JPH02192193A - Ceramic circuit board and manufacture thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a ceramic circuit board, and more particularly to a ceramic circuit board in which the surface of a conductor formed on a ceramic insulating substrate is metalized by nickel plating, and a method for manufacturing the same. .

[Conventional technology]

Conventionally, circuit boards have been known in which a circuit pattern of a high melting point metal such as molybdenum, tungsten, or tantalum formed on a ceramic substrate is metalized with a boron-containing nickel plating film. This boron-containing nickel plating film.

It is formed by an electroless plating method using an amine-boron compound as a reducing agent, but it can withstand high temperature heat treatment better than conventional nickel-phosphorous plating films, and the surface is relatively oxidized. Because of its excellent adhesion properties, it is being considered as a plating film for metallizing the conductor surface of ceramic substrates for high-density mounting in recent years. However, this boron-containing nickel plating film has high stress on its own.

Cracks were likely to occur in the film, which was an obstacle in the subsequent plating process. Therefore, 9 For example, JP-A-58-3
As described in No. 962, the conductor layer that forms the boron-containing nickel plating film contains a small amount of glass material in advance, and boron, which is thought to be the main factor in stress generation, is diffused into this to reduce the amount of boron in the film. Measures are taken to prevent an increase in film stress due to heat treatment.

[Problem to be solved by the invention]

As described in the above section of the prior art, it is effective to reduce the amount of boron in the nickel plating film by thermally diffusing boron into the glass material in the underlying conductor layer of the nickel plating film. However, it is not preferable to include a non-conductive material such as glass in the underlying conductive layer from the viewpoint of electrical conductivity. In addition, cracks that occur in the nickel plating film itself can be suppressed by reducing the amount of boron through thermal diffusion, but this depends on the material of the ceramic substrate.

A new problem arose in that cracks occurred during heat treatment. In other words, the ceramic is alumina (Al1203)
There is no problem in the case of materials with high mechanical strength such as mullite (3JO3, 2Si○2) or mullite ceramics whose main component is mullite, but after the formation of this nickel plating film, It was found that heat treatment significantly increases the incidence of cracks. Furthermore, on the surface of the nickel plating film.

A gold plating layer is formed on the surface of this nickel plating film in order to improve the bonding properties of various types of I10 pins, LSIs, sealing caps, etc. After gold plating, the gold plating layer is formed after various heating processes. No consideration was taken to prevent the film from diffusing into the nickel plating film, making it difficult to maintain the thickness of the gold plating film sufficient for bonding and maintain sufficient bonding properties until the final process. there were.

The purpose of the present invention is to solve these problems,
The first objective is to create a highly reliable ceramic circuit board with a boron-containing nickel plating film that does not cause cracks even when mullite or mullite-based ceramics containing mullite as the main component are used as the ceramic substrate. The third purpose is to create a ceramic circuit board that suppresses the diffusion of the gold plating film layer formed on the nickel plating film surface regardless of the composition of the ceramic substrate, and the fourth purpose is to create a method for manufacturing the same. The aim is to provide each of these.

[Means to solve the problem]

The first object is to provide a circuit board comprising a high melting point metal conductor circuit pattern provided on a ceramic insulating substrate and a nickel film electrolessly plated on the circuit pattern. This is achieved by a ceramic circuit board made of mullite or mullite-based ceramics containing mullite as a main component, and characterized in that the amount of boron contained in the nickel film is 0.71 wt% or less.

The second purpose is to print a high melting point metal paste in a predetermined wiring circuit pattern shape on a mullite or mullite-based ceramic insulating substrate mainly composed of mullite, and to print the circuit pattern in a reducing or inert atmosphere. The boron content is 0.7 on the sintered circuit pattern by sintering and then electroless plating.
This is achieved by a method for manufacturing a ceramic circuit board characterized by comprising a step of forming a nickel plating film of 1 wt % or less.

In addition, what is the boron content in the nickel plating film?

Due to electroless nickel plating using an amine-boron compound as a reducing agent, it cannot be reduced to zero, and in order to maintain the nickel plating rate, the lower limit is about 0.02 wt%. Therefore, the acceptable content is 0.02~0
．． 71tgt%, preferably 0.2-0.5wt%. In order to adjust the amount of boron to this level.

