JP2020047854A - Ceramic circuit board and semiconductor device arranged by use thereof - Google Patents

Abstract

To provide a ceramic circuit board which allows a resin molded semiconductor device to be improved in TCT characteristic.SOLUTION: A ceramic circuit board comprises a ceramic substrate with a circuit metal plate joined to one face and a heat-dissipation metal plate joined to the other face. In the ceramic circuit board, 90% or more of a creepage distance of the heat dissipation metal plate is within a range of over -0.1 mm and less than +0.05 mm. Supposing that a maximum height roughness Rz on a circuit metal plate side from a center of a side face of the ceramic substrate is Rz1, and a maximum height roughness Rz on a heat dissipation metal plate side from the center of the ceramic substrate side face is Rz2, the following relation holds: |Rz1-Rz2|≤10 μm. It is preferred that the ceramic substrate is a silicon nitride substrate having a thermal conductivity of 50 W/mK or more, and a three-point-bending strength of 600 MPa or more.SELECTED DRAWING: Figure 1

Description

  Embodiments generally relate to a ceramic circuit board and a semiconductor device using the same.

In recent years, the output of semiconductor devices has been increased, and the operation compensation temperature (junction temperature) has been increased. The junction temperature is about 150 ° C., but is 170 to 200 ° C. Accordingly, TCT characteristics at high temperatures (heat-resistant cycle characteristics) are also required for ceramic circuit boards on which semiconductor elements are mounted.
WO 2017/056360 (Patent Document 1) discloses a ceramic circuit board in which a ceramic substrate and a copper plate are joined via an active metal brazing material layer. In Patent Document 1, in order to improve the TCT characteristics of the ceramic circuit board, a protruding portion of the active metal brazing material layer from the end of the copper plate is provided. Thus, the ceramic circuit board of Patent Document 1 has improved TCT characteristics.
Further, a semiconductor device in which a semiconductor element is mounted on a ceramic circuit board is resin-molded to ensure insulation. As the junction temperature rises, a destruction mode starting from the mold resin has occurred. Japanese Patent Application Laid-Open No. 2006-179538 (Patent Document 2) controls the Young's modulus of the resin in order to improve the destruction mode by the mold resin. As in Patent Literature 2, by controlling the Young's modulus of the mold resin, an improvement in the destruction mode was observed.
However, even when the ceramic circuit board of Patent Document 1 is used, as the junction temperature increases, a destruction mode starting from the mold resin occurs. Further, the use of two types of mold resins as in Patent Document 2 has caused a cost increase.

WO 2017/056360 A JP 2006-179538 A

The semiconductor device is arranged on a mounting board. The resin mold is provided so as to cover the semiconductor device. When the ceramic circuit board of Patent Document 1 is used, a destruction mode starting from the mold resin occurs around the back metal plate. In Patent Document 1, a brazing material protrusion is provided. In order to provide the brazing material protruding portion, the creepage distance of the back metal plate was required. If there is a creepage distance on the back metal plate, the resin is not sufficiently filled during resin molding, and bubbles are easily formed. The presence of air bubbles caused the resin to come off. As a result, destruction by the mold resin occurred around the back metal plate.
The present invention is directed to addressing such a problem, and provides a ceramic circuit board suitable for a resin mold.

  The ceramic circuit board according to the embodiment has a ceramic circuit board in which a circuit metal plate is joined to one surface of the ceramic substrate and a heat dissipation metal plate is joined to the other surface. The maximum height roughness Rz from the center of the side surface of the ceramic substrate to the circuit metal plate side is Rz1, and the maximum height roughness Rz from the center of the side surface of the ceramic substrate is Rz1. When the maximum height roughness Rz is Rz2, | Rz1−Rz2 | ≦ 10 μm.

  In the ceramic circuit board according to the embodiment, since 90% or more of the creepage distance of the back metal plate is in the range of more than -0.1 mm and not more than +0.05 mm, air bubbles around the back metal plate when resin molding is performed. Can be suppressed from being formed. Further, the difference between the maximum height roughness Rz on the upper side and the lower side on the side surface of the ceramic substrate is reduced. Thereby, peeling of the resin mold can be prevented.

FIG. 1 is a view showing an example of a ceramic circuit board according to an embodiment. The figure which shows another example of the ceramics circuit board concerning embodiment. FIG. 2 is a diagram illustrating an example of the semiconductor device according to the embodiment.

The ceramic circuit board according to the embodiment is a ceramic circuit board in which a circuit metal plate is joined to one surface of the ceramic substrate and a heat dissipation metal plate is joined to the other surface.
90% or more of the creepage distance of the metal plate for heat radiation is in the range of more than -0.1 mm and less than +0.05 mm,
When the maximum height roughness Rz on the circuit metal plate side from the center of the ceramic substrate side surface is Rz1 and the maximum height roughness Rz on the heat dissipation metal plate side from the center of the ceramic substrate side surface is Rz2, | Rz1−Rz2 | ≦ 10 μm.
FIG. 1 shows an example of the ceramic circuit board according to the embodiment. In the figure, 1 is a ceramic circuit board, 2 is a ceramic substrate, 3 is a ceramic substrate side surface, 3A is a circuit metal plate side from the center of the ceramic substrate side surface, 3B is a heat dissipation metal plate side from a center of the ceramic substrate side surface, and 4 is Circuit metal plate, 5 is a heat dissipation metal plate, 6 is a brazing material layer (circuit metal plate side brazing material layer), 7 is a brazing material layer (radiation metal plate side brazing material layer), T is a heat dissipation metal plate Creepage distance.

