JPS62211398A - Method for adjusting fluctuation of current density in electroplating - Google Patents

Abstract

PURPOSE:To decrease the fluctuation range of current density by providing a main conductor roll to the inlet side of a plating cell, providing an auxiliary conductor roll to the outlet side, and changing the current distribution to these rolls according to the thickness of a strip. CONSTITUTION:The main conductor roll 3a is provided to the inlet side of the plating cell 5 and the auxiliary conductor roll 3b is provided to the outlet side. The increase and decrease of the electric resistance in the respective positions of the strip 4 according to the fluctuation in the thickness of the strip 4 are held intact and the intensity of the currents to flow to the respective conductor rolls 3a, 3b is adjusted to meet such increase and decrease. The fluctuation of the current density in electroplating is thereby adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for adjusting current density fluctuations in electroplating to reduce the width of current density fluctuations due to strip thickness fluctuations.

[Conventional technology]

The structure of the electroplating apparatus is as shown in Fig. 5-), in which electrodes (11 (2) are arranged and a strip (3) negatively charged by a conductor roll (3) is placed in a bath filled with a plating bath. 4) and electroplating its surface. [Problems to be solved by the invention] Of these, the electrodes (1) and (2) are arranged parallel to the strip (4), and there is no space between them. While a constant distance is maintained between the anti-conductor rolls (3) of the electrodes (1) (2)
The current that flows from the side end to the strip (4) and reaches the last conductor roll (3) flows from the conductor roll (3) side end of the electrode (13 (2) to the strip (4). Compared to the current reaching 3), the electrode (
1) (2) The electrical resistance when flowing through the strip (4) increases by an amount corresponding to the length L and decreases accordingly. Therefore, from the electrodes (1) and (2)
The current density distribution of the current flowing to the J tube (4) becomes non-uniform in the length direction of the electrode (L bar 2).

Furthermore, in general, the smaller the cross-sectional shape of the conductor, the higher the electrical resistance of the current flowing through the conductor, and the larger the cross-sectional area, the higher the electrical resistance.
Electrical resistance becomes smaller. Therefore, the electrical resistance of the strip (4) changes depending on the thickness of the strip (4), and therefore, the variation width of the current density is non-uniform in the length direction of the electrodes (1) and (2) as described above. will further vary depending on the thickness of the strip (4).

On the other hand, the present inventors developed and proposed a new means to prevent non-uniformity of current density in the length direction of the electrode (11). It is assumed that the electrical resistance of the current flowing from each point to the conductor roll (3) increases in proportion to the distance between the strips (4).
) The plating liquid resistance, which was constant at any point in the length direction, was
As shown in FIG. The sum of the electrical resistance and the plating solution resistance) is kept constant in the length direction of the electrodes (1) and (2).

However, one or more of the above methods are effective when the thickness of the strip (4) is constant, and when the thickness changes, the electrical resistance of the IJ tube (4) changes, Variations in current density will occur again.

In contrast to this G, Fe-Zn%Zn Ni, Zn-M
In the fabrication of alloy electroplated steel sheets such as n, the alloy composition in the plating film, film performance, etc. change depending on the current density, so it is necessary to make the current density uniform.

The present invention was devised in view of the above-mentioned problems, and an object of the present invention is to reduce the range of variation in current density due to variations in the thickness of the strip.

[Means for solving inter-group points]

The electrode (I
J (2) There will be variations in the current density distribution in the length direction, and when there is this variation, the change in the ′vL current density IJiJ width will change depending on the thickness of the strip (4), as mentioned above. It is.

That is, if the thickness of the IJ knob (4) becomes thicker, then
The electrical resistance of the IJ tube (4) is reduced, and therefore, in the case of the conventional electrodes (1) (2) shown in FIG. 5 (IL), the range of variation in current density is also reduced. On the other hand, the thinner the plate thickness is, the larger the fluctuation range of the current density becomes.

Furthermore, when electroplating is performed using the improved electrode (11(2)) shown in FIG. 5(b), the current density distribution is made uniform at a certain thickness of the strip (4), and The fluctuation range is 0, but if the plate thickness changes, the current density distribution will vary, and the current density fluctuation range will increase.

First, we focused on the fact that the electrical resistance of the strip (4) differs depending on the distance from each point of the strip (4) to the conductor roll (3). We decided to reconsider a configuration that can reduce the variation in electrical resistance at each position in the length direction of the strip (4), regardless of its length.Here, we achieved the above objective by providing a completely new configuration. Instead, we considered whether the purpose could be achieved using a configuration that utilized existing equipment, and in the end, we decided to install a plating tank (see Fig. 1 (a)).
5) A main conductor roll (3a) is provided on the inlet side, and an auxiliary conductor roll (3b) is provided on the outlet side.

With the above configuration, the current flows from each point of the strip (4) not only to the main conductor roll (3a) but also to the auxiliary conductor roll (3b), so that the electric current at each point of the strip (4) This will reduce resistance fluctuations.

