Ceramic circuit board, semiconductor device, and method of using the semiconductor device

Abstract

To provide ceramic circuit boards that improve the cooling efficiency of semiconductor devices and offer good manufacturability. [Solution] The ceramic circuit board according to the embodiment consists of a ceramic substrate and metal plates bonded to both sides of the ceramic substrate. The metal plate bonded to at least one of the two sides of the ceramic substrate is a cooling channel metal plate having a cooling channel portion. The thickness of the ceramic substrate is preferably smaller than the thickness of the cooling channel metal plate. Furthermore, the ceramic substrate comprises a first ceramic substrate and a second ceramic substrate bonded to a metal plate bonded to the first ceramic substrate, wherein one side of the second ceramic substrate is bonded to the cooling channel metal plate bonded to the first ceramic substrate, and the metal plate is bonded to the other side of the second ceramic substrate.

Description

Technical Field

[0001] The embodiments described below generally relate to a ceramic circuit board, a semiconductor device, and a method of using the semiconductor device.

Background Art

[0002] In recent years, with the improvement in the performance of industrial equipment, the output of power modules mounted thereon has been increasing. Along with this, the output of semiconductor elements has been increasing. The guaranteed operating temperature of semiconductor elements is 125°C to 150°C, but there is a possibility that it will rise to 175°C or higher in the future with the increase in output. As a circuit board for mounting semiconductor elements, a ceramic circuit board is used. A ceramic circuit board is formed by joining a metal plate on a ceramic substrate. For example, in Japanese Patent No. 6789955 (Patent Document 1), there is an overhanging portion where the bonding layer protrudes from the end of the metal plate. In Patent Document 1, the TCT characteristics (thermal cycle characteristics) are improved by controlling the hardness and size of the overhanging portion of the bonding layer.

[0003] In order to improve the cooling efficiency of a semiconductor element which is a heat generating body, a method using cooling water has been studied. For example, in Japanese Unexamined Patent Application Publication No. 2001-148451 (Patent Document 2), a water channel is provided in a heat sink on which a ceramic circuit board is mounted to dissipate heat generated from the semiconductor element. Also, in International Publication No. 2015 / 147071 (Patent Document 3), a water channel is provided in a ceramic substrate.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

[0005] The methods described in Patent Documents 2 and 3 allow for water cooling, thus improving the cooling efficiency of semiconductor elements. However, Patent Document 2 is unsuitable for miniaturizing modules because it leads to a larger heat sink. Furthermore, imparting a three-dimensional shape to the ceramic substrate, as in Patent Document 3, is a factor that increases costs.

[0006] This invention addresses these challenges and aims to provide a ceramic circuit board that improves the cooling efficiency of semiconductor devices and offers good manufacturability. [Means for solving the problem]

[0007] The ceramic circuit board according to this embodiment comprises a ceramic substrate and metal plates bonded to both sides of the ceramic substrate. The metal plate bonded to at least one of the two sides of the ceramic substrate is a cooling channel metal plate having a cooling channel portion. [Brief explanation of the drawing]

[0008] [Figure 1] A side view showing an example of a ceramic circuit board according to the embodiment. [Figure 2] A side view showing another example of a ceramic circuit board according to the embodiment. [Figure 3] A diagram showing an example of a cooling passage. [Figure 4] A diagram showing another example of a cooling passage. [Figure 5] A side view showing an example of a semiconductor device according to the embodiment. [Figure 6] A side view showing another example of a semiconductor device according to the embodiment. [Modes for carrying out the invention]

[0009] The following describes in detail embodiments of ceramic circuit boards, semiconductor devices, and methods for using semiconductor devices, with reference to the drawings.

[0010] The ceramic circuit board according to this embodiment comprises a ceramic substrate and metal plates bonded to both sides of the ceramic substrate. The metal plate bonded to at least one of the two sides of the ceramic substrate is a metal plate having a cooling channel (hereinafter referred to as the "cooling channel metal plate"). By providing a cooling passage in a metal plate bonded to a ceramic substrate, the number of components such as heat sinks can be reduced.

[0011] Furthermore, in the embodiment, it is desirable that the thickness of the ceramic circuit board is smaller than the thickness of the cooling channel metal plate. In other words, it is preferable that the ceramic circuit board satisfies the condition (thickness of the ceramic substrate) < (thickness of the cooling channel metal plate).

[0012] Furthermore, the ceramic circuit board according to the embodiment comprises a first ceramic substrate and a second ceramic substrate bonded to a metal plate bonded to the first ceramic substrate. One side of the second ceramic substrate is bonded to the cooling channel metal plate bonded to the first ceramic substrate, and the metal plate is bonded to the other side of the second ceramic substrate, and it is preferable that the thickness of the second ceramic substrate is smaller than that of the cooling channel metal plate. In addition, the ceramic substrate is usually in the shape of a flat plate. The ceramic substrate may have a three-dimensional structure with partial irregularities. If it has a three-dimensional structure, the thickness of the ceramic substrate is the thinnest part at the joint with the metal plate.

[0013] Figures 1 and 2 show an example of a ceramic circuit board according to the embodiment. In the figures, reference numeral 1 denotes a ceramic circuit board, reference numeral 2 denotes the first ceramic substrate among the ceramic substrates, reference numerals 3 and 8 denotes metal plates that do not have a cooling passage (hereinafter referred to as "non-cooling passage metal plate"), reference numeral 4 denotes the cooling passage metal plate among the metal plates, reference numeral 5 (shown in Figure 3, etc.) denotes the cooling passage, reference numeral 5A denotes the inlet of the cooling passage 5, reference numeral 5B denotes the outlet of the cooling passage 5, and reference numeral 7 denotes the second ceramic substrate among the ceramic substrates.