The amount of the amine-boron compound added to the plating bath can be adjusted, but if it is too small, a sufficient plating rate will not be obtained. A sulfur-containing organic compound such as thiourea (at least S, C,
By adjusting the amount of added and dissolved N (including each element), the amount of boron contained in the nickel plating film can be regulated to an appropriate value.

The third object is to (1) provide a high melting point metal conductor circuit pattern provided on a ceramic insulating substrate;

In a circuit board comprising a nickel film plated on the circuit pattern and a gold film further plated on the nickel film, the total amount of impurity elements contained in the nickel film is 0.96 wt% or less. (2) more preferably, the amount of boron contained as one of the impurity elements is 0.71 wt% or less. (3) This is achieved by a ceramic circuit board characterized in that the ceramic insulating substrate is made of mullite or mullite-based ceramics containing mullite as a main component.

The invention that achieves this third objective is that, regardless of the material of the ceramic, if the total amount of impurities contained in the nickel plating film exceeds 0.96 tit;%, a gold plating film will be formed on the surface of the film. This was done based on the inventors' knowledge that a significant amount of heat diffuses into the underlying nickel film during subsequent heat treatment.

These impurities are mixed in from various raw materials that make up the plating bath. If a material is used, the amount of impurities other than boron and phosphorus can be reduced as much as possible.

The fourth purpose is to (1) print a high melting point metal paste onto a ceramic insulating substrate into a predetermined wiring circuit pattern, and sinter 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 vt% or less on the sintered circuit pattern by electroless plating.

A method for manufacturing a ceramic circuit board, further comprising the step of forming a gold plating film on the nickel plating film by electroless plating, and preferably (2) forming the ceramic insulating board with mullite or mullite. A method for producing a ceramic circuit board, characterized in that the main component is mullite ceramic, and the content of boron, which is one of the impurity elements contained in the nickel plating film, is 0.71 wt% or less. This is achieved by

[Effect]

The reason why nickel-boron plating (meaning nickel plating containing boron, hereinafter the same) is applied to the surface of high-melting point metals such as tungsten, molybdenum, and tantalum is to obtain high bonding strength with the high-melting point metal. For example, when a conductor pattern made of the above-mentioned high-melting point metal is plated with nickel and boron to a thickness of about 5 layers, a bonding strength of 2 kg/mm2 is obtained. In addition, after nickel/boron plating, when heated at 750℃ for 10 minutes in an inert gas, the bonding strength: 4kg/
Obtain high bonding strength of mm2 or more. This bonding is caused by mutual diffusion of the high melting point metal and nickel, and the same bonding strength can be obtained with a high melting point metal that does not contain a glass component and nickel plating, or with a high melting point metal that contains a glass component.

Boron content: 0.71wt on the high melting point metal conductor surface
The reason for applying a plating film of less than % is to prevent an increase in film stress after heat treatment. As a result, even in mullite-based ceramic substrates with low mechanical strength that contain a large amount of silicon oxide (SiO2), the strain between the high-melting point metal and the nickel/boron plating film is small, and as a result, cracks in the substrate can be avoided. It will no longer occur. In addition, prevention of diffusion of gold and nickel slows down the diffusion of gold into the plating film by reducing the total amount of impurities in the nickel/boron plating film. The gold plating layer is maintained even after various heating processes such as gluing, brazing, and wire bonding, enabling a variety of high-quality connections.

〔Example〕

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

(1) Plating bath composition: NiSO4.6H200,076mo Q/Q glycine 0.013-0.4 gluconic acid
0.038~0.5E D T A -2Na
O~0.003 dimethylamine borane 0.
0085-0.085 II sulfur-containing organic compound 0
．． 5-100 mg/fl water
Amount to be IQ (2) Plating conditions: Plating bath temperature 52 to 70°C Plating bath pH 6 to 8 By combining the above nine composition conditions, the boron content in the nickel-boron plating film is 0.02 to 3.0 wt%. I got something. Nickel/phosphorus plating was performed using Nippon Kanigen Co., Ltd., trade name S-680. In addition.

The evaluation of each plating film is based on approximately five layers of plating thickness.

(3) Ceramic substrate used: The presence or absence of cracks in the ceramic substrate was determined by the following method. The ceramic substrate used has a crystal structure of 3A11203.2Sio2 identified from X-ray diffraction, and is called a mullite ceramic substrate. Although this ceramic substrate has the disadvantage of having a low bending strength of about 173 compared to an alumina ceramic substrate and a low mechanical strength, it has a relative dielectric constant of about 30% and is suitable for high-density packaging. W paste was printed on this ceramic substrate as a high melting point metal conductor and sintered by a conventional method to form a conductor pattern.

