JP3035763B2 - Electroless palladium plating solution - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electroless palladium plating solution.

[0002]

2. Description of the Related Art Conventionally, it has been effective to apply a surface coating to an electrical contact portion of an electronic component with a noble metal having corrosion resistance and excellent electrical characteristics. The surface coating method using a noble metal, which is currently widely used in industry, is a noble metal plating method, but it is impossible to coat a surface that is electrically isolated by this method. On the other hand, according to the electroless plating method, the surface coating can be performed even on an electrically isolated portion, so that noble metal surface coating on an electrically isolated portion is conventionally performed by electroless gold plating. I have. However, since the market price of gold is remarkably high, surface coating with other noble metals has been considered as an alternative to gold. Especially, palladium is the cheapest among the platinum group, so it is widely used as a new functional material not only as a contact material Industrial use in a range.

Conventionally used electroless palladium plating solutions include, for example, an electroless palladium plating solution comprising divalent palladium salt, ethylenediaminetetraacetic acid, ethylenediamine and sodium hypophosphite (Japanese Patent Publication No. Sho.
No. 6-26764). Electroless palladium plating solution containing as essential components at least one of a palladium compound, ammonia and an amine compound, an organic compound containing a divalent sulfur compound, and at least one of a hypophosphorous compound and a borohydride compound ( JP-A-62-12
No. 4280) is known.

[0004]

SUMMARY OF THE INVENTION The above mentioned Japanese Patent Publication No. Sho 46-2676.
The No. 4 electroless palladium plating solution had poor storage stability and had a defect of decomposing in a short time. Also,
Each of the plating films obtained from this plating solution has many cracks and poor solderability, and thus has a difficulty in application to electronic components. Further, the electroless palladium plating solution disclosed in Japanese Patent Application Laid-Open No. Sho 62-124280 discloses a phosphorous compound derived from a hypophosphorous compound or a boron compound as a reducing component.
Since boron was mixed in the plating film, there was a defect that the hardness and the like were significantly varied as compared with the pure palladium plating film.

In view of the above situation, the present inventors have conducted intensive studies to obtain an electroless palladium plating solution that can be used on an industrial scale and that can form a highly pure palladium film. As a result, formic acid, sodium formate and formic acid were used as reducing agents for the electroless palladium plating solution.
An electroless palladium plating solution composed of potassium or the like and using at least one of ammonia and an amine compound as a stabilizer has an appropriate deposition rate, is excellent in stability, and the obtained plating film has cracks. It has been found that the plating film is a high-purity palladium film having almost no impurities derived from the reducing agent, and has a good solderability, and has a low purity.

[0006]

That is, the present invention relates to (1) (a) 0.0001 to 0.5 mol / l of a palladium compound, and (b) 0.0005 to 8 mol of at least one of ammonia and an amine compound. / L (c) formic acid, sodium formate
An electroless palladium plating solution comprising at least one member selected from the group consisting of lithium and potassium formate in an amount of 0.005 to 5 mol / l, (2) an electroless palladium plating solution wherein component (c) contains citric acid or tartaric acid. An object of the present invention is to provide an electroless palladium plating solution according to claim 1.

Hereinafter, the present invention will be described in more detail. The palladium compound used in the present invention is palladium chloride,
Sodium palladium chloride, potassium palladium chloride,
It is a water-soluble palladium compound such as palladium ammonium chloride, palladium sulfate and palladium acetate. The use concentration of the palladium compound in the electroless palladium plating solution is preferably in the range of 0.0001 to 0.5 mol / l. A concentration of 0.0001 mol / l or less is not preferable because the deposition rate of the plating film becomes slow, and a concentration of 0.5 mol / l or more is not practical because the deposition rate does not further improve.

In the plating solution of the present invention, at least one of ammonia and an amine compound is used to maintain the stability of the solution. Ammonia and the amine compound form a complex with palladium in the plating solution to stably hold these components in the solution, thereby contributing to the stabilization of the solution. The concentration of the ammonia and the amine compound is 0.0
005 to 8 mol / l, preferably 0.01 to 5 mol / l
It is. When using ammonia alone, the concentration is more preferably 0.05 mol / l or more in order to improve the stability of the plating solution. The higher the concentration of ammonia and the amine compound, the better the stability of the plating solution. However, if the concentration is higher than the above, it is uneconomical. Particularly when ammonia is used, the working environment is deteriorated due to odor and the like, which is not preferable. . On the other hand, if the concentration is lower than the above, the stability of the plating solution is lowered and the palladium complex is easily separated, which is not preferable.

