Prepreg, laminate, metal-clad laminate, printed wiring board, semiconductor package, method for producing prepreg, and method for producing metal-clad laminate

Abstract

To provide a prepreg capable of realizing a metal-clad laminate having high thickness accuracy even when a fiber base material having a thickness of 40 μm or more is used, and to provide a laminate, a metal-clad laminate, a printed wiring board, and a semiconductor package obtained using the prepreg, and further to provide a method for manufacturing the prepreg and a method for manufacturing the metal-clad laminate.SOLUTION: A prepreg made by impregnating a fiber base material having a thickness of 40 μm or more with a thermosetting resin composition has regions impregnated with the thermosetting resin composition and regions not impregnated with the fiber base material, and a surface waviness (Wa) of 5.0 μm or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a prepreg, a laminate, a metal-clad laminate, a printed wiring board, a semiconductor package, and a method for producing a prepreg and a method for producing a metal-clad laminate. [Background technology]

[0002] Many prepregs for printed wiring boards are produced by immersing a fiber base material in a resin varnish and then drying it (see, for example, Patent Document 1). In recent years, with the increasing density of semiconductor packages and the increasing communication speed, there is a strong demand for printed wiring boards with low warpage, high reliability, and improved impedance control. In order to meet this demand, it is necessary to reduce the variation in thickness of copper-clad laminates compared to the past. However, copper-clad laminates manufactured using prepregs obtained by the conventional method of immersing a fiber base material in a resin varnish and then drying it tend to have a variation in thickness. On the other hand, a method is known in which, instead of immersing a fiber substrate in a resin varnish, a resin film is first prepared from a thermosetting resin composition, and then the fiber substrate and the resin film are bonded together by heating and pressurization to produce a prepreg (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 01-272416 [Patent Document 2] JP 2011-132535 ​​A Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 2 describes that a prepreg with excellent thickness accuracy can be manufactured. However, the present inventors conducted further studies and found that, although the prepreg indeed has excellent thickness accuracy when the fiber base material has a small thickness, for example, 35 μm or less, the prepreg has poor thickness accuracy when the fiber base material has a greater thickness, and thus tends to have poor thickness accuracy of the copper-clad laminate.

[0005] Therefore, an object of the present disclosure is to provide a prepreg capable of realizing a metal-clad laminate with high thickness accuracy even when a fiber base material with a thickness of 40 μm or more is used, and to provide a laminate, a metal-clad laminate, a printed wiring board, and a semiconductor package obtained using the prepreg, and further to provide a method for manufacturing the prepreg and a method for manufacturing the metal-clad laminate. [Means for solving the problem]

[0006] As a result of extensive research, the present inventors have found that the above object can be achieved by the present disclosure. The present disclosure includes the following [1] to

[12] . [1] A prepreg obtained by impregnating a fiber base material having a thickness of 40 μm or more with a thermosetting resin composition, the fiber base material having impregnated areas and unimpregnated areas of the thermosetting resin composition, and a surface waviness (Wa) of 5.0 μm or less. [2] The prepreg according to the above [1], wherein the ratio of the impregnated regions is 25 to 98% as calculated according to the following method: Calculation method: Observe the surface of the prepreg at a magnification of 50 times using an optical microscope to obtain a surface observation image. The obtained surface observation image is 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 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 (manufactured by Microsoft Corporation), and the areas of the black part (RGB value = 255) and the white part (RGB value = 0) are calculated. From these values, the area ratio of the black part to the total of the black part and the white part is calculated. The area ratio of the black part thus obtained is regarded as the presence ratio of the impregnated region. [3] The prepreg according to the above [2], wherein the ratio of the impregnated regions is 35 to 90%. [4] The prepreg according to any one of the above [1] to [3], having a surface roughness (Ra) of 0.1 to 5 μm. [5] The prepreg according to any one of the above [1] to [4], wherein the fiber base material has a thickness of 70 to 120 μm. [6] A laminate comprising one or more prepregs according to any one of [1] to [5] above. [7] A metal-clad laminate comprising a metal foil and one or more sheets of the prepreg according to any one of [1] to [5] above. [8] A printed wiring board comprising the laminate described in [6] above or the metal-clad laminate described in [7] above. [9] A semiconductor package comprising the printed wiring board according to [8] above and a semiconductor element.

[10] A method for producing a prepreg by impregnating a fiber base material having a thickness of 40 μm or more with a film of a thermosetting resin composition by lamination, wherein the fiber base material has regions impregnated with the thermosetting resin composition and regions not impregnated with the thermosetting resin composition, thereby producing a prepreg having a surface waviness (Wa) of 5.0 μm or less.

[11] The method for producing a prepreg according to the above

[10] , wherein the ratio of the impregnated regions is 25 to 98% as calculated by the following method: Calculation method: Observe the surface of the prepreg at a magnification of 50 times using an optical microscope to obtain a surface observation image. The obtained surface observation image is 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 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 (manufactured by Microsoft Corporation), and the areas of the black part (RGB value = 255) and the white part (RGB value = 0) are calculated. From these values, the area ratio of the black part to the total of the black part and the white part is calculated. The area ratio of the black part thus obtained is regarded as the presence ratio of the impregnated region.

