JP2002185092A - Aluminum nitride circuit board and high power modular board comprising the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of an aluminum nitride circuit board that the average particle size of aluminum nitride crystal particles increasing up to about 10 μm in order to enhance heat dissipation but, when the particle size of aluminum nitride crystal particles is increased, the particle size of aluminum nitride crystal particles is varied or pores are generated to cause partial discharge. SOLUTION: The aluminum nitride circuit board comprises an aluminum nitride substrate and a metal circuit layer, wherein (thermal conductivity of the aluminum nitride substrate/thickness of the aluminum nitride substrate) is 300 kW/m2.K or above, extinction voltage (10 pC) of partial discharge is 6.0 kV or above, and 95% or more of aluminum nitride particles in the aluminum nitride substrate has a particle size in the range of 3-7 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum nitride circuit board, and more particularly to an aluminum nitride circuit board capable of suppressing a partial discharge when a large amount of electric power is applied, and a high-power module board using the same.

[0002]

2. Description of the Related Art Ceramic materials are superior to metal materials in various properties such as strength, heat resistance, corrosion resistance, abrasion resistance, and light weight. It is widely used as a machine part, a functional part, and a horizontal construction material used under severe temperature, stress, and abrasion conditions which are inferior to metal materials, such as materials for high-speed cutting tools, nozzles, and bearings.

[0003] Among them, beryllium oxide (BeO) has been conventionally used as a substrate material used for a semiconductor substrate or the like. Beryllium oxide has a thermal conductivity of 272 W / m · K
(300 K), which is very high, so that it was suitable for a substrate material that generates heat due to high integration.

[0004] However, beryllium oxide is very toxic when inhaled, so there is a danger in production, and there is a problem in terms of disposal even after commercialization. In recent years, such beryllium oxide has been replaced by a ceramic material that is non-toxic, has excellent handling, and can be safely disposed of. Among these ceramic materials, aluminum nitride (AlN) is an insulator having high thermal conductivity, and is used instead of beryllium oxide.

[0005] Such aluminum nitride is, for example, I
It is used for power modules (high power modules) such as C packages, IGBTs, and GTOs. In the field of semiconductors, the amount of heat generated by silicon chips is increasing steadily due to the fact that LSIs are being integrated and operated at higher speeds, and applications of power devices such as GTOs and IGBTs are expanding.

As the power module is adopted in fields requiring long-term reliability, such as large industrial equipment and vehicles, a circuit board on which a silicon chip is mounted or a module on which a circuit board is mounted Has become a more serious problem.

In order to improve heat dissipation, it is effective to reduce the thermal resistance of the aluminum nitride substrate by reducing the thickness of the substrate. However, when the aluminum nitride substrate is made thin, partial discharge may occur.

[0008] The partial discharge is a corona discharge, which indicates a local dielectric breakdown phenomenon, and is controlled more strictly than the dielectric strength in general withstand voltage. This partial discharge is carried out by JEC-0401 in Japan and IEC (International Electrotechnical Commit
tee) -1287.

[0009]

Although there are various methods for improving the partial discharge characteristics, it is easy and effective to increase the thickness of the aluminum nitride substrate. However, as described above, when the thickness of the aluminum nitride substrate is increased, the thermal resistance of the substrate is increased and the heat dissipation is reduced.

In order to achieve both partial discharge characteristics and heat dissipation, it is necessary to improve the thermal conductivity of aluminum nitride itself. The aluminum nitride substrate has excellent thermal conductivity in the first place, and is 160 W / m · K or more, and in recent years, 190 W / m.
-Commercialized to about K.

However, the conventional thermal conductivity of 190 W /
An aluminum nitride substrate of about m · K has an average crystal grain size of 10 to improve the thermal conductivity.
It was increased to about μm.

If the particle size of the aluminum nitride crystal particles is increased, the thermal conductivity is certainly increased, but on the other hand, the size of the aluminum nitride crystal particles varies, and pores may be generated in the aluminum nitride substrate. Was.
Such pores cause partial discharge, and it is necessary to minimize the pores.

