JPH0621610A - Manufacture of ceramic board having copper circuit - Google Patents

Abstract

PURPOSE:To obtain a ceramic board with a copper circuit suitable for mass production, which has improve heat shock resistance and heat cycle resistance. CONSTITUTION:A copper circuit is formed on one surface of a ceramic board. On the other surface, a copper plate is attached and it is etched, with the board used as a resist, so that creeping distance may become 0-0.5mm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a ceramic substrate having a copper circuit used for power modules of electronic parts.

[0002]

2. Description of the Related Art As a circuit board for power modules,
There are ceramic substrates with copper circuits. This is a method in which a copper circuit is provided on an alumina substrate or an aluminum nitride substrate. The manufacturing method of the copper circuit is roughly divided into a mounting method in which a copper foil previously processed into a pattern shape is bonded to a ceramic substrate. And an etching method of forming a circuit pattern by chemical etching after bonding a plate-shaped copper foil to a ceramic substrate.

The former method requires a great deal of labor and attention for positioning because the precision of joining position of the copper foil processed into the pattern is strictly required, and the mass productivity is poor.
On the other hand, the latter is a method that is mass-producible, but still involves some difficulty in positioning the etching resist during screen printing. In particular, the copper plate on the back side is usually a very simple solid pattern for soldering with a heat sink, but the distance from the ceramic edge (hereinafter referred to as the creepage distance) directly affects the circuit board characteristics. Positioning must be done very carefully because it will affect.
The smaller the creepage distance, that is, the closer the ceramic substrate edge and the copper pattern edge are, the more improved the circuit board characteristics such as heat shock resistance and heat cycle resistance.

However, if the copper pattern edge on the back surface protrudes from the edge of the ceramic substrate, the insulation characteristics deteriorate. Therefore, in screen printing, there is a problem that the yield is extremely reduced unless a maximum of about 0.5 mm is inevitable. It was

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above problems in forming a copper pattern on the back surface by screen printing and improves the heat shock resistance and heat cycle resistance of a circuit board. The object is to manufacture a ceramic substrate having a copper circuit with high productivity.

[0006]

That is, the present invention provides a circuit board having a copper plate having a creepage distance of 0 to 0.5 mm on the back surface of a ceramic substrate and a copper circuit on the front surface. Is formed by an etching method, the ceramic substrate itself is used as an etching resist for forming the back surface copper plate, which is a method for producing a ceramic substrate having a copper circuit.

The present invention will be described in more detail below.

The creepage distance in the present invention means the distance between the end portion of the ceramic substrate and the end portion of the back surface copper plate, and a heat sink is usually soldered to the back surface copper plate. This back surface copper plate is generally a so-called solid copper plate having no pattern, but it may have a suitable pattern.

Creepage distance depends on heat shock resistance and heat resistance.
It has a close relationship with heat resistance history such as cycle resistance, and these characteristics improve as the creepage distance decreases. However, when the back surface copper plate is in a state of protruding from the ceramic substrate, the insulating property between the front surface and the back surface is significantly inferior.

The back surface copper plate can also be formed by the mounting method, but the mounting method is difficult to secure the positional accuracy of the pattern and is inferior in mass productivity as compared with the etching method. Therefore, the etching method is adopted in the present invention. . However, even with the etching method, if the copper pattern on the back surface is made small, it becomes considerably difficult to secure the positional accuracy, so in the present invention, in order to eliminate it, the ceramic substrate itself is used as an etching resist. A major feature is that the back copper plate is used for patterning.

The ceramic substrate and the back surface copper plate or the copper plate for forming the copper circuit on the front surface may be bonded by any method such as pressure welding, glass bonding, DBC method, active metal brazing method, etc. And from the viewpoint of joint strength, DBC
The method and the active metal brazing method are preferred.

The DBC method is a method in which an aluminum nitride substrate and a copper plate are heated to a temperature below the melting point of copper and above the eutectic temperature of Cu--O to bond them (for example, JP-A-56-163093). Further, the active metal brazing method is a method in which a brazing material containing an active metal is interposed between a ceramic substrate and a copper plate to perform heat bonding (for example, JP-A-60-177634).
Issue).

In the active metal brazing method, as the kind of the active metal contained in the brazing material, those conventionally known are used, but preferably Ti, TiH ₂ , Zr and / or
It is also ZrH ₂ . Typical examples of metals other than active metals are Ag and Ag.
-Cu alloy. The brazing material may be used in the form of an alloy foil, but with the brazing material metal, for example, methyl cellosolve, ethyl cellosolve, terpineol, isophorone,
Organic solvent such as toluene, ethyl cellulose, methyl cellulose, polymethylmethacrylate as necessary,
It is preferable to use a paste prepared by mixing an organic binder such as polyisobutyl methacrylate. As an example of the composition of the brazing paste, a metal 10 other than the active metal
3 to 40 parts by weight of active metal and 1 part of organic solvent to 0 parts by weight
0 to 30 parts by weight and 0 to 5 parts by weight of organic binder.

