JPH11302894A - Electroplating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always stably obtain plating objects having good solder wettability by managing the concn. of the tin ions in a bath resulted by the intrusion of the tin ions in a tin plating bath accompanying a holder into a nickel plating bath. SOLUTION: The plating objects, for example, electronic parts having electrodes, are taken into the holder in a taking-in station and are successively passed through the Ni plating bath 3 constituting an Ni plating line in an arrow 11 direction, a first recovering tank 4 and a first washing tank 5 and are then transferred via a traversing station 10 to an Sn plating line where the electronic parts successively pass the Sn plating bath 6, a second recovering tank 7 and a second washing tank 8. The electronic parts are taken out of the holder in a taking-out station 9. As a result, there is the possibility that the Sn ions in the Sn plating bath 6 accompanying the holder intrude into the Ni plating bath 3 and, therefore, the concn. of the Sn ions in the Ni plating bath 3 is managed at all times in such a manner that <=500 ppm is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electroplating method, and more particularly to an electroplating method for forming a plating film composed of two layers, a nickel film and a tin film.

[0002]

2. Description of the Related Art For example, a nickel film is first formed on a terminal electrode of an electronic component such as a chip-shaped ceramic capacitor by, for example, electroplating, and then a tin film is formed thereon. The solderability with a wiring board for mounting various electronic components is improved, and a highly reliable electrical connection is obtained.

In order to form such a plating film composed of two layers, a nickel film and a tin film, for example, a plating apparatus 1 having a planar arrangement as shown in FIG. 1 is applied. The plating apparatus 1 is roughly divided into a line for performing nickel plating and a line for performing tin plating. The nickel plating line starts from the intake station 2, the nickel plating bath 3, the first recovery tank 4 and the first
To the washing tank 5. On the other hand, the tin plating line starts with a tin plating bath 6 and continues to a second recovery tank 7, a second cleaning tank 8 and a removal station 9. A traverse station 10 is located between the end of the nickel plating line and the start of the tin plating line.

[0004] Although not shown in FIG. 1, a holder for holding an object to be plated is provided during the plating process.
The above-described intake station 2, nickel plating bath 3, first recovery tank 4, first cleaning tank 5, traverse station 10, tin plating bath 6, second recovery tank 7, second cleaning tank 8, and removal station 9 circulates in a direction indicated by an arrow 11 along a circulation path sequentially passing through.

When the object to be plated is, for example, a chip-shaped ceramic capacitor, when electroplating is performed on its terminal electrode, a plurality of ceramic capacitors are put in a rotary barrel together with a medium made of steel balls. The plating process is performed using the rotating barrel as a holder. That is, the plating process is performed while the rotary barrel serving as the holder circulates along the above-described circulation path in the plating apparatus 1.

More specifically, the following steps are sequentially performed while a holder such as a rotary barrel circulates along the circulation path in the plating apparatus 1 as described above. First, at intake station 2,
A plurality of chip-shaped ceramic capacitors as plating objects are incorporated in the holder.

Next, the holder is immersed in the nickel plating bath 3 to form a nickel film on the terminal electrodes of each ceramic capacitor. Next, in the first recovery tank 4,
For example, nickel ions are recovered by washing with water. Next, in the first cleaning tank 5, the ceramic capacitor is washed with pure water while being held by the holder, for example, while applying ultrasonic waves.

[0008] When the processing in the nickel plating line as described above is completed, the ceramic capacitor as the object to be plated is placed in the traverse station 1 together with the holder.
0 and transferred to a tin plating line. In the tin plating line, first, a plurality of ceramic capacitors as plating objects, which have been subjected to nickel plating, are immersed in a tin plating bath 6 together with a holder, and the nickel capacitors already formed on the terminal electrodes of the respective ceramic capacitors. A tin film is formed on the film.

Next, tin ions are recovered in the second recovery tank 7 by, for example, washing with water. Next, in the second cleaning tank 8, the ceramic capacitor held by the holder is cleaned with pure water while applying ultrasonic waves, for example. Next, in the removal station 9, the plurality of ceramic capacitors that have been subjected to the plating process are removed from the holder.

The holder still circulates along the circulation path starting from the intake station 2 as described above, so that each time the holder circulates one round, at the take-out station 9, two layers of nickel film and tin film are obtained. A plurality of ceramic capacitors having terminal electrodes formed with a plating film consisting of the same are removed from the holder, and then, at the intake station 2, a plurality of ceramic capacitors having terminal electrodes to be plated are introduced into the holder. Thereafter, such a process is repeated.

[0011]

The reason why the tin film is formed on the outermost layer of the terminal electrode of each ceramic capacitor is to improve the solderability of the terminal electrode as described above. When a plating process is continuously performed using the plating apparatus 1 as shown, only a ceramic capacitor having poor solder wettability of terminal electrodes despite passing through a tin plating line for forming a tin film. Often not available.

