Ceramic circuit substrates and semiconductor modules

Abstract

A ceramic circuit substrate, comprising: a ceramic substrate having a thickness of 1.0 mm or less, the ceramic substrate having a first surface and a second surface, the first surface including a first region and a second region; a first metal plate bonded to the first region; and a second metal plate bonded to the second surface. A first waviness curve of the second region measured along a first side of the first surface has one or less extreme values. A second waviness curve of the second region measured along a second side of the first surface has two to three extreme values.

Description

[0001] This application is a divisional application of Chinese patent application No. 201780042696.6, which entered the Chinese national phase of PCT / JP2017 / 025729 with an application date of July 14, 2017. Technical Field

[0002] Embodiments relate to a ceramic circuit substrate and a semiconductor module. Background Art

[0003] In recent years, with the improvement of the performance of industrial equipment, the power modules installed therein have been increasing in output. With this, the output of semiconductor devices has also been developing. The guaranteed operating temperature of semiconductor devices is, for example, 125°C to 150°C. It is predicted that the guaranteed operating temperature will rise to 175°C or more in the future.

[0004] As the operating temperature of semiconductor devices increases, ceramic circuit boards are required to have thermal cycle test (TCT) characteristics. In TCT, the durability of ceramic circuit boards is measured with low temperature → room temperature → high temperature → room temperature as one cycle.

[0005] A ceramic circuit substrate having no voids in the solder protrusion is disclosed. A ceramic circuit substrate having a silicon nitride substrate has shown durability of 5000 cycles. By eliminating the voids in the solder protrusion, the TCT characteristics can be improved. However, it is predicted that the operation guarantee temperature will reach 175°C or more as the performance of semiconductor devices increases.

[0006] On the other hand, in order to increase the current carrying capacity (current carrying capacity) as the performance of semiconductor devices improves, the use of large external terminals is being studied. It is known that the thickness of the joint portion of the conventional external terminal is set to 3 mm or more.

[0007] External terminals have various shapes such as lead frames and pins. In order to increase the current carrying capacity, it is effective to use a relatively thick lead frame instead of a thin wire such as a bonding wire. However, if a thick lead frame is used, the ceramic circuit substrate may be greatly bent. If the ceramic circuit substrate is bent, it is easy to cause poor installation when it is installed in the heat dissipation component. In addition, it is difficult to obtain good characteristics when a ceramic circuit substrate with pins (lead terminals) is subjected to TCT at a high temperature of 175°C. This is because: the thicker the lead frame, the higher the stress applied to the ceramic circuit substrate. Therefore, a ceramic circuit substrate that does not bend even when a thick lead frame is bonded to the terminal and has good TCT characteristics is required.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: International Publication No. 2011 / 034075

[0011] Patent Document 2: Japanese Patent Application Publication No. 2004-134703 Summary of the invention

[0012] A ceramic circuit substrate of an embodiment includes: a ceramic substrate having a thickness of 1.0 mm or less, the ceramic substrate having a first surface and a second surface, the first surface including a first region and a second region; a first metal plate bonded to the first region; and a second metal plate bonded to the second surface. A first waviness curve of the second region measured along a first side of the first surface has one or less extreme values. A second waviness curve of the second region measured along a second side of the first surface has two to three extreme values. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a top view showing an example of a ceramic circuit substrate.

[0014] Figure 2 This is a side view showing another example of the ceramic circuit substrate.

[0015] Figure 3 This is a diagram showing an example of a waviness curve.

[0016] Figure 4 This is a diagram showing another example of the waviness curve.

[0017] Figure 5 This is a diagram showing another example of the waviness curve.

[0018] Figure 6 This is a diagram showing an example of the arrangement structure of the metal plates.

[0019] Figure 7 This is a side view showing an example of a ceramic circuit substrate with pins.

[0020] Figure 8 This is a side view showing an example of a semiconductor module.

[0021] Fig. 9 It is a diagram showing an example of the shape of the metal plate side surface and the joining layer. DETAILED DESCRIPTION

[0022] Figure 1 An example of the upper surface of the ceramic circuit board according to the embodiment is shown. Figure 2 An example of a side surface of the ceramic circuit board according to the embodiment is shown. Figure 1The figure shows a ceramic circuit substrate 1, a ceramic substrate 2, metal plates (front metal plate 3, back metal plate 4), the length L1 of the long side of the ceramic substrate 2, the length L2 of the short side of the ceramic substrate 2, and a measurement position W of the waviness curve. Figure 1 and Figure 2 , an example in which a ceramic circuit substrate 1 has two surface metal plates 3 and one back metal plate 4 is shown. The structure of the ceramic circuit substrate of the embodiment is not limited to the above structure, for example, the ceramic circuit substrate 1 may also have one surface metal plate 3 or three or more surface metal plates 3. Similarly, the ceramic circuit substrate 1 may also have two or more back metal plates 4.

[0023] The ceramic substrate 2 has a surface 2a and a surface 2b facing each other. The surface 2a and the surface 2b extend in a first direction and a second direction, respectively. The second direction intersects the first direction. When the surface 2a and the surface 2b are each a rectangular surface, for example, the first direction is, for example, the long side direction of the rectangle, and the second direction is, for example, the short side direction of the rectangle.

[0024] The surface 2a includes an area 21 for receiving the surface metal plate 3 and an area 22 around the area 21. The area 22 extends from the area 21 to the end of the surface 2a, for example. In addition, when a plurality of surface metal plates 3 are bonded to the ceramic substrate 2, the area 22 may also include the area between the plurality of surface metal plates 3. The surface 2b may also have an area 23 for receiving the back metal plate 4 and an area 24 around the area 23. The area 23 extends from the area 23 to the end of the surface 2b, for example. In addition, when a plurality of back metal plates 4 are bonded to the ceramic substrate 2, the area 24 may also include the area between the plurality of back metal plates 4.

