Substrate, printed circuit board, and semiconductor package

Abstract

This substrate has a metal-clad layered board having a metal foil and a prepreg cured product and an insulating layer layered on at least one side of the metal-clad layered board. The metal-clad layered board has an average thickness T1 of 400 μm or greater as determined by a predetermined method using a laser displacement gauge, and the absolute value D1 of the difference between maximum and minimum thickness is 10 μm or less. This printed circuit board and this semiconductor package include said substrate.

Description

Substrates, printed wiring boards and semiconductor packages

[0001] The present disclosure relates to a substrate, a printed wiring board, and a semiconductor package.

[0002] 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-scale computers are increasing year by year. Accordingly, the substrate materials for the printed wiring boards used in these electronic devices are required to suppress variations in characteristic impedance in order to improve transmission characteristics.

[0003] Patent Document 1 discloses a semi-cured synthetic resin sheet that is used as a material for the insulating layer of a multilayer wiring board, and that is characterized by containing cured synthetic resin spheres, and that this semi-cured synthetic resin sheet is a material for the insulating layer of the multilayer wiring board, making it possible to fabricate a multilayer wiring board that facilitates impedance matching of electronic components.

[0004] Japanese Patent Application Laid-Open No. 2002-141670

[0005] However, in recent years, signal speeds have increased dramatically, and more advanced control of characteristic impedance is required to maintain signal quality. In particular, the inventors' studies have revealed that substrates using thick laminates tend to have larger variations in characteristic impedance, and improvements are desired.

[0006] In view of the current situation, an object of this embodiment is to provide a substrate with small variations in characteristic impedance, and a printed wiring board and a semiconductor package using this substrate.

[0007] The present inventors have conducted research to solve the above-mentioned problems and have found that the problems can be solved by the following embodiment: [1] A substrate comprising a metal-clad laminate having a metal foil and a cured product of a prepreg, and an insulating layer laminated on at least one surface of the metal-clad laminate, wherein the metal-clad laminate has an average thickness T measured by the following method using a laser displacement meter. １is 400 μm or more, and the absolute value D of the difference between the maximum and minimum thickness values １ The substrate has an average thickness T of 10 μm or less. １ and the absolute value D of the difference between the maximum and minimum thickness values １ Measurement method) In a plan view of the metal-clad laminate, four rectangular thickness measurement areas measuring 60 mm in length and 60 mm in width are set at any positions that do not overlap each other. In the rectangular thickness measurement areas, 12 vertical measurement lines are set every 5 mm, starting from a position 2.5 mm away from the left edge. On each vertical measurement line, thickness measurements are performed at 1 mm intervals in the vertical direction, starting from a position less than 1 mm (but not 0 mm) from the top edge. In addition, in the rectangular thickness measurement area, 12 horizontal measurement lines are set every 5 mm, starting from a position 2.5 mm away from the top edge. On each horizontal measurement line, thickness measurements are performed at 1 mm intervals in the horizontal direction, starting from a position less than 1 mm (but not 0 mm) from the left edge. For each of the four thickness measurement areas, the absolute value of the difference between the maximum and minimum thickness values ​​is calculated, and the average value obtained is called the absolute value D of the difference between the maximum and minimum thickness values. １ Furthermore, the average thickness of all points in the four thickness measurement regions is calculated, and this is the average thickness T of the metal-clad laminate. １ [2] The substrate according to the above [1], wherein the metal-clad laminate has metal foil on both sides and one or more sheets of the cured prepreg between the metal foils on both sides. [3] The substrate according to the above [1] or [2], wherein the metal-clad laminate has 2 to 20 sheets of the cured prepreg. [4] The substrate according to any one of the above [1] to [3], wherein the prepreg is a prepreg containing a fiber base material having a thickness of 40 μm or more and a thermosetting resin composition. [5] The substrate according to any one of the above [1] to [4], wherein the insulating layer is laminated on both sides of the metal-clad laminate. [6] The substrate according to any one of the above [1] to [5], wherein the insulating layer is a cured film-like thermosetting resin composition. [7] The average thickness T of the insulating layer ２[8] A printed wiring board having the substrate according to any one of [1] to [7] above. [9] A semiconductor package having the printed wiring board according to [8] above and a semiconductor element.

[0008] According to this embodiment, it is possible to provide a substrate with small variations in characteristic impedance, and a printed wiring board and a semiconductor package using the substrate.

[0009] 1 is a schematic diagram ((a) and (b)) illustrating a method for measuring the thickness of a metal-clad laminate. FIG. 2 is a perspective view of an example of a measurement site of a non-contact and clamping type laser displacement meter used in measuring the thickness of a metal-clad laminate. FIG. 3 is a schematic diagram of an example of a sensor head of a laser displacement meter used in measuring the thickness of a metal-clad laminate. FIG. 4 is a schematic cross-sectional view showing one embodiment of a prepreg used in a metal-clad laminate. FIG. 5 is a surface observation image converted into black and white mode from the surface observation image used in calculating the abundance ratio of impregnated regions in the prepreg produced in Example 1. FIG. 6 is a schematic diagram illustrating a method for specifying thickness measurement regions (N1 to N4) from predetermined regions at the four corners of the metal-clad laminate when measuring the thickness of the metal-clad laminate in Examples and Comparative Examples.

[0010] In this specification, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. For example, a numerical range "X to Y" (X and Y are real numbers) means a numerical range that is equal to or greater than X and equal to or less than Y. In this specification, the term "X or greater" means X and a numerical value that exceeds X. In addition, the term "Y or less" in this specification means Y and a numerical value that is less than Y. The lower limit and upper limit of a numerical range described in this specification can be arbitrarily combined with the lower limit or upper limit of another numerical range. In the numerical ranges described in this specification, the lower limit or upper limit of that numerical range may be replaced with a value shown in the examples.

[0011] Unless otherwise specified, each of the components and materials exemplified in this specification may be used alone or in combination of two or more. In this specification, when a resin composition contains a plurality of substances corresponding to each component, the content of each component in the resin composition means the total amount of the plurality of substances present in the resin composition, unless otherwise specified.

[0012] In this specification, the term "solid content" refers to components other than the solvent, and components that are liquid at 25°C are also considered to be solid content.

[0013] In this specification, "(meth)acrylate" means "acrylate" and its corresponding "methacrylate." Similarly, "(meth)acrylic" means "acrylic" and its corresponding "methacrylic," and "(meth)acryloyl" means "acryloyl" and its corresponding "methacryloyl."

[0014] In this specification, the term "semi-cured product" is synonymous with a resin composition in a B-stage state according to JIS K 6800 (2006), and the term "cured product" is synonymous with a resin composition in a C-stage state according to JIS K 6800 (2006).

