Plating apparatus and plating method

A plating apparatus includes a plating tank and a plating unit that performs electrolytic plating on an object. The plating unit includes a workpiece passage region including a partition wall that allows passage of the plating solution but does not allow passage of the object, the workpiece passage region passing the object from above toward below, an injection unit that injects the plating solution from below toward above, a mixing unit that mixes the plating solution injected by the injection unit and the object to be plated passing through the workpiece passage region, an anode outside the workpiece passage region, a cathode inside the workpiece passage region including a hollow region through which a mixed fluid of the plating solution and the object to be plated passes from below toward above, and a guidance unit that guides the mixed fluid to the workpiece passage region.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a plating apparatus and a plating method.

2. Description of the Related Art

In an electronic component, such as a chip multilayer capacitor, Ni plating and Sn Plating is typically performed on a surface of an external electrode included in the electronic component for the purpose of preventing solder corrosion and improving reliability of mounting by soldering.

When plating, such as the Ni plating and the Sn plating, is performed on the electronic component, a barrel plating method is frequently used as disclosed in Japanese Patent Application Laid-Open No. 10-212596.

In performing the barrel plating, a negative electrode terminal is disposed in a barrel to contact a group of objects to be plated in the barrel such that the object to be plated becomes a negative electrode, a positive electrode terminal is disposed outside the barrel so as to be immersed in a plating solution, and current is applied to both of the electrodes to make energization, thus plating the object to be plated.

However, in the conventional barrel plating method, nonuniformity of a current density distribution in the barrel is high, and a variation in thickness of the formed plating film is large.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide plating apparatuses and plating methods each capable of preventing the variation in thickness of the plating film.

According to a preferred embodiment of the present invention, a plating apparatus includes a plating tank in which a plating solution is stored; and a plating unit provided in the plating tank to perform electrolytic plating on an object to be plated. The plating unit includes a workpiece passage region in which at least a portion of the workpiece passage region is surrounded by a partition wall that allows passage of the plating solution but does not allow passage of the object to be plated, the object to be plated being passed from above toward below in the workpiece passage region; an injection unit that injects the plating solution from below toward above; a mixing unit above the injecting unit and below the workpiece passage region, the plating solution injected by the ejection unit and the object to be plated passed through the workpiece passage region being mixed in the mixing unit; an anode outside the workpiece passage region; a cathode inside the workpiece passage region and including a hollow region through which a mixed fluid of the plating solution and the object to be plated mixed by the mixing unit passes from below toward above; and a guidance unit that guides the mixed fluid passing through the hollow region of the cathode to the workpiece passage region.

The partition wall may surround the cathode, the anode may surround the partition wall, and the cathode, the partition wall, and the anode may be concentrically disposed. The partition wall, the mixing unit, the cathode, and the guidance unit may be structured to be separated from the plating apparatus as an integral unit.

The guidance unit may include a plating solution passage unit that allows the passage of the plating solution but does not allow the passage of the object to be plated.

According to a preferred embodiment of the present invention, a plating method includes (a) a step of guiding a mixed fluid including a plating solution and an object to be plated to a workpiece passage region in which at least a portion of the workpiece passage region is surrounded by a partition wall that allows passage of the plating solution but does not allow passage of the object to be plated; (b) a step of performing electrolytic plating on the object to be plated by applying voltage between an anode disposed outside the workpiece passage region and a cathode disposed inside the workpiece passage region when the object to be plated passes through the workpiece passage region from above toward below; and (c) a step of mixing an injected plating solution and the object to be plated passing through the workpiece passage region by injecting the plating solution from below toward above below the cathode, and of passing the mixed fluid of the plating solution and the object to be plated through a hollow region provided inside the cathode from below toward above.

The electrolytic plating may be performed on the object to be plated by repeating the steps (a), (b), and (c).

