JP7067114B2 - Insulated circuit board and its manufacturing method - Google Patents

Description

The present invention relates to an insulated circuit board on which elements such as power elements, LED elements, and thermoelectric elements are mounted, and a method for manufacturing the same.

As an insulating circuit board formed by joining a metal member and a ceramic member, for example, a ceramic substrate such as AlN (aluminum nitride), _Al2O3 (alumina) _{, Si3N4 (} silicon nitride), and one of the ceramic substrates. A circuit layer made of a metal having excellent conductivity such as aluminum (Al) or copper (Cu) bonded to the surface of the surface is known. In this type of insulated circuit board, a metal layer made of a metal having excellent thermal conductivity may be formed on the other surface of the ceramic substrate, for example, a substrate for a power module on which a power element is mounted. A heat dissipation layer (heat sink) is also joined via a metal layer.

For example, Patent Document 1 discloses a circuit board (insulated circuit board) in which a copper circuit is formed on the surface of a ceramic substrate (ceramic substrate), or a heat-dissipating copper plate is formed on the back surface of the ceramic substrate together with the copper circuit. There is.

Various modules are manufactured by soldering (mounting) elements such as power elements, LED elements, and thermoelectric elements to the surface (upper surface) of the circuit layer of the insulated circuit board configured in this way. Further, the module on which the element is mounted is also sealed with a potting resin or a molding resin from the viewpoint of ensuring insulation and protecting wiring.

Japanese Patent No. 3211856

By the way, inspecting the junction interface between the circuit layer and the element and the junction interface between the circuit layer and the ceramic substrate in various modules, the element and the insulating circuit are inspected by using an ultrasonic exploration imaging device (SAT: Scanning Acoustic Tomograph). It is known that it is performed via each layer of the substrate.
However, when a metal such as copper is bonded to a ceramic substrate to form a circuit layer, for example, when a copper (Cu) plate to be a circuit layer is bonded to a ceramic substrate, the activity of Ag-Cu-Ti system or the like is usually used. It is necessary to use a metal brazing material and heat it at a temperature of 800 ° C. or higher. When heated in such a temperature range, the copper crystal grains become coarser than before heating. Therefore, when the junction interface (solder junction) between the circuit layer and the element is inspected by the ultrasonic exploration imaging device via the insulating circuit board (circuit layer), the reflection of ultrasonic waves in the circuit layer becomes large. The problem is to reduce the inspection accuracy.

On the other hand, as a countermeasure, it is conceivable to use a material for the circuit layer in which the crystal grains do not easily become coarse even when high heat is applied. However, in this case, the surface roughness (surface roughness) of the circuit layer surface becomes small. When a module in which an element is mounted on an insulating circuit board is sealed with a resin, it becomes a problem to reduce the adhesion between the resin and the circuit layer.

The present invention has been made in view of such circumstances, and is an insulating circuit capable of ensuring good inspection accuracy of the joint interface of each component constituting the module and good adhesion between the circuit layer and the resin. It is an object of the present invention to provide a substrate and a method for manufacturing the same.

The insulating circuit board of the present invention includes a ceramic substrate and a circuit layer made of either copper or aluminum formed on one surface of the ceramic substrate, and the circuit layer is one surface of the ceramic substrate. It has a laminated structure having a first circuit layer bonded to the first circuit layer and a second circuit layer bonded to the surface of the first circuit layer, and the average crystal grain size of the second circuit layer is the first circuit layer. It is provided larger than the average crystal grain size of.

In this insulated circuit board, the circuit layer has a laminated structure including a first circuit layer bonded to a ceramics substrate and a second circuit layer bonded to the first circuit layer, and elements are mounted (mounted). The average crystal grain size of the second circuit layer is made larger than the average crystal grain size of the first circuit layer. As described above, in the insulated circuit board, the surface of the circuit layer on which the element is mounted is formed by the second circuit layer by combining the first circuit layer and the second circuit layer having different average crystal grain sizes. Since the second circuit layer has a larger average crystal grain size than the first circuit layer, the surface roughness (surface roughness) of the surface of the second circuit layer is also larger than that of the first circuit layer. When a module in which an element is mounted on a circuit layer (second circuit layer) is sealed with resin, stress tends to concentrate on the corners of the molded resin, especially on the peripheral edges of the circuit layer (periphery of the second circuit layer). In the insulating circuit board of the present invention, the average crystal grain size of the second circuit layer is large and the surface roughness of the surface thereof is large, so that the mold resin can be firmly fixed to the peripheral edge of the second circuit layer and the mold can be molded. Good adhesion between the resin and the circuit layer can be ensured.
Further, as described above, since the circuit layer is formed by the first circuit layer and the second circuit layer, the ratio of the second circuit layer to the entire circuit layer is small, that is, to the entire circuit layer. The thickness of the second circuit layer can be made thin. Therefore, when the junction interface between the element and the circuit layer (second circuit layer) is inspected by the ultrasonic exploration imaging device via the circuit layer, the ratio of ultrasonic reflection in the second circuit layer can be greatly reduced. Therefore, the reflection of ultrasonic waves in the entire circuit layer can be greatly reduced, and the inspection accuracy can be ensured satisfactorily.
Further, as the entire circuit layer, a sufficient thickness can be secured by combining the first circuit layer and the second circuit layer. Therefore, it is possible to satisfactorily secure the electrical transmission performance and heat dissipation performance, which are the functions required for the circuit layer.

