JPH11346037A - Substrate for heat radiation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a crack from being generated and developed, by jointing a ceramic plate where at least one of aluminum, aluminum nitride, silicon nitride, and silicon carbide is used as a main constituent onto a bus bar part. SOLUTION: In a substrate for heat radiation, a semiconductor element- mounting part 11 made of metal and a busbar part 16 are provided on both surfaces or one surface of a ceramic substrate 10 where at least one of aluminum, aluminum nitride, silicon nitride, and silicon carbide is used as a main constituent, and at the same time a ceramic plate 20 where at least one of aluminum, aluminum nitride, silicon nitride, and silicon carbide is used as the main constituent is jointed onto the bus bar part 16. At least one type of junction materials 12 and 19 being selected from silver copper brazing alloy, silver brazing metal, aluminum brazing metal, aluminum, and polyimide are provided between the bus bar part 16 and the ceramic substrate 10 and/or the ceramic plate 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric car, a hybrid car, a bullet train, a subway, a commuter train, an elevator,
IGBT (Insulated Gate Bipolar Transisto) is a power device mounted on robots, cranes, air conditioners, etc.
r), and a large current can flow in a semiconductor device housing package in which semiconductor devices are housed and mounted, or in a hybrid integrated circuit device in which various electronic components such as capacitors and resistors are mounted in addition to semiconductor devices. The present invention relates to a heat dissipation substrate having a low-resistance wiring conductor.

[0002]

2. Description of the Related Art Power devices are the oldest semiconductor devices, but in recent years, high voltage, large current, high speed, high frequency, and high performance have been remarkably advanced, and IGBT, GTO, IPM, power MOS FET And other high-speed MOS power devices. These power devices are widely used in automobiles, inverter trains, strobes, microwave ovens, golf carts, and the like. However, in recent years, hybrid vehicles and electric vehicles are becoming popular due to environmental problems, and these power devices, especially IGBTs, are required to withstand high voltages, to be smaller, thinner, and lighter.

The structure of a heat dissipation substrate in a conventional power device will be described with reference to FIG. On a ceramic substrate 1 made of AlN, a semiconductor element mounting portion 2 and a bus bar portion 7 are formed. The semiconductor element mounting section 2
The Al plate 4 is joined to the ceramic substrate 1 made of AlN by the Al brazing 3. Further, a semiconductor element 6 is joined on the Al plate 4 by a solder layer 5. In the bus bar portion 7, the Al plate 9 is joined to the ceramic substrate 1 made of AlN via the Al brazing material 8. The Al plate 9 of the bus bar portion 7 is formed several times thicker than the Al plate 4 of the semiconductor element mounting portion 2.

The bus bar portion 7 is wire-bonded from the semiconductor element 6 (not shown), and electricity is supplied through the wire bar. Further, heat generated at the time of energization is radiated through the ceramic substrate 1 made of AlN having high thermal conductivity.

[0005]

The heat dissipation substrate as described above has a thermal expansion coefficient of 4.7 × 10 ⁻⁶ / ° C. for the ceramic substrate 1 made of AlN and a thermal expansion coefficient of the Al plates 4 and 9. Is significantly different from 23.9 × 10 ⁻⁶ / ° C. Therefore, when a temperature change occurs during use, a tensile stress is particularly applied to the ceramic substrate 1 made of AlN.
There is a problem that cracks occur in the ceramic substrate 1 made of N or the metal layers of the semiconductor element mounting portion 2 and the bus bar portion 7 are broken.

For this reason, it is required that a large current of, for example, 100 A or more can be passed, and it is difficult to use it in a cold environment of -40 ° C. to 150 ° C. For example, it could not be applied to applications such as hybrid vehicles, electric vehicles, and various control devices used in the next Shinkansen, which have been forced to appear due to environmental issues.

If the above-mentioned conventional heat dissipation substrate is used for the applications described above, a thermal stress is generated between the metal layer and the ceramic substrate 1 due to a difference in thermal expansion between the two. Stress concentrates on the ceramics near the end of the metal layer, resulting in a large residual stress.As a result, when a thermal cycle or an external force is applied to the heat dissipation substrate, the residual stress becomes extremely large in combination with the residual stress, causing cracks in the ceramic substrate. Or the cracks may develop and break other wiring conductors.

