TECHNICAL FIELD

The present invention relates to a bonded substrate, a metal circuit board and a circuit board.

BACKGROUND ART

A circuit board as follows is known. That is, a circuit pattern is formed on a metal plate of a bonded substrate including a substrate made of ceramics and the metal plate bonded to the substrate with a bonding member such as a brazing material. Then, an electronic component is mounted on a portion of the circuit pattern (see Patent Documents 1 and 2).

In a case where such a circuit board is manufactured, the electronic component is mounted on the circuit pattern formed on the metal plate, with solder, for example. Therefore, heat is generated when the electronic component is mounted on the metal plate on which the circuit pattern is formed. In a case where such a circuit board is assembled in, for example, a portion of a product (not illustrated), and is operated, heat is generated from the electronic component. For these reasons, the bonded substrate and the circuit board are required to satisfy the heat cycle characteristics which are equal to or higher than predetermined criteria.

A semiconductor element such as so-called a power IC is used as the electronic component of such a circuit board. In recent years, the power of power ICs has been increasing. The semiconductor element such as the power IC may generate heat at a high temperature (for example, 200° C.) during an operation of a circuit board. For the above reasons, the bonded substrate and the circuit board are required to satisfy the heat cycle characteristics higher than the predetermined criteria.

Here, Patent Document 1 discloses a semiconductor device including a ceramic-copper circuit board (a ceramic substrate and a copper plate on which a circuit pattern is formed), a brazing material which is disposed between the ceramic substrate and the copper plate and bonds the ceramic substrate and the copper plate to each other, and a semiconductor chip mounted on the circuit pattern. Specifically, Patent Document 1 discloses that the protrusion length of the brazing material from the edge of the copper plate is set to be equal to or more than 10 (μm) and equal to or less than 150 (μm), the peripheral surface of the copper plate is set to an inclined surface shape, and the thickness of the copper plate is set to be equal to or more than 0.2 (mm) and equal to or less than 1.0 (mm). Patent Document 1 discloses that, in this case, when the area of the right-angled isosceles triangle of a portion corresponding to the end portion of the cross section of the copper plate is defined as an area D, and the area of a portion excluding the right-angled isosceles triangle from the end portion is defined as an area C, C/D is set to be equal to or more than 0.2 and equal to or less than 0.6 (see FIG. 3 in Patent Document 1).

Patent Document 2 discloses a circuit board that includes a ceramic substrate, a metal circuit, and a bonding layer for bonding the metal circuit to the ceramic substrate, and is for mounting an electronic component on the metal circuit. Specifically, Patent Document 2 discloses that the protrusion length of the bonding layer from the edge of the metal circuit is set to equal to or less than 30 (μm), the peripheral surface of the metal circuit is set to an inclined surface, and the thickness of the metal circuit is set to be equal to or more than 0.3 (mm) and equal to or less than 0.5 (mm).

RELATED DOCUMENT

Patent Document

[Patent Document 1] Japanese Unexamined Patent Publication No. 2016-174165

[Patent Document 2] Japanese Patent Application Laid-Open No. 10-326949

SUMMARY OF THE INVENTION

Technical Problem

Regarding the bonded substrate, the metal circuit board, and the circuit board, the thickness of the metal plate is required to increase (for example, increase to a thickness which is equal to or more than 0.5 (mm)) in order to improve heat dissipation.

In the case of the ceramic-copper circuit board disclosed in Patent Document 1, when the thickness of the copper plate is increased in a state of satisfying the above conditions regarding the range of C/D, the width of a portion having an inclined surface shape in the end portion of the copper plate increases. With such an increase, the mounting region for electronic components on the copper plate is reduced.

Further, as described above, Patent Document 2 does not disclose a case where the thickness of the metal plate is increased (for example, a case where the thickness is equal to or more than 0.8 (mm)). Therefore, Patent Document 2 does not disclose the optimum design conditions for the circuit board in consideration of the heat cycle characteristics in a case where the thickness of the metal circuit is increased.

An object of the present invention is to provide a bonded substrate having excellent heat cycle characteristics while securing a mounting region for electronic components even in a case where a metal plate has a large thickness. Another object of the present invention is to provide a metal circuit board having excellent heat cycle characteristics while securing the mounting region for the electronic components even in a case where the metal plate has a large thickness. Still another object of the present invention is to provide a circuit board having excellent heat cycle characteristics while securing the mounting region for the electronic components even in a case where the metal plate has a large thickness.

