US20190093252A1

US20190093252A1 - Electroplating apparatus

Info

Publication number: US20190093252A1
Application number: US16/032,522
Authority: US
Inventors: Kun-Cheng Peng; Po-Yan Su; Chun-Ying Lee; Kuan-Hsien CHEN; Wai-Hon KU; Yu-Shen TU
Original assignee: Ming Chi University of Technology
Current assignee: Ming Chi University of Technology
Priority date: 2017-09-22
Filing date: 2018-07-11
Publication date: 2019-03-28
Also published as: CN109537031B; TWI658174B; CN109537031A; TW201915223A

Abstract

An apparatus for electroplating which is applicable to the electroplating of workpiece is disclosed. The apparatus includes: an electroplating solution container, a target, an absorbent piece, and a power supply. All the electroplating solution, workpiece, absorbent piece, and target are placed inside the electroplating solution container with at least partial portions of each workpiece, absorbent piece and target submerged in the electroplating solution. The positive electrode of the power supply is electrically connected to the target while its negative electrode is electrically connected to the workpiece and absorbent piece simultaneously. When the power supply imposes a current through the circuit, the target releases metal ions into the electroplating solution and metal ions reduce and a metal coating is formed on the workpiece. In the meantime, carbocations in the electroplating solution are adsorbed on the absorbent piece.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan Patent Application Serial Number 106132632, filed on Sep. 22, 2017, the full disclosure of which is incorporated herein by reference.

BACKGROUND

Technical Field

This disclosure is related to the technical filed of electroplating, and more particular to an electroplating apparatus using an absorbent piece to adsorb the carbocations in the electroplating solution.

Related Art

With the continuous development of consumer electronic gadgets, function is not the only determining factor for the consumers. The gadget's appearance has become another important factor as well. In this regards, the structural and exterior parts of most the consumer electronic products are made of Al or Al—Mg alloys. However, for aesthetic consideration, the exterior parts of mobile phones, computers and digital cameras require further surface treatment. Among the commonly used surface treatments, electroplating usually gives the product metallic appearance with better touch quality and durability.
Electroplating is the frequently used surface treatment in which the workpiece is submerged in a container filled with electroplating solution and the externally applied electric current reduced the metal ions onto workpiece's surface to form a coating. The metallic coating can have both functional (e.g. anti-corrosion) and aesthetic effects.
However, for the quality stability of electroplated coating, additives are usually added into most electroplating solutions. For instances, brightener, stabilizer, softener, wetting agent, and leveling agent, etc. Most of these agents contain carbon elements. The electrochemical reactions involved in the electroplating process can ionize the carbon elements and cause the carbocations to deposit onto the workpiece, which degrades the workpiece's aesthetic appearance.
Moreover, if the electroplating solution is organic in essence, the carbon content in the electroplating solution is even higher. More carbocations are ionized in the electroplating solution and more carbons are electrodeposited on the workpiece. Therefore, the color tone appearance of the workpiece becomes carbon-black instead of the anticipated brightness of metal. Usually, the thus electroplated workpiece cannot fulfill the quality requirement on its appearance in the market.
Therefore it is desirous to develop an electroplating apparatus in terms of the possible problem and limitation faced by the conventional electroplating industry.

