Method for producing plated article, plating device, and electroplating method

Abstract

This method for producing a plated object includes: generating cavitation bubbles in a plating solution stored in a plating tank; and plating an object in the plating solution under an influence of the cavitation bubbles. The growth rate of a plating film that grows on the surface of the object is greater than the depletion rate of the plating film associated with disappearance of the cavitation bubbles.

Description

Method for manufacturing plated products, plating apparatus, and electroplating method

[0001] This disclosure relates to a method for manufacturing plated products, a plating apparatus, and an electroplating method.

[0002] In recent years, various efforts have been made to improve the quality of plated films. For example, Patent Document 1 discloses a technique to improve the adhesion of the interface between the plated film and the substrate, by performing mechanical or magnetic stirring simultaneously with electroplating to improve the quality of the plated film. Patent Document 2 discloses a plated film with improved quality, disclosing that the elemental ratio changes with the thickness of the plated film (see Figure 4 in the same document) and that no clear interface is formed between the plated film and the substrate (see Figures 6 and 23 in the same document).

[0003] Patent Document 3 discloses a method for forming a film on an object to be plated in a processing tank, in which microbubbles are supplied to the processing tank and the processing solution is stirred while the film is formed. As shown in Figure 1 of Patent Document 3, the object to be plated is suspended from a hanger and a microbubble generator is immersed in the plating solution. Paragraph 0018 of Patent Document 3 states, "By supplying an excessive amount of nitrogen gas in this manner, a large amount of microbubbles are generated, and the processing solution in the processing tank 1 can be sufficiently stirred." Paragraph 0019 states, "A large amount of microbubbles 19 are continuously generated from the microbubble generator 13 and spread throughout the entire processing tank 1."

[0004] Patent Document 4 discloses that the plating solution is stirred using ultrasonic waves without generating cavitation. Patent Document 5 discloses that when pickling a metal product, high-frequency vibration is applied to the metal product by an electromagnet facing the metal product, and specifically discloses that "the frequency and amplitude of the high-frequency vibration are selected such that a cavitation phenomenon occurs in the reactive solution near the surface of the metal product" (see claim 2 of the same document). Paragraph 0011 of Patent Document 5 describes that the invention can also be used for surface treatments other than pickling, for example, plating of moving products, but as is clear from the description that "the wettability of the strip is improved", it is merely used as a pretreatment for plating. Incidentally, Patent Document 6 discloses a nanofluid flow system configured to generate cavitation in a nanofluid.

[0005] International Publication No. 2018 / 189916, International Publication No. 2018 / 190202, Japanese Patent No. 6029537, Japanese Unexamined Patent Publication No. Hei 6-256998, Japanese Patent No. 3209362, Japanese National Publication of International Patent Application No. 2019-503855

[0006] As disclosed in Patent Document 4, there is a demand for avoiding cavitation during electroplating. The inventor of the present application conceived the present invention contrary to this common general technical knowledge.

[0007] A method for producing a plated product according to one aspect of the present disclosure includes generating cavitation bubbles in a plating solution stored in a plating tank, and plating a plating target in the plating solution under the influence of the cavitation bubbles. A growth rate of a plating film growing on the surface of the plating target is larger than an erosion rate of the plating film accompanying the extinction of the cavitation bubbles. That is, the supply conditions of cavitation bubbles and the plating conditions are selected as such. In the case of electroplating, the plating conditions include energization conditions. The supply conditions of cavitation bubbles include the number and positions of cavitation bubble generation means.

[0008] In this manufacturing method, a plating film can be formed on the object to be plated, with its surface smoothed or flattened by the shock waves generated by the collapse of cavitation bubbles. In other words, cavitation bubbles can act to reduce the growth rate and surface roughness of the plating film growing on the surface of the object to be plated, thereby promoting the formation of a higher quality plating film more uniformly.

[0009] Cavitation is a physical phenomenon in which a group of tiny bubbles (called cavitation bubbles) are generated in a liquid due to pressure fluctuations, and then disappear. A shock wave is generated when the cavitation bubbles disappear. The adverse effects of this shock wave are widely known as the corrosion of pump impellers. Thus, cavitation is generally perceived as a "negative" physical phenomenon. Contrary to this perception, the inventors of this application have conceived the above-mentioned method for manufacturing plated products and have demonstrated its usefulness.

[0010] In detail, when cavitation bubbles disappear near an object during electroplating or electroless plating, the resulting shock waves erode (damage) the plating film growing on the object, inhibiting its growth. In worse cases, the surface of the object itself may erode. Therefore, it is usually impossible to perform "cavitation (or cavitation bubble generation)" and the "plating process" simultaneously. However, contrary to this conventional consideration, the inventors of this application have newly discovered that the following technical effects can be obtained by introducing "cavitation (or cavitation bubble generation)" under conditions that do not severely hinder the progress of the plating process (e.g., electroplating or electroless plating) (i.e., under conditions inferior to plating).

[0011] One technical effect is the smoothing or planarization of the surface of the plating film formed on the object being plated. The surface of the plating film is struck and smoothed or planarized by the shock waves formed when cavitation bubbles disappear (i.e., a burnishing effect is obtained). This increases the glossiness of the plating film and promotes an improvement in the commercial value of the plated object (the object after plating). It should be noted that the smoothing or planarization referred to here does not mean a perfectly smooth or flat surface, but rather a reduction in surface roughness (for example, compared to the case using pin media described later).

[0012] To elaborate, when polishing an object to be plated during electroplating using an abrasive material called pin media, even if the surface of the object can be polished by the pin media, there is a risk of uneven polishing (i.e., non-uniform polishing or burnishing) due to the physical size of the pin media, the frequency of collisions, etc. The same applies when the pin media is moved randomly in an alternating magnetic field. Cavitation bubbles are physically minute, and therefore promote a more dense and smooth surface of the plated film.

[0013] Another technical benefit may be the ability to standardize the thickness and / or quality of the plating film when the object to be plated has cavities, recesses, or concave surfaces. Cavitation bubbles are tiny bubbles with growing nuclei, such as nanobubbles, where each bubble has a size (maximum diameter) of less than 1 micrometer. Therefore, even if the object to be plated has cavities, recesses, or concave surfaces, cavitation bubbles can approach the interior of the cavity, the bottom of the recess, or the vicinity of the concave surface. When the cavitation bubbles disappear inside the cavity, at the bottom of the recess, or near the concave surface, the resulting shock waves can sufficiently reach the cavity wall, the bottom of the recess, or the concave surface. This promotes the formation of more uniform plating films on objects of various shapes. For example, it promotes the uniform formation of high-quality plating films with suppressed pinholes and cracks, regardless of the location of unevenness on the surface of the object to be plated.