[0013] Even if there are no pores in the aluminum nitride substrate, if the aluminum nitride crystal grains become large, the triple point existing between the crystal grains becomes unnecessarily large. The triple point is substantially composed of a liquid phase component mainly containing a sintering aid, impurities, and the like. Since the aluminum nitride crystal particles themselves are insulators, partial discharge is caused by this liquid phase component (grain boundary phase). It is also affected by the state.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides an aluminum nitride circuit board capable of suppressing occurrence of partial discharge without lowering thermal conductivity. It is intended to be. Another object of the present invention is to provide a high-power module substrate that is manufactured using the aluminum nitride circuit board and can operate stably even when used at high power.

[0015]

An aluminum nitride circuit board according to the present invention is a circuit board comprising an aluminum nitride board and a metal circuit layer, wherein [thermal conductivity of the aluminum nitride board / plate thickness of the aluminum nitride board] ] Is 3
00 kW / m ² · K or more and the partial discharge extinction voltage (1
0pC) is 6.0 kV or more.

The aluminum nitride circuit board of the present invention comprises:
[Thermal conductivity of the aluminum nitride substrate / the thickness of the aluminum nitride substrate] is 300 kW / m ² · K or more, which is excellent in heat dissipation, and has a partial discharge extinction voltage (10 p
C) is as high as 6.0 kV or more and partial discharge hardly occurs, so that it is particularly effective for use at high power.

In the aluminum nitride substrate, 95% or more of the total aluminum nitride particles are preferably made of aluminum nitride particles having a particle size of 3 to 7 μm. By increasing the number of particles having such a particle size, the volume of pores and triple junctions can be reduced, and the thermal conductivity can be improved and partial discharge can be suppressed.

The aluminum nitride substrate preferably has a thickness of 0.5 to 1 mm. Set the thickness to 0.
By setting the thickness to 5 to 1 mm, it is possible to secure necessary strength and to improve heat dissipation (thermal conductivity of the aluminum nitride substrate / plate thickness of the aluminum nitride substrate).

Further, the aluminum nitride substrate preferably has a thermal conductivity of 190 W / m · K or more.
By setting the thermal conductivity of the aluminum nitride substrate to 190 W / m · K or more, it becomes easy to secure the heat radiation required for the aluminum nitride circuit board.

The metal circuit layer is formed, for example, by forming a metal plate on DBC.
It is bonded to the aluminum nitride substrate by a direct bonding method or an active metal bonding method. In the present invention, the metal circuit layer can be formed by a known method, for example, using a thick film method. However, from the viewpoint of the bonding strength between the metal circuit layer and the aluminum nitride substrate, easiness, etc.
It is preferably a metal plate joined by the method C or the active metal joining method. In particular, by using a metal plate having a plate thickness of 0.1 mm or more, a current carrying capacity can be ensured, so that it is suitable for a high-power module to be described later. As the metal plate, a copper plate or an aluminum plate having high conductivity is preferable.

The aluminum nitride circuit board of the present invention can be used, for example, as a module board for high power. As described above, the aluminum nitride circuit board of the present invention is excellent in heat dissipation and suppression of partial discharge, generates a large amount of heat, and is used in a high-power module board used at a high voltage. Can be secured.

[0022]

Embodiments of the present invention will be described below. FIG. 1 shows an aluminum nitride circuit board of the present invention. The aluminum nitride circuit board 1 of the present invention has a metal circuit layer 2 and an aluminum nitride substrate 3 as shown in FIG.

The aluminum nitride substrate 3 is [thermal conductivity of aluminum nitride substrate / plate thickness of aluminum nitride substrate].
Is 300 kW / m ² · K or more, and the extinction voltage (10 pC) of the partial discharge is 6.0 kV or more.

[Thermal conductivity of aluminum nitride substrate / plate thickness of aluminum nitride substrate] represents heat dissipation, and the unit [kW / m ² · K] is as follows: It is obtained as follows. [kW / m ² · K] = [W / m · K] · [10 ^-3 m]

In the present invention, by setting the heat dissipation ([thermal conductivity of the aluminum nitride substrate / plate thickness of the aluminum nitride substrate]) to 300 kW / m ² · K or more,
In addition to ensuring heat dissipation, the partial discharge extinction voltage (10
By setting pC) to 6.0 kV or more, use at a higher voltage becomes possible.

