JP7484422B2 - Prepreg, laminate, metal-clad laminate and semiconductor package, and method for manufacturing laminate and metal-clad laminate - Google Patents

Description

The present invention relates to prepregs, laminates, metal-clad laminates and semiconductor packages, as well as methods for manufacturing laminates and metal-clad laminates.

In recent years, with the advancement of higher wiring density and higher integration in printed wiring boards, warping caused by the difference in thermal expansion coefficient between the chip and the board during component mounting and package assembly has become a major issue, especially in semiconductor package substrate applications. Warping is considered to be one of the factors that cause poor connections between semiconductor elements and printed wiring boards, and there is a demand to reduce it.

One of the factors that causes semiconductor packages to warp is the difference in the thermal expansion coefficient between the semiconductor element and the printed wiring board. Generally, the thermal expansion coefficient of the printed wiring board is greater than that of the semiconductor element, so stress is generated due to the thermal history applied when mounting the semiconductor element, resulting in warping. Therefore, in order to prevent semiconductor packages from warping, it is necessary to reduce the thermal expansion coefficient of the printed wiring board and reduce the difference with the thermal expansion coefficient of the semiconductor element.

It is generally known that the thermal expansion coefficient of a prepreg obtained by impregnating a glass cloth with a resin composition follows the Scapery equation shown below.
A≈(ArErFr+AgEgFg)/(ErFr+EgFg)
(In the above formula, A represents the thermal expansion coefficient of the prepreg, Ar represents the thermal expansion coefficient of the resin composition, Er represents the elastic modulus of the resin composition, Fr represents the volume fraction of the resin composition, Ag represents the thermal expansion coefficient of the glass cloth, Eg represents the elastic modulus of the glass cloth, and Fg represents the volume fraction of the glass cloth.)
From the above Scampery equation, it is considered that when glass cloth having the same physical properties is used at any volume fraction, it is possible to reduce the thermal expansion of the prepreg by reducing the elastic modulus and thermal expansion coefficient of the resin composition.

As a material with excellent low thermal expansion properties, a resin composition containing a modified imide resin obtained by modifying a polybismaleimide resin with a siloxane compound has been investigated (see, for example, Patent Document 1). On the other hand, in order to make products using printed wiring boards less likely to catch fire, a flame retardant has been blended into the prepreg contained in the printed wiring board. However, the incorporation of the flame retardant reduces adhesion to the metal foil, causing peeling at the interface between the metal foil and the resin layer, and it has not been easy to achieve both flame retardancy and adhesion to the metal foil.

JP 2014-129521 A

Furthermore, the inventors' research led them to try to increase the flame retardancy of the laminate or metal-clad laminate while also improving adhesion to the metal foil by using a highly flame-retardant prepreg such as that described in Patent Document 1 only inside the laminate and using a prepreg with high adhesion to the metal foil on the surface. However, they encountered a problem in that the laminate and metal-clad laminate themselves were prone to warping due to the difference in thermal expansion coefficients between the prepregs, which have different compositions, being in contact with each other.

In view of the current situation, the object of the present invention is to provide a laminate or metal-clad laminate that has high flame retardancy, high adhesion to metal foil, and suppressed warping, to provide a prepreg that can provide such a laminate or metal-clad laminate, to provide a printed wiring board that contains the laminate or metal-clad laminate, and to provide a method for producing such a laminate or metal-clad laminate.

As a result of intensive research into achieving the above object, the present inventors have found that the above problems can be solved by the following invention, and have completed the present invention.
That is, the present invention provides the following [1] to [9].
[1] A prepreg having a fiber substrate layer containing a fiber substrate, a first resin layer formed on one surface of the fiber substrate layer, and a second resin layer formed on the other surface of the fiber substrate layer;
The first resin layer is an adhesion layer 1 formed by forming a layer of a resin composition (I) containing a thermosetting resin,
The second resin layer is a flame-retardant layer 2 formed by forming a layer of a flame-retardant resin composition (II).
[2] The prepreg according to the above-mentioned [1], wherein the flame-retardant resin composition (II) contains a flame retardant in an amount of 0.5 to 5 mass% based on the resin component.
[3] The prepreg according to the above [1] or [2], wherein the resin composition (I) does not contain a flame retardant, or even if it contains a flame retardant, the content thereof is less than 0.5 mass% based on the resin component.
[4] A laminate obtained by laminating and molding the prepreg according to any one of [1] to [3] above,
A laminate in which identical layers are laminated so as to face each other, and the surface is the adhesion layer 1.
[5] A metal-clad laminate having a metal foil on the surface of the laminate described in [4] above.
[6] A printed wiring board comprising the laminate according to [4] above or the metal-clad laminate according to [5] above.
[7] A semiconductor package comprising the printed wiring board according to [6] above and a semiconductor element mounted thereon.
[8] A method for producing a laminated board by laminating and molding the prepregs according to any one of [1] to [3] above so that the same layers face each other and the surface becomes the adhesion layer 1.
[9] A method for producing a metal-clad laminate by laminating and molding the prepregs according to any one of [1] to [3] above so that the same layers face each other and the adhesion layer 1 is in contact with a metal foil.

According to the present invention, it is possible to provide a laminate or metal-clad laminate that has high flame retardancy, high adhesion to metal foil, and suppressed warping, to provide a prepreg that can provide such a laminate or metal-clad laminate, to provide a printed wiring board that contains the laminate or metal-clad laminate, and to provide a method for manufacturing such a laminate or metal-clad laminate.

FIG. 1 is a schematic cross-sectional view of a prepreg of the present invention. FIG. 2 is a schematic diagram for explaining the thickness of each layer of the prepreg of the present invention. FIG. 2 is a schematic diagram showing how prepregs are layered when producing a copper-clad laminate in Example 1. FIG. 2 is a schematic diagram showing how prepregs are layered when producing a copper-clad laminate in Comparative Example 1. FIG. 1 is a schematic diagram showing how prepregs are layered when producing a copper-clad laminate in Comparative Example 2. FIG. 4 is a schematic diagram showing how prepregs are layered when producing a copper-clad laminate in Example 2. FIG. 2 is a schematic diagram showing how prepregs are layered when producing a copper-clad laminate in Reference Example 1. FIG. 1 is a schematic diagram showing how prepregs are layered when producing a copper-clad laminate in Comparative Example 3.

[Prepreg]
As shown in Figs. 1 and 2, the prepreg of the present invention is a prepreg 100 having a fiber substrate layer 10 containing a fiber substrate 11, a first resin layer 1 formed on one surface of the fiber substrate layer 10, and a second resin layer 2 formed on the other surface of the fiber substrate layer 10.
The first resin layer 1 is an adhesion layer 1 formed by forming a layer of a resin composition (I) containing a thermosetting resin,
The present invention relates to a prepreg, wherein the second resin layer 2 is a flame-retardant layer 2 formed by forming a layer of a flame-retardant resin composition (II).
As described later, a portion of the fiber base material layer 10 is typically impregnated with the first resin layer 1 (adhesion layer 1) on the side in contact with the first resin layer 1 (adhesion layer 1), and is impregnated with the second resin layer 2 (flame-retardant layer 2) on the side in contact with the second resin layer 2 (flame-retardant layer 2).

The mechanism by which the prepreg of the present invention provides a laminate or metal-clad laminate having high flame retardancy, high adhesion to metal foil, and suppressed warping is presumed to be as follows.
The prepreg of the present invention has a first resin layer (adhesion layer) formed by forming a layer of a resin composition (I) containing a thermosetting resin, which has excellent adhesion to metal foil, on one side of a fiber substrate layer. Therefore, by making the adhesion layer the outermost layer of a laminate, a laminate or metal-clad laminate having excellent adhesion to metal foil is obtained.
On the other hand, the prepreg of the present invention has a flame-retardant layer 2, which is a second resin layer, on the other surface of the fiber base material layer. It is considered that the presence of the flame-retardant layer 2 inside the laminate or metal-clad laminate imparts sufficient flame retardancy to the laminate or metal-clad laminate.
Furthermore, the presence of layers with different compositions makes the laminate or metal-clad laminate more susceptible to warping due to differences in the thermal expansion coefficients of those layers, but in the present invention, since the prepreg has the adhesion layer and the flame-retardant layer on either side of the fiber base layer, it is believed that the influence of distortion caused by the difference in the thermal expansion coefficients of the upper and lower layers of the fiber base layer is eliminated or reduced when manufacturing the laminate or metal-clad laminate, and the occurrence of warping is suppressed. As a result, it is believed that a laminate or metal-clad laminate having high flame retardancy, high adhesion to metal foil, and suppressed warping can be provided.

<Fiber Base Layer>
The fiber substrate layer is a layer that contains a fiber substrate.
As the fiber substrate, well-known materials used in various laminates for electrical insulating materials can be used. Examples of the material of the fiber substrate include natural fibers such as paper and cotton linters; inorganic fibers such as glass fibers and asbestos; organic fibers such as aramid, polyimide, polyvinyl alcohol, polyester, tetrafluoroethylene, and acrylic; and mixtures thereof. Among these, glass fibers are preferred from the viewpoint of flame retardancy. As the substrate using glass fibers, glass cloth is preferred, and examples thereof include glass cloth using E glass, C glass, D glass, S glass, etc., or glass cloth in which short fibers are bonded with an organic binder; glass cloth in which glass fibers and cellulose fibers are mixed, etc. Among these, glass cloth using E glass is more preferred.
These fiber substrates have the form of woven fabric, nonwoven fabric, roving, chopped strand mat, surfacing mat, and the like.
The material and shape of the fiber substrate are appropriately selected depending on the intended use, performance, etc. of the molded product. One type may be used alone, or two or more types of materials and shapes may be combined as necessary.
The thickness of the fiber substrate is, for example, 10 μm to 0.5 mm, and from the viewpoint of ease of handling and enabling high-density wiring, is preferably 10 to 100 μm, more preferably 11 to 50 μm, even more preferably 12 to 30 μm, and particularly preferably 13 to 25 μm. When two or more types of fiber substrates are used, the thickness of the fiber substrate is the total value of the thicknesses of the two or more types of fiber substrates.
The fiber substrate may be a single-layer fiber substrate or a multi-layer fiber substrate.
Here, a fiber substrate consisting of one layer means a fiber substrate consisting of only entangled fibers, and when a fiber substrate that is not entangled exists, it is classified as a fiber substrate consisting of multiple layers.
From the viewpoints of heat resistance, moisture resistance, processability, etc., these fiber substrates may be surface-treated with a silane coupling agent or the like, or may be mechanically opened.

The fibrous substrate layer usually contains a resin composition. That is, the fibrous substrate layer usually contains a fibrous substrate and a resin composition impregnated into the fibrous substrate.
Examples of the resin composition contained in the fiber substrate layer include resin composition (I), resin composition (II), and mixtures thereof, which will be described later.
The prepreg of the present invention has a first resin layer on one side and a second resin layer on the other side, but usually, the resin composition (I) forming the first resin layer is also present in the interior of the fiber substrate layer continuously from the first resin layer, and the resin composition (II) forming the second resin layer is also present in the interior of the fiber substrate layer continuously from the second resin layer. In addition, a mixture in which the resin composition (I) and the resin composition (II) are in contact with each other may be present. However, the prepreg of the present invention is not limited to this embodiment, and may have a fiber substrate layer containing a third resin composition different from the resin composition (I) and the resin composition (II), and may have a first resin layer on one side and a second resin layer on the other side. The third resin composition in that case can be a known resin composition used in prepregs, but in the present invention, it is preferable that the fiber substrate layer does not contain the third resin composition.
The content (total content) of the resin composition contained in the fiber substrate layer is preferably from 40 to 90% by mass, more preferably from 60 to 85% by mass, and even more preferably from 65 to 80% by mass.

From the viewpoints of ease of handling and enabling high-density wiring, the thickness of the fiber base material layer is preferably 10 to 100 μm, more preferably 11 to 50 μm, further preferably 12 to 30 μm, and particularly preferably 13 to 25 μm.
Here, the thickness of the fiber substrate layer means the thickness shown by region B containing the fiber substrate in a cross section perpendicular to the planar direction of the prepreg shown in Fig. 2. The thickness of the fiber substrate layer can be determined by, for example, exposing the cross section of the prepreg by a known method such as mechanical polishing or ion milling, observing it with a scanning electron microscope (SEM), measuring the thickness of the fiber substrate layer at any 10 points, and averaging the measured values.

<First Resin Layer>
The first resin layer is a layer formed on one surface of the fiber base material layer, and is a layer formed of a resin composition (I) containing a thermosetting resin.
The thickness of the first resin layer is not particularly limited, but is, for example, 5 to 50 μm, preferably 5 to 30 μm, more preferably 8 to 20 μm, further preferably 8 to 15 μm, and particularly preferably 8 to 13 μm.
Here, the thickness of the first resin layer means the thickness of the region a1 not containing the fiber base material in the cross section perpendicular to the planar direction of the prepreg shown in Fig. 2, and for convenience, the portion of the first resin layer impregnated in the fiber base material layer is not taken into consideration. The thickness of the first resin layer can be measured by the same method as the thickness of the fiber base material layer.

[Resin composition (I)]
The resin composition (I) contains a thermosetting resin. Hereinafter, examples of each component that may be contained in the resin composition (I) will be described.

(Thermosetting Resin (a))
Examples of the thermosetting resin (a) include epoxy resins, phenolic resins, unsaturated imide resins (but not including the component (c) described below), cyanate resins, isocyanate resins, benzoxazine resins, oxetane resins, amino resins (but not including the component (b) described below), unsaturated polyester resins, allyl resins, dicyclopentadiene resins, silicone resins, triazine resins, melamine resins (but not including the component (b) described below), etc. Among these, from the viewpoints of moldability and electrical insulation, and adhesive strength with a metal circuit, one or more types selected from the group consisting of epoxy resins and cyanate resins are preferred, and epoxy resins are more preferred.
As the thermosetting resin (a), one type may be used alone, or two or more types may be used in combination.

Examples of epoxy resins include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, α-naphthol/cresol novolac type epoxy resins, bisphenol A novolac type epoxy resins, bisphenol F novolac type epoxy resins, stilbene type epoxy resins, triazine skeleton-containing epoxy resins, fluorene skeleton-containing epoxy resins, triphenol methane type epoxy resins, biphenyl type epoxy resins, xylylene type epoxy resins, biphenyl aralkyl type epoxy resins, naphthalene type epoxy resins, dicyclopentadiene type epoxy resins, alicyclic epoxy resins, diglycidyl ether compounds of polyfunctional phenols and polycyclic aromatics such as anthracene, and phosphorus-containing epoxy resins in which phosphorus compounds are introduced into these. These may be used alone or in combination of two or more. Among these, biphenyl aralkyl type epoxy resins and α-naphthol/cresol novolac type epoxy resins are preferred from the viewpoint of heat resistance and flame retardancy.

The content of the thermosetting resin (a) in the resin composition (I) is not particularly limited, but is preferably 1 to 30 parts by mass, more preferably 5 to 25 parts by mass, and even more preferably 10 to 20 parts by mass, per 100 parts by mass of the resin component in the resin composition (I).
In this specification, the term "resin component" does not include inorganic compounds such as an inorganic filler (f) described below, but includes a thermosetting resin (a), an amine compound (b) described below, a maleimide compound (c) described below, a (meth)acrylic elastomer (d) and a curing accelerator (e) described below, and other organic components that may be contained as necessary.

(Amine compound (b) having at least two primary amino groups)
The amine compound (b) is not particularly limited as long as it is an amine compound having at least two primary amino groups.
The amine compound (b) is preferably an amine compound having two primary amino groups, and more preferably a diamine compound represented by the following general formula (b-1).

(In general formula (b-1), X ^b1 is a group represented by the following general formula (b1-1), (b1-2) or (b1-3).)

(In general formula (b1-1), each R ^b1 is independently an aliphatic hydrocarbon group having 1 to 5 carbon atoms or a halogen atom. p is an integer of 0 to 4.)

(In general formula (b1-2), R ^b2 and R ^b3 each independently represent an aliphatic hydrocarbon group having 1 to 5 carbon atoms or a halogen atom. X ^b2 represents an alkylene group having 1 to 5 carbon atoms, an alkylidene group having 2 to 5 carbon atoms, an ether group, a sulfide group, a sulfonyl group, a carbonyloxy group, a keto group, a single bond, or a group represented by the following general formula (b1-2-1). q and r each independently represent an integer of 0 to 4.)

(In general formula (b1-2-1), R ^b4 and R ^b5 each independently represent an aliphatic hydrocarbon group having 1 to 5 carbon atoms or a halogen atom. X ^b3 each independently represents an alkylene group having 1 to 5 carbon atoms, an alkylidene group having 2 to 5 carbon atoms, an ether group, a sulfide group, a sulfonyl group, a carbonyloxy group, a keto group, or a single bond. s and t each independently represent an integer of 0 to 4.)

(In general formula (b1-3), R ^b6 , R ^b7 , R ^b8 , and R ^b9 each independently represent an alkyl group having 1 to 5 carbon atoms, a phenyl group, or a substituted phenyl group. X ^b4 and X ^b5 each independently represent a divalent organic group, and u is an integer of 2 to 100.)

In the general formula (b1-1), examples of the aliphatic hydrocarbon group represented by R ^b1 include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, an n-pentyl group, etc. The aliphatic hydrocarbon group is preferably an aliphatic hydrocarbon group having 1 to 3 carbon atoms, more preferably a methyl group. In addition, examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.
Among the above, R ^b1 is preferably an aliphatic hydrocarbon group having 1 to 5 carbon atoms.
p is an integer of 0 to 4, and from the viewpoint of availability, is preferably an integer of 0 to 2, and more preferably 2. When p is an integer of 2 or more, multiple R ^b1 may be the same or different.

In general formula (b1-2), examples of the aliphatic hydrocarbon group having 1 to 5 carbon atoms and the halogen atom represented by R ^b2 and R ^b3 include the same as those for R ^b1 . The aliphatic hydrocarbon group is preferably an aliphatic hydrocarbon group having 1 to 3 carbon atoms, more preferably a methyl group or an ethyl group, and even more preferably an ethyl group.
Examples of the alkylene group having 1 to 5 carbon atoms represented by X ^b2 include a methylene group, a 1,2-dimethylene group, a 1,3-trimethylene group, a 1,4-tetramethylene group, a 1,5-pentamethylene group, etc. From the viewpoints of heat resistance and low thermal expansion, the alkylene group is preferably an alkylene group having 1 to 3 carbon atoms, and more preferably a methylene group.
Examples of the alkylidene group having 2 to 5 carbon atoms represented by X ^b2 include an ethylidene group, a propylidene group, an isopropylidene group, a butylidene group, an isobutylidene group, a pentylidene group, an isopentylidene group, etc. Among these, an isopropylidene group is preferred from the viewpoints of heat resistance and low thermal expansion.
Among the above options, X ^b2 is preferably an alkylene group having 1 to 5 carbon atoms, or an alkylidene group having 2 to 5 carbon atoms. More preferred ones are as described above.
Each of q and r is independently an integer of 0 to 4, and from the viewpoint of availability, each is preferably an integer of 0 to 2, more preferably 0 or 2. When q or r is an integer of 2 or more, multiple R ^b2s or multiple R ^b3s may be the same or different.

In the general formula (b1-2-1), examples of the aliphatic hydrocarbon group having 1 to 5 carbon atoms and the halogen atom represented by R ^b4 and R ^b5 include the same as those in the case of R ^b2 and R ^b3 , and the preferred examples are also the same.
Examples of the alkylene group having 1 to 5 carbon atoms and the alkylidene group having 2 to 5 carbon atoms represented by X ^b3 include the same as the alkylene group having 1 to 5 carbon atoms and the alkylidene group having 2 to 5 carbon atoms represented by X ^b2 , and the preferred examples are also the same.
Among the above options, X ^b3 is preferably an alkylidene group having 2 to 5 carbon atoms, and more preferably, the same as described above.
Each of s and t is an integer of 0 to 4, and from the viewpoint of availability, each is preferably an integer of 0 to 2, more preferably 0 or 1, and further preferably 0. When s or t is an integer of 2 or more, multiple R ^b4s or multiple R ^b5s may be the same or different.
The general formula (b1-2-1) is preferably represented by the following general formula (b1-2-1').

(X ^b3 , R ^b4 , R ^b5 , s and t in general formula (b1-2-1') are the same as those in general formula (b1-2-1), and the preferred ones are also the same.)

The group represented by general formula (b1-2) is preferably a group represented by the following general formula (b1-2'), more preferably a group represented by any of the following formulas (b1-i) to (b1-iii), and even more preferably a group represented by the following formula (b1-ii) or (b1-iii).

(X ^b2 , R ^b2 , R ^b3 , q and r in general formula (b1-2') are the same as those in general formula (b1-2), and the preferred ones are also the same.)

Examples of the alkyl group having 1 to 5 carbon atoms represented by R ^b6 , R ^b7 , R ^b8 and R ^b9 in general formula (b1-3) include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, an n-pentyl group, etc. As the alkyl group, an alkyl group having 1 to 3 carbon atoms is preferable, and a methyl group is more preferable.
Examples of the substituent that the phenyl group has in the substituted phenyl group include an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, and an alkynyl group having 2 to 5 carbon atoms. Examples of the alkyl group having 1 to 5 carbon atoms include the same as those described above. Examples of the alkenyl group having 2 to 5 carbon atoms include a vinyl group and an allyl group. Examples of the alkynyl group having 2 to 5 carbon atoms include an ethynyl group and a propargyl group.
Each of R ^b6 , R ^b7 , R ^b8 and R ^b9 is preferably an alkyl group having 1 to 5 carbon atoms, and more preferably a methyl group.
Examples of the divalent organic group represented by X ^b4 and X ^b5 include an alkylene group, an alkenylene group, an alkynylene group, an arylene group, -O-, or a divalent linking group formed by combining these. Examples of the alkylene group include alkylene groups having 1 to 10 carbon atoms, such as a methylene group, an ethylene group, or a propylene group. Examples of the alkenylene group include alkenylene groups having 2 to 10 carbon atoms. Examples of the alkynylene group include alkynylene groups having 2 to 10 carbon atoms. Examples of the arylene group include arylene groups having 6 to 20 carbon atoms, such as a phenylene group or a naphthylene group.

In the general formula (b-1), X ^b1 may be any of the groups represented by the general formulas (b1-1), (b1-2) and (b1-3). Among these, from the viewpoints of low thermal expansion and adhesive strength with a metal circuit, it is preferably a group represented by general formula (b1-3).

Specific examples of component (b) include diaminobenzidine, diaminodiphenylmethane, diaminodiphenyl ether, diaminodiphenyl sulfone, 3,3'-dichloro-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl-6,6'-disulfonic acid, 2,2',5,5'-tetrachloro-4,4'-diaminobiphenyl, 4,4'-methylene-bis(2-chloroaniline), 1,3'-bis(4-aminophenoxy)benzene, and 2,2'-bis[4-(4-aminophenoxy)phenyl]. Examples of the modified siloxane include propane, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, 4,4'-bis(4-aminophenoxy)biphenyl, 2,2'-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 1,4'-bis(4-aminophenoxy)benzene, 4,4'-diaminodiphenyl sulfide, 2,2'-dimethyl-4,4'-diaminobiphenyl, 4,4'-diamino-3,3'-biphenyldiol, 9,9'-bis(4-aminophenyl)fluorene, o-tolidine sulfone, and modified siloxane compounds having primary amino groups at the molecular terminals. Among these, modified siloxane compounds having primary amino groups at the molecular terminals are preferred from the viewpoints of heat resistance, desmear resistance, low thermal expansion, and adhesive strength with metal circuits.

The modified siloxane compound having a primary amino group at the molecular terminal is preferably a modified siloxane compound having primary amino groups at both molecular terminals (hereinafter also referred to as a "dual-terminal diamine-modified siloxane"), and more preferably a compound having a group represented by the general formula (b1-3) as X ^b1 in the general formula (b-1).
As the diamine-modified siloxane at both ends, commercially available products can be used. For example, modified siloxane compounds having primary amino groups at both ends, such as "PAM-E" (functional group equivalent of amino group: 130 g/mol), "KF-8010" (functional group equivalent of amino group: 430 g/mol), "X-22-161A" (functional group equivalent of amino group: 800 g/mol), and "X-22-161B" (functional group equivalent of amino group: 1.50 0 g/mol), "KF-8012" (amino functional group equivalent 2,200 g/mol), "KF-8008" (amino functional group equivalent 5,700 g/mol) [all manufactured by Shin-Etsu Chemical Co., Ltd.], "BY16-871" (amino functional group equivalent 130 g/mol), "BY16-853U" (amino functional group equivalent 460 g/mol) [all manufactured by Dow Corning Toray Co., Ltd.], etc. Among these, "X-22-161A" and "X-22-161B" are preferred from the viewpoint of high reactivity and lower thermal expansion.

There is no particular restriction on the functional group equivalent weight of the amino group of the modified siloxane compound having a primary amino group at the molecular end, but it is preferably 300 to 3,000 g/mol, more preferably 400 to 2,500 g/mol, and even more preferably 600 to 2,000 g/mol.

From the viewpoint of low thermal expansion and adhesive strength with the metal circuit, the content of component (b) is preferably 3 to 50 parts by mass, more preferably 5 to 30 parts by mass, and even more preferably 7 to 20 parts by mass, per 100 parts by mass of the resin component in resin composition (I).

(Maleimide Compound (c) Having at Least Two N-Substituted Maleimide Groups)
The maleimide compound (c) is not particularly limited as long as it has at least two N-substituted maleimide groups.
As the maleimide compound (c), a maleimide compound having two N-substituted maleimide groups is preferred, and a compound represented by the following general formula (c-1) is more preferred.

(In general formula (c-1), X ^c1 is a group represented by the following general formula (c1-1), (c1-2), (c1-3) or (c1-4).)

(In general formula (c1-1), each R ^c1 is independently an aliphatic hydrocarbon group having 1 to 5 carbon atoms or a halogen atom. p1 is an integer of 0 to 4.)

(In general formula (c1-2), R ^c2 and R ^c3 each independently represent an aliphatic hydrocarbon group having 1 to 5 carbon atoms or a halogen atom. X ^c2 represents an alkylene group having 1 to 5 carbon atoms, an alkylidene group having 2 to 5 carbon atoms, an ether group, a sulfide group, a sulfonyl group, a carbonyloxy group, a keto group, a single bond, or a group represented by the following general formula (c1-2-1). q1 and r1 each independently represent an integer of 0 to 4.)

