electroless deposition

Electroplating is generally cheaper than ED.{{Greenwood&Earnshaw2nd|page=514}} Unlike ED, electroplating only deposits on other conductive or semi-conductive materials. Requiring an applied current, the instrumentation for electroplating is more complex.G. O. Mallory and J. B. Hajdu, editors (1990): Electroless Plating: Fundamentals and applications. 539 pages. {{isbn|9780936569079}} Electroless deposition deposits metals onto 2D and 3D structures, whereas other plating methods such as Physical vapor deposition (PVD), Chemical Vapor Deposition (CVD) are limited to 2D surfaces.{{Cite journal |last1=Siddikali |first1=Palaiam |last2=Sreekanth |first2=P. S. Rama |date=2022-08-18 |title=Performance Evaluation of CNT Reinforcement on Electroless Plating on Solid Free-Form-Fabricated PETG Specimens for Prosthetic Limb Application |journal=Polymers |language=en |volume=14 |issue=16 |pages=3366 |doi=10.3390/polym14163366 |issn=2073-4360 |pmc=9415912 |pmid=36015623|doi-access=free }} Electroless deposition is advantageous in comparison to PVD, CVD, and electroplating deposition methods because it can be performed at ambient conditions. Electroless deposition can also produce very conformal coatings on complex structures like porous membranes.{{cite journal | last=Aminu | first=Temitope Q. | last2=Juybari | first2=Hamid Fattahi | last3=Warsinger | first3=David M. | last4=Bahr | first4=David F. | title=Electroless Deposition for Robust and Uniform Copper Nanoparticles on Electrospun Polyacrylonitrile (PAN) Microfiltration Membranes | journal=Membranes | volume=14 | issue=9 | date=2024-09-20 | issn=2077-0375 | pmid=39330539 | pmc=11434320 | doi=10.3390/membranes14090198 | doi-access=free | page=198}}

File:19.electroless.nickel.jpg

The discovery of electroless deposition is attributed to Charles Wurtz who, in 1846, noticed a nickel-phosphorus solution spontaneously formed a black powder. 70 years later François Auguste Roux rediscovered the electroless deposition process and patented it in United States as the 'Process of producing metallic deposits'.Charles R. Shipley Jr. (1984): "[https://www.pfonline.com/cdn/cms/1805_Printable_Version.pdf Historical highlights of Electroless plating]". Plating and Surface Finishing, volume 71, issue 6, pages 24-27. {{issn|0360-3164}} Roux deposited nickel-phosphorus (Ni-P) electroless deposition onto a substrate but his invention went uncommercialized.{{Cite book |last=Zhang |first=B. |title=Amorphous and Nano Alloys Electroless Depositions |publisher=Washington State University Pullman |year=2016}} In 1946 the process was re-discovered by Abner Brenner and Grace E. Riddell while at the U.S. National Bureau of Standards.{{Cite journal |last1=Ferrar |first1=W. T. |last2=O'Brien |first2=D. F. |last3=Warshawsky |first3=A. |last4=Voycheck |first4=C. L. |title=Metalization of lipid vesicles via electroless plating |url=https://pubs.acs.org/doi/abs/10.1021/ja00209a046 |journal=Journal of the American Chemical Society |year=1988 |language=en |volume=110 |issue=1 |pages=288–289 |doi=10.1021/ja00209a046 |issn=0002-7863|url-access=subscription }}{{Cite journal |date=1891-06-06 |title=Annual Convention of the American Society of Civil Engineers |url=http://dx.doi.org/10.1038/scientificamerican06061891-352 |journal=Scientific American |volume=64 |issue=23 |pages=352–353 |doi=10.1038/scientificamerican06061891-352 |issn=0036-8733|url-access=subscription }} They presented their discovery at the 1946 Convention of the American Electroplaters' Society (AES); a year later, at the same conference they proposed the term "electroless" for the process and described optimized bath formulations,{{Cite journal |date=1947 |title=Reports of committees: Annual Meeting |url=http://dx.doi.org/10.1017/s0272504500101861 |journal=Proceedings of the American Society of International Law at Its Annual Meeting |volume=41 |pages=163–165 |doi=10.1017/s0272504500101861 |issn=0272-5045 |url-access=subscription }} that resulted in a patent.{{Cite journal |last1=Brenner |first1=A. |last2=Riddell |first2=G.E. |date=1946 |title=Nickel plating on steel by chemical reduction |journal=Journal of Research of the National Bureau of Standards |volume=37 |issue=1 |pages=31 |doi=10.6028/jres.037.019 |issn=0091-0635|doi-access=free }}{{Cite journal |date=2009 |title=Coalescers |url=http://dx.doi.org/10.1016/s0026-0576(09)80396-6 |journal=Metal Finishing |volume=107 |issue=11 |pages=52 |doi=10.1016/s0026-0576(09)80396-6 |issn=0026-0576|url-access=subscription }} However, neither Abner nor Riddell benefited financially from the filed patent.{{Cite web |title=Reminiscences of Early Electroless Plating |url=https://www.pfonline.com/articles/reminiscences-of-early-electroless-plating |access-date=2023-02-16 |website=www.pfonline.com |date=6 April 2018 |language=en}} Deposition of Ni-P was commerciallized by Leonhardt Plating Company in Cincinnati followed by the Kannigen Co. Ltd in Japan, with revolutionary impact. The Leonhardt company designed and patented of several deposition baths including plating of metals such as Pt, Sn, Ag, and their alloys.

