JPH081980B2 - Printed wiring board and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board and its manufacturing method.

[0002]

BACKGROUND OF THE INVENTION In a printed wiring board on which electronic parts are mounted, the density is high, it is difficult to route the lead wire for plating, the connector part of the contact or terminal and the part mounting part are mixed, and the parts fall. Occurs, and after passing through the mounting reflow furnace several times, after applying electroless nickel plating,
Substitution type electroless gold plating is performed to form a nickel plating film on a copper conductor pattern and a gold plating film on the nickel plating film.

However, the conventional technique of performing substitutional electroless gold plating on a self-catalytic electroless nickel plating film has poor soldering characteristics, and in particular, even if heat history is applied even once, the soldering characteristics (solder wetting) are significantly increased. There is a defect that the (sex) is deteriorated. For this reason, strict control of assembly conditions and flux conditions is required in the component mounting process, resulting in higher production costs.

Further, after electroless nickel plating is applied on the copper conductor pattern, autocatalytic electroless palladium plating is applied to form a palladium layer having a predetermined thickness on the electroless nickel plating film. Three layers (Ni layer-Pd layer-Au) such as providing a gold plating film on the palladium layer.
Layer) construction techniques have been proposed. Although it has been reported that this product has better soldering characteristics than the two-layer structure (Ni-Au) technique, it is difficult to control palladium plating and gold plating and the cost is extremely high. , Has not been put to practical use.

[0005]

DISCLOSURE OF THE INVENTION As a result of earnestly studying the above-mentioned problems, as a result of forming a palladium layer on an electroless nickel plating film, Pd and Au are in a multi-island sea shape (in the field of electroless plating). Then, a structure such as a multi-island sea-like structure is also called a porous structure), and this structure is rich in abrasion resistance and has good soldering characteristics. It has been found that each of these techniques can utilize existing ones, is extremely simple, and has a low cost.

The present invention has been achieved based on such knowledge, and an object of the present invention is to provide excellent wear resistance characteristics.
Moreover, it is an object of the present invention to provide a technique capable of obtaining a printed wiring board having good soldering characteristics at low cost. An object of the present invention is that a nickel plating film is formed on a conductor pattern provided on a substrate, and gold having an island structure and palladium having an island structure are mixedly formed on the nickel plating film. Is achieved by a printed wiring board.

Further, a step of electroless nickel plating a substrate provided with a conductor pattern, a step of performing substitutional electroless gold plating on a substrate plated with electroless nickel, and an electroless nickel plating And a step of performing substitutional electroless palladium plating on the substrate subjected to the above step.

Hereinafter, the present invention will be described in detail. The printed wiring board is generally a plastic or ceramic substrate such as phenol resin or epoxy resin, on which a predetermined pattern is formed with copper foil. Then, this copper foil pattern is gold-plated for the above-mentioned reason. Also in the present invention, gold plating is applied.

However, before being plated with gold,
A nickel plating film is formed on the copper foil pattern by means of electroless nickel plating using a bath in which a nickel salt such as nickel chloride or nickel sulfate is dissolved.
This electroless nickel plating means has been well known in the past, and the technique can be used. The electroless nickel plating may be preceded by substitutional electroless palladium plating.

In the present invention, the nickel plating film formed by means of electroless nickel plating has a film thickness of about 1 to 7 μm, preferably about 3 to 5 μm.
After that, substitution type electroless palladium plating is performed using a plating bath in which a palladium salt is dissolved. As the plating bath, for example, an acid such as palladium chloride or hydrochloric acid, and optionally a reducing agent and a stabilizer are added. The temperature of the plating bath is controlled at about 10 ° C. or higher, and the time is about 10 seconds or longer.
Then, Pd having a convex height of about 1/100 to 10/100 μm, like a multi-island sea island, is formed on the nickel-plated film.
Is deposited. That is, Pd like a continuous film
Instead of a layer, spotted Pd is formed on the nickel plating film.

Next, displacement type electroless gold plating is performed using a gold plating bath in which a complex salt such as potassium cyanide is dissolved. As the plating bath, for example, potassium cyanide, a salt of an organic acid such as citric acid, and a stabilizer added if necessary are used. The temperature of the plating bath is controlled above about 70 ° C, and about 12
It takes 0 seconds or more. Then, between the Pd formed like the archipelago on the nickel plating film, the convex height is about 1/100 like the archipelago.
Au of about 10/100 μm is deposited. That is,
Instead of the Au layer like a continuous film, Au is formed in spots in the spots of Pd on the nickel plating film.