[0014] To elaborate, when polishing an object to be plated during electroplating using an abrasive called pin media, the relative physical size of the pin media to the physical size of the cavities, recesses, or concave surfaces of the object to be plated may prevent the pin media from reaching the inside of cavities, the bottom of recesses, or concave surfaces of the object to be plated, resulting in a lack of polishing (or burnishing) effect. Cavitation bubbles are physically minute, and therefore promote the formation of a uniform plating film on objects of various shapes. If burrs are present inside the cavities of the object to be plated, a deburring effect can also be obtained (along with the formation of the plating film).

[0015] Other technical benefits, as demonstrated in the examples described later, include high adhesion of the plating film to the object to be plated (substrate) and thinning of the plating film.

[0016] The objects to be plated can vary in size from large to small. In some cases, the object to be plated is a metal product held stationary in a plating solution. In other cases, the object to be plated is a group of metal parts. In either case, the aforementioned technical effects can be obtained by employing the manufacturing method described above. However, it is also clear that the value of the aforementioned technical effects is relatively higher for smaller objects or objects with decorative features such as protrusions and indentations. In some cases, the group of metal parts may be slider bodies for slide fasteners, pull tabs to be attached to the slider bodies, or button parts.

[0017] The slider body for a slide fastener has a Y-shaped element passage for the left and right rows of fastener elements. After plating the slider body, the walls of its element passages are covered with a smooth outer plating film. More specifically, a plating film is formed on the inner wall surface of the element passages, with the surface smoothed or flattened by shock waves generated by the collapse of cavitation bubbles. In this case, the sliding of the fastener elements is smoothed, the sliding resistance of the slider is reduced, and the smooth opening and closing of the slide fastener is promoted. Also, if burrs have formed in the element passages of the slider body, they are removed by shock waves generated by the collapse of cavitation bubbles, further smoothing the sliding of the fastener elements. Pull tabs often have raised and recessed decorative parts, and this is also true for button parts. On recesses or concave surfaces, a plating film is formed, with the surface smoothed or flattened by shock waves generated by the collapse of cavitation bubbles. Thus, even if the pull tab or button part has a recess or concave surface, a plating film can be uniformly formed on the bottom or concave surface of the recess, thereby achieving an appearance quality that meets commercial needs.

[0018] Inducing cavitation bubbles in the plating solution stored in a plating tank can be carried out using various methods. Typically, cavitation bubbles are generated when the liquid flow discharged from a pump passes through a cavitation generator. The cavitation generator includes a restricted channel whose width or diameter is reduced to induce cavitation bubble generation. In the restricted channel, the velocity of the liquid flow increases, and (according to Bernoulli's principle) the static pressure of the liquid flow decreases. The saturated water vapor pressure decreases, and therefore, bubble nuclei are formed, which grow into cavitation bubbles. Although the bubble nuclei and cavitation bubbles can only survive for a certain period of time until the static pressure of the liquid flow increases, they are carried by the liquid flow and diffuse in the plating solution. It has been confirmed through simulations that cavitation bubbles are generated in the downstream area of ​​the restricted channel. It is also possible to generate cavitation bubbles by other methods or means, such as ultrasound (e.g., ultrasonic homogenizer) or high-speed rotation of an impeller.

[0019] The pump described above is preferably a circulating pump that draws the plating solution from the plating tank and returns it to the plating tank via a cavitation generator. This avoids increasing the amount of solution required for plating. An electrolyte solution without a brightener can be used as the plating solution, reducing the processing burden or environmental impact of the plating solution. The omission of the brightener became possible due to the burnishing effect described above. In some cases, the burnishing effect described above also makes it possible to omit the polishing process after plating.

[0020] Plating an object in a plating solution under the influence of cavitation bubbles can be carried out by electroplating, electroless plating, or other types of plating. Electroplating involves setting the object to be plated to a cathode potential and setting the anode electrode in the plating solution (the source of the metal elements for the plating film) to an anode potential. Electroless plating forms a plating film on the object to be plated by reducing metal ions in the solution through a chemical reaction.

[0021] For clarification, plating an object in a plating solution under the influence of cavitation bubbles may mean that the object is plated while cavitation bubbles are present around it and while the cavitation bubbles are disappearing around it. Additionally or alternatively, plating an object in a plating solution under the influence of cavitation bubbles may mean that the object is plated while the cavitation bubbles are disappearing continuously or in a chain reaction around it. Cavitation bubbles can no longer exist as bubbles when the pressure in the plating solution recovers, and shock waves are generated when the cavitation bubbles disappear, impacting the object being plated.

[0022] Plating an object in a plating solution under the influence of cavitation bubbles may mean that the object is plated at a slower rate (or at a slower rate than plating in the absence of cavitation bubbles) due to the shock waves generated when the cavitation bubbles disappear. As mentioned above, cavitation bubbles inhibit the growth of the plating film. Therefore, plating in the presence or supply of cavitation bubbles is slower than plating in the absence of cavitation bubbles. In other words, according to the manufacturing method of this disclosure, the time required to obtain a plating film of the target thickness will be longer, which will lead to an increase in manufacturing costs. However, it is clear from the above explanation that there are benefits that outweigh these disadvantages. Specifically, thinning of the plating film can be promoted for one or more reasons, including improved adhesion between the plating film and the underlying layer, improved smoothness (leveling) of the plating film, and / or prevention of pinhole occurrence due to densification of the plating film (and consequently improved corrosion resistance of the plating film). In other words, according to the manufacturing method of this disclosure, sufficient adhesion, sufficient smoothness, and / or sufficient corrosion resistance can be obtained even with a thin plating film (for example, 100 nm or less, or 80 nm or less, or 60 nm or less, or 55 nm or less, or 50 nm or less).

[0023] Smoothness can be expressed by one or more surface roughness measurements, such as arithmetic mean roughness (Sa) and / or maximum height roughness (Sz). For this measurement, a Hitachi High-Technologies Corporation, model AFM5500M, product name "Medium Probe Microscope System" can be used. Preferably, in a 1 μm × 1 μm observation field, Sa is less than 1.4 nm, less than 1.3 nm, less than 1.2 nm, and less than 1.1 nm. Additionally or alternatively, in a 1 μm × 1 μm observation field, Sz is less than 18 nm, less than 16 nm, less than 14 nm, and less than 12 nm.

