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Innovation is crucial for progress in the fast-changing realm of microelectronics. A revolutionary advancement is the zincate-free electroless nickel deposition method on aluminum substrates like rolled, extruded, and foil. The industry’s critical challenges are being addressed by new approaches that streamline the manufacturing process.
Aluminum has long been the material of choice in microelectronic devices, thanks to its excellent conductivity and cost-effectiveness. However, the formation of an oxide layer on aluminum surfaces presents a significant obstacle for subsequent metal deposition processes. Traditionally, this challenge has been addressed through a multi-step zincate treatment, which involves immersing the aluminum substrate in a concentrated sodium hydroxide solution containing zinc ions.
While effective, the zincate process comes with its own set of drawbacks:
Process complexity
Exposure to undesirable metal ion contaminants
Potential for non-uniform deposition
These limitations have prompted researchers to explore alternative methods for activating aluminum surfaces for electroless nickel deposition. In high-performance microelectronics, the most common metals used for plating include:
Gold:
Excellent conductivity, corrosion resistance, and solderability.
Often used for connectors, contacts, and bonding pads.
Nickel:
Typically used as a barrier layer under gold to prevent diffusion.
Provides good mechanical strength and corrosion resistance.
Silver:
Has the highest electrical and thermal conductivity of all metals.
Used in RF and microwave components, though it tarnishes easily.
Palladium / Palladium-Nickel Alloys:
Provides similar benefits to gold but at a lower cost.
Often used as an alternative to gold for connector finishes.
Copper:
Used as a base layer or interconnect material due to its excellent conductivity.
It is typically plated with a diffusion barrier like nickel before being coated with gold or another finish metal.
Tin:
Used for solderable finishes, often applied over a nickel or copper layer.
Less expensive but prone to whisker formation, which can cause short circuits.
These metals are selected based on their electrical, thermal, and corrosion properties to ensure reliability and performance in demanding microelectronic applications.
Zincate-Free ElectroplatingThe concept of zincate-free electroplating extends beyond the specific application of electroless nickel deposition on aluminum. It represents a broader trend in advanced surface finishing techniques, particularly for aluminum substrates.
Traditional Zincate Process: Limitations and Challenges
The conventional zincate process, while effective, has several drawbacks: Adhesion Issues:
Environmental Concerns:
Time-Intensive:
Several innovative approaches have been developed to overcome these limitations:
Direct Nickel Plating:
Ionic Liquid-Based Plating:
Electroless Deposition:
Advantages of Zincate-Free ElectroplatingThe benefits of zincate-free electroplating extend beyond those specific to electroless nickel deposition:
Enhanced Adhesion:
Environmental Benefits:
Streamlined Processing:
Superior Coating Properties:
Applications in Modern ManufacturingThe potential applications of zincate-free electroplating techniques extend across various industries:
Automotive:
Aerospace:
Electronics:
Construction:
ConclusionThe advancement of zincate-free electroless nickel deposition for aluminum substrates, along with other zincate-free electroplating techniques, is a breakthrough in microelectronic manufacturing and surface finishing technology. By addressing the limitations of traditional methods, these innovative approaches offer:
These innovations will be essential in shaping the future of technology as the demand for smaller, more reliable, and more complex microelectronic devices increases. The potential to apply high-quality metal layers to aluminum surfaces without complicated pretreatment offers new opportunities for device design and manufacturing efficiency.
Additional research and optimization are needed before widespread industrial use, but the work of numerous researchers has paved the way. Zincate-free electroless nickel deposition and electroplating will play a crucial role in tackling future challenges in microelectronics and surface finishing. The pursuit of better manufacturing processes continues, with zincate-free techniques being a major step forward. With ongoing research and exploration, we can anticipate remarkable advancements in advanced surface finishing and microelectronics manufacturing.
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High Strength, Low Stress Nickel Sulfamate Plating for Aerospace and Automotive Applications |
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Silver plating has always been crucial in the metal finishing industry due to its ability to improve conductivity, corrosion resistance, throwing power properties and visual appeal. Nevertheless, the use of cyanide-based solutions has presented major environmental and safety issues. The industry has witnessed a revolutionary shift towards cyanide-free silver-plating technologies in recent years, offering a safer and more sustainable future.
Understanding Silver PlatingSilver plating is an electrochemical process that deposits a thin layer of silver onto various substrates, typically metals like copper, brass, or nickel. This technique is widely used across multiple industries, including electronics, automotive, aerospace, and jewelry manufacturing.
Applications of Silver PlatingElectronics: Silver-plated components are essential for ensuring optimal electrical conductivity in switches, connectors, and printed circuit boards. Automotive: The automotive sector utilizes silver-plated parts in various electrical systems to enhance performance and reliability. Aerospace: Silver plating is crucial in aerospace applications where high conductivity and corrosion resistance are paramount. Jewelry: In the world of decorative arts, silver plating provides an economical way to achieve the lustrous appearance of solid silver. Medical Instruments: Silver's antimicrobial properties make silver-plated instruments valuable in fighting infections in medical settings.
Cyanide-Based Silver PlatingFor decades, the industry has relied on cyanide-based solutions for silver plating due to their current efficiency, throwing power, and cost-effectiveness. These solutions typically contain silver cyanide complexes ([Ag(CN)2]-) dissolved in a potassium cyanide electrolyte.
High Efficiency: Cyanide-based solutions offer rapid plating speeds and excellent throwing power, ensuring uniform coverage even on complex shapes. Bright Deposits: The plated silver layer often exhibits a bright, lustrous finish directly out of the bath, minimizing the need for post-plating polishing. Wide Operating Window: These baths are relatively forgiving in terms of operating conditions, making them easier to manage in production environment. Cost-Effectiveness: The chemicals used in cyanide-based plating are relatively inexpensive, contributing to lower overall production costs.