The heat dissipation and the partial discharge extinction voltage are defined as described above for the following reasons.
If the heat radiation is less than 300 kW / m ² · K, the generated heat cannot be efficiently dissipated when used at high power, so that heat accumulates on the aluminum nitride circuit board and causes equipment malfunction. Operation may be caused. Further, when the annihilation voltage (10 pC) is less than 6.0 kV,
Even at a low voltage, partial discharge occurs, which may also cause malfunction of the device. Considering use at high power, it is necessary to satisfy both improvement of heat dissipation and suppression of partial discharge at the same time. Therefore, in the present invention, the heat dissipation and the extinction voltage of the partial discharge are defined as described above. In the present invention, more preferably, the extinction voltage (10
pC) is 7.0 kV or more.

The thermal conductivity of the aluminum nitride substrate is measured, for example, by a laser flash method. The extinction voltage is measured by a method according to JEC 0401.

In the above-described aluminum nitride substrate, 95% or more of the total aluminum nitride particles have a particle size of 3 to
It is preferable to use 7 μm aluminum nitride particles. This is because, when the particle size exceeds 7 μm, the triple point becomes unnecessarily large and the number of pores tends to increase, which causes partial discharge. Also,
This is because an increase in the number of particles having a particle size of less than 3 μm causes a decrease in thermal conductivity. The ratio of the aluminum nitride crystal particles having a particle size of 3 to 7 μm or less is selected, for example, from any three locations of the aluminum nitride substrate, and the respective aluminum nitride crystal particles contained in each unit area (100 μm × 100 μm) of the three locations Is measured, and the maximum particle size of all aluminum nitride crystal particles is 3 to 7
It can be obtained by calculating the ratio of those having a size of μm or less.

The thickness of the aluminum nitride substrate is preferably 0.5 to 1 mm. Set the thickness to 0.
By setting the thickness to 5 to 1 mm, it is possible to secure necessary strength and suppress partial discharge and also ensure heat radiation.

When the thickness is less than 0.5 mm, the heat radiation can be improved, but partial discharge is likely to occur. On the other hand, when the plate thickness is more than 1 mm, it is possible to suppress the partial discharge and improve the strength, but there is a possibility that the heat radiation property is reduced. Therefore, in the present invention, the thickness of the aluminum nitride substrate is specified to be 0.5 to 1 mm.

Further, the aluminum nitride substrate preferably has a thermal conductivity of 190 W / m · K or more.
In the present invention, the heat dissipation is set to 300 kW / m ² · K or more.
By setting the value to 0 W / m · K or more, the heat radiation property can be further improved.

The metal circuit layer 2 of the aluminum nitride circuit board 1 of the present invention is made of, for example, copper, aluminum, or an alloy thereof. This metal circuit layer is formed by, for example, a thick film method, a DBC method, an active metal method, or the like. In the present invention, the method of forming the metal circuit layer is not particularly limited, and it is needless to say that a known method can be applied. It is preferable to bond to the aluminum nitride substrate by a method, an active metal method or the like.

Although the aluminum nitride circuit board of the present invention can be used for various applications, it is preferably used, for example, as a module board for high power. As described above, the aluminum nitride circuit board of the present invention is excellent in heat dissipation and suppression of partial discharge, and generates intense heat,
By using the module for a high-power module used at a high voltage, its reliability can be ensured.

Next, a method for manufacturing the aluminum nitride circuit board of the present invention will be described. In the present invention, aluminum nitride powder is used as a main raw material, and a material obtained by adding a rare earth oxide, an alkaline earth oxide, or the like as a sintering aid to the powder is used.

In the present invention, for example, 1 to 10 wt% of Y ₂ O ₃ powder, 0.5 to 10 wt% of CaO powder and 0.1 to 0.1 wt% of Al ₂ O ₃ powder are added to aluminum nitride powder, for example.
It is preferable to use a raw material mixed powder to which 〜1 wt% and SiO ₂ powder 0.5 wt% or less are added.

The coloring compounds Ti, Hf, Z
0.1 to 1 wt% of oxides, carbides and nitrides such as r and Cr
% Or less, but these compounds do not form a glass phase in the aluminum nitride sintered body and exist as particles of carbide or nitride having high conductivity. When such a compound having high conductivity is present in the grain boundary phase, it causes a decrease in partial discharge characteristics. Therefore, it is preferable not to include such a coloring compound.

