JP6007016B2 - Circuit board laminate and metal base circuit board - Google Patents

Description

  The present invention relates to a circuit board laminate and a metal base circuit board.

  In recent years, the development of electronics technology has been remarkable, and the performance and miniaturization of electrical and electronic equipment are rapidly progressing. Along with this, the amount of heat generated by components mounted with electrical elements and / or electronic elements is increasing. Under such circumstances, a metal base circuit board on which so-called power devices such as a MOSFET (metal-oxide-semiconductor field-effect transistor) and an IGBT (insulated-gate bipolar transistor) are typically mounted is sufficient. In addition to heat resistance, excellent heat dissipation is required.

  The metal base circuit board has a structure in which an insulating layer and a circuit pattern are laminated in this order on a metal board. In order to improve the heat dissipation of the metal base circuit board, a resin composition in which insulating hexagonal boron nitride (h-BN) having high thermal conductivity and insulation is dispersed in the insulating layer for the insulating layer. Is widely used.

  This hexagonal boron nitride has a layered crystal structure similar to that of graphite and has a scaly shape. And it has anisotropic thermal conductivity that the thermal conductivity in the major axis direction (crystal direction) is high and the thermal conductivity in the minor axis direction (layer thickness direction) is low. Therefore, if the insulating layer is formed into a sheet shape by a known molding method such as press molding method, injection molding method, extrusion molding method, calendar molding method, roll molding method, doctor blade molding method, etc., pressure and flow during molding Therefore, the scaly boron nitride in the resin is tilted in the insulating layer, that is, as shown in FIG. 7, the major axis direction of the scaly boron nitride 5 is easily oriented so as to coincide with the sheet surface direction of the insulating layer. There is a tendency. The heat conductive insulating layer thus obtained has excellent heat conductivity in the surface direction of the insulating layer, and the heat conductivity is not sufficient in the usage form in which the thickness direction of the insulating layer is the heat conduction path. was there.

  In addition, if the major axis direction of all the scaly boron nitrides is oriented parallel to the thickness direction of the insulating layer, the thermal conductivity is significantly reduced instead of improving the thermal conductivity. The orientation of the flaky boron nitride in the thermally conductive insulating layer must be adjusted in consideration of the balance with the above.

  Therefore, primary particles of flaky boron nitride agglomerate in order to provide an insulating heat-radiating sheet excellent in thermal conductivity and insulation by orienting the major axis direction of flaky boron nitride dispersed in the resin in a balanced manner. Insulated heat-radiating sheets containing the secondary aggregated particles have been proposed (see, for example, Patent Documents 1 to 3).

JP-A-11-26661 Japanese Patent Laid-Open No. 11-60216 JP 2010-157563 A

  In the above-described method using secondary aggregated particles in which primary particles of flaky boron nitride are aggregated, there is a limit to orienting the major axis direction (crystal direction) of flaky boron nitride parallel to the thickness direction of the insulating layer, It has been difficult to sufficiently improve the thermal conductivity in the thickness direction of the insulating layer. In addition, since the secondary aggregate has a number of pores, even if an insulating layer is formed using a resin composition in which such secondary aggregate is dispersed, it is used for a metal base circuit board. There has been a problem that sufficient insulation cannot be obtained as an insulating heat dissipation sheet.

  In view of such circumstances, the present invention has an object to provide a laminate for a circuit board excellent in thermal conductivity and insulation, and a metal base circuit board formed using the laminate for a circuit board. And

  According to a first aspect of the present invention, there is provided a circuit board laminate comprising a metal substrate, an insulating layer provided on the metal substrate, and a metal foil provided on the insulating layer. There is provided a laminated board for a circuit board, wherein a groove is formed on the surface of the substrate on the insulating layer side, and the insulating layer contains a non-spherical inorganic filler having an aspect ratio of 2 or more and a resin. .

