Ceramic circuit board and manufacturing method thereof

Abstract

Ceramic copper circuit boards, which have thick copper circuits formed on a thin ceramic substrate, tend to warp. [Solution] In a ceramic copper circuit board having a copper plate formed as a circuit part on one side of a ceramic substrate and a copper plate formed as a heat dissipation part on the other side, the hardness of the copper plate is 45 Hv or more, and the amount of warping of the ceramic copper circuit board is 2 μm / mm or less. Also, in a method for manufacturing a ceramic copper circuit board, copper plates are bonded to both sides of a ceramic substrate, and an etching process is used to form a circuit part on one side of the ceramic substrate and a heat dissipation part on the other side, forming the ceramic copper circuit board. After forming the ceramic copper circuit board, a striking force is applied to the ceramic copper circuit board to increase the hardness of the copper plate to 45 Hv or more and reduce the amount of warping of the ceramic copper circuit board to 2 μm / mm or less.

Description

[Technical Field]

[0001] The embodiments generally relate to ceramic circuit boards and methods of manufacturing the same. [Background technology]

[0002] Ceramic circuit boards are used in semiconductor devices equipped with semiconductor elements such as power elements, and the ceramic substrate and metal circuit are bonded to each other via a bonding layer using a brazing material or the like. As reliability has improved, ceramic circuit boards are used in automobiles (including electric vehicles), electric railway vehicles, solar power generation facilities, inverters for industrial machinery, and the like. In semiconductor devices such as power modules, semiconductor elements are mounted on metal circuits. Wire bonding or metal terminals may also be bonded to ensure electrical continuity of the semiconductor elements. In the manufacture of semiconductor devices, semiconductor elements, wire bonding, metal terminals, and the like are bonded to metal circuits.

[0003] With the emergence of power semiconductors such as SiC and GaN, there are more cases where larger amounts of electricity need to be conducted than before. In order to pass a large current through the metal circuit and dissipate the heat generated by the semiconductor, the metal circuit tends to be thicker and the ceramic substrate thinner. Furthermore, as power modules become smaller, lighter, and more densely packed, the ceramic substrate tends to become thinner and the metal circuit thicker.

[0004] As ceramic substrates have become thinner, they have become more susceptible to warping. There are many methods for reducing the warping of ceramic circuit substrates, and one method disclosed is to heat multiple stacked laminates while applying pressure (Patent Document 1). According to Patent Document 1, it is possible to reduce the warping that occurs during the manufacture of a power module substrate with a heat sink.

[0005] Furthermore, we have developed a method to control the warpage of ceramic circuit boards by adjusting the hardness of the metal circuit. A method for reducing the warpage of a ceramic circuit board has been disclosed (Patent Document 2). According to Patent Document 2, the amount of warpage of a ceramic circuit board can be kept within a certain range by lowering the hardness of the metal circuit board. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5649489 [Patent Document 2] Patent No. 3949270 Summary of the Invention [Problem to be solved by the invention]

[0007] On the other hand, issues arising from thinner ceramic substrates and thicker metal circuits have become apparent. Metal circuits rarely have the same shape on both sides, and the metal circuit section (front side) on which semiconductor elements are mounted has a complex shape divided into several parts. The side opposite the side on which these semiconductor elements are mounted (back side) is often a heat sink (flat plate) without a circuit shape for the purpose of heat dissipation. This causes complex warping due to the difference in shape between the front and back sides. Because the warping that occurs in this way is not uniform, it has been difficult to find a method to suppress it or correct any warping that has occurred.