As a preferred embodiment of the insulating circuit board of the present invention, the other surface of the ceramic substrate is provided with a metal layer made of the same metal as the circuit layer, and the metal layer is bonded to at least the other surface of the ceramic substrate. It is preferable that the first metal layer is provided, and the first metal layer is provided with an average crystal grain size equivalent to that of the first circuit layer.

Even in an insulating circuit board having a metal layer on the other surface of the ceramics substrate, the first metal layer constituting the metal layer is provided with an average crystal grain size equivalent to that of the first circuit layer, so that an ultrasonic exploration image can be obtained. When the device inspects the junction interface between the element and the circuit layer (second circuit layer) via the insulating circuit board, the reflection of ultrasonic waves can be reduced not only in the circuit layer but also in the metal layer. Therefore, it is possible to ensure good inspection accuracy by the ultrasonic exploration imaging device.

As a preferred embodiment of the insulating circuit board of the present invention, the metal layer has a laminated structure including the first metal layer and the second metal layer bonded to the surface of the first metal layer. It is preferable that the second metal layer is provided with an average crystal grain size equivalent to that of the second circuit layer.

By forming the metal layer as a laminated structure of the first metal layer and the second metal layer and providing the second metal layer with a large average crystal grain size equivalent to that of the second circuit layer, the surface of the surface of the second metal layer is provided. A large roughness can be provided. When the surface roughness of the surface of the metal layer is increased in this way, the wettability between the metal layer and the solder is improved when the heat dissipation layer (heat sink) is superposed on the metal layer and bonded by solder or the like. Therefore, the adhesion between the metal layer and the heat radiating layer and the joining reliability can be improved, and heat can be smoothly radiated from the metal layer to the heat radiating layer. Further, even when the metal layer and the heat radiating layer are laminated with the heat conductive grease sandwiched between them, by increasing the surface roughness of the surface of the metal layer, the heat conductivity between the metal layer and the heat radiating layer is increased. The grease can be retained and the heat conductive grease can be prevented from coming out. Therefore, since the adhesion between the metal layer and the heat radiating layer can be satisfactorily secured, the thermal resistance between the metal layer and the radiating layer can be reduced, and the heat radiating performance can be satisfactorily secured.
Further, since the metal layer is formed by the first metal layer and the second metal layer, the ratio of the second metal layer to the entire metal layer can be reduced. Therefore, the ratio of ultrasonic reflection in the second metal layer when inspecting the joint interface of each component of the module by the ultrasonic exploration imaging device can be greatly reduced, and the reflection of ultrasonic waves in the entire metal layer can be greatly reduced. Therefore, good inspection accuracy can be ensured.

As a preferred embodiment of the insulated circuit board of the present invention, when the circuit layer is copper, the average crystal grain size of the first circuit layer is preferably less than 250 μm. Further, when the circuit layer is made of aluminum, the average crystal grain size of the first circuit layer is preferably less than 375 μm.

When the circuit layer is copper or aluminum, by adjusting the average crystal grain size of the first circuit layer within the above range, both the inspection accuracy by the ultrasonic exploration imaging device and the adhesion at the time of resin encapsulation can be improved. , Can be secured well.

The method for manufacturing an insulated circuit board of the present invention is a circuit for forming a circuit layer having a first circuit layer bonded to one surface of a ceramics substrate and a second circuit layer bonded to the surface of the first circuit layer. It has a layer forming step, and among the circuit layers, as the first metal material to be the first circuit layer, from the second metal material to be the second circuit layer bonded to the surface of the first circuit layer. In addition, a crystal grain suppressing material in which coarsening of crystal grains due to heating is suppressed is prepared, and a clad material in which the first metal material and the second metal material are pressure-bonded is formed, and in the circuit layer forming step. In a state where the first metal material of the clad material is superposed on one surface of the ceramic substrate via a brazing bonding material, the first metal material of the clad material is pressurized and heated in the stacking direction of the ceramic substrate and the clad material. Thereby, the first metal material of the clad material and the ceramic substrate are joined to form the circuit layer having the first circuit layer and the second circuit layer on one surface of the ceramic substrate. ..

As described above, by using the crystal grain suppressing material in which the coarsening of the crystal grains due to heating is suppressed as compared with the second metal material as the first metal material, the circuit layer including the first circuit layer and the second circuit layer is provided. Can be formed. Further, by forming a clad material in which the first metal material and the second metal material are crimped in advance, the clad material and the ceramic substrate are joined by one heating in the circuit layer forming step, and the first metal material is bonded to the ceramic substrate. A circuit layer including one circuit layer and a second circuit layer can be easily formed. Therefore, the manufacturing process of the insulated circuit board can be simplified.

