Showing papers in "Plating and Surface Finishing in 1997"

Chemistry & theory of chromium deposition : Part I - Chemistry

Abstract: Although electrodeposition of chromium has been practiced for 75 years, the mechanism is still open to conjecture. Part of the reason is the complexity of the chemistry of chromic acid and its existence in aqueous solution in the form of coordinated octahedral complexes. These complexes vary both structurally and kinetically at different CrO 3 concentrations. The chemistry of tri- and hexavalent chromium is discussed, including polymerization and related mechanisms relative to the overall deposition mechanism.

Properties of nickel-tungsten alloys electrodeposited from sulfamate electrolyte

Abstract: Tungsten and its alloys are of interest in both theoretical and applied aspects because of their specific tribological, magnetic, electrical and electro-erosion properties. Electrodeposited Ni-W alloys successfully vie even with ceramics and graphite by virtue of high thermo-resistance. Another perspective is their application in magnetic heads, bearings, magnetic relays, catalysis of the processes of oxygen- and carbon-containing components of tungsten, electrodes for hydrogen energetics, etc. Interest in these alloys has expanded unusually rapidly in recent years because of scientific and industrial applications in electrodeposition of compositionally modulated multilayers (CMM).

A study of SiC/Ni composite plating in the watts bath

Abstract: Codeposition behavior of SiC powders with Ni under various conditions was studied. In the low-current-density region, codeposition follows the two successive adsorption steps first proposed by Guglielmi. On the other hand, codeposition is a function of powder transfer control in the high-current-density region. These predictions were verified experimentally. In addition,the effect of stir on the volume fraction of SiC powders in the deposit was also investigated.

Evaluation of sealing methods for anodized aluminum alloys with electrochemical impedance spectroscopy (EIS)

Abstract: Al alloys 2024, 6061 and 7075 have been anodized in H 2 SO 4 solutions of two different concentrations and sealed in either boiling water or solutions of nickel acetate, cerium acetate or yttrium acetate at two different temperatures. The same aluminum alloys were anodized in Boeing's Boric-Sulfuric Acid Anodizing (BSAA) process and sealed in a dilute chromate solution or boiling water. The properties of the sealed oxide layers and their changes during exposure to 0.5 N NaCl were monitored using EIS. From the impedance spectra, the pore resistance, R po , and the specific admittance, As, were determined as a function of exDosure time extending up to 14 days. At the end of exposure, the anodized surfaces were examined by visual observation to determine the total pitted area, A pit . Sealing in cerium acetate solutions produced samples with a corrosion resistance comparable to that determined for sealing in nickel acetate.

Investigation of electroless Ni-P-SiC composite coatings

Abstract: Electroless Ni-P-SiC composite coatings were investigated from the viewpoint of bath formulation, technology and coating properties. A sound and homogeneous deposit containing 25-30 vol. percent SiC can be produced, using an optimum bath formulation and technology. In comparison with Ni-P coatings, Ni-P-SiC composite coatings possess greater hardness and higher porosity, as well as lower adhesion and corrosion resistance. It is a significant advantage that the wear resistance of the composite coating is considerably increased. Heat treatment at high temperature can improve adhesion and wearability of the composite coating. Structural analysis confirms that a new phase of Ni 3 Si compound exists in the Ni-P-SiC deposits annealed at 650 °C for 1 hr. In this paper, formation of the Ni 3 Si compound and wear mechanism of the coatings are discussed.

Optimizing palladium conversion in electroless palladium plating of alumina membranes

Abstract: Electroless palladium (Pd) plating on alumina membranes was investigated with the aim of obtaining very high Pd conversions and pure Pd films. Interactions among operating variables including Pd source, temperature, reducing agent concentration, stabilizer concentration and buffer pH, require proper choice of these variables to ensure plating solution stability and to maximize the conversion of Pd salt to Pd metal. A preliminary investigation of these variables readily enabled conversions exceeding 80 percent to be obtained after three hr of plating. Near optimal values (>95%) were also achieved within a three-hr reaction period for a very specific choice of variables. Surface uniformity and purity of the deposited film were excellent. The operating concentration of the stabilizer (Na EDTA) appears to be the most significant consideration in the plating process. Varying Na EDTA concentration results in an optimal region of Pd conversion. Conversions quickly decreased when the system became unstable or if the system had too great a stability.

Practical & Theoretical Aspects of Regeneration of Chromic Acid Plating Solutions via Electrolytic Purification (Porous Pot Method).

