A method for manufacturing a copper terminal electrode of an MLCC capacitor

Abstract

The application discloses a preparation method of a copper terminal electrode of an MLCC capacitor, and relates to the technical field of multilayer ceramic capacitors. The preparation method of the copper terminal electrode of the MLCC capacitor comprises the following steps: (1) placing the MLCC capacitor on a workpiece rack in a vacuum chamber, and performing vacuumizing; (2) starting an anode layer ion source; (3) stopping the anode layer ion source, starting a double-pole HiPIMS power supply, adjusting copper target source process parameters, and preparing an interface mixed layer; (4) keeping the gas flow and gas pressure of inert gas unchanged, adjusting copper target double-pole HiPIMS power supply parameters, and preparing a copper electrode layer; and (5) stopping the double-pole HiPIMS power supply and the inert gas, so that the copper terminal electrode of the MLCC capacitor is obtained. The application adopts a novel low-temperature high-ionization plating film technology, and solves the problems of poor compactness, low bonding force and thermal stress failure of the terminal electrode caused by copper burning during the preparation process of the MLCC capacitor.

Description

Technical Field

[0001] This invention relates to the technical field of multilayer ceramic capacitors, and more particularly to a method for preparing copper terminal electrodes of MLCC capacitors. Background Technology

[0002] Multilayer ceramic capacitors (MLCCs) are among the most important electronic components, and their performance directly affects the overall functionality of electronic products. As MLCCs develop towards miniaturization and higher capacitance, the thickness of the dielectric layer decreases while the number of layers increases. Therefore, the reliability of the connection between the internal and external electrodes has become a crucial factor in the stability of MLCC capacitance values. Currently, MLCCs commonly use nickel as the internal electrode and copper as the terminal electrode. The copper terminal electrode is prepared by high-temperature sintering of copper electrode paste. The copper sintering process typically occurs above 800℃. Due to the difference in thermal expansion coefficients between the ceramic dielectric and the nickel electrode inside the MLCC, thermal stress easily forms at the interface between the internal electrode and the ceramic dielectric under the thermal shock of this high-temperature treatment, leading to significant thermal stress failure. Furthermore, the copper sintering paste is composed of a mixture of copper powder, glass powder, and organic carriers, which is prone to defects such as voids and poor bonding after sintering, resulting in abnormal MLCC performance. Therefore, developing new low-temperature, high-density, and high-bonding terminal electrode preparation technologies is an important measure to improve the quality and reliability of MLCC capacitors.

[0003] To address the issue of MLCC end-cap burning, patent CN115692017A proposes an electrochemical deposition method for preparing aluminum end electrodes. In this method, the aluminum electrode layer preferentially grows on the inner electrode, gradually expanding and connecting over time to cover the entire dielectric ceramic layer and the inner electrode. This method has two main drawbacks: first, because a metal coating cannot grow simultaneously on the dielectric ceramic layer, defects such as discontinuities or voids in the end electrode layer may occur; second, electrochemical deposition uses an electrolyte, which is a wet deposition process, leaving electrolyte residue between the end electrode and the ceramic layer, leading to a significant decrease in the adhesion of the end electrode coating over time.

[0004] Patent CN115786847A discloses a method for magnetron sputtering inside a slender tube using a DC-DC composite bipolar pulse. This method combines the high deposition rate and discharge stability of DC with the high ionization rate and high particle energy of bipolar discharge, thereby achieving rapid fabrication of high-quality films inside slender tubes. While the method allows switching between DC, pulse, bipolar pulse, and DC-DC composite bipolar pulse discharge modes, it is only applicable to magnetron sputtering deposition on the inner wall of slender tubes. Furthermore, this patent addresses the instability of bipolar pulse magnetron sputtering discharge within the narrow space of slender tubes by modifying the bipolar pulse power supply and adding a DC discharge module to increase the stability of the magnetron sputtering discharge inside the slender tube. The main focus of this patent is the modification of the power supply, leading to a magnetron sputtering method for slender tubes. Although the power supply modification improves discharge stability, the DC module discharge significantly reduces the ionization rate of the plasma per unit time for the overall plasma.