In such a terminal electrode having poor solder wettability, it appears that the solder is repelled, and a more detailed examination reveals that the tin film, which should have adhered in a uniform layer on the nickel film. The spots were observed to be spotted in an island shape and the underlying nickel film was directly exposed on the surface. From this, it can be seen that in order to improve the solder wettability, it is necessary to prevent such tin precipitation in an island shape.

Accordingly, an object of the present invention is to provide an electroplating method capable of solving the above-mentioned problems when forming a plating film composed of two layers, a nickel film and a tin film.

[0014]

According to the present invention, an object to be plated is provided by a holder circulating along a circulation path which sequentially passes at least a nickel plating bath, a first cleaning tank, a tin plating bath, and a second cleaning tank. In the state in which the plating film is formed, a plating film composed of two layers of a nickel film and a tin film is formed on the plating object, and the plating film is formed each time the holder circulates once along the circulation path. It is intended to be an electroplating method that repeats taking in a new object to be plated into the holder after taking out the object from the holder, and the present inventor has proposed an electroplating method including such a process. In particular, the present inventors have found that the above-described problem is likely to occur, and have accomplished the present invention.

To solve these problems, the inventor has
As a result of intensive studies on the plating treatment for forming a plating film consisting of two layers of a nickel film and a tin film, a predetermined amount or more of tin ions were mixed into a nickel plating bath,
After the first layer of nickel film is formed, when immersed in a tin plating bath to form a second layer of tin film, tin is not deposited in a layer form but in an island form. It has been found that a problem of deteriorating the solder wettability of the electrode occurs. On the other hand, it has been found that even if nickel ions are mixed in the tin plating bath, the solder wettability is hardly affected.

[0016] Based on these findings, the tin ion concentration in the nickel plating bath is an important factor that determines the success or failure of the subsequent tin plating treatment. It can be seen that the tin plating process cannot be performed well. Here, paying attention again to the electroplating method of repeating the nickel plating and the tin plating as described above to which the present invention is directed, the holder holding the plating object circulates along the circulation path for the plating process. Therefore, it is sufficiently conceivable that tin ions in the tin plating bath are mixed into the nickel plating bath along with the holder and cause the above-described problems in the tin plating.

Therefore, in the electroplating method according to the present invention, the step of controlling the concentration of tin ions in the nickel plating bath caused by mixing the tin ions in the tin plating bath into the nickel plating bath with the holder. It is characterized by having. In the step of controlling the tin ion concentration as described above, preferably, the tin ion concentration is 5
It is controlled so as to be 00 ppm or less.

The managing step may include a step of controlling the tin ion concentration to be lower. This controlling step includes, for example, a step of immersing a dummy plating object in a nickel plating bath to perform electroplating. The present invention is particularly advantageously applied when a nickel film is first formed on a plating object and then a tin film is formed on the nickel film in the step of forming a plating film. In this case, as the plating object,
Typically, it is an electronic component having an electrode to be plated.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The plating apparatus 1 shown in FIG. 1 is also used for carrying out an electroplating method according to one embodiment of the present invention. As described above, in the intake station 2, the object to be plated is a holder (not shown).
Then, the plating object held by the holder passes through the nickel plating bath 3, the first recovery tank 4, and the first cleaning tank 5 constituting the nickel plating line, and then passes through the traverse station 10. , And passes through a tin plating bath 6, a second recovery tank 7 and a second cleaning tank 8 in this order, and finally, a removal station 9.
Is removed from the holder. On the plating object thus taken out, a two-layer plating film is formed, in which a nickel film is located on the first layer and a tin film is located on the second layer.

In such a plating apparatus 1, since the holder is continuously plated while being circulated in the direction of the arrow 11, tin ions in the tin plating bath 6 are accompanied by the holder to cause the tin ions in the nickel plating bath 3. There is a good possibility that it will be mixed in. Therefore, in this embodiment, the tin ion concentration in the nickel plating bath 3 is always controlled so that a good tin film can always be formed on the nickel film.

This control is intended to control the tin ion concentration to be positively lowered even when the tin ion concentration exceeds a predetermined value. It may be management. When controlling the latter to lower the tin ion concentration, for example,
A method of reducing the tin ion concentration by immersing the dummy plating object in the nickel plating bath 3 and electroplating at a relatively low current density is advantageously employed. Another method is to replace the nickel plating bath 3 with a new one.

As described above, when managing the tin ion concentration in the nickel plating bath 3, it is efficient to determine an allowable range of the tin ion concentration in advance and manage based on the allowable range. Therefore, the following experiment was conducted in order to obtain such an allowable range of the tin ion concentration.
This experiment was a beaker scale experiment, and the following nickel plating bath and tin plating bath were prepared. (1) Nickel plating bath: Nickel sulfate: 300 g / L Nickel chloride: 50 g / L Boric acid: 35 g / L pH: 4 Bath temperature: 50 ° C. (2) Tin plating bath Tin sulfate: 70 g / L Diammonium hydrogen citrate 100 g / l Ammonium sulfate 100 g / l pH 5 Bath temperature 30 ° C. On the other hand, 10 mm × 30 mm × 0.3
mm copper plate was prepared.

