JPH06310825A - Metal-base circuit board and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a metal-base circuit board possessing together a high dielectric strength and a low heat resistance and a method of manufacturing the metal-base circuit board by a method wherein the structure of an insulating layer is formed into a multilayer structure having a layer consisting of a low content of a filling material. CONSTITUTION:When an insulating layer 2, which consists of a filling material 3 and a resin 4, is formed on a metal substrate 1, the structure of the layer 2 is formed into a multilayer structure, which material and a layer consisting of a high filling rate of the filling material. By forming the layer consisting of the low filling rate of the filling material, bubbles, which cause a reduction in a dielectric strength, can be confined in the layer consisting of the high filling rate of the filling material. As a result, a metal-base circuit board having a high dielectric strength and a high heat conductivity (a low heat resistance) can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal base circuit board used for electronic parts used in electric equipment, communication devices, automobiles and the like.

[0002]

2. Description of the Related Art Since a metal base circuit board is used in the field of high power, the insulating layer of the board is required to have high withstand voltage and high thermal conductivity. In order to develop thermal conductivity, in a conventional metal base circuit board, a resin highly filled with an inorganic filler is applied and laminated on a metal board to form an insulating layer.

[0003]

However, in an insulating layer formed of a resin highly filled with such an inorganic filler, defects at the interface between the resin and the filler become higher as the filling rate of the filler becomes higher. In addition, the number of voids is increased and the number of voids is increased, so that the insulating property is lowered and the withstand voltage is lowered. Therefore, in order to improve the withstand voltage, it is necessary to reduce the filling rate of the filler, which is contrary to the case of improving the thermal conductivity, but the thermal conductivity naturally decreases. As described above, the conventional metal-based circuit board has a problem that it is difficult to combine high withstand voltage and high thermal conductivity (low thermal resistance).

An object of the present invention is to provide a metal base circuit board having high thermal conductivity and high withstand voltage.

[0005]

A feature of the present invention is that in a metal base circuit board having a circuit formed on an insulating layer laminated on a metal substrate, the insulating layer is formed of a mixture of a filler and a resin. A metal-based circuit board having two or more layers having different filler contents. In particular, among the layers having different filler content in the insulating layer, the layer having the lowest filler content has a value that can be represented by F / L shown in (a) below is 0.4 or less. Thickness is 0.1 μm
The effect is remarkable when the thickness is from 10 μm. (A) A straight line parallel to the metal substrate is drawn on the insulating layer, and the straight line cuts the filling material (F).
Is represented by (F / L).

The method of manufacturing the metal-based circuit board of the present invention is characterized in that an insulating material made of a mixture of a filler and a resin is laminated on the metal substrate, and the filler in the insulating material is allowed to settle and harden. Another feature of the present invention is that an insulating layer having two or more layers having different filler contents is formed, and a circuit made of a conductive metal foil is formed on the insulating layer. Is an insulating material made of a mixture of a filler and a resin, on which an insulating material made of a mixture of the filler and a resin is laminated on a metal substrate, and on which a content of the filler is different from that of the insulating material. Is sequentially laminated to form an insulating layer having two or more layers having different filler contents, and then a circuit made of a conductive metal foil is formed on the insulating layer.

The present invention will be described in detail below with reference to the drawings. In the metal base circuit board of the present invention, as shown in FIGS. 1, 2 and 3, the insulating layer 2 formed on the metal board 1 is made of a mixture of a filler and a resin. It has two or more layers 3, 4, and 5 having different contents.
The object of the present invention can be achieved even when there are more than three layers. The content of the filler is generally expressed as a volume content, but since it is difficult to measure, the content of the filler is represented by the proportion of the filler that can be determined by observing a photograph of a cross section shown in (a) below. This method of displaying the content rate is not the volume content itself, but can be regarded as a parameter of the volume content rate.

The boundary surface of each of these layers is a surface on which the change in the content of the filler is large, and the determination method is as follows.
For example, by observing the cross section of the insulating layer with a naked eye on a scanning micrograph, a method in which the surface with a large change in the filler content is used as the boundary surface, and the cross section of the insulating layer by the scanning micrograph is several μ
For example, there is a method of drawing a straight line parallel to the metal substrate at m intervals and determining a surface in which the ratio of the length of the cut line of the filler to the total length changes largely. In, it is preferable that the width of parallel straight lines at intervals of several μm is as small as possible.

