JP7341756B2 - Device mounting board - Google Patents

Description

The present invention relates to a device mounting substrate on which devices such as semiconductor devices (SiC devices, etc.) and LEDs are mounted.

Devices such as semiconductor devices (for example, SiC devices) and LEDs are usually mounted on metal substrates and used. By mounting the device on a metal substrate, heat generated from the device is dissipated by the substrate. That is, the metal substrate functions as a heat sink for the device (see Patent Document 1, etc.).

Here, when mounting a device on a metal substrate, it is necessary to electrically insulate between the substrate and the device.

Therefore, when mounting a device on a metal substrate, an insulating layer is provided on the device mounting surface of the substrate, and the device is mounted on this insulating layer.

In recent years, with the demand for higher power and higher withstand voltage in devices, it is necessary to increase the electrical insulation (withstand voltage) between the device and the substrate, and the thickness of the insulating layer between the device and the substrate has to be increased. It needed to be thicker.

Japanese Patent Application Publication No. 11-145376

However, if the thickness of the insulating layer between the device and the substrate is increased, the amount of heat generated in the device cannot be sufficiently transferred to the substrate, causing the problem that the temperature of the device rises and makes it unusable. there were.

The present invention was made in view of the problems of the conventional technology described above, and it is possible to improve electrical insulation (withstand voltage) without increasing the thickness of the insulating layer provided between the device and the device. The purpose is to provide device mounting boards.

[1] In order to achieve the above object, the device mounting substrate of the first aspect of the present invention includes a conductive substrate body made of metal, ceramics, or a composite thereof;
an insulating layer formed on the surface of the substrate body and having a mounting surface on which the device is mounted;
a plurality of conductive layers extending along the mounting surface inside the insulating layer;
Equipped with
The plurality of conductive layers are formed in an electrically floating state and are spaced apart from each other in the thickness direction of the insulating layer,
The plurality of divided insulating layers formed by dividing the insulating layer by the plurality of conductive layers have an equal thickness.
[2] In order to achieve the above object, the device mounting substrate according to the second aspect of the present invention includes:
a conductive substrate body made of metal, ceramics, or a composite thereof;
an insulating layer formed on the surface of the substrate body and having a mounting surface on which the device is mounted;
a plurality of conductive layers extending along the mounting surface inside the insulating layer;
Equipped with
The plurality of conductive layers are formed in an electrically floating state, are spaced apart from each other in the thickness direction of the insulating layer, and are formed so as not to be exposed from the insulating layer. .

According to the device mounting substrate of the present invention having the above characteristics, the insulating layer is divided into a plurality of layers by the conductive layer extending inside the insulating layer, so that one of the plurality of divided layers Even when voltage breakdown occurs, it is possible to maintain electrical insulation with the remaining layers, improving the reliability of electrical insulation. Moreover, compared to the case where the insulating layer is not divided, the average value of withstand voltage (average value of Weibull distribution) becomes higher, and the reliability of electrical insulation improves.
Here, "equal" means that when comparing the divided insulating layers, the thickness of one divided insulating layer is in the range of 90% to 110% of the thickness of the other divided insulating layer.

[ 3 ] Furthermore, in the device mounting substrate of the present invention,
Preferably, the conductive layer is formed so as to cover a region where the device is mounted when viewed from a direction perpendicular to the mounting surface.

According to the device mounting substrate of the present invention having the above features, the above effects can be more reliably achieved.

FIG. 1 is a vertical cross-sectional view schematically showing a state in which a device is mounted on a device mounting substrate according to an embodiment of the present invention. FIG. 2 is an enlarged vertical cross-sectional view of an insulating layer portion of the device mounting substrate shown in FIG. 1; FIG. 2 is an enlarged vertical cross-sectional view of an insulating layer portion of a device mounting substrate according to a modified example of the embodiment shown in FIG. 1; FIG. 2 is an enlarged vertical cross-sectional view of an insulating layer portion of a device mounting substrate according to another modification of the embodiment shown in FIG. 1;

DESCRIPTION OF THE PREFERRED EMBODIMENTS A device mounting board according to an embodiment of the present invention will be described below with reference to the drawings. Note that the aspect ratio of each member shown in the drawings has been changed from the actual value for convenience to facilitate understanding of the contents shown in the drawings.