[0015] The mechanism of action described in this specification is speculation and does not limit the mechanism by which the effects of this embodiment are achieved.

[0016] Any combination of the features described in this specification is also included in this embodiment.

[0017] [Substrate] The substrate of the present embodiment is a substrate having a metal-clad laminate having a metal foil and a cured product of a prepreg, and an insulating layer laminated on at least one surface of the metal-clad laminate, and the metal-clad laminate has an average thickness T １ is 400 μm or more, and the absolute value D of the difference between the maximum and minimum thickness values １ The average thickness T of the metal-clad laminate is 10 μm or less. １ and the absolute value D of the difference between the maximum and minimum thickness values １Measurement method) In a plan view of the metal-clad laminate, four rectangular thickness measurement areas measuring 60 mm in length and 60 mm in width are set at any positions that do not overlap each other. In the rectangular thickness measurement areas, 12 vertical measurement lines are set every 5 mm, starting from a position 2.5 mm away from the left edge. On each vertical measurement line, thickness measurements are performed at 1 mm intervals in the vertical direction, starting from a position less than 1 mm (but not 0 mm) from the top edge. In addition, in the rectangular thickness measurement area, 12 horizontal measurement lines are set every 5 mm, starting from a position 2.5 mm away from the top edge. On each horizontal measurement line, thickness measurements are performed at 1 mm intervals in the horizontal direction, starting from a position less than 1 mm (but not 0 mm) from the left edge. For each of the four thickness measurement areas, the absolute value of the difference between the maximum and minimum thickness values ​​is calculated, and the average value obtained is called the absolute value D of the difference between the maximum and minimum thickness values. １ Furthermore, the average thickness of all points in the four thickness measurement regions is calculated, and this is the average thickness T of the metal-clad laminate. １ In the present embodiment, "average" refers to an arithmetic mean. Furthermore, the cured prepreg refers to a cured prepreg.

[0018] The thickness of the metal-clad laminate can be measured, for example, using a non-contact or clamp-type laser displacement meter as shown in Figure 2. This type of laser displacement meter measures the thickness by irradiating laser light from both sides of the object to be measured and detecting the distance from the reflected light to each surface. More specifically, the thickness of the metal-clad laminate can be measured using the laser displacement meter and conditions described in the Examples.

[0019] As described above, the average thickness T of the metal-clad laminate of this embodiment １ and the absolute value D of the difference between the maximum and minimum thickness values １In the measurement method described above, four rectangular thickness measurement areas measuring 60 mm long x 60 mm wide are set. On the other hand, if the size of the metal-clad laminate does not allow for four rectangular thickness measurement areas measuring 60 mm long x 60 mm wide, the thickness measurement areas may be determined using the following method, and the average thickness of the metal-clad laminate and the absolute value of the difference between the maximum and minimum thickness values ​​may be calculated from the thickness measurement areas according to the above method. Even if the average thickness of the metal-clad laminate calculated using this method is 400 μm or more and the absolute value of the difference between the maximum and minimum thickness values ​​is 10 μm or less, the same effect as the substrate of this embodiment can be achieved. However, the lower limit of the thickness measurement area using this method is 20 mm long x 20 mm wide. For example, if only three or fewer rectangular thickness measurement areas measuring 60 mm long x 60 mm wide can be set, the maximum number of rectangular thickness measurement areas measuring 60 mm long x 60 mm wide that can be set is used as the measurement target. Furthermore, when the surface size of the metal-clad laminate is a square with a length of less than 60 mm and a width of less than 60 mm, this is used as the thickness measurement area. Furthermore, when the surface size of the metal-clad laminate is a rectangle with a length of less than 60 mm or a width of less than 60 mm, the largest identifiable square is used as the thickness measurement area. Even when the length and width of the thickness measurement area are less than 60 mm, the width of the measurement line is the same as above, but the total number of measurement lines may be less than 12 lines depending on the length and width. The average thickness of the metal-clad laminate calculated by the above method and the preferred range of the absolute value of the difference between the maximum and minimum thickness values ​​are the average thickness T of the metal-clad laminate in the substrate of this embodiment. １ , and the absolute value D of the difference between the maximum and minimum thickness values １ The preferred range is the same as that of

[0020] <Metal-clad laminate> The metal-clad laminate has a metal foil and a cured product of a prepreg. The metal-clad laminate has a metal foil on at least one side, and preferably has metal foil on both sides and has one or more cured products of a prepreg between the metal foils on both sides. Furthermore, the metal-clad laminate may or may not have metal foil on sides other than both sides.

[0021] (Average thickness T of the metal-clad laminate １ ) The average thickness T of the metal-clad laminate measured by the above method１ The substrate of this embodiment has an average thickness T １ When the average thickness T of the metal-clad laminate is 400 μm or more, the rigidity of the metal-clad laminate is sufficiently high when semiconductor chips are mounted, thereby suppressing the amount of warping, making the metal-clad laminate particularly suitable as a substrate for a large semiconductor package. １ is preferably 500 μm or more, more preferably 700 μm or more, and even more preferably 1,000 μm or more. １ From the viewpoint of size reduction and cost reduction, it is desirable that the thickness is not more than necessary, and it is preferably 2,500 μm or less, more preferably 2,000 μm or less, and even more preferably 1,500 μm or less.

[0022] (The absolute value D of the difference between the maximum and minimum thicknesses of the metal-clad laminate １ ) The absolute value D of the difference between the maximum and minimum thicknesses of the metal-clad laminate measured by the above method １ The absolute value D of the difference between the maximum and minimum thicknesses of the metal-clad laminate is 10 μm or less. １ By keeping the thickness of the metal-clad laminate at 10 μm or less, the variation in the characteristic impedance of the substrate of this embodiment is reduced. １ is preferably 8 μm or less, more preferably 6 μm or less, and even more preferably 5 μm or less. １ The smaller the better, and may be 0 μm, but from the viewpoint of ease of production, it may be 0.1 μm or more, 0.5 μm or more, or 1 μm or more.

[0023] (Metal Foil) Examples of the metal foil contained in the metal-clad laminate include copper foil, aluminum foil, tin foil, tin-lead alloy foil, and nickel foil. Other examples include a three-layer composite foil in which an intermediate layer of nickel, nickel-phosphorus, nickel-tin alloy, nickel-iron alloy, lead, or lead-tin alloy is provided on both sides with a 0.5-15 μm copper layer and a 10-300 μm copper layer, and a two-layer composite foil in which aluminum and copper foil are combined. Among these, copper foil is preferred. The thickness of the metal foil is preferably 1-200 μm, more preferably 2-100 μm, even more preferably 3-50 μm, and particularly preferably 3-20 μm.