Environmental and Safety ConcernsDespite its effectiveness, cyanide-based silver plating poses significant risks: Toxicity: Cyanide is highly toxic to humans and aquatic life, even in small concentrations. Environmental Hazards: Accidental releases or improper handling can lead to severe environmental damage. Disposal Challenges: The disposal of cyanide-containing waste requires specialized treatment processes, adding to operational costs and complexity.
Conversion to Cyanide-Free Silver PlatingThe development of cyanide-free silver-plating processes represents a significant step forward in making the industry more sustainable. This innovation aligns with broader trends towards a green electroplating process, which aim to reduce hazardous chemical use, lower energy consumption, and minimize waste.
Cyanide-Free Silver-Plating SolutionsSeveral types of cyanide-free silver-plating solutions have emerged as viable alternatives: Thiosulfate Solutions: These baths use silver thiosulfate complexes and are known for their stability and ability to produce bright, uniform deposits. Sulfite Solutions: Silver sulfite complexes form the basis of these baths, offering good throwing power and excellent electrical properties. Succinimide Solutions: These newer formulations use silver succinimide complexes and have shown promising results in terms of deposit quality and plating efficiency Pyrophosphate Solutions: While less common, these baths have found niche applications, particularly where specific deposit properties are required.
Advantages of Cyanide-Free Plating SolutionsThe adoption of cyanide-free silver-plating processes presents several key benefits: Environmental Impact: Cyanide-free solutions eliminate the need for hazardous waste disposal protocols, reducing the environmental footprint of plating facilities. Health and Safety: By removing cyanide from the equation, workers in the plating industry are exposed to fewer health risks, contributing to a safer workplace. Regulatory Compliance: Companies can more easily comply with stringent environmental regulations, avoiding costly fines and potential legal issues. Process Efficiency: Many cyanide-free technologies maintain or even improve upon the efficiency and quality of traditional silver-plating methods.
Challenges in Implementing Cyanide-Free PlatingDespite the numerous benefits, transitioning to cyanide-free silver plating is not without its challenges: Cost of Transition: Implementing new technologies often requires significant upfront investment in equipment, training, and process redesign. Stability of the electrolyte, shelf line, and metals turn over are a few factors one must take into account. Performance Parity: Some industries may be hesitant to adopt new methods without assurance that they perform as well as traditional techniques, especially for applications requiring exceptionally high conductivity or corrosion resistance. Process Stability: Maintaining the stability and consistency of cyanide-free plating baths can be more challenging than with cyanide-based solutions, requiring careful control of the plating environment.
Comparative Analysis of Cyanide-Free and Traditional MethodsWhen evaluating the shift from traditional cyanide-based methods to cyanide-free alternatives, several key factors come into play: Plating Efficiency and Quality: Many cyanide-free solutions can now match or even exceed the plating speed and deposit quality of cyanide baths, though performance can vary depending on the specific application and bath chemistry. Cost Considerations: While initial transition costs may be higher, long-term savings can be realized through reduced waste treatment costs and simplified safety protocols. Environmental Impact: Cyanide-free solutions significantly reduce the risk of environmental contamination and typically require less intensive waste treatment processes. Safety Profile: The elimination of cyanide dramatically improves workplace safety, reducing the need for specialized handling procedures and emergency response plans. Versatility: While cyanide baths are known for their wide operating window, many cyanide-free alternatives are catching up in terms of versatility and ease of use.
The Future of Cyanide-Free Silver PlatingAs environmental regulations continue to tighten, the demand for cyanide-free silver plating is expected to grow. Companies at the forefront of this innovation will likely lead the way in developing and commercializing these technologies. Emerging Technologies Advances in related fields, such as additive manufacturing and nanotechnology, could further enhance the performance of cyanide-free plating processes. For instance, the use of nanoparticles in plating baths has shown promise in improving deposit quality and bath stability, addressing some of the challenges currently facing cyanide-free methods. Collaborative Efforts As the industry evolves, collaboration between academic researchers, plating companies, and regulatory bodies will be critical to ensuring the success of cyanide-free technologies. By working together, these stakeholders can accelerate the adoption of safer, more sustainable silver-plating processes that meet the needs of modern industry while protecting the environment. ConclusionThe move to cyanide-free silver plating is a major step towards more environmentally friendly and safer industrial practices. Despite challenges in cost, performance, and process stability, ongoing research will likely overcome these obstacles.
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Zincate-Free Nickel Electroless Deposition for High-Performance Microelectronics As the benefits of cyanide-free technologies become more widely recognized, we can expect to see increased adoption across industries that rely on silver plating. Ultimately, these innovations will help to create a more sustainable and responsible future for the metal finishing industry, aligning with global efforts to reduce environmental impact and enhance workplace safety. The industry’s adoption of cyanide-free silver-plating solutions addresses environmental and safety concerns while ensuring long-term success in an eco-conscious global market. The future of silver plating is bright, sustainable, and cyanide-free. |
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In recent years, significant advancements in the field of plating on plastics (POP) have revolutionized various industries, ranging from automotive to electronics. This paper delves into the latest trends, technologies, and applications in POP, underscoring its burgeoning importance in contemporary manufacturing.
At the forefront of this revolution is electroless plating, a chemical process that deposits a thin metallic layer onto plastic surfaces without the need for electricity. This technique facilitates uniform coating on complex shapes and non-conductive materials, thereby enhancing the durability, conductivity, and aesthetic appeal of plastic parts.
Another groundbreaking method is physical vapor deposition (PVD), which produces extremely thin, highly adherent metallic coatings on plastic substrates. PVD coatings can impart properties such as increased hardness, improved wear resistance, and specific optical characteristics, all while maintaining the lightweight nature of the plastic base material.
