JPH08167768A - Forming method for circuit pattern, and paste used therefor - Google Patents

Abstract

PURPOSE: To form a circuit pattern with a fine line at a high pitch, and to bond it firmly to a board, and further, to form the circuit pattern easily at a low cost without use of metallic fine particles, and moreover, to increase the kinds of the boards whereto this forming method for circuit patterns can be applied. CONSTITUTION: A forming method for circuit patterns includes the process for forming a coating film on a board by the application of a paste wherein metallic oxides reduced to the metals by their heatings in atmosphereat 100-1200 deg.C are distributed uniformly, the process for reducing the metal oxides contained in this coating film to the metals through heating at the foregoing temperature, and the process for depositing electroless platings while these reduced metals are used as nucleuses. The paste is so prepared that the metal oxides of 10-80wt.% which are reduced to the metals by heating in atmosphere at 100-1200 deg.C are distributed uniformly in a vehicle of 90-20wt.% which contains organic binder and organic solvent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a circuit pattern on a substrate for manufacturing a circuit board and a paste for forming the pattern. More specifically, the present invention relates to a method suitable for forming a fine circuit pattern having a fine pitch on a fine line by thermally decomposing a noble metal oxide, and a paste thereof.

[0002]

2. Description of the Related Art In recent years, the mounting density of chip components on a circuit board has increased due to miniaturization of electronic equipment, and circuit patterns are required to be fine lines and fine pitches. Conventionally, as a method of forming a conductive circuit pattern on a non-conductive substrate, for example, a thick film forming method by screen printing is known. In this method, when the substrate is ceramics, a step of preparing a conductive paste by dissolving an organic binder in an organic solvent and mixing metal powder and glass frit, and this conductive paste in a predetermined pattern on a non-conductive substrate. A step of applying by a screen printing method,
This screen-printed conductive paste is dried and then heat-treated to adhere the coating film to the non-conductive substrate. According to this method, when the conductive paste is heat-treated, the metal powders come into contact with each other, and the printed coating film becomes conductive, and at the same time, the glass adheres the coating film to the substrate.

Further, in this method, when the substrate is a resin, a step of dissolving a thermosetting resin in an organic solvent and mixing a metal powder to prepare a conductive paste, and the conductive paste is predetermined on a non-conductive substrate. And a step of applying the screen-printed conductive paste by drying to bond the coating film to the non-conductive substrate with a resin. According to this method, when the conductive paste is dried, the metal powders come into contact with each other, the printed coating film becomes conductive, and at the same time, the resin causes the coating film to adhere to the substrate.

However, when the pattern formed by screen printing is a fine line, there is a risk of pattern breakage due to shrinkage of the paste during drying.
Therefore, in the conventional thick film forming method, it was necessary to set the pattern width to at least about 100 μm when screen printing so as not to cause pattern breakage. Further, when the pattern is formed by the conductive paste, the metal powder in the conductive paste has a large specific gravity, and thus it is apt to settle down due to its own weight to cause sagging of the paste. Therefore, if the pattern interval is narrowed to a fine pitch, there is a risk that the patterns may short-circuit due to sagging. Therefore, in the conventional thick film forming method, when the screen printing is performed so that the patterns are not short-circuited, the pattern interval is at least 1.
It was necessary to keep the thickness to about 00 μm. Therefore, in this method, the pattern width and the pattern interval are each 100
Only a pattern of about μm or more could be formed, and as a result, the circuit pattern could not be made fine with a fine line and a fine pitch.

In order to improve these points, the present applicant has filed a patent application for "a method for forming a circuit on a ceramic substrate" for forming a fine pattern (Japanese Patent Laid-Open No. 4-2499).
0). That is, this method of forming a fine pattern is performed by dispersing fine metal particles having a particle size of 5 μm or less, such as gold, silver, copper, or tungsten, in a metal alkoxide solution of silicon, lead, zinc, aluminum, etc. Alternatively, a ceramic substrate coated with a mask made of a hydrophobic material is immersed in this metal alkoxide solution and pulled up, and after removing this mask from the ceramic substrate, the gel coating film remaining on the non-masked portion of this substrate is removed by air. 800 to 9 in
This is a method of heating to about 00 ° C. and firing. According to this method, when a ceramic substrate is dipped in a metal alkoxide solution and pulled up, a gel coating film composed of gel oxide and metal fine particles is formed on the substrate. Then, after removing the mask from the ceramic substrate, when the gel coating film remaining on the non-mask portion is baked, the gel oxide further shrinks to become a normal oxide, which softens or melts in this baking temperature range, and at the same time The metal fine particles are sintered. Therefore,
A conductive fine pattern having a pattern width and a pattern interval of about 10 to 30 μm can be firmly formed on a ceramic substrate.