Among the layers formed by the boundary layer determined by the above method, if the value represented by F / L of the layer having the lowest filler content exceeds 0.4, the interface between the resin and the filler is reached. In this case, the number of defects is increased and air bubbles are entrained, so that the withstand voltage is significantly reduced. Further, the thickness of the layer having the lowest content of the filler is preferably as thick as possible from the viewpoint of improving the withstand voltage, but in consideration of thermal conductivity, it is 0.1 μm or more.
10 μm is desirable. More preferably 0.5 μm
It is 5 μm. If it exceeds 10 μm, the thermal conductivity will decrease,
The characteristic of high thermal conductivity of the metal base circuit board cannot be fully exhibited. When the thickness is 0.1 μm or less, dielectric breakdown due to bubbles in the insulating layer cannot be prevented, which is not preferable.

The content of the filler is F.L.
As a method of forming a low layer of 4 or less, a method of precipitating the filler or a method of coating and laminating is possible. In the case of the method of allowing the filler to settle, the particle size, shape,
By properly selecting the filling rate, the viscosity of the resin, the temperature conditions, etc., the filler in the insulating layer can be settled, and two layers having different filler content can be formed in the insulating layer.

For example, when an epoxy resin is used as the resin for forming the insulating material, the epoxy resin containing the filler is added at a resin curing temperature of 150 to 200 ° C.
Since the viscosity of the epoxy resin is lowered and the filler is settled by rapidly raising the temperature at a temperature rising rate of ℃ / min or more, the content of the filler is as low as 0.4 or less. Layers can be formed.

In the case of a method of coating or laminating two or more layers of insulating materials having different filling rates of the filler on the metal substrate,
For example, first, an insulating material having a high filling rate of a filler is applied on a metal substrate, and a resin curing temperature of 150 to 200 ° C. is applied.
The temperature is slowly raised at a heating rate slower than ° C / min, and the temperature is kept at 150 to 200 ° C for about 2 to 5 minutes to be cured to form a first layer. Further, an insulating material having a filler content different from that of the first layer is applied onto the layer, laminated, and the second layer is cured under the same conditions as the first layer. When three or more layers are formed, this may be repeated further. When the temperature is raised at such a slow heating rate or maintained at a low temperature in this way, the settling of the filler does not occur because the viscosity of the epoxy resin is high.

The types of resin and filler which compose each layer in the insulating layer formed as described above may be the same or different. If the content of the filler is the lowest, only the resin not containing the filler may be used.

The type of filler is aluminum oxide,
Aluminum nitride, silicon nitride, silica, boron nitride, etc. are used. Moreover, these may be mixed and used. Further, the particle size of the filler is preferably as large as the average particle size in order to cause the filler to settle, but normally, the particle size is preferably about 0.1 to 20 μm. More preferably, it is 1 to 10 μm.

The type of resin is epoxy resin,
Phenolic resins and polyimide resins can be used, but low viscosity resins are preferably used. Further, the content of the filler in the entire insulating layer is related to the thickness of the layer having a low content of the filler and the like, but it is 30 to 80% by volume in terms of both thermal conductivity and insulation. preferable.

The metal substrate 1 used in the present invention is
A metal or metal alloy plate of aluminum, copper, stainless steel, iron or the like having a plate thickness of about 0.3 to 5.0 mm is used. The conductive metal foil 6 is made of copper, aluminum, nickel,
Any one of iron, tin, silver, and titanium, or an alloy containing two or more kinds of these metals and a clad foil using each metal are used. The method for producing the foil at this time may be either an electrolytic method or a rolling method.

[0017]

[Function] By forming the insulating layer into a multi-layer structure including a layer having a low content of the filler, it is possible to prevent a decrease in withstand voltage because the layer having a high content of the filler is often involved. This is because the dielectric breakdown caused by the bubbles can be prevented by the presence of the layer having a small filler content. Moreover, since the above structure can be formed without lowering the filling rate of the filler in the insulating layer, the insulating property can be improved without lowering the thermal conductivity.

[0018]

EXAMPLES Examples will be specifically described below. Example 1 An insulating layer having a thickness of 82 μm was formed on an aluminum substrate having a thickness of 1.5 mm by using an epoxy resin containing 50% by volume of aluminum oxide as a filler (average particle size; 5 μm, crushed powder). After forming, raising the temperature at a heating rate of 60 ° C./min to 150 ° C. and holding for 5 minutes in a B stage state, a 35 μm-thick copper foil was laminated and then at 150 ° C. for 5 hours. The insulating layer was cured to produce a metal base circuit board.

This substrate was cut and its cross section was taken by a scanning electron microscope (DS-130, manufactured by Akashi Beam Technology).
Then, as shown in the model diagram of the structure confirmed in the photograph taken under the conditions of the acceleration voltage of 20 kV and the magnification of 506 times, two layers were recognized in the insulating layer. Here, the content of the filler for each layer in the insulating layer was determined by the following method.

