Claims:We Claim:

1. A method of copper plating on mild steel/ferrous/iron based metallic substrate from a non-cyanide based electrolyte comprising the steps of:
preparing the electrolyte bath;
preparing the surface of substrate;
plating of the substrate;
treating of the substrate; and
drying the substrate,
wherein the electrolyte bath includes Copper pyrophosphate Potassium pyrophosphate, , Etidronic acid, Potassium Citrate, Ammonium citrate tribasic and diethylene diamine,
wherein preparation of surface includes mechanical cleaning and chemical cleaning.
2. The method of copper plating on mild steel substrate from a Non-cyanide based electrolyte as claimed in claim 1, wherein electrolyte bath comprises of:
Copper pyrophosphate (Cu2P2O7.4H2O) - 60-75gm/L
Potassium pyrophosphate (K4P2O7) - 295-305 gm/L
Etidronic acid (HEDP) (C2H8O7P2) - 40-50gm/L
Potassium Citrate (C6H5K3O7) - 10-15gm/L
Ammonium Citrate tribasic (C6H17N3O7) - 10-15gm/L
Diethylenediamine (C4H13N3) - 1-5 ml/L
3. The method of copper plating on mild steel substrate from a Non-cyanide based electrolyte as claimed in claim 1, wherein pH of the electrolyte bath is maintained in a range of 8.5-9.5 by adding Potassium Hydroxide.
4. The method of copper plating on mild steel substrate from a Non-cyanide based electrolyte as claimed in claim 1, wherein mechanical cleaning includes grinding the substrate with sand paper to remove all the rust or oxides.
5. The method of copper plating on mild steel substrate from a Non-cyanide based electrolyte as claimed in claim 1, wherein chemical cleaning includes cleaning by organic solvent including acetone or ethanol followed by rinsing in demineralized water, acid pickling in 10% to 20% Hydrochloric acid (HCl) solution for 20 - 25 seconds and rinsing in demineralized water.
6. The method of copper plating on mild steel substrate from a Non-cyanide based electrolyte as claimed in claim 1, wherein copper plating is done between 0.6V to 0.7V for 15 to 30 minutes for a plating thickness of 5 to 6 microns.
7. The method of copper plating on mild steel substrate from a Non-cyanide based electrolyte as claimed in claim 1, wherein treating of substrate comprises rinsing with demineralized water.
8. The method of copper plating on mild steel substrate from a Non-cyanide based electrolyte as claimed in claim 1, wherein the substrate is dried by compressed air.
9. The method of copper plating on mild steel substrate from a Non-cyanide based electrolyte as claimed in claim 1, wherein copper striking is done at 1.5V for a period of 25 to 30 seconds.
10. The method of copper plating on mild steel substrate from a Non-cyanide based electrolyte as claimed in claim 1, wherein copper plating luster is orange- yellow in color. , Description:A METHOD OF NON-CYANIDE BASED COPPER PLATING

FIELD OF INVENTION
[001] The present subject matter described herein, relates to electroplating and a method of copper plating on mild steel substrate using Non-cyanide based electrolyte. More particularly, the present subject matter relates to a Non-cyanide based Copper Plating process on mild steel plates/components that generates a bright and adherent layer of copper.
BACKGROUND AND PRIOR ART OF THE INVENTION
[002] Electroplating, also known as electrodeposition is the process of coating a metal object with another metal, using an electrical current passed through a chemical solution. This system comprises a cathode – the material to be plated/substrate; an anode – the plating metal or inert conductor; an electrolytic solution – a salt solution used to immerse the anode and cathode containing metal ions to be coated. An electrical current – provided by an electrical source such as a battery or other power unit.
[003] This process results in a thin layer of metal being deposited onto the surface of a work piece called the substrate. In this process, the target is connected to anode and substrate is connected to cathode and are dipped in an electrolytic solution. If the process is used for copper deposition on substrate, it is known as Copper Electroplating. Copper is regarded as the most electrically conductive of all the metals. Copper plating offers a variety of benefits due to its malleability, conductivity, and corrosion resistance, lubricious and anti-bacterial qualities. Additional copper plating benefits include good corrosion resistance and heat conductivity, as well as low-contact resistance. Hence it is common among the electrical industries to copper plate the electrical components.