Abstract: Most common metallic impurities, such as Ni, Zn, Fe, Cu and Cr(III) ions found in decorative (bright) or functional (hard) hexavalent chromium plating solutions can be effectively removed and concentrated as a sludge by electrolytic coagulation, using a porous ceramic separator. Experiments were carried out in a laboratory-scale porous pot at two current levels. The Sargent type, hard chromium plating solution containing simulated metallic impurities was used. In the same process, Cr(III) is effectively oxidized to Cr(VI) at the outside insoluble lead anode. The results show that optimum conditions for efficient operation depend on current density, initial pH and nature of the cathode. From cyclic voltammograms, pH measurements, metal removal rates and theoretical principles, complex electrochemical and chemical processes involved were analyzed. They are presented as much as possible in simplified form. A set of practical guidelines is detailed.

Chemistry & theory of chromium deposition: Part II-Theory of deposition

Abstract: In Part II, various theories of chromium electrodeposition, based on wide-ranging research, are discussed, and an effort is made to show the complexity of chromium deposition and that it is still not completely understood. Part I was published in the May 1997 issue of P&SF.

Zeta potential & codeposition of PTFE particles suspended in electroless nickel solution

Abstract: The relation between the Zeta potential and codeposition of PTFE particles was investigated by studying the effects of various kinds of surfactants on dispersion and the Zeta potential of the treated PTFE particles. The results show that the Zeta potential of PTFE particles is more positive, the PTFE particles are easier to codeposit with Ni-P and the PTFE content in coatings is greater. In this experimental process, the PTFE content is about 25 volume percent on average.

Electrodeposition of zinc-cobalt alloy from cyanide-free alkaline plating bath

Abstract: Zinc-cobalt alloy coating having 0.3 to 1.0 percent cobalt has been deposited from a conventional non-cyanide alkaline zinc plating bath containing zinc, NaOH, and proprietary addition agents. The alloying element, cobalt, is added to the bath together with a complexing agent. The influence of plating bath and process variables, such as temperature, agitation and current density on alloy deposition was studied in detail. The deposit characteristics and corrosion resistance of the Zn-Co coating were evaluated and compared with conventional alkaline zinc. The Zn-Co alloy accepts all usual chromate conversion coatings with a modification in composition, pH and time of immersion.

Performance characteristics of zinc alloys

Abstract: Electroplated alloys of zinc with iron, cobalt or nickel are being used to improve the corrosion resistance of coatings, compared with normal zinc coatings. Acidic and basic plating solutions are being used to deposit these alloy coatings, resulting in a wide array of choices for the electroplater and the parts designer. This paper explores the characteristics of the plating baths used to deposit the zinc alloys and describes the properties of the resulting deposits.

A study of the effects of diammonium citrate on electroformed nickel-tungsten alloy

Abstract: The effect of diammonium citrate on electroformed nickel-tungsten alloy from a sulfamate bath was studied, using citric acid as a buffer. Addition of diammonium citrate in the alloy bath increased the percentage of tungsten in the alloy electroforms, but the internal stress was concurrently increased. To overcome the increased internal stress, two stress reducers, namely sodium benzene sulfonate and benzene sulfonamide were tested. Moreover, the effect of diammonium citrate on the hardness after thermal treatment of the alloy electroforms was also considered.

The evaluation of tungsten carbide thermal spray coatings as replacements for electrodeposited chrome plating ion aircraft landing gear

Abstract: Tungsten carbide (WC) thermal spray coatings applied hy the high velocity oxy-fuel (HVOF) process are considered the leading candidates for replacement of hard chrome plating. This article describes the decision-making process followed to establish the acceptability of WC thermal spray coatings for aircraft landing gear applications. Descriptions of both the laboratory testing phase and the in-service evaluation phase are given.

Preparation of anisotropic conductive particles by electroless plating

Abstract: The problem of connection reliability with large-scale integrated circuits was studied via preparation of conductive particles from electroless nickel solutions. Uniformly covered particles were obtained from an electroless nickel bath, with glycine as a complexing agent. Uniformity was further improved by the addition of a cationic surfactant in the plating bath.

Electroforming of electronic devices

Abstract: Lubomyr Romankiw, who was the AESF Scientific Achievement Award recipient in 1991, was judged by the attendees at the March 1996 AESF Electroforming Symposium as being the excellence in presentation winner among the individuals who presented papers at that event. This is an edited version of his informative discussion of plating through mask technology (one of the names electroforming in electronics is known by). In traditional electroforming, the object is an entity by itself and is expected to part readily from the substrate after plating. In plating through mask technology in electronics, the electroformed metal has to adhere very strongly to the substrate, and it usually represents only one layer of a multilayer structure. Dr. Romankiw's paper covers a history of the development of platingthrough-mask technology in electronics, patterning and pattern transfer, plating through lithographic masks as used in thin film heads, thin film chip carrier manufacture and in fabrication of a prototype of an integrated magnetic minimotor.