According to preferred embodiments of the present invention, electrolytic plating is performed while the object to be plated is passed through the workpiece passage region sandwiched between the anode and the cathode, so that satisfactory plating is able to be performed with a stable current density. Consequently, variations in thickness of the formed plating film are able to be prevented.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, a multilayer ceramic capacitor that is a representative chip electronic component is used as an object to be plated, and a plating apparatus used to perform electrolytic plating on an external electrode provided on a surface of the multilayer ceramic capacitor will be described.

FIG. 1is a front sectional view illustrating a plating apparatus100according to a preferred embodiment of the present invention, andFIG. 2is a sectional view taken along a line II-II inFIG. 1.

As illustrated inFIGS. 1 and 2, the plating apparatus100includes a plating tank10that stores a plating solution1and a plating unit20that is provided in the plating tank10to perform the electrolytic plating on an object to be plated2.

When the electrolytic plating is performed on the object to be plated2, the plating solution1is stored in the plating tank10up to a position above an upper end of a cathode26(to be described later).

The plating unit20includes a workpiece passage region23in which at least a portion of the workpiece passage region23is surrounded by a partition wall22that allows passage of the plating solution1but does not allow passage of the object to be plated2, the object to be plated being passed from above toward below in the workpiece passage region; an injection unit24that injects the plating solution1from below toward above; a mixing unit25disposed above the injection unit24and below the workpiece passage region23to mix the plating solution1injected by the injection unit24and the object to be plated2passing through the workpiece passage region23; an anode21disposed outside the workpiece passage region23; a cathode26disposed inside the workpiece passage region23and including a hollow region26athrough which a mixed fluid3of the plating solution1and the object to be plated2mixed by the mixing unit25passes from below toward above; and a guidance unit27that guides the mixed fluid3passing through the hollow region26aof the cathode26to the workpiece passage region23.

Voltage is applied from a power supply31to the anode21and the cathode26. At this point, the anode21is used as a positive electrode, and the cathode26is used as a negative electrode.

The partition wall22defining the workpiece passage region23preferably has a cylindrical or substantially cylindrical shape, and is made of, for example, a mesh. As described above, the plating solution1is able to pass through the partition wall22, but the object to be plated2cannot pass through the partition wall22. In the present preferred embodiment, an upper portion and a lower portion of the partition wall22do not have liquid permeability. The workpiece passage region23is a region between the partition wall22and the cathode26(to be described later) disposed inside the partition wall22.

The injection unit24includes a circulation line32, a pump33, and a filter34.

The circulation line32is a flow channel of the plating solution1in order to inject the plating solution1in the plating tank10from an injection port24aprovided at a bottom of the plating tank10.

The pump33is provided in the circulation line32, and causes the plating solution1in the plating tank10to be injected from the injection port24athrough the circulation line32.

The filter34removes foreign matter included in the plating solution1flowing through the circulation line32.

The mixing unit25is disposed above the injection unit24and below the workpiece passage region23and the cathode26. The mixing unit25preferably has a truncated cone shape in which a diameter of a top surface is larger than a diameter of a bottom surface. The diameter of the top surface is preferably greater than or equal to an inner diameter of a portion, which does not have liquid permeability and is provided below the partition wall22. The diameter of the bottom surface is preferably equal or substantially equal to the diameter of the injection port24aof the injection unit24. The top surface of the mixing unit25is open and communicates with the workpiece passage region23and the hollow region26aof the cathode26. The bottom surface of the mixing unit25is also open and communicates with the injection port24a. The truncated cone-shaped air gap defining the mixing unit25is formed by drilling a through hole corresponding to the truncated cone shape of the mixing unit25in a member25ahaving the same or substantially the same thickness as a height dimension of the mixing unit25.

