JP2015048529A - Catalyst liquid for electroless plating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a palladium ion catalyst aqueous solution for electroless metal plating, not containing tin having an adverse effect on an environment, not using toxic 2-aminopyridine, dispensing with high-temperature aging, and having a stable bath for an extended period at a service temperature.SOLUTION: A catalyst liquid for electroless plating contains a complex of palladium ion and 2-aminoethyl pyridine with pH of 8.5-12, and further contains nano-particles including palladium ion and 2-aminoethyl pyridine with pH of 8.5-12.

Description

  The present invention relates to a stable catalyst solution for electroless plating. More particularly, the present invention relates to a stable aqueous palladium ion catalyst solution for electroless metal plating that is tin-free and stabilized with certain compounds.

  Electroless metal plating is a well-known method for depositing a metal layer on a substrate surface. Electroless metal plating is used in various industries, including decorative plating and the manufacture of electronic components. Electroless metal plating is also widely used in the formation of electrical circuits on printed circuit boards. When electroless plating is performed on the surface of a non-conductive article, it is necessary to deposit a catalyst on the surface in advance. Conventionally, a palladium-tin colloidal catalyst has been used as this catalyst. The palladium-tin colloidal catalyst is made by mixing tin (II) chloride and palladium chloride in an acidic solution.

  However, palladium-tin colloidal catalysts tend to agglomerate, and agglomerated colloids (particle diameter of several hundred nanometers) are scattered on the surface of the object to be plated, resulting in an extremely large amount of plating deposited around the colloid. It is said that the electroless plating deposition on the object to be plated becomes non-uniform, resulting in a decrease in adhesion between the plating film and the substrate and a decrease in insulation. In addition, development of a catalyst containing no tin has been demanded due to recent environmental problems.

  Instead of palladium-tin colloidal catalysts, catalysts comprising noble metal ions and amine complexing agents have been developed. For example, Japanese Patent Application Laid-Open No. 61-15983 (Patent Document 1) dissolves at least one compound of palladium (II), silver (I), copper (I), copper (II), and nickel (II) in an amide. A catalyst for electroless plating containing the complex obtained in this manner is disclosed. International Publication No. 2007/066460 (Patent Document 2) discloses a catalyst comprising a palladium complex formed by a basic amino acid and palladium. JP-A-1-195281 (Patent Document 3) discloses a catalyst obtained by mixing a divalent palladium compound, a lower alkylamine and an aminopyridine in an alkaline aqueous solution. Here, it is described that 2-aminopyridine, 3-aminopyridine, and 4-aminopyridine are used as aminopyridine. JP 2007-138218 (Patent Document 4) discloses a catalyst concentrate for electroless plating containing a divalent palladium compound and an amine complexing agent. Examples of amine complexing agents include pyridine, 2-aminopyridine, 3-aminopyridine, 4-aminopyridine and the like. US Pat. No. 4,248,632 (Patent Document 5) discloses a catalyst comprising a complex compound of a noble metal, and pyridine, 2-aminopyridine, 2-aminomethylpyridine and the like are disclosed as ligands. ing. US Pat. No. 5,503,877 (Patent Document 6) discloses a complex compound containing a metal having at least one organic ligand, wherein the complex exists in the form of an oligomer or polymer. 2-amino-6-methylpyridine is used for ligand formation.

  However, in these prior art documents, there are problems such that the solution temperature after the bathing is increased to 50 ° C. and aging is performed for 2 hours, and two or more complexing agents must be used. Further, 2-aminopyridine is toxic and therefore undesirable to use. Further, according to the study of the present inventors, 2-aminomethylpyridine has a weak complexing ability with palladium ions under an alkaline condition, and therefore, a catalyst bath. It has been found that holding the water at its use temperature (55 ° C.) for several hours can cause the bath to decompose and cause problems in industrial use situations.

Japanese Patent Application Laid-Open No. Sho 61-15983 International Publication No. 2007/066460 JP-A-1-195281 JP 2007-138218 A US Pat. No. 4,248,632 US Pat. No. 5,503,877

  Accordingly, an object of the present invention is to provide a catalyst which does not use toxic 2-aminopyridine, does not need to be aged at high temperature, and has a stable bath for a long time at the use temperature.

As a result of intensive studies, the present inventors can only deposit an electroless metal plating film uniformly by containing 2-aminoethylpyridine and palladium ions and adjusting the pH to a range of 8.5 to 12. In addition, the present inventors have found that a practical catalyst solution can be obtained that is stable for a long time even when the catalyst bath is at a high temperature, and the present invention has been completed.
That is, this invention relates to the catalyst liquid for electroless plating which is a catalyst liquid containing the complex of palladium ion and 2-aminoethyl pyridine, and pH is 8.5-12.

The present invention also relates to a catalyst solution for electroless plating, which is a catalyst solution containing nanoparticles containing palladium ions and 2-aminoethylpyridine, and has a pH of 8.5-12.
Furthermore, this invention relates to the method of forming a plating film on the surface of a to-be-plated object using the said catalyst liquid.