[0005] Patents CN105355430A and CN113096961A both mention using sputtering technology to prepare end electrodes. Magnetron sputtering is one of the commonly used coating technologies, capable of preparing coatings of metals, alloys, and various ceramic materials. It features fast deposition speed, low coating temperature rise, and minimal damage to the substrate. The resulting film has good adhesion to the substrate, high film purity, and allows for precise control of the coating thickness. Furthermore, the particle size of the film can be controlled by changing parameters, resulting in good density. Sputtering coating processes are highly repeatable, allowing for the acquisition of uniformly thick films on large-area substrates, making it one of the most promising technologies to replace copper-fired end electrodes. However, current research and engineering studies show that the capacitance yield of MLCCs with end electrodes prepared by conventional magnetron sputtering is far lower than that of copper-fired end electrodes. The core challenge lies in the fact that for the micron-wide nickel internal electrodes of MLCCs, some electrodes are recessed within the dielectric ceramic layer, and a thin oxide layer forms on the electrode surface. High-temperature diffusion at the copper end electrode can overcome these barriers, allowing for a good connection between the copper end electrode and the nickel inner electrode. However, conventional magnetron sputtering involves atomic or neutral particle deposition, with particles carrying only a few eV of kinetic energy. Furthermore, since the MLCC capacitor body is made of non-conductive ceramic material, it is difficult to accelerate copper particles by applying an electric field to the workpiece. Such low energy is insufficient to bombard the recesses and oxide layer, thus preventing the copper particles from overcoming the aforementioned barriers to form a good contact between the inner and outer electrodes. This results in a significant decrease in capacitance and end electrode bonding performance. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing copper terminal electrodes for MLCC capacitors. This invention employs a novel low-temperature, high-ionization coating technology to solve the problems of poor electrode density, low adhesion, and thermal stress failure caused by copper burning during MLCC capacitor manufacturing. It also overcomes the problem of significant capacitance reduction caused by the inability of traditional vacuum coating to achieve good contact between the terminal electrodes and the internal electrodes.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] This invention provides a method for preparing copper terminal electrodes of an MLCC capacitor, comprising the following steps:

[0009] (1) Ultrasonic cleaning, rinsing and drying of MLCC capacitors;

[0010] (2) Place the cleaned MLCC capacitor on the workpiece rack in the vacuum chamber;

[0011] (3) Close the vacuum chamber, evacuate the vacuum chamber, and remove the residual polluting gas inside the vacuum chamber;

[0012] (4) Introduce inert gas, then turn on the ion source of the anode layer and ion clean the workpiece;

[0013] (5) Turn off the ion source of the anode layer, introduce inert gas, and then turn on the bipolar HiPIMS power supply. Adjust the copper target source process parameters as follows: frequency 100-200Hz, negative pulse voltage 700-900V, pulse width 50-75μs, positive voltage 300-400V, pulse width 100-200μs. Ground the workpiece frame to avoid charge accumulation and prepare the interface mixing layer.

[0014] (6) Keep the gas flow rate and pressure of the inert gas constant, and adjust the power supply parameters of the copper target bipolar HiPIMS as follows: frequency 100-200Hz, negative pulse voltage 700-800V, pulse width 100-150μs, positive voltage 100-150V, pulse width 100-200μs, ground the workpiece holder, and prepare the copper electrode layer.

[0015] (7) Turn off the bipolar HiPIMS power supply and the inert gas, cool the workpiece, open the furnace and take out the workpiece to obtain the copper terminal electrode of the MLCC capacitor.

[0016] This invention enables the copper electrode to form a bilayer structure through energy control: In the initial stage, a short negative high-voltage pulse generates low-density, highly ionized copper ions, while a higher positive acceleration pulse accelerates the copper ions to high energy, allowing them to be injected into the subsurface layer of the end face, forming an interfacial mixing layer. In the later stage, a long negative high-voltage pulse is used, with an appropriate reduction in the positive acceleration pulse, allowing for the deposition of a highly dense, low-stress copper film at a higher speed. Using this invention's bipolar high-ionization coating technology, the entire process temperature does not exceed 200℃, preventing damage to the functional layers inside the MLCC capacitor. This completely solves the problems of poor density, low adhesion, and thermal stress failure caused by copper burning at the MLCC capacitor manufacturing process.

[0017] Preferably, the ion source power in step (4) is 1.5 to 3.0 kW.

