WO2024202564A1 - Multilayer resin sheet - Google Patents

Abstract

Provided is a novel technique capable of providing an insulating layer that has good surface smoothness and comprises a via hole having a reduced smear and a good shape, even when desmear treatment is performed after a support is peeled off. This multilayer resin sheet comprises two or more layers of resin composition layers having a first resin composition layer which is one outermost layer and a layer excluding the first resin composition layer, wherein: RD/RA is 5 or more and less than 100, where the etching rate of a cured product of the first resin composition layer by a desmear treatment is RA, and the etching rate of a cured product of a resin composition layer which is the outermost layer on the opposite side from the first resin composition layer by a desmear treatment is RD; and the arithmetic average roughness Ra of the cured product of the first resin composition layer after desmear treatment is less than 50 nm.

Description

Multi-layer resin sheet

The present invention relates to a multilayer resin sheet. It also relates to a multilayer resin sheet with a support, a printed wiring board, and a semiconductor device obtained using the multilayer resin sheet. The present invention also relates to a method for producing a printed wiring board using the multilayer resin sheet.

A known manufacturing technique for printed wiring boards is a build-up method in which insulating layers and conductor layers (circuit layers) are alternately stacked. In a build-up manufacturing method, an insulating layer is generally formed by laminating a resin composition layer onto a circuit board using a resin sheet or the like containing a resin composition layer, and curing the resin composition layer. For example, Patent Document 1 discloses a technique in which a resin composition layer is laminated onto a circuit board using a resin sheet having multiple resin composition layers, the resin composition layer is thermally cured to obtain a cured product, and then the cured product is roughened to form a thin insulating layer with excellent mechanical strength.

International Publication No. 2009/119621

With regard to the technology described in Patent Document 1, when forming via holes with a laser to form wiring, it is necessary to carry out a desmear process to remove resin residue (smear) in the via holes. However, if the intensity of the desmear process is increased to improve the ability to remove smears in the via holes, the resin surface may become rough and the smoothness of the insulating layer surface may be impaired. If the insulating layer surface is poorly smooth, the adhesion between the pattern forming dry film and the insulating layer may easily decrease when a conductor layer (wiring layer) is formed on the insulating layer, which may result in poor formation of fine wiring.

To solve this problem, a technique has been proposed in which via holes are formed with a laser while the insulating layer surface is protected by a support, and the support is peeled off after desmearing. This technique makes it possible to remove smears in the via holes while leaving the insulating layer surface smooth. However, this technique has the problem that the support needs to be peeled off after desmearing, which requires a change from the conventional process, and also has the problem that a release agent remains on the insulating layer surface after the support is peeled off, making a separate process of washing off the release agent necessary.

The present invention provides a novel technology that can produce an insulating layer with good surface smoothness, reduced smearing, and well-shaped via holes, even when a desmear treatment is performed after peeling off the support.

As a result of extensive research into the above problems, the inventors discovered that the above problems could be solved by using a multilayer resin sheet having the following configuration, and thus completed the present invention.

That is, the present invention includes the following.
＜1＞
A multilayer resin sheet having two or more resin composition layers including a first resin composition layer which is an outermost layer on one side and a layer other than the first resin composition layer,
an etching rate by a desmear treatment of a cured product of the first resin composition layer is defined as RA, and an etching rate by a desmear treatment of a cured product of the resin composition layer that is the outermost layer on the opposite side to the first resin composition layer is defined as RD, RD/RA is 5 or more and less than 100,
A multilayer resin sheet, wherein the arithmetic mean roughness Ra of a cured product of a first resin composition layer after a desmear treatment is less than 50 nm.
＜2＞
The multilayer resin sheet according to <1>, wherein D1 is an average particle size (μm) of the inorganic filler in the first resin composition layer and D2 is an average particle size (μm) of the inorganic filler in the layers other than the first resin composition layer, and D1 is <D2.
＜3＞
The multilayer resin sheet according to <1> or <2>, wherein the content of the inorganic filler in the first resin composition layer is 5% by mass or less, when the non-volatile components in the first resin composition layer are 100% by mass.
＜4＞
The multilayer resin sheet according to any one of <1> to <3>, wherein the etching rate RA is 0.1% or more and less than 1%.
＜5＞
<1> to <4>, wherein t<(T-t), where T is the thickness (μm) of the multilayer resin sheet and t is the thickness (μm) of the first resin composition layer.
＜6＞
The multilayer resin sheet according to any one of <1> to <5>, which is used by laminating on a target member such that the surface opposite to the first resin composition layer is joined to the target member.
＜７＞
The multilayer resin sheet according to any one of <1> to <6>, which is for use as an insulating layer in a printed wiring board.
＜8＞
A multilayer resin sheet with a support, comprising: the multilayer resin sheet according to any one of <1> to <7>; and a support bonded to the first resin composition layer of the multilayer resin sheet.
＜9＞
A method for producing a printed wiring board, comprising the following steps (I) to (IV):
(I) a step of laminating the multilayer resin sheet according to any one of <1> to <7> on an inner layer substrate so that the surface of the multilayer resin sheet opposite to the first resin composition layer is bonded to the inner layer substrate; (II) a step of curing the multilayer resin sheet to form an insulating layer; (III) a step of forming via holes in the insulating layer by a laser and performing a desmear treatment; and (IV) a step of forming a metal film on the surface of the insulating layer after the desmear treatment. <10>
A printed wiring board comprising an insulating layer made of a cured product of the multilayer resin sheet according to any one of <1> to <7>.
<11>
A semiconductor device comprising the printed wiring board according to <10>.

The present invention provides a novel technology that can produce an insulating layer with good surface smoothness, reduced smearing, and well-shaped via holes, even when a desmear treatment is performed after peeling off the support.

The present invention also provides an insulating layer with little change in thickness before and after the desmear process, even when the desmear process is performed after the support is peeled off.

The present invention will be described in detail below with reference to preferred embodiments. However, the present invention is not limited to the following embodiments and examples, and may be modified as desired without departing from the scope of the claims of the present invention and their equivalents.

[Multi-layer resin sheet]
The multilayer resin sheet of the present invention is characterized in that it comprises two or more resin composition layers including a first resin composition layer which is one of the outermost layers and a layer other than the first resin composition layer, and in that, when an etching rate by a desmear treatment of a cured product of the first resin composition layer is defined as RA and an etching rate by a desmear treatment of a cured product of the resin composition layer which is the outermost layer opposite to the first resin composition layer is defined as RD, RD/RA is 5 or more and less than 100, and the cured product of the first resin composition layer after the desmear treatment has an Ra of less than 50 nm.

The multilayer resin sheet of the present invention has a structure in which two or more resin composition layers are laminated on top of each other. Here, in a multilayer resin sheet having a structure in which two resin composition layers, a first resin composition layer and a second resin composition layer, are laminated, both the first resin composition layer and the second resin composition layer are the outermost layers. Also, in a multilayer resin sheet having a structure in which N resin composition layers (here, N is an integer of 3 or more) are laminated, when the layers are numbered in ascending order from one outermost layer to the other outermost layer as 1st, 2nd, ... Nth, the first resin composition layer and the Nth resin composition layer are the outermost layers.

The multilayer resin sheet of the present invention is used by laminating it to a member to be laminated (for example, an inner layer substrate described later), and at this time, the surface opposite to the first resin composition layer, which is the outermost layer of one side (the other outermost layer; in a multilayer resin sheet consisting of two resin composition layers, the second resin composition layer corresponds to this, and in a multilayer resin sheet consisting of N resin composition layers, the Nth resin composition layer corresponds to this) is laminated to the member to be laminated. Therefore, when laminated to the member to be laminated, the first resin composition layer becomes the outside (external environment side), and therefore, hereinafter, the first resin composition layer may be simply referred to as the "outer layer". In addition, among the multiple resin composition layers constituting the multilayer resin sheet of the present invention, the layers other than the first resin composition layer are located between the first resin composition layer and the member to be laminated after being laminated to the member to be laminated, and therefore, hereinafter, the layers other than the first resin composition layer may be collectively simply referred to as the "inner layer".

In the multilayer resin sheet of the present invention, the resin composition layer may be two or more layers, and may be three or more layers. The multilayer resin sheet of the present invention may be formed by causing differences in the content of each component in essentially one resin sheet. In this case, the part where there is a difference in the content of each component can be interpreted as the layer interface.

The multilayer resin sheet of the present invention is characterized in that, when the etching rate by the desmear treatment of the cured product of the first resin composition layer, which is one of the outermost layers, is RA and the etching rate by the desmear treatment of the cured product of the resin composition layer, which is the outermost layer on the opposite side to the first resin composition layer, is RD/RA is 5 or more and less than 100. As a result, even when the desmear treatment is performed after peeling off the support, the multilayer resin sheet of the present invention can provide an insulating layer with good surface smoothness, reduced smears, and well-shaped via holes. Furthermore, even when the desmear treatment is performed after peeling off the support, the multilayer resin sheet of the present invention can provide an insulating layer with little change in film thickness before and after the desmear treatment.

In the present invention, the "etching rate by desmear treatment of the cured product" in reference to the resin composition layer refers to the mass reduction rate (mass %) calculated by the formula: [(M'-M")/M'] x 100, where M' is the mass of the cured product of the resin composition layer before desmear treatment, and M" is the mass of the cured product of the resin composition layer after desmear treatment. Therefore, the etching rate RA by desmear treatment of the cured product of the first resin composition layer is calculated by the formula: [(MA'-MA")/MA'] x 100, where MA' is the mass of the cured product of the first resin composition layer before desmear treatment, and MA" is the mass of the cured product of the first resin composition layer after desmear treatment. In addition, the etching rate RD by desmearing of the cured product of the resin composition layer that is the outermost layer opposite the first resin composition layer is calculated by the formula: [(MD'-MD")/MD'] x 100, where MD' is the mass of the cured product of the resin composition layer that is the outermost layer opposite the first resin composition layer before desmearing, and MD" is the mass of the cured product of the resin composition layer that is the outermost layer opposite the first resin composition layer after desmearing. Here, the "resin composition layer that is the outermost layer opposite the first resin composition layer" corresponds to the second resin composition layer in a multilayer resin sheet consisting of two resin composition layers, and the Nth resin composition layer in a multilayer resin sheet consisting of N resin composition layers.

In the present invention, the etching rates RA and RD can be measured according to the method described in the section "Measurement of Etching Rate" below. In detail, when the target resin composition layer is thermally cured by heating at 100°C for 30 minutes and then at 170°C for 30 minutes, and the resulting cured product is subjected to a desmear treatment in which the product is immersed in a swelling liquid at 60°C for 10 minutes, in an oxidizing agent liquid at 80°C for 20 minutes, and in a neutralizing liquid at 40°C for 10 minutes, the etching rates RA and RD can be determined by measuring the mass of the cured product before and after the desmear treatment and substituting the results into the above formula.

Even if a desmear treatment is performed after peeling off the support, from the viewpoint of providing an insulating layer with good surface smoothness, reduced smears, and well-shaped via holes, it is important that the etching rate RA is sufficiently smaller than the etching rate RD, and the RD/RA ratio is 5 or more, preferably 5.5 or more or 6 or more, more preferably 6.5 or more or 7 or more, and even more preferably 8 or more, 9 or more, 10 or more, 12 or more, 14 or more, or 15 or more. In particular, an RD/RA ratio of 10 or more is preferable because it is likely to provide an insulating layer with particularly good surface smoothness.

Even if desmearing is performed after peeling off the support, from the viewpoint of obtaining an insulating layer having good surface smoothness, reduced smears, and well-shaped via holes, it is important that the etching rate RD is not too large compared to the etching rate RA, and the RD/RA ratio is less than 100, and is preferably 98 or less, 96 or less, or 95 or less, more preferably 94 or less, 92 or less, 90 or less, 88 or less, or 86 or less, and even more preferably 85 or less, 84 or less, 82 or less, or 80 or less. In particular, an RD/RA ratio of 85 or less is preferable because it is easy to obtain an insulating layer having particularly well-shaped via holes with little dimensional change in the thickness direction of the insulating layer while suitably reducing smears.

Even if the desmear treatment is performed after peeling off the support, from the viewpoint of providing an insulating layer with better surface smoothness, reduced smears, and well-shaped via holes, and further from the viewpoint of providing an insulating layer with little change in film thickness before and after the desmear treatment, in addition to the RD/RA ratio being within a specific range, the etching rate RA by the desmear treatment of the cured product of the first resin composition layer is preferably 1% or less or less than 1%, more preferably 0.9% or less, and even more preferably 0.9% or less. Preferably, it is in the range of 0.85% or less or 0.8% or less, more preferably 0.75% or less, 0.7% or less, 0.65% or less, 0.6% or less, or 0.55% or less, and even more preferably 0.5% or less, 0.48% or less, 0.46% or less, 0.45% or less, 0.44% or less, 0.42% or less, or 0.4% or less, and the lower limit is preferably 0.05% or more, more preferably 0.06% or more or 0.08% or more, and even more preferably 0.1% or more. Therefore, in a preferred embodiment, the etching rate RA is 0.1% or more and less than 1%.

The etching rate RD by the desmear treatment of the cured product of the resin composition layer, which is the outermost layer opposite to the first resin composition layer, is not limited as long as the RD/RA ratio is within the above-mentioned specific range in relation to the etching rate RA. In particular, since it is easy to obtain an insulating layer having via holes with a particularly good shape (cross-sectional shape) with small dimensional change in the thickness direction of the insulating layer while suitably reducing smears, the etching rate RD is preferably in the range of 20% or less, more preferably 18% or less, 16% or less, or 15% or less, even more preferably 14% or less, 12% or less, or 10% or less, and even more preferably less than 10%, 9.5% or less, or 9% or less, and the lower limit is preferably 0.5% or more, more preferably 0.6% or more, or 0.8% or more, and even more preferably 1% or more, 1.2% or more, 1.4% or more, or 1.5% or more.

In the multilayer resin sheet of the present invention, the first resin composition layer, which is one of the outermost layers, when desmeared after curing, produces a cured product with small surface roughness and good surface smoothness. In the multilayer resin sheet of the present invention, the arithmetic mean roughness Ra of the cured product of the first resin composition layer after desmearing is less than 50 nm. If the Ra of the cured product of the first resin composition layer after desmearing is less than 50 nm, even if the thickness of the metal film provided thereon as a plating seed layer is made thinner, plating burn during wiring formation is suppressed and a uniform conductor layer (wiring) is easily formed, which is advantageous from the viewpoint of fine wiring. The Ra of the cured product of the first resin composition layer after desmearing may be even smaller, and may be preferably 45 nm or less, 40 nm or less, or 35 nm or less, more preferably 30 nm or less, 28 nm or less, 26 nm or less, or 25 nm or less. The lower limit of the Ra is not particularly limited, and may be, for example, 1 nm or more, 2 nm or more, 3 nm or more, etc.

In the present invention, the Ra of the cured product of the first resin composition layer after the desmear treatment can be measured according to the method described below in the section [Measurement of surface roughness]. In detail, the first resin composition layer is thermally cured by heating at 100°C for 30 minutes and then at 170°C for 30 minutes, and the resulting cured product is subjected to a desmear treatment in which the product is immersed in a swelling liquid at 60°C for 10 minutes, an oxidizing agent liquid at 80°C for 20 minutes, and a neutralizing liquid at 40°C for 10 minutes. The arithmetic average roughness Ra of the cured product of the first resin composition layer after the desmear treatment is measured and found.

In the multilayer resin sheet of the present invention, it is preferable that the layers other than the first resin composition layer contain an inorganic filler from the viewpoint of obtaining a cured product with a low linear thermal expansion coefficient and from the viewpoint of obtaining a cured product with a low dielectric tangent (and thus a cured product with low transmission loss when operated in a high frequency environment). Details of the inorganic filler will be described later.

In the multilayer resin sheet of the present invention, the first resin composition layer may or may not contain an inorganic filler.
In one embodiment, the first resin composition layer contains an inorganic filler from the viewpoint of providing a cured product with a low linear thermal expansion coefficient and a low dielectric loss tangent. When the first resin composition layer contains an inorganic filler, it is preferable that the inorganic filler contained in the first resin composition layer has a smaller average particle size than the inorganic filler contained in the layers other than the first resin composition layer from the viewpoint of providing a cured product with a lower surface roughness and good smoothness after the desmear treatment. Therefore, in a preferred embodiment, when the average particle size (μm) of the inorganic filler in the first resin composition layer is D1 and the average particle size (μm) of the inorganic filler in the layers other than the first resin composition layer is D2, D1<D2. From the viewpoint of further enjoying the effects of the present invention, the above D1 and D2 preferably satisfy the relationship D1≦0.9D2, more preferably D1≦0.8D2, D1≦0.7D2, D1≦0.6D2, D1≦0.55D2 or D1≦0.5D2. A method for measuring the average particle size of the inorganic filler will be described later.
In another embodiment, the first resin composition layer may be substantially free of inorganic fillers. For example, when the non-volatile components in the first resin composition layer are taken as 100% by mass, the content of inorganic fillers may be 5% by mass or less, 4% by mass or less, 3% by mass or less, 2% by mass or less, 1% by mass or less, or 0.5% by mass or less, or the first resin composition layer may be free of inorganic fillers.

Even when a desmear treatment is performed after peeling off the support, from the viewpoint of providing an insulating layer with better surface smoothness, reduced smears, and well-shaped via holes, it is preferable that the layers other than the first resin composition layer in the multilayer resin sheet of the present invention are thicker than the first resin composition layer. Therefore, in a preferred embodiment, when the thickness (μm) of the multilayer resin sheet is T and the thickness (μm) of the first resin composition layer is t, t<(T-t). From the viewpoint of being able to enjoy the effects of the present invention even more, the above t and T preferably satisfy the relationship t≦0.2T, more preferably t≦0.15T, t≦0.1T, t≦0.08T, t≦0.06T, or t≦0.05T. In addition, t and T preferably satisfy the relationship of 0.005T≦t, 0.01T≦t, or 0.02T≦t, from the viewpoint of obtaining an insulating layer with better surface smoothness, reduced smears, and well-shaped via holes even when the desmear treatment is performed after peeling off the support, and further from the viewpoint of obtaining an insulating layer with little change in film thickness before and after the desmear treatment. In the multilayer resin sheet of the present invention, when the thickness (μm) of the resin composition layer that is the outermost layer on the side opposite to the first resin composition layer is t', t' preferably satisfies the relationship of t'≧0.1(T-t) in the relationship with the above t and T, and more preferably satisfies the relationship of t'≧0.2(T-t), t'≧0.3(T-t), t'≧0.4(T-t), or t'≧0.5(T-t).

The suitable value of the thickness T of the multilayer resin sheet of the present invention varies depending on the application, and may be determined appropriately depending on the application. For example, from the viewpoint of thinning the printed wiring board, the thickness T of the multilayer resin sheet is preferably 200 μm or less, more preferably 150 μm or less, 120 μm or less, 100 μm or less, 80 μm or less, 60 μm or less, or 50 μm or less. The lower limit of the thickness T is not particularly limited, but can usually be 5 μm or more, 10 μm or more, etc.

The resin composition layers constituting the multilayer resin sheet of the present invention will be described in detail below. In the following, when it is preferable to apply different blending components or blending amounts between the first resin composition layer and the other resin composition layers, this will be specified separately. Unless otherwise specified, the blending components and blending amounts of the first resin composition layer may be applied by reading the "resin composition layer" described below as the "first resin composition layer", and the blending components and blending amounts of the layers other than the first resin composition layer may be applied by reading the "resin composition layer" described below as the "layers other than the first resin composition layer". When the multilayer resin sheet of the present invention is a multilayer resin sheet having a structure in which N layers (where N is an integer of 3 or more) of resin composition layers are laminated, the blending amounts of the blending components of the layers other than the first resin composition layer refer to the blending amounts of each blending component in the entire layers (the number of layers is N-1) other than the first resin composition layer, and the physical properties of the blending components of the layers other than the first resin composition layer refer to the average physical properties of each blending component in the entire layers (the number of layers is N-1) other than the first resin composition layer.

- Inorganic filler -
In the multilayer resin sheet of the present invention, the resin composition layer may contain an inorganic filler as described above.

Examples of inorganic filler materials include silica, alumina, glass, cordierite, silicon oxide, barium sulfate, barium carbonate, talc, clay, mica powder, zinc oxide, hydrotalcite, boehmite, aluminum silicate, aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, magnesium oxide, boron nitride, aluminum nitride, manganese nitride, aluminum borate, strontium carbonate, strontium titanate, calcium titanate, magnesium titanate, bismuth titanate, titanium oxide, zirconium oxide, barium titanate, barium zirconate titanate, barium zirconate, calcium zirconate, zirconium phosphate, and zirconium tungstate phosphate. Among these, silica is particularly suitable. Examples of silica include amorphous silica, fused silica, crystalline silica, synthetic silica, and hollow silica. Moreover, spherical silica is preferred as the silica. The inorganic filler may be used alone or in combination of two or more types.

Commercially available inorganic fillers include, for example, "SP60-05" and "SP507-05" manufactured by Nippon Steel Chemical & Material Co., Ltd.; "YC100C", "YA050C", "YA050C-MJE", "YA010C", "SC2500SQ", "SO-C4", "SO-C2", and "SO-C1" manufactured by Admatechs Co., Ltd.; "UFP-30", "DAW-03", and "FB-105FD" manufactured by Denka Co., Ltd.; "Silfil NSS-3N", "Silfil NSS-4N", and "Silfil NSS-5N" manufactured by Tokuyama Corporation; "Cellspheres" and "MGH-005" manufactured by Taiheiyo Cement Corporation; and "Sfereek" and "BA-1" manufactured by JGC Catalysts and Chemicals Co., Ltd.

The average particle size of the inorganic filler is not particularly limited, but is preferably 10 μm or less, more preferably 5 μm or less, even more preferably 3 μm or less, 2 μm or less, 1 μm or less, 0.8 μm or less, or 0.7 μm or less. The lower limit of the average particle size is not particularly limited, but is preferably 0.01 μm or more, more preferably 0.05 μm or more, even more preferably 0.07 μm or more, 0.1 μm or more, or 0.2 μm or more. The average particle size of the inorganic filler can be measured by a laser diffraction/scattering method based on the Mie scattering theory. Specifically, the particle size distribution of the inorganic filler is created on a volume basis using a laser diffraction/scattering particle size distribution measuring device, and the median diameter is used as the average particle size. The measurement sample can be prepared by weighing 100 mg of the inorganic filler and 10 g of methyl ethyl ketone into a vial and dispersing it with ultrasound for 10 minutes. The measurement sample was measured using a laser diffraction type particle size distribution measuring device with blue and red light source wavelengths and a flow cell method to measure the volumetric particle size distribution of the inorganic filler, and the average particle size was calculated as the median diameter from the obtained particle size distribution. An example of a laser diffraction type particle size distribution measuring device is the "LA-960" manufactured by Horiba, Ltd.

As described above, when the first resin composition layer contains an inorganic filler, it is preferable that D1<D2, where D1 is the average particle size (μm) of the inorganic filler in the first resin composition layer and D2 is the average particle size (μm) of the inorganic filler in the layers other than the first resin composition layer. The preferred relationship between D1 and D2 is as described above. In particular, even when the desmear treatment is performed after peeling off the support, from the viewpoint of obtaining a cured product with lower surface roughness and better smoothness after the desmear treatment, D1 is preferably 1 μm or less, more preferably 0.8 μm or less, 0.7 μm or less, or 0.6 μm or less, and even more preferably 0.5 μm or less, 0.4 μm or less, 0.3 μm or less, or 0.2 μm or less. The lower limit of D1 is as described above, and can be, for example, 0.01 μm or more, 0.02 μm or more, etc.

The inorganic filler is preferably surface-treated with an appropriate surface treatment agent. By performing the surface treatment, the moisture resistance and dispersibility of the inorganic filler can be improved. Examples of the surface treatment agent include silane coupling agents such as vinyl silane coupling agents, epoxy silane coupling agents, styryl silane coupling agents, (meth)acrylic silane coupling agents, amino silane coupling agents, isocyanurate silane coupling agents, ureido silane coupling agents, mercapto silane coupling agents, isocyanate silane coupling agents, and acid anhydride silane coupling agents; non-silane coupling-alkoxysilane compounds such as methyltrimethoxysilane and phenyltrimethoxysilane; and silazane compounds. The surface treatment agents may be used alone or in combination of two or more.

Commercially available surface treatment agents include, for example, "KBM403" (3-glycidoxypropyltrimethoxysilane), "KBM803" (3-mercaptopropyltrimethoxysilane), "KBE903" (3-aminopropyltriethoxysilane), "KBM573" (N-phenyl-3-aminopropyltrimethoxysilane), and "SZ-31" (hexamethyldisilazane), all manufactured by Shin-Etsu Chemical Co., Ltd.

The degree of surface treatment with the surface treatment agent is preferably within a specified range from the viewpoint of improving the dispersibility of the inorganic filler. Specifically, it is preferable that 100 parts by mass of the inorganic filler is surface-treated with 0.2 to 5 parts by mass of the surface treatment agent.

The degree of surface treatment with the surface treatment agent can be evaluated by the amount of carbon per unit surface area of the inorganic filler. From the viewpoint of improving the dispersibility of the inorganic filler, the amount of carbon per unit surface area of the inorganic filler is preferably 0.02 mg/m ² or more, more preferably 0.1 mg/m ² or more, and even more preferably 0.2 mg/m ² or more. On the other hand, from the viewpoint of preventing an increase in the melt viscosity of the resin composition or the melt viscosity in a sheet form, it is preferably 1.0 mg/m ² or less, more preferably 0.8 mg/m ² or less, and even more preferably 0.5 mg/m ² or less. The amount of carbon per unit surface area of the inorganic filler can be measured after the inorganic filler after the surface treatment is washed with a solvent (e.g., methyl ethyl ketone (MEK)). Specifically, a sufficient amount of MEK as a solvent is added to the inorganic filler surface-treated with the surface treatment agent, and ultrasonic cleaning is performed at 25 ° C. for 5 minutes. After removing the supernatant and drying the solid content, the amount of carbon per unit surface area of the inorganic filler can be measured using a carbon analyzer, such as "EMIA-320V" manufactured by Horiba, Ltd.

In the multilayer resin sheet of the present invention, the content of the inorganic filler in the resin composition layer may be determined according to the properties required for the multilayer resin sheet. From the viewpoint of easily adjusting the RD/RA ratio to a suitable range and from the viewpoint of realizing a cured product exhibiting an even lower linear thermal expansion coefficient and dielectric loss tangent, when the non-volatile components in the resin composition layer are taken as 100 mass%, the content C2 of the inorganic filler in the layers other than the first resin composition layer is preferably 40 mass% or more or 45 mass% or more, more preferably 50 mass% or more, 55 mass% or more or 60 mass% or more, and even more preferably 65 mass% or more, 66 mass% or more, 68 mass% or more, 70 mass% or more, 72 mass% or more, or 74 mass%. The upper limit of the content C2 is as described above, but is preferably 80 mass% or less, 75 mass% or less, or 70 mass% or less.

In one embodiment, the content C1 (mass%) of the inorganic filler in the first resin composition layer and the content C2 (mass%) of the inorganic filler in the layers other than the first resin composition layer satisfy the relationship C1 < C2. When C1 and C2 satisfy the above relationship, it is preferable because it is easy to adjust the RD/RA ratio to a suitable range. The suitable range for C2 is as described above.

As mentioned above, the first resin composition layer may be substantially free of inorganic fillers. For example, when the non-volatile components in the first resin composition layer are taken as 100% by mass, the content C1 of inorganic fillers in the first resin composition layer may be 5% by mass or less, 4% by mass or less, 3% by mass or less, 2% by mass or less, 1% by mass or less, or 0.5% by mass or less. Alternatively, the first resin composition layer may be free of inorganic fillers.

-Thermosetting component-
In the multilayer resin sheet of the present invention, the resin composition layer preferably contains a thermosetting resin.

Examples of thermosetting resins include epoxy resins, benzocyclobutene resins, epoxy acrylate resins, urethane acrylate resins, urethane resins, cyanate resins, unsaturated polyester resins, melamine resins, and silicone resins. Thermosetting resins may be used alone or in combination of two or more types.

In particular, from the viewpoint of providing an insulating layer with better surface smoothness, reduced smears, and well-shaped via holes even when the desmear treatment is performed after peeling off the support, and further from the viewpoint of providing an insulating layer with little change in film thickness before and after the desmear treatment, it is preferable that the thermosetting resin contains an epoxy resin.

Examples of epoxy resins include bisphenol-type epoxy resins, dicyclopentadiene-type epoxy resins, trisphenol-type epoxy resins, naphthol novolac-type epoxy resins, phenol novolac-type epoxy resins, tert-butyl-catechol-type epoxy resins, naphthalene-type epoxy resins, naphthol-type epoxy resins, anthracene-type epoxy resins, glycidylamine-type epoxy resins, glycidyl ester-type epoxy resins, cresol novolac-type epoxy resins, biphenyl-type epoxy resins, linear aliphatic epoxy resins, epoxy resins having a butadiene structure, alicyclic epoxy resins, heterocyclic epoxy resins, spiro ring-containing epoxy resins, cyclohexane-type epoxy resins, cyclohexane dimethanol-type epoxy resins, naphthylene ether-type epoxy resins, trimethylol-type epoxy resins, and tetraphenylethane-type epoxy resins. Bisphenol-type epoxy resins refer to epoxy resins having a bisphenol structure, and examples include bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, bisphenol S-type epoxy resins, and bisphenol AF-type epoxy resins. Biphenyl-type epoxy resin refers to an epoxy resin having a biphenyl structure, where the biphenyl structure may have a substituent such as an alkyl group, an alkoxy group, or an aryl group. Therefore, bixylenol-type epoxy resins and biphenylaralkyl-type epoxy resins are also included in biphenyl-type epoxy resins. The epoxy resins may be used alone or in combination of two or more types.

As the epoxy resin, aromatic epoxy resin is preferred. Here, aromatic epoxy resin means an epoxy resin that has an aromatic ring in its molecule.

The epoxy resin preferably has two or more epoxy groups in one molecule. When the non-volatile components of the epoxy resin are taken as 100% by mass, the proportion of the epoxy resin having two or more epoxy groups in one molecule is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more.

Epoxy resins include those that are liquid at a temperature of 20°C (hereafter referred to as "liquid epoxy resins") and those that are solid at a temperature of 20°C (hereafter referred to as "solid epoxy resins").

The liquid epoxy resin is preferably one that has two or more epoxy groups in one molecule.

Preferred liquid epoxy resins are bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol AF type epoxy resins, naphthalene type epoxy resins, glycidyl ester type epoxy resins, glycidyl amine type epoxy resins, phenol novolac type epoxy resins, alicyclic epoxy resins such as alicyclic epoxy resins having an ester skeleton, cyclohexane type epoxy resins, cyclohexane dimethanol type epoxy resins, and epoxy resins having a butadiene structure.

Specific examples of liquid epoxy resins include DIC's "HP-4032", "HP-4032D", and "HP-4032SS" (naphthalene type epoxy resins); Mitsubishi Chemical's "828US", "jER828EL", "825", and "Epicoat 828EL" (bisphenol A type epoxy resins); Mitsubishi Chemical's "jER807" and "1750" (bisphenol F type epoxy resins); Mitsubishi Chemical's "jER152" (phenol novolac type epoxy resin); Mitsubishi Chemical's "630" and "630LSD" (p-aminophenol type epoxy resins, glycidyl ether type epoxy resins). amine type epoxy resin); "ZX1059" (a mixture of bisphenol A type epoxy resin and bisphenol F type epoxy resin) manufactured by Nippon Steel Chemical &Material; "EX-721" (glycidyl ester type epoxy resin) manufactured by Nagase ChemteX; "Celloxide 2021P" (alicyclic epoxy resin with an ester structure) manufactured by Daicel; "PB-3600" (epoxy resin with a butadiene structure) manufactured by Daicel; "ZX1658" and "ZX1658GS" (liquid 1,4-glycidylcyclohexane type epoxy resin) manufactured by Nippon Steel Chemical & Material.

As the solid epoxy resin, a solid epoxy resin having three or more epoxy groups in one molecule is preferable, and an aromatic solid epoxy resin having three or more epoxy groups in one molecule is more preferable.

Preferred solid epoxy resins are bixylenol type epoxy resins, naphthalene type epoxy resins, naphthalene type tetrafunctional epoxy resins, cresol novolac type epoxy resins, dicyclopentadiene type epoxy resins, trisphenol type epoxy resins, naphthol type epoxy resins, biphenyl type epoxy resins, naphthylene ether type epoxy resins, anthracene type epoxy resins, bisphenol A type epoxy resins, bisphenol AF type epoxy resins, and tetraphenylethane type epoxy resins.

Specific examples of solid epoxy resins include DIC's "HP-4032H" (naphthalene type epoxy resin); DIC's "HP-4700" and "HP-4710" (naphthalene type tetrafunctional epoxy resin); DIC's "N-690" (cresol novolac type epoxy resin); DIC's "N-695" (cresol novolac type epoxy resin); DIC's "HP-7200HH", "HP-7200H", and "HP-7200" (dicyclopentadiene ether type epoxy resins); DIC Corporation's "EXA-7311", "EXA-7311-G3", "EXA-7311-G4", "EXA-7311-G4S", and "HP6000" (naphthylene ether type epoxy resins); Nippon Kayaku Co., Ltd.'s "EPPN-502H" (trisphenol type epoxy resin); Nippon Kayaku Co., Ltd.'s "NC-7000-L" (naphthol novolac type epoxy resin); Nippon Kayaku Co., Ltd.'s "NC-3000-H", "NC-3000", and "NC-30 00-L, "NC-3100" (biphenyl type epoxy resin); "ESN475V" (naphthol type epoxy resin) manufactured by Nippon Steel Chemical & Material Co., Ltd.; "ESN485" (naphthol novolac type epoxy resin) manufactured by Nippon Steel Chemical & Material Co., Ltd.; "YX4000H", "YX4000", "YL6121" (biphenyl type epoxy resin) manufactured by Mitsubishi Chemical Co., Ltd.; "YX4000HK" (bixylenol type epoxy resin) manufactured by Mitsubishi Chemical Co., Ltd. "YX8800" (anthracene type epoxy resin) manufactured by Osaka Gas Chemicals; "PG-100" and "CG-500" manufactured by Osaka Gas Chemicals; "YL7760" (bisphenol AF type epoxy resin) manufactured by Mitsubishi Chemical; "YL7800" (fluorene type epoxy resin) manufactured by Mitsubishi Chemical; "jER1010" (solid bisphenol A type epoxy resin) manufactured by Mitsubishi Chemical; and "jER1031S" (tetraphenylethane type epoxy resin) manufactured by Mitsubishi Chemical.

