JP7589487B2 - Metal circuit board and semiconductor cooling device - Google Patents

Description

The present invention relates to a metal circuit board on which a semiconductor element is mounted, and a semiconductor cooling device using the metal circuit board.

Metal circuit boards are used as semiconductor cooling devices equipped with metal heat dissipation members to dissipate heat generated by the mounted semiconductor elements. In semiconductor cooling devices, electrical insulation must be maintained between the metal circuit board and the heat dissipation member, so an insulating member with high thermal conductivity is placed between the two. In recent years, the operating voltage of this type of semiconductor cooling device has tended to increase. As the operating voltage increases, there is a growing concern that partial discharges will occur between the metal circuit board and the insulating member, causing deterioration of the insulating member, and there is a demand for improved voltage resistance in semiconductor cooling devices. In particular, if burrs protrude from the side, insulation breakdown is more likely to occur due to localized electric field concentration.

Patent document 1 describes a semiconductor device in which a conductor layer is provided on an insulating member to improve the reliability of voltage resistance, and the insulating member on a heat dissipation member, the conductor layer, a metal circuit board, and a semiconductor element are sealed with resin.

Patent No. 6536129

The sealing material described in Patent Document 1 is a resin composition in which a curing agent and inorganic filler are blended with a base material such as epoxy resin, and techniques such as transfer molding and potting are used as the sealing method. However, sealing materials blended with inorganic fillers have poor fluidity, so they do not adequately fill gaps in metal burrs on the sides and bottom of metal circuit boards or unevenness caused by processing, and there is a high possibility that voids will occur. For this reason, it is not possible to sufficiently improve insulation reliability.

In view of the above-mentioned technical background, the present invention aims to provide a metal circuit board that can reliably improve insulation reliability against burrs present on the surface of the metal circuit board, and a semiconductor cooling device that uses the metal circuit board.

That is, the present invention has the configurations described in [1] to [10] below.

[1] A metal plate has a first surface on which a semiconductor element is mounted, a second surface opposite to the first surface, and a side surface excluding the first surface and the second surface,
A metal circuit board, characterized in that the side surface and/or the second surface of the metal plate are covered with an insulating coating layer.

[2] The metal circuit board described in the preceding paragraph 1, in which both the side surface and the second surface of the metal plate are covered with an insulating coating layer.

[3] The metal circuit board according to paragraph 1 or 2 above, in which the insulating coating layer is made of resin or ceramics.

[4] A metal circuit board according to any one of paragraphs 1 to 3 above, in which the thickness t1 of the insulating coating layer covering the side surface of the metal plate and the surface roughness Rz1 of the side surface of the metal plate satisfy the relationship Rz1≦t1.

[5] A metal circuit board according to any one of paragraphs 1 to 4 above, in which the thickness t2 of the insulating coating layer covering the second surface of the metal plate and the surface roughness Rz2 of the second surface of the metal plate satisfy the relationship Rz2≦t2≦3Rz2.

[6] A metal circuit board according to any one of items 1 to 5 above, in which the insulating coating layer has a surface shape that conforms to the surface shape of the side surface of the metal plate.

[7] A metal circuit board according to any one of items 1 to 5 above, in which the insulating coating layer has a flat surface.

[8] A semiconductor cooling device comprising a metal circuit board according to any one of paragraphs 1 to 7 above, an insulating member bonded to the second surface of the metal plate of the metal circuit board, and a heat dissipation member bonded to the surface of the insulating member opposite the metal circuit board.

[9] The semiconductor cooling device according to paragraph 8, wherein the insulating member is a cured product of an adhesive insulating resin sheet.

[10] A semiconductor cooling device according to paragraphs 8 or 9, in which the dielectric constant of the insulating coating layer of the metal circuit board is greater than the dielectric constant of the insulating member.

