JP7149061B2 - Electroless palladium plating solution - Google Patents

Description

The present invention relates to an electroless palladium plating solution and an electroless palladium plating film.

Electroless nickel that can provide excellent effects on plating film properties such as solderability and wire bonding as a surface treatment method for printed circuit boards, mounting parts and terminal parts of IC packages in the field of electronics industry / electroless The palladium / displacement gold method (Electroless Nickel Electroless Palladium Immersion Gold: ENEPIG) is widely used, and the ENEPIG process produces an electroless nickel plating film (hereinafter sometimes referred to as "Ni plating film"), an electroless palladium plating film (hereinafter , sometimes referred to as "Pd plating film"), immersion gold plating film (hereinafter sometimes referred to as "Au plating film") sequentially applied plating film (hereinafter referred to as "electroless Ni/Pd/Au plating film") ) are commonly used.

In recent years, in order to respond to the plating film properties required with the miniaturization and high density of electronic parts, for example, electroless palladium plating solution (hereinafter sometimes referred to as "electroless Pd plating solution") is improved. A technique for improving the properties of the plating film has been proposed.

For example, in Patent Document 1, by using bismuth or a bismuth compound instead of a sulfur compound as a stabilizer, bath stability is as high as when a sulfur compound is used, and corrosion resistance, solderability, and wire bondability An electroless Pd plating solution has been proposed in which a film having an excellent ductility can be obtained.

Patent No. 4596553

Commonly used electroless Ni/Pd/Au plating films exhibit excellent wire bondability before exposure to high temperature heat history such as reflow treatment, but the wire bondability drops significantly after high temperature heat history. There was a problem of

The present invention has been made in view of the above circumstances, and its object is to obtain an electroless Pd plating film that constitutes a Pd plating film having excellent wire bonding properties even after high-temperature heat history. An object of the present invention is to provide a plating solution and a Pd plating film.

The electroless palladium plating solution of the present invention, which has solved the above problems, comprises a palladium compound, at least one selected from the group consisting of a hypophosphite compound and a phosphorous acid compound, an amine borane compound, and a hydroboron compound. The gist is to contain at least one selected from the group and a complexing agent.

Preferred embodiments of the electroless palladium plating solution of the present invention also include configurations in which the following requirements are arbitrarily combined.
(i) the amine borane compound is at least one selected from the group consisting of dimethylamine borane and trimethylamine borane;
(ii) the hydroboron compound is a borohydride salt;
(iii) the complexing agent is at least one selected from the group consisting of ammonia and amine compounds;

The present invention also includes an electroless palladium plating film characterized by containing phosphorus and boron. A structure having an electroless gold plating film on the surface of the electroless palladium plating film is also a preferred embodiment of the electroless palladium plating film.

The present invention also includes an electronic device component having the electroless palladium plating film.

By using the electroless Pd plating solution of the present invention, a Pd plating film that constitutes a plating film having excellent wire bonding properties even after high-temperature heat history such as reflow treatment can be obtained.

When the laminated plating film (hereinafter sometimes referred to as "Pd/Au laminated plating film") is exposed to high temperature heat history such as reflow, the connection success rate of subsequent wire bonding The present inventors diligently investigated the cause of the significant decrease in the . As a result, Pd diffuses to the surface of the Au plating film when exposed to a high-temperature thermal history, and the Pd—Au solid solution formed on the surface of the Au plating film reduces the connection success rate of wire bonding. As one solution to this problem, it is conceivable to form a thick Au plating film, but this greatly increases the cost.

As a result of further studies by the present inventors, a Pd plating film containing both P and B as an underlying layer of the Au plating film (hereinafter sometimes referred to as "PB-Pd ternary alloy film") It was found that the wire bondability after high-temperature thermal history can be improved by forming That is, when both P and B are contained in the Pd plating film, it is possible to suppress the formation of a Pd-Au solid solution on the surface of the Au plating film even if it is subjected to a high-temperature heat history. , or even with a thickness less than that, it has been found that a wire bonding property superior to that of the prior art can be obtained.

