Development of High Speed Lead Plating and its Applications

A high speed lead plating process has been developed. The bath contains, per gal US, Pb(BF₄)₂ 62·5 oz, HBF₄ and H₂BO₂ ach 6 oz and hydroquinone 1·3 oz. The optimum temperature is 160°F and cathode surface velocities of 0–150 ft/min have been evaluated. Limiting current densities up to 3100 A/ft² and average operating current densities up to 1000 A/ft² are possible. Deposits are fine grained and cover basis metal defects even with coatings 0·1 mil or less. Brushing the basis metal and especially interrupting the lead deposition to brush the deposit reduces porosity. Coatings 0·05 to 0·1 mil thick so produced on steel when tested resisted corrosion by shellac better than terne and tinplate and were satisfactory in water-base paints. However, lead coatings on steel have poor solderability. Salt spray tests confirm the superiority of the deposits produced from the hydroquinone bath with or without brushing treatments. Copper and tin strikes were of no value in corrosion or solderability tests. Power and metal cost is lower for the lead coatings than for zinc coatings of equal thickness. Production facilities for lead-plating steel strip of various gauges are discussed.     

The Faraday Centenary Exhibition, 1931

Solderability of a selection of coatings on copper foil, stored under various conditions, has been determined using both the minimum wetting-time test and area of spread tests. Pure tin and tin-lead alloy plated coatings about 0·3 mils thick withstand all the storage treatments with no loss in solderability. A flash of gold over the same thickness of tin-nickel alloy plating was next in order of merit. 0·2 mils of various alloy gold coatings lost solderability under some conditions but in any case caused embrittlement of the solder, thus confirming other work. A brittle bond was also obtained with a thick palladium coating. All of the very thin metallic coatings, the lacquer film and the chemical preservative treatment, allowed a serious loss of solderability during storage. The results are considered to be of direct application in the electronic industry, especially in the field of printed circuitry and it is suggested that the wetting-time test gives the most accurate assessment of solderability for printed circuit material.     

The Nickel and Chromium Plating of Tinplate

Tinplate, as a base for chromium plated sheet required for fabrication, offers the advantage over steel of being easily polished, but difficulties have arisen, especially with coke grades of tinplate, in obtaining nickel deposits sufficiently adherent to withstand chromium plating and fabrication without flaking.

These difficulties are attributed to two effects:—(1) the mechanical effect during straining of variations in thickness of the tin coating, (2) the effects of hydrogen produced during plating, particularly the disruptive effect produced by the conversion of atomic hydrogen (diffusing through the nickel) into gas at the site of discontinuities (foreign particles, fissures, etc.) at the interface—nickel/tin.

The diffusion of hydrogen to the tin surface can be prevented by depositing a film of copper before nickel plating. Tinplate which has been coated with a composite deposit of copper, nickel and chromium can be fabricated without flaking of the deposit. If the deposit is brittle, however, it is liable to crack on deformation, giving an unsightly appearance. Certain nickel deposits may be seriously embrittled by chromium plating.

The porosity of composite deposits of copper, nickel and chromium on tinplate is considerably lower than on steel of average quality, but their protective value may be destroyed at bends formed during fabrication especially with coke grades of tinplate. Tinplate of charcoal quality offers the advantages of superior finish, better adhesion of the deposit and a lower tendency for the protective value of the coating to be destroyed on deformation.

Tinplate may also be satisfactorily plated with chromium alone. The plated sheet can be pressed without flaking of the coating, the protective value of which is less readily reduced by deformation than that of the composite nickel-chromium coatings, but it is more difficult to obtain a good finish in the absence of a nickel undercoating.     