Further, a copper plate can be bonded as the bus bar portion 7 by a DBC method (Direct Bonding Copper method). In this case, the bonding strength between the metal layer forming the bus bar portion 7 and the AlN ceramic substrate 1 is reduced. Not enough,
The metal layer peels off from the ceramic substrate due to thermal fatigue.
In order to strengthen the bonding, an active metal method can be used. However, in this method, cracks may occur in the outer peripheral portion of the metallized portion of the ceramic substrate 1 and the wiring portion may be disconnected.

[0009]

According to the present invention, there is provided a ceramic substrate comprising at least one selected from alumina, aluminum nitride, silicon nitride, and silicon carbide as a main component on both surfaces or one surface of a ceramic substrate. By providing an element mounting portion and a bus bar portion, and by joining a ceramic plate containing at least one or more selected from alumina, aluminum nitride, silicon nitride, and silicon carbide on the bus bar portion, the bus bar portion is formed. The generation of stress based on the difference in thermal expansion between the formed metal layer and the ceramic substrate can be reduced, cracks can be prevented from occurring and developing, and disconnection of the wiring conductor can be prevented.

Further, the wiring conductor can be reduced in resistance without peeling the wiring conductor from the ceramic substrate, and a large current of 100 A or more can be passed. In a cold environment of -40.degree. C. to 150.degree. Provided is a highly reliable heat dissipation substrate that does not cause any trouble even when used repeatedly.

Further, when at least one kind of joining material selected from silver-copper brazing, silver brazing, aluminum brazing, aluminum, and polyimide is provided between the bus bar portion and the ceramic substrate and / or the ceramic plate, the reliability is further improved. A heat-radiating substrate can be obtained.

[0012]

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

FIG. 1 is a perspective view of a heat dissipation wiring board of the present invention. The heat-dissipating wiring board of the present invention comprises a semiconductor element mounting portion 11 on a ceramic substrate 10 mainly containing AlN or the like.
And a bus bar section 16. The semiconductor element mounting portion 11 is made of a metal plate 13 made of Al or the like and a bonding material 12 made of Al brazing or the like.
It is joined by. Further, a semiconductor element 15 is mounted on the metal plate 13 via a solder layer 14. The busbar portion 16 is formed by joining a metal plate 18 such as copper with a joining material 17 such as Ag brazing.
A ceramic plate 20 made of AlN is joined thereon with a metal material 19 such as Ag braze.

A ceramic substrate 10 usually made of AlN
When a metal plate 18 made of copper or the like is joined, a tensile stress is applied to the ceramic substrate 10 due to a difference in thermal expansion between the two, and cracks occur in the ceramic substrate 10.
By providing a ceramic plate 20 on the upper surface of the ceramic substrate 20 and holding the ceramic plate from both sides, thermal stress applied to the ceramic substrate 10 is dispersed and cracks are prevented from occurring.

The area of the ceramic plate 20 is at least 60%, preferably 80%, of the area of the metal plate 18.
Above. This is because when the area of the ceramic plate 20 is less than 60% of the area of the copper plate 18, the stress due to the difference in thermal expansion between the metal plate 18 and the ceramic substrate 10 cannot be supported,
This is because cracks occur in the ceramic substrate 10.

Further, it is preferable that the shape of the ceramic plate 20 is as much as possible along the outer periphery of the metal plate 18. The portion to be electrically connected to the metal plate 18 by wire bonding is the end face of the metal plate 18 or the ceramic plate 2
A hole is made in the center of the hole 0 so that the metal plate 18 is exposed. Usually, three semiconductor element mounting portions 11 are connected to one bus bar portion 16 by a method such as wire bonding.

The present invention is characterized in that one or more semiconductor element mounting portions 11 and bus bar portions 16 are formed on one ceramic substrate 10, respectively.
This is because the structure in which the semiconductor element mounting portion 11 and the bus bar portion 16 are integrated on the ceramic substrate 11 is indispensable for a power device, particularly for an application such as an IGBT.