In the metal circuit board described in [1] above, the burrs are embedded in the insulating coating layer on the surface of the metal plate covered with the insulating coating layer. This improves the insulation reliability in a semiconductor cooling device in which the metal circuit board, insulating member, and metal heat dissipation member are stacked. That is, on the side surface of the metal plate, the electric field concentration at the tip of the burr is restricted, and insulation breakdown is prevented, thereby improving insulation reliability. Also, on the second surface of the metal plate, insulation reliability is improved by preventing the burr from biting into the insulating member.

The metal circuit board described in [2] above can provide improved insulation reliability on both the side and second surfaces.

The metal circuit boards described in [3], [4], [5] and [6] above can further improve insulation reliability.

According to the metal circuit board described in [6] above, the tip of the burr on the side can be covered with an insulating material of the same thickness as the other parts, and the tip of the burr can be reliably buried. As a result, the insulation reliability can be reliably improved.

According to the metal circuit board described in [7] above, burrs and minute irregularities on the side and second surfaces can be covered with an insulating coating layer, so that insulation reliability can be reliably improved. The insulating coating layer with a flat surface can be produced by a wet process.

The semiconductor cooling device described in [8] above provides the various effects of the metal circuit board described above.

According to the semiconductor cooling device described in [9] above, the adhesive insulating resin sheet can be produced at a relatively low temperature of 200°C or less, which makes it possible to suppress warping and distortion of the product.

The semiconductor cooling device described in [10] above can further improve insulation reliability.

FIG. 1 is a perspective view of a semiconductor cooling device using the metal circuit board of the present invention. FIG. 1 is a cross-sectional view of one embodiment of a metal circuit board. FIG. 2 is a cross-sectional view of another embodiment of a metal circuit board. FIG. 2 is a cross-sectional view of yet another embodiment of a metal circuit board. FIG. 2C is a partially enlarged view of FIG. 2B. FIG. 2 is a cross-sectional view of yet another embodiment of a metal circuit board.

Figure 1 shows one embodiment of a semiconductor cooling device using the metal circuit board of the present invention.

The semiconductor cooling device 1 comprises metal circuit boards 10A, 10B, and 10C, an insulating member 20, and a heat dissipation member 21, which are joined in a stacked state. The semiconductor cooling device 1 is structured to dissipate heat generated by a semiconductor element 2 mounted on the first surface of the metal circuit boards 10A, 10B, and 10C to the heat dissipation member 21.

As shown in Figures 2A, 2B and 2C, the metal circuit boards 10A, 10B and 10C are composed of a metal plate 11 and insulating coating layers 12a and 12b. The metal plate 11 has a first surface 11a on which a semiconductor element 2 is mounted, a second surface 11b opposite the first surface 11a, and a side surface 11c other than the first surface 11a and the second surface 11b. The first surface 11a and the second surface 11b of the metal plate 11 are also the first surface and the second surface of the metal circuit boards 10A, 10B and 10C, and an insulating member 20 is joined to the second surface side of the metal circuit boards 10A, 10B and 10C.

In the metal circuit boards 10A, 10B, and 10C of the present invention, the side surface 11c and/or the second surface 11b of the metal plate 11 are covered with insulating coating layers 12a and 12b. That is, at least one of the surfaces except the first surface 11a on which the semiconductor element 2 is mounted is covered with the insulating coating layer 12a and 12b. In the metal circuit board 10A of FIG. 2A, only the side surface 11c of the metal plate 11 is covered with the insulating coating layer 12a. In the metal circuit board 10B of FIG. 2B, the side surface 11c of the metal plate 11 is covered with the insulating coating layer 12a, and the second surface 11b is covered with the insulating coating layer 12b. In the metal circuit board 10C of FIG. 2C, only the second surface 11b of the metal plate 11 is covered with the insulating coating layer 12b.

