Method for measuring dielectric withstand voltage of ceramic circuit board

Abstract

The present invention improves measurement efficiency of dielectric withstand voltage of a ceramic circuit board having a plurality of metal plates joined to one face of a ceramic substrate. According to the present invention, in a method for measuring dielectric withstand voltage of a ceramic circuit board, the ceramic circuit board includes: a ceramic substrate having a first face and a second face on a reverse side from the first face; a plurality of first metal plates joined to the first face; and at least one second metal plate joined to the second face. The method includes: disposing a conductive rubber member covering the plurality of first metal plates on the plurality of first metal plates; and disposing a measurement electrode on the conductive rubber member.

Description

Method for measuring the dielectric strength of ceramic circuit boards

[0001] The embodiment relates to a method for measuring the dielectric strength of a ceramic circuit board.

[0002] Ceramic circuit boards are used in circuit boards for mounting semiconductor elements. Examples of ceramic circuit boards include those with improved side profiles compared to metal plates. Ceramic circuit boards have a pattern on the metal plate. In recent years, the pattern shapes of ceramic circuit boards have become more complex. A ceramic circuit board has multiple metal plates bonded to one side of the ceramic plate.

[0003] Dielectric breakdown voltage (DVM) measurement is used to evaluate the reliability of ceramic circuit boards. DVM breakdown voltage can be measured by placing electrodes on the metal plates on both the front and back surfaces of the ceramic circuit board and measuring the voltage at which the ceramic circuit board undergoes dielectric breakdown. For example, a method is known in which electrodes are placed on the two front metal plates of the ceramic circuit board to measure the DVM breakdown voltage. Another known method involves placing multiple electrodes on the metal plates on both the front and back surfaces of the ceramic circuit board to measure the DVM breakdown voltage.

[0004] Patent No. 7332588 Patent No. 5720860 Patent No. 7540210

[0005] The dielectric strength of a ceramic circuit board having multiple metal plates bonded to one side of a ceramic substrate is measured by placing electrodes on each individual metal plate. As the number of metal plates on one side of the ceramic substrate increases, the number of electrodes that need to be placed on each metal plate also increases, which reduces measurement efficiency. Furthermore, when manufacturing ceramic circuit boards by dividing a large circuit board containing multiple ceramic circuit boards, the number of electrodes required to measure the dielectric strength of the large circuit board before division also increases, making the process more complex.

[0006] The problem that this embodiment aims to solve is to improve the efficiency of measuring the dielectric strength of a ceramic circuit board having multiple metal plates bonded to one surface of a ceramic substrate.

[0007] The method for measuring the dielectric strength of a ceramic circuit board according to the embodiment comprises a ceramic circuit board having a first surface and a second surface opposite to the first surface, a plurality of first metal plates bonded to the first surface, and at least one second metal plate bonded to the second surface, a conductive rubber member covering the plurality of first metal plates placed on the plurality of first metal plates, and measuring electrodes placed on the conductive rubber member.

[0008] This is a schematic cross-sectional diagram showing an example of a ceramic circuit board. This is a schematic cross-sectional diagram illustrating an example of a method for measuring the dielectric strength of a ceramic circuit board. This is a schematic top view diagram illustrating an example of the arrangement structure of conductive rubber members. This is a schematic top view diagram illustrating an example of the arrangement structure of conductive rubber members. This is a schematic top view diagram illustrating an example of the arrangement structure of conductive rubber members. This is a schematic top view diagram showing an example of a conductive rubber member having a metal part. This is a schematic top view diagram showing an example of a conductive rubber member having a metal part.

[0009] The method for measuring the dielectric strength of a ceramic circuit board according to this embodiment is a method for measuring the dielectric strength of a ceramic circuit board in which metal plates are bonded to both sides of a ceramic circuit board, characterized in that a plurality of metal plates are provided on at least one side of the ceramic circuit board, a conductive rubber member is provided so as to cover the plurality of metal plates, and measuring electrodes are laminated on the conductive rubber member.