[0008] The embodiments are intended to solve such problems, and relate to a ceramic copper circuit board in which the amount of warping is small and in which any warping that occurs is corrected even when a thick copper circuit is formed on a thin ceramic substrate, and a method for manufacturing the same. [Means for solving the problem]

[0009] The ceramic copper circuit board according to the embodiment is a ceramic copper circuit board in which a copper plate is formed as a circuit portion on one side of a ceramic substrate and a copper plate is formed as a heat dissipation portion on the other side. The hardness of the copper plate of the ceramic copper circuit board is 45 Hv or more, and the amount of warpage of the ceramic copper circuit board is 2 μm / mm or less. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing an example of a ceramic copper circuit board according to an embodiment. [Figure 2] Cross-sectional view showing the warpage of a ceramic copper circuit board [Figure 3] 1 is a cross-sectional view showing an example of a method for manufacturing a ceramic copper circuit board according to an embodiment. [Figure 4] 1 is a cross-sectional view showing an example of a method for manufacturing a ceramic copper circuit board according to an embodiment. [Figure 5] 1 is a cross-sectional view showing an example of a method for manufacturing a ceramic copper circuit board according to an embodiment. [Figure 6] 1 is a cross-sectional view showing an example of a method for manufacturing a ceramic copper circuit board according to an embodiment. [Figure 7] 1 shows ceramic copper circuit boards of Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0011] The ceramic copper circuit board according to the embodiment is a ceramic copper circuit board in which a copper plate is formed as a circuit portion on one side of a ceramic substrate and a copper plate is formed as a heat dissipation portion on the other side. The hardness of the copper plate of the ceramic copper circuit board is 45 Hv or more, and the amount of warpage of the ceramic copper circuit board is 2 μm / mm or less.

[0012] FIG. 1 is a cross-sectional view showing an example of a ceramic copper circuit board according to an embodiment. In FIG. 1, 1 denotes a ceramic copper circuit board, 2 denotes a ceramic substrate, 3 denotes a circuit section on the upper surface (front surface, one side), 4 denotes a bonding layer, and 5 denotes a heat dissipation section on the lower surface (back surface, other side). The ceramic substrate 2 has a ceramic substrate upper surface (front surface, one side) and a ceramic substrate lower surface (back surface, other side). The circuit section 3 and the heat dissipation section 5 are bonded to the ceramic substrate upper surface and the ceramic substrate lower surface via a bonding layer 4. In the example of FIG. 1, multiple circuit sections 3 are bonded to the ceramic substrate upper surface via multiple bonding layers 4, respectively. The embodiment is not limited to the illustrated form. One circuit section 3 or three or more circuit sections 3 may be bonded to the ceramic substrate upper surface. One or more heat dissipation sections 5 may also be formed on the lower surface heat dissipation section 5.

[0013] Figure 2 is a cross-sectional view showing the state of warpage of a ceramic copper circuit board. The difference between the maximum and minimum heights of the circuit part or heat dissipation part when the ceramic copper circuit board is placed on a flat surface with the convex side facing up is the amount of warpage (W). Note that the amount of warpage is a positive value when the circuit part is convex as shown in Figure 2, and a negative value when it is concave.

[0014] The circuit section 3 and the heat dissipation section 5 are mainly composed of copper or a copper alloy, and are preferably made of any one of oxygen-free copper, tough pitch copper, phosphorus-deoxidized copper, etc.

[0015] The hardness of the copper plates of the circuit section 3 and the heat dissipation section 5 is 45 Hv or more. In the ceramic copper circuit board according to this embodiment, warping of the ceramic copper circuit board is reduced by increasing the hardness of the copper plate, as described below. In a ceramic-copper bonded body, warping occurs due to the difference in thermal expansion. Because the copper plate has a lower hardness than the ceramic substrate, it is easy for the copper plate to deform along the warp caused by the difference in thermal expansion. Therefore, by increasing the hardness of the copper plate, it is possible to suppress warping of the copper plate and correct warping of the ceramic copper circuit board. If the hardness is less than 45 Hv, the effect of correcting warping is reduced. In this case, the hardness (Hv) of the copper plate may be measured in accordance with JIS Z 2244-2009.

[0016] In the ceramic copper circuit board according to the embodiment, the copper plates of the circuit section and the heat dissipation section have a thickness greater than the thickness of the ceramic substrate.

[0017] The impact increases the hardness of the copper plate, correcting the warp, so the warp of the ceramic substrate follows the copper plate. For this reason, it is preferable that the copper plate is thicker than the ceramic substrate. If the ceramic substrate is thicker than the copper plate, the force required to correct the warp of the ceramic substrate is insufficient, and the warp cannot be corrected. For this reason, by making the copper plate thicker than the ceramic substrate, the hardness of the copper plate is increased, allowing the ceramic substrate to follow the copper plate whose warp has been corrected.

