JP2013253282A - Electroless plating bath and electroless plated film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electroless plating bath, which is free from boric acid used as a pH buffer, has a low nickel content, and can be provided as a condensed solution.SOLUTION: An electroless plating bath 1 includes: copper sulfide hemihydrate 0.03 M; nickel sulfide 0.01 M; trisodium citrate 0.06 M as a complexing agent; sodium hypophosphite 0.18 M as a reducing agent, sodium carbonate 0.25 M as a buffer; lithium hydroxide as a pH adjuster, and a surfactant and the like which are not essential.

Description

  The present invention relates to an electroless plating bath containing hypophosphorous acid containing copper ions and nickel ions, and an electroless copper nickel plating film formed by the electroless plating bath.

  The electroless plating method is widely used as a method for forming a metal film on a conductive material such as metal or an electrical insulator such as resin or ceramic. In order to form a copper film having excellent characteristics as a conductor by an electroless plating method, it is common to use formalin (formaldehyde) as a reducing agent. However, formalin is harmful to the human body and regulations are being investigated.

  On the other hand, an electroless copper plating bath using hypophosphite as a reducing agent has been studied. However, it is not easy to reduce copper ions directly with hypophosphite. The inventor disclosed in Japanese Patent Application Laid-Open No. 2000-212762 that a continuous copper-nickel film can be deposited by adding nickel ions to an electroless copper plating bath using hypophosphite as a reducing agent. Disclosure. In the nickel ion addition bath, nickel metal reduced and precipitated by hypophosphite serves as a catalyst, and copper deposition proceeds.

In the above electroless copper plating bath, boric acid is a pH buffer that suppresses pH fluctuations in the vicinity of the cathode, and is an important component for stable deposition. However, since boric acid has low solubility, the electroless copper plating bath cannot be shipped as a concentrated solution, and cannot be said to be easy to transport.
Boron contained in boric acid is regulated as a substance that may cause damage to human health. However, it is not easy to reduce the boron concentration in wastewater treatment.

  For this reason, there has been a demand for an electroless plating bath that can be provided in a concentrated solution, particularly an electroless plating bath that does not contain boric acid. Further, since the resistance increases as the nickel content of the plating film increases, a plating film having a low nickel content has been demanded.

Japanese Unexamined Patent Publication No. 2000-212762

  An object of an embodiment of the present invention is to provide an electroless plating bath that can be provided in a concentrated solution and a low-resistance plated film manufactured using the electroless plating bath.

  The electroless plating bath according to the embodiment of the present invention includes copper ions, nickel ions, complexing agent ions, hypophosphite ions, and carbonate ions.

  Moreover, the plating film of another embodiment is formed using an electroless plating bath containing copper ions, nickel ions, complexing agent ions, hypophosphite ions, and carbonate ions.

  According to the embodiment of the present invention, it is possible to provide an electroless plating bath that can be provided in a concentrated solution and a plating film manufactured using the electroless plating bath.

It is a schematic diagram for demonstrating a plating state. It is a figure for demonstrating the pH buffer function of carbonate ion. It is a figure which shows the relationship between the carbonate ion concentration of an electroless-plating bath, and the nickel content rate of a copper nickel film. It is a figure which shows the relationship between the carbonate ion density | concentration of an electroless-plating bath, and precipitation rate. It is a figure which shows the relationship between the carbonate ion concentration of an electroless-plating bath, and a resistivity.

Hereinafter, the plating bath 1 of the embodiment will be described.
As shown below, the plating bath 1 contains copper ions, nickel ions, complexing agent ions, hypophosphite ions, and carbonate ions. M represents mol / liter (mol / L).

<Plating bath 1>
Copper sulfate pentahydrate 0.03M
Nickel sulfate hexahydrate 0.01M
Trisodium citrate anhydrous 0.06M
Sodium carbonate 0.25M
Sodium hypophosphite monohydrate 0.18M
Surfactant appropriate amount Lithium hydroxide 0.1 g / liter Bath temperature: 45 ° C
pH 9.0

  For comparison, a plating film 103 similar to that of the plating bath 1 was formed on a plating bath 101 of a comparative example using boric acid as a pH buffer, as shown below, to obtain a plating film 103. Also, in the plating bath 1, the amount of sodium carbonate added was increased or decreased to form a plating film. Further, film formation was performed using potassium carbonate instead of sodium carbonate.

<Plating bath 101>
Instead of sodium carbonate boric acid, the same amount of 0.25M
Otherwise, it is the same as plating bath 1.