According to the present invention, it is possible to ensure good inspection accuracy of the joint interface of each component constituting the module and good adhesion between the circuit layer and the resin.

It is a vertical sectional view schematically showing the power module using the insulation circuit board of 1st Embodiment of this invention. It is a vertical sectional view of the insulation circuit board shown in FIG. It is a vertical sectional view which shows the manufacturing method of the insulation circuit board shown in FIG. 2 in the order of a process. It is a vertical sectional view schematically showing the insulation circuit board of 2nd Embodiment of this invention. It is a vertical sectional view schematically showing the insulation circuit board of 3rd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a power module 101 using an insulated circuit board (power module substrate) 10 manufactured by the method for manufacturing an insulated circuit board according to the first embodiment of the present invention. The power module 101 includes an insulating circuit board 10 and an element 91 mounted on the surface of the insulating circuit board 10, and the element 91 and the insulating circuit board 10 are resin-sealed with a mold resin 81 made of an epoxy resin or the like. It is a thing. Reference numeral 92 in FIG. 1 indicates a bonding layer such as a solder material to which the element 91 is fixed. In this power module 101, the exposed surface of the power module 101 (exposed surface of the insulating circuit board 10) is pressed against the surface of a heat sink (not shown) or the like via heat conductive grease, or via a solder material, an adhesive or the like. It is used in a state where it is adhered and fixed.

As shown in FIG. 2, the insulating circuit board 10 includes a ceramic substrate 11, a circuit layer 12 formed on one surface of the ceramic substrate 11, and a metal layer 13 formed on the other surface of the ceramic substrate 11. It is equipped with. The ceramic substrate 11 is formed of a ceramic material such as AlN (aluminum nitride), Al ₂ O ₃ (alumina), and Si ₃ N ₄ (silicon nitride).

The circuit layer 12 is formed of copper (pure copper or copper alloy) or aluminum (pure aluminum or aluminum alloy), and a metal plate made of these metals is placed on one surface of the ceramic substrate 11 with Ag-Cu-Ti or Al-. It is formed by joining with a brazing material such as Si. Further, as shown in FIGS. 1 and 2, the circuit layer 12 is a first circuit layer 121 bonded to one surface of the ceramic substrate 11 and a second circuit bonded to the surface of the first circuit layer 121. It has a laminated structure having a layer 122, and the element 91 is mounted on the surface of the second circuit layer 122 arranged on the surface of the circuit layer 12. The average crystal grain size of the second circuit layer 122 is larger than the average crystal grain size of the first circuit layer 121.

When the circuit layer 12 is copper (Cu), the average crystal grain size of the first circuit layer 121 is preferably less than 250 μm, and the average crystal grain size of the second circuit layer 122 is preferably 250 μm or more. On the other hand, when the circuit layer 12 is made of aluminum (Al), it is preferable that the average crystal grain size of the first circuit layer 121 is less than 375 μm and the average crystal grain size of the second circuit layer 122 is 375 μm or more. By adjusting the average crystal grain size of the first circuit layer 121 within the above range, the reflection of ultrasonic waves in the first circuit layer 121 can be greatly reduced.

On the other hand, since the second circuit layer 122 has a larger average crystal grain size than the first circuit layer 121, the surface roughness (surface roughness, surface roughness) of the surface of the second circuit layer 122 is larger than that of the first circuit layer 121. Arithmetic mean roughness Ra) is provided large. As described above, in the insulating circuit board 10, the surface of the circuit layer 12 on which the element 91 is mounted is formed by the second circuit layer 122 by combining the first circuit layer 121 and the second circuit layer 122 having different average crystal grain sizes. Is forming. Further, since the circuit layer 12 is formed by the first circuit layer 121 and the second circuit layer 122, the ratio of the second circuit layer 122 to the entire circuit layer 12 is small, that is, the ratio to the entire circuit layer 12 is small. Therefore, the thickness of the second circuit layer 122 can be made thin. Therefore, when the junction interface of each component of the power module 101 is inspected by the ultrasonic exploration imaging device (SAT) performed via the circuit layer 12, the ratio of ultrasonic reflection in the second circuit layer 122 can be greatly reduced. .. Therefore, the reflection of ultrasonic waves in the entire circuit layer 12 can be greatly reduced, and the inspection accuracy can be ensured satisfactorily. The thickness of the second circuit layer 122 is preferably smaller than the thickness of the first circuit layer 121.

On the other hand, when the power module 101 in which the element 91 is mounted on the circuit layer 12 is resin-sealed, stress tends to be concentrated on the corners arranged on the peripheral edge of the circuit layer 12. However, since the insulating circuit board 10 is provided with a large surface roughness of the second circuit layer 122 arranged on the surface of the circuit layer 12, the mold resin 81 can be firmly fixed to the peripheral edge of the circuit layer 12. Therefore, both the inspection accuracy by the ultrasonic exploration imaging device and the adhesion at the time of resin encapsulation can be sufficiently ensured.