The Tollens' reaction is often used in scientific demonstrations of ED. Tollen's reagent deposits a reflective metallic silver layer on glass, thus its reference as silvering mirrors.{{Cite journal |last1=Benet |first1=William E. |last2=Lewis |first2=Gabriella S. |last3=Yang |first3=Louise Z. |last4=Hughes |first4=D. E. Peter |date=2011 |title=The Mechanism of the Reaction of the Tollens Reagent |journal=Journal of Chemical Research |language=en |volume=35 |issue=12 |pages=675–677 |doi=10.3184/174751911X13206824040536 |s2cid=101079977 |issn=1747-5198|doi-access=free }}{{Cite journal |last=Tollens |first=B. |date=1882 |title=Ueber ammon‐alkalische Silberlösung als Reagens auf Aldehyd |url=https://onlinelibrary.wiley.com/doi/10.1002/cber.18820150243 |journal=Berichte der Deutschen Chemischen Gesellschaft |language=en |volume=15 |issue=2 |pages=1635–1639 |doi=10.1002/cber.18820150243 |issn=0365-9496}} This reaction was once used to test for aldehydes in a basic solution of silver nitrate.

The ED process can be analyzed as four steps:

1. Pretreatment or functionalization of the substrate cleans the surface of the substrate to remove any contaminants which affects nanoparticle size resulting in poor plating. Pretreatment determines the porosity of the elemental metal deposition, and the initiation site of elemental deposition.{{Cite journal |last1=Afzali |first1=Arezoo |last2=Mottaghitalab |first2=Vahid |last3=Motlagh |first3=Mahmood Saberi |last4=Haghi |first4=Akbar Khodaparast |date=2010-07-01 |title=The electroless plating of Cu-Ni-P alloy onto cotton fabrics |url=https://doi.org/10.1007/s11814-010-0221-8 |journal=Korean Journal of Chemical Engineering |language=en |volume=27 |issue=4 |pages=1145–1149 |doi=10.1007/s11814-010-0221-8 |s2cid=55179900 |issn=1975-7220|url-access=subscription }}
2. Sensitization is an activator ion that can reduce the active metal in the deposition bath giving catalytic sites for the further deposition ("templation").
3. Activation accelerates the deposition by acting as a catalytic seed on the substrate surface for the final electroless deposition bath metal.
4. Electroless deposition is the process by which metal cation is reduced to elemental metal with a powerful reducing agent.

File:Electroless_deposition_process.png

A typical electroless deposition bath consists of many components:

1. A source of metal cation which is provided by a metal salt (e.g.. Cu²⁺ from CuSO₄ and Ni²⁺ from NiCl₂). The metal salts as their hydrate are first dissolved in the bath. Typical concentrations of metal salt are 30 g/L.
2. Reducing agent (or reductant), which donates electrons to the metal cation. Common reducing agents include formaldehyde, sodium borohydride, glucose, sodium hypophosphite, [hydrogen peroxide, and ascorbic acid.
3. Other reagents, many in fact, are added to modify the rate of deposition and the nature of the resulting films. Some provide buffering action, others are "stabilizers" to control the rate of deposition. Surfaces are prepared for ED by ''sensitization", often with a pretreatment of stannous chloride.

From the perspective of thermodynamics, the process is governed by the Nernst equation:

$E=E^0-(\{0.592\}|\{2\})log(Q)$

E is the potential of the reaction, E⁰ is the standard reduction potential of the redox reaction, and Q is the concentration of the products divided by the concentration of the reactants $[Products/Reactants]$.

The rate of deposition is determined by the kinetics of the autocatalysis, i.e. the efficiency at which the initially deposited islands of metal (or alloy) facilitate the further reduction of the metal salts. In a nickel chloride-sodium hypophosphite bath at 90 °C, the deposition rate is 15 mm/h.