[0024] (Prepreg) The prepreg preferably contains a fiber base material and a thermosetting resin composition. The number of cured prepregs contained in the metal-clad laminate may be appropriately determined depending on the application of the substrate, and may be, for example, 1 to 25 sheets, 2 to 20 sheets, 5 to 18 sheets, 8 to 16 sheets, or 10 to 14 sheets.

[0025] [Surface waviness (Wa) of prepreg] From the viewpoint of reducing thickness variation of the metal-clad laminate, the surface waviness (Wa) of the prepreg is preferably 5.0 μm or less, more preferably 3.0 μm or less, and even more preferably 2.0 μm or less. The lower limit of the surface waviness (Wa) of the prepreg is not particularly limited, but may be 0.01 μm or more, 0.1 μm or more, or 0.2 μm or more. The surface waviness (Wa) is the arithmetic mean height (Wa) that can be obtained from the waviness curve according to ISO 4287 (1997). JIS B 0601 (2001) may be used instead of ISO 4287 (1997). The surface waviness (Wa) can be measured as follows. -Method for measuring the surface waviness (Wa) of a prepreg- Using a shape analysis laser microscope "VK-X100" (manufactured by Keyence Corporation), shape measurement is performed automatically using an observation application to obtain a waviness curve conforming to ISO 4287 (1997) or JIS B 0601 (2001). The obtained waviness curve is subjected to surface roughness analysis using an analysis application, and the surface waviness (Wa) can be calculated. Here, the waviness curve is a curve obtained by applying a phase-compensated high-pass filter λc (λc = 80 μm) to the cross-sectional curve and removing wavelengths less than 80 μm from the cross-sectional curve. The analysis range is 1,000 μm x 1,000 μm. Unless otherwise specified, the surface waviness (Wa) of a prepreg refers to the surface waviness on both sides of the prepreg.

[0026] [Unimpregnated Regions of Prepreg] From the viewpoint of reducing thickness variation of the metal-clad laminate, it is preferable that the prepreg have regions impregnated with the thermosetting resin composition and unimpregnated regions in the fiber substrate. By forming regions impregnated with the thermosetting resin composition and unimpregnated regions in the fiber substrate, the surface waviness (Wa) of the prepreg tends to be reduced even when the fiber substrate is thick. Specifically, for example, even when a fiber substrate having a thickness of 40 μm or more is used, the surface waviness (Wa) tends to be suppressed to 5.0 μm or less. The mechanism behind this effect is unclear, but is thought to be as follows. FIG. 4 shows a schematic cross-sectional view of one embodiment of a prepreg 10 used in a metal-clad laminate. By intentionally providing unimpregnated regions 3 in the fiber substrate 2 where the thermosetting resin composition 1 is not impregnated, as in the prepreg 10, the layer of the thermosetting resin composition 1 near the surface (hereinafter also referred to as the "resin layer") does not follow the waviness of the fiber substrate 2. As a result, it is thought that large waviness of the fiber base material 2 is less likely to be reflected on the surface of the prepreg 10, thereby reducing the surface waviness (Wa) of the prepreg 10. Even when an unimpregnated region is provided in the prepreg, the thermosetting resin composition flows in the thickness direction and into the unimpregnated region during press molding to produce the metal-clad laminate, thereby sufficiently suppressing the generation of voids in the metal-clad laminate.

[0027] The presence of unimpregnated regions can be confirmed by determining the ratio of impregnated regions of the thermosetting resin composition in the fiber substrate. In other words, if the ratio of impregnated regions is not 100%, it means that there are unimpregnated regions. The ratio of impregnated regions can be measured, for example, by the following measurement method. From the viewpoint of reducing thickness variation in the metal-clad laminate, the ratio of impregnated regions determined based on the following method is preferably 20 to 99%, more preferably 30 to 98%, and even more preferably 50 to 95%. -Method for measuring the impregnated regions of prepreg- A surface observation image is obtained by observing the surface of the prepreg at 50x magnification using an optical microscope. The observation conditions, specifically those described in the Examples, are adopted from the viewpoint of capturing images at appropriate brightness. The obtained surface observation image is converted to black and white mode using image editing software and saved in BMP (Microsoft Windows Bitmap Image) format. Next, the black-and-white mode surface observation image saved in BMP format is converted to RGB (Red, Green, Blue) values ​​for each pixel using image conversion software, and then saved in CSV (comma-separated values) format. The RGB data saved in CSV format is pasted into Microsoft Excel (Microsoft Corporation), and the areas of the black areas (RGB value = 255) and white areas (RGB value = 0) are calculated. From these values, the area ratio of the black areas to the total area of ​​the black and white areas is calculated. The area ratio of the black areas thus obtained is used as the proportion of the impregnated areas. Examples of image editing software that can be used include "Microsoft Paint" (Microsoft Corporation). Examples of image conversion software that can be used include free software such as "bmp2csv." Note that in the above observation, when the surface observation image captured at an appropriate brightness is converted to black-and-white mode, the surface where the thermosetting resin composition-unimpregnated areas exist below the observation surface is represented as "white" because it is a void area that easily reflects light, while the other surfaces are represented as "black."Here, when capturing a surface observation image, it is preferable to adjust the exposure time during surface imaging within the range of 60 to 100 ms to capture an image with appropriate brightness that adequately reflects the impregnated and unimpregnated regions. In a surface observation image of a prepreg, the areas with the strongest color are "areas in the resin layer where no glass cloth is present," "areas in which the glass cloth is sufficiently impregnated with the thermosetting resin composition," and "areas in which the glass cloth is insufficiently impregnated with the thermosetting resin composition." In this embodiment, "areas in the resin layer where no glass cloth is present" are also included in the impregnated regions. If the surface observation image is too bright, not only areas in which the glass cloth is insufficiently impregnated with the resin but also areas in which the glass cloth is sufficiently impregnated with the resin tend to appear white in the black-and-white mode surface observation image. Furthermore, if the image is too bright, the surface observation image in black-and-white mode tends to appear white overall. On the other hand, if the surface observation image is too dark, the surface observation image in black-and-white mode tends to appear black overall, making it difficult to reflect the presence of unimpregnated regions. Therefore, it is preferable to capture images with appropriate brightness. As an example of a surface observation image captured at an appropriate brightness and converted into black and white mode, the surface observation image converted into black and white mode obtained in Example 1 is shown in Fig. 5. The area ratio of the white areas to the total area of ​​the white and black areas can be easily calculated using the COUNTIF function in Microsoft Excel (manufactured by Microsoft Corporation).