  The ceramic circuit board 1 has a circuit metal plate 4 on one surface of a ceramic substrate 2 and a heat dissipating metal plate 5 on the other surface. For convenience, the circuit metal plate 4 is called a front metal plate, and the heat dissipation metal plate is called a back metal plate. FIG. 1 illustrates an example in which a metal plate is joined via a brazing material layer 6 and a brazing material layer 7. As described later, the ceramic circuit board is preferably formed by joining a metal plate via a brazing material layer. FIG. 1 illustrates an example in which one circuit metal plate 4 is provided. The ceramic circuit board according to the embodiment may be provided with a plurality of circuit metal plates 4. When a plurality of circuit metal plates 4 are provided, a semiconductor element is mounted on at least one metal plate.

90% or more of the creeping distance T from the end of the ceramic substrate 2 of the heat-dissipating metal plate 5 is in the range of more than -0.1 mm and not more than +0.05 mm. In addition, the creepage distance T of the heat-dissipating metal plate 5 from the end of the ceramic substrate 2 is simply referred to as “the creepage distance of the heat-dissipation metal plate”. Further, 100% of the creepage distance T of the heat-dissipating metal plate indicates the creepage distance of the entire outer periphery of the heat-dissipation metal plate. A creeping distance T of minus indicates that the end of the metal plate for heat dissipation is inside the end of the ceramic substrate. When the creepage distance T is plus, it indicates that there is an end of the metal plate for heat radiation outside the end of the ceramic substrate. That is, if the creepage distance T is minus, it indicates that the heat dissipation metal plate is smaller than the ceramic substrate. Conversely, if the creepage distance T is positive, it indicates that the heat dissipating metal plate is larger than the ceramic substrate. When the creepage distance T is 0 mm, it indicates that the metal plate for heat radiation and the ceramic substrate have the same size.
The fact that 90% or more of the creepage distance T of the heat-dissipating metal plate is within the range of more than -0.1 mm and not more than +0.05 mm indicates that the creepage distance T is reduced. Thereby, it is possible to suppress the formation of bubbles in the creepage distance region when performing resin molding. This is because, by reducing the creepage distance T, the region where the mold resin enters the back side of the ceramic substrate can be reduced.
In addition, when the TCT test is performed, the occurrence of cracks on the back surface of the ceramic substrate can be suppressed. The thermal stress between the ceramic substrate and the metal plate is caused by the difference between the coefficients of thermal expansion of the materials. In particular, it becomes larger at the joint end. By reducing the creepage distance T, the bending moment of the ceramic substrate portion is suppressed when the resin molding is performed and the TCT test is performed, and the thermal stress at the joint end can be reduced. Further, when T is small, it also leads to suppression of resin peeling.
Further, it is preferable that 100% of the creepage distance of the metal plate for heat radiation is in the range of more than -0.1 mm and not more than +0.05 mm. In addition, it is preferable that 100% of the creepage distance of the metal plate for heat radiation is in the range of −0.05 mm or more and 0 mm or less. In addition, it is preferable that the creeping distance of the metal plate for heat radiation is 0 mm.

  The creeping distance T of the heat-dissipating metal plate is measured by magnifying the ceramic circuit board 20 times from the rear surface direction with a tool microscope. When measurement is performed in the state of a resin-molded semiconductor device, X-ray CT is used.

When the maximum height roughness Rz on the circuit metal plate side from the center of the ceramic substrate side surface is Rz1 and the maximum height roughness Rz on the heat dissipation metal plate side from the center of the ceramic substrate side surface is Rz2, | Rz1- Rz2 | ≦ 10 μm.
The maximum height roughness Rz indicates what is defined as the maximum height roughness Rz in JIS-B-0601 (2013). Further, as shown in FIG. 1, the side region from the center of the side surface of the ceramic substrate 2 to the side of the circuit metal plate is 3A. The side surface area from the center of the side surface of the ceramic substrate 2 toward the metal plate for heat radiation is 3B. The maximum height roughness Rz of the side surface region 3A is Rz1, and the maximum height roughness Rz of the side surface region 3B is Rz2. The ceramic circuit board according to the embodiment is characterized in that | Rz1−Rz2 | ≦ 10 μm. The maximum height roughness Rz is the sum of the largest peak and the largest valley of the roughness curve.
| Rz1−Rz2 | ≦ 10 μm indicates that the difference in the maximum height roughness Rz of the side surface of the ceramic substrate is small. If there is a difference in Rz on the side surface of the ceramic substrate 2, the adhesion to the mold resin varies. A TCT test of the resin-molded semiconductor device has revealed that a phenomenon occurs in which the resin peels off from the weakly adherent portion. The maximum height roughness Rz is the sum of the largest peak and the largest valley of the roughness curve. The maximum height roughness Rz is an important factor for obtaining the anchor effect.