[0010] Figure 1 is a schematic cross-sectional view showing an example of a ceramic circuit board. Figure 1 shows a ceramic circuit board 1, a ceramic substrate 2, a metal plate 3, a metal plate 4, and a bonding layer 5. The ceramic circuit board 1 has a ceramic substrate 2, a metal plate 3, a metal plate 4, and a bonding layer 5. The metal plate 3 is sometimes called the front metal plate (first metal plate). The metal plate 4 is sometimes called the back metal plate (second metal plate). Figure 1 shows an example in which three metal plates 3 are bonded to the front surface (first surface) of the ceramic substrate 2, and one metal plate 4 is bonded to the back surface (second surface opposite the first surface). Figure 1 shows an example in which the metal plate 3 is used as a metal circuit board and the metal plate 4 is used as a heat sink. The ceramic circuit board 1 is not limited to this form, and the number of metal plates 3 is not particularly limited as long as there are two or more. The number of metal plates 4 may also be two or more. Furthermore, the metal plate 4 may be used as a metal circuit board. Furthermore, while Figure 1 shows an example of joining metal plates 3 and 4 via a bonding layer 5, the metal plates 3 and 4 may also be directly joined to the ceramic substrate 2 without using the bonding layer 5. Alternatively, a metallization layer or thin film may be used instead of metal plates.

[0011] Figure 2 is a schematic cross-sectional view illustrating an example of a method for measuring the dielectric strength of a ceramic circuit board according to an embodiment. Figure 2 shows a ceramic circuit board 1, a conductive rubber member 6, and a measuring electrode 7. The description of the ceramic circuit board 1 can be appropriately referenced from the description of the ceramic circuit board 1 shown in Figure 1. Figure 2 shows an example in which the conductive rubber member 6 covering a plurality of metal plates 3 is placed in contact with the plurality of metal plates 3, and the measuring electrode 7 is placed in contact with the conductive rubber member 6. Also, Figure 2 shows an example in which the conductive rubber member 6 covering a metal plate 4 is placed in contact with the metal plate 4, and the measuring electrode 7 is placed on the conductive rubber member 6. In Figure 2, the conductive rubber member 6 is also placed on the metal plate 4, but when the metal plate 4 is a single metal plate, it is not necessarily required to place the conductive rubber member 6, and the measuring electrode 7 may be placed in contact with the metal plate 4. When multiple metal plates are joined to one surface of the ceramic substrate 2, it is effective to cover the multiple metal plates with the conductive rubber member 6.

[0012] Providing the conductive rubber member 6 so as to cover multiple metal plates means that the conductive rubber member 6 is arranged across two or more metal plates. The conductive rubber member 6 may be arranged so as to overlap at least a portion of each of the multiple metal plates provided on one surface in the thickness direction. It is most preferable that the conductive rubber member 6 is arranged so as to cover all of the multiple metal plates provided on one surface. By covering all of the multiple metal plates, the dielectric strength of the area where all the metal plates are provided can be measured together.

[0013] Because the conductive rubber member 6 is flexible, it adheres well even if the metal plates 3 and 4 have irregularities. Furthermore, even if the ceramic circuit board 1 is warped, the conductive rubber member 6 can be placed in close contact with it. In addition, the conductive rubber member 6 also adheres well to the measuring electrode 7. In conventional methods, where the measuring electrode 7 is placed directly on each of the multiple metal plates 3, adhesion decreases if there are minute irregularities on the surface of the metal plates 3. This decrease in adhesion can lead to measurement errors.

[0014] Figures 3, 4, and 5 are schematic top views illustrating an example of the arrangement structure of the conductive rubber member 6. Figures 3, 4, and 5 show a ceramic circuit board 1, a metal plate 3, and a conductive rubber member 6. Figure 3 shows the surface (first surface) of the ceramic circuit board 1 on the metal plate 3 side. Figure 3 shows an example of a ceramic circuit board formed by joining five metal plates 3. Figure 4 shows an example of covering five metal plates 3 with a conductive rubber member 6. Figure 5 shows an example of covering five metal plates 3 with two conductive rubber members 6. The arrangement is not limited to these, and the same applies when a conductive rubber member 6 is provided on the surface (second surface) on the metal plate 4 side. There may be one conductive rubber member 6 on each surface or multiple conductive rubber members 6. Furthermore, when multiple conductive rubber members 6 are provided, the measuring electrode 7 is arranged so as to straddle each conductive rubber member 6. By arranging the measuring electrode 7 so as to straddle multiple conductive rubber members 6, the dielectric strength can be measured with a single measuring electrode 7.

[0015] The volume resistivity of the conductive rubber member 6 is not particularly limited as long as the dielectric strength can be measured, but in the unpressurized state it is 1 × 10⁻⁶.６ It is preferable that the resistance is Ω·cm or less. Furthermore, the volume resistivity of the conductive rubber member 6 is 1 × 10⁻¹⁰ in the unpressurized state. ３ It is preferable that the volume resistivity is Ω·cm or less. A lower volume resistivity of the conductive rubber member 6 improves the accuracy of the dielectric strength measurement. The lower limit of the volume resistivity of the conductive rubber member 6 is not particularly limited, but it is 1 × 10⁻⁶. －６ A value of Ω·cm or higher is preferred. An example of a method for measuring the volume resistivity of the conductive rubber member 6 includes the double-ring electrode method in accordance with JIS-K-6271. JIS-K-6271 corresponds to ISO 14309.