[0024] When the object to be plated includes a group of metal parts, it is preferable to agitate the group of metal parts in the plating solution. This promotes the flow of the metal parts in the plating solution, thereby facilitating the formation of a more uniform plating film. Agitation can be performed, for example, by (i) rotating an agitator blade, (ii) rotating a magnetic rotating part, (iii) generating ultrasonic waves, and (iv) generating microbubbles. The group of metal parts may be, for example, a group of slider bodies for slide fasteners, a group of pull tabs, a group of button parts, or a mixture thereof.

[0025] (i) With regard to rotating the impeller, the metal parts will sink to the bottom of the plating tank due to gravity. Therefore, it is preferable to install the impeller at the bottom of the plating tank. However, it is not limited to this, and the impeller can also be installed near the surface or at an intermediate depth of the plating solution stored in the plating tank. The rotation speed of the impeller should be such that the rotation of the impeller itself does not cause cavitation, for example, within the range of rotation speeds where the fluid static pressure ≥ the fluid vapor pressure.

[0026] (ii) Regarding the rotation of the magnetic rotating part, the magnetic rotating part has one or more magnets, such as neodymium magnets or electromagnets, around its axis of rotation. As the magnetic rotating part rotates (rotates) around its axis of rotation, the magnets revolve around the axis of rotation, and the metal parts are carried along by the magnets. If the magnetic rotating part has magnets with the north pole facing upward and magnets with the south pole facing upward alternately in the circumferential direction, an alternating magnetic field is generated, causing the metal parts to flow randomly and promoting the formation of a more uniform plating film. Furthermore, when employing the rotation of the magnetic rotating part, magnetic stirring materials such as pin media can also be used for the purpose of stirring the metal parts.

[0027] (iii) Regarding the generation of ultrasonic waves, the use of an ultrasonic homogenizer can be cited as an example. Furthermore, an ultrasonic homogenizer can be used not only for stirring metal parts but also for generating cavitation bubbles.

[0028] (iv) Regarding the generation of microbubbles, an example can be created by generating a multiphase flow of cavitation bubbles and microbubbles. A multiphase flow of cavitation bubbles and microbubbles can be generated by injecting gas (e.g., air) into the liquid flow that flows into or is discharged from the cavitation generator. Microbubbles generated by the injection of gas into the liquid flow are supplied to the downstream area of ​​the cavitation generator. In the multiphase flow obtained by injecting gas into the liquid flow that flows through the restricted channel of the cavitation generator, the shock waves generated when cavitation bubbles collapse cause microbubbles in the vicinity of the cavitation bubbles to collapse, thereby obtaining a stronger burnishing effect on the surface of the object to be plated. If the burnishing effect of cavitation bubbles alone is insufficient, a more effective burnishing effect can be obtained by creating a multiphase flow of cavitation bubbles and microbubbles.

[0029] A group of metal parts may include two or more metal parts that flow randomly in the plating solution in response to the aforementioned agitation. When at least some of the cavitation bubbles are supplied between two or more metal parts (located in close proximity to each other) and disappear, the resulting shock waves propagate toward the individual metal parts of the two or more metal parts. As a result, the vanishing effect is obtained as described above. It is generally believed that the direction of the shock wave propagation is omnidirectional.

[0030] In some embodiments, the plating (preferably electroplating) of the object to be plated is started in the plating solution before cavitation bubbles are generated. This promotes the stable initial formation of the plating film.

[0031] Further details regarding the manufacturing process described above will be discussed later.

[0032] An electroplating method according to another aspect of the present disclosure includes growing a plating film on an object to be plated under the influence of cavitation bubbles. Optionally, the method includes smoothing or planarizing the surface of the plating film by eliminating the cavitation bubbles. Optionally, the cavitation bubbles are generated when a liquid stream discharged from a pump passes through a cavitation generator, which includes a restricted channel whose channel width or diameter is reduced to generate cavitation bubbles. Optionally, multiple cavitation generators are used. The advantages of the method described herein are similarly understandable from the above description and will not be repeated.

[0033] A further different embodiment of the present disclosure includes a plating tank for storing a plating solution, a circulation pump that takes the plating solution from the plating tank and returns it to the plating tank, and a cavitation generator provided in the flow path between the discharge port of the circulation pump and the plating tank, through which the liquid flow of the plating solution discharged from the circulation pump passes. The cavitation generator includes a restricted flow path with reduced flow path width or diameter, and is configured to generate cavitation bubbles in the plating solution stored in the plating tank and in the downstream area of ​​the restricted flow path. Such a plating apparatus is optimal for carrying out the above-described manufacturing method.

[0034] In some embodiments, the plating apparatus further includes a power supply that sets the plating tank to cathode potential and sets the anode electrode, which is immersed in the plating solution of the plating tank, to anode potential.

[0035] In some embodiments, the cavitation generator includes a main channel through which a flow of plating solution discharged from a circulation pump passes, a main channel including a restricting channel, a gas injection channel for injecting gas into the liquid flow through the restricting channel, and an on / off valve for adjusting the degree of opening and closing of the gas injection channel.

[0036] In some embodiments, the plating apparatus further includes an additional cavitation generator, which is located in another flow path between the discharge port of a circulation pump and the plating tank, or in another flow path between the discharge port of another circulation pump and the plating tank.

[0037] In some embodiments, the plating apparatus further includes one or more stirring devices, the one or more stirring devices including at least one of (i) a stirring blade, (ii) a magnetic rotating unit, (iii) an ultrasonic generating unit, or (iv) a microbubble generating unit.

[0038] Details regarding the plating equipment will be described later.

[0039] According to one aspect of this disclosure, it is possible to form a high-quality plating film more uniformly.

[0040] This is a schematic diagram of an electroplating apparatus according to one aspect of the present disclosure. This is a conceptual diagram for explaining cavitation. This is a schematic cross-sectional diagram of a cavitation generator. This is a schematic cross-sectional diagram of a cavitation generator of another example. This is a schematic diagram of an electroplating apparatus equipped with two or more cavitation generators. This is a schematic top view showing the arrangement of cavitation generators. This is a schematic diagram of an electroplating apparatus equipped with a stirring blade. This is a schematic diagram of an electroplating apparatus equipped with a magnetic stirring device. This is a schematic diagram of an electroplating apparatus that serves as the premise for the simulation. This is the result of a steady-state analysis of a simulation of pressure distribution using a gas-liquid multiphase flow as the analytical model. This is the result of a steady-state analysis of a simulation of cavitation distribution using a gas-liquid multiphase flow as the analytical model. This is a perspective view showing a slider for a slide fastener as an example of an object to be plated. This is a perspective view showing the pull tab of a slider for a slide fastener as another example of an object to be plated. This is a perspective view showing a cap for a button as yet another example of an object to be plated. This is a perspective view showing the button body as yet another example of an object to be plated. This is a schematic cross-sectional diagram of an object to be plated in which a plating film is formed on both the outer and inner surfaces. This is a graph showing the change in elemental density in the thickness direction of the plating film (using a JAMP9500F Auger electron spectrometer manufactured by JEOL Ltd). This is a TEM image showing a cross-section of the plated object (the object to be plated) according to Example 1 (observation magnification 200,000x, observation field 0.64 μm × 0.43 μm). This image was acquired using a transmission electron microscope (model number: TalosF200X) manufactured by Japan FEI Co., Ltd. This is a TEM image showing a cross-section of the plated object according to the comparative example, with an observation magnification of 50,000x. This image was acquired using a transmission electron microscope (model number: TalosF200X) manufactured by Japan FEI Co., Ltd. This is a SEM image showing the surface of the plated object according to Example 1, with an observation magnification of 50,000x. This image was acquired using a scanning electron microscope (model number: JSM-IT800SHL) manufactured by JEOL Ltd. This is an SEM image showing the surface of the plated object according to the comparative example, with an observation magnification of 50,000x. These images were acquired using a scanning electron microscope (model number: S-4800) manufactured by Hitachi High-Technologies Corporation. The photographs show differences in the surface gloss of plated objects.This is a time chart for one example of electroplating and cavitation treatment. This is a time chart for another example of electroplating and cavitation treatment. This graph shows the change in arithmetic mean roughness (Ra) when the cavitation treatment time is changed, with respect to the time chart shown in Figure 23. This is an SEM image showing the surface condition of the plated film of sample No. 1 shown in Figure 25. This is an SEM image showing the surface condition of the plated film of sample No. 2 shown in Figure 25. This is an SEM image showing the surface condition of the plated film of sample No. 3 shown in Figure 25.

[0041] The following describes various embodiments and features with reference to the drawings. Those skilled in the art will understand that each embodiment and / or feature can be combined without needing excessive explanation, and that the synergistic effects of such combinations can be understood. Duplication of explanation between embodiments will be omitted in principle. The reference drawings are primarily for describing the invention and have been simplified for ease of drawing.

[0042] As shown in Figure 1, the plating apparatus 1 includes a plating tank 2 for storing a plating solution, a circulation pump 3 that takes the plating solution from the plating tank 2 and returns it to the plating tank 2, a cavitation generator 4 provided in the flow path F1 between the discharge port of the circulation pump 3 and the plating tank 2, through which the liquid flow of the plating solution discharged from the circulation pump 3 passes, and a power supply 5.

[0043] The plating tank 2 is a cylindrical tank made of insulating material. The circulation pump 3 takes in the plating solution from the intake section 31 and discharges the plating solution. The cavitation generator 4 is connected between the pump 3 and the plating tank 2, and the liquid flow discharged from the pump 3 flows through it, thereby generating cavitation bubbles in the plating solution. The cavitation generator 4 is installed to the side of the plating tank 2, but it can also be installed in another location, for example, above or below the plating tank 2.

[0044] The cathode of a power source 5 is connected to a plating object P, and the plating object P is set to a cathode potential. The anode of the power source 5 is connected to an anode electrode 6 (for example, rod-shaped or massive tin (Sn), etc.), and the anode electrode 6 is set to an anode potential. When the power source 5 is turned on, metal ions (for example, Sn ions) eluted from the anode electrode 6 migrate toward the plating object P, receive electrons on the surface of the plating object P, and precipitate as metal. A plating film is formed through continuous metal precipitation. Note that the anode electrode 6 is placed in a mesh basket and held in the plating solution, but the present invention is not limited thereto, and a ring-shaped anode electrode can also be adopted. The plating object P is typically a slide fastener part (slider body, pull tab, metal fastener element), a semi-finished product of these parts, or a clothing accessory such as a button. However, the plating object P is not limited to these, and may be any circuit element such as a semiconductor substrate; a circuit board such as a printed wiring board; or a capacitor chip. Whether or not to plate a group of plating objects P flowing through stirring is merely an option. Further, the anode electrode 6 may be an insoluble electrode.

[0045] In the present embodiment, an object to be plated is plated in a plating solution under the influence of cavitation bubbles. In Fig. 1, part of the cavitation bubbles are schematically depicted as circles in the plating solution. Furthermore, a supply region (existing range) R of cavitation bubbles is schematically depicted by a dotted line. Some cavitation bubbles disappear near the surface of the plating object P during electroplating and generate shock waves. The action of these shock waves improves the quality of the plating film (for example, adhesion to the plating object P and smoothness of the surface of the plating film). It also enables the formation of thinner plating films.

[0046] The principle and structural example of the cavitation generator 4 will be described with reference to FIGS. 2 to 4. As shown in FIG. 2, a liquid flow flows into the cavitation generator 4 at a predetermined velocity from a discharge port of a pump 3. The cavitation generator 4 comprises: an introduction flow path Z1 whose flow path width or diameter gradually decreases along the direction of the liquid flow; a restriction flow path Z2 whose flow path width or diameter is reduced to generate cavitation bubbles (in short, the restriction flow path Z2 has a constant minimum flow path width or diameter along the direction of the liquid flow); and optionally a discharge flow path Z3 whose flow path width or diameter gradually increases along the direction of the liquid flow. The cavitation generator 4 (and the restriction flow path Z2) is configured such that cavitation bubbles are generated in the plating solution stored in a plating tank and in a downstream area of the restriction flow path.

[0047] The liquid flow discharged from the pump 3 increases in velocity as it progresses through the introduction flow path Z1, and flows faster in the restriction flow path Z2. In the restriction flow path Z2, the static pressure of the liquid flow decreases, bubble nuclei are generated, and grow into cavitation bubbles in a downstream area of the restriction flow path Z2 (for example, in the discharge flow path Z3, and the plating solution in the plating tank 2). Cavitation bubbles cannot persist for a long time, and naturally disappear as the static pressure in the liquid recovers, generating shock waves.