SUMMARY

The electroplating apparatus of this disclosure is to reduce the possible problems in aesthetic appearance caused by the deposition of carbocations onto the workpiece during electroplating.
According to one embodiment of the disclosure, an electroplating apparatus is disclosed to be adapted for the electroplating treatment on workpiece. The apparatus includes: an electroplating solution container, a target, an absorbent piece, and a power supply. All the electroplating solution, workpiece, absorbent piece, and target are placed inside the electroplating solution container with at least partial portions of each workpiece, absorbent piece and target submerged in the electroplating solution. The positive electrode of the power supply is electrically connected to the target while its negative electrode is electrically connected to the workpiece and absorbent piece simultaneously. When the power supply imposes a current through the circuit, the target releases metal ions into the electroplating solution and metal ions reduce and a metal coating is formed on the workpiece. In the meantime, carbocations in the electroplating solution are adsorbed on the absorbent piece.
In one embodiment, the material of the absorbent piece in the electroplating apparatus of this disclosure can be metals, ceramics, or fabrics.
In one embodiment, in the electroplating apparatus of this disclosure, the material of the target can be copper alloy or nickel alloy, and the material for the absorbent piece can be porous nickel.
In one embodiment, in the electroplating apparatus of this disclosure, the material of target can be gold or platinum, and the material for the absorbent piece can be non-woven fabric.
In one embodiment, in the electroplating apparatus of this disclosure, the range of the operating current density is between 0.001-0.005 A/cm².
In one embodiment, in the electroplating apparatus of this disclosure, the electroplating solution includes choline chloride, nitrogenous compound, metal chloride, bio-bacteria and inorganic acid agent.
In one embodiment, in the electroplating apparatus of this disclosure, the electroplating solution includes saccharin.
In one embodiment, in the electroplating apparatus of this disclosure, the nitrogenous compound in the electroplating solution is selected from ammonia, urea or uric acid.
In one embodiment, in the electroplating apparatus of this disclosure, the metal chloride in the electroplating solution is selected from nickel chloride, copper chloride, cobalt chloride, zinc chloride, gold chloride or silver chloride.
In one embodiment, in the electroplating apparatus of this disclosure, the inorganic acid agent in the electroplating solution is selected from nitric acid (HNO₃), boric acid (H₃BO₃), hydrobromic acid (HBr) or perchloric acid (HClO₄).
In one embodiment, in the electroplating apparatus of this disclosure, the electroplating solution further includes glycerol (C₃H₈O₃), which is added into the inorganic acid agent to form compound lipid.
In one embodiment, in the electroplating apparatus of this disclosure, the range of volume fraction of the inorganic acid agent to glycerol in the electroplating solution is between 4:1 and 3:1.
In one embodiment, in the electroplating apparatus of this disclosure, the bio-bacteria in the electroplating solution is Saccharomycetes, Lactobacillus casei strain shirota, photosynthetic bacteria, Lactobacillus, Bacillus and its combination, or fermented milk.
In one embodiment, in the electroplating apparatus of this disclosure, the electroplating solution further contains chitin ((C8H13O5N)n) additive which is mixed with the used inorganic acid agent first.
In one embodiment, in the electroplating apparatus of this disclosure, a magnetic stirrer is further displaced in the electroplating solution container to stir and mix the electroplating solution.
In contrast to the prior art, the coating electroplated on the workpiece from the electroplating apparatus of this disclosure not only can prevent the workpiece from possible corrosion, but also can retain its metallic quality and glossiness required by the market. The electrostatic function of the charged absorbent piece adsorbs the carbocations in the electroplating solution to its surface and spares most of the influence of carbocations on the workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

The features of the exemplary embodiments believed to be novel and the elements and/or the steps characteristic of the exemplary embodiments are set forth with particularity in the appended claims. The Figures are for illustration purposes only and are not drawn to scale. The exemplary embodiments, both as to organization and method of operation, may best be understood by reference to the detailed description which follows taken in conjunction with the accompanying drawings in which:

FIG. 1 depicts the schematic diagram of an exemplary electroplating apparatus of this disclosure;

FIG. 2A to FIG. 2F are the pictures of the workpieces and the absorbent pieces before and after the electroplating of different metals using an exemplary electroplating apparatus of this disclosure; and