The mixing unit25is a region in which a fluid including the object to be plated2and the plating solution1that passes through the workpiece passage region23while sinking, the fluid having high percentage of the sedimentation-thickening object to be plated2, and the plating solution1injected upward from the injection port24aare mixed together, and is a region in which a fluid including the object to be plated2at a high rate by the injection force of the plating solution1injected from the injection port24ais mixed with the plating solution1in a process of guiding the fluid to the hollow region26a.

The cathode26is preferably a metal pipe, for example, and disposed inside the workpiece passage region23. The cathode26includes an inner hollow portion, and the inner hollow portion defines a hollow region26athrough which the mixed fluid3of the plating solution1and the object to be plated2pass from below toward above. The upper end of the cathode26is located above the upper end of the partition wall22.

The anode21preferably has a cylindrical or substantially cylindrical shape, and is disposed outside the workpiece passage region23. As illustrated inFIG. 2, the partition wall22surrounds the cathode26, and the anode21surrounds the partition wall22. As illustrated inFIG. 2, the cathode26, the partition wall22, and the anode21are concentric such that center axes of the cathode26, the partition wall22, and the anode21are aligned with one another.

That is, a region between an inner circumferential surface of the partition wall22and the outer circumferential surface of the cathode26, which are concentrically surrounded, define the workpiece passage region23. Consequently, current density is made uniform during the plating, and a uniform plating film is able to be formed. Because of the uniform current density, a region in which the current density exceeds the limiting current density does not exist as long as the current density is increased within a limiting current density range, so the current density is able to be set higher to enhance productivity.

In order to make the current density in the workpiece passage region23uniform, a mask member is provided between the partition wall22and the anode21so as to surround the lower portion of the workpiece passage region23.

The guidance unit27includes a truncated cone unit27aand a plating solution passage unit27b. The plating solution passage unit27bhaving an annular shape is provided on the truncated cone unit27a, and is structured such that the plating solution1is able to pass through the plating solution passage unit27bbut the object to be plated2cannot pass through the plating solution passage unit27b. The truncated cone unit27apreferably has a truncated cone shape in which the top surface is larger than the bottom surface. The top and bottom surfaces of the truncated cone unit27aare open surfaces, and a side surface of the truncated cone unit27ais structured such that both of the plating solution1and the object to be plated2cannot pass through the side surface. The diameter of the bottom surface of the truncated cone unit27ais preferably less than or equal to the inner diameter of a portion, which does not have liquid permeability and is above the partition wall22. With this structure, in the mixed fluid3of the plating solution1and the object to be plated2injected from the upper end of the hollow region26aof the cathode26, the object to be plated2is able to be naturally guided to the workpiece passage region23.

Above the cathode26, a top plate28is provided such that the object to be plated2included in the mixed fluid3injected from the upper end of the hollow region26aof the cathode26is prevented from jumping to the outside of the guidance unit27.

As illustrated inFIG. 3, the partition wall22, the mixing unit25, the cathode26, and the guidance unit27are structured to be separated from the plating apparatus100as an integral unit. Hereinafter, the partition wall22, the mixing unit25, the cathode26, and the guidance unit27defining the separable integral unit, are also referred to as a separation unit30.

As illustrated inFIG. 4, the lower portion of the separation unit30, namely, a leading end40provided below the mixing unit25is able to be removed. A diaphragm40a, through which the plating solution1is able to pass but the object to be plated2cannot pass, is provided at the leading end40. While the object to be plated2is currently subjected to the plating, the object to be plated2does not drop in the injection port24abecause the diaphragm40ais provided.

A method for performing the plating on the object to be plated2according to a preferred embodiment of the present invention using the plating apparatus100having the above-described configuration will be described below.