It is preferable to use aluminum nitride powder having an average particle diameter of 1 μm or less. By using such a powder, 95% or more of the particles in the aluminum nitride substrate can be easily converted into aluminum nitride particles having a particle size of 3 to 7 μm, and partial discharge can be easily suppressed.

Next, such raw material mixed powder is mixed,
It is formed by a doctor blade method or a slurry casting method to form a thin or sheet-like molded product, or a raw material mixture is press-formed to form a thin or large molded product. The thickness of the compact is preferably such that the thickness of the aluminum nitride substrate after sintering is about 0.5 to 1 mm. With such a thickness, it is possible to obtain an aluminum nitride substrate which has excellent heat dissipation and can suppress partial discharge.

The obtained molded body is heated and degreased in an atmosphere of air or nitrogen gas, and the hydrocarbon component used as the organic binder is removed from the molded body. The degreased molded body is fired in a nitrogen gas atmosphere or the like at 1600 ° C. or more and 1800 ° C. or less for 1 hour or more and 10 hours or less to produce the aluminum nitride substrate of the present invention.

In the present invention, 1600 ° C. or more and 180
By firing at a relatively low temperature of 0 ° C or less,
Grain growth is suppressed, and 9% of all particles in the aluminum nitride substrate
5% or more is easily converted to aluminum nitride particles having a particle size of 3 to 7 μm, and partial discharge is also easily suppressed.

Further, by bonding a copper plate to the obtained aluminum nitride substrate by, for example, the DBC method, the aluminum nitride circuit board of the present invention can be manufactured.

In the production of the aluminum nitride circuit board of the present invention, it is possible to use an aluminum plate or an alloy plate thereof instead of the copper plate. In addition, instead of the DBC method, it is also possible to join the metal plates using an active metal method or the like.

When performing the active metal method, T is used as a brazing material.
It is preferable to use an Ag-Cu brazing material containing 0.2 to 5 wt% of at least one of i, Zr, and Hf. In addition, when a metal plate having a thickness of 0.1 mm or more, preferably 0.2 to 0.7 mm is used as the metal circuit board, the current carrying capacity of the metal circuit board is improved, so that it is effective as a high power module substrate. .

[0044]

EXAMPLES (Examples 1 to 4, Comparative Examples 1 to 3) Examples 1 to 4 Aluminum nitride powder having an average particle diameter of 1 μm or less was used, and Y ₂ O ₃ powder of 1 to 7 wt% was added thereto. And
After mixing, molding and degreasing, 1650-1800 ° C,
AlN having a particle size of 3 to 7 μm is fired for 1 to 10 hours.
An AlN substrate in which the crystal grains accounted for 95% or more of all the AlN crystal grains and in which the thermal conductivity and the plate thickness were changed was produced. The thermal conductivity was measured by changing the amount of the Y ₂ O ₃ powder, the firing temperature, and the firing time. Furthermore, this A
A 0.2 mm-thick Cu plate was joined to the 1N substrate by the active metal method to produce an AlN circuit board.

Next, the extinguishing voltage of this AlN circuit board was measured and the heat dissipation (thermal conductivity of AlN board / plate thickness of AlN board) was calculated. The thermal conductivity was measured by a laser flash method, and the extinguishing voltage was a voltage according to JEC-0401 when the voltage became 10 pC or less, which was taken as the extinguishing voltage.

Comparative Examples 1 to 3 Aluminum nitride powder having an average particle size of 1.5 to 2 μm
The following range is used, and Y ₂ O ₃ powders 1 to 1
After adding 0 wt% and mixing, molding and degreasing, 18
After firing at 20 to 1900 ° C. for 1 to 15 hours, AlN crystal particles having a particle size of 3 to 7 μm are 80% of all AlN crystal particles.
%, And an AlN substrate in which the thermal conductivity and the plate thickness were changed was manufactured. A Cu plate having a thickness of 0.2 mm was joined to the AlN substrate by an active metal method to produce an AlN circuit board.

The extinction voltage was measured and the heat dissipation was calculated for these AlN circuit boards in the same manner as in Example 1. Table 1 shows the results.

