JP2001172769A - Reducing activation treatment solution for electroless nickel plating and method for producing printed wiring board using the same - Google Patents

Abstract

(57) [Summary] [PROBLEMS] The present invention suppresses the occurrence of white unevenness,
An object of the present invention is to provide a reducing activation treatment solution for electroless nickel plating for enabling formation of a nickel-gold plating film having excellent mounting reliability and a method for manufacturing a printed wiring board using the same. is there. SOLUTION: The reducing agent is dissolved in an aqueous solution of an inorganic base, and in particular, the reducing agent comprises sodium hypophosphite or potassium hypophosphite, and the aqueous solution of the inorganic base is sodium hydroxide and / or It is characterized by being an aqueous solution having a pH of 9 to 13 in which a hydroxide composed of potassium hydroxide is dissolved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroless nickel plating for selectively forming a nickel plating layer on a copper surface, and more particularly to a reducing activation treatment solution for electroless nickel plating used for pretreatment thereof, and The present invention relates to a method for manufacturing a printed wiring board using such a reducing activation treatment solution.

[0002]

2. Description of the Related Art In recent years, as electronic devices such as information communication equipment and information communication terminal equipment have become smaller, the density of printed wiring boards has increased, multilayer wiring boards, CSP and BGA mounting on small-diameter lands have advanced technologies, and low cost. Is required.

In response to these demands, electroless plating technology has been adopted in place of electrolytic plating as a surface treatment of copper. This electroless plating technique will be described with reference to FIGS.

Conventionally, in order to form a nickel plating layer on the surface of copper wiring or copper land 3 disposed on the surface layer of the printed wiring board 1 by this electroless nickel plating, the copper surface must be pretreated before plating. Degreasing, soft etching and PdCl ₂ or Pd called activator
After an activation treatment (palladium nucleus 9 attachment) with Pd containing SO ₄ or the like, the substrate is immersed in an electroless nickel plating solution 11 to form a nickel plating film 12, on which oxidation of the nickel plating film 12 is prevented. In addition, the flash gold plating film 13 for preventing the solderability from being deteriorated is formed by electroless gold plating. In the figure, 4 is a solder resist, 5 is a conductive via, 7 is an inner copper wiring, and 8 is an insulating resin layer.

[0005]

However, as the printed wiring board 1 becomes thinner and more multilayered at the same time as high-density wiring, an abnormal phenomenon may occur in plating deposition depending on the pattern configuration. In particular, it occurs on a specific copper land or copper wiring, for example, a thin copper wiring or a small copper land 2 connected to an inner copper pattern 6 having a large area in FIGS.

[0006] This is because the deposition of nickel is delayed, and when electroless gold plating is performed thereon, the replacement of gold with a nickel film proceeds abnormally, and the plating surface looks abnormally whitish when compared with other lands. Call them white spots)
Becomes

For example, when nickel is formed by plating with a thickness of 5 μm, the plating thickness of the normal copper wiring or copper land 3 is set to b, and the thin copper wiring or the small copper land 2 connected to the inner copper pattern 6 having a large area is set to b1. Then
When b = 5 μm, b1 = 1.5 to 2 μm.

Further, it has been found that the nickel plating film 12 is easily attacked by electroless gold plating, the substitution of gold is intense as compared with a normal nickel plating film, and it looks whitish as compared with other gold plating films. Furthermore, the solder ball pull strength after soldering is weak, and there has been a phenomenon that the solder joint strength is reduced.

The present invention solves the above-mentioned conventional problems, and provides a reducing activation treatment solution for electroless nickel plating for forming a nickel-gold plating film having excellent mounting reliability, and a printed wiring board using the same. It is intended to provide a manufacturing method.

[0010]

In order to solve the above-mentioned problems, the present invention provides a reducing activation solution for electroless plating, characterized in that a reducing agent is dissolved in an aqueous solution of an inorganic base. A reducing agent consisting of sodium hypophosphite or potassium hypophosphite, which is a hypophosphite, and an aqueous solution of an inorganic base in which a hydroxide consisting of sodium hydroxide and / or potassium hydroxide is dissolved; It is characterized by the following aqueous solutions of to 13.

