JP3201737B2 - Platinum plating bath and plating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a platinum plating bath and a plating method therefor.

[0002]

2. Description of the Related Art Platinum plating has a large internal strain in a deposited layer and a high internal stress, so that it is difficult to increase the plating thickness. However, platinum plating can be used in a high-temperature atmosphere, and because of its various properties as platinum, such as good thermal conductivity and good electrical conductivity, switches used in high-temperature environments, various sensor materials, and electrode materials Widely used for such applications.

[0003]

However, the platinum plating baths which have been used in the past are rarely strongly alkaline baths, but are generally constructed with chloroplatinic acid, amino nitrite, tetrachloroammonium salt and the like. The strongly acidic baths that were used were the mainstream.

[0004] Therefore, since the pH of the platinum plating bath is strongly acidic or strongly alkaline, there has been a problem that the plating object itself is attacked by the plating solution and a product defect easily occurs. Therefore, there has been a demand for a platinum plating bath which has a pH closer to neutrality and which has a long-term stability so that the plating object itself is not affected by the plating solution.

[0005] Further, in the conventional water-soluble platinum plating bath, there are problems that an oxide is generated on the anode side, and the plating solution is unstable and easily decomposed. In addition, the current efficiency is about 65% at the maximum, and the maximum deposition efficiency cannot be obtained unless the current density is very low. Therefore, there is a problem that the plating rate is very low. Furthermore, this conventional platinum plating bath is susceptible to fluctuations in various factors such as fluctuations in solution temperature and bath composition concentration during plating, and causes variations in plating speed. I couldn't get it. As a result, quality control is complicated, and the product yield is reduced.

The present invention has been made in view of such problems in the prior art, and is practical and stable, hardly decomposed, and capable of achieving high current efficiency and high plating rate. It provides a platinum plating bath.

[0007]

The platinum plating bath according to the present invention comprises, as a platinum compound, a platinum (II) complex salt, disodium malonate, malonamide, acetic acid, oxalic acid, tartaric acid, sodium propionate, and urea. One obtained by adding one or more compounds selected from the group and stirring the mixture is used.

The platinum concentration is 1 to 200 as platinum.
g / l, preferably 10 to 20 g / l
Can be present. If the platinum concentration is less than 1 g / l, the upper limit of the current density becomes small and it becomes difficult to put the alloy to practical use. If the platinum concentration is more than 200 g / l, the amount exceeds the saturation dissolution amount, and the cost becomes high, which is not suitable for practical use. Platinum (II)
As salts, tetrachloroplatinate (II), tetrabromoplatinate (II), tetraammineplatinate (II), bisoxalatoplatinate (II) and the like can be used.

Further, at least one compound selected from the group consisting of disodium malonate, malonamide, acetic acid, oxalic acid, tartaric acid, sodium propionate and urea at a concentration of 0.001 to 1.0 mol / l, It should be added to the above-mentioned platinum (II) salt, preferably from 0.01 to
The addition amount is 0.20 mol / l. When the amount of addition is 0.
001 to 1.0 mol / l is 0.001 mol
When the amount is less than 1 / l, the effect of stabilizing the platinum plating solution by the addition hardly appears, and when it is more than 1.0 mol / l, the precipitation is hindered. Of the compounds mentioned herein, it is desirable to use disodium malonate. And in the platinum plating solution according to the present invention,
Add 40 g / l of boric acid.

[0010] In addition, the plating conditions in the platinum plating method according to the present invention are set as follows. In the following, each value range described as preferable is
It is determined in consideration of the desired performance of platinum plating and the easiness of process control in actual operation.

The pH value of the plating solution is in the range of 1 to 8, preferably in the range of 4 to 5. Here, the solution pH was set in the range of 1 to 8 because if the pH is less than 1, the upper limit of the usable current density becomes small, and the plating rate cannot be increased. This causes precipitation to occur, which shortens the life of the plating solution.

The temperature of the plating solution is in the range of 50 to 98 ° C., and the temperature is 80 to 90 ° C. Here, the reason why the lower limit temperature is set to 50 ° C. is that when the temperature is lower than this temperature, the deposition rate of platinum becomes extremely slow, and when the upper limit temperature is set to 98 ° C., the evaporation rate of water increases, and the fluctuation of the plating solution concentration is reduced. This is because it tends to occur.

Next, the current density used during plating is:
And 0.01~3.0A / dm ^2, preferably in the range of current density 0.10~0.20A / dm ^2. This is because when the current density is lower than 0.01 A / dm ² , the deposition rate of platinum becomes extremely low, and 3.0 A / dm ^2.
At higher current densities, the polarization ratio between hydrogen and platinum is reversed, most of the supply current is consumed by the polarization of hydrogen, and the generation of hydrogen gas takes precedence over the deposition of platinum, significantly reducing the current efficiency. Because it will be.

[0014]

The present invention will be described in more detail with reference to the following examples.
I will tell.Example 1 Sodium tetrachloroplatinate (II) (at metal concentration) 10 g / l Boric acid 40 g / l Disodium malonate 0.02 mol / l pH 5.0 Temperature 85 ° C Current density 0.15 A / dm²  In this example, the above-mentioned tetrachloro white
Sodium gold (II) salt as a “dicarboxylate”
Add disodium malonate and keep at 85 ° C in a hot bath.
While stirring with a magnetic stirrer for 1 hour
Using.

[0015] Then, a gold strike plating is applied to a test brass piece which is an object to be plated in advance, and a 1 µm
After gold plating, plating was carried out under the above conditions, and a bright platinum plating layer having an average film thickness of 8 μm was obtained. Then, it was confirmed that this platinum plating layer had practically sufficient characteristics in hardness, adhesion, heat resistance, bonding property and the like. At this time, the current efficiency is 10
0%, and the plating rate was 1.5 μm / h on average.