Plasma-enhanced chemical vapor deposition (PECVD) pushes these boundaries even further. This technique employs plasma to aid in the deposition of various materials onto plastic surfaces, enabling the creation of coatings with tailored properties such as hydrophobicity, optical transparency, or specific electrical characteristics.
The implications of these advanced plating techniques are profound. In the automotive industry, plastic components can now replace heavier metal parts without compromising strength or durability, leading to improved fuel efficiency.
The electronics sector benefits from plastic housings that provide electromagnetic shielding, a crucial feature in our increasingly connected world. Medical device manufacturers are leveraging these technologies to create implants and instruments that combine the biocompatibility of certain plastics with the requisite strength and wear resistance of metals. In the realm of consumer goods, designers are exploring new aesthetic possibilities, producing plastic products with metallic finishes indistinguishable from their all-metal counterparts.
As these plating techniques continue to evolve, we can expect even more innovative applications. The ability to selectively functionalize specific areas of plastic components opens possibilities for integrated circuitry and sensors embedded directly into structural parts. This could lead to a new generation of smart products with enhanced capabilities and improved resource efficiency. However, challenges remain. Ensuring strong adhesion between the plating and the plastic substrate across a wide range of environmental conditions is an ongoing area of research. Additionally, as the industry moves towards more sustainable practices, developing eco-friendly plating processes and improving the recyclability of plated plastics are becoming increasingly important considerations.
The plastic metamorphosis driven by these cutting-edge plating techniques is more than just a technological advancement; it represents a paradigm shift in how we approach material selection and product design. As these technologies mature and become more widely adopted, they promise to blur the lines between traditional material categories, offering designers and engineers an expanded palette of possibilities to create the products of tomorrow. The revolution in plastic plating techniques is ushering in a new era of manufacturing, where the versatility of plastics is enhanced by the properties of metals. This synergy is not only pushing the boundaries of what’s possible in product design but also contributing to more efficient, lightweight, and potentially more sustainable manufacturing processes. As research in this field continues to advance, we can anticipate even more exciting developments that will further transform the landscape of modern manufacturing. The Rise of Double-Shot MoldingOne of the most exciting developments in POP is the adoption of double-shot (or twin-shot) molding techniques. This process involves creating parts with both plateable and non-plateable plastic resins, offering several advantages:
Reduced assembly costs
Double-shot molding requires expertise in etching and activation to achieve controlled and highly selective plating without yield loss. This technique has found applications in various industries, including medical devices, consumer electronics, automotive components, and more.
Weight Reduction: A Key DriverAs industries strive for more efficient and environmentally friendly products, weight reduction has become a crucial factor. POP technologies enable the replacement of metal components with lighter plastic alternatives, particularly in automotive applications like door handles.
MID Metallization Technologies Molded Interconnect Devices (MID) represent another frontier in POP. Several MID metallization technologies have emerged:
These technologies are driven by cost and cycle time considerations, with applications spanning cell phone antennas, electronic connectors, medical devices, automotive components, and LED lighting.
Surface Preparation: The Key to SuccessRegardless of the specific POP technique, proper surface preparation is crucial for successful metal deposition. Various methods are employed, including:
Three main types of POP pretreatment processes are currently in commercial use:
Each process has its own sequence of steps, from chromic etching to electroplating.
The Advantage of Ionic Palladium ActivationIonic palladium activation systems offer several benefits over traditional colloidal systems: Reduced pre-plate process steps Expanding Material Horizons POP techniques have been successfully applied to a wide range of plastics, including: ABS and PC/ABS This versatility has opened new possibilities for designers and engineers across multiple industries.
The Future of Plating on PlasticsAs global demand for POP continues to grow, driven primarily by the automotive sector, we can expect further innovations in this field. While conventional colloidal systems remain widely trusted, ionic systems offer flexibility and cost reduction potential for the future. The ongoing advancements in POP technologies promise to deliver lighter, more intricate, and more cost-effective components across various industries. As research continues and new applications emerge, plating on plastics will undoubtedly play a crucial role in shaping the future of manufacturing and product design. By exploring the latest advancements and trends in POP, this paper aims to provide valuable insights for professionals and enthusiasts in the manufacturing sector. For those looking to stay ahead of the curve, understanding and leveraging these cutting-edge techniques is essential.
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The metal finishing industry plates hard and decorative hexavalent chromium processes from 1920s. It is an acknowledged industry standard and preferred choice because of its exceptional physical characteristics. US Environmental Protection Agency (EPA) and Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH) had listed chromium trioxide as a hazardous chemical because of its carcinogenic property.
ApplicationsMany aerospace components use hard chromium, the automotive sector primarily uses decorative and other sectors use both decorative and hard chromium plating deposits. A deposit thicker than 1.2 micron are functional (hard) and any lesser are decorative. The industry favors chromium because of its oxidation resistance properties. Among groups 4, 5, and 6 elements of periodic table we plate only chromium using an aqueous solution. Ionic liquids can deposit most of the transition elements. Aqueous hexavalent Cr deposit has exceptional tribological and corrosion resistance (not all formulations) properties. We plate the deposit on high strength steels and nickel alloys (with Wood’s nickel strike). This deposit exists in alpha phase, is crystalline and forms limited compounds or components with occlusion of hydrogen and carbon developing internal deposit stress (refer ASM Handbook for more information). The electrolytes’ low cathode current efficiency allows greater tribological properties. This is because the deposit has hydride and carbide compounds. These hydrides and carbides develop deposit intrinsic stress and effect deformation property of the deposit (Hooke’s law describes elastic properties of materials or deposit).