[12] A method for producing a metal-clad laminate, comprising providing metal foil on both sides of a single prepreg obtained by the method described in

[10] or

[11] above, or on both sides of a prepreg laminate containing at least one of the prepregs, and then press-molding the laminate. Effect of the Invention

[0007] According to the present disclosure, it is possible to provide a prepreg that can realize a metal-clad laminate with high thickness accuracy even when a fiber base material with a thickness of 40 μm or more is used, and to provide a laminate, a metal-clad laminate, a printed wiring board, and a semiconductor package obtained using the prepreg, and further to provide a method for manufacturing the prepreg and a method for manufacturing the metal-clad laminate. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a schematic cross-sectional view showing one aspect of the prepreg of the present embodiment. [Diagram 2]FIG. 1 is a schematic cross-sectional view of a prepreg produced by a conventional method in which a fiber substrate is immersed in a resin varnish and then dried. [Diagram 3] FIG. 2 is a cross-sectional view of the prepreg of the present embodiment for explaining the thickness of the fiber base material and the resin thickness on the front and back sides. [Figure 4] 1 is a surface observation image converted into black and white mode and used to calculate the abundance ratio of the impregnated region in the prepreg produced in Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] One embodiment of the present disclosure will be described in detail below, but the present disclosure is not limited to the embodiment described below. In the numerical ranges described in this disclosure, the lower limit or upper limit of the numerical range may be replaced with the values ​​shown in the examples. The lower limit and upper limit of a numerical range may be arbitrarily combined with the lower limit or upper limit of another numerical range. In the expression "AA to BB", the numerical values ​​AA and BB at both ends are included in the numerical range as the lower limit and upper limit, respectively. In addition, the expression "over CC to DD" indicates that the numerical range is over CC and is equal to or less than DD. In the present disclosure, for example, the description "10 or more" means 10 and a numerical value exceeding 10, and the same applies when the numerical values ​​are different. Also, for example, the description "10 or less" means 10 and a numerical value less than 10, and the same applies when the numerical values ​​are different. In addition, unless otherwise specified, each component and material exemplified in the present disclosure may be used alone or in combination of two or more. In the present disclosure, the content of each component in the thermosetting resin composition means the total amount of the multiple substances present in the thermosetting resin composition when multiple substances corresponding to each component are present in the thermosetting resin composition, unless otherwise specified.

[0010] In the present disclosure, the term "resin component" is defined as all components among the solid contents constituting the thermosetting resin composition, excluding inorganic compounds such as inorganic fillers described below, and flame retardants and flame retardant assistants. In the present disclosure, the term "solid content" refers to components in a thermosetting resin composition other than water, volatile substances such as the solvent described below, etc. In other words, the solid content includes those that are liquid, syrup-like, or waxy at around 25°C, and does not necessarily mean that they are solid. The expression "containing XX" described in the present disclosure includes both the meaning of containing XX in a reacted state when XX is capable of reacting, and the meaning of simply containing XX. Any combination of the descriptions in this disclosure is also included in this disclosure and this embodiment.

[0011] [Prepreg] The prepreg of this embodiment is a prepreg obtained by impregnating a fiber base material having a thickness of 40 μm or more with a thermosetting resin composition, and has impregnated areas and unimpregnated areas of the thermosetting resin composition in the fiber base material, and has a surface waviness (Wa) of 5.0 μm or less. The surface waviness (Wa) in this disclosure refers to the arithmetic mean height (Wa) that can be obtained from a waviness curve according to ISO 4287 (1997). JIS B 0601 (2001) may be used instead of ISO 4287 (1997). The surface waviness (Wa) in this disclosure can be measured as follows. 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). For the obtained waviness curve, a surface roughness analysis is performed using an analysis application to calculate the surface waviness (Wa). Here, the waviness curve is a curve obtained by applying a phase compensation 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 the prepreg in the present disclosure refers to the surface waviness of at least one surface of the prepreg, and the "surface" refers to the surface that will be overlapped when a plurality of prepregs are laminated to produce a metal-clad laminate, or the surface opposite thereto. For example, the surface waviness (Wa) of at least one surface of the prepreg is preferably 5.0 μm or less, and from the viewpoint of the thickness accuracy of the metal-clad laminate, it is more preferable that the surface waviness (Wa) of both surfaces of the prepreg is 5.0 μm or less.

