JP2018041868A - Heat dissipation substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat dissipation substrate capable of restraining curvature deformation after brazing.SOLUTION: In a heat dissipation substrate 10A where Cu layers 12, 14, 16 and metal A layers 18 composed of metal A are laminated alternately, the Cu layers 12, 14, 16 are laminated asymmetrically in the thickness direction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a heat dissipation substrate applied to an electronic component.

  In electric vehicles, hybrid vehicles and wind power generation, power modules are used as power control components. In power modules, an insulating substrate made of ceramics and a heat dissipation substrate made of metal are joined together, and semiconductor devices, especially LSIs, ICs, power transistors, etc. that operate at high power are connected via a joining material. It is brazed. Semiconductor devices that operate with high power generate heat during use.

  The heat dissipation substrate is required to efficiently diffuse and dissipate heat generated from these semiconductor devices. However, since the power module is a joined body made of different materials as described above, an internal stress is generated not only at the time of manufacture but also by temperature change at the time of use. There is a problem that the heat dissipation substrate is deformed by the internal stress. Therefore, it is desired that the heat dissipation substrate has high mechanical strength and high thermal conductivity.

  On the other hand, for example, Patent Document 1 discloses a clad material in which a Cu layer, a Mo layer, and a Cu layer are sequentially laminated as a heat dissipation substrate having a three-layer structure. By changing the volume ratio of Mo in this three-layer clad material in the range of 20% to 99.6%, the thermal conductivity and thermal expansion coefficient are controlled, higher thermal conductivity than Mo alone, and higher than Cu alone. Also obtained with a small thermal expansion coefficient.

Patent Document 2 discloses a relationship between a thermal expansion coefficient of a clad material having a three-layer structure in which a Cu layer, a Mo layer, and a Cu layer are sequentially laminated and a volume ratio of Cu. In the clad material having this structure, when the Mo layer is one layer, for example, in order to make the thermal expansion coefficient 12 × 10 ⁻⁶ / K or less, the amount of Mo having low thermal conductivity is reduced to the total mass. Must be 20% or more. Therefore, the thermal conductivity in the thickness direction of this clad material is only about 230 W / (m · K).

  Further, Patent Document 3 discloses a clad material in which five or more Cu layers and Mo layers are alternately laminated. In this case, by laminating five or more layers, a clad material having a smaller thermal expansion coefficient and a higher thermal conductivity can be obtained.

Japanese Patent Laid-Open No. 2-102551 JP-A-6-268115 JP 2007-115731 A

  In order to ensure the reliability of the semiconductor device to be joined, the heat dissipation substrate needs to be close to the thermal expansion coefficient of the semiconductor device at a temperature around 150 ° C., which is the operating temperature of the semiconductor device. For this reason, the heat dissipation substrate needs to have a volume ratio exceeding 10% of the entire layer composed of a metal having a low thermal expansion coefficient. The heat dissipation substrate configured as described above has a smaller coefficient of thermal expansion than the ceramic substrate. Therefore, the heat dissipation substrate is warped and deformed after cooling because the ceramic substrate undergoes thermal deformation more greatly at the heating temperature (for example, 800 ° C.) during brazing during assembly.

  An object of this invention is to provide the thermal radiation board which can suppress the curvature deformation after brazing.

  The heat dissipation substrate according to the present invention is characterized in that, in a heat dissipation substrate in which Cu layers and metal A layers made of metal A are alternately stacked, the Cu layers are stacked asymmetrically in the thickness direction.

  According to the present invention, since the Cu layer is laminated asymmetrically in the thickness direction, warpage deformation after silver brazing is suppressed in the heat dissipation substrate.