The metal plate 11 may have fine burrs on its surface during processing. In addition to the burrs, there are also fine irregularities inherent to the material. In the metal circuit boards 10A, 10B, and 10C, the side surface 11c and/or the second surface 11b of the metal plate 11 are covered with insulating coating layers 12a and 12b, and the burrs (including fine protrusions) 13 are embedded in the insulating coating layers 12a and 12b. Since air is a good conductor of electricity, if the burrs 13 protrude from the side surface 11c of the metal plate 11, insulation breakdown due to electric field concentration at the tip of the burrs 13 is likely to occur. However, by covering the side surface 11c with the insulating coating layer 12a, the electric field concentration can be regulated, insulation breakdown can be prevented, and insulation reliability can be improved. Furthermore, if burrs 13 protrude from the second surface 11b of the metal plate 11, there is a risk that the burrs 13 will cut into the insulating member 20 and reduce the insulating performance of the insulating member 20. However, by covering the second surface 11b with an insulating coating layer 12b to prevent the burrs from cutting into the insulating member 20, the insulation reliability can be improved (see FIG. 2B).

The insulating material constituting the insulating coating layers 12a and 12b may be a thermosetting resin, a thermoplastic resin, a photocurable resin, rubber, ceramics, or the like. In addition, it is preferable that the insulating coating layers 12a and 12b are made of a material having a higher relative dielectric constant than the insulating member 20 of the semiconductor cooling device 1, which can further improve the insulation reliability. The relative dielectric constant of the insulating coating layers 12a and 12b is preferably 5.0 to 1000, and the relative dielectric constant of the insulating member 20 is preferably 1.0 to 3.0.

Examples of the thermosetting resin include epoxy resin, cyanate resin, polyimide resin, benzoxazine resin, unsaturated polyester resin, phenol resin, melamine resin, silicone resin, bismaleimide resin, and acrylic resin.

Examples of the thermoplastic resin include polyolefin, polyvinyl chloride resin, methyl methacrylate resin, nylon, fluororesin, etc.

Examples of the rubber include acrylic rubber, nitrile rubber, isoprene rubber, urethane rubber, ethylene propylene rubber, styrene-butadiene rubber, butadiene rubber, fluororubber, butyl rubber, and silicone rubber.

Examples of the ceramics include powders of inorganic compounds such as silica, alumina, barium sulfate, aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, magnesium oxide, cerium oxide, hafnium oxide, zirconium oxide, boron nitride, aluminum nitride, silicon nitride, barium titanate, strontium titanate, calcium titanate, magnesium titanate, bismuth titanate, titanium oxide, and diamond-like carbon.

Among the insulating materials mentioned above, metal oxides with high relative dielectric constants are preferred, and titanate-based materials such as titanium oxide, barium titanate, calcium titanate, and strontium titanate are also recommended. These titanate-based coating materials turn into metal oxides when heated, making it possible to create a dense coating layer without voids or cracks.

The method for forming the insulating coating layer is not limited, and it can be formed by, for example, the following method. In the case of a thermosetting resin, a curing agent is added to a base resin, and a solvent is further added to prepare a resin composition having fluidity, which is then applied to the metal plate 11 and aged to harden. In the case of a thermoplastic resin, a solvent is added to prepare a resin composition having fluidity, which is then applied to the metal plate 11, and the solvent is then removed. In the case of rubber, a vulcanizing agent and a solvent are appropriately added in addition to the monomer components that form the rubber to prepare a rubber precursor composition having fluidity, which is then applied to the metal plate 11 and aged to harden.
In the case of ceramics, a low-viscosity precursor coating material containing the above-mentioned inorganic compound that forms a ceramic layer by resin or heating is prepared, and after applying this precursor coating material, the insulating layer is formed through a process of solvent drying and thermal decomposition.

The above-mentioned resin, rubber and precursor coating material coating materials have high fluidity and can fill even the small gap between the side surface 11c and/or second surface 11b of the metal plate 11 and the burr 13, and can completely cover the burr 13 by embedding it in the insulating coating layers 12a, 12b without generating voids. By completely covering the burr 13, it is possible to prevent dielectric breakdown caused by the burr 13. As referred to in Patent Document 1, when sealing all the members on the heat dissipation member including the semiconductor element, the sealing material after curing is required to have mechanical strength, so it is necessary to contain a large amount of inorganic filler, which inevitably reduces the fluidity of the sealing material. On the other hand, when the side surface 11c and/or second surface 11b of the metal plate 11 is covered with the insulating coating layers 12a, 12b to a thickness such that the burr 13 is embedded, high mechanical strength is not required, so there is no need to contain a large amount of inorganic filler, and a coating material with high fluidity can be selected.