[0012] The prepreg of this embodiment has a surface waviness (Wa) of 5.0 μm or less, even though it uses a "fiber base material with a thickness of 40 μm or more" that has a larger surface waviness than a thin fiber base material. This was achieved by adopting a method of "deliberately providing an area not impregnated with the thermosetting resin composition in the fiber base material of the prepreg." This method is generally difficult to adopt, given the conventional technical common sense that void generation is suppressed by increasing the impregnation rate of the thermosetting resin composition into the fiber base material as much as possible during the prepreg manufacturing stage. And, by using the prepreg, it was successful in significantly improving the thickness accuracy of the metal-clad laminate of this embodiment. Although the mechanism of success is unclear, it is considered as follows. As shown in FIG. 1, when the resin film is impregnated into the fiber substrate, a region in which the thermosetting resin composition is not impregnated is intentionally provided in the fiber substrate, so that the layer of the thermosetting resin composition near the surface (hereinafter, abbreviated as the resin layer) exists without following the waviness of the glass cloth. As a result, the large waviness of the fiber substrate having a thickness of 40 μm or more is difficult to be reflected on the surface of the prepreg, and the surface waviness (Wa) of the prepreg is 5.0 μm or less. Then, by press molding using the prepreg with a surface waviness (Wa) of 5.0 μm or less, the thickness of the metal-clad laminate is prevented from becoming uneven due to the small surface waviness (Wa) of the prepreg, and high thickness accuracy can be achieved. On the other hand, in the conventional method of immersing a fiber substrate in a resin varnish and then drying it, as shown in FIG. 2, the thermosetting resin composition follows the undulation of the glass cloth, so that the surface undulation of the prepreg becomes large. In other words, in the prepreg, the thickness of the resin layer in the surface direction becomes more uneven. Since the prepreg is pressurized in the thickness direction during the production of the metal-clad laminate, the thermosetting resin composition is likely to flow in the thickness direction, but if it does not flow sufficiently in the surface direction, it will lead to unevenness in the thickness of the metal-clad laminate. However, it is technically difficult to control the flow of the thermosetting resin composition in the surface direction to such an extent that the unevenness in the thickness of the resin layer is reduced or eliminated. In the prepreg of this embodiment, the resin layer near the surface does not follow the undulations of the glass cloth, and therefore, as described above, the surface undulations are small, that is, the thickness variation is small. Therefore, it is considered that the thickness variation of the metal-clad laminate is small even if there is no flow of the thermosetting resin composition in the surface direction during the production of the metal-clad laminate.

[0013] In this embodiment, an unimpregnated region of the thermosetting resin composition is provided in the fiber base material of the prepreg. During press molding to manufacture the metal-clad laminate, the thermosetting resin composition flows in the thickness direction and into the unimpregnated region, thereby sufficiently suppressing the generation of voids in the metal-clad laminate.

[0014] From the above viewpoints, the surface waviness (Wa) of the prepreg of this embodiment is preferably 5.0 μm or less, more preferably 3.0 μm or less, and even more preferably 1.0 μm or less. The lower limit of the surface waviness (Wa) of the prepreg of this embodiment is not particularly limited, but may be 0.01 μm or more, 0.1 μm or more, or 0.2 μm or more. In other words, the surface waviness (Wa) of the prepreg of this embodiment may be 0.01 to 5.0 μm, 0.1 to 3.0 μm, or 0.2 to 1.0 μm.

[0015] (Regarding the presence of regions in the fiber substrate that are not impregnated with the thermosetting resin composition) As described above, the prepreg of this embodiment has an impregnated region and an unimpregnated region of the thermosetting resin composition in the fiber base material, and is particularly characterized by having the unimpregnated region. The presence of the unimpregnated region can be confirmed by determining the ratio of the impregnated region of the thermosetting resin composition in the fiber base material. In other words, if the ratio of the impregnated region is not 100%, it means that the prepreg has an unimpregnated region. The method for determining the ratio of the impregnated region of the thermosetting resin composition in the fiber base material can be, for example, the following calculation method. From the viewpoint of the thickness accuracy of the metal-clad laminate, the ratio of the impregnated region determined based on the following calculation method is not particularly limited, but may be 25 to 98%, 30 to 98%, 30 to 95%, 35 to 95%, 35 to 90%, 40 to 90%, 40 to 85%, or 40 to 80%. When the ratio is 98% or less, the effect of improving the thickness accuracy of the metal-clad laminate tends to be large, and when it is 95% or less, this tendency becomes even greater. In addition, when the ratio is 30% or more, the thermosetting resin composition does not fall off from the prepreg, so that the secondary effect of good handleability tends to be obtained.