[0016] Figures 4 and 5 show an example using a conductive rubber member 6 having a rectangular planar shape. As will be described later, a rectangular conductive rubber member 6 makes it easier to control the angle of the metal part 9, which will be described later. The planar shape of the conductive rubber member 6 is not limited to a rectangular shape, but may be various shapes such as a circle (including an ellipse), a triangle, a polygon, or an L-shape.

[0017] The dielectric strength of the ceramic circuit board 1 may be measured in insulating oil, if necessary.

[0018] The conductive rubber member 6 can be formed by mixing a conductive substance with rubber, which is an insulator. The conductive substance can be any substance that has conductivity. Examples of conductive substances include metal powder, metal pieces, metal wires, and metal fillers. Metal powder refers to a small aspect ratio of 2 or less. Metal fillers refer to needle-shaped or fibrous materials with an aspect ratio greater than 2. Metal pieces can be, for example, metal plates that have been cut. The shape of the metal pieces can be various, such as square, disc-shaped, or triangular. Metal wires can be, for example, elongated. Metal wires may also be long metal wires that have been cut to a predetermined size. Furthermore, the conductive member is preferably a metal piece or a metal wire. Using a metal piece or a metal wire makes it easier to form the anisotropic conductive rubber member described later. Furthermore, the short diameter of the metal piece or metal wire is preferably 0.5 mm or more.

[0019] The conductive rubber member 6 is preferably anisotropic conductive rubber. Anisotropic conductive rubber has the characteristic of conducting in a certain direction but not in a direction other than the aforementioned certain direction. An example of anisotropic conductive rubber is one that conducts in the thickness direction of the conductive rubber member 6 but does not conduct in the short side direction or long side direction of the conductive rubber member 6. The thickness direction of the conductive rubber member 6 refers to the stacking direction of the metal plate 3 or metal plate 4, the conductive rubber member 6, and the measuring electrode 7. By using anisotropic conductive rubber that has conductivity in the thickness direction of the conductive rubber member 6 for the conductive rubber member 6, it is possible to prevent conduction in the lateral direction such as the short side direction or long side direction of the conductive rubber member 6. This improves measurement accuracy and safety. If the conductive rubber of the conductive rubber member 6 does not have anisotropic conductivity in the thickness direction, the sides of the conductive rubber member 6 will also be conductive. Conduction on the sides may cause unnecessary leakage current. From this point of view as well, it is preferable that the conductive rubber member 6 is anisotropic conductive rubber that has conductivity in the thickness direction.

[0020] The rubber used in the conductive rubber member 6 preferably satisfies the requirements of JIS-K-6200. JIS-K-6200 corresponds to ISO 1382. JIS-K-6200 defines rubber as an elastomer that is essentially insoluble (but can swell) in a boiling solvent such as benzene, methyl ethyl ketone, or an ethanol-toluene azeotropic mixture, and that can be modified or has already been modified. Examples of rubbers used in the conductive rubber member 6 include silicone rubber, fluoropolymer rubber, ethylene propylene rubber, and nitrile rubber. These rubbers have a volume resistivity of 10 １１ ~10 １８ It has high insulating properties, approximately Ω·cm.

[0021] Examples of conductive materials used in the conductive rubber member 6 include copper, copper alloys, aluminum, aluminum alloys, and carbon. The volume percentage of the conductive material in the conductive rubber member 6 is preferably within the range of 10% to 80% by volume. If the conductive material is less than 10% by volume, the conductivity may be insufficient. If the conductive material exceeds 80% by volume, the strength of the conductive rubber member 6 may decrease. It is more preferable that the conductive material in the conductive rubber member 6 is within the range of 20% to 70% by volume.

[0022] The thickness 8 of the conductive rubber member 6 is preferably, for example, within the range of 0.15 mm to 5 mm. By controlling the thickness 8 of the conductive rubber member 6, it is possible to suppress damage due to pressing force and to impart anisotropic conductivity at the same time. If the thickness 8 of the conductive rubber member 6 is less than 0.15 mm, it may be damaged by the pressing force when the metal plate 3 or metal plate 4 is laminated with the conductive rubber member 6 and measuring electrode 7. Also, if the thickness 8 of the conductive rubber member 6 exceeds 5 mm, it may be difficult to make it anisotropic conductive rubber. The thickness of the conductive rubber member 6 is more preferably within the range of 0.2 mm to 2 mm.

[0023] The conductive rubber member 6 preferably has a metal part. Figures 6 and 7 are schematic top views showing an example of a conductive rubber member 6 having a metal part. Figures 6 and 7 show the conductive rubber member 6, the metal part 9, the width 10 of the conductive rubber member 6, the pitch width 11 of the metal part 9 within the conductive rubber member 6, and the angle 12 of the metal part 9. Figures 6 and 7 show the mounting surface of the metal plate 3 or metal plate 4 in the conductive rubber member 6. It is preferable that there is one metal part 9 in the thickness direction of the conductive rubber member 6. This can suppress damage due to pressing force.

[0024] An example of the metal part 9 is at least one selected from the group consisting of metal powder, metal pieces, metal wires, and metal fillers. The metal part 9 is preferably a metal piece or a metal wire. If the metal part 9 is a metal piece or a metal wire, it is easier to form anisotropic conductive rubber. The metal part 9 is arranged on or near the surface of the conductive rubber member 6. When a pressing force is applied to the conductive rubber member 6, the metal part 9 makes the conductive rubber member 6 conductive in the thickness direction, thereby imparting anisotropic conductivity. The metal piece may have a square cross-section. The metal wire may have a circular (including elliptical) cross-section. By using a metal piece or a metal wire, a contact area can be secured when pressed. It is also preferable that a part of the metal part 9, such as a metal piece or metal wire, is exposed on the surface of the conductive rubber member 6. The metal part 9, such as metal powder, metal pieces, metal wires, or metal fillers, can be formed using copper or aluminum.

[0025] Figures 6 and 7 show an example in which multiple metal parts 9 are arranged along the long side direction of the conductive rubber member 6, but the number of multiple metal parts 9 is not limited to the number shown in Figures 6 and 7. Multiple metal parts 9 may also be arranged along the short side direction of the conductive rubber member 6. The pitch width 11 of the metal parts 9 is preferably in the range of 0.03 mm or more and 0.1 mm or less. The pitch width 11 of the metal parts 9 is the shortest distance between adjacent metal parts 9 when viewed from the pressing surface of the conductive rubber member 6. The pressing surface of the conductive rubber member 6 is the surface shown by the long side (X axis) × short side (Y axis) when the long side (X axis), short side (Y axis), and thickness (Z axis) of the conductive rubber member 6 are defined. The long side and short side of the conductive rubber member 6 are perpendicular to the thickness direction of the conductive rubber member 6. By controlling the pitch width 11 of the metal parts 9, both conductivity and flexibility of the conductive rubber member 6 can be achieved. If the pitch width 11 of the metal parts 9 is less than 0.03 mm, the flexibility of the conductive rubber member 6 may decrease. If the flexibility decreases, the adhesion to the multiple metal plates may decrease. Also, if the pitch width 11 of the metal parts 9 is larger than 0.1 mm, the conductivity may decrease.

[0026] Furthermore, it is preferable that the aspect ratio of the metal part 9 is 2 or greater. The aspect ratio of the metal part 9 is the ratio of the long side to the short side of the metal piece or metal wire. If the metal part 9 has an aspect ratio of 2 or greater, it is easier to arrange it at a predetermined pitch width 11 on the pressing surface of the conductive rubber member 6 (the surface indicated by the long side (X axis) × short side (Y axis)). There is no particular upper limit to the aspect ratio of the metal part 9, but it is preferable that it does not protrude from the side surface of the conductive rubber member 6.

[0027] The metal part 9 may be positioned diagonally, as shown in Figure 7. Positioning diagonally means that the long side of the metal part 9 is not parallel to either the long side (X-axis) or the short side (Y-axis) of the conductive rubber member 6.

[0028] The angle 12 of the metal part 9 is preferably within the range of 10° to 80°. The angle 12 of the metal part 9 is the angle of the long side of the metal part 9 relative to the long side of the conductive rubber member 6, with the long side (X-axis) of the conductive rubber member 6 being set to 0°. By giving the metal part 9 an angle, the strength of the conductive rubber member 6 can be improved. In addition, by arranging the metal part 9 diagonally, the metal part 9 will straddle multiple metal plates 3, thereby improving measurement accuracy. If the planar shape of the conductive rubber member 6 is not rectangular, the angle of the long side of the metal part 9 can be determined by setting the angle of the long side of the ceramic substrate 2 to 0°.

[0029] An example of a method for manufacturing the conductive rubber member 6 is to perform a mixing step, a molding step, and a heating step, which involve mixing the elastomer, which will serve as the rubber base material, with the conductive substance and the material for the metal part. If necessary, the conductive rubber member 6 can also be cut to control its size.

[0030] To adjust the pitch width 11 and angle 12 of the metal part 9, a method can be used in which the metal parts 9 are arranged in a mold beforehand and elastomer is poured in to form them. Alternatively, a method can be used in which a large conductive rubber member 6 is made using a long metal part 9 and then cut to the required size. With this method, a structure can be made in which the metal part 9 is exposed on the surface of the conductive rubber member 6.

[0031] With the dielectric strength measurement method for a ceramic circuit board according to the embodiment, the maximum applied voltage during measurement (voltage applied to the ceramic circuit board 1) can be set to 2kV or more. The dielectric strength is measured until the ceramic circuit board 1 undergoes dielectric breakdown. For example, if the dielectric strength of a ceramic circuit board 1 using a silicon nitride substrate with a thickness of 0.32 mm is 25kV / mm, the applied voltage at the time of dielectric breakdown will be 8kV (= 25kV / mm × 0.32 mm). With the conductive rubber member 6 described above, damage can be suppressed even if the applied voltage is increased. Therefore, it can be used repeatedly. The dielectric strength measurement method in which the applied voltage is increased until dielectric breakdown occurs is called the first dielectric strength measurement method. The second dielectric strength measurement method is a method in which the applied voltage is not increased until dielectric breakdown occurs. It is preferable to set the applied voltage within a range of 20% to 80% (range confirmation) of the catalog value of the dielectric strength of the ceramic circuit board 1.

[0032] For example, if the catalog value of the dielectric strength of a ceramic circuit board 1 using a silicon nitride substrate with a thickness of 0.32 mm is 20 kV / mm, the applied voltage is set within the range of 1.28 kV to 5.12 kV (calculated to be within the range of 20-80%). By setting the applied voltage to 20 kV / mm (catalog value), a lower value will be detected if the product is defective. By not increasing the applied voltage until dielectric breakdown occurs, defective products can also be sorted out. The first dielectric strength measurement method is a destructive test. Therefore, the first dielectric strength measurement method is for sampling inspection and is not suitable for 100% inspection. On the other hand, the second dielectric strength measurement method does not increase the applied voltage until dielectric breakdown occurs, making it suitable for sorting out defective products. Therefore, the second dielectric strength measurement method can also be applied to 100% inspection. The second dielectric strength measurement method may also be used for sampling inspection. Furthermore, with the second dielectric strength measurement method, the ceramic circuit board 1 after measurement can be used in semiconductor devices.

[0033] An example of the ceramic substrate 2 is one selected from, for example, a silicon nitride substrate, an aluminum nitride substrate, an aluminum oxide substrate, and a zirconium oxide substrate.

[0034] The thermal conductivity of the silicon nitride substrate is 50 W / m·K or higher, and even 80 W / m·K or higher. Furthermore, the three-point bending strength of the silicon nitride substrate is 600 MPa or higher, and even 700 MPa or higher.

[0035] The thermal conductivity of aluminum nitride substrates is 150 W / m·K or higher, and even 200 W / m·K or higher. The three-point bending strength of aluminum nitride substrates is approximately 300 MPa to 450 MPa. The three-point bending strength of aluminum oxide substrates is approximately 300 MPa to 450 MPa, but aluminum oxide substrates are cheaper than other substrates. Furthermore, the thermal conductivity of aluminum oxide substrates is approximately 20 W / m·K to 30 W / m·K. The three-point bending strength of zirconium oxide substrates is high at approximately 550 MPa, but the thermal conductivity is approximately 30 W / m·K to 50 W / m·K.

[0036] The thickness of the ceramic substrate 2 is preferably between 0.2 mm and 3 mm, and more preferably between 0.2 mm and 1 mm. If the thickness of the ceramic substrate 2 is less than 0.2 mm, the strength may be insufficient. Also, if the thickness of the ceramic substrate 2 exceeds 3 mm, it may become a thermal resistor and its heat dissipation may decrease. Furthermore, since silicon nitride substrates have high strength, their thickness can be within the range of 0.2 mm to 0.5 mm. From the viewpoint of thinning the substrate, it is preferable to use a silicon nitride substrate.

[0037] As the metal plates 3 and 4, one or more selected from copper plates (including copper alloy plates) and aluminum plates (including aluminum alloy plates) can be mentioned. As the metal plates 3 and 4, a copper plate is preferable. Moreover, an oxygen-free copper plate is preferable. Oxygen-free copper has a copper purity of 99.96 wt% or more as shown in JIS-H-3100. The thermal conductivity of copper is about 400 W / m·K, and the thermal conductivity of aluminum is about 240 W / m·K. Copper has a higher thermal conductivity than aluminum. By using a copper plate as the metal plates such as the metal plates 3 and 4, the heat dissipation property of the metal plate is improved. Also, the aluminum plate is preferably pure aluminum. Pure aluminum is shown in JIS-H-4000. Note that JIS-H-4000 corresponds to ISO6361. JIS-H-3100 corresponds to ISO197 and the like.

[0038] The ceramic substrate 2 and the metal plates 3 and 4 are preferably joined via a joining layer 5. The joining layer 5 is preferably a member formed by using an active metal joining method. The active metal joining method is a joining method using one or more active metals selected from Ti (titanium), Zr (zirconium), and Hf (hafnium). Also, when the metal plates 3 and 4 are copper plates, it is preferable to use an active metal brazing filler metal mainly composed of copper (Cu) or silver (Ag) and containing an active metal selected from Ti, Zr, and Hf. Also, when the metal plates 3 and 4 are aluminum plates, the active metal becomes Si (silicon), and it is preferable to use an active metal brazing filler metal mainly composed of Al and containing Si. The main component mentioned here is the component most contained among the metal components of the brazing filler metal.

[0039] The active metal brazing filler metal mainly composed of Ag or Cu contains Ag (silver) of 0 mass% or more and 80 mass% or less, Cu (copper) of 15 mass% or more and 70 mass% or less, and Ti (titanium) or TiH ２ (titanium hydride) of 1 mass% or more and 15 mass% or less, preferably. Ti and TiH ２When both are used, the total of these shall be within the range of 1% by mass or more and 15% by mass or less. If necessary, one or both of Sn (tin) or In (indium) may be contained in the active metal brazing filler metal within the range of 1% by mass or more and 50% by mass or less. Also, if necessary, C (carbon) may be contained in the active metal brazing filler metal within the range of 0.1% by mass or more and 2% by mass or less.

[0040] When both Ag and Cu are used, Ag shall be within the range of 20% by mass or more and 60% by mass or less, Cu shall be within the range of 15% by mass or more and 40% by mass or less, and one or both of Sn or In shall be within the range of 5% by mass or more and 30% by mass or less, and Ti or TiH ２ is preferably within the range of 1% by mass or more and 15% by mass or less.

[0041] When Ag is the main component, Ag shall be within the range of 50% by mass or more and 80% by mass or less, and one or both of Sn or In shall be within the range of 5% by mass or more and 30% by mass or less, and Ti or TiH ２ is preferably within the range of 1% by mass or more and 15% by mass or less. The main component is the component with the largest amount among the constituent components.

[0042] When Cu is the main component, Cu shall be within the range of 40% by mass or more and 70% by mass or less, and one or both of Sn or In shall be within the range of 5% by mass or more and 50% by mass or less, and Ti or TiH ２ is preferably within the range of 1% by mass or more and 15% by mass or less.

[0043] The ratio of the active metal brazing filler metal composition is calculated with the total of the raw materials to be mixed as 100% by mass. For example, when the active metal brazing filler metal is composed of three kinds of Ag, Cu, and Ti, Ag + Cu + Ti = 100% by mass. Ag, Cu, TiH ２ When the active metal brazing filler metal is composed of four kinds of In, Ag + Cu + TiH ２ + In = 100% by mass. When the active metal brazing filler metal is composed of five kinds of Ag, Cu, Ti, Sn, and C, Ag + Cu + Ti + Sn + C = 100% by mass.

[0044] Ag or Cu are components that form the base material of the brazing material. Sn or In have the effect of lowering the melting point of the brazing material. C (carbon) has the effect of controlling the fluidity of the brazing material and controlling the structure of the bonded layer by reacting with other components. For this reason, examples of brazing material components include Ag-Cu-Ti, Ag-Cu-Sn-Ti, Ag-Cu-Ti-C, Ag-Cu-Sn-Ti-C, Ag-Ti, Cu-Ti, Ag-Sn-Ti, Cu-Sn-Ti, Ag-Ti-C, Cu-Ti-C, Ag-Sn-Ti-C, and Cu-Sn-Ti-C. In may be used instead of Sn. Both Sn and In may be used.