It is a perspective view which shows typically the structure of the thermal radiation board which concerns on this embodiment. It is a side view which shows the use condition of the heat sink which concerns on this embodiment. It is a perspective view which shows typically the structure of the thermal radiation board | substrate which concerns on a modification.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  The heat dissipation substrate 10A shown in FIG. 1 has a rectangular shape, and Cu layers 12, 14, 16 made of Cu or Cu alloy and metal A layers 18 made of metal A are alternately stacked. As shown in the thickness direction, the heat dissipation substrate 10A has four sides that are linear. In the case of this figure, the heat dissipation substrate 10A has a Cu layer 14 at the center in the thickness direction, a metal A layer 18 on both sides of the Cu layer 14, and Cu layers 12 and 16 on the outer surface. Is formed. The metal A is Mo or W.

  The heat dissipation board 10A is formed asymmetrically in the thickness direction. That is, in the heat dissipation substrate 10A, the Cu layers 12 and 16 at the same position counted from the center in the thickness direction have different thicknesses. In the case of this figure, the thickness of the Cu layer 12 arranged on one surface side is thicker than the thickness of the Cu layer 16 arranged on the other surface side opposite to the one surface. The metal A layers 18 have the same thickness. The thickness of the Cu layer 12 is preferably at least 0.02 mm thicker than the thickness of the Cu layers 14 and 16. The thickness of the Cu layer 12 can be selected, for example, in the range of 0.30 to 0.60 mm, and the thickness of the Cu layers 14 and 16 can be selected in the range of, for example, 0.25 to 0.55 mm. If the thickness of the Cu layer 12 is equal to or less than the above upper limit, the effect of low thermal expansion by the metal A layer 18 can be obtained, and reliability is not impaired. If the thickness of the Cu layer 12 is equal to or greater than the above lower limit, sufficient mechanical strength can be obtained. The thickness of the metal A layer 18 can be 0.03 to 0.10 mm.

  Next, a method for manufacturing the heat dissipation board 10A configured as described above will be described. The heat dissipation substrate 10A can be manufactured by a step of bonding a Cu plate and a metal A plate and a step of cutting out the heat dissipation substrate 10A.

  In the process of joining the Cu plate and the metal A plate, hot pressing is performed in which five layers of the Cu plate and the metal A plate are alternately stacked and pressed in a uniaxial direction at a high temperature. Specifically, it is performed using a press machine under conditions of a pressure of 1 to 10 MPa and a temperature of 925 to 1025 ° C. The atmosphere during hot pressing is preferably an atmosphere that does not contain oxygen in order to prevent Cu oxidation. For example, a reducing gas atmosphere, a nitrogen atmosphere, an argon atmosphere, a helium atmosphere, or a vacuum is preferred. . By the above-described process, a bonded body composed of five layers in which the Cu layers 12, 14, 16 and the metal A layers 18 are alternately overlapped is obtained.

  Next, a process of cutting out the heat dissipation substrate 10A will be described. In this step, the heat dissipation substrate 10A having a predetermined size is cut out from the joined body obtained as described above by punching. In other words, the male die is brought into contact with the lowermost layer of the joined body, the female die is brought into contact with the uppermost layer of the joined body, and the male die is moved in the female die direction, thereby punching the heat dissipation substrate 10A.

  As shown in FIG. 2, the ceramic substrate 20 is bonded to one surface of the heat dissipation substrate 10 </ b> A manufactured as described above via a bonding portion 21 containing silver brazing. Usually, when the heat dissipation substrate 10A and the ceramic substrate 20 are joined by silver brazing, the substrate is heated to 800 ° C to 830 ° C.

  By being heated, the heat dissipation substrate 10A and the ceramic substrate 20 are thermally expanded. When the heating temperature is 800 ° C. or higher, the silver solder is melted, flows between the heat dissipation substrate 10A and the ceramic substrate 20, and solidifies to bond the heat dissipation substrate 10A and the ceramic substrate 20.

  When cooled, the heat dissipation substrate 10A and the ceramic substrate 20 each thermally contract. In the case of the present embodiment, in the heat dissipation substrate 10A, the Cu layers 12, 14, and 16 are laminated asymmetrically in the thickness direction, so that warpage deformation after silver brazing is suppressed.