In one embodiment of the present invention, the non-spherical inorganic filler is, for example, in a scale shape, a plate shape, or a fiber shape.
In another embodiment of the present invention, the non-spherical inorganic filler is, for example, scaly boron nitride, and the average particle diameter thereof is, for example, in the range of 1 μm to 50 μm.

  In another embodiment of the present invention, the grooves formed on the surface of the metal substrate have, for example, a depth of 10 to 150 μm and a pitch of 0.1 μm or more.

  In another embodiment of the present invention, the grooves on the surface of the metal substrate are formed in a stripe shape, a lattice shape, or a dot shape, for example.

  In another embodiment of the present invention, the groove on the surface of the metal substrate has a cross-sectional shape of, for example, a V shape, a U shape, or a rectangular shape.

  According to the 2nd side surface of this invention, the metal base circuit board obtained by patterning the metal foil of the laminated board for circuit boards mentioned above is provided.

  According to the present invention, it is possible to provide a circuit board laminate excellent in thermal conductivity and insulation, and a metal base circuit board formed using the circuit board laminate.

Sectional drawing which shows schematically the laminated board for circuit boards which concerns on 1 aspect of this invention. Sectional drawing which shows schematically an example of the metal base circuit board obtained from the laminated board for circuit boards shown in FIG. Sectional drawing which shows typically a part of laminated board for circuit boards which concerns on 1 aspect of this invention. The SEM photograph which replaces drawing which shows a part of cross section of the laminated board for circuit boards which concerns on 1 aspect of this invention. The SEM photograph which replaces drawing which shows a part of cross section of the laminated board for circuit boards which concerns on 1 aspect of this invention. The SEM photograph which replaces drawing which shows a part of cross section of the laminated board for circuit boards which concerns on 1 aspect of this invention. Sectional drawing which showed the conventional insulation thermal radiation sheet typically.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
A laminated board for a circuit board according to the present invention includes a metal substrate having a groove formed on a surface thereof, an insulating layer provided on the surface of the metal substrate having a groove formed thereon, and a metal provided on the insulating layer. The insulating layer contains a non-spherical inorganic filler and a resin.

  As described above, when a non-spherical inorganic filler such as flaky boron nitride is used as the inorganic filler dispersed in the resin constituting the insulating layer, the major axis direction (in-plane direction) of the particles is insulated. It is easily oriented so as to coincide with the plane direction of the layer. On the other hand, when the thermal conductivity in the major axis direction (in-plane direction) of the non-spherical inorganic filler is high and the thermal conductivity in the minor axis direction (thickness direction) is low, such as scaly boron nitride, In a conventional insulating layer formed using a spherical inorganic filler, heat conduction in the thickness direction of the insulating layer is easy because the major axis direction (in-plane direction) of the particles tends to be aligned with the surface direction of the insulating layer. There was a problem that the sex was not enough.

  As shown in FIG. 1, the circuit board laminate 1 according to the present invention has grooves formed on the surface of the metal substrate 2 on the insulating layer 3 side. For this reason, for example, as schematically shown in FIG. 3, the major axis direction of the non-spherical inorganic dispersion material 5 dispersed in the matrix resin 6 of the insulating layer 3 formed on the metal substrate 2 is Oriented in the depth direction. As a result, the thermal conductivity in the thickness direction of the insulating layer can be improved without reducing the insulating properties.

  The inorganic filler used for the insulating layer is non-spherical inorganic particles, and examples thereof include a scale shape, a plate shape, and a fiber shape. However, the shape is not limited to these, and the aspect ratio is 2 or more. If it is. Here, the aspect ratio is an index indicating whether or not the shape of the particle is close to a sphere or a cube. For example, in the case of scaly or plate-like particles, the aspect ratio is expressed as the ratio of particle diameter to particle thickness (particle diameter / particle thickness). Here, the particle diameter represents an average particle diameter (D50) described later, and the particle thickness represents an average thickness measured from a cross-sectional image of 10 particles obtained by SEM. For example, in the case of fibrous particles, the aspect ratio is expressed as the ratio of the long side to the short side (long side / short side) of the fibrous particle. Here, the ratio (long side / short side) represents an average length obtained from fiber length distribution measurement (ISO16065-2 standard) by a non-polarized light source method.

  If the aspect ratio of the inorganic filler is less than 2, the shape is close to a sphere or a cube, so even if the resin flows into the groove formed on the surface of the metal substrate, the major axis direction of the particles is oriented in the depth direction of the groove. Therefore, the desired thermal conductivity cannot be obtained. In one embodiment of the present invention, the aspect ratio of the inorganic filler is preferably 5 to 60, for example, and more preferably 10 to 30.

  Specific examples of the non-spherical inorganic filler include boron nitride, aluminum nitride, silicon nitride, alumina, silica, carbide, metal fiber, and resin fiber. In one embodiment of the present invention, the non-spherical inorganic filler is preferably scaly boron nitride (hexagonal boron nitride [h-BN]).

  In one embodiment of the present invention, the average particle diameter of the non-spherical inorganic filler is preferably 1 μm or more and 50 μm or less, and more preferably 5 μm or more and 25 μm or less.

  Here, the average particle diameter is a particle diameter at a point at which the cumulative curve is 50% in a cumulative curve obtained by obtaining a particle size distribution on a volume basis and setting the total volume to 100%. D50). The particle size is measured by the light transmission centrifugal sedimentation method when the average particle size (D50) is 1 μm or less, and is measured by the laser diffraction / scattering method when it exceeds 1 μm.

  In one embodiment of the present invention, the content (filling rate) of the non-spherical inorganic filler in the insulating layer is preferably 40 to 80% by volume based on the resin contained in the insulating layer, and 50 to 70% by volume. More preferably. If the filling rate is too low, there may be a problem that it is difficult to form a heat transfer path because the number of contact points between the particles is reduced even if the orientation can be achieved. On the other hand, if the filling rate is too high, the viscosity becomes too high, which may cause a problem that the fluidity of the resin is lowered.

  The resin that becomes the matrix of the insulating layer is not particularly limited as long as it is a resin that exhibits fluidity when heated and / or pressurized. Examples thereof include polyamide imide, liquid crystal polyester, polyether ether ketone, polysulfone, polyphenyl sulfone, polyether sulfone, polyphenylene sulfide, epoxy resin, and imide resin. These resins can be used alone or in combination.

  The resin composition forming the insulating layer contains, for example, a solvent in addition to the above-described non-spherical inorganic filler and resin. For example, 10 to 9900 parts by mass, and more preferably 100 to 1900 parts by mass of the solvent is contained with respect to 100 parts by mass of the resin. When the amount of the solvent is excessively large, a large amount of the solvent must be removed from the coating film, which tends to cause a poor appearance of the coating film. In addition, productivity is reduced because a lot of drying time is required. On the other hand, when the amount of the solvent is excessively small, the composition tends to increase in viscosity, and the handleability and the like deteriorate. Examples of the solvent include N-methylpyrrolidone, dimethylacetamide, tetrafluoroisopropanol, methyl ethyl ketone, ethylene diglycol acetate, propylene glycol monomethyl ether acetate, and methyl isobutyl ketone.

  The resin composition may further contain various additives. Examples of the additive include coupling agents such as a silane coupling agent and a titanium coupling agent, and an ion adsorbent.

  The surface on the side where the insulating layer is formed in the metal substrate is an uneven surface due to the formation of grooves (recesses). The depth (d), pitch (p), shape, and the like of the groove are appropriately set depending on the particle size of the inorganic filler to be used and the balance between heat dissipation and insulation in the use as a metal base circuit board. In order to increase the degree of orientation, the groove pitch can be reduced and the depth can be increased within a range in which the resin can flow sufficiently. The depth (d) of the groove is, for example, preferably 10 to 150 μm, and more preferably 20 to 100 μm. The pitch (p) of the grooves is preferably 1 μm or more, more preferably 1 to 300 μm, still more preferably 60 to 250 μm, for example. The cross-sectional shape of the groove is not limited, but is, for example, V-shaped, U-shaped, or rectangular. The shape of the groove on the substrate surface is not limited, but is, for example, a stripe shape. , Grid or dot.

  The metal substrate is made of, for example, a single metal or an alloy. As a material of the metal substrate, for example, aluminum, iron, copper, aluminum alloy, or stainless steel can be used. The metal substrate may further contain a nonmetal such as carbon. For example, the metal substrate may contain aluminum combined with carbon. The metal substrate may have a single layer structure or a multilayer structure.

The metal substrate has a high thermal conductivity. Typically, the metal substrate has a thermal conductivity of 60 W · m ⁻¹ · K ⁻¹ or more.
The metal substrate may have flexibility or may not have flexibility. The thickness of the metal substrate is, for example, in the range of 0.2 to 5 mm.

  The method for forming the groove on the surface of the metal substrate is not particularly limited, and for example, known methods such as etching, press molding, cutting, dicing, knurling, and sandblasting can be used.

As shown in FIG. 1, the metal foil 4 is provided on the insulating layer 3. The metal foil 4 faces the metal substrate 2 with the insulating layer 3 interposed therebetween.
The metal foil 4 is made of, for example, a single metal or an alloy. As a material of the metal foil 4, for example, copper or aluminum can be used. The thickness of the metal foil 4 is in the range of 10 to 50 μm, for example.

The circuit board laminate 1 according to the present invention is manufactured, for example, by the following method.
First, the above-described resin is dissolved in a solvent to obtain an optically isotropic solution. Next, the non-spherical inorganic filler described above is dispersed in the solution to obtain a dispersion. The inorganic filler may be dispersed in the solution while being pulverized using, for example, a ball mill, a three roll, a centrifugal stirrer or a bead mill. Prior to adding the inorganic filler to the solution, an additive such as a silane coupling agent or an ion adsorbent may be added to the solution.

  Next, this dispersion is applied to at least one of the metal substrate 2 and the metal foil 4 having grooves formed on the surface. For the application of the dispersion, for example, a roll coating method, a bar coating method, or a screen printing method can be used. You may carry out by a continuous type and may carry out by a single plate type.

  After drying a coating film as needed, it overlap | superposes so that the metal substrate 2 and metal foil 4 may face each other on both sides of a coating film. Furthermore, they are hot pressed. As described above, the circuit board laminate 1 is obtained.

In this method, a coating film is formed by applying a dispersion liquid, which is a resin composition, to at least one of the metal substrate 2 and the metal foil 4, but in another embodiment, the dispersion liquid is applied to a substrate such as a PET film. Then, a coating film may be formed in advance by drying and thermally transferred to one of the metal substrate 2 and the metal foil 4.
When the resin composition is applied to the metal substrate 2 or when the coating film made of the resin composition is heated and pressurized to the metal substrate 2, the grooves (concave portions) formed on the surface of the metal substrate 2 are filled with non-spherical inorganic material. The resin in which the material is dispersed flows and the major axis direction of the non-spherical inorganic filler is oriented in the thickness direction of the insulating layer along the shape of the groove. As a result, an effect of improving heat dissipation and insulation is brought about.

Next, a metal base circuit board 1 ′ obtained from the above-described circuit board laminate 1 will be described.
A metal base circuit board 1 ′ shown in FIG. 2 is obtained from the circuit board laminate shown in FIG. 1, and includes a metal board 2, an insulating layer 3, and a circuit pattern 4 ′. The circuit pattern 4 ′ is obtained by patterning the metal foil 4 of the circuit board laminate described with reference to FIG. 1. This patterning can be obtained, for example, by forming a mask pattern on the metal foil 4 and removing the exposed portion of the metal foil 4 by etching. The metal base circuit board 1 ′ can be obtained, for example, by performing the above-described patterning on the metal foil 4 of the circuit board laminate 1 and performing processing such as cutting and drilling as necessary. it can.

  Since this metal base circuit board 1 ′ is obtained from the circuit board laminate 1 described above, it is excellent in heat dissipation and insulation.

Examples of the present invention will be described below. The present invention is not limited to these.
<Preparation of resin composition>
Synthesis Example 1: Resin composition 1
Boron nitride (manufactured by Denki Kagaku Kogyo, “SGP”, average particle size 20 μm, aspect ratio 20) is applied to a polyamideimide resin solution (Hitachi Chemical Co., Ltd., “HPC9000” / solvent: dimethylacetamide) having a solid content of 30% by mass. An insulating resin composition was prepared by blending to 60% by volume based on the resin solid content.

Synthesis Example 2: Resin composition 1 for control
Aggregation in which boron nitride (manufactured by Denki Kagaku Kogyo Co., Ltd., “SGP”, average particle size 20 μm) is aggregated by a spray drying method to a polyamideimide resin solution (manufactured by Hitachi Chemical Co., Ltd., “HPC9000”) having a solid content of 30% by mass Boron nitride (average particle size: 50 μm, aspect ratio: 1.3) was added in a total amount of 65% by volume based on the resin solid content to produce an insulating resin composition.

  The average particle size was measured by a laser diffraction / scattering method. The aspect ratio represents particle diameter / particle thickness, the particle diameter is the average particle diameter (D50) described above, and the particle thickness is an average thickness measured from a cross-sectional image of 10 particles obtained by SEM. However, the aspect ratio in the case of an agglomerate is a value obtained from the average value of the longest diameter / the average value of the diameters perpendicular to the longest diameter measured from a cross-sectional image of 10 particles obtained by SEM.

<Metal substrate>
As a metal substrate, a V-shaped groove having a pitch (p) and a depth (d) shown in the following table is striped on one surface of an aluminum alloy plate having a thermal conductivity of 140 W / mk and a thickness of 2.0 mm. The formed aluminum substrates (a), (b) and (c) were used. For comparison, a smooth aluminum substrate (thermal conductivity 140 W / mk, aluminum alloy plate having a thickness of 2.0 mm) that was not grooved was used.

<Evaluation>
The density, BN orientation, thermal resistance, and withstand voltage of the circuit board laminate were evaluated according to the following evaluation methods.
[density]
Each of the insulating resin compositions obtained by the above-described method was stirred for 5 minutes with a planetary stirring and defoaming machine, and then applied on a copper foil having a thickness of 70 μm so that the thickness after thermal bonding was about 100 μm. Dry at 220 ° C. until the solvent is gone. The copper foil on which this coating film was formed was laminated on each of the above-described aluminum substrates so that the coating film became an intermediate layer, and thermally bonded at a pressure of 20 MPa and a temperature of 270 ° C. Using the obtained laminate for circuit board as a sample, the copper foil and the aluminum plate were chemically etched to take out only the insulating layer.

The insulating layer obtained as described above was cut into a sheet size of 50 × 50 mm, and the density of the dried coating film was measured by Archimedes method. The value was made into the coating-film density (g / cm < ³ >).

[BN orientation]
Each of the insulating resin compositions obtained by the above-described method was stirred for 5 minutes with a planetary stirring and defoaming machine, and then applied on a copper foil having a thickness of 70 μm so that the thickness after thermal bonding was about 100 μm. Dry at 220 ° C. until the solvent is gone. The copper foil on which this coating film was formed was laminated on each of the above-described aluminum substrates so that the coating film became an intermediate layer, and thermally bonded at a pressure of 20 MPa and a temperature of 270 ° C. Using the obtained laminate for circuit board as a sample, the copper foil and the aluminum plate were chemically etched to take out only the insulating layer.

A sheet size of 50 × 50 mm is cut out from the insulating layer obtained as described above, and the peak intensities of the a-axis (100) and c-axis (002) of boron nitride obtained by X-ray diffraction are obtained. The degree of BN orientation (I.O.P) was determined.

[Thermal resistance]
Each of the insulating resin compositions obtained by the above-described method was stirred for 5 minutes with a planetary stirring and defoaming machine, and then applied on a copper foil having a thickness of 70 μm so that the thickness after thermal bonding was about 100 μm. Dry at 220 ° C. until the solvent is gone. The copper foil on which this coating film was formed was laminated on each of the above-described aluminum substrates so that the coating film became an intermediate layer, and thermally bonded at a pressure of 20 MPa and a temperature of 270 ° C. Using the obtained laminate for circuit board as a sample, thermal resistance was evaluated by the following method.

A substrate having a sheet size of 30 × 40 mm was cut out from the laminate obtained as described above, and a land size of 14 × 10 mm was arranged in the center of the substrate. Transistor C2233 (made by Toshiba) is attached to this board with solder, and the temperature of the surface of the transistor and the surface of the cooling device that generate heat when supplying 30 W of power using a thermally conductive silicone grease on the back side of the substrate and setting it in a water cooling device. Was measured. And thermal resistance (degreeC / W) was calculated | required from Formula (2).

[Withstand voltage]
Each of the insulating resin compositions obtained by the above-described method was stirred for 5 minutes with a planetary stirring and defoaming machine, and then applied on a copper foil having a thickness of 70 μm so that the thickness after thermal bonding was about 100 μm. Dry at 220 ° C. until the solvent is gone. The copper foil on which this coating film was formed was laminated on each of the above-described aluminum substrates so that the coating film became an intermediate layer, and thermally bonded at a pressure of 20 MPa and a temperature of 270 ° C. Using the obtained laminate for circuit board as a sample, thermal resistance was evaluated by the following method.

  A substrate having a sheet size of 50 × 50 mm was cut out from the laminate obtained as described above, and a land size φ20 mm was arranged in the center of the substrate. This substrate was immersed in insulating oil, and an AC voltage was applied to the copper foil at room temperature to measure the voltage (kV) at which dielectric breakdown occurred.

  The evaluation results are shown in Table 2. Moreover, the SEM photograph of the cross section of each sample produced in evaluation of Examples 1-3 is each shown to FIGS. 4-6.

Shown in Table 2

  From Table 2, it was found that by using an Al substrate having a grooved surface, the density and BN orientation were increased, and the thermal conductivity and withstand voltage were excellent. In addition, it can confirm also from FIGS. 4-6 that BN orientation degree increases by using the Al substrate by which the groove process was given to the surface. That is, in FIG. 4-6, the major axis direction of the scaly BN is oriented in the thickness direction of the insulating layer along the shape of the groove formed on the surface of the Al substrate.

  DESCRIPTION OF SYMBOLS 1 ... Circuit board laminated board, 1 '... Metal base circuit board, 2 ... Metal substrate, 3 ... Insulating layer, 4 ... Metal foil, 4' ... Circuit pattern, 5 ... Non-spherical inorganic filler, 6 ... Resin

Claims (6)

And the metal substrate, an insulating layer provided on the metal substrate, a circuit laminate board having a metal foil disposed on the insulating layer, the depth to the metal substrate of the insulating layer side of the surface Grooves having a thickness of 30 to 100 μm are formed at a pitch of 60 to 250 μm , and the insulating layer contains a non-spherical inorganic filler having an average particle diameter of 5 μm to 25 μm and an aspect ratio of 2 or more and a resin. The laminated board for circuit boards characterized.   The circuit board laminate according to claim 1, wherein the non-spherical inorganic filler has a scale shape, a plate shape, or a fiber shape.   The circuit board laminate according to claim 1, wherein the non-spherical inorganic filler is scaly boron nitride. 4. The circuit board laminate according to claim 1 , wherein the groove is formed in a stripe shape, a lattice shape, or a dot shape on the surface of the metal substrate. 5. The cross-sectional shape of the groove | channel formed in the said metal substrate surface is V shape, U shape, or a rectangular shape, The laminated board for circuit boards of any one of Claims 1-4 characterized by the above-mentioned. The metal base circuit board by which the said metal foil of the laminated board for circuit boards of any one of Claims 1-5 is patterned .

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