In a plating method according to a preferred embodiment of the present invention, the plating is performed on the object to be plated2by sequentially repeating the following steps: (a) a step of guiding the mixed fluid3of the plating solution1and the object to be plated2to the workpiece passage region23in which at least a portion of the workpiece passage region23is surrounded by the partition wall22that allows the passage of the plating solution1but does not allow the passage of the object to be plated2, (b) a step of performing the electrolytic plating on the object to be plated2by applying a voltage between the anode21disposed outside the workpiece passage region23and the cathode26disposed inside the workpiece passage region23when the object to be plated2passes through the workpiece passage region23from above toward below, and (c) a step of mixing an injected plating solution1and the object to be plated2passing through the workpiece passage region23by injecting the plating solution1from below the cathode26toward above, and of passing the mixed fluid3of the plating solution1and the object to be plated2through the hollow region26aprovided inside the cathode26from below toward above.

The step (a) is a step of guiding the mixed fluid3of the plating solution1and the object to be plated2to the workpiece passage region23in the guidance unit27. In the mixed fluid3of the plating solution1and the object to be plated2that passes through the hollow region26aof the cathode26, a portion of the plating solution1flows out to the outside of the guidance unit27through the plating solution passage unit27b. While the object to be plated2included in the mixed fluid3sinks due to its own weight, and the object to be plated2is guided to the workpiece passage region23along the shape of the truncated cone unit27a.

That is, in the mixed fluid3of the plating solution1and the object to be plated2injected from the upper end of the cathode26, the object to be plated2is separated from the plating solution1by sedimentation. The object to be plated2is separated from the plating solution1without applying external force, so that scratching on the surface of the object to be plated2and other damage is prevented after the plating treatment. The guidance unit27includes the plating solution passage unit27b, which allows a portion of the plating solution1included in the mixed fluid3to flow out to the outside of the guidance unit27through the plating solution passage unit27bto quickly separate the plating solution1from the object to be plated2.

In the step (b), the object to be plated2guided to the workpiece passage region23in the step (a) passes through the workpiece passage region23from above toward below. At this point, by applying voltage between the anode21and the cathode26, the electrolytic plating is performed on the object to be plated2as it moves in the workpiece passage region23.

More specifically, in the step (b), the object to be plated2guided to the workpiece passage region23is deposited in the workpiece passage region23, and gradually lowered while deposited. As described above, the cathode26, the partition wall22, and the anode21are concentrically disposed such that the center axes of the cathode26, the partition wall22, and the anode21are aligned with one another, so that the stable and satisfactory plating is able to be performed on the object to be plated2passing through the workpiece passage region23with high uniformity of a current density distribution. Consequently, the variation in thickness of the plating film is prevented and a plating film having uniform thickness is formed.

As described above, the upper portion and the lower portion of the partition wall22do not have liquid permeability. The upper portion of the partition wall22does not have liquid permeability, which prevents an influence of the liquid flow from the truncated cone unit27adisposed on the upper side of the workpiece passage region23. The lower portion of the partition wall22does not have liquid permeability, which prevents an influence of the liquid flow of the plating solution1injected from below the workpiece passage region23. Consequently, the object to be plated2is able to stably pass through the workpiece passage region23.

In the step (c), the plating solution1in the plating tank10is injected from the injection port24athrough the circulation line32in the injection unit24. The object to be plated2that passes through the workpiece passage region23is mixed with the plating solution1injected from the injection port24ain the mixing unit25by suction force of a jet flow from the injection port24a. At this point, the object to be plated2that is lowered while being deposited in the workpiece passage region23is loosened by shearing force of the jet flow from the injection port24ain the mixing unit25, and dispersed in the plating solution1to form the mixed fluid3. By the jet flow from the injection port24a, the mixed fluid3of the plating solution1and the object to be plated2passes through the hollow region26aof the cathode26from below toward above, and is injected upward from the upper end of the hollow region26a.

In this manner, in the injection unit24, the plating solution1is injected from the injection port24aby actuating the pump33, such that the mixed fluid3of the plating solution and the object to be plated2is passed through the hollow region26aof the cathode26and injected upward from the upper end of the hollow region26a.

The mixed fluid3of the plating solution1and the object to be plated2that is injected upward from the upper end of the hollow region26ais guided to the workpiece passage region23in the step (a).

