JP2003309210A - Ceramic circuit board and method of manufacturing the same - Google Patents

Abstract

[PROBLEMS] To provide a ceramic circuit board which prevents cracks generated in a ceramic substrate after brazing and has improved thermal conductivity and temperature cycle life, and a method of manufacturing the same. SOLUTION: A metal circuit board 12 having a thickness of 3 mm or less is provided on a surface of a ceramic substrate 11 having a thickness of 0.2 to 0.9 mm via a brazing material 14 containing an active metal. A metal radiator plate 13 is provided via a brazing material 14 containing at least one of which has been subjected to at least one cooling treatment at a temperature of −110 ° C. or less. Warpage is 5
It is 100 μm or less per 0 mm. Further, a ceramic circuit board having a residual stress applied to the ceramic substrate of 650 MPa or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic circuit board and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, with the progress of miniaturization, high power consumption, and high performance of motors, power converters, etc., circuit boards for power semiconductor devices mounted on them have high thermal conductivity capable of handling higher power. And long-term high reliability of temperature cycle life is required. In order to meet this demand, various proposals have been made for ceramic circuit boards for power semiconductor devices having high thermal conductivity and high reliability.

For example, Japanese Unexamined Patent Publication No. 9-246691 discloses a method of manufacturing a ceramic circuit board having a metal circuit with improved temperature cycle life. It discloses a method of relaxing a residual stress by cooling a joined body obtained by brazing a metal circuit board and a ceramics substrate at −70 ° C. and improving a temperature cycle life.

[0004]

In order to handle a large amount of power, it is necessary to increase the thickness of the metal circuit board on which the power semiconductor element is mounted, reduce the thermal resistance, and improve the thermal conductivity. The bonded body in which the metal circuit board thus thickened is brazed to the ceramics substrate increases the residual stress and the amount of warp, and the cracks easily occur on the ceramics substrate.
Even if this bonded body is cooled at -70 ° C, the residual stress and the amount of warpage are not sufficiently relaxed, and there is a problem that the temperature cycle life is short. Therefore, improvement of thermal conductivity and temperature cycle life is awaited while preventing cracks generated in the ceramics substrate after the brazing and bonding.

In view of the above, an object of the present invention is to provide a ceramics circuit board having improved thermal conductivity and temperature cycle life while preventing cracks generated in the ceramics board after brazing and bonding, and a method for manufacturing the same. Especially.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present inventors have studied the relationship between the thickness of a metal circuit board and the thickness of a metal heat dissipation plate, and the brazed area of the metal circuit board and the metal heat dissipation. The relationship between the brazed area of the plate, the amount of warpage and the residual stress that occur when brazing the metal circuit board and the metal heat dissipation plate and the ceramics substrate can be suppressed, and the amount of warpage and the residual stress that occur- Cooling at −110 ° C. or lower can be more relaxed than cooling at 70 ° C., that is, heat dissipation and temperature cycle life of the ceramic circuit board can be improved while preventing cracks after brazing. The present invention has been completed and the present invention has been achieved.

The ceramic circuit board of the present invention is a bonded body in which a metal circuit board is provided on the front surface of the ceramic substrate via a brazing material, and a metal radiator plate is provided on the back surface of the ceramic substrate via a brazing material. , The joint is -1
The amount of warpage at room temperature is 5 after cooling at 10 ° C or below.
It is characterized in that it is 100 μm or less per 0 mm.

The residual stress applied to the ceramic substrate at this time is 650 MPa or less. Furthermore, the thickness of the ceramic substrate is 0.2
˜0.9 mm, the thickness of the metal circuit board is 3.0 mm or less, and the relationship between the thickness (tc) of the metal circuit board and the thickness (tr) of the metal heat dissipation plate is tc> tr. It is preferable that the relationship between the brazed area (sc) and the brazed area (sr) of the metal heat sink is sc <sr.