FIG. 3A to FIG. 3E are the results of composition analyses on coatings of different metals electroplated using an exemplary electroplating apparatus of this disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to representative embodiments illustrated in accompanying drawings to further understand the purpose, characteristics and functions of this invention.
FIG. 1 depicts the schematic diagram of an exemplary electroplating apparatus used in this disclosure. The electroplating apparatus 100 applies to electroplating process with both electrodes on the workpiece 110. The electroplating apparatus 100 of this embodiment includes an electroplating container 120, an target 130, an absorbent piece 140 and a power supply 150. The electroplating solution 121 is contained in the electroplating container 120 of the electroplating apparatus 100. The workpiece 110 to be plated and the target 130 are all supported inside the electroplating container with at least partial submersion in the electroplating solution 121. The absorbent piece 140, which can be made of metal, ceramic or fabric, is also supported in the electroplating container 120 with at least partial submersion in the electroplating solution 121.
While connected electrically to the anode of an electrical power supply 150, the target 130 must consist of conductive material. The workpiece 110 and the absorbent piece 140 are electrically connected to the cathode of the power supply 150. In the electroplating process, the power supply 150 provides direct current to the target 130, the absorbent piece 140 and the workpiece 110. The reactions at the anode and cathode are oxidation M→Mⁿ⁺+ne⁻ and reduction Mⁿ⁺+ne⁻→M, respectively. More specifically, the target releases electrons ne⁻ and becomes metal ions Mⁿ⁺ which are dissolved into the electroplating solution 121. On the other hand, the metal ions Mⁿ⁺ in the electroplating solution 121 receive electrons ne⁻ from the cathode, reduce into metal atoms and deposit on the surface of the workpiece 110 to form a coating. In the meantime, because the power supply 150 also provides the current to the absorbent piece 140, an electrostatic attraction is developed therein. The attraction adsorbs the carbocations (for example, the carbocations contained in the additives to the electroplating solution 121) in the electroplating solution 121 and spares them from deposition on the surface of the workpiece 110.
The following embodiment presents the examples of the workpiece 110 and the absorbent piece 140 used in this disclosure. If the material of target 130 is copper alloy or nickel alloy, the absorbent piece 140 can be made of porous nickel. In the other case, if the material of target 130 is gold or platinum, the absorbent piece 140 can be made of non-woven fabric.
The purpose of choosing different combinations of the workpiece 110 and the absorbent piece 140 is to create a potential difference between the workpiece 110 and its neighboring absorbent piece 140. The metal ions in the electroplating solution 121 only are attracted to and reduced on the surface of the workpiece 110. The metal ions are not adsorbed on the absorbent piece 140. On the contrary, when the carbocations diffuse through the absorbent piece 140, they are captured by the electrostatic adsorption and can hardly reach the surface of the workpiece 110. Any person skilled in the related art can choose the workable material pairs for these workpiece 140 and absorbent piece 110 accordingly. The workpiece 110 and the absorbent piece 140 only have to be in certain potential difference. Their selections should not be limited by the material types of this disclosure.
It should be mentioned that the current density used in the described electroplating process is very low. It is usually in the range of 0.001-0.005 A/cm². The corresponding deposition rate of the coating is around 4 μm/hr. However, the working current density in different applications can be easily adjusted according to the required deposition rate by any persons skilled in this electroplating field. The disclosed current density should not limit the applicability of this disclosure.
Before the electroplating process, the workpiece 110 is usually ground by emery papers or rinsed by diluted hydrochloric acid to remove the oxidation stain on its surface. Subsequently, the workpiece 110 is submerged in sodium hydroxide solution to remove grease residues. Finally, the pretreatment to the workpiece 110 is completed with fully rinse of distilled water. After the electroplating is finished, the workpiece 110 is taken out from the electroplating container 120. Then, the residual electroplating solution on workpiece 110 is washed away with distilled water followed by acetone rinse to remove the distilled water. A metal workpiece deposited with a coating is thus obtained.
Mostly, the electroplating is conducted at room temperature. No heating to the electroplating solution 121 is required. Further, for usual practice a magnetic stirrer 160 is used to enhance the mixing in the electroplating solution 121. The rotating speed of the stirrer 160 can influence the internal stress of the coating plated on the workpiece 110. Moreover, the faster the stirrer 160 agitates the glossier appearance the plated coating becomes. In one embedment, the rotating speed may be from 300 rpm (revolution per minute) to 1,000 rpm.