Thereafter, the steps (a), (b), and (c) are repeated in this order, so that the electrolytic plating is performed on the object to be plated2. Consequently, because the object to be plated2passes through the workpiece passage region23a plurality of times, the variation in thickness of the plating film in each object to be plated2is decreased, and the plating film having a desired thickness is able to be obtained.

As described above, according to the plating apparatus100of the present preferred embodiment, the object to be plated2flows in the vertical direction, so that the plating apparatus100has a vertically long shape. Thus, as compared with the conventional plating apparatus in which a rotating barrel including a rotating shaft in the horizontal direction is used, a floor area required to install the apparatus is able to be reduced, and area productivity is improved.

Additionally, because a driving source that fluidizes the object to be plated2includes only the pump33that fluidizes the plating solution1, the structure of the plating unit20is simplified and the maintenance costs are reduced.

When the electrolytic plating is completed, the plated object to be plated2is cleaned. In order to clean the object to be plated2, the separation unit30, namely, the partition wall22, the member25adefining the mixing unit25, the cathode26, and the guidance unit27are removed, as an integral unit, from the plating tank10. When the separation unit30is removed, the plating solution1flows out to the outside through the partition wall22. On the other hand, the object to be plated2does not flow out to the outside, but remains in the workpiece passage region23and the mixing unit25.

After the plating solution1flows out to the outside through the partition wall22, the separation unit30is set in a separately-prepared cleaning tank50as illustrated inFIG. 5. Specifically, the leading end40of the separation unit30is connected to an injection port51aprovided at the bottom of the cleaning tank50. In the cleaning tank50, a cleaning solution is stored up to the position above the upper end of the cathode26.

Although the injection unit24is provided in the plating apparatus100inFIG. 1, an injection unit51having the same or substantially the same configuration is also provided in the cleaning tank. The injection unit51includes a circulation line52, a pump53, and a filter54that removes the foreign matter.

During the cleaning of the plated object to be plated2, the pump53is actuated to inject the cleaning solution in the cleaning tank50from an injection port51athrough the circulation line52. Consequently, in the mixing unit25, the cleaning solution injected from the injection port51aand the object to be plated2are mixed and flow through the hollow region26aof the cathode26from below toward above. In the mixed fluid of the cleaning solution and the object to be plated2that exits out from the upper end of the hollow region26a, a portion of the cleaning solution passes through the plating solution passage unit27bof the guidance unit27, and flows to the outside of the guidance unit27. Although the object to be plated2included in the mixed fluid sinks down due to its own weight, the object to be plated2is guided to the workpiece passage region23along a shape of the truncated cone unit27aof the guidance unit27at that time.

The object to be plated2that moves from above toward below in the workpiece passage region23is mixed with the cleaning solution in the mixing unit25, and flows again from below toward above in the hollow region26aof the cathode26. In this manner, the object to be plated2is cleaned while being circulated, which allows the object to be plated2to be cleaned in a short time.

Because the object to be plated2is able to be cleaned while cleaning liquid is circulated, a small amount of the cleaning liquid is able to be used, and an amount of drained cleaning liquid is reduced.

After the object to be plated2is cleaned, the separation unit30is moved upward, and the leading end40is removed, which allows the plated object to be plated2to be removed from below the mixing unit25. Consequently, the plated object to be plated2is easily removed. Whether the object to be plated2remains in the partition wall22is able to be visually confirmed, so that the plating treatment is prevented from being performed on another type of an object to be plated while the object to be plated2remains in the separation unit30.

In Example 1 of a preferred embodiment of the present invention, a multilayer ceramic capacitor having a length of about 2.0 mm, a width of about 1.25 mm, and a thickness of about 1.25 mm, for example, was prepared as the object to be plated2, and Ni plating and Sn plating were performed on the external electrodes of the multilayer ceramic capacitor. As described later, after the Ni plating was performed on the object to be plated2, the Sn plating was performed on the object to be plated2.

