JP2642723B2 - Manufacturing method of ceramic circuit board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a ceramic circuit board,
In particular, the present invention relates to a method of manufacturing a ceramic circuit board in which a conductor surface formed on a ceramic insulating substrate is metallized by nickel plating.

[Conventional technology]

Conventionally, there has been known a circuit board in which a high melting point metal conductor circuit pattern such as molybdenum, tungsten, or tantalum formed on a ceramic substrate is metallized with a boron-containing nickel plating film. This boron-containing nickel plating film is formed by an electroless plating method using an amine-boron compound as a reducing agent, but is more resistant to high-temperature heat treatment than a conventional nickel-phosphorus plating film, and its surface is relatively less oxidized. Due to its excellent solderability and silver brazing properties, it has been studied as a plating film for metallizing the conductor surface of ceramic substrates for high-density mounting in recent years. However, since the boron-containing nickel plating film has a large stress on the film itself, cracks easily occur in the film, which is an obstacle to the subsequent plating process. Therefore, for example, as described in Japanese Patent Application Laid-Open No. 58-3962, a conductor layer for forming a boron-containing nickel plating film is made to contain a small amount of glass material in advance, and boron, which is considered to be a main factor of stress generation, is expanded. At least, measures have been taken to reduce the amount of boron in the film to prevent the film stress from increasing due to heat treatment.

[Problems to be solved by the invention]

As described in the section of the prior art, it is effective to reduce the amount of boron in the nickel plating film by thermally expanding boron in the glass material in the underlying conductor layer of the nickel plating film. However, including a non-conductive material such as glass in the base conductor layer is not preferable from the viewpoint of electric conductivity. In addition, although cracks generated in the nickel plating film itself can be suppressed by reducing the amount of boron due to thermal diffusion, a new problem arises in that cracks are generated during heat treatment depending on the material of the ceramics used as the substrate. In other words, there is no problem if the ceramic has high mechanical strength such as alumina (Al ₂ O ₃ ), but it has high strength such as mullite (3Al ₂ O ₃ .2SiO ₂ ) or mullite ceramics containing mullite as a main component. It was found that, when the value of was small, the rate of crack generation was significantly increased by the heat treatment after the formation of the nickel plating film. Furthermore, I / O pins, LSI,
A gold plating layer is formed on the surface of the nickel plating film to improve various bonding properties such as sealing caps. After the gold plating, the gold plating film diffuses into the nickel plating film after each heating process. However, it was difficult to maintain a sufficient thickness of the gold plating film for bonding and maintain sufficient bonding properties until the final process.

An object of the present invention is to solve these problems, and a first object of the present invention is to provide a boron-containing nickel plating film which does not crack even when mullite or a mullite ceramic containing mullite as a main component is used as a ceramic substrate. The second object is to provide a method for manufacturing a highly reliable ceramic circuit board having a high reliability, and a second purpose is to provide a method for manufacturing a ceramic circuit board in which diffusion of a gold plating film layer formed on a nickel plating film surface is suppressed regardless of the composition of the ceramic substrate. To provide each.

[Means for solving the problem]

The first object is to print a high melting point metal paste on a mullite or a mullite ceramic insulating substrate containing mullite as a main component in a predetermined wiring circuit pattern shape, and to form the circuit pattern in a reducing or inert atmosphere. And then a boron content of 0.71 on the sintered circuit pattern by electroless plating.
a method of manufacturing a ceramic circuit board having a step of forming a nickel plating film of wt% or less, wherein a sulfur-containing organic compound is added to a plating bath in the step of forming a nickel plating film and contained in the nickel plating film. This is achieved by a method for manufacturing a ceramic circuit board, wherein the amount of boron is regulated to the above-mentioned appropriate value.

