JPH036679B2 - - Google Patents

Description

[Detailed Description of the Invention] Technical field to which the invention pertains The present invention relates to a substrate material for forming electronic circuits such as integrated circuits and resistance circuits, particularly a substrate material having a glass insulating layer attached to a part or the entire surface of an iron alloy substrate. Regarding circuit boards.

Conventional technology Ceramic materials such as alumina have traditionally been most commonly used as heat-resistant insulating substrates for integrated circuits, but ceramics have low mechanical strength and
It has disadvantages such as poor processability and inability to make large substrates, which limits its applications.

Therefore, recently, iron substrates, which have excellent strength, workability, and can be made large, have been attracting attention. When using this iron as a circuit board, it is basically necessary to electrically insulate the iron and the circuit. To insulate, a glass insulating layer is usually formed over the entire surface of the iron substrate, or only in areas that require insulation, but the adhesive strength is weak even if glass is applied directly, so nickel or cobalt, like iron enamel, is used. Pre-plated or
After forming a specific oxide such as cobalt oxide, glazing is applied, or as disclosed in Japanese Patent Publication No. 56-36597, the substrate is first heat treated to form a metal oxide film, and then glass is applied on top of it. form a layer. Further, Japanese Patent Application Nos. 61-40722 and 40723 have adhesive structures in which only a portion of the glass and oxide layer react.

Problems to be Solved by the Invention However, the glass insulating film formed by these methods still does not have sufficient adhesive strength with the iron substrate, and the glass film may crack once the substrate is bent or a strong impact is applied. If the glass layer enters the substrate, separation between the substrate and the glass layer is likely to occur. Also, when forming a thick film circuit on a substrate,
It is common for glass layers to be fired several times in an oxidizing or non-oxidizing atmosphere, or more than 10 times for multilayer circuits, but when glass layers are formed using conventional methods, the strength deteriorates as the number of firings increases. It is easy to cause and peel off.

An object of the present invention is to provide a glass-coated iron circuit board that has excellent adhesion between a glass insulating layer and an iron base, does not deteriorate even after repeated firing, and can withstand severe temperature shock. .

Means for Solving the Problems The present invention involves heat treating an iron alloy substrate containing aluminum at a temperature of 500°C or higher in a nitrogen atmosphere, and then forming a glass insulating layer on a part or the entire surface of the substrate. This is a characteristic method of manufacturing a circuit board.

The second invention is to heat-treat an aluminum-containing iron alloy substrate at a temperature of 500°C or higher in a nitrogen atmosphere, then heat-treat it in an oxidizing atmosphere, and then apply a glass insulating layer on a part or the entire surface of the substrate. This is a method of manufacturing a circuit board, characterized in that:

Effect: Prior to forming a glass insulating layer on an iron substrate containing aluminum, the substrate is heat-treated in nitrogen, resulting in an iron circuit board with extremely strong adhesion between the glass layer and the iron substrate compared to conventional methods. can get. This insulating layer can withstand repeated firing in oxidizing or non-oxidizing atmospheres during thick film circuit formation.
Furthermore, the strength will not deteriorate even if subjected to severe temperature shock or mechanical shock.

It is not clear why heat treatment in nitrogen improves adhesive strength, but thin-film X-ray diffraction has shown that when an iron alloy containing aluminum is heated to high temperatures in nitrogen, aluminum nitride is formed on the substrate surface. It is thought that this contributes in some way to the adhesion between the glass insulating layer and the iron substrate. The heat treatment temperature depends on the type of base alloy, but it should be about 500℃ or higher, and practically 800℃ or higher.
A temperature of about 1000°C is preferable. The heat treatment time varies depending on the temperature, and the higher the temperature, the shorter the time required. For example, in the case of 900°C, it is appropriate to hold the temperature for about 5 to 30 minutes. In addition, if heat treatment is performed in nitrogen and then heat treatment is performed again in an oxidizing atmosphere such as air, the strength tends to further improve, and no deterioration in strength is observed even if the heat treatment is repeated. The heat treatment in an oxidizing atmosphere is preferably performed at a temperature of about 500°C or higher.

The glass insulating layer is formed after the iron substrate is subjected to the above heat treatment, and any known method may be used to form the glass insulating layer. Typically, a paste or slurry in which glass powder is dispersed in a liquid vehicle is applied to the surface of an iron substrate by screen printing, dipping, spraying, etc., dried, and then heated to a temperature above the melting point of glass according to conventional methods. Perform firing. Alternatively, a glass green sheet or glass plate may be placed directly on the iron substrate and fired. The composition of the glass has almost no effect on the effects of the present invention and is not particularly limited. Amorphous glass, crystalline glass, mixtures thereof, mixtures of glass and ceramic fillers, etc. can all be used.

Examples of the substrate containing aluminum include general heat-resistant steel.

Examples Example 1 15% chromium, 4% aluminum and 0.2 titanium
A plate-shaped iron alloy substrate (50 mm x 50 mm, thickness 0.6 mm) containing 1% was heat-treated at 900°C for 10 minutes in a nitrogen atmosphere with an oxygen concentration of 10 ppm or less.