[0014] Figure 1 shows a structure in which a non-cooling passage metal plate 3 is bonded to one side of the first ceramic substrate 2, and a cooling passage metal plate 4 is bonded to the other side. Figure 2 shows a structure in which a non-cooling passage metal plate 3 is bonded to one side of the first ceramic substrate 2, a cooling passage metal plate 4 is bonded to the other side, one side of the second ceramic substrate 7 is bonded to the cooling passage metal plate 4, and a non-cooling passage metal plate 8 is bonded to the other side of the second ceramic substrate 7. Although not shown, a structure in which cooling passage metal plates 4 are provided on both sides of the first ceramic substrate 2 is also possible. In that case, through holes may be provided in the first ceramic substrate 2 to connect the cooling passage portions of the front and back cooling passage metal plates 4 via the through holes.

[0015] Examples of ceramic substrates 2 and 7 include silicon nitride substrates, aluminum nitride substrates, alumina substrates, zirconia substrates, and algil substrates. Algil substrates are ceramic sintered bodies made by mixing alumina and zirconia.

[0016] The thickness T1 of the first ceramic substrate 2 and the thickness T3 of the second ceramic substrate 7 are preferably within the range of 0.2 mm or more and 4 mm or less. If the thicknesses T1 and T3 of the ceramic substrates 2 and 7 are less than 0.2 mm, the strength may be insufficient. Further, if the thicknesses T1 and T3 of the ceramic substrates 2 and 7 exceed 4 mm, the heat dissipation may decrease. Therefore, the thicknesses T1 and T3 of the ceramic substrates 2 and 7 are 0.2 mm or more and 4 mm or less. Further, when the ceramic substrates 2 and 7 are silicon nitride substrates or aluminum oxide substrates, the thicknesses T1 and T3 are preferably within the range of 0.2 mm or more and 1 mm or less. In the case shown in FIG. 2, the thickness T1 of the first ceramic substrate 2 and the thickness T3 of the second ceramic substrate 7 may be the same or different.

[0017] The silicon nitride substrate as the ceramic substrates 2 and 7 preferably has a three-point bending strength of 600 MPa or more. Further, the thermal conductivity is preferably 80 W / m·K or more. By increasing the strength of the silicon nitride substrate, the substrate thickness can be reduced. For this reason, the three-point bending strength of the silicon nitride substrate is preferably 600 MPa or more, and more preferably 700 MPa or more. The silicon nitride substrate can be made thinner to 2 mm or less, and more preferably 0.40 mm or less in terms of substrate thickness.

[0018] The aluminum nitride substrate as the ceramic substrates 2 and 7 has a three-point bending strength of about 300 to 450 MPa. On the other hand, the thermal conductivity of the aluminum nitride substrate is 160 W / m·K or more. Since the aluminum nitride substrate has low strength, the substrate thickness is preferably 0.60 mm or more.

[0019] The aluminum oxide substrate as the ceramic substrates 2 and 7 has a three-point bending strength of about 300 to 450 MPa, but is inexpensive. Further, the aldyl substrate has a relatively high three-point bending strength of about 550 MPa, but the thermal conductivity is about 30 to 50 W / m·K.

[0020] Incidentally, the ceramic substrates 2 and 7 are preferably silicon nitride substrates. This is because silicon nitride substrates have high strength, enabling them to be made thinner. Also, by using a silicon nitride substrate with a thermal conductivity of 80 W / m·K or more, heat dissipation can be improved.

[0021] The metal plates, namely, the non-cooling path metal plates 3 and 8 and the cooling path metal plate 4, include one or more selected from copper plates, copper alloy plates, aluminum plates, and aluminum alloy plates. As the metal plate, a copper plate is preferred. Furthermore, it is more preferable that the copper plate is an oxygen-free copper plate. Oxygen-free copper has a copper purity of 99.96 wt% or more as shown in JIS-H-3100. The thermal conductivity of copper is approximately 400 W / m·K, and the thermal conductivity of aluminum is approximately 240 W / m·K. Since copper has a higher thermal conductivity than aluminum, heat dissipation is improved. Also, it is preferable that the aluminum plate is pure aluminum. Pure aluminum is shown in JIS-H-4000. The aluminum plate is suitable for weight reduction. Note that JIS-H-4000 corresponds to ISO6361. Also, JIS-H-3100 corresponds to ISO197 etc.

[0022] By providing a cooling path portion 5 (shown in FIG. 3) in the metal plate joined to the ceramic substrates 2 and 7, it is possible to reduce the number of components such as a heat sink for dissipating heat generated from the semiconductor element.

[0023] Also, in the ceramic circuit board 1 according to the embodiment, the thickness T1 of the first ceramic substrate 2 is smaller than the thickness T2 of the cooling path metal plate 4. That is, the ceramic circuit board 1 satisfies T1 < T2. Also, it is preferable that the thickness T3 of the second ceramic substrate 7 of the ceramic circuit board 1 is also smaller than the thickness T2 of the cooling path metal plate 4. That is, it is preferable that the ceramic circuit board 1 satisfies T3 < T2. Let the thickness of the first ceramic substrate 2 be T1, the thickness of the cooling path metal plate 4 be T2, and the thickness of the second ceramic substrate 7 be T3.