In the ceramic circuit board of the present invention,
It is preferable that the ceramic substrate is silicon nitride, aluminum nitride, or alumina, and the metal circuit board and the metal radiator plate are copper or a copper alloy containing copper as a main component, or aluminum or an aluminum alloy containing aluminum as a main component. At this time, it is preferable to use a brazing material containing an active metal or an Al alloy brazing material as the brazing material.

According to the method of manufacturing a ceramics circuit board of the present invention, a metal plate is joined to the front surface and the back surface of the ceramics substrate with a brazing material, the metal plate on the front surface is etched to form a circuit pattern, and the metal plate on the back surface is formed. A bonded body is formed as a heat dissipation plate, or a metal circuit board having a circuit pattern formed on the surface of a ceramic substrate and a metal heat dissipation plate are bonded to the back surface of the ceramic substrate with a brazing material containing an active metal to form a bonded body. It is characterized in that it is manufactured and the joined body is cooled to −110 ° C. or lower. Here, the cooling is preferably performed by vacuum-packing the bonded body, or by cooling in an inert gas at a temperature lowering rate of 80 ° C./minute or less to −110 ° C. or less and holding for 20 minutes or more.

Further, in the method for manufacturing a ceramics circuit board of the present invention, the metal plates are joined to the front and back surfaces of the ceramics substrate with a brazing material, cooled to -110 ° C. or lower and returned to room temperature, and the metal plate on the surface is etched. And forming a circuit pattern by using the metal plate on the back surface as a heat dissipation plate to form a bonded body, or further cooling the bonded body to −110 ° C. or lower. Here, the cooling is preferably performed by vacuum-packing the bonded body, or by cooling in an inert gas at a temperature lowering rate of 80 ° C./minute or less to −110 ° C. or less and holding for 20 minutes or more. As the brazing material described above, it is preferable to use a brazing material containing an active metal or an Al alloy brazing material.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a ceramic circuit board of the present invention. In the ceramic circuit board 10 of the present invention, a metal circuit board 12 is provided on the surface of a ceramic substrate 11 via a brazing material containing an active metal or an Al alloy brazing material 14, while the back surface of the ceramic substrate 11 contains an active metal. This is a joined body in which the metal heat dissipation plates 13 are respectively provided via the brazing material or the Al alloy brazing material 14, and the obtained joined body is cooled at -110 ° C or lower. According to this bonded body, the warp amount (tw) of the ceramic substrate 11 at room temperature can be 100 μm or less per 50 mm, and the residual stress applied to the ceramic substrate 11 can be 650 MPa or less. The amount of warp may be on either side of the metal circuit board or the metal heat dissipation plate. In order to prevent the residual stress from concentrating, it is desirable that the end faces and the end corners of the metal circuit board 12 and the metal heat dissipation plate 13 are provided with taper and / or radius.

When the warp amount of the ceramic circuit board 10 is large, when the metal radiator plate 13 side is attached to the radiator or the housing of the equipment by using screws or low-temperature brazing material, the adhesion is deteriorated and the heat radiation performance is deteriorated. to degrade. Therefore, in order to improve the adhesiveness and improve the heat dissipation, it is more preferable that the warp amount (tw) per 50 mm is 50 μm or less, which is smaller. In addition, when the ceramic circuit board 10 is mounted on a radiator plate or the like using screws, the warp of the ceramic circuit board 10 is concave (metal) on the metal circuit board 12 side rather than convex (metal concave 13 side). When the heat dissipation plate 13 side is convex, the adhesion is better and the heat dissipation is better. Further, since the residual stress is relaxed, the temperature cycle life can be improved, which is more preferable.

The ceramic substrate 11 used in the present invention
Examples of the material include silicon nitride, aluminum nitride, alumina and the like. If the thickness is too thin, the strength and durability will be small, and if it is too thick, the thermal resistance will be large. Preferably there is. Further, as the metal circuit board 12 and the metal heat dissipation plate 13,
Examples thereof include copper, a copper alloy containing copper as a main component, aluminum, and an aluminum alloy containing aluminum as a main component. The thickness of the metal circuit board 12 is preferably 3.0 mm or less. The reason for this will be described later.