It is a photograph which shows the state of the copper coat | covered with the glass cloth when the backlight test is done about the glass epoxy copper clad laminated board after the electroless copper plating of Example 1. FIG.

  In the present specification, the terms “catalyst solution” and “catalyst bath” are used interchangeably, and “plating solution” and “plating bath” are used interchangeably. ° C means degrees Celsius, g / L means gram per liter, mg / L means milligram per liter, and μm means micrometer. Percentage (%) means% by weight unless otherwise specified herein.

  The electroless plating catalyst solution of the present invention contains palladium ions and 2-aminoethylpyridine having the following structure.

Palladium ions can be obtained by dissolving a palladium compound that generates palladium ions in water in water. Examples of such palladium compounds include palladium chloride, palladium fluoride, palladium bromide, palladium iodide, palladium nitrate, palladium sulfate, palladium oxide, palladium sulfide and the like, and these are used alone or in combination. May be.
The content of palladium ions is preferably 0.05 g / L or more, more preferably 0.1 g / L or more, based on the total amount of the catalyst aqueous solution. At the same time, the content of palladium ions is preferably 1 g / L or less, more preferably 0.5 g / L or less, based on the total amount of the catalyst aqueous solution.

  2-Aminoethylpyridine stabilizes palladium ions and enables use as a practical palladium ion catalyst. According to the study by the present inventors, when 2-aminomethylpyridine, 3-aminomethylpyridine and 2-amino-3-methylpyridine, which are similar compounds of 2-aminoethylpyridine, were used, all were catalysts. It has been found that the bath does not stabilize at high temperatures and decomposes, or the electroless plating film obtained is not uniform and some areas are not plated (skip plating). Without being bound by theory, the presence of an amino group at the 2-position of the pyridine ring via a hydrocarbon chain having 2 carbon atoms allows the nitrogen atom of the pyridine ring and the nitrogen atom of the amino group to be complexed with palladium. It can be positioned at an optimum distance for formation, and it is considered that a catalyst bath that is stable for a long time even at a high temperature as shown in the present invention can be obtained.

  Further, although not limited by theory, in the catalyst solution of the present invention, palladium ions become nanoparticles stabilized by 2-aminoethylpyridine and are considered to exist stably in the catalyst solution. . For this reason, it is considered that the catalyst particles can be uniformly adsorbed on the substrate surface as catalyst particles that are much smaller than the palladium-tin colloidal catalyst, and a uniform and highly adhesive plating film can be obtained.

  The content of 2-aminoethylpyridine is preferably 0.05 g / L or more, more preferably 0.1 g / L or more, preferably 1 g / L or less, more preferably 0.5 g / L or less. .

  The molar ratio of palladium ion to 2-aminoethylpyridine is preferably 1.0: 0.7 to 1.0: 1.5. By setting it within this range, the obtained catalyst solution is stable for a long time even at a high temperature. If the molar ratio of 2-aminoethylpyridine to palladium ions is too small, palladium ions are deposited without being chelated, and precipitation occurs in the catalyst bath. On the other hand, if the molar ratio of 2-aminoethylpyridine to palladium ions is too large, the amount of catalyst adhering to the substrate surface is reduced, causing problems in subsequent electroless plating deposition. In the present invention, even if the catalyst solution is maintained at 55 ° C. for 4 hours, the catalyst solution in which no turbidity or precipitation is observed is assumed to be stable at a high temperature for a long time. The molar ratio of palladium ion to 2-aminoethylpyridine is more preferably 1.0: 1.0 to 1.0: 1.2 from the viewpoint of further stability of the resulting aqueous catalyst solution.

  The catalyst particles contained in the catalyst solution of the present invention are preferably nanoparticles. The diameter of the nanoparticles is preferably 1 to 100 nanometers, more preferably 1 to 50 nanometers, and even more preferably 1 to 10 nanometers.

  The aqueous catalyst solution of the present invention has a pH of 8.5 or higher, preferably 10 or higher. Moreover, pH is 12 or less. The pH can be adjusted to a desired value with a known pH adjusting agent. Since the palladium compound is usually dissolved in water under acidic conditions, the pH is adjusted to the above range by adding an alkaline aqueous solution to the obtained aqueous solution containing palladium ions and 2-aminoethylpyridine. The alkaline aqueous solution is not particularly limited, and sodium hydroxide, potassium hydroxide, sodium carbonate and the like can be used.

  The catalyst aqueous solution of the present invention is prepared, for example, by adding palladium chloride to hydrochloric acid, stirring the solution until the palladium chloride is completely dissolved, adding 2-aminoethylpyridine, adding water to a specified amount, and further adding sodium hydroxide. It can be prepared by adjusting the pH to the desired value with an aqueous solution.