[0028] [Prepreg Thickness] The thickness of the prepreg may be determined appropriately depending on the thickness of the fiber substrate, etc., but is preferably 50 to 300 μm, more preferably 60 to 200 μm, and even more preferably 70 to 150 μm. The prepreg thickness refers to the thickness of one prepreg. The prepreg thickness is the average value of values ​​obtained by measuring five arbitrary locations with a Digimatic indicator.

[0029] [Thermosetting Resin Composition] The thermosetting resin composition is not particularly limited as long as it contains a thermosetting resin.

[0030] -Thermosetting Resin- Examples of thermosetting resins include epoxy resins, polyimide resins, maleimide resins, modified maleimide resins, phenol resins, polyphenylene ether resins, bismaleimide triazine resins, cyanate resins, isocyanate resins, benzoxazine resins, oxetane resins, amino resins, unsaturated polyester resins, allyl resins, dicyclopentadiene resins, silicone resins, triazine resins, and melamine resins. Among these, from the viewpoints of moldability and electrical insulation, epoxy resins, polyimide resins, maleimide resins, modified maleimide resins, and cyanate resins are preferred, and epoxy resins, maleimide resins, and modified maleimide resins are more preferred. One type of thermosetting resin may be used alone, or two or more types may be used in combination.

[0031] Examples of modified maleimide resins include reaction products of maleimide resins having two or more N-substituted maleimide groups with one or more compounds selected from the group consisting of monoamine compounds and diamine compounds. As the maleimide resins having two or more N-substituted maleimide groups, bismaleimide resins having two N-substituted maleimide groups are preferred, and aromatic bismaleimide resins having two N-substituted maleimide groups are more preferred. As the monoamine compounds, monoamine compounds having acidic substituents such as aminophenol and aminobenzoic acid are preferred. As the diamine compounds, diamine compounds having two primary amino groups are preferred, and aromatic diamine compounds having two primary amino groups are more preferred.

[0032] The epoxy resin is preferably an epoxy resin having two or more epoxy groups per molecule. Here, epoxy resins are classified into glycidyl ether-type epoxy resins, glycidyl amine-type epoxy resins, glycidyl ester-type epoxy resins, etc. Among these, glycidyl ether-type epoxy resins are preferred. Epoxy resins are also classified into various epoxy resins based on differences in their main skeletons. For example, each of the above types of epoxy resins is further classified into bisphenol-type epoxy resins, alicyclic epoxy resins, aliphatic linear epoxy resins, novolac-type epoxy resins, stilbene-type epoxy resins, naphthalene-skeleton-containing epoxy resins, biphenyl-type epoxy resins, xylylene-type epoxy resins, and dihydroanthracene-type epoxy resins. Among these, naphthalene-skeleton-containing epoxy resins are preferred from the viewpoints of insulation reliability and heat resistance.

[0033] From the viewpoints of heat resistance and moldability, the content of the thermosetting resin in the thermosetting resin composition is preferably 10 to 100 mass%, more preferably 20 to 80 mass%, and even more preferably 30 to 70 mass%, relative to the total solid content (100 mass%) of the thermosetting resin composition.

[0034] -Curing Accelerator- The thermosetting resin composition preferably further contains a curing accelerator. A typical curing accelerator used for curing thermosetting resins can be used as the curing accelerator. For example, when the thermosetting resin contains an epoxy resin, examples of the curing accelerator include imidazole compounds and derivatives thereof, phosphorus-based compounds, tertiary amine compounds, and quaternary ammonium compounds. Among these, imidazole compounds and derivatives thereof are preferred from the viewpoint of accelerating the curing reaction. Examples of imidazole compounds and derivatives thereof include imidazole compounds such as 2-methylimidazole, 2-ethylimidazole, 2-undecylimidazole, 2-phenylimidazole, 1,2-dimethylimidazole, and 2,4-diamino-6-[2'-undecylimidazolyl-(1)']-ethyl-S-triazine; salts of the above imidazole compounds with trimellitic acid such as 1-cyanoethyl-2-phenylimidazolium trimellitate; salts of the above imidazole compounds with isocyanuric acid; and salts of the above imidazole compounds with hydrobromic acid. Among these, imidazole compounds are preferred, and 2,4-diamino-6-[2'-undecylimidazolyl-(1)']-ethyl-S-triazine is more preferred.

[0035] When the thermosetting resin composition contains a curing accelerator, the content of the curing accelerator in the thermosetting resin composition is preferably 0.01 to 20 parts by mass, more preferably 0.1 to 10 parts by mass, and even more preferably 0.5 to 3 parts by mass, relative to 100 parts by mass of the thermosetting resin, from the viewpoints of the curing acceleration effect and storage stability.

[0036] -Inorganic Filler- The thermosetting resin composition preferably further contains an inorganic filler. 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, clay, talc, aluminum borate, and silicon carbide. Among these, silica, alumina, aluminum hydroxide, mica, and talc are preferred from the viewpoints of low thermal expansion, heat resistance, and flame retardancy, and silica and aluminum hydroxide are more preferred. As silica, fused silica is preferred from the viewpoints of dispersibility and moldability. The inorganic filler may be surface-treated with a surface treatment agent such as a silane coupling agent to improve moisture resistance, or may be hydrophobized to improve dispersibility.

[0037] When the thermosetting resin composition contains an inorganic filler, the content of the inorganic filler in the thermosetting resin composition is preferably 10 to 90 mass%, more preferably 20 to 80 mass%, and even more preferably 30 to 70 mass%, relative to the total amount of solids (100 mass%), from the viewpoints of low thermal expansion and moldability.

[0038] -Other Components- The thermosetting resin composition may further contain other components, such as resin materials other than the above components, flame retardants, antioxidants, heat stabilizers, antistatic agents, UV absorbers, pigments, colorants, lubricants, organic solvents, and other additives, as needed. Each of these other components may be used alone, or two or more may be used in combination. The content of the above other components in the thermosetting resin composition is not particularly limited, and they may be used as needed within a range that does not impair the effects of this embodiment. Furthermore, the thermosetting resin composition may not contain the above other components, depending on the desired performance.

[0039] The thermosetting resin composition can be produced by mixing the components. In this process, the components may be dissolved or dispersed with stirring, using an organic solvent as needed. The mixing conditions, such as the order of mixing, temperature, and time, are not particularly limited and may be set as desired depending on the types of raw materials, etc.

