CROSS-REFERENCE TO RELATED APPLICATION
This application claims the benefit of the filing date under 35 U.S.C. § 119(a)-(d) of Chinese patent application Ser. No. 20/231,0072318.X, filed on Jan. 17, 2023.
FIELD OF THE INVENTION
The present invention relates to an electroplating device, in particular to an electroplating device suitable for forming a solid nanocrystalline coating on a surface of a workpiece.
BACKGROUND
The industrialization of metal electroplating (electrochemical deposition) has a history of nearly 200 years. In order to obtain a flat, uniform, firm, and dense electroplating layer, in addition to optimizing the plating solution formula, the most commonly used method is to replace direct current electroplating with pulse electroplating. The current of pulse electroplating, which is relatively constant and unchanging in direct current, is on/off or alternates between positive and negative according to a certain waveform cycle. Its mechanism and advantages are as follows:
- 1) Flat and uniform electrodeposition: When the current is interrupted or reversed intermittently, the metal ions and auxiliary additives (leveling agents, dispersants, wetting agents, etc.) in the electroplating solution have the opportunity to fully diffuse and transfer mass to the surface of the plating body, maintaining a high and stable concentration of the plating solution when the surface of the plating body is electrified. The crystal nucleus obtains smoother and more uniform electrocrystallization through diffusion adsorption and dislocation growth;
- 2) Strong coverage ability: Adequate diffusion and mass transfer reduces the impedance of the plating solution near the plating body, allowing it to withstand higher peak current density impacts, increase the overpotential on the surface of the cathode (plating body), increase the power (or concentration) of electro adsorption of metal ions, and make it easier to form new crystal nuclei to quickly cover the surface of the cathode plating body;
- 3)The purity of the coating is high: the carbon (organic additive) and trace foreign metal impurities that are instantly co deposited will also be continuously physically or electrolytically dissolved during intermittent circuit breaks or reverse currents, or simply cannot be co deposited due to short power on time (or extremely small pulse width at constant duty cycle, i.e., high-frequency pulse), thereby improving the purity of the metal coating.
- 4) Strong adhesion, fine crystallization, and strong deep plating ability: In the process of continuous power on and off, especially when the on/off ratio (duty cycle) is very small, the generation rate of crystal nuclei is much faster than the growth rate of crystal nuclei. The electrodeposited crystals are small and numerous, making it easier to nucleate at the grain boundaries or holes or defects of the cathode plating body. The deep ability is strong, and the coating is firm and dense.
- 5) Suitable for high current density selective electroplating: By appropriately increasing peak current density and reducing duty cycle, electrodeposition in low current density areas can be suppressed, thus achieving high current density selective electroplating, such as saving precious metals such as gold plating or controlling non plating areas.
From the above mechanisms and advantages, it can be seen that, in order to obtain finer grains such as a flat, uniform, and firm coating at the nanocrystalline level, we should minimize the power on duty cycle and pulse width of pulse electroplating as much as possible, as well as increase the peak current density and pulse frequency. However, in practical applications, almost no electroplating solution can always blindly reduce the duty cycle and pulse width of pulse electroplating, as well as infinitely increase the peak current density. The low stability of high-frequency pulse rectifiers also limits the pulse frequency to not be too high, and it is not recommended to use too high current density for high temperature rise. In order to balance multiple technological bottlenecks, pulse electroplating production in industry can only slightly increase the peak current density and pulse frequency, and slightly reduce the power on duty cycle and pulse width. Therefore, it is difficult to obtain nanocrystalline coatings, and even if it is barely obtained in the laboratory, it is difficult to achieve stable mass production.
The existing pulse electroplating is used for mass production. In order to improve electroplating efficiency and facilitate management, a single pulse rectifier is often used. The technical bottleneck that limits its ability to obtain nanocrystalline coatings is:
- 1) High peak current density and high duty cycle lead to coating scorching and reduced deep plating ability. Taking pulse electroplating of nickel on copper substrate as an example, when the current density exceeds 100 A/dm2 and the duty cycle is greater than 20%, the applied driving potential of the electrodeposition far exceeds the ion conductivity of the nickel plating solution, leading to severe scorching of the plating area with high current density (such as the tip and protrusion of the part).