However, even if it is possible to reduce the variation in the electrical resistance at each point of the strip (4) with this configuration, if the thickness of the strip (4) changes and the electrical resistance of the strip (4) changes. In this case, the fluctuation of the electrical resistance at each point of the strip (4) increases again. Therefore, as described above, the present invention provides a main conductor roll (3a) on the entrance and exit sides of the plating tank (5). and an auxiliary conductor roll (3b), as well as a strip (4).
The increase or decrease in electrical resistance at each position of the strip (4) due to changes in plate thickness remains unchanged, and the current is adjusted by adjusting the strength of the current flowing to each conductor roll (3a) (3b) in accordance with the increase or decrease. This is intended to reduce the fluctuation range of density.Therefore, both conductor rolls (3a) (
The flow distribution of 1 to 3b) will be changed according to the thickness of the IJ tube (4).

Among these, the current distribution ratio (y) to the auxiliary conductor roll (3b) changes the lengthwise distance of the electrodes (1) and (2) that the auxiliary conductor roll (3b) has, depending on the thickness of the strip (4). This is calculated based on the idea that the current density change can be kept below the allowable value depending on the situation, and is determined by the following formula.

Plate thickness t′ of T Ni strip (4) Two reference plate J4 (plate thickness that produces an allowable M&X current density change) Also, as shown in Figure 1 (b), an improved type with a certain curvature on the electrode surface The same applies when electrodes (1) and (2) are used.

Here, a constant curvature means that when the thickness of the strip (4) is a certain value, as mentioned above, the thickness of the strip (4) at each point (S) IJ tube (S) depending on the electrical resistance of the strip (4) I
J knob (4) - electrode (1) (2) distance between electrode (1)
(2) It is provided so that the sum of the electrical resistance and liquid resistance of the strip (4) can be made constant by varying it in the length direction, and is determined by the following formula.

ρ1 (-z knee a'/zL) = Constant P determined by the electrical resistance of the strip (4): Constant determined by the liquid resistance X: From the tip of the main contactor roll (3a) side electrode (1 bar 2) distance h: curvature L: electrode (IJ (2) length [Example 1]) The inventors first developed a continuous double-sided electroplating apparatus with a length of 140
A conventional electrode and an improved electrode made of 0 m of g11 silver (Pb-Ag) were installed, respectively, and filled with a plating solution rich in zinc sulfate (ZH5O4).

An experiment was conducted to examine the current density distribution in the length direction of each electrode by changing the thickness of the strip serving as the material to be plated in the range of 0.4 to 1.6 cm. At this time, the distance between the strip and the electrode is 1
There are 5 items. Also, the surface of the improved electrode is provided with a curvature along its length. Furthermore, the plating liquid resistivity is 11.1 ACIn, and the strip resistivity is 12.5
It was 10-'Qcm.

From the above experiments, the results shown in FIG. 2(a) Q)) were obtained. Figure (a) is a graph showing current density fluctuations corresponding to strip thickness fluctuations when electroplating is carried out by equipping a conductor roll only on the inlet side of the plating bath where each pole is installed. In the figure, the actual gland shows the conventional electrode, and the broken line shows the case of the improved electrode. On the other hand, in the same method, a main conductor roll and an auxiliary conductor roll are installed on the inlet and outlet sides of the plating bath in which each of the above electrodes is installed separately, and both are installed in accordance with the variation in the thickness of the strip. Implementing the method of the present invention that changes the current distribution to the conductor roll (the current distribution rate to the auxiliary conductor roll is determined by the above-mentioned formula),
FIG. 2 is a graph diagram showing current density fluctuations corresponding to IJ knob plate thickness fluctuations.

Looking at the conventional electrodes in these graphs, we find that (i) If the thickness of the IJ tube is below a certain value (the value represented by t in the drawings), the method of the present invention is not implemented; The fluctuation range of current density is inversely proportional to the strip thickness,
When the strip thickness is 0.4 mm, the current density fluctuation range is the maximum of 16.5%, whereas when the method of the present invention is implemented, the current density fluctuation range is 16.5%, regardless of the strip thickness fluctuation. The fluctuation range is uniformly 8%, and the effect is visible. In addition, S) In the range where the IJ tube thickness exceeds the above-mentioned certain value, the current density fluctuation width is small in inverse proportion to the strip thickness at exactly the same rate, regardless of whether the method of the present invention is implemented or not. At a plate thickness of 1.6 m, the above fluctuation range is the minimum of 4.5%.

Furthermore, regarding the improved electrode, except for the fact that current density fluctuations disappear at a certain strip thickness (same < 1), the above fluctuations occur at all strip thicknesses, but within the range below the above-mentioned certain value, the current density fluctuations disappear. If the invention method is not implemented, the current density fluctuation range is inversely proportional to the IJ tube thickness, and the current density fluctuation range is
, 4, the maximum value is 8%, but when the method of the present invention is implemented, the width of current density fluctuation is also inversely proportional to the strip thickness.

It can be seen that the effect of the method of the present invention is evident when the thickness of the plate is 1.5 cm at a thickness of 0.4 m. In addition, in the range where the strip thickness exceeds the above-mentioned certain value, the current density fluctuation width increases in proportion to the strip thickness at the same rate regardless of whether the method of the present invention is implemented or not. At .6 wag, the above fluctuation range is approximately 5%.