[0018] The thickness of the ceramic substrate is preferably 0.7 mm or less. By making the ceramic circuit substrate thinner and the metal circuit thicker, heat dissipation performance is improved. The thickness here refers to the dimension in the direction connecting the upper surface of the ceramic substrate and the lower surface of the ceramic substrate. These ceramic substrates may be single-layered or may have a three-dimensional structure such as a multilayer structure. There is no particular lower limit for the thickness, but it is preferably 0.1 mm or more. This is to ensure the electrical insulation of the ceramic substrate.

[0019] In the ceramic copper circuit board according to the embodiment, the difference in thickness between the copper plate of the circuit portion and the copper plate of the heat dissipation portion is 0.05 mm or more.

[0020] Among the types of warpage in ceramic copper circuit boards, warpage caused by the difference in thickness between the copper plate in the circuit section and the copper plate in the heat dissipation section is close to a simple shape. In other words, the warpage is caused by the difference in thermal expansion due to the difference in thickness of the copper plate, causing the thinner side of the copper plate to warp convexly. When this type of warpage occurs, applying a striking force to the ceramic circuit board increases the hardness of the copper plate, making it possible to correct the warpage. When the difference in thickness between the copper plate in the circuit section and the copper plate in the heat dissipation section is 0.05 mm or more, the difference in thickness of the copper plates tends to make the warpage uniform, making it easier to correct. Furthermore, a thickness difference of 0.1 mm or more is even more preferable.

[0021] The ceramic substrate according to the embodiment is a silicon nitride substrate.

[0022] The ceramic substrate 2 is preferably one of a silicon nitride substrate, an aluminum nitride substrate, and an aluminum oxide substrate. An aridil substrate is also a type of aluminum oxide substrate. Aridil is a sintered body made by adding 10 to 30 wt% zirconium oxide to aluminum oxide. The three-point bending strength of an aluminum nitride substrate or an aluminum oxide substrate is approximately 300 to 450 MPa. The strength of an aridil substrate is also around 550 MPa. The three-point bending strength of a silicon nitride substrate can be increased to 600 MPa or more, even 700 MPa or more. Therefore, a silicon nitride substrate is ideal because it is less likely to be damaged even when a striking force is applied to correct warpage. Furthermore, the thermal conductivity of a silicon nitride substrate can be increased to 50 W / m·K or more, even 80 W / m·K or more. In recent years, silicon nitride substrates that combine both high strength and high thermal conductivity have become available. Because of their high strength, silicon nitride substrates can be made thinner, enabling improved heat dissipation. For this reason, the thickness of the silicon nitride substrate is preferably 0.635 mm or less, and more preferably 0.3 mm or less.

[0023] In the method for manufacturing a ceramic copper circuit board according to the embodiment, copper plates are bonded to both sides of a ceramic substrate, and an etching process is used to form a circuit section on one side of the ceramic substrate and a heat dissipation section on the other side to form a ceramic copper circuit board. After this, an impact force is applied to the ceramic copper circuit board to increase the hardness of the copper plates to 45 Hv or more and reduce the amount of warping of the ceramic copper circuit board to 2 μm / mm or less.

[0024] In the manufacturing method for a ceramic copper circuit board according to the embodiment, the ratio (Ha / Hb) of the hardness (Ha) of the copper plate when the impact force is applied to the hardness (Hb) before the impact force is applied is 1.1 or more. The hardness of the copper plate can be increased by applying an impact. Copper undergoes work hardening when impacted, increasing its hardness. Work hardening is a phenomenon in which copper crystal grains become finer due to deformation, increasing the number of grain boundaries and increasing strength. If the hardness ratio (Ha / Hb) is less than 1.1, the increase in hardness is insufficient, and warpage correction may be insufficient.

[0025] In the method for manufacturing a ceramic copper circuit board according to the embodiment, the impact force is 3 J or more and 12 J or less.