(In general formula (c1-2-1), R ^c4 and R ^c5 each independently represent an aliphatic hydrocarbon group having 1 to 5 carbon atoms or a halogen atom. X ^c3 represents an alkylene group having 1 to 5 carbon atoms, an alkylidene group having 2 to 5 carbon atoms, an ether group, a sulfide group, a sulfonyl group, a carbonyloxy group, a keto group, or a single bond. s1 and t1 each independently represent an integer of 0 to 4.)

(In general formula (c1-3), n1 is an integer from 1 to 10.)

(In general formula (c1-4), R ^c6 and R ^c7 each independently represent a hydrogen atom or an aliphatic hydrocarbon group having 1 to 5 carbon atoms. u1 represents an integer of 1 to 8.)

In the general formula (c1-1), examples of the aliphatic hydrocarbon group represented by R ^c1 include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, an n-pentyl group, etc. The aliphatic hydrocarbon group is preferably an aliphatic hydrocarbon group having 1 to 3 carbon atoms, more preferably a methyl group. In addition, examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.
Among the above, R ^c1 is preferably an aliphatic hydrocarbon group having 1 to 5 carbon atoms.
p1 is an integer of 0 to 4, and from the viewpoint of availability, is preferably an integer of 0 to 2, more preferably 0 or 1, and even more preferably 0. When p1 is an integer of 2 or more, multiple R ^c1 may be the same or different.

In the general formula (c1-2), examples of the aliphatic hydrocarbon group having 1 to 5 carbon atoms and the halogen atom represented by R ^c2 and R ^c3 include the same as those for R ^c1 . The aliphatic hydrocarbon group is preferably an aliphatic hydrocarbon group having 1 to 3 carbon atoms, more preferably a methyl group or an ethyl group, and even more preferably an ethyl group.
Examples of the alkylene group having 1 to 5 carbon atoms represented by ^Xc2 include a methylene group, a 1,2-dimethylene group, a 1,3-trimethylene group, a 1,4-tetramethylene group, a 1,5-pentamethylene group, etc. From the viewpoints of heat resistance and low thermal expansion, the alkylene group is preferably an alkylene group having 1 to 3 carbon atoms, more preferably a methylene group.
Examples of the alkylidene group having 2 to 5 carbon atoms represented by ^Xc2 include an ethylidene group, a propylidene group, an isopropylidene group, a butylidene group, an isobutylidene group, a pentylidene group, an isopentylidene group, etc. Among these, an isopropylidene group is preferred from the viewpoints of heat resistance and low thermal expansion.
Among the above options, ^Xc2 is preferably an alkylene group having 1 to 5 carbon atoms, or an alkylidene group having 2 to 5 carbon atoms. More preferred ones are as described above.
Each of q1 and r1 is independently an integer of 0 to 4, and from the viewpoint of availability, each is preferably an integer of 0 to 2, more preferably 0 or 2. When q1 or r1 is an integer of 2 or more, multiple R ^c2s or multiple R ^c3s may be the same or different.

In the general formula (c1-2-1), examples of the aliphatic hydrocarbon group having 1 to 5 carbon atoms and the halogen atom represented by R ^c4 and R ^c5 include the same as those in the case of R ^c2 and R ^c3 , and the preferred examples are also the same.
Examples of the alkylene group having 1 to 5 carbon atoms and the alkylidene group having 2 to 5 carbon atoms represented by X ^c3 include the same as the alkylene group having 1 to 5 carbon atoms and the alkylidene group having 2 to 5 carbon atoms represented by X ^c2 , and the preferred ones are also the same.
Among the above options, X ^c3 is preferably an alkylidene group having 2 to 5 carbon atoms, and more preferably is as described above.
Each of s1 and t1 is an integer of 0 to 4, and from the viewpoint of availability, each is preferably an integer of 0 to 2, more preferably 0 or 1, and further preferably 0. When s1 or t1 is an integer of 2 or more, multiple R ^c4s or multiple R ^c5s may be the same or different.
Moreover, the general formula (c1-2-1) is preferably represented by the following general formula (c1-2-1').

(X ^c3 , R ^c4 , R ^c5 , s1 and t1 in general formula (c1-2-1') are the same as those in general formula (c1-2-1), and the preferred ones are also the same.)

The group represented by the general formula (c1-2) is preferably a group represented by the following general formula (c1-2'), more preferably a group represented by any of the following (c1-i) to (c1-iii), and even more preferably a group represented by the following (c1-i) or (c1-ii).

(X ^c2 , R ^c2 , R ^c3 , q1 and r1 in general formula (c1-2') are the same as those in general formula (c1-2), and the preferred ones are also the same.)

In the general formula (c1-3), n1 is an integer of 1 to 10, and from the viewpoint of availability, is preferably an integer of 1 to 5, and more preferably an integer of 1 to 3.
In the general formula (c1-4), examples of the aliphatic hydrocarbon group having 1 to 5 carbon atoms represented by R ^c6 and R ^c7 include the same as those in the case of R ^c1 in the general formula (c1-1), and the preferred ones are also the same. u1 is an integer of 1 to 8, preferably an integer of 1 to 3, and more preferably 1.

In the general formula (c-1), X ^c1 may be any of the groups represented by the general formulas (c1-1), (c1-2), (c1-3) and (c1-4). Among these, from the viewpoints of low thermal expansion and bending elastic modulus, it is preferable that X c1 is a group represented by (c1-2).

Specific examples of the component (c) include bis(4-maleimidophenyl)methane, polyphenylmethane maleimide, bis(4-maleimidophenyl)ether, bis(4-maleimidophenyl)sulfone, 3,3'-dimethyl-5,5'-diethyl-4,4'-diphenylmethane bismaleimide, 4-methyl-1,3-phenylene bismaleimide, m-phenylene bismaleimide, and 2,2-bis[4-(4-maleimidophenoxy)phenyl]propane.
Among these, from the viewpoint of high reactivity and ability to achieve higher heat resistance, bis(4-maleimidophenyl)methane, bis(4-maleimidophenyl)sulfone, 3,3'-dimethyl-5,5'-diethyl-4,4'-diphenylmethane bismaleimide, and 2,2-bis[4-(4-maleimidophenoxy)phenyl]propane are preferred, from the viewpoint of solubility in solvents, 3,3'-dimethyl-5,5'-diethyl-4,4'-diphenylmethane bismaleimide and bis(4-maleimidophenyl)methane are more preferred, and from the viewpoint of production costs, bis(4-maleimidophenyl)methane is even more preferred.

From the viewpoint of elastic modulus and low thermal expansion, the content of component (c) is preferably 20 to 90 parts by mass, more preferably 30 to 70 parts by mass, and even more preferably 40 to 60 parts by mass, per 100 parts by mass of the resin component in resin composition (I).

Components (b) and (c) may be mixed directly with component (a), or, if necessary, components (b) and (c) may be heated and reacted to form an amino-modified polyimide resin (hereinafter referred to as amino-modified polyimide resin (X)) before mixing with component (a). By reacting components (b) and (c) in advance to form amino-modified polyimide resin (X), the molecular weight can be controlled and low cure shrinkage and low thermal expansion can be improved. The amino-modified polyimide resin (X) is described below.

(Amino-modified polyimide resin (X))
There is no particular restriction on the method for reacting component (b) with component (c). From the viewpoints of productivity and allowing the reaction to proceed sufficiently, the reaction temperature is preferably 70 to 200° C., more preferably 80 to 150° C., and even more preferably 100 to 130° C. In addition, there is no particular restriction on the reaction time, but it is preferably 0.5 to 10 hours, and more preferably 1 to 6 hours.

The reaction between the (b) component and the (c) component is preferably carried out in an organic solvent. Examples of the organic solvent include alcohol-based solvents such as ethanol, propanol, butanol, methyl cellosolve, butyl cellosolve, and propylene glycol monomethyl ether; ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester-based solvents such as ethyl acetate and γ-butyrolactone; ether-based solvents such as tetrahydrofuran; aromatic solvents such as toluene, xylene, and mesitylene; nitrogen-containing solvents such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone; and sulfur-containing solvents such as dimethylsulfoxide. These may be used alone or in combination of two or more.
Among these, from the viewpoint of solubility, cyclohexanone, propylene glycol monomethyl ether, methyl cellosolve, and γ-butyrolactone are preferred, and from the viewpoints of low toxicity and high volatility that make it unlikely to remain as a residual solvent, cyclohexanone, propylene glycol monomethyl ether, and dimethylacetamide are preferred, and propylene glycol monomethyl ether is more preferred.
The amount of the organic solvent used is not particularly limited, but from the viewpoints of solubility and reaction rate, the amount is preferably 25 to 1,000 parts by mass, more preferably 50 to 500 parts by mass, and even more preferably 50 to 200 parts by mass, per 100 parts by mass of the total of the components (b) and (c).

After the reaction is completed, the reaction mixture is mixed with other components without any purification to prepare a resin composition (I) containing an amino-modified polyimide resin (X).