Extensive applications and good properties make environmental directions a challenge to meet. Before we get deeper, let us get a historical perspective.
HistoryAround 1910, a researcher accidentally developed the original hexavalent chromium plating formula comprising chromium trioxide and sulfuric acid. He assumed chromium trioxide was a trivalent salt until another scientist corrected the misinterpretation within two years.
ResearchFrom that time substitute methods such as trivalent chromium plating, cobalt alloy deposits, electroless Ni deposits with P or B alloys were developed and are a focus of continuing research. High temperature and room temperature ionic liquids for deposits such as trivalent chromium, niobium, aluminum, molybdenum is in study.
Alternate ChoicesTrivalent Chromium PlatingDecorative trivalent and hexavalent deposits have similar properties because of the thickness limit and electrolysis mechanisms of the respective electrolytes. Electrolysis mechanisms change as electrolysis progresses and the deposit characteristics vary with thickness. There are scientific papers on this phenomenon. On hard Cr applications major variation is on macro-cracks, which develops after baking. When analyzing macro-cracks, a seldom adhered to practice is to compare the microstructure on transverse sections. Refer to ASTM E3 – Microstructure and Properties for more information. A few applications use nickel undercoat to negate the effect of macro-cracks.
Other Electrolytic MethodsA few specialists recommend electroless Ni-P, electroless Co – P and electroless Co as substitutes to hexavalent hard chromium plating deposit. But the author of this paper doesn’t consider these as dependable alternatives. Only electroless Ni-B (mid boron) deposit possesses tribological properties, but it doesn’t offer comparable wear and corrosion resistance properties of hard hexavalent Cr plating deposit.
Ionic Liquid MethodsRoom temperature ionic liquid electrolysis is an effective alternate. Aluminum deposit offers many unique advantages. However, it is still an emerging technology.
Vapour Deposition MethodsThere are two types of vapour deposition methods – physical vapour deposition (PVD) and chemical vapour deposition (CVD). We can apply CVD on several transition metals. Of particular interest to this topic are CVD deposits of Ta and Nb.
Thermal Spray CoatingOn economy, versatility and diversity of options, the thermal spray coating processes is the best alternate to hexavalent Cr plating method. There are five different methods available in the market – oxyfuel wire (OFW) spray, electric arc wire (EAW) spray, oxyfuel powder (OFP) spray, plasma arc (PA) powder spray, and high velocity oxyfuel (HVOF) powder spray. Refer to ASM Handbook Volume 18 for more information on this subject. However, on many applications the line-of-sight characteristic will limit the thermal spray method. There is continuous research in this field, and recently a few companies have taken the processes to a new level.
SummaryBottom line, trivalent chromium plating, vapour deposition, and thermal spray methodologies are operative substitutes to hexavalent hard chromium plating process. Application demand, cost and the required physical characteristics determine the value of a specific method.
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Electronics Manufacturing through Reel to Reel Plating | Advint Incorporated
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Acknowledgement of the influential in electroplating develops our learning of the fundamentals, and it improves our research. There are thousands of contributors who served the electroplating industry and academia for over a century. Who tops your list? What did they do? Why is it important? What did we learn?
his short paper lists 8 innovators, two focused on electrochemistry and the rest on industrial plating (electrolytic, autocatalytic, ionic & aqueous). Their contributions enabled our understanding, improved our applications, and helped us to advance the technology.
Let us see who they are, when and what did they offer to the field and its benefits.
Michael Faraday
During 1832 Faraday published a paper relating the quantity of electricity with the amount of metal liberated at the electrodes resulting in two laws. When we think of electroplating, Faraday’s laws are probably the first to come to our mind. Mastering a process or shining at customer satisfaction does not end without due consideration of an electrolyte’s current efficiency and the feasibility of a deposit.
Walther Nernst
Nernst equation is the fundamental equation of electrochemistry and for the electrode processes. An ardent electroplating researcher shall begin and ensure a thorough understanding of Nernst equation and its concept. We can plate several transition metals, post transition metals, and metalloids. Some using aqueous electrolytes and room temperature ionic liquids, and most using high temperature ionic liquids. A modest approach to choose the electrolyte and the element for the deposition process is to comprehend Nernst equation and its concept. An interstitial or interatomic alloy electrodeposit choice is no exception to this subject.
Abner Brenner
Brenner conducted many studies on electroplating deposits. We conspicuously recognize for his preliminary contributions on electroless nickel plating invention around 1946. Though he got black non-adherent dendrites in the initial testing, his research allowed significant growth in electroless Ni-P and Ni-B deposition processes, and plating on plastics.
Richard Hull
Hull cell device is common in most electroplating laboratories. Most platers gain Hull cell testing skills or aspire to become good at it! Hull around 1930s invented a testing cell and derived a formula to calculate the effective current density of an electrolyte. Hull cell unit and its formula is quite easy to use! Is the design of the unit and its formula an ordinary achievement?
Oliver Watts
Professor Watts reported on 1931 his work on nickel plating bath comprising nickel sulfate, nickel chloride and boric acid at a higher temperature. Many used nickel-plating electrolyte using the same inorganic constituents at room temperature or at 120ºF. Watts was the first to report the benefits of thick and uniform deposit at 145ºF and 160ºF. Since then we began calling this electrolyte a Watts nickel plating solution.
Donald Wood
Wood was an expert in cyanide silver plating, and that is what he did for most of his career. We know him for his invention of chloride-based nickel strike bath during early 1940s. The Wood’s nickel strike formulation enabled the global industry to plate on all ferrous, nickel, titanium and aluminum alloys.