[0026] The impact force varies depending on the thickness of the ceramic substrate and copper plate, and the amount of warping of the ceramic-copper circuit board, but it is generally preferable to be between 3J and 12J. If it is less than 3J, it will take too long to harden the copper plate, and if it is more than 12J, the hardness of the copper plate will increase, but there is a possibility that it will damage the ceramic substrate. For this reason, an impact force of 5J or more and 10J or less is more preferable.

[0027] The impact force (J) is calculated using the following formula 1. Impact force (J) = 0.5 x mass (kg) x (velocity (m / s)) 2 Formula 1 In other words, the impact force (J) when hitting with a 1 kg hitting part at a speed of 2 (m / sec) is 2J.

[0028] 3 to 6 are cross-sectional views of an example of a method for manufacturing a ceramic copper circuit board according to an embodiment. In FIG. 3, a warped ceramic copper circuit board 1 is placed on a base 6, and a striking unit 7 is moved up and down from above to strike the board, thereby increasing the hardness of the copper plate and correcting the warp. If the warp of the ceramic copper circuit board is small, the warp can be corrected with a few strikes. If the amount of warp is large, the strikes are applied in multiple steps. If a large amount of warp is struck across the entire board, the ceramic substrate may not be able to keep up with the impact and may break. For this reason, the amount of warp before striking is preferably 10 μm / mm or less, and more preferably 8 μm / mm or less.

[0029] In Fig. 4, the impact part 7 moves while impacting parts of the ceramic copper circuit board 1. Compared to Fig. 3, it is possible to deal with cases where the warp is large, but if the amount of warp is large, it is preferable to impact in multiple steps.

[0030] In Figure 5, a ceramic copper circuit board is sandwiched between a base 6 and a buffer material 8, and the hardness of the copper plate is increased by applying a blow to the buffer part, thereby correcting the warp. In Figure 5, the striking part moves while applying a blow to a part of the board, as in Figure 4, but the striking part may also cover the entire ceramic copper circuit board, as in Figure 3.

[0031] In Figure 5, the ceramic copper circuit board 1 is sandwiched between a base 6 and a buffer material 8, and a strike is applied to the buffer material to increase the hardness of the copper plate and correct the warp. Because the strike is applied while the warp is forced by the weight of the buffer material 8, it is possible to correct the warp with a smaller striking force. Also, in Figure 5, the striking part moves while striking partially as in Figure 4, but it is also possible for the striking part 7 to cover the entire ceramic copper circuit board 1 as in Figure 3.

[0032] In Figure 6, the same effect as applying a blow is achieved by applying vibration while applying pressure from above using the impact unit 7. It is possible to correct warping with a small impact force such as vibration, rather than a blow.

[0033] The striking part 7 is preferably made of a material that will not scratch the copper circuit when struck. Examples of materials that can be used for the striking part 7 include resins such as polyacetal (POM), polyamide (PA), polycarbonate (PC), polyvinyl chloride (PVC), thermoplastic elastomer (TPE), and hard rubber, as well as metals such as iron. If scratches or abrasions occur when struck, this can be prevented by sandwiching thin paper or rubber between the striking part 7 and the ceramic copper circuit board 1.

[0034] It is preferable that the base 6 be made of a material that will not scratch the copper circuit when struck or deform when struck. Materials for the base 6 include resins such as polyacetal (POM), polyamide (PA), polycarbonate (PC), polyvinyl chloride (PVC), thermoplastic elastomer (TPE), and hard rubber, metals such as iron, and ceramics such as granite and high-purity alumina. If scratches or abrasions occur when struck, this can be prevented by sandwiching thin paper or rubber between the base 6 and the ceramic copper circuit board 1.

[0035] In Figures 3 to 6, the circuit section faces the striking section, but it is also possible to have the circuit section 3 facing the base 6 and the heat dissipation section 5 facing the striking section 7. Also, instead of striking a single ceramic copper circuit board 1, it is also possible to strike multiple or multi-cavity boards. Also, in Figures 3 to 6, the base 6 is fixed and the striking section 7 moves up and down to strike, but it is also possible for the striking section 7 to be fixed and the base 6 to move up and down. Furthermore, the base 6 and striking section 7 may be installed vertically, and the ceramic copper circuit board 1 may be placed upright and struck horizontally.

