Resin sheet, prepreg, insulating resin member, and printed wiring board

Abstract

The present disclosure provides a resin sheet (3) which can be used to form an insulating layer in which a conductor is embedded, makes it easy to embed the conductor in the insulating layer, and is less likely to deteriorate in moldability. The resin sheet (3) contains an uncured product or a semi-cured product of a thermosetting resin composition (X1). The melt viscosity measured using a Koka flow tester is 10 Pa·s to 2000 Pa·s under measurement conditions of 130°C and 1 MPa, and 6 Pa·s to 1200 Pa·s under measurement conditions of 130°C and 4 MPa.

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to resin sheets, prepregs, insulating resin members, and printed wiring boards. More specifically, the present disclosure relates to resin sheets and prepregs that can be used to form insulating layers of printed wiring boards, insulating layers including the resin sheets and prepregs, and printed wiring boards including the insulating layers formed from the resin sheets and prepregs. BACKGROUND

[0002] Patent Document 1 teaches manufacturing a multilayer printed wiring board by forming a laminate by interposing a heat-fusible and thermosetting resin sheet between an exposed surface of a via of a substrate and a prepreg containing an inorganic filler.

[0003] LIST OF CITATIONS

[0004] PATENT LITERATURE

[0005] Patent Document 1: JP 2003-37362 A SUMMARY

[0006] The problem to be solved by the present disclosure is to provide resin sheets and prepregs that can be used to form insulating layers in which a conductor is buried, making it easier to bury the conductor in the insulating layer and reducing the likelihood of causing a decrease in moldability, insulating resin members including the resin sheets and prepregs, and printed wiring boards including the insulating layers formed from the resin sheets and prepregs.

[0007] A resin sheet according to one aspect of the present disclosure includes an uncured product or semi-cured product of a thermosetting resin composition (X1). The resin sheet has a melt viscosity equal to or greater than 10 Pa s and equal to or less than 2000 Pa s when measured using a Koka flow tester under measurement conditions including 130°C and 1 MPa, and a melt viscosity equal to or greater than 6 Pa s and equal to or less than 1200 Pa s when measured using a Koka flow tester under measurement conditions including 130°C and 4 MPa.

[0008] A prepreg according to another aspect of the present disclosure is used together with the above-described resin sheet and includes: a base material; and an uncured product or semi-cured product of a thermosetting resin composition (X2) impregnated into the base material. The uncured product or semi-cured product of the thermosetting resin composition (X2) has a melt viscosity equal to or greater than 500 Pa s and equal to or less than 6000 Pa s when measured using a Koka flow tester under measurement conditions including 130°C and 4 MPa.

[0009] The insulating resin member according to still another aspect of the present disclosure includes the resin sheet described above; and the prepreg laminated on the resin sheet.

[0010] The printed wiring board according to yet another aspect of the present disclosure includes a core member including an insulating base and a conductor located above the insulating base; and an insulating layer laminated on the core member and covering the conductor. The insulating layer includes a first layer arranged in contact with the core member and being a cured product of the resin sheet described above; and a second layer laminated on the first layer and being a cured product of the prepreg described above. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a schematic cross-sectional view of a prepreg, resin sheet, and core member according to one exemplary embodiment of the present disclosure, and a laminate composed of the prepreg, resin sheet, and core member; and

[0012] Figure 2 is a schematic cross-sectional view of a printed wiring board according to an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION

[0013] The inventors found that, in the case where a printed wiring board is formed by laminating a resin sheet and a prepreg on a conductor and integrating the resin sheet and the prepreg with each other, thereby forming an insulating layer on the conductor from cured products of the resin sheet and the prepreg, and by burying the conductor into the cured product of the resin sheet, if the conductor is rather thick, it is difficult to sufficiently bury the conductor into the cured product of the resin sheet. Alternatively, even if the conductor can be sufficiently buried into the cured product of the resin sheet, when the insulating layer is molded from the resin sheet and the prepreg, moldability tends to decrease.

[0014] Accordingly, the inventors conducted research and development to provide a resin sheet that can be used to form an insulating layer in which a conductor is buried, so that it is easier to bury the conductor into the insulating layer and the possibility of causing moldability to decrease is reduced, thereby conceiving the idea of the present disclosure.

[0015] Exemplary embodiments of the present disclosure will now be described. Note that the following described embodiments are merely exemplary embodiments of the various embodiments of the present disclosure and should not be construed as limiting. Rather, the exemplary embodiments can be easily varied in various ways according to design choice or any other factor without departing from the scope of the present disclosure.

[0016] The resin sheet 3 according to the present embodiment includes an uncured product or a semi-cured product of a thermosetting resin composition (X1) (hereinafter simply referred to as "composition (X1)"). The melt viscosity of the resin sheet is equal to or greater than 10 Pa-s and equal to or less than 2000 Pa-s when measured using a Koka flow tester under measurement conditions including 130°C and 1 MPa, and the melt viscosity of the resin sheet is equal to or greater than 6 Pa-s and equal to or less than 1200 Pa-s when measured using a Koka flow tester under measurement conditions including 130°C and 4 MPa. Note that the uncured product can be the composition (X1) itself. Alternatively, if the composition (X1) contains a solvent, the uncured product can also be a product generated by volatilizing the solvent from the composition (X1) without allowing the curing reaction of the composition (X1) to proceed. On the other hand, the semi-cured product as used herein refers to a product generated by partially curing the composition (X1), and corresponds to a product in a so-called "Stage B" stage.