Further, in the ceramic circuit board of the present invention, in order to prevent damage and warpage of the joined body due to relaxation of the residual stress generated in the joined body by brazing, and to improve the temperature cycle life, the metal circuit board 12 is Thickness (tc)
And the thickness (tr) of the metal radiator plate 13 is tc> tr
And the brazed area of the metal circuit board 12 (s
The relationship between c) and the brazed area (sr) of the metal heat dissipation plate 13 is preferably sc <sr. The reason for this is considered as follows.

The warp of the joined body after brazing is determined by the thickness (tc) of the metal circuit board 12 and the thickness (t) of the metal heat dissipation plate 13.
It depends on the relationship with r). For example, the above area is sc = sr
Under the condition, warp does not occur when the thickness is tc = tr. When the thickness is tc> tr, the metal circuit board 12 side is warped to be concave (the metal heat dissipation plate 13 side is convex). When the thickness is tc <tr, the metal circuit board 12 side is convex (the metal heat dissipation plate 13 side is concave). Furthermore, the above area is sc <s
Under the condition of r, the thickness is tc = tr or tc <t.
In the case of r, the metal circuit board 12 side is convex (the metal heat dissipation plate 13 side is concave). If the thickness is tc> tr, no warpage occurs, the metal circuit board 12 side is convex (the metal heat dissipation plate 13 side is concave), or the metal circuit board 12 side is concave (the metal heat dissipation plate 13 side is convex). ) Is either warped. The amount of warp tends to increase as the difference between the thicknesses tc and tr increases and as the difference between the areas sc and sr increases. That is, in order to control at least the metal circuit board 12 side to be concave (the metal heat dissipation plate 13 side is convex) and to control the warp amount to be small, sc <sr and tc> tr are necessary conditions.
The optimum constant may be selected from the conditions.

As the ceramic substrate 11 in the present invention, a silicon nitride substrate having a high bending strength of 650 MPa or more and good thermal conductivity is particularly preferable because it must withstand the residual stress applied. Further, as the metal circuit board 12 and the metal heat dissipation plate 13, oxygen-free copper having good electrical conductivity, thermal conductivity and elongation is preferable.

Further, the ceramic circuit board 10 of the present invention.
In the manufacturing method of A, a metal plate is provided on the front surface and the back surface of the ceramic substrate 11 and a brazing material containing an active metal such as titanium, or A
They are brought into contact with each other via the 1-alloy brazing material 14, and the temperature is raised to a temperature at which the brazing material 14 is melted to join them. After that, after returning to room temperature at a temperature lowering rate of 5 ° C./min or less so that cracks do not occur, the metal plate on the front surface is etched to form a circuit pattern, and the metal plate on the back surface is directly used as a heat dissipation plate to form a bonded body ( 1) or a metal circuit board 12 having a circuit pattern formed in advance on the surface of the ceramic substrate 11 by pressing or the like and a metal radiator plate 13 are brought into contact with the back surface of the ceramic substrate 11 via the brazing material 14. Then, the temperature is raised to a temperature at which the brazing material 14 is melted and the brazing material 14 is bonded. After that, the bonded body (2) is manufactured by returning the temperature to room temperature at a temperature lowering rate of 5 ° C./minute or less so that cracks do not occur. Next, this bonded body is vacuum-packed or cooled in an inert gas to a temperature of -110 ° C. or lower at a temperature lowering rate of 80 ° C./minute or less and kept for 20 minutes or more so that cracks do not occur in the bonded body. , So that cracks do not occur in the joined body after cooling 80
It is manufactured by returning to room temperature at a temperature rising rate of not more than ° C / min. In addition, in order to alleviate the residual stress, it is more preferable to cool to around -190 ° C. The cooling treatment for manufacturing the joined body (1) may be performed only once after the metal plates are joined before forming the circuit pattern, or may be performed again after forming the circuit pattern. In particular, the method of cooling after joining metal plates before forming a circuit pattern is effective in preventing cracks during the formation of a circuit pattern by reducing residual stress. Further improvement of life can be expected.