[0016] -Calculation method- A surface observation image is obtained by observing the surface of the prepreg using an optical microscope at a magnification of 50. The observation conditions are those described in detail in the Examples from the viewpoint of photographing in an appropriate brightness. The obtained surface observation image is converted to black and white mode by 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 is converted to RGB (Red, Green, Blue) values ​​for each pixel by 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 parts (RGB value = 255) and the white parts (RGB value = 0) are calculated. From these values, the area ratio of the black parts to the total of the black parts and the white parts is calculated. The area ratio of the black parts thus obtained is regarded as the abundance ratio of the impregnated region. As the image editing software, for example, "Microsoft Paint" (manufactured by Microsoft Corporation) can be used. Furthermore, as the image conversion software, for example, free software "bmp2csv" can be used. In the above observation, when the surface observation image taken at a moderate brightness is converted to a black and white mode, the surface where the unimpregnated region of the thermosetting resin composition exists below the observation surface is a void portion that is easily reflective of light, and is therefore represented as "white", and the other surfaces are represented as "black". Here, when taking a surface observation image, it is preferable to adjust the exposure time during surface photography within a range of 60 to 100 ms, so that the image can be taken at a moderate brightness that can fully reflect the impregnated and unimpregnated regions. In the surface observation image of the prepreg, the areas in order of intensity of color are "areas in the resin layer where no glass cloth exists", "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, the "areas in the resin layer where no glass cloth exists" are also included in the impregnated area. If the surface observation image is too bright, not only the parts where the resin is not sufficiently impregnated into the glass cloth but also the parts where the resin is sufficiently impregnated into the glass cloth tend to be shown in white in the surface observation image in the black and white mode, and if the image is even brighter, the surface observation image in the black and white mode tends to be white overall. On the other hand, if the surface observation image is too dark, the surface observation image in the black and white mode tends to be black overall, making it difficult to reflect the presence of unimpregnated areas. Therefore, it is preferable to take the image at a moderate brightness. As an example of converting a surface observation image taken at a moderate brightness into a black and white mode, the surface observation image converted into the black and white mode obtained in Example 2 is shown in FIG. 4. In addition, the area ratio of the white areas to the total area of ​​the white and black areas can be easily calculated by using the COUNTIF function in Microsoft Excel (Microsoft Corporation).

[0017] (Surface roughness (Ra)) The prepreg of the present embodiment is not particularly limited, but preferably has a surface roughness (arithmetic mean roughness Ra; hereinafter sometimes simply referred to as "Ra") of 0.1 to 5 μm. The surface roughness (Ra) in this disclosure refers to the arithmetic mean height (Ra) that can be obtained from a roughness curve according to ISO 4287 (1997). Instead of ISO 4287 (1997), JIS B 0601 (2001) may be used. The surface roughness (Ra) in this disclosure refers to the surface roughness (Ra) obtained by measuring with a shape analysis laser microscope "VK-X100" (manufactured by Keyence Corporation). Here, the roughness curve measured in this embodiment is a curve obtained by applying a phase compensation high-pass filter λc (λc=80 μm) to the cross-sectional curve and removing wavelengths of 80 μm or more from the cross-sectional curve. The analysis range is 1,000 μm x 1,000 μm.

[0018] In the prepreg of this embodiment, by setting Ra to 0.1 μm or more, appropriate unevenness is imparted to the surface of the prepreg, which makes it possible to suppress the amount of static electricity to a low level and makes the prepreg easy to handle. On the other hand, by setting Ra to 5 μm or less, the thickness precision of the metal-clad laminate tends to be improved. From this viewpoint, the Ra of the prepreg of the present embodiment may be 0.15 to 3 μm, 0.2 to 2 μm, 0.2 to 1.6 μm, or 0.2 to 1.0 μm. Unless otherwise specified, the Ra of the prepreg in the present disclosure is the Ra of at least one surface of the prepreg, and the "surface" refers to the surface that will be laminated when a metal-clad laminate is produced by laminating a plurality of prepregs or the surface opposite thereto. It is preferable that the Ra of at least one surface of the prepreg is within the above range, and it is more preferable that the Ra of both surfaces is within the above range.

[0019] (Relationship between the thickness of resin protruding from the fiber base material on the front and back of the prepreg) The prepreg of this embodiment is not particularly limited, but by setting the difference in thickness of the resin protruding from the fiber substrate on the front and back of the prepreg to preferably 0 to 10 μm, it is possible to suppress warping of the prepreg itself and reduce the amount of warping of the metal-clad laminate. In this disclosure, the thickness of the thermosetting resin composition protruding from the fiber substrate on the front and back of the prepreg is sometimes referred to as the "resin thickness", and the difference between the resin thickness on the front surface of the prepreg and the resin thickness on the back surface of the prepreg is sometimes referred to as the "resin thickness difference". From the viewpoint of reducing the amount of warping of the metal-clad laminate, the difference in resin thickness is more preferably 0 to 7 μm, even more preferably 0 to 5.5 μm, particularly preferably 0 to 3.5 μm, and most preferably 0 to 2.5 μm. The lower limit of the difference in resin thickness may be 0.1 μm, 0.3 μm, 0.5 μm, or 0.8 μm. The resin thickness is the shortest distance from a resin end on the front or back of the prepreg to the glass cloth in an image of a cross section of the prepreg observed with a metallurgical microscope as shown in Fig. 3. For convenience, the thermosetting resin composition impregnated in the fiber substrate is not shown in Fig. 3. By reducing the difference in the thickness of the resin protruding from the fiber base material as described above, the difference in the amount of thermal expansion between the front and back of the prepreg during press molding is reduced, so it is believed that the metal-clad laminate tends to be less prone to warping when made into a metal-clad laminate. Reducing the amount of warping of the metal-clad laminate contributes to improving the connection reliability of printed wiring boards and semiconductor packages.