In the plating apparatus100having the configuration shown inFIGS. 1 and 2, a portion having liquid permeability in the cylindrical partition wall22was made of a mesh material of about 80 mesh, the diameter of the portion was about 70 mm, and the length of the portion was about 100 mm, for example. Portions which do not have the liquid permeability are located above and below the liquid-permeability portion, and the portions were defined by a pipe having the diameter of about 70 mm and the length of about 40 mm, for example.

A truncated cone unit27ahaving an apex angle of about 90 degrees, for example, is provided above the partition wall22. The diameter of the opening lower surface of the truncated cone unit27ais equal or substantially equal to the diameter of the partition wall22. The plating solution passage unit27bmade of a mesh material is disposed above the truncated cone unit27. The mixing unit25having the apex angle of about 90 degrees, for example, was provided below the partition wall22.

A stainless steel pipe having an outer diameter of about 35 mm and an inner diameter of about 25 mm, for example, was used as the cathode26disposed inside the partition wall22. The gap between the lower end of the pipe and the lower end of the mixing unit25having a truncated cone shape is several tens millimeters, and the upper end of the pipe is disposed near the center in the height direction of the truncated cone unit27a. The pipe was suspended from above, and connected to the negative electrode of the power supply31.

On the outside of the partition wall22, a titanium anode case having an annular shape was disposed with a spacing of about 60 mm, for example, therebetween. A space that is able to be filled with a Ni chip was provided in the anode case, and the space was filled with the Ni chip. The anode case filled with the Ni chip was connected to the positive electrode of the power supply31to define the anode21.

A Watt bath was used as the plating solution stored in the plating tank10. As described above, the injection port24ais provided at the bottom of the plating tank10. The leading end40provided below the mixing unit25was mounted so as to be fitted in the injection port24a. The plating solution was stored in the plating tank10up to a position above the upper end of the cathode26.

By actuating the pump33of the injection unit24, the plating solution1in the plating tank10is injected upward from the injection port24athrough the circulation line32. The plating solution1injected from the injection port24apasses through the hollow region26aof the cathode26, and is injected upward from the upper end of the cathode26.

About 70000 multilayer ceramic capacitors as the object to be plated2and about 300 cc conductive medium having a diameter of about 1.5 mm, for example, were input to the plating tank10, more specifically, to the inside of the plating solution passage unit27bhaving an annular shape. The input object to be plated2sank, and was gradually lowered while deposited in the workpiece passage region23. The object to be plated2was attracted to the mixing unit25by the jet flow of the plating solution1from the injection port24a, mixed with the plating solution1in the mixing unit25, and injected upward through the hollow region26aof the cathode26. In the mixed fluid3of the ejected plating solution1and the object to be plated2, a portion of the plating solution1passed through the plating solution passage unit27bof the guidance unit27, flowed out to the outside of the guidance unit27, and was injected from the injection port24athrough the circulation line32. On the other hand, the object to be plated2was guided to the workpiece passage region23through the truncated cone unit27aof the guidance unit27together with the other portion of the plating solution1, namely, the plating solution1that does not flow out to the outside of the guidance unit27, and gradually lowered in the workpiece passage region23while being deposited.

In this manner, while the object to be plated2was repeatedly circulated, the power supply31was turned on, energization was performed at about 24 A, for example, and the voltage was applied between the anode21and the cathode26. The energization was made for about 90 minutes to supply a predetermined integrated current, and then the power supply31was turned off. The separation unit30was removed from the plating tank10, and the plating solution1in the plating tank10was drained. Then, the separation unit30was immersed in the cleaning tank50filled with pure water used as a cleaning solution.