[0019]

EXAMPLES The present invention will be specifically described below with reference to examples. (Examples 1 to 3) 50 m in size as a ceramic substrate
m × 30mm × (thickness) 0.64mm and thermal conductivity is 80
An oxygen-free copper plate with a size of 40 mm x 25 mm x (thickness) of 1.0 mm as a metal circuit board on the surface of a W / mK silicon nitride substrate, and a size of 40 mm x 25 mm as a metal heat dissipation plate on the back surface.
× (thickness) 0.8 mm oxygen-free copper plate, silver containing active metal, which is cut into a circuit pattern shape and a heat dissipation plate shape,
The brazing filler metal foil made of copper and titanium having a thickness of 50 μm is contacted and heated in a vacuum of 1.33 Pa or less at 850 ° C. for 10 minutes, and then cooled at a temperature lowering rate of 4 ° C./minute to obtain no silicon nitride substrate. A bonded body of oxygen copper plates was obtained.

Next, a circuit pattern was formed by etching an oxygen-free copper plate as a circuit metal plate. Here, the ratio (sc / sr) of the brazing area (sc) of the metal circuit board and the brazing area (sr) of the metal heat dissipation plate was 0.8.

Further, this was vacuum packed and at a temperature lowering rate of 60 ° C./min, the temperature was −110 ° C. or less, specifically −191 ° C., −
After cooling to 150 ° C. and −110 ° C., respectively, holding for 30 minutes, and then returning to room temperature at a temperature rising rate of 60 ° C./min to obtain a ceramic circuit board. Liquid nitrogen was used as a coolant for cooling at -191 ° C.

(Comparative Examples 1 to 4) After obtaining the same bonded bodies as in the above-mentioned Examples, these were vacuum-packed and cooled to -70 ° C, -50 ° C, -25 ° C at a temperature decreasing rate of 60 ° C / min. After that, hold for 30 minutes, and then return to room temperature at a heating rate of 60 ° C./minute,
A ceramic circuit board was obtained. In addition, ceramic circuit boards that were not cooled with the same bonded body were prepared for comparison.

(Example 4) After obtaining a bonded body similar to the above-mentioned example, first, the first cooling treatment was performed at -191 ° C, and then a circuit metal plate was etched to form a circuit pattern. . A ceramic circuit board was obtained in the same manner as in Example 1 except for the above.

(Embodiment 5) After obtaining a bonded body similar to that of the above embodiment, first cooling treatment is performed at -191 ° C., and then a metal plate for a circuit is subjected to etching processing to form a circuit pattern. . After that, the second cooling process-
Performed at 191 ° C. A ceramic circuit board was obtained in the same manner as in the above example except for the above.

(Embodiment 6) A ceramic circuit board is obtained in the same manner as in Embodiment 1 except that the method is such that the metal plate for a circuit is preliminarily pressed to be joined. It was

(Examples 7 and 8) Ceramic ceramic substrates having dimensions of 50 mm × 30 mm × (thickness) 0.64 mm, aluminum nitride substrates and alumina substrates respectively having metal circuit boards with a thickness of 40 mm × 25 mm × (thickness) 0. After obtaining a bonded body under the same brazing conditions as in Example 1, using an oxygen-free copper plate of 0.6 mm and an oxygen-free copper plate of 40 mm × 25 mm × (thickness) 0.4 mm as a metal radiator plate on the back surface, respectively, First, the first cooling treatment was performed at -191 ° C., and then the circuit metal plate was etched to form a circuit pattern to obtain a ceramic circuit board.