[0036] In the method for manufacturing a ceramic copper circuit board according to the embodiment, the copper plates of the circuit section and the heat dissipation section have a thickness greater than the thickness of the ceramic substrate.

[0037] As mentioned above, the hardness of the copper plate is increased by striking to correct the warp, so the warp of the ceramic substrate follows the copper plate. For this reason, it is preferable that the copper plate is thicker than the ceramic substrate. If the ceramic substrate is thicker than the copper plate, the force to correct the warp of the ceramic substrate is insufficient, and the warp cannot be corrected. For this reason, by making the copper plate thicker than the ceramic substrate, the hardness of the copper plate is increased, allowing the ceramic substrate to follow the copper plate whose warp has been corrected.

[0038] In the method for manufacturing a ceramic copper circuit board according to the embodiment, the difference in thickness between the copper plate in the circuit portion and the copper plate in the heat dissipation portion is 0.05 mm or more.

[0039] As mentioned above, the warpage of ceramic copper circuit boards caused by the difference in thickness between the copper plate in the circuit section and the copper plate in the heat dissipation section is close to a simple shape. In other words, the warpage is caused by the difference in thermal expansion due to the difference in thickness of the copper plate, so the thinner side of the copper plate warps convexly. In this type of warpage, applying a striking force to the ceramic circuit board increases the hardness of the copper plate, making it possible to correct the warpage.

[0040] In the method for manufacturing a ceramic copper circuit board according to the embodiment, the ceramic substrate is a silicon nitride substrate.

[0041] As mentioned above, the three-point bending strength of silicon nitride substrates can be increased to over 600 MPa, and even to over 700 MPa. This makes silicon nitride substrates ideal for correcting warpage, as they are less likely to be damaged when impact forces are applied. Furthermore, the thermal conductivity of silicon nitride substrates can be increased to over 50 W / m·K, and even to over 80 W / m·K. In recent years, silicon nitride substrates have become available that combine both high strength and high thermal conductivity. Because silicon nitride substrates are so strong, they can be made thinner, enabling them to dissipate heat better.

[0042] Next, a method for manufacturing a ceramic copper circuit board according to an embodiment will be described in detail. Copper plates are bonded to both sides of a ceramic substrate, and an etching process is used to form a circuit section on one side of the ceramic substrate and a heat dissipation section on the other side. After forming the ceramic copper circuit board, a striking force is applied to the ceramic copper circuit board to set the hardness of the copper plate to 45 Hv or more and the amount of warping of the ceramic copper circuit board to 2 μm / mm or less. Here, an example of a method for obtaining ceramic circuit boards with a high yield will be given.

[0043] First, a ceramic substrate and a copper plate are prepared. The ceramic substrate is preferably one selected from an aluminum oxide substrate, an aluminum nitride substrate, and a silicon nitride substrate. In particular, considering the heat dissipation properties of the entire circuit board, the ceramic substrate is preferably a silicon nitride substrate with a thermal conductivity of 50 W / m·K or more and a three-point bending strength of 600 MPa or more. Furthermore, when through holes are used to connect the circuits on the upper surface and the lower surface of the ceramic substrate, a ceramic substrate with through holes is prepared. When through holes are provided in the ceramic substrate, they may be provided in advance at the molded body stage. Alternatively, through holes may be provided in the ceramic substrate (ceramic sintered body). The through holes are provided by laser processing, cutting, etc. Cutting processes include drilling using a drill or the like.

[0044] The copper plate is preferably one selected from copper or a copper alloy. When the copper plates are joined individually without etching, the copper circuit components are preferably processed into the individual shapes of the circuit section and heat dissipation section on the upper and lower surfaces. When the copper circuit is formed using etching, the copper plate is preferably one having the same thickness on the upper and lower surfaces.