[0006]

However, in the above method for forming a fine pattern, it is difficult to prepare metal fine particles of 5 μm or less, and the metal fine particles are uniformly dispersed in the metal alkoxide solution when dipping the substrate. However, it is difficult to keep them in place, and since metal fine particles are used, the manufacturing cost is high. The above method is 800-
Since it has a baking step at 900 ° C., it was not possible to use an organic plastic substrate having poor heat resistance as the non-conductive substrate. Furthermore, since it is a mechanism to obtain conductivity by contact with metal powder, a large amount of metal must be filled and the coating thickness of the paste must be sufficiently thick, so further refinement could not be accommodated. . Further, since the conductivity is obtained by the contact of the metal powder, contact resistance is generated and there is a limit to the high frequency.

An object of the present invention is to form a circuit pattern on a fine line and at a fine pitch,
Moreover, it is an object of the present invention to provide a method of forming a circuit pattern that can be firmly adhered to a substrate and a paste thereof. Another object of the present invention is to provide a method for forming a circuit pattern easily and inexpensively without using fine metal particles, and a paste thereof. Still another object of the present invention is to provide a method of forming a circuit pattern and a paste thereof which can be applied to many types of substrates.

[0008]

In order to achieve the above object, the method for forming a circuit pattern according to the present invention is performed in the atmosphere at 100%.
A step of forming a coating film by applying a paste obtained by uniformly dispersing a metal oxide that is reduced to a metal by heating at a temperature of ~ 1200 ° C, and the metal oxide contained in the coating film. It is a method including a step of reducing to a metal by heat treatment in the atmosphere at the above temperature, and a step of depositing electroless plating using the reduced metal as a nucleus. The circuit pattern forming paste of the present invention is a vehicle 90 containing at least an organic binder and an organic solvent in an amount of 10 to 80% by weight of a metal oxide which is reduced to a metal by heating at a temperature of 100 to 1200 ° C. in the atmosphere.
It is evenly dispersed to 20% by weight.

The present invention will be described in detail below. (a) Circuit Pattern Forming Paste The paste of the present invention is prepared by uniformly dispersing in a vehicle a metal oxide that is reduced to a metal by heating in air at a temperature of 100 to 1200 ° C. The metal oxide preferably has an average particle size of 5 μm or less. When the average particle size of the metal oxide is larger than 5 μm, it becomes difficult to cope with fine line and fine pitch. Generally, metal oxides are produced from an aqueous solution by a precipitation method, so primary particles are fine powders with a particle size of 5 μm or less, and even if they agglomerate, they are not spreadable and brittle, so they can be easily crushed to make fine lines and fine pitches. Is suitable. On the other hand, the metal powder used in the conventional method is generally produced from an aqueous solution by a reduction precipitation method, but it is difficult to control the particle size by controlling the reduction reaction, and primary particles easily grow and aggregation easily occurs.
Further, since it has spreadability, it is difficult to disintegrate, and it is very difficult to obtain fine powder of 5 μm or less.

The content of the metal oxide is 10 to 80% by weight based on 100% by weight of the paste. If the content is less than 10% by weight, it is difficult to obtain a continuous plating film, and if it exceeds 80% by weight, the fluidity of the paste is lost and it becomes difficult to adapt to fine lines. Here, the metal oxide is not particularly limited as long as it can be reduced to a metal by heating in the atmosphere, but the metal species of the metal oxide is preferably Au, Pd or Ag.

