JPH08144061A - Metallizing of insulating material - Google Patents

Abstract

PURPOSE: To provide a metallizing method by the electroless plating of an insulating material which unnecessitates surface roughening process and facilitates the control of a catalyst solution. CONSTITUTION: A metal oxide coating film is formed on an insulating material substrate by forming a metallic complex (example of a complexing agent; triethanol amine, ammonia) of a metal constituting a metal oxide (e.g. ZnO, SnO2 , TiO2 , In2 O3 ) in an alkali aq. solution, allowing the insulating material substrate (e.g. substrate for printed circuit board) to contact with the solution containing the metallic complex and decomposing under heating the metallic complex. After that, a metal coating film (e.g. copper) is formed thereon in an electroless plating bath after palladium is imparted to the metal oxide coating film in the alkali catalyst solution and, if necessary, further a metal coating film (e.g. copper) is formed thereon by electroplating. The metallizing layer having high adhesion is finely patterned with a low cost and at a low temp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for metallizing an insulator, and more particularly to a method for forming an insulator substrate characterized by a combination of forming a metal oxide film by a wet method and subsequent electroless plating. Regarding metallization technology. Here, metallization means forming a metal (including alloy) film on the surface of the insulator.

[0002]

2. Description of the Related Art In the field of materials such as electronic devices, automobiles and aircrafts, it is often necessary to metallize an insulator. Up to now, several methods have been proposed as a method of metallizing an insulator. For example, the following method has been proposed as a dry method. The "high melting point metal method" is a method of sintering an ink or paste containing a high melting point metal powder such as molybdenum on the surface of an alumina base material to form a metallized layer, and an improved method thereof is disclosed in JP-A-55-15438.
No. 3 added Mo to the fine and coarse powders, preferably mainly Mn powders, and applied a paste containing an organic liquid onto the calcined Al ₂ O ₃ at 1500 ° C. in hydrogen. It describes to sinter. The "thick film method" is a method in which a suspension containing a metal compound is applied to the surface of a ceramic, the applied layer is baked, and then the metal compound is reduced. For example, Japanese Patent Laid-Open No. 59-92979 discloses, as an example, a mixture of a Cu compound powder and a SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —Na ₂ O high-melting-point glass powder mixed with water. % Al ₂ O
₃ It describes that a metal coating layer is formed by printing and coating on a porcelain, firing at 1100 to 1200 ° C. in the atmosphere, and reducing by immersing in kerosene. "Direct bond method"
Is Al ₂ O ₃ covered with a copper foil having a copper oxide layer on the surface, as described in JP-A-57-82181, for example.
The sintered plate is heated at the eutectic temperature of Cu and Cu ₂ O while controlling the O ₂ partial pressure in a vacuum furnace. The "physical vapor deposition method" is a method in which a metal layer is directly formed on a substrate by a vapor deposition method, a sputtering method, or the like.

The refractory metal method is a high temperature process (up to 150
Since 0 ° C.) is used, it cannot be applied to a metal (Cu or the like) having a melting point equal to or lower than the process temperature, and the metallized layer is limited to a refractory metal. In the thick film method, fine patterning of the metallized layer is impossible due to the size of the paste particles used (currently 200 μm width). In addition, high temperature process (~ 100
0 ° C) is required. Although the direct bond method can form a metallized layer having good adhesiveness in terms of quality,
It is not suitable for industrialization because it is difficult to control the process. This method also requires a high temperature process (up to 1000 ° C.). The physical vapor deposition method can form a metallized layer with high adhesion and is applicable to almost all metals.
A low temperature process (270 ° C.) is also possible if a means is selected.
However, the cost is high because an expensive vacuum device is used.

As an alternative to the dry / high temperature process, there is an electroless plating method as a wet / low temperature process. In the electroless plating method, for example, as described in JP-A-52-914, after the substrate is roughened by etching or the like, S
The surface of the substrate is activated with an nCl ₂ , PdCl ₂ solution or the like, and a metal layer is formed by electroless plating. Further, in JP-A-6-61619, when a zinc oxide layer is formed on a ceramic or glass substrate and brought into contact with a solution in which a metal salt of a metal serving as a catalyst for electroless plating is dissolved, a zinc oxide dissolution reaction occurs. At the same time, by utilizing the phenomenon that the metal ions in the metal salt are taken into the surface and inside, the metal layer is laminated on the surface of the ceramic or glass substrate by putting it in the electroless plating bath. The manufacturing method of the circuit board described above is described.