Selection of process parameters for mass plating of discrete electronic components

The miniaturisation of electronic components coupled with requirements for high temperature lead-free soldering has forced the improvement of the termination finish of surface mount components to meet the critical demands of the electronic industry. In the present work the processing parameters necessary to plate miniature multilayer varistors (MLVs) with nickel and tin layers have been explored. The tooling selected was a ‘rotary flow-thru’ plater which achieved high volume plating with <0·5% rejects. The anode selection proved critical and Nickel S rounds only were suitable with the chosen parameters. A very tight plating distribution with nickel thickness average 2·2 µm (±0·28 µm) and tin thickness average 3·5 µm (±0·31 µm) was achievable in production size quantities. An evaluation of product by examining solder fillet heights and tombstoning in mass board mounting trials concluded that the nickel tin finish is effective for high speed soldering applications.     

Zinc Alloy Die Castings—Quality,Design and Plating Procedures

Pressure die casting in zinc alloy is a method of production eminently suited for components required in very large numbers. Particularly when they are to be plated, strict attention must be given to the design of the die and to conditions of casting if die castings of a suitably high standard are to be produced. Freedom from sub-superficial porosity and a flawless surface are required—the smooth matte “hardware” finish. It is desirable that the plater be consulted at an early stage in the designing of a die casting if his interests are to be safeguarded, otherwise unnecessary difficulties may be created for him. Preparation for plating should imply a minimum of emery bobbing, light pressure in polishing and only a brief electrolytic cleaning in mildly alkaline solution. On significant surfaces a primary deposit of copper not less than 0–0003” in thickness is necessary. The copper deposits most satisfactory for bright nickel plating are not necessarily those of highest lustre.     

A novel electrolyte for the high speed electrodeposition of bright pure tin at elevated temperatures

A new tin electroplating process capable of producing fully bright, pure tin deposits from an electrolyte operated at temperatures of up to 50°C has been developed. Unlike conventional bright tin deposits, the tin deposit from the new process has an increased grain size and low carbon content. In addition, the deposit demonstrates excellent ductility, solderability, and low tendency for whisker growth. Production trials conducted by various industries have proven that the new pure tin deposit is suitable for connector applications, as well as for corrosion protection and decorative uses. In this article, the characteristics of the tin electrolyte and the bright tin deposit are described.Electrodeposition of bright tin, characterized by its silvery-white decorative appearance, excellent solderabilty, conductivity, good corrosion and tarnish resistance, and non-toxic nature, has been widely used in the electronic industry and protective-decorative applications. The industrial importance of tin electrodeposition has been markedly extended with the introduction of lead-free solder in the electronic marketplace. However, certain drawbacks of commonly used bright tin plating processes have limited the acceptance of electrodeposited bright tin. The operation and control of bright tin plating solutions is more difficult compared to that of matte tin processes, since the additive system of conventional bright tin electrolytes usually contains many volatile organic components that act as brightening agents. Because of the volatile nature of the organic brightening agents, a cooling system is usually required in conventional bright tin plating baths, in order to maintain the bath temperature between 20 to 25°C where most brightening agents are effective. For high-speed plating, the use of a cooling system becomes essential since the bath temperature naturally rises rapidly during plating. A key concern with the use of bright tin in certain applications is the relatively low ductility often associated with bright deposits and the reportedly higher tendency towards tin whisker growth compared to matte deposits. For demanding automotive applications, where the use of bright tin-lead has been permitted for a limited period of time, continuing efforts are being made by both the electronics industry and suppliers of plating chemistry to replace bright tin-lead with bright pure tin. Tin whisker performance has become one of the most critical characteristics in qualification of any bright pure tin plating process for use in the electronics industry.The newly developed plating bath, SOLDERON? BHT-350 bright tin, has been designed to be operated at temperatures between room temperature and 50°C, while producing ductile, bright deposits with low whisker growth tendency. Production trials conducted by different industries have demonstrated that the new process is able to produce bright tin deposits under high speed reel-to-reel plating conditions, and the simple additive system facilitates automatic or manual dosing during operation. The resulting bright tin deposits are suitable for connectors, contacts, wire and other items requiring a bright tin finish. In this article, the characteristics of the electrolyte and the properties of the bright tin deposit, including microstructure, carbon content, ductility, texture, solderability and whisker performance are described in detail.     

