GB2259523A

GB2259523A - Electroplating miniature parts in bulk

Info

Publication number: GB2259523A
Application number: GB9219336A
Authority: GB
Inventors: Masaaki Ono; Kiyoshi Nakagawa; Norio Sakai; Kazuma Tanaka; Yuko Yamaguchi; Shoichi Kawabata
Original assignee: Murata Manufacturing Co Ltd
Current assignee: Murata Manufacturing Co Ltd
Priority date: 1991-09-13
Filing date: 1992-09-11
Publication date: 1993-03-17
Anticipated expiration: 2012-09-11
Also published as: JPH0570999A; GB9219336D0; JP2745892B2; GB2259523B

Abstract

The parts eg. electronic components are introduced with a plurality of steel balls 4 into a container comprising an electrode, and the container dipped in a plating bath, the container being supplied with horizontal and vertical swing motions, thereby stirring the parts and the steel balls, and the container further containing a plurality of insulating bodies 31 which are larger in volume than the parts to further improve the stirring effect for the parts and the steel balls, thereby uniformly plating the respective parts. Swing motion is generated by rotation of eccentric load 17 rotated by motor 15 acting on part 14 held through springs 19 with respect to housing 18. <IMAGE>

Description

TITLE OF THE INVENTION Method of Plating Miniature Parts BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method of plating miniature parts, and more particularl though not exclusively, it relates to a method of plating miniature parts while supplying horizontal and vertical swing motions to a container containing the miniature parts to be plated.

Description of the Background Prt For example, a multilayer ceramic capacitor is provided with external electrodes on both longitudinal ends thereof. In order to form such external electrodes, silver paste, for example, is generally applied onto prescribed positions of a chip for defining the multilayer ceramic capacitor, and baked. However, since silver oxidizable and solde--leachable, surface layers of tin or nickel are formed on substrate layers containing silver such as the silver paste. These surface layers are often formed by plating.

I order to efficiently plate miniature electric parts such as the aforementioned multilayer ceramic capacitors or miniature parts other than electronic parts, a plurality of parts to be plated are generally individually introduced into a proper container, wic in turn is dipped in a plating path for simultaneously plating the plurality of parts. In such a plating method, the container is provided with a cathode or serves as a cathode itself, while an anode is arranged in an appropriate position of the plating bath. Thus, the parts are plated in the container when the same are electrically connected with the cathode.In order to promote such electric connection between the parts and the zathode, the container contains a plurality of steel balls Ln addition to the parts.

In the aforementioned plating method, the parts and the steel balls contained in the container are properly stirred during plating, so that the respective parts are uniformly plated. Barrel plating is known as - method of plating a number of miniature parts while stirring the same. In such barrel plating, a container called a barrel, which is prepared from a net in the fcrm of a hexagonal pole, is employed to contain a plurality of parts to be plated and steel balls. The container is dipped in a plating bath so that its central taxis is horizontally directed, and rotated about the central axis.

Thus, the parts and the steel balls contained in the container are stirred.

In the aforementioned barrel plating method, however, the parts and the steel balls are not necessarily uniformly stirred. Among such parts and steel balls, those in regions close to the wall surfaces of the container tend to remain in such regions, and relatively hardly change places with those in other regions.

Consequently, it is difficult to uniformly plate the parts, while two or more parts and/or steel balls may be plated in sticking states.

Fig. 1 shows a plating apparatus 1, which has been proposed in order to solve this problem. Referring to Fig. 1, a container 2 which is formed by a net, for example, contains a plurality of miniature parts 3 to be plated and a plurality of steel balls 4. The parts 3 such as multilayer ceramic capacitors, for example, are provided on both ends thereof with external electrodes 5.

The container 2 is positioned in a plating vessel 7 containing a plating solution 6.

In order to stir the parts 3 and the steel balls a, this container 2 is coupled to a vibrating head 9 through a coupling rod 8. The vibrating head 9 supplies the container 2 with a reciprocating angular motion in a small angular range about the coupling rod 8, i.e., a horizontal swing motion as shown by arrow 10, thereby stirring the parts 3 and the steel balls 4. In order to upset the parts 3 in such a stirring state, the container 2 is provided with a baffle 11.

In the plating apparatus 1 shown in Fig. 1, however, the parts 3 and the steel balls 4 may be caught in a cavity, which is inevitably defined between the baffle 11 and the wall surface of the container 2. Thus, specific ones of the parts 3 may remain in such a cavity while the other ones are being plated, leading to dispersion in thickness of plating films which are formed on the parts 3 upon completion of plating.

ig. 2 shows another plating apparatus 12 which can solve the aforementioned problem. This plating apparatus 12 comprises a container 13 which is provided with no baffle.

Referring to Fig 2, the plating apparatus 12 comprises a swing motion generating part 14. A motor 15 is mounted on the swing motion generating part 14, while an eccentric load 17 is mounted on a rotary shaft 16 of the motor 15. The swing motion generating part 14 is contained in a fixed housing 18, and hld through a plurality of springs 19 with respect to the housing 18.