- 2) High peak current density increases the difficulty of heat dissipation and reduces the stability of long-term use of pulse rectifiers: High peak current density requires pulse rectifiers to output high current and power, and the temperature rise is fast and high after long-term use, which increases the difficulty of system heat dissipation and increases instability and high cost for continuous production 24 hours a day. For example, low power consumption can only be achieved by air cooling, while high power consumption systems must be cooled with ice water.
- 3) Low peak current density and low duty cycle can lead to plating leakage in areas with low current density: appropriately reducing the duty cycle can undoubtedly reduce the average current density within a certain period of time, thereby improving the maximum tolerance of peak current density. Conversely, reducing the peak current density can also tolerate higher duty cycles, but it is difficult to achieve balance and harmony between the two. The conservative approach is to use a combination of low peak current density and low duty cycle, the electric potential of the external driving electrodeposition is too low to penetrate into low current density areas (such as holes and depressions in parts), resulting in plating leakage.
- 4) Small pulse width and high frequency pulse can lead to poor adhesion, difficulty in plating, and overall loss of plating: Pulse electroplating with small pulse width and low duty cycle has a particularly high requirement for the conductivity of the entire plating circuit (including wires, cathode contacts, anodes, and plating solution). The electrification time of small pulse width and high frequency pulse is extremely short, and it is consumed on the high resistance circuit before it can drive the electrodeposition. Even if given multiple cycles of pulses, electrons cannot rush to the cathode to reduce metal ions into metal atoms. Without the initial driving force for the formation of crystal nuclei, it can lead to poor adhesion and difficulty in plating, resulting in overall loss of plating.
SUMMARY
An electroplating device includes an electroplating pool containing an electroplating solution, a first anode plate immersed in the electroplating solution, and a first pulse rectifier having a positive electrode electrically connected to the first anode plate and a negative electrode electrically connected to a workpiece to be electroplated that is immersed in the electroplating solution. The first pulse rectifier periodically outputs a first set of pulse currents during electroplating of the workpiece. The first set of pulse currents includes a plurality of first different pulse currents that differ in a peak current density and a duty cycle.
BRIEF DESCRIPTION OF THE DRAWINGS
Features of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the accompanying drawings, in which:
FIG. 1 shows an illustrative view of an electroplating device according to an exemplary embodiment of the present invention;
FIG. 2 shows an illustrative view of an electroplating device according to another exemplary embodiment of the present invention;
FIG. 3 shows an illustrative view of an electroplating device according to another exemplary embodiment of the present invention;
FIG. 4 shows an illustrative view of the pulse current waveform output by the first pulse rectifier according to an exemplary embodiment of the present invention;
FIG. 5 shows an illustrative view of the first set of pulse currents output by the first pulse rectifier according to an exemplary embodiment of the present invention;
FIG. 6 shows an illustrative view of the pulse current waveform output by a second pulse rectifier according to an exemplary embodiment of the present invention; and
FIG. 7 shows an illustrative view of the second set of pulse currents output by a second pulse rectifier according to an exemplary embodiment of the present invention.
DETAILED DESCRIPTION OF EMBODIMENTS
Exemplary embodiments of the present disclosure will be described hereinafter in detail with reference to the attached drawings, wherein like reference numerals refer to like elements. The present disclosure may however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that the present disclosure will convey the concept of the disclosure to those skilled in the art.
In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing.
As shown in FIGS. 1 to 3, in an exemplary embodiment of the present invention, an electroplating device is disclosed. The electroplating device comprises an electroplating pool 13, a first anode plate 110, and a first pulse rectifier 11. The electroplating pool 13 is used to contain electroplating solution. The first anode plate 110 is immersed in the electroplating solution of the electroplating pool 13 and serves as the anode for electroplating. The positive pole of the first pulse rectifier 11 is electrically connected to the first anode plate 110. The negative electrode of the first pulse rectifier 11 is electrically connected to the workpiece 130 to be electroplated, which is immersed in the electroplating solution. The workpiece 130 serves as the cathode for electroplating.
