JPH0423340Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to an enameled printed circuit board that has good heat dissipation and excellent insulation performance. As shown in Figure 1, a conventional enamel printed circuit board is made by coating the surface of a metal core 1 with enamel enamel, covering the entire surface with an enamel enamel layer 2, which is a heat-resistant electrical insulating layer, and adding a thick layer to the surface. A structure in which an electric circuit 3 such as a membrane circuit is formed is known.

One of the characteristics of this enamel board is that it has good heat dissipation properties, but air bubbles and pinholes may occur in the enamel, and these air bubbles can cause areas where the wall thickness is particularly thin. This can cause the enamel enamel layer to have a low withstand voltage compared to its thickness, and when printing and firing circuit conductors, iron can migrate from the core steel sheet through pinholes, impairing its properties. Yes, and must be coated with a thick layer of enamel to ensure electrical insulation. For example, in the case of 1000V withstand voltage, the thickness of enamel is 100μm ~
200 μm, but when the enamel layer becomes thick like this, the heat dissipation effect decreases because the enamel has low thermal conductivity, making it difficult to dissipate the heat generated in the electrical circuit, which is an inherent characteristic of the enamel board. It has the disadvantage of losing

In order to reduce the above-mentioned drawbacks, for example, as shown in FIG.
The pressure resistance can be increased by a relatively thin layer of enamel enamel that does not compensate for pinholes. However, in this method, the thickness of the enamel layer other than the portions where the dielectric strength needs to be increased increases, resulting in a decrease in heat dissipation.

The present invention was developed in view of the above-mentioned situation, and as shown in FIG. This is an enamel printed circuit board in which a crystalline enamel enamel layer 2C-2 and an electric circuit 3 are sequentially provided on the enamel enamel, and the crystalline enamel enamel is crystallized.

Now, in the present invention, the crystalline enamel enamel is, for example, an enamel containing crystallized glass as shown below, but the present invention is not limited to this composition.

(a) about 6 to 25 mole percent barium oxide; (b) about 30 _to 60 mole percent MO; (c) about 13 to 35 mole percent _B2O3 ; and (d) about 10 to 25 mole percent. The MO has an oxide composition consisting of SiO ₂ and is selected from the group consisting of magnesium oxide, magnesium oxide, zinc oxide, and calcium oxide.

Specific examples include MgO58.0 mol%, BaO7.0
A composition having 21.0 mol% of B ₂ O _{3 and} 14.0 mol% of SiO ₂ melts at about 700°C, crystallizes at 850°C for about 10 minutes, and has a remelting temperature of 950°C or higher.

For this reason, bonding can be performed in the same process as the normal thick film process, making the enamel coating more efficient.
Has heat resistance of 850℃ or higher.

Referring to a specific example of implementing the present invention,
The surface of the metal core 1 is coated with the above crystallizable enamel to a thickness of 20 μm to 100 μm to form an enamel layer 2C-1, and a portion 2C-2 where an electric circuit 3 such as a thick film circuit is formed. 800~900℃ as above
Glass frit which melts and crystallizes at 800 to 900
Amorphous glass frit, which melts at ℃ and solidifies at about 700 ℃, is screen-printed as a paste, and after drying or drying and firing, a circuit conductor is layered, screen-printed, and fired to form the electrical circuit 3. You can get an enameled printed circuit board.

In another embodiment of the present invention, an organic compound that forms a film of silicon oxide (SiO ₂ ) or aluminum oxide (Al ₂ O ₃ ) when fired, for example, can be used instead of the glass paste. In this case, since the formed film is thin, it is not necessary to limit the coating to just below the portion where the electric circuit is to be formed.

Since the present invention has the above structure, it has the following effects.

(1) Since crystallized enamel is used as the enamel, it is inherently heat resistant.Even if the enamel enamel layer contains air bubbles, the heat resistance has improved due to crystallization, so the substrate can be refired. However, the bubbles will not increase or grow.

(2) The lower side of the circuit conductor 3 is a crystalline enamel enamel layer 2C-1 and a crystalline enamel enamel layer 2C-
Since it has a two-layer structure with 2, even if bubbles or pinholes exist in both layers, there is little possibility that the same weak point will occur in the same part, so there is a complementary relationship, and the electrical insulation can be improved.

(3) Parts that do not require electrical insulation are covered only with the crystalline enamel enamel layer 2C-1 and are thin, so heat is easily dissipated through the metal core 1.
Moreover, due to the coating of 20μm to 100μm, even if the metal core 1 is exposed to high temperature and high humidity atmosphere,
Further, it is not oxidized even in a high temperature atmosphere during the formation of a thick film circuit.

(4) Since the enamel printed circuit board of the present invention can be manufactured in the same manner as printing and firing of ordinary thick film circuits, it is relatively easy to carry out in terms of equipment and work.

The enamel enamel layer 2C-1, which is the first layer preferred in the present invention, melts and crystallizes at 800 to 900° C., and preferably has a thickness of 20 μm to 100 μm.
That is, if it is less than 20 μm, it is too thin and the metal core is likely to be oxidized through bubbles or pinholes, whereas if it is thicker than 100 μm, there is no effect in reducing the amount of material and the heat dissipation property tends to decrease, which is not preferable.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a conventional enamel printed circuit board, FIG. 2 is a sectional view showing another example of the same, and FIG. 3 is a sectional view showing an example of the enamel printed circuit board of the present invention. 1...Metal core, 2C-1...Crystalline enamel enamel layer, 2C-2...Crystalline enamel enamel layer. or a second insulating layer such as an amorphous enameled enamel layer or an insulating oxide layer.

Claims (1)

[Scope of utility model registration request] A crystalline enamel enamel layer covering the surface of the metal core is provided, and a crystalline or non-crystalline enamel layer or an electrically insulating oxide film layer and an electrical circuit are sequentially provided on the electrical circuit formation portion. Enamel printed circuit board.