[0018] The ion source power determines the energy required for ion cleaning of the workpiece. Low-energy cleaning fails to remove surface contaminants, while excessively high energy can bombard the surface, causing defects or even damaging the internal electrodes, leading to abnormal capacitance values. Therefore, this invention controls the ion source power within the aforementioned range to better remove contaminants from the workpiece surface, thus minimizing the impact on the fabrication of the copper terminal electrodes of the MLCC capacitor.

[0019] Preferably, the copper target source process parameters in step (5) are: frequency 100-120Hz, negative pulse voltage 700-800V, pulse width 50-60μs, positive voltage 300-350V, pulse width 150-200μs.

[0020] More preferably, the copper target source process parameters in step (5) are: frequency 120Hz, negative pulse voltage 800V, pulse width 60μs, positive voltage 350V, pulse width 150μs.

[0021] By employing the aforementioned specific power pulse parameters, this invention facilitates the ionization of copper and the energy of copper ions, enabling better interfacial mixing between the plating layer and the electrode, thereby achieving a good connection between the end electrode and the inner electrode.

[0022] Preferably, the copper target bipolar HiPIMS power supply parameters in step (6) are: frequency 180-200Hz, negative pulse voltage 700-750V, pulse width 100-120μs, positive voltage 100-120V, pulse width 100-120μs.

[0023] More preferably, the copper target bipolar HiPIMS power supply parameters in step (6) are: frequency 180Hz, negative pulse voltage 700V, pulse width 120μs, positive voltage 120V, and pulse width 120μs.

[0024] By employing the aforementioned specific power supply parameters, this invention can better achieve the goal of high-speed copper film deposition. Furthermore, while ensuring the film density, appropriately reducing the positive pulse voltage (reducing ionization) and negative pulse voltage (reducing energy) can reduce the bombardment of ions on the film surface, thereby increasing the deposition speed.

[0025] Preferably, in step (4), the flow rate of the inert gas is 60-100 SCCM and the gas pressure is 0.1-0.3 Pa.

[0026] In this invention, ion cleaning involves an ion source emitting electrons, which collide with an inert gas and ionize into positive ions. A negative voltage is applied to the workpiece holder, attracting these positive ions to bombard the workpiece surface. Therefore, if the inert gas content is too low, fewer positive ions are generated, resulting in poor bombardment; conversely, excessive inert gas content can easily damage the workpiece. Thus, controlling the inert gas flow rate within the aforementioned range is beneficial for ion source cleaning.

[0027] Preferably, in step (5), the flow rate of the inert gas is 100-150 SCCM and the pressure is 0.3-0.5 Pa.

[0028] Preferably, in step (3), the vacuum is evacuated to 3×10⁻⁶. -3 Below Pa.

[0029] Vacuum up to 3×10 -3 Below Pa, the residual gas in the vacuum chamber, such as oxygen, can be reduced, avoiding oxidation on the surface of the metal electrode and improving the adhesion between the coating and the electrode.

[0030] More preferably, in step (3), the MLCC capacitor is first heated to 100-200°C, and then evacuated again to 3×10⁻⁶ °C. -3 Below Pa.

[0031] Heating the MLCC capacitor to 100-200℃ is to release contaminants adsorbed in the atmosphere from the vacuum chamber walls, fixtures, and workpieces, and then re-evacuating to 3×10⁻⁶. -3 Below Pa, the heating temperature can remove polluting gases released during the heating process, making the coating process less susceptible to interference. If the heating temperature is too low, it will hinder gas release; if the heating temperature is too high, it will easily cause fixture deformation.

[0032] Preferably, the inert gas is argon.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] (1) The present invention generates copper positive ions by high-energy negative pulses and accelerates copper ions by positive pulses. The high-energy copper ions break through the barrier on the surface of the inner electrode and can be injected into the subsurface layer of the inner electrode, forming an interface mixing layer between the copper electrode and the inner electrode, which greatly improves the connection and bonding strength of the inner and outer electrodes.

[0035] (2) By adjusting the waveform parameters of high-energy negative pulses and positive pulses, the generation and energy of copper ions can be easily adjusted. High energy and low speed form an interface mixing layer, and low energy and high speed grow a copper electrode layer.

[0036] (3) Bipolar high energy density pulsed magnetron sputtering end electrode preparation technology can deposit copper electrodes at a lower temperature (not exceeding 200℃), avoiding thermal stress damage between the multilayer internal electrodes and ceramic dielectric inside the capacitor. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the bipolar high-energy-density pulse waveform in this invention.

