JPS63137497A - Manufacture of ceramic wiring circuit board - 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] [Technical Field] Unlike the conventional ceramic wiring circuit board in which a circuit is formed on a flat board, the present invention enables a circuit to be formed on an irregularly or three-dimensionally shaped board, and is used for cases such as cases of electronic devices. The present invention relates to the selection and manufacturing process of ceramic materials that are used to make electronic devices more compact and lightweight.

[Background technology]

In recent years, the demand for smaller and lighter electronic devices has become stricter year by year, and the miniaturization of electronic components is progressing day by day. Electronic circuit boards have also progressed from single-sided wiring to double-sided wiring to multilayer wiring, and flexible wiring boards are being used to pack more functions into the limited space of electronic devices.

Furthermore, as a method of integrating functions, a method has been adopted in which the case of the electronic device and the wiring are integrated, that is, a wiring circuit is provided on the surface of the case. In this case, the material used is a metal substrate with an aluminum base and an epoxy resin as an insulating layer. First, a circuit is formed on the flat metal substrate, and then a case is formed by pressing. As products, it is used in calculators, small radios, etc.

In other words, conventional irregularly shaped (non-planar) printed circuit boards are almost entirely made of plastic or a composite material of plastics and metal, and printed circuit boards made of ceramics are limited to planar ones. It was getting worse.

[Purpose of the invention]

This invention forms a circuit on a ceramic green sheet before firing, presses it into a non-planar shape, and then fires it to create a printed circuit board with an irregular shape that is useful for making electronic devices more compact and lightweight. The purpose is to provide a method for manufacturing.

[Disclosure of the invention]

In order to make a non-planar ceramic wiring circuit board, it is possible to first mold and fire the non-planar ceramic and then form the circuit by printing or other methods. There is the troublesome problem of printing.

Therefore, the present inventors solved this problem by forming a circuit before firing the ceramic and firing the ceramic and the four-body circuit simultaneously.

Hereinafter, this invention will be explained in detail following the process.

(1) Process of preparing ceramic green sheets Any ceramic can be used as long as it has electrically insulating properties, high mechanical strength, and strong moisture and water resistance after forming and firing. However, commonly used alumina porcelain, steatite porcelain, glass ceramic porcelain, etc. can be used.

For example, in the case of alumina-based ceramics, the raw materials include 92% to 99.5% alumina (preferably those with an average particle size of 0.5μ to 5μ) and flux.
Clays, clays, silicas, calcium carbonates, magnesium carbonates and/or mixtures thereof, such as
A mixture of 5 to 8%, pulverized and dried is used. In the case of glass ceramics, the main component is fine powder of insulating glass, and insulating inorganic powders such as alumina, steatite, silica, and forsterite are added to the powder, mixed, and ground. Use dried ones.

There are two main methods for producing green sheets from these ceramic powders: extrusion molding and doctor blade molding.

In the extrusion molding method, first, ceramic raw material powder is mixed with binder, plasticizer, dispersant, water (or solvent), etc.
The mixture is kneaded and extruded into a sheet from an extrusion mold using an extrusion molding machine. It is possible to extrude a thin sheet of 0.2W and a thick sheet of several dragons.

On the other hand, in the doctor blade molding method, ceramic raw material powder is mixed with a binder, a dispersant, a plasticizer, and a solvent, and the slurry is poured out through the gap between a knife called a doctor blade and a polyester film, and then coated. The slurry is then dried on the film and then peeled off to create a sheet. Advantageous for forming thin sheets, o.

A sheet of 5 dragons to 1 crane can be formed.

For the purpose of the present invention, any method may be used, but a combination of binder, plasticizer, and dispersant suitable for each method must be selected.As the binder used for sheet forming, cellulose-based (methyl cellulose, ethyl cellulose, etc.), PVA, acrylic, polyvinyl butyral, etc. are mainly used.

As the plasticizer, dibutyl phthalate, dioctyl phthalate, glycerin, etc. are used, and as the dispersant, a nonionic surfactant, etc. are used.

(2) A method of forming a conductor circuit on a green sheet.

Broadly speaking, two methods are effective for the purpose of the present invention.

First, the method of printing directly onto a green sheet is to first process the holes in the green sheet (if necessary), then print a conductive paste that matches the ceramics using screen printing, and then apply transfer paper. There is a way to set it. By screen printing or transfer printing in advance,
Conductive paste is a method in which a transfer paper obtained by printing conductive paste on a polymer film with good thermal decomposition is set or pasted on a green sheet before press molding. The choice must be made according to the binding characteristics.