Referring to FIG. 1 again, the electroplating solution 120 used in the electroplating apparatus 100 in this disclosure can be conventional inorganic solution. Additives such as brightener, stabilizing agent, softener, wetting agent and leveling agent can be employed as required. Or an organic, pollution-free electroplating solution as described in the following can be used. The pollution-free electroplating solution according to one embodiment of the disclosure includes choline chloride, nitrogenous compound, metal chloride, bio-bacteria and inorganic acid agent.
The nitrogenous compounds used in this embodiment can be selected from ammonia, urea or uric acid. For example, the choline chloride concentration is 560 g/L or 4M in molar concentration. The urea concentration is 480 g/L or 8M in molar concentration. The ratio between their molar concentrations equals 1:2. Nevertheless, the concentrations of choline chloride and urea employed in this embodiment can vary between 460 g/L to 660 g/L and 380 g/L to 580 g/L, respectively. In one embodiment, an ionic liquid having the mixing of 560 g/L choline chloride and 480 g/L urea may be selected.
The molar concentration of metal chloride in ionic liquid is controlled within 0.005M to 0.5M. More specifically, in this embodiment the metal chloride can be nickel chloride (NiCl₂), copper chloride (CuCl₂), cobalt chloride (CoCl₂), zinc chloride (ZnCl₂), gold chloride (AuCl₃) or silver chloride (AgCl). It should be noted that the purpose of adding metal chloride is simply to provide the source of metal ion for the reduction of coating on workpiece. Therefore, the only requirement is to add the chemical which can dissolve and provide the same metal ions as the target metal in the electroplating. The use of metal chloride as of this disclosure is not a limitation in application. Taking nickel chloride as an example, the concentration of adding NiCl₂—6H₂O in the ionic liquid is 120 g/L or 0.5M in molar concentration. The feasible range of adding nickel chloride in the ionic liquid in this invention is from 90 g/L to 150 g/L and the preferred concentration is 120 g/L.
If zinc chloride is used as the metal chloride mentioned in the ionic liquid, the concentration is 27 g/L or 0.2M in molar concentration, for example. For copper chloride, the concentration of copper(II) chloride dihydrate (CuCl₂—2H₂O) in ionic liquid is 1 g/L or 0.006M in molar concentration. For gold chloride, its concentration is 500 mg/300 mL or 0.005M in molar concentration.
The weight fraction of added bio bacteria in ionic liquid is between 7 wt % to 11 wt % while the molar concentration of the added inorganic agent is between 0.7M to 2M. The purpose of adding inorganic agent in the electroplating solution 121 of this disclosure is mainly to stabilize the pH value (hydrogen ion concentration index). After adding bio bacteria and inorganic agent, the electroplating solution 121 of this disclosure becomes weak acidic and its pH is around 4.
The bio bacteria 224 used in this embodiment can be Saccharomycetes, Lactobacillus casei strain shirota, photosynthetic bacteria, Lactobacillus, Bacillus and its combination. In addition, bio bacteria 224 can also be fermented milk, e.g. yogurt. The inorganic acid agent employed in this embodiment can be, but not limited to, weak acidic agent such as nitric acid (HNO₃), boric acid (H₃BO₃), hydrobromic acid (HBr) or perchloric acid (HClO₄). The concentration of the bio bacteria in this embodiment for instance is 20 mL/200 mL or 9 wt % in weight fraction. The concentration of boric acid used is 20 g/200 mL or 1.62M in molar concentration. Moreover, their concentration ranges of in this embodiment can be from 15 mL/200 mL to 25 mL/200 mL for the bio bacteria and 15 g/200 mL to 25 g/200 mL for the boric acid, respectively. In one embodiment, the concentrations are 20 mL/200 mL for bio bacteria and 20 g/200 mL for the boric acid, respectively for example. The mixing of bio bacteria and inorganic acid agent in the ionic liquid is performed by using magnetic stirrer 160 at room temperature.
If nitric acid is used as the inorganic acid agent, its concentration ranges from 15 g/200 mL to 25 g/200 mL or 1.2M to 1.98M in molar concentration. If hydrobromic acid is used instead, the range is from 15 g/200 mL to 25 g/200 mL or 0.9M to 1.54M in molar concentration. Or if perchloric acid is employed, the concentration range is from 15 g/200 mL to 25 g/20 mL or 0.7M to 1.24M in molar concentration.
In this embodiment, when the quality of the electroplating on the workpiece 110 degrades, further addition of inorganic acid agent in the electroplating solution 121 to dilute the concentration of metal ions can rejuvenate its function. Therefore, the electroplating solution 121 of this disclosure can overcome the problem associated with discarding old electroplating solution in the conventional practice.
Moreover, the electroplating electroplating solution 121 can be further modified by adding saccharin. The molar concentration of saccharin can be from 0.05M to 0.2M. The purpose of adding saccharin in this disclosed electroplating solution 121 is mainly to reduce the grain and consequently the internal stress of the electroplated coating on the workpiece 110. An improvement in the surface finish of the workpiece 110 can also be obtained.
