JP2001044577A - Circuit board - Google Patents

Abstract

(57) [Problem] To provide a circuit board excellent in both heat cycle resistance and partial discharge characteristics. A circuit board comprising a metal circuit formed on one surface of a aluminum nitride substrate and a metal radiator plate formed on the other surface, and satisfying the following conditions. (1) The thickness of the aluminum nitride substrate is 1 to 5 mm (2) The material of the metal circuit and the metal heat sink is aluminum or an aluminum alloy (3) The metal circuit and the metal heat sink are nitrided with the metal plate (4) The difference in creepage distance between the metal circuit and the metal radiator plate is 1 mm or less (including 0) in any part (5). ) On the side surfaces of the metal circuit and the metal heat sink, the apex angle has an acute angle of less than 90 degrees, and there is no convex portion having a height exceeding 30 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high withstand voltage circuit board used for a power module or the like of an electronic component.

[0002]

2. Description of the Related Art In recent years, a circuit board for a power module, in which a copper circuit is formed on one surface of an aluminum nitride substrate and a heat-dissipating copper plate is formed on the other surface, has attracted attention with the development of semiconductor elements. In addition, its use has been diversified from industrial inverters to motor control for electric trains, electric vehicles, and the like, and high voltage reliability is required.

[0003] Aluminum nitride substrates have high thermal conductivity and high insulation properties. Therefore, they have various advantages such as reliability against heat cycle resistance as insulating substrates for circuit boards for power modules, but are required today. However, the reliability of the partial discharge characteristics when the operating voltage was high as described above was unknown.

Conventionally, methods for evaluating insulation failure include an insulation resistance test and a withstand voltage test. In the insulation resistance test, since the applied voltage is about 0.5 to 1.0 kV, it is not possible to detect a defect or a void in the insulating substrate. In the withstand voltage test, a voltage as high as 10 kV or more can be applied, so that the presence or absence of dielectric breakdown can be detected, but a small discharge current cannot be detected, and partial discharge occurs for a long time. It is not possible to detect the insulation failure due to this.

[0005]

The partial discharge characteristics are such that if the amount of discharge charge is 10 pC or less at a voltage obtained by multiplying the voltage to be used by a safety factor, insulation failure will not occur even if partial discharge occurs for a long time. However, for example, in the case of a power module for controlling a drive motor of a train, the partial discharge starting voltage exceeding 10 pC is 6 kV or more, particularly preferably 9 kV.
That is all. However, in a circuit board in which a copper circuit is formed on one surface of an aluminum nitride substrate and a heat-dissipating copper plate is formed on the other surface, there is no prior art describing specific means for realizing the withstand voltage.

The present invention has been made in view of the above, and an object of the present invention is to maintain excellent heat cycle resistance,
In addition, it is an object of the present invention to provide a circuit board having a good partial discharge characteristic in which the partial discharge starting voltage is 6 kV or more when the discharge charge between the metal circuit and the metal radiator plate exceeds 10 pC.

[0007]

That is, the present invention provides an aluminum nitride substrate in which a metal circuit is formed on one surface and a metal radiator plate is formed on the other surface, and satisfies the following conditions. It is a circuit board characterized by the above-mentioned. (1) The thickness of the aluminum nitride substrate is 1 to 5 mm. (2) The material of the metal circuit and the metal heat sink is aluminum or an aluminum alloy. (3) The metal circuit and the metal heat sink are nitrided with the metal plate. (4) The difference in creepage distance between the metal circuit and the metal radiator plate is 1 mm or less (including 0) in any part. (5) ) On the side surfaces of the metal circuit and the metal heat sink, the apex angle has an acute angle of less than 90 degrees, and there is no convex portion having a height exceeding 30 μm.