[004] Most commonly used chemicals for preparing copper plating electrolyte is potassium and Sodium cyanide because of its high throughput. In India large number of plating industries uses potassium cyanide/sodium cyanide for copper plating of various components including its aesthetic uses like jewelry applications. However, there are many health and environmental hazards involved with cyanide based copper plating. And as awareness towards these hazards is increasing, law and regulations are being formulated by different governments for the use of cyanide based electrolyte in copper plating. In this situation, it is obvious that industrial copper plating business may get hampered badly in the near future if sustainable alternative to cyanide based copper plating is not developed immediately.
[005] Copper electro-plating is used extensively in a variety of industrial applications including electroforming, electro refining, soldering, printing rolls and decorative plating of zinc die castings. Since then and now, majority of commercial copper plating solutions are cyanide based. This has been the case due to its numerous advantages like cyanide is an excellent complexing agent making it more tolerant to metal contamination and it can guarantee a pure orangish yellow bright deposit which are desired by customers. But due to hazardous nature of Cyanide, there is a gradual shift towards non-cyanide based copper plating. Currently Cyanide based copper plating so are being used to plate the components of Turbo generator. However, these cyanide baths are highly toxic in nature. This has to lead to the development of bright copper plating using a non-cyanide bath.
[006] Cyanide based Copper Electroplating has been in use for decades due to its ability to generate high quality, adherent and bright Copper plating. But use of Cyanide has been a serious concern from operator’s health and environmental hazards point of view. Exposure to cyanide can cause serious health issues. Besides the threat to the operator's health, the disposal of the exhausted plating bath and waste water treatment, are becoming more and more expensive and critical. If not treated properly, disposed waste from plating industry can contaminate the underground and river water of the area which comes in its contact. Hence law bodies and governments have started taking preventive steps to avoid such hazards from cyanide based Copper plating.
[007] Reference may also be made to the following prior arts:
[008] With reference to European patent reference No: EP0163131A2, a brightening agent 2- mercaptobenzothiazole is being used for FGD acid based copper plating solution. In connection to US patent reference No: 3161575A & 3157586A a brightening agent 2- mercaptobenzothiazole or 1, 3, 4-Thiadiazoles or alkyl mercaptobenzothiazole is being used for alkali based copper pyrophosphate plating solution with a single complexing agent i.e pyrophosphate based copper plating electrolyte.
[009] In particular to US patent No: US3075856A a brightening agent diethylenetriamine is being used for alkali based copper plating solution with a single complexing agent i.e Formaldehyde & ethylene tetra aminoacetic acid (EDTA) based.
[0010] Researches have been done in this field and found that Copper Sulphate with Glycerol and Ethylenediaminetetraacetic acid (EDTA) based non-cyanide solutions are able to generate promising Copper plating. Moreover, these Acid bath corrodes the steel being used as a substrates for Copper plating. Many kinds of copper electroplating with excellent properties have been reported. These methods mainly focused on single-complexing system, such as pyrophosphate, citrates, EDTA and Etidronic acid, which still have many disadvantages compared to cyanide alkaline technology. Single-complexing copper plating system is difficult to replace cyanide copper plating because of the low current efficiency and weak adhesion. Hence, a mixed complexing agent system has become one of the main research area.
[0011] Pyrophosphate and Etidronic acid is good complexing agent for copper electroplating and will form stable mixed complex in alkaline solution. Moreover, pyrophosphate and Etidronic acid has the strong adsorption and activation on the electrode surface. When pyrophosphate and Etidronic acid are used together, the effect is more obvious.
[0012] None of the above prior arts can fulfil the requirements of the invention for which it is designed. Hence, the present invention has been introduced.
OBJECTS OF THE INVENTION
[0013] It is therefore the object of the invention to overcome the aforementioned and other drawbacks in prior art.
[0014] The principal objective of the present invention is to develop a non-cyanide based copper plating process which is having better adhesion, bright and low porosity copper coating on steel substrate and is less hazardous than Cyanide based copper plating and at last complies with the government regulatory norms.
[0015] These and other objects and advantages of the present subject matter would be apparent to a person skilled in the art after consideration of the following detailed description taken into consideration with accompanying drawings in which preferred embodiments of the present subject matter are illustrated.
SUMMARY OF THE INVENTION
[0016] One or more drawbacks of the conventional technology based on existing apparatus and processes are overcome, and additional advantages are provided through a novel method of copper plating on mild steel substrate using Non-cyanide based electrolyte.
[0017] Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be a part of the claimed disclosure.
[0018] In accordance with an embodiment of the present subject matter, a method of copper plating on mild steel substrate from a non-cyanide based electrolyte comprising the steps of preparing the electrolyte bath; preparing the surface of substrate; plating of the substrate; treating of the substrate and drying the substrate, wherein the electrolyte bath includes Potassium pyrophosphate, Copper pyrophosphate, Etidronic acid, Potassium Citrate, Ammonium citrate tribasic and diethylene diamine, wherein preparation of surface includes mechanical cleaning and chemical cleaning.
[0019] In another embodiment of the present subject matter, the pH of the electrolyte bath is maintained in a range of 8.5-9.5 by adding Potassium Hydroxide.
[0020] In another embodiment of the present subject matter, the mechanical cleaning includes grinding the substrate with sand paper to remove all the rust or oxides.
[0021] In another embodiment of the present subject matter, the copper plating is done between 0.6V to 0.7V for 15 to 30 minutes for a plating thickness of approximately 5 to 6 microns.
[0022] In another embodiment of the present subject matter, the chemical cleaning includes cleaning by organic solvent, rinsing in demineralized water, acid pickling in 10% - 20% Hydrochloric acid (HCl) solution for 20 - 25 seconds and rinsing in demineralized water.
[0023] In another embodiment of the present subject matter, the treating of substrate comprises rinsing with demineralized water.
[0024] In another embodiment of the present subject matter, the substrate is dried by compressed air.
[0025] In another embodiment of the present subject matter, the copper striking is done at 1.5V for a period of 25 to 30 seconds.
[0026] In another embodiment of the present subject matter, the copper plating luster is orange- yellow in color.
[0027] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.
[0028] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0029] It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter, and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the accompanying figures. In the figures, a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system or methods or structure in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
[0030] Figure 1 illustrates a schematic view of a metallic substrate before and after plating;
[0031] Figure 2 illustrates a schematic view of a copper plated substrate after a bend test in accordance with an embodiment of the present disclosure;
[0032] Figure 3 illustrates a schematic view of micro structure of copper plated substrate in accordance with an embodiment of the present disclosure;
[0033] Figure 4 illustrates of a schematic view of XRD pattern of copper plated sample in accordance with an embodiment of the present disclosure;
[0034] Figure 5 illustrates a schematic view of XRD pattern of Copper plated sample & mild steel pattern in accordance with an embodiment of the present disclosure;
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
[0035] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein are not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the present disclosure as defined by the appended claims.
[0036] It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
[0037] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a",” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
[0038] It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
[0039] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0040] The present disclosure discloses a novel method of Non-cyanide based copper plating on mild steel substrate. Electrolytic solution is based on Potassium pyrophosphate, Copper pyrophosphate, Etidronic acid, Potassium Citrate, Ammonium citrate tribasic and diethylene diamine. All these chemicals are dissolved in demineralized water to prepare the electrolytic solution. Later Diethylenediamine is mixed in the solution as brightening agent. pH of the solution is maintained ~ 9 by adding potassium hydroxide. Once electrolyte is ready, surface preparation of the mild steel plates is done by grinding it with sand paper followed by chemical cleaning and acid pickling. Copper plate (Anode) and mild steel plate (Cathode) were dipped inside the electrolyte. A rectifier was then used to supply the DC current through anode, cathode and electrolyte. Voltage striking was done for 30 seconds at1.5 volts followed by copper plating for 30 minutes at 0.6 volts. After 30 minutes of plating, mild steel substrate is removed from the electrolyte and rinsed by De-mineralized water.
TECHNICAL ADVANTAGES:
[0041] The main advantage of complex system with pyrophosphate, Etidronic acid and diethylenediamine in copper plating aid in high brightness, excellent adhesion and low porosity copper deposition on steel substrate. High deposition rate is also achieved due to high formation of copper pyrophosphate complex in this electrolytic solution.
[0042] These and other advantages of the present subject matter would be described in greater detail with reference to the following figures. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope.
