JPH06330398A - Method for plating and device therefor - Google Patents

Abstract

PURPOSE:To provide a method and device for plating capable of suppressing the oxidation of a metallic ion in a plating bath and prolonging the life of the plating bath. CONSTITUTION:At the time of electroplating by dipping electronic parts 13 as a member to be plated in the plating bath 11, an inert gas is supplied from an inert gas introducing pipe 17 and a plating metal aq. solution 12 is bubbled by inert gas bubbles 18. Thus, products are plated in the same plating bath over a long time.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dipping a member to be plated in a plating bath for electroplating and an apparatus therefor, and in particular, it is provided with a process and a structure capable of preventing deterioration of the plating bath over time. And a plating apparatus.

2. Description of the Related Art Conventionally, a plating method has been adopted as one of methods for forming external electrodes of electronic parts. Figure 2
It is sectional drawing which shows the multilayer capacitor as an example of an electronic component. In the multilayer capacitor 1, a plurality of internal electrodes 3 to 6 are arranged in a ceramic sintered body 2 so as to overlap with each other with a ceramic layer interposed therebetween. External electrodes 7 and 8 are formed on both end surfaces of the ceramic sintered body 2, respectively. The external electrodes 7 and 8 are respectively composed of first external electrode layers 7a and 8a made of Ag, second external electrode layers 7b made of Ni, and
8b and the third outer electrode layers 7c and 8c made of tin or solder formed on the outermost layer. As described above, the external electrodes 7 and 8 having the three-layer structure are formed because the solder is eroded by Ag during the mounting process by the second Ni electrode.
This is to prevent the external electrode layers 7b and 8b and to form the third external electrode layers 7c and 8c made of tin or solder on the outermost layer to improve the solderability. By the way, the outermost external electrode layers 7c and 8c are formed by electroplating tin or solder, but the plating bath deteriorates with time as will be described below by taking tin plating as an example. There was a problem. That is, as a tin plating bath used when forming an external electrode of an electronic component, a neutral bath is generally used in order to prevent performance deterioration of the electronic component. However, tin ions are easily oxidized from divalent ions to tetravalent ions in a neutral aqueous solution to cause precipitation. Therefore, a method has been adopted in which an organic acid or the like is mixed in the plating bath to complex-ionize the divalent tin ions to stabilize the divalent tin ions in the plating bath. However, even if the tin ions are complex-ionized and stabilized as described above, the divalent tin ions are gradually oxidized while the tin plating bath is used for a long period of time.
It is inevitable that the number of tin ions will increase. This tetravalent tin ion does not participate in the electrochemical reaction for plating, and when the tetravalent tin ion increases, it interferes with the plating reaction of the divalent tin ion and hydrogen gas is easily generated. As a result, there has been a problem that poor quality of electronic components and poor plating occur. Therefore, conventionally, when the tetravalent tin ion concentration increased with time, it was necessary to replace the entire plating bath. Although the above description has been made by taking the tin plating bath as an example, in the case of the solder plating bath as well, the increase of tetravalent tin ions similarly compels the complicated replacement work of the plating bath. An object of the present invention is to provide a plating method and a plating apparatus capable of preventing the plating bath from deteriorating due to the oxidation of metal ions involved in plating in the plating bath and extending the life of the plating bath. To provide.

The invention according to claim 1 is characterized in that when the member to be plated is immersed in a plating bath for electroplating, the plating bath is bubbled with an inert gas. It is a plating method. Further, the invention according to claim 2 is an apparatus used in the above plating method, which comprises a plating bath for dipping and electroplating a member to be plated, and a bubbling of an inert gas in the plating bath. A plating apparatus comprising an inert gas introducing unit. The plating method and the plating apparatus of the present invention are common in that they have the characteristic of bubbling an inert gas in the plating bath as described above, and the bubbling by the inert gas is performed with the metal ions and oxygen to be plated. This is done to suppress the contact of As the inert gas, for example, nitrogen, helium, neon, argon or the like can be used. The bubbling condition cannot be uniquely determined because it varies depending on the size of the plating bath, the type of plating bath, etc., but is not particularly limited as long as the inert gas can be sufficiently dispersed in the plating bath. Absent. Further, as the above-mentioned inert gas introducing means in the plating apparatus of the present invention, for example, a structure in which an inert gas introducing pipe is immersed in a plating bath, or a structure for introducing an inert gas from a hole opened in the wall surface of the plating bath, etc. It is possible to adopt an appropriate structure capable of bubbling an inert gas in the plating bath.
Further, the plating method and the plating apparatus of the present invention are preferably used when tin or solder is plated as an external electrode of an electronic component, but the member to be plated is not particularly limited to the electronic component, and a general component is required. It can be used for plating on plated members, and the metal to be plated is not limited to tin or solder, but can also be used for plating tin alloy such as tin-bismuth or iron. it can.