Note that the lower limit of the boron content in the nickel plating film cannot be reduced to zero because of the relationship between electroless nickel plating using an amine-boron compound as a reducing agent and that it is necessary to maintain the nickel plating rate. It is the limit. Therefore, the acceptable content is 0.02 to 0.71 wt%, preferably 0.2 to 0.5 wt%. In order to adjust the amount of boron to this level, the amount of the amine-boron compound added to the plating bath may be adjusted. However, if the amount is too small, a sufficient plating speed cannot be obtained. By adjusting the addition and dissolution amount of sulfur-containing organic compounds (including at least each element of S, C, and N) such as thiourea that dissolve in the plating bath. The amount of boron contained in the plating film can be regulated to an appropriate value.

The second object is (1) a step of printing a refractory metal paste on a ceramic insulating substrate in a predetermined wiring circuit pattern shape, and a step of sintering the circuit pattern in a reducing or inert atmosphere. Next, a step of forming a nickel plating film having a total content of impurity elements of 0.96 wt% or less on the sintered circuit pattern by electroless plating, and further gold plating by electroless plating on the nickel plating film. A method for manufacturing a ceramic circuit board having a step of forming a film, wherein a sulfur-containing organic compound is added to a plating bath in the step of forming a nickel plating film, and Preferably (2) the ceramic insulating substrate is mullite or mullite containing mullite as a main component. And ceramics, and, by the method of manufacturing a ceramic circuit board, characterized in that the content of boron which is one of the impurity element contained in the nickel plating film is less 0.71 wt%, is achieved.

[Action]

The reason why nickel and boron plating (meaning of boron-containing nickel plating, the same applies hereinafter) is applied to the surface of a refractory metal such as tungsten, molybdenum, or tantalum is to obtain high bonding strength with the refractory metal. For example, when a nickel-boron plating is applied to the conductor pattern made of the high melting point metal with a thickness of about 5 μm, a bonding strength of 2 kg / mm ² is obtained. In addition, after nickel-boron plating, 750
When heated at ℃ for 10 minutes, a high bonding strength of 4 kg / mm ² or more is obtained. This bonding is caused by mutual diffusion of the high-melting-point metal and nickel. The same bonding strength can be obtained regardless of whether the high-melting-point metal does not include a glass component and the nickel plating or the high-melting-point metal includes a glass component.

The reason why the plating film having a boron content of 0.71 wt% or less is applied to the surface of the refractory metal conductor is to prevent an increase in the film stress after the heat treatment. As a result, even for a mullite ceramic substrate containing a large amount of silicon oxide (SiO ₂ ) with a low mechanical strength, the refractory metal and nickel
The distortion between the substrate and the boron plating film is small, and as a result, cracks are not generated on the substrate. Also, the diffusion of gold and nickel is prevented by reducing the total amount of impurities in the nickel and boron plating films, thereby delaying the diffusion of gold into the plating films. The gold plating layer is maintained even after various heating processes such as brazing, brazing, and wire bonding, thereby enabling various kinds of high connection.

〔Example〕

Example 1 Various nickel / boron plating films were formed under the following conditions.

(1) Plating bath _{composition: NiSO 4 · 6H 2 O 0.076} mol / glycine 0.013 to 0.4 mol / gluconate 0.038 ~0.5 mol / EDTA-2Na 0 ~0.003mol / dimethylamine borane 0.0085～0.085Mol / containing ionic organic compounds 0.5 (2) Plating conditions: Plating bath temperature 52-70 ° C Plating bath pH 6-8 Combination of the above composition and conditions, boron content in nickel-boron plating film 0.02-3.0 wt %.
Nickel-phosphorus plating is manufactured by Nippon Kanigen S-68
Performed using 0. The evaluation of each plating film is based on a plating thickness of about 5 μm.

(3) Ceramic substrate used: The presence or absence of cracks in the ceramic substrate was determined by the following method. The ceramic substrate used had a crystal structure of 3Al ₂ O ₃ .2SiO ₂ identified by X-ray diffraction and is called a mullite ceramic substrate. This ceramic substrate has a drawback strength of about 1/3 that of an alumina ceramic substrate and a small mechanical strength. However, it has a relative dielectric constant of about 30% and is suitable for high-density mounting. is there. A W paste was printed on the present ceramic substrate as a high-melting metal conductor, and sintered by an ordinary method to form a conductor pattern.