[0020] <Fiber base material> As the fiber substrate having a thickness of 40 μm or more contained in the prepreg of this embodiment, a well-known one used in various laminates for electrical insulating materials can be used. Examples of the material of the fiber substrate include natural fibers such as paper and cotton linters; inorganic fibers such as glass fibers and asbestos; organic fibers such as aramid, polyimide, polyvinyl alcohol, polyester, tetrafluoroethylene, and acrylic; and mixtures thereof. Among these, inorganic fibers are preferred from the viewpoint of flame retardancy, and glass fibers are more preferred. Furthermore, examples of glass fibers include glass cloth using E glass, C glass, D glass, S glass, etc.; glass cloth in which short fibers are bonded with an organic binder; and a mixture of glass fibers and cellulose fibers. Among these, glass cloth using E glass is preferred as the glass fiber. 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, etc. Among these, in the case of a woven fabric, the effect of the present embodiment tends to be more remarkable. The material and shape may be appropriately selected according to the intended use and performance of the molded product. As the fiber substrate, one type may be used alone, or two or more types of materials and two or more types of shapes may be used in combination as necessary. The fiber substrate may be a fiber substrate made of one layer or a fiber substrate made of multiple layers. The fiber substrate made of one layer means a fiber substrate made of only entangled fibers, and when there is a fiber substrate that is not entangled, it is classified as a fiber substrate made of multiple layers. The material and shape of the fiber substrate of two or more layers may be the same or different.

[0021] (Thickness of fiber base material) The thickness of the fiber base material contained in the prepreg of this embodiment (see FIG. 3) is set to "40 μm or more", which was found to tend to deteriorate the thickness precision of the metal-clad laminate in the conventional method. The thickness of the fiber base material may be 40 to 120 μm, 50 to 120 μm, 60 to 120 μm, 70 to 120 μm, or 70 to 100 μm. The larger the thickness of the fiber base material, the larger the surface waviness of the fiber base material itself tends to be, so the thickness precision of the metal-clad laminate decreases in the conventional method. However, in the case of the prepreg of this embodiment, even if the thickness of the fiber base material is large as described above, the surface waviness (Wa) of the prepreg is suppressed to be small, and as a result, the thickness precision of the metal-clad laminate increases. In the present disclosure, the thickness of the fiber base material is the thickness at the portion shown in FIG. 3, and is the average value of values ​​obtained by measuring five arbitrary portions of the fiber base material with a micrometer.

[0022] (Surface waviness of fiber substrate (Wa)) The surface waviness (Wa) of the fiber substrate contained in the prepreg of this embodiment is not particularly limited, but may be more than 5.0 μm, 6.0 μm or more, 7.0 μm or more, 10.0 μm or more, or 15.0 μm or more. The upper limit of the surface waviness (Wa) of the fiber substrate of this embodiment is not particularly limited, but may be 40 μm or less, 30 μm or less, or 25 μm or less. In other words, the surface waviness (Wa) of the fiber substrate may be more than 5.0 to 40 μm, 6.0 to 30 μm, 7.0 to 30 μm, 10 to 25 μm, or 15 to 25 μm. According to this embodiment, even if the surface waviness (Wa) of the fiber base material is within the above range, the surface waviness (Wa) of the prepreg can be kept within the above range, and the thickness accuracy of the metal-clad laminate can be maintained at a high level.

[0023] <Thermosetting resin composition> As described above, the prepreg of this embodiment is a prepreg obtained by impregnating a fiber base material having a thickness of 40 μm or more with a thermosetting resin composition. The thermosetting resin composition contains at least a thermosetting resin. The components contained in the thermosetting resin composition are not particularly limited, but it is preferable that the thermosetting resin composition contains at least one selected from the group consisting of a curing agent, a curing accelerator, an inorganic filler, an organic filler, a coupling agent, a leveling agent, an antioxidant, a flame retardant, a flame retardant assistant, a thixotropy imparting agent, a thickener, a flexible material, a surfactant, and a photopolymerization initiator in addition to the thermosetting resin. Hereinafter, each component contained in the thermosetting resin composition will be described in order.

[0024] (thermosetting resin) Examples of the thermosetting resin include epoxy resin, polyimide resin, maleimide resin, modified maleimide resin, phenol resin, polyphenylene ether resin, bismaleimide triazine resin, cyanate resin, isocyanate resin, benzoxazine resin, oxetane resin, amino resin, unsaturated polyester resin, allyl resin, dicyclopentadiene resin, silicone resin, triazine resin, melamine resin, etc. Examples of the modified maleimide resin include a reaction product of a maleimide compound having at least two N-substituted maleimide groups and at least one compound selected from the group consisting of a monoamine compound and a diamine compound. In addition, the thermosetting resin is not particularly limited to these, and a known thermosetting resin can be used. The thermosetting resin may be used alone or in combination of two or more types. Among these, from the viewpoints of moldability and electrical insulation, it is also preferable to contain, as the thermosetting resin, at least one selected from the group consisting of epoxy resins, polyimide resins, maleimide resins, modified maleimide resins, cyanate resins, polyphenylene ether resins, and bismaleimide triazine resins.