The insulating coating layer 12a on the side surface 11c of the metal plate 11 is also useful when sealing all the members on the heat dissipation member 21 of the semiconductor cooling device 1 with a material with high mechanical strength. The small gap between the side surface 11c and the burr 13 is already filled with the insulating coating layer 12a, making it unnecessary to fill the narrow gap with a sealing material with low fluidity, and therefore a sealing material with high mechanical strength even if it has low fluidity can be selected.
(Thickness of insulating coating layer)
FIG. 3 shows a partial enlarged view of the metal circuit board 10B.

The surface roughness (maximum height) of the side surface 11c of the metal plate 11 is Rz1, and the thickness of the insulating coating layer 12a covering the side surface 11c is t1. The surface roughness Rz1 of the side surface 11c and the thickness t1 of the insulating coating layer 12a preferably satisfy the relationship Rz1≦t1. This relationship indicates a state in which the burr 13 is completely embedded in the insulating coating layer 12a up to its tip, and the effect of improving the insulation reliability is large. When Rz1>t1, the tip of the burr 13 protrudes from the surface of the insulating coating layer 12a, and the effect of improving the insulation reliability is small. The particularly preferable thickness t1 of the insulating coating layer 12a is three times or more Rz1. In addition, there is no particular upper limit to the thickness t1 of the insulating coating layer 12a.

The surface roughness (maximum height) of the second surface 11b of the metal plate 11 is Rz2, and the thickness of the insulating coating layer 12b covering the second surface 11b is t2. The surface roughness Rz2 of the second surface 11b and the thickness t2 of the insulating coating layer 12b preferably satisfy the relationship Rz2≦t2≦3Rz2. The reason why the lower limit of the thickness t2 is the surface roughness Rz2 is that, like the side surface 11c, the burrs 13 are completely embedded in the insulating coating layer 12b up to the tip to improve the insulation reliability. On the other hand, the upper limit of the thickness t2 of the insulating coating layer 12b is set because the second surface 11b becomes a heat transfer path to the heat dissipation member 21, and the insulating coating layer 12b becomes an obstacle to heat transfer, so that the thicker the insulating coating layer 12b, the lower the cooling performance. If the thickness t2 is 3 times or less than the surface roughness Rz2, the cooling performance can be maintained. The thickness t2 is particularly preferably 1 to 3 times the surface roughness Rz2.

FIG. 3 shows a metal circuit board 10B in which both the side surface 11c and the second surface 11b of the metal plate 11 in FIG. 2B are covered with insulating coating layers 12a, 12b. However, even when the insulating coating layers 12a, 12b are formed on only one of the surfaces (see FIGS. 2A and 2C), the preferred ranges of the thicknesses t1, t2 are the same.
(Surface morphology and formation method of insulating coating layer)
4 and 2B show two types of surface morphology of the insulating coating layers 12c and 12a covering the side surface 11c of the metal plate 11. FIG.

The insulating coating layer 12c in FIG. 4 has a surface shape in which the burr 13 protrudes following the surface shape of the side surface 11c, and the thickness of the insulating coating layer 12c is approximately constant. The burr 13 is covered up to its tip with an insulating material of the same thickness as the other parts, so that the burr 13 can be reliably embedded in the insulating coating layer 12c. In turn, the insulation reliability can be reliably improved. The insulating coating layer 12c with such a surface shape is obtained by forming a film using a dry process. A dry process is a method of forming a film by ionizing, radicalizing, gasifying, and monomolecularizing chemical species using PVD, CVD, vapor deposition, electron beam deposition, etc.