The metal layer 13 is made of the same metal as the circuit layer 12, and is formed by joining a metal plate to the other surface of the ceramic substrate 11 with a brazing material in the same manner as the circuit layer 12. Further, as shown in FIGS. 1 and 2, the metal layer 13 includes at least a first metal layer 131 bonded to the other surface of the ceramic substrate 11, and the first metal layer 131 and the first circuit layer 121. It is provided with the same average crystal grain size. Further, in the insulating circuit board 10 of the present embodiment, the metal layer 13 has a laminated structure including a first metal layer 131 and a second metal layer 132 bonded to the surface of the first metal layer 131. .. The average crystal grain size of the second metal layer 132 is provided to be the same as the average crystal grain size of the second circuit layer 122.

The average crystal grain size of the first circuit layer 121 and the average crystal grain size of the first metal layer 131 are equivalent to the average crystal grain size of the first circuit layer 121 based on the average crystal grain size of the first metal layer 131. It shall include not only the case where it exactly matches the diameter but also the case where there is a difference of ± 20%. Similarly, the average crystal grain size of the second circuit layer 122 and the average crystal grain size of the second metal layer 132 are equivalent to each other in the second circuit layer 122 based on the average crystal grain size of the second metal layer 132. It shall include not only the case where it exactly matches the average crystal grain size but also the case where there is a difference of ± 20%. As with the first circuit layer 121, the average crystal grain size of the first metal layer 131 is preferably less than 250 μm when the circuit layer 12 is copper (Cu), and the circuit layer 12 is made of aluminum (Al). It is preferably less than 375 μm. Further, the average crystal grain size of the second metal layer 132 is preferably 250 μm or more when the circuit layer 12 is copper, and 375 μm or more when the circuit layer 12 is aluminum, as in the second circuit layer 122. Is preferable.

Although the metal layer 13 is formed in the same flat area as the circuit layer 12 in FIG. 1 and the like, the metal layer 13 may be formed in a flat area different from that of the circuit layer 12.

The average crystal grain size of each of the first circuit layer 121 and the second circuit layer 122, the first metal layer 131 and the second metal layer 132 is measured by using, for example, an optical microscope. In the present embodiment, the average crystal grain size of the first circuit layer 121 and the second circuit layer 122 of the circuit layer 12 is the plane of the second circuit layer 122 and the first circuit layer 121 by polishing the circuit layer 12 in the thickness direction. Was exposed in order, and the crystal grains in the planes of the layers 122 and 121 were measured using an optical microscope. Similarly, the average crystal grain size of the first metal layer 131 and the second metal layer 132 of the metal layer 13 is the plane surface of the second metal layer 132 and the first metal layer 131 by polishing the metal layer 13 in the thickness direction. Was exposed in order, and the crystal grains on the planes of the layers 132 and 131 were measured using an optical microscope. Then, the number of crystal grains completely contained in the measurement range of a known area (for example, 5000 mm ² ) observed by an optical microscope, and half the number of crystal grains cut around the measurement range. The total number of crystal grains is taken as the total number of crystal grains, and the equivalent circle diameter (diameter of the circle having the same area as the unit area of the metal particles) is calculated from the area obtained by dividing the area of the measurement range by the total number of crystal grains. The equivalent diameter was taken as each average crystal grain size.

As an example of the various dimensions of the insulating circuit board 10 configured in this way, the thickness (plate thickness) of the ceramic substrate 11 made of Si ₃ N ₄ (silicon nitride) is 0.1 mm to 1.5 mm, and Cu ( The thickness of the circuit layer 12 and the metal layer 13 made of copper) is 0.05 mm to 3.0 mm. The thickness of the first circuit layer 121 and the first metal layer 131 is 0.025 mm to 2.975 mm, and the thickness of the second circuit layer 122 and the second metal layer 132 is 0.025 mm to 2.975 mm. However, these dimensions are not limited to the above numerical range.

The element 91 is an electronic component provided with a semiconductor, and is an IGBT (Integrated Gate Bipolar Transistor), a MOSFET (Metal Oxide Semiconductor Detector Field Effect Transistor), various FWD (Free Node), etc., depending on the required function. The semiconductor element is selected. In this case, although not shown, the element 91 is provided with an upper electrode portion at the upper portion, a lower electrode portion at the lower portion, and the lower electrode portion is provided on the upper surface of the circuit layer 12 (second circuit layer 122). The element 91 is mounted on the upper surface of the circuit layer 12 by being joined by soldering or the like. Further, the upper electrode portion of the element 91 is connected to the circuit electrode portion of the circuit layer 12 via a lead frame (not shown) or the like.

Further, the power module 101 is integrated with the element 91 and the insulating circuit board 10 by being resin-sealed with a mold resin 81 except for the back surface side of the metal layer 13. As the mold resin 81, for example, an epoxy resin containing a SiO ₂ filler can be used, and the mold resin 81 is molded by, for example, a transfer mold.