In the multilayer resin sheet of the present invention, the resin composition layer may contain only liquid epoxy resin as the epoxy resin, may contain only solid epoxy resin, or may contain a combination of liquid epoxy resin and solid epoxy resin. From the viewpoint of easily adjusting the above RD/RA ratio to a suitable range, it is preferable that the resin composition layer contains a solid epoxy resin. When a liquid epoxy resin and a solid epoxy resin are used in combination, the ratio by mass between them (liquid epoxy resin:solid epoxy resin) is preferably 1:0.5 to 1:50, more preferably 1:1 to 1:30, and even more preferably 1:2 to 1:20. From the viewpoint of easily adjusting the RD/RA ratio to a suitable range, the mass ratio X1 of the solid epoxy resin/liquid epoxy resin in the first resin composition layer is preferably higher than the mass ratio X2 of the solid epoxy resin/liquid epoxy resin in the layers other than the first resin composition layer, and for example, the difference (X1-X2) between the mass ratio X1 and the mass ratio X2 may be 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more. The upper limit of the difference (X1-X2) may usually be 20 or less, 15 or less, 14 or less, 12 or less, etc.

The epoxy equivalent of the epoxy resin is preferably 50 g/eq. to 5000 g/eq., more preferably 50 g/eq. to 3000 g/eq., even more preferably 80 g/eq. to 2000 g/eq., and even more preferably 110 g/eq. to 1000 g/eq. The epoxy equivalent is the mass of an epoxy resin containing one equivalent of epoxy groups. This epoxy equivalent can be measured according to JIS K7236.

The weight average molecular weight (Mw) of the epoxy resin is preferably 100 to 5000, more preferably 250 to 3000, and even more preferably 400 to 1500. The Mw of the epoxy resin can be measured as a polystyrene-equivalent value by gel permeation chromatography (GPC).

From the viewpoint of easily adjusting the RD/RA ratio to a suitable range, providing an insulating layer with better surface smoothness, reduced smears, and well-shaped via holes, the content of the thermosetting resin in the resin composition layer is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 12% by mass or more, 14% by mass or more, or 15% by mass or more, when the resin component in the resin composition layer is taken as 100% by mass. The upper limit of the content is not particularly limited and may be determined according to the properties required of the resin composition, but may be, for example, 60% by mass or less, 50% by mass or less, 45% by mass or less, or 40% by mass or less.

In the present invention, the "resin component" of the resin composition layer refers to the solids (non-volatile components) constituting the resin composition layer, excluding the inorganic filler described below.

In the multilayer resin sheet of the present invention, the resin composition layer may contain, in addition to the thermosetting resin and inorganic filler, one or more selected from a curing agent, a thermoplastic resin, a radical polymerizable resin, and a curing accelerator.

- Hardener -
In the multilayer resin sheet of the present invention, the resin composition layer preferably contains a curing agent. The curing agent usually has a function of reacting with the thermosetting resin to cure the resin composition layer.

Examples of the curing agent include active ester curing agents, phenolic curing agents, naphthol curing agents, acid anhydride curing agents, cyanate ester curing agents, carbodiimide curing agents, and amine curing agents. The curing agents may be used alone or in combination of two or more.

In particular, from the viewpoint of obtaining an insulating layer having better surface smoothness, reduced smears, and well-shaped via holes even when a desmear treatment is performed after peeling off the support, it is preferable that the curing agent contains one or more selected from the group consisting of active ester-based curing agents, phenol-based curing agents, and naphthol-based curing agents, and from the viewpoint of obtaining an insulating layer having better surface smoothness, reduced smears, and well-shaped via holes, it is preferable that the curing agent contains an active ester-based curing agent, since it is easy to adjust the RD/RA ratio to a suitable range and it is possible to obtain an insulating layer having better surface smoothness, reduced smears, and well-shaped via holes. Therefore, in one embodiment, the curing agent contains one or more selected from the group consisting of active ester-based curing agents, phenol-based curing agents, and naphthol-based curing agents, and more preferably contains an active ester-based curing agent.

As the active ester curing agent, a compound having one or more active ester groups in one molecule can be used. Among them, as the active ester curing agent, a compound having two or more highly reactive ester groups in one molecule, such as phenol esters, thiophenol esters, N-hydroxyamine esters, and esters of heterocyclic hydroxy compounds, is preferred. The active ester curing agent is preferably one obtained by a condensation reaction between a carboxylic acid compound and/or a thiocarboxylic acid compound and a hydroxy compound and/or a thiol compound. In particular, from the viewpoint of improving heat resistance, an active ester curing agent derived from a carboxylic acid compound is preferred, an active ester curing agent obtained from a carboxylic acid compound and a hydroxy compound is more preferred, and an active ester curing agent obtained from a carboxylic acid compound and an aromatic hydroxy compound is even more preferred.

As the carboxylic acid compound, either an aromatic carboxylic acid compound or an aliphatic carboxylic acid may be used, and examples thereof include benzoic acid, acetic acid, succinic acid, maleic acid, itaconic acid, phthalic acid, isophthalic acid, terephthalic acid, pyromellitic acid, etc.

Examples of aromatic hydroxy compounds include (i) polyaddition products of unsaturated aliphatic cyclic compounds containing two double bonds in one molecule with phenols, (ii) various bisphenol compounds, (iii) aromatic polyols having two or more hydroxy groups bonded to a carbon atom on an aromatic ring, and (iv) aromatic monools having one hydroxy group bonded to a carbon atom on an aromatic ring. Examples of polyaddition products of unsaturated aliphatic cyclic compounds with phenols include polyaddition products of unsaturated aliphatic cyclic compounds such as dicyclopentadiene, tetrahydroindene, norbornadiene, limonene, and vinylcyclohexene with phenols that may have a substituent (e.g., phenol, cresol, xylenol, ethylphenol, propylphenol, vinylphenol, allylphenol, phenylphenol, benzylphenol, halophenols, etc.), and specific examples thereof include polyaddition products of dicyclopentadiene and phenols. Examples of bisphenol compounds include bisphenol A, bisphenol F, bisphenol AF, bisphenol AP, bisphenol B, bisphenol BP, bisphenol C, and bisphenol M. Examples of aromatic polyols having two or more hydroxy groups bonded to carbon atoms on an aromatic ring include hydroquinone, resorcinol, catechol, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, dihydroxybenzophenone, trihydroxybenzophenone, tetrahydroxybenzophenone, phloroglucinol, benzenetriol, and phenol novolak. Examples of aromatic monools having one hydroxyl group bonded to a carbon atom on an aromatic ring include phenol, cresol, xylenol, ethylphenol, propylphenol, vinylphenol, allylphenol, phenylphenol, benzylphenol, halophenol, naphthol, methylnaphthol, dimethylnaphthol, ethylnaphthol, propylnaphthol, vinylnaphthol, allylnaphthol, phenylnaphthol, benzylnaphthol, and halonaphthol.

Specific examples of suitable active ester-based curing agents include active ester compounds containing a dicyclopentadiene-type diphenol structure, active ester compounds containing a naphthalene structure, active ester compounds containing an acetylated product of phenol novolac, and active ester compounds containing a benzoylated product of phenol novolac. Among these, active ester compounds containing a naphthalene structure and active ester compounds containing a dicyclopentadiene-type diphenol structure are more preferred. The term "dicyclopentadiene-type diphenol structure" refers to a divalent structural unit consisting of phenylene-dicyclopentalene-phenylene.

Commercially available active ester curing agents include active ester resins containing a dicyclopentadiene-type diphenol structure, such as "EXB-9451", "EXB-9460", "EXB-9460S", "HPC-8000-65T", "HPC-8000H-65TM", and "HPC-8000L-65TM" (manufactured by DIC Corporation); active ester resins containing a naphthalene structure, such as "EXB-8100L-65T", "EXB-8150-60T", "EXB-8150-62T", "EXB-9416-70BK", "HPC-8150-60T", and "HPC-8150-62T". , "HP-B-8151-62T", "HP-C-8151-62T" (manufactured by DIC Corporation); "EXB9401" (manufactured by DIC Corporation) is a phosphorus-containing active ester resin; "DC808" (manufactured by Mitsubishi Chemical Corporation) is an active ester resin that is an acetylated product of phenol novolac; "YLH1026", "YLH1030", "YLH1048" (manufactured by Mitsubishi Chemical Corporation) are active ester resins that are benzoylated products of phenol novolac; and "PC1300-02-65MA" (manufactured by Air Water Inc.) is an active ester resin that contains a styryl group and a naphthalene structure.

From the viewpoint of heat resistance and water resistance, phenol-based and naphthol-based hardeners having a novolac structure are preferred. From the viewpoint of adhesion to the conductor layer, nitrogen-containing phenol-based and nitrogen-containing naphthol-based hardeners are preferred, and triazine-skeleton-containing phenol-based and triazine-skeleton-containing naphthol-based hardeners are more preferred.

Specific examples of phenol-based and naphthol-based hardeners include "MEH-7700", "MEH-7810", "MEH-7851", and "MEH-8000H" manufactured by Meiwa Kasei Co., Ltd.; "NHN", "CBN", and "GPH" manufactured by Nippon Kayaku Co., Ltd.; and "SN-170", "SN-180", "SN-190", "SN-475", "SN-485", "SN-495", "SN-495V", and "SN-3" manufactured by Nippon Steel Chemical & Material Co., Ltd. 75" and "SN-395" manufactured by DIC Corporation; "TD-2090", "TD-2090-60M", "LA-7052", "LA-7054", "LA-1356", "LA-3018", "LA-3018-50P", "EXB-9500", "HPC-9500", "KA-1160", "KA-1163", and "KA-1165" manufactured by Gun-ei Chemical Co., Ltd.; "GDP-6115L", "GDP-6115H", and "ELPC75" manufactured by Gun-ei Chemical Co., Ltd.

Acid anhydride curing agents include those that have one or more acid anhydride groups in one molecule. Specific examples of acid anhydride curing agents include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, hydrogenated methylnadic anhydride, trialkyltetrahydrophthalic anhydride, dodecenyl succinic anhydride, 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, trimellitic anhydride, pyromellitic anhydride, and benzophenonetetracarboxylic dianhydride. Examples of acid anhydrides include polymeric acid anhydrides such as biphenyltetracarboxylic dianhydride, naphthalenetetracarboxylic dianhydride, oxydiphthalic dianhydride, 3,3'-4,4'-diphenylsulfonetetracarboxylic dianhydride, 1,3,3a,4,5,9b-hexahydro-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-C]furan-1,3-dione, ethylene glycol bis(anhydrotrimellitate), and styrene-maleic acid resins in which styrene and maleic acid are copolymerized. Examples of commercially available acid anhydride-based hardeners include "MH-700" manufactured by New Japan Chemical Co., Ltd.

Examples of cyanate ester curing agents include bifunctional cyanate resins such as bisphenol A dicyanate, polyphenol cyanate, oligo(3-methylene-1,5-phenylene cyanate), 4,4'-methylenebis(2,6-dimethylphenyl cyanate), 4,4'-ethylidene diphenyl dicyanate, hexafluorobisphenol A dicyanate, 2,2-bis(4-cyanate)phenylpropane, 1,1-bis(4-cyanate-3,5-dimethylphenyl)methane, 1,3-bis(4-cyanate-phenyl-1-(methylethylidene))benzene, bis(4-cyanate-phenyl)thioether, and bis(4-cyanate-phenyl)ether; multifunctional cyanate resins derived from phenol novolac and cresol novolac; prepolymers in which these cyanate resins have been partially converted to triazine; and the like. Specific examples of cyanate ester-based hardeners include arxada's "PT30" and "PT60" (phenol novolac-type multifunctional cyanate ester resins), "ULL-950S" (multifunctional cyanate ester resin), "BA230" and "BA230S75" (prepolymers in which part or all of bisphenol A dicyanate has been triazine-converted into a trimer).

Specific examples of carbodiimide-based curing agents include Carbodilite (registered trademark) V-03 (carbodiimide group equivalent: 216 g/eq.), V-05 (carbodiimide group equivalent: 262 g/eq.), V-07 (carbodiimide group equivalent: 200 g/eq.), V-09 (carbodiimide group equivalent: 200 g/eq.), and Stavaxol (registered trademark) P (carbodiimide group equivalent: 302 g/eq.), all manufactured by Nisshinbo Chemical Co., Ltd.

Amine-based curing agents include curing agents having one or more amino groups in one molecule, such as aliphatic amines, polyether amines, alicyclic amines, and aromatic amines. Specific examples of amine-based curing agents include 4,4'-methylenebis(2,6-dimethylaniline), diphenyldiaminosulfone, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, m-phenylenediamine, m-xylylenediamine, diethyltoluenediamine, 4,4'-diaminodiphenylether, 3,3'-dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dihydroxybenzidine, 2,2-bis(3-amino-4-hydroxyphenyl)-2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dihydroxybenzidine, and 2,2-bis(3-amino-4-hydroxyphenyl)-2,2'-dimethyl-4,4'-diaminobiphenyl. bis(4-aminophenoxy)phenyl)propane, 3,3-dimethyl-5,5-diethyl-4,4-diphenylmethanediamine, 2,2-bis(4-aminophenyl)propane, 2,2-bis(4-(4-aminophenoxy)phenyl)propane, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)biphenyl, bis(4-(4-aminophenoxy)phenyl)sulfone, bis(4-(3-aminophenoxy)phenyl)sulfone, and the like. Commercially available amine-based curing agents may be used, such as "KAYABOND C-200S", "KAYABOND C-100", "KAYAHARD A-A", "KAYAHARD A-B", and "KAYAHARD A-S" manufactured by Nippon Kayaku Co., Ltd., and "Epicure W" manufactured by Mitsubishi Chemical Corporation.

Even if the desmear treatment is performed after peeling off the support, from the viewpoint of obtaining an insulating layer with better surface smoothness, reduced smears, and well-shaped via holes, the content of the curing agent in the resin composition is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, 35% by mass or more, or 40% by mass or more, assuming that the resin component in the resin composition is 100% by mass. The upper limit of the content is not particularly limited and may be determined according to the properties required of the resin composition, but may be, for example, 80% by mass or less, 75% by mass or less, or 70% by mass or less.

As described above, the curing agent preferably contains an active ester curing agent, from the viewpoint of easily adjusting the RD/RA ratio to a suitable range, providing an insulating layer with better surface smoothness, reduced smears, and well-shaped via holes. In the multilayer resin sheet of the present invention, when the resin composition layer contains an active ester curing agent as a curing agent, the content of the active ester curing agent in the curing agent is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, 75% by mass or more, or 80% by mass or more, from the viewpoint of being able to enjoy the effects of the present invention more effectively and from the viewpoint of obtaining a cured product exhibiting particularly excellent dielectric properties, when the non-volatile components of the curing agent are taken as 100% by mass. The upper limit of the content of the active ester curing agent in the curing agent is not particularly limited, and may be 100% by mass, but may also be, for example, 95% by mass or less, 90% by mass or less, etc.

When the resin composition layer in the multilayer resin sheet of the present invention contains an active ester-based curing agent as a curing agent, the mass ratio of the active ester-based curing agent to the thermosetting resin (active ester-based curing agent/thermosetting resin) is preferably 0.5 or more, more preferably 0.6 or more, and even more preferably 0.8 or more, 1 or more, 1.1 or more, 1.2 or more, 1.3 or more, 1.4 or more, or 1.5 or more, from the viewpoint of being able to enjoy the effects of the present invention more effectively and from the viewpoint of exhibiting particularly excellent dielectric properties. The upper limit of the mass ratio (active ester-based curing agent/thermosetting resin) may be, for example, 5 or less, 4.5 or less, 4 or less, etc. In particular, from the viewpoint of easily adjusting the etching rate RA to a suitable range, and thus easily adjusting the RD/RA ratio to a suitable range, the mass ratio (active ester-based curing agent/thermosetting resin) in the first resin composition layer is preferably 1 or more, more preferably 1.2 or more or 1.4 or more, and even more preferably 1.5 or more, 16 or more, 1.8 or more, or 2 or more.

- Thermoplastic resin -
In the multilayer resin sheet of the present invention, the resin composition layer may contain a thermoplastic resin.

Examples of thermoplastic resins include phenoxy resins, polyimide resins, polyvinyl acetal resins, acrylic resins, polyolefin resins, polybutadiene resins, polyamideimide resins, polysulfone resins, polyethersulfone resins, polyphenylene ether resins, polyetherimide resins, polycarbonate resins, polyetheretherketone resins, and polyester resins. Among these, resins selected from phenoxy resins, polyimide resins, acrylic resins, polyphenylene ether resins, and polycarbonate resins are preferred. Thermoplastic resins may be used alone or in combination of two or more.

--Phenoxy resin--
Examples of the phenoxy resin include phenoxy resins having one or more skeletons selected from the group consisting of bisphenol A skeleton, bisphenol F skeleton, bisphenol S skeleton, bisphenolacetophenone skeleton, novolac skeleton, biphenyl skeleton, fluorene skeleton, dicyclopentadiene skeleton, norbornene skeleton, naphthalene skeleton, anthracene skeleton, adamantane skeleton, terpene skeleton, and trimethylcyclohexane skeleton. The terminal of the phenoxy resin may be any functional group such as a phenolic hydroxyl group or an epoxy group. The phenoxy resin may be used alone or in combination of two or more kinds. Specific examples of the phenoxy resin include "1256" and "4250" (both of which are phenoxy resins containing a bisphenol A skeleton), "YX8100" (phenoxy resin containing a bisphenol S skeleton), and "YX6954" (phenoxy resin containing a bisphenol acetophenone skeleton) manufactured by Mitsubishi Chemical Corporation, "FX280" and "FX293" manufactured by Nippon Steel Chemical & Material Co., Ltd., and "YX7200B35", "YX7500BH30", "YX6954BH30", "YX7553", "YX7553BH30", "YL7769BH30", "YL6794", "YL7213", "YL7290", and "YL7482" manufactured by Mitsubishi Chemical Corporation.

--Polyimide resin--
The polyimide resin may be a resin having an imide structure. The polyimide resin may generally be obtained by an imidization reaction between a diamine compound and an acid anhydride, or an imidization reaction between a diisocyanate compound and an acid anhydride. Specific examples of the polyimide resin include modified polyimides such as linear polyimides (polyimides described in JP-A-2006-37083) obtained by reacting a bifunctional hydroxyl group-terminated polybutadiene, a diisocyanate compound, and a tetrabasic acid anhydride, polysiloxane skeleton-containing polyimides (polyimides described in JP-A-2002-12667 and JP-A-2000-319386, etc.). The polyimide resin may be a commercially available product, such as "Rikacoat SN20" and "Rikacoat PN20" manufactured by New Japan Chemical Co., Ltd.

An example of a particularly suitable polyimide resin is shown below. In a preferred embodiment, the polyimide resin contains a structural unit represented by the following formula (1) (hereinafter also referred to as "structural unit (1)"). The number of structural units (1) contained per molecule of the polyimide resin is 1 or more, and is not particularly limited, but may be 100 or less, 50 or less, or 30 or less.

［式（１）中、
　Ｒ_１は、下記式（１－１）で表される４価の基であり、
　Ｒ_２は、下記式（１－２）で表される２価の基である。

[In formula (1),
R ₁ is a tetravalent group represented by the following formula (1-1):
_R2 is a divalent group represented by the following formula (1-2).

　（式（１－１）中、
　Ａｒ_１１、Ａｒ_１２、Ａｒ_１３及びＡｒ_１４は、それぞれ独立に、置換基を有していてもよい芳香環を表し、
　Ｌ_１１、Ｌ_１２及びＬ_１３は、それぞれ独立に、２価の連結基を表し、
　ｎｃ１は、０以上の整数を表す。）

(In formula (1-1),
Ar ₁₁ , Ar ₁₂ , Ar ₁₃ and Ar ₁₄ each independently represent an aromatic ring which may have a substituent;
L ₁₁ , L ₁₂ and L ₁₃ each independently represent a divalent linking group;
nc1 represents an integer of 0 or more.

　（式（１－２）中、
　Ａｒ_２１、Ａｒ_２２、Ａｒ_２３及びＡｒ_２４は、それぞれ独立に、置換基を有していてもよい芳香族環を表し、
　Ｌ_２１、Ｌ_２２及びＬ_２３は、それぞれ独立に、２価の連結基を表し、
　ｎｃ２は、１以上の整数を表す。）］

(In formula (1-2),
Ar ₂₁ , Ar ₂₂ , Ar ₂₃ and Ar ₂₄ each independently represent an aromatic ring which may have a substituent;
L ₂₁ , L ₂₂ and L ₂₃ each independently represent a divalent linking group;
nc2 represents an integer of 1 or more.

In formula (1-1), the aromatic rings represented by Ar ₁₁ , Ar ₁₂ , Ar ₁₃ and Ar ₁₄ (hereinafter also referred to as "aromatic ring C") are preferably aromatic rings having 6 to 100 carbon atoms, more preferably 6 to 50 carbon atoms, still more preferably 6 to 100 carbon atoms, and even more preferably 6 to 50 carbon atoms. In a preferred embodiment, in formula (1-1), Ar ₁₁ , Ar ₁₂ , Ar ₁₃ and Ar ₁₄ are each independently an aromatic carbocyclic ring having 6 to 14 carbon atoms which may have a substituent. Here, the term "aromatic ring" as used herein means a ring according to the Huckel rule in which the number of electrons contained in the π electron system on the ring is 4n+2 (n is a natural number), and includes a monocyclic aromatic ring and a fused aromatic ring in which two or more monocyclic aromatic rings are fused. The aromatic ring may be a carbocyclic ring or a heterocyclic ring. Examples of the aromatic ring include monocyclic aromatic rings such as a benzene ring, a furan ring, a thiophene ring, a pyrrole ring, a pyrazole ring, an oxazole ring, an isoxazole ring, a thiazole ring, an imidazole ring, a pyridine ring, a pyridazine ring, a pyrimidine ring, and a pyrazine ring; fused rings in which two or more monocyclic aromatic rings are fused, such as a naphthalene ring, an anthracene ring, a benzofuran ring, an isobenzofuran ring, an indole ring, an isoindole ring, a benzothiophene ring, a benzimidazole ring, an indazole ring, a benzoxazole ring, a benzisoxazole ring, a benzothiazole ring, a quinoline ring, an isoquinoline ring, a quinoxaline ring, an acridine ring, a quinazoline ring, a cinnoline ring, and a phthalazine ring; and fused rings in which one or more monocyclic aromatic rings are fused to one or more monocyclic non-aromatic rings, such as an indane ring, a fluorene ring, and a tetralin ring. Of these, aromatic carbon rings having 6 to 14 carbon atoms are preferred, with a benzene ring being more preferred.

In formula (1-1), when Ar ₁₁ , Ar ₁₂ , Ar ₁₃ and Ar ₁₄ represent an aromatic ring having a substituent, the number of the substituents is not limited. Such substituents (hereinafter also referred to as "substituent S") include, independently of one another, a halogen atom, an alkyl group, a cycloalkyl group, an alkoxy group, a cycloalkyloxy group, an aryl group, an aryloxy group, an arylalkyl group, an arylalkoxy group, a monovalent heterocyclic group, an alkylidene group, an amino group, a silyl group, an acyl group, an acyloxy group, a carboxy group, a sulfo group, a cyano group, a nitro group, a hydroxy group, a mercapto group and an oxo group.

In formula (1-1), the divalent linking group represented by L ₁₁ , L ₁₂ and L ₁₃ is preferably a divalent group consisting of one or more (e.g., 1 to 3000, 1 to 1000, 1 to 100, 1 to 50) skeletal atoms selected from carbon atoms, oxygen atoms, nitrogen atoms, sulfur atoms and silicon atoms. Examples of the divalent linking group include _-SO2- , -CO-, -COO-, -O-, -S-, -O- _{C6H4 -O-} (wherein _-C6H4- represents a phenylene group), -O- _{C6H4 -} C( _CH3 ) _{2 - C6H4} -O-, -COO-( _CH2 ) _q -OCO- (wherein q represents an integer of 1 to 20), -COO- _H2C -HC(-O- _C (=O) _-CH3 ) _-CH2- OCO-, an alkylene group, an alkenylene group, an alkynylene group, an arylene group, a heteroarylene group, -C(=O)-, -C(=O)-O-, ^-NR0- (wherein R ⁰ represents a hydrogen atom, an alkyl group having 1 to 3 carbon atoms. ) and -C(=O)-NR ⁰ - are included. The number of carbon atoms of the alkylene group is preferably 1 to 10, more preferably 1 to 6, even more preferably 1 to 5 or 1 to 4. The number of carbon atoms of the alkenylene group is preferably 2 to 10, more preferably 2 to 6, and even more preferably 2 to 5. The number of carbon atoms of the arylene group is preferably 6 to 20, more preferably 6 to 10, and the number of carbon atoms of the heteroarylene group is preferably 2 to 20, more preferably 3 to 10, 4 to 10, or 5 to 10. The above-mentioned alkyl group, alkylene group, alkenylene group, alkynylene group, arylene group, and heteroarylene group may further have a substituent. Examples of the substituent include the above-mentioned substituent S. It is preferable that the divalent linking group represented by _{L 11} , L ₁₂ , and L ₁₃ does not contain an aromatic ring. In one embodiment, the divalent linking group represented by L ₁₁ and the divalent linking group represented by L ₁₃ are the same as each other, and the divalent linking group represented by L ₁₁ and the divalent linking group represented by L ₁₂ are different from each other. In a preferred embodiment, in formula (1-1), L ₁₁ and L ₁₃ are -O-, and L ₁₂ is an alkylene group which may have a substituent, and in a more preferred embodiment, in formula (1-1), Ar ₁₁ , Ar ₁₂ , Ar ₁₃ and Ar ₁₄ are each independently an aromatic carbon ring having 6 to 14 carbon atoms which may have a substituent, and L ₁₁ and L ₁₃ are -O-, and L ₁₂ is an alkylene group which may have a substituent. In a further preferred embodiment, in formula (1-1), L ₁₁ and L ₁₃ are -O-, and L ₁₂ is a dimethylmethylene group.

In formula (1-2), examples of the aromatic rings represented by Ar ₂₁ , Ar ₂₂ , Ar ₂₃ and Ar ₂₄ and the substituents which the aromatic rings may have are the same as those of the aromatic ring C and the substituent S. Thus, in a preferred embodiment, in formula (1-2), Ar ₂₁ , Ar ₂₂ , Ar ₂₃ and Ar ₂₄ are each independently an aromatic carbocyclic ring having 6 to 14 carbon atoms which may have a substituent. In a preferred embodiment, in formula (1-2), L ₂₁ and L ₂₃ are -O-, and L ₂₂ is an alkylene group which may have a substituent, and in a more preferred embodiment, in formula (1-2), Ar ₂₁ , Ar ₂₂ , Ar ₂₃ , and Ar ₂₄ are each independently an aromatic carbocycle having 6 to 14 carbon atoms which may have a substituent, and L ₂₁ and L ₂₃ are -O-, and L ₂₂ is an alkylene group which may have a substituent. In a further preferred embodiment, in formula (1-2), L ₂₁ and L ₂₃ are -O-, and L ₂₂ is a dimethylmethylene group.

In a particularly preferred embodiment, in formula (1-1), Ar ₁₁ , Ar ₁₂ , Ar ₁₃ and Ar ₁₄ are each independently an aromatic carbocyclic ring having 6 to 14 carbon atoms which may have a substituent, and in formula (1-2), Ar ₂₁ , Ar ₂₂ , Ar ₂₃ and Ar ₂₄ are each independently an aromatic carbocyclic ring having 6 to 14 carbon atoms which may have a substituent. In a particularly preferred embodiment, in formula (1-1), L ₁₁ and L ₁₃ are -O-, L ₁₂ is an alkylene group which may have a substituent, and in formula (1-2), L ₂₁ and L ₂₃ are -O-, and L ₂₂ is an alkylene group which may have a substituent.

In formula (1-1), nc1 preferably represents an integer of 1 or more. The upper limit of the integer represented by nc1 is not particularly limited, but may be, for example, 50, 40, 30, or 20.

In formula (1-2), nc2 preferably represents an integer of 2 or more. The upper limit of the integer represented by nc2 is not particularly limited, but may be, for example, 60, 50, 40, or 30.

The structural unit (1) can be obtained, for example, by a known method for producing a polyimide resin, typically a method for polymerizing a monomer composition containing a tetracarboxylic dianhydride and a diamine compound to form an imid, or a method for polymerizing a monomer composition containing a tetracarboxylic dianhydride and a diisocyanate compound to form an imid. It is acceptable for the polyimide resin to contain a portion of a polyamic acid structure that may be generated during the imidization process.

The structural unit (1) may be obtained, for example, by reacting 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (a compound represented by the following formula (I); hereinafter, also referred to as "BPADA") with 4,4'-[1,4-phenylenebis[(1-methylethylidene)-4,1-phenyleneoxy]]bisbenzeneamine (a compound represented by the following formula (II); hereinafter, also referred to as "BPPAN"). That is, in the structural unit (1), R ₁ is a skeleton derived from BPADA, and R ₂ is a skeleton derived from BPPAN.

The polyimide resin may further include a structural unit represented by the following formula (2) (hereinafter also referred to as "structural unit (2)"). Thus, in one embodiment, the polyimide resin further includes a structural unit represented by the following formula (2). The number of structural units (2) contained per molecule of the polyimide resin is 0 or more, and is not particularly limited, but may be 100 or less, 50 or less, or 30 or less.

　（式（２）中、
　Ｒ_３は、置換基を有していてもよい４価の脂肪族基又は置換基を有していてもよい４価の芳香族基を表し、
　Ｒ_４は、置換基を有していてもよい２価の脂肪族基又は置換基を有していてもよい２価の芳香族基を表す。但し、Ｒ_３がＲ_１と同じ場合、Ｒ_４はＲ_２とは異なり、Ｒ_４がＲ_２と同じ場合、Ｒ_３はＲ_１とは異なる。）

(In formula (2),
_R3 represents a tetravalent aliphatic group which may have a substituent or a tetravalent aromatic group which may have a substituent;
_R4 represents a divalent aliphatic group which may have a substituent or a divalent aromatic group which may have a substituent. However, when _R3 is the same as _R1 , _R4 is different from _R2 , and when _R4 is the same as _R2 , _R3 is different from _R1 .

In formula (2), the tetravalent aliphatic group represented by R ₃ contains at least a carbon atom, and is preferably a tetravalent group consisting of one or more (e.g., 1 to 3000, 1 to 1000, 1 to 100, 1 to 50) skeletal atoms selected from carbon atoms, oxygen atoms, nitrogen atoms, sulfur atoms, and silicon atoms. In formula (2), the tetravalent aliphatic group represented by R ₃ is more preferably a tetravalent aliphatic group having 1 to 100 carbon atoms, and even more preferably 1 to 50 carbon atoms. In formula (2), when R ₃ represents a tetravalent aliphatic group having a substituent, examples of the substituent are the same as the examples of the substituent S.

In formula (2), the tetravalent aromatic group represented by R ₃ is preferably a tetravalent aromatic group having 6 to 100 carbon atoms, more preferably 6 to 50 carbon atoms. The aromatic group contains at least an aromatic ring. Examples of the aromatic ring contained in the aromatic group are the same as the examples of the aromatic ring represented by Ar ₁₁ , Ar ₁₂ , Ar ₁₃ and Ar ₁₄ in formula (1-1). In formula (2), when R ₃ represents a tetravalent aromatic group having a substituent, examples of the substituent are the same as the examples of the substituent S.

The tetravalent aromatic group represented by _R3 may be a group obtained by removing two acid anhydride groups from a tetracarboxylic dianhydride having an aromatic group which may have a substituent. Specific examples of the tetracarboxylic dianhydride having an aromatic group which may have a substituent include BPADA, pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride.

In formula (2), the divalent aliphatic group represented by R ₄ contains at least a carbon atom, and is preferably a divalent group consisting of one or more (e.g., 1 to 3000, 1 to 1000, 1 to 100, 1 to 50) skeletal atoms selected from carbon atoms, oxygen atoms, nitrogen atoms, sulfur atoms, and silicon atoms. In formula (2), the divalent aliphatic group represented by R ₄ is more preferably a divalent aliphatic group having 1 to 100 carbon atoms, and even more preferably 1 to 50 carbon atoms. In formula (2), when R ₄ represents a divalent aliphatic group having a substituent, examples of the substituent are the same as the examples of the substituent S, and are, for example, an alkyl group having 1 to 6 carbon atoms. Therefore, in one embodiment, R ₄ is a divalent aliphatic group which may have a substituent, and one of the substituents is an alkyl group having 1 to 6 carbon atoms. In one embodiment, R ₄ is a divalent aliphatic group which may have a substituent, and is a divalent group obtained by removing two amino groups from isophoronediamine.

When R ₄ represents a divalent aliphatic group which may have a substituent, it may be a group obtained by removing two amino groups from a diamine compound having a linear aliphatic group which may have a substituent, selected from 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine, 1,10-decanediamine, 1,11-undecanediamine, and 1,12-dodecanediamine.

When R ₄ represents a divalent aliphatic group which may have a substituent, it may be a group obtained by removing two amino groups from a diamine compound having a branched aliphatic group which may have a substituent selected from 1,2-diaminopropane, 1,2-diamino-2-methylpropane, 1,3-diamino-2-methylpropane, 1,3-diamino-2,2-dimethylpropane, 1,3-diaminopentane, and 1,5-diamino-2-methylpentane.

When R ₄ represents a divalent aliphatic group which may have a substituent, it may be a group obtained by removing two amino groups from a diamine compound having an aliphatic group which may have a substituent selected from 5-amino-1,3,3-trimethylcyclohexanemethylamine (isophoronediamine), 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, 1,4-cyclohexanebis(methylamine), 1,3-cyclohexanebis(methylamine), 4,4'-diaminodicyclohexylmethane, bis(4-amino-3-methylcyclohexyl)methane, 3(4),8(9)-bis(aminomethyl)tricyclo[5.2.1.0 ^2,6 ]decane, 2,5(6)-bis(aminomethyl)bicyclo[2.2.1]heptane, 1,3-diaminoadamantane, 3,3'-diamino-1,1'-biadamantyl, and 1,6-diaminoadamantane. These diamine compounds are characterized in that the aliphatic groups contain alicyclic carbon rings.

