JPS6244592A - High-speed electrolytic sliver plating method - Google Patents

Abstract

PURPOSE:To form a smooth and thick silver plating film in a short period by using a plating liquid which is specified in silver soncn. and does not contain cyan compd. except silver cyan compd. and using DC current regulated in frequency and pulse ratio to make electrolysis. CONSTITUTION:The silver plating liquid which has 40-80g/l silver concn. and does not contain the cyan compd. except the silver cyan compd. is prepd. the electrolytic treatment is executed by using such plating bath and using the pulse current regulated to 50-5,000ms frequency of DC pulse and 0.5-0.9 range of the ratio of the DC current pulse occupying in the repeating period. The diffusion of the silver ions to the electrode surface takes place in the quiescent time of the pulse according to such pulse electrolysis. As a result, the silver ion concn. is restored near the material to be plated. The generation of gaseous hydrogen is consequently suppressed and the generation of dendrite is made hard. The silver plating having the excellent surface characteristic is thus formed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is capable of forming a smooth and thick plating film on the surfaces of electrical contact parts such as contacts, sliders, busbars, etc. of electric relays and decorative items in a short period of time. Regarding the high-speed electrolytic grudge formation method.

[Conventional technology]

The electrolytic reaction in high-speed electrolytic silver plating is usually performed using direct current. The direct current is lO~100A/
Electricity is applied at a current density of approximately dm2, and plating is performed to a maximum thickness of 100 μm.

[Problem that the invention seeks to solve]

In such conventional grudges using direct current,
When the current density is increased in order to increase the plating speed, the degree of silver ion concentration on the surface of the object to be plated decreases significantly, and hydrogen gas is generated.

This generation of hydrogen gas disturbs the diffusion layer near the surface of the object to be plated, causing dendrites to precipitate. This dendrite precipitation is not so noticeable when the film thickness is about 0 μm, but becomes noticeable when the film thickness exceeds 100 μm, causing deterioration of the surface quality. Therefore, in order to obtain a smooth and thick coating, electrolysis is required at low current density and for a long time.

In view of these problems, the present invention provides a film with a thickness of 100 μm.
To obtain a ruptured film with excellent surface properties in a short time by electrolysis at a high TJ and flow density, even when forming a thick resistant film that exceeds 100 mL.

[Means for Solving the Problems]] In order to achieve the object, the present invention has a silver concentration of 40 to 40.
Using a silver plating bath containing no cyanide other than silver cyanide at 80 g/l, the frequency of the DC pulse is 50 ~
Electrolysis is carried out using a pulse current having a duration of 5000 ms and a ratio of DC current pulses to the repetition period of 0.5 to 0.9.

The value of electrolytic current density in this case is the silver concentration in the plating bath,
It can be increased in proportion to the bath temperature and flow rate of the plating bath. On the other hand, if the silver concentration and bath temperature are low and the plating solution flows slowly, it is necessary to reduce the value. By the way, in the present invention, by making the applied plating current a controlled pulse, the plating film can be smoothed within the range of 10 to 150 A/dm2 with an average cathode current density (?) specified by 2fil. The effect of increasing

I=ヱ, × t/θ ・−1−−−−−−・−−−−・
-(1) However, ip: pulse current density, θ: pulse repetition period, t: width of current pulse The various electrolytic conditions in the present invention have the following meanings.

When the pulse repetition period is shorter than 50m5 and 5S
If the length is longer than , the effect of smoothing the plating film will not be observed and dendrites will occur.

From this, the pulse repetition period is 50ma to 5S.
is appropriate.

Next, the ratio of DC pulses to the pulse repetition period (
When the ratio of the width of the current pulse to the pulse repetition period = pulse current radius / pulse repetition period) becomes smaller than 0.5, a large pulse current is required if the plating speed (average current density) is the same. . For this reason, the formation of dendrites becomes significant. If an attempt is made to reduce the pulse current to prevent this, the average current density will also become smaller and the plating speed will decrease. On the other hand, if the ratio of DC current pulses to the pulse repetition period is greater than 0.9, only a plating film equivalent to that obtained by DC electrolysis can be obtained. From the above, the ratio of pulse current is 0.5~
0.9 is appropriate.

Furthermore, the plating bath used for plating under the pulsed electrolysis conditions of the present invention needs to be a low cyanide plating bath that does not contain any cyanide compounds other than anticyanide so that it can be operated at high current density. The silver concentration in the bath is 40-80 g/j!
is appropriate. If the silver concentration is less than 40g71, the plating surface becomes rough and the current density cannot be increased.
If g/1 or more, a large amount of silver component is pumped out from the plating bath, which is economically disadvantageous.

[Effect]

When pulse electrolysis is performed in which direct current is applied intermittently, silver ions diffuse to the electrode surface during pulse rest periods. As a result, the concentration of negative ions is restored in the vicinity of the object to be plated. Therefore, hydrogen gas generation is suppressed and dendrites are less likely to be generated.

The conditions for pulse electrolysis to suppress dendrite precipitation vary depending on the type of plating metal, but in the case of silver plating, the repetition period of DC pulses is 5Qms to 5s;
The ratio of pulse current energization time to the repetition period is 0
．． Pulse electrolysis conditions in the range of 5 to 0.9 are most effective in suppressing dendrite formation.