A PB-Pd ternary system alloy film exhibiting such effects can be easily formed by using the electroless Pd plating solution of the present invention. Specifically, the electroless Pd plating solution of the present invention is selected from the group consisting of at least one selected from the group consisting of a palladium compound, a hypophosphite compound, and a phosphorous acid compound, an amine borane compound, and a hydroboron compound. It is an electroless Pd plating solution containing at least one selected and a complexing agent.

A plurality of reducing agents used in the electroless Pd plating solution are known, and the hypophosphite compound, the phosphite compound, the amine borane compound, and the hydroboron compound used in the plating solution of the present invention are some of them. be. However, conventionally, when a plurality of reducing agents having different reducing powers are used in combination, the stability of the plating solution deteriorates, abnormal deposition occurs, and the properties of the plating film deteriorate. In particular, since the hypophosphite compound and the phosphorous acid compound alone have sufficient reducing power, there was no need to use them in combination with other reducing agents. However, the effect of suppressing the solid solution of Pd in the Au plating film due to thermal history cannot be obtained by adding a reducing agent alone or in combination with reducing agents other than the above, and the above problem occurs only in the above-mentioned specific combination of the present invention. It has been clarified that a Pd plating film can be formed on a practical level, and such a solid solution suppression effect is a unique effect that can be obtained only with the above combination.

Palladium compounds Palladium compounds are sources of palladium ions for obtaining palladium plating. Palladium compounds may be water-soluble, for example, inorganic water-soluble palladium salts such as palladium chloride, palladium sulfate, and palladium acetate; Organic water-soluble palladium salts such as nitrates and dichlorodiethylenediamine palladium can be used. You may use these palladium compounds individually or in mixture of 2 or more types. The Pd ion concentration in the electroless Pd plating solution is not limited, but if the Pd ion concentration is too low, the deposition rate of the plating film may be significantly reduced. On the other hand, if the Pd ion concentration is too high, there is a risk that the physical properties of the film will deteriorate due to abnormal precipitation or the like. Therefore, the content of the palladium compound in the plating solution is preferably 0.01 g/L or more, more preferably 0.1 g/L or more, still more preferably 0.3 g/L or more, and still more preferably 0 as Pd ion concentration. 5 g/L or more, preferably 10 g/L or less, more preferably 5 g/L or less, still more preferably 3 g/L or less. The Pd ions are measured by atomic absorption spectrometry (AAS) using an atomic absorption spectrophotometer.

In the electroless Pd plating solution of the present invention, (1) at least one selected from the group consisting of a hypophosphite compound and a phosphite compound (hereinafter referred to as “phosphorus (2) at least one selected from the group consisting of an amine borane compound and a hydroboron compound (hereinafter sometimes referred to as a "boron compound").

(1) Hypophosphite compounds and at least one selected from the group consisting of phosphite compounds These are P supply sources for the Pd plating film, and are reducing agents for precipitating Pd in the electroless Pd plating solution. acts as Examples of hypophosphite compounds include hypophosphorous acid and hypophosphites such as sodium hypophosphite. Phosphite compounds include phosphorous acid and phosphites such as sodium phosphite. are exemplified. A hypophosphite compound and a phosphite compound may be used alone or in combination. If the content of the hypophosphite compound and/or the phosphite compound in the electroless Pd plating solution is too low, the deposition rate during the plating process will decrease, and Pd will not solidify on the Au plating film due to high-temperature heat history. A sufficient melting suppression effect cannot be obtained, and the wire bondability may deteriorate. As the content of the hypophosphite compound and the phosphite compound in the electroless Pd plating solution increases, the effect of suppressing solid solution improves, but the stability of the electroless Pd plating solution may decrease. The content of the hypophosphite compound and the phosphite compound in the electroless Pd plating solution (when contained alone, it is a single amount, and when two or more are contained, it is a total amount.) is preferably 0 .1 g/L or more, more preferably 0.5 g/L or more, still more preferably 1 g/L or more, still more preferably 2 g/L or more, preferably 100 g/L or less, more preferably 50 g/L or less , more preferably 20 g/L or less, still more preferably 15 g/L or less.

