JP2016160504A - ELECTROLESS Ni/Au PLATED FILM FORMING METHOD, AND ELECTROLESS Ni/Au PLATED FILM OBTAINED BY THE FORMING METHOD - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of stabilizing the reaction rate of an electroless Ni/Au plating precipitation reaction at the time of forming an electroless Ni/Au plating film, within a controllable range, and forming an electroless Ni/Au plating film having an excellent corrosion resistance.SOLUTION: In a Ni/Au plated film forming method for forming a nickel coating on the circuit surface of a wiring circuit board and forming a gold plating film on the surface of said nickel coating, there is adopted an electroless Ni/Au plating film forming method or the like, which is characterized in that said nickel coating is formed by subjecting the circuit surface of the wiring circuit board to an electroless Ni strike plating and then to an electroless Ni plating.SELECTED DRAWING: Figure 1

Description

  The present application relates to a method for forming an electroless Ni / Au plating film and an electroless Ni / Au plating film obtained by the forming method. The electroless Ni / Au plating film here is used particularly on the surface of a wiring circuit, the surface of a connection terminal of a semiconductor chip, and the like.

  In recent years, wiring boards, semiconductor chips, and the like incorporated in personal computers, mobile communication devices, and the like have been required to have high functionality as well as downsizing and weight reduction. Therefore, high density and high speed signal are required for wiring boards and semiconductor chip mounting substrates mounted thereon. In such a case, an electroless Ni / Au plating layer that eliminates the need to form a plating lead or the like has been used for the wiring board and the semiconductor chip mounting substrate.

  The electroless Ni / Au plating layer has an electroless nickel film on the base and a gold plating film (at least a displacement gold plating film) on the surface thereof. For the formation of the electroless nickel plating film at this time, a solution using hypophosphite as a reducing agent (hereinafter referred to as “hypophosphite plating solution”) has been widely used. In the case of this hypophosphite plating solution, phosphorus and nickel contained in hypophosphite are co-deposited in an amorphous state in the bulk of the formed electroless nickel film. -"Phosphorus alloy film" is formed. Such an electroless nickel plating film is used as an undercoat for displacement gold plating, and prevents the components of metal conductor wiring made of copper, copper alloy, etc. from diffusing into the gold plating film and degrading its physical properties. As well as providing excellent corrosion resistance and wear resistance.

  The replacement gold plating film (thickness: 0.01 μm to 0.1 μm) provided on the surface of the electroless nickel plating film is formed by thin gold plating on the electroless nickel plating film by a substitution reaction. Improves corrosivity and contributes to improving solder wettability of metal conductor wiring. In order to increase the bonding strength between the gold plating film and the gold wire in wire bonding and improve the connection reliability, an electroless gold plating film (thickness: 0. 1 μm to 1.0 μm) may be provided to increase the thickness.

  Adjacent to the electroless Ni / Au plating layer provided on the circuit surface as the density of the circuit using the above electroless Ni / Au plating film increases and the signal current flowing through the circuit increases in speed. There is a demand for accuracy to avoid as much as possible the occurrence of short-circuit defects between circuits and the deterioration of insulation reliability.

  From such a viewpoint, Patent Document 1 provides a semi-additive etchant that can maintain a good circuit cross-sectional shape even in a fine circuit, a semi-additive method using the same, and a method for manufacturing a wiring board. In the case of performing electroless Ni / Au plating, if metal residue remains on the surface of the insulating layer, the plating metal is deposited on the surface of the insulating layer, resulting in short circuit failure or insulation reliability. It is disclosed to prevent the occurrence of the decrease. That is, Cr, Ni, and the like, which are rust preventive components on the surface of the copper foil used for wiring board formation, are likely to remain on the surface of the insulating resin even after the copper foil is etched. Therefore, in order to remove the metal residue from the insulating resin, a method of removing the metal residue with a ferricyanide metal salt and an etching solution containing a chelating agent has been proposed.

  However, the above-described metal ferricyanide salt is easily decomposed and highly toxic, increasing the burden of waste liquid. And since the etching liquid containing a chelating agent is strongly acidic, there exists a problem that the damage given to the interface of a circuit and an insulating resin layer becomes large. Therefore, in Patent Document 2, metal residues such as Cu, Ni, and Cr remaining on the surface of the insulating layer can be removed, and a “chelating agent” is used as a metal residue removing solution that suppresses precipitation abnormality such as electroless Ni / Au plating. And a metal residue removing solution characterized by exhibiting alkalinity.