Shear Tests of The Adhesion of Electrodeposited Chromium to Steel

The solderability of various coatings of tin, of alloys of tin with lead, zinc, cadmium, and of cadmium and silver has been compared. A spread-of-drop type test was employed which was thought to give the best assessment of solderability of surfaces. For most types of coating, the influence of coating thickness, basis metal, undercoat layers, and after-treatment was studied, and some specimens were stored for periods up to two years to examine the effect of storage on solderability. Mot-dipped tin or electroplated tin coatings of 0·0003 in. thickness or more were found to be superior and least influenced by basis metal, undercoat or storage. There seemed to be no advantage in using tin alloy coatings if solderability is the only criterion. Coatings on steel or over a nickel undercoat were not appreciably affected by storage whereas coatings on copper or over a copper underlayer slowly decreased in solderability especially at 50°C resulting from formation of inter-metallic compound and consequent loss of free tin. This deterioration was only serious with coatings of less than 0·0003 in. thickness. Soldering difficulties with tin coated brass, said to be encountered in practice, were not found in the present tests. General recommendations are made from the results of the investigation for achieving high initial solderability and retainment of solderability during storage.     

The Electrodeposition of Rhodium

As part of a continuing effort to improve the durability of decorative plated automobile parts, a deleterious type of chromium cracking and the changes in the microstructure of nickel brought about by addition of a sulphur-containing additive have been studied. Type Y cracking of 0·02–0·05 mil chromium deposits was found to result from interaction of the internal stress of the deposit with tensile stress induced by directional abrasion of the nickel substrate. A similar type of cracking was found to occur in a bright nickel plus chromium plate on directionally abraded steel. Reduction of the stress by annealing or removal of the stress layer by electropolishing eliminated this type of cracking. The size of the columnar structure of a Watts deposit was found to decrease when sodium allyl sulphonate was added to the bath. With increasing concentration, the columns gradually disappeared leaving visible only a laminar structure. The transition from columnar to laminar structure occurred well below the normally used additive concentration. In a fully bright deposit, perpendicular faults associated with scratches in the basis metal were observed. These were duplicated in deposits on electro-formed precision roughness standards. The effects of these phenomena on corrosion of decorative plated coatings are discussed.     

Effect of direct current and pulse plating parameters on tin whisker growth from tin electrodeposits on copper and brass substrates

Abstract

Electroplated tin finishes are widely utilised in the electronics industry due to their advantageous properties such as excellent solderability, electrical conductivity and corrosion resistance. However, the spontaneous growth of tin whiskers during service can be highly deleterious, resulting in localised electrical shorting or other harmful effects. The formation of tin whiskers, widely accepted as resulting from the formation of compressive stresses within the electrodeposit, has been responsible for a wide range of equipment failures in consumer products, safety critical industrial and aerospace based applications. The numbers of failures associated with tin whiskers is likely to increase in the future following legislation banning the use of lead in electronics, the latter when alloyed with tin, being an acknowledged tin whisker mitigator. Using a bright tin electroplating bath, the effect of process parameters on the characteristic structure of the deposit has been evaluated for deposition onto both brass and copper substrates. The effect on whisker growth rate of process variables, such as current density and deposit thickness, has been evaluated. In addition, the effect of pulse plating on subsequent whisker growth rates has also been investigated, particularly by varying duty cycle and pulse frequency. Whisker growth has been investigated under both ambient conditions and also using elevated temperature and humidity to accelerate the growth of whiskers. Studies have shown that whisker formation is strongly influenced by pulse plating parameters. Furthermore, increasing both current density and thickness of the deposit reduce whisker growth rates. It is also observed that whisker formation is greatly accelerated on brass substrates compared with copper. The basis for this observation is explained.     