In the present invention, the metal plate 13 and the bonding material 12 forming the semiconductor element mounting portion 11 or the metal plate 18 and the bonding materials 17 and 19 forming the bus bar portion 16 are made of molybdenum, tungsten, copper, aluminum, or the like. And at least one dense or porous metal selected from silver. This is because these metals have low resistance and
This is because even if the porosity is selected and the Young's modulus is lowered and at the same time the specific resistance is lowered, it can be used as a sufficiently large current wiring conductor.

The selection of the porosity depends on the ceramic substrate 1
Is important in suppressing the generation of stress due to the difference in the coefficient of thermal expansion between the metal layer and each metal layer. For example, in the case of a ceramic substrate 1 made of aluminum nitride ceramics, when silver or copper is used as each metal layer, 5-30%,
Desirably, a porosity of 7-15%, ideally 8-12% is required. As a method of adjusting the porosity, generally, the baking temperature at the time of joining the ceramic substrate 11 and each metal layer is adjusted. However, in order to accurately obtain a desired porosity, the baking temperature is adjusted in advance. There is a method in which a suitable amount of plastic beads having a desired shape and a desired size are mixed in a metal layer before the bonding.

Hereinafter, a method of measuring the porosity of the metallized portion of each metal layer will be described. Since the metallized portion has a very small thickness of about 50 μm, it is difficult to measure the porosity by a usual method.

Therefore, in the present invention, the porosity was measured using a porosimeter. In this measurement method, a metallized silicon nitride is inserted into a glass container (a dilatometer), the glass container is filled with mercury (Hg), and a pressure is applied to the mercury from the outside. The porosity is calculated from Due to the surface tension of mercury, mercury does not penetrate into the pores of the metallization as it is.
When pressure is applied from the outside, mercury penetrates into the pores according to the following equation, and the pore volume (K) can be measured by measuring the permeation amount. This time, the external pressure was increased to 100 atm, and the porosity was measured.

Mercury intrusion pore diameter (μm) = 15 / pressure applied to mercury (atm) The metallized thickness (t) of the metallized portion is measured using a surface roughness meter or an optical interference thickness meter, and the width (h) is measured. And the length (L) were measured with a measure scope, the volume (V) of the metallized portion was calculated by the formula V = t × h × L, and the porosity (A) was calculated by the following formula. .

Porosity (A) = K / V Here, since the ceramic substrate 11 made of silicon nitride or the like is dense, its porosity is neglected. However, when non-negligible porosity can be expected in the ceramic substrate 11, the surface area and volume are reduced. The same dummy as the measurement test piece is prepared, and the value obtained by subtracting the amount of porosity of the dummy may be used as the amount of porosity of the metallized portion.

In the present invention, the ceramic plate 20 containing at least one selected from the group consisting of alumina, aluminum nitride, silicon nitride, and silicon carbide is bonded on the bus bar portion 16 for the following reasons. . That is, the bus bar section 16 is usually provided with a plurality of semiconductor element mounting sections 11.
Since it is connected as a large current path by wire bonding or the like, it has a cross-sectional area 2 to 10 times that of the metal plate 13 of the semiconductor element mounting portion 11. In other words, the busbar portion 16 generates more stress due to the coefficient of thermal expansion between the busbar portion 16 and the ceramic substrate 10 than the semiconductor element mounting portion 11. In order to prevent the ceramic substrate 10 from being broken due to the generation of the stress, it has been found that it is sufficient to join the ceramic plate 20 for relaxing the stress on the bus bar portion 16. The invention was not completed. And, due to these synergistic effects,
Provided is a heat-radiating substrate used as a high-reliability large-current printed circuit board that does not cause any trouble even when repeatedly used in a cold environment at a temperature of ° C.

Further, the joining materials 17 and 19 between the metal plate 18 and the ceramic substrate 10 and / or the ceramic plate 20 in the bus bar portion 16 are selected from silver copper brazing, silver brazing, aluminum brazing, aluminum, and polyimide. If at least one kind is used, it can be joined effectively.