[0045] The active metal brazing material may contain one or more elements selected from tungsten (W), molybdenum (Mo), and rhenium (Re) in an amount of 0.1% to 10% by mass. The fluidity of the active metal brazing material can be controlled by adding tungsten, molybdenum, or rhenium. Magnesium (Mg) may also be added to the active metal brazing material. An example of an active metal mainly composed of Al is one in which Si is 0.01% to 20% by mass and the remainder is Al.

[0046] The activated metal bonding method involves applying an activated metal brazing paste onto a ceramic substrate 2, placing a metal plate 3 or 4 on top of it, and performing heat bonding. The heat bonding process is preferably performed at a temperature between 600°C and 950°C. This process allows for the production of a bonded body. By applying an etching process to the resulting bonded body, a circuit shape can be imparted to the metal plate. By imparting a circuit shape to the metal plate, a ceramic circuit board 1 is formed. Alternatively, the ceramic circuit board 1 may have a metallized layer or a thin film instead of a metal plate.

[0047] The longest side of the ceramic substrate 2 may be 150 mm or more, and even 200 mm or more. A ceramic substrate with a longest side of 150 mm or more, and even 200 mm or more, is called a large substrate. A ceramic circuit board using a large substrate may be used as a circuit board as is, or it may be made into multiple pieces. Making multiple pieces means dividing the ceramic circuit board using a large substrate into individual ceramic circuit boards. For example, this can be done by scribing. A ceramic circuit board or assembly using a large substrate before making multiple pieces is sometimes called a master card (or master substrate).

[0048] The dielectric strength measurement method for a ceramic circuit board according to this embodiment uses a conductive rubber member 6, allowing measurement to be performed in a single measurement regardless of the size of the ceramic circuit board 1. In other words, it can be measured as a master card, or each individual ceramic circuit board 1 can be measured after it has been divided. Furthermore, because a conductive rubber member 6 is used, it can accommodate various circuit shapes. Note that since dielectric strength measurement is a destructive test, a sampling inspection is performed by selecting a sample from a certain number. The dielectric strength measurement shall be performed in accordance with the method described in "15. Dielectric breakdown strength test" of JIS-C-2141. In one example of the dielectric strength measurement method, conductive rubber members 6 are placed on both sides of the ceramic circuit board 1. Measuring electrodes 7 are placed on the conductive rubber members 6. The measuring electrodes 7 are made of brass, but are not limited to this. The clamping force of the measuring electrodes 7 is in the range of 2N to 4N.

[0049] (Examples 1-6, Comparative Examples 1-3) As ceramic circuit board 1, ceramic circuit boards A, B, C, and D shown in Table 1 were prepared. Ceramic circuit boards A-D are formed by bonding copper plates to both sides of a silicon nitride substrate (thermal conductivity 90 W / m·K, three-point bending strength 650 MPa) with an activated metal brazing material containing Ti, and then applying a circuit shape by etching. Ceramic circuit board A is a master card for obtaining 10 ceramic circuit boards B by division processing. Similarly, ceramic circuit board D is also a master card for obtaining individual ceramic circuit boards by division. The amount of warpage of ceramic circuit boards A-D is the amount of warpage of the long side of the ceramic substrate 2, and the largest value measured with a three-dimensional shape measuring instrument is shown.

[0050]

[0051] Next, conductive rubber members A, B, C, and D shown in Table 2 were prepared. Conductive rubber members A to D have a planar shape with a rectangular shape between the long side (X axis) and the short side (Y axis). A metal wire is embedded in conductive rubber members A to D to form a metal part 9. Also, conductive rubber members A to D are all rectangular in shape. Conductive rubber member 6 has a volume resistivity of 10 in the unpressurized state. ６ The conductivity is less than or equal to Ω·cm. Conductive rubber members A to D are formed using copper wire and silicone rubber. Conductive rubber members A to D are arranged one by one so as to cover the front and back surfaces of the ceramic circuit board 1, as shown in Figure 4. Measuring electrodes 7 are also placed one by one on each of the conductive rubber members A to D on the front and back surfaces.

[0052]

[0053] Next, as shown in Table 3, the dielectric strength of the ceramic circuit boards according to the embodiment was measured by combining the ceramic circuit boards A to D and conductive rubber members A to D. As a comparative example, the dielectric strength was measured by placing the measuring electrodes 7 in contact with each of the metal plates of the ceramic circuit boards A to C without any conductive rubber members being used. The dielectric strength was measured by applying a voltage until dielectric breakdown was observed. The dielectric strength measurement was performed in insulating oil. The results are shown in Table 3.