As described above, the injection port51ais provided in the cleaning tank50, and the leading end40of the separation unit30is connected to the injection port51ato actuate the pump53, such that the object to be plated2was cleaned while being circulated through the path of the workpiece passage region23, the mixing unit25, the hollow region26aof the cathode26, and the guidance unit27. Then, the separation unit30was removed and moved to another cleaning tank, and the same washing process was performed. This washing treatment was repeated three times.

After the object to be plated2is cleaned, the separation unit30was immersed in the plating tank10filled with the Sn plating solution, and the Sn plating was performed on the object to be plated2by a procedure similar to the Ni plating. The condition that the anode21and the cathode26were energized was set to about 17 A for about 60 minutes, for example.

After the Sn plating was performed on the object to be plated2, the object to be plated2was cleaned similarly to after the Ni plating.

After the cleaning of the object to be plated2, as illustrated inFIG. 6, the separation unit30was removed from the injection port51aof the cleaning tank50while the cleaning water was immersed at least up to the upper end of the partition wall22, and a recovery container60made of a mesh material having a structure in which a main portion did not allow the passage of the object to be plated2but allowed the passage of the plating solution1was disposed below the removed separation unit30. The leading end40(seeFIGS. 3 and 4) provided below the separation unit30was removed. Consequently, the object to be plated2deposited in the workpiece passage region23and the mixing unit25sank and was recovered in the recovery container60. At this point, the entire object to be plated2was recovered in the recovery container60by allowing the cleaning water to flow from above the separation unit30.

As described above, the recovery container60included the liquid passage portion made of the mesh material which allowed the passage of the plating solution1but did not allow the passage of the object to be plated2, so that the cleaning water could flow out to the outside of the recovery container60to recover only the plated object to be plated2when the recovery container60was moved upward.

After the object to be plated2was recovered in the recovery container60, the separation unit30was moved upward and observed from above, which enables checking that the object to be plated2did not remain in the hollow region26aof the cathode26and the workpiece passage region23. The cathode26and the region holding the cathode26in the upper portion were removed, and the outer surface of the cathode26was observed to check whether the object to be plated2adhered thereto.

When the thickness of the Sn film of the object to be plated2recovered in the recovery container60was measured at30locations with a fluorescent x-ray film thickness meter, the average film thickness was about 3.95 μm, and CV (standard deviation/average value) was as good as about 6.7%. On the other hand, in the case that the plating film was formed by the conventional barrel plating method in which the rotating barrel was used, CV was greater than or equal to about 10% and less than or equal to about 15%. That is, with the plating apparatus100of the present preferred embodiment, the variation in thickness of the formed plating film is significantly decreased.

In the conventional barrel plating method in which the rotating barrel is used, a ridgeline of the object to be plated2is smoothed by scratching between the objects to be plated or collision between the object to be plated and the inner wall of the barrel. However, according to the plating method of Example 1, it was confirmed that the scratching did not occur by observing the surface of the Sn plating film, particularly the ridgeline. That is, with the plating apparatus100of the present preferred embodiment, impact force applied to the object to be plated2during the plating treatment is reduced.

In the conventional barrel plating apparatus in which the rotating barrel is used, the rotating barrel rotates around the horizontal axis. In order to avoid extreme concentration of current density, the anode is required to be disposed in parallel or substantially in parallel with the rotation axis at a position at which the anode stays at a predetermined distance from the barrel. For this reason, in the case of the conventional barrel plating apparatus in which the rotating barrel is used, the floor area of the plating tank is enlarged, for example, a floor area of about 500 mm in length×about 600 mm in width is required. On the other hand, with the plating apparatus100of the present preferred embodiment, the floor area of the plating tank10is, for example, about 300 mm in length×about 300 mm in width, and the floor area is reduced to less than or equal to about ⅓ as compared with the conventional barrel plating apparatus in which the rotating barrel is used.

