction occurred due to consumption of the reducing agent. When the adsorbed amount of Ni-complex on the nanodiamond particles was large, a large amount of nanodiamond was co-deposited with the nickel. The results are interpreted to indicate that the adsorbed Ni-complex precipitates the incorporation of nanodiamond particles into the nickel matrix. In addition, incorporation becomes more probable when the adsorbed amount of Ni-complex on the nanodiamond particles was large.     

Gold wire bondability of electroless gold plating using disulfiteaurate complex

Generally, contact or terminal areas are coated with nickel as a barrier layer; subsequently, gold plating is performed to maintain reliability of electrical interconnection. Treatment using dilute solutions of palladium ions have been applied to initiate electroless nickel plating on copper substrates because copper has no catalytic action for the oxidation of hypophosphite. However, trace amounts of palladium ions may remain on the unwanted areas and extraneous nickel deposits are often observed. We confirmed that nickel films without extraneous deposits can be formed using the activation solutions containing dimethyl amine borane (DMAB). Bondability on the electrolessly deposited gold was greatly influenced by the phosphorus contents of the deposited nickel films as the underlayer. Bonding strength after electroless gold plating was increased with increasing phosphorus contents in the nickel films. Stabilizers in the electroless gold plating also influenced the bonding strength. Baths containing cupferron or potassium nickel cyanide as a stabilizer showed superior bondability. Gold deposits having strong orientation with Au(220) and Au(311) indicated high bond strength.     

Ni–Zn–P alloy deposition from sulfate bath: inhibitory effect of zinc

Electroless Ni–Zn–P alloy deposition from a sulphate bath, containing sodium hypophosphite as reducer, was investigated. To increase the plating rate, the deposition parameters were optimized. The effect of process parameters (T, pH and [Zn²⁺]) on the plating rate and deposit composition was examined and it was found that the presence of zinc in the bath has an inhibitory effect on the alloy deposition. As a consequence, the percentage of zinc in the electroless Ni–Zn–P alloys never reaches high values. Using cyclic voltammetry the electrodeposition mechanism of Ni–Zn–P alloys was investigated. It was observed that the zinc deposition inhibits the nickel discharge and, as a consequence, its catalytic activity on hypophosphite oxidation. It was also found that increase in temperature or pH leads to the deposition of nickel rich alloys.     

Establishing relationships between bath chemistry, electrodeposition and microstructure of Co-W alloy coatings produced from a gluconate bath

Electrodeposited Fe group: W and Mo alloys have the potential to replace hard Cr coatings for use in engineering applications where wear and corrosion resistance are needed. Electrochemical studies have concentrated in the past on Ni-W alloy deposition, but now interest in Co-W alloys has developed as they possess lower coefficients of friction when in contact with another metal. The most attractive coating composition is in the range 14-20 at.% W, if controlled deposition promotes crystalline alloys of high hardness, rather than softer amorphous alloys containing >20 at.% W. This paper employs ammonia free baths with low concentrations of cobalt and sodium tungstate and varying additions of sodium gluconate to produce alloys at close to 50% efficiency. Voltammetry, UV and visible spectrometry, and potentiostatic deposition have been performed on such baths, whilst XRD, SEM and TEM observations have been made on the deposits. This aims to optimise the process and to understanding the relationships between bath contents, electrochemical kinetics and alloy composition. Efficient deposition of coatings with hardness values up to 1000 kgf mm⁻² occurred from a bath containing a high concentration of gluconate. Such deposits arise from concentrations of Co-W-gluconate complexes which promote the formation of nanoscale alloy grains. Current densities up to 2.75 A dm⁻² in the agitated bath promoted deposition kinetics to form these highly orientated structures. These kinetics produced nano-segregation of W which may be assisted by the migration of Co-W clusters to boundary sites during the growth of the deposit.     

Electroless thin film CoNiFe-B alloys for integrated magnetics on Si

Electroless magnetic thin films have been deposited from borane-based baths suitable for use in integrated magnetics on Si applications. The baths were developed for compatibility with standard photoresist for microfabrication of integrated magnetics on Si. The specific formulations, which differ from those reported previously, yield uniform, high saturation magnetisation (up to 2.15 T) deposits with low coercivity (<2 Oe). The resistivity of the film can be increased to minimise eddy current losses by using higher dimethylamine borane (DMAB) content or the inclusion of a second reducing agent, hypophosphite, to facilitate phosphorus codeposition of up to 7 at.%. The Ni content in the plating bath has been shown to exert significant influence over the composition, deposition rate and coercivity. XRD analysis suggests that the deposits consist of nanocrystalline phase with grains <20 nm. Such small grains are consistent with the observed low coercivity of the deposits.     

Effect of halide ions on electroless nickel plating

The effect of halide ions (F^–, Cl^–, Br, I^–) on nickel deposition in acidic electroless nickel plating baths is investigated. Halide ions were found to have a significant effect on the nickel deposition and the results could not fully be explained using mixed-potential theory. A correlation between the stability constants of halide ions with palladium (ii) ions and the plating rate is proposed to explain the observations. Various parameters, such as the activation energy, deposit microstructure and phosphorus contents of the plating bath in the presence of various halide ions, were also studied.