[0025] The thickness of the ceramic substrate 2 is preferably 1.0 mm or less. If the thickness of the ceramic substrate 2 exceeds 1.0 mm, it becomes difficult to achieve a specified waviness curve. By reducing the thickness of the ceramic substrate 2, it is easy to achieve a specified waviness curve. The three-point bending strength of the ceramic substrate 2 is preferably 500 MPa or more. By using a ceramic substrate having a three-point bending strength of 500 MPa or more, the thickness of the substrate can be thinned to less than 0.4 mm. Examples of ceramic substrates having a three-point bending strength of 500 MPa or more include silicon nitride substrates. Examples of the above-mentioned ceramic substrates include high-strength aluminum nitride substrates, high-strength alumina substrates, and high-strength alumina substrates containing zirconium oxide.

[0026] As a ceramic substrate, a silicon nitride substrate is particularly preferred. The three-point bending strength of a common aluminum nitride substrate and an aluminum oxide substrate is about 300 to 450 MPa. For a substrate with a strength lower than 500 MPa, if the thickness is reduced to less than 0.4 mm, the TCT characteristics are reduced. In particular, when the temperature in the high temperature state of TCT is increased to above 175°C, the durability is reduced. As a silicon nitride substrate, there are high-strength silicon nitride substrates with a three-point bending strength of more than 500 MPa, and further more than 600 MPa. As a silicon nitride substrate, there are silicon nitride substrates with a thermal conductivity of more than 50 W / m·K, and further more than 80 W / m·K. In recent years, there are also silicon nitride substrates that have both high strength and high thermal conductivity. If it is a silicon nitride substrate with a three-point bending strength of more than 500 MPa and a thermal conductivity of more than 80 W / m·K, the substrate thickness can also be reduced to less than 0.33 mm. The three-point bending strength was measured in accordance with JIS-R-1601, and the thermal conductivity was measured in accordance with JIS-R-1611.

[0027] The surface metal plate 3 is joined to the region 21. The back metal plate 4 is joined to the region 23. That is, the region 21 represents the region joined to the surface metal plate 3 in the surface 2a. The region 23 represents the region joined to the back metal plate 4 in the surface 2b. The surface metal plate 3 and the back metal plate 4 preferably contain copper, aluminum or an alloy with them as the main component. These metal plates are easy to use in circuits because of their low resistance. In addition, the thermal conductivity of copper and aluminum is high, which is 398W / m·K and 237W / m·K respectively. Therefore, the heat dissipation can be improved. It is preferred to effectively utilize these characteristics and set the thickness of the metal plate (the surface metal plate 3 and the back metal plate 4) to 0.6mm or more, and further preferably to 0.8mm or more. By thickening the metal plate, it is possible to achieve both ensuring the conduction capacity and improving the heat dissipation. In addition, the upper limit of the thickness of the metal plate is not particularly limited, but is preferably less than 5mm. If it is larger than 5mm, it will lead to the enlargement of the semiconductor module when the pins are installed. Examples of methods for bonding the ceramic substrate and the metal plate include a method of bonding via a bonding layer and a method of directly bonding without a bonding layer. It should be noted that, as described later, in order to improve TCT characteristics, a structure with a bonding layer is preferred.

[0028] The waviness curve (first waviness curve) of the region 22 measured along the first side of the surface 2a extending in the first direction has one or less extreme values. That is, the number of extreme values ​​of the above-mentioned waviness curve is 1. The waviness curve (second waviness curve) of the region 22 measured along the second side of the surface 2a extending in the second direction has 2 to 3 extreme values. That is, the number of extreme values ​​of the above-mentioned waviness curve is 2 or 3. Each extreme value is a maximum value or a minimum value. It is also possible that the waviness curve measured along the first side of the surface 2b has one or less extreme values, and the waviness curve measured along the second side of the surface 2b has 2 to 3 extreme values.

[0029] When the surface 2a is a rectangular surface, it is preferred that one of the waviness curve along the long side and the waviness curve along the short side of the surface 2a is substantially arc-shaped, and the other is substantially M-shaped or substantially S-shaped. The surface refers to the ceramic surface from the end of the surface 2a to the outermost periphery of the pattern (e.g., copper pattern) of the surface metal plate 3.

[0030] The waviness profile is measured according to JIS-B0601. The waviness profile is a profile curve obtained by sequentially applying profile filters with cutoff values ​​of λf and λc to the cross-sectional curve, and is different from the roughness profile. Examples of measurement methods include laser method and contact method. The waviness profile along the long side of the surface 2a is gradually measured. It is preferred to measure the long side at one time. If the measurement cannot be performed at one time due to the substrate size or the device size, the measurement is performed multiple times, and the result is a measured value of the waviness profile. The same is true for the short side. In addition, the same is true when the waviness profile is measured on the surface 2b. In addition, the measurement location of the waviness profile is within the range of 0.5 to 1 mm from the end of the ceramic substrate 2.

[0031] One of the waviness curve along the long side and the waviness curve along the short side of the surface 2 a is in a substantially arc shape, and the other is in a substantially M-shape or a substantially S-shape. Figures 3 to 5 An example of a waviness curve is shown. Figure 3 A substantially arc-shaped waviness curve is exemplified. Figure 4 A substantially M-shaped waviness curve is shown as an example. Figure 5 A substantially S-shaped waviness curve is illustrated.

[0032] A roughly circular arc shape refers to a shape that gradually rises in a curved line, and gradually descends in a curved line after passing the maximum point (the uppermost point). At this time, there is only one extreme point. The extreme point can be either the surface side or the back side. In addition, when the extreme point is toward the back side, it becomes the following shape: gradually descending in a curved line, and gradually rising in a curved line after passing the minimum point (the lowermost point). In addition, the beginning and end parts of the waviness curve may also be an extended shape like the foot of Mount Fuji. That is, a roughly circular arc shape refers to a shape in which there is one extreme value in the waviness curve.