For example, when a large number of ceramic circuit boards are to be obtained, scribe processing of a line shape or a dot line is performed. The substrate is divided along the scribe marks. The side surfaces of the divided ceramic substrate differ in the maximum height roughness in the scribed marks and in the other areas. As a result, | Rz1−Rz2 | was a value exceeding 10 μm.
It is preferable that | Rz1−Rz2 | ≦ 4 μm. The smaller the difference between Rz1 and Rz2, the more the variation in adhesion to the mold resin can be reduced.
Rz1 and Rz2 are preferably 0.3 μm or more and 20 μm or less. When Rz1 and Rz2 are less than 0.3 μm, the surface may be too flat and the anchor effect may be insufficient. On the other hand, if Rz1 and Rz2 are larger than 20 μm, it is difficult for the resin to enter the valley and bubbles are easily formed. If bubbles are present on the side surface of the substrate, the resin may peel off. Therefore, Rz1 and Rz2 are preferably from 0.3 μm to 20 μm, more preferably from 3 μm to 15 μm.
By setting the maximum height roughness Rz of the side surface of the ceramic substrate 2 to | Rz1−Rz2 | ≦ 10 μm and 0.3 μm to 20 μm, the strength of the ceramic substrate 2 can be improved. If Rz on the side of the ceramic substrate varies, the strength of the ceramic substrate tends to vary. For example, in the half scribe processing, scribe marks are formed up to half of the side surface of the ceramic substrate. In this case, the strength of the ceramic substrate is changed by turning the scribe mark upward or downward. In other words, in the ceramic circuit board according to the embodiment, Rz on the side surface of the board is within a predetermined range. Therefore, the strength does not decrease due to the directionality of the substrate. Further, by setting Rz on the side surface of the substrate to a predetermined range, the strength can be improved.

  The maximum height roughness Rz is measured by measuring the side surface of the ceramic substrate 2 in the thickness direction. It shall be measured along the lateral direction of the substrate side. Measurement is performed for an arbitrary 5 mm in the lateral direction of the side surface region 3A. Similarly, measurement is performed for an arbitrary 5 mm in the lateral direction of the side surface region 3B. Each of the four sides is measured, and the largest | Rz1−Rz2 | value among them is taken as the | Rz1−Rz2 | value of the ceramic circuit board. Further, the values of Rz1 and Rz2 are both preferably 0.3 μm or more and 20 μm or less.

Examples of the ceramic substrate 2 include a silicon nitride substrate, an aluminum nitride substrate, an aluminum oxide substrate, and an azyl substrate. For example, the thickness of the ceramic substrate is 0.2 to 0.8 mm. For example, a silicon nitride substrate has a thermal conductivity of 50 W / m · K or more and a three-point bending strength of 600 MPa or more. For example, the aluminum nitride substrate has a thermal conductivity of 150 W / m · K or more and a three-point bending strength of 300 to 550 MPa. For example, the aluminum oxide substrate has a thermal conductivity of 20 to 40 W / m · K and a three-point bending strength of 400 to 500 MPa.
Further, the azil substrate is an aluminum oxide substrate containing zirconium oxide.
The thermal conductivity of the azil substrate is 20 to 40 W / m · K, and the three-point bending strength is 450 to 600 MPa. Since the silicon nitride substrate has high strength, the thickness of the substrate can be reduced to 0.33 mm or less. Aluminum nitride substrates have high thermal conductivity. Although the aluminum oxide substrate and the azil substrate have low thermal conductivity, these substrates are inexpensive. The type of the ceramic substrate can be appropriately selected according to the purpose. Further, the silicon nitride substrate and the aluminum nitride substrate are referred to as nitride ceramics. The aluminum oxide substrate and the azil substrate are referred to as oxide ceramics.
The ceramic substrate 2 is preferably a silicon nitride substrate having a thermal conductivity of 50 W / m · K or more and a three-point bending strength of 600 MPa or more. If the substrate has high strength as described above, it can be made thin. By reducing the thickness, the thermal resistance can be reduced. Further, it is preferable that the silicon nitride substrate has a thermal conductivity of 80 W / m · K or more. By increasing the thermal conductivity, the thermal resistance can be reduced.
In addition, by using a ceramic substrate having a three-point bending strength of 600 MPa or more, high reliability can be maintained even when the metal plate is thickened. By increasing the thickness of the metal plate, it is possible to improve current carrying capacity, reduce inductance, and improve heat dissipation. From this point, it is preferable that the silicon nitride substrate has a thermal conductivity of 50 W / m · K or more and a three-point bending strength of 600 MPa or more.

Further, it is preferable that the thickness of the circuit metal plate and the heat radiation metal plate is 0.1 mm or more. If the thickness of the metal plate is less than 0.1 mm, the current carrying capacity cannot be obtained. If current carrying capacity cannot be obtained, it becomes difficult to mount a high-power semiconductor element. The thickness of the metal plate is preferably 0.1 mm or more, more preferably 0.5 mm or more. The upper limit of the thickness of the metal plate is not particularly limited, but is preferably 3 mm or less. If the thickness of the metal plate exceeds 3 mm, it may be difficult to apply a manufacturing method for cutting a joined body as described later.
Further, the metal plate for circuit and the metal plate for heat dissipation are preferably a copper plate (Cu plate) or an aluminum plate (Al plate). It is assumed that the copper plate contains a copper alloy. The aluminum plate contains an aluminum alloy. Copper has a thermal conductivity of about 400 W / m · K. Aluminum has a thermal conductivity of about 240 W / m · K. Both are higher than the thermal conductivity of the ceramic substrate. For this reason, heat dissipation can be improved by thickening a copper plate or an aluminum plate.
Further, the maximum height roughness Rz of the side surface of the metal plate 5 for heat radiation is preferably in the range of 0.3 μm or more and 20 μm or less. By setting Rz on the side surface of the heat-dissipating metal plate 5 to a predetermined value, the adhesion to the mold resin can be improved.