  Sources of copper and nickel ions include various aqueous salts such as copper sulfate pentahydrate and nickel sulfate hexahydrate, such as chloride, sulfate, formate, acetate, carbonate, Use hydroxides or other salts.

  The concentration C (M) of the copper ion is preferably 0.005 to 0.3M. If the concentration is not less than the above range, the precipitation reaction proceeds stably, and if it is not more than the above range, precipitation such as copper sulfate occurs. There is no. Further, the nickel ion concentration N (M) is preferably C / N of 1-10. If it is more than the said range, copper precipitation reaction will advance continuously, and if it is less than the said range, the nickel content rate in a plating film is low and it is low resistance.

  Sources of complexing agent ions include various water soluble compounds such as trisodium citrate anhydrate, such as Rochelle salt, ethylenediaminetetraacetic acid (EDTA), aspartic acid, glutamic acid, succinic acid, citric acid, or A salt or derivative of the above compound is used. The concentration of the complexing agent ion is preferably 0.5 to 4 with respect to (C + N). If the concentration is higher than the above range, precipitation does not occur. If the concentration is lower than the above range, the concentrate can be easily manufactured. .

  Hypophosphorous acid (phosphinic acid) ion is a reducing agent, and sodium hypophosphite or potassium hypophosphite is used as a supply source. The concentration of hypophosphite ion is preferably 1 to 10 with respect to (C + N). If the concentration is higher than the above range, the precipitation reaction proceeds stably. If the concentration is lower than the above range, the plating bath is self-decomposed. There is no.

  Lithium hydroxide is added to adjust pH and improve conductivity, but is not an essential component, and sodium hydroxide or the like may be used. The plating bath 1 preferably has a pH in the range of pH 8 to pH 11, and the precipitation reaction proceeds stably. If the plating bath is within the above range, the plating bath will not self-decompose.

  A surfactant is not an essential component, but is preferably added to improve wettability with a substrate. As the surfactant, a cationic, anionic, nonionic or amphoteric surfactant that has been conventionally added to the plating bath is used.

And the carbonate ion which is the characteristic of the plating bath 1 has a pH buffer function in the range of pH8-pH11, as shown in FIG. As a carbonate ion supply source, carbonate such as sodium carbonate or potassium carbonate is preferably used, but carbonated water in which carbon dioxide gas is dissolved by bubbling or the like may be used, or carbon dioxide gas is bubbled into the plating bath 1. It may be dissolved.
<Film formation method>
As shown in FIG. 1, COP (cyclofin polymer) is used as a substrate, and after immersion in an electroless plating bath 1 for 7 minutes after ultraviolet irradiation treatment, alkali treatment, conditioning treatment, palladium ion treatment, and reduction treatment, a plating film 3 Got.

<Evaluation>
EPMA was used for composition analysis and thickness measurement of the plating film 3. On the other hand, after performing heat treatment at 80 ° C. for 30 minutes, 20 μm-thick electrolytic copper plating was formed using the plating film 3 as the underlying conductive layer, and after performing heat treatment at 80 ° C. for 30 minutes, the adhesion strength was measured. It was.

  As shown in FIG. 3, when the carbonate ion concentration is 0.5 M or less, the nickel content of the electroless copper nickel plating film is 15 wt% or less. Moreover, as a carbonic acid supply source, the nickel content of the electroless copper nickel plating film was smaller in potassium carbonate (K) than in sodium carbonate (Na).

  The phosphorus content was 0.4 wt at a carbonate ion concentration of 0.25M, but increased as the carbonate ion concentration increased and exceeded 1 wt% when the carbonate ion concentration exceeded 1.0M.

  On the other hand, as shown in FIG. 4, when the carbonate ion concentration is 0.1 M or more, the precipitation reaction starts, and when the concentration is 0.2 M or more, the deposition rate is sufficiently compatible with practical use. If it exceeds, the effect of improving the deposition rate becomes small.

  Moreover, as shown in FIG. 5, if the carbonate ion concentration is 1.0 M or less, preferably 0.6 M or less, the resistivity of the electroless copper nickel plating film does not increase greatly.

In addition, the nickel content of the electroless copper nickel plating film of the comparative example formed from the plating bath 101 of the comparative example using boric acid is 20.7 wt%, the phosphorus content is 3.1 wt%, and the deposition rate is 28 It was 0.4 μg / cm ² / min, and the resistivity was 63 μΩ · cm.

  From the above results, it was found that the carbonate ion concentration is preferably 0.1 to 1.0M, and particularly preferably 0.20 to 0.60M. In applications where the nickel content is not a problem, there is no particular upper limit for the carbonate ion concentration, and it may be contained up to the solubility limit.