Donald Cook
Even if you are well read in the industry, you might not have heard about Dr. Donald Cook! Cook coined the term ‘metaliding’. Metal finishing industry did not see the effects of his research. But if I didn’t mention his name with others, it would be amiss as he is alike Nernst and Brenner. No one would have worked on more transition elements and diffused into others than him! His knowledge in electrochemistry and chemistry of halides was impeccable, and he distinguished the ins and outs of transition metals of group 3 to 11 of the periodic table. But his only focus was in high temperature ionic liquids.
Seymour Senderoff
We know Dr. Senderoff for his invention of spiral contractometer used in hard hexavalent chromium and nickel sulfamate plating applications to detect internal stress in the deposit. He worked for Dr. Brenner for several years and later focused on high temperature ionic liquid tantalum plating. It was my source of pride to continue on his research and improvise his formulation.
So, what is the learning?
Recognizing these pioneers and their work must transcend awareness and dwell on a deeper understanding of their explanations and research outputs. Faraday and Nernst focussed on the fundamental of electrochemistry. Cook and Senderoff concentrated mostly on high temperature ionic liquid electrolysis (plating and diffusion). Brenner, Hull, Watts and Wood dedicated their research on commercial electrolysis. Nevertheless, all played a revolutionary role in electroplating applications.
Here are the examples of teachings from a few of these pioneers’ work: Nernst’s invention allowed us to relate electrode potential, valency of the metal ion and current. Hull’s work brought to light Tafel’s, Butler’s and Volmer’s work. Wood’s invention signified electromotive force (emf) series and distinguished strike, flash plating, and plating. Cook’s and Senderoff’s developments emphasized the importance of eutectic temperature, phase diagram, liquidus temperature of salts, fluxing effect and ionic conductivity of electrolytes.
Hope you find this paper valuable and you dig deeper on these matters! Post your comments and write about who tops your list.
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Managing time with a data-driven approach offers incredible value in process management and customer service on electroplating and anodizing applications. Analytical data, awareness of chemicals and deposit properties with a historical context add value to engineers and aspiring scientists in the metal finishing field.
Spot and quick tests offer incredible insights for the metal finishing processes. What is a spot test? Are these tests reliable?
High temperature oxidation resistance is a valuable elemental and deposit property. What does it mean? Which elements possess this property? We will review the value of this physical property.
Surface and metal finishing offer a variety of options such as plating, anodizing, coloring of metals and electropolishing. Plating on several substrates such as plastic, steel, stainless steel, Invar, Kovar, nickel, aluminum, and titanium alloys are common. Elements like gold, silver, nickel, chromium, zinc and cadmium are plated. We choose the deposit based on consideration for cost, corrosion resistance and tribology properties.
Other than plating, we can electropolish and anodize metals such as stainless alloys. Applicators anodize on aluminum, magnesium, titanium, niobium, tantalum, etc.
Anodising is an electrolytic process in which we make an Al alloy anodic with a metal cathode on an acidic electrolyte. There are three classes of coating. We anodize with and without sealing.
This short paper explains which element to choose as deposit or substrate. It lists spot and quick tests available in the market. Review brightener chemistry and history. Discuss inhibitors, chemicals used for coloring metals and chromium conversion coatings.
Spot Tests
Several wet and instrumental analyses methods are used to conduct qualitative and quantitative analysis of elements. The advantage of these methods are accuracy and data reliability. But these test methods are time consuming and some are expensive. When you need a quick feedback, consider conducting spot tests on deposits and effluents. The sensitivity of spot test reaction can be at ppm levels. Elements such as aluminum, stannous tin, gold, silver, iron, nickel, palladium, lead, zinc, cadmium, chromium and copper can be tested. Many of these tests can take less than 5 minutes. We can detect heavy metals, hexavalent ions and cyanide content in the effluent. You can distinguish between cadmium or zinc plating deposits using spot tests.
Here is a list of some organic chemicals used for spot tests: Diphenyl carbazone Dimethyl glyoxime Tri-ammonium aurine-tricarboxylate Nitro-bruciquinone hydrate p-Dimethylamino benzylidene rhodamine diphenyl thiocarbozone sym-Diphenyl-carbazide (1-2-Hydroxy-5-sulpho-phenyl)-3 phenyl-5-(2-carboxy-phenyl)-formzan) sodium salt 1-(2-Pydridyl-azo)-2-naphthol Refer to Chem Spider for further information on any chemicals.
For further information on spot tests, read the book - Analysis of Metal Finishing Effluents and Effluent Treatment Solutions. This is a book written by Duncan MacArthur, Fred Stevens, and G. W. Fischer. ChemicalsDid you know tobacco and licorice were one of the earlier brighteners used? Several decades ago, or even a century back, the use of brighteners or additives were very limited. Even the awareness of organic brightener science did not exit. Like many inventions, use of organic chemicals as a brightener was an accident. Tobacco was one of earlier recorded chemical used as additive. More than a century ago a plating operator who had the habit of chewing tobacco drooled the juice onto a plating solution during electroplating. Later noticed that a plated lot had a brighter appearance. Further investigation revealed the brightness influence of tobacco on plating deposit. People used licorice during earlier days. It had a presence in the industry for some time and even now to an extent. Licorice extract is a carbohydrate and its chemical name is glycyrrhizin. They used it as an additive.
The additive was prepared by weighing a known quantity of licorice root and steep in a boiling water until colour saturation occurred. For 100 L plating solution, 100 grams of root was steeped in 0.5 L of boiling water. Pickling and acid activation are a very common process at a steel mill, metal foundry, and a metal finishing processing plant. Conditional on activation and deposition bonding requirements, a substrate such as copper alloys or steel alloys would require activation under strongly acidic conditions. Use of strong acids such as hydrochloric acid, sulfuric acid and hydrofluoric acid can etch the substrates.