When plating was carried out under the same composition and conditions as described above, except that disodium malonate was replaced with the following compounds, the results shown in Table 1 were obtained. Here, acetic acid is used as a monocarboxylic acid, oxalic acid is used as a dicarboxylic acid, and tartaric acid is used as a hydroxycarboxylic acid. With respect to other characteristics such as the appearance other than the characteristics shown in Table 1, the same effects as in the case of using the above disodium malonate were obtained.

[0017]

[Table 1]

Example 2 Sodium tetrachloroplatinate (II) 10 g / l Boric acid 40 g / l Disodium malonate 0.02 mol / l pH 5 Temperature 85 ° C. Current density 0.5 A / dm ² In the examples, as the platinum compound, a compound obtained by adding disodium malonate to the above sodium tetrachloroplatinate (II) and stirring with a magnetic stirrer for 30 minutes while maintaining at 85 ° C. in a hot bath was used.

The test brass piece to be plated is subjected to gold strike plating in advance, and a 1 μm
After gold plating, plating was performed under the above conditions, and a bright platinum plating layer having an average film thickness of 3 μm was obtained. Then, it was confirmed that this platinum plating layer had practically sufficient characteristics in hardness, adhesion, heat resistance, bonding property and the like. At this time, the current efficiency is 98
%Met.

In the same composition and under the same conditions as above, disodium malonate was replaced with monocarboxylate sodium propionate 0.2 mol / l,
Plating was performed. As a result, the current efficiency was 60%, the film thickness was 0.1 μm, the plating rate was 0.9 μm / h, and the other effects such as the appearance were the same as those obtained when disodium malonate was used.

Example 3 Sodium tetrachloroplatinate (II) (at a metal concentration) 10 g / l Boric acid 40 g / l Oxalic acid 0.02 mol / l pH 5 Temperature 85 ° C. Current density 1.0 A / dm ² As the platinum compound, a compound obtained by adding oxalic acid to the above sodium tetrachloroplatinate (II) and stirring with a magnetic stirrer for 1 hour while maintaining at 85 ° C. in a hot bath was used.

Then, a gold strike plating is applied to a test brass piece to be plated in advance, and a 1 μm
After gold plating, plating was performed under the above conditions, and a bright platinum plating layer having a thickness of 5 μm was obtained. Then, it was confirmed that this platinum plating layer had practically sufficient characteristics in hardness, adhesion, heat resistance, bonding property and the like. At this time, the current efficiency was 90%.

[0023]Example 4 Sodium tetrachloroplatinate (II) 10g / l Boric acid 40g / l Malonamide 0.2mol / l pH5 Temperature 85 ° C Current density 0.15A / dm²  In this example, the above-mentioned tetrachloro white
Add malonamide to sodium gold (II) salt and add hot
1 hour by magnetic stirrer while keeping at 85 ° C by bus
What was stirred for a while was used.

The test brass piece to be plated is subjected to gold strike plating in advance, and a 1 μm
After gold plating, plating was performed under the above conditions, and a bright platinum plating layer having a thickness of 3 μm was obtained. Then, it was confirmed that this platinum plating layer had practically sufficient characteristics such as hardness, adhesion, heat resistance and bonding property. At this time, the current efficiency was 84%.

In the same composition and conditions as above, instead of malonamide, 0.2 mol of propionamide was used.
When plating was performed using 1 / l, the current efficiency was 77
%, And a film thickness of 0.1 μm. Similarly, when urea 0.2 mol / l was used instead of malonamide, the current efficiency was 85%.
%, And a film thickness of 2.8 μm. With respect to other characteristics such as appearance, the same effects as in the case of using the above malonamide were obtained.

[0026]

As described above, the platinum plating bath and the plating method according to the present invention include disodium malonate,
By using a platinum (II) complex salt obtained by adding and reacting at least one compound selected from the group consisting of malonamide, acetic acid, oxalic acid, tartaric acid, sodium propionate, and urea, it has a nearly neutral pH value. In addition, there is an effect that the plating bath is hardly decomposed and the stability of the bath is increased. Furthermore,
INDUSTRIAL APPLICABILITY The plating bath and the plating method according to the present invention make it possible to achieve high current efficiency in platinum plating and obtain a good plating rate.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-90672 (JP, A) JP-A-2-107794 (JP, A) JP-A-4-333587 (JP, A) JP-A-4- 333588 (JP, A) JP-A-4-333589 (JP, A) JP-A-6-316786 (JP, A) JP-A 8-319595 (JP, A) Patent 2577832 (JP, B2) Patent 2972567 (JP) , B2) JP-B-61-58557 (JP, B2) JP-B-41-16412 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) C25D 3/50

Claims (2)

(57) [Claims] Claims: 1. Use of any one of tetrachloroplatinate (II), tetrabromoplatinate (II), tetraammineplatinate (II) and bisoxalatoplatinum (II) containing a divalent platinum salt In an aqueous solution having a concentration of 1 to 200 g / l, 0.001 or more of one or more compounds selected from the group consisting of disodium malonate, malonamide, acetic acid, oxalic acid, tartaric acid, sodium propionate, and urea are added.
A platinum plating bath having a pH of 4 to 5 containing a platinum compound obtained by adding and stirring to a concentration of 1.0 mol / l and reacting by stirring, and 40 g / l of boric acid. 2. The plating bath according to claim 1, wherein the temperature is 50 to 98 ° C. and the current density is 0.01 to 3.0 A / dm.
Platinum plating method performed under condition ² .