FIG. 4 shows an illustrative view of the pulse current waveform output by the first pulse rectifier 11 according to an exemplary embodiment of the present invention. FIG. 5 shows an illustrative view of the first set of pulse currents P1 output by the first pulse rectifier 11 according to an exemplary embodiment of the present invention.
As shown in FIGS. 4 and 5, the first pulse rectifier 11 is set to periodically output the first set of pulse currents P1 when electroplating the workpiece 130. The first set of pulse currents P1 includes various different pulse currents P11 to P13. The peak current density and duty cycle of various pulse currents P11 to P13 in the first set of pulse currents P1 are different from each other. In the illustrated embodiment, the first set of pulse currents P1 includes three different pulse currents P11, P12, and P13. However, the present invention is not limited to the illustrated embodiments, for example, the first set of pulse currents P1 may also include two, four, five, or more different pulse currents.
As shown in FIGS. 4 and 5, in the illustrated embodiment, various different pulse currents P11 to P13 in the first set of pulse currents P1 are generated in chronological order. The peak current density of a pulse current generated first in the first set of pulse currents P1 is higher than that of another pulse current generated later in the first set of pulse currents P1. For example, in the illustrated embodiment, the peak current density of the first generated pulse current P11 in the first set of pulse currents P1 is higher than that of the subsequent generated pulse currents P12 and P13, and the peak current density of the first generated pulse current P12 in the first set of pulse currents P1 is higher than that of the subsequent generated pulse current P13.
As shown in FIGS. 4 and 5, in the illustrated embodiment, various different pulse currents P11 to P13 in the first set of pulse currents P1 are generated in chronological order. The duty cycle of a pulse current generated first in the first set of pulse current P1 is lower than that of another pulse current generated later in the first set of pulse current P1. For example, in the illustrated embodiment, the duty cycle of the pulse current P11 generated first in the first set of pulse currents P1 is lower than that of the pulse currents P12 and P13 generated later, while the duty cycle of the pulse current P12 generated first in the first set of pulse currents P1 is lower than that of the pulse current P13 generated later.
As shown in FIGS. 4 and 5, in an exemplary embodiment of the present invention, at least one of the amplitudes A11 to A13, pulse widths W11 to W13, and pulse frequencies f11 to f13 of various different pulse currents P11 to P13 in the first set of pulse currents P1 is different from each other. For example, in the illustrated embodiment, the amplitudes A11˜A13, pulse widths W11˜W13, and pulse frequencies f11 to f13 of various different pulse currents P11˜P13 in the first set of pulse currents P1 are different from each other.
As shown in FIGS. 1 to 3, in the illustrated embodiments, the electroplating device further includes a second anode plate 120 and a second pulse rectifier 12. In the illustrated embodiment, the electroplating device includes two independent pulse rectifiers 11 and 12. However, the present invention is not limited to the illustrated embodiments, for example, the electroplating device may include three or more pulse rectifiers.
As shown in FIGS. 1 to 3, in the illustrated embodiments, the second anode plate 120 is immersed in the electroplating solution of the electroplating pool 13 and serves as the anode for electroplating. The positive pole of the second pulse rectifier 12 is electrically connected to the second anode plate 120, and the negative pole of the second pulse rectifier 12 is electrically connected to the workpiece 130 to be electroplated that is immersed in the electroplating solution.
FIG. 6 shows an illustrative view of the pulse current waveform output by the second pulse rectifier 12 according to an exemplary embodiment of the present invention. FIG. 7 shows an illustrative view of the second set of pulse currents P2 output by the second pulse rectifier 12 according to an exemplary embodiment of the present invention. In the illustrated embodiments, the second pulse rectifier 12 is set to periodically output a second set of pulse currents P2 when electroplating the workpiece 130. The second set of pulse currents P2 includes various different pulse currents P21 to P23. The peak current density and duty cycle of various pulse currents P21 to P23 in the second set of pulse currents P2 are different from each other.