Nickel electrodeposition from novel lactate bath

Abstract

A new electroplating bath for nickel deposition has been developed. Lactic acid was used as a complexing agent in the bath replacing boric acid. The effect of bath composition, current density, pH and temperature on the cathodic polarisation, cathodic current efficiency, morphology and structure of the deposit was carried out. Optimum conditions for producing sound and satisfactory nickel deposits were: 0·30M NiSO₄.7H₂O, 0·50–1·0M lactic acid and 0·3M Na₂SO₄ at pH=10, c.d.=0·98 to 9·80 mA cm^?2 and 25°C. The surface morphology of the deposited nickel was investigated using SEM. The crystal structure was examined by X-ray diffraction analysis. The results showed that the nickel deposits have a face centred cubic structure.     

The Effect of Addition Agents upon the Conductivity,Cathodic Polarisation and Grain Size of Deposits Obtained from the Cell: Cu/CuSo4, H2So4/Cu

The outdoor corrosion resistance of chromium plated, polished Watts nickel is compared with that of bright nickel, and the following systems of composite plates are also reviewed. 1. Bright, crack-free chromium in thicknesses of 0·03 to 0·08 mil (0·75 to 2 micron) on nickel or copper+nickel plate. 2. The usual 0·01 mil chromium on dual or duplex nickel plate consisting predominantly of a thin overlay of bright nickel on a deposit of soft, semi-bright, sulphur-free nickel. 3. Dual or duplex microscopically cracked bright chromium plate of 0·03 to 0·1 mil thickness deposited on nickel or copper+nickel. 4. Chromium+nickel+chromium composite deposits. Systems 2 and 3 are the best in use to date. System 2 is well established and in more widespread use than the newer system 3. The latter system appears to offer considerable promise, but the outdoor exposure tests (1 year) are not yet of sufficient duration for its proper evaluation. System 4 has not yet been tried under production conditions, but the results of extended outdoor exposure tests (4 years) indicate that it is capable of showing the best overall corrosion resistance. Combinations of all these systems are also discussed.     

Properties of welded joints made of Weldox 1100 steel

This study evaluated both the joint strength of copper wire on a copper substrate with tin plating and the joint reliability of copper wire bonding after heat treatment. The suitable tin thickness and bonding conditions, which are stage temperature, wire bonding power and bonding time, were chosen by the peel test after copper wire bonding. Tin thickness of 10 m showed a high bonding rate under the conditions of stage temperature 373 K, bonding power 500–700 mW and bonding time 30 50 ms. Before heat treatment, the peel strength of the copper wire on the copper substrate with tin plating conditions was weaker than that of gold wire on a gold substrate. After heat treatment for more than 70 h at 298 K, the peel strength of the copper wire became higher than that of the gold wire and twice as high as the initial bonding strength. The tin layer remained between the copper wire and copper substrate before heat treatment. When the samples were held at 298 K, tin reacted with copper and turned into a Cu–Sn intermetallic compound. Upon completion of this reaction at 298 K for over 70 h, the soft tin layer between the copper wire and copper substrate disappeared. Therefore, the peel strength of copper wire after heat treatment increased. These results were observed by scanning electron microscope images of the interface between the copper wire and copper substrate before and after heat treatment.     

Electrodeposition and corrosion behaviour of some Zn–Fe group metal alloys by pulsed current

Abstract

The corrosion and electrochemical behaviour of pulse plated Zn–Fe group metal alloy deposits obtained from chloride bath have been studied as a function of pulse parameters such as duty cycle, frequency and average current density. The frequencies of electric current, T _on, T _off, pulse duty cycles have large effects on the chemical composition and surface morphology of the deposits. Results of the electrochemical tests indicate that the corrosion resistance of pulse plated Zn–Fe group metal alloy coatings is superior to that of the alloy deposited by the direct current technique. The on time and off time had no significant influence on the deposit characteristics. Characterisations of deposits were carried out by cyclic voltammetry and the surface morphology was studied by scanning electron microscopy. The composition of the alloy deposits were analysed by spectrophotometry. Refinements in grain size and deposit composition have been made for better corrosion performance with the advent of pulse plating. A minimum corrosion rate was observed at 50% duty cycle and pulse frequency range of 100 Hz in all cases and is proposed as optimal conditions for development of a bright, smooth and uniform deposit of Zn–Fe group metal alloy over steel.     