(4) Electroless plating: The W conductor of this substrate is subjected to conventional plating and plating treatment with catalyst addition, nickel-boron, nickel-phosphorus plating, and then 750 ° C in a nitrogen gas atmosphere. Then, a heat treatment was performed for 10 minutes, and the occurrence of cracks on the mullite ceramic substrate was observed based on the change in the plating film stress before and after the heat treatment.

(5) Crack generation and stress measurement evaluation: As a method for evaluating crack generation, of the 268 conductors, the percentage of cracked conductors was determined as a percentage and expressed as the crack generation rate.

The presence or absence of cracks in each nickel-boron plating film itself and the stress of the plating film were determined by plating on a pure tungsten plate having a thickness of 0.2 mm.

The stress of the plating film before and after the heat treatment was measured by the following method. After plating 5 μm of various types of nickel and boron, the tungsten plate was cut into a length of 50 mm and a width of 10 mm, and the amount of warping after plating and heat treatment of the tungsten plate was measured with a surface roughness meter, and calculated by the following equation.

E: Young's modulus of tungsten plate t: Plate thickness h: Warpage amount l: Tungsten plate length d: Plating film thickness (6) Measurement of impurities in plating film: Impurity in nickel-boron plating film Was measured using the following method. After dissolving the plated sample in nitric acid, this solution was used as an analytical sample, and the analysis was performed using an emission spectrometer.

(7) Result: The above results are shown in Tables 1 and 2.

The first sample No. 1 shows nickel-phosphorus plating as a comparative example. The content of impurities in the nickel-phosphorus plating film is as large as 7.62 wt%. Although no cracks occur in the plating film, the film stress after heat treatment reaches 150 kg / mm ² ,
The mullite ceramic substrate had 100% cracks.

Samples No. 2 to No. 13 show the presence or absence of cracks in the nickel-boron plating film and the crack occurrence rate of the mullite ceramic substrate due to the increase in the film stress after heat treatment.

When the boron content was remarkably large as shown in Sample Nos. 2 and 3, cracks occurred in the plating film after plating, and it was found that the plating film was not practical. Therefore, the film stress could not be measured.

As shown in Sample Nos. 4 to 6, the boron content was 1.1 wt%
Under the following conditions, the film stress and the occurrence of cracks on the ceramic substrate could be measured without cracks in the plating film. As a result, the smaller the boron content, the lower the film stress after heat treatment, and the lower the crack generation rate of the ceramic substrate.

As shown in Sample Nos. 7 to 13, the boron content was 0.71 wt%
By the following, the film stress after heat treatment is 31.6kg
/ mm ² or less, and no cracks occurred on the ceramic substrate. Therefore, it was found that it is necessary for the mullite ceramic substrate that passes through the step of applying high heat after nickel-boron plating to have a boron content of 0.71 wt% or less in the nickel-boron plating film. Thus, boron content 0.71 ~ 0.02wt%
In, it is possible to obtain a film stress 31.6kg / mm ² ~7.6kg / mm ² after the heat treatment, of course it cracks do not occur in a nickel-boron plating film, a ceramic substrate mullite (3Al ₂ O · 2SiO ₂ ) It was found that there was no crack generation rate on the substrate even when using the ceramics.

Example 2 In this example, the surface of the nickel-boron plating film obtained in Example 1 was subjected to gold plating, and when the gold plating film was subjected to heat treatment, the heat diffusion into the underlying nickel plating film was performed. It has been considered.

The conditions for the diffusion of gold into the underlying nickel plating film by gold plating and heat treatment are as follows.

The degree of diffusion between the nickel-boron plating film and the gold plating film was determined by nickel electroplating on a tungsten plate as described above.
Using the product name Rekutororesu D ₁ of Engineers, Inc.,
The sample was subjected to displacement gold plating with a thickness of about 0.2 μm, and then heat-treated at 650 to 850 ° C. for 10 minutes in a nitrogen gas atmosphere, and was determined from the characteristic X-ray intensity ratio of the surface. That is,
The higher the nickel / gold strength ratio, the more gold diffused into the nickel-boron plating film, indicating that the gold plating layer on the surface disappeared.