FIG. 1 schematically shows a state in which a device is mounted on a device mounting substrate according to an embodiment of the present invention.

The device mounting board 1 according to this embodiment includes a board body 2. As shown in FIG. The substrate body 2 can have various shapes suitable for the shape of the device, such as a rectangular plate shape and a disk shape.

The substrate body 2 is made of a conductive material such as metal, ceramics, or a composite of these metals and/or ceramics. Here, examples of the metal forming the base body 2 include copper (Cu), aluminum (Al), and the like. Furthermore, examples of the electrically conductive ceramic forming the base body 2 include silicon carbide (SiC).

An insulating layer 3 is provided on the surface of the substrate body 2.

FIG. 2 shows an enlarged view of the insulating layer 3 of the device mounting substrate 1 shown in FIG. The surface of the insulating layer 3 on the side opposite to the substrate body 2 forms a device mounting surface 3a on which the device 4 is mounted. The insulating layer 3 includes a base 5 made of an insulating material and a conductive layer 6 made of a conductive material buried inside the base 5.

The insulating material constituting the base 5 of the insulating layer 3 may be an organic material or an inorganic material such as a ceramic material. Examples of inorganic materials include alumina (Al ₂ O ₃ ), aluminum nitride (AlN), yttrium oxide (Y ₂ O ₃ ), forsterite (2MgO・SiO ₂ )), other oxides, nitrides, and other oxides and nitrides thereof. Examples include composite materials.

The conductive material constituting the conductive layer 6 is preferably a metal, such as nickel (Ni), tungsten (W), molybdenum (Mo), platinum (Pt), or the like. The material for the conductive layer 6 is selected depending on the heat resistance of the film forming process for forming the conductive layer 6, for example. As a film forming method, various film forming methods such as chemical vapor deposition (CVD), thermal spraying such as plasma spraying, physical vapor deposition (PVD), etc. can be suitably used. It is also possible to use multiple film forming methods.

In the device mounting substrate 1 according to the present embodiment, a plurality of conductive layers 6 (three in this example) are provided, and the plurality of conductive layers 6 are spaced apart from each other in the thickness direction of the base 5 of the insulating layer 3. It is located.

Each of the plurality of conductive layers 6 is surrounded by an insulating material constituting the base 5, and is in an electrically floating state.

Further, each of the plurality of conductive layers 6 extends along the direction in which the device mounting surface 3a extends. Each conductive layer 6 is formed so as to include a region where the device 4 is mounted (device mounting region) when viewed from a direction perpendicular to the device mounting surface 3a.

The base 5 of the insulating layer 3 is partitioned by a plurality of conductive layers 6, so that at least a portion corresponding to the device mounting area has a plurality of regions (in this example, four 2) divided insulating layers 5a are formed.

The thicknesses of the plurality of divided insulating layers 5a are made equal. That is, the intervals between the plurality of conductive layers 6 are approximately the same, and the interval between the device mounting surface 3a of the insulating layer 3 and the conductive layer 6 closest to the device mounting surface 3a is the same as the interval between the plurality of conductive layers 6. The distance between the back surface 3b of the insulating layer 3 and the conductive layer 6 closest to the back surface 3b is substantially the same as the distance between the plurality of conductive layers 6.

Here, when the plurality of divided insulating layers 5a are "equal" in thickness, when comparing the divided insulating layers 5a, the thickness of one divided insulating layer 5a is 90% of the thickness of the other divided insulating layer 5a. It means something in the range of ~110%.

Further, in the device mounting substrate 1 according to the present embodiment, each of the plurality of conductive layers 6 is formed so as not to be exposed to the outside from the base 5 of the insulating layer 3. That is, each conductive layer 6 extending along the extending direction of the device mounting surface 3 inside the base 5 of the insulating layer 3 has an edge that does not reach the side circumferential surface 3c of the insulating layer 3, and is not insulating. It terminates inside the base body 5 of the layer 3.

