JPH06264284A - Method for forming wiring board - Google Patents

Abstract

PURPOSE:To improve the brazing property of solder, etc., by forming an electroless Ni-B plating film on a wiring pattern formed on a ceramic wiring board and on a connecting pad, heat-treating the film and then forming an Ni-P plating film. CONSTITUTION:An electroless Ni-B plating film is formed on a wiring pattern, consisting of W or Mo formed on a ceramic wiring board and on a connecting pad. The film is heat-treated at 65-850 deg.C in a reducing atmosphere (e.g. about hydrogen:nitrogen= 2:1 to 1:2), and then an Ni-P plating film (contg. 6% P and having 0.3-2mum thickness) is formed. Consequently, a wiring board is obtained without the joining strength in brazing solder, etc., and wettability being lowered. Besides, a gold plating film is formed on the Ni-P plating film in 0.05-0.5mum thickness to further improve the solder wettability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to nickel-boron plating, heat treatment, nickel-phosphorus, for imparting brazing property of solder or the like on a wiring pattern formed of a refractory metal such as tungsten or molybdenum. The present invention relates to a method for forming a wiring board in which a nickel plating film is formed in the order of plating.

[0002]

2. Description of the Related Art Since refractory metals such as tungsten and molybdenum used as wiring materials for ceramic wiring boards are extremely susceptible to oxidation, it is difficult to carry out brazing such as soldering as they are. Therefore, a method of plating nickel on tungsten or molybdenum is generally used. Tungsten, molybdenum and nickel cannot provide sufficient bonding strength in the as-plated state, so heat treatment is performed at a temperature of 600 ° C. or higher to form a tungsten-nickel compound or molybdenum-nickel compound at the interface between the two. It is joined. As a nickel plating method, since the wiring pattern is electrically isolated, it is difficult to apply electroplating, and electroless plating is used.

There are two types of electroless nickel plating, nickel-phosphorus and nickel-boron, both of which are fine crystals after plating and are excellent in brazing property of solder or the like. However, when heat treatment is performed at a temperature of 300 ° C. or higher, crystallization progresses, a nickel-phosphorus compound and a nickel-boron compound are generated, and there is a drawback that brazing property such as soldering is deteriorated. Therefore, a method of performing nickel plating again after the heat treatment is used. As an example thereof, JP-A-60-1
There is a technique described in Japanese Patent Publication No. 97894.

In the above-mentioned Japanese Patent Laid-Open No. 60-197894, primary nickel plating is formed to a thickness of 0.3 to 1.0 .mu.m, heat treated at 800 to 1200.degree. A method of performing nickel plating is described, and effects such as a large bond between the plated film and the base that does not cause peeling are described.

[0005]

[Problems to be Solved by the Invention]
In the method described in 0-197894, when the secondary nickel plating is electroless nickel-phosphorus plating, when the phosphorus content in the secondary nickel plating is too large or the plating thickness is too thick, the solder In brazing such as brazing, there is a drawback that the joint strength is reduced due to the concentration of phosphorus. Further, if the plating thickness is too thin, there is a drawback that the wettability of solder or the like is deteriorated.

An object of the present invention is to perform a heat treatment after a primary nickel plating and then a secondary nickel plating, in which electroless nickel-phosphorus plating is used as the secondary nickel plating, and the phosphorus content and the plating film are An object of the present invention is to provide a method for forming a wiring board in which the bonding strength and wettability are not deteriorated by brazing solder or the like by defining the thickness.

[0007]

In order to achieve the above object, the present invention uses a nickel-phosphorus plating having a strong precipitation force for the secondary nickel plating which is performed after the heat treatment of the primary nickel plating. And a phosphorus content of 6% or less and a plating film of 0.3 to
By setting the thickness to 2 μm, a decrease in the bonding strength due to the concentration of phosphorus at the bonding interface during brazing of solder, gold-tin or the like is prevented, and sufficient solder wettability is secured.