Either of the substitution type electroless palladium plating and the substitution type electroless gold plating performed after the electroless nickel plating may be performed first. That is, electroless nickel plating → substitution type electroless palladium plating → substitution type electroless gold plating or electroless nickel plating → substitution type electroless gold plating → substitution type electroless palladium plating may be performed in this order. . That is, whichever comes first, Au formed by the substitution electroless gold plating and Pd formed by the substitution electroless palladium plating are spotted, so that one is not covered by the other. However, both Au and Pd are exposed on the surface. The underlying Ni layer is preferably covered with Au and Pd and is not exposed.

The surface structure on the conductor pattern of the printed wiring board is based on Ni, and Au and Pd are formed on the surface.
Those having a mixture of and like spots were rich in wear resistance and corrosion resistance, and further had good soldering characteristics. Moreover, each plating technique itself carried out in the present invention is a well-established technique, and it is not difficult at all, and it can be easily implemented, has high productivity, and can be implemented at low cost.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

[0015]

【Example】

[Examples 1 to 6] FIG. 1 is a schematic view of a printed wiring board according to the present invention. In the figure, 1 is a printed circuit board substrate,
2 is a copper foil formed in a predetermined pattern.

Numeral 3 is Pd formed on the copper foil 2 by substitutional electroless palladium plating. Reference numeral 4 is a Ni plating layer having a thickness of about 3 to 5 μm formed by electroless nickel plating performed after the step of substitutional electroless palladium plating. Then, the printed wiring board on which the Ni plating layer 4 was formed was immersed in a palladium plating bath having the following composition.

[Palladium plating bath] Palladium chloride 60 to 120 ppm Hydrochloric acid (35%) 60 to 120 cc / l Reducing agent 0.5 to 2 g / l Stabilizer 0.2 to 2 g / l [Palladium plating conditions] Bath temperature 25 to 35 ° C. time 15 to 120 seconds By such substitution type electroless palladium plating, N
Pd5 is formed on the surface of the i-plated layer 4 in the form of a multi-island sea (spots).

The printed wiring board on which Pd5 was formed was washed with water and then immersed in a gold plating bath having the following composition. [Gold plating bath] Potassium cyanide 1 to 4 g / l Citrate 80 to 120 g / l Stabilizer 0.1 to 1 g / l [Gold plating conditions] Bath temperature 90 to 100 ° C. Time 180 to 300 seconds By the electroless gold plating, Au6 is formed in the inter-island sea-like (spot-like) shape in the interstices of the multi-island sea-like Pd5 on the surface of the Ni-plated layer 4, and the surface is substantially covered with Pd and Au. A printed wiring board is obtained.

Comparative Example 1 A printed wiring board was obtained in the same manner as in Example 1 except that the substitutional electroless palladium plating step performed after the electroless nickel plating step was omitted. [Characteristics] The printed wiring boards obtained in each of the above examples were held at 150 ° C for 5 hours, and the solder wettability was examined thereafter. The results are shown in Table 1 below.

Table-1 Palladium plating time Gold plating time Solder wettability Example 1 15 seconds 180 seconds Good Example 2 30 seconds 180 seconds Good Example 3 60 seconds 180 seconds Good Example 4 120 seconds 180 seconds Good Example 5 60 Second 240 seconds Good Example 6 60 seconds 300 seconds Good Comparative example 1 0 180 seconds Poor

[0021]

According to the present invention, it is possible to obtain a printed wiring board having excellent wear resistance and good soldering properties at low cost.

[Brief description of drawings]

FIG. 1 is a schematic view of a printed wiring board.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Copper foil 4 Ni plating layer with a thickness of about 3 to 5 μm 5 Multi-island sea-shaped (spotted) Pd 6 Multi-island sea-shaped (spotted) Au

Continuation of front page (56) References JP-A-63-224290 (JP, A) JP-A-5-327187 (JP, A) JP-A-6-350227 (JP, A)

Claims (2)

[Claims] 1. A print characterized in that a nickel plating film is formed on a conductor pattern provided on a substrate, and gold having an island structure and palladium having an island structure are mixedly formed on the nickel plating film. Wiring board. 2. A step of performing electroless nickel plating on a substrate provided with a conductor pattern, a step of performing substitutional electroless gold plating on a substrate subjected to electroless nickel plating, and electroless nickel plating And a step of performing substitutional electroless palladium plating on the substrate subjected to the above step.