In the device mounting substrate 1 according to the present embodiment having the above configuration, even if a high voltage is applied during use of the device 4 and breakdown occurs, the breakdown of the breakdown voltage is caused by the breakdown of the plurality of divided insulating layers 5a. It stays in my first tier. That is, voltage breakdown does not occur in the other divided insulating layers 5a, and sufficient electrical insulation can be maintained as a whole of the insulating layer 3 by these healthy divided insulating layers 5a.

As described above, according to the device mounting board 1 according to the present embodiment, reliability regarding prevention of withstand voltage breakdown that would make it impossible to use the device 4 can be improved compared to a device mounting board with a conventional structure, that is, a single-layer insulating layer. It can be made more expensive than a device mounting board with. In other words, in the device mounting substrate 1 according to the present embodiment, the thickness of the insulating layer can be made thinner than that of the conventional device when ensuring voltage breakdown performance equivalent to that of the device mounting substrate of the conventional structure.

In other words, in the case of a conventional device mounting substrate with a single insulating layer, if the thickness of the insulating layer is d and the potential difference in the thickness direction is V, then the electric field strength E of the insulating layer is E=V/d. becomes.

Then, the electric field strength value E (breakdown voltage value) when breakdown voltage breakdown occurs is arranged according to the Weibull distribution of the following equation.

F(E)=1-exp{-(E/E ₀ ) ^m (V _eff /V ₀ )}
F: Weibull distribution function m: Shape parameter E ₀ : Scale parameter V _eff : Effective volume V ₀ : Reference volume

At this time, the average value of the intensity values in the Weibull distribution is expressed as
E (average) = E ₀ (V _eff /V ₀ ) ^-1/m Γ (1+1/m)
It can be expressed as

As a result, the ratio between the average value E ₂ of the Weibull distribution in the case of the conventional device mounting substrate with a single insulating layer and the average value E 1 of the Weibull distribution of the device mounting substrate ₁ according to the present embodiment is , the effective volume of the insulating layer in the conventional structure is V _eff2 , and the effective volume of each divided insulating layer 5a of the insulating layer 3 in this embodiment is V _eff1 ,
E1/E2=(V _eff1 /V _eff2 ) ^-1/m
becomes. It should be noted here that there is no difference in the film quality of the insulating layer itself between the conventional structure and this embodiment, and the m value (shape parameter) remains the same.

V _eff1 /V _eff2 is calculated by assuming that a uniform electric field is formed in the thickness direction of the insulating layer, and when the insulating layer is divided into n layers,
V _eff1 /V _eff2 = (V/n)/V=1/n
becomes.

Therefore, since m>1 and n>1,
E1/E2=(1/n) ^-1/m >1
becomes.

That is, the average withstand voltage E ₁ of the insulating layer 3 divided into n layers as in this embodiment is higher than the average withstand voltage E ₂ of the single-layer insulating layer of the conventional structure.

As described above, according to the device mounting board 1 according to the present embodiment, even if voltage breakdown occurs in one of the plurality of divided insulating layers 5a, the entire insulating layer 3 is covered by the other healthy divided insulating layers 5a. It is possible to maintain the electrical insulation properties as described above, and the average value of withstand voltage can be increased compared to the conventional structure.

This increases the reliability (reliability of electrical insulation) in preventing voltage breakdown that would make devices unusable, compared to conventional device mounting substrates with a single insulating layer. Therefore, the breakdown voltage performance can be improved without increasing the thickness of the insulating layer.

As a modification of the above embodiment, as shown in FIG. 3, each end of the plurality of conductive layers 6 may be configured to be exposed at the side circumferential surface 3c of the insulating layer 3. Alternatively, the end portions of some of the plurality of conductive layers 6 may be exposed at the side circumferential surface 3c of the insulating layer 3.

As another modification of the above embodiment, as shown in FIG. 4, a conductive layer 6 may be provided inside the base 5 of the insulating layer 3. The conductive layer 6 is formed at the center of the insulating layer 3 in the thickness direction of the base 5 . Note that the number of conductive layers 6 formed inside the base 5 of the insulating layer 3 is arbitrary.