  The adhesion strength was 0.8 kN / m for the plating film formed from the plating bath 101 of the comparative example, whereas 0.8 kN / m for the plating film formed from the plating bath 1. It was equivalent.

  Here, the solubility (20 ° C.) of boric acid is 47.2 g / liter (0.76 M). Furthermore, since the solubility of sodium borate is 26.0 g / liter (0.13 M), the solubility of boric acid in the sodium-containing solution is further lowered, the dissolution rate is slow, and the time required for dissolution is increased.

On the other hand, the solubility of sodium carbonate is 216 g / liter (2.04 M), which is 2 times or more, and the solubility of potassium carbonate is 1120 g / liter (8.10 M), which is 10 times or more. For this reason, potassium carbonate is particularly preferred as the carbonate ion supply source. In addition, even if an excessive amount of carbonate is added, since it is released as a gas, no precipitation or the like occurs.

  In the plating bath 1, the copper ion supply source, the nickel ion supply source, the complexing agent ion supply source, and the hypophosphite ion supply source have the same solubility as sodium carbonate, which is the carbonate ion supply source. Is 200 g / liter (20 ° C.) or more.

That is, the solubility (20 ° C.) is as follows.
Copper sulfate pentahydrate 317 g / liter Nickel sulfate hexahydrate 650 g / liter Trisodium citrate anhydrous 730 g / liter Sodium hypophosphite monohydrate 1000 g / liter

  For this reason, when the plating bath 101 of the comparative example was concentrated twice, boric acid was precipitated. The concentration ratio N of the concentrated liquid is the volume of the concentrated liquid / the volume of the solution before the concentration. On the other hand, the plating bath 1 was stable without precipitation for a long time even when concentrated 10 times.

  Even when the plating bath 1 concentrated 10 times was diluted with water, the same result as the plating bath 1 not concentrated was obtained. In addition, you may concentrate the plating bath 1 to the range which can melt | dissolve all the components.

  In addition, the concentrated solution of the plating bath 1 may be a so-called one-component type that concentrates in a state including all compounds except for the pH adjusting agent, or is composed of a plurality of concentrated solutions according to solubility and stability. It may be. In addition, it is preferable to mix the hypophosphorous acid which is a reducing agent, and a metal salt as separate concentrates, and to mix at the time of a bath.

  For example, the plating bath 1 can be a two-component concentrate comprising the following concentrate A and concentrate B.

<Concentrate A>
Copper sulfate pentahydrate 0.3M
Nickel sulfate hexahydrate 0.1M
Trisodium citrate anhydrous 0.4M
Sodium carbonate 2.5M
Lithium hydroxide 1.0 g / liter Surfactant 10 times the appropriate amount

<Concentrate B>
Sodium hypophosphite monohydrate 1.8M
Trisodium citrate anhydrous 0.2M

  The electroless plating bath 1 is prepared by adding 0.1 liter of concentrate A and 0.1 liter of concentrate B to 0.8 liter of water, and adjusting the pH with sodium carbonate as necessary. Is done.

  In the above-described two-component concentrate, the total concentration required for 1 liter of the electroless plating bath 1 is 0.2 liter, and the concentration rate is five times.

  Since the electroless plating bath 1 is prepared by diluting a concentrated solution of 2 times or more, for example, 10 times with water, transportation and the like are easy.

  As described above, the electroless plating bath 1 according to the embodiment does not contain boron and can be provided as a concentrated solution. Moreover, according to the electroless plating bath of the embodiment, a low resistance copper nickel plating film having a low nickel content can be produced.

  The present invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the scope of the present invention.

Claims (7)

Copper ions,
With nickel ions,
A complexing agent ion;
Hypophosphite ions,
An electroless plating bath comprising carbonate ions.   The electroless plating bath according to claim 1, wherein the carbonate ion is contained in an amount of 0.1 mol / liter or more.   The electroless plating bath according to claim 2, wherein the carbonate ion is contained in an amount of 1.0 mol / liter or less.   The water solubility of the copper ion source, nickel ion source, complexing agent ion source, hypophosphite ion source, and carbonate ion source are all 200 g / liter (20 ° C.) or higher. The electroless plating bath according to claim 3.   The electroless plating bath according to claim 4, wherein the electroless plating bath is prepared by diluting a concentrated solution having a concentration ratio of 2 times or more with water.   An electroless plating film formed by using the electroless plating bath according to any one of claims 1 to 5. It forms into a film using the electroless-plating bath of any one of Claims 3-5,
An electroless plating film having a nickel content of 15 wt% or less.

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