Although the composition of the vehicle varies depending on the heat treatment temperature, an organic binder such as ethyl cellulose is dissolved in an organic solvent such as terpineol and pentyl carbitol, and if necessary, a metal alkoxide such as silicon alkoxide, titanium alkoxide and aluminum alkoxide is added. Use the added one.

(B) Formation of coating film of predetermined pattern It is necessary that the non-conductive substrate for forming the circuit pattern of the present invention is not deteriorated or deformed by the subsequent heat treatment at 100 to 1200 ° C. The non-conductive substrate may be an organic plastic material, an inorganic ceramic material, or an inorganic / organic composite material. Examples of the organic plastic material include paper phenol, glass epoxy, polyimide, fluororesin, polysulfonide, and the like, and examples of the inorganic ceramic material include alumina, silicon carbide,
Examples of boron nitride, silicon nitride, crystallized glass,
Further, examples of the inorganic / organic composite material include quartz-epoxy. As a method of forming a coating film on the substrate in a predetermined pattern, a method of directly drawing a pattern on the substrate by a screen printing method and performing electroless plating after heat treatment (full additive method), a spin coater or dipping on the entire surface of the substrate Apply paste,
After heat treatment, a pattern is formed by etching and electroless plating is performed (semi-additive method), paste is applied to the entire surface of the substrate by spin coater or dipping, heat treatment is performed, then electroless plating is performed, and electroplating is further performed if necessary. , A method of forming a pattern by etching (subtract method) is used.

(C) Reduction of Metal Oxide in Coating Film The metal oxide contained in the coating film is 100
The metal oxide is reduced to a metal by heat treatment at a temperature of up to 1200 ° C. For example, oxidized Ag (II) (A
gO) is 100 ° C or higher, and oxidized Ag (I) (Ag ₂ O) is 1
60 ℃ or higher, 250 ℃ for Au (III) oxide (Au ₂ O ₃ )
As described above, the oxidized Pd (II) (PdO) is gradually decomposed at 700 ° C. or higher and reduced to Ag, Au or Pd which is a metal. Therefore, by using Ag (I) (II) oxide for reduction at a low temperature, it becomes possible to use a substrate made of an organic plastic material. When an inorganic ceramic material is used as the substrate, any metal oxide can be used.

(D) Adhesion of Coating Film to Substrate The adhesion mechanism between the coating film and the substrate differs depending on the composition of the paste and the substrate material used. For example, when the vehicle does not contain metal alkoxide and the substrate is an inorganic ceramic material, the organic binder is decomposed by heat treatment at high temperature and only the reduced metal remains on the substrate and the core of the electroless plating is Then, the reduced metal adheres the plating film to the substrate by the anchor effect. When the adhesion is insufficient, the vehicle is made to contain a metal alkoxide, and heat treatment is performed in the atmosphere to cause hydrolysis or polycondensation, and the reaction product is changed to a metal oxide to adhere the coating film to the substrate. When an organic plastic material is used as the substrate, heat treatment is performed at a low temperature, so that the organic binder serves as an adhesive to bond the coating film to the substrate. Furthermore, when a metal alkoxide is contained, the organic binder functions as a viscosity adjuster, and the adhesion is mainly performed by hydrolysis or polycondensation of the metal alkoxide.

(E) Electroless Plating on Coating Film The coating film thus formed is subjected to electroless plating to deposit a metal layer. Electroless plating is performed using reduced metals such as Au, Pd, and Ag as nuclei, but if the catalytic property that can start the electroless plating reaction is insufficient, initial drive is performed by Pd substitution or galvanic initiation if necessary. The electroless plating reaction is started by applying a force. For example, if the reduced metal is Ag, replace this metal with Pd. The electroless plating metal species include Au, Pd, Ag, Cu,
Although Ni and the like can be mentioned, Cu or Ni is particularly preferable in terms of precipitation rate, cost, and handling. The metal layer deposited by electroless plating is strongly adhered to the lower coating film and laminated.

[0016]

The metal powder used in the conventional method is generally produced from an aqueous solution by the reduction precipitation method, but it is difficult to control the particle size by controlling the reduction reaction, and primary particles easily grow and agglomerate easily. Further, since it has spreadability, it is difficult to disintegrate, and it is very difficult to obtain fine powder of 5 μm or less. On the other hand, since the metal oxide used in the method of the present invention is produced from an aqueous solution by a precipitation method, the primary particles are basically fine powder having a particle size of 5 μm or less, and even if they are aggregated, they are fragile because they are not spreadable and brittle. It is also easy to handle fine lines and fine pitches.