[0048] As shown in FIG. 3, similar to FIG. 2, the cavitation generator 4 can have the introduction flow path Z1, the restriction flow path Z2, and the discharge flow path Z3 as a main flow path through which the flow of the plating solution discharged from a circulation pump passes. Alternatively, as shown in FIG. 4(a), the cavitation generator 4 has the introduction flow path Z1 and the restriction flow path Z2 as the main flow path through which the flow of the plating solution discharged from the circulation pump passes, but does not have the discharge flow path Z3. The role of the discharge flow path Z3 for generating cavitation bubbles (increasing static pressure) is assumed by the plating tank 2 or a pipe connecting the cavitation generator 4 and the plating tank 2. As shown in FIG. 4(b), the discharge flow path Z3 may have a constant flow path diameter.

[0049] As can be seen from Figures 4(a) and (b), the cavitation generator 4 may have a gas injection passage Z6 for injecting gas (typically air) into the restricting passage Z2, and an on-off valve 46 for adjusting the degree of opening and closing of the gas injection passage Z6. When the on-off valve 46 is closed, the liquid flow in Z3 becomes negative pressure and cavitation occurs. In contrast, by slightly opening the on-off valve 46, microbubbles (bubbles larger than 1 μm) are generated in the cavitation generator 4 or downstream of the restricting passage Z2, that is, a multiphase flow containing cavitation bubbles and microbubbles can be supplied to the plating solution in the plating tank 2. The microbubbles promote agitation of the metal parts, and the burnishing effect due to the disappearance of cavitation bubbles is also promoted, allowing a stronger impact force to be applied more evenly to the metal parts. However, if the opening of the on-off valve 46 is increased too much, almost no cavitation bubbles will be generated, and only micro-sized or millimeter-sized bubbles will be generated. The flow rate (L / min) of the liquid flow passing through the cavitation generator 4 is, for example, 30 L / min. The flow rate (L / min) of the gas injected into the liquid flow in the cavitation generator 4 is, for example, 0.1 to 2.0 L / min. When the former is A and the latter is B, (A / B) is 5 or more, and this provides an optimal mixed flow.

[0050] The liquid flow discharged from pump 3 flows into the plating solution in plating tank 2 via cavitation generator 4. This liquid flow has a flow velocity corresponding to the discharge performance of the (adjustable) pump 3, and therefore, cavitation bubbles flow through the plating solution at a certain speed. Depending on the type, structure, and size of the object to be plated P, it is possible to uniformly supply cavitation bubbles to the object to be plated P solely by the diffusion of cavitation bubbles based on the flow of the liquid. However, cavitation bubbles inherently disappear in a short time and do not persist permanently in the plating solution. Furthermore, if the diameter or width of the plating tank 2 is large, the supply area for cavitation bubbles may be insufficient. Moreover, if the object to be plated P is a group of metal parts, there is a risk that some of the metal parts may escape from the supply area for cavitation bubbles.

[0051] In the embodiment shown in Figure 5, the object to be plated P is a group of metal parts, and the plating apparatus 1 further includes an additional cavitation generator 4', which facilitates the sufficient supply of cavitation bubbles to each individual metal part. The additional cavitation generator 4' is provided in another flow path F2 between the discharge port of the circulation pump 3 and the plating tank 2. The cavitation generator 4' has the same configuration as the cavitation generator 4, and a redundant explanation is omitted. As shown by the dotted line in Figure 5, the cavitation generator 4' can also be provided in another flow path F3 between the discharge port of another circulation pump 3' and the plating tank 2.

[0052] In the embodiment shown in Figure 5, the cathode of the power supply 5 is connected to the plating tank 2, and the plating tank 2 is set to the cathode potential. The anode of the power supply 5 is connected to an anode electrode 6 (for example, a rod-shaped or lump-shaped tin (Sn), etc.), and the anode electrode 6 is set to the anode potential. When the power supply 5 is turned on, the plating tank 2 is set to the cathode potential, and the object to be plated P in contact with the plating tank 2 is set to the cathode potential. Among the objects to be plated P that are not in direct contact with the plating tank 2, there are some that are electrically connected to the plating tank 2 (cascadingly) via one or more other objects to be plated P. Even if the object to be plated P is electrically insulated from the plating tank 2 by the flow of the object to be plated P, as long as the cathode potential is maintained, the growth of the plating film there is possible. The characteristics of electrical connection described in this paragraph are also applicable to the apparatus shown in Figures 7 and 8, which will be described later.

[0053] In the embodiment shown in Figure 6, a plurality of cavitation generators 4 (four in the illustrated example) are used, and these are arranged so that the plating solution circulates in the circumferential direction of the cylindrical plating tank 2. The plating solution circulates counterclockwise. Circulating the plating solution clockwise or counterclockwise is merely one example. To achieve a stirring effect, the first subset and the second subset of cavitation generators 4 can be switched on complementaryly. For example, suppose a first pump supplies liquid flow to the two cavitation generators 4 of the first subset, and a second pump supplies liquid flow to the two cavitation generators 4 of the second subset. By complementary on / off control of the first and second pumps, turbulence is generated in the plating solution, and different stirring effects can be obtained. Of course, such control is not necessarily required, and therefore, whether to use a common pump 3 for the plurality of cavitation generators 4 or to provide individual pumps 3 can be appropriately determined by those skilled in the art depending on the need. Needless to say, the piping configuration connecting the common or individual pumps 3 to each cavitation generator 4 is a matter that a person skilled in the art can appropriately determine.

[0054] If the object to be plated P is a group of metal parts, the plating apparatus 1 may further have one or more stirring devices. The one or more stirring devices may be at least one of (i) a stirring blade, (ii) a magnetic rotating unit, (iii) an ultrasonic generating unit, or (iv) a microbubble generating unit.

[0055] A group of metal parts may include two or more metal parts that flow randomly in the plating solution in response to agitation. The relative positions and distances of the two or more metal parts change randomly moment by moment along the time axis due to the agitation. Typically, a large number of metal parts are introduced into the plating solution stored in the plating tank 2, and therefore, there can always be one or more other metal parts around a given metal part. When cavitation bubbles are supplied into the plating solution, at least some of the cavitation bubbles will naturally be supplied between the two or more metal parts. Subsequently, when at least some of these cavitation bubbles disappear at a position between these two or more metal parts, the resulting shock wave propagates toward the individual metal parts of the two or more metal parts. As a result, the vanishing effect is obtained as described above. Note that the individual metal parts may change their own flow direction and / or orientation due to the shock wave. The distance between the two or more metal parts may be 3 cm or less, or 2 cm or less, or 1 cm or less at any given moment.