[0024] The cooling path metal plate 4 dissipates heat by allowing a cooling medium such as cooling water to flow through or come into contact with the cooling path portion 5 (shown in FIG. 3). By setting T1 < T2, the heat dissipation performance of the cooling path metal plate 4 can be improved. Also, by setting T3 < T2, the heat dissipation performance of the cooling path metal plate 4 can be improved. As will be described later, the non-cooling path metal plate 3 or the non-cooling path metal plate 8 can be used for the circuit portion on which the semiconductor element is mounted. Comparing the ceramic substrate and the metal plate, the metal plate has a higher thermal conductivity. By setting T1 < T2, the heat dissipation performance can be improved. Similarly, the heat dissipation performance can also be improved for T3 < T2. Note that at least one of the non-cooling path metal plate 3 and the non-cooling path metal plate 8 may be replaced with a cooling path metal plate, and the cooling path metal plate may be used for the circuit portion on which the semiconductor element is mounted.

[0025] Also, it is preferable that the ratio of the thickness T2 of the cooling path metal plate 4 to the thickness T1 of the first ceramic substrate 2, that is, T2 / T1, is within the range of 2 or more and 40 or less. Also, it is preferable that the ratio of the thickness T2 of the cooling path metal plate 4 to the thickness T3 of the second ceramic substrate 7, that is, T2 / T3, is within the range of 2 or more and 20 or less. By satisfying either or both of 2 ≤ T2 / T1 ≤ 40 or 2 ≤ T2 / T3 ≤ 40, it is possible to achieve both heat dissipation performance and warpage suppression.

[0026] Conventionally, as in Patent Document 2, a ceramic circuit board and a heat sink having a cooling path portion were provided separately. Since the ceramic circuit board 1 according to the embodiment has a cooling path structure provided in the metal plate 4 joined to the ceramic substrates 2 and 7, it can also be configured without using a heat sink. Therefore, the effect of reducing the number of components as a semiconductor device can also be obtained.

[0027] Furthermore, the thickness T2 of the cooling passage metal plate 4 is preferably 1 mm or more. Making the thickness T2 of the cooling passage metal plate 4 1 mm or more makes it easier to form the cooling passage portion 5 in the metal plate 4. There is no particular upper limit to the thickness T2 of the cooling passage metal plate 4, but it is preferably 20 mm or less. If it is thicker than 20 mm, it may lead to an increase in the size of the ceramic circuit board 1. For this reason, the thickness T2 is preferably 1 mm or more and 20 mm or less, and furthermore, if the ceramic substrates 2 and 7 are silicon nitride substrates, the thickness T2 is preferably 3 mm or more and 10 mm or less.

[0028] Furthermore, the thickness of the uncooled path metal plate 3 is set to T4, and the thickness of the uncooled path metal plate 8 is set to T5. The thicknesses T4 and T5 of the uncooled path metal plates 3 and 8 may be the same or different, but it is preferable that each be 0.2 mm or more. The uncooled path metal plates 3 and 8 form the circuit portion on which semiconductor elements are mounted. Also, the uncooled path metal plates 3 and 8 are metal plates that do not have a cooling path portion 5. By making the metal plates thicker, current conductivity and heat dissipation can be provided. Furthermore, there is no particular upper limit to the thickness of the uncooled path metal plates 3 and 8, but it is preferable that they be 10 mm or less. If the thickness of the uncooled path metal plates 3 and 8 exceeds 10 mm, it may lead to an increase in the size of the ceramic circuit board 1. Also, it may become difficult to form the circuit shape. Figures 1 and 2 illustrate a case in which one uncooled path metal plate 3 is bonded to one side of the first ceramic substrate 2, and one uncooled path metal plate 8 is bonded to one side of the second ceramic substrate 7. However, the ceramic circuit board 1 according to this embodiment is not limited to this form, and a plurality of uncooled path metal plates 3 (Figure 4 shows the joining of three uncooled path metal plates 3) may be provided on one side of the ceramic substrates 2, 7. In other words, circuit shapes may be given to the uncooled path metal plates 3, 8.

[0029] Furthermore, the thickness T2 of the cooling passage metal plate 4 relative to the thickness T4 of the non-cooling passage metal plate 3, i.e., T2 / T4, is preferably within the range of 0.5 to 50. By reducing the difference between the thickness T2 of the cooling passage metal plate 4 and the thickness T4 of the non-cooling passage metal plate 3 to a certain extent, such that 0.5 ≤ T2 / T4 ≤ 50, the effect of suppressing warping of the ceramic circuit board 1 can be obtained.

[0030] Furthermore, as shown in Figure 2, it is preferable that the ceramic circuit board 1 includes a second ceramic substrate 7 and a non-cooled passage metal plate 8. The ceramic circuit board 1 shown in Figure 2 has a structure in which ceramic substrates are bonded to both sides of the cooling passage metal plate 4. By bonding ceramic substrates 2 and 7 to both sides of the cooling passage metal plate 4, the flatness of the ceramic circuit board 1 can be improved. The flatness of the ceramic circuit board 1 is indicated by the difference between the highest and lowest points on the surface of the non-cooled passage metal plate 3. Similarly, it is indicated by the difference between the highest and lowest points on the surface of the non-cooled passage metal plate 8. By using a structure in which ceramic substrates 2 and 7 are bonded to both sides of the cooling passage metal plate 4, the flatness can be reduced to 1.0 mm or less. In addition, the flatness can also be improved by using a silicon nitride substrate. Flatness can be measured using a three-dimensional shape measuring machine. Flatness indicates the difference between the highest and lowest points of the metal plate. For example, the highest and lowest points of the cooling passage metal plate 4 are measured, and the difference is taken as the flatness.

[0031] Furthermore, similar to the ratio of the thickness T2 of the cooling passage metal plate 4 to the thickness T4 of the non-cooled passage metal plate 3, the ratio T2 of the thickness T2 of the cooling passage metal plate 4 to the thickness T5 of the non-cooled passage metal plate 8, i.e., T2 / T5, is preferably within the range of 0.5 to 50. By reducing the difference between the thickness T2 of the cooling passage metal plate 4 and the thickness T5 of the non-cooled passage metal plate 8 to a certain extent, and setting 0.5 ≤ T2 / T5 ≤ 50, the effect of suppressing warping of the ceramic circuit board 1 can be obtained.