(Comparative Examples 5 and 6) Ceramic circuit boards each having the same bonded body as those in Examples 7 and 8 but not subjected to cooling treatment were prepared for comparison.

(Embodiments 9 and 10) Ceramic substrates having a size of 50 mm × 30 mm × (thickness) of 0.64 mm and silicon nitride substrates and aluminum nitride substrates each having a thickness of 40 mm × 25 mm × (thickness) as metal circuit boards. 0.6mm pure aluminum plate and 40mm x 25mm x (thickness) 0.4 on the back as metal heat sinks
mm pure aluminum plate, thickness 5 made of Al-Si
630 ° C. while contacting through a 0 μm brazing material foil and applying a load of 16 kPa in a vacuum of 1.33 Pa or less.
After heating for × 10 minutes, it was cooled at a temperature decrease rate of 4 ° C./minute to obtain a bonded body of a silicon nitride substrate and an aluminum plate and a bonded body of an aluminum nitride substrate and an aluminum plate, respectively. After obtaining the above-mentioned bonded body, first the first cooling treatment-
The process was performed at 191 ° C., and then the circuit metal plate was etched to form a circuit pattern. The circuit pattern shape and sc / sr were the same as in Example 1 to obtain a ceramics circuit board.

(Comparative Examples 7 and 8) Ceramic circuit boards each having the same bonded body as those in Examples 9 and 10 but not subjected to cooling treatment were prepared for comparison. Table 1 shows the specifications and dimensions of the ceramic substrates, metal circuit boards, and metal heat sinks of the above Examples and Comparative Examples.

[0030]

[Table 1]

Next, with respect to the ceramic circuit board thus manufactured, the amount of warpage (A) per 50 mm of the silicon nitride substrate was measured, and the residual stress (B) generated in the silicon nitride substrate was analyzed. Also, the temperature cycle life (C) test was held in the atmosphere at −40 ° C. for 20 minutes, left at room temperature 25 ° C. for 10 minutes, and further held at 125 ° C. for 20 minutes.
One cycle was carried out at 25 ° C. for 10 minutes, and the number of cycles until defects such as cracks occurred in the silicon nitride substrate part was measured. The results are shown in Table 2.

[0032]

[Table 2]

As shown in Table 1, in the case of a silicon nitride ceramics circuit board using an oxygen-free copper plate as a metal plate, the residual stress, the amount of warpage, and the temperature cycle life have a cooling temperature of −.
The examples according to the present invention at -110 ° C or lower are improved over the comparative examples at 70 ° C or higher, and among them, -191.
It was found that the ° C example was the most improved.

Next, the above Examples 1 to 3 and Comparative Examples 1 to 4
Figure 2 shows a graph of the relationship between the amount of warp and the cooling temperature.
Shown in. According to this, in order to suppress the warp amount to 100 μm or less, it is necessary to set the cooling temperature to −110 ° C. or less.

Further, in all of Examples 4, 5 and 6, the residual stress, the amount of warpage and the temperature cycle life were improved as compared with the comparative example. Among them, the residual stress, the amount of warpage and the amount of warpage of the example of the present invention in Example 5 were improved. It can be seen that the temperature cycle life is most improved.

Next, when an aluminum nitride substrate or an alumina substrate is used as the ceramic substrate of Examples 7 and 8, as compared with Comparative Examples 5 and 6, the ceramic circuit boards according to the Examples of the present invention are not warped. It can be seen that the residual stress and the temperature cycle life are both improved.
However, since the bending strength of the aluminum nitride substrate and the alumina substrate is lower than that of silicon nitride, when a thick copper plate is joined, the joining temperature and joining should be done so that the ceramic substrate is not damaged by the residual stress during brazing. It is necessary to select the thickness of the metal plate under appropriate conditions.