[0040] [Fiber Substrate] The fiber substrate contained in the prepreg can be any well-known material used in various laminates for electrical insulating materials. Examples of the material for the fiber substrate include natural fibers such as paper and cotton linters; inorganic fibers such as glass fibers and asbestos; organic fibers such as aramid, polyimide, polyvinyl alcohol, polyester, tetrafluoroethylene, and acrylic; and mixtures thereof. Among these, inorganic fibers are preferred from the viewpoint of flame retardancy, and glass fibers are more preferred. Examples of glass fibers include glass fibers made from E-glass, C-glass, D-glass, and S-glass. The shape of the fiber substrate is not particularly limited, and may be a woven fabric, a nonwoven fabric, a roving, a chopped strand mat, a surfacing mat, or the like. Among these, a woven fabric is preferred. That is, glass cloth is preferred as the fiber substrate.

[0041] The thickness of the fiber substrate is preferably 40 μm or more from the viewpoint of the handleability of the prepreg. That is, the prepreg is preferably a prepreg containing a fiber substrate having a thickness of 40 μm or more and a thermosetting resin composition. From the same viewpoint as above, the thickness of the fiber substrate is more preferably 60 μm or more, even more preferably 70 μm or more, and particularly preferably 80 μm or more. Furthermore, from the viewpoint of thinning the substrate, the thickness of the fiber substrate is preferably 120 μm or less, more preferably 110 μm or less, and even more preferably 100 μm or less. The greater the thickness of the fiber substrate, the greater the surface waviness of the fiber substrate itself tends to be. However, as described above, by providing impregnated regions and unimpregnated regions in the prepreg, even when the thickness of the fiber substrate is 40 μm or more, the surface waviness (Wa) of the prepreg can be kept small, and the thickness variation of the metal-clad laminate can be reduced.

[0042] [Method for producing prepreg] The method for producing a prepreg may be, for example, a method of laminating a film-like thermosetting resin composition (hereinafter also referred to as a "resin film") on a fiber substrate (hereinafter also referred to as a "lamination method"), or a method of immersing a fiber substrate in a thermosetting resin composition diluted with an organic solvent and then drying (hereinafter also referred to as an "immersion method"). Among these, the lamination method is preferred from the viewpoint of easily reducing the thickness variation of the metal-clad laminate. The lamination method will be described below.

[0043] The resin film used in the lamination method is preferably a supported resin film having a support on one side. Supported resin films can be produced, for example, by applying a varnish-like thermosetting resin composition (hereinafter also referred to as "resin varnish") to one side of a support and then drying. The resin varnish can be applied using a known coating device such as a comma coater, bar coater, kiss coater, roll coater, gravure coater, or die coater. The drying temperature and drying time after application of the resin varnish can be determined appropriately depending on the type and amount of organic solvent used, etc. For example, in the case of a resin varnish containing 30 to 70% by mass of organic solvent, a resin film can be suitably formed by drying at 50 to 160°C for 1 to 8 minutes.

[0044] The thickness of the resin film may be appropriately determined depending on the thickness of the prepreg, etc. For example, when the thickness of the fiber substrate is 40 to 120 μm, the thickness of the resin film is preferably 10 to 100 μm, more preferably 15 to 70 μm, and even more preferably 20 to 50 μm.

[0045] Examples of the support include organic films such as polyethylene terephthalate (PET), biaxially oriented polypropylene (OPP), polyethylene, polyvinyl fluorate, and polyimide; and metal foils of metals such as copper and aluminum, or alloys thereof. These supports may be release-treated with a release agent. The thickness of the support is, for example, 10 to 200 μm from the viewpoints of ease of handling and economy when applying the thermosetting resin composition.

[0046] To laminate a resin film onto a fiber substrate, first, a supported resin film is placed on at least one side of the fiber substrate so that the resin film and the fiber substrate are in contact with each other. Next, the supported resin film and the fiber substrate are heated and pressurized to impregnate the fiber substrate with the resin film. It is preferable to laminate the supported resin film on both sides of the fiber substrate. Examples of lamination methods include (a) roll lamination and (b) lamination under reduced pressure.

[0047] (a) When performing roll lamination, the heating temperature may be 80 to 180°C or 100 to 150°C. The applied pressure may be 0.05 to 1.0 MPa or 0.2 to 0.6 MPa. The feed rate may be 0.5 to 7.0 m / min or 1.0 to 4.0 m / min. (b) When performing lamination under reduced pressure, the heating temperature may be 80 to 180°C or 100 to 150°C. The vacuum time may be 10 to 120 seconds or 20 to 80 seconds. The applied pressure may be 10 to 120 seconds or 20 to 80 seconds. The pressure may be 0.05 to 1.0 MPa or 0.1 to 0.6 MPa. Lamination under reduced pressure can be performed using a vacuum laminating device.

[0048] A method for providing an unimpregnated region of the thermosetting resin composition in the fiber substrate can be, for example, by adjusting the conditions for heating and pressurizing the supported resin film and the fiber substrate. Here, when the same lamination conditions are used for a thin fiber substrate and a thick fiber substrate, the thick fiber substrate tends to be more difficult for the resin film to impregnate the fiber substrate. Therefore, even if the lamination conditions of this embodiment are similar to those of the conventional thin fiber substrate when laminating a resin film, this embodiment can provide an unimpregnated region of the thermosetting resin composition in the fiber substrate. A specific method for adjusting the heating and pressurizing conditions is, for example, to first prepare a prepreg under predetermined heating and pressing conditions, and then determine the ratio of the impregnated region of the thermosetting resin composition in the fiber substrate based on the above-mentioned calculation method. If the impregnated region is 100%, that is, if there is no unimpregnated region, lower the heating temperature or the pressing pressure, or lower both the heating temperature and the pressing pressure, reprepare the prepreg, and then determine the ratio of the impregnated region again. By repeating this process as necessary, the conditions for producing a prepreg having unimpregnated regions can be easily determined. Furthermore, if it is desired to adjust the proportion of unimpregnated regions to a lower value, the prepreg can be re-prepared by increasing the heating temperature or the pressurizing pressure, or by increasing both the heating temperature and the pressurizing pressure. When laminating under reduced pressure, the proportion of unimpregnated regions can also be adjusted by adjusting the degree of vacuum.

[0049] (Method for manufacturing metal-clad laminate) Metal-clad laminate can be manufactured by stacking prepregs and metal foils in the desired order and press-molding them. The heating temperature during press-molding is preferably 130 to 350°C, more preferably 150 to 300°C, and even more preferably 170 to 250°C. The holding time at the maximum temperature during press-molding is preferably 10 to 240 minutes, more preferably 30 to 180 minutes, and even more preferably 60 to 120 minutes. The pressure during press-molding is preferably 0.5 to 10 MPa, more preferably 1 to 7 MPa, and even more preferably 2 to 5 MPa.