[0005]

The electroless plating method is a low temperature process, but requires roughening of the substrate to obtain the adhesion of the metallized layer. Therefore, there is a limit to fine patterning of the metallized layer. Further, the roughening treatment may cause blistering of the metallized layer.
JP-A-6-61619 uses the dissolution reaction of zinc oxide to improve the adhesion to the plating film, but the solubility of zinc oxide is greatly affected by pH. Z for catalyst liquid
Since nO is dissolved, it is difficult to control the pH and the liquid life is short. There is also a spray coating method as a method for forming a zinc oxide film, but the obtained zinc oxide film is too smooth and Cu
Can not get close contact with. Therefore, it is necessary to roughen the surface of zinc oxide, but since the roughening solution dissolves zinc oxide as described above, it is difficult to control the solution. Further, the life of the liquid is short and the cost is high.

In view of such circumstances, an object of the present invention is to develop a method of metallizing an insulator by electroless plating which does not require a roughening step and facilitates control of a catalyst solution, and through which a low cost and low temperature process is achieved. Therefore, it is to establish a metallizing method having a large adhesive force and capable of forming a fine pattern of the metallized layer.

[0007]

As a result of studies for solving the above-mentioned problems, as a result, a metal complex of a metal forming a metal oxide is formed in an alkaline aqueous solution, and an insulator substrate is brought into contact with a solution containing the metal complex. And when a metal oxide film is formed on the insulating substrate by thermally decomposing the metal complex,
The surface is moderately rough, and therefore roughening treatment is not required, and electroless plating can be suitably performed using a commercially available catalyst solution. This method is low cost, low temperature process, high adhesion, fine pattern It was concluded that it is the most suitable for satisfying all the requirements for conversion. Thus, the present invention forms a metal complex of a metal forming a metal oxide in an alkaline aqueous solution, brings an insulator substrate into contact with a solution containing the metal complex, and thermally decomposes the metal complex to form the insulator. A metal oxide film is formed on a substrate, and then palladium is applied on the metal oxide film in an alkali catalyst solution, and then a metal film is formed in an electroless plating solution. Provide a metallization method. Further, thereafter, a metal film can be formed by electroplating.

The metal oxide film is preferably ZnO, Sn
It is a mixture of one or more selected from O ₂ , TiO ₂ and In ₂ O ₃ , and ZnO is particularly preferable.
The complexing agent for forming the metal complex is preferably triethanolamine or ammonia. The insulator substrate is
It is made of ceramics, glass, or plastic, and one of its suitable applications is a printed wiring board substrate.

[0009]

Action: ZnO, SnO ₂ , TiO in alkaline aqueous solution
A metal complex of a metal forming a mixture of one or more selected from ₂ and In ₂ O ₃ is formed. By adding a complexing agent, the metal hydroxide usually forms and dissolves a metal complex. The insulating metal substrate is brought into contact with a solution containing the metal complex, and the metal complex is thermally decomposed to form a conductive metal oxide film having good adhesion on the insulating substrate at a rate of about 1 to 2 μm / hr. To form a film. When the metal oxide film is formed in this manner, the surface is moderately roughened, and therefore roughening treatment is not required, and electroless plating can be suitably performed using a commercially available catalyst solution. Then, if necessary, a metal coating is formed by electroplating. These process steps are low cost, low temperature process, high adhesion,
Satisfy all requirements for fine patterning.

[0010]

DETAILED DESCRIPTION OF THE INVENTION Examples of the insulating substrate used in the present invention include ceramics such as alumina and aluminum nitride, glass, epoxy, and plastics such as phenol resin. Specifically, for example, application to metallization on a substrate for a printed wiring board or the like can be considered. Hybrid IC substrates and electrodes for plasma displays are examples of applications.

As oxides, ZnO, SnO ₂ , Ti
O ₂ , In ₂ O _{3 and the} like and mixtures thereof can be mentioned. Therefore, as a metal ion source that forms these oxides,
An aqueous solution containing Zn salt, Sn salt, Ti salt, In salt and the like is used. The concentration is usually 0.01 to 1 though it depends on the conditions.
0 mol / l is preferred. If the concentration is too low, the final deposition rate of the metal oxide film will be slow, while if the concentration is too high, a uniform metal oxide film will not be formed.