(Determination of Filler Content F / L) It was determined by statistically processing the abundance ratio of the filler in the photograph of each layer when photographed with a scanning electron microscope at a magnification of 10500 times. That is, when a straight line parallel to the substrate is drawn as shown in FIG. 4 and the total length F ₁ , f ₂ , ..., F _n of the filler is F, the filler content = F / L And Here, F is F = f ₁ + f ₂ + ... + f _n .

Specifically, the length of the filler occupying a line segment having a length of 10 cm was calculated, and the ratio to the total length was statistically calculated.

As a result of the measurement, a layer having a low content of the filler was recognized as the second layer, the thickness of the layer was 4 μm, and the content of the filler was 0.33 in F / L. It was or,
Dielectric breakdown voltage and thermal resistance were measured using this substrate.
The dielectric breakdown voltage was measured by the step-up method (AC voltage) specified in JIS C2110. The thermal resistance was measured by the following method. The results are shown in Table 1. The dielectric breakdown voltage was 5.0 kV and the thermal resistance was 0.68 ° C / W.

(Measurement Method of Thermal Resistance) A conductive metal foil of a metal base insulating substrate is etched to form a pad portion of 10 × 15 mm, and a transistor (TO220, manufactured by Toshiba Corporation) is soldered on the pad portion. The metal plate surface side was cooled, the transistor was energized, and the thermal resistance was measured from the temperature difference between the transistor side and the metal plate side with the insulating layer sandwiched between them and the amount of energization (Denka HITT plate catalog manufactured by Denki Kagaku Kogyo Co., Ltd.). Method described in.

Example 2 An epoxy resin containing 50% by volume of aluminum oxide as a filler (average particle size: 5 μm, crushed powder) was first formed on an aluminum substrate having a thickness of 1.5 mm to give a thickness of 54 μm. Thus, the insulating layer was formed, heated at a heating rate of 60 ° C./min, and held at 200 ° C. for 5 minutes to be cured. Next, an insulating layer was formed thereon using an epoxy resin having the same filler content so as to have a thickness of 30 μm, and the insulating layer was held at 80 ° C. for 5 minutes to be cured to a B stage state. After adhering 35 μm copper foil, the insulating layer was cured at 150 ° C. for 5 hours to produce a metal base circuit board.

This substrate was cut and observed under a scanning electron microscope under the same conditions as in Example 1. This photograph is shown in FIG. Further, as shown in the model view of the structure confirmed in this photograph, three layers were recognized in the insulating layer. As a result of measuring the content of the filler in each layer, a layer having a low content of the filler was observed in the second layer, the thickness of the layer was 6 μm, and the content of the filler had a value represented by F / L. It was 0.36. Moreover, the dielectric breakdown voltage and the thermal resistance were measured using this substrate. The results are shown in Table 1. The breakdown voltage was 5.5 kV and the thermal resistance was 0.73 ° C / W.

Example 3 An epoxy resin containing 50% by volume of aluminum oxide as a filler (average particle diameter: 5 μm, crushed powder) was first used on an aluminum substrate having a thickness of 1.5 mm, and a thickness of 32 μm was obtained. An insulating layer was formed so that the temperature was increased to 200 ° C. at a temperature increase rate of 40 ° C./min, and the temperature was held for 5 minutes to cure the insulating layer. Next, an insulating layer was formed thereon with an epoxy resin containing 35% by volume of aluminum oxide as a filler so as to have a thickness of 9 μm, and the temperature was 40 ° C.
The temperature was raised to 200 ° C. at a heating rate of 1 minute / minute and held for 5 minutes for curing. Further, an insulating layer is formed thereon by using the epoxy resin used first so as to have a thickness of 42 μm.
After holding at 0 ° C. for 5 minutes to cure it into a B-stage state, a 35 μm-thick copper foil was attached, and then 15
The insulating layer was cured at 0 ° C. for 5 hours to produce a metal base circuit board.

This substrate was cut and observed under a scanning electron microscope under the same conditions as in Example 1. As shown in the model diagram confirmed in this photograph as shown in FIG. 3, three layers were recognized in the insulating layer. As a result of measuring the content of the filler in each layer, a layer having a low content of the filler was recognized as the third layer, and the thickness of the layer was 9 μm.
The content of the filler is 0.33 which can be represented by F / L.
Met. Moreover, the dielectric breakdown voltage and the thermal resistance were measured using this substrate. The results are shown in Table 1. The breakdown voltage was 6.1 kV and the thermal resistance was 0.85 ° C / W.

Comparative Example 1 As Comparative Example 1, 1.5 mm
Epoxy resin containing 50% by volume of aluminum oxide filler is used on a thick aluminum plate and has a thickness of 80 μm.
m insulating layer is formed and held at 80 ° C for 5 minutes to cure B
A copper foil having a thickness of 35 μm was laminated on the stage-shaped one, and the insulating layer was cured at 150 ° C. for 5 hours to produce a metal base circuit board. After this substrate was cut and made into a mirror surface with a cross-section polishing machine, a cross-sectional photograph was taken with a scanning electron microscope as in Example 1. From the photograph, the distribution of the filler in the insulating layer was uniform, and the presence of layers having different filler contents was not recognized. Moreover, the dielectric breakdown voltage and the thermal resistance were measured by the same measurement method as in Example 1. The results are shown in Table 1. The breakdown voltage is 3.8 kV and the thermal resistance is 0.7.
It was 2 ° C / W.

Comparative Example 2 As Comparative Example 2, 1.5 mm
An insulating material having the same content as in Example 1 was applied on a thick aluminum plate to a thickness of 52 μm, and the temperature rising rate was 30 ° C./min.
It was cured under the conditions of 00 ° C. for 5 minutes. Subsequent operations were the same as in Example 2 to produce a metal base substrate. The cross-section observation, the dielectric breakdown voltage, and the thermal resistance were measured by the same measurement method as in Example 1. The thickness of the layer having a low filler content was 1 μm, and the content thereof was 0.43 in terms of F / L. Also, the dielectric breakdown voltage is 4.2 kV,
The thermal resistance was 0.72 ° C / W (see Table 1).

Comparative Example 3 As Comparative Example 3, 1.5 mm
45 aluminum oxide filler on thick aluminum plate
The epoxy resin containing 52% by volume was applied to a thickness of 52 μm and cured at a temperature rising rate of 70 ° C./minute, 200 ° C. for 5 minutes, and the subsequent operation was performed in the same manner as in Example 2 to prepare a metal base substrate. It was made. The cross-section observation, the dielectric breakdown voltage, and the thermal resistance were measured by the same measurement method as in Example 1. As a result, the layer with a low content of the filler has a thickness of 14 μm, the content has a value that can be represented by F / L of 0.25, the dielectric breakdown voltage is 6.2 kV, and the thermal resistance is 1.09 ° C./W. There was (Table 1
reference).

[0031]

[Table 1]

[0032]

As described above, according to the present invention, since the insulating layer of the metal base circuit board is composed of two or more layers having different filler contents, the thermal conductivity is high (the thermal resistance is high). It is possible to obtain an excellent metal-based circuit board having a high withstand voltage.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a metal base circuit board according to a first embodiment which is an example of the present invention.

FIG. 2 is a diagram showing a structure of a metal base circuit board according to a second embodiment which is an example of the present invention.

FIG. 3 is a diagram showing a structure of a metal base circuit board of Example 3 which is an example of the present invention.

FIG. 4 is a diagram for specifically determining the content F / L of the filler.

5 is a photograph of a scanning microscope at a magnification of 506 times of the portion A in FIG. 2 showing the structure of the metal base circuit board of Example 2 which is an example of the present invention.

[Explanation of symbols]

 1: Metal Substrate 2: Insulating Layer 3: Layer with Different Filling Ratio of Filler 4: Layer with Different Filling Ratio of Filler 5: Layer with Different Filling Ratio of Filler 6: Circuit Made of Conductive Metal Foil 7: Resin 8: Filler

Claims (4)

[Claims] 1. A metal base circuit board having a circuit formed on an insulating layer laminated on a metal substrate, wherein the insulating layer is formed of a mixture of a filler and a resin, and the insulating layer is A metal base circuit board having two or more layers having different filler contents. 2. Among the layers having different filler content in the insulating layer, the layer having the lowest content is F shown in (a) below.
The value represented by / L is 0.4 or less, and the thickness of the layer is 0.1 μm to 10 μm.
The metal-based circuit board described. (A) A straight line parallel to the metal substrate is drawn on the insulating layer, and the straight line cuts the filling material (F).
Is represented by (F / L). 3. An insulating material comprising a mixture of a filler and a resin is laminated on a metal substrate, and the filler is allowed to settle and harden to form an insulating layer having two or more layers having different filler contents. A method of manufacturing a metal base circuit board, further comprising forming a circuit made of a conductive metal foil on the insulating layer. 4. An insulating material composed of a mixture of a filler and a resin is laminated on a metal substrate, and further one or more mixtures of the filler and the resin having a different content of the filler from the insulating material. Characterized in that an insulating layer having two or more layers having different filler contents is sequentially formed, and then a circuit made of a conductive metal foil is formed on the insulating layer. Manufacturing method of metal base circuit board.