In the plating method and the plating apparatus of the present invention, since the inert gas is bubbled in the plating bath, the dissolved oxygen in the plating bath is expelled by the inert gas like nitrogen substitution, or the inert gas is removed. Oxidation of metal ions in the plating bath is suppressed, probably because the bubbles float on the surface of the plating bath. Therefore, since the oxidation of the metal ions in the plating bath is suppressed over time, deterioration of the plating bath can be prevented and the life of the plating bath can be extended.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be clarified by describing non-limiting examples of the present invention. FIG. 1 is a schematic configuration diagram for explaining the plating apparatus of the present invention.
An aqueous solution 12 in which metal ions to be plated, for example, divalent tin ions are dissolved is stored in the plating bath 11. In this aqueous solution 12, an electronic component 1 as a member to be plated
3 is immersed. The electronic component 13 includes an external electrode 14,
The outer surface of each of the external electrodes 14 and 15 is plated with the present plating apparatus as described below to form the outermost external electrode layer. Reference numeral 16 denotes an anode, to which a voltage is applied between the external electrodes 14 and 15. In the plating apparatus of this embodiment, the aqueous solution 12 is used in the above plating apparatus.
An inert gas introducing pipe 17 is inserted therein, and the inert gas introducing pipe 17 is supplied with an inert gas in the direction of arrow A shown by an inert gas supplying means (not shown). Therefore,
An inert gas is bubbled through the aqueous solution 12 from the tip 17a of the inert gas introduction pipe 17, and the inert gas bubble 1
8 is dispersed in the aqueous solution 12. By dispersing the bubbles 18 of the inert gas in the aqueous solution 12, the dissolved oxygen in the aqueous solution 12 is expelled and the oxidation of metal ions is suppressed. Further, it is considered that since the bubbles 18 continuously float on the surface of the aqueous solution 12, the dissolution of oxygen in the air into the aqueous solution 12 is suppressed. Therefore, as is clear from the experimental examples described below, the oxidation of metal ions in the plating bath over time can be suppressed, and the life of the plating bath can be extended. Next, a specific experimental example will be described. In order to confirm the effect of the above example, a neutral tin plating bath storing a divalent tin ion-containing aqueous solution was prepared. The amount of the tin ion aqueous solution in the prepared tin plating bath was 1 liter, and nitrogen gas was supplied at a flow rate of 50 ml / min using an inert gas introduction tube having a tip hole diameter of 5 mm to perform bubbling. The bath temperature of the plating bath was 40 ° C.
The tetravalent tin ion concentration in the plating bath after one month was measured. The results are shown in Table 1 below. For comparison, except that nitrogen gas is not bubbled,
Similarly prepared, the bath temperature of the plating bath was 25 ° C, 40
Each of the plating baths of 50 ° C. and 50 ° C. was prepared and left for one month while maintaining the bath temperature. The concentration of tetravalent tin ions was measured for the plating baths at each bath temperature after standing. The results are also shown in Table 1 below.

[Table 1] As is clear from Table 1, when nitrogen gas was not bubbled, the generation rate of tetravalent tin ions increased as the bath temperature of the plating bath increased. This is presumably because the oxidation reaction from divalent tin ions to tetravalent tin ions progresses faster as the bath temperature increases. On the other hand, even when the bath temperature was 40 ° C., when nitrogen gas was bubbled, the generation rate of tetravalent tin ions was about 1/10 of that when nitrogen gas was not bubbled. That is, by bubbling nitrogen gas, 2
It can be seen that the oxidation reaction from tetravalent tin ions to tetravalent tin ions can be significantly suppressed. Next, in order to stabilize the quality of the member to be plated, the concentration of tetravalent tin ions in the tin plating bath was controlled to, for example, 30 g / l or less. That is, when the tetravalent tin ion concentration exceeds 30 g / l,
Assuming that the life of the plating bath was exhausted, the life of each plating bath was measured. The results are shown in Table 2 below.

[Table 2] As is clear from Table 2, in the case of a neutral tin plating bath,
By bubbling nitrogen gas under the above conditions, it can be seen that the plating bath life can be extended to about 10 times that of the conventional one.

According to the plating method and the plating apparatus of the present invention, bubbling of the inert gas in the plating bath suppresses the oxidation of metal ions in the plating bath. Therefore, deterioration of the plating bath over time is prevented, and the life of the plating bath can be extended. Therefore, the frequency of exchanging the plating bath can be reduced, and the plating cost can be significantly reduced. In addition, since the product can be plated for a long period of time using the same plating bath, the quality of the product to be plated can be stabilized.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram for explaining a plating apparatus according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a multilayer capacitor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Plating bath 12 ... Plating metal aqueous solution 13 ... Electronic component as a member to be plated 17 ... Inert gas introduction pipe 18 ... Bubble

Claims (2)

[Claims] 1. A plating method which comprises bubbling the plating bath with an inert gas when the member to be plated is immersed in the plating bath for electroplating. 2. A plating apparatus comprising a plating bath for immersing and electroplating a member to be plated, and an inert gas introducing means for bubbling an inert gas in the plating bath. .