[0025] The epoxy resin is preferably an epoxy resin having two or more epoxy groups in one molecule. Here, the epoxy resin is classified into glycidyl ether type epoxy resin, glycidyl amine type epoxy resin, glycidyl ester type epoxy resin, etc. Among these, glycidyl ether type epoxy resin is preferable. Epoxy resins are classified into various epoxy resins according to the difference in the main skeleton. For example, the above-mentioned types of epoxy resins are further classified into bisphenol-type epoxy resins, alicyclic epoxy resins, aliphatic chain epoxy resins, novolac-type epoxy resins, stilbene-type epoxy resins, naphthalene skeleton-containing epoxy resins, biphenyl-type epoxy resins, xylylene-type epoxy resins, dihydroanthracene-type epoxy resins, etc. One type of epoxy resin may be used alone, or two or more types may be used in combination from the viewpoints of insulation reliability and heat resistance. The epoxy resin may be a novolac type epoxy resin or a phenol novolac type epoxy resin.

[0026] (hardening agent) For example, when the thermosetting resin contains an epoxy resin, the curing agent may be a phenol-based curing agent, a cyanate ester-based curing agent, an acid anhydride-based curing agent, an amine-based curing agent, or an active ester group-containing compound. When the thermosetting resin contains a resin other than an epoxy resin, a known curing agent for the thermosetting resin may be used. The curing agent may be used alone or in combination of two or more types.

[0027] The phenol-based curing agent is not particularly limited, but preferred examples thereof include cresol novolac type phenolic resins, biphenyl aralkyl type phenolic resins, phenol novolac type phenolic resins, naphthylene ether type phenolic resins, and triazine skeleton-containing phenolic resins.

[0028] The cyanate ester-based curing agent is not particularly limited, but examples thereof include bisphenol A dicyanate, polyphenol cyanate (oligo(3-methylene-1,5-phenylene cyanate)), and the like. The acid anhydride curing agent is not particularly limited, but examples thereof include phthalic anhydride, tetrahydrophthalic anhydride, trimellitic anhydride, and pyromellitic anhydride. The amine-based curing agent is not particularly limited, but examples thereof include aliphatic amines such as triethylenetetramine and tetraethylenepentamine; and aromatic amines such as 4,4'-diaminodiphenylmethane. Moreover, as the hardener, urea resin or the like can also be used.

[0029] When the thermosetting resin composition contains a curing agent, the content thereof is preferably 20 to 200 parts by mass, more preferably 20 to 150 parts by mass, and further preferably 30 to 100 parts by mass, based on 100 parts by mass of the thermosetting resin. In addition, when the thermosetting resin composition contains a curing agent, the content may be expressed by the functional group equivalent. Specifically, the content of the curing agent is preferably an amount that satisfies the formula: (mass of thermosetting resin / functional group equivalent) ≒ (mass of curing agent / functional group equivalent capable of reacting with thermosetting resin) × constant C. The constant C varies depending on the type of functional group of the curing agent, and is preferably 0.8 to 1.2 when the functional group is a phenolic hydroxyl group, preferably 0.2 to 0.4 when the functional group is an amino group, and preferably 0.3 to 0.6 when the functional group is an active ester group. When the thermosetting resin contains an epoxy resin, the above formula becomes (mass of epoxy resin / epoxy group equivalent)≒(mass of curing agent / functional group equivalent capable of reacting with epoxy group)×constant C.

[0030] (Cure accelerator) As the curing accelerator, a general curing accelerator used for curing the thermosetting resin can be used. For example, when the thermosetting resin contains an epoxy resin, the curing accelerator may be an imidazole compound and its derivatives; a phosphorus-based compound; a tertiary amine compound; a quaternary ammonium compound, etc. From the viewpoint of accelerating the curing reaction, an imidazole compound and its derivatives are preferred. Specific examples of the imidazole compound and its derivatives include imidazole compounds such as 2-methylimidazole, 2-ethylimidazole, 2-undecylimidazole, 2-phenylimidazole, 1,2-dimethylimidazole, and 2,4-diamino-6-[2'-methylimidazolyl-(1')]ethyl-s-triazine; salts of the imidazole compounds and trimellitic acid such as 1-cyanoethyl-2-phenylimidazolium trimellitate; salts of the imidazole compounds and isocyanuric acid; salts of the imidazole compounds and hydrobromic acid. One type of imidazole compound may be used alone, or two or more types may be used in combination. The curing accelerator may be an imidazole compound or a derivative thereof, or may be an imidazole compound.