Further, it is preferable that the metal plates are joined via a brazing material layer.
When the metal plate is a copper plate, it is preferably an active metal brazing material layer. The active metal brazing material contains Ag, Cu and an active metal as essential components. Ag and Cu are eutectic combinations. By forming the AgCu eutectic, the bonding strength between the ceramic substrate and the copper plate can be improved. The active metal is one or more selected from Ti (titanium), Zr (zirconium), Hf (hafnium), and Nb (niobium). Among the active metals, Ti is preferred. The active metal reacts with the ceramic substrate to form a strong bond. An active metal nitride phase is formed with a nitride ceramic. For example, when Ti is used as the active metal, a titanium nitride (TiN) phase is formed. The oxide ceramic forms an active metal oxide phase. For example, when Ti is used as the active metal, a titanium oxide (TiO ₂ ) phase is formed. The active metal may be a simple metal or may be added as a hydride.
If necessary, Sn (tin) or In (indium) may be added to the active metal brazing material. Sn and In can lower the melting point of the active metal brazing material. For this reason, the joining temperature can be reduced. Joining at a low temperature can reduce the residual stress of the joined body. Reducing the residual stress is effective for improving the thermal cycle reliability of the joined body.
If necessary, C (carbon) may be added to the active metal brazing material. By adding carbon, the fluidity of the brazing material can be suppressed. Therefore, the thickness of the brazing material layer can be made more uniform.
In the active metal brazing material, the content of Ag is 40 wt% or more and 80 wt% or less, the content of Cu is 15 wt% or more and 45 wt% or less, the content of active metal is 1 wt% or more and 12 wt% or less, and Sn (or In). Is preferably 0 wt% or more and 20 wt% or less, and the C content is preferably 0 wt% or more and 2 wt% or less. The total content of Ag, Cu, Ti, Sn (or In), and C is 100 wt%. When adding Sn or In to the active metal brazing material, the content of Sn or In is preferably 5 wt% or more. When both Sn and In are added, the total content is preferably in the range of 5 to 20 wt%. When carbon is added to the active metal brazing material, it is preferable that the content of carbon is 0.1 wt% or more and 2 wt% or less.

When the metal plate is an Al plate, the active metal brazing material preferably contains Al (aluminum) as a main component. Further, it is preferable that the Al brazing material contains at least one element selected from Si (silicon) and Mg (magnesium). The content of Si or Mg is preferably 0.01 wt% or more and 20 wt% or less, with the balance being Al.
The thickness of the brazing material layer is preferably 10 μm or more and 60 μm or less. If the thickness of the brazing material layer is less than 10 μm, the bonding strength may be insufficient. On the other hand, if the thickness exceeds 60 μm, it is difficult to obtain further effects. In addition, it may cause a cost increase.
In addition, the ceramic substrate, the metal plate for circuit and the metal plate for heat radiation are joined via a brazing material layer, and the creeping distance of the brazing material layer on the metal plate side for heat radiation is more than -0.1 mm and 0 mm or less. Is preferred. This indicates that the brazing material layer on the side of the metal plate for heat radiation does not protrude from the side surface of the ceramic substrate. The protruding portion of the brazing material layer from the end of the metal plate for heat radiation is preferably at least 0 μm and at most 10 μm. By reducing the protruding part of the brazing material on the heat-dissipating metal plate side, it is possible to suppress the formation of bubbles of the mold resin. The protruding portion of the brazing material is formed by heat-treating the active metal brazing material paste. This is because the surface has minute irregularities and bubbles are easily formed.

FIG. 2 shows another example of the ceramic circuit board according to the embodiment. In the figure, 1 is a ceramic circuit board, 2 is a ceramic substrate, 4 is a circuit metal plate, 5 is a heat dissipation metal plate, 6 is a brazing material layer (circuit metal plate side brazing material layer), and 7 is a brazing material layer ( (A metal plate side brazing material layer for heat radiation)).
FIG. 2 shows the case where the creepage distance T is 0 mm.
The fact that the creeping distance of the brazing material layer on the side of the metal plate for heat dissipation is more than -0.1 mm and 0 mm or less indicates that the brazing material layer 7 does not protrude from the side surface of the ceramic substrate 2. With this structure, it is possible to suppress the formation of bubbles when performing resin molding. Further, the effect of controlling Rz on the side surface of the ceramic substrate 2 is easily obtained.