[0033] A roughly M-shaped shape refers to the following shape: it gradually rises in a curved line, gradually falls after passing the first maximum point (uppermost point), gradually rises again after passing the minimum point (lowermost point), and gradually falls after passing the second maximum point (uppermost point). It is a shape that depicts the uppermost point (first maximum point) → the lowermost point (minimum point) → the uppermost point (second maximum point) in a curved line. In addition, the uppermost point and the lowermost point may also be reversed. In this case, it becomes roughly W-shaped. Therefore, a roughly M-shaped shape also includes a roughly W-shaped shape. In addition, the beginning and end parts of the corrugation curve may also be an extended shape like the foot of Mount Fuji. That is, a roughly M-shaped shape refers to a shape with three extreme values ​​in the corrugation curve.

[0034] The roughly S-shaped shape refers to the following shape: it gradually rises in a curved line, gradually falls after passing the maximum point (uppermost point), and gradually rises again after passing the minimum point (lowermost point). It is a shape that draws the uppermost point → the lowermost point in a curved line. In addition, the uppermost point and the lowermost point can also be reversed. In addition, the beginning and end parts of the waviness curve can also be an extended shape like the foot of Mount Fuji. That is, the roughly S-shaped shape refers to a shape in which there are two extreme values ​​in the waviness curve.

[0035] It is preferred that the first waviness curve is in a roughly circular arc shape, and the second waviness curve is in a roughly M-shape or a roughly S-shape. When the surface 2a is a rectangular surface, the surface 2a has two long sides facing each other. It is preferred that at least one of the two first waviness curves measured along the two long sides extends in a roughly circular arc shape, and it is further preferred that the two first waviness curves extend in a roughly circular arc shape. It is sufficient that the two first waviness curves measured along the two opposing long sides each extend in a roughly circular arc shape, and the shapes may not be completely consistent with each other.

[0036] It is preferred that at least one of the two second corrugation curves extends in a substantially M-shape or a substantially S-shape, and it is further preferred that the two second corrugation curves extend in a substantially M-shape or a substantially S-shape. It is sufficient that the two second corrugation curves extend in a substantially M-shape or a substantially S-shape, respectively, and the shapes may not be completely identical to each other. In the case where one second corrugation curve extends in a substantially M-shape, it is preferred that the other second corrugation curve also extends in a substantially M-shape. Similarly, in the case where one second corrugation curve extends in a substantially S-shape, it is preferred that the other second corrugation curve also extends in a substantially S-shape.

[0037] Figures 3 to 5 The figure further shows the difference Z between the maximum and minimum values ​​of the corrugation curve. The difference Z between the maximum and minimum values ​​of the corrugation curve is preferably greater than 10 μm. The maximum value is the largest value among the uppermost points of the corrugation curve. In addition, the minimum value is the smallest value among the lowermost points of the corrugation curve. The difference Z between the maximum and minimum values ​​of the corrugation curve is preferably greater than 10 μm, and more preferably greater than 50 μm. By increasing the difference Z between the maximum and minimum values ​​of the corrugation curve, the corrugation of the ceramic substrate 2 can be reduced after the pins are bonded. In addition, the maximum value of the difference Z between the maximum and minimum values ​​of the corrugation curve is not particularly limited, but is preferably less than 400 μm. If it exceeds 400 μm, the corrugation of the ceramic substrate 2 is large, so there is a possibility that the corrugation remains after the pins are bonded, and the mountability of the heat dissipation component is reduced.

[0038] The ratio of the thickness of the ceramic substrate 2 / the thickness of the metal plate is preferably less than 1.5. When a plurality of metal plates including the surface metal plate 3 and the back metal plate 4 are joined to the ceramic substrate 2, the thickness of the thickest metal plate is used to calculate the above ratio. That is, the thickness of the thickest metal plate is preferably less than 1.5 times the thickness of the ceramic substrate 2. The ratio of the thickness of the ceramic substrate 2 / the thickness of the metal plate is preferably less than 1.5, and more preferably less than 0.5. The ratio of the thickness of the ceramic substrate 2 / the thickness of the metal plate is less than 0.5, indicating that the ceramic substrate 2 is thinned or the metal plate is thickened. Thus, the corrugation curve can be easily controlled. The ratio of the length L1 of the long side of the ceramic substrate to the length L2 of the short side preferably satisfies (L1 / L2) ≥ 1.25. That is, L1 is preferably more than 1.25 times of L2. The longer the long side of the substrate, the easier it becomes to impart the desired corrugation.

[0039] When the thickness of the ceramic substrate 2 is 0.4 mm or less and the thickness of the metal plate is 0.6 mm or more, it is preferred that the waviness curve along the long side is roughly arc-shaped, and the waviness curve along the short side is roughly M-shaped. If it is this shape, the waviness of the ceramic substrate 2 will become a symmetrical structure, so the difference between the maximum value and the minimum value of the waviness curve of the ceramic substrate 2 after the pins are bonded can be reduced. In addition, if it is a silicon nitride substrate, the thickness can be reduced to less than 0.33 mm, and further reduced to less than 0.30 mm. By reducing the thickness of the ceramic substrate 2 to less than 0.4 mm, it becomes easy to control the waviness curve.

[0040] In order to control the first waviness curve along the surface of the long sides and the second waviness curve along the surface of the short sides of the ceramic substrate 2 , it is also effective to adjust the arrangement structure of the metal plates. Figure 6 This is a diagram showing an example of the arrangement structure of the metal plates. Figure 6 The figure shows the ceramic substrate 2, the metal plates 3a, 3b, 3c, and 3d as the surface metal plates 3, the length L1 of the long side of the ceramic substrate 2, the length L2 of the short side of the ceramic substrate 2, and the length M of the long side of the metal plate 3c. 1-1 , the length M of the long side of the metal plate 3d 1-2 , the length M of the short side of the metal plate 3a 2-1 , the length M of the short side of the metal plate 3b 2-2 and the length M of the short side of the metal plate 3d 2-3 .