The aqueous solution of the inorganic base is used for increasing the driving force of the reaction of the reducing agent, and may be any one which does not inhibit this. For example, an aqueous solution of NaOH or KOH can be used. Depending on the concentration of the inorganic base, p
Adjust H. When the pH of the aqueous solution, that is, the pH of the reducing activation treatment solution is pH 9 or less, the activation is reduced, and the adherence of electroless nickel plating is deteriorated. On the other hand, if the pH exceeds 13, the resist mask may be damaged.

Accordingly, the pH of the reducing activation treatment solution is preferably pH 9 or more in consideration of the adherence of electroless nickel plating, and the pH is 13 or less in applications where corrosion of the resist mask is required. It is desirable.

[0013] A first activity in which a surface of copper wiring and / or copper land, which is a conventional electroless plating method, is first degreased, pickled, and soft-etched, and then nucleated with palladium plating. After the activating treatment step, a second activating treatment step of immersing the reducing agent of the present invention in a reducing activation treatment solution for electroless plating in which the reducing agent is dissolved in an aqueous solution of an inorganic base; By applying an electroless nickel plating step according to the process of the present invention in which the surface is immersed in a redox reaction type electroless nickel plating solution while being attached to the surface of the wiring and / or copper land, uniform nickel plating is achieved. In addition to the formation of a film, the nickel film can be replaced by a nickel film for a dense and uniform nickel plating film even in the electroless gold plating process of dipping in an electroless plating solution. Uniformly conducted reliability superior nickel - it becomes possible to produce a printed wiring board, characterized in having a gold coating.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for forming a nickel-gold plating film on the surfaces of copper wiring and copper lands of a printed wiring board according to the present invention will be described with reference to the drawings.

First, the nickel plating method on the copper wiring and copper land surface is based on the following principle. First, a printed wiring board having copper wiring and / or copper land formed on the surface layer is subjected to ordinary degreasing treatment and acid cleaning with 62% sulfuric acid. After that, soft etching is performed with a sodium persulfate / 62% sulfuric acid solution. Subsequently, pre-dip is performed with an ammonium salt, and a first activation process is performed using an activator containing a palladium salt.

Next, a reducing agent such as sodium hypophosphite used in the redox reaction type electroless nickel plating solution in the next step is made of an inorganic material such as sodium hydroxide whose pH is adjusted to 9.0 to 13.0. A second activation process of immersing in a reductive activation treatment solution for electroless plating dissolved in salt is performed.

Further, the copper surface is immersed in an electroless nickel plating solution of an oxidation-reduction reaction type while the reducing activation treatment solution is attached to copper wiring and copper lands, and then immersed in an electroless gold plating solution. And gold plating is performed.

By the way, as the printed wiring board becomes thinner and the printed wiring board is adopted in electronic equipment of higher frequency, very thin wiring or small copper lands are required for noise suppression or impedance matching. It often leads to a wiring pattern with a large area in the inner layer.

When these multilayer wiring boards are immersed in an electroless plating solution, a local battery is formed between a wide wiring pattern and a place other than the wiring pattern. Therefore, depending on the method of forming the local battery, plating does not precipitate, or A phenomenon occurs in which the plating deposition rate is significantly reduced.

Therefore, considering the driving force of the reaction of electroless nickel plating, the reduction potential of Ni ²⁺ is pH on the acidic side.
It is almost constant up to around 4, but fluctuates considerably on the alkali side due to the stability of Ni complex ions. On the other hand, the redox potential of the reducing agent changes linearly over the entire pH range. Therefore, the value of the driving force of the plating reaction, that is, the reduction reaction is pH
Was also changed by

For example, in electroless nickel plating, Ni ²⁺ + 2e ⁻ = Ni at pH 4 E ⁰ = −0.250 V H ₂ PO ₂ ⁻ + H ₂ O = H ₂ PO ₃ ⁻ + 2H ⁺ + 2e ⁻ . ^{...... E 0 '= -0.750V E 0} ' in ^{-E 0 = -0.5V pH12 Ni-cit} + 2e - = Ni ......... E 0 = -0.4V H 2 PO 2 - + H 2 O = H 2 _{^{PO 3 - + 2H + + 2e}} - ......... E 0 '= -1.25V E 0' -E a ⁰ = -0.85 V, it can be seen that the driving force of the reduction reaction higher pH increases.