[0045] The ceramic substrate 2 is bonded to the circuit section 3 on the upper surface and the heat dissipation section 5 on the lower surface via a bonding layer 4. The ceramic substrate and the copper plate are preferably bonded by an active metal bonding method. Examples of active metals include titanium (Ti), zirconium (Zr), hafnium (Hf), and niobium (Nb). In the active metal bonding method, an active metal brazing material containing an active metal such as titanium is used. Examples of the active metal brazing material include a mixture of titanium and copper, and a mixture of titanium, silver, and copper. In the active metal brazing material, for example, the titanium content is 0.1 to 10 wt%, the copper content is 10 to 60 wt%, and the remainder is silver. If necessary, 1 to 15 wt% of one or more selected from the group consisting of indium (In), tin (Sn), aluminum (Al), silicon (Si), carbon (C), and magnesium (Mg) may be added. The active metal brazing material components are mixed with an organic substance to form a paste. In the paste, it is preferable that the active metal brazing material components are mixed uniformly, because if the active metal brazing material components are distributed unevenly, brazing will be unstable, which will cause poor bonding.

[0046] Next, the active metal brazing paste is printed on the ceramic substrate and dried. Next, a copper plate is placed on the dried active metal brazing paste. Next, the ceramic substrate with the copper plate placed thereon is heated at 700 to 900°C to bond it. The heating process is carried out in a vacuum or a non-oxidizing atmosphere as required. When carried out in a vacuum, the temperature is set to 1×10 -2 The pressure is preferably 50 Pa or less. Examples of non-oxidizing atmospheres include a nitrogen atmosphere and an argon atmosphere. By using a vacuum or a non-oxidizing atmosphere, oxidation of the bonding layer can be suppressed, thereby improving the bonding strength. According to the active metal bonding method, the bonding strength between the ceramic substrate and the metal circuit can be 50 MPa or more. When forming a circuit by etching, the copper plate is etched after bonding to form the circuit shape.

[0047] The ceramic copper circuit board can be manufactured by the above-mentioned process. Next, a striking force is applied to the ceramic copper circuit board to reduce the amount of warping of the ceramic copper circuit board to 2 μm / mm or less. The striking force is applied to the ceramic copper circuit board by the methods shown in Figures 3 to 6, as described above. When the thickness of the ceramic copper circuit board is T and the amount of warping is W, if W>T, it is preferable to apply the striking force in multiple steps.

[0048] The method of impact is to place the ceramic copper circuit board on the base 6 and then impact it by lowering the impact unit from above. If a device is used, a stamp mill or the like is used.

[0049] Furthermore, a metal thin film containing one selected from the group consisting of nickel (Ni), silver, and gold (Au) as a main component may be provided on the surface of the metal circuit. Examples of such a metal thin film include a plated film and a sputtered film. By providing a metal thin film, corrosion resistance, solder wettability, and the like can be improved.

[0050] Semiconductor elements and the like are bonded to the ceramic copper circuit board with reduced warpage in this way. A bonding layer is provided at the location where the semiconductor elements are to be bonded. The bonding layer preferably contains solder or brazing material. The required number of semiconductor elements are then provided on the bonding layer. Resin is also provided around the periphery.

[0051] While semiconductor elements continue to become smaller, the amount of heat generated by the chips is increasing. Therefore, improving heat dissipation is becoming increasingly important for ceramic circuit substrates that mount semiconductor elements. Furthermore, to improve the performance of semiconductor devices (semiconductor modules), multiple semiconductor elements can be mounted on ceramic circuit substrates. If even one semiconductor element exceeds its intrinsic temperature, its resistance changes to a negative temperature coefficient. This can lead to thermal runaway, where power flows intensively, resulting in instantaneous destruction of the semiconductor device. Therefore, reducing the amount of warping in ceramic copper circuit substrates and improving the reliability of the bond between the semiconductor element and the circuitry is highly effective. Furthermore, semiconductor devices using ceramic copper circuit substrates according to embodiments can be used in PCUs, IGBTs, and IPM modules used in inverters for automobiles, including electric vehicles, electric railway vehicles, industrial machinery, and air conditioners. Electric vehicles are becoming increasingly popular. The more reliable the semiconductor device, the greater the safety of the automobile. The same is true for electric railway vehicles, industrial equipment, and other applications.

