JPH08269727A - Electroless palladium plating solution and plating method - Google Patents

Abstract

PURPOSE: To improve plating bath stability, depositing rate and plating film property by adding an inorganic sulfur compound such as thiosulfate into an electroless palladium plating solution containing a palladium compound, a reducing agent and a complexing agent. CONSTITUTION: The inorganic sulfur compound is added into the electroless palladium plating solution containing the palladium compound, the reducing agent and the complexing agent. As the palladium compound, a water soluble salt such as palladium chloride is suitable and is used by 0.001-0.5mol/l. Hypophosphorous acid, its salt, phosphorous acid, its salt, a borohydride, aminoborans as the reducing agent and ammonia, amins as the complexing agent are respectively used. As the inorganic sulfur compound, thiosulfate, polythionate, dithionite, sulfite and dithionate or the like is used by 0.01-10mmol/l. A plating film hardly causing cracks is rapidly formed by controlling the pH of the plating solution to 4-10 and dipping a material to be plated thereinto.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroless palladium plating solution and a plating method which are preferably used as plating for bonding electronic parts and the like.

[0002]

2. Description of the Related Art Conventionally, the problems to be solved by the invention
Electroless nickel plating /
The electroless gold plating process is the mainstream, but recently, it has been demanded to reduce the cost of electronic parts etc. Therefore, electroless palladium plating has been attracting attention in place of the costly electroless gold plating. It was

For this reason, various electroless palladium plating solutions have been proposed (JP-A-62-124280, JP-A-1-268877, JP-A-5-214551).

However, the conventional electroless palladium plating film has a problem that cracks are likely to occur and therefore the solder wettability and bonding property are inferior to those of the gold plating film. Further, the conventional electroless palladium plating solutions have problems that the bath stability is poor and the deposition rate is slow.

The present invention has been made in view of the above circumstances.
An object of the present invention is to provide an electroless palladium plating solution and a plating method which provide a plating film which is excellent in bath stability, has a high deposition rate, and is resistant to cracks.

[0006]

Means for Solving the Problems and Actions The inventors of the present invention have conducted extensive studies to achieve the above object, and as a result, have found that palladium compounds, hypophosphorous acid and salts thereof, phosphorous acid and salts thereof, and hydrogenation. A reducing agent selected from boride and amine boranes, and an electroless palladium plating solution containing a complexing agent selected from ammonia and amines, thiosulfate, polythionate, dithionite, sulfite and By adding an inorganic sulfur compound selected from dithionate, the stability of the electroless palladium plating solution is significantly improved, the deposition rate is also improved, and cracks occur in the obtained electroless palladium plating film. It has been found that it is difficult to form a plating film having excellent solder wettability and bondability, and thus the present invention has been accomplished.

The present invention will be described in more detail below. The electroless palladium plating solution of the present invention comprises a palladium compound, hypophosphorous acid and its salt, phosphorous acid and its salt, borohydride and amine boranes. An inorganic sulfur compound is added to an electroless palladium plating solution containing a reducing agent selected and a complexing agent selected from ammonia and amines.

Any palladium compound may be used as long as it is water-soluble, and for example, palladium chloride, palladium sulfate, palladium acetate or the like can be used. The usage amount is 0.001 to 0.5 m
It is preferably ol / l, particularly 0.01 to 0.1 mol / l. If it is too small, the plating rate will decrease, and if it is too large, the physical properties of the coating may deteriorate.

As the reducing agent, as described above,
Hypophosphite, hypophosphite such as sodium hypophosphite,
Any of phosphite, phosphites such as sodium phosphite, borohydrides such as sodium borohydride, and amine boranes such as dimethylamine borane and diethylamine borane are used. The usage is 0.001-5mo
It is preferably 1 / l, particularly 0.2 to 2 mol / l. If it is too small, the deposition rate will decrease, and if it is too large, the bath may become unstable.

Further, ammonia and amines are used as complexing agents. Examples of the amines include methylamine, dimethylamine, trimethylamine, benzylamine, methylenediamine, ethylenediamine, tetramethylenediamine, diethylenetriamine, EDTA, EDTA sodium, N-hydroxyethylenediaminetriacetic acid and its salts, glycine, N-methylglycine, bitantoin. acid,
Examples thereof include imidazoline and 2-methyl-2-imidazoline, and these can be used alone or in combination of two or more. Of these, dimethylamine, ethylenediamine, and N-hydroxyethylenediaminetriacetic acid are particularly preferable. The usage is 0.001-1
It is preferably 0 mol / l, particularly preferably 0.1 to 2 mol / l. If it is too small, the stability of the bath will decrease, and if it is too large, the plating rate will decrease.

The electroless palladium plating solution of the present invention contains
In addition to the above components, thiosulfates (divalent inorganic sulfur compounds), polythionates (for example, in O ₃ S—Sn—SO ₃ , n = 1 to 4 inorganic sulfur compounds), dithionite (3 Valent inorganic sulfur compound), sulfite (tetravalent inorganic sulfur compound), dithionate (pentavalent inorganic sulfur compound) selected from one or more inorganic sulfur compounds, This significantly improves the stability of the plating solution, the deposition rate, and the plating film characteristics. A water-soluble salt such as sodium salt is used as the salt.

The amount of the inorganic sulfur compound added is 0.01 to
10 mmol / mole, especially 0.1-5 mmo
If the amount is too small, the above-mentioned effects cannot be sufficiently achieved, and if the amount is too large, the plating rate tends to decrease.