The present invention also provides an aluminum nitride substrate having a metal circuit formed on one surface and a metal radiator plate on the other surface, wherein the metal circuit and the metal radiator plate are made of aluminum or aluminum. An alloy, wherein the metal circuit and the metal radiator plate are formed by etching a joined body of the metal plate and the aluminum nitride substrate, and the discharge charge between the metal circuit and the metal radiator plate is 10%.
A circuit board characterized in that a partial discharge starting voltage when exceeding pC is 6 kV or more.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

As described above, a circuit board in which a copper circuit is formed on one surface of an aluminum nitride substrate and a heat-dissipating copper plate is formed on the other surface is a circuit board for a power module. Has various advantages. The present invention is to optimize the circuit material, fine shape, and the like of a circuit board having such a skeletal structure, and further impart partial discharge characteristics as required today.

The first condition of the present invention is that the thickness of the aluminum nitride substrate is 1 to 5 mm. The reason why the thickness of the aluminum nitride substrate is required to be 1 mm or more is to reduce the influence of discharge charges due to minute voids or defects by increasing the capacitance of aluminum nitride as an insulating substrate. If the thickness of the aluminum nitride substrate exceeds 5 mm, the capacitance and the dielectric strength will be more than required than required, and the size and cost will increase.

As the aluminum nitride substrate, a mixed powder containing an aluminum nitride powder and a yttria powder (sintering aid) is extruded and fired, and an aluminum nitride sintered body obtained by firing is optionally subjected to honing or the like. Those manufactured by surface treatment are preferred. Among them, those having a thermal conductivity of 10
Those having 0 W / mK or more are preferable. Since there is a commercially available product of such an aluminum nitride substrate, it can be used. Hereinafter, an example of a manufacturing method thereof will be outlined.

100 parts by weight of aluminum nitride powder containing 0.5 to 5% by weight of yttria powder are added to stearic acid, aliphatic carboxylic acid of oleic acid, aliphatic carboxylic acid salts and esters thereof, higher alcohols, sulfonic acids, etc. One or more hydrophobizing agents selected from the group consisting of 0.5 to 5
About parts by weight are blended and mixed with a ball mill, a vibration mill, a Henschel mixer or the like. To achieve uniform mixing,
It is preferable to prepare a masterbatch in which the amount of the surfactant is about 1.5 to 3 times larger than the above amount, and mix the masterbatch and the aluminum nitride powder in the above ratio.

Next, 4 to 14 parts by weight of a water-soluble organic polymer compound such as polyvinyl alcohol, methylcellulose, alginic acid, polyethylene glycol, carboxymethylcellulose, ethylcellulose and the like are added to 100 parts by weight of the aluminum nitride powder subjected to the hydrophobic treatment. Phthalate esters such as dibutyl phthalate, dimethyl phthalate and diethyl phthalate, and plasticizers 1 to 8 such as glycerin
Parts by weight and 5 to 15 parts by weight of water are kneaded using a ball mill, a vibration mill, a high-speed mixer, a screw, or the like.

The kneaded material is vacuum degassed at about 50 to 200 Pa, extruded, and dried at a temperature at which the water-soluble organic polymer does not deteriorate, for example, at 100 ° C. or less, to form an aluminum nitride green sheet. As an extruder, a screw type extruder is generally employed.

Next, the aluminum nitride green sheet is heated and degreased in air at 500 to 600 ° C. for 1 to 10 hours, and then fired to produce an aluminum nitride sintered body. The firing conditions are a temperature of 1700 to 2000 ° C. for 0.5 to 5 hours in a non-oxidizing atmosphere such as nitrogen or argon.

The obtained aluminum nitride sintered body is cleaned, if necessary, with a honing device using an alumina abrasive to form an aluminum nitride substrate.

A second condition of the present invention is that the material of the metal circuit and the metal radiator plate is aluminum or an aluminum alloy. Aluminum or an aluminum alloy has a lower yield strength and is more likely to be plastically deformed than copper or a copper alloy, and therefore has excellent heat cycle resistance and the like. The purity of Al is set to facilitate plastic deformation.
Although it is preferably 99.5% or more, particularly 99.9% or more, an aluminum alloy such as A2017 can be used as long as the thickness is several tens μm or less. The thickness of the metal circuit and the metal heat sink is 0.2 to 0.6 mm, especially 0.3 to 0.6 mm.
It is preferably 0.5 mm. In particular, the thickness of the metal circuit is preferably equal to or less than that of the metal heat sink.