In formula (2), the divalent aromatic group represented by R ₄ is preferably a divalent aromatic group having 6 to 100 carbon atoms, more preferably 6 to 50 carbon atoms. The aromatic group contains at least an aromatic ring. Examples of the aromatic ring contained in the aromatic group are the same as the examples of the aromatic ring C. In formula (2), when R ₄ represents a divalent aromatic group having a substituent, examples of the substituent are the same as the examples of the substituent S.

When _R4 represents a divalent aromatic group which may have a substituent, it may be a group obtained by removing two amino groups from a diamine compound having an aromatic group which may have a substituent selected from 4,4'-diaminodiphenyl ether, 1,4-phenylenediamine, and 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

With the proviso that when _R3 is the same as _R1 , _R4 is different from _R2 , and when _R4 is the same as _R2 , _R3 is different from _R1 . In one embodiment, _R3 is the same as _R1 .

The above-mentioned structural unit (2) can be obtained, for example, according to a known method for producing a polyimide resin. The structural unit (2) can be obtained, for example, by reacting BPADA with isophoronediamine. That is, _R3 in the structural unit (2) is a skeleton derived from BPADA, and _R4 is a skeleton derived from isophoronediamine. When _R3 is the same as _R1 , _R3 and _R1 are skeletons derived from BPADA.

The terminal structure of the polyimide resin is not particularly limited. For example, the terminal structure of the polyimide resin may be an acid anhydride group derived from the raw material compound (e.g., an acid such as BPADA, or an amine compound such as BPPAN), or a carboxyl group or an amino group. If the raw material compound further contains maleic anhydride, the terminal structure of the polyimide resin may be a maleimide group.

The glass transition temperature Tg (°C) of the polyimide resin is preferably 140°C or higher, more preferably 145°C or higher, and even more preferably 150°C or higher, 160°C or higher, or 170°C or higher. There is no particular upper limit, but it can be 300°C or lower, for example. The glass transition temperature Tg (°C) of the polyimide resin can be measured by thermomechanical analysis (TMA).

The content of the structural unit (1) in the polyimide resin is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, 30% by mass or more, or 40% by mass or more. The upper limit of the content may be, for example, 98% by mass or less, 95% by mass or less, 90% by mass or less, or 85% by mass or less. Here, the content (mass percentage) of the structural unit (1) can be calculated from the ratio of the amounts (parts by mass) of each material used in the synthesis of the polyimide resin. Alternatively, the molecular weight of the polyimide resin and the formula weight of the structural unit (1) may be specified, and the content may be calculated as the ratio of the formula weight of the structural unit (1) to the molecular weight. When the polyimide resin is a polymer, it is preferable that the content of the structural unit (1) estimated from the degree of polymerization is within the above range.

When the polyimide resin further contains the structural unit (2), the content of the structural unit (2) may be 0% by mass (i.e., no structural unit (2)), and there is no upper limit as long as the effect of the present invention is not impaired. The content of the structural unit (2) in the polyimide resin may be, for example, 1% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, or 30% by mass or more, and 95% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass or less, or 60% by mass or less. Here, the content of the structural unit (2) is calculated in the same manner as the content of the structural unit (1).

The weight average molecular weight (Mw) of the polyimide resin is 1,000 or more, preferably 1.00 to 10,000, and more preferably 1,000 to 5,000. The weight average molecular weight of the resin can be measured as a polystyrene-equivalent value by gel permeation chromatography (GPC).

--Polyvinyl acetal resin--
Examples of polyvinyl acetal resins include polyvinyl formal resins and polyvinyl butyral resins, with polyvinyl butyral resins being preferred. Specific examples of polyvinyl acetal resins include S-LEC BH series, BX series (e.g., BX-5Z), KS series (e.g., KS-1), BL series, and BM series manufactured by Sekisui Chemical Co., Ltd.

--Acrylic resin--
The acrylic resin refers to a polymer obtained by polymerizing a monomer component including a (meth)acrylic acid ester monomer. The monomer components constituting the acrylic resin may contain, in addition to the (meth)acrylic acid ester monomer, a (meth)acrylamide monomer, a styrene monomer, a functional group-containing monomer, or the like as copolymerization components. Specific examples of acrylic resins include "ARUFON UP-1000", "ARUFON UP-1010", "ARUFON UP-1020", "ARUFON UP-1021", "ARUFON UP-1061", "ARUFON UP-1080", "ARUFON UP-1110", "ARUFON UP-1170", "ARUFON UP-1190", "ARUFON UP-1500", "ARUFON UH-2000", "ARUFON UH-2041", "ARUFON UH-2190", "ARUFON UHE-2012", "ARUFON UC-3510", and "ARUFON UP-1021", all manufactured by Toagosei Co., Ltd. UG-4010", "ARUFON US-6100", "ARUFON US-6170", etc. These may be used alone or in combination of two or more.

--Polyolefin resin--
Examples of polyolefin resins include ethylene-based copolymer resins such as low-density polyethylene, very low-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, and ethylene-methyl acrylate copolymer; and polyolefin-based elastomers such as polypropylene and ethylene-propylene block copolymer.

--Polybutadiene resin--
Examples of polybutadiene resins include hydrogenated polybutadiene skeleton-containing resins, hydroxy group-containing polybutadiene resins, phenolic hydroxy group-containing polybutadiene resins, carboxy group-containing polybutadiene resins, acid anhydride group-containing polybutadiene resins, epoxy group-containing polybutadiene resins, isocyanate group-containing polybutadiene resins, urethane group-containing polybutadiene resins, polyphenylene ether-polybutadiene resins, and the like.

--Polyamide-imide resin--
Specific examples of polyamide-imide resins include "Viromax HR11NN" and "Viromax HR16NN" manufactured by Toyobo Co., Ltd. Specific examples of polyamide-imide resins also include modified polyamide-imides such as "KS9100" and "KS9300" (polysiloxane skeleton-containing polyamide-imide) manufactured by Resonac Corporation.

--Polyethersulfone resin--
A specific example of the polyethersulfone resin is "PES5003P" manufactured by Sumitomo Chemical Co., Ltd.

--Polysulfone resin--
Specific examples of polysulfone resins include polysulfones "P1700" and "P3500" manufactured by Solvay Advanced Polymers.

--Polyphenylene ether resin--
A specific example of the polyphenylene ether resin is Noryl (registered trademark) SA90 manufactured by SABIC, etc. A specific example of the polyetherimide resin is Ultem manufactured by GE, etc.

--Polycarbonate resin--
Examples of polycarbonate resins include hydroxyl group-containing carbonate resins, phenolic hydroxyl group-containing carbonate resins, carboxyl group-containing carbonate resins, acid anhydride group-containing carbonate resins, isocyanate group-containing carbonate resins, and urethane group-containing carbonate resins. Specific examples of polycarbonate resins include Mitsubishi Gas Chemical Company's "FPC0220," Asahi Kasei's "T6002" and "T6001" (polycarbonate diols), and Kuraray's "C-1090,""C-2090," and "C-3090" (polycarbonate diols). Specific examples of polyether ether ketone resins include Sumitomo Chemical's "Sumiploy K." Examples of polyester resins include polyethylene terephthalate resins.

Unless otherwise specified, the weight average molecular weight of the thermoplastic resin is preferably 5,000 or more, more preferably 8,000 or more, even more preferably 10,000 or more, 15,000 or more, or 20,000 or more, and is preferably 200,000 or less, more preferably 150,000 or less, or 100,000 or less, even more preferably 80,000 or less, or 60,000 or less. The weight average molecular weight of the thermoplastic resin can be measured as a polystyrene-equivalent value by gel permeation chromatography (GPC).

In the multilayer resin sheet of the present invention, when the resin composition layer contains a thermoplastic resin, the content of the thermoplastic resin in the resin composition layer is preferably 0.1% by mass or more, 0.3% by mass or more, or 0.5% by mass or more, when the resin component in the resin composition layer is taken as 100% by mass, from the viewpoint of easily adjusting the RD/RA ratio to a suitable range, providing an insulating layer with better surface smoothness, reduced smears, and well-shaped via holes. The upper limit of the thermoplastic resin content is not particularly limited, but is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 6% by mass or less or 5% by mass or less.

-Radical polymerizable resin-
In the multilayer resin sheet of the present invention, the resin composition layer may contain a radical polymerizable resin.

The type of radical polymerizable resin is not particularly limited, so long as it has one or more (preferably two or more) radical polymerizable unsaturated groups in one molecule. Examples of radical polymerizable resins include resins having one or more radical polymerizable unsaturated groups selected from maleimide groups, vinyl groups, allyl groups, styryl groups, vinylphenyl groups, acryloyl groups, methacryloyl groups, fumaroyl groups, and maleoyl groups. Among them, from the viewpoint of providing an insulating layer with better surface smoothness, reduced smears, and well-shaped via holes, and further from the viewpoint of providing an insulating layer with little change in film thickness before and after desmearing, it is preferable that the radical polymerizable resin contains one or more selected from maleimide resins, (meth)acrylic resins, and styryl resins.

The type of maleimide resin is not particularly limited as long as it has one or more (preferably two or more) maleimide groups (2,5-dihydro-2,5-dioxo-1H-pyrrol-1-yl groups) in one molecule. Examples of maleimide resins include (1) "BMI-3000J", "BMI-5000", "BMI-1400", "BMI-1500", "BMI-1700", "BMI-689" (all manufactured by Designer Molecules Inc.), and "SLK6895-T90" (manufactured by Shin-Etsu Chemical Co., Ltd.), which have an aliphatic skeleton (preferably an aliphatic compound having 36 carbon atoms derived from dimer diamine). skeleton); (2) maleimide resins containing an indane skeleton, as described in the Japan Institute of Invention and Innovation's Technical Journal No. 2020-500211; (3) maleimide resins containing an aromatic ring skeleton directly bonded to the nitrogen atom of the maleimide group, such as "MIR-3000-70MT" (manufactured by Nippon Kayaku Co., Ltd.), "BMI-4000" (manufactured by Daiwa Kasei Co., Ltd.), and "BMI-80" (manufactured by Keiai Kasei Co., Ltd.).

The (meth)acrylic resin may be a monomer or an oligomer, and is not particularly limited in type, so long as it has one or more (preferably two or more) (meth)acryloyl groups in one molecule. Here, the term "(meth)acryloyl group" is a general term for acryloyl and methacryloyl groups. Examples of methacrylic resins include (meth)acrylate monomers, as well as (meth)acrylic resins such as "A-DOG" (manufactured by Shin-Nakamura Chemical Co., Ltd.), "DCP-A" (manufactured by Kyoeisha Chemical Co., Ltd.), "NPDGA", "FM-400", "R-687", "THE-330", "PET-30", and "DPHA" (all manufactured by Nippon Kayaku Co., Ltd.).

The type of styryl resin is not particularly limited, and may be a monomer or oligomer, so long as it has one or more (preferably two or more) styryl groups or vinylphenyl groups in one molecule. Examples of styryl resins include styrene monomers, as well as styryl resins such as "OPE-2St", "OPE-2St 1200", and "OPE-2St 2200" (all manufactured by Mitsubishi Gas Chemical Co., Ltd.).

In the multilayer resin sheet of the present invention, when the resin composition layer contains a radically polymerizable resin, the content of the radically polymerizable resin in the resin composition layer is preferably 2% by mass or more, more preferably 4% by mass or more, and even more preferably 5% by mass or more, 6% by mass or more, 8% by mass or more, or 10% by mass or more, when the resin component in the resin composition is taken as 100% by mass, and may be increased to, for example, 12% by mass or more, 14% by mass or more, or 15% by mass or more. The upper limit of the content is not particularly limited and may be determined depending on the properties required of the resin composition, but may be, for example, 60% by mass or less, 50% by mass or less, or 40% by mass or less.

From the viewpoint of providing an insulating layer with better surface smoothness, reduced smears, and well-shaped via holes, and further from the viewpoint of providing an insulating layer with little change in film thickness before and after desmearing, it is preferable that the first resin composition layer of the resin composition layers constituting the multilayer resin sheet of the present invention contains a radical polymerizable resin. Therefore, in a preferred embodiment, the first resin composition layer contains a radical polymerizable resin.

- Hardening accelerator -
In the multilayer resin sheet of the present invention, the resin composition layer may contain a curing accelerator, which makes it possible to efficiently adjust the curing time and the curing temperature.

Examples of the curing accelerator include organic phosphine compounds such as "TPP", "TPP-K", "TPP-S" and "TPTP-S" (manufactured by Hokko Chemical Industry Co., Ltd.); imidazole compounds such as "Curesol 2MZ", "2P4MZ", "2E4MZ", "Cl1Z", "Cl1Z-CN", "Cl1Z-CNS", "Cl1Z-A", "2MZ-OK", "2MA-OK" and "2PHZ" (manufactured by Shikoku Chemical Industry Co., Ltd.); amine adduct compounds such as Novacure (manufactured by Asahi Chemical Industry Co., Ltd.) and Fujicure (manufactured by Fuji Chemical Industry Co., Ltd.); amine compounds such as 1,8-diazabicyclo[5,4,0]undecene-7,4-dimethylaminopyridine, benzyldimethylamine, 2,4,6-tris(dimethylaminomethyl)phenol and 4-dimethylaminopyridine; and organometallic complexes or organometallic salts of cobalt, copper, zinc, iron, nickel, manganese, tin, etc.

When the resin composition layer in the multilayer resin sheet of the present invention contains a curing accelerator, the content of the curing accelerator in the resin composition layer is preferably 12% by mass or less, more preferably 10% by mass or less, 8% by mass or less, 6% by mass or less, or 5% by mass or less, when the resin component in the resin composition is taken as 100% by mass, from the viewpoint of easily adjusting the RD/RA ratio to a suitable range, and the lower limit can be 0.001% by mass or more, 0.01% by mass or more, 0.05% by mass or more, etc.

From the viewpoint of providing an insulating layer with better surface smoothness, reduced smears, and well-shaped via holes, and further from the viewpoint of providing an insulating layer with little change in film thickness before and after desmearing, it is preferable that the content A1 (mass %) of the curing accelerator relative to 100 mass % of the resin components in the first resin composition layer and the content A2 (mass %) of the curing accelerator relative to 100 mass % of the resin components in the layers other than the first resin composition layer satisfy the relationship A1>A2. The difference between A1 and A2 (A1-A2) is preferably 1 mass % or more, more preferably 2 mass % or more, 3 mass % or more, or 4 mass % or more.

-Optional Additives-
In the multilayer resin sheet of the present invention, the resin composition layer may further contain any additive. Examples of such additives include organic fillers such as rubber particles; radical polymerization initiators such as peroxide radical polymerization initiators and azo radical polymerization initiators; organometallic compounds such as organic copper compounds, organic zinc compounds, and organic cobalt compounds; colorants such as phthalocyanine blue, phthalocyanine green, iodine green, diazo yellow, crystal violet, titanium oxide, and carbon black; polymerization inhibitors such as hydroquinone, catechol, pyrogallol, and phenothiazine; leveling agents such as silicone leveling agents and acrylic polymer leveling agents; thickeners such as bentone and montmorillonite; defoamers such as silicone defoamers, acrylic defoamers, fluorine defoamers, and vinyl resin defoamers; ultraviolet absorbers such as benzotriazole ultraviolet absorbers; adhesion improvers such as urea silane; and triazole adhesion imparting agents. Adhesion imparting agents such as tetrazole adhesion imparting agents and triazine adhesion imparting agents; antioxidants such as hindered phenol antioxidants; fluorescent brightening agents such as stilbene derivatives; surfactants such as fluorine-based surfactants and silicone-based surfactants; flame retardants such as phosphorus-based flame retardants (e.g., phosphate ester compounds, phosphazene compounds, phosphinic acid compounds, red phosphorus), nitrogen-based flame retardants (e.g., melamine sulfate), halogen-based flame retardants, and inorganic flame retardants (e.g., antimony trioxide); dispersants such as phosphate ester dispersants, polyoxyalkylene dispersants, acetylene dispersants, silicone-based dispersants, anionic dispersants, and cationic dispersants; stabilizers such as borate-based stabilizers, titanate-based stabilizers, aluminate-based stabilizers, zirconate-based stabilizers, isocyanate-based stabilizers, carboxylic acid-based stabilizers, and carboxylic anhydride-based stabilizers. The content of such additives may be determined according to the properties required for the multilayer resin sheet.

-Method for manufacturing multi-layer resin sheet-
The method for producing the multilayer resin sheet of the present invention is not particularly limited as long as it can realize a structure in which two or more resin composition layers are laminated on each other, and a method known to those skilled in the art may be used. For example, (i) an extrusion molding method in which a resin composition is melt-kneaded using an extruder, extruded, and then molded into a film shape using a T-die or a circular die, (ii) a casting molding method in which a resin composition is dissolved or dispersed in a solvent, and then cast to mold into a film shape, and (iii) other conventionally known film molding methods, etc. are included. Among them, the extrusion molding method or the casting molding method is preferred because it can be made thin. The multilayer resin sheet of the present invention includes two or more resin composition layers laminated on each other. Examples of methods for forming a multilayer resin sheet by laminating two or more resin composition layers on top of each other include (1) a method for forming a multilayer resin sheet by simultaneously or sequentially forming resin composition layers during coating or extrusion, (2) a method for forming a multilayer resin sheet by laminating two or more resin composition layers that are separately prepared with a heat roll laminator or the like, (3) a method for forming a resin sheet having a multilayer structure in a single resin sheet by causing a difference in the content of each component in the resin sheet during casting molding, and (4) other conventionally known methods for forming a multilayer resin sheet.

Below, a suitable example of a method for producing a multilayer resin sheet having two resin composition layers, i.e., a first resin composition layer and a second resin composition layer, is described.

In one embodiment, a method for producing a multilayer resin sheet includes the steps of:
(A1) a step of preparing a support-attached resin sheet including a support and a first resin composition layer bonded to the support; and (B1) a step of applying a second resin composition onto the first resin composition layer and drying the applied film to provide a second resin composition layer (hereinafter, such an embodiment of lamination by coating is also referred to as the "first embodiment").

In step (A1), a resin sheet with a support is prepared, which includes a support and a first resin composition layer bonded to the support. The support is described in the section below titled [Multilayer resin sheet with support].

The resin sheet with support can be produced, for example, by applying the first resin composition onto the support and drying the applied film to provide a first resin composition layer. In detail, the resin sheet can be produced by preparing a resin varnish by dissolving the first resin composition in an organic solvent, applying this resin varnish onto the support using a die coater or the like, and drying the applied film.

Examples of organic solvents include ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester-based solvents such as methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate, isoamyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone; ether-based solvents such as tetrahydropyran, tetrahydrofuran, 1,4-dioxane, diethyl ether, diisopropyl ether, dibutyl ether, and diphenyl ether; alcohol-based solvents such as methanol, ethanol, propanol, butanol, and ethylene glycol; 2-ethoxyethyl acetate, propylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, ethyl diglycol acetate, γ-butyrolactone, and methyl methoxypropionate. Examples of suitable organic solvents include ether ester solvents such as ethyl acetate; ester alcohol solvents such as methyl lactate, ethyl lactate, and methyl 2-hydroxyisobutyrate; ether alcohol solvents such as 2-methoxypropanol, 2-methoxyethanol, 2-ethoxyethanol, propylene glycol monomethyl ether, and diethylene glycol monobutyl ether (butyl carbitol); amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone; sulfoxide solvents such as dimethyl sulfoxide; nitrile solvents such as acetonitrile and propionitrile; aliphatic hydrocarbon solvents such as hexane, cyclopentane, cyclohexane, and methylcyclohexane; and aromatic hydrocarbon solvents such as benzene, toluene, xylene, ethylbenzene, and trimethylbenzene. The organic solvent may be used alone or in combination of two or more.

The coating film may be dried by known drying methods such as heating or blowing hot air. Although this varies depending on the boiling point of the organic solvent in the resin varnish, for example, when a resin varnish containing 30% to 60% by mass of an organic solvent is used, a first resin composition layer can be formed on the support by drying at 80°C to 180°C for 2 to 10 minutes.

In step (B1), a second resin composition is applied onto the first resin composition layer, and the applied film is dried to provide a second resin composition layer. This results in the formation of a multilayer resin sheet with a support, in which a multilayer resin sheet is formed on the support.

The application of the second resin composition and the drying of the coating film may be carried out in the same manner as the application of the first resin composition and the drying of the coating film in step (A1). From the viewpoint of easily adjusting the RD/RA ratio to a suitable range, when the drying temperature (°C) of the coating film in step (A1) is T1 and the drying temperature (°C) of the coating film in step (A2) is T2, it is preferable that the relationship T1>T2 is satisfied, more preferably T1≧(T2+20), and even more preferably T1≧(T2+40) or T1≧(T2+50).

The multilayer resin sheet with a support may further include a protective film similar to the support on the surface of the multilayer resin sheet that is not joined to the support (i.e., the surface opposite the support). When a protective film is provided, the multilayer resin sheet with a support can be used by peeling off the protective film when laminating it to a member to be laminated.

In another embodiment, a method for producing a multilayer resin sheet includes the steps of:
(A2a) preparing a first support-attached resin sheet including a first support and a first resin composition layer bonded to the first support;
(A2b) a step of preparing a second supported resin sheet including a second support and a second resin composition layer bonded to the second support; and (B2) a step of laminating the first supported resin sheet and the second supported resin sheet together such that the first resin composition layer and the second resin composition layer are bonded to each other (hereinafter, such an embodiment of lamination by lamination is also referred to as a "second embodiment").

In the second embodiment, step (A2a) and step (A2b) may each be performed in the same manner as step (A1) in the first embodiment. From the viewpoint of easily adjusting the RD/RA ratio to a suitable range, if the drying temperature (°C) of the coating film in step (A2a) is Ta and the drying temperature (°C) of the coating film in step (A2b) is Tb, it is preferable that the relationship Ta>Tb is satisfied, more preferably Ta≧(Tb+20), and even more preferably Ta≧(Tb+40) or Ta≧(Tb+50).

In step (B2), the first resin sheet with a support and the second resin sheet with a support are laminated so that the first resin composition layer and the second resin composition layer are bonded. This forms a multilayer resin sheet between the first support and the second support. The second support can function as the protective film in the first embodiment. The multilayer resin sheet with a support manufactured in the second embodiment can be used by peeling off the second support (protective film) when laminating it to a member to be laminated.

For the lamination in step (B2), the lamination temperature is preferably in the range of 60°C to 160°C, more preferably 80°C to 140°C, the lamination pressure is preferably in the range of 0.098MPa to 1.77MPa, more preferably 0.29MPa to 1.47MPa, and the lamination time is preferably in the range of 20 seconds to 400 seconds, more preferably 30 seconds to 300 seconds. Lamination may be performed under reduced pressure conditions, preferably at a pressure of 26.7hPa or less.

Lamination can be performed using a commercially available vacuum laminator. Examples of commercially available vacuum laminators include the vacuum pressure laminator manufactured by Meiki Seisakusho Co., Ltd., the vacuum applicator manufactured by Nikko Materials Co., Ltd., and the batch type vacuum pressure laminator.

The multilayer resin sheet of the present invention can provide an insulating layer with good surface smoothness, reduced smears, and well-shaped via holes, even when the desmear treatment is performed after peeling off the support. The multilayer resin sheet of the present invention can also provide an insulating layer with little change in thickness before and after the desmear treatment. Therefore, the multilayer resin sheet of the present invention can be suitably used as a multilayer resin sheet for forming an insulating layer of a printed wiring board (multilayer resin sheet for insulating layer of printed wiring board), and can be more suitably used as a multilayer resin sheet for forming an interlayer insulating layer of a printed wiring board (multilayer resin sheet for interlayer insulating layer of printed wiring board). The multilayer resin sheet of the present invention can also be suitably used when the printed wiring board is a circuit board with built-in components. The resin composition of the present invention can also be suitably used as a multilayer resin sheet for forming an insulating layer (multilayer resin sheet for insulating layer for forming a conductor layer) in contact with the insulating layer on which a conductor layer (including a rewiring layer) will be formed.

[Multi-layer resin sheet with support]
The present invention also provides a supported multi-layer resin sheet in which the multi-layer resin sheet of the present invention is provided on a support.

The multilayer resin sheet with a support of the present invention is
The multilayer resin sheet of the present invention,
The multilayer resin sheet includes a support bonded to the first resin composition layer of the multilayer resin sheet.

The multilayer resin sheet of the present invention is as described above in the [Multilayer resin sheet] section. In the multilayer resin sheet with a support of the present invention, the first resin composition layer of the multilayer resin sheet of the present invention is bonded to the support.

Examples of the support include thermoplastic resin film, metal foil, and release paper, with thermoplastic resin film and metal foil being preferred. Thus, in a preferred embodiment, the support is a thermoplastic resin film or metal foil.

When a thermoplastic resin film is used as the support, examples of the thermoplastic resin include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), acrylics such as polycarbonate (PC) and polymethyl methacrylate (PMMA), cyclic polyolefins, triacetyl cellulose (TAC), polyether sulfide (PES), polyether ketone, polyimide, etc. Among these, polyethylene terephthalate and polyethylene naphthalate are preferred, with inexpensive polyethylene terephthalate being particularly preferred.

When a metal foil is used as the support, examples of the metal foil include copper foil and aluminum foil, with copper foil being preferred. As the copper foil, foil made of a single metal, copper, or an alloy of copper and another metal (e.g., tin, chromium, silver, magnesium, nickel, zirconium, silicon, titanium, etc.) may be used.

The support may be subjected to a matte treatment, a corona treatment, or an antistatic treatment on the surface to be bonded to the first resin composition layer. The support may be a support with a release layer having a release layer on the surface to be bonded to the first resin composition layer. The release agent used in the release layer of the support with a release layer may be, for example, one or more release agents selected from the group consisting of alkyd resins, polyolefin resins, urethane resins, and silicone resins. The support with a release layer may be a commercially available product, for example, "SK-1", "AL-5", and "AL-7" manufactured by Lintec Corporation, "Lumirror T60" manufactured by Toray Industries, "Purex" manufactured by Teijin Limited, and "Unipeel" manufactured by Unitika Limited, which are PET films having a release layer mainly composed of an alkyd resin-based release agent.

The thickness of the support is not particularly limited, but is preferably in the range of 5 μm to 75 μm, and more preferably in the range of 10 μm to 60 μm. When using a support with a release layer, it is preferable that the thickness of the entire support with the release layer is in the above range.

In one embodiment, the multilayer resin sheet with a support may further include an optional layer, if necessary. Such an optional layer may be, for example, a protective film provided on the surface of the multilayer resin sheet that is not joined to the support (i.e., the surface opposite the support). The thickness of the protective film is not particularly limited, but is, for example, 1 μm to 40 μm. By laminating the protective film, it is possible to prevent the adhesion of dirt and the like to the surface of the multilayer resin sheet and to prevent scratches.

The method for producing a multilayer resin sheet with a support is as explained in the "Multilayer resin sheet" section above.

The multilayer resin sheet with support can be wound up in a roll and stored. When the resin sheet with support has a protective film, it can be used by peeling off the protective film. Here, when the adhesive strength between the support and the multilayer resin sheet (specifically, the first resin composition layer) is S1, and the adhesive strength between the protective film and the multilayer resin sheet (specifically, the outermost layer opposite the first resin composition layer) is S2, the relationship S1>S2 is satisfied. This allows the protective film to be peeled off from the multilayer resin sheet before the support, exposing the surface of the multilayer resin sheet opposite the first resin composition layer, and thus allowing the multilayer resin sheet to be laminated so that the surface of the multilayer resin sheet opposite the first resin composition layer is bonded to the member to be laminated.

The multilayer resin sheet with a support of the present invention can be suitably used to form an insulating layer of a printed wiring board (for insulating layers of printed wiring boards), and can be even more suitably used to form an interlayer insulating layer of a printed wiring board (for interlayer insulating layers of printed wiring boards). The sheet-like laminate material of the present invention can also be suitably used as a resin composition for forming an insulating layer (for insulating layers for forming conductor layers) in contact with which a conductor layer (including a rewiring layer) will be formed.

[Printed wiring board]
The printed wiring board of the present invention includes an insulating layer made of a cured product of the multilayer resin sheet of the present invention.

A printed wiring board can be produced, for example, by using the multilayer resin sheet of the present invention, by a method including the following steps (I) to (IV).
(I) a step of laminating the multilayer resin sheet of the present invention on an inner layer substrate such that the surface of the multilayer resin sheet opposite to the first resin composition layer is bonded to the inner layer substrate; (II) a step of curing (e.g., thermally curing) the multilayer resin sheet to form an insulating layer; (III) a step of forming via holes in the insulating layer with a laser and performing a desmear treatment; and (IV) a step of forming a metal film on the surface of the insulating layer after the desmear treatment.

-Step (I)-
In step (I), the multilayer resin sheet of the present invention is laminated on an inner layer substrate so that the surface of the multilayer resin sheet opposite the first resin composition layer is bonded to the inner layer substrate.

The "inner layer substrate" used in step (I) is a member that will be the substrate of the printed wiring board, and examples thereof include glass epoxy substrates, metal substrates, polyester substrates, polyimide substrates, BT resin substrates, and thermosetting polyphenylene ether substrates. The substrate may have a conductor layer on one or both sides, and the conductor layer may be patterned. An inner layer substrate having a conductor layer (circuit) formed on one or both sides of the substrate may be called an "inner layer circuit substrate." In addition, intermediate products on which an insulating layer and/or a conductor layer is to be formed during the manufacture of a printed wiring board are also included in the "inner layer substrate" of the present invention. When the printed wiring board is a circuit board with built-in components, an inner layer substrate with built-in components may be used.

The lamination of the inner layer substrate and the multilayer resin sheet can be carried out, for example, by using the multilayer resin sheet with a support of the present invention and heat-pressing the multilayer resin sheet to the inner layer substrate from the support side. Examples of the member for heat-pressing the multilayer resin sheet to the inner layer substrate (hereinafter also referred to as the "heat-pressing member") include a heated metal plate (such as a SUS panel) or a metal roll (SUS roll). The heat-pressing member may be pressed directly onto the multilayer resin sheet with a support, or may be pressed via an elastic material such as heat-resistant rubber so that the resin sheet can sufficiently follow the surface irregularities of the inner layer substrate.

Lamination of the inner layer substrate and the multilayer resin sheet may be performed by a vacuum lamination method. In the vacuum lamination method, the heat-pressure bonding temperature is preferably in the range of 60°C to 160°C, more preferably 80°C to 140°C, the heat-pressure bonding pressure is preferably in the range of 0.098MPa to 1.77MPa, more preferably 0.29MPa to 1.47MPa, and the heat-pressure bonding time is preferably in the range of 20 seconds to 400 seconds, more preferably 30 seconds to 300 seconds. Lamination may be performed under reduced pressure conditions, preferably at a pressure of 26.7hPa or less.

Lamination can be performed using a commercially available vacuum laminator. Examples of commercially available vacuum laminators include a vacuum pressure laminator manufactured by Meiki Seisakusho Co., Ltd., a vacuum applicator manufactured by Nikko Materials Co., Ltd., and a batch-type vacuum pressure laminator.

After lamination, the laminated multilayer resin sheet may be smoothed under normal pressure (atmospheric pressure), for example by pressing a heat-pressure bonding member from the support side. The pressing conditions for the smoothing treatment may be the same as the heat-pressure bonding conditions for the lamination described above. The smoothing treatment may be performed using a commercially available laminator. Note that lamination and smoothing treatment may be performed consecutively using the commercially available vacuum laminator described above.

The support may be removed between step (I) and step (II), or after step (II). When a metal foil is used as the support, the conductor layer may be formed using the metal foil without peeling off the support.

-Step (II)-
In step (II), the multilayer resin sheet is cured (for example, thermally cured) to form an insulating layer made of a cured product of the multilayer resin sheet.

The curing conditions for the multilayer resin sheet are not particularly limited, and the conditions normally used when forming an insulating layer for a printed wiring board may be used.

For example, the heat curing conditions for the multilayer resin sheet vary depending on the composition of the resin composition layer, but in one embodiment, the curing temperature is preferably 120°C to 250°C, more preferably 150°C to 240°C, and even more preferably 170°C to 230°C. The curing time is preferably 5 minutes to 240 minutes, more preferably 10 minutes to 150 minutes, and even more preferably 15 minutes to 120 minutes.

Before the multilayer resin sheet is thermally cured, it may be preheated at a temperature lower than the curing temperature. For example, prior to thermally curing the multilayer resin sheet, it may be preheated at a temperature of 50°C to 120°C, preferably 60°C to 115°C, and more preferably 70°C to 110°C for 5 minutes or more, preferably 5 minutes to 150 minutes, more preferably 15 minutes to 120 minutes, and even more preferably 15 minutes to 100 minutes.

-Step (III)-
In step (III), a via hole is formed in the insulating layer by a laser, and a desmear treatment is performed.

As a laser light source for forming a via hole in an insulating layer, for example, a carbon dioxide gas laser ( _CO2 laser), a UV-YAG laser, an excimer laser, or the like may be used. Among them, it is preferable to use a _CO2 laser from the viewpoint of obtaining the effects of the present invention more effectively. Therefore, in one embodiment, a via hole is formed in an insulating layer by a _CO2 laser.

The dimensions and shape of the via hole may be appropriately determined depending on the design of the printed wiring board. For example, the shape of the via hole is not particularly limited, but is generally circular (approximately circular). The top diameter of the via hole is preferably 50 μm or less, 40 μm or less, 30 μm or less, or 20 μm or less, and the lower limit can be, for example, 3 μm or more, 5 μm or more, 10 μm or more, etc. Here, the top diameter of the via hole refers to the diameter of the opening of the via hole at the insulating layer surface (the insulating layer surface derived from the first resin composition layer).

By using the multilayer resin sheet of the present invention, it is possible to form a via hole with a good cross-sectional shape with little dimensional change in the thickness direction of the insulating layer. In one embodiment, when observing the cross section of the via hole, the relationship R1 ≧ R2 is satisfied, where R1 is the maximum via diameter (μm) in the insulating layer portion derived from the first resin composition layer, and R2 is the maximum via diameter (μm) in the insulating layer portion derived from the layers other than the first resin composition layer. In a preferred embodiment, R1 and R2 satisfy the relationship R1 ≧ R2 and also satisfy the relationship (R1-R2) ≦ 0.1R1.

After forming via holes in the insulating layer with a laser, a desmear process is performed. This makes it possible to remove resin residue (smear) from within the via holes. The procedure and conditions for the desmear process are not particularly limited, and known procedures and conditions that are typically used when forming insulating layers for printed wiring boards can be used. For example, the desmear process can be performed by carrying out a swelling process using a swelling liquid, a desmear (roughening) process using an oxidizing agent liquid, and a neutralization process using a neutralizing liquid, in that order.

The swelling liquid used in the desmear treatment is not particularly limited, but examples thereof include an alkaline solution, a surfactant solution, etc., and is preferably an alkaline solution, and as the alkaline solution, a sodium hydroxide solution or a potassium hydroxide solution is more preferable. Examples of commercially available swelling liquids include "Swelling Dip Securigant P" and "Swelling Dip Securigant SBU" manufactured by Atotech Japan. The swelling treatment using the swelling liquid is not particularly limited, but can be performed by, for example, immersing the insulating layer in a swelling liquid at 30°C to 90°C for 1 to 20 minutes. From the viewpoint of suppressing the swelling of the resin of the insulating layer to an appropriate level, it is preferable to immerse the insulating layer in a swelling liquid at 40°C to 80°C for 5 to 15 minutes.

The oxidizing agent used in the desmear treatment is not particularly limited, but examples thereof include alkaline permanganate solutions in which potassium permanganate or sodium permanganate is dissolved in an aqueous solution of sodium hydroxide. Roughening treatment using an oxidizing agent such as an alkaline permanganate solution is preferably performed by immersing the insulating layer in an oxidizing agent solution heated to 60°C to 100°C for 10 to 30 minutes. The concentration of permanganate in the alkaline permanganate solution is preferably 5% by mass to 10% by mass. Examples of commercially available oxidizing agents include alkaline permanganate solutions such as "Concentrate Compact CP" and "Dosing Solution Securigans P" manufactured by Atotech Japan.

The neutralizing solution used in the desmear treatment is preferably an acidic aqueous solution, and a commercially available product is, for example, "Reduction Securigant P" manufactured by Atotech Japan. Neutralization with a neutralizing solution can be performed by immersing the surface that has been roughened with an oxidizing agent in a neutralizing solution at 30°C to 80°C for 5 to 30 minutes. From the standpoint of workability, etc., a method in which the object that has been roughened with an oxidizing agent is immersed in a neutralizing solution at 40°C to 70°C for 5 to 20 minutes is preferred.

Here, when the desmear treatment is performed after peeling off the support, the desmear treatment also serves as a roughening treatment for the exposed surface of the insulating layer. As described above, the multilayer resin sheet of the present invention is advantageous because it can provide an insulating layer with good surface smoothness, reduced smears, and well-shaped via holes even when the desmear treatment is performed after peeling off the support. Therefore, in one embodiment, the desmear treatment is performed after peeling off the support. In a preferred embodiment, step (III) is a step of forming via holes in the insulating layer with a laser, peeling off the support, and then performing the desmear treatment.

-Step (IV)-
After the desmear treatment in step (III), a metal film is formed on the surface of the insulating layer in step (IV). The formed metal film can be used as a plating seed layer to form wiring.

The thickness of the metal film (plating seed layer) may be preferably 500 nm or less, more preferably 400 nm or less, and even more preferably 300 nm or less. After a conductor layer is formed on the metal film in a desired pattern, unnecessary parts other than the conductor layer forming parts are removed by etching or the like. In this case, the thinner the metal film is, the easier it is to remove the unnecessary parts of the metal film, and the erosion of the conductor pattern when removing the unnecessary parts can be kept to a minimum, which is advantageous in realizing fine wiring.

In this regard, when a thin metal film is formed on the surface of an insulating layer, there is a tendency for the thickness of the conductor layer formed on the metal film by electrolytic plating to vary, a phenomenon known as plating burn. This is believed to be due to the fact that the thickness of the metal film is likely to be uneven due to the unevenness of the insulating layer surface. In detail, the electrical resistance value of the thin metal film is higher than that of the thick metal film, and it is believed that when a conductor layer is formed on top of this by electrolytic plating, the plating grows slower in the thin metal film and high electrical resistance parts than in other parts, resulting in insufficient formation of the conductor layer and making it difficult to form a uniform conductor layer.

In contrast, by using the multilayer resin sheet of the present invention, an insulating layer with good surface smoothness can be formed, and plating burn can be suppressed even if the thickness of the metal film is made thinner. For example, the thickness of the metal film can be reduced to 280 nm or less, 260 nm or less, or 250 nm or less.

The metal film (plating seed layer) includes at least a conductive seed layer. The conductive seed layer is a layer that functions as an electrode in an electrolytic plating method. The conductive material constituting the conductive seed layer is not particularly limited as long as it exhibits sufficient conductivity, and suitable examples include copper, palladium, gold, platinum, silver, aluminum, and alloys thereof. The metal film may also include a diffusion barrier layer. The diffusion barrier layer is a layer that prevents the conductive material constituting the conductive seed layer from diffusing into the insulating layer and causing insulation breakdown. In addition, the material constituting the diffusion barrier layer is not particularly limited as long as it can suppress or prevent the diffusion of the conductive material constituting the conductive seed layer, and suitable examples include titanium, tungsten, tantalum, and alloys thereof. When the metal film includes a diffusion barrier layer, the "thickness of the metal film" in the present invention refers to the average thickness of the entire metal film including not only the conductive seed layer but also the diffusion barrier layer.

When the metal film includes a diffusion barrier layer, the thickness of the diffusion barrier layer is not particularly limited as long as it can suppress or prevent the diffusion of the conductive material constituting the conductive seed layer, but from the viewpoint of contributing to fine wiring, it is preferably 50 nm or less, more preferably 40 nm or less, and even more preferably 30 nm or less. The lower limit of the thickness of the diffusion barrier layer is not particularly limited, and may be, for example, 1 nm or more, 3 nm or more, 5 nm or more, etc. In this case, the remainder of the metal film is preferably a conductive seed layer, and the thickness of the conductive seed layer may be determined so that the thickness of the entire metal film is in the above-mentioned preferred range in relation to the thickness of the diffusion barrier layer.

The metal film may be formed by dry plating or wet plating. Examples of dry plating include physical vapor deposition (PVD) methods such as sputtering, ion plating, and vacuum deposition, and chemical vapor deposition (CVD) methods such as thermal CVD and plasma CVD. Examples of wet plating include electroless plating. From the viewpoint of facilitating the formation of a thin metal film with a more uniform thickness, sputtering and electroless plating are preferred, and among these, sputtering is particularly preferred from the viewpoint of realizing fine wiring with excellent adhesion strength. Therefore, in a preferred embodiment, the metal film is formed by sputtering in step (IV).

After step (IV), a conductor layer can be formed on the metal film by electrolytic plating. Thus, in one embodiment, the method for producing a printed wiring board of the present invention includes, as step (V), a step of forming a conductor layer on the metal film by electrolytic plating.

The conductor material used for the conductor layer is not particularly limited. In a preferred embodiment, the conductor layer contains one or more metals selected from the group consisting of gold, platinum, palladium, silver, copper, aluminum, cobalt, chromium, zinc, nickel, titanium, tungsten, iron, tin, and indium. The conductor layer may be a single metal layer or an alloy layer, and examples of the alloy layer include layers formed from an alloy of two or more metals selected from the above group (e.g., nickel-chromium alloy, copper-nickel alloy, and copper-titanium alloy). Among these, from the viewpoints of versatility, cost, ease of patterning, etc. of the conductor layer formation, a single metal layer of chromium, nickel, titanium, aluminum, zinc, gold, palladium, silver, or copper, or an alloy layer of a nickel-chromium alloy, a copper-nickel alloy, or a copper-titanium alloy is preferred, a single metal layer of chromium, nickel, titanium, aluminum, zinc, gold, palladium, silver, or copper, or an alloy layer of a nickel-chromium alloy is more preferred, and a single metal layer of copper is even more preferred.

The conductor layer may be a single-layer structure, or a multi-layer structure in which two or more single metal layers or alloy layers made of different types of metals or alloys are laminated. When the conductor layer has a multi-layer structure, the layer in contact with the insulating layer is preferably a single metal layer of chromium, zinc, or titanium, or an alloy layer of a nickel-chromium alloy.

The thickness of the conductor layer depends on the desired printed wiring board design, but is generally between 3 μm and 35 μm, preferably between 5 μm and 30 μm.

The conductor layer may be formed by a so-called semi-additive method. That is, a photoresist (plating resist) is formed on the metal film formed in step (IV) to expose a portion of the metal film corresponding to the desired wiring pattern. Next, a conductor layer is formed on the exposed metal film by electrolytic plating, and the photoresist is then removed. Thereafter, unnecessary metal film other than the conductor layer forming portion is removed by etching or the like, and a conductor layer (wiring) having the desired wiring pattern can be formed.

By using the multilayer resin sheet of the present invention, it is possible to form fine conductor circuits with L/S of, for example, 5/5 μm or less, 4/4 μm or less, 3/3 μm or less, 2/2 μm or less, 1.5/1.5 μm or less, or 1/1 μm or less while suppressing plating burn.

If necessary, the formation of the insulating layer and the conductor layer in steps (I) to (V) may be repeated to form a multilayer wiring board.

[Semiconductor chip package]
A semiconductor chip package can be manufactured using the multilayer resin sheet of the present invention. The present invention also provides such a semiconductor chip package. The semiconductor chip package of the present invention includes an insulating layer (rewiring formation layer) for forming a rewiring layer, which is made of a cured product of the multilayer resin sheet of the present invention.

A semiconductor chip package can be manufactured, for example, by using the multilayer resin sheet of the present invention by a method including the following steps (1) to (6). The multilayer resin sheet of the present invention may be used to form the rewiring formation layer in step (5). An example of forming a rewiring formation layer using a multilayer resin sheet is shown below, but the technology for forming a rewiring formation layer for a semiconductor chip package is publicly known, and a person skilled in the art can manufacture a semiconductor package using the multilayer resin sheet of the present invention according to the publicly known technology.
(1) A step of laminating a temporary fixing film on a substrate;
(2) A step of temporarily fixing a semiconductor chip on a temporary fixing film;
(3) forming an encapsulation layer on the semiconductor chip;
(4) peeling the substrate and the temporary fixing film from the semiconductor chip;
(5) forming a rewiring formation layer as an insulating layer on the surface of the semiconductor chip from which the base material and the temporary fixing film have been peeled off; and (6) forming a rewiring layer as a conductor layer on the rewiring formation layer.

-Step (1)-
The material used for the substrate is not particularly limited. Examples of the substrate include a silicon wafer, a glass wafer, a glass substrate, a metal substrate such as copper, titanium, stainless steel, or cold-rolled steel plate (SPCC), a substrate in which glass fiber is impregnated with epoxy resin or the like and subjected to a heat curing treatment (e.g., an FR-4 substrate), and a substrate made of bismaleimide triazine resin (BT resin).

The material of the temporary fixing film is not particularly limited as long as it can be peeled off from the semiconductor chip in step (4) and can temporarily fix the semiconductor chip. Commercially available products can be used as the temporary fixing film. Examples of commercially available products include Riva Alpha manufactured by Nitto Denko Corporation.

-Step (2)-
The semiconductor chips can be temporarily fixed using known devices such as a flip chip bonder, a die bonder, etc. The layout and number of semiconductor chips can be appropriately set depending on the shape and size of the temporary fixing film, the number of semiconductor packages to be produced, etc., and for example, the semiconductor chips can be temporarily fixed by arranging them in a matrix shape of multiple rows and multiple columns.

-Step (3)-
An encapsulating resin sheet having an encapsulating resin composition layer provided on a support is laminated on a semiconductor chip, or the encapsulating resin composition is applied onto a semiconductor chip and cured (e.g., thermally cured) to form an encapsulating layer.

For example, the semiconductor chip and the encapsulating resin sheet can be laminated by heat-pressing the encapsulating resin sheet onto the semiconductor chip from the support side. The semiconductor chip and the encapsulating resin sheet can also be laminated by a vacuum lamination method, and the lamination conditions are the same as those described in relation to the method for manufacturing a printed wiring board, and the preferred ranges are also the same.

After lamination, the encapsulating resin composition layer is thermally cured to form an encapsulating layer. The thermal curing conditions are the same as those described in relation to the method for manufacturing a printed wiring board.

The support of the sealing resin sheet may be peeled off after the sealing resin sheet is laminated on the semiconductor chip and thermally cured, or the support may be peeled off before the sealing resin sheet is laminated on the semiconductor chip.

When forming a sealing layer by applying the sealing resin composition, the application conditions are the same as those for forming the resin composition layer described in relation to the manufacturing method of the multilayer resin sheet of the present invention, and the preferred ranges are also the same.

-Step (4)-
The method for peeling off the substrate and the temporary fixing film can be appropriately changed depending on the material of the temporary fixing film, and examples include a method in which the temporary fixing film is heated and foamed (or expanded) to peel it off, and a method in which ultraviolet light is irradiated from the substrate side to reduce the adhesive strength of the temporary fixing film and then peeled off.

In the method of heating and foaming (or expanding) the temporary fixing film to peel it off, the heating conditions are usually 100 to 250° C. for 1 to 90 seconds or 5 to 15 minutes. In the method of irradiating the temporary fixing film from the substrate side with ultraviolet light to reduce the adhesive strength of the temporary fixing film to peel it off, the irradiation dose of ultraviolet light is usually 10 mJ/cm ² to 1000 mJ/cm ² .

-Step (5)-
The material for forming the rewiring formation layer (insulating layer) is not particularly limited as long as it has insulating properties when the rewiring formation layer (insulating layer) is formed, and the rewiring formation layer can be formed using the multilayer resin sheet of the present invention. In step (5), the multilayer resin sheet of the present invention is laminated so that the surface opposite to the first resin composition layer is bonded to the surface of the semiconductor chip from which the substrate and the temporary fixing film have been peeled off. Thereafter, the multilayer resin sheet is cured to form the rewiring formation layer.

After forming the redistribution layer, via holes may be formed in the redistribution layer to connect the semiconductor chip to a conductor layer (described later). The via holes may be formed by a known method depending on the material of the redistribution layer.

-Step (6)-
The formation of the conductor layer on the rewiring formation layer may be carried out in the same manner as in step (V) described in relation to the method for producing a printed wiring board. Note that steps (5) and (6) may be repeated to alternately stack (build up) the conductor layer (rewiring layer) and the rewiring formation layer (insulating layer).

In manufacturing the semiconductor chip package, the steps of (7) forming a solder resist layer on the conductor layer (rewiring layer), (8) forming bumps, and (9) dicing and singulating the multiple semiconductor chip packages into individual semiconductor chip packages may be further performed. These steps may be performed according to various methods known to those skilled in the art and used in the manufacture of semiconductor chip packages.

By forming a rewiring formation layer using the multilayer resin sheet of the present invention, a semiconductor chip package can be realized regardless of whether the semiconductor package is a fan-in (Fan-In) type package or a fan-out (Fan-Out) type package. Furthermore, the multilayer resin sheet of the present invention can be applied regardless of whether it is a fan-out type panel level package (FO-PLP) or a fan-out type wafer level package (FO-WLP).

[Semiconductor device]
The semiconductor device of the present invention comprises a layer made of a cured product of the multilayer resin sheet of the present invention. The semiconductor device of the present invention can be produced by using the printed wiring board or semiconductor chip package of the present invention.

Semiconductor devices include various semiconductor devices used in electrical products (e.g., computers, mobile phones, digital cameras, and televisions) and vehicles (e.g., motorcycles, automobiles, trains, ships, and aircraft).

The present invention will be specifically explained below by giving examples and comparative examples. The present invention is not limited to the following examples.

(Thermosetting resin)
(1) Biphenyl type epoxy resin ("NC-3000" manufactured by Nippon Kayaku Co., Ltd.)
(2) Biphenyl type epoxy resin ("NC-3000-H" manufactured by Nippon Kayaku Co., Ltd.)
(3) p-Aminophenol type epoxy resin ("630" manufactured by Mitsubishi Chemical Corporation)
(4) Dicyclopentadiene type epoxy resin (DIC Corporation "HP-7200")

(Hardening agent)
(1) Aminotriazine skeleton cresol novolak resin-containing liquid (DIC Corporation's "LA-3018-50P", containing 50% by mass of non-volatile components and 50% by mass of propylene glycol monoethyl ether)
(2) Triazine skeleton phenol novolak resin-containing liquid (DIC Corporation's "LA-7054", containing 60% by mass of non-volatile components and 40% by mass of methyl ethyl ketone)
(3) Activated ester resin-containing liquid (DIC Corporation's "HPC-8000-65T", containing 65% by mass of non-volatile components and 35% by mass of toluene)

(Cure Accelerator)
(1) Imidazole compound (2-phenyl-4-methylimidazole, "2P4MZ" manufactured by Shikoku Chemical Industry Co., Ltd.)