We commonly use sodium fluoride as an inhibitor. On picking applications, industry used antimony trioxide as an inhibitor.
Copper alloys such as brass tarnish in the presence of oxygen from atmosphere. Brass plated deposit do the same. An organic coating can prevent tarnish. Benzotriazole coating forms a thin layer in an immersion process, and the layer protects copper alloys from tarnish.
Brass plating is an alloy deposition process. The electromotive force potential of copper and zinc makes cyanide brass plating one of the most complex electrolytic processes. Attainment of a consistent and durable colour is tricky. Proper use of current density with an excellent choice of rectifier (IGBT or SCR) with an organic coating ensures great cosmetic appeal with durability. We can also colour brass. One such colour is blue. An immersion process at high temperature in the presence of sodium sulphite and lead acetate colours brass substrates. Other than brass, we can colour stainless steel alloys using dichromate salts.
Yellow chromate on zinc deposit is one of the popular choices. We recognize the yellow chromate for brilliance of colour and corrosion protection. There is a subtle colour difference different between hexavalent and trivalent chromates. Chromates sometimes leaves iridescent finish. A protective coating similar to benzotriazole layer reduces iridescent streaks. One can get a reddish tone on the yellow chromate formulation. Use of a sulfate ions and nitric acid offers a reddish yellow chromate finish.
Occasionally people refer to chromate or chromium plating as chroming. Chroming is a colloquial speech term and we prefer you avoid using informal terms to avoid confusion and for use of clear language communication. Hexavalent Cr and (cyanide) cadmium is listed by Registration Evaluation Authorization and Restriction of Chemicals (REACH). We now replace cadmium plating with zinc / nickel alloy. Sacrificial protection of cadmium under saline conditions are inimitable.
Deposit PropertiesObserving electromotive force series of elements and their potentials (negative or positive / active or noble) suggests evidences on fascinating deposit, material or electrolyte properties. We are referring to properties such as high temperature oxidation resistance and conductivity. Pilling and Bedworth conducted a seminal work on high temperature oxidation. Chromium, tantalum, zirconium and gold possess exceptional high temperature oxidation resistance properties. What is high temperature oxidation resistance? The volume of oxide is greater or lesser than the parent metal, it produces or cannot produce an effective protective property. What does a reference to protective property mean? It refers to the formation of an oxide layer, such as tantalum oxide, chromium oxide and zirconium oxide on the metal or the deposit. The refractory metals offer oxidation resistance up to ~ 600ºF. Oxidation and healing property are the principal reason hexavalent hard chromium plated components had gained wide popularity. Many applications of aerospace and automotive industries require components to posses tribological properties at a higher temperature. Wear, lubrication, and friction are such examples. The oxides can re-form and withstand high temperatures during these mechanical transformations. Tantalum, zirconium, niobium, and chromium metals are a few among the best to possess such a property. Other than oxidation properties, these elements are susceptible to corrosion resistance from acids, alkalis, organic media and other reagents. We measure high temperature oxidation in ratio and Pilling - Bedworth (PB) ratio of corrosion resistant metals range between 0 and 4. Higher the number better the corrosion resistance. PB ratio is the ratio of the metal oxide volume divided by the metal volume. Chromium PB ratio is 2. All chromium electroplating deposits do not have the same corrosion resistance properties. Corrosion resistance of decorative Cr plating is because of nickel undercoat. Most hard chromium deposit do not have any corrosion resistance. However, a few formulations containing fluoride ions in the electrolyte possess high corrosion resistance. Some hard-hexavalent Cr deposits pass 500 hours of neutral salt spray test (NSST). We mainly attribute the variations to formulation, processing, and process control.
Other than refractory metals, precious metals such as gold plating deposit possess high temperature oxidation resistance. Industry uses gold plated components on space applications because of high temperature oxidation resistance, conductivity, high surface stability, high resistance to tarnish, and chemical corrosion. Both trivalent and monovalent salts are used to deposit gold from electrolytes. Precious metals like gold, silver and palladium can be plated on several substrates such as stainless steel, Kovar, Inconel, magnesium, aluminum and titanium alloys efficaciously.
Besides lightweight, the stubborn oxide layer makes aluminum and titanium alloys indispensable in our daily lives.
Previous paragraph mentioned about the conductivity of deposit. What about electrolyte conductivity? Change of ion activities with concentration affects electrolyte conductivity. Understanding interionic attraction theory of electrolytes are essential to improve conductivity.
ValueWhether you are an engineer or a research scientist, understanding element and deposit properties, electrolyte capabilities and limitations, and vitality of unique chemicals are important. A process design engineer with a good understanding on these characteristics can design products with superior corrosion and tribological properties. The matters covered in this paper such as high temperature oxidation resistance can help a designer identify suitable metal as substrate and a deposit.
We identify some chemicals listed in this paper as hazardous or carcinogen per Registration Evaluation Authorization and Restriction of Chemicals (REACH). REACH is a European Union regulation. You can also find additional information on carcinogens by visiting the website of National Institute of Environmental Health Sciences (NIEHS) under the National Toxicology Program (NTP). Observing regulatory compliance and identifying risk mitigation plan will drive an organization’s governance.
REACH, quality demand, and customer requirement will call for a transformed focus on a few facets such as colouring of metals, plating solution additives, chromium conversion coating and anodizing. An ardent electroplating specialist must consider all the services, test methods and fundamental concepts. A leader must prepare electroplating companies to manage complex processes. An agile metal finishing organization aiming to survive even under adverse conditions shall be data driven, ensure speed of business is appreciable, work faster, and inculcate easy-to-use test methods. We know many that plating companies who are not data driven do not grow or adapt to developing changes.