[0032] The cooling passage metal plate 4 has a cavity because it is provided with a cooling passage section 5. Therefore, the cooling passage metal plate 4 is prone to distortion. By providing ceramic substrates 2 and 7 and metal plates 3 and 8 on both sides of the cooling passage metal plate 4, distortion of the cooling passage metal plate 4 can be suppressed. By suppressing distortion of the cooling passage metal plate 4, the mountability of the semiconductor element 11 can be improved.

[0033] Furthermore, the cooling passage metal plate 4 may have the inlet 5A and outlet 5B of the cooling passage 5 on the same side of the cooling passage metal plate 4 (as shown in Figure 3), or on different sides of the cooling passage metal plate 4 (as shown in Figure 4). The positions of the inlet 5A and outlet 5B of the cooling passage 5 shall be determined according to the location where the semiconductor device 12 is installed and the mechanism for introducing cooling water. In addition, it is preferable that the cooling passage 5 of the cooling passage metal plate 4 has a plurality of bent portions (for example, folded portions 9). In particular, when the inlet 5A and outlet 5B of the cooling passage 5 are provided on the same side of the cooling passage metal plate 4 (as shown in Figure 3), it is preferable that it has folded portions 9.

[0034] Figures 3 and 4 show an example of a cooling passage. In the figures, reference numeral 4 denotes a cooling passage metal plate, reference numeral 5 denotes a cooling passage section, reference numeral 5A denotes the inlet of the cooling passage section 5, reference numeral 5B denotes the outlet of the cooling passage section 5, reference numeral 9 denotes the folded-over section, and reference numeral 10 denotes the cover section. Figures 3 and 4 are schematic diagrams showing a cutaway model to explain the structure of the cooling passage section 5.

[0035] Various shapes can be applied to the flow path of the cooling passage section 5. The shape formed by the flow path of the cooling passage section 5 may be a curved shape with bent sections (for example, folded sections 9), as shown in Figure 3. The curved flow path may be a winding structure with multiple folded sections 9, as shown in Figure 3, or it may be a structure with bent sections such as U-shaped, V-shaped, W-shaped, or L-shaped. The flow path of the cooling passage section 5 may also be a straight shape, as shown in Figure 4. Multiple cooling passage sections 5 may be provided. A combination of curved and straight shapes may also be used. The cooling passage section 5 may also be a structure in which multiple cooling passages intersect. Furthermore, when considering the structure of a single cooling passage section 5, it may be a wave shape, not just a straight shape. The cooling passage section 5 may also have a fin structure or adopt a vapor chamber system.

[0036] Furthermore, the cooling passage 5 may have a structure that passes through a region of the cooling passage metal plate 4 that is close to the semiconductor element 11 mounted on the non-cooling passage metal plates 3 and 8, for example, a region directly beneath the semiconductor element 11. This allows for effective cooling of heat from the semiconductor element 11 and improves cooling efficiency.

[0037] The cooling passage metal plate 4 may have the inlet 5A and outlet 5B of the cooling passage 5 on the same side surface. In a structure where the inlet 5A and outlet 5B are on the same side surface of the cooling passage metal plate 4, even when the cooling passage 5 is laid across the entire surface of the cooling passage metal plate 4, the cooling passage 5 has a continuous structure with one inlet 5A and one outlet 5B connected. This makes it easier to manage the cooling medium. For example, if multiple linear cooling passages 5 are provided as shown in Figure 4, multiple inlets 5A and multiple outlets 5B are required. Therefore, the burden of managing the cooling medium increases when multiple inlets 5A and outlets 5B are formed. Also, when providing a cooling passage 5 directly beneath the mounting locations of multiple semiconductor elements, if the cooling passage 5 is a linear type as shown in Figure 4, multiple cooling passages 5 will be required.

[0038] As shown in Figure 3, a curved cooling passage 5 with one inlet 5A and one outlet 5B connected makes it easier to manage the cooling medium and increases the degree of freedom in the mounting location of semiconductor elements. For this reason, it is preferable to use a cooling passage 5 that has a folded portion 9. Also, in Figure 3, the left side of the paper is the inlet 5A and the right side is the outlet 5B, but it is not limited to this. Also, in Figure 4, the front of the paper is the inlet 5A and the back of the paper is the outlet 5B, but it is not limited to this. Note that in Figures 3 and 4, examples are shown where the cross-sections of the inlet 5A and outlet 5B are circular. However, the area around the inlet 5A and outlet 5B may have a rectangular or elliptical shape, not just a circular cross-section, and may also have various shapes such as U-shaped grooves or V-shaped grooves formed from one side or both sides. Note that, as shown in Figure 4, the inlet 5A and outlet 5B of the cooling passage 5 may be provided on different sides of the cooling passage metal plate 4.

[0039] The cooling passage section 5 formed in the cooling passage metal plate 4 may be formed on one or more of the following: one side, both sides, or inside the cooling passage metal plate 4. In the cooling passage section 5 shown in Figure 3, the cross section is formed internally so as to be circular near the inlet 5A and outlet 5B, while in the rest of the main body, a U-groove (a groove with a square cross section or a square with rounded corners at the bottom) is formed on one side. On the other hand, in the cooling passage section 5 shown in Figure 4, the cross section is formed internally so as to be circular. In other words, in the example in Figure 4, the cooling passage section 5 is formed by excavating a hole (tunnel) in the direction of the flow path from a circular cut on the side surface of the cooling passage metal plate 4.