The method of measuring the total amount of impurities in the nickel / boron plating film is the same as that of the first embodiment, and the same as that of the samples described in Tables 1 and 2. The results are as shown in FIG.

In other words, in the figure, the horizontal axis represents the sum of the impurity contents shown in Tables 1 and 2, and the nickel (Ni)
It shows the progress of diffusion of the gold plating layer from the characteristic X-ray intensity ratio of gold and Au (Au). We have found a very good correlation between them. 0.96 total impurity content
At less than wt%, an extremely small Ni / Au intensity ratio was obtained at each heat treatment temperature. In other words, the characteristic X-ray intensity of Au is strong and the Au plating layer diffuses into the nickel / boron plating layer.
Indicates no penetration. Therefore, even if the ceramic substrate provided with the nickel / boron plating film and the gold plating film thereon on the refractory metal conductor such as tungsten or molybdenum is passed through a high heating process thereafter, As a result, the Au plating layer is held as
High joining properties of parts can be maintained.

As described above, it is surprising that the smaller the total content of impurities such as boron, iron, cobalt, sulfur, and copper, the slower the diffusion of gold into the nickel film. Although the exact reason is unknown, it is presumed that this is probably due to the fact that impurities easily react with gold and that the higher the purity of nickel, the larger the crystal grain size of the plating film and the slower the gold diffusion rate. Furthermore, it is surprising that iron, cobalt, sulfur, copper, etc. are mixed into the nickel / boron plating film.
Probably, the chemicals used are various from industrial to high-purity reagents, but they are contained as impurities in these chemicals, and as a result of the plating reaction, it is presumed that they were co-deposited with the nickel and hoe layers. .

As described above, according to the present embodiment, diffusion of gold can be suppressed, so that even if the thickness of the gold plating film is reduced, it is possible to sufficiently contribute to bonding. In this example, mullite ceramics were used for the substrate. However, it can be easily understood that diffusion prevention of gold plating can be generally applied to other well-known materials such as alumina irrespective of the ceramic material.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION According to this invention, a crack does not generate | occur | produce in a nickel-boron plating film, a crack does not generate | occur | produce in a mullite ceramics substrate even after a heat treatment, and the gold plating layer formed on the nickel-boron plating film is maintained. Therefore, it is possible to realize a ceramic substrate that achieves high component bonding properties.

[Brief description of the drawings]

 FIG. 1 is a characteristic curve diagram showing one embodiment of the present invention.

Claims (4)

(57) [Claims] A step of printing a high melting point metal paste on a mullite or mullite ceramic insulating substrate containing mullite as a main component in a predetermined wiring circuit pattern shape, and firing the circuit pattern in a reducing or inert atmosphere. Forming a nickel plating film having a boron content of 0.71 wt% or less on the sintered circuit pattern by an electroless plating method. A method for producing a ceramic circuit board, comprising adding a sulfur-containing organic compound to a plating bath in a step of forming a plating film. 2. The method for manufacturing a ceramic circuit board according to claim 1, wherein a step of forming a gold plating film by electroless plating is added after the step of forming the nickel plating film. 3. A step of printing a refractory metal paste on a ceramic insulating substrate in a predetermined wiring circuit pattern shape, a step of sintering the circuit pattern in a reducing or inert atmosphere, and then an electroless plating method. The content of the impurity element on the sintered circuit pattern is 0.96 wt.
% Of a nickel plating film in a method of manufacturing a ceramic circuit board, the method including a step of forming a nickel plating film of not more than 10% and a step of forming a gold plating film on the nickel plating film by an electroless plating method. A method for producing a ceramic circuit board, characterized in that a sulfur-containing organic compound is added to a plating bath according to (1). 4. The method according to claim 1, wherein the ceramic insulating substrate is made of mullite or a mullite ceramic containing mullite as a main component, and the content of boron, which is one of the impurity elements contained in the nickel plating film, is 0.71 wt% or less. 4. The method for manufacturing a ceramic circuit board according to claim 3, wherein: