JP7804411B2 - Resin film, metal-clad laminate, circuit board and laminate structure - Google Patents

Description

The present invention relates to resin films, metal-clad laminates, circuit boards, and laminate structures that have excellent thermal conductivity and can be used as materials for, for example, semiconductor modules.

In recent years, there has been an increasing demand for smaller and lighter electronic devices, such as mobile phones and smartphones. The miniaturization of electronic devices has led to increased integration in semiconductor modules, and coupled with faster information processing speeds, means of dissipating heat generated within electronic devices have become increasingly important. Accordingly, efforts have been made to improve the thermal conductivity (λz) through the thickness direction by blending thermally conductive fillers into polyimides used in applications such as insulating resin layers on circuit boards (see, for example, Patent Documents 1 to 3).

However, when a large amount of thermally conductive filler is incorporated into an insulating resin layer to increase the thermal conductivity (λz) in the thickness direction, some of the thermally conductive filler protrudes from the surface of the insulating resin layer, causing poor appearance and surface smoothness, and poor adhesion to the metal layer. Furthermore, incorporating a large amount of thermally conductive filler may result in a decrease in the mechanical strength of the insulating resin layer. Therefore, the previous approach of incorporating a large amount of thermally conductive filler to improve the thermal conductivity (λz) in the thickness direction is expected to have limitations.
In addition, in the above Patent Documents 1 to 3, the thickness of the insulating resin layer described in the examples is 20 μm or more, so even if a large amount of thermally conductive filler is added, a decrease in mechanical strength is unlikely to become apparent.

International Publication WO2009/110387 JP 2012-213899 A JP 2019-140094 A

The inventors have found that when the thermal conductivity in the thickness direction (λz) is around 0.6 W/m·K, the effect of increasing the thermal conductivity in the thickness direction (λz) tends to plateau, and that it is more effective to reduce the thickness of the insulating resin layer while limiting the amount of thermally conductive filler added. Furthermore, when applied to applications such as semiconductor modules, as their integration becomes higher, there is likely to be an increasing demand for thinner insulating resin layers containing thermally conductive fillers. On the other hand, there is concern that further thinning the insulating resin layer will significantly reduce its mechanical strength and make it more brittle, making it more susceptible to serious problems such as cracks and breaks.

Therefore, the object of the present invention is to provide a resin film that is thin yet maintains heat dissipation properties and mechanical strength sufficient for practical use.

After extensive research to solve the above problems, the inventors discovered that it is possible to achieve both heat dissipation properties and sufficient mechanical strength even when the film is made thin, leading to the completion of the present invention.

That is, the resin film of the present invention is a resin film comprising a film-like insulating resin and a thermally conductive filler dispersed within the insulating resin. The resin film of the present invention is characterized in that the overall thickness (L) of the resin film is in the range of 8 μm or more and less than 23 μm, the thermal conductivity in the thickness direction (λz) is in the range of 0.3 W/m·K or more and less than 2.0 W/m·K, and the edge tear resistance measured over a 20 mm width is in the range of 0.3 [N] or more and 30.0 [N] or less.

In the resin film of the present invention, the volume average particle diameter of the thermally conductive filler may be in the range of more than 1.0 μm and less than 5 μm, and the ratio of the volume average particle diameter (D) of the thermally conductive filler to the film thickness (L) may be in the range of 0.15 or more and 0.50 or less.

The resin film of the present invention may have a tear propagation resistance in the range of 7.0 mN or more and 30.0 mN or less.

The resin film of the present invention may have a thermally conductive filler content in the range of 10 vol% to 50 vol% relative to the entire resin film.

In the resin film of the present invention, the thermally conductive filler may be alumina particles.

In the resin film of the present invention, the insulating resin may be a polyimide obtained by reacting an acid dianhydride component with a diamine component. In this case, the acid dianhydride component may contain 50 mol% or more of one or more selected from pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and 3,3',4,4'-benzophenonetetracarboxylic dianhydride relative to the total acid dianhydride components, and the diamine component may contain 50 mol% or more of one or more selected from 4,4'-diaminodiphenyl ether and 2,2-bis[4-(4-aminophenoxy)phenyl]propane relative to the total diamine components.

The metal-clad laminate of the present invention is a metal-clad laminate comprising an insulating resin layer consisting of a single layer or multiple layers and a metal layer laminated on one or both sides of the insulating resin layer, and at least one layer of the insulating resin layer is composed of the above-mentioned resin film.

The circuit board of the present invention comprises an insulating resin layer consisting of a single layer or multiple layers, and a conductor circuit layer laminated on one or both sides of the insulating resin layer, and at least one layer of the insulating resin layer is composed of the above-mentioned resin film.

The laminated structure of the present invention is a laminated structure used in a semiconductor module,
a conductor circuit layer electrically connected to an external semiconductor element;
an insulating resin layer consisting of a single layer or multiple layers;
an adhesive layer;
a heat transfer metal layer that mediates heat conduction to an external heat dissipation member;
have a structure in which the above are stacked in this order,
At least one of the insulating resin layers is formed from the resin film.

The resin film of the present invention is thin, yet maintains heat dissipation properties and mechanical strength sufficient for practical use. Therefore, the resin film of the present invention can be widely used industrially as a substrate material for semiconductor modules and circuit boards that require high heat dissipation properties, as well as electronic devices and lighting equipment that use these.

1 is a view showing a cross-sectional structure in a thickness direction of a resin film according to an embodiment of the present invention. 1 is a view showing a cross-sectional structure in a thickness direction of a metal-clad laminate according to an embodiment of the present invention. 1 is a diagram showing a cross-sectional structure in a thickness direction of a circuit board according to an embodiment of the present invention. 1 is a diagram showing a configuration of a laminated structure according to an embodiment of the present invention. 1 is a diagram showing the configuration of a semiconductor module used to evaluate heat dissipation characteristics in Examples and Comparative Examples.

The following describes an embodiment of the present invention, with reference to the drawings as appropriate.

[Resin film]
1 shows a cross-sectional structure in the thickness direction of a resin film according to one embodiment of the present invention. Resin film 10 of this embodiment includes film-like insulating resin 11 and thermally conductive filler 12 dispersed in insulating resin 11. Resin film 10 of this embodiment may be a single layer or may be composed of multiple layers, but is preferably a single layer.

<Insulating resin>
The insulating resin (matrix resin) 11 constituting the resin film 10 is not particularly limited, and examples thereof include polyimide, epoxy resin, urethane resin, and polyethylene terephthalate, among which polyimide is preferred. The case where the matrix resin is polyimide will be described in detail below.

Polyimide is a polymer formed by reacting an acid dianhydride component with a diamine component. The polyimide may contain a structural unit represented by the following general formula (1):

In the above general formula (1), the group Ar represents an acid dianhydride residue derived from an acid dianhydride, and the group R ₁ represents a diamine residue derived from a diamine compound.

In this embodiment, the acid dianhydride from which the group Ar is derived can be any acid dianhydride generally known as a raw material monomer for polyimide, without particular limitation. However, preferred examples of acid dianhydrides include pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), and 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA). Pyromellitic dianhydride (PMDA) has a rigid structure, which enhances the heat resistance of the resin film 10. 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) has a structure that includes moderate flexibility, which enhances the mechanical strength of the resin film 10. 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) has a structure with moderately suppressed flatness, which enhances the thermal conductivity of the resin film 10 in the thickness direction.

Furthermore, the diamine compound from which the group _R1 is derived can be any compound generally known as a raw material monomer for polyimide, without any particular limitation, but preferred diamine compounds include 4,4'-diaminodiphenyl ether (DAPE) and 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP). 4,4'-diaminodiphenyl ether (DAPE) and 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) have appropriate flexibility due to their molecular structures, and therefore have the effect of increasing the toughness of the resin film 10, thereby increasing the mechanical strength of the resin film 10 and improving its adhesiveness.

From the above perspectives, a preferred combination is one in which the acid dianhydride component contains 50 mol% or more, preferably 80 mol% or more, of one or more selected from pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), and 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) relative to the total acid dianhydride components, and the diamine component contains 50 mol% or more, preferably 80 mol% or more, of one or more selected from 4,4'-diaminodiphenyl ether (DAPE) and 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) relative to the total diamine components. Among these, a combination in which the acid dianhydride component is 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and the diamine component is 4,4'-diaminodiphenyl ether (DAPE), or a combination in which the acid dianhydride components are pyromellitic dianhydride (PMDA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and the diamine component is 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) are particularly preferred.

Specific examples of other acid dianhydrides that provide the group Ar in general formula (1) include, for example, naphthalene-2,3,6,7-tetracarboxylic dianhydride (NTCDA), naphthalene-1,2,5,6-tetracarboxylic dianhydride, naphthalene-1,2,4,5-tetracarboxylic dianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride, naphthalene-1,2,6,7-tetracarboxylic dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic dianhydride, and 4,8-dimethyl-1,2,3,5,6 ,7-Hexahydronaphthalene-2,3,6,7-tetracarboxylic dianhydride, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 1,4,5,8-tetrachloronaphthalene-2,3,6,7-tetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3'' ,4,4''-p-Terphenyltetracarboxylic acid dianhydride, 2,2'',3,3''-p-Terphenyltetracarboxylic acid dianhydride, 2,3,3'',4''-p-Terphenyltetracarboxylic acid dianhydride, 2,2-bis(2,3-dicarboxyphenyl)-propane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-propane dianhydride, bis(2,3-dicarboxyphenyl)ether dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, bis(2,3-dicarboxy Bis(3,4-dicarboxyphenyl)sulfone dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, perylene-2,3,8,9-tetracarboxylic dianhydride, perylene-3,4,9,10-tetracarboxylic dianhydride, perylene-4,5,10,11-tetracarboxylic dianhydride, perylene-5,6,11,12-tetracarboxylic dianhydride, phenanthrene-1,2,7,8-tetracarboxylic dianhydride, phenanthrene-1, Examples include 2,6,7-tetracarboxylic dianhydride, phenanthrene-1,2,9,10-tetracarboxylic dianhydride, cyclopentane-1,2,3,4-tetracarboxylic dianhydride, pyrazine-2,3,5,6-tetracarboxylic dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic dianhydride, thiophene-2,3,4,5-tetracarboxylic dianhydride, and 4,4'-oxydiphthalic dianhydride.

Other diamine compounds that provide the group R ₁ in general formula (1) include, for example, 4,6-dimethyl-m-phenylenediamine, 2,5-dimethyl-p-phenylenediamine, 2,4-diaminomesitylene, 4,4'-methylenedi-o-toluidine, 4,4'-methylenedi-2,6-xylidine, 4,4'-methylene-2,6-diethylaniline, 2,4-toluenediamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylpropane, 3,3'-diaminodiphenylpropane, 4,4'-diaminodiphenylethane, 3,3'- Diaminodiphenylethane, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 3,3-diaminodiphenyl ether, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, benzidine, 3,3'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl,3,3'-dimethoxybenzidine,4,4'-diamino-p-terphenyl,3,3'-diamino-p-terphenyl, bis(p-aminocyclohexyl)methane, bis(p-β-amino-t-butylphenyl)ether, bis(p-β-methyl-δ-aminopentyl)benzene, p-bis(2-methyl-4-aminopentyl)benzene, p-bis(1,1-dimethyl-5-aminopentyl)benzene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,4-bis(β- amino-t-butyl)toluene, 2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylenediamine, p-xylylenediamine, 2,6-diaminopyridine, 2,5-diaminopyridine, 2,5-diamino-1,3,4-oxadiazole, piperazine, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,7-diaminodibenzofuran, 1,5-diaminofluorene, dibenzo-p-dioxin-2,7-diamine, and 4,4'-diaminobenzyl.

When synthesizing the polyimide that constitutes the resin film 10, only one type of diamine or acid anhydride may be used, or two or more types may be used in combination.

<Thermal conductive filler>
Any conventionally known thermally conductive filler can be used without any particular limitation as the thermally conductive filler 12. Preferred examples of the thermally conductive filler 12 include alumina, silica, diamond, magnesia, beryllia, boron nitride, silicon nitride, and silicon carbide. Among these, alumina, silica, boron nitride, and silicon nitride are preferred, as they have a significant effect of increasing the thermal conductivity of the resin film 10, and alumina is most preferred.

The content of thermally conductive filler 12 in resin film 10 is preferably in the range of 10 vol% to 50 vol%, and more preferably in the range of 20 vol% to 40 vol%. If the content of thermally conductive filler 12 is less than 10 vol%, sufficient heat dissipation characteristics cannot be obtained when used in electronic components such as semiconductor modules. On the other hand, if the content of thermally conductive filler 12 exceeds 50 vol%, not only will the effect of improving heat dissipation characteristics plateau, but the incorporation of a large amount of thermally conductive filler 12 will have significant adverse effects, such as poor appearance and adhesion of resin film 10, reduced mechanical properties, and excessively increased viscosity of the polyamic acid solution, making it difficult to fabricate resin film 10. In other words, even if the content of thermally conductive filler 12 exceeds 50 vol%, the effect of improving heat dissipation characteristics is not significantly improved compared to when the content is 50 vol% or less, and negative effects such as reduced mechanical strength and handleability will become more significant.

The particle size of the thermally conductive filler 12 is preferably determined taking into consideration the balance with the thickness of the resin film 10. Specifically, from the perspective of uniformly dispersing the filler in the thickness direction of the resin film 10 and improving thermal conductivity, the volume average particle size (D) of the thermally conductive filler 12 is preferably greater than 1.0 μm and less than 5 μm, and more preferably between 1.5 μm and 4.0 μm. Here, the "volume average particle size" refers to the value at which the cumulative value reaches 50% on a frequency distribution curve obtained by measuring the volumetric particle size distribution using a laser diffraction scattering method. If the volume average particle size (D) of the thermally conductive filler 12 is 1.0 μm or less, it is difficult to form a thermal conduction path in the thickness direction, and the improvement in thermal conduction efficiency is likely to be insufficient. On the other hand, if the volume average particle size (D) is 5 μm or more, the mechanical strength is likely to decrease, and the thermally conductive filler 12 may protrude from the surface of the resin film 10, causing problems with appearance and surface smoothness, or problems with adhesion to any layer (e.g., a metal layer) laminated on the resin film 10.

In this embodiment, it is possible to blend two or more types of thermally conductive fillers with different volume average particle diameters (D), as long as the effects of the invention are not impaired. In this case, since fillers with smaller particle diameters are less likely to form filler thermal conduction paths than fillers with larger particle diameters, it is preferable to add the filler with the largest volume average particle diameter (D) at the highest content. In other words, for example, when two types of fillers with different volume average particle diameters (D), D1 and D2, are used in combination and the volume average particle diameter of D1 is larger than the volume average particle diameter of D2, it is preferable to include them in a combination where the content of D1 is greater than the content of D2.

Furthermore, the thermally conductive filler 12 preferably has a 95% cumulative value ( _D95 ) of 15 μm or less, more preferably 10 μm or less, in a frequency distribution curve obtained by measuring the volumetric particle size distribution by a laser diffraction scattering method. When the _D95 of the thermally conductive filler 12 is 15 μm or less, the proportion of coarse particles is controlled to be low, thereby preventing a decrease in the mechanical strength of the resin film 10.

The thermally conductive filler 12 is preferably spherical. Here, "spherical" means a shape that is spherical or nearly spherical, with the ratio of the average major axis to the average minor axis being 1 or nearly 1 (preferably 0.8 or greater). The use of spherical fillers enables high-density filling and uniform dispersion in the resin film 10, improving thermal conductivity.

The thermally conductive filler 12 in the resin film 10 is preferably in a uniformly dispersed state in which the thermally conductive filler 12 is uniformly dispersed and particle aggregation is suppressed. This uniformly dispersed state effectively maximizes the thermal conductivity of the thermally conductive filler 12, and allows the resin film 10 to maintain sufficient mechanical strength for practical use even when made thinner.

The resin film 10 of this embodiment may contain optional components such as processing aids, antioxidants, light stabilizers, flame retardants, antistatic agents, surfactants, dispersants, anti-settling agents, heat stabilizers, UV absorbers, and organic or inorganic fillers other than the thermally conductive filler 12, as long as the effects of the invention are not impaired.

<Thickness>
The overall thickness (L) of the resin film 10 in this embodiment is preferably, for example, in the range of 8 μm or more and less than 23 μm, more preferably 10 μm or more and less than 20 μm, and even more preferably 10 μm or more and 18 μm or less. If the thickness (L) of the resin film 10 is less than 8 μm, the surface smoothness of the film may deteriorate, and the mechanical strength of the resin film 10 may decrease, making it more susceptible to problems such as tearing. Conversely, if the thickness (L) is 23 μm or more, a sufficient heat dissipation effect cannot be obtained.

In addition, in the resin film 10 of this embodiment, the ratio (D/L ratio) of the volume average particle diameter (D) of the thermally conductive filler 12 to the film thickness (L) is preferably in the range of 0.15 to 0.50, more preferably 0.20 to 0.40. When the resin film 10 contains multiple thermally conductive fillers with different volume average particle diameters (D), the D/L ratio is determined based on the filler with the largest volume average particle diameter (D). If the D/L ratio is below 0.15, it is difficult to form a thermal conduction path in the thickness direction, and the improvement in thermal conduction efficiency is likely to be insufficient. On the other hand, if the D/L ratio exceeds 0.50, the mechanical strength is likely to decrease, and the filler may protrude from the surface of the resin film 10, causing problems with appearance and surface smoothness, or problems with adhesion to any layer (such as a metal layer) laminated on the resin film 10.

<Thermal conductivity in the thickness direction (λz)>
The thermal conductivity (λz) in the thickness direction of the resin film 10 of this embodiment is preferably, for example, in the range of 0.3 W/m·K or more and less than 2.0 W/m·K, and more preferably in the range of 0.5 W/m·K or more and 1.8 W/m·K or less. If the thermal conductivity (λz) in the thickness direction is less than 0.3 W/m·K, a sufficient heat dissipation effect cannot be obtained when applied to electronic components such as semiconductor modules. On the other hand, there is no particular upper limit to the thermal conductivity (λz) in the thickness direction, but it is preferable to set it to less than 2.0 W/m·K in consideration of practicality when applied to electronic components such as semiconductor modules.

<Mechanical properties>
The tear propagation resistance of the resin film 10 of this embodiment is preferably in the range of 7.0 mN or more and 30.0 mN or less, and more preferably in the range of 9.0 mN or more and 30.0 mN or less. If the tear propagation resistance is less than 7.0 mN, it may cause breakage, and processability and flexibility may be impaired. There is no particular upper limit for the tear propagation resistance, but if it exceeds 30.0 mN, the thickness must be increased or the filler content must be reduced, making it difficult to ensure sufficient heat dissipation.

In addition, the edge tear resistance of the resin film 10 of this embodiment, measured over a width of 20 mm, is preferably in the range of 0.30 N or more and 30.0 N or less, and more preferably in the range of 0.35 N or more and 30.0 N or less. Resistance below 0.30 N can cause tearing and impair processability and flexibility. There is no particular upper limit for edge tear resistance, but a configuration exceeding 30.0 N requires either a larger thickness or a smaller filler content, making it difficult to ensure sufficient heat dissipation.

In this embodiment, the amount of thermally conductive filler 12 and the relationship between its average particle size and the film thickness of the resin film 10 are appropriately controlled, so the tear propagation resistance and edge tear resistance can be maintained within the above ranges, resulting in mechanical strength sufficient for practical use.

<Method of manufacturing resin film>
The method for producing resin film 10 of the present embodiment is not particularly limited. When insulating resin 11 is polyimide, a preferred method is to apply a filler-containing polyamic acid solution, which is a precursor of polyamic acid, to a substrate and disperse thermally conductive filler 12 in the solution, dry the solution, and imidize the solution to form a film.

The polyamic acid solution containing the thermally conductive filler 12 can be prepared, for example, by adding a predetermined amount of the thermally conductive filler 12 to a polyamic acid solution containing a solvent obtained by prior polymerization and dispersing it using a stirrer or the like, or by adding an acid dianhydride component and a diamine component while dispersing the thermally conductive filler 12 in a solvent and polymerizing the resulting solution. Here, polyamic acid can be produced by a known method in which the acid dianhydride component and the diamine component are polymerized in a solvent in approximately equimolar amounts.

Preferred solvents for use in the polyamic acid solution include, for example, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethyl sulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diglyme, triglyme, cresol, and water. Two or more of these solvents can be used in combination, and aromatic hydrocarbons such as xylene and toluene can also be used in combination. There are no particular restrictions on the solvent content, but it is preferable to adjust the amount so that the polyamic acid concentration is approximately 5 to 70% by weight.

In this embodiment, in order to uniformly disperse the thermally conductive filler 12 in the resin film 10, it is preferable to adjust the viscosity of the polyamic acid solution serving as the dispersion medium to within a range of, for example, 500 cP to 50,000 cP (500 mPa·s to 50,000 mPa·s). This viscosity range allows the thermally conductive filler 12 to be maintained in a uniformly dispersed state.

The substrate is not particularly limited, but metal foils such as copper foil, which are used as conductor layers in heat dissipation substrates and circuit boards, are preferred. The filler-containing polyamic acid solution can be applied to the substrate by a known method, such as bar coating, gravure coating, roll coating, or die coating.

After applying a polyamic acid solution containing thermally conductive filler 12 to the substrate, it is dried, for example, at a temperature of 140°C or less to remove a certain amount of solvent. This is then followed by further heat treatment at a high temperature to imidize the polyamic acid, resulting in a laminate having a substrate on one side of the filler-containing polyimide layer. If a metal foil is used as the substrate, a metal-clad laminate, as described below, can be produced. Thereafter, if necessary, the filler-containing polyimide layer can be peeled off from the substrate to produce the resin film 10 of this embodiment.

The heat treatment for imidization is preferably carried out in stages over a period of approximately 15 to 60 minutes at a heating temperature within the range of 130 to 360°C. Such staged heat treatment minimizes dimensional changes in the resin film 10 and suppresses warping. Note that if the heat treatment temperature is lower than 130°C, the dehydration ring-closing reaction of polyimide will not proceed sufficiently, and conversely, if it exceeds 360°C, the resin film 10 and metal foil may deteriorate due to oxidation, etc.

[Metal-clad laminate]
2 shows a cross-sectional structure in the thickness direction of a metal-clad laminate according to one embodiment of the present invention. The metal-clad laminate 30 of this embodiment includes an insulating resin layer 10A and a metal layer 20 laminated on the insulating resin layer 10A. The metal layer 20 may be laminated on both sides of the insulating resin layer 10A.

<Insulating resin layer>
The insulating resin layer 10A in the metal-clad laminate 30 of this embodiment is composed of a single layer or multiple layers, and at least one layer of the insulating resin layer 10A may be composed of the resin film 10 containing the thermally conductive filler 12. The insulating resin layer 10A may include any layer that does not contain the thermally conductive filler 12, but it is preferable that the entire insulating resin layer 10A be composed only of the resin film 10.

<Metal layer>
The metal layer 20 in the metal-clad laminate 30 of the present invention serves as a conductor layer for a heat dissipation substrate or a circuit board, and examples thereof include conductive metal foils such as copper, aluminum, iron, silver, palladium, nickel, chromium, molybdenum, tungsten, zinc, and alloys thereof. Among these, copper foil or an alloy copper foil containing 90% or more copper is preferably used.

The preferred thickness range of the metal layer 20 can be set depending on the application of the metal-clad laminate 30. When used as a laminate substrate for a semiconductor module, for example, a range of 5 μm to 50 μm is preferable, and a range of 12 μm to 40 μm is even more preferable. Of these, a range of 30 μm to 40 μm is particularly preferable. If the thickness of the metal layer 20 is less than 5 μm, problems such as wrinkling may occur during transportation in the manufacturing process. Conversely, if it exceeds 50 μm, processability may be reduced. Here, the ratio (LR/LM) of the thickness of the insulating resin layer 10A (LR) to the thickness of the metal layer 20 (LM) is preferably in the range of 0.2 to 2.0, more preferably in the range of 0.2 to 1.0, and most preferably in the range of 0.5 to 0.6, from the perspective of suppressing warping of the metal-clad laminate 30. If the ratio (LR/LM) is less than 0.2, the insulating resin layer 10A will be too thin compared to the thickness of the metal layer 20, resulting in poor processability; if it exceeds 2.0, the insulating resin layer 10A will be too thick compared to the thickness of the metal layer 20, resulting in warping.

In addition, to enhance adhesion to the insulating resin layer 10A, the conductive metal foil used as the metal layer 20 preferably has a surface roughness (Rz) of 0.05 to 3.5 μm on the surface that adheres to the insulating resin layer 10A. If the surface roughness (Rz) of the surface that adheres to the insulating resin layer 10A is less than 0.05 μm, the metal layer 20 and the insulating resin layer 10A may be prone to peeling depending on the application of the metal-clad laminate 30, making the metal-clad laminate 30 unsuitable for use as a flexible circuit board material, for example. On the other hand, if the surface roughness (Rz) of the surface that adheres to the insulating resin layer 10A exceeds 3.5 μm, the anchor effect of the roughening will improve adhesion between the metal layer 20 and the insulating resin layer 10A, but there is a concern that the wiring shape may deteriorate when the metal layer 20 is processed into wiring.

<Metal-clad laminate manufacturing method>
The manufacturing method of the metal-clad laminate 30 of this embodiment is as explained in relation to the manufacturing method of the resin film 10, and a single-sided metal-clad laminate can be manufactured in which the metal layer 20 is laminated on one side of the insulating resin layer 10A by using a metal foil as a substrate for manufacturing the resin film 10. Furthermore, it is also possible to form a double-sided metal-clad laminate having a laminated structure of metal foil/insulating resin layer 10A/metal layer 20 by laminating a metal foil on the side of the insulating resin layer 10A opposite to the metal layer 20 by a method such as thermocompression bonding.

The insulating resin layer 10A of the metal-clad laminate 30 of this embodiment has heat dissipation characteristics sufficient for practical use while avoiding the reduction in mechanical strength that results from the incorporation of thermally conductive filler 12. Therefore, by using the metal-clad laminate 30 of this embodiment as a substrate material for semiconductor modules and the like, the reliability of electronic devices can be improved.

[Circuit board]
FIG. 3 shows a cross-sectional structure in the thickness direction of a circuit board according to one embodiment of the present invention. The circuit board 40 of this embodiment includes an insulating resin layer 10A consisting of a single layer or multiple layers, and a conductor circuit layer 21 laminated on the insulating resin layer 10A. The circuit board 40 can be manufactured by processing the metal layer 20 of the metal-clad laminate 30 into a pattern using a conventional method to form the conductor circuit layer 21. The metal layer 20 can be patterned using any method, such as photolithography and etching. The circuit board 40 may have any layer other than those shown in FIG. 3. Furthermore, the circuit board 40 may be a flexible circuit board or a rigid circuit board.

The insulating resin layer 10A of the circuit board 40 of this embodiment has heat dissipation characteristics sufficient for practical use while avoiding the reduction in mechanical strength that results from the incorporation of thermally conductive filler 12. Therefore, by applying the circuit board 40 of this embodiment to semiconductor modules and the like, the reliability of electronic devices can be improved.

[Laminated structure]
4 shows the configuration of a laminated structure according to one embodiment of the present invention. The laminated structure 100 of this embodiment is a laminated structure 100 used, for example, in a semiconductor module. The laminated structure 100 has a structure in which a conductor circuit layer 21 electrically connected to an external semiconductor element 70, an insulating resin layer 10A consisting of a single layer or multiple layers, an adhesive layer 50, and a heat transfer metal layer 60 that mediates heat conduction to an external heat dissipation member (not shown) are stacked in this order. In the laminated structure 100 of this embodiment, the conductor circuit layer 21 and the insulating resin layer 10A have the same configuration as the circuit board 40 described above.

In the laminated structure 100, at least one layer of the insulating resin layer 10A, preferably the entire insulating resin layer 10A, is composed of the above-mentioned resin film 10. Therefore, the insulating resin layer 10A has heat dissipation characteristics sufficient for practical use while avoiding a decrease in mechanical strength caused by the incorporation of the thermally conductive filler 12. Therefore, by using the laminated structure 100 of this embodiment in a semiconductor module or the like, the reliability of electronic devices can be improved. Note that the laminated structure 100 may have any layers other than those shown in FIG. 4.

In addition to increasing density, semiconductor modules are beginning to be used in applications such as automobile daytime running lights, which require higher heat dissipation and heat resistance. By using the laminated structure 100 of this embodiment, the durability of the semiconductor module can be improved because it has better heat dissipation and heat resistance than conventional materials.

The present invention will be explained in detail below based on examples, but the present invention is not limited to the scope of these examples.

The abbreviations used in the examples represent the following compounds.
BTDA: 3,3',4,4'-benzophenonetetracarboxylic dianhydride BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride PMDA: pyromellitic dianhydride DAPE: 4,4'-diaminodiphenyl ether BAPP: 2,2-bis(4-aminophenoxyphenyl)propane m-TB: 2,2'-dimethyl-4,4'-diaminobiphenyl DMAc: N,N-dimethylacetamide

The properties evaluated in the examples were evaluated according to the following evaluation methods.

[Viscosity measurement]
The viscosity of the polyamic acid solution was measured using a cone-plate viscometer equipped with a thermostatic water bath (manufactured by Tokimec Co., Ltd.).
The measurement was carried out at 25°C.

[Measurement of volume average particle diameter _D50 ]
The volume-average particle diameter was determined as the value at which the cumulative value reached 50% on a frequency distribution curve obtained by volume-based particle size distribution measurement using a laser particle size distribution measurement device (Microtrac MT3300EXII manufactured by Microtrac Bell Co., Ltd.) by laser diffraction. In the measurement, alumina was placed in a 0.2% by mass aqueous solution of sodium hexametaphosphate and dispersed for 5 minutes at 40 W using an ultrasonic device built into the device, and the refractive index of the alumina was set to 1.76.

[Thermal conductivity in the thickness direction (λz)]
The polyimide resin film was cut into a size of 20 mm x 20 mm, and the thermal diffusivity in the thickness direction was measured by a laser flash method (trade name: Xenon Flash Analyzer LFA447 Nanoflash device, manufactured by NETZSCH), the specific heat was measured by differential scanning calorimetry (DSC), and the density was measured by a water displacement method. Based on these results, the thermal conductivity (W/m K) was calculated.

Tear Propagation Resistance (TPR)
A polyimide resin film of 63.5 mm x 50 mm was used as a test piece, and a 12.7 mm long notch was made in the test piece, and the tear propagation resistance was measured using a light load tear tester manufactured by Toyo Seiki Co., Ltd.

[End tear resistance]
According to Method B of JIS C2151 (2019), edge tear resistance was measured using a 20 mm × 200 mm polyimide film test piece with a Strograph R1 (trade name) manufactured by Toyo Seiki Seisakusho.

[Workability]
When the copper foil of a 20 cm x 30 cm copper-clad laminate was completely etched, the polyimide film was evaluated as x if it had film defects due to cracks, tears, etc., and the polyimide film was evaluated as ◯ if a good film was obtained without any defects.

[Chip temperature (evaluation of heat dissipation characteristics)]
5, for a semiconductor module S having a structure in which, from the top, an LED chip (LED) as a semiconductor element 70, a copper circuit layer (Cu) as a conductor circuit layer 21, a polyimide layer (PI) as an insulating resin layer 10A, an adhesive layer (AD) as an adhesive layer 50, and an aluminum layer (Al) as a heat-conducting metal layer 60 are stacked in this order, the heat dissipation characteristics were evaluated by measuring the chip temperature when the LED chip (LED) was operated (light-emitting) for one hour. Note that heat dissipation was performed only from the aluminum layer (Al) side.
The LED chip (LED) had a size of 3 mm x 3 mm x 1 mm thick, a heat generation amount of approximately 2 W, and the copper circuit layer (Cu) had a size of 3 mm x 3 mm x 35 μm thick. The polyimide layer (PI), adhesive layer (AD), and aluminum layer (Al) all had a planar size of 50 mm x 100 mm, and the thickness of the polyimide layer (PI) was shown in each example and comparative example. The adhesive layer (AD) had a thermal conductivity of 1 [W/m K] in the thickness direction, a thickness of 100 μm, and a thickness of 1 mm for the aluminum layer (Al).

(Synthesis Example 1)
Under a nitrogen stream, DAPE (17.26 g, 0.086 mol) was dissolved in 255 g of DMAc solvent in a 500 ml separable flask with stirring. BTDA (27.73 g, 0.086 mol) was then added. The solution was then stirred at room temperature for 3 hours to allow polymerization, yielding a pale yellow, viscous polyamic acid solution A with a viscosity of 12,000 cP.

(Synthesis Example 2)
As in Synthesis Example 1, BAPP (29.23 g, 0.071 mol) was dissolved in 255 g of DMAc solvent in a 500 ml separable flask with stirring under a nitrogen atmosphere. PMDA (14.73 g, 0.068 mol) and BPDA (1.05 g, 0.004 mol) were then added. The solution was then stirred at room temperature for 3 hours to carry out a polymerization reaction, yielding a pale yellow, viscous polyamic acid solution B with a viscosity of 10,000 cP.

(Synthesis Example 3)
As in Synthesis Example 1, m-TB (22.21 g, 0.104 mol) was dissolved in 255 g of DMAc solvent in a 500 ml separable flask with stirring under a nitrogen stream. Next, PMDA (22.79 g, 0.104 mol) was added. The solution was then stirred at room temperature for 3 hours to carry out a polymerization reaction, yielding a pale yellow, viscous polyamic acid solution C with a viscosity of 10,000 cP.

(Synthesis Example 4)
As in Synthesis Example 1, DAPE (21.56 g, 0.107 mol) was dissolved in 255 g of DMAc solvent in a 500 ml separable flask with stirring under a nitrogen atmosphere. PMDA (23.44 g, 0.107 mol) was then added. The solution was then stirred at room temperature for 3 hours to carry out a polymerization reaction, yielding a pale yellow, viscous polyamic acid solution D with a viscosity of 13,000 cP.

(Combination example 1)
63.1 parts by weight of polyamic acid solution A with a solids concentration of 15 wt % and 6.9 parts by weight of aluminum oxide particles (manufactured by Sumitomo Chemical Co., Ltd., product name: AA-3, spherical, volume average particle diameter D ₅₀ 3.4 μm) as a thermally conductive filler were mixed until homogeneous using a centrifugal mixer to obtain a filler-containing polyamic acid solution E containing a thermally conductive filler. The content of aluminum oxide particles in the insulating resin layer obtained by curing this filler-containing polyamic acid solution E was 20 vol %.

(Formulation examples 2 to 9)
As in Formulation Example 1, the polyamic acid solution and aluminum oxide particles shown in Table 1 were mixed in a centrifugal mixer until homogeneous, to obtain filler-containing polyamic acid solutions F to M containing thermally conductive fillers.
In Blending Example 4, aluminum oxide particles (manufactured by Sumitomo Chemical Co., Ltd., product name: AA-1.5, spherical, volume average particle diameter D ₅₀ : 1.6 μm) were also used as a thermally conductive filler, and the filler was contained so that the weight ratio of AA-3 to AA-1.5 (AA-3:AA-1.5) was 24:16.

Example 1
The polyamic acid solution E obtained in Formulation Example 1 was applied to copper foil 1 (electrolytic copper foil, manufactured by Fukuda Metal Foil & Powder Co., Ltd., product name: CF-T4MDS-HD-35, thickness: 35 μm, Rz = 1.4 μm) to a thickness of 14.8 μm after curing, and the solution was dried by heating at 90 to 140 °C to remove the solvent. The temperature was then increased stepwise over 30 minutes within a temperature range of 130 to 360 °C to produce a flexible substrate laminate consisting of a polyimide layer on copper foil 1. To evaluate the properties of the polyimide layer in the flexible substrate laminate, copper foil 1 was etched away to produce film M1, and the thickness-wise thermal conductivity (λz), tear propagation resistance (TPR), edge tear resistance, and processability were evaluated. Furthermore, when applied to a semiconductor module S having the configuration shown in FIG. 5, the chip temperature was measured to evaluate the heat dissipation characteristics.