The above is the case where the oxygen-free copper plate is used as the metal plate, but when the pure aluminum plate is used as the metal plate, the residual stress and the temperature cycle are improved from Examples 9 and 10 and Comparative Examples 7 and 8. You can see that the effect is seen.

In the ceramic circuit board of this embodiment, a semiconductor element is mounted on a metal circuit pattern by using a low temperature brazing material, solder or the like, and the ceramic circuit board is made of a heat sink or a metal such as Cu on the metal radiator plate side. It is used by fixing it to a water cooling jacket. In this case, there is a thermal resistance as a measure of the diffusion heat dissipation performance that allows the heat generated by the element to reach the heat sink.

Saturation thermal resistance (heat reaches the heat sink and the thermal resistance value starts to saturate) where the thermal resistance value is saturated with respect to the power application time tp when a certain electric power is continuously applied to this thermal resistance. The thermal resistance value at that time is the saturation thermal resistance value, and the power application time at this time is tp = tp1.)
Is used when a constant power is applied for a short time tp2 (tp2 <tp1), and the thermal resistance value is divided into the transient thermal resistance before saturation. However, the thermal resistance shown here is obtained by dividing the temperature difference between the elements before and after the application of power by the applied power value. Especially when it is used to control motors and power conversion equipment, good heat dissipation characteristics are required in order to apply power to the semiconductor element in a short time tp2 and at the same time to quickly dissipate the heat emitted from the element in a short time. In this case, it is required that the transient thermal resistance be small. That is,
The absolute value of the thermal resistance value is small with the increase of the power application time, and the longer the time (tp1) until the transient thermal resistance (transient thermal resistance value) reaches the saturation value, the smaller the temperature rise of the element, and the heat radiation. It can be said that it is excellent in sex.

Here, when the power applied to the semiconductor element is constant and the power application time is variable from 1 ms to 0.5 s, the thickness of the metal circuit board is 1.0 mm (the thickness of the metal heat sink is 0.8 mm). 3) shows an example of measurement of thermal resistance characteristics of the ceramic circuit board of Example 1. However, the standardized thermal resistance is shown here instead of the thermal resistance value. The normalized thermal resistance is the resistance value of the measurement sample divided by the saturation thermal resistance value of the same sample. Therefore, it was considered that the thermal resistance of the sample was saturated at the power application time (tp1) when the normalized thermal resistance value became 1. In the case of the sample used in the measurement of FIG. 3, it can be seen that the thermal resistance value reaches the saturation value when the power application time is 0.1 sec (= tp1) or more. Therefore, in the case of this sample, the thermal resistance value when tp = tp1 becomes the saturation thermal resistance value.

(Embodiment 11) The ceramic circuit board of the sample for measurement uses silicon nitride as the ceramic board, and the dimensions of the silicon nitride board are 50 mm × 30 mm × (thickness) 0.6.
It is 4 mm, and through holes for screwing of φ3 mm are machined at intervals of 22.5 mm from the center of the surface in the longitudinal direction. The thickness of the metal circuit board is constant at 1.0 mm, the size of the metal heat dissipation plate is 50 mm x 30 mm x (thickness x: variable at 1.0 mm or less), and the length is different from the center of the surface of the metal heat dissipation plate in the longitudinal direction. Φ3 mm screwing through holes are formed at intervals of 22.5 mm. The amount of warpage of the ceramic circuit board in which the thickness (x) of the metal heat dissipation plate was changed was obtained by continuously measuring the surface on the metal heat dissipation plate side. In addition, grease having a good thermal conductivity was applied to the entire surface of the metal heat sink plate attached to the heat sink used as the heat sink in a thickness of 50 μm, and screwed and attached. The radiator was water-cooled and kept constant at 25 ° C. Further, a power semiconductor element having a 10 mm square and a thickness of 0.5 mm was used as the element, and the element was bonded onto the metal circuit board of the ceramic circuit board with a low temperature brazing material so that the saturation thermal resistance characteristics could be measured.