(2) At least one selected from the group consisting of an amine borane compound and a hydroboron compound These are a boron supply source for the Pd plating film and act as a reducing agent for depositing palladium in the electroless Pd plating solution. Examples of amine borane compounds include dimethylamine borane (DMAB) and trimethylamine borane (TMAB), and examples of hydroborane compounds include alkali metal borohydride salts such as sodium borohydride (SBH) and potassium borohydride (KBH). are exemplified. In the present invention, it is preferable to use at least one selected from the group consisting of dimethylamine borane, trimethylamine borane, sodium borohydride, and potassium borohydride. If the content of the boron compound in the electroless Pd plating solution is too low, the deposition rate during the plating process will decrease, and the effect of suppressing the solid solution of Pd in the Au plating film due to the high-temperature heat history will not be sufficiently obtained. Bondability may deteriorate. As the content of the boron compound in the electroless Pd plating solution increases, the effect of suppressing solid solution improves, but the stability of the electroless Pd plating solution may decrease. The content of the boron compound in the electroless Pd plating solution (when it is contained alone, it is the amount alone, and when it contains two or more, it is the total amount) is preferably 0.01 g / L or more, more preferably 0.1 g/L or more, more preferably 0.5 g/L or more, still more preferably 1 g/L or more, preferably 100 g/L or less, more preferably 50 g/L or less, still more preferably 30 g/L Below, more preferably 20 g/L or less.

Complexing Agent The complexing agent mainly has the effect of stabilizing the solubility of Pd in the electroless Pd plating solution. Various known complexing agents may be used as the complexing agent, preferably at least one selected from the group consisting of ammonia and amine compounds, more preferably an amine compound. Examples of amine compounds include methylamine, dimethylamine, trimethylamine, benzylamine, methylenediamine, ethylenediamine, ethylenediamine derivatives, tetramethylenediamine, diethylenetriamine, ethylenediaminetetraacetic acid (EDTA), alkali metal salts thereof, and EDTA derivatives. , glycine and the like. A complexing agent can be used alone or in combination of two or more. The content of the complexing agent in the electroless Pd plating solution (when it is contained alone, it is the single amount, and when it contains two or more kinds, it is the total amount) may be appropriately adjusted so that the above effects can be obtained. preferably 0.5 g/L or more, more preferably 1 g/L or more, still more preferably 3 g/L or more, still more preferably 5 g/L or more, preferably 50 g/L or less, more preferably 30 g /L or less.

Since the electroless Pd plating solution of the present invention exhibits the above effect if it has the above component composition, it may be composed only of the above component composition, but various additives such as pH adjusters and stabilizers may be added as necessary. It may contain an agent.

pH Adjusting Agent If the pH of the electroless Pd plating solution of the present invention is too low, the deposition rate of Pd tends to decrease, while if the pH is too high, the stability of the electroless Pd plating solution may decrease. It is preferably pH 4-10, more preferably pH 6-8. The pH of the electroless Pd plating solution can be adjusted by adding a known pH adjuster. Examples of pH adjusters include acids such as hydrochloric acid, sulfuric acid, nitric acid, citric acid, malonic acid, malic acid, tartaric acid and phosphoric acid, and alkalis such as sodium hydroxide, potassium hydroxide and aqueous ammonia. These can be used alone or in combination of two or more.

Stabilizer Stabilizer is added as necessary for purposes such as plating stability, improvement of appearance after plating, and adjustment of plating film formation speed. The electroless Pd plating solution of the present invention can further contain known sulfur-containing compounds. The sulfur-containing compound is preferably one or more selected from, for example, thioether compounds, thiocyan compounds, thiocarbonyl compounds, thiol compounds, thiosulfuric acid and thiosulfate salts. Specifically, thioether compounds such as methionine, dimethylsulfoxide, thiodiglycolic acid, and benzothiazole; thiocyanates such as thiocyanic acid, potassium thiocyanate, sodium thiocyanate, and ammonium thiocyanate; thiocarbonyls such as thiourea and derivatives thereof. compounds; thiol compounds such as cysteine, thiolactic acid, thioglycolic acid, mercaptoethanol and butanethiol; and thiosulfates such as sodium thiosulfate. These sulfur-containing compounds can be used alone or in combination of two or more. The content of the stabilizer in the electroless Pd plating solution (when it is contained alone, it is a single amount, and when it contains two or more types, it is a total amount) is appropriately adjusted so that effects such as plating stability can be obtained. It may be adjusted, preferably 0.1 mg/L or more, more preferably 0.5 mg/L or more, preferably 500 mg/L or less, more preferably 100 mg/L or less.