In the reaction, the ratio of the (b) component to the (c) component is preferably such that the equivalent of the maleimide group in the (c) component exceeds the equivalent of the primary amino group in the (b) component, from the viewpoints of preventing gelation and heat resistance. In other words, the ratio of the equivalent of the maleimide group in the (c) component to the equivalent of the primary amino group in the (b) component [(c)/(b)] is preferably greater than 1, more preferably 2 to 35, and even more preferably 10 to 35.

When the resin composition (I) contains the amino-modified polyimide resin (X), the content is preferably 40 to 95 parts by mass, more preferably 50 to 80 parts by mass, and even more preferably 60 to 70 parts by mass, per 100 parts by mass of the resin components in the resin composition (I).

((Meth)acrylic elastomer (d))
The prepreg of the present invention, which contains the resin composition (I) containing the (meth)acrylic elastomer (d), can reduce the elastic modulus while maintaining good adhesive strength with the metal circuit. Although the reason for this is unclear, it is thought that the flexible acrylic skeleton of the (d) component and the maleimide skeleton with strong adhesive force of the (c) component form a sea-island structure in an appropriate form, allowing each component to exhibit its respective characteristics without bias.

The (meth)acrylic elastomer (d) is a polymer containing at least a structural unit derived from a (meth)acrylic acid ester. The structural unit derived from a (meth)acrylic acid ester means a structural unit formed when a vinyl bond of a (meth)acrylic acid ester is subjected to addition polymerization. In this specification, "(meth)acrylic acid" means one or more selected from the group consisting of acrylic acid and methacrylic acid.
The (meth)acrylic elastomer (d) may be used alone or in combination of two or more kinds.

Examples of (meth)acrylic acid esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, lauryl (meth)acrylate, and benzyl (meth)acrylate, but are not limited thereto.
The (meth)acrylic elastomer (d) may contain structural units derived from two or more types of (meth)acrylic acid esters, or may be composed of structural units derived from two or more types of (meth)acrylic acid esters.

The (meth)acrylic elastomer (d) may contain a structural unit derived from a monomer other than a (meth)acrylic acid ester.
Examples of the monomer other than the (meth)acrylic acid ester include vinyl monomers such as acrylonitrile, (meth)acrylamide, (meth)acrylic acid, styrene, ethylene, propylene, butadiene, etc. The (meth)acrylic elastomer (d) may contain structural units derived from two or more kinds of monomers other than the (meth)acrylic acid ester.

The (meth)acrylic elastomer (d) may further have a reactive functional group at least at one of the molecular terminal and the molecular chain. Examples of the reactive functional group include an epoxy group, a hydroxyl group, a carboxyl group, an amino group, an amide group, an isocyanato group, a (meth)acrylic group, and a vinyl group. By having these reactive functional groups, the compatibility with other resin components is improved, and the internal stress generated during the curing of the resin composition (I) can be more effectively reduced, and as a result, the warpage of the substrate can be significantly reduced. In particular, from the viewpoint of low thermal expansion and adhesive strength with a metal circuit, it is preferable to have one or more selected from the group consisting of an epoxy group, a hydroxyl group, a carboxyl group, an amino group, and an amide group, and from the viewpoint of heat resistance and insulation reliability, it is more preferable to have one or more selected from the group consisting of an epoxy group, a hydroxyl group, and an amide group.
When the reactive functional group has an epoxy group, the functional group equivalent is preferably from 0.01 to 0.5 eq/kg, more preferably from 0.03 to 0.4 eq/kg, and even more preferably from 0.05 to 0.3 eq/kg.
When the reactive functional group has a hydroxyl group, the hydroxyl value is preferably from 5 to 100 mgKOH/g, more preferably from 10 to 50 mgKOH/g, and even more preferably from 15 to 30 mgKOH/g.

The weight average molecular weight (Mw) of the (meth)acrylic elastomer (d) is not particularly limited, but is preferably 1,000 to 2,000,000, more preferably 10,000 to 1,500,000, even more preferably 100,000 to 1,400,000, and particularly preferably 300,000 to 1,300,000. When the weight average molecular weight (Mw) is equal to or greater than the lower limit, the low elastic modulus tends to be excellent, and when it is equal to or less than the upper limit, the compatibility and flowability tend to be excellent. The weight average molecular weight (Mw) is measured by gel permeation chromatography (GPC) and converted using a calibration curve prepared using standard polystyrene.

From the viewpoints of excellent compatibility with other resin components and effectively reducing the elastic modulus of the cured product, the content of the (meth)acrylic elastomer (d) is preferably 1 to 60 parts by mass, more preferably 5 to 50 parts by mass, and even more preferably 10 to 30 parts by mass, per 100 parts by mass of the resin components in the resin composition (I). When the content of the (meth)acrylic elastomer (d) is within the above range, an appropriate sea-island structure can be formed in the cured product, and both the reduction in elastic modulus due to the flexible (meth)acrylic elastomer (d) and the excellent adhesive strength to the metal circuit due to the maleimide compound (c) can be highly achieved.
Here, the solid content in the present embodiment refers to components in the composition other than water, volatile substances such as the solvent described below, etc. In other words, the solid content includes those that are liquid, syrup-like, or wax-like at room temperature around 25° C., and does not necessarily mean that they are solid.

(Cure Accelerator (e))
The resin composition (I) may further contain a curing accelerator (e).
Examples of the curing accelerator (e) include organometallic salts such as zinc naphthenate, cobalt naphthenate, tin octylate, cobalt octylate, bisacetylacetonate cobalt (II), trisacetylacetonate cobalt (III), etc.; imidazoles and their derivatives; organophosphorus compounds; secondary amines; tertiary amines; quaternary ammonium salts. These may be used alone or in combination of two or more. Among these, imidazoles and their derivatives are preferred from the viewpoint of heat resistance, flame retardancy, and adhesive strength with metal circuit, and organophosphorus compounds are preferred from the viewpoint of low thermal expansion.
As the curing accelerator (e), commercially available products may be used, such as isocyanate mask imidazole (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: G-8009L) and triphenylphosphine triphenylborane (manufactured by Hokko Chemical Industry Co., Ltd., product name: TPP-S).
When the resin composition (I) contains the curing accelerator (e), the content thereof is preferably 0.1 to 10 parts by mass, more preferably 0.3 to 5 parts by mass, and even more preferably 0.5 to 2 parts by mass, relative to 100 parts by mass of the resin component in the resin composition (I). When the content of the curing accelerator (e) is 0.1 parts by mass or more, the heat resistance, flame retardancy, and copper foil adhesion tend to be excellent, and when it is 10 parts by mass or less, the heat resistance, aging stability, and press moldability tend to be excellent.

(Inorganic filler (f))
The resin composition (I) may further contain an inorganic filler (f).
Examples of the inorganic filler (f) include silica, alumina, titanium oxide, mica, beryllia, barium titanate, potassium titanate, strontium titanate, calcium titanate, aluminum carbonate, magnesium hydroxide, aluminum hydroxide, aluminum silicate, calcium carbonate, calcium silicate, magnesium silicate, silicon nitride, boron nitride, clay such as calcined clay, talc, aluminum borate, silicon carbide, quartz powder, glass short fiber, glass fine powder, hollow glass, etc. Examples of glass include E glass, T glass, D glass, etc. These may be used alone or in combination of two or more.
Among these, silica is preferred from the viewpoint of dielectric properties, heat resistance and low thermal expansion. Examples of silica include precipitated silica produced by wet method and having high water content, and dry method silica produced by dry method and containing almost no bound water, etc., and dry method silica is further classified into crushed silica, fumed silica, fused spherical silica, etc., depending on the difference in production method. Among these, fused spherical silica is preferred from the viewpoint of low thermal expansion and flowability when filled in resin.

The average particle size of the inorganic filler (f) is preferably 0.1 to 10 μm, more preferably 0.3 to 8 μm, and even more preferably 0.3 to 3 μm. If the average particle size is 0.1 μm or more, the flowability when highly filled in the resin tends to be good, and if it is 10 μm or less, the probability of coarse particles being mixed in tends to be reduced, and the occurrence of defects caused by coarse particles tends to be suppressed. Here, the average particle size refers to the particle size at the point corresponding to 50% volume when the cumulative frequency distribution curve of the particle size is obtained with the total volume of the particles being 100%, and can be measured by a particle size distribution measuring device using a laser diffraction scattering method, etc.
The inorganic filler (f) may be surface-treated with a coupling agent. The surface treatment method with a coupling agent may be a method of performing a dry or wet surface treatment on the inorganic filler (f) before blending, or may be a so-called integral blend treatment method in which the inorganic filler (f) without surface treatment is blended with other components to form a composition, and then a silane coupling agent is added to the composition.
Examples of the coupling agent include a silane-based coupling agent, a titanate-based coupling agent, and a silicone oligomer.

When the resin composition (I) contains an inorganic filler (f), the content is preferably 10 to 300 parts by mass, more preferably 50 to 250 parts by mass, and even more preferably 70 to 180 parts by mass, per 100 parts by mass of the resin component in the resin composition (I). When the content of the inorganic filler (f) is within the above range, the moldability and low thermal expansion properties are good.

When the resin composition (I) contains an inorganic filler (f), it is preferable to improve the dispersibility of the inorganic filler (f) by treating it with a dispersing machine such as a triple roll mill, a bead mill, or a Nanomizer, as necessary.

(Other ingredients)
The resin composition (I) contained in the prepreg of the present invention may contain other components, such as ultraviolet absorbers, antioxidants, photopolymerization initiators, fluorescent brightening agents, adhesion improvers, etc., to the extent that the thermosetting properties are not impaired.
The ultraviolet absorbing agent may be, for example, a benzotriazole-based ultraviolet absorbing agent.
Examples of the antioxidant include hindered phenol-based antioxidants and hindered amine-based antioxidants.
Examples of the photopolymerization initiator include benzophenones, benzil ketals, and thioxanthone-based photopolymerization initiators.
Examples of the fluorescent whitening agent include fluorescent whitening agents of stilbene derivatives.
Examples of the adhesion improver include urea compounds such as urea silane, and the above-mentioned coupling agents.

The resin composition (I) preferably does not contain a flame retardant, or if it contains a flame retardant, the content is less than 0.5 mass% relative to the resin component. By suppressing the content of the flame retardant in the resin composition (I) to less than 0.5 mass%, it is possible to suppress the adhesion to the metal foil from decreasing. From the same viewpoint, even if the resin composition (I) contains a flame retardant, the content is more preferably 0.3 mass% or less relative to the resin component, even more preferably 0.1 mass% or less, particularly preferably 0.01 mass% or less, and most preferably substantially none.

The resin composition (I) may be in the form of a varnish in which each component is dissolved or dispersed in an organic solvent so that it can be easily used in the production of a prepreg or the like.
Examples of the organic solvent include alcohol-based solvents such as methanol, ethanol, propanol, butanol, methyl cellosolve, butyl cellosolve, and propylene glycol monomethyl ether; ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester-based solvents such as butyl acetate and propylene glycol monomethyl ether acetate; ether-based solvents such as tetrahydrofuran; aromatic solvents such as toluene, xylene, and mesitylene; nitrogen-containing solvents such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone; and sulfur-containing solvents such as dimethylsulfoxide. These organic solvents may be used alone or in combination of two or more.
Among these, from the viewpoint of the solubility of each component, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl cellosolve, and propylene glycol monomethyl ether are preferred, and methyl ethyl ketone is more preferred, and from the viewpoint of low toxicity, methyl isobutyl ketone, cyclohexanone, and propylene glycol monomethyl ether are more preferred.
The solid content of the varnish is preferably 40 to 90% by mass, more preferably 50 to 80% by mass. When the solid content of the varnish is within the above range, good coatability can be maintained and a prepreg having an appropriate amount of the resin composition (I) adhered thereto can be obtained.

<Second Resin Layer>
The second resin layer is a layer formed on the other surface of the fiber substrate layer, and is a layer formed of a flame-retardant resin composition (II).
The thickness of the second resin layer is not particularly limited, but is, for example, 5 to 50 μm, preferably 5 to 30 μm, more preferably 8 to 20 μm, further preferably 8 to 15 μm, and particularly preferably 8 to 13 μm.
Here, the thickness of the second resin layer means the thickness of the region a2 not containing the fiber base material in the cross section perpendicular to the planar direction of the prepreg shown in Figure 2, and for convenience, the portion of the second resin layer impregnated in the fiber base material layer is not taken into consideration. The thickness of the second resin layer can be measured by the same method as the thickness of the fiber base material layer.

In the prepreg of the present invention, the ratio of the thickness of the first resin layer to the thickness of the second resin layer [first resin layer/second resin layer] is not particularly limited, but from the viewpoints of low thermal expansion, heat resistance, moldability and suppression of warping, it is preferably 20/80 to 80/20, more preferably 30/70 to 70/30, even more preferably 40/60 to 60/40, and particularly preferably substantially 50/50.

[Flame-retardant resin composition (II)]
The flame-retardant resin composition (II) is not particularly limited as long as it is a resin composition to which flame retardancy has been imparted, and is preferably a flame-retardant thermosetting resin composition. In order to impart flame retardancy, it is preferable to blend a flame retardant into the resin composition. In addition, from the viewpoint of suppressing warping, it is preferable that the resin composition has a similar composition to the resin composition (I), and it is more preferable that the resin composition (I) is blended with a flame retardant. In other words, with the exception of the flame retardant, each component of the flame-retardant resin composition (II) is as described for each component in the resin composition (I).
Examples of the flame retardant include phosphorus-based flame retardants such as aromatic phosphate ester compounds, phosphazene compounds, phosphinic acid esters, metal salts of phosphinic acid compounds, red phosphorus, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and derivatives thereof, nitrogen-based flame retardants such as guanidine sulfamate, melamine sulfate, melamine polyphosphate, melamine cyanurate, halogen-containing flame retardants containing bromine, chlorine, etc., inorganic flame retardants such as antimony trioxide, etc. Among these, phosphorus-based flame retardants are preferred.

When the flame-retardant resin composition (II) contains a flame retardant, the content is preferably 0.5 to 5 mass%, more preferably 1.0 to 3.5 mass%, further preferably 1.5 to 3.5 mass%, and particularly preferably 1.5 to 3.0 mass%, based on the resin component. If the content of the flame retardant in the flame-retardant resin composition (II) is 0.5 mass% or more, sufficient flame retardancy can be imparted, and if it is 5 mass% or less, deterioration of various properties required for printed wiring board applications, such as low thermal expansion and flexural modulus, can be suppressed.

[Prepreg manufacturing method]
The prepreg of the present invention can be produced, for example, by a method of laminating a first resin film formed from the resin composition (I) on one side of a fibrous base material and laminating a second resin film formed from the flame-retardant resin composition (II) on the other side of the fibrous base material.

The first resin film and the second resin film can be produced, for example, by applying the resin composition (I) and the flame-retardant resin composition (II) to a release film, respectively, and then drying the applied film by heating or the like.

When producing the first resin film and the second resin film, the resin composition (I) and the flame-retardant resin composition (II) may be in the form of a varnish in which each component is dissolved or dispersed in an organic solvent, as necessary, from the viewpoint of facilitating handling and improving the productivity of the resin film and the prepreg of the present invention.
Examples of organic solvents used in the varnish include alcohol-based solvents such as methanol, ethanol, propanol, butanol, methyl cellosolve, butyl cellosolve, and propylene glycol monomethyl ether; ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester-based solvents such as butyl acetate, ethyl acetate, γ-butyrolactone, and propylene glycol monomethyl ether acetate; ether-based solvents such as tetrahydrofuran; aromatic solvents such as toluene, xylene, and mesitylene; nitrogen-containing solvents such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone; and sulfur-containing solvents such as dimethylsulfoxide. These may be used alone or in combination of two or more.
Among these, from the viewpoint of solubility, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl cellosolve, and propylene glycol monomethyl ether are preferred, and from the viewpoint of low toxicity, methyl isobutyl ketone, cyclohexanone, and propylene glycol monomethyl ether are more preferred.
The solid content of the resin composition (I) or the flame-retardant resin composition (II) in the varnish is preferably 40 to 90% by mass, more preferably 50 to 80% by mass, of the entire varnish. By setting the solid content within the above range, the coatability is improved, and the productivity of the resin film and prepreg is excellent.

For coating when preparing a resin film, a known coater such as a die coater, a comma coater, a bar coater, a kiss coater, a roll coater, etc. These coaters may be appropriately selected depending on the desired thickness of the resin film.
Examples of the release film used for the resin film include organic films such as polyethylene terephthalate (PET), biaxially oriented polypropylene (OPP), polyethylene, polyvinyl fluorate, polyimide, etc.; films of copper, aluminum, and alloys of these metals, etc. These release films may be treated with a release agent for release.

The lamination may be performed by a known method such as roll lamination using a pressure roll or vacuum lamination, but from the viewpoint of productivity, roll lamination is preferred. Conditions for roll lamination may be, for example, a heating temperature of 50 to 150°C, a linear pressure of 0.1 to 1.0 MPa, and a speed of 0.5 to 5 m/min. The atmosphere during lamination may be normal pressure or reduced pressure, but from the viewpoint of productivity, normal pressure is preferred.
The lamination of the first resin film and the lamination of the second resin film may be performed separately, but from the viewpoint of productivity, it is preferable to perform them simultaneously. That is, it is preferable to arrange the first resin film on one side of the fiber substrate, arrange the second resin film on the other side of the fiber substrate, and laminate the first resin film and the second resin film simultaneously by roll lamination or the like, thereby forming the first resin layer and the second resin layer while impregnating the fiber substrate with the resin composition (I) and the flame retardant resin composition (II).

The surfaces of the first and second resin films that come into contact with the fiber substrate (resin layer forming surfaces) may be preheated before lamination. The heating position may be adjusted, for example, so that the center of the heating surface of the heater is 10 to 50 mm in front of the pressure roll, and the heating temperature may be adjusted so that the surface temperature at the center of the heating surface is 100 to 150°C, preferably 110 to 140°C.
Similarly, the fiber substrate may be preheated before lamination. The temperature of the fiber substrate may be, for example, 100 to 170°C, preferably 120 to 150°C.
For heating, for example, a halogen heater can be used.

The overall thickness of the prepreg may be adjusted as appropriate depending on the thickness of the inner layer circuitry, etc., but from the viewpoints of thinning the board, moldability and workability, it is preferably 10 μm or more, more preferably 20 μm or more, and preferably 700 μm or less, more preferably 500 μm or less, even more preferably 200 μm or less, even more preferably 100 μm or less, even more preferably 80 μm or less, particularly preferably 50 μm or less, and most preferably 40 μm or less.

[Laminates and metal-clad laminates]
The laminate of the present invention is produced by laminating and molding the prepreg of the present invention.
As for the configuration of the laminate of the present invention, if one prepreg of the present invention is expressed as (adhesion layer 1/flame retardant layer 2) [the fiber base material is indicated by a slash (/)], examples include "(adhesion layer 1/flame retardant layer 2)-(flame retardant layer 2/adhesion layer 1)", "(adhesion layer 1/flame retardant layer 2)-(flame retardant layer 2/adhesion layer 1)-(adhesion layer 1/flame retardant layer 2)-(flame retardant layer 2/adhesion layer 1)", etc. In other words, the same layers of prepregs are laminated so as to face each other, and the surface is the adhesion layer 1.
Here, the term "same layer" refers to a layer in which the same types of components are blended in the same manner, and the content error of the order of experimental error is considered to be the same. Specifically, the content difference of ±5% by mass is considered to be the same.

In addition to the prepreg of the present invention, a prepreg having a structure of (flame retardant layer 2/flame retardant layer 2), a prepreg having a structure of (another functional layer 3/another functional layer 3), a prepreg having a structure of (flame retardant layer 2/another functional layer 3), a prepreg having a structure of (adhesion layer 1/another functional layer 3), etc. can also be used. In that case, examples of the laminate of the present invention include "(adhesion layer 1/flame retardant layer 2)-(flame retardant layer 2/flame retardant layer 2)-(flame retardant layer 2/flame retardant layer 2)-(flame retardant layer 2/adhesion layer 1)", "(adhesion layer 1/flame retardant layer 2)-(flame retardant layer 2/another functional layer 3)-(another functional layer 3/another functional layer 3)-(another functional layer 3/adhesion layer 1)", etc. In these cases, the contact surfaces of the prepregs are in a form in which the same layers are in contact with each other.
The term "another functional layer" means a layer different from the adhesive layer 1 and the flame-retardant layer 2, and its function is not particularly limited.

By making a laminate with the above-mentioned structure, it has high flame retardancy, high adhesion to the metal foil, and also suppresses warping.

[Method of manufacturing laminate and metal-clad laminate]
The laminate of the present invention can be produced, for example, by stacking 2 to 20 sheets of the prepreg of the present invention and other prepregs as necessary so as to obtain the above-mentioned configuration, and laminating and molding the stack with metal foil on one or both sides. There are no particular limitations on the metal foil as long as it is used in laminates for electrical insulating materials. The laminate having metal foil on the surface thereof is called a "metal-clad laminate". The configuration of the metal-clad laminate is a configuration in which metal foil is present on one or both sides of the laminate configuration described above.
The metal of the metal foil is preferably copper, gold, silver, nickel, platinum, molybdenum, ruthenium, aluminum, tungsten, iron, titanium, chromium, or an alloy containing at least one of these metal elements.

The molding conditions can be, for example, the same as those for laminates and multilayer boards for electrical insulating materials, and molding can be performed using a multi-stage press, multi-stage vacuum press, continuous molding, autoclave molding machine, etc., under conditions of a temperature of 100 to 250°C, a pressure of 0.2 to 10 MPa, and a heating time of 0.1 to 5 hours. The laminate board of the present invention can also be manufactured by combining the prepreg of the present invention with an inner layer wiring board and laminating and molding it.

As described above, the present invention also provides a method for producing a laminated board by laminating and molding the prepregs of the present invention so that the same layers face each other and the surface becomes the adhesion layer 1.
The present invention also provides a method for producing a metal-clad laminate by laminating and molding the prepreg of the present invention so that the same layers face each other and the adhesion layer 1 is in contact with a metal foil.
In any of the manufacturing methods, any other prepreg may be used in combination. However, when the any prepreg is laminated with the prepreg of the present invention, or when any prepreg is laminated with another prepreg, the opposing layers are made to be the same layer from the viewpoint of suppressing warpage. In other words, even if any prepreg is used, it is necessary to select a prepreg such that the opposing layers of the two prepregs to be laminated are the same layer.

[Printed wiring board]
The printed wiring board of the present invention contains the laminate of the present invention.
The printed wiring board of the present invention can be manufactured by processing a conductor layer (metal foil) arranged on one or both sides of the laminate of the present invention into a circuit. The method for forming the wiring pattern is not particularly limited, but includes known methods such as a subtractive method, a full additive method, a semi-additive method (SAP: Semi Additive Process), and a modified semi-additive method (m-SAP: modified Semi Additive Process).
Specifically, first, the conductor layer of the laminate of the present invention is wired by the above-mentioned method, then a plurality of laminates wired via the prepreg of the present invention are stacked and hot-pressed to form a multilayer structure. After that, the printed wiring board of the present invention can be manufactured by forming through holes or blind via holes by drilling or laser processing and forming interlayer wiring by plating or conductive paste.

[Semiconductor Package]
The semiconductor package of the present invention is obtained by mounting a semiconductor on the printed wiring board of the present invention. The semiconductor package of the present invention can be produced, for example, by mounting a semiconductor element such as a semiconductor chip or memory at a predetermined position on the printed wiring board of the present invention and sealing the semiconductor element with a sealing resin or the like.

Next, the present invention will be described in more detail with reference to the following examples, but these examples do not limit the present invention.

[Production of amino-modified polyimide resin (X)]
Production Example 1: Production of amino-modified polyimide resin (X-1) In a 2-liter reaction vessel equipped with a thermometer, a stirrer, and a moisture meter equipped with a reflux condenser and capable of being heated and cooled, 72 g of a siloxane modified at both ends with diamines (manufactured by Shin-Etsu Chemical Co., Ltd., product name: X-22-161A, amino functional group equivalent: 800 g/mol, component (b)), 252 g of bis(4-maleimidophenyl)methane (manufactured by K.I. Chemical Co., Ltd., product name: BMI, component (c)), and 270 g of propylene glycol monomethyl ether were placed and reacted at 110° C. for 3 hours to obtain a solution containing amino-modified polyimide resin (X-1).

[Preparation of resin films A1 and B1]
Production Examples 2 and 3
The components shown in Table 1 below were mixed in the blending ratios shown in Table 1 below (the units of values in the table are parts by mass unless otherwise specified, and in the case of a solution, the units are solid content equivalents), and a varnish with a solid content concentration of 65 mass% was prepared using methyl ethyl ketone as a solvent. This varnish was applied to a 580 mm wide PET film (manufactured by Teijin DuPont Films Ltd., product name: G-2) with an application width of 525 mm and an adjusted thickness of the resin layer after drying to 10 μm, to prepare a resin film A1 for an adhesive layer and a resin film B1 for a flame-retardant layer.

(Regarding each component listed in Table 1)
[Thermosetting resin (a)]
Epoxy resin: α-naphthol/cresol novolac type epoxy resin [amino-modified polyimide resin (X)]
X-1: Solution containing amino-modified polyimide resin (X-1) prepared in Production Example 1 [(meth)acrylic elastomer (d)]
- Epoxy group-containing acrylic polymer "SG-P3" with a weight average molecular weight of 850,000 (product name, manufactured by Nagase ChemteX Corporation, epoxy value: 0.21 eq/kg (catalog value))
[Cure Accelerator (e)]
Isocyanate masked imidazole "G-8009L" (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name)
[Inorganic filler (f)]
Spherical fused silica (average particle size: 0.5 μm)
〔Flame retardants〕
Phosphorus-based flame retardant: PX-200 (product name, manufactured by Daihachi Chemical Industry Co., Ltd.)