[0040] A cooling passage section 5 formed on one side of the cooling passage metal plate 4 is created by forming a groove from one side of the cooling passage metal plate 4. Cooling passage sections 5 formed on both sides of the cooling passage metal plate 4 are created by forming grooves from both sides. When grooves are provided on both sides of the cooling passage metal plate 4, the front and back may have the same shape or different shapes. In addition, a cooling passage section 5 formed inside the cooling passage metal plate 4 is created by excavating a hole (tunnel) in the direction of the flow path from the side of the cooling passage metal plate 4. With a cooling passage section 5 excavated in this way, the front and back sides are not open, so it is possible to prevent the cooling medium from leaking out of the cooling passage section 5.

[0041] On the other hand, if a cooling passage 5 is provided by grooves carved from one or both sides of the cooling passage metal plate 4, the cooling medium may easily leak out of the cooling passage 5 because the front and back surfaces are not sealed. Therefore, if necessary, a metal plate may be joined to the cooling passage metal plate 4 as a cover portion 10 to cover the grooves formed in the cooling passage metal plate 4. To provide a cooling passage 5 with a folded portion 9, it is effective to groove one or both sides of the cooling passage metal plate 4. The cooling passage metal plate 4 may have insufficient bonding area with the ceramic substrate 2. In addition, by providing the cover portion 10, the flatness of the non-cooled passage metal plates 3 and 8 can be improved. The area of ​​the non-cooled passage metal plates 3 and 8 directly above the location where the cooling passage 5 is provided is prone to denting. Therefore, the flatness of the non-cooled passage metal plates 3 and 8 may decrease. By using the cover portion 10, the flatness of the non-cooled passage metal plates 3 and 8 can be improved.

[0042] Furthermore, by providing the cover portion 10 on the cooling passage metal plate 4, the bonding area with the ceramic substrate 2 can be secured. In other words, if the bonding area with the ceramic substrate 2 can be secured, the cover portion 10 does not need to be used. Figure 3 shows an example with the cover portion 10 provided. Figure 4 shows an example without the cover portion 10. When the cover portion 10 is provided, the sum of the thickness of the cooling passage metal plate 4 and the thickness of the cover portion 10 is defined as the thickness T2.

[0043] Furthermore, the ratio of the volume of the cooling passage section 5 to the total volume of the cooling passage metal plate 4 is preferably within the range of 10% to 80%. If the volume ratio of the cooling passage section 5 is less than 10%, the effect of providing the cooling passage section may be insufficient. Also, if the volume ratio of the cooling passage section 5 exceeds 80%, the strength of the cooling passage metal plate 4 may decrease. In addition, the bonding area between the ceramic substrates 2,7 and the cooling passage metal plate 4 may be insufficient. For this reason, the ratio of the volume of the cooling passage section 5 to the total volume of the cooling passage metal plate 4 is preferably within the range of 10% to 80%, and more specifically, within the range of 20% to 60%. If multiple cooling passage sections 5 are provided in the cooling passage metal plate 4, the ratio should be based on the total volume of the cooling passages.

[0044] Furthermore, the width of the cooling passage 5 in its cross-section is preferably 1 mm or more. If the cross-section of the cooling passage 5 is circular, the width of the cross-section of the cooling passage 5 refers to the length of the diameter of the cross-section of the cooling passage 5. If the cross-section of the cooling passage 5 is of any other shape, the width of the cross-section of the cooling passage 5 refers to the shortest length between opposing points in the cross-section of the cooling passage 5. If the width of the cooling passage 5 is less than 1 mm, the flow of the cooling medium may be impaired. Also, if the width of the cooling passage 5 is too narrow, it will put a load on the processing and reduce manufacturability. There is no particular upper limit to the width of the cooling passage 5, but it is preferably 10 mm or less. If the width of the cooling passage 5 exceeds 10 mm, it may impair flatness. For this reason, the width of the cooling passage 5 is preferably within the range of 1 mm to 10 mm, and more preferably between 2 mm and 8 mm.

[0045] Furthermore, it is preferable that the creepage distance of the cooling passage 5 be 1 mm or more. The creepage distance of the cooling passage 5 is the shortest distance from the cooling passage 5 to the edge of the cooling passage metal plate 4. If the creepage distance of the cooling passage 5 is less than 1 mm, even a slight expansion of the cooling passage 5 will reach the edge of the cooling passage metal plate 4, reducing the bonding area and potentially causing water leakage. For example, the ceramic substrate 2 and the cooling passage metal plate 4 are bonded using an activated metal bonding method. If the creepage distance is short, there is a possibility of water leakage if there are unbonded areas (voids, etc.) within the bonded layer. Unbonded areas may also be formed when thermal stress is applied, such as in a TCT test. In other words, durability can be improved by setting the creepage distance to 1 mm or more. For this reason, it is preferable that the creepage distance of the cooling passage be 1 mm or more, and more preferably 2 mm or more.

[0046] Furthermore, it is preferable to use an activated metal bonding method for joining the first ceramic substrate 2 to the metal plates 3 and 4, and for joining the second ceramic substrate 7 to the metal plates 4 and 8. The activated metal bonding method is a bonding method that uses one or more activated metals selected from Ti (titanium), Zr (zirconium), and Hf (hafnium). It uses an activated metal brazing material that has copper (Cu) or silver (Ag) as its main component and contains activated metals. The main component here refers to the component that is present in the largest amount among the metal components of the brazing material. When the activated metal bonding method is used, the ceramic substrate 2 and the metal plates 3 and 4 are joined via the activated metal bonding layer, and the second ceramic substrate 7 and the metal plates 4 and 8 are joined.