Adsorption of hydrogen ions on the surface of SiC powder in solution of nickel sulfate during composite coating

Abstract: In codeposition of inert particles with a metal, two processes are involved-adsorption of ions on inert particles and on the cathode. For the first of these processes, for the Ni-SiC system, the pH changes of NiSO 4 and Watts solutions resulting from addition of SiC particles were measured. The influence on the character of pH changes as a function of time was determined for nickel ions, initial pH, SiC particle concentration, dimensions and type, and for preliminary purification in HNO 3 .

Acid sulfate & pyrophosphate copper plating

Abstract: PLATING & SURFACE FINISHING Applications Both acid sulfate and copper pyrophosphate copper plating solutions find use today in several areas. Acid sulfate solutions are the predominant copper plating solutions used in the printed circuit industry, although pyrophosphate solutions are specified by some Federal agencies where ductility of the deposit is of paramount importance. Recent advances in additive systems have resulted in comparable physical properties from acid sulfate solutions. Both solutions are also used in the plating-on-plastics industry after an electroless strike has been applied to the nonconductive surfaces. Acid sulfate copper solutions are also used to plate steel wire, stainless steel cooking utensils and zinc die castings (after a cyanide copper strike). Pyrophosphate solutions are often used in electroforming applications and in the plating of zinc, aluminum, and steel die castings. Pyrophosphate solutions are alkaline and are, therefore, less corrosive to plating equipment than acid sulfate. The deposit has excellent physical properties. The solutions have good throwing power, allowing surface-to-hole ratios of 1:1 to be achieved. Copper pyrophosphate solutions are, however, very difficult to control and are more difficult to waste treat than their acid sulfate counterparts. Acid sulfate solutions are corrosive and must be used in equipment designed for them. With appropriate additives, they are easy to control, have good throwing power (surfaceto-hole ratios close to l:l can be obtained) and are easily waste-treated.

The influence of pulse frequency on the hardness of bright copper electrodeposits

Abstract: The hardness of copper coatings deposited by direct and pulsed currents were measured. The proprietary bright acid solution used contains an agent, SA-LFPP, having high hydrodynamic activity. This additive, with a pulse frequency of 5 Hz, produced a synergistic effect on initial coating hardness values (about 230 HV). These values remained unchanged for more than 270 days. The results obtained prove the validity of the previously described mechanism oflow-frequency pulse plating with brighteners. This mechanism predicts the occurrence of the maximum hardness values at a limiting frequency as a result of an optimal matching of the process rates of nuclear formation, brightener adsorption, and incorporation into deposits.

Materials characterization of a non-cyanide silver electrodeposit

Abstract: This paper presents results of a CRADA (Cooperative Research and Development Agreement) between Technic, Inc., and the Lawrence Livermore National Laboratory, directed at developing a non-cyanide plating solution for deposition of thick (>125 μm) deposits. Results were quite successful with a succinimide-based formulation. Data are included on grain size (transmission electron microscopy), hardness, electrical resistivity, ductility, stress and wear.

Acceleration mechanism of thioglycolic acid for electroless nickel deposition

Abstract: The effect of thioglycolic acid (TA) on the deposition rate of electroless nickel (EN), hydrogen evolution, and activation energy of reaction was investigated. The results show that thioglycolic acid can accelerate reduction of Ni +2 and H + simultaneously, and decrease the activation energy of the EN deposition reaction. The anodic and cathodic polarization curves show that thioglycolic acid accelerates only the anodic oxidation of H 2 PO 2 - and does not affect the cathodic process directly. The elemental composition of Ni-P deposits was determined by XPS and AES. The acceleration mechanism is described as a result of adsorption of thioglycolic acid and its interaction with H 2 PO 2 . on the active metallic surface. Cleavage of the PH bond is accelerated and electrons are easily transported to the metallic surface through the sulfur and hydrogen atoms of the acid, resulting in simultaneous reduction of Ni +2 , H + , and H 2 PO 2 - .

A new low-temperature electroless nickel plating process

Abstract: A new low-temperature electroless nickel plating process was developed by adding some inorganic agents to the plating solution, in which citrate acted as complexing agent. With the optimum process determined, high deposition rate was obtained, resulting in a bright deposit with excellent adhesion.

Characterization of bright/semi-bright nickel electrolytes & corrosion properties of the corresponding nickel deposits

Abstract: The capability of cyclic voltammetry for the characterization of bright and semi-bright nickel electrolytes is reported. Evaluation was made of the effect of various organic additives on the features of the resulting cyclic voltammograms. A method for quantifying of these additives is outlined. In addition, cyclic voltammograms are evaluated in terms of the corrosion performance of the nickel deposits. These data were compared with STEP test data.