Spot testing of effluent, electrolyte or deposit is an under used method, and will help gather data with speed and ease. Other quick tests like pH measurement, specific gravity, litmus, refractometer, and profilometer are all easy and inexpensive. This do not mean volumetric and instrumental analysis offer less value. Both methods are vital for many electroplating operations. The choice depends on their technical ability, product testing requirements and financial capability. The examples of these instruments are atomic absorption spectroscopy, scanning electron microscopy, induced couple plasma (ICP), x-ray diffraction, x-ray fluorescence and electron microprobe analysis. We use these units for elemental analysis at lower concentration with a top-level accuracy. XRD and EPMA can detect light elements such as lithium, oxygen and carbon with an outstanding repeatability and reproducibility. We deliberated chemicals, methods, properties, and data driven approach. Cognizance of these matters without a long-term analysis and reaction plan is not noteworthy! Consider use of run chart, control chart and Process Development and Control (PDC) tools with a visual dashboard. Readers can find a value on other short papers written on this page previously. Please read articles on electrode potential, IGBT and SCR power supplies, current distribution, throwing power, periodic table, Time Change Management (TCM), Process Development & Control (PDC) tools, and communication. A complex electrolysis process requires a multidimensional approach on disciplines such as science, mathematics, technology and management. There are many vital aspects involved in this field such as automation, process control, business development methodologies, and so on. Fundamentals, laws, equations, and concepts govern electrolysis. Though not needed on a day-to-day basis, these are important to be aware and apply. Discipline, observation, data, patterns, and behaviors are critical for one to succeed at a higher level. Though there will be a scientific explanation for all outputs, one needs to treat the work as art! This is imperative because of our limitations – time and knowledge. Hence, at Advint we offer on guidance on subjects related to laboratory practices, equipment engineering, automation, productivity, lean, statistical process control (SPC) tools, and management. Advint’s virtual Electroplating Training explains all these subjects comprehensively.
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Surface profile of the substrate, specifically surface activity and its receptivity to accept electroplating deposit, spontaneously determines the morphology.
A deposit with good morphology will possess an adherent deposit. There is a myth and inadequate science work related to surface profile and adhesion. A few sectors do well with improving surface activity, and a sector is vulnerable. This short paper intends to shine light, dissipate a myth, and suggest improvements with supporting information. Cleaning & Activation
It is a normal practice to blast a metal surface to improve cleanliness. This approach predates the 60s, when cleaner science had made minimal progress. Over the years proprietary plating supply houses like Atotech, MacDermid Enthone and Coventya had conducted extensive research and offer an array of cleaning products. We released a short paper explaining the importance of cleaning on April 1, 2019.
In the absence of an effective cleaning process, blasting the surface is pertinent. It is an important treatment method on applications where we require higher Ra values or unique aesthetic appeal. Rather, if one blasts a surface merely to improve adhesion, then it is time to debunk the myth! Now, I’ll back up the purpose with facts and information.
To get an adherent deposit the metal surface must be clean, active and receive nucleation (form a unimolecular layer) within the first 10 or 20 seconds regardless of the current distribution pattern. A spontaneous and uniform deposit formation is important. The critical nucleation time varies between substrates and the deposit element’s electrode potential. A truly active surface allows effective nucleation. A poor nucleation layer will disrupt crystal growth and cause re-nucleation of the crystals. This disruption leads to deposit non-coherence and inconsistency in physical characteristics, resulting in premature product failure. Impregnated blasted media is very difficult to obliterate the surface and in most cases leaves a residue, hinders nucleation or continuity and uniformity of the deposit. An electropolished surface address this concern and enables epitaxial or pseudomorphic growth when and where applicable. This surface possesses very low Ra values, are active and free from foreign materials. If it drives you to get the most adherent deposit, electropolished surface is one of the best means to achieve this endeavor.
Surface Profile & AdhesionA truly active metal surface can form a thick intermetallic layer and develop a single domain deposit morphology (columnar structure) through the process. A single domain columnar structure deposit will possess a distinct grain boundary.
This mechanism is not independent of process control. The author of this paper had conducted extensive research over a decade on this matter, and so did a few other scientists from our society during the 80s and till now. A deposit with an intermetallic layer forms the most adherent deposit. In order for a non-electropolished surface to form an intermetallic layer, it must possess an active surface. We know that an electropolished surface possesses lower Ra value, but we require more controlled studies to validate the relationship between the surface profile and adhesion. On this subject, good surface profile implies a clean, smooth and active surface.
Morphology & Physical Characteristics
Most adherent deposits possess good morphology. A deposit with an intermetallic layer and undisrupted columnar structure will have greater than 20% improvement in physical characteristics such as hardness, tribology, and corrosion resistance properties.
Summary
Blasting is a valuable pretreatment method, but an ambitious applicant must recognize that residue left on the surface affects the deposit characteristics, and it is not a certain choice in pursuit of an adherent deposit. Electropolishing is not practical on many applications. Exceptional cleaning and activation are viable and important.
Accomplishing an intermetallic layer on all applications is an unreasonable expectation, but a clairvoyance can set that as an aim. This aim is akin to lean’s one-piece flow and six-sigma. In short, be mindful of the relationship between activation, morphology and physical characteristics.
Notes:Material scientists and electrochemists now and then use different terminologies when referring to the same concept. Some terms used in this paper are no exception.
You are welcome to post a comment or email with questions to [email protected] if a concept is abstruse.
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This is the second year of short papers release. Last year, Advint released papers on cyanide ions, properties and
Reel-to-Reel Plating
Electronic industry regularly uses gold, tin, palladium, palladium/nickel and copper on a continuous reel-to-reel plating application. Similar to gold, tin and indium possess comparable properties and advantages. Tin, silver, copper, indium, and gold all possess good conductive property. Indium, a precious metal, we primarily use as an alloying material in plating applications, though they use it as a deposit by itself (without alloying element).