A bonded body similar to that of Example 1 was prepared except that the thickness of the metal radiator plate was changed (1.0 mm or less).
FIG. 2 shows the result of measurement of the normalized saturation thermal resistance characteristic with respect to the warp amount of 0 to 150 μm of the ceramic circuit board when cooled at −191 ° C. Here, the normalized saturation thermal resistance is a value obtained by dividing the saturation thermal resistance value of a sample having an arbitrary warp amount by the saturation thermal resistance value of a sample having a warp amount of 0 (μm).
From the measurement results of the prototype sample according to this example, when the thickness of the metal radiator plate was 0.8 mm, the absolute value of the warp amount was closest to 0, which was a preferable result. Therefore, the thermal resistance was standardized using the saturated thermal resistance value at this time. Of these ceramic circuit boards, of course, the absolute value of the saturation thermal resistance when using a circuit board with a warp amount of 0 (μm) is the smallest, and as the warp amount increases, the gap with the heat sink increases and the saturation thermal resistance increases. The value increases. That is, it can be said that the normalized saturation thermal resistance shown here is as small as possible, and that the closer it is to 1, the more heat is diffused, and the closer to the heat dissipation performance of the circuit board having the warp amount of 0 (μm).

From FIG. 2, the normalized saturation thermal resistance has a warp amount of 5
It can be seen that when the warp amount is 0 μm, the saturation thermal resistance increases by about 5%, and when the warp amount is 100 μm, the saturation thermal resistance increases by about 10%. It can be seen that when the amount of warpage exceeds 100 μm, the normalized saturation thermal resistance rapidly increases. That is, it is necessary to suppress the amount of warpage to 100 μm or less in order to prevent deterioration of the saturated thermal resistance. This agrees with the result of the cooling temperature and the warp amount in FIG.

(Embodiment 12) FIG. 4 shows the measurement results of the thermal resistance characteristics when the input power to the semiconductor element is fixed and the thickness of the metal circuit board is variable for varying the power application time from 1 ms to 0.5 s. Show. Similar to FIG. 3, in this evaluation method, the longer the time (tp1) until the transient thermal resistance reaches the saturation value with respect to the power application time, the smaller the temperature rise of the element and the better the heat dissipation. The normalized thermal resistance in FIG. 4 is obtained by dividing the thermal resistance value of each measurement sample by the saturation thermal resistance value of the same sample. Therefore, it means that the thermal resistance of the sample was saturated in the power application time (tp1) when the normalized thermal resistance value became 1. The measurement sample uses a silicon nitride substrate as the ceramic substrate, and the thickness of the metal circuit board is 0.4.
It was produced in the same manner as in Example 1 except that the thickness was changed to 4 mm (the thickness of the metal heat dissipation plate determines the optimum thickness in the same manner as in Example 11) and the cooling treatment was performed at -191 ° C. next,
A 10 mm square and 0.5 mm thick power semiconductor element was bonded onto the metal circuit board of the ceramic circuit board with a low temperature brazing material so that the saturation thermal resistance characteristics could be measured.

It can be seen from FIG. 4 that when the thickness of the metal circuit board exceeds 3 mm, the extension of the power application time tp1 at which the normalized thermal resistance value is saturated becomes small. That is, even if a metal circuit board having a thickness of more than 3 mm is used, it is not possible to expect a great improvement in heat dissipation. Further, when the thickness is 3 mm or more, the expansion / contraction of the metal circuit board easily damages the ceramics substrate and easily affects the low temperature brazing material for fixing the element. Furthermore, it is not recommended because it is difficult to reduce the weight of the ceramic circuit board and reduce the manufacturing cost.

[0046]

According to the ceramic circuit board and the method for manufacturing the same of the present invention, the thermal resistance, particularly the transient thermal resistance, can be reduced, so that the thermal conductivity can be improved and the temperature cycle life can be improved. Therefore, it is possible to contribute to miniaturization, high power consumption, and high reliability of the circuit board for the power semiconductor element.