For instance, the concentration of adding saccharin into the ionic liquid is 2 g/200 mL or 0.05M in molar concentration. Adding saccharin into the ionic liquid is performed at room temperature and under stirring of magnetic stirrer 160. The range of saccharin concentration in this embodiment is from 2 g/200 mL to 7 g/200 mL (0.2M) and the preferred one is 2 g/200 mL.
Beside bio bacteria and inorganic acid agent added, additional glycerol (C₃H₈O₃) can be added into the electroplating solution 121, which combine with inorganic acid agent and form compound lipid. The volume fraction of the inorganic acid and glycerol is between 4:1 and 3:1. It is noted that the glycerol is not directly involved in the electroplating reaction. Its function is to dilute the concentration of metal ions.
In one embodiment, chitin ((C₈H₁₃O₅N)_n) can be additionally added into the inorganic acid agent in the preparation of the electroplating solution 121 to improve the surface characteristics of the workpiece 110. In general, because the electroplating is conducted under anhydrous environment, no significant temperature rise occurs after certain duration of electroplating. Therefore, the degradation rate of the disclosed electroplating solution 121 in this invention can be alienated.
FIG. 2A to FIG. 2F present the pictures of the workpieces and the absorbent pieces before and after the electroplating of different metals using an exemplary electroplating apparatus of this disclosure. The metals shown in these figures from 2A to 2F are sequentially electroplated nickel, electroplated gold, electroplated copper, electroplated tin, electroplated platinum and electroplated cobalt. It is clearly seen in these figures that without the absorbent piece (porous nickel or non-woven fabric) the surfaces of the electroplated workpieces are in dark grey or red brown colors. No bright and glossy color of any metal appears. However, with the use of the absorbent piece in electroplating, each electroplated coating reveals bright and shiny surface as usually required for metallic coating in industry. The difference can also be noted for the absorbent piece before and after electroplating. The portion of the absorbent piece submerged in the electroplating solution during electroplating shows totally different color tone comparing with the un-submerged portion. The carbon-black color tone of the submerged portion denotes the adsorption of carbocations on the absorbent piece which reduces their deposition on the workpiece.
FIG. 3A to FIG. 3E show the results of composition analyses on coatings of different metals electroplated using an exemplary electroplating apparatus of this disclosure. FIG. 3A to 3E sequentially present the results of electroplated silver, electroplated nickel, electroplated gold, electroplated copper, and electroplated platinum. The microscopic examinations are to confirm the carbocation adsorption function of the absorbent piece. According to the weight fraction (norm. C [wt. %]) or atomic fraction (Atom. C [at. %]) data shown in FIG. 3A to 3E, the electroplated metal contents (Ag, Ni, Au, Cu, Pt) are more dominant than their carbon counterparts. The absorbent piece effectively adsorbs the carbocations in the electroplating solution and reduces their presence in the workpiece.
In summary, the electroplated workpiece produced from the electroplating apparatus disclosed from this disclosure not only can have a better coating to prevent it from corrosion, but also can show better surface appearance with metallic quality of glossiness. All these are obtained by reducing the deposition of carbocations in the electroplating solution to the workpiece with the use of the absorbent piece. The improvement in the appearance of the electroplated workpiece fits the usual requirement in industrial applications.
In addition, the electroplating solution disclosed in embodiment of this invention contains mostly non-toxic ingredients and inorganic acid agents which are weakly acidic. When applied in industrial electroplating product process, it presents no serious threat to working environment and ecological system, most importantly, good electroplating performance. In the previous embodiment, the bio-bacteria used can determine the electrical property of the electroplating solution. Thus, different species and amounts of bio bacteria can be employed to tune the electrical property of the electroplating solution. Moreover, the electrical properties of the electroplating solution of this disclosure can be rejuvenated by adding or adjusting the bio bacteria species or concentrations to obtain its recyclability. Green and environmental friendliness is conserved with this invention.
While the invention has been described with reference to the specific embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention as defined by the appended claims. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, method, or process to the objective, spirit and scope of the invention. All such modifications are intended to be within the scope of the claims appended hereto.