[Example 2] Next, using the conventional electrode and improved electrode with a length of 1400 m used in the previous example in a continuous type double-sided electroplating apparatus consisting of one cell, the strip-to-electrode distance was set to 15 mm and the plate thickness was 0.
．． 4-1.6m) Fe-Zn alloy electroplating was performed on both sides of the IJ tube. In one case, electroplating was carried out by negatively charging the strip using only a conductor roll installed on the plating entry side, while in the other, a main conductor roll and an auxiliary conductor roll were installed on the plating entry and exit sides. In addition, the strip thickness is 0.4
The current distribution to both conductor rolls is changed accordingly when the current distribution varies within the range of ~1.6 ounces (as in the previous embodiment, the current distribution ratio to the auxiliary conductor rolls is determined by the above formula). Electroplating was carried out using the method of the present invention.

The plating layer was then analyzed by GDS to examine the distribution of Fe content in the depth direction, and the results shown in Figure 3 (a) and (b) show the range of Fe content variation in the depth direction of the plating layer due to plate thickness variation. I got it.

The plating conditions at this time were as follows.

Plating conditions used Cell instruction 1 Electrode length 1400m x 2 Average current density 50 A/dm" Line speed 15mpm Deposition i 15 f!/m" Plating solution FeSO4.7H! O/(FesO4・7H2
0+ZnSO4・7H2O) = 0.7PH=
2.5 Strip thickness 0.4 to 1.6 ms F in both figures
The fluctuation range of the e content is determined by determining the difference between the maximum value a and the minimum value of the Fe content in the depth direction of the plating layer, as shown in FIG. 4, for example.

As a result, in the case of conventional electrodes, those who did not implement the method of the present invention found that 1164 ~
While the Fe content varies within the range of 3Ls, the strip thickness of the strip plate using the method of the present invention is 0.4 to 3Ls.
The Fe content is uniformly around 8% in the range of 0.9 gourd,
The range of fluctuation is smaller. Note that the strip thickness is 0.
In a range exceeding 9■, it is the same as when the method of the present invention is not practiced.

Also, in the case of the improved electrode, for those who have not practiced the method of the present invention, the fluctuation range of F content becomes almost 0 at a strip thickness of 0.9 cans, but when the strip thickness is less than that, The range varies inversely with the strip thickness, with the strip thickness being 0.
The range of variation in Fe content reaches its maximum at 5.5% at 4.0 m, and further, in the range where the strip thickness becomes thicker than 0.9 m, the range of variation in Fe content increases in proportion to the thickness of the strip. 6 tar
It becomes 3% at s. On the other hand, those who implemented the method of the present invention showed similar Fet content fluctuation behavior, but especially in the strip thickness range of 0.9 arm or less, it was almost flat, and at the strip thickness of 0.4 tram. The Fe content fluctuation range is 1.
The result was a low value of around 2 inches. In the range where the strip thickness exceeds 0.9 mm, it is the same as when the method of the present invention is not practiced.

〔Effect of the invention〕

As explained above, according to the method of the present invention, by providing conductor rolls on the inlet and outlet sides of the plating tank, (1) the variation in electrical resistance at each position in the length direction of the IJ tube can be minimized, and the strip plate Even if the thickness varies within a certain range and the electrical resistance varies greatly at each strip position, the current can be reduced by changing the current distribution to both conductor rolls and adjusting the strength of the current flowing there. The width of density fluctuation can be reduced. Therefore, when used in alloy electroplating, it has the excellent effect of stabilizing the alloy composition in the plating tank and the film performance.

[Brief explanation of drawings]

Figures 1 (a) and (b) are explanatory diagrams showing the method of implementing the present invention, Figures 2 (a) and (b) are graph diagrams showing the first experimental results of the conventional method and the method of the present invention, and Figure 3 ( a) (b) is a graph showing the results of the conventional method and the present invention method in the second experiment,
Figure 4 is a graph explaining how to determine the fluctuation range of Fe content in Figures 3 (a) and (b), @Figure 5 (a) (b)
FIG. 2 is an explanatory diagram showing the arrangement of conventional electrodes and improved electrodes in a conventional method. In the figure, (IJ) (2) is the electrode, (3X3aX3b) is the conductor roll, (4) is the strip, and (5) is the plating bath. Patent applicant: Nippon Kokan Co., Ltd. Inventor: Toshi Tsujihara 2.
Anan Tatsu Buma
Raw Tenmoku Budo
Blind Okabe
Norihiko Sakamoto Figure 2 (G) Mizumaku - Enter Figure 2 (b) Ohojo - Network Engineering [mml root ↓ [mmJ

Claims (1)

[Claims] The main conductor roll and its parts are installed on the inlet side of the plating tank. An auxiliary conductor roll is provided on the exit side of the The current distribution to these conductor rolls is Change it according to the thickness of the trip The current density in electroplating characterized by Variation adjustment method.