JP7771619B2 - Ceramic substrate laminate and method for manufacturing the same - Google Patents

Description

This disclosure relates to a ceramic substrate laminate and a method for manufacturing a ceramic substrate laminate.

The speed and capacity of signals used in electronic devices such as mobile phones, their base station equipment, servers, routers, and other network infrastructure equipment, and large computers are increasing year by year. Accordingly, the printed wiring boards used in these electronic devices must be able to handle higher frequencies, creating a demand for substrate materials with low dielectric constants and low dielectric dissipation factors that can reduce transmission loss. In recent years, in addition to the electronic devices mentioned above, new systems that handle high-frequency wireless signals have been put into practical use and planned for use in the ITS field (automotive and transportation systems) and indoor short-range communications fields. Going forward, it is expected that there will be even greater demand for low-transmission-loss substrate materials for the printed wiring boards used in these devices.

Ceramic substrates have excellent heat dissipation properties and high-frequency characteristics, and their application to various high-frequency circuit boards is being considered (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2020-80386

Ceramic substrates have large surface irregularities and poor impact resistance, making it difficult to form fine wiring by laminating metal foil on the ceramic substrate. Therefore, the present disclosure aims to provide a ceramic substrate laminate capable of forming fine wiring, and a method for manufacturing a ceramic substrate laminate.

One aspect of the present disclosure relates to a method for manufacturing a ceramic substrate laminate, which includes a step of laminating a metal foil onto a ceramic substrate via a resin layer.

Another aspect of the present disclosure relates to a ceramic substrate laminate comprising a ceramic substrate and a resin layer provided on the ceramic substrate, wherein the resin layer contains a resin composition containing, as component (A), a maleimide compound having a saturated or unsaturated divalent hydrocarbon group and a divalent group having at least two imide bonds, and as component (B), an aromatic maleimide compound.

The present disclosure provides a ceramic substrate laminate capable of forming fine wiring, and a method for manufacturing a ceramic substrate laminate.

1 is a schematic cross-sectional view showing one embodiment of a ceramic substrate laminate. 1 is a schematic cross-sectional view showing an embodiment of a ceramic substrate laminate including metal foil. FIG. 2 is a schematic cross-sectional view showing an embodiment of a ceramic substrate laminate in which vias are formed.

Preferred embodiments of the present disclosure are described in detail below. However, the present disclosure is not limited to the following embodiments. In this specification, the term "process" refers not only to an independent process, but also to processes that cannot be clearly distinguished from other processes as long as the intended effect of the process is achieved. In this specification, the term "layer" encompasses not only a structure that is formed over the entire surface when viewed from a plan view, but also a structure that is formed on only a portion of the surface. In this specification, the high-frequency region refers to the 0.3 GHz to 300 GHz region, and in particular, the 3 GHz to 300 GHz region.

In this specification, numerical ranges indicated using "to" indicate ranges that include the numerical values before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range may be replaced with the upper or lower limit of a numerical range in another stage. Furthermore, in numerical ranges described in this specification, the upper or lower limit of that numerical range may be replaced with a value shown in the examples. When referring to the amount of each component in a composition in this specification, if the composition contains multiple substances corresponding to each component, this refers to the total amount of those multiple substances present in the composition, unless otherwise specified.

[Ceramic substrate laminate]
1 is a schematic cross-sectional view showing one embodiment of a ceramic substrate laminate. The ceramic substrate laminate according to this embodiment includes a ceramic substrate 1 and a resin layer 2 provided on the ceramic substrate 1.

The ceramic substrate laminate may further include a metal foil 4 on the surface of the resin layer 2 opposite the ceramic substrate 1. FIG. 2 is a schematic cross-sectional view showing one embodiment of a ceramic substrate laminate including a metal foil. The laminate includes a ceramic substrate 1, a resin layer 2 provided on the ceramic substrate 1, and a metal foil 4 laminated on the resin layer 2. The ceramic substrate 1 is bonded to the metal foil 4 via the resin layer 2. A resin layer 2 and a metal foil 4 may also be formed on the surface of the ceramic substrate 1 opposite the resin layer 2. In other words, the ceramic substrate laminate according to this embodiment may be a laminate in which a resin layer 2 is formed on one or both surfaces of the ceramic substrate 1, and a metal foil 4 is laminated on the resin layer 2.

One aspect of the manufacturing method for the ceramic substrate laminate (hereinafter sometimes simply referred to as "laminate") according to this embodiment includes a step of laminating metal foil on a ceramic substrate via a resin layer. A ceramic substrate laminate including metal foil may be produced by forming a resin layer on one or both sides of a ceramic substrate, then placing metal foil on the resin layer, and then heating and pressurizing. Alternatively, a ceramic substrate laminate including metal foil may be produced by placing resin-coated metal foil, in which a resin layer has been formed on the metal foil, on one or both sides of a ceramic substrate, and then heating and pressurizing.

The heating and pressurizing conditions for producing the laminate may be, for example, a temperature of 170 to 250°C, a pressure of 0.5 to 5.0 MPa, and a period of 60 to 150 minutes. Heating and pressurizing can be carried out at a vacuum level of 10 kPa or less, preferably 5 kPa or less, and from the perspective of increasing efficiency, it is preferable to carry out the heating and pressurizing in a vacuum.

The laminate according to this embodiment makes it possible to form fine wiring on the ceramic substrate. For example, by laser processing the metal foil 4 and the resin layer 2, vias for interlayer connection can be formed on the ceramic substrate. Figure 3 is a schematic cross-sectional view showing one embodiment of a ceramic substrate laminate in which vias have been formed.

(ceramic substrate)
Examples of ceramic materials constituting the ceramic substrate include alumina, zirconia, magnesia, and titania. From the viewpoint of improving high-frequency characteristics, it is preferable to use low-temperature co-fired ceramics (LTCC) as the ceramic substrate. Examples of LTCC include glass composite low-temperature co-fired ceramics, crystallized glass low-temperature co-fired ceramics, and non-glass low-temperature co-fired ceramics.

The dielectric constant (Dk) of the ceramic substrate may be, for example, 3 to 70. The dielectric dissipation factor (Df) of the ceramic substrate may be, for example, 0.0001 to 0.0010. The Dk and Df of the ceramic substrate can be measured using a cavity resonance method. To improve the insulation reliability and antenna characteristics (characteristic impedance) of the laminate, the thickness of the ceramic substrate may be 100 μm or more, 200 μm or more, or 300 μm or more, and may be 600 μm or less, 500 μm or less, or 450 μm or less.

(Resin layer)
The resin layer according to this embodiment has excellent adhesion to metal foil and ceramic substrates, which improves the impact resistance of the ceramic substrate laminate and makes it easier to form fine wiring.

The thickness of the resin layer 2 is not particularly limited, but may be, for example, 1 to 200 μm, 3 to 180 μm, 5 to 150 μm, 10 to 100 μm, or 15 to 80 μm. By setting the thickness of the resin layer 2 within the above range, it becomes easier to further improve the high-frequency characteristics of the laminate according to this embodiment.

One embodiment of the ceramic substrate laminate comprises a ceramic substrate and a resin layer disposed on the ceramic substrate, wherein the resin layer contains a resin composition containing, as component (A), a maleimide compound having a saturated or unsaturated divalent hydrocarbon group and a divalent group having at least two imide bonds, and as component (B), an aromatic maleimide compound. Each component contained in the resin composition is described in detail below.

Component (A) is a compound having (a) a maleimide group, (b) a divalent group having at least two imide bonds, and (c) a saturated or unsaturated divalent hydrocarbon group. (a) The maleimide group is sometimes referred to as structure (a), (b) the divalent group having at least two imide bonds is sometimes referred to as structure (b), and (c) the saturated or unsaturated divalent hydrocarbon group is sometimes referred to as structure (c). By using component (A), a resin composition with excellent high-frequency properties and adhesive properties can be obtained.

The (a) maleimide group is not particularly limited and is a general maleimide group. The (a) maleimide group may be bonded to an aromatic ring or an aliphatic chain, but from the perspective of dielectric properties, it is preferably bonded to a long-chain aliphatic chain (e.g., a saturated hydrocarbon group having 8 to 100 carbon atoms). When component (A) has a structure in which the (a) maleimide group is bonded to a long-chain aliphatic chain, the high-frequency properties of the resin composition can be further improved.

There are no particular limitations on the structure (b), but examples include groups represented by the following formula (I): The structure (b) is a group that does not have a maleimide group.

In formula (I), _R1 represents a tetravalent organic group. _R1 is not particularly limited as long as it is a tetravalent organic group, but from the viewpoint of handleability, it may be, for example, a hydrocarbon group having 1 to 100 carbon atoms, a hydrocarbon group having 2 to 50 carbon atoms, or a hydrocarbon group having 4 to 30 carbon atoms.

_R1 may contain a substituted or unsubstituted siloxane moiety. Examples of the siloxane moiety include structures derived from dimethylsiloxane, methylphenylsiloxane, diphenylsiloxane, etc.

When _R1 is substituted, examples of the substituent include an alkyl group, an alkenyl group, an alkynyl group, a hydroxyl group, an alkoxy group, a mercapto group, a cycloalkyl group, a substituted cycloalkyl group, a heterocyclic group, a substituted heterocyclic group, an aryl group, a substituted aryl group, a heteroaryl group, a substituted heteroaryl group, an aryloxy group, a substituted aryloxy group, a halogen atom, a haloalkyl group, a cyano group, a nitro group, a nitroso group, an amino group, an amido group, -CHO, -NR _x C(O)-N(R _x ) ₂ , -OC(O)-N(R _x ) ₂ , an acyl group, an oxyacyl group, a carboxyl group, a carbamate group, and a sulfonamide group. Here, R _x represents a hydrogen atom or an alkyl group. One or more of these substituents can be selected depending on the purpose, application, etc.

_R1 is preferably, for example, a tetravalent residue of an acid anhydride having two or more anhydride rings in one molecule, i.e., a tetravalent group obtained by removing two acid anhydride groups (-C(=O)OC(=O)-) from an acid anhydride. Examples of acid anhydrides include compounds described below.

From the viewpoint of mechanical strength, _R1 is preferably aromatic, and more preferably a group obtained by removing two acid anhydride groups from pyromellitic anhydride. That is, structure (b) is more preferably a group represented by the following formula (III):

From the viewpoint of fluidity and circuit embedding ability, it is preferable for multiple structures (b) to be present in component (A). In this case, the structures (b) may be the same or different. The number of structures (b) in component (A) is preferably 2 to 40, more preferably 2 to 20, and even more preferably 2 to 10.

From the viewpoint of dielectric properties, the structure (b) may be a group represented by the following formula (IV) or (V):

Structure (c) is not particularly limited and may be linear, branched, or cyclic. From the perspective of high-frequency characteristics, structure (c) is preferably an aliphatic hydrocarbon group. Furthermore, the saturated or unsaturated divalent hydrocarbon group may have 8 to 100 carbon atoms. Structure (c) is preferably an optionally branched alkylene group having 8 to 100 carbon atoms, more preferably an optionally branched alkylene group having 10 to 70 carbon atoms, and even more preferably an optionally branched alkylene group having 15 to 50 carbon atoms. When structure (c) is an optionally branched alkylene group having 8 or more carbon atoms, the molecular structure is easily three-dimensional, increasing the free volume of the polymer and facilitating low density. In other words, the dielectric constant can be reduced, which facilitates improved high-frequency characteristics of the resin composition. Furthermore, when component (A) contains structure (c), the flexibility of the resin composition is improved, enabling the handleability (tackiness, cracking, powder shedding, etc.) and strength of the resin layer (resin film) produced from the resin composition to be improved.

Examples of structure (c) include alkylene groups such as nonylene, decylene, undecylene, dodecylene, tetradecylene, hexadecylene, octadecylene, and nonadecylene; arylene groups such as benzylene, phenylene, and naphthylene; arylene alkylene groups such as phenylenemethylene, phenyleneethylene, benzylpropylene, naphthylenemethylene, and naphthyleneethylene; and arylene dialkylene groups such as phenylenedimethylene and phenylenediethylene.

From the viewpoints of high frequency characteristics, low thermal expansion characteristics, adhesion to ceramic substrates and metal foils, heat resistance, and low moisture absorption, a group represented by the following formula (II) is particularly preferred as structure (c).

In formula (II), _R2 and _R3 each independently represent an alkylene group having 4 to 50 carbon atoms. From the viewpoint of further improving flexibility and ease of synthesis, _R2 and _R3 each independently represent an alkylene group having 5 to 25 carbon atoms, more preferably an alkylene group having 6 to 10 carbon atoms, and even more preferably an alkylene group having 7 to 10 carbon atoms.

In formula (II), _R4 represents an alkyl group having 4 to 50 carbon atoms. From the viewpoint of further improving flexibility and ease of synthesis, _R4 is preferably an alkyl group having 5 to 25 carbon atoms, more preferably an alkyl group having 6 to 10 carbon atoms, and even more preferably an alkyl group having 7 to 10 carbon atoms.

In formula (II), _R5 represents an alkyl group having 2 to 50 carbon atoms. From the viewpoint of further improving flexibility and ease of synthesis, _R5 is preferably an alkyl group having 3 to 25 carbon atoms, more preferably an alkyl group having 4 to 10 carbon atoms, and even more preferably an alkyl group having 5 to 8 carbon atoms.

From the standpoint of fluidity and circuit embedding ability, it is preferable for multiple structures (c) to be present in component (A). In this case, the structures (c) may be the same or different. For example, it is preferable for 2 to 40 structures (c) to be present in component (A), more preferably 2 to 20 structures (c), and even more preferably 2 to 10 structures (c).

The content of component (A) in the resin composition is not particularly limited. From the standpoint of heat resistance, the content of component (A) is preferably 2 to 98 mass% of the total mass of the resin composition, more preferably 10 to 50 mass%, and even more preferably 10 to 30 mass%.

The molecular weight of component (A) is not particularly limited. From the standpoints of handleability, fluidity, and circuit embedding ability, the weight average molecular weight (Mw) of component (A) is preferably 500 to 10,000, more preferably 1,000 to 9,000, even more preferably 1,500 to 9,000, even more preferably 1,500 to 7,000, and particularly preferably 1,700 to 5,000.

The Mw of component (A) can be measured by gel permeation chromatography (GPC).

The GPC measurement conditions are as follows.
Pump: L-6200 type [manufactured by Hitachi High-Technologies Corporation]
Detector: L-3300 RI [manufactured by Hitachi High-Technologies Corporation]
Column oven: L-655A-52 [manufactured by Hitachi High-Technologies Corporation]
Guard column and column: TSK Guard column HHR-L + TSK gel G4000HHR + TSK gel G2000HHR [all manufactured by Tosoh Corporation, product names]
Column size: 6.0 x 40 mm (guard column), 7.8 x 300 mm (column)
Eluent: tetrahydrofuran Sample concentration: 30 mg/5 mL
Injection volume: 20μL
Flow rate: 1.00mL/min Measurement temperature: 40℃

The method for producing component (A) is not limited. Component (A) may be produced, for example, by reacting an acid anhydride with a diamine to synthesize an amine-terminated compound, and then reacting the amine-terminated compound with excess maleic anhydride.

Examples of acid anhydrides include pyromellitic anhydride, maleic anhydride, succinic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride. Depending on the purpose, application, etc., one type of acid anhydride may be used alone, or two or more types may be used in combination. As mentioned above, a tetravalent organic group derived from an acid anhydride such as those listed above can be used as R ₁ in the above formula (I). From the viewpoint of better dielectric properties, the acid anhydride is preferably pyromellitic anhydride.

Examples of diamines include dimer diamine, 2,2-bis(4-(4-aminophenoxy)phenyl)propane, 1,3-bis(4-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-diamino-3,3'-dihydroxybiphenyl, 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene, 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene, polyoxyalkylenediamine, and [3,4-bis(1-aminoheptyl)-6-hexyl-5-(1-octenyl)]cyclohexene. Depending on the purpose and application, one type of diamine may be used alone, or two or more types may be used in combination.

The component (A) may be, for example, a compound represented by the following formula (XIII).

In formula (XIII), R and Q each independently represent a divalent organic group. R can be the same as in the structure (c) above, and Q can be the same as R1 above. n represents an integer of ₁ to 10.

Commercially available compounds can also be used as component (A). Examples of commercially available compounds include products manufactured by Designer Molecules Inc., specifically BMI-1500, BMI-1700, BMI-3000, BMI-5000, and BMI-9000 (all trade names). From the perspective of obtaining better high-frequency characteristics, it is more preferable to use BMI-3000 as component (A).

The aromatic maleimide compound serving as component (B) in this embodiment is a maleimide compound different from component (A). A compound that can be classified as both component (A) and component (B) is considered to belong to component (A). However, when two or more compounds that can be classified as both component (A) and component (B) are included, one of them is considered to belong to component (A) and the others are considered to belong to component (B). For example, a compound having an aromatic ring contained in the group represented by formula (I) may be considered component (A), and a compound having an aromatic ring other than the aromatic ring contained in the group represented by formula (I) may be considered component (B). The use of component (B) can reduce the hygroscopicity of the resin composition. A cured product of a resin composition containing components (A) and (B) can maintain good dielectric properties while improving its low hygroscopicity by containing a polymer having structural units composed of component (A), which has low dielectric properties, and structural units composed of component (B), which has low hygroscopicity.

It is preferable that component (B) has a lower thermal expansion coefficient than component (A). Examples of components (B) with a lower thermal expansion coefficient than component (A) include maleimide group-containing compounds with a lower molecular weight than component (A), maleimide group-containing compounds with more aromatic rings than component (A), and maleimide group-containing compounds with a shorter main chain than component (A).

The content of component (B) in the resin composition is not particularly limited. From the standpoint of low moisture absorption and dielectric properties, the content of component (B) is preferably 1 to 95 mass% of the total mass of the resin composition, more preferably 3 to 90 mass%, and even more preferably 5 to 85 mass%.

The blending ratio of component (A) to component (B) in the resin composition is not particularly limited. From the standpoint of low moisture absorption and dielectric properties, the mass ratio of component (A) to component (B), (B)/(A), is preferably 0.01 to 3, more preferably 0.03 to 2, and even more preferably 0.05 to 1.

Component (B) is not particularly limited as long as it contains an aromatic ring. Because aromatic rings are rigid and have low thermal expansion, using a component (B) containing an aromatic ring can reduce the thermal expansion coefficient of the resin composition. The maleimide group may be bonded to either an aromatic ring or an aliphatic chain, but from the perspective of low thermal expansion, it is preferably bonded to an aromatic ring. Component (B) may also be a polymaleimide compound containing two or more maleimide groups. Component (B) may be used alone or in combination of two or more types.

Examples of component (B) include 1,2-dimaleimidoethane, 1,3-dimaleimidopropane, bis(4-maleimidophenyl)methane, bis(3-ethyl-4-maleimidophenyl)methane, bis(3-ethyl-5-methyl-4-maleimidophenyl)methane, 2,7-dimaleimidofluorene, N,N'-(1,3-phenylene)bismaleimide, N,N'-(1,3-(4-methylphenylene))bismaleimide, bis(4-maleimidophenyl)sulfone, bis(4-maleimidophenyl)sulfide, bis(4-maleimidophenyl)ether, 1,3-bis(3-maleimidophenoxy)benzene, 1,3-bis(3-(3-maleimidophenoxy)phenoxy)benzene, bis( bis(4-maleimidophenoxy)phenyl)ketone, 2,2-bis(4-(4-maleimidophenoxy)phenyl)propane, bis(4-(4-maleimidophenoxy)phenyl)sulfone, bis[4-(4-maleimidophenoxy)phenyl]sulfoxide, 4,4'-bis(3-maleimidophenoxy)biphenyl, 1,3-bis(2-(3-maleimidophenyl)propyl)benzene, 1,3-bis(1-(4-(3-maleimidophenoxy)phenyl)-1-propyl)benzene, bis(maleimidocyclohexyl)methane, 2,2-bis[4-(3-maleimidophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, and bis(maleimidophenyl)thiophene. To further reduce moisture absorption and the coefficient of thermal expansion, bis(3-ethyl-5-methyl-4-maleimidophenyl)methane may be used as component (B). To further increase the breaking strength and metal foil peel strength of the resin film formed from the resin composition, 2,2-bis(4-(4-maleimidophenoxy)phenyl)propane may be used as component (B).

From the viewpoint of moldability, a compound represented by the following formula (VI) may be used as component (B).

In formula (VI), _A4 represents a residue represented by the following formula (VII), (VIII), (IX) or (X), and _A5 represents a residue represented by the following formula (XI): From the viewpoint of low thermal expansion, _A4 may be a residue represented by the following formula (VII), (VIII) or (IX).

In formula (VII), each R ₁₀ independently represents a hydrogen atom, an aliphatic hydrocarbon group having 1 to 5 carbon atoms, or a halogen atom.

In formula (VIII), R ₁₁ and R ₁₂ each independently represent a hydrogen atom, an aliphatic hydrocarbon group having 1 to 5 carbon atoms, or a halogen atom, and A ₆ represents an alkylene group or alkylidene group having 1 to 5 carbon atoms, an ether group, a sulfide group, a sulfonyl group, a carbonyl group, a single bond, or a residue represented by the following formula (VIII-1):

In formula (VIII-1), R ₁₃ and R ₁₄ each independently represent a hydrogen atom, an aliphatic hydrocarbon group having 1 to 5 carbon atoms, or a halogen atom, and A ₇ represents an alkylene group having 1 to 5 carbon atoms, an isopropylidene group, an ether group, a sulfide group, a sulfonyl group, a carbonyl group, or a single bond.

In formula (IX), i is an integer of 1 to 10.

In formula (X), R ₁₅ and R ₁₆ each independently represent a hydrogen atom or an aliphatic hydrocarbon group having 1 to 5 carbon atoms, and j represents an integer of 1 to 8.

In formula (XI), R ₁₇ and R ₁₈ each independently represent a hydrogen atom, an aliphatic hydrocarbon group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, a hydroxyl group, or a halogen atom, and A ₈ represents an alkylene group or alkylidene group having 1 to 5 carbon atoms, an ether group, a sulfide group, a sulfonyl group, a carbonyl group, a fluorenylene group, a single bond, a residue represented by the following formula (XI-1) or a residue represented by the following formula (XI-2):

In formula (XI-1), R ₁₉ and R ₂₀ each independently represent a hydrogen atom, an aliphatic hydrocarbon group having 1 to 5 carbon atoms, or a halogen atom, and A ₉ represents an alkylene group having 1 to 5 carbon atoms, an isopropylidene group, an m-phenylenediisopropylidene group, a p-phenylenediisopropylidene group, an ether group, a sulfide group, a sulfonyl group, a carbonyl group, or a single bond.

In formula (XI-2), each R ₂₁ independently represents a hydrogen atom, an aliphatic hydrocarbon group having 1 to 5 carbon atoms, or a halogen atom, and each A ₁₀ and A ₁₁ independently represents an alkylene group having 1 to 5 carbon atoms, an isopropylidene group, an ether group, a sulfide group, a sulfonyl group, a carbonyl group, or a single bond.

Component (B) may be a compound having an amino group and a maleimide group from the viewpoints of solubility in organic solvents, high-frequency characteristics, and high adhesion to ceramic substrates and metal foils. A compound having an amino group and a maleimide group can be obtained, for example, by subjecting a bismaleimide compound to a Michael addition reaction with an aromatic diamine compound having two primary amino groups in an organic solvent.

Examples of aromatic diamine compounds include 4,4'-diaminodiphenylmethane, 4,4'-diamino-3,3'-dimethyl-diphenylmethane, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2-bis(4-(4-aminophenoxy)phenyl)propane, 4,4'-[1,3-phenylenebis(1-methylethylidene)]bisaniline, and 4,4'-[1,4-phenylenebis(1-methylethylidene)]bisaniline. These may be used alone or in combination of two or more.

From the viewpoints of high solubility in organic solvents, high reaction rate during synthesis, and high heat resistance, the aromatic diamine compound may be 4,4'-diaminodiphenylmethane or 4,4'-diamino-3,3'-dimethyl-diphenylmethane.

Examples of organic solvents include alcohol compounds such as methanol, ethanol, butanol, butyl cellosolve, ethylene glycol monomethyl ether, and propylene glycol monomethyl ether; ketone compounds such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; aromatic hydrocarbons such as toluene, xylene, and mesitylene; ester compounds such as methoxyethyl acetate, ethoxyethyl acetate, butoxyethyl acetate, and ethyl acetate; and nitrogen-containing compounds such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone. One organic solvent may be used alone, or two or more may be mixed together. Among these, methyl ethyl ketone, cyclohexanone, propylene glycol monomethyl ether, N,N-dimethylformamide, and N,N-dimethylacetamide are preferred from the standpoint of solubility.

The resin composition according to this embodiment may further contain a catalyst to promote the curing of component (A). The amount of catalyst is not particularly limited, but may be 0.1 to 5% by mass relative to the total mass of the resin composition. Examples of catalysts that can be used include peroxides and azo compounds.

Examples of peroxides include dicumyl peroxide, dibenzoyl peroxide, 2-butanone peroxide, tert-butyl perbenzoate, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, bis(tert-butylperoxyisopropyl)benzene, and tert-butyl hydroperoxide. Examples of azo compounds include 2,2'-azobis(2-methylpropanenitrile), 2,2'-azobis(2-methylbutanenitrile), and 1,1'-azobis(cyclohexanecarbonitrile).

The resin composition according to this embodiment may further contain an inorganic filler. By adding any appropriate inorganic filler, the resin layer can be improved in low thermal expansion properties, high elastic modulus, heat resistance, flame retardancy, and the like. Examples of inorganic fillers 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, calcined clay, talc, aluminum borate, and silicon carbide. These may be used alone or in combination of two or more.

There are no particular restrictions on the shape or particle size of the inorganic filler. The particle size of the inorganic filler may be, for example, 0.01 to 20 μm or 0.1 to 10 μm. Particle size refers to the average particle size, and is the particle size at the point corresponding to 50% volume when a cumulative frequency distribution curve is calculated based on particle size, with the total volume of the particles being 100%. The average particle size can be measured using a particle size distribution measuring device that uses the laser diffraction scattering method.

When an inorganic filler is used, there are no particular restrictions on the amount used. However, for example, the inorganic filler content is preferably 3 to 75 volume % of the total solid content in the resin composition, and more preferably 5 to 70 volume %. When the inorganic filler content in the resin composition is within the above range, good curability, moldability, and chemical resistance are more likely to be achieved.

When inorganic fillers are used, a coupling agent can be used in combination as needed to improve the dispersibility of the inorganic filler and its adhesion to organic components. Examples of coupling agents that can be used include silane coupling agents and titanate coupling agents. These can be used alone or in combination of two or more. The amount of coupling agent added can be, for example, 0.1 to 5 parts by mass or 0.5 to 3 parts by mass per 100 parts by mass of the inorganic filler used. Within these ranges, there is little deterioration in various properties, making it easier to effectively utilize the benefits of using inorganic fillers.

When using a coupling agent, the so-called integral blending method can be used, in which the inorganic filler is blended into the resin composition and then the coupling agent is added. However, it is preferable to use an inorganic filler that has been surface-treated in advance with a coupling agent using a dry or wet method. This method allows the above-mentioned characteristics of the inorganic filler to be more effectively expressed.

The resin composition of this embodiment may further contain, as component (C), a thermosetting resin (C) different from components (A) and (B). Compounds that may fall under component (A) or component (B) are not considered to belong to component (C). By including component (C), the low thermal expansion properties of the resin composition can be further improved. Examples of component (C) include epoxy resins and cyanate ester resins. One type of component (C) may be used alone, or two or more types may be used in combination.

Examples of epoxy resins include bisphenol A epoxy resins, bisphenol F epoxy resins, bisphenol S epoxy resins, alicyclic epoxy resins, linear aliphatic epoxy resins, naphthalene skeleton-containing epoxy resins such as phenol novolac epoxy resins, cresol novolac epoxy resins, bisphenol A novolac epoxy resins, phenol aralkyl epoxy resins, naphthol novolac epoxy resins, and naphthol aralkyl epoxy resins, as well as difunctional biphenyl epoxy resins, biphenyl aralkyl epoxy resins, dicyclopentadiene epoxy resins, and dihydroanthracene epoxy resins. From the perspective of high-frequency characteristics and thermal expansion characteristics, naphthalene skeleton-containing epoxy resins or biphenyl aralkyl epoxy resins may also be used.

Examples of cyanate ester resins include 2,2-bis(4-cyanatophenyl)propane, bis(4-cyanatophenyl)ethane, bis(3,5-dimethyl-4-cyanatophenyl)methane, 2,2-bis(4-cyanatophenyl)-1,1,1,3,3,3-hexafluoropropane, α,α'-bis(4-cyanatophenyl)-m-diisopropylbenzene, cyanate ester compounds of phenol-added dicyclopentadiene polymer, phenol novolac-type cyanate ester compounds, and cresol novolac-type cyanate ester compounds. Considering the overall balance of low cost, high-frequency characteristics, and other properties, 2,2-bis(4-cyanatophenyl)propane may also be used.

When the resin composition according to this embodiment contains component (C), it may further contain a curing agent for component (C). This allows the reaction to proceed smoothly when obtaining a cured product of the resin composition, and also makes it possible to appropriately adjust the physical properties of the resulting cured product of the resin composition. One type of curing agent may be used alone, or two or more types may be used in combination.

Examples of epoxy resin curing agents include polyamine compounds such as diethylenetriamine, triethylenetetramine, diaminodiphenylmethane, m-phenylenediamine, and dicyandiamide; polyphenol compounds such as bisphenol A, phenol novolac resin, cresol novolac resin, bisphenol A novolac resin, and phenol aralkyl resin; acid anhydrides such as phthalic anhydride and pyromellitic anhydride; carboxylic acid compounds; and active ester compounds.

Examples of curing agents for cyanate ester resins include monophenol compounds, polyphenol compounds, amine compounds, alcohol compounds, acid anhydrides, and carboxylic acid compounds.

The resin composition according to the present embodiment may further contain a curing accelerator depending on the type of component (C). Examples of curing accelerators for epoxy resins include imidazole-based curing accelerators, _BF3 amine complexes, and phosphorus-based curing accelerators. From the viewpoints of the storage stability of the resin composition, the handleability of the semi-cured resin composition, and solder heat resistance, imidazole-based curing accelerators and phosphorus-based curing accelerators are preferred.

The resin composition according to this embodiment may further contain a thermoplastic resin to improve the handleability of the resin film. There are no particular limitations on the type of thermoplastic resin, and there are no limitations on the molecular weight either. However, in order to further enhance compatibility with component (A), it is preferable that the number average molecular weight (Mn) be 200 to 60,000.

From the standpoint of film-forming properties and moisture absorption resistance, the thermoplastic resin is preferably a thermoplastic elastomer. Examples of thermoplastic elastomers include saturated thermoplastic elastomers, such as chemically modified saturated thermoplastic elastomers and unmodified saturated thermoplastic elastomers. Examples of chemically modified saturated thermoplastic elastomers include styrene-ethylene-butylene copolymers modified with maleic anhydride. Specific examples of chemically modified saturated thermoplastic elastomers include Tuftec M1911, M1913, and M1943 (trade names, manufactured by Asahi Kasei Corporation). On the other hand, examples of unmodified saturated thermoplastic elastomers include unmodified styrene-ethylene-butylene copolymers. Specific examples of unmodified saturated thermoplastic elastomers include Tuftec H1041, H1051, H1043, and H1053 (trade names, manufactured by Asahi Kasei Corporation).

From the standpoint of film-forming properties, dielectric properties, and moisture absorption resistance, it is more preferable for saturated thermoplastic elastomers to have styrene units in their molecules. In this specification, "styrene units" refers to units in a polymer derived from styrene monomers, and "saturated thermoplastic elastomers" refers to elastomers in which the aliphatic hydrocarbon portions of the styrene units, other than the aromatic hydrocarbon portions, are all composed of saturated bond groups.

The content of styrene units in the saturated thermoplastic elastomer is not particularly limited, but is preferably 10 to 80% by mass, and more preferably 20 to 70% by mass, in terms of the mass percentage of styrene units relative to the total mass of the saturated thermoplastic elastomer. When the content of styrene units is within the above range, the film tends to have excellent appearance, heat resistance, and adhesiveness.

A specific example of a saturated thermoplastic elastomer having styrene units in its molecule is a styrene-ethylene-butylene copolymer. A styrene-ethylene-butylene copolymer can be obtained, for example, by hydrogenating the unsaturated double bonds in the butadiene-derived structural units of a styrene-butadiene copolymer.

The amount of thermoplastic resin contained is not particularly limited, but from the perspective of further improving the dielectric properties, it may be 0.1 to 15 mass%, 0.3 to 10 mass%, or 0.5 to 5 mass% of the total solid content of the resin composition.

The resin composition according to this embodiment may further contain a flame retardant. The flame retardant is not particularly limited, but preferred examples include bromine-based flame retardants, phosphorus-based flame retardants, and metal hydroxides. One type of flame retardant may be used alone, or two or more types may be used in combination.

Brominated flame retardants include, for example, brominated epoxy resins such as brominated bisphenol A epoxy resins and brominated phenol novolac epoxy resins; brominated additive flame retardants such as hexabromobenzene, pentabromotoluene, ethylene bis(pentabromophenyl), ethylene bistetrabromophthalimide, 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane, tetrabromocyclooctane, hexabromocyclododecane, bis(tribromophenoxy)ethane, brominated polyphenylene ether, brominated polystyrene, and 2,4,6-tris(tribromophenoxy)-1,3,5-triazine; and brominated reaction flame retardants containing unsaturated double bond groups such as tribromophenylmaleimide, tribromophenyl acrylate, tribromophenyl methacrylate, tetrabromobisphenol A dimethacrylate, pentabromobenzyl acrylate, and brominated styrene.

Phosphorus-based flame retardants include, for example, aromatic phosphate esters such as triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, cresyl diphenyl phosphate, cresyl di-2,6-xylenyl phosphate, and resorcinol bis(diphenyl phosphate); phosphonate esters such as divinyl phenylphosphonate, diallyl phenylphosphonate, and bis(1-butenyl) phenylphosphonate; phosphinate esters such as phenyl diphenylphosphinate, methyl diphenylphosphinate, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide derivatives; phosphazene compounds such as bis(2-allylphenoxy)phosphazene and dicresyl phosphazene; and phosphorus-based flame retardants such as melamine phosphate, melamine pyrophosphate, melamine polyphosphate, melam polyphosphate, ammonium polyphosphate, phosphorus-containing vinylbenzyl compounds, and red phosphorus. Metal hydroxide flame retardants include, for example, magnesium hydroxide and aluminum hydroxide.

The resin composition according to this embodiment can be obtained by uniformly dispersing and mixing the above-described components. There are no particular limitations on the means and conditions for preparing the resin composition. For example, the resin composition may be prepared by thoroughly and uniformly stirring and mixing the predetermined amounts of the components using a mixer or the like, kneading the mixture using a mixing roll, extruder, kneader, roll, extruder, or the like, and then cooling and pulverizing the resulting mixture.

The dielectric constant of the cured product (resin layer after curing) of the resin composition according to this embodiment is not particularly limited, but from the viewpoint of suitable use in the high frequency band, the dielectric constant at 10 GHz is preferably 3.6 or less, more preferably 3.1 or less, and even more preferably 3.0 or less. There is no particular limit on the lower limit of the dielectric constant, but it may be, for example, about 1.0. Furthermore, from the viewpoint of suitable use in the high frequency band, the dielectric loss tangent of the cured product of the resin composition is preferably 0.004 or less, more preferably 0.003 or less. There is no particular limit on the lower limit of the dielectric constant, but it may be, for example, about 0.0001.

To prevent warping of the laminate, the thermal expansion coefficient of the cured resin composition is preferably 10 to 90 ppm/°C, more preferably 10 to 45 ppm/°C, and even more preferably 10 to 40 ppm/°C. The thermal expansion coefficient can be measured in accordance with IPC-TM-650 2.4.24.

The resin layer 2 may be formed by applying a resin composition directly to the ceramic substrate 1, by laminating a resin film on the ceramic substrate 1, or by using a resin-coated metal foil.

The term "resin film" refers to a resin composition in the form of an uncured or semi-cured film. There are no particular restrictions on the method for producing a resin film from a resin composition. For example, a resin film may be obtained by applying the resin composition to a support substrate and drying the resulting resin layer. Specifically, the resin composition according to this embodiment may be applied to a support substrate using a kiss coater, roll coater, comma coater, or the like, and then dried in a heated drying oven or the like at a temperature of, for example, 70 to 250°C, preferably 70 to 200°C, for 1 to 30 minutes, preferably 3 to 15 minutes. This allows for the production of a resin film in which the resin composition is semi-cured.

The semi-cured resin film can be further heated in a heating oven at a temperature of, for example, 170 to 250°C, preferably 185 to 230°C, for 60 to 150 minutes to thermally cure the resin film.

The thickness of the resin film is not particularly limited, but may be 0.01 to 2.0 times, 0.05 to 1.0 times, or 0.1 to 0.9 times the thickness of the ceramic substrate. If the thickness of the resin film is 2.0 times or less, the dielectric constant of the laminate is more likely to be reduced. If the thickness of the resin film is 0.01 times or more, the rigidity and dimensional stability of the laminate are more likely to be improved. The thickness of the resin film may be, for example, 1 to 200 μm, 3 to 180 μm, 5 to 150 μm, 10 to 100 μm, or 15 to 80 μm.

The supporting substrate is not particularly limited, but is preferably at least one selected from the group consisting of glass, metal foil, and PET film. Providing a supporting substrate for the resin film tends to improve storage properties and ease of handling when used to manufacture laminates. When metal foil is used as the supporting substrate, a resin-coated metal foil is obtained.

(metal foil)
In order to reduce transmission loss, a metal foil having a low surface roughness (low-roughening metal foil) can be used as the metal foil according to this embodiment. The surface roughness of the metal foil may be 0.05 to 2 μm, 0.1 to 1.5 μm, or 0.15 to 1 μm. The thickness of the metal foil may be 5 to 100 μm, 8 to 70 μm, 10 to 40 μm, or 15 to 30 μm.

Examples of metal foils include foils of copper, aluminum, iron, gold, silver, nickel, palladium, chromium, molybdenum, or alloys thereof. Copper foil is preferably used as the metal foil from the viewpoints of workability, flexibility, electrical conductivity, etc. As the copper foil, electrolytic copper foil may be used from the viewpoint of peel strength, or peelable copper foil may also be used. Peelable copper foil refers to a multilayer copper foil in which a carrier copper foil and a copper foil (generally an ultra-thin copper foil of 1 to 9 μm) are peelably laminated together. Since the carrier copper foil is peelable, peelable copper foil is also called ultra-thin copper foil with a carrier. The thickness of the carrier copper foil may be, for example, 10 to 80 μm.