The electroless Pd plating solution of the present invention does not contain a surfactant. When a surfactant is added to the electroless Pd plating solution of the present invention, the surfactant is adsorbed on the surface of the resulting Pd plating film, resulting in poor film-forming properties of the Au plating film. As a result, the wire bondability also deteriorates. Surfactants are various known nonionic, cationic, anionic and amphoteric surfactants.

The present invention includes a Pd plating film containing P and B using the above electroless Pd plating solution. The effect of suppressing the solid solution of Pd can be obtained if both P and B are contained in the Pd plating film, so each content is not limited, but if the content of P or B contained in the Pd plating film increases, A more excellent effect of suppressing solid solution of Pd is obtained. The P content in the Pd plating film is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, preferably 10% by mass or less, and more preferably 5% by mass or less. The B content in the Pd plating film is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, preferably 15% by mass or less, and more preferably 10% by mass or less. Further, by appropriately controlling the ratio of P and B, a more excellent effect of suppressing solid solution of Pd can be obtained. The mass ratio (P:B) of the contents of P and B in the electroless Pd plating film is preferably 10:1 to 1:10, more preferably 5:1 to 1:5. The Pd plating film of the present invention should only contain P and B, and may further contain components derived from the various additives described above. The balance is Pb and unavoidable impurities.

The electroless Pd plating solution of the present invention is also suitable for a Pd/Au laminated plating film in which an Au plating film is laminated on a Pd plating film used for plating for bonding of electronic parts. Therefore, it is also a preferred embodiment to form a laminated plating film having the Pd plating film and the Au plating film of the present invention. In the Pd plating film of the present invention, at least the Pd/Au laminated plating film in which the Au plating film is laminated can be confirmed to have the effect of suppressing the solid solution of Pd. Therefore, the substrate for forming the Pd plating film is not limited, and various known substrates such as Al, Al-based alloys, Cu and Cu-based alloys, Fe, Co, Ni, Cu, Zn, Ag, Au, Pt, etc., and A plated film obtained by coating a base material with a metal such as these alloys, which has catalytic properties for reduction deposition of a Pd plated film, can be mentioned. Even metals having no catalytic properties can be used as objects to be plated by various methods.

As another preferred embodiment, the electroless Pd plating solution of the present invention can be applied to the ENEPIG process. In the ENEPIG process, for example, the Pd of the present invention is formed by forming a Ni plating film, a Pd plating film, and then an Au plating film on the Al, Al-based alloy, Cu, or Cu-based alloy that constitutes the electrode. An electroless Ni/Pd/Au plating film containing a plating film is obtained. In addition, the formation of each plating film should just employ|adopt the method currently performed normally. Hereinafter, a method for producing an electroless Ni/Pd/Au plating film having a Pd plating film of the present invention will be described based on the ENEPIG process. can be changed as appropriate based on

Plating conditions and a plating apparatus for electroless Ni plating using an electroless Ni plating solution are not particularly limited, and various known methods can be appropriately selected. For example, the object to be plated may be brought into contact with the electroless Ni plating solution at a temperature of 50 to 95° C. for about 15 to 60 minutes. The film thickness of the Ni plating film may be appropriately set according to the required properties, and is usually about 3 to 7 μm. Various known compositions such as Ni--P alloy and Ni--B alloy can be used for the electroless Ni plating solution.

Plating conditions and a plating apparatus for electroless Pd plating using the electroless Pd plating solution of the present invention are not particularly limited, and various known methods can be appropriately selected. For example, the object to be plated on which the Ni plating film is formed may be brought into contact with the electroless Pd plating solution at a temperature of 50 to 95° C. for about 15 to 60 minutes. The film thickness of the Pd plating film may be appropriately set according to the required properties, and is usually about 0.001 to 0.5 μm.