The third condition is that the metal circuit and the metal radiator are
That is, the metal part of the joined body in which the aluminum plate or the aluminum alloy plate is joined to the front and back surfaces of the aluminum nitride substrate is formed by etching. As a result, irregularities on the side surface (etched surface) can be drastically reduced, and charge concentration when a high voltage is applied can be eliminated.

The joined body is a metal plate and an aluminum nitride substrate
Between, Al-Si alloy foil, Al-Cu alloy foil,
Al-Cu-Mg alloy foil is interposed and carbon
In a vertical direction of the aluminum nitride substrate
From 15 to 60kgf / cm ^TwoWhile applying pressure
At 590-640 ° C for 3-60 minutes.
Can be manufactured. Use of such alloy foil
And by soldering defects (created on the joined metal plate
Worming phenomenon) is significantly reduced, and the partial discharge characteristics are more excellent.
It will be.

The formation of the metal circuit and the metal radiator plate is performed by printing an etching resist having a desired pattern on the upper surface of the metal plate on the front and back of the joined body, and using a ferric chloride solution having a hydrochloric acid concentration of 0.1 to 0.5%. After dissolving the plate, the etching resist can be dissolved, and if necessary, Ni plating can be performed.

The fourth condition is that when a metal circuit and a metal radiator plate are formed by etching the joined body, the difference in the creepage distance between the metal circuit and the metal radiator plate should be 1 mm or less (0 to 0 mm) in any part. Including). The creepage distance in the present invention refers to the distance between the end of the aluminum nitride substrate and the end of the outermost metal circuit or metal heat sink.

In the present invention, the formation position, size, shape, etc. of the metal circuit and the metal radiator plate are completely free, but the difference in the creepage distance is 1 mm or less (0 mm) in any part.
Is very important. When the difference in the creepage distance between the metal circuit and the metal radiator plate exceeds 1 mm, charges concentrate on the metal circuit portion, and the partial discharge starting voltage exceeding 10 pC decreases. The most preferred creepage difference is zero.

The difference in creepage distance can be measured using a commercially available optical microscope equipped with a scale capable of measuring the length.

The fifth condition of the present invention is a regulation on the smoothness of the side surfaces (etched surfaces) of the metal circuit and the metal radiator plate, and expresses the quality of the etched state. This requirement is as important as the fourth condition.

The present inventor has previously found that the partial discharge starting voltage largely depends on the smoothness of the side surfaces of the metal circuit and the metal radiator formed on the aluminum nitride substrate. Therefore, further investigations revealed that the higher the height of the projection, the sharper the apex angle, the lower the partial discharge inception voltage, and the discharge charge was 10 pC.
As a result of further pursuing the conditions for achieving a partial discharge inception voltage of 6 kV or more, a convex portion having an apex angle of less than 90 degrees and a height of more than 30 μm must never be present. That's what I found.

Usually, in addition to the convex portions, concave portions or concave and convex portions in which the concave portions and the convex portions are continuous are formed on the side surfaces (etched surfaces) of the metal circuit and the metal radiating plate. Must have a protruding height of 30 μm from the side
And a projection having an acute angle of less than 90 degrees.
Therefore, in the present invention, the presence of a projection having an acute angle of less than 90 degrees and a height of 30 μm or less is allowed. In the case of continuous irregularities, the sum of the depth of the concave portion and the height of the convex portion is defined as the height of the convex portion, which is 30 μm.
The following are allowed. In the case of the concave portion, the depth may exceed 30 μm, and there is no limitation on the bottom shape such as the rising angle of the side wall from the bottom. The shape of the recess does not cause a reduction in the partial discharge starting voltage.