Further, it is preferable that the side surfaces of the metal plate 5 for heat radiation have a vertical shape. The vertical shape indicates a shape in which the side surface of the heat-dissipating metal plate is straight in the thickness direction. By having a vertical shape, it is possible to suppress the formation of bubbles during resin molding. Further, when Rz on the side surface of the metal plate 5 for heat radiation is set to 0.3 μm or more and 20 μm or less, it becomes easy to improve the adhesion to the mold resin.
The side surface of the circuit metal plate 4 may have a vertical shape or an inclined shape. Further, it is preferable that the brazing material layer 6 protrudes from the circuit metal plate 4. By having the protruding portion of the brazing material, thermal stress can be reduced. The protruding portion of the brazing material is preferably from 0 μm to 100 μm. Further, the protruding portion of the brazing material of the circuit metal plate 4 preferably has a thickness of 0 μm or more and 10 μm or less. By reducing the protruding portion of the brazing material of the circuit metal plate 4, the formation of bubbles in the mold resin can be suppressed.
Further, the side surface of the circuit metal plate 4 preferably has an inclined shape. By having an inclined shape, thermal stress can be reduced. The circuit metal plate 4 is used for mounting a semiconductor element or the like. Also, wires and lead frames are connected. The circuit metal plate 4 is a metal plate on which a heat-generating member is placed. Therefore, it is preferable to provide an inclined shape or a protruding portion of the brazing material. The surface on which the circuit metal plate 4 is provided is the front surface. In resin molding, even if an inclined shape is provided on the circuit metal plate to inject the resin from above, it does not cause bubbles to be formed.
If necessary, a metal coating may be provided on the surface of the circuit metal plate 4 or the heat radiation metal plate 5. As the metal coating, a coating mainly composed of one selected from nickel (Ni), gold (Au), and silver (Ag) is preferable.

The ceramic circuit board as described above is suitable for a semiconductor device on which a semiconductor element is mounted. Further, it is preferable that the semiconductor device is a resin-molded semiconductor device.
FIG. 3 shows an example of a resin-molded semiconductor device. In the figure, 10 is a semiconductor device, 11 is a semiconductor element, 12 is a mounting substrate, and 13 is a mold resin. FIG. 3 shows a semiconductor device mounted on the ceramic circuit board 1 shown in FIG.
The semiconductor element includes a power element such as an IGBT chip. Further, those having a junction temperature of 150 ° C. or higher, more preferably 170 ° C. or higher are preferable. Further, it is preferable that the semiconductor elements are joined by Pb-free solder. Examples of the Pb-free solder include Sn-Ag-Cu-based solder.
In addition, it is assumed that wiring is provided at necessary places. Examples of the wiring include a bonding wire and a lead frame. Further, electrodes are provided as necessary.
Further, the bonding wire preferably has a diameter of 100 to 700 μm. The semiconductor device according to the embodiment suppresses peeling of the mold resin. If the mold resin comes off, it causes cracks in the ceramic circuit board. In addition, it may cause breakage of the bonding wire. In the semiconductor device according to the embodiment, since the peeling of the mold resin is suppressed, disconnection of the bonding wire can be prevented. In other words, it is effective for a semiconductor device having a bonding wire and resin molding.
Further, the semiconductor device 10 is joined to the mounting board 12. The mounting substrate 12 is a heat sink base, a housing, or the like. Examples of the heat sink base include a Cu base and an AlSiC base. The metal plate 5 for heat dissipation of the semiconductor device 10 and the mounting substrate 12 are joined by solder or the like.

The mold resin 13 is an organic material having an insulating property. Fill with viscous organic matter,
It is cured. Examples of the organic substance include a thermosetting resin and a photocurable resin. Examples of such a resin include an epoxy resin and a silicone resin. Potting gels are also examples of viscous organic substances.
Various methods such as a transfer method and a compression method are applied to the molding process. There is also a molding method using a potting gel. In recent years, a transfer method has been used because of its good mass productivity. Transfer molding is a method in which a resin is heated in a plunger to soften the resin, and the softened resin is poured into a mold and cured. Since the softened resin is used, it is easy to fill the resin into the gap of the semiconductor device having a complicated shape. In addition, since the molding resin is solidified at a time, mass productivity and productivity are excellent. On the other hand, since the resin is being filled in the mold, it has not been possible to confirm whether the resin is filled up to the back side of the ceramic substrate without any gap.
For example, the silicon nitride substrate has a coefficient of linear expansion of about 2 to 3 × 10 ⁻⁶ / K. The linear expansion coefficient of the epoxy resin is about 40 to 70 × 10 ⁻⁶ / K. The linear expansion coefficients of the silicon nitride substrate and the epoxy resin are different by about 20 times. The difference in the coefficient of linear expansion tends to cause resin peeling.
In the ceramic circuit board according to the embodiment, since the creeping distance T of the heat-dissipating metal plate is reduced, bubbles are less likely to be formed on the back side of the ceramic substrate. Further, by controlling the maximum height roughness Rz of the side surface of the ceramic substrate, an anchor effect with the mold resin is obtained. Therefore, even when a semiconductor element having a high junction temperature of 150 ° C. or more is mounted, resin peeling can be suppressed.