[0050] <Insulating Layer> The substrate of this embodiment has an insulating layer laminated on at least one surface of the metal-clad laminate. The insulating layer is laminated on at least one surface of the metal-clad laminate, and is preferably laminated on both surfaces of the metal-clad laminate. The insulating layer may be a cured product of a prepreg or a cured product of a film-like thermosetting resin composition. As the prepreg used as the insulating layer-forming material, for example, the same prepreg used in the production of a metal-clad laminate can be used. As the film-like thermosetting resin composition used as the insulating layer-forming material, for example, the same resin film used in the production of a prepreg used in the production of a metal-clad laminate can be used.

[0051] (Average thickness of the insulating layer T ２ ) Average thickness of insulating layer T ２ is preferably 5 to 100 μm, more preferably 6 to 70 μm, and even more preferably 8 to 50 μm. ２ When the average thickness T of the insulating layer is equal to or greater than the above lower limit, the insulating properties tend to be better. ２ When the thickness of the insulating layer is equal to or less than the upper limit, the substrate tends to be thin. The thickness of the insulating layer can be measured by the method described in the examples.

[0052] (The absolute value of the difference between the maximum and minimum thicknesses of the insulating layer D ２ ) Absolute value D of the difference between the maximum and minimum thicknesses of the insulating layer ２ is preferably 10 μm or less, more preferably 8 μm or less, and even more preferably 6 μm or less. ２ When the thickness of the insulating layer is equal to or greater than the lower limit, the variation in the characteristic impedance tends to be smaller. ２ The smaller the value, the better, and it may be 0 μm, but from the viewpoint of ease of manufacture, it may be 0.2 μm or more, 0.5 μm or more, or 1.0 μm or more. ２ can be measured by the method described in the Examples.

[0053] <Substrate Manufacturing Method> The substrate of this embodiment can be manufactured by laminating an insulating layer on at least one side of a metal-clad laminate. Specifically, for example, an insulating layer-forming material is layered on one or both sides of the metal-clad laminate, and then metal foil is layered on both outer sides as needed, followed by press molding to laminate an insulating layer on at least one side of the metal-clad laminate. The metal foil can be the same as the metal foil that can be used in metal-clad laminates. The heating temperature during press molding is preferably 130 to 350°C, more preferably 150 to 300°C, and even more preferably 170 to 250°C. The compression pressure during press molding is preferably 0.5 to 10 MPa, more preferably 1 to 7 MPa, and even more preferably 2 to 5 MPa. The pressing time is preferably 10 to 240 minutes, more preferably 30 to 180 minutes, and even more preferably 60 to 120 minutes.

[0054] [Printed Wiring Board] The printed wiring board of this embodiment is a printed wiring board having the substrate of this embodiment. The printed wiring board of this embodiment can be manufactured by forming a conductor circuit on the substrate of this embodiment. The conductor circuit is preferably formed at least on the insulating layer of the substrate of this embodiment. The conductor circuit can be formed, for example, by appropriately performing hole drilling, metal plating, etching of metal foil, etc. using a known method. A multilayer printed wiring board can also be manufactured by performing a multilayer adhesive process as necessary.

[0055] [Semiconductor Package] The semiconductor package of this embodiment is a semiconductor package including the printed wiring board of this embodiment and a semiconductor element. The semiconductor package of this embodiment can be manufactured, for example, by mounting a semiconductor chip, a memory, etc. on the printed wiring board of this embodiment by a known method.

[0056] The present embodiment will be specifically described below with reference to examples, although the present embodiment is not limited to the following examples.

[0057] [Surface waviness (Wa)] Using a shape analysis laser microscope "VK-X100" (manufactured by Keyence Corporation), the shape of the prepreg prepared in each example was measured automatically using an observation application, and a waviness curve conforming to ISO 4287 (1997) was obtained. The obtained waviness curve was subjected to surface roughness analysis using an analysis application, and the surface waviness (Wa) of the prepreg was calculated. Here, the waviness curve is a curve obtained by applying a phase-compensated high-pass filter λc (λc = 80 μm) to the cross-sectional curve and removing wavelengths less than 80 μm from the cross-sectional curve. The analysis range was 1,000 μm x 1,000 μm. The surface waviness (Wa) was measured on both sides of the prepreg, and the larger value was used.

[0058] [Ratio of Impregnated Regions] The ratio (%) of the impregnated regions of the thermosetting resin composition in the fiber base material of the prepreg produced in each example was determined based on the following calculation method. - Calculation Method - Using an optical microscope (Olympus Corporation, product name: MX61L-F), the surface of the prepreg was observed under the following conditions to obtain a surface observation image. <Observation Conditions> - Magnification: 50x - Observation Mode: Dark Field - Sensitivity: ISO 400 - Exposure Time for Surface Photography: 60 to 100 ms - Brightness of Observation Environment: Two 35W fluorescent lamps installed 2 m above the observation stage. The obtained surface observation image was converted to black and white mode using image editing software and then saved in BMP (Microsoft Windows Bitmap Image) format. Next, the black and white mode surface observation image saved in BMP format was converted to RGB (Red, Green, Blue) values ​​for each pixel using image conversion software and then saved in CSV (comma-separated values) format. The RGB data saved in CSV format was pasted into Microsoft Excel (Microsoft Corporation), and the areas of the black areas (RGB value = 255) and white areas (RGB value = 0) were calculated. From these values, the area ratio of the black areas to the total of the black and white areas was calculated. The area ratio of the black areas thus obtained was taken as the abundance ratio (%) of the impregnated areas. When photographing the surface observation images, the exposure time for photographing the surface was adjusted between 60 and 100 ms as described above to ensure adequate reflection of the impregnated and unimpregnated areas, and the images were taken at an appropriate brightness. "Microsoft Paint" (Microsoft Corporation) was used as the image editing software. The free software "bmp2csv" was used as the image conversion software.