Further, since the metal oxide has a small specific gravity, it becomes a uniform paste, and even if a fine line is drawn by screen printing or the like, the sagging of the paste does not occur due to the precipitation of the solid content, and the fine line is formed and the fine pitch is obtained by the full additive method. Can be realized. Alternatively,
It is also applicable to the subtractive method and semi-additive method using etching. In either case, the metal oxide is reduced to a metal by performing a heat treatment at a temperature of 100 to 1200 ° C. in the atmosphere, and becomes a nucleus of the electroless plating in the next step. Furthermore, an electroconductive plating is performed to obtain an integrated conductive layer, which has excellent adhesion to the substrate.

[0018]

EXAMPLES Next, examples of the present invention will be described together with comparative examples. <Example 1> 15 g of ethyl cellulose was dissolved in 85 g of a 35% ethyl silicate ethanol solution, and 20 g of Ag ₂ O having an average particle size of 0.3 µm was uniformly dispersed in the solution to prepare a paste. This paste was applied to the surface of an Al ₂ O ₃ substrate by a screen printing method so that the pattern width was 50 μm and the space between patterns was 100 μm. After screen printing, the substrate was dried at 125 ° C. for 10 minutes and then heat-treated at 850 ° C. for 10 minutes to reduce Ag ₂ O to Ag. This is 200ppm Pd
After substituting Ag and Pd by immersing in a Cl ₂ aqueous solution, electroless Cu plating was performed to obtain a pattern having a film thickness of 5 μm.

<Example 2> 10 g of ethyl cellulose was dissolved in 90 g of terpineol, and this solution had an average particle size of 0.
80 g of 1 μm Ag ₂ O was uniformly dispersed using a bead mill to prepare a paste. This paste was applied to the surface of the Al ₂ O ₃ substrate with a spin coater. This board 15
Ag ₂ O was reduced to Ag by drying at 0 ° C. for 10 minutes and then heat-treating at 850 ° C. for 10 minutes. A resist is applied to the surface of the substrate by screen printing so that the pattern width is 50 μm and the distance between the patterns is 100 μm.
The Ag in the portion not coated with the resist was removed by etching. After removing the resist, 200ppm Pd
After substituting Ag and Pd by immersing in a Cl ₂ aqueous solution, electroless Cu plating was performed to obtain a pattern having a film thickness of 5 μm.

Example 3 10 g of ethyl cellulose was dissolved in 90 g of terpineol, and this solution had an average particle size of 0.
80 g of 1 μm Ag ₂ O was uniformly dispersed using a bead mill to prepare a paste. This paste was applied to the surface of the Al ₂ O ₃ substrate with a spin coater. This board 15
Ag ₂ O was reduced to Ag by drying at 0 ° C. for 10 minutes and then heat-treating at 850 ° C. for 10 minutes. 2 this board
After substituting Ag and Pd by immersing in a PdCl ₂ aqueous solution of 00 ppm, electroless Cu plating is performed, and then electric C
u plating was performed to form a Cu film having a film thickness of 5 μm on the entire surface of the substrate. A pattern was formed on this substrate with a positive resist so that the pattern width was 50 μm and the pattern interval was 100 μm, and Cu in the portion where the resist was not applied was removed by etching. 5μ film thickness after removing resist
A Cu pattern of m was obtained.

Example 4 20 g of a novolac phenolic resin was dissolved in 80 g of ethanol, and 20 g of AgO having an average particle size of 0.2 μm was uniformly dispersed in this solution using a triple roll to prepare a paste. This paste was applied to the surface of a glass epoxy substrate by screen printing so that the pattern width was 50 μm and the distance between patterns was 100 μm. After screen printing, the substrate was heat-treated at 150 ° C. for 2 hours to reduce AgO to Ag. This is 2
After substituting Ag with Pd by immersing in a PdCl ₂ aqueous solution of 00 ppm, electroless Cu plating was performed to obtain a pattern having a film thickness of 5 μm. Comparative Example 1 15 g of ethyl cellulose was dissolved in 85 g of a 35% ethyl silicate ethanol solution, and 20 g of Cu powder having an average particle size of 8 μm was uniformly dispersed in this solution using a bead mill to prepare a paste. This paste was applied to the surface of the Al ₂ O ₃ substrate by screen printing so that the pattern width was 50 μm and the space between patterns was 100 μm, but pattern breakage was observed.