When electroless metal plating is performed on a non-conductive substrate using the aqueous catalyst solution of the present invention, it can be performed according to the following process. As an example, the case where electroless copper plating is performed will be described. First, the substrate is degreased by washing with an acid or alkali solution, washed with deionized water, and then microetched with a known etching solution. Subsequently, after performing deionized water cleaning, acid cleaning, and deionized water cleaning, a catalyst is applied to the substrate surface using the aqueous catalyst solution of the present invention. The catalyst is applied by bringing the substrate into contact with an aqueous catalyst solution adjusted to 20 to 60 ° C. for 2 to 5 minutes. Subsequently, the substrate is washed with deionized water and brought into contact with the reducing agent solution. As the reducing agent, sodium hypophosphite, formaldehyde, stannous chloride, dimethylamine borane, lithium aluminum hydride, lithium borohydride, sodium borohydride and the like can be used. Although content of the reducing agent in a reducing agent solution changes with kinds of reducing agent to be used, when using sodium hypophosphite, for example, they are 20 g / L-100 g / L. Then, it wash | cleans with deionized water and performs electroless copper plating. In the electroless copper plating, a known electroless copper plating solution such as CUPOSIT ^™ 328 (manufactured by Rohm and Haas Electronic Materials Co., Ltd.) can be used.

  Examples of the non-conductive substrate to be plated include a resin substrate using a thermosetting resin, a thermoplastic resin, or a combination thereof. The resin used for the resin substrate is not limited to these, but acetal resin, acrylic resin, cellulose resin, epoxy resin, polyimide resin, phenol resin, cyanate resin, ABS, bismaleimide / triazine resin, polyimide, and mixtures thereof Etc. The non-conductive substrate used in the present invention is not limited to a resin substrate, for example, a substrate using materials including inorganic and organic substances such as glass, ceramic, porcelain, resin, paper, cloth, and combinations thereof. Also good. A substrate using a metal-clad material or an unclad material is also a substrate that can be metal-plated using the catalyst solution of the present invention.

  Examples of the substrate include a printed circuit board. Such printed circuit boards include thermosetting resins, thermoplastic resins, and combinations thereof, including mixtures of resins and fibers such as glass fibers. Specific examples of resins that can be used include, but are not limited to, the above resins.

  EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, these Examples do not limit the scope of the present invention.

  An FR-4 substrate (MCL-E67, thickness 1.6 mm, manufactured by Hitachi Chemical Co., Ltd.), which is a glass epoxy resin substrate, was used as a test substrate and processed according to the process shown in Table 1 below.

Example 1
0.3 g of palladium chloride powder was added to 6 mL of hydrochloric acid and stirred for about 3 hours until the palladium chloride powder was completely dissolved. Thereafter, 0.22 g of 2-aminoethylpyridine was added, and the mixture was further stirred for 10 minutes, and then diluted to 1 liter with deionized water. Subsequently, the pH was adjusted to 12 using an aqueous sodium hydroxide solution to obtain a catalyst solution.

  When the deposition state after performing electroless copper plating according to the process of Table 1 was visually confirmed, a beautiful bright copper-colored uniform deposition film was confirmed. Moreover, it was 0.45 micrometer when the film thickness was measured with the fluorescent X-ray film thickness apparatus (SEIKO SFT9450XRF). A glass epoxy copper-clad laminate R-1705 (FR-4, thickness 1.6 mm, through-hole diameter 0.9 mm) with through-holes was subjected to the same treatment and a backlight test was conducted. It was uniformly coated (FIG. 1).

Examples 2-8, Comparative Examples 1-19
The same operation as in Example 1 was performed except that the compounds shown in Tables 2 to 8 were used instead of 2-aminoethylpyridine of Example 1 and the pH was adjusted to the values shown in Tables 2 to 8. In Examples 7 and 8 and Comparative Examples 16 to 19, 50 g / L sodium hypophosphite was used instead of 1 g / L dimethylaminoborane as a reducing agent in the treatment process. The obtained results are shown in Tables 2-8.

Structure of 2-amino-5-chloropyridine used in Comparative Examples 1-3

Structure of 2-aminomethylpyridine used in Comparative Example 4

Structure of 3-aminomethylpyridine used in Comparative Example 5

Structure of sulfacetamide used in Comparative Example 6

Hydantoin structure used in Comparative Example 7

Structure of picoline used in Comparative Example 8

Structure of nicotinic acid used in Comparative Example 9

Structure of 1,3-di (4-pyridyl) propane used in Comparative Example 10

Structure of hexamethylenediamine used in Comparative Example 11

Structure of 2-amino-3-methylpyridine used in Comparative Examples 12-13 and 16-17

Structure of 2-amino-6-methylpyridine used in Comparative Examples 14-15 and 18-19

Claims (6)

  A catalyst solution for electroless plating containing a complex of palladium ion and 2-aminoethylpyridine and having a pH of 8.5-12.   A catalyst solution for electroless plating, containing nanoparticles containing palladium ions and 2-aminoethylpyridine, and having a pH of 8.5-12.   The catalyst solution for electroless plating according to claim 1 or 2, wherein the molar ratio of palladium ion to 2-aminoethylpyridine is 1.0: 0.7 to 1.0: 1.5.   The catalyst solution for electroless plating according to any one of claims 1 to 3, wherein the pH is 10 to 12.   The catalyst solution for electroless plating according to any one of claims 1 to 4, wherein no precipitation occurs after heating at 55 ° C for 4 hours.     A method for performing electroless plating on a non-conductive substrate using the electroless plating catalyst solution according to claim 1.

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