JP 2004-277854 A JP 2006-245199 A

Tajima, K .; Surface Technology, 62 (8), 387 (2011).

  However, as disclosed in Patent Literature 1 and Patent Literature 2, even if the problem of the metal residue on the surface of the insulating layer is solved, Ni nodules are generated in the electroless Ni plating film, and the deposition state of the subsequent displacement gold plating There was a problem that affected it. In particular, when electroless Ni / Au plating is performed on a fine copper wiring circuit, a bridge phenomenon (hereinafter referred to as “Ni bridge phenomenon”) that occurs when electroless Ni plating is performed as the wiring pitch is narrowed. Is a big problem. In order to solve this problem, in recent years, application of a Ni thinning process in the formation of an electroless Ni / Au plating film has been studied.

  When forming an electroless Ni / Au plating film using this Ni thinning process, the Ni particles deposited by the electroless method are non-uniform, so when performing substitution Au plating on the surface of the electroless nickel film, Local corrosion phenomenon of electroless nickel film is likely to occur. Further, the precipitation of Ni particles by the electroless nickel method is easily influenced by the surface state of the base and the adsorption state of the Pd catalyst. Pd used as a catalyst has a very high hydrogen storage property and excellent substitution reactivity. Therefore, depending on the adsorption state of Pd, the precipitation reaction of electroless Ni plating proceeds rapidly, making it difficult to control and generating Ni nodules. There was a trend.

  As can be understood from the above, the reaction rate of the electroless Ni plating deposition reaction when forming the electroless Ni / Au plating film is stabilized within a controllable range, and the deposited Ni particles are uniform and Ni nodules. Therefore, there has been a demand for a method capable of forming an electroless Ni / Au plating film that suppresses the occurrence of oxidization and has good corrosion resistance.

  Therefore, the inventors of the present application pay attention to Ni that has a lower hydrogen storage property than Pd used as a catalyst and causes an oxidation reaction of hypophosphorous acid, and the conventional method for forming an electroless Ni / Au plating film. As an alternative, the following invention has been conceived.

Electroless Ni / Au plating film forming method: The electroless Ni / Au plating film forming method according to the present application is formed by forming a nickel film on a circuit surface of a printed circuit board and applying a gold plating film to the surface of the nickel film. In the forming method of the Ni / Au plating film to be formed, the nickel film is formed by performing electroless Ni plating after performing electroless Ni strike plating on the circuit surface of the printed circuit board.

  The electroless Ni strike plating used in the method of forming an electroless Ni / Au plating film according to the present application contains 1 g / L to 10 g / L of dimethylamine borane and 10 ppm to 200 ppm of Ni as an electroless Ni strike plating solution. An aqueous solution is used.

  In the method for forming an electroless Ni / Au plating film according to the present application, the gold plating film is formed by an electroless gold plating method.

Electronic component material: The electronic component material according to the present application is obtained by using the above-described method for forming an electroless Ni / Au plating film.

  The method for forming the electroless Ni / Au plating film according to the present application is to perform electroless Ni strike plating instead of the conventional Pd catalyst for the formation of the electroless Ni plating film, and then perform electroless Ni plating. The deposition rate of electroless Ni plating is controlled to precipitate uniform Ni particles and suppress the generation of Ni nodules. Therefore, the electroless Au plating film finally applied is also uniform, and an electroless Ni / Au plating film having good corrosion resistance can be formed. Moreover, since the electroless Ni / Au plating film forming method according to the present application does not include electrolytic plating, the manufacturing cost can be reduced. In addition, an electronic component material obtained by using the electroless Ni / Au plating film forming method according to the present application has an electroless Ni / Au plating film having a uniform thickness on the surface, and has good corrosion resistance. To prepare. Furthermore, since the electroless Ni / Au plating film forming method according to the present application uses an electroless plating method, even if the surface shape of the electronic component material is complicated, the surface of the electroless Ni / Au plating film is uniform. / Au plating film can be provided.

It is a scanning electron microscope image which shows the surface state of the electroless nickel membrane before performing the electroless gold plating of an Example and a comparative example. It is a figure which shows the result of the barrier property test using the constant potential electrolysis method of an Example and a comparative example.