The ceramic substrate used in the present invention usually contains alumina or aluminum nitride as a main component. Aluminum nitride is particularly suitable for the present invention because it has high thermal conductivity.

There are no particular restrictions on the type and shape of the copper plate used in the present invention. For the type, see DBC
In the method, a tough pitch copper plate is preferable, and in the active metal brazing method, an oxygen-free copper plate having an oxygen content of 30 ppm or less is preferable.

As for the shape of the copper plate, in the case of the back surface copper plate, a size that is slightly larger than the width of the ceramic substrate after joining is selected. Therefore, it is preferable to use a copper plate having the same size as the ceramic substrate in consideration of the ease of setting before joining. As a result, after joining, the copper plate is slightly off the ceramic substrate due to the difference in thermal expansion coefficient between the two. On the other hand, also in the case of the copper plate for forming the copper circuit on the front surface, there is no need to make a distinction from that on the back surface, and the same size as the ceramic substrate is preferably used.

A resist for etching to form a circuit pattern is applied to the ceramic substrate obtained as described above and a bonded body in which copper plates are bonded to both surfaces of the ceramic substrate. It is general to use screen printing or the like for the surface circuit, but there is no problem even if it is performed by other methods. The resist used is not particularly limited as long as it can withstand the etching process.

On the other hand, the resist coating on the back copper plate is performed on the entire surface. As the coating method, screen printing, roll coating
Although a coater, a sprayer, a brush coater, etc. are adopted, the roll coater method is most suitable in consideration of production on an industrial scale.

In the bonded body coated with the resist as described above, unnecessary portions are removed by etching and the circuit pattern is formed.
However, the copper circuit on the surface is formed by the same etching method as the conventional one. On the other hand, in the case of the back surface, the resist is not applied to one surface of the copper plate protruding from the ceramic substrate, so that part is dissolved by the etching solution, and the size is slightly smaller than that of the ceramic substrate. Creepage distance is 0
A circuit board of 0.5 mm is manufactured.

[0020]

EXAMPLES Examples of the present invention will be described below.

Example 1 A brazing paste (Ag-Cu-TiH ₂ + organic vehicle) was applied at 8 mg / both on both sides of an alumina substrate of 60 × 30 × 0.635 mm.
It was applied using a roll coater so that the applied amount was cm ² . Both sides are sandwiched by 0.3 mm and 0.2 mm copper plates, a weight of 200 g is placed, and under a vacuum of 1 × 10 ^-5 torr,
A joined body was manufactured by holding at 850 ° C. for 20 minutes.

After sufficiently aligning the 0.3 mm copper plate of the obtained joined body, the circuit pattern on the surface was screen-printed. On the other hand, 62 for a 0.25 mm copper plate
A resist was applied to the entire copper plate using a × 32 mm screen plate. Since the screen size is sufficiently larger than that of the copper plate, no labor was required for positioning.

Next, the bonded body coated with this resist was put into an etching machine using a ferric chloride solution as an etcher and etched for about 20 minutes. The creeping distance of the copper pattern on the back surface of the obtained circuit board was 0.1 mm, and there was almost no variation. Further, no protrusion from the alumina substrate was observed at all.

Example 2 A circuit board was manufactured in the same manner as in Example 1 except that an aluminum nitride substrate was used instead of the alumina substrate. The creepage distance of the copper pattern on the back surface was 0.1 mm, and there was almost no variation. There was no. Further, no protrusion from the aluminum nitride substrate was observed at all.

[0025]

According to the present invention, the creepage distance of the copper plate on the back surface is 0 to 0.5 very easily without lowering the yield.
A circuit board having a size of mm, that is, a circuit board having excellent heat shock resistance and heat cycle resistance can be manufactured with good mass productivity. Moreover, in the case of double-sided etching, a double-sided shower etching machine is required, but in the present invention, a single-sided shower machine enables patterning of both sides.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshihiko Tsujimura 1 Shinkai-cho, Omuta-shi, Fukuoka Electric Machinery Co., Ltd. Omuta Plant

Claims (1)

[Claims] 1. A creepage distance of 0 is provided on the back surface of the ceramic substrate.
In forming a circuit board having a copper plate of 0.5 mm or less and a copper circuit on the surface by an etching method, the ceramic substrate itself is used as an etching resist for forming the back copper plate. A method for manufacturing a ceramic substrate having a copper circuit.