Showing papers in "Plating and Surface Finishing in 1998"

Nickel plating on steel by chemical reduction

Abstract: A process has been developed for the production of adherent nickel deposits of good quality on steel without the use of an electric current. The deposition of nickel is brought about by chemical reduction of a nickel salt with hypophosphites in a hot ammoniacal solution. The reaction is catalytic and, under the prescribed conditions of concentration and pH, no reduction occurs in the solution unless certain metals, such as steel or nickel, are introduced into the bath. The reduction then occurs only at the surface of the immersed metal with the production of a coating of nickel of 96 to 97 percent purity.

Electropolishing of titanium and titanium alloys in perchlorate-free electrolytes

Abstract: A new perchlorate-free electrolyte electropolishing process for titanium and titanium alloys has been developed, using a sulfuric acid-methanol mixture as electrolyte. Electrolyte composition and polishing conditions were optimized by measuring current-voltage curves on a rotating disk electrode at temperatures of -10 to 25 °C. Mass-transport-controlled limiting current plateaus were observed for sulfuric acid concentrations between 2 and 4 M. Best polishing was obtained in an electrolyte containing 3 M sulfuric acid at an applied potential of 8 V against a saturated mercurous sulfate reference electrode. The topography of the polished surfaces was characterized by optical microscopy, optical profiling and by atomic force microscopy.

Co-W alloys for replacement of conventional hard chromium

Abstract: The influence of deposition conditions on bath stability and some coating properties was investigated. Using the Rochelle salt-ammonium chloride bath electroplating, with the soluble tungsten anode, was possible only at elevated temperatures of about 90 °C and resulted in current efficiency at 92 to 96 percent. With an inert platinum anode, deposition temperature could be reduced to 50 °C, but with significant decrease in current efficiency and much faster deterioration of the bath. Deposits obtained from the bath with the tungsten anode were fine-grained, with crystallite size 90 to 150 A, while plating at 50 °C with an inert platinum anode yielded nanocrystalline coatings. Thermal treatment of deposits at 400 to 500 °C in air led to the formation of a Co 3 O 4 surface layer, 3-5 μm thick. The oxide coating was distinguished by good protective characteristics, capable of enhancing corrosion resistance substantially. Properties of alloy deposits are compared with those of conventional hexavalent chromium.

Composite electroless nickel coatings for the aerospace & airline industries

Abstract: This paper discusses in depth the variety of composite electroless coatings used in the aerospace and airline industry. Included are (1) Composites with wear-resistant particles, including diamond, aluminum oxide, tungsten carbide, silicon carbide and boron carbide for hardness, wear and impact resistance; (2) composites with self-lubricating particles, including PTFE, as well as harder inorganic materials that provide greater wear resistance with a low coefficient of friction and are capable of withstanding high temperatures; and (3) composites with light-emitting particles for wear-indicating layers, as well as product authentication. Test results, a cross sectional photomicrograph and patent references are also included.

Cathode process in nickel-cobalt alloy deposition from sulfamate electrolytes : Application to electroforming

Abstract: Electroforming is a specialized application of electroplating for the production of finished components and unique articles that cannot be made by any other method. Sulfamate electrolytes for Ni-Co deposition form highly efficient and stable solutions, but their wide use for electroforming has been hampered by the fact that the mechanism of Ni +2 and Co +2 codeposition is as yet imperfectly understood. Study was made of the effect of electrolyte composition and operating conditions on the Ni-Co alloy constitution and the mechanism of its electrodeposition. It was shown that the Faradaic efficiency of the deposition is characterized by a complicated dependence on pH with a maximum of 98.5 percent at pH 3.5 to 3.8. The concentration of cobalt in the deposit decreases by as much as five to seven percent for a pH rise from 2 to 5.2. A minor increase of cobalt concentration in the electrolyte is followed by a steep rise in the cobalt content of the alloy. At a ratio of cobalt to nickel of 0.1, the alloy contains 45 percent cobalt; at equal cation concentrations, the alloy contains 73 percent Co. This is because of the faster kinetics of Co +2 reduction. By rotating-disk-electrode and chronopotentiometric methods, it was demonstrated that the rate-determining step of alloy deposition is the electrochemical reaction, complicated by adsorption. It is believed that the codeposition of Ni +2 and Co +2 is explained by the formation of heteronuclear surface complexes with sulfamate anion as the bidentate ligand. The alloy structure and physical and mechanical properties, such as hardness, internal stress, tensile strength, elongation and thermal stability were also studied. An optimum was found between alloy characteristics and operating conditions. Parts having complex shapes (molds, miniature nozzles and other electronic and aircraft components) were produced by Ni-Co electroforming.