Various nonionic, cationic, anionic and amphoteric surfactants may be added to the plating solution of the present invention for the purpose of improving the uniformity of the plating film. In this case, the added amount can be 0.01 to 10 g / l.

The plating solution of the present invention has a pH of 4 to 10, especially 6
It is preferably -8, and if the pH is too low, the stability of the bath will be reduced, and if the pH is too high, cracks will tend to occur in the plating film.

The above-mentioned electroless palladium plating solution is suitably used as a plating for bonding electronic parts, etc. When plating is performed using this, the object to be plated may be immersed in this plating solution. Examples of the material of the liquid to be plated include iron, cobalt, nickel, copper, tin, silver, gold, platinum, palladium and the like, and alloys thereof, which have catalytic properties for reducing and depositing the electroless palladium plating film. . If the metal has no catalytic property, so-called galvanic initiation is performed (electricity is applied to the object to be plated until reduction precipitation occurs), or plating is performed after forming a plating film of the above-mentioned catalytically active metal. It suffices to carry out, and for glass, ceramics, plastics, or the like, or metals having no catalytic activity as described above, plating can be carried out after attaching metal catalyst nuclei such as palladium nuclei according to a conventional method.

The plating temperature is 30 to 80 ° C., especially 5
The temperature is preferably 0 to 70 ° C. Further, the plating solution can be stirred if necessary.

[0017]

The electroless palladium plating solution of the present invention is
High stability of the bath makes it possible to carry out plating work at high temperature without any problems. In addition to having a high deposition rate, it has excellent physical properties of the film, no cracks occur, and a plating film with excellent solder wettability and bondability is obtained. To give.

[0018]

EXAMPLES The present invention will be described below in detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

Comparative Example 1 PdCl ₂ 5 g / L Ethylenediamine 25 g / L Sodium hypophosphite 20 g / L pH 8 Bath temperature 50 ° C.

Comparative Example 2 PdCl ₂ 3 g / L Ethylenediamine 25 g / L Sodium hypophosphite 20 g / L Thiodiglycolic acid 20 mg / L pH 8 Bath temperature 50 ° C.

Comparative Example 3 PdCl ₂ 3 g / L ethylenediamine 25 g / L thiodiglycolic acid 20 mg / L dimethylamineborane 10 g / L pH 8 bath temperature 50 ° C.

Example 1 PdCl ₂ 3 g / L ethylenediamine 25 g / L sodium hypophosphite 20 g / L sodium thiosulfate 50 mg / L pH 8 bath temperature 50 ° C.

Example 2 PdCl ₂ 3 g / L Ethylenediamine 25 g / L Sodium hypophosphite 20 g / L Sodium dithionate 40 mg / L pH 8 Bath temperature 70 ° C.

Example 3 PdCl ₂ 3 g / L ethylenediamine 25 g / L dimethylamine borane 10 g / L sodium sulfite 40 mg / L pH 8 bath temperature 70 ° C.

Example 4 PdCl ₂ 3 g / L Ethylenediamine 25 g / L Dimethylamine borane 10 g / L Sodium dithionite 50 mg / L pH 8 Bath temperature 70 ° C.

The above components were dissolved in water to prepare a plating solution for each example, and the stability was examined by the following method. 90 ° C. heating test : 100 ml of plating solution is hermetically stored in a beaker in a 90 ° C. high temperature tank. Room temperature test : 1 liter of plating solution is sealed and stored in a polyethylene container at room temperature. Next, an iron plate having nickel-boron electroless nickel plating on its surface (Ni4 μm) was dipped in each of the above plating solutions, plated for 1 hour at the bath temperature described in each example, and the deposition rate was evaluated. did. Also,
0.5μm electroless palladium plating film under the same conditions
Then, the presence or absence of cracks was examined by SEM observation.

Further, solder wettability and bond
The dinging property was evaluated. Solder wettability : 10 x 50mm 42 alloy meniscogula
Apply the same nickel plating to the test piece, and then
After applying a palladium plating film of 0.5 μm, a meniscus
It was evaluated by cograph. In this case, the nickel / gold process
Evaluation was made on the basis of the solder wetness.Bondability : Plating on the evaluation piece (plating conditions
Is the same as above), and the strength is evaluated by bonding with a gold wire.
did. In this case, the nickel / gold process is used as the basis for evaluation.
Was. Table 1 shows the above results.

[0028]

[Table 1]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hirokazu Masamoto 1-5-1, Exit Hirakata, Osaka Prefecture Uemura Industrial Co., Ltd. Central Research Laboratory

Claims (4)

[Claims] 1. A palladium compound, a reducing agent selected from hypophosphorous acid and salts thereof, phosphorous acid and salts thereof, borohydrides and amine boranes, and a complexing agent selected from ammonia and amines. Electroless palladium plating characterized in that an inorganic sulfur compound selected from thiosulfate, polythionate, dithionite, sulfite and dithionate is added to the contained electroless palladium plating solution. liquid. 2. The amount of the inorganic sulfur compound added is 0.01 to 1.
The plating solution according to claim 1, which is 0 mmol / l. 3. The plating solution according to claim 1, which has a pH of 4 to 10. 4. An electroless characterized in that an object to be plated is immersed in the plating solution according to any one of claims 1 to 3 to form an electroless palladium plating film on the object to be plated. Palladium plating method.