  A thermal stress is generated between the heat dissipation substrate 10A and the ceramic substrate 20 according to the difference in thermal expansion coefficient between the heat dissipation substrate 10A and the ceramic substrate 20. Since the Cu layer 12 on one surface side in contact with the ceramic substrate 20 is thicker than the Cu layer 16 on the other surface side, the thermal expansion substrate 10A has a higher thermal expansion coefficient on the one surface side than on the other surface side. Accordingly, the heat dissipation substrate 10A has a smaller difference in thermal expansion from the ceramic substrate 20 on one surface side than the conventional heat dissipation substrate 10A that is symmetric in the thickness direction, so that the thermal stress between the heat dissipation substrate 10A and the ceramic substrate 20 is reduced. As described above, since the thermal stress between the heat dissipation substrate 10A and the ceramic substrate 20 is small, warpage is suppressed. Furthermore, since Cu is easily plastically deformed, it is considered that the warpage of the heat dissipation substrate 10A is suppressed when the Cu layer 12 is plastically deformed.

  In the case of the present embodiment, the heat dissipation board 10A is a conventional heat dissipation board that includes the laminated Cu layers 12, 14, 16 and the metal A layer 18 so as to include a composite alloy composed of Cu and Mo as a core material. In comparison, a higher mechanical strength can be obtained with the thinner metal A layer 18. Therefore, since the heat dissipation substrate 10A can make the metal A layer 18 thinner, higher thermal conductivity can be obtained.

(Modification)
The present invention is not limited to the above-described embodiment, and can be appropriately changed within the scope of the gist of the present invention.

  In the case of the above embodiment, the case where the metal A layer 18 has the same thickness has been described, but the present invention is not limited to this. A modification will be described with reference to FIG. 3 in which the same components as those in FIG. As shown in this figure, the heat dissipating substrate 10B has the metal disposed on the other surface side opposite to the one surface from the thickness of the metal A layer 18 disposed on the one surface side to which the ceramic substrate is bonded. The A layer 22 is thick. The thickness of the metal A layer 22 is preferably at least 0.02 mm thicker than the thickness of the metal A layer 18. The thickness of the metal A layer 22 can be selected, for example, in the range of 0.05 to 0.15 mm. The heat dissipation substrate 10B can further suppress warpage by disposing the metal A layer 22 having high mechanical rigidity on the other surface side. If the thickness of the metal A layer 22 is not more than the above upper limit, warpage due to the difference in thermal expansion coefficient between the heat dissipation substrate 10B and the ceramic substrate can be suppressed by the effect of the present invention. Moreover, if the thickness of the metal A layer 22 is equal to or greater than the above lower limit, the effect of reducing thermal expansion and the effect of high mechanical rigidity due to the metal A layer 22 can be obtained.

  In the case of the above-described embodiment, the case where the heat dissipation substrate 10A has five layers has been described, but the present invention is not limited to this, and may be nine layers or thirteen layers. In any case, the outermost surface is preferably a Cu layer. Since the heat dissipation substrate 10A has five layers, it includes two or more metal A layers. Therefore, as shown in the modification, warping can be further suppressed by changing the thicknesses of the metal A layers 18 and 22 on the one surface side and the other surface side.

10A, 10B Heat dissipation substrate 12, 14, 16 Cu layer 18, 22 Metal A layer 20 Ceramic substrate

Claims (5)

A heat dissipation substrate in which Cu layers and metal A layers made of metal A are alternately stacked, wherein the Cu layer is stacked asymmetrically in the thickness direction. The heat dissipation substrate according to claim 1, wherein the Cu layer and the metal A layer are laminated in a total of 5, 9 or 13 layers in the thickness direction. The thickness of the Cu layer disposed on the one surface side to which the ceramic substrate is bonded is thicker than the thickness of the Cu layer disposed on the other surface side opposite to the one surface. The heat dissipation board of 1 or 2. The heat dissipation substrate according to claim 3, wherein a thickness of the metal A layer disposed on the other surface side is larger than a thickness of the metal A layer disposed on the one surface side. The heat dissipation substrate according to any one of claims 1 to 4, wherein the metal A is Mo or W.

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