Claims

What is claimed is:

1. An electroplating apparatus, applicable to a workpiece to be electroplated, comprising:

an electroplating container, which contains an electroplating solution and the workpiece to be electroplated at least partially submerged in the electroplating solution;

a target, which is made of conductive material and is contained in the electroplating container with at least partial submersion in the electroplating solution;

an absorbent piece, which is contained in the electroplating container with at least partial submersion in the electroplating solution; and

a power supply, which is equipped with a positive electrode and a negative electrode, connected electrically to the target and the workpiece, respectively;

when the power supply imposes an operating current, the target dissolves metal ions into the electroplating solution, the metal ions reduce into metal atoms and a coating is formed on the surface of the workpiece to be electroplated, and the absorbent piece adsorbs the carbocations in the electroplating solution.

2. The electroplating apparatus of claim 1, wherein the absorbent piece is select from made of metal, ceramic or fabric.

3. The electroplating apparatus of claim 2, wherein the material of the target is selected from copper alloy or nickel alloy, and the absorbent piece comprises porous nickel.

4. The electroplating apparatus of claim 2, wherein the material of the target is selected from gold or platinum, and the absorbent piece comprises non-woven fabric.

5. The electroplating apparatus of claim 1, wherein the range of the operating current density is between 0.001-0.005 A/cm².

6. The electroplating apparatus of claim 1, wherein the electroplating solution comprises choline chloride, nitrogenous compound, metal chloride, bio bacteria and inorganic acid agent.

7. The electroplating apparatus of claim 6, wherein the electroplating solution further comprises saccharin.

8. The electroplating apparatus of claim 6, wherein the nitrogenous compound is selected from ammonia, urea or uric acid.

9. The electroplating apparatus of claim 6, wherein the metal chloride is selected from nickel chloride, copper chloride, cobalt chloride, zinc chloride, gold chloride or silver chloride.

10. The electroplating apparatus of claim 6, wherein the inorganic acid agent is selected from nitric acid, boric acid, hydrobromic acid or perchloric acid.

11. The electroplating apparatus of claim 6, wherein the electroplating solution further comprises glycerol (C3H8O3) which combines with the inorganic acid agent to form compound lipid.

12. The electroplating apparatus of claim 11, wherein the volume fraction between inorganic acid agent and the glycerol is within 4:1 to 3:1.

13. The electroplating apparatus of claim 6, wherein the bio bacteria is selected from Saccharomycetes, Lactobacillus casei strain shirota, photosynthetic bacteria, Lactobacillus, Bacillus and their combination, or fermented milk.

14. The electroplating apparatus of claim 6, wherein the electroplating solution further comprises chitin ((C8H13O5N)n) which is added into the inorganic acid agent.

15. The electroplating apparatus of claim 1 further comprising a magnetic stirrer, which is placed in the electroplating container and can rotate to mix the electroplating solution.