The reducing power of reagents is pH dependent. At pH 0, the E⁰ of formaldehyde is 0.056 V, but at pH=14 the E⁰=-1.070.{{Citation |title=Electroless Copper Plating |date=1994 |url=https://dl.asminternational.org/books/book/20/chapter/289695/electroless-copper-plating |work=Surface Engineering |pages=311–322 |editor-last=Cotell |editor-first=C.M. |publisher=ASM International |language=en |doi=10.31399/asm.hb.v05.a0001265 |osti=872041 |isbn=978-1-62708-170-2 |access-date=2023-02-23 |editor2-last=Sprague |editor2-first=J.A. |editor3-last=Smidt |editor3-first=F.A.|url-access=subscription }} The formaldehyde (pH 14) is a more suitable reducing agent than at pH=0 because of the lower negative standard potential which makes it a powerful reducing agent. The potential dependence on pH is described by the Pourbaix Diagram.

Several mechanisms for ED have been discussed. In the case of nickel hypophosphorous acid, the following summarizes the net equation:

:{{chem2|Ni(2+) + 2 H2PO2- + 2 H2O -> Ni + H2 + 2 H3PO3}}

{{main|Electroless nickel-phosphorus plating}}

Mirrors for furniture, astronomy, and solar collectors, are produced by silvering using ED. A typical precursor is an ammoniacal solution of silver nitrate as the metal source and glucose or hydrazine as the reducing agent.{{cite book |doi=10.1002/14356007.a16_641.pub2 |chapter=Mirrors |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2014 |last1=Schiller |first1=Matthias |pages=1–7 |isbn=978-3-527-30673-2 }}

Platinum-based catalysts are widely used in fuel cells for hydrogen production, methanol oxidation, and oxygen reduction. Many catalysts have been produced by ED, e.g. from platinum halides and using hydrazine. Platinum salts even more so than nickel salts are easily reduced in an electrochemical sense, so they are suited for ED.{{cite journal |doi=10.1021/cr9003902 |title=Platinum-Based Nanostructured Materials: Synthesis, Properties, and Applications |date=2010 |last1=Chen |first1=Aicheng |last2=Holt-Hindle |first2=Peter |journal=Chemical Reviews |volume=110 |issue=6 |pages=3767–3804 }}

Plastics are typically metallized by nickel-phosphorus, nickel gold, nickel-boron, palladium, copper, and silver. Metallized plastics are used to lower the weight of metal product and minimize the cost associated with the use of precious metals.{{Cite web |title=Pretreatment for the metallzation of polymers/ plastics |url=https://www.polymer-surface.com/en/examples/metallization-of-plastics.html |access-date=2023-02-15 |website=Fraunhofer Institute for Applied Polymer Research |language=en}} Electroless nickel plating is used in a variety of industries including aviation, construction, textiles, and oil and gas industries.{{Cite web |last=Electro-Coating |title=Differences & Advantages Between Electroplating & Electroless Plating {{!}} Electro-Coating |url=https://www.electro-coatings.com/electroless-plating-vs-electro-plating.php |access-date=2023-02-24 |website=www.electro-coatings.com |language=en}}

Electromagnetic interference shielding (EMI shielding) refers to the process by which devices are protected from interference from the electromagnetic radiation.{{Cite web |title=What is EMI Shielding and Why is it Important for Your Design? |url=https://www.modusadvanced.com/resources/blog/what-is-emi-shielding-and-why-is-it-important-for-your-design |access-date=2023-02-22 |website=www.modusadvanced.com |language=en-us}} The interference negatively affects the function of the devices; EMI sources include radiowaves, cell phones, and TV receivers. The Federal Aviation Administration and the Federal Communications Commission prohibit the use of cellphones after an airplane is airborne to avoid interference with navigation.{{Cite web |title=Portable Electronic Devices |url=https://www.faa.gov/about/initiatives/ped/ |access-date=2023-02-22 |website=www.faa.gov |language=en-us}}{{Cite web |title=47 CFR § 22.925 - Prohibition on airborne operation of cellular telephones. |url=https://www.law.cornell.edu/cfr/text/47/22.925 |access-date=2023-02-22 |website=LII / Legal Information Institute |language=en}} Elemental Ni, Cu, and Ni/Cu coating on planes absorb noise signals in the 14 Hz to 1 GHz range.

Elemental nickel coating prevents corrosion of the steel tubulars used for drilling. At the core of this industry nickel coats pressure vessels, compressor blades, reactors, turbine blades, and valves.

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• Electroless copper deposition
• Electroless nickel-boron deposititon
• Nanomaterials
• Nanotechnology

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Category:Metal plating

Category:Corrosion prevention

Category:Printed circuit board manufacturing