Improved copper plating through the use of current pulsing & ultrasonic agitation

Abstract: High-frequency and high-current pulse plating, as well as ultrasonic agitation, have been used to improve the smoothness and microhardness of copper coatings produced by electroplating from a sulfate bath in the absence of brightening agents. By carrying out pulse reversal plating at higher pulse frequencies (200 kHz) than have previously been reported for copper plating, coatings have been produced with VHN microhardness values (50 g load) slightly above 200, normally achievable only with the addition of brightening agents. Pulse reversal plating has consistently been found to produce a smoother and harder deposit than pulsed current plating. The best results have been achieved by combining an ultrasonic field having a strength of 60 watts with current reversal plating at 200 kHz, 80 percent duty cycle and 10 A/dm 2 average cathodic current density. This yielded a deposit with a microhardness of 230 VHN and a mirror smooth finish without having to do any mechanical polishing.

A study of zinc-iron alloy electrodeposition using a rotating cylinder hull cell

Abstract: A study has been made of the zinc-iron alloy electrodeposition system, using chloride solutions, to establish the composition dependence upon the deposition parameters of current density and agitation achieved by rotation of cylindrical cathodes. It is shown that a deposit composition of approximately 10 to 80 percent iron in zinc can be consistently obtained, thereby enabling two layer deposits to be obtained from a single solution by varying these two parameters. Additions of ammonium chloride act not only as conductivity salts, but as deposit grain refiners.

Bright Tin-Silver Alloy Electrodeposition from an Organic Sulfonate Bath Containing Pyrophosphate, Iodide & Triethanolamine as Chelating Agents

Abstract: A new tin-silver alloy plating bath was investigated to obtain a lead-free solderable coating. Bright tin-silver electrodeposits having compositions close to eutectic were obtained from an organic sulfonate bath containing pyrophosphate, iodide and triethanolamine as chelating agents, and an amine-aldehyde reaction product as a brightener. A suitable bath composition was determined and the relationship between silver content in the deposit and bath composition and operating conditions were investigated. Properties of the deposits (i.e., solderability and whisker growth) were also investigated.

Alloys are promising as chromium or cadimum substitutes

Abstract: A Significant amount of work on electrodeposited alloys is available. Browsing the Internet and pointing the browser on alloys can get over 40,000 hits. The commercial database STN' gets more than 400,000 hits on the term alloy. One article cannot cover all of the available alloys. This one discusses the alloys that are being used or evaluated as replacements for cadmium and chromium.

Microstructural morphology of Zn-Fe alloy electrodeposited coatings

Abstract: The morphologies of zinc-iron alloy electrodeposits, produced from a chloride solution, have been studied over a wide composition range, using current density and electrode rotational agitation as the main process parameters. Change of current density was the greatest influence on morphology and can be correlated with changes of deposit composition. Rotational agitation should be high for compositions of less than 10 wt percent Fe and low for compositions of greater than 10 wt percent Fe. Additions of ammonium chloride act as a grain refiner.

Electrochemical preparation & mechanical properties of amorphous nickel-SiC composites

Abstract: In this study, an attempt was made to incorporate SiC particles into an amorphous nickel-phosphorus alloy matrix by electrodeposition. The bath composition and operating conditions of electrodeposited Ni-P-SiC composite coatings were studied and the structure and mechanical properties of the deposits were determined.

Electrodeposition, growth morphology & melting characteristics of gold-tin eutectic alloys

Abstract: Eutectic Au-Sn (80/20 percent by weight) solders have good electrical and heat conducting properties, as well as superior thermal fatigue strength as compared to other material used in microelectronics assembly, such as SnPb-solders and conducting epoxies. A chemistry has been developed to electroplate high quality Au-Sn deposits and to characterize the coatings in terms of alloy and phase composition, structure, and melting characteristics. An operating window and the long-term stability of the plating process have been established.

Multilayer composition-modulated deposits of Zn-Fe alloy

Abstract: Composition-modulated multilayer alloys of Zn-Fe have been produced from a single chloride-based solution, using current density and agitation as the parameters of modulation. SEM examination has shown that the multilayer structure was developed in a predictable manner and that solution and deposition parameters can affect the leveling and regularity of the multilayers. Comparison has been made with multilayers produced by a dual bath technique.

Why use electroless nickel today

Abstract: The unique properties of electroless have resulted in the steady growth of both the number of applications and consumption of electroless nickel (EN) since it recovered from a lull in the mid-1980s. Today, there are approximately 1,000 facilities in North America that are processing EN-most of which are jobshops using proprietary bath formulations. The original Kanigen (catalytic nickel generation) process mixed by the user, however, is still in widespread use, particularly for the petroleum industry. Also, the use of specialized high- and low-phos processes and composite processes has grown rapidly.

An alternative surface finish for tin-lead solders

Abstract: A novel tin electrodeposition chemistry and process has been developed. This process produces smooth, satin bright tin deposits that have stable, large grain structures. The deposits contain very low organic content and, as a consequence, exhibit excellent ductility, solderability and reflowability. The chemistry is capable of operating at elevated temperatures over a wide range of current densities, and is thus applicable to rack, barrel and reel-to-reel operations. All chemical components, including breakdown products, are fully analyzable with conventional analytical methods. Extensive bath life studies show that the deposit appearance and material properties, including grain structures, are stable in relation to the age of the electroplating chemistry. In addition, the grain refiners used are highly stable, and have few breakdown products as the chemistry ages. All these features imply a robust process that has been confirmed in various manufacturing environments. This tin electroplating process has been utilized in plating coatings for connectors, solder bumps, PWBs and components for semiconductor applications.

A new method of etching ABS plastic for plating by ultrasound

Abstract: An ultrasonic etching method is effective for pretreatment of ABS plastic for plating with fewer chemicals and lower cost of wastewater treatment. After ultrasonic etching for 40 min, the improvement of adhesion strength can increase by 30 percent, compared with that of chromic acid etching in the same or other conditions. The mechanism of adhesion improvement was studied by examination of weight loss, surface roughness, image analysis, SEM and XPS.

How chelating resins behave

Abstract: Chelating resins are gaining as the best avallable technology for the of transition and heavy metal cations from ground water and from plating waters. These specialty exchange resins are of removing metals in the presence of ions such as calcium, magnesium and sodium. This paper describes the various of chelating resins that are commercially available, the conditions under they will and will not and explores the input require-ments necessary to a system design.

The role of electroless plating bath constituents in the catalytic oxidation of the hypophosphite ion

Abstract: Oxidation of the hypophosphite ion by water at the surface of a standard reference nickel catalyst (EuroNi-1) has been studied at 80 °C and pH 4. The effects of a number of bath additives, commonly used in electroless plating bath formulations, have been studied by measurements of the hydrogen evolved and the phosphorus deposited on the catalyst. This reaction occurs concurrently with the plating reaction in electroless plating baths, using hypophosphite as reducing agent. The results of this work are discussed in terms of their relevance to the mechanism of electroless plating.

Structure & properties of electroless Ni-P-B4C composite coatings

Abstract: The surface image and inner structure of electroless Ni-P-B 4 C deposit layers were observed and analyzed by SEM, optical microscope and X-ray diffractometer. The results showed that with increase of the amount of B 4 C particles in the plating solution, the number of the surface nodular protrusions increased. The particles of B 4 C evenly dispersed on the Ni-P matrix and adhered well in the coatings. The presence of the B 4 C particles does not change the phase composition. The mechanical properties of composite coatings were measured. The results indicated that with increase of the content of B 4 C, the hardness and wear resistance were obviously improved, but the critical load was decreased.

Electroless copper plating on PZT ceramic

Abstract: A PZT [Pb(Zr,Ti)O 3 ] ceramic has been used in electronic devices such as pressure sensors, resonators and capacitors, because it holds piezoelectricity. Conductive paste is generally applied for the construction of circuits or electrodes on the PZT ceramic. In small electronic devices, however, its application to micro-circuits or electrodes is not easy. Accordingly, applicability of electroless copper plating on the ceramic was evaluated. Etching with a mineral acid is generally applied for obtaining good adhesion of deposited copper on the ceramic. This may cause deterioration of the electronic properties of the ceramic, however, and for this reason, electroless copper plating without etching becomes important. In this study, the use of the optimum pretreatment process and bath composition under best plating conditions allowed us to obtain electroless copper of sufficient adhesion strength, with no blisters.

Gold-plated contacts : Effect of thermal aging on contact resistance

Abstract: A study was made of the effect of thermal aging on the contact resistances of pure gold platings, as well as of cobalt- and nickel-hardened gold platings (Hard Golds), on copper. Samples were aged at several temperatures, and contact resistance was determined by probing according to ASTM B-667. It was found that, although nickel underplate retards the rate of increase of contact resistance of pure gold, it may accelerate the rate for Hard Golds. This effect becomes more pronounced with increasing hardener content and Hard Gold thickness. Nickel-golds are more stable than cobalt-golds.

Effect of isomeric dipyridyls on electroless copper deposition from EDTA solutions

Abstract: The effect of 2,2'-, 2,4'- and 4,4'-dipyridyl on the rate of electroless copper deposition from EDTA solutions was examined. It was found that, of all dipyridyls examined, only 2,2'-dipyridyl increases the copper plating rate at concentrations of 5 x 10 -5 to 8 x 10 -4 mol/dm 3 , The results were compared to those obtained by chronovolt-amperometric method from solutions of similar composition and pH.

Composition dependence of some physical properties of Fe-Tm-B (TM = Mo, W, Mo-W) alloys obtained by electroless plating

Abstract: Composition dependence of some physical properties of Fe-TM-B (TM = Mo, W, Mo-W) alloy deposits obtained by electroless plating has been studied. Their microhardness increases continuously with increase of the B content. The Fe-Mo-W-B alloy deposits possess higher glass formability and simultaneously lower magnetic losses in the range of B content from 9.8 to 27.3 atomic percent. The magnetic losses of the deposits depend strongly on the physical phase composition and its content.

Toward understanding nickel activation & chromium reverse etching

Abstract: A contribution is offered for better understanding of cathodic activation of nickel prior to decorative chromium plating and for reverse etching before hard chromium plating. Causes and cures for nickel passivity are given. Anodic etching prior to hard chromium plating is analyzed in relation to the influence of the base metal, and plating chromium over chromium is detailed. Practical aspects are given and theoretical explanations are presented for electrochemistry related to activation and reversing mechanisms.

Hard anodizing behavior of aluminum alloy DTD 5124 containing varying amounts of impurities under different electrolytic conditions

Abstract: The influence of various additives in hard-anodizing electrolytes to counteract the detrimental behavior of Al 12 (FeMn) 3 Si particles in aluminum alloy DTD 5124 has been investigated. Studies reveal that the addition of a small amount of hydrochloric acid, nitric acid or ammonium nitrate in sulfuric or sulfuric-oxalic acid electrolyte is capable of counteracting the inhibition of hard-anodic film growth resulting from the presence of constituent particles of impurities. The small amounts of these additives enables the electrolyte to dissolve the constituent Al 12 (FeMn) 3 Si particles during film growth. The optimum concentration of additives and other hard anodizing parameters have been evaluated.

Electro-oxidation of ascorbic acid in an aqueous citrate buffer solution

Abstract: Ascorbic acid is a non-toxic reducing agent with potential applications in the electroless deposition of metals. Reducing agents can be consumed through (i) homogeneous reactions in solution (e.g., reaction with gold thiosulfate, oxygen or peroxide) and (ii) heterogeneous surface reactions, leading either to the deposition of metal or non-metal depositing reactions. The chemical and electrochemical oxidation of ascorbic acid has been investigated in an aqueous citrate solution at pH 6.4 and 25 °C to quantify its consumption rate in electroless processes. Ascorbic acid undergoes a homogeneous reaction with dissolved oxygen in a pseudo first-order reaction having a rate constant of (1.75 x 10 -3 )/min. This is equivalent to consuming five percent of the initial ascorbic acid concentration in 30 min. Hydrogen peroxide is one of the possible side products of ascorbic acid oxidation. The addition of hydrogen peroxide on gold surfaces does not significantly accelerate the reaction between dissolved oxygen and ascorbic acid. The diffusion coefficient was found to be 6.46 x 10 -6 cm 2 /sec.

The mechanism of electrodeposition of chromium coatings with different phase structure

Abstract: Study of chromium phase structure and the surface composition of chromium deposited by pulsed current has shown that when the hcp structure forms, the thickness of oxy-hydroxide Cr(III) compounds film increases on the deposit surface. Increase of this film thickness over some value (about 100 A) results in maintenance of the hydride CrH as the first stage of chromium crystallization. Study of the phase structure of chromium from solutions with formic acid has shown that formation of the hcp structure is promoted by oxidation of the organic additive by chromic acid (i. e., by increasing the Cr(III) concentration in the solution and by decreasing its acidity). This intensifies the formation of oxy-hydroxide Cr(III) compounds on the chromium surface during electrolysis.

Theoretical and practical aspects of electrodeposition of metal coatings with improved properties. (Part 1)

Abstract: The properties of electrodeposits, such as adhesion, corrosion and wear resistance, hardness, electrical conductivity and brightness, are important and even mandatory for a broad spectrum of applications. Many of these properties depend on the specific procedure for electrodeposition, because alternative procedures produce significantly different properties. In general, electrodeposited metal coatings with excellent properties must have fine-grained structure. A fine-grained structure, however, is only one of the conditions necessary for a metal coating with good decorative and functional properties. Leveling power is suggested as an additional adequate measure for quality estimation and as a criterion of discovering the best plating regime. Part 1 of this paper lays out the theoretical principles at work in the electrodeposition of metal coatings with fine-grained structure. It also offers a model for precise experimental determination of those plating parameters and hydrodynamic conditions under which fine-grained metal coatings with maximum leveling power are electrodeposited.

Mass transfer of components of zinc chromating solutions. Part 1; Mass transfer of species containing Cr(VI), Cr(III) & Zn(II)

Abstract: The concentration profiles of the components of a chromating solution were calculated on the basis of a mass transfer model, taking into account the mobile chemical equilibria. The data on the composition model of the diffusion layer, together with the analysis of the solubility of certain Cr(III) and Zn(II) compounds, allowed determination of the composition of conversion coatings formed on the surface of Zn in the chromating solutions.

Modeling for sludge estimation & reduction

Abstract: Sludge reduction is one of the most important environmental issues in electroplating plants. The most effective way of sludge reduction is to minimize the sludge generated from each plating line. In this paper, a set of sludge models is developed to characterize the sludge generation in parts cleaning and rinsing. These models, together with a set of dynamic models for characterizing cleaning solutions, rinsewater, and parts, can be used to develop strategies for sludge reduction and quality assurance for cleaning and rinsing. Model-based simulation has demonstrated the desirability of adopting them in real processes.