On the other hand, the insulating coating layer 12a in FIG. 2B has a flat surface, and the portion covering the burrs 13 is thinner than the other portions. The insulating coating layer 12a with this surface has the advantage that it covers metal burrs and minute irregularities on the side of the metal circuit board with an insulating layer. In addition, this surface shape can be obtained by forming the film using a wet process. A wet process is a method that uses dipping, spin casting, and spray pyrolysis dispenser application alone or in combination.

The surface configuration of the insulating coating layer on the side surface 11c of the metal plate 11 may be either of the above two types. However, it is preferable that the insulating coating layer on the second surface 11b has a flat surface configuration in consideration of the bonding with the insulating member 20.
(Semiconductor cooling device)
As shown in FIG. 1, the semiconductor cooling device 1 of the present invention comprises the above-mentioned metal circuit boards 10A, 10B, 10C, an insulating member 20 joined to the second surface side of the metal circuit boards 10A, 10B, 10C, and a heat dissipation member 21 joined to the surface of the insulating member 20 opposite to the metal circuit boards 10A, 10B, 10C.

The insulating member 20 can be made of any insulating material such as resin or ceramics, and a cured adhesive insulating resin sheet is recommended. The adhesive insulating resin sheet can be produced at a relatively low temperature of 200°C or less, which helps prevent warping and distortion of the product.

It is also preferable to design the dielectric constant of the insulating coating layers 12a and 12b of the metal circuit boards 10A, 10B, and 10C to be greater than the dielectric constant of the insulating member 20.

The heat dissipation member 21 can be made of any material with good thermal conductivity, such as aluminum or copper. The cooling method, such as liquid cooling or air cooling, is not limited.

The metal circuit board of the present invention can be suitably used in semiconductor cooling devices equipped with metal heat dissipation members.

1...Semiconductor cooling device 2...Semiconductor element 10A, 10B, 10C...Metal circuit board 11...Metal plate 11a...First surface 11b...Second surface 11c...Side surface 12a, 12b, 12c...Insulating coating layer 13...Burrs 20...Insulating member 21...Heat dissipation member t1...Thickness of insulating coating layer on side surface t2...Thickness of insulating coating layer on second surface Rz1...Surface roughness of side surface Rz2...Surface roughness of second surface

Claims (8)

A semiconductor cooling device comprising: a metal circuit board; an insulating member bonded to a second surface side of a metal plate of the metal circuit board; and a heat dissipation member bonded to a surface of the insulating member opposite to the metal circuit board,
The metal circuit board is a metal plate having a first surface on which a semiconductor element is mounted, a second surface opposite to the first surface, and a side surface excluding the first surface and the second surface;
The side surface and/or the second surface of the metal plate is covered with an insulating coating layer;
4. A semiconductor cooling device, wherein the insulating coating layer is made of resin. The semiconductor cooling device according to claim 1 , wherein both the side surface and the second surface of the metal circuit board are covered with an insulating coating layer. 3. The semiconductor cooling device according to claim 1, wherein the metal circuit board has an insulating coating layer covering a side surface of the metal plate with a thickness t1 and a surface roughness Rz1 of the side surface of the metal plate that satisfy the relationship Rz1 ≦t1. The semiconductor cooling device according to any one of claims 1 to 3, wherein the metal circuit board has a thickness t2 of an insulating coating layer covering the second surface of the metal plate and a surface roughness Rz2 of the second surface of the metal plate that satisfies the relationship Rz2≦t2≦3Rz2. 5. The semiconductor cooling device according to claim 1 , wherein the metal circuit board has a surface configuration in which the insulating coating layer conforms to the surface configuration of the side surface of the metal plate. 5. The semiconductor cooling device according to claim 1 , wherein the insulating coating layer of the metal circuit board has a flat surface. 7. The semiconductor cooling device according to claim 1, wherein the insulating member is a cured product of an adhesive insulating resin sheet. 8. The semiconductor cooling device according to claim 1, wherein the insulating coating layer of the metal circuit board has a higher dielectric constant than the insulating member.

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