Next, a method for manufacturing the ceramic circuit board according to the embodiment will be described. The manufacturing method of the ceramic circuit board according to the embodiment is not limited as long as it has the above configuration, but the following methods can be used to obtain a good yield.
First, a ceramic substrate is prepared. Examples of the ceramic substrate include a silicon nitride substrate, an aluminum nitride substrate, an aluminum oxide substrate, and an aryl substrate. Further, as the size of the ceramic substrate, one having a desired vertical and horizontal size may be used in advance, or a large size for obtaining a large number of pieces may be used. In order to improve mass productivity, it is preferable to use a large-sized substrate. The ceramic substrate is preferably a silicon nitride substrate having a thermal conductivity of 50 W / m · K or more and a three-point bending strength of 600 Mpa or more. Such a silicon nitride substrate can be made as thin as 0.33 mm or less. When the substrate is thin, it is easy to perform a bonding body cutting step described later.
Next, a metal plate is prepared. Examples of the metal plate include a copper plate and an aluminum plate. The thickness of the metal plate is preferably 0.1 mm or more and 3 mm or less, more preferably 0.4 mm or more and 2 mm or less. If the thickness of the metal plate is less than 0.1 mm, the current carrying capacity cannot be obtained. If the thickness is more than 3 mm, the cutting step of the joined body may be difficult.
The front metal plate used for the circuit metal plate may be the same as the vertical and horizontal sizes of the ceramic substrate, or may be a plate processed in advance in a pattern shape. Further, it is preferable that the back metal plate used as the heat radiating metal plate has the same vertical and horizontal size as the ceramic substrate. Further, the size of the heat-dissipating metal plate may be a target creeping distance T in advance. Further, when multiple pieces are taken, it is preferable to use a metal plate having the same vertical and horizontal size as the ceramic substrate before the multiple pieces are taken.

Next, a brazing material is prepared. Preferably, the brazing material is an active metal brazing material. When the metal plate is a copper plate, the active metal brazing material contains Ag, Cu and an active metal as essential components. The active metal is one or more selected from Ti (titanium), Zr (zirconium), Hf (hafnium), and Nb (niobium). If necessary, Sn (tin) or In (indium) may be added to the active metal brazing material. If necessary, C (carbon) may be added to the active metal brazing material. By adding carbon, the fluidity of the brazing material can be suppressed. Therefore, the thickness of the brazing material layer can be made more uniform.
In the active metal brazing material, the content of Ag is 40 wt% or more and 80 wt% or less, the content of Cu is 15 wt% or more and 45 wt% or less, the content of active metal is 1 wt% or more and 12 wt% or less, and Sn (or In). Is preferably 0 wt% or more and 20 wt% or less, and the C content is preferably 0 wt% or more and 2 wt% or less. The total content of Ag, Cu, Ti, Sn (or In), and C is 100 wt%. When adding Sn or In to the active metal brazing material, the content of Sn or In is preferably 5 wt% or more. When both Sn and In are added, the total content is preferably in the range of 5 to 20 wt%. When carbon is added to the active metal brazing material, it is preferable that the content of carbon is 0.1 wt% or more and 2 wt% or less.

When the metal plate is an Al plate, the active metal brazing material preferably contains Al (aluminum) as a main component. Further, it is preferable that the Al brazing material contains at least one element selected from Si (silicon) and Mg (magnesium). The content of Si or Mg is preferably 0.01 wt% or more and 20 wt% or less, with the balance being Al.
The components of the active metal brazing material are mixed into a paste. An active metal brazing material paste is applied on a ceramic substrate. The active metal brazing material paste is applied so that the thickness of the brazing material layer is 10 μm or more and 60 μm or less.
A metal plate is placed on the applied active metal brazing material layer. After that, a heat bonding step is performed. The heating temperature is preferably, for example, in the range of 600 to 900C. Further, it is preferable to perform the treatment in a vacuum (1 × 10 ⁻³ Pa or less). By this step, a joined body in which the ceramic substrate and the metal plate are joined is produced.

Next, a step of processing the circuit metal plate (front metal plate) into a target pattern shape is performed. Etching is preferable for processing into a pattern shape. If it is an etching process, it is easy to adjust the inclined shape of the side surface of the metal plate and the protruding portion of the brazing material. In addition, a front metal plate processed in a pattern shape in advance may be joined.
Next, a step of adjusting the creeping distance T of the metal plate for heat radiation is performed. When a large substrate is used, it is effective to cut the joined body. The cutting may be performed using a cutting blade or a laser. The cutting blade may be a dicer blade. By cutting the joined body, a large number of metal plates for heat dissipation having a creeping distance T of 0 mm can be obtained.

Further, it is preferable to cut the joined body without performing scribe processing on the ceramic substrate. According to this method, the maximum height roughness Rz of the side surface of the ceramic substrate can be set to | Rz1−Rz2 | ≦ 10 μm.
Conventionally, when the joined body is divided, the ceramic substrate is scribed. For the scribe processing, a half scribe method or a dot scribe method in which scribe marks are provided on about half of the substrate is used. In such a method, | Rz1−Rz2 | on the side surface of the ceramic substrate has a large value of 10 μm.

For example, there is a method of polishing the side surface of the ceramic substrate so that | Rz1−Rz2 | ≦ 10 μm. However, when the side surface of the joined body is polished, the metal plate is softer than the ceramic substrate, so that the metal plate is more often removed. For this reason, there is a possibility that the creeping distance T becomes -0.1 mm or less. In other words, in the scribing method, it is difficult to obtain a large number of ceramic circuit boards having a creepage distance T exceeding -0.1 mm and not more than +0.05 mm.
When a ceramic substrate 2 having a target size is prepared in advance, a method of polishing the side surface of the ceramic substrate to remove scribe marks may be applied. In this case, the cost increases because the number of steps for polishing the side surface of the ceramic substrate increases.