A container 13 is coupled to the swing motion generating part 14 through a coupling rod 21 extending through a hole 20 which is provided in the housing 18.

When the eccentric load 17 is rotated following rotation of the motor 15, therefore, the swing motion generating part 14, being held through the springs 19 with respect to the housing 18, makes horizontal and vertical swing motions, which are transmitted to the container 13 through the coupling rod 21.

The container 13 contains a plurality of miniature parts 3 such as multilayer ceramic capacitors, for example, and a plurality of steel balls 4. This container 13 is positioned in a plating vessel 23 confiainin- a plating solution 22.

Fig. 3 is a plan view showing the container ;, which is integrally formed of resin with the coupling rod 21. A plurality of holes 25 and 26 are provided on a bottom wall 24 of the container 13. Nets 27 are fitted in the holes 25 respectively, to allow passage of the plating solution 22 while preventing falling o the parts 3 and the steel balls 4 from the container 13. On the other hand, cathode members 28 are fitted in the holes 26 respectively. As shown in Fig. 2, the cathode members 28 are connected -with lead wires 29, which are wired through the interior of the hollow coupling rod 21.

Fig. 4 shows a flow locus 30 formed by the parts 3 and the steel balls 4 when the parts 3 are plated in the container 13 of the plating apparatus 12. Thus, the parts 3 and the steel balls 4 are sufficiently stirred in the container 13 along the flow locus 30, so that the respective parts 3 can be uniformly plated.

When the parts 3 are plated in the plating apparatus 12, however, the parts 3 may be separated from the steel balls 4 as shown in Fig. 5, such that the steel balls 4 can apply no action on the parts 3. More specifically, the parts 3 tend to gather on the central portion o the container 13, while the steel balls 4 tend to gather on the outer peripheral side of the container 13. Thus, it may be difficult to uniformly plate the respective parts 3 even by the plating apparatus 12.

The inventors have investigated the cause fr the phenomenon shown in Fig. 5, to infer that this phenomenon may be caused by difference in specific gravity between the parts 3 and the steel balls 4. The specific gravity of the parts 3 such as multilayer ceramic capacitors is 3 to 6, while that of the steel balls 4 is about c. On the basis of such difference in specific gravity, it is inferred that the parts 3 gather on the central portion of the container 13 due to the smaller specific gravity, while the steel balls 4 gather on the outer peripheral side of the container 13 due.to the larger specific gravity.

SUMEURY OF THE INVENTION Accordingly, an object of the present invention is, in a method of plating a plurality of miniature parts while supplying horizontal and vertical swing motions to a container containing the miniature parts to be plated and a plurality of steel balls, to enable proper mixture of the parts and the steel balls.

A method of plating miniature parts according to the present invention is characterized in that a container containing a plurality of miniature parts to be plated and a plurality of steel balls further contains a plurality of insulating bodies, respective ones of which are larger in volume than the miniature parts.

The container containing the miniature parts, the steel balls and the insulating bodies is dipped in a plating solution, to be supplied with horizontal and vertical swing motions in this state.

According to the present invention, therefore, it is possible to introduce the insulating bodies bee the respective ones of the parts and the steel balls, while the insulating bodies can be vibrated by the swing motions supplied from the container. Thus, it is possible to sufficiently stir the parts and the steel balls, thereby uniformly plating the parts.

The present invention is effectively applied when the steel balls have the largest specific gravity among the parts, the steel balls and the insulating bodies while the parts and the insulating bodies are substantial lv identical in specific gravity to each other.

The present invention is also effectively applied to plating of electronic parts such as multi layer ceramic capacitors each comprising a plurality of external electrodes on its outer surfaces. The external electrodes comprise substrate layers, and surface layers which are formed by plating.

The insulating bodies preferably have spherical shapes. These insulating bodies are formed of alumina, or by metal bodies covered with silicone resin.

The above and further features of the present invention are set forth with particularity in the appended claims an should become clearer from consideration of the following detailed description of an embodiment of the invention given with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE D?:WINGS Fig. 1 is an illustratIve sectional view showing a conventional plating apparatus 1; Fig. 2 is an illustratIve sectional view showing another conventional plating apparatus 12; Fig. 3 is a plan view cf a container 13 shown in Fig.

2; Fig. 4 is an illustratIve plan view showing a flow locus 30 of parts 3 and steel balls 4 in the container 13 shown in Fig. 2; Fig. 5 is an illustrative sectional view showing the container 13, for illustrating a problem in a plating method which is carried out with. the plating apparatus 12 shown in Fig. 2; Fig. 6 is a sectional view corresponding to Fig. 2, for illustrating a plating method according to an embodiment of the present invention; and Fig. 7 is a sectional view for illustrating movements of parts 3, steel balls 4 and insulating bodies 31 which are made in a container 13 by the plating method shown in Fig. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 6 shows a plating apparatus 12, which is substantially similar to that shown in Fig. 2. This plating apparatus 12 is adapted to carry out a plating method according to an embodiment of the present invention. Referring to Fig. 6, elements corresponding to those shown in Fig. 2 are denoted by similar reference numerals. As to the structure of the plating apparatus i2 shown in Fig. 6, refer to the above description with reference to Figs. 2 to 4.