Next, a method of manufacturing the insulated circuit board 10 will be described in order of steps with reference to FIG.
As shown in FIGS. 1 and 2, for the insulating circuit board 10 having the circuit layer 12 and the metal layer 13 on both sides of the ceramic substrate 11, the circuit layer forming step for forming the circuit layer 12 and the metal layer 13 are provided. The metal layer forming step to be formed can be performed at the same time. In the circuit layer forming step, a metal plate (clad material) to be a circuit layer 12 is bonded to one surface of the ceramic substrate 11, and the first circuit layer 121 bonded to one surface of the ceramic substrate 11 and its first. A circuit layer 12 having a second circuit layer 122 joined to the surface of the circuit layer 121 is formed. Further, in the metal layer forming step, the metal plate (clad material) to be the metal layer 13 is bonded to the other surface of the ceramic substrate 11, and the first metal layer 131 bonded to the other surface of the ceramic substrate 11 and its like. A metal layer 13 having a second metal layer 132 joined to the surface of the first metal layer 131 is formed.

As a metal plate to be the circuit layer 12, as shown in FIG. 3A, a first metal material 221a to be a first circuit layer 121 and a second metal material 222a to be a second circuit layer 122 are crimped together. The clad material 251 is formed. The clad material 251 can be formed, for example, by stacking the base material of the first metal material 221a and the base material of the second metal material 222a and rolling them with a roll or the like. The clad material 251 is formed into a desired outer shape by punching a plate material by press working.

As the first metal material 221a, a crystal grain suppressing material in which coarsening of crystal grains due to heating is suppressed as compared with the second metal material 222a is used. As the crystal grain suppressing material, if it is a copper material, a copper material that suppresses coarsening of crystal grains when heated at 800 ° C. and has an average crystal grain size of less than 250 μm can be preferably used. Specifically, GOFC manufactured by Furukawa Electric Co., Ltd. can be used as the crystal grain suppressing material for the first metal material 221a. On the other hand, oxygen-free copper (OFC) of a general rolled plate can be used for the second metal material 222a. When the second metal material 222a is heated at 800 ° C., the crystal grains become coarse and the average crystal grain size becomes 250 μm or more.

Further, in the present embodiment, the metal plate to be the metal layer 13 is formed to have the same configuration as the metal materials 221a and 222a to be the circuit layer 12. That is, as the metal plate to be the metal layer 13, the clad material 252 to which the first metal material 221b having the same structure as the first metal material 221a and the second metal material 222b having the same structure as the second metal material 222a are crimped is used. Use.

Further, as the brazing bonding material 224 for joining these clad materials 251,252 and the ceramic substrate 11, for example, an Ag-Cu-Ti brazing material can be used. In this case, the brazing joint material 224 can be easily handled by applying it to the joint surface of the clad material 251 and the joint surface of the clad material 252 in advance. In FIG. 3B, the brazing bonding material 224 is previously applied to the lower surface of the first metal material 221a and the upper surface of the first metal material 221b.

As shown in FIG. 3C, the clad material 251 forming the circuit layer 12 is placed on one surface of the ceramic substrate 11 via the brazing joint material 224. Similarly, the clad material 252 forming the metal layer 13 is placed on the other surface of the ceramic substrate 11 so as to be overlapped with each other via the same brazing bonding material 224. In this state, as shown by the white arrows in FIG. 3C, the ceramic substrate 11 and the clad material 251,252 are pressurized and heated in the stacking direction.

As a result, the first metal material 221a of the clad material 251 that becomes the circuit layer 12 and the ceramic substrate 11 are joined. At this time, the clad material 251 is heated so that the metal of the first metal material 221a and the metal of the second metal material 222a are interatomicly bonded and firmly bonded. As a result, the circuit layer 12 having the first circuit layer 121 and the second circuit layer 122 is formed on one surface of the ceramic substrate 11. At the same time, the first metal material 221b of the clad material 252 to be the metal layer 13 and the ceramic substrate 11 are bonded, and the first metal material 221b and the second metal material 222b are firmly bonded to form the ceramic substrate 11. A metal layer 13 having a first metal layer 131 and a second metal layer 132 is formed on the other surface. As a result, as shown in FIG. 3D, an insulated circuit board 10 in which the metal layer 13, the ceramic substrate 11, and the circuit layer 12 are laminated in this order is manufactured.

As described above, as the first metal materials 221a and 221b, the crystal grain suppressing materials in which the coarsening of the crystal grains due to heating is suppressed more than those of the second metal materials 222a and 222b are used, whereby the first circuit layer 121 and the second circuit layer 121 and the second. The circuit layer 12 including the circuit layer 122 and the metal layer 13 including the first metal layer 131 and the second metal layer 132 can be formed. Further, by forming the clad materials 251,252 to which the first metal materials 221a and 221b and the second metal materials 222a and 222b are crimped in advance, one heating in the circuit layer forming step and the metal layer forming step is performed. The metal having the circuit layer 12 including the first circuit layer 121 and the second circuit layer 122 and the metal including the first metal layer 131 and the second metal layer 132 by joining the clad material 251,252 and the ceramic substrate 11 The layer 13 can be easily formed. Therefore, the manufacturing process of the insulated circuit board 10 can be simplified.