[0047] Furthermore, the active metal brazing material composition preferably contains 0% to 60% by mass of Ag (silver), 15% to 70% by mass of Cu (copper), and 1% to 15% by mass of Ti (titanium) or TiH2 (titanium hydride). When both Ti and TiH2 are used, the total amount should be within the range of 1% to 15% by mass. When both Ag and Cu are used, it is preferable that Ag be within the range of 20% to 60% by mass and Cu be within the range of 15% to 40% by mass.

[0048] Furthermore, if necessary, one or two of Sn (tin) or In (indium) may be included in an amount of 1% to 50% by mass. The Ti or TiH2 content is preferably in the range of 1% to 15% by mass. Furthermore, if necessary, C (carbon) may be included in an amount of 0.1% to 2% by mass. Additionally, the active metal brazing material may contain one or more selected from tungsten (W), molybdenum (Mo), and rhenium (Re) in an amount of 0.1% to 10% by mass. Carbon, tungsten, molybdenum, and rhenium can control the fluidity of the active metal brazing material.

[0049] The ratio of the active metal brazing material composition shall be calculated by considering the total value of the raw materials to be mixed as 100% by mass. For example, if it is composed of three types of materials, Ag, Cu, and Ti, then Ag + Cu + Ti = 100% by mass. If it is composed of four types of materials, Ag, Cu, TiH2, and In, then Ag + Cu + TiH2 + In = 100% by mass. If it is composed of five types of materials, Ag, Cu, Ti, Sn, and C, then Ag + Cu + Ti + Sn + C = 100% by mass.

[0050] Ag or Cu are the base material components of the brazing material. Sn or In have the effect of lowering the melting point of the brazing material. C (carbon) has the effect of controlling the fluidity of the brazing material and controlling the structure of the bonded layer by reacting with other components. For this reason, possible components of the brazing material include Ag-Cu-Ti, Ag-Cu-Sn-Ti, Ag-Cu-Ti-C, Ag-Cu-Sn-Ti-C, Ag-Ti, Cu-Ti, Ag-Sn-Ti, Cu-Sn-Ti, Ag-Ti-C, Cu-Ti-C, Ag-Sn-Ti-C, and Cu-Sn-Ti-C. In may also be used instead of Sn. In addition, both Sn and In may be used.

[0051] The above-mentioned activated metal brazing material is effective for joining copper plates. Furthermore, it is preferable that the metal part is a copper component, and that the ceramic substrates 2 and 7 and the copper component are joined via an Ag-free bonding layer. An Ag-free bonding layer means using an activated metal brazing material that does not contain added Ag. The amount of Ag as an unavoidable impurity may be 0.01% by mass or less (including zero). By using an Ag-free bonding layer, the occurrence of Ag ion migration can be suppressed. Ag ion migration is a phenomenon in which Ag in the bonding layer ionizes and moves when a voltage is applied in a humid environment. Ag ions move and precipitate in other locations. This causes insulation failure. Among activated metal brazing materials, Ag is the most likely to cause ion migration. By not using Ag in the bonding layer, Ag ion migration can be suppressed.

[0052] Furthermore, when metal plates 3, 4, and 8 are aluminum plates, it is preferable to use Al-Si or AlMg type brazing materials as the active metal brazing material. The content of one or two of Si or Mg in the active metal brazing material is preferably in the range of 0.1% by mass or more and 20% by mass or less. The activated metal bonding method can increase the bonding strength between the ceramic substrates 2 and 7 and the metal plates 3, 4, and 8. Therefore, when the cooling channel metal plate 4 is bonded to the ceramic substrates 2 and 7 on one or both sides, airtightness can be ensured.

[0053] The ceramic circuit board 1 described above can be used in a semiconductor device on which semiconductor elements are mounted. Figure 5 shows an example of a semiconductor device according to the embodiment. Figure 5 illustrates a case in which the semiconductor device according to the embodiment has an inlet 5A and an outlet 5B on the same side surface of the cooling passage metal plate 4. Cases in which the inlet 5A and outlet 5B are on different side surfaces of the cooling passage metal plate 4 are not illustrated, but are equivalent to Figure 5, so no explanation is given. In the figure, reference numeral 1 denotes a ceramic circuit board, reference numeral 11 denotes a semiconductor element, and reference numeral 12 denotes a semiconductor device. In Figure 5, a case in which semiconductor elements 11 are mounted on both sides is illustrated, but semiconductor elements 11 may be mounted on only one side. Furthermore, multiple semiconductor elements 11 may be mounted on one side. Bonding wires, lead frames, etc., which are not shown, may also be provided.

[0054] A cooling medium is introduced from the inlet 5A of the cooling passage 5 of the semiconductor device 12. Examples of cooling mediums include cooling water and cooling gas. By introducing the cooling medium from the inlet 5A to the outlet 5B of the cooling passage 5, a semiconductor device 12 with high cooling efficiency can be achieved. Furthermore, since a cooling passage metal plate 4 is provided on the back surface of the ceramic substrate 2, the semiconductor device 12 can be made thinner. Thus, both cooling efficiency and thinness can be achieved.

[0055] Furthermore, the ceramic circuit board 1 according to this embodiment can be mounted in a power module without using a heat sink. In other words, the ceramic circuit board 1 can be directly mounted to the mounting board (or base plate). Since a heat sink is not required, this is effective in reducing the number of components.

[0056] Conventionally, ceramic circuit boards are installed on a cooler provided on the power module side via a TIM (Thermal Interface Material) layer. With the ceramic circuit board 1 according to this embodiment, it is possible to mount it to the cooling passage metal plate 4 without providing a TIM layer. Examples of TIM layers include thermal grease. In other words, it is also possible to mount the ceramic circuit board without providing grease between the ceramic circuit board and the mounting board. Not having to use a TIM layer is also effective in reducing the number of components.