[0041] The sum of the lengths of the long sides of the metal plates is ΣM. n When ΣM n The ratio relative to L1 preferably satisfies 0.50≤ΣM n / L1≤0.95.ΣM n is the total length of the metal plates closest to the long side of the ceramic substrate 2. n depends on the number of metal plates to be targeted. Figure 6 In terms of the metal plate 3c and the metal plate 3d, the edges of the long sides of the ceramic substrate 2 are closest. n M 1-1 +M 1-2 When the length of a metal plate is represented by M, it is preferred that M / L1≤0.5. Figure 6 The middle figure shows the metal plate 3c and the metal plate 3d, but the number of metal plates may be three or more.

[0042] The sum of the lengths of the short sides of the metal plate is ΣM. m When ΣM m The ratio relative to L2 preferably satisfies 0.50≤ΣM m / L2≤0.95.ΣMm is the total length of the metal plates closest to the short side of the ceramic substrate 2. n depends on the number of metal plates to be targeted. Figure 6 In terms of the metal plates 3a, 3b, 3d, the edges of the short sides of the ceramic substrate 2 are closest. m M 2-1 、M 2-2 and M 2-3 In addition, when the length of one metal plate is represented by M, it is preferred that M / L2≤0.5. Figure 6 The middle figure shows the metal plate 3a, the metal plate 3b, and the metal plate 3d, but the number of the metal plates may be four or more.

[0043] ΣM is controlled by the lengths L1 and L2 relative to the ceramic substrate 2 n Value, ΣM m The shape of the waviness curve can be controlled by adjusting the M value. Thus, even if the number of metal plates is increased to more than 3, the shape of the waviness curve can be made into a preferred shape. That is, even if the number of surface metal plates 3 is more than 3 in a complex pattern shape, the waviness curve can be controlled.

[0044] Figure 6 The figure shows three metal plates (3a, 3b, 3d) arranged on the edge of the short side of the ceramic substrate 2. A gap can be formed between the metal plate 3a and the metal plate 3b and between the metal plate 3b and the metal plate 3d. The extreme value of the corrugation curve becomes easy to form in the gap. The same is true for the long side. It is also possible to set 0.50≤ΣM n / L1≤0.95、0.50≤ΣM m Any one of M / L2≤0.95, M / L1≤0.5, and M / L2≤0.5, or a combination of two or more thereof.

[0045] The ceramic circuit substrate 1 is preferably a ceramic circuit substrate with pins. Figure 7 This is a diagram showing an example of a ceramic circuit board with pins. Figure 8 This is a diagram showing an example of a semiconductor module. Figure 7 and Figure 8 The figure shows a ceramic circuit substrate 1 , pins 5 , a semiconductor device 6 , a heat dissipation member 7 , a ceramic circuit substrate 10 with pins, and a semiconductor module 20 .

[0046] The ceramic circuit substrate 10 with pins includes a ceramic circuit substrate 1, a surface metal plate 3 bonded to the ceramic circuit substrate 1, and a pin 5 bonded to the surface metal plate 3. The pin 5 has a function as an external electrode for conducting with the outside. Examples of the shape of the pin 5 include a lead frame type and a lead pin type. The number of pins 5 bonded is not particularly limited. If necessary, the pins can also be used in combination with wire bonding.

[0047] The ceramic circuit substrate 10 with pins is suitable for a structure in which a pin 5 with a thickness of 0.2 mm or more is joined to a surface metal plate 3. The thickness of the pin 5 is preferably 0.2 mm or more, and more preferably 0.4 mm or more. In addition, the thickness of the pin 5 is defined by the thickness of the lead frame plate in the case of a lead frame type, and is defined by the width of the pin in the case of a pin type. The pin 5 preferably contains a material with good conductivity such as copper, aluminum or their alloys. Examples of methods for joining the surface metal plate 3 to the pin 5 include solder joining, brazing joining, ultrasonic joining and crimping joining (compression welding joining). By thickening the pin 5, the current carrying capacity can be increased and the inductance can be reduced. As a result, the advantages of high-performance semiconductor devices can be effectively utilized.

[0048] The ceramic circuit substrate 10 with pins can reduce the difference Z between the maximum and minimum values ​​of the waviness curve to less than 40 μm. If it is joined to the pin 5 with a thickness of more than 0.2 mm, the surface metal plate 3 will be locally thickened. In the case of such a structure, the waviness of the ceramic substrate 2 is large. The ceramic substrate 2 has a predetermined waviness along the long side or the short side. Thereby, the waviness generated by the joining of the pin 5 can be offset. As a result, the difference Z between the maximum and minimum values ​​of the waviness curve of the ceramic circuit substrate with pins can be set to less than 40 μm, and further to less than 20 μm.

[0049] The upper limit of the thickness of the pin is not particularly limited, but is preferably 3 mm or less. If the pin has a thickness of 0.2 mm to 3 mm, the waviness can be reduced by joining at any position on the surface of the surface metal plate 3. By reducing the waviness of the ceramic substrate 2, the mountability to the heat dissipation member 7 can be improved.

[0050] The semiconductor module 20 includes a ceramic circuit substrate 10 with pins, a semiconductor device 6 mounted on the ceramic circuit substrate 10 with pins, and a heat dissipation member 7. The semiconductor device 6 is bonded to the surface metal plate 3. The number and mounting position of the semiconductor device 6 are optional as long as they are on the surface metal plate 3.