[0017] The insulating layer 8 in which the conductor 9 is embedded can be formed of the resin sheet 3. This enables, for example, the insulating layer 8 of the printed wiring board 5 to be formed using the resin sheet 3. According to the present embodiment, forming the insulating layer 8 in which the conductor 9 is embedded from the resin sheet 3 makes it easier to embed the conductor 9 into the insulating layer 8, and reduces the likelihood of causing a decrease in moldability.

[0018] The prepreg 2 according to the present embodiment is used for lamination on the resin sheet 3. The prepreg 2 includes: a base material 4; and an uncured product or a semi-cured product of a thermosetting resin composition (X2) (hereinafter simply referred to as "composition (X2)") impregnated into the base material 4. The melt viscosity of the uncured product or semi-cured product of the composition (X2) is equal to or greater than 500 Pa-s and equal to or less than 6000 Pa-s when measured using a Koka flow tester under measurement conditions including 130°C and 4 MPa. Note that the uncured product can be the composition (X2) itself. Alternatively, if the composition (X2) contains a solvent, the uncured product can also be a product generated by volatilizing the solvent from the composition (X2) without allowing the curing reaction of the composition (X2) to proceed. On the other hand, the semi-cured product as used herein refers to a product generated by partially curing the composition (X2), and corresponds to a product in a so-called "Stage B" stage.

[0019] The insulating layer 8 in which the conductor 9 is embedded can be formed from the prepreg 2 and the resin sheet 3. For example, this makes it possible to use the prepreg 2 and the resin sheet 3 to form the insulating layer 8 of the printed wiring board 5. According to the present embodiment, forming the insulating layer 8 in which the conductor 9 is embedded from the prepreg 2 and the resin sheet 3 makes it easier to embed the conductor 9 in the insulating layer 8, and significantly reduces the likelihood of causing a decrease in moldability.

[0020] Next, how the insulating layer 8 is formed and how the printed wiring board 5 is manufactured will be described with reference to Figure 1 and 2

[0021] To form the insulating layer 8 from the prepreg 2 and the resin sheet 3, specifically, for example, as shown in Figure 1 a core member 11 including a conductor 9 such as a conductor line is provided. The core member 11 includes, for example, an insulating base 10 and the conductor 9 located above the insulating base 10. Any material can be used for the insulating base 10 and the conductor 9, as long as the material can be used as a material for a printed wiring board. The insulating base 10 can be, for example, a resin base such as an epoxy resin base including a glass base material. The conductor 9 can be a copper line formed by, for example, an additive method or a subtractive method.

[0022] In the example shown in Figure 1 , as the conductor 9, the core member 11 includes a first conductor 91 located above one surface (first surface 101) of the insulating base 10 and a second conductor 92 located above a second surface 102 of the insulating base 10 opposite the first surface 101.

[0023] An electronic component 13 can be mounted on each surface of the core member 11 having the conductor 9. The electronic component 13 can be, but is not limited to, an IC and an LSI.

[0024] As shown in Figure 1 , the core member 11, the resin sheet 3, and the prepreg 2 are sequentially laminated to each other with the conductor 9 facing the resin sheet 3, thereby forming a laminate 12. Optionally, as shown in Figure 1 , the laminate 12 can further include a metal foil sheet 14. In this case, the core member 11, the resin sheet 3, the prepreg 2, and the metal foil sheet 14 are sequentially laminated to each other with the conductor 9 facing the resin sheet 3, thereby forming the laminate 12 as shown in Figure 1 . The metal foil sheet 14 can be, but is not limited to, a copper foil sheet.

[0025] In the example shown in Figure 1 ​In the example shown, one resin sheet 3, one prepreg 2, and one metal foil sheet 14 are sequentially stacked on each other on the first conductor 91 of the core member 11, and another resin sheet 3, another prepreg 2, and another metal foil sheet 14 are sequentially stacked on each other on the second conductor 92 of the core member 11. That is, one metal foil sheet 14, one prepreg 2, one resin sheet 3, the core member 11, another resin sheet 3, another prepreg 2, and another metal foil sheet 14 are sequentially stacked on each other. Alternatively, the resin sheet 3 and the prepreg 2 can be stacked only on one side of the core member 11.

[0026] Next, the hot-press laminate 12 is pressed, and the resin sheet 3 softens or melts and becomes to have a reduced viscosity and starts to flow along the shape of the conductor 9. If the electronic component 13 is mounted on the core member 11, the resin sheet 3 also flows along the shape of the electronic component 13. In this way, the conductor 9 is embedded into the resin sheet 3. If the electronic component 13 is mounted on the core member 11, the electronic component 13 is also embedded into the resin sheet 3. Subsequently, the resin sheet 3 is cured. As a result, the first layer 7 is formed as a cured product of the resin sheet 3, and the conductor 9 is embedded into the first layer 7. If the electronic component 13 is mounted on the core member 11, the electronic component 13 is also embedded into the first layer 7.