Commercially available ultra-thin copper foil with a carrier includes, for example, FUTF-5DA-5, FUTF-5DA-3, FUTF-5DA-2, and FUTF-5DA-1.5 manufactured by Fukuda Metal Foil & Powder Co., Ltd.; and MT18Ex and MT18FL manufactured by Mitsui Mining & Smelting Co., Ltd. The surface roughness (Rz) may be 2 μm or less or 1.5 μm or less, and the copper foil thickness may be 1.5 to 5 μm.

Preferred embodiments of the present disclosure have been described above, but these are merely examples for the purpose of explaining the present disclosure and are not intended to limit the scope of the present invention to these embodiments alone. The present invention can be implemented in various forms different from the above-described embodiments without departing from the spirit of the present invention.

The present disclosure will be explained in more detail below based on examples. However, the present invention is not limited to the following examples.

(Preparation of Resin Composition)
As the component (A), a maleimide compound having the structure represented by the following formula (XII-3) (manufactured by Designer Molecules Inc., trade name: BMI-1500) was prepared. As the component (B), 2,2-bis(4-(4-maleimidophenoxy)phenylpropane (manufactured by Daiwa Chemical Industry Co., Ltd., trade name: BMI-4000) was prepared.

104.4 g of silica slurry (manufactured by Admatechs Co., Ltd., product name: SC-2050KNK), 9.1 g of toluene, 21.3 g of component (A), 5.1 g of component (B), and 0.53 g of catalyst (2,5'-dimethyl-2,5-di(t-butylperoxy)hexane, manufactured by NOF Corporation, product name: Perhexyne 25B) were placed in a container equipped with a stirrer and mixed by stirring at 25°C for 1 hour. The mixture was filtered using a #200 nylon mesh to obtain a resin composition.

[Example 1]
A carrier-attached copper foil (manufactured by Mitsui Mining & Smelting Co., Ltd., product number: MT18FL-1.5) was prepared, which had a 1.5 μm ultrathin copper foil provided on an 18 μm carrier copper foil. The resin composition was applied to the ultrathin copper foil surface of the carrier-attached copper foil using a comma coater, and then dried at 130°C to produce a resin-attached copper foil having a semi-cured resin layer. The thickness of the resin layer was 25 μm.

The resin-coated copper foil was placed on both sides of a ceramic substrate (manufactured by KOA Corporation, product name: KLC, thickness: 400 μm) so that the resin layer was in contact with the ceramic substrate. The resulting laminate was then pre-laminated using a vacuum laminator and vacuum pressed at 230°C/2.0 MPa/90 minutes to produce a ceramic substrate laminate.

(Via formation)
The carrier copper foil was peeled off from one side of the produced laminate to expose the ultrathin copper foil surface. Vias were then processed in the exposed ultrathin copper foil and resin layer using a direct UV laser (manufactured by Via Mechanics Co., Ltd., product name: LU-2L), followed by a wet desmear treatment using a _KMnO4 aqueous solution to form vias with a hole diameter of 30 μm in the ceramic substrate. When the laminate was inspected after via formation, no cracks or breakage were found in the ceramic substrate.

1...ceramic substrate, 2...resin layer, 4...metal foil.

Claims (10)

The method includes a step of laminating a metal foil on a ceramic substrate via a resin layer ,
A method for producing a ceramic substrate laminate, wherein the resin layer comprises a resin composition containing, as a component (A), a maleimide compound having a saturated or unsaturated divalent hydrocarbon group and a divalent group having at least two imide bonds, and as a component (B), an aromatic maleimide compound . The method according to claim 1 , wherein the aromatic maleimide compound has a structure in which a maleimide group is bonded to an aromatic ring. 3. The method according to claim 1 , wherein the saturated or unsaturated divalent hydrocarbon group has 8 to 100 carbon atoms. The method according to any one of claims 1 to 3 , wherein the saturated or unsaturated divalent hydrocarbon group is a group represented by the following formula (II):

[In formula (II), _R2 and _R3 each independently represent an alkylene group having 4 to 50 carbon atoms, _R4 represents an alkyl group having 4 to 50 carbon atoms, and _R5 represents an alkyl group having 2 to 50 carbon atoms.] The method according to any one of claims 1 to 4 , wherein the divalent group having at least two imide bonds is a group represented by the following formula (I):

[In formula (I), _R1 represents a tetravalent organic group.] a ceramic substrate; a resin layer provided on the ceramic substrate; and a metal foil laminated on a surface of the resin layer opposite to the ceramic substrate ,
a ceramic substrate laminate, wherein the resin layer comprises a resin composition containing, as a component (A), a maleimide compound having a saturated or unsaturated divalent hydrocarbon group and a divalent group having at least two imide bonds, and as a component (B), an aromatic maleimide compound. The ceramic substrate laminate according to claim 6 , wherein the aromatic maleimide compound has a structure in which a maleimide group is bonded to an aromatic ring. 8. The ceramic substrate laminate according to claim 6 , wherein the saturated or unsaturated divalent hydrocarbon group has 8 to 100 carbon atoms. The ceramic substrate laminate according to any one of claims 6 to 8 , wherein the saturated or unsaturated divalent hydrocarbon group is a group represented by the following formula (II):

[In formula (II), _R2 and _R3 each independently represent an alkylene group having 4 to 50 carbon atoms, _R4 represents an alkyl group having 4 to 50 carbon atoms, and _R5 represents an alkyl group having 2 to 50 carbon atoms.] The ceramic substrate laminate according to any one of claims 6 to 9 , wherein the divalent group having at least two imide bonds is a group represented by the following formula (I):

[In formula (I), _R1 represents a tetravalent organic group.]