As shown in FIG. 1, the element 91 is mounted on the insulating circuit board 10 manufactured in this manner. The element 91 is bonded to the upper surface of the second circuit layer 122 of the circuit layer 12 via, for example, a bonding layer 92 made of silver sintering or a solder bonding material. Further, although not shown, the power module 101 is manufactured by connecting necessary wiring or the like to the element 91 and electrically connecting the circuit layer 12 and the element 91. After that, the entire power module 101 excluding the lower surface of the metal layer 13 is sealed with the mold resin 81. Since the surface of the second circuit layer 122 provided on the peripheral edge of the circuit layer 12 has a larger surface roughness than the surface of the first circuit layer 121, the mold resin 81 is largely exposed on the surface of the circuit layer 12. It adheres to the surface of the second circuit layer 122 and is firmly bonded.

In the insulated circuit board 10 of the power module 101 configured in this way, the circuit layer 12 is bonded to the ceramic substrate 11 and the first circuit layer 121, and the second circuit layer 122 is bonded to the first circuit layer 121. The average crystal grain size of the second circuit layer 122 on which the element 91 is mounted (mounted) is made larger than the average crystal grain size of the first circuit layer 121. As described above, in the insulating circuit board 10, the surface of the circuit layer 12 on which the element 91 is mounted is formed by the second circuit layer 122 by combining the first circuit layer 121 and the second circuit layer 122 having different average crystal grain sizes. Is forming. Since the second circuit layer 122 has a larger average crystal grain size than the first circuit layer 121, the surface roughness (surface roughness) of the surface of the second circuit layer 122 is also larger than that of the first circuit layer 121. Become. When the power module 101 in which the element 91 is mounted on the circuit layer 12 (second circuit layer 122) is resin-sealed, the corners formed on the peripheral edge of the circuit layer 12 (the peripheral edge of the second circuit layer 122) of the mold resin 81 in particular. Although stress tends to be concentrated on the portion, in the insulating circuit board 10 of the present embodiment, the average crystal grain size of the second circuit layer 122 is provided large, and the surface roughness of the surface thereof is provided large, so that the mold resin 81 is used. It can be firmly fixed to the peripheral edge of the two circuit layers 122, and good adhesion between the mold resin 81 and the circuit layer 12 can be ensured.

Further, as described above, since the circuit layer 12 is formed by the first circuit layer 121 and the second circuit layer 122, the ratio of the second circuit layer 122 to the entire circuit layer 12 can be reduced. Therefore, the ratio of ultrasonic reflection in the second circuit layer 122 when inspecting the junction interface between the element 91 and the circuit layer 12 (second circuit layer 122) via the circuit layer 12 by the ultrasonic exploration imaging device is determined. It can be greatly reduced, and the reflection of ultrasonic waves in the entire circuit layer 12 can be greatly reduced. Therefore, good inspection accuracy can be ensured.

Further, as the entire circuit layer 12, a sufficient thickness can be secured by combining the first circuit layer 121 and the second circuit layer 122. Therefore, it is possible to satisfactorily secure the electric transmission performance and the heat dissipation performance, which are the functions required for the circuit layer 12.

Further, in the insulating circuit board 10, since the first metal layer 131 constituting the metal layer 13 is provided with an average crystal grain size equivalent to that of the first circuit layer 121, the insulating circuit board 10 is provided by an ultrasonic exploration imaging device. When inspecting the junction interface between the element 91 and the circuit layer 12 via the circuit layer 12, the reflection of ultrasonic waves can be reduced not only by the circuit layer 12 but also by the metal layer 13. Further, since the metal layer 13 is formed by the first metal layer 131 and the second metal layer 132, the ratio of the second metal layer 132 to the entire metal layer 13 can be reduced. Therefore, the ratio of the reflection of the ultrasonic wave in the second metal layer 132 when inspecting the joint interface of each component of the power module 101 by the ultrasonic exploration imaging device can be greatly reduced, and the reflection of the ultrasonic wave in the entire metal layer 13 can be greatly reduced. It can be greatly reduced. Therefore, it is possible to ensure good inspection accuracy by the ultrasonic exploration imaging device.

Further, as described above, the metal layer 13 has a laminated structure of the first metal layer 131 and the second metal layer 132, and the second metal layer 132 is formed with a large average crystal grain size equivalent to that of the second circuit layer 122. Therefore, the surface roughness of the surface of the second metal layer 132 can be made large. When the surface roughness of the surface of the metal layer 13 is increased in this way, the wettability between the metal layer 13 and the solder is improved when the heat dissipation layer (heat sink) is superposed on the metal layer 13 and bonded by solder or the like. Therefore, the adhesion between the metal layer 13 and the heat radiating layer and the joining reliability can be improved, and heat can be smoothly radiated from the metal layer 13 to the heat radiating layer. Further, even when the metal layer 13 and the heat radiating layer are laminated with the heat conductive grease sandwiched between them, the surface roughness of the surface of the metal layer 13 is increased so that the metal layer 13 and the heat radiating layer are sandwiched between the metal layer 13 and the heat radiating layer. The heat conductive grease can be retained, and the heat conductive grease can be prevented from coming out to the outside. Therefore, since the adhesion between the metal layer 13 and the heat radiating layer can be satisfactorily secured, the thermal resistance between the metal layer 13 and the radiating layer can be reduced, and the heat radiating performance can be satisfactorily secured.