In the illustrated embodiment, the second set of pulse current P2 output by the second pulse rectifier 12 is different from the first set of pulse current P1 output by the first pulse rectifier 11. As shown in FIGS. 6 to 7, in an exemplary embodiment of the present invention, the peak current density of at least one pulse current P21 to P23 in the second set of pulse currents P2 is different from that of any pulse current P11 to P13 in the first set of pulse currents P1. The duty cycle of at least one pulse current P21˜P23 in the second set of pulse currents P2 is different from the duty cycle of any pulse current P11˜P13 in the first set of pulse currents P1. In the illustrated embodiments, the peak current density of any pulse current P21 to P23 in the second set of pulse currents P2 is different from that of any pulse current P11 to P13 in the first set of pulse currents P1. The duty cycle of any pulse current P21˜P23 in the second set of pulse currents P2 is different from that of any pulse current P11˜P13 in the first set of pulse currents P1.
As shown in FIGS. 6 and 7, in the illustrated embodiment, the second set of pulse currents P2 includes three different types of pulse currents P21, P22, and P23. However, the present invention is not limited to the illustrated embodiments, for example, the second set of pulse currents P2 may also include two, four, five, or more different types of pulse currents.
As shown in FIGS. 6 and 7, in the illustrated embodiment, various different pulse currents P21 to P23 in the second set of pulse currents P2 are generated in chronological order. The peak current density of a pulse current generated first in the second set of pulse currents P2 is higher than that of another pulse current generated later in the second set of pulse currents P2. For example, in the illustrated embodiment, the peak current density of the first generated pulse current P21 in the second set of pulse currents P2 is higher than that of the later generated pulse currents P22 and P23, and the peak current density of the first generated pulse current P22 in the second set of pulse currents P2 is higher than that of the later generated pulse current P23.
As shown in FIGS. 6 and 7, in the illustrated embodiment, various different pulse currents P21 to P23 in the second set of pulse currents P2 are generated in chronological order. The duty cycle of a pulse current generated first in the second set of pulse currents P2 is lower than that of another pulse current generated later in the second set of pulse currents P2. For example, in the illustrated embodiment, the duty cycle of the first generated pulse current P21 in the second set of pulse currents P2 is lower than that of the subsequent generated pulse currents P22 and P23, while the duty cycle of the first generated pulse current P22 in the second set of pulse currents P2 is lower than that of the subsequent generated pulse current P23.
As shown in FIGS. 6 and 7, in an exemplary embodiment of the present invention, at least one of the amplitudes A21 to A23, pulse widths W21 to W23, and pulse frequencies f21 to f23 of various different pulse currents P21 to P23 in the second set of pulse currents P2 is different. For example, in the illustrated embodiment, the amplitudes A21˜A23, pulse widths W21˜W23, and pulse frequencies f21˜f23 of various different pulse currents P21˜P23 in the second set of pulse currents P2 are different from each other.
As shown in FIGS. 1 to 3, in the illustrated embodiments, the electroplating device comprises at least one pair of first anode plates 110, each pair of first anode plates 110 being respectively arranged on the front and rear sides of the workpiece 130 to be electroplated. The electroplating device includes at least one pair of second anode plates 120, each pair of which is respectively arranged on the front and back sides of the workpiece 130 to be electroplated.
As shown in FIG. 1, in the illustrated embodiment, the electroplating device includes a pair of first anode plates 110 and a pair of second anode plates 120. One of the first pair of anode plates 110 and one of the second pair of anode plates 120 are arranged side by side on the front side of the workpiece 130 to be electroplated. The other of the pair of first anode plates 110 and the other of the pair of second anode plates 120 are arranged side by side on the rear side of the workpiece 130 to be electroplated.