[0051] The heat dissipation member 7 is a member for mounting the back metal plate 4. The heat dissipation member 7 is provided on the back metal plate 4. Examples of the heat dissipation member 7 include a heat sink, a bottom plate, and a heat sink. The heat dissipation member 7 may be in various shapes such as a plate, a comb, a groove, or a needle. The heat dissipation member 7 may be made of a material having good heat dissipation properties such as copper, Al, or AlSiC.

[0052] An interlayer of solder, grease, etc. may also be provided between the heat dissipation member 7 and the back metal plate 4. Since the difference Z between the maximum value and the minimum value of the waviness curve of the ceramic circuit substrate 10 with pins is small, the gap between the heat dissipation member 7 and the back metal plate 4 becomes small. Therefore, the uneven coating of the interlayer of solder, grease, etc. disappears. Thus, it is possible to prevent the occurrence of misalignment, protrusion of inclusions, and other installation defects.

[0053] The semiconductor module 20 may also have a mounting structure that applies stress to the ceramic circuit substrate, such as a screw fixing structure. Even with a screw fixing structure, the gap between the heat dissipation member 7 and the back metal plate 4 is small, so the tightness can be improved. Thus, stress concentration during screw fixing can be suppressed, so poor installation can be reduced.

[0054] Improving the closeness between the heat dissipation member 7 and the back metal plate 4 will also improve the heat dissipation. The improvement of heat dissipation will improve the TCT characteristics of the semiconductor module. With the high performance of semiconductor devices, the operation guarantee temperature has become as high as 175°C or more. In order to improve the heat dissipation, thickening the metal plate and thinning the ceramic substrate 2 are being studied. The ceramic circuit substrate of the embodiment is given a predetermined corrugation curve, so that the heat dissipation can be improved even if it is made into a structure with pins.

[0055] In order to improve the TCT characteristics, the ceramic substrate 2 and the metal plate are preferably bonded via a bonding layer. Fig. 9 It is a diagram showing an example of the shape of the metal plate side surface and the joining layer. Fig. 9 The figure shows the ceramic substrate 2, the metal plate (the surface metal plate 3), the bonding layer 8, and the contact angle θ between the bonding layer and the side surface of the metal plate. Fig. 9 Although the front metal plate 3 is illustrated in FIG. 1 , the back metal plate 4 is also the same.

[0056] The bonding layer preferably contains an active metal. The active metal includes at least one element selected from Ti (titanium), Zr (zirconium), Hf (hafnium), Nb (niobium) and Al (aluminum). A brazing paste containing an active metal is used for bonding. When the metal plate is a copper plate (including a copper alloy plate), it is preferably included at least one element selected from Ti (titanium), Zr (zirconium), Hf (hafnium) and Nb (niobium). Ti is preferred among these active metals. In addition, the bonding layer containing these active metals preferably contains the following active metal brazing material, which contains the following components totaling less than 100 mass%: 40 mass% to 80 mass% of Ag, 20 mass% to 60 mass% of Cu, 0.1 mass% to 12 mass% of active metal, 0 mass% to 20 mass% of Sn and 0 mass% to 20 mass% of In. When the metal plate is an aluminum plate (including an aluminum alloy plate), a brazing material with Al as the main component is used. The Al brazing material preferably contains 0.1 mass% to 12 mass% of Si.

[0057] The bonding layer 8 preferably has a bonding layer protrusion protruding from between the ceramic substrate 2 and the metal plate 3. The bonding layer protrusion is preferably arranged in a region 10 μm to 100 μm away from the end of the metal plate. In addition, the contact angle θ between the bonding layer 8 and the side of the metal plate 3 is preferably 80 degrees or less, more preferably 60 degrees or less. By controlling the bonding layer protrusion and the contact angle θ, the TCT characteristics can be improved. In particular, as a ceramic circuit substrate with pins, the TCT characteristics can be improved. The shape of the bonding layer protrusion and the side of the metal plate can be controlled by etching.

[0058] Resin sealing can also be performed as needed. The resin sealing process can use a method such as transfer molding. Since the semiconductor module of the embodiment is bonded with thick pins, the pins will not be broken during the resin sealing process. On the other hand, since the wires are thin in lead bonding, wire breakage is likely to occur in methods with high molding pressure such as transfer molding. In other words, by using thick pins, a module structure that is easy to be resin sealed can be made.

[0059] Next, a method for producing the ceramic circuit board will be described. The method for producing the ceramic circuit board is not particularly limited as long as the ceramic circuit board has the above-mentioned configuration, but the following method can be cited as a method for obtaining a good yield.

[0060] The first manufacturing method is a method of processing a ceramic molded body (green sheet) and then sintering it in order to obtain a target waviness curve. Examples of the processing method include die pressing using a die having a waviness for obtaining the target waviness curve. There is also a method of using a die having a waviness for obtaining the target waviness curve when punching the green sheet. There is also a method of using a die having a waviness for obtaining the target waviness curve in a drying process after punching.

[0061] The second manufacturing method is a method of giving waviness to a sintered ceramic substrate in order to obtain a target waviness curve. The usual warpage correction process of a ceramic substrate is to flatten the substrate by heating while applying a load. In this case, a method of heating while applying a load using a mold having a waviness for obtaining a target waviness curve is effective.

[0062] The third manufacturing method is a method of imparting waviness for obtaining a target waviness curve in the bonding process of the metal plate and the ceramic substrate. When the metal plate and the ceramic substrate are bonded, tensile stress is imparted to the metal plate. By imparting tensile stress to the metal plate, the metal plate contracts in the bonding process, and waviness is imparted to the ceramic substrate. Examples of methods of imparting tensile stress to the metal plate include honing.

[0063] The fourth manufacturing method is to perform honing on the metal plate of the ceramic circuit board. By performing the honing linearly, the portion can be made convex.

[0064] The fifth manufacturing method is a method of controlling the volume ratio of the front and back metal plates. The first to fifth manufacturing methods described above may be performed individually or in combination.