As the alkaline aqueous solution used in the present invention, NaOH or KOH is generally within a range suitable for metal hydroxide formation depending on the metal ion source concentration, and is generally 0.5 to 10.
Add so that it becomes mol / l. As a result, a metal hydroxide is formed, which may result in precipitation.

Triethanolamine or ammonia is used as the complexing agent. The concentration of the complexing agent added is preferably 0.1 to 10 mol / l. By adding a complexing agent, the metal hydroxide usually forms and dissolves a metal complex. The concentration of the complexing agent is sufficient to form the metal complex.

The solution containing the metal complex is brought into contact with the insulating substrate, and the insulating substrate is immersed in the solution containing the metal complex, for example, and heated at 40 to 100 ° C. for about 0.5 to 10 hours. By this heat treatment, a metal oxide film is formed on the insulating substrate. The heating temperature and heating time are appropriately selected depending on the metal so as to form a metal oxide film having a predetermined thickness. For example, when forming a zinc oxide film, 5
Heat to 0-95 ° C. The film formation rate of the metal oxide film is about 1 to 2 μm / hour. Thickness of oxide film is 1
It is generally about 10 μm, but the invention is not limited to this. The thickness of the film can be adjusted by repeating the dipping operation a desired number of times.

A catalyst is applied as a pretreatment for electroless plating. The catalyst may be applied according to a generally practiced method, for example, the following pretreatment steps are performed: (a) Conditioning A weak alkaline conditioner is used to stain the surface with a component such as a surfactant. To give a charge to the surface,
d Makes colloid adsorption easy. (B) Washing with water (c) Pre-dip By dipping in a weak alkaline (pH 10.5) pre-dip solution containing an organic chelating agent, the catalyst solution in the next step is prevented from being diluted. (D) Addition of catalyst This is a step of attaching a Pd catalyst using a weak alkaline (pH 10.5) catalyst liquid, and the Pd-organic complex is adsorbed on the surface. (E) Reduction treatment The Pd-organic complex adsorbed in the catalyst step is reduced to leave Pd nuclei and remove the organic chelating agent. (F) Washing with water

After that, an electroless plating process is carried out.
In this case, a metal layer (Cu, Ni, etc.) is formed by performing electroplating after performing thin electroless plating or performing thick electroless plating. Use an alkaline plating solution to prevent the oxides from dissolving. A typical example of the electroless plating solution is copper plating,
Examples of the conditions are as follows: (Electroless copper plating conditions) CuSO ₄ .5H ₂ O: 0.5 to 10 g / l as Cu: 5 to 15 g / l HCHO: 37% solution of 5 to 30 ml / Stabilizer (eg EDTA): Appropriate amount Additive: Appropriate amount

Thereafter, if necessary, an insulating substrate with an electroless plating film is used as a cathode electrode on the insulating substrate by an electrolytic method to form a noble metal such as copper, nickel, platinum group metal, gold or silver, or a metal such as solder. A film is formed. The bath used is
Any conventional plating bath can be used. For example, in the case of copper plating, the following conditions can be used: (Copper pyrophosphate plating conditions) Copper pyrophosphate: 80-100 g / l Potassium pyrophosphate: 300-400 g / l Ammonia: 2.5-5. 0 ml / l Additive: Appropriate amount pH: 8.4 to 9.0 Temperature: 45 to 55 ° C. Current density: 2.0 to 3.5 A / dm ²

After this, patterning, surface treatment, additional film formation and other necessary treatments are performed.

[0019]

Example 1 Alumina substrate (96% Al ₂ O ₃ , 5 cm
An example in which copper is metallized on (× 5 cm square) will be shown. Alumina substrate with 1 mol / l ZnCl ₂ +3.5 mol / l
60% in NaOH + 50 ml 25% aqueous ammonia solution
A zinc oxide film was formed by dipping at 3 ° C. for 3 hours.