As shown in FIG. 2, in the illustrated embodiment, the electroplating device includes a pair of first anode plates 110 and a pair of second anode plates 120. One of the first pair of anode plates 110 and one of the second pair of anode plates 120 are overlapped on the front side of the workpiece 130 to be electroplated. The other of the pair of first anode plates 110 and the other of the pair of second anode plates 120 are overlapped at the rear side of the workpiece 130 to be electroplated.
As shown in FIG. 3, in the illustrated embodiment, the electroplating device includes two pairs of first anode plates 110. Two first anode plates 110 in the two pairs of first anode plates 110 are arranged on the front side of the workpiece 130 to be electroplated, and the two first anode plates 110 arranged on the front side of the workpiece 130 are staggered and electrically connected to each other. The other two first anode plates 110 in the two pairs of first anode plates 110 are arranged on the rear side of the workpiece 130 to be electroplated, and the other two first anode plates 110 are staggered and electrically connected to each other on the rear side of the workpiece 130.
As shown in FIG. 3, in the illustrated embodiment, the electroplating device includes two pairs of second anode plates 120. Two second anode plates 120 of the two pairs of second anode plates 120 are arranged on the front side of the workpiece 130 to be electroplated, and the two second anode plates 120 arranged on the front side of the workpiece 130 are staggered and electrically connected to each other. The other two second anode plates 120 in the two pairs of second anode plates 120 are arranged on the rear side of the workpiece 130 to be electroplated, and the other two second anode plates 120 are staggered and electrically connected to each other on the rear side of the workpiece 130.
As shown in FIG. 3, in the illustrated embodiment, any first anode plate 110 in two pairs of first anode plates 110 is overlapped with a corresponding second anode plate 110 in two pairs of second anode plates 120.
In the illustrated embodiment, the material of the first anode plate 110 is different from that of the second anode plate 110.
In an embodiment, the electroplating device also includes a filter bag. The first anode plate 110 and/or the second anode plate 110 are contained in a filter bag to prevent foreign powder particles dissolved from the first anode plate 110 and/or the second anode plate 110 from entering the electroplating solution.
The present invention uses multiple sets of pulse combinations, each with different pulse widths, peak current densities, duty cycles, and number of pulses. The combination of pulses can weaken a single upper limit parameter to a certain extent, resulting in burnt, sponge like, and porous loose coatings. It can also avoid the bottleneck of missing plating, poor adhesion, and even failure to plating caused by lower limit parameters to a certain extent; Double anodes or (multiple anodes) are connected separately to different pulse rectifiers, and each pulse rectifier is equipped with different combination pulses to jointly provide electrodeposition driving force on the same plating body (i.e., workpiece 130). This further reduces the bottleneck of parameter upper or lower limits, widens the working window, and the power consumption of each pulse rectifier is less than 50% or even lower when only a single pulse rectifier is used, effectively reducing the difficulty of heat dissipation in pulse rectifiers, and enhancing the stability of long-term use. It is crucial that the present invention can first use high current density and low duty cycle to promote nucleation, and then use medium to high current density and high duty cycle to promote grain growth. Nucleation and grain growth are not simple alternating effects. Multiple anode pulses not only promote grain growth, but also add new nucleation. The grains will not grow excessively, and nucleation can fill all grain boundaries in a timely manner, with multiple pulse combinations repeating themselves, gradually accumulate into dense nanocrystals of target thickness. In short, the present invention can enable the parameters of nanocrystals to be obtained theoretically or in the laboratory to participate in electrodeposition work steadily in practice, with a wide working window and stable and controllable process. It is a sustainable and stable method for depositing nanocrystalline coatings in mass production.
As mentioned above, the present invention can solve at least one of the following technical problems:
- 1) There are many hidden dangers in the quality of plating: due to technical bottlenecks, the working window is narrow, or it is difficult to balance various technical parameters, resulting in some plating risks, such as protruding and burning at the tip, insufficient deep plating ability, leakage of plating at deep hole depressions, poor adhesion, difficulty in plating, and overall loss of plating;
- 2) Poor stability in mass production: difficult heat dissipation and poor stability in long-term use of pulse rectifiers;
- 3) It is difficult to obtain stable nanocrystalline coatings: nanocrystalline coatings may be occasionally obtained in the laboratory, but it is difficult to obtain stable nanocrystallines through mass production.