Rapidly solidified thick cobalt-based alloy deposit with carbide particles produced by plasma spraying

Abstract

Thermal spraying can produce rapidly solidified thick layers, because the droplets that accumulate on the substrate experience cooling rates of 10⁵–10⁸ K s^–1. It is thus an attractive method to produce composite deposits containing fine particles formed in situ. In the present work, Co–1·5C, Co–1·5C–14Cr and Co–1·5C–29Cr (wt-%) alloy powders produced by argon atomisation were low-pressure plasma sprayed onto water cooled or uncooled substrates. The as sprayed Co–1·5C deposit formed on a water-cooled substrate consists of a metastable β-Co phase, supersaturated with carbon due to the high cooling rate. Heat treatment at >673 K led to the formation of α-Co and graphite. The deposit heat treated at 1073 K contained graphite particles ～0·8 μm in size. At higher treatment temperatures, coarsening of graphite and the elimination of carbon supersaturation result in lower hardness. As-sprayed Co–1·5C deposit on uncooled substrates consisted of β-Co, α-Co and graphite. As-sprayed deposit of Co–1·5C–14Cr and Co–1·5C–29Cr powders on uncooled substrates consisted of β-Co, α-Co, Cr₃C₂, Cr₇C₃ and graphite. The fine (0·5 μm) precipitates in the as-sprayed Co–1·5C–14Cr deposit on uncooled substrates were identified as chromium carbide. As-sprayed Co–1·5C–29Cr deposits on uncooled substrates contained many precipitates ～0·6 μm in size and showed the highest microhardness of ～600 HV (2·94 N).     

锡青铜化学镀 Ni-P 合金工艺及镀层性能

目的在锡青铜基体上化学镀Ni-P合金镀层,提高锡青铜的耐磨性和耐腐蚀性。方法以酸性含锌活化液活化锡青铜试样,在相同的条件下实施化学镀,并对镀态试样进行不同温度(250,400,500℃)下的热处理。对比基体、镀态试样和热处理试样的性能,研究热处理温度对锡青铜化学镀Ni-P合金层微观结构、显微硬度、耐磨性和耐腐蚀性的影响。结果锡青铜表面形成了Ni-P合金镀层,并且镀层无孔隙缺陷,与基体结合良好,沉积速率较快,为10.00μm/h。经热处理后,镀层的微观结构由非晶态向晶态转变,在500℃热处理的镀层显微硬度最大,耐磨性最好。镀态镀层和经250℃热处理的镀层在10%HNO3溶液和10%H2SO4溶液(10%均为体积分数)中的耐腐蚀性明显好于锡青铜基体,镀态镀层在两种介质溶液中的腐蚀速率分别为0.225,0.146 mg/(cm2·d)。结论采用酸性含锌活化液活化锡青铜基体,可以在锡青铜表面制备出化学镀Ni-P合金镀层,且镀覆效果较好。这表明紫铜化学镀Ni-P合金工艺同样适用于锡青铜。     

The effect of additives on the pulsed electrodeposition of copper

Abstract

The pulsed electrodepostion of copper has been systematically investigated from a copper sulphate bath. Pulse duty cycles of 5–80%, at frequencies from 10 to 100 Hz with current densities ranging from 2·5 to 7·5 A dm^?2 were employed. The influences of pulsed current duty cycle, peak current density and frequency on the thickness and hardness of the copper deposit, current efficiency and throwing power of the plating process were studied. The effect of additives, polyethylene glycol and di-sodium EDTA on the properties of deposit were investigated.     