[Brief description of drawings]

FIG. 1 shows a cross-sectional view of a ceramics circuit board of the present invention.

FIG. 2 is a diagram showing an example of normalized saturation thermal resistance and cooling temperature characteristics with respect to the amount of warpage of the ceramic circuit board of the present invention.

FIG. 3 is a diagram showing an example of normalized thermal resistance characteristics of the ceramic circuit board of the present invention with respect to power application time.

FIG. 4 is a diagram showing normalized thermal resistance characteristics with respect to power application time when the thickness of a metal circuit board is changed in the ceramic circuit board of the present invention.

[Explanation of symbols]

10: Ceramics circuit board 11: Ceramics substrate 12: Metal circuit board 13: Metal heat sink 14: brazing material

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H05K 3/22 H01L 23/12 C (72) Inventor Yasutoshi Kurihara 7-1 Omika-cho, Hitachi-shi, Ibaraki F-term in Hitachi Research Laboratory, Hitachi, Ltd. (reference) 4G026 BA03 BA16 BA17 BB22 BB23 BB27 BF11 BF16 BF20 BF24 BF42 BG02 BG23 BH07 5E338 AA01 AA18 EE02 EE26 5E339 AB06 BC55BD06 BB31 BB76 BB31 BB23 BB23 ER54

Claims (8)

[Claims] 1. A joined body in which a metal circuit board is provided on a front surface of a ceramic substrate via a brazing material, and a metal heat dissipation plate is provided on a back surface of the ceramic substrate via a brazing material, the joined body being- A ceramic circuit board which is cooled at 110 ° C. or less and has a warp amount at room temperature of 100 μm or less per 50 mm. 2. The ceramic circuit board according to claim 1, wherein the residual stress applied to the ceramic board is 650 MPa or less. 3. The ceramic substrate has a thickness of 0.2 to
The ceramic circuit board according to claim 1 or 2, wherein the thickness is 0.9 mm and the thickness of the metal circuit board is 3.0 mm or less. 4. The relationship between the thickness (tc) of the metal circuit board and the thickness (tr) of the metal heat dissipation plate is tc> tr, and the brazed area (sc) of the metal circuit board and the metal heat dissipation are further defined. The relation with the brazed area (sr) of the plate is sc <sr
The ceramic circuit board according to any one of claims 1 to 3, wherein 5. The ceramic substrate is silicon nitride, aluminum nitride or alumina, and the metal circuit board and the metal heat dissipation plate are copper or a copper alloy containing copper as a main component or aluminum or an aluminum alloy containing aluminum as a main component. Claims 1 to 4 characterized in that
The ceramic circuit board according to any one of 1. 6. A metal plate is joined to a front surface and a back surface of a ceramic substrate with a brazing material, the front surface metal plate is etched to form a circuit pattern, and a bonded body is formed by using the back surface metal plate as a heat dissipation plate, or Alternatively, a metal circuit board having a circuit pattern formed on the front surface of the ceramics substrate and a metal heat radiating plate on the back surface of the ceramics substrate are respectively joined with a brazing material to form a joined body, and the joined body is cooled to −110 ° C. or lower. A method of manufacturing a ceramics circuit board, comprising: 7. A metal plate on the back surface is formed by bonding metal plates to the front and back surfaces of a ceramic substrate with a brazing material, cooling to −110 ° C. or lower and returning to room temperature, and etching the metal plate on the front surface to form a circuit pattern. A method for manufacturing a ceramic circuit board, characterized in that the plate is used as a heat dissipation plate to form a bonded body, or the bonded body is further cooled to -110 ° C or lower. 8. The joined body is vacuum-packed or cooled to −110 ° C. or lower in an inert gas at a temperature lowering rate of 80 ° C./min or lower and held for 20 minutes or longer. Alternatively, the method for manufacturing a ceramics circuit board according to Item 7.