(Example)
[Example 1]
Insulating layer formation using thermal spray coating
(i) A square plate-shaped substrate body 2 made of copper (Cu) with dimensions of 50 mm (length of one piece) x 5 mm (thickness) is prepared.
(ii) Alumina (Al ₂ O ₃ ) is sprayed onto the surface of the substrate main body 2 to form an alumina sprayed film with a thickness of 30 μm.
(iii) Nickel (Ni) is sprayed onto the alumina sprayed film to form a nickel sprayed film with a thickness of 10 μm.
(iv) Alumina is sprayed onto the nickel sprayed film to form an alumina sprayed film with a thickness of 30 μm.
Repeat steps (iii) and (iv) until the alumina sprayed surface is finally formed.
Then, the total thickness of the alumina sprayed film is set to 150 μm.

[Comparative example 1]
Insulating layer formation using thermal spray coating
(i) A square plate-shaped copper (Cu) substrate body measuring 50 mm (length of one piece) x 5 mm (thickness) is prepared.
(ii) Alumina (Al ₂ O ₃ ) is sprayed onto the surface of the substrate body to form an alumina sprayed film with a thickness of 150 μm.

[Example 2]
Insulating layer formation using CVD film
(i) A square plate-shaped substrate body 2 made of copper (Cu) with dimensions of 50 mm (length of one piece) x 5 mm (thickness) is prepared.
(ii) A 30 μm thick yttrium oxide (Y ₂ O ₃ ) film is formed on the surface of the substrate body 2 by CVD.
(iii) A platinum (Pt) film with a thickness of 3 μm is formed on the yttrium oxide film by PVD.
(iv) A 30 μm thick yttrium oxide film is formed on the platinum film by CVD.
Repeat steps (iii) and (iv) until finally a yttrium oxide film is formed.
Then, the total thickness of the yttrium oxide film is set to 150 μm.

[Comparative example 2]
Insulating layer formation using CVD film
(i) A square plate-shaped copper (Cu) substrate body measuring 50 mm (length of one piece) x 5 mm (thickness) is prepared.
(ii) A 150 μm thick yttrium oxide (Y ₂ O ₃ ) film is formed on the surface of the substrate body by CVD.

For the above-mentioned Examples 1 and 2 and Comparative Examples 1 and 2, a withstand voltage test was conducted at 50 locations using a needle electrode, plotted on Weibull probability paper, and the average dielectric strength was calculated. The results are shown in Table 1.

As shown in Table 1, the average withstand voltage of Example 1 (divided insulating layer) is larger than the average withstand voltage of Comparative Example 1 (single insulating layer). Further, the average withstand voltage value of Example 2 (divided insulating layer) is larger than the average withstand voltage value of Comparative Example 2 (single insulating layer).

In this way, it was confirmed that by forming the base 5 of the insulating layer 3 into a divided structure by the conductive layer 6, the average value of withstand voltage could be increased compared to a single insulating layer.

1 Device mounting board 2 Board body 3 Insulating layer 3a Device mounting surface (surface of insulating layer)
3b Back surface of insulating layer 3c Side peripheral surface of insulating layer 4 Device 5 Base of insulating layer 5a Divided insulating layer of base 6 Conductive layer

Claims (3)

A device mounting board on which a device is mounted,
a conductive substrate body made of metal, ceramics, or a composite thereof;
an insulating layer formed on the surface of the substrate body and having a mounting surface on which the device is mounted;
a plurality of conductive layers extending along the mounting surface inside the insulating layer;
Equipped with
The plurality of conductive layers are formed in an electrically floating state and are spaced apart from each other in the thickness direction of the insulating layer,
The plurality of divided insulating layers formed by dividing the insulating layer by the plurality of conductive layers have an equal thickness.
Board for mounting devices. A device mounting board on which a device is mounted,
a conductive substrate body made of metal, ceramics, or a composite thereof;
an insulating layer formed on the surface of the substrate body and having a mounting surface on which the device is mounted;
a plurality of conductive layers extending along the mounting surface inside the insulating layer;
Equipped with
The plurality of conductive layers are formed in an electrically floating state, are spaced apart from each other in the thickness direction of the insulating layer, and are formed so as not to be exposed from the insulating layer.
Board for mounting devices. 3. The device mounting substrate according to claim 1 , wherein the conductive layer is formed to cover a region where the device is mounted when viewed from a direction perpendicular to the mounting surface.

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