(Examples 2 to 8, Comparative Examples 1 and 2)
By changing the type and thickness of the polyamic acid solution used, films M2 to M10 were obtained and evaluated in the same manner as in Example 1. In addition, when applied to a semiconductor module S having the configuration shown in Figure 5, the chip temperature was measured and the heat dissipation characteristics were evaluated.

(Comparative Example 3)
Polyamic acid solution B obtained in Synthesis Example 2 was applied to copper foil 1 to a thickness of 1.5 μm after curing, and the solution was dried by heating at 90 to 140°C to remove the solvent. Next, polyamic acid solution C obtained in Synthesis Example 3 was applied thereon to a thickness of 5.0 μm after curing, and the solution was dried by heating at 120°C to remove the solvent. Next, polyamic acid solution B obtained in Synthesis Example 2 was applied thereon to a thickness of 1.5 μm after curing, and the solution was dried by heating at 90 to 140°C to remove the solvent. The temperature was then increased stepwise over 30 minutes within a temperature range of 130 to 360°C to produce a flexible substrate laminate consisting of three polyimide layers on copper foil 1. The thicknesses of the polyimide layers on copper foil 1 were 1.5 μm/5.0 μm/1.5 μm, in the order B/C/B from the copper foil 1 side. In order to evaluate the characteristics of the polyimide layer in the laminate for flexible substrates, the copper foil 1 was etched away to produce a film M11, and the thickness thermal conductivity λz, tear propagation resistance (TPR), edge tear resistance, and processability were evaluated. In addition, when applied to a semiconductor module S having the configuration shown in Figure 5, the chip temperature was measured to evaluate the heat dissipation characteristics.

The above results are summarized in Table 2.

Comparative Example 1 is an example of a conventional design concept that increases λz, but increasing the filler content to increase λz makes the film brittle, resulting in problems during processing. Comparative Example 3 simulates an example of processability problems caused by thinning when no filler is included. With regard to processability problems, Comparative Example 1 exhibited film defects in the form of cracks, whereas Comparative Example 3 exhibited film tears, demonstrating different modes of failure. From this perspective, the tear mode can be evaluated by tear propagation resistance, and the crack mode by edge tear resistance, and it is believed that maintaining both physical properties above a certain level is necessary to prevent processability problems. It can also be seen that edge tear resistance changes depending on the film thickness and is not simply proportional to the thickness.

In Examples 1 to 8, the resin structure, thickness, filler content, and volume average particle size of the filler were appropriately controlled, thereby minimizing processability problems and achieving better heat dissipation properties than Comparative Example 2, which used a thin film containing no filler.

The above describes in detail an embodiment of the present invention for illustrative purposes, but the present invention is not limited to the above embodiment and various modifications are possible.

10...resin film, 10A...insulating resin layer, 11...insulating resin, 12...thermally conductive filler, 20...metal layer, 21...conductor circuit layer, 30...metal-clad laminate, 40...circuit board, 50...adhesive layer, 60...heat-conducting metal layer, 70...semiconductor element, 100...laminated structure

Claims (6)

A resin film comprising a film-shaped insulating resin and a thermally conductive filler dispersed in the insulating resin,
the thermally conductive filler is alumina particles,
the insulating resin is a polyimide obtained by reacting an acid dianhydride component with a diamine component, the acid dianhydride component contains one or more selected from pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and 3,3',4,4'-benzophenonetetracarboxylic dianhydride in 50 mol % or more of the total acid dianhydride components, and the diamine component contains one or more selected from 4,4'-diaminodiphenyl ether and 2,2-bis[4-(4-aminophenoxy)phenyl]propane in 50 mol % or more of the total diamine components;
The thickness (L) of the entire resin film is in the range of 8 μm or more and less than 23 μm,
a ratio (D/L ) of a volume average particle diameter (D) of the thermally conductive filler to the film thickness (L) is in the range of 0.20 or more and 0.40 or less;
A resin film characterized in that the thermal conductivity (λz) in the thickness direction is in the range of 0.3 W/m K or more and less than 2.0 W/m K, and the edge tear resistance measured at a width of 20 mm is in the range of 0.3 [N] or more and 30.0 [N] or less. The resin film according to claim 1, having a tear propagation resistance in the range of 7.0 mN or more and 30.0 mN or less. The resin film according to claim 1 or 2, wherein the content of the thermally conductive filler relative to the entire resin film is within the range of 10 vol% to 50 vol%. A metal-clad laminate comprising a single or multiple insulating resin layer and a metal layer laminated on one or both sides of the insulating resin layer,
A metal-clad laminate, wherein at least one of the insulating resin layers is formed from the resin film according to claim 1 . A circuit board comprising an insulating resin layer consisting of a single layer or multiple layers, and a conductor circuit layer laminated on one side or both sides of the insulating resin layer,
A circuit board, wherein at least one of the insulating resin layers is formed from the resin film according to claim 1 . A laminated structure for use in a semiconductor module,
a conductor circuit layer electrically connected to an external semiconductor element;
an insulating resin layer consisting of a single layer or multiple layers;
an adhesive layer;
a heat transfer metal layer that mediates heat conduction to an external heat dissipation member;
have a structure in which the above are stacked in this order,
A laminated structure, wherein at least one of the insulating resin layers is formed from the resin film according to claim 1 .