By performing pulse electrolysis under such conditions, a smooth base plating film can be obtained even if the film thickness is as thick as 1.5 mm.

〔Example〕

Next, the features of the present invention will be specifically explained with reference to Examples.

Example 1 - Potassium silver cyanide converted to silver concentration of 80 g/l
.

Potassium citrate 100g/L Hydrolic acid 30g/e
An aqueous solution containing 2 g/l of selenite in terms of selenium concentration was adjusted to pH 8 and used as a plating solution.

Using a copper plate for the cathode and a PT plated Ti plate for the anode, bath fj1
Plating was performed by pulse electrolysis while jetting a 10° C. plating solution from a nozzle toward the cathode. The pulse application conditions at this time are that the pulse repetition period is 50 ma to 5 s.
, 0m mill 5s, pulse 0,9. The average cathode current density is 1
0OA/dm" and 15OA/dm". Also, for comparison, the current density is 100A/dm'' and 15OA/dm
DC electrolysis was carried out at 1,700 C/c.
mz. The thickness of the grudge film obtained at this time is
It was in the range of 1.2 to 1.5 mm. Table 1 shows the surface condition of the sticky coating obtained by this electrolysis.

As is clear from Table 1, the plated film obtained by pulse electrolysis has better surface properties than the plated film obtained by direct current electrolysis at the same current density.
Even when the film thickness exceeded m, the surface smoothness was sufficiently maintained.

Surface condition of the first Omotesama plating film A: Semi-gloss smooth B: Matte smooth C: Unevenness Example 2 - A commercially available high-speed forging plating bath (Silharjet 220 manufactured by Japan Ronal Co., Ltd.) was prepared. Using potassium silver cyanide, the silver concentration was adjusted to 65 g/l, and the pH of the solution was adjusted to 8.
Adjusted to 2. Using a copper plate as the cathode and a PT plated Ti plate as the anode, the plating solution with a bath temperature of 60°C was jetted from the nozzle to the cathode, and the pulse repetition period was 10m3 to 10S1, the pulse ratio was 0.5 to 0.9, and the average cathode current was Pulse electrolysis was performed at a density of 508 dm" and 100 A/dm2. For comparison, direct current electrolysis was performed at a current density of 50 A/dm" and 100 A/dm. At this time, the amount of current applied was 1200 C/cm''. The thickness of the silver plating film thus obtained was in the range of 0.8 to 1.0 mm. The thickness of the grating film obtained by electrolysis of,
Shown in Table 2. As is clear from Table 2, when the pulse ratio is 0.5 to 0.9 and the pulse repetition period is 50
The surface of the plating film obtained by pulse electrolysis at ~5S was smooth, and the surface condition was much better than that of the plating film obtained by direct current electrolysis at the same current density.

Table 2 Surface condition of small plating film A: Mirror gloss B: Smooth C;
With unevenness D: Dendrite precipitation Example 3 - Potassium pyrophosphate 200g/1, Potassium dihydrogen orthophosphate 20g/R, Potassium selenite toppm
, potassium ethylxanthate 20ppm+ ethylenediaminetetraacetic acid 2g/l and potassium silver cyanide as silver? An aqueous solution containing 40 g/1 in terms of M degree and adjusted to pH 9 was used as the plating solution.

A copper plate is used as the cathode, a PT plated Ti plate is used as the anode, and the bath temperature is 50°C.
While jetting the plating solution from the nozzle to the cathode at ℃, the pulse repetition period was 50 to 5 s, and the pulse ratio was 0.5 and
．． 7. Average cathode current density from IOA/dm” to 3OA/dm
Pulse electrolysis was performed under the conditions of 100 dm''. For comparison, direct current electrolysis was performed at a current density of IOA/dm2 to 3 OA/dm2. At this time, the amount of current applied was set to 130C/cm''.The thickness of the silver plating film obtained in this way was:
It was in the range of 100 to 120 μm. Table 3 shows the surface condition of the silver plating film obtained by this electrolysis. As is clear from Table 3, the plated coating obtained by pulse electrolysis was smooth and had a better surface condition than the plated coating obtained by direct current electrolysis at the same current density.

Table 3 Note) Surface condition of plating film A: Semi-gloss smooth B: Matte smooth C: Dendrite precipitation [Effects of the invention] As explained above, according to the silver plating method of the present invention, the appearance is good. A thick coating with a thickness of 100 μm to 1.5 mm can be created in a short time. For this reason, it has become possible to omit the brazing work that was conventionally performed for attaching contact chips to contacts of electromagnetic relays, etc., and to form silver contacts directly on the terminals. Further, the time required for applying thick film plating to the surfaces of electrical contact parts such as sliders and busbars or decorative items can be shortened.

Claims (1)

[Claims] 1. Using a silver plating bath with a silver concentration of 40 to 80 g/l and containing no cyanide other than silver cyanide, the frequency of the DC pulse is in the range of 50 to 5000 ms, and the frequency of the DC pulse in the repetition period is The ratio is 0.5-0.
A high-speed electrolytic silver plating method characterized by electrolyzing using a pulsed current in the range of 9.