[0056] In the embodiment shown in Figure 7 (the pump intake is not shown), the plating apparatus 1 has an agitator 9 having an agitator blade 91. The agitator blade 91 is provided on the bottom side of the plating tank 2. Although not shown, ribs are provided radially on the upper surface of the agitator blade 91 with respect to the rotation axis of the agitator blade 91. The metal parts are agitated by the rotation of the agitator blade 91 around its rotation axis AX. A polishing effect can also be obtained due to collisions between the metal parts. In addition, cavitation bubbles are diffused simultaneously with the agitation of the metal parts. Therefore, even if the metal parts have cavities, such as the slider body, it is possible to effectively supply cavitation bubbles to the inner surface of the cavities. The drive mechanism for the agitator blade 91 is arbitrary, but as shown in the illustrated example, it can have a motor M and a belt B that mechanically connects the output shaft of the motor M and the rotation axis of the agitator blade 91.

[0057] In the embodiment shown in Figure 7, the cathode of the power supply 5 is connected to an annular cathode electrode 7 provided at the bottom of the plating tank 2, and a metal part in contact with it is set to the cathode potential. The anode of the power supply 5 is connected to an annular anode electrode 6, and the anode electrode 6 is set to the anode potential. When the power supply 5 is turned on, the metal part is set to the cathode potential via the cathode electrode 7. Among the objects to be plated P that are not in direct contact with the cathode electrode 7, there are some that are electrically connected to the cathode electrode 7 (in a cascaded manner) via one or more other objects to be plated P. Even if the objects to be plated P are electrically insulated from the cathode electrode 7 by the flow of the objects to be plated P, as long as the cathode potential is maintained, the plating film can grow there.

[0058] In the embodiment shown in Figure 8, the plating apparatus 1 has an agitator 9 having a magnetic rotating section 92. The magnetic rotating section 92 is provided directly below the bottom plate of the plating tank 2. The magnetic rotating section 92 has a rotating plate 92a and two or more (for example, four) magnets 92b, 92c. The magnets 92b are magnets with their north poles facing upward. The magnets 92c are magnets with their south poles facing upward, and these are arranged alternately in the circumferential direction (in short, an annular array of NSNS is formed). When the magnetic rotating section 92 rotates, an alternating magnetic field is generated directly above it. If the object to be plated P is a metal part, the metal part will flow randomly in response to the alternating magnetic field. A polishing effect due to collisions between the metal parts may also be obtained. In addition to metal parts, magnetic agitation media (for example, pins with non-sharp ends) can also be placed in the plating tank 2. The drive mechanism for the magnetic rotating part 92 is arbitrary, but as shown in the illustrated example, it can have a motor M, and the magnetic rotating part 92 is fixed to the output shaft of the motor M in a way that prevents it from rotating.

[0059] Further explanation of other stirring devices is omitted, but they can be appropriately implemented by those skilled in the art in light of the above description. For the sake of clarity, when using an ultrasonic homogenizer, it can be used not only for stirring metal parts but also for generating cavitation bubbles. Microbubbles can be supplied as a multiphase flow of cavitation bubbles and microbubbles. A multiphase flow of cavitation bubbles and microbubbles can be generated by injecting gas (e.g., air) into the liquid flowing into or discharged from the cavitation generator. In addition to cavitation, the microbubbles generated by gas injection are added, enhancing the vanishing effect of cavitation and effectively stirring the metal parts.

[0060] Referring to Figures 9 to 11, the results of a steady-state simulation using a gas-liquid multiphase flow as the analytical model will be explained for reference. As shown in Figure 9, the cavitation generator 4 has an introduction channel Z1, a restricting channel Z2, and a gas injection channel Z6. The flow rate of the liquid flowing through the main channel of the cavitation generator 4 is 30 L / min, and the flow rate of air injected through the gas injection channel Z6 is 2 L / min. The object to be plated P is an elongated rod-shaped member, and a part of it is included in the cavitation bubble supply area (see dotted line in Figure 9). The gas injection channel Z6 functions as a bubble generator that generates microbubbles.

[0061] As can be seen from Figures 10 and 11, cavitation occurs in the plating solution downstream of the cavitation generator 4. The cavitation bubble supply area (existence range) is sufficiently far from the restricting channel Z2. Specifically, the cavitation bubble supply area is located at a distance L5 that is longer than the length L2 of the restricting channel Z2. This makes it easy to set the cavitation bubble supply area within the plating solution of the plating tank 2. The distance L5 can be in the range of 3 to 8 times the length L2. It is understood that the distance L5 is a parameter that depends on the discharge rate of the pump 3, the minimum channel width or diameter of the restricting channel.

[0062] Figures 12 to 15 show examples of objects P to be plated. Figure 12 shows the slider body, in which a Y-shaped element passage 101 is formed by an upper wing plate 201, a lower wing plate 202, and connecting pillars (not shown). Access to the element passage 101 is possible through the front openings on the left and right of the connecting pillars, a single rear opening at the rear of the connecting pillars, and lateral slits through which fastener tape is inserted. However, the slider body is a small part, and the vertical distance between the upper wing plate 201 and the lower wing plate 202 is narrow. Therefore, polishing pins cannot enter, and it may not be possible to form a good plating film on the inner surface defining the element passage of the slider body, nor can deburring be performed. By utilizing cavitation bubbles, these problems can be solved or reduced to a certain extent.

[0063] Figure 13 shows an example of a non-limiting pull handle. The gripping portion of the pull handle has a frame portion 102, a recess 103, and a protrusion 104, with a narrow concave surface 105 formed between the frame portion 102 and the protrusion 104. Even pull handles of this shape can be uniformly plated by utilizing cavitation bubbles. Figures 14 and 15 show a button part as the object to be plated P, and even such a part can be uniformly plated by utilizing cavitation bubbles.