For example, when the ceramic is 92% alumina, the sintering temperature exceeds 1300°C, so it is inconvenient to use low-melting point metal pastes such as gold or silver, and tungsten, molybdenum, manganese, and mixtures (or alloys) thereof are inconvenient. used.

On the other hand, if the ceramic is glass ceramic, it can be fired at approximately 1000°C or less, so gold,
Metal pastes such as silver and copper are used.

According to the direct printing method, the printed metal paste comes into direct contact with the surface of the mold during press molding, and stress is applied to the surface of the mold. Cannot be molded.

On the other hand, in the other method of setting the transfer paper, only the film-like transfer mount comes into contact with the surface of the molding die, so there is almost no possibility of major damage to the circuit.

Although the cost is high, this method is advantageous for ceramics that are highly deformed.

(3) Method of forming a circuit-formed green sheet into an unusual shape.
Press molding is preferable.

The molding conditions are determined depending on the material properties determined by the material composition of the green sheet.

For example, if an alumina-based ceramic material is extruded using a thermoplastic acrylic binder, it is best to heat the sheet in advance to make it flexible, and then press-form it in a cooled mold. used.

In addition, in the case of extrusion-molded sheets of the same alumina-based ceramic material using methylcellulose, which has the property of thermally gelling, as a binder, the sheet is kept at room temperature or below and then press-molded in a heated mold. method is used.

The key to molding is to release the formed thin sheet from the mold without losing its shape. Conditions for this must be established on a case-by-case basis.
- (4) Method of firing When firing a green sheet formed into a non-flat shape, the following points should be kept in mind: ■ Appropriate setting of binder removal conditions; ■ Appropriate setting of sintering temperature; ■ These are: controlling the firing atmosphere; ■ matching the jigs to hold the sheets; The following is a step-by-step explanation.

■ Conditions for removing the binder The binder required for forming must be removed by decomposition and sintering before sintering. If the binder removal is insufficient, the residual aroma of the binder (mainly carbon) will remain, which will have a negative effect on the insulation properties of the fired product.If the temperature applied to remove the binder is too rapid, the sheet may blister. , cranking or deformation may occur. Therefore, a method is generally adopted in which the temperature is raised as slowly (as slowly as possible) in a temperature range where the binder decomposes and sinters. For example, using a methylcellulose binder,
For molded sheets, the temperature is raised to 300°C to 500°C over 2 to 4 hours.

■ Sintering temperature The sintering temperature should be set according to the sintering characteristics determined by the type of ceramic material. For example, alumina ceramics require 1 to 3 hours at a temperature of 1500°C to 1600°C.

Glass ceramics require 30 minutes to 3 hours at a temperature of 800°C to 1000°C.

If sintering is insufficient, the density will not rise to the theoretical density, and therefore voids will remain, resulting in a product with low strength and poor moisture resistance.

If sintering becomes excessive, the sheet may become soft and deformed, the grains of the ceramic may grow excessively, causing a decrease in strength, and the metal used as a conductor may melt, diffuse, or volatilize.

(2) Atmosphere for firing If gold, silver, or palladium-based metals are used as conductors, firing may be performed in air, and there is no need to be very careful about the atmosphere. When copper, tungsten, molybdenum, or manganese is used as a conductor, when fired in an oxidizing atmosphere, the metal turns into an oxide and cannot function as a conductor. Therefore, when copper is used, at least a non-oxidizing atmosphere is required, and nitrogen is often used.

When using m-isomers such as tungsten, molybdenum, and manganese, a mixed gas of hydrogen gas and nitrogen gas is used.
In many cases, the atmosphere is reducing.

■ Firing jig If a shaped sheet with an irregular shape is placed on a flat setter and fired, it may deform under its own weight if exposed to the high temperatures during sintering. In such a case, it is necessary to change the way it is placed or to place a supporting jig so that it does not deform even under its own weight.

Although the present invention has been described above according to the process, it will be described in more detail below, focusing on examples.

Example 1・ ■Preparation of green sheet It was conducted using the following materials and formulations.

Put the above mixture into Polmir, dissolve and mix for 24 hours,
After pulverizing, the mixture was defoamed using a vacuum degassing machine to create a slurry. Approximately 1f of this slurry was processed using the doctor blade method.
It was formed into a green sheet with a thickness of i.

■ Conductor paste printing A circuit was printed on the prepared green sheet by screen printing using a conductor paste whose main ingredients were fine powders of tungsten and molybdenum.