(Thermoplastic resin)
(1) Phenoxy resin-containing liquid ("YX6954BH30" manufactured by Mitsubishi Chemical Corporation, containing 30% by mass of non-volatile components, 35% by mass of methyl ethyl ketone, and 35% by mass of cyclohexanone)
(2) Polyimide resin 1 (polyimide resin synthesized in Synthesis Example 1 below, non-volatile component 20% by mass)

(Radical Polymerizable Resin)
Maleimide resin 1 (SLK6895-T90, an aliphatic skeleton-containing maleimide resin having a structure represented by the following formula (which may contain a partial unsaturated bond), 90% by mass of non-volatile components and 10% by mass of toluene)

(Inorganic filler)
(1) Silica 1 (spherical silica obtained by surface-treating 100 parts by mass of "SO-C4" manufactured by Admatechs Co., Ltd. with 0.4 parts by mass of a silane coupling agent having an N-phenyl-3-aminopropyl group ("KBM-573" manufactured by Shin-Etsu Chemical Co., Ltd.), average particle size 1.0 μm)
(2) Silica 2 (spherical silica obtained by surface-treating 100 parts by mass of "SO-C2" manufactured by Admatechs Co., Ltd. with 0.6 parts by mass of a silane coupling agent having an N-phenyl-3-aminopropyl group ("KBM-573" manufactured by Shin-Etsu Chemical Co., Ltd.), average particle size 0.5 μm)
(3) Silica 3 (spherical silica obtained by surface-treating 100 parts by mass of "YC100C" manufactured by Admatechs Co., Ltd. with 3.0 parts by mass of a silane coupling agent having an N-phenyl-3-aminopropyl group ("KBM-573" manufactured by Shin-Etsu Chemical Co., Ltd.), average particle size 0.10 μm)

(solvent)
(1) Solvent (MEK, methyl ethyl ketone, Fujifilm Wako Pure Chemical Industries, Ltd.)

(Synthesis Example 1: Polyimide resin 1)
A monomer composition was obtained by mixing 49.6 g of 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (hereinafter also referred to as "BPADA"), 50.4 g of 4,4'-[1,4-phenylenebis[(1-methylethylidene)-4,1-phenyleneoxy]]bisbenzenamine (hereinafter also referred to as "BPPAN"), and 40 g of toluene as a solvent into 400 g of N,N-dimethylacetamide (hereinafter also referred to as "DMAc") as a solvent, and the mixture was stirred and reacted at room temperature and atmospheric pressure for 3 hours. As a result, a solution of polyamic acid was obtained.

The polyamic acid solution was then heated and, while maintained at approximately 160°C, the condensed water was removed azeotropically with toluene under a nitrogen stream. It was confirmed that the specified amount of water had accumulated in the moisture content receiver and that no water was leaking out. After this, the reaction solution was further heated and stirred at 200°C for 1 hour. It was then cooled. This resulted in a varnish containing 20% by mass of polyimide resin (hereinafter also referred to as "polyimide resin 1") as a non-volatile component.

From the above reaction pathway, it was estimated that polyimide resin 1 contains a structural unit represented by the following formula (C1a). In addition, from the above reaction pathway, it was estimated that polyimide resin 1 contains a first skeleton derived from BPADA and a second skeleton derived from BPPAN.

The glass transition temperature Tg (TMA method) of polyimide resin 1 was 210°C. Tg was measured using a Rigaku TMA device at a heating rate of 5°C/min from 25°C to 250°C.

Example 1
Biphenyl type epoxy resin ("NC-3000" manufactured by Nippon Kayaku Co., Ltd.) 25 parts by mass, bisphenol type epoxy resin ("ZX1059" manufactured by Nippon Steel Chemical & Material Co., Ltd.) 2 parts by mass, dicyclopentadiene type epoxy resin ("HP-7200" manufactured by DIC Corporation) 7 parts by mass, aminotriazine skeleton cresol novolac resin-containing liquid ("LA-3018-50P" manufactured by DIC Corporation) 5 parts by mass (non-volatile components 2.5 parts by mass), active ester resin-containing liquid ("HPC-8000-65T" manufactured by DIC Corporation) 200 parts by mass of polyimide resin (130 parts by mass of non-volatile component), 10 parts by mass of an imidazole compound ("2P4MZ" manufactured by Shikoku Chemical Industry Co., Ltd.), 10 parts by mass of a phenoxy resin-containing liquid ("YX6954BH30" manufactured by Mitsubishi Chemical Corporation) (3 parts by mass of non-volatile component), 15 parts by mass of maleimide resin (13.5 parts by mass of non-volatile component), 5 parts by mass of polyimide resin 1 (1 part by mass of non-volatile component), and 125 parts by mass of methyl ethyl ketone (MEK) were mixed and stirred at room temperature until a homogeneous solution was obtained, thereby obtaining a resin composition varnish A.

Formation of outer layer (first resin composition layer; layer that becomes the outer layer after lamination):
The obtained resin composition varnish A was mixed with 130 parts by mass of silica 3 (spherical silica obtained by surface-treating 100 parts by mass of "YC100C" manufactured by Admatechs Co., Ltd. with 3.0 parts by mass of a silane coupling agent having an N-phenyl-3-aminopropyl group ("KBM-573" manufactured by Shin-Etsu Chemical Co., Ltd.), and the mixture was stirred at room temperature until a homogeneous solution was obtained, thereby obtaining a resin composition varnish B.

The obtained resin composition varnish B was applied to the release-treated surface of a PET film (thickness 38 μm) using an applicator, and then dried in a gear oven at 170°C for 180 seconds to volatilize the solvent. In this way, a sheet-like molded product A (outer layer; first resin composition layer) with a thickness of 2 μm was obtained on the PET film.

Formation of inner layer (layers other than the first resin composition layer; layers that become the inner layer after lamination): Formation method 1
-Lamination by coating 20 parts by mass of biphenyl type epoxy resin ("NC-3000" manufactured by Nippon Kayaku Co., Ltd.), 3 parts by mass of bisphenol type epoxy resin ("ZX1059" manufactured by Nippon Steel Chemical & Material Co., Ltd.), 10 parts by mass of dicyclopentadiene type epoxy resin ("HP-7200" manufactured by DIC Corporation), 15 parts by mass of aminotriazine skeleton cresol novolac resin-containing liquid ("LA-3018-50P" manufactured by DIC Corporation) (7.5 parts by mass of non-volatile components), active ester resin-containing liquid (DIC A resin composition varnish C was obtained by mixing 80 parts by mass (52 parts by mass of non-volatile component) of an imidazole compound (2P4MZ manufactured by Shikoku Chemical Industry Co., Ltd.), 2 parts by mass of a phenoxy resin-containing liquid (YX6954BH30 manufactured by Mitsubishi Chemical Corporation) (1.5 parts by mass of non-volatile component), 5 parts by mass of polyimide resin 1 (1 part by mass of non-volatile component), and 200 parts by mass of methyl ethyl ketone (MEK). The mixture was stirred at room temperature until a homogeneous solution was obtained, and a resin composition varnish C was obtained.

The obtained resin composition varnish C was mixed with 290 parts by mass of silica 2 (spherical silica surface-treated with 100 parts by mass of "SO-C2" manufactured by Admatechs Co., Ltd. and 0.6 parts by mass of a silane coupling agent having an N-phenyl-3-aminopropyl group ("KBM-573" manufactured by Shin-Etsu Chemical Co., Ltd.) and stirred at room temperature until a homogeneous solution was obtained, to obtain resin composition varnish D.

Then, the obtained resin composition varnish D was applied onto the obtained sheet-like molded body A so that the total thickness was 40 μm, and then it was dried in a gear oven at 100°C for 2 minutes to evaporate the solvent. In this way, a sheet-like molded body C (inner layer; layers excluding the first resin composition layer) having a thickness of 38 μm was formed on the sheet-like molded body A, and a multilayer resin sheet B having a thickness of 40 μm was obtained. The multilayer resin sheet B has a layer structure of sheet-like molded body C/sheet-like molded body A/support.

[Preparation of Evaluation Substrate]
(1) Preparation of inner layer substrate The copper foil on both sides of a glass cloth-based epoxy resin double-sided laminate (copper foil thickness 18 μm, substrate thickness 0.3 mm, size 500 mm x 500 mm, Panasonic "R5715ES") on which an inner layer circuit was formed was etched to produce 25 copper patterns with L/S of 1 mm/1 mm and length of 5 cm, to obtain a textured substrate. The copper surface was then roughened by etching 1 μm using MEC's "CZ8100".

(2) Lamination of multilayer resin sheet to inner layer substrate The obtained multilayer resin sheet B was placed on the substrate surface from the sheet-like molded body C side, and laminated on both sides of the inner layer circuit substrate using a batch type vacuum pressure laminator (Nichigo-Morton Co., Ltd. 2-stage build-up laminator CVP700) so that the sheet-like molded body C was in contact with the inner layer circuit substrate. The lamination was performed by reducing the pressure for 30 seconds to 13 hPa or less, and then pressing at 100°C and a pressure of 0.74 MPa for 30 seconds. Next, a heat press was performed at 100°C and a pressure of 0.5 MPa for 60 seconds.

(3) Curing of the Multilayer Resin Sheet The laminated multilayer resin sheet with the support was heated at 100° C. for 30 minutes and then at 170° C. for 30 minutes to thermally cure the multilayer resin sheet and form an insulating layer. The obtained laminate sample is referred to as “Laminate Sample D”.

(4) Formation of via holes Using a CO2 _laser processing machine "LC-2E21B/1C" manufactured by Hitachi Via Mechanics, laminate sample D was drilled to form via holes in the insulating layer. The top diameter (diameter) of the via hole on the insulating layer surface was 50 μm. The conditions for drilling were mask diameter 1.60 mm, focus offset value 0.050, pulse width 25 μs, energy 0.33 mJ/shot (output 0.66 W, frequency 2000 Hz), aperture 13, number of shots 2, and burst mode.
Next, the support was peeled off from the laminate sample D in which the vias were formed.

(5) Desmear Treatment A desmear treatment was carried out on the laminate sample D having vias formed therein according to the following procedure.

Swelling treatment:
The laminate sample D with the vias formed therein was placed in a swelling liquid at 60° C. (Atotech Japan's "Swelling Dip Securigant P", an aqueous solution of diethylene glycol monobutyl ether and sodium hydroxide) and swung for 10 minutes at a swelling temperature of 60° C. Thereafter, the laminate sample D was washed with pure water.

Roughening treatment:
The swollen laminated sample was placed in an oxidant solution at 80° C. (Atotech Japan's "Concentrate Compact CP", an aqueous solution containing potassium permanganate at a concentration of approximately 6% and sodium hydroxide at a concentration of approximately 4%) and was shaken at a roughening temperature of 80° C. for 20 minutes.

Neutralization process:
Thereafter, the laminated sample was washed with a neutralizing solution (Reduction Securigant P, an aqueous sulfuric acid solution, manufactured by Atotech Japan) at 40° C. for 10 minutes, and then further washed with pure water. The obtained laminated sample is referred to as “Laminated Sample E”.

[Measurement of surface roughness]
For laminate sample E, the Ra value was determined using a non-contact surface roughness meter (WYKO NT3300 manufactured by Beco Instruments) in VSI mode with a 50x lens over a measurement range of 121 μm x 92 μm. The measured value was determined by averaging 10 randomly selected points. The surface roughness was determined based on the arithmetic mean roughness (Ra) and the following criteria.

Criteria for arithmetic mean roughness (Ra):
⊚: arithmetic mean roughness (Ra) is less than 30 nm; ◯: arithmetic mean roughness (Ra) is 30 nm or more and less than 50 nm; ×: arithmetic mean roughness (Ra) is 50 nm or more

[Measurement of Etching Rate]
The obtained resin composition varnish B was applied to the release-treated surface of a PET film (thickness 38 μm) using an applicator, and then dried in a gear oven at 100 ° C. for 2 minutes to volatilize the solvent. In this way, a sheet-shaped molded body A' having a thickness of 38 μm was obtained on the PET film. Separately, a sheet-shaped molded body C' having a thickness of 38 μm was obtained on the PET film in the same manner, except that the resin composition varnish D was used.
Next, the sheet-form molded products A' and C' were each heated at 100° C. for 30 minutes and then at 170° C. for 30 minutes to obtain cured products A' and C'.
The masses of the obtained cured bodies A' and C' were each measured.

Next, the obtained cured bodies A' and C' were subjected to the swelling treatment, roughening treatment, and neutralization treatment in the same manner as described in the above "(5) Desmear treatment", and thus a desmear treatment was carried out. In this way, desmeared cured bodies A" and C" were obtained.
The masses of the cured bodies A″ and C″ after the desmear treatment were measured.

The masses of the obtained cured bodies A', C', A", and C" were used to calculate the etching rate RA by desmearing the cured product of the first resin composition layer and the etching rate RD by desmearing the cured product of the resin composition layer, which is the outermost layer on the opposite side to the first resin composition layer, based on the following formula.

Etching rate RA=100×(mass of A'-mass of A")/mass of A' Etching rate RD=100×(mass of C'-mass of C")/mass of C'

<Evaluation of smear removal ability>
The periphery of the bottom of the via hole was observed with a scanning electron microscope (SEM), and the maximum smear length from the wall surface of the bottom of the via hole was measured from the obtained image. The smear removability was evaluated according to the following criteria.
Evaluation criteria:
○: The maximum smear length is less than 2 μm. ×: The maximum smear length is 2 μm or more.

<Evaluation of the cross-sectional shape of via holes>
The cross section of the via hole was cut out by FIB and observed by a scanning electron microscope (SEM), and the maximum via diameter R1 in the insulating layer portion derived from the first resin composition layer and the maximum via diameter R2 in the insulating layer portion derived from the layer other than the first resin composition layer were measured from the obtained image. The cross-sectional shape of the via hole was evaluated according to the following criteria.

Evaluation criteria:
○: R1≧R2
×: R1<R2

<Evaluation of film thickness change before and after desmear treatment>
Cross sections of laminate sample D (after thermal curing) and laminate sample E (after desmearing) were cut out using an FIB, the insulating layer was observed using a scanning electron microscope (SEM), and the thickness of the insulating layer portion derived from the first resin composition layer was measured from the obtained image. Then, based on the difference between the thickness of the insulating layer portion derived from the first resin composition layer in laminate sample D and the thickness of the insulating layer portion derived from the first resin composition layer in laminate sample E, evaluation was performed according to the following criteria.

Evaluation criteria:
◎: Thickness difference is less than 0.5 μm. ○: Thickness difference is 0.5 μm or more and less than 1.0 μm. ×: Thickness difference is 1.0 μm or more.

Example 2
A sample was produced and evaluated in the same manner as in Example 1, except that the method for forming the inner layer was changed to Formation Method 2 below, and the resulting multilayer resin sheet B' was used.

Formation of inner layer: Formation method 2 - Lamination by lamination Using an applicator, the obtained resin composition varnish D was applied onto a release-treated surface of a PET film (thickness 38 μm), and then dried for 2 minutes in a gear oven at 100° C. to volatilize the solvent. In this way, a sheet-like molded product C having a thickness of 38 μm was obtained on the PET film.

The sheet-like molded body A and the sheet-like molded body C were laminated with their coated surfaces overlapping each other using a vacuum pressure laminator ("MVLP-500" manufactured by Meiki Seisakusho) at a pressure of 0.4 MPa and a temperature of 100°C for 60 seconds to obtain a multilayer resin sheet B'.

(Examples 3 to 5 and Comparative Examples 1 to 3)
Samples were prepared and evaluated in the same manner as in Example 1, except that the compositions of the outer layer and the inner layer were changed as shown in Table 1.

Claims (11)

A multilayer resin sheet having two or more resin composition layers including a first resin composition layer which is an outermost layer on one side and a layer other than the first resin composition layer,
an etching rate by a desmear treatment of a cured product of the first resin composition layer is defined as RA, and an etching rate by a desmear treatment of a cured product of the resin composition layer that is the outermost layer on the opposite side to the first resin composition layer is defined as RD, RD/RA is 5 or more and less than 100,
A multilayer resin sheet, wherein the arithmetic mean roughness Ra of a cured product of a first resin composition layer after a desmear treatment is less than 50 nm. The multilayer resin sheet according to claim 1, in which D1 is the average particle size (μm) of the inorganic filler in the first resin composition layer, and D2 is the average particle size (μm) of the inorganic filler in the layers other than the first resin composition layer, and D1 < D2. The multilayer resin sheet according to claim 1, wherein the content of the inorganic filler in the first resin composition layer is 5% by mass or less, when the non-volatile components in the first resin composition layer are taken as 100% by mass. The multilayer resin sheet according to claim 1, having an etching rate RA of 0.1% or more and less than 1%. The multilayer resin sheet according to claim 1, in which t<(T-t) is satisfied, where T is the thickness (μm) of the multilayer resin sheet and t is the thickness (μm) of the first resin composition layer. The multilayer resin sheet according to claim 1, which is used by laminating it on a member to be laminated so that the surface opposite to the first resin composition layer is bonded to the member to be laminated. The multilayer resin sheet according to claim 1, which is used as an insulating layer for a printed wiring board. A multilayer resin sheet with a support, comprising the multilayer resin sheet according to any one of claims 1 to 7 and a support bonded to the first resin composition layer of the multilayer resin sheet. A method for producing a printed wiring board, comprising the following steps (I) to (IV):
(I) a step of laminating the multilayer resin sheet according to any one of claims 1 to 7 on an inner layer substrate so that the surface of the multilayer resin sheet opposite to the first resin composition layer is bonded to the inner layer substrate; (II) a step of curing the multilayer resin sheet to form an insulating layer; (III) a step of forming via holes in the insulating layer by a laser and performing a desmear treatment; and (IV) a step of forming a metal film on the surface of the insulating layer after the desmear treatment. A printed wiring board comprising an insulating layer made of a cured product of the multilayer resin sheet according to any one of claims 1 to 7. A semiconductor device including the printed wiring board according to claim 10.