(4) Electroless plating: The W conductor of this board is subjected to pre-plating treatment such as cleaning and catalyst application in the usual manner, and is then plated with nickel-boron and nickel-phosphorus at 750°C in a nitrogen gas atmosphere. ,1
A heat treatment was performed for 0 minutes, and the occurrence of cracks in the mullite ceramic substrate was observed based on changes in the stress of the plating film before and after the heat treatment.

(5) Crack occurrence and stress measurement evaluation: As a method for evaluating crack occurrence, the percentage of cracked conductors among the 268 conductors was calculated and expressed as a crack occurrence 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 a pure tungsten plate with a thickness of 0.2 mm.

The stress of the plating film before and after heat treatment was measured by the following method. After plating various nickel and boron to 5μm,
A tungsten plate was cut into pieces of 50 mm in length and @10 mm, and the amount of warpage after plating and heat treatment of the tungsten plate was measured using a 2-surface roughness meter and calculated using the 9th equation.

E: Young's modulus of tungsten plate t: Thickness of plate h: Warpage amount Ω: Length of tungsten plate d: Thickness of plating film (6) Measurement of impurities in plating film: Impurities in nickel/boron plating film The measurement was carried out using the following method. After dissolving the plated sample in nitric acid, this solution was used as an analysis sample for analysis using a dual emission spectrometer.

Table 2 Eyebrow water The above results are shown in Tables 1 and 2.

Note that sample Nα1 in Table 1 shows nickel-phosphorus plating as a comparative example. The impurity content in the nickel-phosphorus plating film is as high as 7.62 wt%. Although no cracks occur in the plating film, the film stress after heat treatment is 150 kg.
/mm2, and 10 for mullite ceramic substrates.
0% crack occurred.

Samples Nα2 to Nα13 are shown in terms of the presence or absence of cracks in the nickel-boron plating film and the rate of crack occurrence in the mullite ceramic substrate due to increase in film stress after heat treatment.

It was found that when the boron content was extremely large as shown in samples Nα2 and Nα3, cracks appeared in the plating film after completion of plating, making it unusable for practical use. Therefore, the film stress could not be measured.

As shown in samples Nα4 to 6, the boron content is 1.1w.
When the amount was t% or less, the coating stress and the occurrence of cracks in the ceramic substrate could be measured without causing any cracks in the plating film. As a result, the lower the boron content, the lower the film stress after heat treatment.

At the same time, the crack occurrence rate of ceramic substrates also decreased.

As shown in samples Nα7 to 13, the boron content is 0.7
By setting the amount to 1 wt% or less, the film stress after heat treatment was as small as 31.6 kg/mm'' or less, and no cracks were generated in the ceramic substrate.

Therefore, after nickel/boron plating, mullite ceramic substrates that undergo a process of applying high heat have a boron content of 0.71w in the nickel/boron plating film.
It has been found that it is necessary to keep it below t%. In this way, with a boron content of 0.71 to 0.02 wt%, the film stress after heat treatment was 31.6 kg/mm2 to 7.6 kg/m.
m”, and not only does the nickel-boron plating film not crack, but even when mullite (3Af1203/2S102) ceramics are used as the ceramic substrate, there is no cracking rate in the substrate. Understood.

Example 2 In this example, gold plating was applied to the surface of the nickel-boron plating film obtained in Example 1, and when this gold plating film was subjected to heat treatment, heat was diffused into the underlying nickel plating film. This is a review of the situation.

The conditions for gold plating and heat treatment to diffuse gold into the base nickel plating film are as follows.

The degree of diffusion between the nickel/boron plating film and the gold plating film was determined by using Retroless D (trade name, manufactured by Nippon Electroblating Engineers Co., Ltd.) after nickel/boron plating on the tungsten plate as described above.
A sample was plated with displacement gold to a thickness of about 0.2 cape and then heat-treated at 650 to 850°C for 10 minutes in a nitrogen gas atmosphere, and the measurement was determined from the characteristic X-ray intensity ratio of the surface. That is, the larger the nickel/total strength ratio, the more the diffusion of gold into the nickel/boron plating film progressed, and the more the gold plating layer on the surface of 9 disappeared.

The method for measuring the total amount of impurities in the nickel-boron plating film was the same as that of Example 1, and the same as that of the samples listed in Tables 1 and 2. Result is,
As shown in Figure 1.