Form of formation method of electroless Ni / Au plating film: The formation method of the electroless Ni / Au plating film according to the present application is to form a nickel film on the circuit surface of the wiring circuit board and to perform gold plating on the surface of the nickel film. In the method of forming a Ni / Au plating film for forming a film, the nickel film is formed by performing electroless Ni plating after performing electroless Ni strike plating on a circuit surface of a printed circuit board. To do. That is, it is as follows when the formation method of this electroless Ni / Au plating film is described according to the process.

Object to which electroless Ni / Au plating film is applied: Electroless Ni / Au plating film is provided on the surface of copper wiring circuit of printed wiring boards, semiconductor wafer plating, terminal plating of connector parts, etc. No limitation is required.

Formation of Electroless Nickel Film: In the method of forming an electroless Ni / Au plating film according to the present application, when forming the electroless nickel film on the surface of the wiring circuit included in the above-described circuit board for testing, the electroless Ni film is first formed. Nickel catalyst nuclei are formed using a strike plating bath.

  As the electroless Ni strike plating solution, an aqueous solution containing 1 g / L to 10 g / L of DMAB (dimethylamine borane) and 10 ppm to 200 ppm of Ni is preferably used. On the other hand, when the DMAB is less than 1 g / L, the formation rate of the nickel catalyst nuclei is slow, and the industrially required productivity cannot be satisfied. Even if DMAB exceeds 10 g / L, there is no particular problem, but the effect of improving the formation rate of nickel catalyst nuclei is saturated, which is not preferable because it wastes resources. If Ni is less than 10 ppm, the amount of nickel catalyst nuclei formed is reduced, and the significance of performing strike plating is lost, which is not preferable. On the other hand, when Ni exceeds 200 ppm, excessive nickel catalyst nuclei are generated on the resin between the copper wirings, and Ni bridge phenomenon occurs, which is not preferable.

  This electroless Ni strike plating solution is preferably used in a temperature range of 20 ° C to 40 ° C. When the liquid temperature is less than 20 ° C., the formation rate of the nickel catalyst nuclei is slow, and the state of the nickel catalyst nuclei adhering to the surface of the wiring circuit is also unfavorable because it varies depending on the location. On the other hand, if the liquid temperature exceeds 40 ° C., the rate of formation of nickel catalyst nuclei becomes excessive, and the evaporation of water from the electroless Ni strike plating solution is large, resulting in large composition fluctuations.

  It is preferable to form a nickel catalyst nucleus by immersing an object to which an electroless Ni / Au plating film is applied in the electroless Ni strike plating solution described above for 30 seconds to 300 seconds. When this immersion time is less than 30 seconds, it is difficult to form good nickel catalyst nuclei with the above electroless Ni strike plating solution. On the other hand, even when the immersion time exceeds 300 seconds, there is no particular problem, but it is not preferable because productivity required industrially cannot be satisfied.

  When electroless Ni strike plating is completed as described above, an electroless Ni plating film having a thickness of 0.01 μm to 3 μm is then formed on the surface on which the nickel catalyst nuclei are formed. Strictly speaking, this electroless Ni plating film contains nickel catalyst nuclei formed by electroless Ni strike plating. If the thickness of the electroless Ni plating film is less than 0.01 μm, the underlying wiring circuit surface cannot be sufficiently covered and the corrosion resistance tends to decrease, which is not preferable. On the other hand, when the electroless Ni plating film thickness exceeds 3 μm, the deposition rate of nickel also becomes slow, the surface of the electroless Ni plating film becomes rough, and the surface state of the subsequent electroless gold plating film is affected. Therefore, it is not preferable.

  And in forming this electroless Ni plating film, it is possible to use all of known electroless Ni plating solutions, but considering the best film thickness uniformity and plating coverage, sulfuric acid It is preferable to use an electroless nickel plating solution having a composition of Ni 23 g / L, malic acid 13 g / L, lactic acid 18 g / L, lead 0.2 ppm, and sodium hypophosphite 23 g / L.

Formation of electroless gold plating film: When the formation of the electroless Ni plating film on the surface of the wiring circuit is completed as described above, an electroless Au plating film is formed on the surface of the electroless Ni plating film. The electroless Au plating film has a thickness of 0.01 μm to 0.2 μm. When the thickness of the electroless Au plating film is less than 0.01 μm, the surface of the electroless Ni plating film may not be uniformly coated, which is not preferable. On the other hand, when the thickness of the electroless Au plating film exceeds 0.2 μm, the surface of the electroless Au plating film becomes rough, which is not preferable.