[Table 1]

As shown in Table 1, it was confirmed that the extinguishing voltage value can be set to 6.0 kV or more while maintaining the thermal conductivity of 190 W / m · K or more in each of the examples of the present invention. In addition, heat dissipation (thermal conductivity of AlN substrate / Al
The thickness of the N substrate is also 300 kW / m ^2.
-It was K or more, and it was recognized that the examples of the present invention were excellent in the suppression of partial discharge and the heat dissipation.

On the other hand, AlN having a particle size of 3 to 7 μm
In Comparative Examples in which the crystal particles were 80% of all AlN crystal particles, in Comparative Examples 1 and 2 in which the thermal conductivity was 170 W / m · K, the disappearance voltage value could be increased because the substrate thickness was relatively large. However, it was recognized that heat dissipation was reduced. In Comparative Example 3, it was recognized that the extinguishing voltage was reduced although the heat dissipation was excellent. As described above, in Comparative Examples 1 to 3, it was recognized that it was difficult to simultaneously improve both the extinguishing voltage value and the heat dissipation.

(Examples 5 to 8, Comparative Examples 4 and 6) Example 1
, And vehicle modules were manufactured using the AlN circuit boards of Comparative Examples 1 to 3. Next, these vehicle modules were continuously operated at a voltage of 5 kV for 100 hours, and the presence or absence of partial discharge and the ratio of the thermal resistance value were measured.

The measurement of the partial discharge was performed by measuring the extinction voltage of the partial discharge on the AlN circuit board after the continuous operation for 100 hours in the same manner as in Example 1.

As a result of the measurement, the extinction voltage (10 pC) was 6.
0 kV or more, partial discharge "No", 6.0 kV
Those that were less than were indicated as "presence" of partial discharge.

In the measurement of the thermal resistance, the thermal resistance of each AlN circuit board was measured, and the thermal resistance of the other AlN circuit board when the thermal resistance of the AlN circuit board of Comparative Example 1 was set to a reference value of 100. The measurement was performed by expressing the resistance value as a ratio (relative value) to a reference value. Therefore, the smaller the ratio of the thermal resistance, the better the heat radiation. Table 2 shows the presence / absence of partial discharge and the ratio of the thermal resistance value.

[Table 2]

As shown in Table 2, no partial discharge occurred in any of the examples of the present invention, and the ratio of the thermal resistance was low. On the other hand, in the comparative example, the module having no partial discharge has a higher thermal resistance value, while the module having no partial discharge has a higher thermal resistance value. Was found to be unsuitable.

[0055]

According to the aluminum nitride circuit board of the present invention, [the thermal conductivity of the aluminum nitride substrate / the thickness of the aluminum nitride substrate] is set to 300 kW / m ² · K or more, and the extinction voltage (10 pC ) Is 6.0k
By setting it to V or more, heat dissipation can be improved and partial discharge can be suppressed. Therefore, it can be used at high power where heat and partial discharge easily occur.

Further, by using the above-mentioned aluminum nitride circuit board for the high power module substrate of the present invention, the reliability in using the high power module substrate at high power can be improved.

[Brief description of the drawings]

FIG. 1 is an external view showing an aluminum nitride circuit board of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Aluminum nitride circuit board 2 ... Metal circuit layer 3 ... Aluminum nitride substrate

Claims (6)

[Claims] 1. A circuit board comprising an aluminum nitride substrate and a metal circuit layer, wherein [thermal conductivity of the aluminum nitride substrate / plate thickness of the aluminum nitride substrate] is 300 kW / m ² · K or more and partial discharge. Wherein the annihilation voltage (10 pC) is 6.0 kV or more. 2. The aluminum nitride circuit board according to claim 1, wherein 95% or more of the total aluminum nitride particles of the aluminum nitride substrate are made of aluminum nitride particles having a particle size of 3 to 7 μm. 3. An aluminum nitride substrate having a thickness of 0.
The aluminum nitride circuit board according to claim 1 or 2, wherein the thickness is 5 to 1 mm. 4. The thermal conductivity of the aluminum nitride substrate is 190 W / m · K or more.
4. The aluminum nitride circuit board according to any one of claims 1 to 3. 5. The metal circuit layer according to claim 1, wherein a metal plate is bonded to the aluminum nitride substrate by a DBC method or an active metal bonding method. Aluminum nitride circuit board. 6. A high power module board comprising the aluminum nitride circuit board according to claim 1. Description: