JP6559136B2 - Insulating sheet - Google Patents

Description

Cross-reference of related applications

  This application claims the priority of Japanese Patent Application No. 2014-153477, and is incorporated into the description of this specification by reference.

  The present invention relates to an insulating sheet.

  Conventionally, an insulating sheet is an adhesive sheet that is used by being bonded to an adherend (for example, an insulating sheet that is interposed between an electronic component and a heat radiating member that releases heat generated by the electronic component to the outside) Etc.) contains an epoxy resin and an inorganic filler.

  For example, Patent Document 1 describes an insulating sheet in which a resin sheet formed of a resin composition containing an epoxy resin and an inorganic filler and a metal layer formed of a metal foil are laminated.

Japanese Unexamined Patent Publication No. 2006-191150

  By the way, in recent years, there are cases where an insulating sheet having even better insulating properties, adhesiveness, and thermal conductivity is required. However, conventional insulating sheets may not sufficiently satisfy such requirements.

  This invention makes it a subject to provide the insulating sheet excellent in insulation, adhesiveness, and heat conductivity in view of the said request point.

The present invention is an insulating sheet having a layer structure of three or more layers,
Used by adhering to the adherend,
A first surface layer adhered to the adherend;
A second surface layer that is a surface opposite to the first surface layer;
An intermediate layer in contact with the first surface layer from the inside,
The first surface layer contains an epoxy resin and an inorganic filler,
The intermediate layer has a higher volume content of inorganic components than the first surface layer, and a higher thermal conductivity than the first surface layer,
The first surface layer is an insulating sheet having a thickness smaller than that of the intermediate layer and having a difference in thermal resistance with the intermediate layer in the thickness direction within ± 5 ° C./W.

  Here, as an aspect of the insulating sheet according to the present invention, the intermediate layer contains an epoxy resin and an inorganic filler.

  Moreover, the said intermediate | middle layer is comprised with the ceramic plate as another aspect of the insulating sheet which concerns on this invention.

  Furthermore, as an aspect of the insulating sheet in which the intermediate layer is formed of a ceramic plate, the ceramic plate is an alumina plate, an aluminum nitride plate, or a silicon nitride plate.

The schematic sectional drawing of the insulating sheet which concerns on one Embodiment. The schematic sectional drawing which shows a coating apparatus.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

  The insulating sheet according to the present embodiment is an insulating sheet having a layer structure of three or more layers. Further, the insulating sheet according to the present embodiment is used by being adhered to an adherend. Furthermore, the insulating sheet according to the present embodiment includes a first surface layer that is bonded to the adherend, a second surface layer that is a surface opposite to the first surface layer, and the first surface layer. And an intermediate layer in contact with the inside. The first surface layer contains an epoxy resin and an inorganic filler. The intermediate layer has a higher volume content of inorganic components than the first surface layer, and a higher thermal conductivity than the first surface layer. The first surface layer has a smaller thickness than the intermediate layer, and a difference in thermal resistance with the intermediate layer in the thickness direction is within ± 5 ° C./W.

  Hereinafter, the insulating sheet according to the present embodiment will be described using an insulating sheet having a three-layer structure as an example.

  The insulating sheet according to the present embodiment is an insulating sheet that is used by being interposed between an electronic component and a heat radiating member that releases heat generated by the electronic component to the outside.

  As shown in FIG. 1, the insulating sheet 1 according to the present embodiment includes a first surface layer 2 on one side, a second surface layer 3 on the other side, the first surface layer 2 and the second surface layer. 3 and an intermediate layer 4 in contact with the first surface layer 2 and the second surface layer 3.

  The first surface layer 2, the second surface layer 3, and the intermediate layer 4 each contain an epoxy resin and an inorganic filler.

The first surface layer 2 and the second surface layer 3 are layers each having a smaller volume content of an inorganic filler that is an inorganic component than the intermediate layer 4.
Since the first surface layer 2 and the second surface layer 3 each have a smaller volume content of the inorganic filler than the intermediate layer 4, the volume of the epoxy resin in the first surface layer 2 and the second surface layer 3. The content can be made larger than the volume content of the epoxy resin in the intermediate layer 4. Moreover, the epoxy resin has excellent adhesiveness unlike the inorganic filler which is an inorganic component. Therefore, the said 1st surface layer 2 and the said 2nd surface layer 3 become the thing excellent in adhesiveness, As a result, the insulating sheet 1 which concerns on this embodiment becomes the thing excellent in adhesiveness.
In addition, the first surface layer and the second surface layer are less likely to cause cracks because the volume content of the inorganic filler, which is an inorganic component, is smaller than that of the intermediate layer. Therefore, the first surface layer 2 and the second surface layer 3 are excellent in insulation, and as a result, the insulating sheet 1 according to the present embodiment is excellent in insulation.
In the intermediate layer 4, the volume content of the inorganic filler is preferably 50% by volume or more, and more preferably 50 to 70% by volume.
Each layer of the first surface layer 2 and the second surface layer 3 has an inorganic filler volume content of preferably 60% by volume or less, more preferably 30 to 60% by volume.
The volume means the volume at 20 ° C.

The intermediate layer 4 has higher thermal conductivity than the first surface layer and the second surface layer.
The intermediate layer 4 has a thermal conductivity of preferably 10 to 50 W / (m · K), more preferably 10 to 30 W / (m · K).
The first surface layer has a thermal conductivity of preferably 10 to 50 W / (m · K), more preferably 10 to 30 W / (m · K). The second surface layer has a thermal conductivity of preferably 10 to 50 W / (m · K), more preferably 10 to 30 W / (m · K).
In addition, thermal conductivity can be measured by the method prescribed | regulated to JISA1412-1: 1999.

The first surface layer 2 and the second surface layer 3 each have a smaller thickness than the intermediate layer 4. The insulation sheet 1 which concerns on this embodiment becomes the thing excellent in heat conductivity by such structure.
The intermediate layer 4 has a thickness of preferably 100 to 300 μm, more preferably 100 to 200 μm.
The first surface layer 2 has a thickness of preferably 30 to 100 μm, more preferably 30 to 80 μm. The second surface layer 3 has a thickness of preferably 30 to 100 μm, more preferably 30 to 80 μm.
The thickness can be measured with a micrometer.

The difference in thermal resistance between the first surface layer 2 and the intermediate layer 4 in the thickness direction is within ± 5 ° C./W. In the insulating sheet 1 according to the present embodiment, such a configuration makes it difficult for heat accumulation to occur. As a result, the insulating sheet 1 according to the present embodiment is excellent in thermal conductivity.
The second surface layer 3 preferably has a difference in thermal resistance within ± 5 ° C./W with respect to the intermediate layer 4 in the thickness direction.
The first surface layer 2 has a thermal resistance of preferably 75 ° C./W or less, more preferably 6 to 20 ° C./W. Each of the second surface layers 3 has a thermal resistance of preferably 75 ° C./W or less, more preferably 6 to 20 ° C./W. The intermediate layer 4 has a thermal resistance of preferably 75 ° C./W or less, more preferably 6 to 20 ° C./W.
The first surface layer 2 preferably has a difference in thermal resistance with the intermediate layer 4 in the thickness direction within ± 3 ° C./W. The second surface layer 3 preferably has a difference in thermal resistance with the intermediate layer 4 in the thickness direction within ± 3 ° C./W.
The ratio of the resistance in the thickness direction of the intermediate layer 4 to the thermal resistance in the thickness direction of the first surface layer 2 is preferably 8/10 to 10/8, more preferably 9/10 to 10 /. Nine. The ratio of the resistance in the thickness direction of the intermediate layer 4 to the thermal resistance in the thickness direction of the second surface layer 3 is preferably 8/10 to 10/8, more preferably 9/10 to 10 /. Nine.
The thermal resistance can be measured by the method defined in JIS A1412-1: 1999.
The properties (thermal resistance, thickness, thermal conductivity, etc.) of each layer can be measured by polishing the insulating sheet and exposing the layer to be measured.

The dielectric breakdown voltage (BDV) of the insulating sheet according to the present embodiment is preferably 2 kV or more, and more preferably 3 kV or more.
BDV can be measured based on JIS K6911: 1995.

  The insulating sheet according to the present embodiment is used by being interposed between an electronic component such as a power transistor and a heat radiating member such as a heat radiating fin.

  The insulating sheet according to the present embodiment is configured as described above. Next, a manufacturing method for manufacturing the insulating sheet according to the present embodiment will be described.

  In the manufacturing method, a hot pressing step is performed in which the first resin sheet to be the first surface layer 2, the third resin sheet to be the intermediate layer 4, and the second resin sheet to be the second surface layer 3 are hot pressed. Thus, the insulating sheet according to the present embodiment can be obtained.

First, the manufacturing method of the resin sheet (1st resin sheet, 2nd resin sheet, and 3rd resin sheet) is demonstrated.
The resin sheet manufacturing method is a resin composition preparation step of preparing a resin composition by mixing an inorganic filler, an epoxy resin, and if necessary, a volatile solvent and other components by a general method, A resin sheet forming step of forming the resin composition by forming the resin composition into a sheet shape.

  As a method for preparing the resin composition in the resin composition preparation step, for example, a method in which an epoxy resin is dissolved in a volatile solvent and an inorganic filler or other component is added and mixed can be employed. Further, for example, a method of mixing the inorganic filler, the heated and melted epoxy resin and other components with a mixer or the like while heating and melting the epoxy resin can be employed.

  Examples of the epoxy resin include bisphenol A type epoxy resin, modified bisphenol A type epoxy resin, bisphenol F type epoxy resin, modified bisphenol F type epoxy resin, triphenylmethane type epoxy resin, cresol novolac type epoxy resin, biphenyl type epoxy resin, Various epoxy resins such as dicyclopentadiene type epoxy resin, phenol novolac type epoxy resin, and phenoxy resin can be used alone or in combination of two or more.

The inorganic filler is not particularly limited as long as it has a thermal conductivity higher than that of the epoxy resin. For example, boron nitride, aluminum nitride, silicon nitride, gallium nitride, aluminum oxide, silicon carbide, silicon dioxide, magnesium oxide, diamond, etc. Particles.
The inorganic filler preferably has an average particle size of 10 to 50 μm.

The resin composition can be provided with a thermosetting property by containing a curing agent and a curing accelerator.
The curing agent is not particularly limited, and examples thereof include amine curing agents such as diaminodiphenyl sulfone, dicyandiamide, diaminodiphenylmethane, and triethylenetetramine, phenol novolac resins, aralkyl-type phenol resins, and dicyclopentadiene-modified phenols. Resin, phenolic curing agents such as naphthalene type phenolic resin and bisphenolic phenolic resin, acid anhydrides and the like can be used.
Among these, phenol novolac resin and diaminodiphenyl sulfone are preferable in that it is easy to ensure reliability in electrical characteristics.
The curing accelerator is not particularly limited, but amine-based curing accelerators such as imidazoles, triphenyl phosphate (TPP), and boron trifluoride monoethylamine are preferable in terms of storage stability.

  The other components are generally used as plastic compounding chemicals such as dispersants, tackifiers, anti-aging agents, antioxidants, processing aids, stabilizers, antifoaming agents, flame retardants, thickeners, pigments, etc. Other components that can be added can be appropriately added as long as the effects of the present invention are not impaired.

The volatile solvent is used to uniformly disperse components contained in the resin composition.
Although it does not specifically limit as said volatile solvent, A boiling point of 120 degrees C or less is preferable at the point that volatilization removal is easy at the time of a resin sheet formation process. Moreover, it is preferable to use methyl ethyl ketone, acetone, toluene, etc. at the point that there is no reactivity with a resin composition.

  In the resin sheet forming step, for example, when a volatile solvent is used and a resin composition that is liquid at room temperature is used, the resin sheet is formed by a general coating apparatus as shown in FIG. A resin sheet can be formed on the support layer 6 by coating the resin composition 5 to be formed on one side of the support layer 6 and then drying the resin composition 5.

  The method for applying the resin composition 5 is not particularly limited, and a doctor blade method, a coater method, an extrusion molding method, a screen printing method, a metal mask printing method, and the like can be employed.

  As a method of drying the resin composition 5, a method of removing the volatile solvent in the resin composition 5 by volatilization and removal under vacuum conditions can be employed in addition to a drying method by heating at normal pressure. When a volatile solvent is contained in the resin composition 5, the resin composition 5 is usually dried and solidified by this drying. The temperature for drying the resin composition 5 is not particularly limited, but is preferably a temperature not lower than the boiling point of the volatile solvent blended in the resin composition 5 and not higher than the complete curing temperature of the epoxy resin, usually 70 to 130 ° C is suitable.

  In the resin sheet forming step, when the support layer 6 is used as shown in FIG. 2, the support layer 6 may be, for example, a sheet-like sheet that has been subjected to surface roughening treatment and surface release treatment in addition to surface untreatment. Things can be used. The material of the support layer 6 is not particularly limited, and examples thereof include plastics such as polyester, polyolefin, and polyimide, metals such as copper, aluminum, and nickel. Among these, polyethylene terephthalate (PET) is preferable in terms of good peelability, good external formability, and low cost. The thickness of the support layer 6 is typically 25 to 188 μm.

  In the resin sheet forming step, for example, the support layer 6 is fed out on one side and wound up on the other side, and the liquid resin composition 5 is continuously applied and dried between the feeding and winding. A so-called “roll-to-roll” method with excellent productivity can be employed.

  The resin sheet has a void. Since the voids of the resin sheet can be reduced by hot pressing the resin sheet, the thickness of the resin layer formed after the hot pressing is smaller than that of the resin sheet. Therefore, in consideration of such a change in thickness, for example, by appropriately setting the thickness when the resin composition is applied to the support layer, the thickness of the desired resin layer can be obtained.

In addition, when the mass of the resin layer per unit area of the surface where the resin layer is laminated is w, the thickness of the resin layer is m, and the density of the resin layer is ρ, it is expressed by the following formula (1).
w = m × ρ (1)
Further, the density ρ of the resin layer can be calculated from the sum of the density of each component of the resin layer multiplied by the volume ratio of each component in the resin layer in the resin sheet. Alternatively, a resin layer may be separately formed and the mass and volume may be measured to calculate the density ρ of the resin layer.
Furthermore, the mass of the resin layer can be calculated by subtracting the mass of the component that volatilizes during hot pressing from the mass of the resin composition used to form the resin layer.
Therefore, by forming the resin sheet so that the mass per unit area after drying is w, the thickness of the resin layer after the hot pressing step in the subsequent stage can be set to the target thickness m.

In the hot pressing step, first, the first resin sheet with the support layer and the third resin with the support layer are first brought into contact with the first resin sheet that becomes the first surface layer and the third resin sheet that becomes the intermediate layer. A resin sheet is laminated and hot-pressed to join the first resin sheet and the third resin sheet, thereby producing a joined body having support layers on both sides.
And the support layer by the side of the 3rd resin sheet is peeled from this joined body.
Next, the second resin sheet with the support layer and the joined body with the support layer are laminated so that the second resin sheet to be the second surface layer and the third resin sheet to be the intermediate layer are in contact with each other. The insulating sheet which has a support layer on both surfaces is produced by pressing and joining a 2nd resin sheet and a 3rd resin sheet.
And an insulating sheet can be obtained by peeling a support layer from both surfaces of an insulating sheet.

  The pressure in the hot press is preferably 1 to 20 MPa, more preferably 2 to 15 MPa.

Although it does not specifically limit as conditions of the said hot press other than a pressure, The temperature of 40-160 degreeC and 2 second-10 hours can be illustrated. It is preferably 40 ° C. or higher in terms of further promoting thermal curing, and 160 ° C. or lower in terms of preventing the epoxy resin curing reaction from proceeding excessively so that the electricity cannot be bonded between the media to be insulated. It is preferable that
Further, it is more preferable to perform hot pressing under reduced pressure in that voids can be efficiently removed.

  After the hot pressing step, the epoxy resin is preferably in an uncured state, more specifically in a semi-cured state that is not completely cured. As the semi-cured state, the calorific value of the epoxy resin that is not cured at all in DSC measurement is 100%, and the calorific value of the epoxy resin after the hot pressing step is in the range of 20 to 85%. Is preferred.

In addition to the heating device, the hot pressing step can be performed by, for example, a press machine equipped with a decompression device, a press machine equipped with a cooling device, and other multistage press machines.
In addition, as a specific method for carrying out the heat press, there are a method of heating and natural cooling, a method of consistently heating and cooling by heat exchange, a method of separating the heating press and the cooling press and performing a cooling press after the heating press, etc. Illustrated.

  By the way, since the 3rd resin sheet has high volume content of an inorganic filler, it is easy to produce a crack. However, in the manufacturing method, since the third resin sheet is covered with the first resin sheet and the second resin sheet and hot-pressed, the cracked portion of the epoxy resin of the first resin sheet and the second resin sheet is hot-pressed. Can be filled. As a result, an insulating sheet with few cracks can be obtained.

  Since the insulating sheet of the present embodiment is configured as described above, it has the following advantages.