[0052] (Examples 1 to 11, Comparative Examples 1 to 7, Reference Example 1) The ceramic copper circuit substrates shown in Table 1 were prepared. The ceramic substrates were silicon nitride substrates, aluminum nitride substrates, aluminum oxide (alumina) substrates, and alu-silica substrates. The silicon nitride substrates had a thermal conductivity of 90 W / m·K and a three-point bending strength of 650 MPa. The aluminum nitride substrates had a thermal conductivity of 170 W / m·K and a three-point bending strength of 300 MPa. The aluminum oxide substrates had a thermal conductivity of 25 W / m·K and a three-point bending strength of 400 MPa. The alu-silica substrates had a thermal conductivity of 25 W / m·K and a three-point bending strength of 650 MPa. The ceramic substrates in the examples and comparative examples measured 30 mm x 60 mm. In Table 1, aluminum nitride substrates were abbreviated as AlN.

[0053] Next, copper plates with the thicknesses shown in Table 1 were prepared for use in the circuit and heat dissipation sections. The copper plates were 30 mm x 60 mm in size. The ceramic substrate and copper plate were joined using the active metal joining method. The metal components of the active metal brazing material were 2 wt% titanium, 10 wt% tin, 30 wt% copper, and the remainder silver. The active metal brazing material paste was made by mixing the materials to be used and then adding organic components. The brazing material paste was printed and dried on both sides of the ceramic substrate, and the copper plate was placed on top of it and placed in a vacuum (1 x 10 -2 The substrate was heated at 830°C or higher for 10 minutes at a pressure of 1000 kJ / cm2 or less (less than 100 kJ / cm2). Next, the circuit section and heat dissipation section as shown in Figure 7 were formed by etching to obtain a ceramic copper circuit board. Figure 7(a) is a top view of the ceramic copper circuit board, Figure 7(b) is a cross-sectional view of Figure 7(a) AA', and Figure 7(c) is a bottom view. The circuit section is 20mm x 20mm in two places, and the heat dissipation section is 20mm in size. m x 50mm.

[0054] Next, five ceramic copper circuit boards were sampled and their warpage and hardness were measured. The amount of warpage was determined by placing the ceramic copper circuit board on a flat surface with the convex side facing up and measuring the difference between the maximum and minimum heights of the circuit or heat dissipation area, averaging the measured values. Note that the amount of warpage was determined as positive (+) when the circuit area was convex, and negative (-) when the circuit area was concave. The hardness (Hv) of the copper plate was measured using a method conforming to JIS Z 2244-2009. Measurements were taken at approximately the center of one circuit area and approximately the center of the heat dissipation area, and the average values ​​were used to determine the circuit area hardness (HbS) and the heat dissipation area hardness (HbB). A measuring jig with a window at the measurement area was used, and the measuring jig was fixed with screws to temporarily level the measurement area. The hardness and amount of warpage are shown in Table 1.

[0055] [Table 1]

[0056] Next, impact force was applied to the ceramic copper circuit board to increase the hardness of the copper circuit and reduce warpage. The ceramic copper circuit board was placed on a base with clean paper placed on both sides as a cushioning material. A carbon steel impactor was then struck from above, varying the weight and speed of the impactor. The impactor was 30 mm long x 60 mm wide and had heights of 30 mm, 60 mm, and 90 mm. The impact speed from above was 3 to 5 m / s. The number of impacts ranged from 10 to 30. For the 30 impacts, the impact location was shifted from one edge to the other, taking into account the magnitude of the warpage. For example, the ceramic copper circuit board was struck by inserting approximately 1 / 3 of the board horizontally on one side, followed by another approximately 2 / 3 of the board, including the impacted area, and finally the entire board was struck. The impact force and number of impacts are shown in Table 2.

[0057] Next, five samples of the ceramic copper circuit boards that had been subjected to the impact force were taken, and the hardness (Hv) of the copper plate was measured using the same method as before the impact. The measurement locations were approximately the same as the locations measured before the impact, namely, approximately the center of one circuit section and approximately the center of the heat dissipation section, and the values ​​were averaged to determine the circuit section hardness after impact (HaS) and the heat dissipation section hardness after impact (HaB). The hardness ratio of the circuit section (HaS / HbS) and the heat dissipation section (HaB / HbB) before and after the impact were also calculated. The hardness and hardness ratios are shown in Table 2.

[0058] [Table 2]

[0059] The hardness of the circuit section and heat dissipation section in the examples increased to 45 Hv or more. This is because work hardening occurred due to the application of impact force, increasing the hardness. For example, in Example 1, 20 impacts of 3.8 J were applied, resulting in a total of 76 J of impacts. In contrast, in the comparative examples, the hardness increase was small or nonexistent, being less than 45 Hv. This is because the impact force was small and insufficient to increase the hardness of the copper. For example, in Comparative Example 1, 10 impacts of 2.6 J were applied, resulting in a total of only 26 J of impacts.

[0060] Next, in the same way as before the impact, the ceramic copper circuit board was placed on a flat surface with the convex side facing up, and the difference between the maximum and minimum heights of the circuit part or heat dissipation part was measured and averaged to obtain the amount of warpage after the impact. Note that the amount of warpage was positive (+) when the circuit part was convex, and negative (-) when it was concave.

[0061] In addition, the withstand voltage (3 kV) on both sides was measured in insulating oil, and a withstand voltage test was conducted on the circuit part and heat dissipation part of the ceramic copper circuit board. If all five pieces had a withstand voltage of 3 kV, it was rated as passed (◯), and if any shorted out, it was rated as failed (×). The amount of warping after impact and the results of the withstand voltage test are shown in Table 3.

[0062] [Table 3]

[0063] The amount of warpage of the ceramic copper circuit board of the example was within the preferred range. This is because the increase in copper hardness caused the hardness of the copper, which had been plastically deformed, to increase, correcting the warpage of the ceramic copper circuit board. In contrast, the amount of warpage of the comparative example was outside the preferred range. No increase in hardness occurred, and the correction of warpage was insufficient. This was because the impact force was small and insufficient to increase the hardness of the copper.

[0064] Furthermore, the voltage resistance test of the examples was favorable. This is because the impact force corrected the warpage, but the impact force did not damage the ceramic substrate, and insulation was maintained. In contrast, comparative examples 2, 4, and 6 failed the voltage resistance test. When the copper plate and etching layer of these failed products were dissolved, cracks were observed in the ceramic substrate. This is because the impact force was too strong, damaging the ceramic substrate and causing it to lose insulation.

[0065] From these experimental results, it can be said that the present embodiment can correct the warpage and reduce the amount of warpage even when a thick copper circuit is formed on a thin ceramic substrate.

[0066] Although several embodiments of the present invention have been described above, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other. [Explanation of symbols]

[0067] 1...Ceramic copper circuit board 2...Ceramic substrate 3...Circuit section 4...Joining layer 5...Heat radiation part 6...Pedestal 7...Striking section 8…Cushioning material

Claims

1. A ceramic copper circuit board comprising a copper plate formed as a circuit portion on one side of a ceramic substrate and a copper plate formed as a heat dissipation portion on the opposite side, the copper plate being work-hardened to a hardness of 45 Hv or more, characterized in that the amount of warpage of the ceramic copper circuit board is 2 μm / mm or less and the withstand voltage is 3 kV or more.

2. 2. The ceramic copper circuit board according to claim 1, wherein the thickness of the copper plates in the circuit section and the heat dissipation section is greater than the thickness of the ceramic substrate.

3. 3. The ceramic copper circuit board according to claim 1, wherein the difference in thickness between the copper plate of the circuit portion and the copper plate of the heat dissipation portion is 0.05 mm or more.

4. 3. The ceramic copper circuit board according to claim 1, wherein the ceramic substrate is a silicon nitride substrate.

5. 4. The ceramic copper circuit board according to claim 3, wherein the ceramic substrate is a silicon nitride substrate.

6. 3. The ceramic copper circuit board according to claim 1, wherein the copper plate is bonded to the ceramic substrate by an active metal bonding method.

7. 4. The ceramic copper circuit board according to claim 3, wherein the copper plate is bonded to the ceramic substrate by an active metal bonding method.

Images