[0057] Figure 6 illustrates a structure in which a ceramic circuit board 1 is mounted on a mounting board. In the figure, reference numeral 1 denotes a ceramic circuit board, reference numeral 8 denotes a metal plate (back metal plate), reference numeral 11 denotes a semiconductor element, reference numeral 12 denotes a semiconductor device, reference numeral 13 denotes a mounting board, and reference numeral 14 denotes a power module. The ceramic circuit board 1 on which the semiconductor element 11 is mounted becomes a semiconductor device 12. Furthermore, when the semiconductor device 12 is mounted on the mounting board 13, it becomes a power module 14.

[0058] Conventionally, a thermal grease layer was provided between the ceramic circuit board and the heat sink, or between the ceramic circuit board and the mounting board. Thermal grease is made by adding fillers to silicone resin, etc. Its thermal conductivity is about 1 to 2 W / m·K. By using grease, which has a lower thermal conductivity than the ceramic substrate or metal plate, it becomes more difficult for heat to dissipate from the semiconductor element. The ceramic circuit board 1 according to this embodiment has a cooling passage 5, so the heat dissipation of the ceramic circuit board 1 itself is good. For this reason, it is possible to attach the ceramic circuit board 1 to the mounting board 13 without using thermal grease between the non-cooled passage metal plate 8 and the mounting board 13. Note that a structure that does not use a heat sink is sometimes called a heat sink-less structure. Also, a structure that does not use grease is sometimes called a grease-less structure. Attachment to the mounting board 13 may be done using screws or other methods as needed. Molding resin may also be provided as needed.

[0059] The above examples illustrate structures without heat sinks or grease, but these may be used as needed. This demonstrates that it is possible to implement solutions even without heat sinks or grease. Furthermore, if the ceramic circuit board 1 has the shape shown in Figure 1, the cooling passage metal plate 4 may be attached to the mounting board 13. Furthermore, the method of using the semiconductor device 12 according to this embodiment involves controlling the temperature by circulating or bringing a cooling medium into contact with the cooling passage 5. This allows for efficient dissipation of heat generated during the operation of the semiconductor device.

[0060] (Examples) (Examples 1-8) For the ceramic circuit board 1 according to Examples 1 to 8, silicon nitride substrates, aluminum oxide substrates, and aluminum nitride substrates were prepared as ceramic substrates 2. The silicon nitride substrate had a thermal conductivity of 90 W / m·K, a three-point bending strength of 650 MPa, and dimensions of 100 mm x 90 mm. The aluminum oxide substrate had a thermal conductivity of 20 W / m·K, a three-point bending strength of 430 MPa, and dimensions of 100 mm x 90 mm. The aluminum nitride substrate had a thermal conductivity of 170 W / m·K, a three-point bending strength of 400 MPa, and dimensions of 100 mm x 90 mm. A copper plate was also prepared as the metal plate. The copper plate was an oxygen-free copper plate. The ceramic circuit board 1 according to Examples 1 to 7 includes a second ceramic substrate 7, as shown in Figure 2. On the other hand, the ceramic circuit board 1 according to Example 8 does not include a second ceramic substrate 7 and a non-cooled path metal plate 8, as shown in Figure 1.

[0061] A ceramic substrate 2 and a copper plate were joined using an activated metal brazing method. An Ag-Cu-Sn-Ti type brazing material was used as the activated metal brazing material.

[0062] Table 1 shows the thickness of the copper plates corresponding to the non-cooled path metal plate 3, the cooled path metal plate 4, and the non-cooled path metal plate 8, as well as the thickness of the ceramic substrate 2, in the ceramic circuit board 1 according to Examples 1 to 7. Table 2 shows the length and width dimensions of the non-cooled path metal plate 3, the cooled path metal plate 4, and the non-cooled path metal plate 8. The non-cooled path metal plate 3 is referred to as the front metal plate, and the non-cooled path metal plate 8 is referred to as the back metal plate. Table 3 shows the shape of the cooling path portion 5 provided in the copper plate corresponding to the cooled path metal plate 4. The ceramic circuit board 1 in Examples 1 to 7 has the structure shown in Figure 2.

[0063] Furthermore, a ceramic circuit board 1 with the structure shown in Figure 1 was fabricated as part of Example 8. The ceramic circuit board 1 consists of a silicon nitride substrate with a front metal plate on the surface and a cooling channel metal plate 4 on the back surface, bonded using an activated metal bonding method. The non-cooling channel metal plate 3 is also referred to as the front metal plate. Both the front metal plate and the cooling channel metal plate 4 were made of copper (oxygen-free copper).

[0064] [Table 1]

[0065] [Table 2]

[0066] [Table 3]

[0067] Table 2 shows the dimensions of the front and back metal plates, indicated as length mm × width mm. The cooling passage metal plate 4 has a groove formed on one side. The lid 10 is made of 0.3 mm thick copper plate. The curved cooling passage 5 has one inlet 5A and one outlet 5B. The straight cooling passage 5 has multiple passages so that the volume ratio is a predetermined value. In all cases, the width of the cooling passage 5 is within the range of 1 mm to 10 mm. The creepage distance of the cooling passage 5 is 1 mm or more.

[0068] The flatness of the ceramic circuit boards 1 according to Examples 1 to 8 was investigated. The flatness of the front metal plate and the back metal plate was measured. In the ceramic circuit boards 1 according to Examples 1 to 7, the flatness of the uncooled path metal plate 3 as the front metal plate and the uncooled path metal plate 8 as the back metal plate was measured. On the other hand, in the ceramic circuit board 1 according to Example 8, the flatness of the uncooled path metal plate 3 as the front metal plate and the cooled path metal plate 4 was measured. The difference between the highest and lowest points on the surface of the front metal plate was measured using a 3D shape measuring machine. The same measurement was performed for the back metal plate. The results are shown in Table 4.