Next, this copper plate was first plated with nickel
Immerse in a bath for 2 minutes, 5A / dm ^TwoAt the current density of
Perform nickel plating to form a 2μm thick nickel film
And then immersed in a tin plating bath for 2 minutes, 4 A / dm
^TwoTin plating with a current density of 4 μm and a thickness of 4 μm
Was formed. In the above plating process, nickel
The tin ion concentration in the plating bath is zero.

Similarly, the plating operation as described above was carried out for the case where tin ions were mixed at a concentration of 500 ppm in the nickel plating bath and the case where tin ions were mixed at a concentration of 1000 ppm. Then, as described above, the tin ion concentration in the nickel plating bath was 0 ppm, 500 ppm, and 1000 ppm.
In each case, the sample obtained was evaluated for solder wettability. In this evaluation, H60A was used as solder,
The soldering temperature was set to 230 ° C., and a zero-cross time was determined by a meniscograph method using a low-activity rosin flux as a flux.

As a result, the zero crossing time is less than 5 seconds when the tin ion concentration is 0 ppm,
In the case of 00 ppm, it was 5 seconds or more and less than 20 seconds, and in the case of 1000 ppm, it was 20 seconds or more.
Here, the zero cross time is preferably shorter,
Less than a second is acceptable, and from this,
It can be seen that the tin ion concentration in the nickel plating bath should be controlled so as to be 500 ppm or less.

Therefore, in the plating apparatus 1 shown in FIG. 1, the tin ion concentration in the nickel plating bath is 500 p.
pm or less while controlling an electronic component such as a chip-shaped ceramic capacitor as a plating object, and forming a nickel film and a tin film on a terminal electrode thereof.
If a plating film composed of layers is formed, the solder wettability of the terminal electrode can always be made excellent.

[0027]

As described above, according to the present invention, the holder circulating along the circulation path sequentially passing at least the nickel plating bath, the first cleaning tank, the tin plating bath, and the second cleaning tank. When a plating film composed of two layers, a nickel film and a tin film, is formed on a plating object in a state where the plating object is held, tin ions in the tin plating bath are accompanied by the holder and are formed in the nickel plating bath. Although it is inevitably mixed in, the tin ion concentration in the nickel plating bath is controlled, so that the phenomenon that the tin film is not formed well when the tin ion concentration in the nickel plating bath exceeds a predetermined value. This can be prevented from occurring. Therefore, the yield of products manufactured by applying such an electroplating method can be improved.

In the present invention, the tin ion concentration in the nickel plating bath is preferably lower,
When controlling such tin ion concentration, this is 500p
If the permissible reference value is clarified to be equal to or less than pm, such management can be performed more easily and reliably. Further, in the present invention, when controlling the tin ion concentration so as to actively lower the tin ion concentration, the plating process can be continuously performed for a longer time.

As a method of controlling the tin ion concentration to be lower as described above, if a method of immersing a dummy plating object in a nickel plating bath and performing electroplating is adopted, it is relatively easy. At the same time, the tin ion concentration can be controlled to be lower at low cost. Also,
In the present invention, when a nickel film is first formed on an object to be plated, and then a tin film is formed on the nickel film, the subsequent tin plating treatment is more susceptible to the adverse effects of tin ions in the nickel plating bath. Therefore, the effect of the present invention can be more remarkably exhibited.

According to the present invention, when the tin film is formed on the nickel film and the object to be plated is an electronic component having an electrode to be plated, as described above. Thus, an electronic component including an electrode having good solder wettability can always be stably obtained.

[Brief description of the drawings]

FIG. 1 is a plan layout view of a plating apparatus 1 used for performing an electroplating method according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plating apparatus 2 Intake station 3 Nickel plating bath 5 First washing tank 6 Tin plating bath 8 Second washing tank 9 Removal station

Claims (6)

[Claims] In a state where an object to be plated is held by a holder circulating along a circulation path sequentially passing through at least a nickel plating bath, a first cleaning bath, a tin plating bath, and a second cleaning bath. While forming a plating film consisting of two layers of a nickel film and a tin film on a plating object,
Each time the holder circulates one round along the circulation path,
An electroplating method in which the plating object on which the plating film is formed is taken out of the holder, and then a new plating object is repeatedly introduced into the holder, wherein the tin ions in the tin plating bath contain the holder. Controlling the concentration of tin ions in the nickel plating bath caused by mixing in the nickel plating bath with the process. 2. The electroplating method according to claim 1, wherein, in the step of controlling, the tin ion concentration is controlled to be 500 ppm or less. 3. The electroplating method according to claim 1, wherein the managing step includes a step of controlling the tin ion concentration to be lower. 4. The electroplating method according to claim 3, wherein said controlling step includes a step of immersing a dummy plating object in said nickel plating bath to perform electroplating. 5. In the step of forming the plating film, the nickel film is first formed on the plating object, and then the tin film is formed on the nickel film.
The electroplating method according to claim 1. 6. The electroplating method according to claim 5, wherein the object to be plated is an electronic component having an electrode to be plated.