[0065] The first manufacturing method is particularly effective for thin ceramic substrates with a thickness of 0.4 mm or less. If the thickness of the ceramic substrate is 0.6 mm or more, the shrinkage of the ceramic molded body during the sintering process becomes large, making it difficult to control the waviness curve.

[0066] The second manufacturing method is also particularly effective for thin ceramic substrates with a thickness of 0.4 mm or less, as in the first manufacturing method. If waviness is to be imparted to a ceramic substrate with a thickness of 0.6 mm or more, the substrate may be damaged. In particular, if the strength is less than 400 MPa and the thickness is greater than 0.6 mm, the substrate is not flexible enough and thus easily damaged.

[0067] The third manufacturing method is particularly effective for a thick metal plate having a thickness of 0.6 mm or more. If the thickness of the metal plate is as thin as 0.3 mm or less, the tensile stress is unlikely to increase, and thus the waviness is likely to be insufficient.

[0068] The fourth manufacturing method is particularly effective for a thick metal plate having a thickness of 0.6 mm or more. If the thickness of the metal plate is as thin as 0.3 mm or less, the tensile stress is unlikely to increase, and thus the waviness is likely to be insufficient.

[0069] The fifth manufacturing method is effective when there is a difference in thickness between the front and back metal plates. Therefore, a combination of a silicon nitride substrate having a thickness of 0.33 mm or less and a metal plate having a thickness of 0.6 mm or more (eg, a copper plate) is an easy combination to manufacture.

[0070] The method for joining the ceramic substrate and the metal plate may be any one of a joining method via a joining layer and a joining method of directly joining without a joining layer. The joining method via a joining layer is preferably an active metal joining method. The active metal joining method is a method using an active metal brazing material containing an active metal.

[0071] The active metal preferably contains at least one element selected from Ti (titanium), Zr (zirconium), Hf (hafnium), Nb (niobium) and Al (aluminum). When the metal plate is a copper plate (including a copper alloy plate), it preferably contains at least one element selected from Ti (titanium), Zr (zirconium), Hf (hafnium) and Nb (niobium). Among these active metals, Ti is preferred.

[0072] The bonding layer containing the above-mentioned active metal is preferably formed using the following active metal brazing filler metal, which contains 40% to 80% by mass of Ag, 20% to 60% by mass of Cu, 0.1% to 12% by mass of active metal, 0% to 20% by mass of Sn and 0% to 20% by mass of In, and their total content is less than 100% by mass. The active metal brazing filler metal containing Ti reacts with nitride ceramics (silicon nitride substrate, aluminum nitride substrate) to form TiN. Thus, the bonding strength can be improved. When the metal plate is an aluminum plate (including an aluminum alloy plate), a brazing filler metal with Al as the main component is used. The Al brazing filler metal preferably contains 0.1% to 12% by mass of Si.

[0073] An active metal brazing paste is applied on a ceramic substrate and a metal plate is placed. The coating thickness of the active metal brazing paste is preferably 10 μm to 40 μm. The bonding process is preferably carried out at a temperature of 600°C to 950°C. In the case where the active metal contains at least one element selected from Ti, Zr, Hf and Nb, it is preferably carried out at a temperature of 800°C to 950°C. In the case where the active metal contains Al, it is preferably carried out at a temperature of 600°C to 800°C. The heating atmosphere is preferably a non-oxidizing atmosphere. As needed, a pattern shape can also be formed by etching. The side of the metal plate can be etched to control the contact angle θ between the protrusion of the bonding layer and the metal plate.

[0074] The ceramic substrate and the metal plate can also be joined by a direct joining method without the aid of a joining layer. When the metal plate is a copper plate, a direct joining method using a eutectic of copper and oxygen can be used. When the ceramic substrate is a nitride, an oxide film is formed on the surface. When the metal plate is an Al plate, an AlSi alloy plate is used for direct joining.

[0075] By performing the above steps, the waviness curve of the ceramic substrate can be controlled, for example, the waviness curve of the long side or the short side of the ceramic substrate can be made into a substantially arc shape, and the other can be made into a substantially M shape or a substantially S shape. In addition, the difference Z between the maximum value and the minimum value of the waviness curve can be adjusted by adjusting the conditions of the first to third manufacturing methods.

[0076] Next, a method for manufacturing the ceramic circuit board with pins is described. The ceramic circuit board with pins is manufactured by bonding pins to the ceramic circuit board.

[0077] Examples of the pins include lead frame type pins and lead pin type pins. Examples of the shape of the pins include plate shape, needle shape, S shape, and L shape. The pins preferably contain copper, Al, or an alloy thereof.

[0078] The pin is bonded to the surface metal plate of the ceramic circuit board. Examples of methods for bonding the pin to the surface metal plate include methods using bonding materials, ultrasonic bonding, and pressure bonding. Examples of bonding materials include solder and brazing materials.

[0079] By giving the ceramic circuit substrate a predetermined waviness curve, the ceramic circuit substrate can be prevented from bending when the thickness of the pin is enlarged to 0.2 mm or more, and further to 0.4 mm or more. Therefore, the ceramic circuit substrate with pins can reduce the difference Z between the maximum value and the minimum value of the waviness curve of the long side and the short side to less than 40 μm, and further to less than 20 μm.

[0080] As described above, it is preferable to give 0.50≤ΣM n / L1≤0.95、0.10≤ΣM m Any one or more of M / L2≤0.95, M / L1≤0.5, and M / L2≤0.5. By setting it within such a range, the waviness curve can be controlled even if the number of the surface metal plates 3 reaches three or more. For example, by joining two or more surface metal plates 3 and setting a gap between the metal plates, it becomes easy to give an extreme value of the waviness curve. Even if the creepage distance between the ceramic substrate 2 and the surface metal plate 3 is narrowed to 1 mm to 2 mm, a predetermined waviness curve can be given.