[0054]

[0055] As can be seen from Table 3, the dielectric strength could be measured using the methods of the Examples and Comparative Examples. In the Comparative Examples, measuring electrodes 7 had to be placed on each metal plate. In contrast, the Examples use conductive rubber members A to D, which simplifies the installation of measuring electrodes 7. Furthermore, in the Examples, dielectric strength could be measured even if the number of metal plates was different. In addition, in the Examples, dielectric strength could be measured even if the ceramic circuit board 1 was warped.

[0056] Furthermore, the applied voltage during the measurement of dielectric strength could be set to 2kV or higher in all cases. In addition, the embodiment was able to measure the dielectric strength even when the ceramic circuit board 1 was warped. As a result, the measurement time was shortened. Moreover, the dielectric strength of both the embodiment and the comparative example was 25±2kV / mm, and there was no significant difference in the measurement results. Therefore, it was found that the measurement method of the embodiment is reliable in terms of measurement results. Similar results were also obtained when the second dielectric strength measurement method was used, in which 20-80% of the catalog value of dielectric strength was applied.

[0057] Although several embodiments of the present invention have been illustrated above, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. Modifications of these embodiments are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. Furthermore, the embodiments described above can be implemented in combination with each other.

Claims

1. A method for measuring the dielectric strength of a ceramic circuit board, wherein the ceramic circuit board comprises: a ceramic substrate having a first surface and a second surface opposite to the first surface; a plurality of first metal plates bonded to the first surface; and at least one second metal plate bonded to the second surface, and the measurement method comprises: placing a conductive rubber member covering the plurality of first metal plates on the plurality of first metal plates; and placing measuring electrodes on the conductive rubber member.

2. The method for measuring dielectric strength according to claim 1, wherein the conductive rubber member is an anisotropically conductive rubber member having conductivity in the thickness direction of the conductive rubber member.

3. The method for measuring dielectric strength according to claim 1 or claim 2, wherein the thickness of the conductive rubber member is 0.15 mm or more and 5 mm or less.

4. The dielectric strength measurement method according to claim 1 or claim 2, wherein the conductive rubber member has a plurality of metal parts, the plurality of metal parts are arranged in a direction perpendicular to the thickness direction of the conductive rubber member, and the pitch width of the plurality of metal parts is 0.03 mm or more and 0.1 mm or less.

5. The method for measuring dielectric strength according to claim 3, wherein the conductive rubber member has a plurality of metal parts, the plurality of metal parts are arranged in a direction perpendicular to the thickness direction of the conductive rubber member, and the pitch width of the plurality of metal parts is 0.03 mm or more and 0.1 mm or less.

6. The method for measuring dielectric strength according to claim 4, wherein the angle between the long side of each of the plurality of metal parts and the long side of the conductive rubber member is 10° or more and 80° or less.

7. The method for measuring dielectric strength according to claim 5, wherein the angle between the long side of each of the plurality of metal parts and the long side of the conductive rubber member is 10° or more and 80° or less.

8. A method for measuring dielectric strength according to claim 1 or 2, comprising placing a second conductive rubber member covering the at least one second metal plate on the at least one second metal plate, and placing a second measuring electrode on the second conductive rubber member.

9. The method for measuring dielectric strength according to claim 5, comprising placing a second conductive rubber member covering the at least one second metal plate on the at least one second metal plate, and placing a second measuring electrode on the second conductive rubber member.

10. The method for measuring dielectric strength according to claim 7, comprising placing a second conductive rubber member covering the at least one second metal plate on the at least one second metal plate, and placing a second measuring electrode on the second conductive rubber member.

11. The method for measuring dielectric breakdown voltage according to claim 1 or claim 2, wherein the voltage applied to the ceramic circuit board when measuring the dielectric breakdown voltage is 2 kV or more.

12. The method for measuring dielectric breakdown voltage according to claim 8, wherein the voltage applied to the ceramic circuit board when measuring the dielectric breakdown voltage is 2 kV or more.

13. The method for measuring dielectric strength according to claim 1 or claim 2, wherein each of the plurality of first metal plates is a copper plate or an aluminum plate.

14. The method for measuring dielectric strength according to claim 8, wherein each of the plurality of first metal plates is a copper plate or an aluminum plate.

15. The method for measuring dielectric strength according to claim 10, wherein the metal part is made of copper or aluminum.

16. The method for measuring dielectric strength according to claim 1 or claim 2, wherein the long side of the ceramic substrate is 200 mm or more.

17. The method for measuring dielectric strength according to claim 8, wherein the long side of the ceramic substrate is 200 mm or more.

18. The method for measuring dielectric strength according to claim 10, wherein the long side of the ceramic substrate is 200 mm or more.

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