A glass paste containing glass particles of the following composition was screen printed on the entire surface of one side of this substrate, and
After drying at ℃ for 10 minutes, peak temperature 850℃ for 10 minutes,
Firing was performed in a 40-minute cycle to produce an iron circuit board with a glass insulating layer. The thickness of the insulating layer after firing is 40 μm.

[Glass composition] (wt%) SiO ₂ 40 Al ₂ O ₃ 20 B ₂ O ₃ 10 CaO 15 ZnO 10 TiO ₂ 5 The following tests were conducted on the obtained substrate to examine the adhesive strength between the glass and the iron substrate. I went there.

Peeling test (initial strength): The substrate was bent at the center and the glass layer was forcibly peeled off. The peeled part was gray in color, and when the surface was observed using an electron microscope, it was found that a glass layer was attached. That is, the glass layer cracks and is destroyed by the tensile force caused by bending, but the glass layer remains at the interface because the adhesive strength between the iron base and the glass layer is greater than the breaking strength of the glass.

Repeated firing test: The iron circuit board with the glass insulating layer manufactured by the above method was repeatedly fired 10 times in air at a peak temperature of 850°C for 10 minutes and one cycle of 40 minutes, and then the peel test described above was performed. I did, but the results were the same.

Thermal shock test: A steel circuit board with the same glass insulation layer was placed in cold water from a red-hot state of 800℃.
Thereafter, the above peel test was performed, but the results were the same.

Example 2 An iron circuit board having a glass insulating layer was manufactured in the same manner as in Example 1 except that the composition of the glass was as follows.

[Glass composition] (wt%) SiO ₂ 52 Al ₂ O ₃ 8 B ₂ O ₃ 10 PbO 30 When the adhesive strength of the obtained substrate was examined in the same manner as in Example 1, it was found that there was a glass layer on the peeled surface. The adhesive strength between the iron substrate and the glass layer was extremely strong.

Example 3 The same iron substrate as in Example 1 was heat treated at 900°C for 10 minutes in a nitrogen atmosphere and then heated at 850°C in air.
Heat treated for 10 minutes. The same glass paste as in Example 1 was screen printed on the entire surface of one side of the substrate,
After drying at 150°C for 10 minutes, baking was performed at a peak temperature of 850°C for 10 minutes in a 40-minute cycle to produce an iron circuit board with a glass insulating layer.

A peel test was conducted on the obtained substrate in the same manner, and the results showed that the glass layer was attached to the peeled surface, and the adhesive strength between the iron base and the glass layer was extremely strong.

Example 4 A circuit board was manufactured in the same manner as in Example 1, except that the heat treatment conditions in nitrogen were 600° C. for 4 hours.

As a result of a peel test, the glass layer was found to be attached to the peeled surface, and the adhesive strength between the iron substrate and the glass layer was extremely strong.

Example 5 An iron circuit board having a glass insulating layer was manufactured in the same manner as in Example 1 except that an iron alloy containing 12% chromium and 3.5% aluminum was used as the base.

As a result of a peel test, the adhesive strength between the iron substrate and the glass layer was extremely strong.

Comparative Example 1 The same iron alloy substrate as in Example 1 was heat treated at 900° C. for 10 minutes in air to form an oxide film. A glass paste having the same composition as in Example 1 was screen printed on the entire surface of one side of this substrate, and then heated at 150°C.
After drying for 10 minutes, peak temperature 850℃ for 10 minutes, 40
Firing was performed in a minute cycle to produce an iron circuit board having a glass insulating layer.

When the obtained substrate was subjected to a peel test in the same manner as in Example 1, the glass was completely peeled off and the peeled surface had a metallic luster. Observation using an electron microscope revealed that no glass remained. This indicates that the adhesive strength between the iron substrate and the glass layer is extremely weak. Further, when a thermal shock test was conducted in the same manner as in Example 1, the glass layer peeled off after being immersed in cold water.

Comparative Example 2 The same iron substrate as in Example 1 was heat-treated at 400° C. for 5 hours in a nitrogen atmosphere, and then glass paste was printed and fired on the entire surface of one side in the same manner as in Example 1 to produce a circuit board.

The results of the peel test were the same as in Comparative Example 1.

Comparative Example 3 A circuit board was manufactured using aluminum-free stainless steel SUS304 as a substrate and performing the same treatment as in Example 1.

The results of the peel test were the same as in Comparative Example 1.

Effects of the Invention As is clear from the examples, the glass-coated iron substrate manufactured by the method of the present invention has extremely strong adhesive strength between the glass coating layer and the iron alloy substrate compared to the conventional method. Furthermore, since the strength does not deteriorate even after repeated firing, it is particularly excellent as a thick film integrated circuit board that is subjected to multiple firings. It also withstands severe mechanical shock and temperature shock, making it suitable for applications with severe usage conditions.

Claims (1)

[Scope of Claims] 1. A circuit board characterized in that an iron alloy substrate containing aluminum is heat treated at a temperature of 500°C or higher in a nitrogen atmosphere, and then a glass insulating layer is formed on a part or the entire surface of the substrate. manufacturing method. 2 The iron alloy substrate containing aluminum is heat-treated at a temperature of 500°C or higher in a nitrogen atmosphere, then heat-treated in an oxidizing atmosphere, and then a glass insulating layer is formed on a part or the entire surface of the substrate. A method of manufacturing a circuit board.