Investigations on the Electro-Deposition of Silver,with Special Reference to the use of Sodium Cyanide

The results of an investigation on the deposition of tin-zinc alloys, ranging in composition from 92/8 to 28/72, are discussed, and instructions are given for the deposition of the alloy containing 78% of tin, which appears to be the most serviceable. The electrolyte contains sodium stannate, zinc cyanide, sodium hydroxide, and sodium cyanide and is operated at 70°C., using tin-zinc alloy anodes of approximately the same composition as the deposit. A feature of the process is polarisation of the anodes so as to ensure dissolution of the tin as stannate. The influence of changes in the composition of the electrolyte, in cathode current density, and in temperature on the composition of the deposit have been examined and measurements have been made of the effect of alteration in the working conditions on anode and cathode efficiency. Chemical methods for the analytical control of the plating bath and alloy deposit are given.     

Influence of microalloying additions on Al–Mg alloy. Part 1: Corrosion and electrochemical response

A range of custom alloys based on the Al–4Mg–0·4Mn system were produced with selected quaternary microalloying additions. Alloying elements studied include silicon, zinc, lead, titanium, tin, zirconium, strontium and neodymium. To characterise the corrosion response, electrochemical tests were carried out in 0·1M NaCl, supplemented by constant immersion tests and basic microstructural characterisation by means of scanning electron microscopy (SEM). Optical profilometery was used to determine the form and intensity of localised corrosion. The results indicate that low level quaternary alloying additions can have a marked influence on specific aspects of the first order correlation between chemistry, microstructure, hardness and corrosion.     

Examination of Oxides on Tin Surfaces by Cathodic Reduction

Abstract

Oxides formed on tin surfaces were examined by electrochemical reduction in galvanostatic and potentiodynamic experiments and also by electron diffraction. Reduction of oxide occurred at three distinct potentials (NHE scale): ?0·115 ?0·06 pH, ?0·150 ?0·06 pH and ?0·345 ?0·06 pH, although sometimes only one or two of them were observed. The most negative reduction step rarely appeared for electrodeposited tin coatings oxidised in air but was well developed for pure tin sheet and for hot-dipped tin coatings. Impurities in tin modified both the speed of oxidation and the form of the oxide reduction curves but their effect cannot account for the difference between electrodeposiied coatings and other tin surfaces. This difference is probably due to exposure of differing crystal faces. The two less negative reduction steps appeared for all forms of tin, but were not always clearly separated and they cover the possible reduction of both SnO and SnO₂. The most negative step is associated with SnO₂ only and its development is favoured by chemical or electrochemical oxidation, which may produce it for electrodeposited tin, or by high humidity of air. SnO₂ is also formed on all surfaces during long term storage at room temperature. Some thicker oxide films, formed during long storage or by anodic oxidation, may be partly undermined during reduction and the total reduction charge is not an accurate measure of their character.     

The Structure of Electrodeposited Nickel

Here are presented the results of laboratory studies on various types of acid rhodium plating electrolyte, with particular reference to sulphate and phosphate-sulphate solutions, but including exploratory trials on phosphate, fluoborate and sulphamate electrolytes. The sulphate electrolyte is preferred for general purposes.

For the first two electrolytes, examination is made of the effects of variations in preparative procedure on the characteristics of electrolytes of the same nominal composition, and the influence of composition and deposition factors on the internal stress of deposits.

Factors affecting the incidence of cracking of thick rhodium deposits are discussed, and on the basis of laboratory and field experience, practical recommendations are made concerning the formulation of sulphate electrolytes and the optimum operating conditions for the production of rhodium deposits in the thickness range 0·002-0·002” from this type of solution. Procedures are detailed for either the rhodium or silver/rhodium plating of the basis metals most commonly involved in industrial applications.