[0038] Figure 2 This is a schematic diagram of the bipolar high-energy copper plating process before and after in this invention.

[0039] Figure 3 This is a schematic diagram showing the connection between the copper end electrode and the inner electrode in this invention. Detailed Implementation

[0040] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments, but the scope of protection and implementation of the present invention are not limited thereto.

[0041] Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0042] Example 1

[0043] A method for fabricating copper terminal electrodes of an MLCC capacitor includes the following steps:

[0044] (1) Place the MLCC capacitor without terminal electrodes (model 0805X / 106K6R3NBT) in the cleaning solution (neutral cleaning agent from Borer, Switzerland) for ultrasonic cleaning for 15 minutes, rinse it with deionized water three times with ultrasonic cleaning, and dry it with hot air at 80°C.

[0045] (2) Place the MLCC capacitor in a special fixture and load it onto the workpiece rack in the vacuum chamber. Adjust the target-base distance to 100mm. After checking the rotation status, close the furnace door.

[0046] (3) Start the mechanical pump and molecular pump respectively to evacuate the vacuum to a back-bottom vacuum of 3×10⁻⁶. -3 Below Pa, start the workpiece holder rotation and heat the workpiece to 100℃, then turn off the heating power and evacuate the vacuum again to 3×10. -3 Below Pa;

[0047] (4) Introduce 60 SCCM of argon gas at a pressure of 0.1 Pa; turn on the ion source of the anode layer at a power of 1.5 kW and ion clean the workpiece for 5 min;

[0048] (5) Turn off the ion source of the anode layer, adjust the argon flow rate to 100 SCCM and the gas pressure to 0.3 Pa, turn on the bipolar high energy density pulse power supply, and the copper target source process parameters are: frequency 100 Hz, negative pulse voltage 700 V, pulse width 50 μs, positive voltage 300 V, pulse width 100 μs. Ground the workpiece holder to avoid charge accumulation, and prepare the interface mixing layer for 5 min.

[0049] (6) Keep the gas flow rate and pressure constant, and adjust the parameters of the bipolar high energy density pulse power supply for the copper target: frequency 100Hz, negative pulse voltage 700V, pulse width 100μs, positive pulse voltage 100V, pulse width 100μs, ground the workpiece holder, prepare a low-stress dense copper electrode layer for 20min, and turn off the bipolar high energy density pulse power supply after completion.

[0050] (7) A nickel barrier layer and a tin solder layer are deposited in the same vacuum chamber using a vacuum coating method. After the deposition is completed, the power supply and argon gas are turned off. The workpiece is cooled to below 80°C, and the furnace is opened to remove the workpiece, thus obtaining the copper terminal electrode of the MLCC capacitor.

[0051] Example 2

[0052] A method for fabricating copper terminal electrodes of an MLCC capacitor includes the following steps:

[0053] (1) Place the MLCC capacitor without terminal electrodes (model 0805X / 106K6R3NBT) in the cleaning solution and ultrasonically clean it for 15 minutes. Then, rinse it with deionized water three times and dry it with hot air at 80°C.

[0054] (2) Place the MLCC capacitor in a special fixture and load it onto the workpiece rack in the vacuum chamber. Adjust the target-base distance to 100mm. After checking the rotation status, close the furnace door.

[0055] (3) Start the mechanical pump and molecular pump respectively to evacuate the vacuum to a back-bottom vacuum of 3×10⁻⁶. -3 Below Pa, start the workpiece holder rotation and heat the workpiece to 200℃, then turn off the heating power and evacuate the vacuum again to 3×10. -3 Below Pa;

[0056] (4) Introduce 100 SCCM of argon gas at a pressure of 0.3 Pa; turn on the ion source of the anode layer at a power of 3.0 kW and ion clean the workpiece for 5 min;

[0057] (5) Turn off the ion source, adjust the argon flow rate to 150 SCCM and the gas pressure to 0.5 Pa, turn on the bipolar high energy density pulse power supply, and the copper target source process parameters are: frequency 200 Hz, negative pulse voltage 900 V, pulse width 75 μs, positive voltage 400 V, pulse width 200 μs. Ground the workpiece holder to avoid charge accumulation, and prepare the interface mixing layer for 5 min.

[0058] (6) Keep the gas flow rate and pressure constant, adjust the parameters of the bipolar high energy density pulse power supply for the copper target: frequency 200Hz, negative pulse voltage 800V, pulse width 150μs, positive pulse voltage 150V, pulse width 200μs, ground the workpiece holder, prepare a low-stress dense copper electrode layer for 20min, and turn off the bipolar high energy density pulse power supply after completion.

[0059] (7) A nickel barrier layer and a tin solder layer are deposited in the same vacuum chamber using a vacuum coating method. After the deposition is completed, the power supply and argon gas are turned off. The workpiece is cooled to below 80°C, and the furnace is opened to remove the workpiece, thus obtaining the copper terminal electrode of the MLCC capacitor.

[0060] Example 3

[0061] The difference from Example 1 is that the copper target source process parameters in step (5) are: frequency 120Hz, negative pulse voltage 800V, pulse width 60μs, positive voltage 350V, pulse width 150μs, and the rest are the same as in Example 1.

[0062] Example 4

[0063] The difference from Example 1 is that the copper target bipolar HiPIMS power supply parameters in step (6) are: frequency 180Hz, negative pulse voltage 700V, pulse width 120μs, positive voltage 120V, pulse width 120μs, and the rest are the same as in Example 1.

[0064] Comparative Example 1

[0065] A method for fabricating copper terminal electrodes of an MLCC capacitor includes the following steps:

[0066] (1) Place the MLCC capacitor without terminal electrodes (model 0805X / 106K6R3NBT) in the cleaning solution and ultrasonically clean it for 15 minutes. Then, rinse it with deionized water three times and dry it with hot air at 80°C.

[0067] (2) Place the MLCC in a special fixture and load it onto the workpiece rack in the vacuum chamber. Adjust the target-base distance to 100mm and close the cavity to evacuate the vacuum.

[0068] (3) Start the mechanical pump and molecular pump respectively to evacuate the vacuum to a back-bottom vacuum of 3×10⁻⁶. -3 Below Pa, start the workpiece holder rotation and heat the workpiece to 120°C. Then, turn off the heating power and evacuate the vacuum to 3×10⁻⁶. -3 Below Pa;

[0069] (4) Introduce argon gas at 80 SCCM and a pressure of 0.15 Pa; turn on the ion source of the anode layer at a power of 2.0 kW and ion clean the workpiece for 5 min;

[0070] (5) Turn off the ion source, adjust the argon flow rate to 120 SCCM and the gas pressure to 0.4 Pa, and use conventional magnetron sputtering to complete the copper layer sputtering. The sputtering voltage is a constant 400 V and the sputtering time is 25 min. After completion, turn off the conventional magnetron sputtering power supply.

[0071] (6) Deposit a nickel barrier layer and a tin solder layer in the same vacuum chamber using a vacuum coating method. After the deposition is completed, turn off the power and argon gas, cool the workpiece to below 80°C, and then open the furnace to remove the workpiece.

[0072] Comparative Example 2

[0073] The difference from Example 1 is that the copper target source process parameters in step (5) are: frequency 80Hz, negative pulse voltage 600V, pulse width 40μs, positive voltage 250V, pulse width 90μs, and the rest are the same as in Example 1.

[0074] Comparative Example 3

[0075] The difference from Example 1 is that the copper target source process parameters in step (5) are: frequency 250Hz, negative pulse voltage 950V, pulse width 80μs, positive voltage 450V, pulse width 250μs, and the rest are the same as in Example 1.

[0076] Comparative Example 4

[0077] The difference from Example 1 is that the copper target bipolar HiPIMS power supply parameters in step (6) are: frequency 90Hz, negative pulse voltage 650V, pulse width 80μs, positive voltage 70V, pulse width 80μs, and the rest are the same as in Example 1.

[0078] Comparative Example 5

[0079] The difference from Example 1 is that the copper target bipolar HiPIMS power supply parameters in step (6) are: frequency 250Hz, negative pulse voltage 850V, pulse width 200μs, positive voltage 200V, pulse width 250μs, and the rest are the same as in Example 1.

[0080] Comparative Example 6

[0081] The difference from Example 1 is that the copper target source process parameters in step (5) are: frequency 100Hz, negative pulse voltage 700V, pulse width 100μs, positive pulse voltage 100V, pulse width 100μs;

[0082] In step (6), the power supply parameters of the copper target bipolar HiPIMS are as follows: frequency 100Hz, negative pulse voltage 700V, pulse width 50μs, positive voltage 300V, pulse width 100μs, and others are the same as in Example 1.

[0083] experiment

[0084] Ten samples were randomly selected from Examples 1-4 and Comparative Examples 1-6 to measure the end bonding force and capacitance of the copper terminals of MLCC capacitors (VICTOR 4090A LCR bridge).

[0085] Table 1 Sample Tolerances (Unit: μF)

[0086]

[0087] Note: Any value indicating capacitor failure or abnormally excessive capacitance is considered a sign of capacitor damage.

[0088] Table 2. Sample bonding strength (unit: pounds)

[0089]

[0090]

[0091] Table 3. Copper end electrode thickness of samples (unit: μm)

[0092]

[0093] According to the comparison between Comparative Example 1 and Example 1 in Tables 1 and 2, the copper layer sputtering in Comparative Example 1, which directly uses conventional magnetron sputtering, results in a lower capacitance value and bonding strength of the copper terminal electrode of the MLCC capacitor compared to Example 1. This indicates that using conventional magnetron sputtering to sputter the copper layer cannot solve the problems of poor terminal electrode density, low bonding strength, and thermal stress failure caused by copper burning during the MLCC capacitor fabrication process. In contrast, in Example 1, step (5) uses a short negative high-voltage pulse, and step (6) also uses a short negative high-voltage pulse, with an appropriate reduction in the positive acceleration pulse. This allows for the deposition of a high-density, low-stress copper film at a higher speed, thereby improving the capacitance value and bonding strength of the copper terminal electrode of the MLCC capacitor.

[0094] Comparing Comparative Examples 2-3 with Example 1, it can be seen that the copper target source process parameters in step (5) of Comparative Example 2 are not within the scope of protection of this application. The capacitance value of the copper terminal electrode of the MLCC capacitor is lower than that of Example 1, and the bonding force of the copper terminal electrode of the MLCC capacitor is also lower than that of Example 1. In Comparative Example 3, high-energy coating was used, and the bonding force of the copper terminal electrode of the MLCC capacitor was higher than that of Example 1. However, bombardment with excessively high energy will cause damage to the internal electrode of the capacitor, resulting in abnormal capacitance value. This shows that not all copper target source process parameters can achieve the effect of this invention. In this invention, the negative voltage generates highly ionized copper plasma, and the positive voltage accelerates copper ions and increases ion energy. If the negative voltage is too low, the copper ion content generated will be low. If the positive voltage is too low, the injection effect will be poor, which is not conducive to interface mixing. If the positive voltage is too high, the electric field will interact violently with the plasma, causing abnormal discharge and damaging the film layer. If the negative pulse width is too narrow, the voltage will stop before reaching the peak value, and the voltage will not yet reach a high ionization state. If the negative pulse width is too wide, continuous discharge will also increase the gas ion content. Therefore, this invention controls the pulse voltage and pulse width within a certain range, which can improve the ionization of copper and the energy of copper ions, so that the coating and the electrode can form a better interface mixing, thereby achieving a good connection between the end electrode and the inner electrode.

[0095] Comparing Comparative Examples 4-5 with Example 1, it can be seen that the copper target bipolar HiPIMS power supply parameters in step (6) of Comparative Example 4 are not within the scope of protection of this application. The capacitance of the copper terminal electrode of the MLCC capacitor is lower than that of Example 1, and the bonding force of the copper terminal electrode of the MLCC capacitor is also lower than that of Example 1. The copper target bipolar HiPIMS power supply parameters in step (6) of Comparative Example 5 are also not within the scope of protection of this application. Although the capacitance and bonding force of the copper terminal electrode of the MLCC capacitor are higher than those of Example 1, the thickness of the copper terminal electrode of the MLCC capacitor in Comparative Example 5 is lower than that of Example 1, resulting in a less dense terminal electrode coating. This shows that not all copper target bipolar HiPIMS power supply parameters can achieve the effects of this invention. If the voltage is too low, the plasma generated by the discharge has a low ion content and cannot form an ionized coating; if the voltage is too high, the ion content will increase, which will increase the emission of secondary electrons and increase the content of gas ions. This invention, while ensuring the density of the film layer, appropriately reduces the negative pulse voltage (reducing ionization) and the positive pulse voltage (reducing energy), which can reduce the bombardment of ions on the film surface, increase the film deposition speed, and thus better achieve the purpose of high-speed copper film deposition.

[0096] Comparing Comparative Example 6 with Example 1, it can be seen that in Comparative Example 6, a long negative high-voltage pulse is used in step (5), and a short negative high-voltage pulse is used in step (6). Furthermore, the positive acceleration pulse in step (6) is higher than that in step (5). Compared to Example 1, the long negative pulse in step (5) generates excessive gas ions. Although the bonding strength is slightly improved compared to Example 1, excessive ion bombardment may damage the internal electrode, leading to abnormal capacitance values ​​in some cases. This demonstrates that in this invention, only by using a short negative high-voltage pulse in the early stage and a long negative high-voltage pulse in the later stage, and appropriately reducing the positive acceleration pulse, can an interface mixing layer be formed between the copper electrode and the internal electrode, thereby improving the connection and bonding strength between the internal and external electrodes.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for fabricating copper terminal electrodes of an MLCC capacitor, characterized in that, Includes the following steps: (1) Ultrasonic cleaning, rinsing and drying of MLCC capacitors; (2) Place the cleaned MLCC capacitor on the workpiece rack in the vacuum chamber; (3) Close the vacuum chamber, evacuate the vacuum chamber, and remove the residual polluting gases inside the vacuum chamber; (4) Introduce inert gas, then turn on the ion source of the anode layer and ion clean the workpiece; (5) Turn off the ion source of the anode layer, introduce inert gas, and then turn on the bipolar HiPIMS power supply. Adjust the copper target source process parameters as follows: frequency 100-200Hz, negative pulse voltage 700-900V, pulse width 50-75μs, positive voltage 300-400V, pulse width 100-200μs. Ground the workpiece frame to avoid charge accumulation and prepare the interface mixing layer. (6) Keep the gas flow rate and pressure of the inert gas constant, and adjust the power supply parameters of the copper target bipolar HiPIMS as follows: frequency 100-200Hz, negative pulse voltage 700-800V, pulse width 100-150μs, positive voltage 100-150V, pulse width 100-200μs, ground the workpiece holder, and prepare the copper electrode layer. (7) Turn off the bipolar HiPIMS power supply and the inert gas, cool the workpiece, open the furnace and take out the workpiece to obtain the copper terminal electrode of the MLCC capacitor.

2. The method for preparing the copper terminal electrode of an MLCC capacitor as described in claim 1, characterized in that, The copper target source process parameters in step (5) are: frequency 100-120Hz, negative pulse voltage 700-800V, pulse width 50-60μs, positive voltage 300-350V, pulse width 150-200μs.

3. The method for preparing the copper terminal electrode of an MLCC capacitor as described in claim 2, characterized in that, The copper target source process parameters in step (5) are: frequency 120Hz, negative pulse voltage 800V, pulse width 60μs, positive voltage 350V, pulse width 150μs.

4. The method for preparing the copper terminal electrode of an MLCC capacitor as described in claim 1, characterized in that, The copper target bipolar HiPIMS power supply parameters in step (6) are: frequency 180-200Hz, negative pulse voltage 700-750V, pulse width 100-120μs, positive voltage 100-120V, pulse width 100-120μs.

5. The method for preparing the copper terminal electrode of an MLCC capacitor as described in claim 4, characterized in that, The copper target bipolar HiPIMS power supply parameters in step (6) are: frequency 180Hz, negative pulse voltage 700V, pulse width 120μs, positive voltage 120V, pulse width 120μs.

6. The method for preparing the copper terminal electrode of an MLCC capacitor as described in claim 1, characterized in that, In step (4), the flow rate of the inert gas is 60-100 SCCM and the pressure is 0.1-0.3 Pa.

7. The method for preparing the copper terminal electrode of an MLCC capacitor as described in claim 1, characterized in that, In step (5), the flow rate of the inert gas is 100-150 SCCM and the pressure is 0.3-0.5 Pa.

8. The method for preparing the copper terminal electrode of an MLCC capacitor as described in claim 1, characterized in that, In step (3), a vacuum is drawn to 3×10 -3 Below Pa.

9. The method for preparing the copper terminal electrode of an MLCC capacitor as described in claim 8, characterized in that, In step (3), the MLCC capacitor is first heated to 100-200℃, and then evacuated to 3×10℃. -3 Below Pa.

10. The method for preparing the copper terminal electrode of an MLCC capacitor as described in claim 1, characterized in that, The inert gas is argon.

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