That is, the insulating sheet 1 of this embodiment is an insulating sheet having a layer structure of three or more layers. Further, the insulating sheet according to the present embodiment is used by being adhered to an adherend. Furthermore, the insulating sheet according to the present embodiment includes a first surface layer 2 that is bonded to the adherend, a second surface layer 3 that is a surface opposite to the first surface layer 2, and the first surface layer 2. And an intermediate layer 4 in contact with the surface layer 2 from the inside. The first surface layer 2 contains an epoxy resin and an inorganic filler. The intermediate layer 4 has a higher volume content of inorganic components than the first surface layer 2 and a higher thermal conductivity than the first surface layer 2. The first surface layer 2 has a thickness smaller than that of the intermediate layer 4, and a difference in thermal resistance with the intermediate layer 4 in the thickness direction is within ± 5 ° C./W.
In the insulating sheet 1, since the first surface layer 2 has a smaller volume content of the inorganic component than the intermediate layer 4, the volume content of the epoxy resin in the first surface layer 2 is set in the intermediate layer 4. It can be made larger than the volume content of the epoxy resin. Moreover, an epoxy resin has the outstanding adhesiveness unlike an inorganic component. Therefore, the first surface layer 2 is excellent in adhesiveness, and as a result, the insulating sheet 1 is excellent in adhesiveness.
The first surface layer 2 is less prone to cracks due to the smaller volume content of the inorganic component than the intermediate layer 4. Therefore, the first surface layer 2 has excellent insulating properties, and as a result, the insulating sheet 1 has excellent insulating properties.
In the insulating sheet 1, the intermediate layer 4 has a volume content of the inorganic filler larger than that of the first surface layer 2. Moreover, an inorganic component is more excellent in heat conductivity than an epoxy resin. Therefore, the intermediate layer 4 is excellent in thermal conductivity. As a result, the insulating sheet 1 is excellent in thermal conductivity.
Further, in the insulating sheet 1, the first surface layer 2 is smaller in thickness than the intermediate layer 4, so that the insulating sheet 1 is excellent in thermal conductivity.
Furthermore, in the insulating sheet 1, the first surface layer 2 has a difference in thermal resistance with the intermediate layer 4 in the thickness direction within ± 5 ° C./W. Therefore, in such an insulating sheet 1, it is difficult for heat accumulation to occur. As a result, the insulating sheet 1 is excellent in thermal conductivity.
As described above, according to this embodiment, it is possible to provide an insulating sheet that is further excellent in insulation, adhesiveness, and thermal conductivity.

  Moreover, in the insulating sheet 1 of this embodiment, the said intermediate | middle layer 4 contains an epoxy resin and an inorganic filler.

  The insulating sheet according to the present invention is not limited to the above embodiment. In addition, the insulating sheet according to the present invention is not limited to the above-described effects. The insulating sheet according to the present invention can be variously modified without departing from the gist of the present invention.

For example, in the insulating sheet according to the present embodiment, the intermediate layer 4 contains an epoxy resin and an inorganic filler, but in the insulating sheet according to the present invention, the intermediate layer may be formed of a ceramic plate. Although the ceramic plate itself has a low mechanical strength, the insulating sheet according to the present invention has an advantage that the mechanical strength is increased because the ceramic plate is covered with two surface layers.
In this case, the intermediate layer 4 has a thickness of preferably 100 to 300 μm, more preferably 100 to 200 μm. The first surface layer 2 has a thickness of preferably 30 to 200 μm, more preferably 50 to 150 μm. The second surface layer 3 has a thickness of preferably 30 to 200 μm, more preferably 50 to 150 μm.

  The ceramic plate is preferably an alumina plate, an aluminum nitride plate, or a silicon nitride plate, and an aluminum nitride plate is particularly preferable from the viewpoint of excellent heat dissipation and low cost.

  1: insulating sheet, 2: first surface layer, 3: second surface layer, 4: intermediate layer, 5: resin composition, 6: support layer

Claims (4)

An insulating sheet having a layer structure of three or more layers,
Used by adhering to the adherend,
A first surface layer adhered to the adherend;
A second surface layer that is a surface opposite to the first surface layer;
An intermediate layer in contact with the first surface layer from the inside,
The first surface layer contains an epoxy resin and an inorganic filler,
The intermediate layer has a higher volume content of inorganic components than the first surface layer, and a higher thermal conductivity than the first surface layer,
The first surface layer is an insulating sheet having a thickness smaller than that of the intermediate layer, and a difference in thermal resistance with the intermediate layer in the thickness direction is within ± 5 ° C / W.   The insulating sheet according to claim 1, wherein the intermediate layer contains an epoxy resin and an inorganic filler.   The insulating sheet according to claim 1, wherein the intermediate layer is made of a ceramic plate.   The insulating sheet according to claim 3, wherein the ceramic plate is an alumina plate, an aluminum nitride plate, or a silicon nitride plate.

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