As described above, in the plating apparatus100of the preferred embodiment, the partition wall22, the mixing unit25, the cathode26, and the guidance unit27are structured to be define an integral unit that is able to be separated as the separation unit30. Thus, after the plating treatment, the separation unit30is removed from the plating tank10, and transferred to the cleaning tank50, which enables easy cleaning of the object to be plated2.

The cleaning is performed by circulating the object to be plated2in the cleaning tank50, so that the cleaning is able to be performed in a short time. The uniformity of the cleaning solution in the cleaning tank is also achieved in a short time by circulating the cleaning solution, so that an excellent cleaning effect is obtained.

In Example 2 of a preferred embodiment of the present invention, the Ni plating and the Sn plating were performed on the external electrodes of the multilayer ceramic capacitor having the length of about 4.5 mm, the width of about 3.2 mm, and the thickness of about 2.0 mm, for example, using the same plating apparatus100as that of Example 1. The presence or absence of cracking and chipping of the multilayer ceramic capacitor after the plating treatment was observed. The method for performing the Ni plating and the Sn plating was the same or substantially the same as Example 1.

Similarly to Example 1, the smoothing of the surface of the Sn film after the Sn plating was not observed, but the deposited Sn film remained. On the other hand, in the conventional barrel plating method in which the rotating barrel was used, the smoothing is produced at the ridgeline of the object to be plated, the Sn film was peeled off, and the inside external electrode was visible.

In either one of the plating method according to a preferred embodiment of the present invention and the conventional barrel plating method in which the rotating barrel is used, the cracking and the chipping were not observed when the appearance of 1000 plated objects to be plated were observed.

The plated object to be plated was returned to the plating apparatus again, a mixing treatment was additionally performed for about 10 hours, and the appearance of the object to be plated was observed. That is, the plated object to be plated using the plating apparatus100according to a preferred embodiment of the present invention was returned to the plating apparatus100, the plated object to be plated by the conventional barrel plating method was returned to the rotating barrel, and the mixing treatment was performed. The mixing treatment is similar to the plating treatment, but the mixing treatment differs from the plating treatment in that the energization is not provided to the anode and the cathode.

When the mixing processing was performed in the rotating barrel, the chipping was generated in the ridgelines of three objects to be plated out of the 1000 objects to be plated. On the other hand, in the case that the mixing treatment was performed using the plating apparatus100, the cracking and the chipping were not generated in any of the 1000 objects to be plated.

That is, in the plating apparatus100, the external force applied to the object to be plated during the plating treatment is reduced, and the cracking and the chipping of the object to be plated were not generated.

In the above-described preferred embodiments, by way of example, the multilayer ceramic capacitor is used as the object to be plated, and the plating is performed on the external electrode. However, there is no particular limitation on a type of the object to be plated and the object that should be plated. For example, a laminated coil component may be used as the object to be plated, and the plating may be performed on the surface conductor of the laminated coil component.

In the above-described preferred embodiments, the cathode26, the partition wall22, and the anode21are concentrically disposed such that the center axes of the cathode26, the partition wall22, and the anode21are aligned with one another. However, the cathode26, the partition wall22, and the anode21are not necessarily concentrically disposed. For example, the center axis of each of the cathode26, the partition wall22, and the anode21may not be aligned with one another, or sectional shapes of the cathode26, the partition wall22, and the anode21in the horizontal direction may not be circular or substantially circular, and instead, may be an elliptical, for example. Even in such a configuration, the electrolytic plating is performed while the object to be plated2is passed through the workpiece passage region23sandwiched between the anode21and the cathode26, which enables good plating with stable current density. Thus, the variation in thickness of the plating film is able to be prevented. However, when the cathode26, the partition wall22, and the anode21are concentrically disposed, the current density distribution is able to be more uniform during the plating, and the formed plating film is more uniform. Thus, preferably the cathode26, the partition wall22, and the anode21are concentrically disposed.

The present invention is not limited to the above-described preferred embodiments in other respects, but various applications and modifications may be made within the scope of the present invention.