[0043] With reference to Figure 1 to Figure 5, the present disclosure discloses a method of copper plating on mild steel substrate using Non-cyanide based electrolyte comprising the steps of-
ELECTROLYTE PREPARATION:
[0044] The Electrolyte bath comprises of the following chemicals:
Copper pyrophosphate (Cu2P2O7.4H2O) - 60-75gm/L
Potassium pyrophosphate (K4P2O7) - 295-305 gm/L
Etidronic acid (HEDP) (C2H8O7P2) - 40-50gm/L
Potassium Citrate (C6H5K3O7) - 10-15gm/L
Ammonium Citrate tribasic (C6H17N3O7) - 10-15gm/L
Diethylenediamine (C4H13N3) - 1-5 ml/L
Potassium Hydroxide (KOH) - to maintain pH~ 9
Potassium pyrophosphate is first dissolved in demineralized water to a half of the electrolyte bath volume. Copper pyrophosphate is dissolved in Potassium pyrophosphate dissolved solution as it is not soluble in demineralized water. Once Copper pyrophosphate is dissolved, Etidronic acid is mixed with the pyrophoshate solution. Potassium Citrate, Ammonium Citrate tribasic and Diethylenediamine is mixed slowly in the solution directly. pH of the bath is measured and maintained in a range of 8.5-9.5 by adding Potassium Hydroxide.
[0045] Once Electrolyte is ready, surface of the steel substrate is to be prepared for Copper plating. Surface preparation can be categorized into two parts:
Mechanical Cleaning: Mechanical cleaning of the substrate comprises grinding of the substrate with sand paper to remove all the rust or oxides. This process exposes and makes ready the substrate surface for chemical cleaning.
Chemical Cleaning: Mechanical cleaning is followed by chemical cleaning. Substrate is first cleaned by organic solvent like Acetone for removal of any oily substance. Substrate is then rinsed in demineralized water followed by acid pickling in 20% Hydrochloric acid (HCl) for 20 - 25 seconds. At last substrate is again rinsed in DM water before copper plating.
COPPER PLATING:
[0046] After surface preparation, substrate is then transferred into the electrolyte solution for plating. Substrate is connected to the cathode and pure copper is connected to the anode terminal of the rectifier. Both mild steel substrate (Cathode) and Pure copper (Anode) is dipped into the electrolyte bath before starting the plating. After switching on the rectifier, striking is done first at 1.5V for approximately 30 Seconds followed by copper plating at 0.6V for 30 minutes to get the plating thickness of approximately 5 to 6 microns.
POST-PLATING TREATMENT:
[0047] After copper plating of 30 minutes, substrate is removed from electrolyte bath and rinsed with demineralized water. It is then dried by compressed air.
BEND TEST AND EXPERIMENTAL RESULTS:
[0048] Three cycles of 90-degree bend test is performed to check the adhesion of the plating.
[0049] No crack or flaking observed near the bent area.
[0050] Thickness is measured through optical microscope and found in the range of 5-6 microns.
[0051] Crystallinity phase of copper was characterized through XRD analysis and found that, copper deposited on mild substrate is crystalline in nature.
[0052] Working of invention
[0053] A method of Non-cyanide based copper plating on mild steel substrate. Electrolytic solution is based on Potassium pyrophosphate, Copper pyrophosphate, Etidronic acid, Potassium Citrate, Ammonium citrate tribasic and diethylene diamine. All these chemicals are dissolved in demineralized water to prepare the electrolytic solution. Later Diethylenediamine is mixed in the solution as brightening agent. pH of the solution is maintained ~ 9 by adding potassium hydroxide. Once electrolyte is ready, surface preparation of the mild steel plates is done by grinding it with sand paper followed by chemical cleaning and acid pickling. Copper plate (Anode) and mild steel plate (Cathode) were dipped inside the electrolyte. A rectifier was then used to supply the DC current through anode, cathode and electrolyte. Voltage striking was done for 30 seconds at 1.5 volts followed by copper plating for 30 minutes at 0.6 volts. After 30 minutes of plating, mild steel substrate is removed from the electrolyte and rinsed by De-mineralized water.
[0054] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”
[0055] It will be further appreciated that functions or structures of a plurality of components or steps may be combined into a single component or step, or the functions or structures of one-step or component may be split among plural steps or components. The present invention contemplates all of these combinations. Unless stated otherwise, dimensions and geometries of the various structures depicted herein are not intended to be restrictive of the invention, and other dimensions or geometries are possible. In addition, while a feature of the present invention may have been described in the context of only one of the illustrated embodiments, such feature may be combined with one or more other features of other embodiments, for any given application. It will also be appreciated from the above that the fabrication of the unique structures herein and the operation thereof also constitute methods in accordance with the present invention. The present invention also encompasses intermediate and end products resulting from the practice of the methods herein. The use of “comprising” or “including” also contemplates embodiments that “consist essentially of” or “consist of” the recited feature.
[0056] Although embodiments for the present subject matter have been described in language specific to structural features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the system/component of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations, which fall within the scope of the present subject matter.