[0081] Next, a method for manufacturing a semiconductor module will be described. The method for manufacturing a semiconductor module includes the following steps: a step of mounting a semiconductor device on the above-mentioned ceramic circuit substrate with pins; and a step of mounting the semiconductor device on a heat dissipation member.

[0082] In the process of installing the semiconductor device, the semiconductor device is installed on the surface metal plate. The semiconductor device is preferably joined via a bonding layer such as solder. In the process of installing on the heat dissipation component, the back metal plate of the ceramic circuit substrate is installed on the heat dissipation component. Grease, solder, brazing material, etc. may also be sandwiched between the back metal plate and the heat dissipation component as needed.

[0083] The ceramic substrate may be screwed as required. Examples of the screw-fixing structure include a structure in which a screw hole is provided on the ceramic substrate, and a structure in which the end of the ceramic substrate is fixed with a clamp for screwing.

[0084] The difference Z between the maximum and minimum values ​​of the waviness curves of the long side and the short side of the ceramic circuit substrate with pins is small. Therefore, when mounted on the heat dissipation component, the gap between the back metal plate and the heat dissipation component can be reduced. Therefore, the heat dissipation between the back metal plate and the heat dissipation component can be improved.

[0085] Since the closeness between the back metal plate and the heat dissipation component is improved, even if a fixing method such as threaded fixing that applies stress to the ceramic substrate is used, it is not easy to cause poor installation such as misalignment and breakage. In contrast, a resin sealing process can also be performed as needed. Examples of resin sealing processes include transfer molding. Transfer molding is a sealing method that increases molding pressure to improve mass productivity. By joining pins with a thickness of more than 0.2 mm, it is possible to prevent the pins from being broken in the transfer molding process. In other words, a ceramic circuit substrate with pins and a semiconductor module formed using the ceramic circuit substrate with pins are suitable for a transfer molding process.

[0086] Example

[0087] (Examples 1 to 8, Comparative Examples 1 to 3)

[0088] The silicon nitride circuit substrate shown in Table 1 was produced. As a silicon nitride substrate, a silicon nitride substrate with a thermal conductivity of 90 W / m·K and a three-point bending strength of 700 MPa was prepared. As a surface metal plate and a back metal plate, a copper plate was prepared. An active metal brazing material containing Ti was used to join the silicon nitride substrate and the copper plate. As an active metal brazing material, a brazing material made of Ag (remainder), Cu (30 mass%), Ti (5 mass%), and Sn (10 mass%) was used. The active metal brazing paste was applied with a thickness of 20 μm, and the silicon nitride substrate and the copper plate were joined by heating at 850°C in a non-oxidizing atmosphere. After joining the copper plates, the size of the protrusion of the joining layer and the contact angle θ between the side end of the copper plate and the protrusion of the joining layer were adjusted by etching. The length of the protrusion of the joining layer was adjusted to 20 to 40 μm, and the contact angle θ between the side end of the copper plate and the protrusion of the joining layer was adjusted to 40 to 60 degrees. The distance between the copper plates of the surface copper plate is set to 1.5 to 3.0 mm. The creepage distance between the surface copper plate and the ceramic substrate was unified to 1.5 mm. In the embodiment, as the waviness imparting process, the second manufacturing method (a method of imparting the target waviness to the ceramic substrate) or the fourth manufacturing method (a method of linearly honing the metal plate) was performed. Comparative Example 1 eliminated the waviness by the warpage correction process. In addition, Comparative Examples 2 and 3 imparted waviness by the same method as the embodiment.

[0089] [Table 1]

[0090]

[0091] The ΣM n / L1,ΣM m / L2, M / L1, M / L2. These measurements were performed based on the surface metal plate located closest to the surface on the long side (L1 side) and the short side (L2 side) of the ceramic substrate. In addition, when metal plates of different sizes were joined, M / L1 and M / L2 showed the largest values. The results are shown in Table 2.

[0092] [Table 2]

[0093]

[0094] As can be seen from Table 2, the silicon nitride circuit substrate of the embodiment satisfies 0.50≤ΣM n / L1≤0.95、0.50≤ΣM m One or more of M / L2≤0.95, M / L1≤0.5, M / L2≤0.5.

[0095] Next, the waviness curves of the long sides and short sides of the ceramic circuit substrates of the embodiment and the comparative example were measured. The waviness curve was measured by laser scanning the portion 1 mm inside from the end of the ceramic substrate. The measurement results were made into a waviness curve according to JIS-B0601. In addition, the difference Z between the maximum value and the minimum value of the waviness curve was also measured. The results are shown in Table 3.

[0096] [Table 3]

[0097]

[0098] Pins were bonded to the ceramic circuit substrates of the embodiment and the comparative example. The pins shown in Table 4 were used. In addition, all the pins were made of copper. The lead frame type was made into a flat plate shape, and the pin type was made into a cylindrical shape. In the case of the pin type, the thickness of the pin became the diameter.

[0099] [Table 4]

[0100] shape size Pin 1 Lead frame type Length 10mm×width 3mm×thickness 0.5mm Pin 2 Lead frame type 8mm in height x 2mm in width x 0.8mm in thickness Pin 3 Pin type Length 5mm × Diameter 2mm

[0101] Next, the pins shown in Table 4 are joined to the ceramic circuit substrates of the embodiments and comparative examples. The number of joined pins is expressed as the number joined on one surface metal plate. That is, since there are two surface metal plates, the actual number of connections is doubled. For example, in Embodiment 1, two pins 1 are joined on one metal plate. In Embodiment 1, since two surface metal plates are provided, the total number of connections of pin 1 is 4. Thereafter, the difference Z between the maximum value and the minimum value of the corrugation curve on the long side (the first corrugation curve) and the corrugation curve on the short side (the second corrugation curve) is measured. The results are shown in Table 5.