[0027] In the same way, the prepreg 2 also softens or melts and becomes to have a reduced viscosity and starts to flow, and then is cured, thereby forming the second layer 6. In this way, the printed wiring board 5 as shown is manufactured. Figure 2

[0028] The printed wiring board 5 includes the insulating substrate 10, the conductor 9, and the insulating layer 8, which are sequentially stacked on each other. If the laminate 12 includes the metal foil sheet 14, the printed wiring board 5 further includes the foil sheet 14 stacked on the insulating layer 8. For example, the conductor line can be formed by patterning the metal foil sheet 14 with an etching process. In this case, the printed wiring board 5 including the conductor line above the insulating layer 8 is obtained. If the electronic component 13 is mounted on the core member 11, the printed wiring board 5 further includes the electronic component 13. The insulating layer 8 includes the second layer 6 as a cured product of the prepreg 2 and the first layer 7 as a cured product of the resin sheet 3. The conductor 9 is located opposite to the second layer 6 with respect to the first layer 7. In the present embodiment, the conductor 9 and the electronic component 13 are embedded into the first layer 7.

[0029] ​The printed wiring board 5 is manufactured in this way to enable the conductor 9 to be embedded into the insulating layer 8 by flowing the resin sheet 3 that has been softened or melted, and to reduce the possibility of the conductor 9 in the insulating layer 8 coming into contact with the base material 4 in the prepreg 2, thereby making it easier to improve reliability when the printed wiring board 5 is heated. In addition, in the insulating layer 8, the base material 4 is not included in the first layer 7 but is included in the second layer 6, thereby enabling the amount of base material 4 used to be reduced and making it easier to reduce the thickness of the insulating layer 8.

[0030] The conditions of the hot-pressing laminate 12 can be appropriately adjusted, for example, in accordance with the respective chemical compositions of the compositions (X1) and (X2), but can include, for example, a heating temperature equal to or higher than 150°C and equal to or lower than 250°C, a pressing pressure equal to or higher than 0.5 MPa and equal to or lower than 5 MPa, and a treatment time equal to or longer than 60 minutes and equal to or shorter than 120 minutes.

[0031] As described above, the melt viscosity η1 of the resin sheet 3 is equal to or greater than 10 Pa s and equal to or less than 2000 Pa s when measured using the Koka flow tester under measurement conditions including 130°C and 1 MPa, and the melt viscosity η2 of the resin sheet 3 is equal to or greater than 6 Pa s and equal to or less than 1200 Pa s when measured using the Koka flow tester under measurement conditions including 130°C and 4 MPa. Thus, making the melt viscosity η1 at 1 MPa equal to or greater than 10 Pa s and making the melt viscosity η2 at 4 MPa equal to or greater than 6 Pa s reduces the possibility of leaving unfilled voids in the first layer 7 or generating air bubbles in the first layer 7. This contributes to improving the reliability of the printed wiring board 5. In addition, making the melt viscosity η1 at 1 MPa equal to or less than 2000 Pa s and making the melt viscosity η2 at 4 MPa equal to or less than 1200 Pa s reduces the possibility of resin flowing out when the first layer 7 is formed. This can reduce the dispersion of the thickness of the insulating layer 8, and also reduces the possibility of causing failure in long-term insulation reliability tests by preventing the conductor 9 from coming into contact with the base material 4 in the prepreg 2. Specifically, arranging the conductor 9 too close to the base material 4 in the prepreg 2 makes it easier for ions to move along the base material 4, thereby possibly causing ion migration. In contrast, interposing the first layer 7 between the conductor 9 and the prepreg 2 reduces the possibility of causing ion migration. A specific exemplary method for measuring the melt viscosity will be described later in the “Examples” section.

[0032] The melt viscosity η2 under measuring conditions including 130°C and 4 MPa is one of factors that roughly determine the flowability of the resin sheet 3, particularly the flowability when the resin sheet 3 flows along the conductor 9, i.e., specifically, the filling property thereof. During the molding process, a relatively high pressure is applied to the portion of the resin sheet 3 that surrounds the conductor 9. However, setting the melt viscosity η2 within this range will increase the flowability of the portion, and ultimately improve the filling property. On the other hand, the melt viscosity η1 under measuring conditions including 130°C and 1 MPa is one of factors that roughly determine how smoothly the resin can flow out from the resin sheet 3 (i.e., the thickness accuracy of the insulating layer 8). During the molding process, for example, a relatively low pressure is applied to the end portion of the resin sheet 3. However, setting the melt viscosity η1 within this range will reduce the possibility of excessive flow of the resin in the portion, thereby making it less likely for the resin in the resin sheet 3 to flow out.

[0033] The melt viscosity η1 under measuring conditions including 130°C and 1 MPa is more preferably equal to or greater than 30 Pa-s, and even more preferably equal to or greater than 50 Pa-s. In addition, this melt viscosity η1 is more preferably equal to or less than 1000 Pa-s, and even more preferably equal to or less than 500 Pa-s. The melt viscosity η2 under measuring conditions including 130°C and 4 MPa is more preferably equal to or greater than 10 Pa-s, and even more preferably equal to or greater than 20 Pa-s. In addition, this melt viscosity η2 is more preferably equal to or less than 600 Pa-s, and even more preferably equal to or less than 300 Pa-s.

[0034] The thixotropic index (TI) of the resin sheet 3 is preferably equal to or greater than 1.1. This particularly significantly reduces the possibility of flow-out of the resin when the first layer 7 is formed. The thixotropic index is defined as the ratio (η1 / η2) of the melt viscosity η1 under measuring conditions including 130°C and 1 MPa to the melt viscosity η2 under measuring conditions including 130°C and 4 MPa. In addition, this thixotropic index is preferably equal to or less than 15. This will particularly significantly improve the filling property of the insulating layer 8. The thixotropic index is more preferably equal to or greater than 1.2 and equal to or less than 8.0, and particularly preferably equal to or greater than 1.3 and equal to or less than 4.0.

[0035] The resin flowability of the resin sheet 3 measured by the Glynis method under measurement conditions including 130°C and 0.5 MPa is preferably equal to or lower than 40%. This will further reduce the flow-out of the resin when the first layer 7 is formed from the resin sheet 3, further improve the thickness accuracy of the insulating layer 8, and further reduce the possibility of the conductor 9 contacting the base material 4 in the prepreg 2. The resin flowability is more preferably equal to or less than 35%, and even more preferably equal to or less than 30%. A specific exemplary method for measuring the resin flowability will be described later in the "Examples" section.

[0036] As described above, the melt viscosity of the uncured product or semi-cured product of the composition (X2) of the prepreg 2 is equal to or greater than 500 Pa-s and equal to or less than 6000 Pa-s when measured using the Koka flow tester under measurement conditions including 130°C and 4 MPa. This makes it easier to further improve the thickness accuracy of the insulating layer 8, and further reduce the possibility of the conductor 9 contacting the base material 4 in the prepreg 2. It is presumed that this is because reducing the excessive flow of the prepreg 2 when the second layer 6 is formed from the prepreg 2 will enable the reduction of the excessive flow of the resin sheet 3 due to the flow of the prepreg 2. A specific exemplary method for measuring the melt viscosity will be described later in the "Examples" section.

[0037] This melt viscosity is more preferably equal to or greater than 700 Pa-s, and even more preferably equal to or greater than 1000 Pa-s. In addition, this melt viscosity is more preferably equal to or less than 5000 Pa-s, and even more preferably equal to or less than 4000 Pa-s.

[0038] The melt viscosity of the prepreg 2 under measurement conditions including 130°C and 4 MPa is preferably higher than the melt viscosity of the resin sheet 3 under measurement conditions including 130°C and 4 MPa. In particular, the melt viscosity of the prepreg 2 is preferably equal to or greater than 2000 Pa-s.

[0039] The prepreg 2 and the resin sheet 3 will be described in more detail.

[0040] As described above, the resin sheet 3 is an uncured product or semi-cured product of the composition (X1). Any material can be used without limitation as the composition (X1) as long as the material can be used to form the insulating layer 8 of the printed wiring board 5.

[0041] The composition (X1) contains a thermosetting resin. As used herein, the thermosetting resin can include at least one selected from the group consisting of monomers, oligomers, and prepolymers, all of which have thermosetting properties. The thermosetting resin includes at least one selected from the group consisting of, for example, an epoxy resin, a polyimide resin, a phenol resin, a bismaleimide triazine resin, and a thermosetting polyphenylene ether resin. The epoxy resin includes at least one component selected from the group consisting of, for example, a bisphenol A epoxy resin, a bisphenol F epoxy resin, a cresol-novolak epoxy resin, a bisphenol A novolak epoxy resin, a bisphenol F novolak epoxy resin, a naphthalene epoxy resin, a biphenyl epoxy resin, a dicyclopentadiene epoxy resin, and a multifunctional epoxy resin. The epoxy equivalent weight of the epoxy resin is preferably equal to or greater than 120 g / eq and equal to or less than 800 g / eq, and more preferably equal to or greater than 170 g / eq and equal to or less than 600 g / eq. Note that these are merely exemplary components that can be included in the thermosetting resin, and should not be construed as limiting.

[0042] The composition (X1) can also contain a suitable additive selected from the group consisting of a curing agent, a curing accelerator, a flame retardant, a rubber component, and an inorganic filler. The composition (X1) can also contain a solvent.

[0043] The curing agent includes at least one selected from the group consisting of, for example, a diamine-based curing agent, a difunctional or higher functional phenolic curing agent, an acid anhydride-based curing agent, a dicyandiamide, and a low molecular weight polyphenylene ether compound. The difunctional or higher functional phenolic curing agent includes, for example, a bisphenol A novolak phenol-aldehyde resin. The diamine-based curing agent includes, for example, at least one selected from the group consisting of a primary amine and a secondary amine. The functional group equivalent of the curing agent is preferably equal to or greater than 20 g / eq and equal to or less than 500 g / eq.

[0044] The curing accelerator includes at least one selected from the group consisting of, for example, an imidazole compound, a tertiary amine compound, an organic phosphine compound, and a metal soap. The imidazole compound includes, for example, 2-ethyl-4-methylimidazole (2E4MZ).

[0045] The flame retardant includes at least one selected from the group consisting of, for example, a halogen-based flame retardant and a non-halogen-based flame retardant. The halogen-based flame retardant includes, for example, a bromine-containing compound. The non-halogen-based flame retardant includes at least one selected from the group consisting of, for example, a phosphorus-containing compound and a nitrogen-containing compound.

[0046] The rubber component contains, for example, an elastomer fine particle. The elastomer fine particle can have, for example, a core-shell structure including a core layer and a shell layer, and contains a core-shell fine particle in which the shell layer is compatible with the epoxy resin. The polymer forming the shell layer contains, for example, at least one selected from the group consisting of polymethyl methacrylate and polystyrene. The polymer forming the core layer contains at least one selected from the group consisting of, for example, an acrylic polymer, a silicone polymer, a butadiene polymer, and an isoprene polymer.

[0047] The inorganic filler contains at least one selected from the group consisting of, for example, silicon dioxide, aluminum hydroxide, magnesium hydroxide, aluminum silicate, magnesium silicate, talc, clay, mica, and a molybdenum compound. The silicon dioxide contains at least one selected from the group consisting of, for example, spherical silicon dioxide and pulverized silicon dioxide. The molybdenum compound includes, for example, molybdenum trioxide. The content of the inorganic filler is preferably equal to or greater than 20 mass parts and equal to or less than 1400 mass parts with respect to 100 mass parts in total of the thermosetting resin and the curing agent.

[0048] The solvent contains at least one selected from the group consisting of, for example, a suitable organic solvent and water. The organic solvent contains, for example, at least one selected from the group consisting of benzene, toluene, N,N-dimethylformamide (DMF), acetone, methyl ethyl ketone, methanol, ethanol, and cellosolve.

[0049] Note that these are merely exemplary components of the composition (X1), and should not be construed as limiting.

[0050] For example, the composition (X1) can contain a phenoxy resin. The phenoxy resin imparts flexibility to the prepreg 2 formed from the composition (X1), and reduces the likelihood of causing chalking.

[0051] In forming the resin sheet 3, the composition (X1) is shaped into a sheet shape by, for example, a coating method. Examples of the coating method include a dip coating method, a spray coating method, a spin coating method, a roll coating method, a curtain coating method, and a screen printing method. Subsequently, the resin sheet 3 is formed by heating and thereby drying or semi-curing the composition (X1).

[0052] By appropriately setting the type and corresponding content of the components forming the composition (X1) and the heating conditions of the composition (X1) during the formation of the resin sheet 3, the resin sheet 3 can be made to have the melt viscosity and resin flowability within the aforementioned range. For example, by adding a low-viscosity component to the composition (X1), increasing the content of the low-viscosity component in the composition (X1), decreasing the heating temperature, and / or shortening the heating time, the resin sheet 3 can have a reduced melt viscosity and increased resin flowability. Furthermore, the melt viscosity under measurement conditions including 130°C and 1 MPa and the melt viscosity under measurement conditions including 130°C and 4 MPa can be adjusted by changing the type, particle size, and content of the inorganic filler in the composition (X1).

[0053] For example, the thickness of resin sheet 3 is equal to or greater than 50 μm and equal to or less than 200 μm. Although in Figure 1 The example shown uses a single resin sheet 3, but two or more resin sheets 3 can be stacked on top of each other.

[0054] As described above, the prepreg 2 includes a substrate 4 and an uncured or semi-cured product of the composition (X2) impregnated in the substrate 4.

[0055] Substrate 4 can be, for example, a sheet of inorganic fiber fabric, inorganic fiber nonwoven fabric, organic fiber fabric, or organic fiber nonwoven fabric. Inorganic fibers can be, for example, glass fibers or fibers of inorganic materials other than glass. Examples of glass as a constituent material of glass fibers include E glass, D glass, S glass, NE glass, T glass, and quartz. Examples of organic fibers include aramid fibers, poly(p-phenylenebenzodioxazole) (PBO) fibers, poly(benzimidazole) (PBI) fibers, poly(tetrafluoroethylene) (PTFE) fibers, poly(p-phenylenebenzobisthiazole) (PBZT) fibers, and fully aromatic polyester fibers.

[0056] Any material can be used in the composition (X2) without limitation, as long as the material can be used to form the insulating layer 8 of the printed circuit board 5.

[0057] The composition (X2) contains a thermosetting resin. The thermosetting resin includes at least one selected from the group consisting of, for example, an epoxy resin, a polyimide resin, a phenol resin, a bismaleimide triazine resin, and a thermosetting polyphenylene ether resin. The epoxy resin includes at least one component selected from the group consisting of, for example, a bisphenol A epoxy resin, a bisphenol F epoxy resin, a cresol-novolak epoxy resin, a bisphenol A novolak epoxy resin, a bisphenol F novolak epoxy resin, a naphthalene epoxy resin, a biphenyl epoxy resin, a dicyclopentadiene epoxy resin, and a multifunctional epoxy resin. The epoxy equivalent of the epoxy resin is preferably equal to or greater than 120 g / eq and equal to or less than 800 g / eq, and more preferably equal to or greater than 170 g / eq and equal to or less than 600 g / eq. Note that these are merely exemplary components that can be included in the thermosetting resin, and should not be construed as limiting.

[0058] The composition (X2) can also contain a suitable additive selected from the group consisting of a curing agent, a curing accelerator, a flame retardant, and a rubber component. The composition (X2) can also contain a solvent.

[0059] The curing agent includes at least one selected from the group consisting of, for example, a diamine-based curing agent, a difunctional or higher functional phenolic curing agent, an acid anhydride-based curing agent, a dicyandiamide, and a low molecular weight polyphenylene ether compound. The difunctional or higher functional phenolic curing agent includes, for example, a bisphenol A novolak phenol resin. The diamine-based curing agent includes, for example, at least one selected from the group consisting of a primary amine and a secondary amine. The functional group equivalent of the curing agent is preferably equal to or greater than 20 g / eq and equal to or less than 500 g / eq.

[0060] The curing accelerator includes at least one selected from the group consisting of, for example, an imidazole compound, a tertiary amine compound, an organic phosphine compound, and a metal soap. The imidazole compound includes, for example, 2-ethyl-4-methylimidazole (2E4MZ).

[0061] The flame retardant includes at least one selected from the group consisting of, for example, a halogen-based flame retardant and a non-halogen-based flame retardant. The halogen-based flame retardant includes, for example, a bromine-containing compound. The non-halogen-based flame retardant includes at least one selected from the group consisting of, for example, a phosphorus-containing compound and a nitrogen-containing compound.

[0062] The rubber component contains, for example, an elastomer fine particle. The elastomer fine particle can have, for example, a core-shell structure including a core layer and a shell layer, and contains a core-shell fine particle in which the shell layer is compatible with the epoxy resin. The polymer forming the shell layer contains, for example, at least one selected from the group consisting of polymethyl methacrylate and polystyrene. The polymer forming the core layer contains at least one selected from the group consisting of, for example, an acrylic polymer, a silicone polymer, a butadiene polymer, and an isoprene polymer.

[0063] The solvent contains at least one selected from the group consisting of, for example, a suitable organic solvent and water. The organic solvent contains, for example, at least one selected from the group consisting of benzene, toluene, N,N-dimethylformamide (DMF), acetone, methyl ethyl ketone, methanol, ethanol, and cellosolve.

[0064] Note that these are merely exemplary components of the composition (X2), and should not be construed as limiting.

[0065] For example, the composition (X2) can contain a phenoxy resin. The phenoxy resin imparts flexibility to the resin sheet 3 formed from the composition (X2), and reduces the likelihood of causing chalking.

[0066] Optionally, the composition (X2) can contain an inorganic filler. If the composition (X2) contains an inorganic filler, the content of the inorganic filler is suitably adjusted within a range not impairing the advantages of the present embodiment.

[0067] The prepreg 2 is formed by impregnating the composition (X2) into the base material 4, and then heating the composition (X2), thereby drying the composition (X2) or converting the composition (X2) into a semi-cured product. The conditions for heating the composition (X2) can be suitably adjusted depending on the chemical composition of the composition (X2) and the physical properties to be imparted to the prepreg 2.

[0068] For example, by suitably adjusting the types and respective contents of the components forming the composition (X2) and the conditions for heating the composition (X2) when forming the prepreg 2, the uncured product or semi-cured product of the composition (X2) in the prepreg 2 has a melt viscosity within the range defined above. For example, the melt viscosity of the uncured product or semi-cured product of the composition (X2) can be adjusted by adding a low-viscosity component to the composition (X2), increasing the content of the low-viscosity component in the composition (X2), lowering the heating temperature, and / or shortening the heating time.

[0069] The insulating resin member 1 including the resin sheet 3 and the prepreg 2 laminated on the resin sheet 3 can be formed by laminating the prepreg 2 on the resin sheet 3 and then heat-pressing the laminate.

[0070] As described above, the insulating layer 8 can be formed of the resin sheet 3 and the prepreg 2, and the printed wiring board 5 including the insulating layer 8 can be manufactured.

[0071] For example, the thickness of the conductor 9 (i.e., the conductor 9 of the core member 11) embedded into the insulating layer 8 at the time of manufacturing the printed wiring board 5 can be equal to or greater than 70 μm and equal to or less than 500 μm. Even if the conductor 9 is relatively thick, the present embodiment still makes it easier to embed the conductor 9 into the insulating layer 8, and reduces the likelihood of causing a decrease in moldability. In addition, if the conductor 9 is thick enough, the amount of current allowed to flow through the conductor 9 can be increased accordingly. This enables the printed wiring board 5 to be applied to, for example, industrial equipment and in-vehicle equipment that require a large amount of current to flow therethrough. The thickness of the conductor 9 is more preferably equal to or greater than 100 μm and equal to or less than 450 μm, and even more preferably equal to or greater than 130 μm and equal to or less than 420 μm. Note that these thickness ranges of the conductor 9 are merely examples, and should not be construed as limiting.

[0072] If the core member 11 includes the electronic component 13 mounted thereon, the thickness of the electronic component 13 can be, for example, equal to or greater than 100 μm and equal to or less than 500 μm. As used herein, the thickness of the electronic component 13 refers to the maximum height of the electronic component 13 measured from the surface of the insulating base 10 of the core member 11. Even if the thickness of the electronic component 13 is within such a range, the present embodiment still makes it easier to embed the electronic component 13 into the insulating layer 8, and reduces the likelihood of causing a decrease in moldability. The thickness of the electronic component 13 is more preferably equal to or greater than 100 μm and equal to or less than 450 μm, and even more preferably equal to or greater than 130 μm and equal to or less than 420 μm. Note that these thickness ranges of the electronic component 13 are merely examples, and should not be construed as limiting.

[0073] Embodiment

[0074] Next, a more specific example of the present embodiment will be provided. Note that the following described embodiment is merely an example of the present embodiment, and should not be construed as limiting.

[0075] 1. Resin Sheet

[0076] (1) Formation of Resin Sheet

[0077] A composition was prepared by mixing each component shown in the "Chemical Composition" column of the resin sheets in Tables 1 and 2. Details of those components shown in Tables 1 and 2 are as follows:

[0078] • Brominated epoxy resin: Brominated bisphenol A epoxy resin, product name "EPICLON 1121N-80M", manufactured by DIC Corporation;

[0079] • Bisphenol A epoxy resin: product name "1051-75M", manufactured by DIC Corporation;

[0080] • Cresol novolak epoxy resin: product name "EPICLON N-690-75M", manufactured by DIC Corporation;

[0081] • DICY: Dicyandiamide;

[0082] • 2E4MZ: 2-ethyl-4-methylimidazole;

[0083] • Phenoxy resin: product number "YP50EK35", manufactured by NIPPON STEEL Chemical & Materials Co., Ltd.;

[0084] • Acrylate polymer: product name "Teisan Resin SG-P3", manufactured by Nagase Chemtex Corporation; and

[0085] • Solvent: mixed solvent containing methyl ethyl ketone (MEK), propylene glycol monomethyl ether (PGME), and N,N-dimethylformamide (DMF).

[0086] The composition was coated onto a PET film, and heated to the heating temperature shown in the "Heating Conditions" column in Tables 1 and 2, and for the heating time shown. In this way, resin sheets having any of the thicknesses shown in Tables 1 and 2 were obtained.

[0087] (2) Property tests on the resin sheets

[0088] The resin sheets were subjected to the following property tests. The results are summarized in Tables 1 and 2.

[0089] (2-1) Film properties

[0090] The resin sheets were subjected to a bending test by the cylindrical mandrel method using a bending tester. Resin sheets in which no cracks were identified when the diameter of the mandrel was 10 mm were evaluated as "A". Resin sheets in which some cracks were identified when the diameter of the mandrel was 10 mm but in which no cracks were identified when the diameter of the mandrel was 20 mm were evaluated as "B". Resin sheets in which some cracks were identified when the diameter of the mandrel was 20 mm were evaluated as "C".

[0091] (2-2) Melt viscosity and TI

[0092] A sample was obtained by peeling the resin sheet from the PET film. The melt viscosity η1 of this sample was measured using a Koka flow tester (Model "FT-500D / 100D", manufactured by Shimadzu Corporation) under measurement conditions including a temperature of 130°C and a pressure of 1 MPa.

[0093] In the same manner, the melt viscosity η2 of the sample was also measured under measurement conditions including a temperature of 130°C and a pressure of 4 MPa.

[0094] In addition, based on the results of these melt viscosity measurements, the thixotropic index (η1 / η2) was also calculated.

[0095] (2-3) Resin flowability

[0096] The resin sheet was peeled from the PET film and cut into a test piece having dimensions of 100 mm x 100 mm.

[0097] The test piece was sandwiched between two sheets of release film. Then, they were placed in the gap between two hot plates and heat-pressed under conditions including 130°C, 0.5 MPa, and 300 seconds.

[0098] The weight (W1) of the test piece before heat-pressing was measured. In addition, a sample having a diameter of 80 mm was punched out from the test piece that had been heat-pressed. The weight (W2) of this sample was measured. Based on this result, the resin flowability was calculated by the following formula: Resin flowability = (W1 - 2 x W2) / W1 x 100 (%).

[0099] 2. Prepreg

[0100] (1) Formation of the prepreg

[0101] A composition was prepared by mixing each component shown in the "Chemical composition" column of the prepregs in Tables 1 and 2. Details of those components shown in Tables 1 and 2 are as follows:

[0102] • Brominated epoxy resin: Brominated bisphenol A epoxy resin, product name "EPICLON 1121N-80M", manufactured by DIC Corporation;

[0103] • Cresol novolak epoxy resin: Product name "EPICLON N-690-75M", manufactured by DIC Corporation;

[0104] • DICY: Dicyandiamide;

[0105] • 2E4MZ: 2-ethyl-4-methylimidazole;

[0106] • SO-25R: Spherical silica, product name "SO-25R", manufactured by Admatechs;

[0107] • R974: Fumed silica, product name "R974", manufactured by Nippon Aerosil Co., Ltd.;

[0108] • Silane coupling agent: 3-glycidyloxypropyltrimethoxysilane, product number "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.;

[0109] • Phenoxy resin: product number "YP50EK35", manufactured by NIPPON STEEL Chemical & Materials Co., Ltd.; and

[0110] • Solvent: mixed solvent containing methyl ethyl ketone (MEK), propylene glycol monomethyl ether (PGME), and N,N-dimethylformamide (DMF).

[0111] A glass cloth of E glass (#1080) was provided as a substrate, which was impregnated with the composition, and then the composition was heated to the heating temperature shown in Tables 1 and 2, and for the heating time shown. In this way, a prepreg having the resin content and thickness shown in Tables 1 and 2 was obtained.

[0112] (2) Melt Viscosity

[0113] A sample was obtained by removing the substrate from the prepreg. The melt viscosity of this sample was measured using a Koka flow tester (model "FT-500D / 100D", manufactured by Shimadzu Corporation) under measurement conditions including a temperature of 130°C and a pressure of 4 MPa. The results are summarized in Tables 1 and 2.

[0114] 3. Evaluation Test

[0115] (1) Filling Property

[0116] A core member was provided which included an insulating substrate and a conductor circuit provided on each of both surfaces of the insulating substrate. The insulating substrate was an epoxy resin substrate including glass cloth as its base material. Each conductor circuit was made of copper and had a residual copper rate of 60%. In addition, a core member on which an electronic component had been mounted was also used. For the core member on which no electronic component was mounted, the thickness of the conductor of the core member is shown in the column of "Thickness of conductor or electronic component of core member" in Tables 1 and 2. For the core member on which an electronic component was mounted, the thickness of the electronic component is shown in the column of "Thickness of conductor or electronic component of core member" in Tables 1 and 2.

[0117] On each of both surfaces of the core member, a single or multiple resin sheet, a prepreg, and a copper foil sheet having a thickness of 35 μm were sequentially laminated to each other. In other words, a copper foil sheet, a prepreg, a single or multiple resin sheet, a core member, a single or multiple resin sheet, another prepreg, and another copper foil sheet were sequentially laminated to each other. The number of resin sheets was as shown in Tables 1 and 2. In this way, a laminate was obtained. Then, a printed wiring board was formed by hot-pressing the laminate under conditions including 200°C, 22 MPa, and 60 minutes.

[0118] The printed wiring board was cut. The cross section thus exposed was polished, and then observed to see whether any air gap was left between the insulating layer and the conductor circuit or the electronic component.

[0119] A printed wiring board in which the residual copper rate of the conductor circuit was 80% was also evaluated in the same way.

[0120] A printed wiring board in which no air gap was identified at a residual copper rate of 60% and at a residual copper rate of 80% was evaluated as "A". A printed wiring board in which some air gap was identified at a residual copper rate of 60% but no air gap was identified at a residual copper rate of 80% was evaluated as "B". A printed wiring board in which air gap was identified at a residual copper rate of 60% and at a residual copper rate of 80% was evaluated as "C".

[0121] (2) Thickness accuracy

[0122] A printed wiring board was obtained under the same conditions as in the above "(1) Filling property" section (except that the residual copper rate of each conductor circuit was only 60%).

[0123] The thickness of the printed wiring board is measured at five points on the printed wiring board using a micrometer. If the difference between the maximum and minimum of the five measurements thus obtained is equal to or less than 10% of the theoretical thickness value of the printed wiring board, such a printed wiring board is evaluated as "A". If the difference between the maximum and minimum is greater than 10% and equal to or less than 20% of the theoretical thickness value of the printed wiring board, such a printed wiring board is evaluated as "B". If the difference between the maximum and minimum is greater than 20% of the theoretical thickness value of the printed wiring board, such a printed wiring board is evaluated as "C".

[0124] [Table 1]

[0125]

[0126]

[0127] [Table 2]

[0128]

[0129]

[0130] List of Reference Numerals

[0131] 1 Insulating resin member

[0132] 2 Prepreg

[0133] 3 Resin sheet

[0134] 4 Base material

[0135] 5 Printed wiring board

[0136] 6 Second layer

[0137] 7 First layer

[0138] 8 Insulating layer

[0139] 9 Conductor

[0140] 10 Insulating base

[0141] 11 Core member

[0142] 13 Electronic component

[0143] 14 Metal foil

Claims

1. An insulating resin member comprising: a resin sheet; and a prepreg laminated on the resin sheet, the resin sheet comprising an uncured product or semi-cured product of a thermosetting resin composition (X1), a melt viscosity of the resin sheet being equal to or greater than 10 Pa-s and equal to or less than 2000 Pa-s when measured using a Koka flow tester under measurement conditions including 130°C and 1 MPa, and a melt viscosity of the resin sheet being equal to or greater than 6 Pa-s and equal to or less than 1200 Pa-s when measured using a Koka flow tester under measurement conditions including 130°C and 4 MPa, a resin flow of the resin sheet being equal to or less than 40% measured by the Glynis method under measurement conditions including 130°C and 0.5 MPa, the prepreg comprising: a base material; and an uncured product or semi-cured product of a thermosetting resin composition (X2) impregnated into the base material, a melt viscosity of the uncured product or semi-cured product of the thermosetting resin composition (X2) being equal to or greater than 500 Pa-s and equal to or less than 6000 Pa-s when measured using a Koka flow tester under measurement conditions including 130°C and 4 MPa, the thermosetting resin composition (X1) containing a thermosetting resin, a curing agent, and a phenoxy resin.

2. A printed wiring board comprising: a core member comprising an insulating base and a conductor positioned above the insulating base; and an insulating layer laminated on the core member and covering the conductor, the insulating layer comprising: a first layer arranged in contact with the core member and being a cured product of the resin sheet in the insulating resin member of claim 1; and a second layer laminated on the first layer and being a cured product of the prepreg in the insulating resin member of claim 1.

3. The printed wiring board of claim 2, wherein a thickness of the conductor is equal to or greater than 70 μm and equal to or less than 500 μm.

4. The printed wiring board of claim 2 or 3, further comprising an electronic component mounted on the core member, wherein the electronic component is embedded in the insulating layer.

5. The printed wiring board of claim 4, wherein a thickness of the electronic component is equal to or greater than 70 μm and equal to or less than 500 μm.

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