[0069] [Table 4]

[0070] As shown in Table 4, in the ceramic circuit boards 1 according to Examples 1 to 8, the metal plates all had a flatness of 1.5 mm or less, thus ensuring sufficient flatness. Of Examples 1 to 8, in the ceramic circuit boards 1 according to Examples 1 to 6, the flatness of both the front and back metal plates was 1.0 mm or less. Furthermore, in the ceramic circuit boards 1 according to Examples 2, 3, and 5, which used the lid portion 10, the flatness of both the front and back metal plates was small, at 0.4 mm or less. In addition, in the ceramic circuit boards 1 according to Examples 2 and 3, which used a silicon nitride substrate and the lid portion 10, the flatness of the front and back metal plates was even smaller, at 0.2 mm or less.

[0071] On the other hand, in Example 7, the flatness of both the front and back metal plates exceeded 1.0 mm. In the ceramic circuit board 1 according to Example 7, the thickness of the cooling passage metal plate 4 was thin, resulting in greater distortion of the ceramic circuit board 1. Furthermore, the ceramic circuit board 1 according to Example 8 has a structure that does not use the second ceramic substrate 7. In this case, the flatness of the front metal plate was good. On the other hand, the flatness of the cooling passage metal plate 4 exceeded 1.0 mm. Therefore, it can be seen that the flatness of the metal plates is better when the second ceramic substrate is used.

[0072] Next, the cooling efficiency was investigated. A semiconductor device 12 was fabricated by mounting semiconductor elements 11 on a ceramic circuit board 1 according to Examples 1 to 8. Next, a semiconductor device 12 according to Examples 1 to 8 was fabricated by attaching it to a mounting board via grease (hereinafter referred to as semiconductor device A). The grease was applied to a thickness of 0.7 mm. In addition, a semiconductor device 12 according to Examples 1 to 8 was fabricated by attaching it to a mounting board without using grease (hereinafter referred to as semiconductor device B). Each semiconductor device A and B was energized, and the temperature rise after reaching a steady state was measured. During temperature measurement, cooling water was flowed through the cooling passage 5 as a cooling medium. Five of each device were fabricated, and the lower and upper limits of the temperature rise were recorded. The results are shown in Table 5.

[0073] [Table 5]

[0074] As can be seen from Table 5, the ceramic circuit board 1 according to Examples 1 to 8 has improved cooling efficiency because it is provided with a cooling passage 5. Furthermore, the ceramic circuit board 1 according to Examples 1 to 8 does not require the use of a heat sink or water cooling sink, as described in Patent Document 2. Therefore, it is possible to make the semiconductor device thinner. In addition, since a separate heat sink or water cooling sink is not required, the thermal resistance can be reduced. Moreover, it could be used even without grease. Accordingly, the ceramic circuit board according to Examples 1 to 8 can improve cooling efficiency.

[0075] As described above, the ceramic circuit board 1 according to the embodiment can provide a ceramic circuit board that improves the cooling efficiency of the semiconductor element 11 and has good manufacturability.

[0076] Although several embodiments of the present invention have been illustrated above, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. Modifications of these embodiments are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. Furthermore, the embodiments described above can be implemented in combination with each other.

Claims

1. A semiconductor device comprising a ceramic circuit board consisting of a ceramic substrate and copper plates bonded to both sides of the ceramic substrate, The ceramic circuit board is such that a copper plate bonded to one of the two surfaces of the ceramic substrate is a cooling-pass copper plate having a cooling passage portion with a plurality of folded portions, and a copper plate bonded to the other surface is a non-cooling-pass copper plate that does not have the cooling passage portion. The thickness of the cooling path copper plate of the ceramic circuit board is 1 mm or more and 20 mm or less. A semiconductor device characterized in that a semiconductor element is mounted on the uncooled copper plate of the ceramic circuit board.

2. The semiconductor device according to claim 1, characterized in that the thickness of the ceramic substrate is smaller than the thickness of the cooling path copper plate.

3. The ceramic substrate comprises a first ceramic substrate and a second ceramic substrate bonded to the cooling passage copper plate bonded to the first ceramic substrate. One side of the second ceramic substrate is bonded to the cooling passage copper plate which is bonded to the first ceramic substrate. The semiconductor device according to claim 1, characterized in that the uncooled copper plate is bonded to the other surface of the second ceramic substrate.

4. The semiconductor device according to claim 1, characterized in that the inlet and outlet of the cooling passage portion of the cooling passage copper plate are provided on the same side surface of the cooling passage copper plate.

5. The semiconductor device according to claim 1, characterized in that the ceramic substrate is a silicon nitride substrate.

6. The semiconductor device according to claim 1, characterized in that the space between the ceramic substrate and the cooling path copper plate and the space between the ceramic substrate and the non-cooling path copper plate are joined via an active metal junction layer.

7. The semiconductor device according to claim 1, characterized in that the thickness of the ceramic substrate is smaller than the thickness of the cooling path copper plate.

8. A semiconductor device according to any one of claims 1 to 7, A mounting board or base plate attached to the ceramic circuit board of the semiconductor device, A power module equipped with [a specific feature / feature].

9. The semiconductor device has a structure in which the mounting board or the base plate is directly attached to the ceramic circuit board without a heat sink. The power module according to claim 8.

10. The structure is such that no grease is used between the ceramic circuit board and the mounting board or the base plate. The power module according to claim 9.

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