[0064] Figure 16 is a schematic diagram showing a state in which plating films 302 and 303 are formed on both sides (e.g., the upper and lower surfaces) of a plate portion 301 (e.g., an upper or lower wing plate) of the object to be plated P, which is part of the object to be plated P. In Figure 16, the boundary between the plate portion 301 and the plating films 302 and 303 is clearly shown by solid lines, but as will be described later, the interface between the two cannot be clearly observed in the TEM image, and therefore, the high adhesion of the plating film to the object to be plated P can be confirmed. As can be seen from the explanation below, the above manufacturing method facilitates the formation of a thin plating film with sufficient adhesion to the object to be plated P and sufficient surface smoothness or flatness, and promotes the production of highly glossy plated products at low cost, not only improving durability or wear resistance.

[0065] Example 1 A slider with a handle made of CuZn alloy (brass) was electroplated at room temperature using the electroplating apparatus shown in Figure 7 (however, the power connection was as shown in Figure 5). A tin ingot (Sn) was used as the anode electrode. A near-neutral electrolyte (pH = 5) without a brightener was used as the plating solution. The volume of the plating tank was 40 L, and 30 L of plating solution was stored. The total weight of the sliders with handles placed in the plating solution was 20 kg, and the weight of each slider with a handle was 1.8 g. Pump 3 was set to a discharge rate of 30 L / min. The rotation speed of motor M was set to 120 rpm. A current of 10 A was applied.

[0066] Figure 17 is a graph showing the change in elemental density in the thickness direction of the plating film of the plated object (plated object P) obtained in Example 1. The plating film is formed to be extremely thin, at 40 nm. The constituent elements Cu and Zn of the object P slowly decrease toward the surface of the plating film, while complementary to this, the metal (Sn) originating from the anode electrode slowly increases toward the surface of the plating film. Thus, the plating film is a gradient plating film in which the density of metal elements originating from the metal elements of the object gradually decreases toward the surface, and the density of metal elements originating from the anode electrode gradually increases toward the surface. This characteristic is understood to be equivalent to that disclosed in Patent Documents 1 and 2. Therefore, it is inferred that the same level of adhesion between the object and the plating film as disclosed in Patent Documents 1 and 2 is ensured.

[0067] Figure 18 is a TEM image of the plated object obtained in Example 1. Although it is 10 nm thicker than the one shown in Figure 17, the plating film is extremely thin at 50 nm. As can be seen from Figure 18, no clear interface is formed between the plating film and the base material (object to be plated).

[0068] Figure 19 shows a TEM image of a plated product obtained by electroplating without supplying cavitation bubbles in a comparative example. The crystal grains of the plated film were coarse, pinholes were formed, and corrosion resistance in the salt spray test could not be maintained unless the plated film was formed to a thickness of 800 nm.

[0069] Figure 20 is an SEM image showing the surface of a plated object according to Example 1. From Figure 20, the largest crystal grain or precipitate size observed on the surface is approximately the same size as a circle with an inscribed circle diameter of 100 nm (0.1 μm). Figure 21 is an SEM image showing the surface of a plated object according to Patent Documents 1 and 2. Figure 21 is a surface observation image of a plated object plated without using cavitation bubbles, and the largest crystal grain or precipitate size is approximately the same size as a circle with an inscribed circle diameter of 0.25 μm. Furthermore, compared with the SEM surface observation image of Figure 20, it is clear that there is a large variation in crystal grain or precipitate size. Compared with the plated object in Figure 21, the plated object in Figure 20 shows a larger burnishing effect (compression adhesion effect) due to cavitation bubbles, and it is clearly observed that the crystal grains or precipitates are denser and the variation in crystal grain size or precipitate size is smaller. As is clear from the comparison of Figures 20 and 21, in the embodiment, the surface of the plated object has fine particulate protrusions uniformly and densely formed, resulting in a higher degree of smoothness or flatness. As shown in Figure 22, the plated object according to Embodiment 1 (i.e., the slider with a pull handle on the right) has a higher gloss than the plated object plated by conventional "barrel electroplating" (i.e., the slider with a pull handle on the left).

[0070] Figure 23 is a time chart of an example relating to electroplating and cavitation treatment in a configuration using the electroplating apparatus 1 shown in Figure 1. As shown in Figure 23, electroplating is started at time t1. For example, by turning on a switch (not shown), a voltage is applied between the anode electrode 6 and the object to be plated P by the power supply 5, causing metal ions to dissolve from the soluble electrode anode electrode 6 into the plating solution. These metal ions then migrate through the plating solution, receiving electrons on the surface of the object to be plated P and depositing there. Subsequently, cavitation treatment is started at time t2. Specifically, the circulation pump 3 is activated, and the plating solution taken from the water intake unit 31 is flowed into the cavitation generator 4, generating cavitation bubbles in the plating solution in the plating tank 2. The plating film grows on the object to be plated P under the action of these cavitation bubbles. As described above, the growth rate of the plating film growing on the surface of the object to be plated is greater than the erosion rate of the plating film due to the disappearance of the cavitation bubbles. At time t3, the electroplating process ends when the switch is turned off, and the cavitation treatment ends simultaneously or almost simultaneously when the circulation pump 43 stops operating.

[0071] Preferably, as can be seen from the example in Figure 23, electroplating is started (on the time axis) before the cavitation treatment, thereby promoting stable initial film formation of the plating film. Also, by ending electroplating at a later point in time than the cavitation treatment, sufficient action of cavitation bubbles on the plating film can be ensured. Optimally, the end time of electroplating and the end time of cavitation treatment are substantially, nearly, or completely the same, thereby avoiding excessive exposure of the plating film to cavitation bubbles. Typically, the electroplating period at time t1-t2 is longer than the electroplating and cavitation period at time t2-t3, thereby promoting stable growth of the initial plating film. As shown in Figure 24, electroplating can also be ended at a point t2' slightly earlier than the end time of the cavitation treatment. Although not shown in the figure, the cavitation treatment can also be ended at a point slightly earlier than the end time of electroplating.

[0072] Figure 25 is a graph showing the change in the arithmetic mean roughness (Ra) of the plated object surface when the cavitation treatment time is changed, with respect to the time chart shown in Figure 23. The discharge time in the figure is equal to the operating period of the circulation pump 3 and can be said to be equal to the cavitation treatment period. In order to clearly demonstrate the smoothing effect of cavitation bubbles, the effect verification was performed in all experiments in Figure 25 using a plating solution without added brightener. It can be seen that Ra decreases in proportion to the discharge time, and the decrease in Ra slows down after a discharge time of 60 seconds. As confirmed in this experiment, it can be seen that there is an optimal discharge time for cavitation bubbles. A semiconductor chip with a copper film deposited on its surface was used as the plated object P.