Taking nickel plating as an example, the present invention can achieve the following technical effects:
The commonly used pulse electroplating methods currently exist, where the nickel flash coating has a rough and loose surface with a porosity ratio of about 20 nanometers, resulting in incomplete coverage and inadequate deposition. The nickel flash coating of the present invention is evenly and finely dispersed into the texture of the copper substrate. The extremely thin coating of about 20 nanometers has almost no particle sensation, completely restoring the clear texture of the copper substrate. The nanocrystalline film is flexible and undulating with the texture without interruption, tightly biting the substrate. Whether it is used as a base coating to increase the adhesion with the substrate, or as an intermediate or surface coating to enhance the corrosion protection and friction durability of parts, nanocrystalline coatings are undoubtedly superior to non nanocrystalline coatings. The grain size of nanocrystals is too small, and EBSD can only measure grains larger than 100 nm. Here, the grain size of nanocrystals can only be measured using TEM.
As shown in FIGS. 1 to 3, the schematic diagram of the dual anode (multi anode) structure and pulse waveform of the present invention have been detailed in FIGS. 4 to 7. The implementation process of the present invention is explained in detail using nano nickel as an example:
Installation of anodes and pulse rectifiers—The multiple anode arrangement methods of the present invention can be in various ways (as shown in FIGS. 1-3), which can be left and right spacing, parallel front and rear, or staggered front and rear. Each group of anodes corresponds to a pulse rectifier, which is independently controlled. The anode material should be selected from a plating metal with corresponding electrolytic solubility. For example, nickel anode can be used for nickel plating, or materials without electrolytic solubility can be used, such as graphite, titanium, etc. In this invention, it is recommended to use titanium material with better conductivity for platinum or niobium plating, or materials without electrolytic solubility can be combined with nickel anode, such as platinum plating or niobium titanium basket loading nickel balls. Each group of anodes can use different materials, especially when electroplating alloys. It is recommended that each rectifier control different anode materials to control the proportion of coating alloys. The anode is covered with a polymer filter bag that is acid and alkali resistant to prevent foreign particles dissolved from the anode from entering the electroplating solution and adsorbing onto the plating body. The selection of pulse rectifier range is based on practical application, so that the actual power consumption falls between 20%-80% of the range. If the range is too small, the current cannot rise, and if the range is too large, the accuracy is not enough. The large volume of the equipment also occupies a large working space.
Preparation of Electroplating Solution—Electroplating solution can be a commercially mature formula or self-made. The nickel used in the present invention is self-formulated and does not add any organic additives to ensure the purity of the nickel. Set the corresponding electroplating temperature and cycle exchange stirring speed.
Setting pulse electroplating parameters for electrodeposition—Each pulse rectifier can be used to set different or the same waveform in practical applications. High current density and low duty cycle can be used to nucleate the plating first, and then medium to high current density and high duty cycle can be used to promote grain growth. Nucleation and grain growth alternate, and the grains will not grow excessively. Nucleation can fill all grain boundaries in a timely manner, and multiple pulse combinations cycle through, dense nanocrystals can accumulate to the target thickness. The example of nickel in the present invention is only 20 nanometers, which better reflects the coverage and depth capabilities.
The present invention has developed a multi pulse dual (multi) anode co plating device and method, which successfully obtains a perfect nanocrystalline coating and can be applied to stable mass production.
It should be appreciated for those skilled in this art that the above embodiments are intended to be illustrative, and not restrictive. For example, many modifications may be made to the above embodiments by those skilled in this art, and various features described in different embodiments may be freely combined with each other without conflicting in configuration or principle.
Although several exemplary embodiments have been shown and described, it would be appreciated by those skilled in the art that various changes or modifications may be made in these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the claims and their equivalents.
As used herein, an element recited in the singular and preceded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property.
Patent Application
20240240350