■Press molding Preheat the above green sheet to approximately 70°C (put it in a dryer set at 70°C for 15 minutes), then put it into a mold kept below 20°C and form it into an irregular shape using direct pressure press molding. did. The shape of the obtained product is shown in FIG.

■ In a firing box-shaped electric furnace, air is passed from room temperature to 500℃, nitrogen is passed from 500℃, and then the temperature is increased to 1000℃.
A mixture of nitrogen and hydrogen gas is passed through, and the maximum temperature is 1550℃.
It was kept for 1 hour and fired. The temperature was increased for 3 hours in the binder removal region from 300°C to 500°C.

As a result of the above process, an irregularly shaped ceramic printed circuit board with a conductive circuit formed on the back surface of the case was obtained.

Example 2 ■ Creation of transfer film printed with conductor paste Polymethylmethacrylic resin sheet (thickness 10μ)
A circuit was printed using a screen printing method using a w-type paste mainly composed of fine powders of tungsten and molybdenum.

■ Simultaneous molding of transfer film and green sheet in close contact.

A transfer film was set on the green sheet prepared in Example 1, and after preheating to about 70°C, it was put into a mold kept at 20°C or lower, and molded into an irregular shape by direct pressure press molding. The shape of the obtained product is shown in FIG.

(2) Firing Firing was carried out under the same conditions as in Example 1 to obtain an irregularly shaped ceramic wiring circuit board.

Example 3 ■ Preparation of green sheet It was conducted using the following materials and formulations.

Glass powder 100 parts by weight Methyl cellulose 10 Wax emulsion
5 Diethylene glycol 3
〃Wed 23
The composition of the glass powder used in the above formulation was as follows.

S, 0. 57.1 parts by weight Aj! z
c) + 23.8 〃B2O34
, 8〃 CaO1,9 // MgO12,4〃 The above mixture was mixed and kneaded for about 30 minutes using a pressurized knee gun, and then applied to an extruder to form a green sheet with a thickness of 1.5H.

(2) Printing of conductive paste A conductive paste containing silver as a main component was printed on the green sheet prepared in (2) above by screen printing to form a circuit.

■Press molding The green sheet described above was introduced into a mold heated to 100° C. without preheating, and molded into an irregular shape by direct pressure press molding. The shape of the obtained product is shown in FIG.

(2) Firing The product was fired in a box-shaped electric furnace in an air atmosphere at a maximum temperature of 950°C for 1 hour.

To remove the binder, the temperature is 300℃ to 500℃ during the temperature increase process.
It took 3 hours to cover the area. Through the above process, a ceramic circuit board on which an irregularly shaped conductor circuit was formed was obtained.

Example 4 A ceramic circuit board was obtained in which an irregularly shaped conductor circuit was formed in the same manner as in Example 3 using gold paste as the conductor paste.

Example 5 ■ Creation of transfer film printed with conductive paste A circuit was printed on a polymethyl methacrylate resin (thickness: 10 μm) using gold paste by screen printing.

■ Simultaneous adhesion molding of transfer film and green sheet The transfer film was set on top of the green sheet prepared in Example 3, and introduced into a mold set at 100°C.
It was molded into an irregular shape by direct pressure press molding. The shape of the obtained product is shown in FIG.

■ Baking Firing was performed under the same conditions as in Example 3.

Through the above process, a ceramic circuit board on which a conductor circuit of an irregular shape was formed was obtained.

〔Effect of the invention〕

As shown above, it is now possible to create irregularly shaped ceramic circuit boards, which were previously difficult to create, through a simple process by applying co-firing technology with conductors. Ta. This part is used in electronic equipment.
For example, it can be used for the case itself, and has the effect of greatly contributing to the miniaturization and weight reduction of electronic devices, for example.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of a ceramic circuit board manufactured by the method of the present invention. 1 is ceramic, 2 is conductor

Claims (4)

[Claims] (1) A method for producing a non-flat ceramic wiring circuit board, which comprises forming an electric circuit on a ceramic green sheet, press-molding it into a non-flat shape, and then firing it. (2) A method for manufacturing a ceramic wiring circuit board according to claim (1), wherein a method of screen printing on a green sheet is selected as the circuit forming method. (3) As the circuit formation method, a method is selected in which a transfer paper on which a circuit is printed by screen printing is attached to a green sheet and transferred.
) The manufacturing method of the ceramic wiring circuit board described in item 2. (4) 1000℃ as a ceramic green sheet
A ceramic wiring circuit board according to claims (1) to (3), characterized in that a ceramic material is sintered in the following manner, and gold, silver, palladium, or copper is used as a circuit conductor. manufacturing method.