As described above, the heat dissipation board of the present invention can be suitably used as a large current heat dissipation wiring board for passing a large current. In particular, it can be suitably used as a heat dissipation board for a power module on which a power element such as an IGBT is mounted.

[0027]

EXAMPLES Specific examples are shown below. All board dimensions were B6 size. A W paste is printed in a desired shape in a thickness of 15 to 40 μm on an AlN tape having a thickness of 1 to 3 mm, and N ₂ -H is applied at 1750 to 1900 ° C. for 3 hours.
₂ Simultaneous firing in a mixed gas to obtain a ceramic substrate 11 made of AlN having a W metallized portion provided on the surface. Then, on the W metallization, an Ag brazing material as the bonding material 17, a Cu plate having a thickness of 0.5 to 1 mm as the metal plate 18, a bonding material 1
9 as Ag brazing, and ceramic plate 20 as thickness 1
３3 mm AlN plates are sequentially stacked and simultaneously placed in a vacuum furnace for 80
The joining was performed at 0 to 860 ° C. to form the bus bar portion 16. Thereafter, an Al plate having a thickness of 0.5 mm as a metal plate 13 is joined with an Al brazing material as a joining material 12, and the semiconductor element mounting portion 11
Was formed to obtain a heat dissipation substrate of the present invention. And then
The semiconductor element 15 was mounted on the metal plate 13 by solder bonding.

Further, the ceramic substrate 1, the metal plate 18 forming the bus bar portion 16, the joining material 17, the ceramic plate 2
As shown in Table 1, various materials having different material Nos. 0 were prototyped in the same manner and subjected to a thermal test.

In the cooling / heating test, two kinds of liquid tanks of -40 ° C. and 150 ° C. were prepared, and a durability test in which a cycle (one cycle and one hour) in which the heat radiation substrate was left in each liquid tank for 30 minutes was performed. The number of cycles until cracks occurred was determined.

The results are shown in Table 1.
In the example of the present invention in which the ceramic plate 20 was bonded to the substrate, the severe cycle test was cleared up to 1000 cycles, and the resistance value after the test was not affected at all.
On the other hand, in the comparative example in which the ceramic plate 20 was not bonded, cracks were observed without clearing 1000 cycles.

[0031]

[Table 1]

[0032]

As described above, according to the present invention, a metal substrate is formed on both surfaces or one surface of a ceramic substrate mainly containing at least one selected from alumina, aluminum nitride, silicon nitride, and silicon carbide. By providing an element mounting portion and a bus bar portion, and by joining a ceramic plate containing at least one or more selected from alumina, aluminum nitride, silicon nitride, and silicon carbide on the bus bar portion, the bus bar portion is formed. The generation of stress based on the difference in thermal expansion between the formed metal layer and the ceramic substrate can be reduced, cracks can be prevented from occurring and developing, and disconnection of the wiring conductor can be prevented.

Therefore, a highly reliable heat-dissipating substrate which can flow a large current of 100 A or more and which does not cause any trouble even when repeatedly used in a cold environment of -40 ° C. to 150 ° C. is provided.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a heat dissipation substrate of the present invention.

FIG. 2 is a perspective view showing a conventional heat dissipation substrate.

[Explanation of symbols]

 10: Ceramic substrate 11: Semiconductor element mounting part 12: Bonding material 13: Metal plate 14: Solder layer 15: Semiconductor element 16: Bus bar part 17, 19: Bonding material 18: Metal plate 20: Ceramic plate

Claims (2)

[Claims] An alumina, aluminum nitride, silicon nitride,
A semiconductor element mounting portion made of metal and a bus bar portion are provided on both surfaces or one surface of a ceramics substrate containing at least one or more selected from silicon carbide as a main component, and alumina, aluminum nitride, and silicon nitride are provided on the bus bar portion. A heat dissipation substrate, wherein a ceramic plate containing at least one selected from silicon carbide as a main component is bonded. 2. The method according to claim 1, wherein at least one kind of a joining material selected from silver copper brazing, silver brazing, aluminum brazing, aluminum, and polyimide is provided between the bus bar portion and the ceramic substrate and / or the ceramic plate. The heat dissipation substrate according to claim 1.