In order to form a metal circuit and a metal radiator plate whose side surfaces satisfy the fifth condition by etching, it is necessary to manufacture a joined body having no brazing defects. When a joined body having a brazing defect is etched, an etchant enters the part, and a flat surface that is not good for increasing the partial discharge starting voltage is formed. The method for producing a joined body having no brazing defects has been described above.

In order to satisfy the fifth condition, etching conditions are important. Aluminum has a very high dissolution rate in a normal etching solution, so that it is difficult to control the etching rate. Therefore, in the present invention, a ferric chloride solution having a low hydrochloric acid concentration is used as an etching solution. In ordinary etching solutions, the concentration of hydrochloric acid in the ferric chloride solution is maintained at about 1% in order to prevent precipitation of iron hydroxide called sludge and to increase the etching rate. As a result, unevenness occurs which has an adverse effect on increasing the partial discharge starting voltage. In the present invention, the concentration of hydrochloric acid in the ferric chloride solution is 0.1 to 0.1.
It is preferably 5%, particularly preferably 0.2 to 0.3%.
If it is less than 0.1%, sludge is generated, and the etching nozzle is easily clogged, so that uniform etching cannot be performed.

Whether the side surfaces (etched surface) of the metal circuit and the metal radiator plate satisfy the fifth condition is determined by wrapping the metal circuit and the side surface (etched surface) of the metal radiator plate with an acrylic resin. After burying and polishing, 2
This can be done by taking a photograph at a magnification of 00 times and measuring the height and the apex angle of the convex portion.

The circuit board satisfying the above five conditions is:
The discharge charge between the metal circuit and the metal heat sink is 10p
The partial discharge starting voltage when exceeding C becomes 6 kV or more. If the conditions are more carefully selected, it can be increased to 9 kV or more.

In the present invention, the partial discharge starting voltage is measured according to JEC-0401, for example, by using a partial discharge meter “DAC-6018” manufactured by Soken Electric Co., Ltd., and attaching electrodes to the metal circuit surface and the metal heat radiation surface. By applying a voltage at a boosting rate of 1 kV / min, measuring the amount of discharge charge every 1 kV, and reading the voltage when it exceeds 10 pC,
It can be carried out.

[0033]

The present invention will be described more specifically below with reference to examples and comparative examples.

Example 1 96 parts by weight of aluminum nitride powder having an oxygen content of 1.2% by weight and an average particle diameter of 2.0 μm and 4 parts by weight of yttria powder were mixed in a ball mill for 30 minutes, and then 2 parts by weight of oleic acid was added. The mixture was further mixed for 30 minutes to subject the aluminum nitride powder to a hydrophobic treatment. After adding 8 parts by weight of methylcellulose to this powder and mixing for 1 minute with a high-speed mixer, further add a mixed solution of 6 parts by weight of glycerin and 14 parts by weight of water while continuing to stir, mix for 2 minutes and knead with a roll. Was manufactured.

The kneaded material is 130 P with a rotary pump.
After forming into a sheet with a die having a width of 120 mm using a screw-type extruder while performing vacuum deaeration to about a, drying at 80 ° C. for 20 minutes in a belt-type drying furnace, and nitriding with a thickness of 1.2 mm An aluminum green sheet was formed. This was punched out with a die to a size of 55 mm × 55 mm, and BN powder was applied to the surface of each sheet, and five sheets were placed in a degreasing furnace and placed in air at a temperature of 500 ° C.
Treated for time and degreased.

Then, it was placed in a nitrogen atmosphere at normal pressure and at a temperature of 1
After firing at 900 ° C. for 30 minutes, the temperature was 1700.
The temperature was cooled to room temperature at a cooling rate of 1.5 ° C./min to a temperature of 43 ° C. to produce a 43 mm × 43 mm × 1.0 mm aluminum nitride sintered body. The surface of the sintered body was removed by a honing treatment to remove 2 μm to obtain an aluminum nitride substrate. Its thermal conductivity is 180W / mK, room temperature 3-point bending strength is 40kg
f / mm ² .

On both sides of the aluminum nitride substrate, Al
0.4 thickness with Cu-based alloy foil (A2017) interposed
mm Al plate (A1085), set it on a carbon jig, and apply 60 kgf / c in the vertical direction of the laminate.
It was heated in a vacuum at 630 ° C. for 10 minutes while applying a pressure of m ² to produce a joined body.

An etching resist was applied to the joined body so that the difference between the creepage distances of the metal circuit and the metal radiator plate was 0.8 mm, and was etched with a ferric chloride solution having a hydrochloric acid concentration of 0.2%. Plating was performed to produce a circuit board.

Examples 2 to 4 Comparative Examples 1 to 4 Applied pressure in manufacturing a joined body, thickness of aluminum nitride substrate, concentration of hydrochloric acid in ferric chloride solution, and difference in creepage distance between metal circuit and metal radiator plate Was made in the same manner as in Example 1 except that the conditions shown in Table 1 were used.

Example 5 In Example 1, an Al-Cu alloy foil (A2017) was used.
Instead, using an Al-10% Si-2% Mg alloy powder, an Al plate having a thickness of 100 μm was formed at 600 ° C. × 10 minutes for 6 minutes.
After pressure bonding at a pressure of 0 kgf / cm ² , a clad plate of Cu and Ni is further laminated on both the front and back surfaces so that Al and Ni are in contact with each other, and 10 kgf / cm.
A pressure of mm ² was applied to perform pressure bonding to produce a bonded body. It was etched in the same manner as in Example 1 to produce a circuit board.

The partial discharge starting voltage of the obtained circuit board was measured according to the above method. After the measurement of the partial discharge, the smoothness of the side surfaces (etch etching surfaces) of the metal circuit and the metal radiator plate was measured according to the above method. Further, after a 13 mm Si chip was soldered to the center of the circuit board, a heat cycle test was performed. The heat cycle test was performed at −40 ° C. × 30 minutes → room temperature × 10 minutes → 125 ° C. × 30
Min → room temperature × 10 minutes as one cycle, and 3000 cycles were performed. After the heat cycle test, the appearance was checked for solder cracks, pattern peeling, and the like. Table 1 shows these results.
Shown in

[0042]

[Table 1]

[0043]

According to the present invention, a circuit board excellent in both heat cycle resistance and partial discharge characteristics is provided.

Continuation of the front page (72) Inventor Yoshihiko Tsujimura 1 Shinkaicho, Omuta-shi, Fukuoka F-term in the Omuta Plant of Electrochemical Industry Co., Ltd. (Reference) 4E351 AA09 BB01 BB24 BB30 DD10 DD21 DD54 GG04 GG06 5E338 AA01 AA18 BB71 CC01 EE02

Claims (2)

[Claims] 1. A circuit board comprising a metal circuit formed on one surface of a aluminum nitride substrate and a metal radiator plate formed on the other surface, wherein the following conditions are satisfied. (1) The thickness of the aluminum nitride substrate is 1 to 5 mm. (2) The material of the metal circuit and the metal heat sink is aluminum or an aluminum alloy. (3) The metal circuit and the metal heat sink are nitrided with the metal plate. (4) The difference in creepage distance between the metal circuit and the metal radiator plate is 1 mm or less (including 0) in any part. (5) ) On the side surfaces of the metal circuit and the metal heat sink, the apex angle has an acute angle of less than 90 degrees, and there is no convex portion having a height exceeding 30 μm. 2. A metal circuit formed on one surface of an aluminum nitride substrate and a metal radiator plate formed on the other surface, wherein the metal circuit and the metal radiator plate are made of aluminum or an aluminum alloy. The metal circuit and the metal radiator plate are formed by etching a joined body of the metal plate and the aluminum nitride substrate, and the portion where the discharge charge between the metal circuit and the metal radiator plate exceeds 10 pC A circuit board having a discharge starting voltage of 6 kV or more.