Palladium and nickel are neighbors in the periodic table. We consider palladium to be a precious metal and it also possess properties comparable with nickel. It
Plating on Plastics (PoP)
The demand for nickel on other hand is rapidly growing in the automotive industry, particularly in plating on plastics applications. The wide acceptability of nickel is because of its refractory properties, though it does not belong to elements of the refractory group (periodic table). Nickel release and its allergic properties are an issue in certain demographics and on applications such as eyeglass frame, earring, necklace, ring, bracelet.
On PoP applications, plastic substrate preparation using a colloidal catalyst is one of the most important steps. On acrylonitrile butadiene styrene (ABS) plastics, it follows preparation of the substrate with electrolytic copper, nickel and chromium deposits. Among Ni use, electroless Ni is gaining wider acceptance in recent decades. The industry also now replaces hexavalent Cr with trivalent chromium.
Electrode potentials are distinct between hexavalent and trivalent Cr plating applications. The trend is the same on other metals such as Ni, Au, Sn, In, Cu and Pd. The properties are distinct not only because of electrode potentials but also because of transportation of ions and ionic mobility. Similar to chromium, ionic mobility of electrolytes of electro-polishing and anodizing are also less. This is one reason these require a very high DC voltage from the rectifier during processing. Note: A paper on rectifier is coming soon.
Summary
Different metals deposition mechanisms vary because of their electrode potentials and other properties like ionic mobility and concentration of metal ions. Among many elements of reel-to-reel plating and PoP applications reviewed in this paper, Pd The recognition goes beyond plating applications.
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Electroless Ni-P and Ni-B process management had improved significantly within the last two decades. In this paper I’ll write about the science of autocatalytic plating as practiced now and the criterions for advancement at a higher level. The purpose is to offer reader’s deeper information to achieve consistent deposit physical characteristics and the functional properties of electroless nickel plating. We will go over the functions of a reducing agent, stabilizer (or catalytic inhibitor), and complexing agent related to thermodynamic property of an electrolyte and mixed potential theory.
Temperature (energy), electrolyte flow (current density), solution volume, and the concentrations balance determine the effectiveness of the deposition mechanism and consistency of the deposit in the long term. Gibbs free energy and its relationship with volume, temperature, and energy influence the required concentrations and ratios of a reducing agent, stabilizer, and the complexing agent. An understanding of Gibbs ∆G value with the stability, instability and absolute stability of the electrolyte is imperative. Per mixed potential theory, the deposition reaction is a combination of cathodic and anodic partial reactions taking place at separate electrodes. Redox potentials of sodium hypophosphite, dimethyl amine borane (DMAB), and sodium borohydride play a significant role in a reduction step and the concentrations of stabilizers and complexing agents.
To confirm sustained deposit characteristics, electrolysis mechanism and control or management of by products release are important. Geometrical properties such as
will ensure stability.
When Gibbs free energy and partial electrode reactions (anodic and cathodic) are within the optimum range plating rate, deposit composition (Ni and P or B weight percentages), and formation of uniform eutectic compounds of Ni-P or Ni-B will be effective and consistent. Corrosion and tribology properties depend on the consistency of the deposit composition and phase formation. Out of range ∆G value can lead to unstable or absolute stability of the electrolyte. This will lead to either electrolyte decomposition or very low plating rate. The concentrations of a reducing agent, stabilizer, and the complexing agent determine the stability of the electrolyte. Plating rate depends on electrolyte temperature and pH.
Summary:
Other than simple control and changes done to temperature and chemical constituents, due diligence on the following variables considering the aforementioned concepts will advance the attained deposit characteristics:
One can improve the bath life and the effectiveness of any deposit by giving more attention to the fundamental concepts and conscientiousness on the input variables. Though the examples cited in this paper are for electroless Ni, the recommendations apply to all electroless processes including Cu, Ag, Pd, Au, etc.
Readers - You are welcome to post questions, comments or thoughts.
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Evolution of Cleaner Formulations in the Industry
Unlike quite a few decades ago, current cleaner formulations contain methodically investigated inorganic and organic ingredients which are effective and comply with the environmental regulations. Different sectors and industries use solvent, alkaline This blog highlights the value of a good cleaner, identifies a simple step in choosing a cleaner, and list a few potential ingredients and their properties. A carefully chosen cleaner can remove organic residues from the substrate thoroughly. Decrease the cleaning time and (or) improve cleanliness. Cut cost by increasing the cleaner life and minimize environmental impact.
Go over a material safety data sheet (MSDS) to select a cleaner, however, a proprietary chemical supplier could throw a curve ball. Section 2 of an MSDS must contain hazardous ingredient listed with Chemical Abstracts Service (CAS) registry number and the concentration. The reader can find specific CAS related information on this link.
Before considering the inorganic and organic ingredients, process owner must know their processes and supply chain well. Knowing and considering the substrate Alkalinity, buffer, water softening, chelation, and surface tension are a few important solution properties to observe. The process owner should assess the presence and concentrations of sodium hydroxide, carbonate, phosphate, silicate, amines, and surfactants and relate to the application (s). A surfactant can be anionic, non-ionic and (or) amphoteric. It changes the surface tension and wettability of the solution.
Learn More
Rhodium Plating Techniques | Advint Incorporated
Briefly put, irrespective of reasons and justifications, focussing on cleaners and improving the cleaning performance is worth the effort and not a hard nut to crack using the listed suggestions. |
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Venkat Raja 40 September 29, 2024 |
Charles G Graham 10 August 20, 2024 |