  As this electroless gold plating solution, all known electroless gold plating solutions can be used. However, using a cyan substitutional electroless Au plating solution of potassium gold cyanide 2.8 g / L, citric acid 3K 30 g / L, phosphoric acid 8 g / L, ethylenediaminetetraacetic acid 58 g / L, the film thickness is uniform. It is preferable for obtaining an electroless Au plating film having excellent properties. In consideration of environmental load and workability improvement, when using a non-cyanide substitution type electroless Au plating solution, for example, sodium gold sulfite 5 g / L, sodium sulfite 25 g / L, sodium thiosulfate 30 g / L, It is preferable to use a composition of sodium L-ascorbate 15 g / L and ammonium chloride 5 g / L.

  The electroless Au plating solution for forming the electroless Au plating film is preferably used in a temperature range of 70 ° C. to 95 ° C. When the liquid temperature is less than 70 ° C., the deposition rate of the electroless Au plating film is extremely decreased, which is not preferable. On the other hand, when the liquid temperature exceeds 95 ° C., the composition variation of the electroless Au plating solution is large, and the surface state of the electroless Au plating film varies, which is not preferable.

  It is preferable to perform electroless Au plating by immersing an object to which an electroless Ni / Au plating film is applied in the electroless Au plating solution described above for 60 seconds to 20 minutes. When this immersion time is less than 60 seconds, the electroless Au plating film becomes 0.01 μm, which is not preferable because the electroless Ni plating film may not be sufficiently coated. On the other hand, when the immersion time exceeds 20 minutes, an electroless Au plating film having a thickness of more than 0.2 μm is formed and the surface becomes rough.

Form of Electronic Component Material: The electronic component material according to the present application is obtained by using the above-described method for forming an electroless Ni / Au plating film. Here, “electronic component material” is described as requiring any conductive terminal plating such as a printed wiring board, a semiconductor chip mounting substrate, a chip component, and a connector component. By using the method for forming an electroless Ni / Au plating film according to the present application, it is possible to improve the corrosion resistance of bonding parts, connection terminal portions, and the like of electronic component materials.

Preparation of test wiring board: The copper foil layer on the surface of the double-sided copper-clad laminate is pickled with dilute hydrochloric acid, dry film lamination is performed on the surface of the cleaned copper foil layer, and a 100 μm pitch (circuit) A test linear circuit having a width of 50 μm and an inter-circuit gap of 50 μm was formed. Thereafter, a desmut treatment was performed using a desmut solution containing phosphoric acid and hydrogen peroxide to obtain a test circuit board.

Formation of electroless nickel coating: A nickel catalyst core was formed on the surface of a copper circuit included in the above-described test circuit board using electroless Ni strike plating. The electroless Ni strike plating at this time was an aqueous solution containing 4 g / L of DMAB and 20 ppm of Ni, and a test circuit board was immersed therein for 60 seconds to form a nickel catalyst nucleus. Thereafter, an electroless Ni plating film having a thickness of 0.5 μm was formed on the surface on which the nickel catalyst core was formed. In this case, the electroless Ni plating film was formed by treatment with Ni sulfate 23 g / L, malic acid 13 g / L, lactic acid 18 g / L, lead 0.2 ppm, and hypophosphorous acid Na 23 g / L.

Formation of electroless gold plating film: An electroless Au plating film was formed on the surface of the electroless Ni plating film using a test circuit board in which the electroless Ni plating film was formed on the surface of the copper circuit. Here, a cyanide substitution type electroless Au plating solution of potassium gold cyanide 2.8 g / L, citric acid 3K 30 g / L, phosphoric acid 8 g / L, and ethylenediaminetetraacetic acid 58 g / L is used. A test circuit board having an electroless Ni plating film formed on the surface thereof is immersed for 300 seconds to selectively form an electroless Au plating film having a thickness of 0.05 μm only on the electroless Ni plating film. An electroless Ni / Au plating film was provided on the copper wiring circuit.

Comparative example

Formation of electroless nickel coating: Palladium catalyst nuclei were formed on the surface of a copper circuit provided in the above-described test circuit board using a Pd chloride catalyst solution. The Pd chloride catalyst solution at this time was an aqueous solution containing 50 ppm of Pd, and the test circuit board was immersed therein for 60 seconds to form Pd catalyst nuclei. Thereafter, an electroless Ni plating film having a thickness of 0.5 μm was formed on the surface on which the Pd catalyst was formed. The same solution as in the example was used for forming the electroless Ni plating film.

Formation of electroless gold plating film: An electroless Au plating film was formed on the surface of the electroless Ni plating film using a test circuit board in which the electroless Ni plating film was formed on the surface of the copper circuit. Here, a test circuit board in which an electroless Ni plating film is formed on the surface of a copper circuit is immersed for 300 seconds using the same cyan-based substitutional electroless Au plating solution as in the example. An electroless Au plating film having a thickness of 0.05 μm was selectively formed only on the plating film, and an electroless Ni / Au plating film was provided on the fine copper wiring circuit.

<Evaluation method of electroless Ni / Au plating film>
As the evaluation of the electroless Ni / Au plating film, “Ni and Au film surface morphology observation”, “underlying Ni local corrosion state observation”, and “barrier property test using constant potential electrolysis method” were performed. The test methods for each test are described below.

Ni and Au film surface morphology observation method: Each plating surface was observed using a field emission scanning electron microscope (FE-SEM).
Observation of underlying Ni local corrosion state: The Au coating was dissolved and removed from the sample applied up to the Au plating film using a cyan-based gold stripping solution, and the surface of the underlying Ni was observed by FE-SEM. For the analysis of the P-rich layer formed by the underlying Ni local corrosion, the film depth direction analysis was performed using an Auger electron spectroscopy analyzer.
Barrier property test using constant potential electrolysis method: A sample subjected to Au plating was used as an anode, a platinum coil as a counter electrode, and a silver / silver chloride electrode as a reference electrode. These electrodes were immersed in a 10 vol% sulfuric acid aqueous solution, a voltage of −50 mV was applied, and the current flowing at that time was read.

<Contrast between Example and Comparative Example>
Comparison of Ni and Au film surface morphology observation: Each surface state of “electroless nickel film before electroless gold plating of example” and “electroless nickel film before electroless gold plating of comparative example” Were observed with a scanning electron microscope, and there was no significant difference in their surface morphology. However, when each surface state of "the gold plating surface after electroless gold plating of the example" and "the gold plating surface after electroless gold plating of the comparative example" is observed with a scanning electron microscope, it can be understood from FIG. Thus, it can be seen that the Au particles constituting the electroless gold plating of the comparative example are rough, and the Au particles constituting the electroless gold plating of the example have a finer and smoother surface.

Contrast in observation of underlying Ni local corrosion state: As a result of observation of underlying Ni local corrosion state, the electroless Ni / Au plating film of the example is more electroless than the electroless Ni / Au plating film of the comparative example. There was little local Ni local corrosion after film peeling.

Comparison in barrier property test using constant potential electrolysis method: As can be understood from FIG. 2, it can be seen that the elution current is smaller in the example than in the comparative example. Therefore, it can be said that the example is equipped with dense electroless gold plating with less surface defects such as pinholes than the comparative example.

  From the above, by using the electroless Ni strike plating when forming the electroless nickel film as in the electroless Ni / Au plating film forming method according to the present application, in a uniform precipitation state compared to the conventional method, In addition, it is possible to form an electroless Ni / Au plating film having excellent corrosion resistance.

  Since the method for forming an electroless Ni / Au plating film according to the present application does not use a conventional Pd catalyst and does not employ an electrolytic plating method, the manufacturing cost is low. The method for forming an electroless Ni / Au plating film according to the present application is to form an electroless Ni / Au plating film having good corrosion resistance on a circuit surface on a printed wiring board, a connector terminal, or a silicon wafer. Is possible. Therefore, an electronic component material provided with a high quality electroless Ni / Au plating film can be supplied to the market.

Claims (4)

In a method for forming a Ni / Au plating film in which a nickel film is formed on a circuit surface of a printed circuit board, and a gold plating film is formed on the surface of the nickel film,
The method for forming an electroless Ni / Au plating film, wherein the nickel film is formed by performing electroless Ni strike plating on a circuit surface of a printed circuit board, followed by electroless Ni plating. The electroless Ni strike plating uses an aqueous solution containing 1 g / L to 10 g / L of dimethylamine borane and 10 ppm to 200 ppm of Ni as an electroless Ni strike plating solution. Method for forming Au plating film. The method for forming an electroless Ni / Au plating film according to claim 1, wherein the gold plating film is formed by an electroless gold plating method. An electronic component material obtained by using the electroless Ni / Au plating film forming method according to claim 1.