[0073] Figure 26 is an SEM image showing the surface condition of the plating film of sample No. 1 shown in Figure 25. Figure 27 is an SEM image showing the surface condition of the plating film of sample No. 2 shown in Figure 25. Figure 28 is an SEM image showing the surface condition of the plating film of sample No. 3 shown in Figure 25. These images were acquired using a laser microscope (model: OPTECS HYBTID) manufactured by Lasertec Corporation. A comparison of Figures 27 and 28 shows that the surface irregularities have decreased. Although the surface irregularities in Figure 26 appear smaller than in Figure 27, in reality, large protrusions are formed locally, and because there is no smoothing effect from the brightener, Ra is larger when there is no burnishing effect due to cavitation bubbles.

[0074] Based on the above teachings, those skilled in the art can make various modifications to each embodiment and feature. The reference numerals included in the claims are for reference only and should not be used to limit the scope of the claims.

[0075] 1: Plating apparatus, 2: Plating tank, 3: Circulation pump, 4: Cavitation generator, 9: Stirring device, P: Object to be plated

Claims

1. A method for manufacturing a plated object, comprising generating cavitation bubbles in a plating solution stored in a plating tank, and plating an object to be plated in the plating solution under the influence of the cavitation bubbles, wherein the growth rate of the plating film growing on the surface of the object to be plated is greater than the erosion rate of the plating film due to the disappearance of the cavitation bubbles.

2. The method for manufacturing a plated product according to claim 1, wherein the cavitation bubbles are generated when a liquid flow discharged from a pump passes through a cavitation generator, and the cavitation generator includes a restricted flow path whose flow path width or diameter is reduced in order to generate the cavitation bubbles.

3. The method for manufacturing a plated product according to claim 2, wherein the cavitation generator includes a main flow path through which the liquid flow passes, a main flow path including the restricting flow path, a gas injection passage for injecting gas into the liquid flow flowing through the restricting flow path, and an on / off valve for adjusting the degree of opening and closing of the gas injection passage.

4. The method for manufacturing a plated product according to claim 3, wherein microbubbles generated by the injection of the gas into the liquid flow are supplied to the downstream region of the cavitation generator.

5. The method for manufacturing a plated product according to any one of claims 2 to 4, wherein the pump is a circulation pump that takes the plating solution from the plating tank and returns it to the plating tank.

6. A method for manufacturing a plated product according to any one of claims 1 to 5, wherein the object to be plated includes a group of metal parts, the method further comprising stirring the group of metal parts in the plating solution.

7. The method for producing a plated product according to claim 6, wherein stirring the group of metal parts in the plating solution includes at least one of the following: (i) rotating an agitator, (ii) rotating a magnetic rotating part, (iii) generating ultrasonic waves, and (iv) generating microbubbles.

8. The method for manufacturing a plated product according to claim 6 or 7, wherein the group of metal parts includes at least one of a slider body for a slide fastener, a pull tab to be attached to the slider body, and a button part.

9. The method for manufacturing a plated product according to claim 6 or 7, wherein the group of metal parts is a slider body for a slide fastener, and includes a slider body with element passages, and a plated film is formed on the inner wall surface of the element passages, the surface of which is smoothed or flattened by shock waves generated by the disappearance of the cavitation bubbles.

10. The method for manufacturing a plated product according to claim 6 or 7, wherein the group of metal parts is a pull handle attached to a slider body for a slide fastener, and includes a pull handle having at least one recess or concave surface, and a plated film is formed on the recess or concave surface, the surface of which is smoothed or flattened by shock waves generated by the collapse of the cavitation bubbles.

11. The method for manufacturing a plated product according to any one of claims 6 to 10, wherein the group of metal parts includes two or more metal parts that flow randomly in the plating solution in response to the stirring, at least a portion of the cavitation bubbles are supplied between the two or more metal parts and disappear, and the resulting shock waves propagate toward the individual metal parts of the two or more metal parts.

12. The method for manufacturing a plated product according to any one of claims 1 to 11, wherein the plating solution does not contain a brightener.

13. A method for manufacturing a plated object according to any one of claims 1 to 12, wherein the plating of the object to be plated is started in the plating solution before the cavitation bubbles are generated.

14. A plating apparatus comprising: a plating tank for storing a plating solution; a circulation pump for taking the plating solution from the plating tank and returning it to the plating tank; and a cavitation generator provided in a flow path between the discharge port of the circulation pump and the plating tank, through which the liquid flow of the plating solution discharged from the circulation pump passes, wherein the cavitation generator includes a restricted flow path with reduced flow path width or diameter, and is configured to generate cavitation bubbles in the plating solution stored in the plating tank and in the downstream area of ​​the restricted flow path.

15. The plating apparatus according to claim 14, further comprising a power supply for setting the plating tank to cathode potential and setting the anode electrode immersed in the plating solution of the plating tank to anode potential.

16. The plating apparatus according to claim 14 or 15, wherein the cavitation generator includes a main flow path through which the liquid flow of the plating solution discharged from the circulation pump passes, the main flow path including the restricting flow path, a gas injection passage for injecting gas into the restricting flow path, and an on / off valve for adjusting the degree of opening and closing of the gas injection passage.

17. The plating apparatus according to any one of claims 14 to 16, further comprising an additional cavitation generator, the additional cavitation generator being provided in another flow path between the discharge port of the circulation pump and the plating tank, or in another flow path between the discharge port of another circulation pump and the plating tank.

18. The plating apparatus according to any one of claims 14 to 17, further comprising one or more stirring devices, wherein the one or more stirring devices include at least one of (i) a stirring blade, (ii) a magnetic rotating unit, (iii) an ultrasonic generating unit, or (iv) a microbubble generating unit.

19. An electroplating method for growing a plating film on an object to be plated under the influence of cavitation bubbles.

20. The electroplating method according to claim 19, further comprising smoothing or planarizing the surface of the plating film by eliminating the cavitation bubbles.

21. The electroplating method according to claim 19 or 20, wherein the cavitation bubbles are generated by a liquid flow discharged from a pump passing through a cavitation generator, and the cavitation generator includes a restricted flow path whose flow path width or diameter is reduced in order to generate the cavitation bubbles.

22. The electroplating method according to claim 21, wherein a plurality of cavitation generators are used.

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