[0102] [Table 5]

[0103]

[0104] As can be seen from the table, the difference Z between the maximum value and the minimum value of the waviness curve of the ceramic circuit board with pins of the example is as small as 20 μm or less, while the values ​​of the comparative examples are large.

[0105] Next, the ceramic circuit substrate with pins of the embodiment and the comparative example was subjected to a TCT characteristic and mounting confirmation test. TCT is -40℃×30 minutes→room temperature×10 minutes→175℃×30 minutes→room temperature×10 minutes as one cycle, and the defect generation rate after 5000 cycles was measured. The defect generation rate caused by TCT is 0% for no defect and 100% for all defective products (cracks on the bonding layer or ceramic substrate).

[0106] The confirmation test of the mounting performance measured the defect rate when the heat dissipation component was fixed by screw fixing. The screw fixing was performed by sandwiching grease between the back metal plate and the heat dissipation component. The thermal resistance (K / W) was also measured. The results are shown in Table 6.

[0107] [Table 6]

[0108]

[0109] As can be seen from the table, the ceramic circuit substrate with pins of the embodiment obtained good results in TCT characteristics and mounting properties. In contrast, the comparative example had a large waviness, so the characteristics were reduced. Therefore, it can be seen that the embodiment is suitable for a ceramic circuit substrate with thick pins. Even if the silicon nitride substrate is thinned to less than 0.32 mm, and further to less than 0.25 mm, it still shows excellent durability.

[0110] Several embodiments of the present invention are illustrated above, but these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other ways, and various omissions, substitutions, changes, etc. can be made without departing from the scope of the main purpose of the invention. These embodiments and their modifications are included in the scope and main purpose of the invention, and are included in the invention recorded in the claims and their equivalents. In addition, the above-mentioned embodiments can be implemented in combination with each other.

Claims

1. A ceramic circuit substrate, comprising: A ceramic substrate having a thickness of 1.0 mm or less, the ceramic substrate having a first surface and a second surface, the first surface including a first region and a second region; a first metal plate bonded to the first region via a first bonding layer; and a second metal plate, the second metal plate being bonded to the second surface via a second bonding layer, The first surface extends along a first direction and a second direction intersecting the first direction, a first waviness curve of the second region measured along a first side of the first surface extending along the first direction has one or less extreme values, a second waviness curve of the second region measured along a second side of the first surface extending along the second direction has two to three extreme values; The first bonding layer is disposed on the first surface, and has a first protrusion extending from a first interface between the first bonding layer and a side surface of the first metal plate, the length of the first protrusion is 10 μm to 100 μm, and an angle formed by the first interface and the side surface of the first metal plate is less than 80 degrees. The second bonding layer is arranged on the second surface and has a second protrusion extending from the second interface between the second bonding layer and the side of the second metal plate, the length of the second protrusion is 10μm to 100μm, and the angle formed by the second interface and the side of the second metal plate is less than 80 degrees.

2. The ceramic circuit substrate according to claim 1, in, The first waviness curve is substantially in the shape of an arc. The second waviness curve is substantially M-shaped or substantially S-shaped.

3. The ceramic circuit substrate according to claim 1 or claim 2, in, At least one of the first metal plate and the second metal plate has a thickness of 0.6 mm or more.

4. The ceramic circuit substrate according to claim 1 or claim 2, in, A ratio of the thickness of the ceramic substrate to the thickness of the thickest metal plate of the first metal plate and the second metal plate is 1.5 or less.

5. The ceramic circuit substrate according to claim 4, in, The length of the first side is 1.25 times or more the length of the second side.

6. The ceramic circuit substrate according to claim 5, in, The ceramic substrate is a silicon nitride substrate having a thickness of 0.33 mm or less.

7. The ceramic circuit substrate according to claim 1, in, The first waviness curve is substantially in the shape of an arc. The second waviness curve is substantially M-shaped or S-shaped. The thickness of at least one of the first metal plate and the second metal plate is 0.6 mm or more. The ceramic substrate is a silicon nitride substrate having a thickness of 0.33 mm or less. 8 . The ceramic circuit board according to claim 1 , further comprising a pin having a thickness of 0.2 mm or more and joined to the first metal plate.

9. A ceramic circuit substrate comprising: A ceramic substrate having a thickness of 1.0 mm or less, the ceramic substrate having a first surface and a second surface, the first surface including a first region and a second region; a first metal plate joined to the first region; and a second metal plate, the second metal plate being bonded to the second surface, The thickness of at least one of the first metal plate and the second metal plate is 0.6 mm or more. The ratio of the thickness of the ceramic substrate to the thickness of the thickest metal plate of the first metal plate and the second metal plate is 1.5 or less. The first surface extends along a first direction and a second direction intersecting the first direction, a first waviness curve of the second region measured along a first side of the first surface extending along the first direction has one or less extreme values, a second waviness curve of the second region measured along a second side of the first surface extending along the second direction has two to three extreme values; The difference between the maximum value and the minimum value of at least one of the first waviness curve and the second waviness curve is greater than 10 μm. The first waviness curve is substantially in an arc shape, and the second waviness curve is substantially in an M shape or a S shape.

10. A semiconductor module comprising: The ceramic circuit substrate according to claim 8, a semiconductor device disposed on the first metal plate, and A heat dissipation member is provided on the second metal plate.

11. The semiconductor module according to claim 10, in, The first waviness curve is substantially in the shape of an arc. The second waviness curve is substantially M-shaped or S-shaped. The thickness of at least one of the first metal plate and the second metal plate is 0.6 mm or more. The ceramic substrate is a silicon nitride substrate having a thickness of 0.33 mm or less.

12. A semiconductor module comprising: The ceramic circuit substrate according to claim 9, a semiconductor device disposed on the first metal plate, and A heat dissipation member is provided on the second metal plate.

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