<Comparative Example 2> The conductive paste prepared in Comparative Example 1 has a pattern width of 100 μm and a pattern interval of 100 μm.
The resulting pattern was applied to the surface of the Al ₂ O ₃ substrate by screen printing so that a pattern break was observed.

<Comparative Example 3> The conductive paste prepared in Comparative Example 1 has a pattern width of 200 μm and a pattern interval of 200 μm.
Was applied to the surface of the Al ₂ O ₃ substrate by screen printing. After screen printing, the substrate is dried in a reducing atmosphere at 125 ° C. for 10 minutes and then in a reducing atmosphere at 850.
Heat treatment was performed at 10 ° C. for 10 minutes. This is 200ppm Pd
After substituting Cu and Pd by immersing in a Cl ₂ aqueous solution, electroless Cu plating was performed to obtain a pattern having a film thickness of 5 μm.

The circuit patterns of Examples 1 to 4 and Comparative Examples 1 to 3 were measured for pattern breakage, presence or absence of pattern short circuit, pattern width, pattern spacing, and adhesion strength by peeling test. Table 1 shows the results.

[0025]

[Table 1]

In Examples 1 to 4, since the particle size of the metal oxide powder dispersed in the paste was small and the specific gravity was also small, there was no pattern breakage or pattern short circuit, whereas in Comparative Examples 1 to 3, Line width 100 due to large particle size
Pattern breaks occurred up to μm, and there were no pattern breaks at a line width of 200 μm, but since the filling amount of the metal powder was large and the specific gravity was large, spread of the pattern occurred due to sagging paste. Further, the adhesion strengths in all of the examples exceeded the practical strength of 2 kg / 2 mm □, but in Comparative Example 3, the practical strength of 1.3 kg / 2 mm □ was not reached.

[0027]

As described above, according to the present invention, after heat-treating a coating film formed by a paste in which fine powder of metal oxide which is reduced to a metal by heating in air is uniformly dispersed, By performing the electroless plating, it is possible to form a circuit pattern on a fine line and at a fine pitch without causing a paste break or a paste sag. Further, the coating film can be firmly adhered to the substrate by the anchor effect of electroless plating and the effect of the adhesive component such as metal alkoxide. In particular, since the metal fine particles are not used as compared with the conventional method of forming a fine pattern, the circuit pattern can be formed easily and inexpensively, and further, the heat treatment from a relatively low temperature in the atmosphere is possible, There is also an advantage that there are many types of applicable substrates.

Claims (5)

[Claims] 1. A step of forming a coating film by applying a paste obtained by uniformly dispersing a metal oxide that is reduced to a metal by heating at a temperature of 100 to 1200 ° C. in the atmosphere, A method of forming a circuit pattern, comprising: a step of reducing the metal oxide contained in to a metal by heat treatment in the atmosphere at the temperature; and a step of depositing electroless plating using the reduced metal as a nucleus. 2. The metal species of the metal oxide is Au, Pd or A.
The method for forming a circuit pattern according to claim 1, wherein the method is g. 3. The method for forming a circuit pattern according to claim 1, wherein the metal species of the electroless plating for depositing the reduced metal on the nucleus as a metal layer is either Cu or Ni. 4. A paste for forming a circuit pattern on a non-conductive substrate, wherein at least 10 to 80% by weight of a metal oxide reduced to a metal by heating at a temperature of 100 to 1200 ° C. in the atmosphere is used as an organic binder. A paste characterized by being uniformly dispersed in a vehicle containing 20 to 20% by weight of an organic solvent. 5. The paste according to claim 4, wherein the average particle size of the metal oxide is 5 μm or less.