Examples of the amine compound used in the present invention include monoamines such as methylamine, ethylamine, propylamine, trimethylamine and dimethylethylamine, methylenediamine, ethylenediamine, and the like.
Diamines such as tetramethylenediamine, hexamethylenediamine, diaminetriamine, polyamines such as pentaethylenehexamine, and other amino acids, ethylenediaminetetraacetic acid and its sodium salt, potassium salt, ammonium salt, nitrilotriacetic acid and its sodium salt, Potassium salt, ammonium salt, glycine,
And iminodiacetic acid. In the present invention, at least one of the above-mentioned ammonia and amine compounds may be used. However, when ammonia is used alone, the time until plating starts to be deposited may be long. In this case, the time can be shortened by adding an amine compound as an acetylating agent. With the plating solution to which the above-mentioned amine compound is added, the appearance of the plating film when the plating film is thickened is particularly good.

Next , formic acid and sodium formate used in the present invention.
The concentration of chromium and potassium formate used in the plating solution is 0.005 to 5 mol / l, preferably 0.01 to 1 mol / l.
Mol / l. At a concentration of 0.005 mol / l or less,
If the plating film is not sufficiently formed, and if the concentration is 5 mol / l or more, the deposition rate is in an equilibrium state and cannot be further improved, so that it is not practical.

The plating solution of the present invention can be used in a pH range of 3 to 10. In this pH range, a good plating film can be formed. The pH of the plating solution is adjusted with an acid such as hydrochloric acid or sulfuric acid or an alkaline substance such as sodium hydroxide or potassium hydroxide.

The plating solution of the present invention can be plated at a wide temperature range of 20 to 90 ° C.
When the solution temperature is 0 to 80 ° C., a smooth, glossy and good plating film is obtained. Also, the higher the liquid temperature, the higher the deposition rate of the plating film tends to be, and an arbitrary deposition rate can be obtained by appropriately setting the temperature within the above-mentioned temperature range. Furthermore, in the plating solution of the present invention,
Since the deposition rate of the plating film depends not only on the temperature of the plating solution but also on the palladium concentration, the deposition rate of the plating film can be adjusted by appropriately setting the palladium concentration. Is easy.

In order to form a plating film with the plating solution of the present invention, a substrate having a catalytic property for reductive deposition of the palladium film may be immersed in the plating solution within the above-mentioned temperature range. Examples of the catalytic substrate include, for example,
Examples include iron, nickel, cobalt, gold, silver, copper, platinum, palladium, and alloys thereof. In addition, even a substrate having no catalytic property such as resin, glass, and ceramics may be immersed in a plating solution in the same manner as described above by imparting catalytic property by a known method such as a sensitizing-activator method. Thus, a plating film can be formed. The deposition of the palladium film by the electroless palladium plating solution of the present invention proceeds autocatalytically. Therefore, a film having a low porosity and excellent adhesion can be obtained.

[0014]

The electroless palladium plating solution of the present invention comprises:
Since the storage stability of the liquid is extremely good and precipitation can be performed at a low temperature, the workability is good and the working environment is good. Further, since the deposition rate depends on the palladium concentration and the solution temperature, it is easy to control the plating film thickness. Since no phosphorus, boron, or the like is mixed into the plating film, high-purity palladium having good catalytic activity can be obtained. The plating film obtained by the plating solution of the present invention has very few cracks and is excellent in solderability and wire bonding. Since the plating solution of the present invention has excellent characteristics as described above, it has a great practical value as a plating material for various electronic components requiring high reliability.

[0015]

The present invention will be described below in detail with reference to examples.

Example 1 Composition of plating solution Palladium chloride 0.02 mol / l Ethylenediamine 0.08 mol / l Sodium formate 0.15 mol / l The above plating solution was adjusted to pH with hydrochloric acid and sodium hydroxide.
It was adjusted to 6.0, and at a liquid temperature of 70 ° C., a copper plate preliminarily subjected to electroless nickel plating was immersed for 60 minutes. As a result, a 1.1 μm-thick palladium plating was obtained.