Solution to Problem

According to a first aspect of the present invention, a bonded substrate includes a substrate, a metal plate that forms a stacked state along with the substrate, has a first surface on the substrate side and a second surface on an opposite side of the first surface, and has an edge of the first surface, which is located outside an edge of the second surface when viewed in a stacking direction, and a bonding member that is disposed between the substrate and the metal plate, so as to bond the metal plate to the substrate, and protrudes from the edge over an entire periphery of the metal plate when viewed from the stacking direction. In a case where, in at least one of a plurality of cut surfaces obtained by cutting the bonded substrate along the stacking direction, a length from a portion corresponding to a peripheral edge of the first surface to a portion corresponding to a peripheral edge of the second surface in an orthogonal direction orthogonal to the stacking direction is defined as a peripheral surface length A (mm), a length of a protruding portion of the bonding member in the orthogonal direction is defined as a protrusion length B (mm), and a distance from the first surface to the second surface is defined as a thickness C (mm) of the metal plate, the following first expression and the following second expression are satisfied.
0.032≤B/(A+B)≤0.400  (First Expression)
0.5(mm)≤C≤2.0(mm)  (Second Expression)

According to a second aspect of the present invention, in the bonded substrate in the first aspect, the metal plate is a polygon having four or more corners when viewed from the stacking direction, and the at least one cut surface is a cut surface obtained by cutting the bonded substrate along a diagonal line of the metal plate when viewed from the stacking direction.

According to a third aspect of the present invention, in the bonded substrate in the second aspect, in all cut surfaces obtained by cutting the bonded substrate along all diagonal lines along the stacking direction, the peripheral surface length A (mm) and the protrusion length B (mm) satisfy the first expression.

According to a fourth aspect of the present invention, in the bonded substrate in anyone of the first to third aspects, a peripheral surface of the metal plate, which connects an entire peripheral edge of the first surface and an entire peripheral edge of the second surface is a surface including an inclined surface.

According to a fifth aspect of the present invention, in the bonded substrate in the fourth aspect, in at least one of the plurality of cut surfaces obtained by cutting the bonded substrate along the stacking direction, an inclination angle θ (°) of a portion corresponding to the inclined surface with respect to the orthogonal direction satisfies the following third expression.
θ>45(°)  (Third Expression)

According to a sixth aspect of the present invention, in the bonded substrate in the fifth aspect, in all cut surfaces obtained by cutting the bonded substrate along all diagonal lines along the stacking direction, the inclination angle θ (°) of the portion corresponding to the inclined surface with respect to the orthogonal direction satisfies the third expression.

According to a seventh aspect of the present invention, in the bonded substrate in any one of the first to sixth aspects, the peripheral surface length A (mm) is any length in a range of being equal to or more than 0.15 (mm) and equal to or less than 0.30 (mm).

According to an eighth aspect of the present invention, in the bonded substrate in any of the first to seventh aspects, the protrusion length B (mm) is any in a range of being equal to or more than 10×10−6(mm) and equal to or less than 100×10−6(mm).

According to the first aspect of the present invention, there is provided a metal circuit board in which a circuit pattern is formed on the metal plate of the bonded substrate in any one of the first to eighth aspects.

According to the first aspect of the present invention, a circuit board includes the bonded substrate in any one of the first to eighth aspects, and an electronic component mounted on the metal plate on which a circuit pattern is formed.

According to the second aspect of the present invention, in the circuit board in the first aspect, an operation temperature of the electronic component is in a range of being equal to or higher than 100° C. or equal to or lower than 250° C.

Advantageous Effects of Invention

The bonded substrate in the present invention has excellent heat cycle characteristics while securing a mounting region for the electronic component even in a case where the metal plate has a large thickness.

The metal circuit board in the present invention has excellent heat cycle characteristics while securing the mounting region for the electronic component even in a case where the metal plate has a large thickness.

The circuit board in the present invention has excellent heat cycle characteristics while securing the mounting region for the electronic component even in a case where the metal plate has a large thickness.