[0008]

The electroless nickel plating applicable to the secondary nickel plating includes nickel-phosphorus plating and nickel-boron plating. Nickel-boron plating has a low boron content of generally 0.3 to 1.0% and a high nickel purity, so that it is excellent in brazing property of solder or the like. However, since the deposition force of plating is small, it is difficult to reliably deposit on the primary nickel plating film after the heat treatment. In particular, a few 100 μm-order minute connection pads
In the case of a wiring board having 100 or more, a pad on which nickel-boron plating is not deposited appears. As a countermeasure, there is a method of activating with a palladium solution before the secondary plating, which makes it possible to reliably deposit nickel-boron plating. However, in this method, since the palladium layer by the activation treatment exists between the primary plating film and the nickel-boron plating film,
The bonding strength between the two becomes extremely small.

On the other hand, since nickel-phosphorus plating has a large deposition force, it is possible to reliably deposit on all connection pads even in the wiring board having a large number of fine connection pads as described above. A large value is also obtained for the bonding strength with the next nickel-boron plated film. For example,
When a copper wire with a diameter of 0.5 mm is soldered and pulled, nickel-phosphorus cuts the copper wire with a force of 1 kg or more, whereas nickel-boron has a force of 0.1 kg or less for primary plating and secondary It will peel off from the plating. in this way,
Nickel-phosphorus plating is suitable as the secondary nickel plating.

However, since the nickel-phosphorus plating film contains 3 to 12% of phosphorus, solder, gold-tin, gold-germanium, tin-on the nickel-phosphorus plating film.
When brazing is performed using a brazing material such as silver, phosphorus in the nickel-phosphorus plating film is concentrated as an impurity at the bonding interface, which lowers the bonding strength. FIG. 1 is a diagram showing the results of examining the relationship between the phosphorus content in the nickel-phosphorus plating film and the joint strength with the solder. The joint strength is remarkably reduced at a phosphorus content of 6% or more.

Further, as the nickel-phosphorus plating film thickness increases, the amount of phosphorus diffused in the brazing material also increases, so that the bonding strength decreases. This relationship is shown in FIG. The bonding strength is almost constant up to a film thickness of 2 μm, but 2 μm
It has fallen above.

FIG. 3 shows the results of examining the solder wettability of the nickel-phosphorus plated film as the wetting spread length of a solder disk having a diameter of 1.5 mm. As for the wetting spread length, if the film thickness is 0.3 μm or more, a value of 10 mm or more is obtained, which indicates that the film has sufficient wettability.

As can be seen from the above, the nickel-phosphorus plated film has a phosphorus content of 6% or less and a film thickness of 0.3-2.
μm is a preferable range. The solder wettability is further improved by further forming gold plating to a thickness of 0.05 to 0.5 μm on the nickel-phosphorus plating film, and even when the nickel-phosphorus plating film thickness is 0.1 μm. A solder wetting spread length of 10 mm or more can be obtained.

As the primary nickel plating, nickel-boron plating, which has a high nickel purity and therefore produces a small amount of nickel compounds by heat treatment and has a small plating film stress, is suitable. The film thickness of the primary nickel plating is preferably from 1 to 10 μm, and when the thickness is 1 μm or less, tungsten cannot be completely covered, and when the thickness is 10 μm or more, the stress becomes large, which causes a crack in the plating film and peeling of the connection pad.

The heat treatment after the primary plating is 650 to 850.
A temperature of ℃ is preferable, and at 650 ° C or lower, a compound of nickel and tungsten is not sufficiently formed, and the bonding strength cannot be obtained.

On the other hand, at 850 ° C. or higher, the above-mentioned compound is unnecessarily produced in a large amount, and the nickel-boron plating film thickness is reduced. The heat treatment atmosphere is preferably a reducing atmosphere from the viewpoint of preventing oxidation of the nickel-boron plated film surface and from the viewpoint of productivity. For example, hydrogen: nitrogen = 2: 1 to 1: 2.
Is suitable.

As the pretreatment after the secondary plating, only acid treatment is sufficient. For example, immersion in 5 to 10% sulfuric acid or 10 to 50% hydrochloric acid at room temperature for about 30 seconds to 3 minutes is suitable.

[0018]

EXAMPLES The present invention will be described in detail below based on examples.