[0059] [Metal-clad laminate average thickness T １ , the absolute value D of the difference between the maximum and minimum thicknesses of the metal-clad laminate １Measurement method] From the four corners of the metal-clad laminate prepared in each example (see Figure 6), rectangular thickness measurement areas (N1 to N4) measuring 60 mm long x 60 mm wide were set in a planar view of the metal-clad laminate. Next, using a non-contact and clamp-type laser displacement meter "CL-3000 Series (sensor head: CL-L015)" (multi-color laser coaxial displacement meter, manufactured by Keyence Corporation), the thickness of the thickness measurement areas (N1 to N4) was measured according to the following procedure. The measurement conditions were: measurement speed; 10 mm / s, measurement range; diameter 300 μm, resolution; 0.003 μm, repeatability 0.3 μm or less, and sensor head size (arrow portion in Figure 3); diameter 26 mm. Repeatability refers to the degree of variation when measurements are repeatedly taken at a fixed point on the object to be measured; the smaller the repeatability, the smaller the degree of variation in values ​​due to repeated measurements. First, as shown in FIG. 1( a), 12 vertical measurement lines were set every 5 mm in a rectangular thickness measurement area, starting from a position 2.5 mm away from the left edge. Then, on each vertical measurement line, thickness measurements were performed at 1 mm intervals in the vertical direction, starting from a position less than 1 mm (but not 0 mm) from the top edge. Next, as shown in FIG. 1( b), 12 horizontal measurement lines were set every 5 mm in a rectangular thickness measurement area, starting from a position 2.5 mm away from the top edge. Then, on each horizontal measurement line, thickness measurements were performed at 1 mm intervals in the horizontal direction, starting from a position less than 1 mm (but not 0 mm) from the left edge. This resulted in thickness measurements at 1,440 points per thickness measurement area (however, even if there were overlapping measurement points on the vertical and horizontal measurement lines, each was counted as one point). From the thickness obtained by the above method, the absolute value of the difference between the maximum and minimum thickness values ​​for each of the four thickness measurement areas (N1 to N4) was calculated, and the average value obtained was used as the absolute value D of the difference between the maximum and minimum thickness values ​​of the metal-clad laminate. １ The average value of all the thicknesses measured in the four thickness measurement regions (N1 to N4) was taken as the average thickness T １ It was decided.

[0060] [Average thickness of insulating layer T ２, the absolute value D of the difference between the maximum and minimum thicknesses of the insulating layer ２ Measurement method for the average thickness T of the metal-clad laminate １ , the absolute value D of the difference between the maximum and minimum thicknesses of the metal-clad laminate １ In the measurement method for [Measurement Method for the Substrates], the average thickness of the substrate and the absolute value of the difference between the maximum and minimum thicknesses of the substrate were determined in the same manner as above, except that the measurement object was changed to the substrate obtained in each example. Next, the thickness of the insulating layer was determined from the thickness of the substrate and the thickness of the metal-clad laminate at the same point based on the following formula: Insulating layer thickness = [Substrate thickness - Metal-clad laminate thickness - Copper foil thickness] / 2 Note that the "copper foil thickness" in the above formula refers to the thickness of the copper foil laminated on the opposite side of the insulating layer from the metal-clad laminate. From the thickness obtained by the above method, the average thickness T of the insulating layer was calculated using the same procedure as for the metal-clad laminate. ２ , and the absolute value D of the difference between the maximum and minimum thicknesses of the insulating layer ２ was calculated.

[0061] [Production of Metal-Clad Laminate] Production Example 1 <Production of Metal-Clad Laminate 1> (Preparation of Modified Maleimide Resin) 595.8 g of bis(4-maleimidophenyl)methane, 54.2 g of 4,4′-diaminodiphenylmethane, and 350.0 g of propylene glycol monomethyl ether were placed in a 2 L reaction vessel equipped with a thermometer, a stirrer, and a moisture content monitor with a reflux condenser, and the contents were allowed to react for 5 hours under reflux to obtain a solution of a modified maleimide resin (solid concentration: 65% by mass).

[0062] (Preparation of Resin Varnish) 107 parts by mass of the modified maleimide resin solution obtained above, 30 parts by mass of tetrafunctional naphthalene-type epoxy resin "EXA-4710" (manufactured by DIC Corporation), 17.5 parts by mass of aluminum hydroxide, 130 parts by mass of fused silica, 0.5 parts by mass of 2,4-diamino-6-[2'-undecylimidazolyl-(1)']-ethyl-S-triazine, and methyl isobutyl ketone and cyclohexanone as dilution solvents were added and mixed to prepare Resin Varnish A with a solids concentration of 65% by mass (aluminum hydroxide content: 8% by volume, fused silica content: 41.5% by volume).

[0063] (Preparation of Resin Film) The resin varnish A obtained above was applied to a PET film (manufactured by Toray Industries, Inc., thickness: 50 μm, product name: S10) using a comma coater. At this time, the amount of application was adjusted so that the application width was 530 mm and the thickness after drying was 30 μm. Thereafter, a resin film with a PET film was prepared by heating and drying at 130° C. for 2 minutes.

[0064] (Preparation of prepreg) A glass cloth “IPC#2116” (manufactured by Nitto Boseki Co., Ltd., basis weight: 104 g / m) having a length of 530 mm and a width of 530 mm was used. ２ The PET film-attached resin film was placed on both sides of a glass cloth (substrate width: 530 mm, thickness: 91 μm) so that the resin film of the PET film-attached resin film abutted against the glass cloth. This "PET film / resin film / glass cloth / resin film / PET film" laminate was heated and pressurized under vacuum using a vacuum laminating device to obtain a PET film-attached prepreg in which the glass cloth was impregnated with the thermosetting resin composition of the resin film. The vacuum lamination conditions were a heating plate temperature of 130°C, a pressure of 0.5 MPa, a vacuum degree of 100 kPa or less, a vacuum time of 30 seconds, and a heating time of 30 seconds. The PET film was peeled off from the obtained PET film-attached prepreg to obtain prepreg 1 (thickness 125 μm, surface waviness (Wa) 0.5 μm, and an impregnated region abundance ratio of 62%). The thickness of the prepreg was determined as the average value of the values ​​measured at five arbitrary points using a base adjusted to be horizontal and a Digimatic Indicator (manufactured by Mitutoyo Corporation). The content of the thermosetting resin composition in prepreg 1 was calculated as follows: The mass of the resin film (w ｒ The mass of the resin film (w ｒ ) and the mass of prepreg 1 (w ｐ ) was used to calculate the content of the thermosetting resin composition according to the following formula: Content of the thermosetting resin composition (mass%) = (w ｒ / w ｐ ) x 100

[0065] (Preparation of Metal-Clad Laminate) Twelve sheets of the prepreg 1 obtained above were stacked, and 12 μm thick copper foil "GTHMP-12" (manufactured by Furukawa Circuit Foil Taiwan Corporation) was placed on top and bottom of them. Next, pressing was performed under the following conditions, and the edges of the obtained metal-clad laminate were cut to prepare a rectangular metal-clad laminate 1 measuring 500 mm x 500 mm in plan view. - Pressing conditions - Heating conditions: The temperature was raised from 25°C to 230°C at a rate of 3°C / min, and the laminate was held at 230°C for 90 minutes, followed by cooling for 30 minutes. Pressure conditions (pressure applied to the 12 prepregs sandwiched between the copper foils): 4 MPa (from the start of heating to the end of cooling)