Example 2 Composition of plating solution Palladium chloride 0.02 mol / l Ethylenediamine 0.08 mol / l Formic acid 0.15 mol / l Citric acid 0.05 mol / l The above plating solution was treated with hydrochloric acid and sodium hydroxide. By pH
It was adjusted to 6.0, and at a liquid temperature of 70 ° C., a copper plate preliminarily subjected to electroless nickel plating was immersed for 60 minutes. As a result, 2.4 μm-thick palladium plating was obtained.

Example 3 A plating solution having the same composition as in Example 2 was adjusted to pH 6.0 with hydrochloric acid and sodium hydroxide, and the solution temperature was 55 ° C. and 61 ° C.
C, 70 ° C. and 80 ° C., the copper plate pre-electroless nickel plated was immersed for 10 minutes, resulting in a film thickness of 0.1 μm, 0.2 μm, 0.4 μm, and 0.6 μm
Palladium plating was obtained.

Example 4 A plating solution having the same composition as in Example 2 was adjusted to pH 6.0 with hydrochloric acid and sodium hydroxide. At a solution temperature of 70 ° C., a copper plate preliminarily subjected to electroless nickel plating was treated for 10 minutes and 20 minutes. , 30 minutes and 60 minutes immersion resulted in film thicknesses of 0.3 μm, 0.6 μm, 1.1 μm, and 2.3.
A μm palladium plating was obtained. The result is shown in FIG. From FIG. 1, it can be seen that the immersion time and the plating thickness are in a proportional relationship, the deposition proceeds autocatalytically, and the stability of the deposition rate is extremely good. Further, the plating solution was heated to 90 ° C., but the plating solution did not decompose, and the plating solution did not decompose even when stored tightly at room temperature for one year.

[0020]

FIG.

The hydrochloric acid and potassium hydroxide Example 5 Plating solution composition palladium chloride 0.04 mol / l ethylenediamine 0.08 mol / l potassium formate 0.30 mol / l tartaric acid 0.05 mol / l The above plating solution By pH
Adjusted to 6.0, at a liquid temperature of 70 ° C., a copper plate preliminarily subjected to electroless nickel plating was immersed for 8 hours, and the section hardness of the thick palladium plating was measured. As a result, the Vickers hardness was 170 Hv. In addition, 300
Vickers hardness 170H after heating for 2 hours
v.

Example 6 Composition of plating solution Ammonium palladium chloride 0.02 mol / l Ethylenediaminetetraacetic acid 0.03 mol / l Sodium formate 0.15 mol / l Aqueous ammonia (28%) 0.05 mol / l PH of plating solution with hydrochloric acid and sodium hydroxide
It was adjusted to 6.0, and at a liquid temperature of 60 ° C., a copper plate previously subjected to electroless nickel plating was immersed for 20 minutes. As a result, palladium plating having a thickness of 0.2 μm was obtained.

Comparative Example Composition of plating solution Palladium chloride 0.01 mol / l Ethylenediamine 0.03 mol / l Thiodiglycolic acid 20 mg / l Sodium hypophosphite 0.06 mol / l The above plating solution was treated with hydrochloric acid and water. PH by sodium oxide
It was adjusted to 8.0, and at a liquid temperature of 50 ° C., a copper plate previously subjected to electroless nickel plating was immersed for 24 hours, and the cross-sectional hardness of the thick palladium plating was measured. As a result, the Vickers hardness was 450 Hv. In addition, 300
C. Vickers hardness 700H after heating for 2 hours
v. From the above Example 5 and Comparative Example, it can be seen that the hardness of the palladium film obtained from the plating solution of the present invention does not change even after heat treatment, and that the stability is excellent.

[0024]

[Brief description of the drawings]

FIG. 1 is a view showing a relationship between a plating time and a deposited plating film when a plating solution of Example 4 is used.

Claims (2)

(57) [Claims] (A) a palladium compound 0.0001 to
0.5 mol / l, (b) at least one of ammonia and an amine compound 0.0005 to 8 mol / l (c) selected from formic acid, sodium formate and potassium formate
Electroless palladium plating solution, characterized in that it comprises at least one 0.005 mol / l was. 2. The component (c) contains citric acid or tartaric acid.
The electroless palladium plating solution according to claim 1.