Electrochemical porosity measurement of electroless nickel coatings on ferrous substrates : Information resulting from AESF Research Project

Abstract: A non-destructive electrochemical method is used to measure the porosity of electroless nickel (EN) coatings on steel and gray cast iron. The method is based on determining the mixed potential of a duplex metal surface consisting of an EN coating and the ferrous substrate exposed by the pores in a corrosive electrolyte; the measured porosity is quantitatively expressed in terms of the fraction of pore area on the coating surface. The accuracy of this method is compared to the conventional ferroxyl and salt fog spray tests. The electrochemical technique is found to be more sensitive than the ferroxyl test, and provides the porosity information comparable to that of the salt fog test in a much shorter time without destroying the appearance of test samples. The electrochemical porosity measurement is subsequently used to examine the effect of substrate preparation, including surface polishing and an electrolytic nickel strike, on the porosity of EN coating on carbon steel and gray cast iron substrates. It is found that the porosity of EN coatings decrease with decreasing roughness of the substrate surface. Mechanically polishing the substrates to 1-μm smoothness prior to EN plating eliminates nodular EN deposits and reduces the porosity of the EN coating. Electropolishing of the substrate surface also results in EN deposits with low porosity. An electrolytic nickel strike on carbon steel and gray cast iron prior to EN plating decreases the porosity of the EN coating by covering exposed graphite and other non-catalytic inclusions on the substrate surface with a catalytic nickel layer. The porosity of an EN coating,decreases with increasing thickness of the nickel strike. A nickel strike of 1 μm in thickness virtually eliminates nodular EN deposits and reduces the coating porosity by a factor of 100 to an area fraction of pores less than 10 -5 .

Application of precision filtration to an electroless copper plating bath

Abstract: Electrolytic and electroless plating are becoming extremely important for forming functional thin films. Printed circuit boards are indispensable as elements of electronic equipment, and the boards are shrinking in size. Accordingly, the full additive process can be attractive as a substitute for the subtractive process. Extraneous deposition occurs easily on the circuits, however, when copper is deposited using the additive process. The sulfate and formate ions accumulated during the plating reaction are the cause of extraneous deposition, or plate-out. Nascent hydrogen is also a possible cause inasmuch as extraneous deposition develops with the evolution of hydrogen gas, as shown in Fig. 1. 1 Extraneous deposition still occurred, however, even when these related factors were eliminated. Fine inorganic particles in the plating bath are also a possible cause of extraneous deposition. 2 Accordingly, elimination of the extraneous deposition by filtration was investigated, as well as the inhibiting effect of the filtering media.

Metallization of piezoelectric ceramic surfaces

Abstract: This paper reports metallization of PZT (lead zirconate titanate) piezoelectric ceramic surfaces accomplished by an electroless plating process with proper after-treatment With this method, nickel electrodes can be formed on PZT piezoelectric ceramic components used in piezoelectric ceramic wave filters The main mechanical and electric properties of the piezoelectric ceramic components with this type of plated Ni electrode are as good as, or even better than, those with fired-on Ag electrodes This paper introduces the detailed process of pretreatment, electroless plating and after-treatment, and discusses the principles, results and various effective factors in each process, and indicates preferred operating conditions and control methods feasible in practical production

Properties of Ni-WC electrocomposites

Abstract: A significant increase in hardness and wear resistance was observed by incorporation of WC particles in nickel deposits. These properties were not drastically altered, even after annealing up to 800 °C, unlike nickel deposits. This has been attributed to Ni-W solid solution formation. Also, the oxidation resistance of the composite was found to be better than that of pure nickel deposits.

Interference coloring of dual-anodized films on aluminum containing electrolytically deposited thin metal layers

Abstract: This study concerns the properties and structure of oxide films on aluminum, anodized in a sulfuric acid bath, first by DC, and next by AC in the same bath; Sn-Ni metal was then deposited electrolytically into the micropores. Each film showed fine colors that varied from blue, green, and to gold in medium tones as thickness of the AC films increased. EPMA line analyses disclosed that Sn deposited cleanly at the bottom of the micropores, with maximum intensity increasing with the kind of colors. In observations with SEM, the back-scattered electron images proved clearly the difference for AC films; also, the secondary electron images exhibited metal deposition like tree twigs in very fine micropores. The colors obtained indicated good corrosion resistance and light fastness.

Advanced techniques for replacing chromium : Third information exchange

Abstract: Because this issue of Plating and heels of the environmental and resource-oriented programs of AESF Week 1997, it is a good time to note another program that took place last November 4-6, 1996, at the venerable, but at the time snowless, Seven Springs Ski Resort, in the Laurel Highlands of Pennsylvania. The third annual information exchange on Advanced Techniques for Replacing Chromium dealt with the issue of substitutes for chromium-based coatings derived from hexavalent processes.