(Examples 1 to 3) An electroless nickel-boron plating film having a thickness of 3.5 μm was formed on a tungsten wiring or a connection pad formed on a ceramic substrate made of alumina or alumina and silica, and then, hydrogen:
Heat treatment was performed at 700 ° C. for 10 minutes in a reducing atmosphere of nitrogen = 1: 1. Next, after pretreatment with 10% sulfuric acid at 25 ° C. for 1 minute, it was washed with water to form a nickel-phosphorus plating film with a thickness of 1 μm.
It was formed to a thickness of m. As the nickel-phosphorus plating solution, three kinds of plating solutions having different compositions are used, and the phosphorus content is 3,
A 4.5% and 6% plated film and an 8% plated film as a comparative example were formed. About these plating films, the diameter is about 0.3
A joint strength test based on shear strength when a solder ball of mm was connected, and a solder wet spread test using a solder disk having a diameter of 1.5 mm were performed. As a result, as shown in Table 1, solder wetting spread values of 10 mm or more were obtained and sufficient wettability was shown, but the bonding strength was 3%, 4.5%, 6% phosphorus content. A value of 190 g or more was obtained for the film, but 83 g was obtained for the 8% film, and the strength was decreased due to the concentration of phosphorus at the bonding interface.

[0020]

[Table 1]

(Examples 4 to 6) After nickel-boron plating and heat treatment were performed in the same manner as in Example 1, nickel-
Secondary nickel plating was performed while changing the phosphorous plating film to 0.3, 1 and 2 μm, and the joint strength and the solder wetting spread were investigated. The phosphorus content is about 4.5%. As a result, in each case, a bonding strength of 200 g or more and a solder wetting spread of 10 mm or more were obtained. However, although the bonding strength of 200 g or more was obtained at the film thickness of 0.1 μm performed as a comparative example, the solder wetting spread was too small,
It was an insufficient value of 6.8 mm. Further, when the film thickness was 3 μm, the solder wetting spread showed a good value of 13.1 mm, but the bonding strength was an insufficient value of 89 g due to the effect of phosphorus concentration.

[0022]

[Table 2]

(Examples 7 to 9) After performing secondary nickel-phosphorus plating in the same manner as in Example 1, a gold plating film was formed to a thickness of 0.1 μm using a displacement gold plating solution.
The nickel-phosphorus plating film thickness is 0.1, 1 or 2 μm,
As a comparative example, 0.05 and 3 μm were also examined. As a result, even with a nickel-phosphorus plating film thickness of 0.1 μm, a good result of solder wetting spread of 10 mm or more was obtained, and the effect of gold plating was confirmed. Regarding the bonding strength, the effect of gold plating was not recognized, and the same results as in Examples 4 to 6 were obtained.

[0024]

[Table 3]

[0025]

According to the present invention described above, nickel-phosphorus plating is applied to the secondary nickel plating so that the phosphorus content is 6% or less and the plating film thickness is 0.3 to 2 μm.
As a result, when solder, gold-tin, gold-germanium, tin-silver, etc. is brazed, a strong bond can be obtained without lowering the bond strength due to the concentration of phosphorus diffused from the nickel-phosphorus plating film. It has become possible to obtain extremely good wettability with respect to a brazing filler metal such as a solder. As a result, the bonding yield and bonding reliability of the wiring board can be significantly improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a phosphorus content rate and a bonding strength.

FIG. 2 is a diagram showing a relationship between a nickel-phosphorus plating film thickness and a bonding strength.

FIG. 3 is a diagram showing a relationship between a nickel-phosphorus plating film thickness and solder wetting spread.

Claims (3)

[Claims] 1. A wiring pattern made of tungsten or molybdenum formed on a ceramic wiring substrate,
A method for forming a wiring board, comprising forming an electroless nickel-boron plating film on a connection pad, performing heat treatment, and then forming a nickel-phosphorus plating film. 2. The method for forming a wiring board according to claim 1, wherein the nickel-phosphorus plated film has a phosphorus content of 6% or less and the plated film has a thickness of 0.3 to 2 μm. 3. The method for forming a wiring board according to claim 1, wherein a gold plating film is further formed on the nickel-phosphorus plating film to a thickness of 0.05 to 0.5 μm.