[Preparation of prepregs and copper-clad laminates]
Example 1
The resin film A1 (for adhesion layer) prepared in Production Example 2 was placed on one side of a fiber substrate, glass cloth (thickness 15 μm, basis weight 13 g/ ^m2 , IPC#1017, substrate width 530 mm, manufactured by Nitto Boseki Co., Ltd.), and the resin film B1 (for flame retardant layer) prepared in Production Example 3 was placed on the other side, with the resin layer forming surface facing the glass cloth.
The fiber substrate was sandwiched between pressure rolls and laminated, and the resin composition was pressurized and impregnated from both sides of the fiber substrate. The prepreg was then cooled with a cooling roll and wound up. The conditions of the pressure roll were a roll temperature of 100° C., a linear pressure of 0.2 MPa, and a speed of 2.0 m/min. The lamination was performed under normal pressure.
The surfaces of the resin film A1 and the resin film B1 that contact the glass cloth (the surfaces on which the resin layer is formed) were preheated before lamination. The heating position was adjusted so that the center of the heating surface of the heater was 30 mm in front of the pressure roll, and the heating temperature was adjusted so that the surface temperature at the center of the heating surface was 135°C. The glass cloth itself was heated in the same manner, and the temperature of the glass cloth was adjusted to 140°C. A halogen heater (manufactured by Ushio Inc., device name: UH-USF-CL-700) was used for heating.
The total thickness of the obtained prepreg was 30 μm, the thickness of the first resin layer was 7.5 μm, and the thickness of the second resin layer was 7.5 μm. The thickness of each layer was measured by observing with a scanning electron microscope (SEM) and measuring the thickness of each layer at any 10 points, and averaging the measured values.
As shown in FIG. 3 , four prepregs obtained above were stacked so that the first resin layers (adhesion layers 1) faced each other and the second resin layers (flame-retardant layers 2) faced each other, and electrolytic copper foils having a thickness of 12 μm were placed on top and bottom of the stacked prepregs. The stacked prepregs were pressed at a pressure of 3.0 MPa and a temperature of 240° C. for 60 minutes to obtain a copper-clad laminate.
The copper-clad laminate thus obtained was subjected to various measurements according to the methods described below. The results are shown in Table 2.

[Preparation of prepregs and copper-clad laminates]
Comparative Example 1
A prepreg was obtained by carrying out the same operation as in Example 1, except that the resin film A1 (for adhesive layer) produced in Production Example 2 was placed on both sides of the glass cloth.
Four prepregs obtained above were stacked as shown in FIG. 4, and electrolytic copper foils having a thickness of 12 μm were placed on top and bottom. The laminate was pressed at a pressure of 3.0 MPa and a temperature of 240° C. for 60 minutes to obtain a copper-clad laminate.
The copper-clad laminate thus obtained was subjected to various measurements according to the methods described below. The results are shown in Table 2.

[Preparation of prepregs and copper-clad laminates]
Comparative Example 2
A prepreg was obtained by carrying out the same operation as in Example 1, except that the resin film B1 (for flame retardant layer) produced in Production Example 3 was placed on both sides of the glass cloth.
Four prepregs obtained above were stacked as shown in FIG. 5, and electrolytic copper foils having a thickness of 12 μm were placed on top and bottom. The laminate was pressed at a pressure of 3.0 MPa and a temperature of 240° C. for 60 minutes to obtain a copper-clad laminate.
The copper-clad laminate thus obtained was subjected to various measurements according to the methods described below. The results are shown in Table 2.

[Measurement methods for each physical property]
(1) Copper foil peel strength After forming a 3 mm wide resist on the outer copper foil of the copper-clad laminate prepared in each example, the laminate was immersed in a copper etching solution to prepare an evaluation board having an outer copper foil of 3 mm wide as a peel strength measurement part. One end of the copper foil in the peel strength measurement part was peeled off at the interface between the copper foil and the board and gripped with a gripper, and the load when peeled off in the vertical direction at a pulling speed of 50 mm/min at room temperature (25°C) was measured using a tensile tester (Shimadzu Corporation, product name: Autograph S-100).

(2) Flame Retardancy The copper-clad laminate prepared in each example was immersed in a 10% by mass solution of ammonium persulfate (manufactured by Mitsubishi Gas Chemical Company, Inc.) as a copper etching solution to remove the copper foil, from which a test piece 127 mm in length and 12.7 mm in width was cut out. The test piece was used to test and evaluate flame retardancy in accordance with the UL94 test method (V method).
That is, the lower end of the test piece was held vertically and exposed to a 20 mm flame for 10 seconds twice. The evaluation was performed according to the UL94 V method standard.

As is clear from Table 2, the laminate (copper-clad laminate) obtained in Example 1 had both copper foil peel strength and flame retardancy. On the other hand, the laminates obtained in Comparative Examples 1 and 2 did not have both copper foil peel strength and flame retardancy.

[Preparation of prepregs and copper-clad laminates]
Example 2
A copper-clad laminate was produced in the same manner as in Example 1, except that only two second resin layers (flame-retardant layers 2) were stacked so that the second resin layers (flame-retardant layers 2) faced each other as shown in FIG.
The amount of warping of the obtained copper-clad laminate was measured according to the method described below. The results are shown in Table 3.

[Preparation of prepregs and copper-clad laminates]
Reference Example 1
In Example 2, a copper-clad laminate was produced in the same manner, except that only two sheets were stacked so that the first resin layer (adhesion layer 1) and the second resin layer (flame-retardant layer 2) faced each other, as shown in Figure 7.
The amount of warping of the obtained copper-clad laminate was measured according to the method described below. The results are shown in Table 3.

[Preparation of prepregs and copper-clad laminates]
Comparative Example 3
In the same manner as in Comparative Example 1, a prepreg was prepared by disposing the resin film A1 (for adhesion layer) produced in Production Example 2 on both sides of a glass cloth, and in the same manner as in Comparative Example 2, a prepreg was prepared by disposing the resin film B1 (for flame-retardant layer) produced in Production Example 3 on both sides of a glass cloth.
Next, as shown in FIG. 8, a copper-clad laminate was produced in the same manner as in Example 1, except that four of these prepregs were alternately stacked.
The amount of warping of the obtained copper-clad laminate was measured according to the method described below. The results are shown in Table 3.

(3) Warpage A test piece measuring 510 mm x 410 mm was cut from the center of each copper-clad laminate prepared in each example. The test piece was placed on a flat surface plate at 20°C, and the warpage of the four corners was measured with a dial gauge. The largest value was taken as the warpage.

As is clear from Table 3, the laminate (copper-clad laminate) obtained in Example 2 was sufficiently suppressed in warping. On the other hand, the laminate obtained in Reference Example 1 could not suppress warping because the resin compositions of the opposing surfaces of the prepregs were different. From this, it can be said that it is necessary to laminate the prepregs of the present invention in the above-mentioned appropriate overlapping manner.
Furthermore, in Comparative Example 3 in which a prepreg having high adhesion to copper foil and a prepreg having high flame retardancy were alternately laminated, warping became large.

The prepreg of the present invention provides laminates or metal-clad laminates that have high flame retardancy, high adhesion to metal foil, and reduced warping, making it useful as highly integrated semiconductor packages, printed wiring boards for electronic devices, etc.

1 First resin layer (adhesion layer)
2 Second resin layer (flame retardant layer)
10 Fiber substrate layer 11 Fiber substrate 100 Prepreg

Claims (8)

A laminated plate obtained by laminating and molding a prepreg, the prepreg having a fiber substrate layer containing a fiber substrate, a first resin layer formed on one surface of the fiber substrate layer, and a second resin layer formed on the other surface of the fiber substrate layer, the first resin layer being an adhesion layer 1 formed by forming a layer of a resin composition (I) containing a thermosetting resin, and the second resin layer being a flame-retardant layer 2 formed by forming a layer of a flame-retardant resin composition (II) ,
A laminate in which identical layers are laminated so as to face each other, and the surface is the adhesion layer 1. The laminate according to claim 1, wherein the flame-retardant resin composition (II) contains a flame retardant in an amount of 0.5 to 5% by mass based on the resin component. The laminate according to claim 1 or 2, wherein the resin composition (I) does not contain a flame retardant, or even if it contains a flame retardant, the content thereof is less than 0.5 mass% based on the resin component. A metal-clad laminate comprising the laminate according to any one of claims 1 to 3 and a metal foil on the surface thereof. A printed wiring board comprising the laminate according to any one of claims 1 to 3 or the metal-clad laminate according to claim 4 . A semiconductor package comprising the printed wiring board according to claim 5 and a semiconductor element mounted thereon. A method for producing a laminated plate, comprising laminating and molding a prepreg having a fiber substrate layer containing a fiber substrate, a first resin layer formed on one side of the fiber substrate layer, and a second resin layer formed on the other side of the fiber substrate layer, the first resin layer being an adhesion layer 1 formed by layering a resin composition (I) containing a thermosetting resin, and the second resin layer being a flame-retardant layer 2 formed by layering a flame-retardant resin composition (II) so that identical layers face each other and the surface is the adhesion layer 1. A method for producing a metal-clad laminate, comprising laminating and molding a prepreg having a fiber substrate layer containing a fiber substrate, a first resin layer formed on one side of the fiber substrate layer, and a second resin layer formed on the other side of the fiber substrate layer, the first resin layer being an adhesion layer 1 formed by layering a resin composition (I) containing a thermosetting resin, and the second resin layer being a flame-retardant layer 2 formed by layering a flame-retardant resin composition (II) , so that the same layers face each other and so that the adhesion layer 1 is in contact with a metal foil.