[0066] Production Example 2 <Production of Metal-Clad Laminate 2> A laminate of "PET film / resin film / glass cloth / resin film / PET film" was produced using the same procedure as in Production Example 1. Next, the laminate was heated and pressurized using a pressure roll to obtain a prepreg with a PET film, in which the glass cloth was impregnated with the thermosetting resin composition of the resin film. The pressure roll conditions were a roll temperature of 130°C, a pressure of 0.40 MPa, and a speed of 2.0 m / min. The PET film was peeled from the obtained prepreg with a PET film to obtain prepreg 2 (thickness 125 μm, surface waviness (Wa) 0.5 μm, and a proportion of impregnated regions 68%). The thickness and content of the thermosetting resin composition of prepreg 2 were determined in the same manner as in Production Example 1. Using the prepreg 2 obtained above, a metal-clad laminate 2 was produced using the same procedure as in Production Example 1.

[0067] Production Example 3 <Production of Metal-Clad Laminate 3> The same glass cloth as used in Production Example 1 was immersed in the resin varnish A prepared in Production Example 1, then removed and heated at 140°C for 3.5 minutes to dry, yielding prepreg 3 (thickness 125 µm, surface waviness (Wa) 5.7 µm). Using this prepreg 3, metal-clad laminate 3 was produced using the same procedure as in Production Example 1.

[0068] [Production of Substrate] Examples 1 to 8, Comparative Examples 1 to 5 A resin film (manufactured by Resonac Corporation, product name "AS-400HS", average thickness T of the insulating layer shown in Table 1) was attached to the top and bottom of a metal-clad laminate of the type shown in Table 1. ２A sheet of copper foil (manufactured by Mitsui Mining & Smelting Co., Ltd., product name MT18FL, roughened surface roughness Rz: 1.3 μm) was then placed on both outer sides of the sheet, and the resulting sheet was press-molded at a temperature of 230°C, a pressure of 3.0 MPa, and a time of 80 minutes to obtain a metal-clad laminate having insulating layers laminated on both sides.

[0069] [Measurement of Characteristic Impedance] Holes were drilled at desired positions on the substrate obtained in each example, and through-holes were formed by electroless copper plating. Furthermore, one side of the substrate was patterned by etching to form five microstrip lines with a line length of 50 mm. A pattern for contacting a high-frequency probe was formed on one side of the signal line, and this substrate was used for characteristic impedance measurement. The line width was designed to achieve a characteristic impedance of 50 Ω, taking into account the thickness of the insulating layer of each substrate. The characteristic impedance was measured using a high-frequency probe (manufactured by Form Factor, product name "ACP-65 GSG-250") and an oscilloscope equipped with a TDR module (manufactured by Keysight Technologies, product names "54750A" and "54754A") connected via a coaxial cable (manufactured by HUBER-SUHNER, product name "SUCOFLEX104"). A high-frequency signal with a pulse rise time of 30 ps was input from an oscilloscope, and the high-frequency probe was pressed against the pattern on the characteristic impedance measurement board fabricated above, and the characteristic impedance was calculated from the measured voltage. The difference between the maximum and minimum values ​​of the characteristic impedance of the 20 lines was taken as the variation in characteristic impedance (maximum value - minimum value). The results are shown in Table 1.

[0070]

[0071] From Table 1, it can be seen that the substrates of Examples 1 to 8 of this embodiment have small variations in characteristic impedance. On the other hand, the absolute value D of the difference between the maximum and minimum thicknesses of the metal-clad laminate １ The substrates of Comparative Examples 1 to 5, in which the thickness exceeded 10 μm, had large variations in characteristic impedance.

[0072] REFERENCE SIGNS LIST 1 Thermosetting resin composition 2 Fiber substrate 3 Unimpregnated region 10 Prepreg

Claims

1. A substrate having a metal-clad laminate having a metal foil and a cured product of a prepreg, and an insulating layer laminated on at least one surface of the metal-clad laminate, wherein the metal-clad laminate has an average thickness T measured according to the following method using a laser displacement meter. １ is 400 μm or more, and the absolute value D of the difference between the maximum and minimum thickness values １ The average thickness T of the metal-clad laminate is 10 μm or less. １ and the absolute value D of the difference between the maximum and minimum thickness values １ Measurement method of thickness measurement) In a plan view of the metal-clad laminate, four rectangular thickness measurement areas of 60 mm length x 60 mm width are set at any positions that do not overlap each other. In the rectangular thickness measurement areas, 12 vertical measurement lines are set every 5 mm, starting from a position 2.5 mm away from the left side. On each vertical measurement line, thickness measurements are performed at 1 mm intervals in the vertical direction, starting from a position less than 1 mm (but not 0 mm) from the top side. In addition, in the rectangular thickness measurement area, 12 horizontal measurement lines are set every 5 mm, starting from a position 2.5 mm away from the top side. On each horizontal measurement line, thickness measurements are performed at 1 mm intervals in the horizontal direction, starting from a position less than 1 mm (but not 0 mm) from the left side. For each of the four thickness measurement areas, the absolute value of the difference between the maximum and minimum thickness values ​​is calculated, and the average value obtained is called the absolute value D of the difference between the maximum and minimum thickness values. １ Furthermore, the average thickness of all the points in the four thickness measurement regions is calculated, and this is defined as the average thickness T of the metal-clad laminate. １ Let us assume that.

2. The substrate according to claim 1, wherein the metal-clad laminate has metal foil on both sides and one or more sheets of the cured prepreg between the metal foils on both sides.

3. The substrate according to claim 1 or 2, wherein the metal-clad laminate comprises 2 to 20 sheets of the cured prepreg.

4. The substrate according to claim 1 or 2, wherein the prepreg is a prepreg containing a fiber base material having a thickness of 40 μm or more and a thermosetting resin composition.

5. The substrate according to claim 1 or 2, wherein the insulating layer is laminated on both sides of the metal-clad laminate.

6. The substrate according to claim 1 or 2, wherein the insulating layer is a cured product of a film-like thermosetting resin composition.

7. Average thickness T of the insulating layer ２ The substrate according to claim 1 or 2, wherein the thickness of the first insulating layer is 5 to 100 μm.

8. A printed wiring board comprising the substrate according to claim 1 or 2.

9. A semiconductor package comprising the printed wiring board according to claim 8 and a semiconductor element.