Through the above steps, the ceramic circuit board according to the embodiment can be manufactured.
A semiconductor device can be manufactured by mounting a semiconductor element on a ceramic circuit board. The semiconductor element is mounted on the circuit metal plate 4. Further, it is preferable to mount the semiconductor element using Pb-free solder. Further, a plurality of semiconductor elements may be provided.
Further, a step of providing wiring is performed. Examples of the wiring include a bonding wire and a lead frame. Further, electrodes are provided as necessary.
Next, a resin molding step is performed. Various methods such as a transfer method and a compression method are applied to the molding process. There is also a molding method using a potting gel. A resin molding process is performed so that the surface of the heat-dissipating metal plate 5 is not covered with the resin. In addition, a molding process is performed so that wiring is formed from the molding resin.
In recent years, a transfer method has been used because of its good mass productivity. Transfer molding is a method in which a resin is heated in a plunger to soften the resin, and the softened resin is poured into a mold and cured. Since the softened resin is used, it is easy to fill the resin into the gap of the semiconductor device having a complicated shape. In addition, since the molding resin is solidified at a time, mass productivity and productivity are excellent.
The compression method is a resin sealing method in which a resin is directly injected into a mold, melted, and then a semiconductor device is immersed therein to mold the resin. Since the required amount of resin is injected into the mold, the usage efficiency of the resin is high. Further, since the fluidity of the resin is suppressed, disconnection of the bonding wire can be suppressed.
The potting method is a method in which a resin is dropped and molded. Since the resin can be dropped on a portion to be molded, it is effective when it is desired to form a partial mold structure. On the other hand, mass productivity is low.
In the ceramic circuit board according to the embodiment, the creeping distance T of the metal plate for heat radiation is reduced to 0 mm or more and less than 0.1 mm, so that it is possible to suppress the formation of bubbles in the resin mold on the back side of the ceramic substrate. For this reason, the resin-molded semiconductor device can suppress the resin peeling due to the thermal stress.
Next, the mounting board 12 and the metal plate 5 for heat dissipation are joined. In the joining step, solder, brazing, an adhesive, or the like can be used.

  Although the semiconductor device is bonded to the mounting substrate 12 after performing the molding process, the molding process may be performed after bonding to the mounting substrate 12.

(Example)
(Examples 1 to 12, Comparative Examples 1 to 4)
The ceramic substrate shown in Table 1 was used. In addition, the vertical and horizontal sizes were unified to 170 mm × 150 mm.

Further, a copper plate or an Al plate was prepared as a metal plate. The joining between the metal plate and the ceramics substrate was performed using an active metal brazing material.
For joining the copper plate and the ceramic substrate, an active metal brazing material made of Ag (60 wt%)-Cu (27 wt%)-Sn (10 wt%)-Ti (3 wt%) was used. The thickness of the brazing material layer was set to 30 μm, and the members were joined by heating at 830 ° C. in a vacuum (1 × 10 ⁻³ Pa or less).
In addition, for joining the Al plate and the ceramic substrate, an active metal brazing material made of Al (99 wt%)-Si (1 wt%) was used. The thickness of the brazing material layer was set to 30 μm, and the members were heated and joined at 630 ° C. in a vacuum (1 × 10 ⁻³ Pa or less).
Through this process, a joined body was manufactured. The same horizontal and vertical size of the metal plate for heat radiation as that of the ceramic substrate was used. The circuit metal plate used was previously processed into a pattern shape. The side surface of the metal plate for circuit was inclined, and the length of the protruding portion of the brazing material was a value shown in Table 2.
Next, the joined body was cut and divided into a length of 50 mm and a width of 30 mm. If necessary, the side surface of the heat-dissipating metal plate was etched to adjust the creeping distance T. Through this step, a ceramic circuit board according to the example was manufactured.
As a comparative example, in Comparative Examples 1 and 4, a ceramic substrate was subjected to half-scribe processing and divided processing. In Comparative Examples 1 to 4, the back metal plate was prepared by etching to make the creepage distance T −0.2 mm or −0.3 mm.
Examples 1 to 8 and Comparative Examples 1 to 4 were cut by laser. Examples 9 to 12 are cut by a dicer.
Through the above steps, ceramic circuit boards according to the example and the comparative example were prepared. The creepage distance T and the length of the protruding portion of the brazing material of the heat-dissipating metal plate were confirmed by a tool microscope at a magnification of 20 times. In addition, Rz1 and Rz2 were measured along the lateral direction of the side surface of the ceramic substrate. Each side was measured and showed the largest value among them. Rz was measured according to JIS-B-0601.
Table 2 shows the results.