Therefore, it is important to utilize the driving force of this reaction to generate a reducing force exceeding the potential difference between the copper lands and the copper wiring patterns having different plating areas. That is, the surface of the copper wiring pattern having a different plating area is defined as e ⁻ (H ₂ PO ₂ ⁻ + H ₂ O = H ₂ PO ₃ ⁻ + 2H ⁺ +2).
In order to make e ⁻ ) rich and promote the reaction of Ni ₂ ⁺ + 2e ⁻ = Ni, the pH of the surface of the copper land and the copper wiring pattern having different plating areas is increased (alkaline side) and the reducing agent is used. It is important to keep the amount of sodium hypophosphite rich as well.

According to the present invention, a reducing agent (eg, sodium hypophosphite) contained in a nickel plating solution is dissolved in a sodium hydroxide solution which does not interfere with the plating operation even when brought into the next nickel plating. If redox-type electroless nickel plating is performed immediately with the chemical activation treatment liquid directly attached to the copper wiring and copper land, a large reducing power can be obtained on the copper surface, and the nucleus is first placed on the copper wiring and copper. A nickel film is deposited around the attached palladium particles. By performing the second activation process as described above, when the printed wiring board having the copper wiring and the copper wiring enters the plating solution, the initial nickel deposition is facilitated. It was also confirmed that if this nickel plating could be performed, plating treatment such as electroless gold plating could be performed on this nickel film without any problem.

As the electroless plating solution, for example, an electroless Ni-P plating solution or an electroless Ni-B plating solution can be used.

As the electroless nickel plating solution, not only an alkaline plating solution using sodium hypophosphite as a reducing agent but also an acidic plating solution can be used. In the present invention, it has been experimentally found that the pH of the acidic plating solution is 4.0 to 6.8 in order to uniformly form a nickel plating film on each copper wiring and copper land.
When the pH exceeds 7, nickel hydroxide precipitates and becomes cloudy. However, since the pH of the alkaline solution containing the reducing agent of the present invention is adjusted to 9.0 to 13.0, in the treatment of the present invention, The plating does not exceed 7 and can be plated very well. Further, as the plating progresses and the nickel ions are consumed, the pH drops. However, even with this drop in pH, the pH was suppressed to some extent by bringing in the alkaline solution by the above treatment, and good results were obtained for plating adhesion. Further, when the pH of the reducing activation treatment solution is set to 13.0 or more, adverse effects such as attack of organic substances such as a solder resist are caused.

Hereinafter, specific embodiments of the present invention will be described with reference to FIGS.
The same components as those in the related art are denoted by the same reference numerals, and description thereof is omitted.

First, as shown in FIG. 1A, a multilayer printed wiring board 1 having copper wiring or copper lands 3 formed thereon was prepared in the same manner as in the prior art.

Next, as shown in FIG. 1 (b), the copper surface of the copper wiring or the copper land 3 of the multilayer printed wiring board 1 is first subjected to ordinary degreasing treatment, followed by acid cleaning with 62% sulfuric acid.
Perform a soft etch with a sodium persulfate-post 62% sulfuric acid solution. Subsequently, the multilayer printed wiring board 1 is pre-dipped with an ammonium salt, and immersed in the first activation treatment solution for 3 minutes with an activator containing a palladium salt, and a palladium nucleus 9 is formed on the exposed copper surface. Pure and washed.

Next, as shown in FIG. 1C, as a second activation treatment solution, 25 g of sodium hypophosphite as a reducing agent was dissolved in 750 mL of water, and then pH 9.0 with sodium hydroxide solution. After adding pure water while adjusting to ~ 13.0, immersing in the reducing activation treatment solution 10 having a total of 1000 mL for 10 seconds, or immediately or immersed in pure water, the multilayer printed wiring board 1 was prepared as follows. Further, several ppm of a sulfur compound such as thioglycolic acid is added as a reaction accelerator, 5 ppm of lead acetate is further added as a stabilizer, the pH is adjusted to 4.0 to 6.8, and the temperature is adjusted to 80. Immersion in an oxidation-reduction type electroless nickel plating solution of about 90 ° C. for about 25 minutes to form a nickel plating film 12 containing phosphorus of 5 to 6 μm on the exposed copper wiring or copper land 3. .

Further, as shown in FIG. 2 (e), the multilayer printed wiring board is washed with pure water and a substitution reaction type electroless gold plating solution (for example, OPC Muden Gold, pH5, manufactured by Okuno Pharmaceutical Co., Ltd.) .8, a liquid temperature of 90 ° C.) for about 10 minutes, and a thickness of 0.05 μm is formed on the surface of the nickel plating film 12.
m of the flash gold plating film 13 was formed.