In other words, the figure shows the total impurity content shown in Tables 1 and 2 on the horizontal axis, and the nickel (Ni) content at each heat treatment temperature.
The progress of diffusion in the gold-plated layer is shown from the characteristic X-ray intensity ratio of gold (A u ) and gold (A u ). We have found that an extremely good correlation can be obtained between these. When the total impurity content was 3.96 wt% or less, an extremely small N]/Au intensity ratio was obtained at each heat treatment temperature. In other words, the characteristic X-ray intensity of Au is strong<the Au plating layer is nickel/
Indicates that boron has not diffused or penetrated into the plating layer. Therefore, the above-mentioned nickel/boron plating film is applied on a high melting point metal conductor such as tungsten or molybdenum.

Furthermore, even if the ceramic substrate with the gold-plated film on it passes through a high-temperature heating process.

As a result of retaining the Au plating layer as described above, high bondability between the two parts can be maintained.

As mentioned above, boron, iron, cobalt, and sulfur.

It is surprising that the smaller the total content of impurities such as copper, the slower the diffusion of gold into the nickel film.

The exact reason is unknown, but probably.

This is presumed to be due to the fact that impurities and gold easily react with each other, and that the crystal grain size of the plating film becomes larger when using highly pure nickel, which slows down the diffusion rate of gold. Furthermore, it is surprising to find that iron, cobalt, sulfur, copper, etc. are mixed into the nickel/boron plating film. The chemicals used were probably various, ranging from industrial ones to high-purity reagents, but it is presumed that these chemicals contained them as impurities, and were eutectoided with the nickel and boron layers as a result of the plating reaction. .

As described above, according to this embodiment, since the diffusion of gold can be suppressed, even if the gold plating film is made thin, it can sufficiently contribute to bonding. Further, in this example, mullite-based ceramics were used for the substrate, but it is easy to understand that the prevention of diffusion of gold plating can be applied to other well-known materials, including alumina, regardless of the material of the ceramic.

〔Effect of the invention〕

According to the present invention, no cracks occur in the nickel/boron plating film, no cracks occur in the mullite ceramic substrate even after 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 with high component bondability.

[Brief explanation of the drawing]

FIG. 1 is a characteristic curve diagram showing one embodiment of the present invention. Representative Patent Attorney Junnosuke Nakamura

Claims (7)

[Claims] 1. A circuit board comprising a high melting point metal conductor circuit pattern provided on a ceramic insulating substrate and a nickel film electrolessly plated on the circuit pattern,
The ceramic insulating substrate is made of mullite or mullite-based ceramics containing mullite as a main component, and the amount of boron contained in the nickel film is 0.71w.
A ceramic circuit board characterized by having a content of t% or less. 2. A process of printing a high melting point metal paste in a predetermined wiring circuit pattern shape on a mullite or a mullite-based ceramic insulating substrate mainly composed of mullite, and a process of sintering the circuit pattern in a reducing or inert atmosphere, A method for manufacturing a ceramic circuit board, comprising the step of: forming a nickel plating film having a boron content of 0.71 wt% or less on the sintered circuit pattern by electroless plating. 3. A circuit board comprising a high melting point metal conductor circuit pattern provided on a ceramic insulating substrate, a nickel film plated on the circuit pattern, and a gold film plated on the nickel film. The total amount of impurity elements contained in the nickel film is 0.96wt%.
A ceramic circuit board characterized by the following: 4. The amount of boron contained as one of the above impurity elements is
The ceramic circuit board according to claim 3, characterized in that the content is 0.71 wt% or less. 5. 5. The ceramic circuit board according to claim 3, wherein the ceramic insulating substrate is made of mullite or mullite-based ceramics containing mullite as a main component. 6. A process of printing a high melting point metal paste in a predetermined wiring circuit pattern shape on a ceramic insulating substrate, a process of sintering the circuit pattern in a reducing or inert atmosphere, and then a process of printing the sintered metal paste by an electroless plating method. The total content of impurity elements on the circuit pattern was 0.96wt.
% or less, and further forming a gold plating film on the nickel plating film by electroless plating. 7. The ceramic insulating substrate is made of mullite or a mullite ceramic whose main component is mullite, and the content of boron, which is one of the impurity elements contained in the nickel plating film, is 0.71 wt% or less. 7. The method of manufacturing a ceramic circuit board according to claim 6.