In Examples 1, 3 to 6, 8 to 9, and 11 to 12, Rz on the side surface of the metal plate for heat radiation was in the range of 1 to 10 μm. On the other hand, Rz of the side surfaces of the metal plates for heat radiation of Examples 2, 7, 10 and Comparative Examples 1 to 4 were 0.1 μm or less. This is because the side surface of the metal plate was etched.
Semiconductor elements were mounted on the ceramic circuit boards according to the examples and comparative examples. The semiconductor elements were mounted using Sn-Ag-Cu-based Pb-free solder. The bonding wire was performed using an Al wire having a diameter of 400 μm. Two lead frames were joined.
Next, a resin molding process was performed. In Examples 1 to 6, Examples 9 to 12, and Comparative Examples 1 to 4, resin molding was performed by transfer molding. In Example 7, a resin molding process was performed by a potting method. In Example 8, a resin molding process was performed by a compression method. In each case, the end of the lead frame was formed so as to protrude from the mold resin. The back surface of the metal plate for heat radiation was not covered with the mold resin.
Next, the heat-dissipating metal plate was joined to the mounting substrate (heat sink base). Through this step, a semiconductor device having a resin mold was manufactured.
The presence or absence of bubbles (voids) in the mold resin of the obtained semiconductor device was examined. Further, the TCT characteristics of the semiconductor device having the resin mold were examined.
The presence or absence of bubbles was measured by X-ray CT. Judgment was made based on whether or not air bubbles could be observed around the side surface of the metal plate for heat radiation and around the side surface of the metal plate for circuit.
In addition, the TCT test was performed at -40 ° C. × 30 minutes → room temperature (25 ° C.) × 10 minutes → 175 ° C. × 30 minutes → room temperature (25 ° C.) × 10 minutes, and 1000 cycles were performed. The withstand voltage before and after the TCT test was measured. The withstand voltage was measured by measuring the withstand voltage between the front and back metal plates (the voltage at which dielectric breakdown occurs when held for 1 minute). Table 3 shows the results.

As can be seen from the table, the semiconductor device according to the example had a small decrease in withstand voltage. This is because the formation of bubbles in the mold resin is suppressed. Further, since the maximum height roughness Rz of the side surface of the ceramic substrate is controlled, the anchor effect with the resin is improved.
The presence / absence of bubbles is indicated by “absence” of bubbles in which no bubbles were confirmed (below the detection limit) by the X-ray CT image. An X-ray CT image in which the shadow of a small bubble was reflected was defined as “somewhat”. Those in which air bubbles were clearly observed were indicated as "Yes".
On the other hand, in the comparative example, since the creepage distance T was as large as −0.1 mm or less, bubbles were formed on the back metal plate side. In addition, since | Rz1−Rz2 | is large, resin peeling was induced by TCT, and the withstand voltage was reduced. When the protruding part of the brazing material was larger than 10 μm, air bubbles were easily formed in the mold resin.

  While some embodiments of the present invention have been described above, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. These novel embodiments can be implemented in other various forms, and various omissions, replacements, changes, and the like can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and equivalents thereof. The above-described embodiments can be implemented in combination with each other.

DESCRIPTION OF SYMBOLS 1 ... Ceramic circuit board 2 ... Ceramic substrate 3 ... Ceramic substrate side surface 3A ... Side side region from the center of the ceramic substrate side surface to the circuit metal plate side 3B ... Side region 4 from the center of the ceramic substrate side surface to the heat dissipation metal plate side 4 ... Circuit Metal plate 5: Metal plate for heat dissipation 6: Brazing material layer (Metal plate side brazing material layer for circuit)
7. Brazing material layer (Metal plate side brazing material layer for heat dissipation)
T: creepage distance of metal plate for heat dissipation 10: semiconductor device 11: semiconductor element 12: mounting substrate 13: mold resin

Claims (11)

In a ceramic circuit board in which a circuit metal plate is joined to one surface of a ceramic substrate and a heat dissipation metal plate is joined to the other surface,
90% or more of the creepage distance of the metal plate for heat radiation is in the range of more than -0.1 mm and less than +0.05 mm,
When the maximum height roughness Rz on the circuit metal plate side from the center of the ceramic substrate side surface is Rz1 and the maximum height roughness Rz on the heat dissipation metal plate side from the center of the ceramic substrate side surface is Rz2, | Rz1−Rz2 | A ceramic circuit board characterized by ≦ 10 μm. 2. The ceramic circuit board according to claim 1, wherein 100% of the creepage distance of the metal plate for heat radiation is in the range of more than -0.1 mm and not more than +0.05 mm. 3. The ceramic circuit board according to claim 1, wherein 100% of the creepage distance of the metal plate for heat radiation is in a range of not less than -0.07 mm and not more than 0 mm. 4. The ceramic circuit board according to claim 1, wherein a creepage distance of the metal plate for heat radiation is 0 mm. The ceramic circuit board according to any one of claims 1 to 4, wherein Rz1 and Rz2 are in a range from 0.3 m to 20 m. The ceramic circuit board according to any one of claims 1 to 5, wherein the thickness of the circuit metal plate and the heat radiation metal plate is 0.1 mm or more. The ceramic circuit board according to any one of claims 1 to 6, wherein the ceramic substrate, the metal plate for a circuit, and the metal plate for heat radiation are joined via a brazing material layer. The ceramic circuit board according to any one of claims 1 to 7, wherein a maximum height roughness (Rz) of a side surface of the metal plate for heat radiation is 0.3 µm or more and 20 µm or less. The ceramic circuit substrate according to any one of claims 1 to 8, wherein the ceramic substrate is a silicon nitride substrate having a thermal conductivity of 50 W / m · K or more and a three-point bending strength of 600 MPa or more. A semiconductor device comprising a semiconductor element mounted on the ceramic circuit board according to claim 1. The semiconductor device according to claim 10, wherein the semiconductor device is resin-molded.

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