Here, the composition of the oxidation-reduction type electroless nickel plating solution used in this experimental example is shown below.

(Composition of Redox Reaction Type Electroless Nickel Plating Solution) Nickel sulfate 7.4 g / L Sodium hypophosphite 13 g / L Rossel salt 14 g / L Malic acid 10 g / L Sodium acetate 6 g / L L sodium hydroxide aqueous solution to add pH 4.0 to pH 6.0.
8 By the above plating process, Ni (5 to 5) is applied to the surface of all exposed copper wiring or copper land 3 of multilayer printed wiring board 1.
6 μm) -Au (0.05 μm) plating film was formed. This nickel plating film 12 adhered extremely firmly to the exposed copper wiring or copper land 3, and further, a dense nickel film was formed. Further, when the plating ball solder ball pull test was performed, as shown in FIG. 3, a very good solder ball pull strength was exhibited.

As described above, according to the present embodiment, it has been difficult to perform conventional plating with an extremely simple operation. That is, for example, the copper pattern 6 having a large area in FIGS.
The thin copper wiring or the small copper land 2 connected to the same can obtain almost the same plating thickness as the other exposed copper wiring or the copper land 3. For example, if the nickel plating thickness a is 5 μm in FIG. 2E, the nickel plating film 12 can be formed stably with a plating thickness a1 of 5 ± 0.5 μm. In addition, the formed nickel film is formed very densely, the formation of the Ni-Sn alloy layer by soldering is small, and the solder bonding property is excellent, and the reliability for the solder mounting strength of CSP, BGA, etc. is high. Excellent implementation has become possible.

[0034]

As described above, according to the present invention, it is possible to suppress the occurrence of white unevenness and to apply nickel-gold plating having excellent mounting reliability to the copper surface of a copper wiring or a copper land of a printed wiring board. Can be formed.

[Brief description of the drawings]

FIG. 1 is a process schematic cross-sectional view schematically showing a state of a plating process of a multilayer printed wiring board according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view of the same process.

FIG. 3 is a characteristic diagram showing solder ball pull strength in the embodiment.

FIG. 4 is a process schematic cross-sectional view schematically showing a state of a plating process of a conventional multilayer printed wiring board.

FIG. 5 is a schematic sectional view of the same process.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Multilayer printed wiring board 2 Fine copper wiring or small copper land connected to wide area inner layer copper pattern 3 Copper wiring or copper land 4 Solder resist 5 Conducting via 6 Large area inner layer copper pattern 7 Inner layer copper wiring 8 Insulating resin Layer 9 Palladium nucleus 10 Reducing activation treatment solution 11 Electroless nickel plating solution 12 Nickel plating film 13 Flash gold plating film

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Junji Mizukoshi 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. 72) Inventor Izumi Okamoto 1006 Kadoma, Kazuma, Osaka Pref.F-term in Matsushita Electric Industrial Co., Ltd. (Reference) EE02 GG06 GG13

Claims (4)

[Claims] 1. A treatment solution for activating a surface of copper wiring and / or copper land formed on a surface layer of a printed wiring board, wherein a reducing agent is dissolved in an aqueous solution of an inorganic base. Activating solution for electroless nickel plating. 2. The reducing activation treatment solution for electroless nickel plating according to claim 1, wherein the reducing agent is hypophosphite. 3. The electroless nickel plating solution according to claim 1, wherein the aqueous solution of the inorganic base is an aqueous solution having a pH of 9 to 13 in which a hydroxide composed of sodium hydroxide and / or potassium hydroxide is dissolved. Reductive activation treatment solution. 4. When the surface of the copper wiring and / or copper land formed on the surface layer of the printed wiring board is subjected to electroless plating, the surface of the copper wiring and / or copper land is degreased, pickled, After the soft etching treatment, a first activation treatment step of nucleating the palladium plating, and a second activation treatment of immersing in a reducing activation treatment solution for electroless plating in which a reducing agent is dissolved in an aqueous solution of an inorganic base. A step of immersing the surface in an oxidation-reduction type electroless nickel plating solution and electroless nickel plating with the reducing activation treatment solution adhered to the surface of the copper wiring and / or copper land; and A method of immersing in an electroless gold plating solution to perform electroless gold plating.