Referring to Fig. 6, a container 13 contains a plurality of insulating bodies 31, in addition to a plurality of miniature parts 3 and a plurality of steel balls 4. The number of the insulating bodies 31, which are sufficiently larger in volume than the parts 3, is properly decided in consideration of the dimensions of the container 13, the stirring state of the parts 3, and the like. The insulating bodies 31 are preferably formed by balls of alumina, or iron balls which are covered with silicone resin. The insulating bodies 31 are not restricted to the aforementioned spherical shapes, but the same may have polygonal shapes.

The miniature parts 3, such as multilayer ceramic capacitors provided with external electrodes 5, for example, may have lengths o several mm to not more than 1 mm along the longest edges. Such multilayer ceramic capacitors generally have specific gravity c 3 to 6. On the other hand, the steel balls 4 have diameters of about 0.7 to 1.2 mm and specific gravity of about 8, while the insulating bodies 31 have diameters of 10 to 15 mm and specific gravity of 3 to 6. Thus, the insulating bodies 31 are larger in volume than the respective parts 3.

Among the parts 3, the steel balls 4 and the insulating bodies 31, the steel balls 4 have the largest specific gravity, while the parts 3 and the insulating bodies 31 are substantially identical in specific gravity to each other.

Referring to Fig. 7, the parts 3, the steel balls 4 and the insulating bodies 31 flow along the flow locus 30 shown in Fig. 4, when the container 13 is supplied witn horizontal and vertical swing motions. At this time, the insulating bodies 31 are introduced between the parts 3 and the steel balls 4, which tend to gather independently of each other. Further, the insulating bodies 31 which are vibrated by the swing motions of the container 13 stir the parts 3 and the steel balls 4. Thus, the parts 3 and the steel balls 4 appropriately flow along the flow locus 30 shown in Fig. 4, to be properly mixed with each other.

Particularly in this embodiment, the insulating bodies 31 being substantially identical in specific gravity to tn.e parts 3 apply larger actions on the parts 3, which ted to gather on the central portion of the container 13 as shown in Fig. 5.

Thus, the parts 3 are electrically connected with cathode members 28 directly or through the steel balls 4 with a certain probability, whereby plating fIlms are formed to define surface layers of external electrodes 5.

Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being limited only by the terms of the appended claims.

Claims

CLAIMS:

1. A method of plating miniature parts, the method comprising: preparing a container or containing a plurality of miniature parts to be plated, said container comprising an electrode; preparing a plurality of steel balls for promoting electric connection between said miniature parts, being contained in said container, and said electrode; preparing a plurality o insulating bodies being larger in volume than said miniature parts; introducing said miniature parts, said steel balls and said insulating bodies into said container; positioning said container ln a plating vessel containing a plating solution; and supplying said container, being positioned in said plating vessel, with horizontal and vertical swing motions.

2. A plating method in accordance with claim 1, wherein said steel balls have the largest specific gravity among said miniature parts, said steel balls and said insulating bodies, said miniature parts and said insulating bodies being substantially identical in specific gravity to each other.

3. A plating method in accordance with claim 1 or 2, wherein said miniature parts are electronic parts each provided on its outer surfaces with a plurality of external electrodes comprising substrate layers and surface layers, said surface layers being formed by plating.

4. A plating method in accordance with claim 3, wherein said electronic parts are multilayer ceramic capacitors.

5. A plating method in accordance with any preceding claim, wherein said insulating bodies have spherical shapes.

6. A plating method in accordance with any preceding claim , wherein said insulating bodies are made of alumina.

7. A plating method in accordance with any of claims 1 to 5, wherein said insulatina bodIes are formed hy metal bodies being covered with silicone resin.

8. A method of plating miniature components, the method comprising placing a plurality of said components in a container together with electrically insulating bodies which are larger in size than said components and electrically conductive bodies, placing said container in a plating bath and agitating said container.

9. An apparatus for plating miniature components, the apparatus comprising: a plating bath; a container for retaining said components, a plurality of electrically insulating bodies and electrically conductive bodies, the insulating bodies being larger in size than said components and the conductive bodies making an electrical connection between a plating electrode and at least some of said components; and means for agitating said container within said bath, wherein said agitating means causes said insulating bodies to move, said movement resulting in irregular motion of said components with respect to the conductive bodies thereby promoting substantially uniform plating of said components.

10. An apparatus or method substantially as described herein with reference to the accompanying drawings.