[0031] When the thermosetting resin composition contains a curing accelerator, the content thereof is preferably 0.1 to 20 parts by mass, and more preferably 0.1 to 10 parts by mass, based on 100 parts by mass of the thermosetting resin.

[0032] (Inorganic filler) The inorganic filler can reduce the thermal expansion coefficient and improve the strength of the coating film. Examples of inorganic fillers include silica, alumina, barium sulfate, talc, mica, kaolin, boehmite, beryllia, barium titanate, potassium titanate, strontium titanate, calcium titanate, aluminum carbonate, magnesium hydroxide, aluminum hydroxide, aluminum borate, aluminum silicate, calcium carbonate, calcium silicate, magnesium silicate, zinc borate, zinc stannate, aluminum oxide, zirconia, mullite, magnesia, zinc oxide, titanium oxide, silicon carbide, silicon nitride, boron nitride, clay (e.g., calcined clay, etc.), molybdic acid compounds such as zinc molybdate, glass short fibers, glass powder, and hollow glass beads. Examples of glass, which is a material for glass short fibers, glass powder, and hollow glass beads, include E glass, T glass, and D glass. One type of inorganic filler may be used alone, or two or more types may be used in combination. Among these, silica and alumina are preferred from the viewpoint of reducing the coefficient of thermal expansion, the relative dielectric constant and the dielectric loss tangent, and aluminum hydroxide is preferred from the viewpoint of heat resistance, with silica and aluminum hydroxide being more preferred. Examples of the silica include precipitated silica produced by a wet method and having a high water content, and dry method silica produced by a dry method and containing almost no bound water, etc. Dry method silica further includes crushed silica, fumed silica, and fused silica (fused spherical silica) depending on the production method. The inorganic filler may be surface-treated with a surface treatment agent such as a silane coupling agent in order to improve moisture resistance, and may be hydrophobized in order to improve dispersibility.

[0033] When the thermosetting resin composition contains an inorganic filler, its content varies depending on the purpose of addition, but is preferably 0.1 to 65% by volume. If it is 0.1% by volume or more, the thermal expansion coefficient tends to be small. On the other hand, by suppressing it to 65% by volume or less, the viscosity during blending of the resin components does not become too high, and it tends to be easy to suppress a decrease in workability. From the same viewpoint, the content of the inorganic filler is more preferably 10 to 60% by volume, further preferably 15 to 55% by volume, and particularly preferably 30 to 55% by volume.

[0034] (Coupling Agent) The inclusion of a coupling agent has the effect of improving the dispersibility of the inorganic filler and the organic filler, and improving the adhesion to the reinforcing substrate and the metal foil. The coupling agent may be used alone or in combination of two or more kinds. The coupling agent may be a titanate coupling agent, a silane coupling agent, or the like.

[0035] (Organic solvent) From the viewpoint of ease of handling, the thermosetting resin composition may further contain an organic solvent. In the present disclosure, the thermosetting resin composition containing an organic solvent may be referred to as a resin varnish. The organic solvent is not particularly limited, but examples thereof include alcohol-based solvents such as methanol, ethanol, methyl cellosolve, butyl cellosolve, and propylene glycol monomethyl ether; ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, butanone, cyclohexanone, and 4-methyl-2-pentanone; ester-based solvents such as ethyl acetate, butyl acetate, and propylene glycol monomethyl ether acetate; ether-based solvents such as tetrahydrofuran; aromatic solvents such as toluene, xylene, and mesitylene; nitrogen-containing solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; sulfur-containing solvents such as dimethyl sulfoxide; and ester-based solvents such as γ-butyrolactone. The organic solvent may be used alone or in combination of two or more kinds.

[0036] From the viewpoint of ease of application, for example, the content of the organic solvent may be adjusted so that the non-volatile content of the thermosetting resin composition is preferably 20 to 85 mass %, more preferably 40 to 80 mass %. Although the resin varnish may be prepared using an organic solvent, in the method for producing the prepreg of this embodiment described below, a resin film is produced and then the resin film is impregnated into a fiber substrate to obtain the prepreg, so that the organic solvent volatilizes during the resin film production stage. As a result, almost no organic solvent remains in the prepreg of this embodiment, specifically 5 mass % or less.

[0037] The method for preparing the thermosetting resin composition is not particularly limited, and any conventionally known preparation method can be used. For example, a thermosetting resin and other components as necessary are added to the organic solvent, and then the mixture is mixed and stirred using various mixers to prepare a resin varnish. Examples of the mixer include ultrasonic dispersion type, high-pressure collision type dispersion type, high-speed rotation dispersion type, bead mill type, high-speed shear dispersion type, and rotation-revolution type dispersion type mixers.