In the above-mentioned first embodiment, the insulating circuit board 10 is configured to include the metal layer 13 formed on the other surface of the ceramic substrate 11, but the insulating circuit of the second embodiment shown in FIG. 4 is provided. The present invention also includes a configuration in which only the circuit layer 12 formed on one surface is provided without providing the metal layer on the other surface of the ceramic substrate 11 as in the substrate 20.

Further, in the above-mentioned first embodiment, the metal layer 13 is configured to include the first metal layer 131 and the second metal layer 132, but as in the insulated circuit board 30 of the third embodiment shown in FIG. In addition, the metal layer 33 may be composed of only the first metal layer 131. In the second embodiment and the third embodiment, the same reference numerals are given to the common elements with those of the first embodiment, and the description thereof will be omitted.

The present invention is not limited to the configuration of the above embodiment, and various changes can be made to the detailed configuration without departing from the spirit of the present invention.
For example, in the above embodiment, one side (lower electrode portion) of the element 91 is mounted on the circuit layer 12 of the insulating circuit board 10, but by arranging the insulating circuit boards 10 on both sides of the element 91, respectively. It is also possible to have a double-sided cooling structure.

Further, in the above embodiment, the circuit layer 12 and the metal layer 13 having different average crystal grain sizes for each region are formed of copper (pure copper or copper alloy), but aluminum (pure aluminum or aluminum alloy) is used. The circuit layer 12 and the metal layer 13 can be formed by making the average crystal grain size different for each region.
For example, the average crystal grain size can be controlled by adjusting the rolling reduction rate per pass in the rolling process of rolling an ingot of aluminum to a desired plate thickness. Specifically, the average crystal grain size can be increased by increasing the reduction rate per pass. Then, by using the rolled material having the average crystal grain size adjusted in this way, it is possible to easily manufacture an insulated circuit substrate having a circuit layer having a different average crystal grain size between the first circuit layer and the second circuit layer.

Hereinafter, the effects of the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples.

As shown in Tables 1 and 2, Examples 1-1 to 1-3 and 2-1 to 2-3 of the power module in which the element and the insulating circuit board are joined, and Comparative Examples 1-1 to 1-3 and 2-1 to 2-3 were prepared. As the insulating circuit board, a circuit board having the circuit layers shown in Tables 1 and 2 formed on one surface of the ceramics substrate was used. In Examples 1-1 to 1-3 and 2-1 to 2-3, the circuit layer is formed by forming the second circuit layer on which the element is mounted having an average crystal grain size larger than that of the first circuit layer. .. On the other hand, in Comparative Examples 1-1 to 1-2 and 2-1 to 2-2, the second circuit layer of the circuit layer was formed with the average crystal grain size smaller than that of the first circuit layer.

As the ceramic substrate, a rectangular plate made of Si _{3N 4 (} silicon nitride) having a plate thickness of 0.32 mm and a plane size of 30 mm × 30 mm was used. As the clad material forming the circuit layer, a rectangular plate having a plate thickness of 1.6 mm and a plane size of 28 mm × 28 mm is used, the thickness of the first metal material portion is 1.2 mm, and the thickness of the second metal material portion is 0. It was set to 0.4 mm. If the metal plate to be the circuit layer is copper, an Ag-Cu-Ti brazing material is used, and if it is aluminum, an Al-Si brazing material is used to separate the ceramic substrate and the clad material. Insulated circuit boards were manufactured by joining them.

The surface roughness of the upper surface of the circuit layer of each of the obtained insulated circuit boards was measured, and the surface roughness of the circuit layer surface was measured. Next, an element was bonded to the surface of the circuit layer (second circuit layer) of each insulated circuit board with a solder material (Sn—Cu-based solder material) to manufacture a power module. Then, with respect to the obtained power module, the solder joint layer was inspected from both the element side not passing through the circuit layer and the insulating circuit board side via the circuit layer, and the void area ratio in the solder joint layer was measured. .. Further, in the obtained power module, the element and the insulating circuit board were sealed with a resin, and the adhesion between the resin and the circuit layer was evaluated. An epoxy resin was used as the resin, and the resin was sealed by a transfer mold.

(Measurement of surface roughness of circuit layer surface)
The surface roughness Ra (μm) of the surface of the circuit layer (second circuit layer) was measured using a surf tester (SJ-410 manufactured by Mitutoyo). The results are shown in Tables 1 and 2.