Plating conditions and a plating apparatus for electroless gold plating using an electroless gold plating solution are not particularly limited, and various known methods can be appropriately selected. For example, the object to be plated on which the Pd plating film is formed may be brought into contact with the electroless gold plating solution at a temperature of 40 to 90° C. for about 3 to 20 minutes. The film thickness of the gold plating film may be appropriately set according to the required properties, and is usually about 0.01 to 2 μm.

If the Pd plating film of the present invention is used, the diffusion and solid solution of palladium from the Pd plating film to the Au plating film can be suppressed due to the thermal history in the mounting process after the formation of the plating film such as reflow treatment. Excellent wire bondability can be realized. The temperature of the thermal history is the temperature assumed in the mounting process, and is not particularly limited. By using the Pd plating film of the present invention, it is possible to realize excellent wire bonding properties even after a high temperature heat history of, for example, 50° C. or higher, more preferably 100° C. or higher.

Electronic Equipment Components The present invention also includes electronic equipment components having the plating film. Electronic device components include, for example, chip components, crystal oscillators, bumps, connectors, lead frames, hoop materials, semiconductor packages, and printed circuit boards. In particular, it is suitably used for UBM (Under Barrier Metal) forming technology for the purpose of soldering and wire bonding (W/B) bonding to Al electrodes or Cu electrodes on wafers. By laminating an Au plating film on a Pd plating film using the electroless Pd plating solution of the present invention, excellent wire bonding properties can be realized even after thermal history.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited by the following examples, and can be modified appropriately within the scope that can conform to the gist of the above and later descriptions. It is of course possible to implement them, and all of them are included in the technical scope of the present invention.

A BGA substrate (Ball Grid Array: manufactured by Uemura Kogyo Co., Ltd., 5 cm x 5 cm) was subjected to the pretreatment and plating treatment shown in Table 1 in order, and a test piece on which a Ni plating film, a Pd plating film, and an Au plating film were formed in order from the substrate side. 1-18 were produced. The wire bondability of the obtained test piece was examined.

Wire bonding property Wire bonding was performed using a tester (a semi-automatic wire bonder HB16 manufactured by TPT), and evaluated by a bond tester SERIES4000 manufactured by Dage under the following measurement conditions with 20 points per condition. In addition, the measurement was performed before the heat treatment and after the heat treatment (holding at 175° C. for 16 hours). As a wire bonding property evaluation, "excellent" when the wire bonding average strength after heat treatment is 9.0 g or more, "good" when it is 8.5 g or more and less than 9.0 g, and 7.5 g or more and less than 8.5 g. "Fair", and the case of less than 7.5 g was defined as "Poor".

[Measurement condition]
Capillary: B1014-51-18-12 (manufactured by PECO)
Wire: 1 mil-Au wire (manufactured by SPM)
Stage temperature: 150°C
Ultrasonic (mW): 250 (1st), 250 (2nd)
Bonding time (ms): 200 (1st), 50 (2nd)
Tensile force (gf): 25 (1st), 50 (2nd)
Step (length from 1st to 2nd): 0.7mm
Measurement method: Wire pull test device: Universal bond tester #4000 (manufactured by Nordson Advanced Technologies)
Test speed: 170 μm/sec

As shown in Table 2, the [complexing agent] defined in the present invention, [hypophosphorous acid compound and/or phosphorous acid compound], and [amine borane compound and/or hydroboron compound] The test piece No. using the electroless Pd plating solution containing All of the wire bondability after the heat treatment of Nos. 1 to 9 were evaluated as "good" or better.

On the other hand, the test piece No. using the Pd plating solution that does not satisfy the provisions of the present invention. Wire bondability after heat treatment of Nos. 10 to 18 were all evaluated as "Poor".

Claims (3)

a palladium compound;
at least one selected from the group consisting of a hypophosphite compound and a phosphite compound;
at least one selected from the group consisting of an amine borane compound and a hydroboron compound;
An electroless palladium plating solution characterized by containing a complexing agent. 2. The electroless palladium plating solution according to claim 1, wherein said amine borane compound is at least one selected from the group consisting of dimethylamine borane and trimethylamine borane, and said hydroborane compound is a borohydride salt. 3. The electroless palladium plating solution according to claim 1, wherein said complexing agent is at least one selected from the group consisting of ammonia and amine compounds.