The following steps were carried out as a pretreatment for electroless plating: (a) Conditioning: CP-1025 conditioner, manufactured by Japan Energy, used at 70 ° C. for 5 minutes. (B) Washing with water (c) Pre-dip: Japan Energy, trade name CP
-3040 Pre-dip solution was used and carried out at 25 ° C for 1 minute. (D) Application of catalyst: Japan Energy, trade name CP-3
Using 340 catalyst solution, 5 minutes at 60 ℃. (E) Washing with water (f) Reduction: manufactured by Japan Energy, trade name CP-404
1 Using reducing solution, 5 minutes at 25 ℃. (G) Washing with water

Next, thinning electroless plating was performed under the following conditions: (Thinning electroless copper plating conditions) CuSO ₄ .5H ₂ O: 10 g / l NaOH: 10 g / l HCHO: 37% solution of 15 ml / l EDTA · 4Na · 4H ₂ O: 30 g / l Additive: appropriate amount Temperature and time: 25 ° C. × 15 minutes The adhesion of the thin electroless copper plating film was good.

[0022]

Example 2 Following Example 1, after washing with water, electrolytic copper plating was performed using a copper pyrophosphate plating bath. The electrolytic plating conditions were as follows: (Copper pyrophosphate electrolytic plating conditions) Copper pyrophosphate: 90 g / l Potassium pyrophosphate: 350 g / l Ammonia: 3 ml / l Additive: Appropriate amount pH: 8.8 Temperature: 50 ° C Current density: 2.8 A / dm ²

After washing with water, the sample prepared under the above conditions was
A pull test was performed after patterning to a size of 2 mm × 2 mm. As a result, the adhesion strength was 4 kgf in 2 mm square.

[0024]

EFFECTS OF THE INVENTION When a metal oxide such as zinc oxide is formed, the surface is appropriately roughened, so that it is not necessary to roughen it. Therefore, since a commercially available catalyst solution can be used, the management is easy and the solution life is long. Since it is a low temperature process, a low melting point substance can be metallized. Further, the cost is lower than that of the physical vapor deposition method. Since the substrate does not need to be roughened, the metallized layer can be finely patterned and the metallized layer does not swell.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H05K 3/18 B 7511-4E

Claims (10)

[Claims] 1. An insulating substrate by forming a metal complex of a metal forming a metal oxide in an alkaline aqueous solution, contacting an insulating substrate with a solution containing the metal complex, and thermally decomposing the metal complex. A metallization of an insulator, characterized in that a metal oxide film is formed on the metal oxide film, palladium is then applied to the metal oxide film in an alkali catalyst solution, and then a metal film is formed in an electroless plating solution. Method. 2. An insulator substrate is formed by forming a metal complex of a metal forming a metal oxide in an alkaline aqueous solution, contacting an insulator substrate with a solution containing the metal complex, and thermally decomposing the metal complex. A metal oxide film is formed on the metal oxide film, palladium is then applied to the metal oxide film in an alkaline catalyst solution, a metal film is formed in an electroless plating solution, and then a metal film is formed by electroplating. A method of metallizing an insulator, comprising: 3. The metal oxide film is ZnO, SnO ₂ , T
The method for metallizing an insulator according to claim 1 or 2, wherein the method is a mixture of one or more selected from iO ₂ and In ₂ O ₃ . 4. The method for metallizing an insulator according to claim 1, wherein the complexing agent for forming the metal complex is triethanolamine or ammonia. 5. A zinc complex is formed by forming a hydroxide of zinc in an alkaline aqueous solution and adding a complexing agent selected from triethanolamine or ammonia to the hydroxide. An insulating substrate is brought into contact with the solution, and a zinc oxide film is formed on the insulating substrate by thermally decomposing the zinc complex, and then palladium is applied on the zinc oxide film in an alkaline catalyst solution, A method for metallizing an insulator, which comprises forming a metal film in an electroless plating solution. 6. A zinc complex is formed by forming a zinc hydroxide in an alkaline aqueous solution and adding a complexing agent selected from triethanolamine or ammonia to the hydroxide. An insulating substrate is brought into contact with the solution, and a zinc oxide film is formed on the insulating substrate by thermally decomposing the zinc complex, and then palladium is applied on the zinc oxide film in an alkaline catalyst solution, A method of metallizing an insulator, which comprises forming a metal film in an electroless plating solution and further forming the metal film by electroplating. 7. The method for metallizing an insulator according to claim 1, wherein the insulator is ceramics. 8. The method of metallizing an insulator according to claim 1, wherein the insulator is glass. 9. The method of metallizing an insulator according to claim 1, wherein the insulator is plastic. 10. The method for metallizing an insulator according to claim 1, wherein the insulator is a printed wiring board substrate.