(Measuring method of void diameter in solder joint layer)
For the obtained power module, the bonding interface (solder bonding layer) between the circuit layer and the element was observed using an ultrasonic exploration video device (SAT, ES5000 manufactured by Hitachi Engineering and Service Co., Ltd.). Observation of the junction interface between the circuit layer and the element is performed from both the insulated circuit board side via the circuit layer and the element side not via the circuit layer, and the diameter of the void observed by the ultrasonic exploration imaging device is determined for each. Measured from the direction. For the diameter of the void, the diameter of a circle having the same area was calculated from the area of the observed void, and the diameter corresponding to this circle was taken as the diameter of the void. When there were a plurality of voids in one bonding interface, the average value (average diameter) of the diameters of each void was calculated. Further, the ratio (D1 / D2) × 100 [%] of the average diameter D1 of the voids when observed from the element side and the average diameter D2 of the voids when observed from the insulating circuit board side was calculated.

The smaller the value of the obtained ratio, the smaller the difference between the average diameter of the voids when observed from the element side and the average diameter of the voids when observed from the insulating circuit board side, and good inspection accuracy can be obtained. .. In this case, the inspection accuracy is evaluated as good "○" if the ratio value is less than ± 10% (ratio is more than 90% and less than 110%), and ± 10% or more (ratio is 90% or less or 110%). The case of (above) was evaluated as “x”. The results are shown in Tables 3 and 4.

(Adhesion evaluation by pudding cup test)
The adhesion between the mold resin and the insulating circuit board was evaluated by a pudding cup test. The pudding cup test was carried out in accordance with the international standard ISO19095-1-4 of the resin-metal bonding property evaluation test method. Specifically, a pudding cup-shaped resin was formed on the surface of the circuit layer of the insulating circuit board, and a shear peel strength test of the resin was carried out. When the obtained shear peel strength was 15 MPa or more, the adhesion between the mold resin and the insulating circuit board was evaluated as “◯”, and when the shear peel strength was less than 15 MPa, it was evaluated as “×”. The results are shown in Tables 3 and 4.

As can be seen from the results in Tables 3 and 4, when the circuit layer is copper, the average crystal grain size of the first circuit layer is set to less than 250 μm, so that the inspection accuracy by the ultrasonic exploration imaging device and the resin encapsulation can be obtained. Both the adhesion at the time can be secured well. When the circuit layer is made of aluminum, the average crystal grain size of the first circuit layer region is set to less than 375 μm, so that both the inspection accuracy by the ultrasonic exploration imaging device and the adhesion at the time of resin encapsulation can be improved. Can be secured well.

10, 20, 30 Insulated circuit board 11 Ceramic substrate 12 Circuit layer 13, 33 Metal layer 81 Molded resin 91 Element 92 Bonding layer 101 Power module (module)
121 First circuit layer 122 Second circuit layer 131 First metal layer 132 Second metal layer 221a, 221b First metal material 222a, 222b Second metal material 224 Wax joint material 251,252 Clad material

Claims (6)

A ceramic substrate and a circuit layer made of either copper or aluminum formed on one surface of the ceramic substrate are provided.
The circuit layer has a laminated structure including a first circuit layer bonded to one surface of the ceramic substrate and a second circuit layer bonded to the surface of the first circuit layer.
An insulating circuit board characterized in that the average crystal grain size of the second circuit layer is larger than the average crystal grain size of the first circuit layer. A metal layer made of the same metal as the circuit layer is provided on the other surface of the ceramic substrate.
The metal layer comprises at least a first metal layer bonded to the other surface of the ceramic substrate.
The insulating circuit board according to claim 1, wherein the first metal layer is provided with an average crystal grain size equivalent to that of the first circuit layer. The metal layer has a laminated structure including the first metal layer and the second metal layer bonded to the surface of the first metal layer.
The insulating circuit board according to claim 2, wherein the second metal layer is provided with an average crystal grain size equivalent to that of the second circuit layer. The insulating circuit board according to any one of claims 1 to 3, wherein when the circuit layer is copper, the average crystal grain size of the first circuit layer is less than 250 μm. The insulating circuit board according to any one of claims 1 to 3, wherein when the circuit layer is aluminum, the average crystal grain size of the first circuit layer is less than 375 μm. It has a circuit layer forming step of forming a circuit layer having a first circuit layer bonded to one surface of a ceramic substrate and a second circuit layer bonded to the surface of the first circuit layer.
Among the circuit layers, as the first metal material to be the first circuit layer, the coarsening of crystal grains due to heating is larger than that of the second metal material to be the second circuit layer bonded to the surface of the first circuit layer. A suppressed crystal grain suppressing material is prepared, and a clad material in which the first metal material and the second metal material are pressure-bonded is formed.
In the circuit layer forming step, in a state where the first metal material of the clad material is superposed on one surface of the ceramic substrate via a brazing bonding material, the laminating direction of the ceramic substrate and the clad material. The first metal material of the clad material and the ceramic substrate are joined to each other by pressurizing and heating the ceramic substrate, and the ceramic substrate has the first circuit layer and the second circuit layer on one surface of the ceramic substrate. A method for manufacturing an insulated circuit board, which comprises forming the circuit layer.

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