[0038] (Prepreg thickness) The thickness of the prepreg of this embodiment may be appropriately determined according to the thickness of the fiber base material, and may be 50 to 300 μm, 50 to 250 μm, 55 to 200 μm, 60 to 180 μm, 60 to 170 μm, or 60 to 150 μm. Here, the thickness of the prepreg refers to the thickness of one prepreg. When the thickness of the prepreg is equal to or greater than the lower limit, the effect of reducing surface waviness according to this embodiment tends to be significantly obtained. When the thickness of the prepreg is equal to or less than the upper limit, the generation of voids after the production of the laminate tends to be suppressed in this embodiment. In the present disclosure, the thickness of the prepreg is the average value of values ​​obtained by measuring any five points with a Digimatic indicator.

[0039] [Prepreg manufacturing method] The method for producing the prepreg of the present embodiment is not particularly limited, and from the viewpoint of improving thickness accuracy, the following production method is preferred. In other words, a method for producing a prepreg is preferred in which a film of a thermosetting resin composition is impregnated into a fiber base material having a thickness of 40 μm or more by lamination, and a surface waviness (Wa) of 5.0 μm or less is achieved by providing impregnated areas and unimpregnated areas of the thermosetting resin composition in the fiber base material. In this manufacturing method, a film of a thermosetting resin composition (hereinafter, sometimes referred to as a "resin film") is used. Note that, in the method of immersing a fiber substrate in a resin varnish and then drying it, it is difficult to intentionally provide an unimpregnated region in the fiber substrate, and the surface waviness (Wa) tends to be large (see FIG. 2), so the above manufacturing method is preferable. In the method for producing the prepreg, the fiber base material, the thermosetting resin composition, and the surface waviness (Wa) are as described above.

[0040] The resin film can be produced by forming a layer (resin layer) of a thermosetting resin composition on one side of a release film. The resin layer can be formed, for example, by applying the resin varnish to one side of the release film and then drying it. The method of applying the resin varnish is not particularly limited, and can be carried out using a known coating device such as a comma coater, a bar coater, a kiss coater, a roll coater, a gravure coater, a die coater, etc. It is preferable to appropriately select these coating devices depending on the film thickness of the resin layer. The drying temperature and drying time will vary depending on the amount of organic solvent used, the boiling point of the organic solvent, etc., but for example, in the case of a resin varnish containing 30 to 70 mass % of an organic solvent, a resin film can be suitably formed by drying at 50 to 160°C for 1 to 8 minutes. The film thus produced is sometimes called a resin film with a release film.

[0041] (Thickness of resin film) 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 in the range of 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. In the present disclosure, the thickness of the resin film is a value measured as follows. First, the total thickness of the resin-attached film after coating is measured using a Digimatic indicator at any five points. The resin layer at the measurement points is peeled off with an adhesive tape, and the thickness of the release film is measured using a Digimatic indicator, and the average value of the values ​​obtained by subtracting the thickness of the release film from the total thickness is obtained. When the thickness of the resin film is equal to or greater than the lower limit, a sufficient amount of resin for impregnating a thick glass cloth having a thickness of 40 μm or more tends to be secured. When the thickness of the resin film is equal to or less than the upper limit, the resin film tends to be easily produced.

[0042] (Release film) Examples of the release film include organic films such as polyethylene terephthalate (PET), biaxially oriented polypropylene (OPP), polyethylene, polyvinyl fluoride, polyimide, etc.; metal or alloy films such as copper and aluminum, etc. These release films may be treated with a release agent for release. The thickness of the release film is not limited, and from the viewpoints of ease of handling when applying the thermosetting resin composition and economic efficiency, it is preferably 10 to 200 μm, more preferably 20 to 100 μm, and even more preferably 30 to 70 μm. As the release film, a commercially available product can be used.

[0043] (Method of impregnating a fiber substrate with a resin film) Next, a method for impregnating the fiber base material with the resin film by lamination will be described. First, the resin film with release film is placed on at least one surface of the fiber substrate so that the resin film is in contact with the fiber substrate. Then, the resin film with release film and the fiber substrate are heated and pressurized to impregnate the fiber substrate with the resin film. At this time, an area not impregnated with the thermosetting resin composition is provided in the fiber substrate. In this way, the prepreg of this embodiment with a release film is obtained. The heating and pressure application here is preferably carried out by lamination, which can be performed by (a) roll lamination or (b) a method of laminating under reduced pressure such as vacuum lamination.

[0044] (a) The conditions for roll lamination are not particularly limited, but the heating temperature is preferably 80 to 180° C., and the pressing pressure is preferably 0.05 to 1.0 MPa / m. (b) The conditions for the method of laminating under reduced pressure are not particularly limited, but the heating temperature is preferably 50 to 170°C, more preferably 110 to 160°C, the pressurizing time is preferably 10 to 120 seconds, more preferably 20 to 80 seconds, and the pressurizing pressure is preferably 0.05 to 1.0 MPa, more preferably 0.1 to 0.6 MPa.

[0045] (Method of Providing Unimpregnated Region) The method for providing the fiber substrate with the non-impregnated region of the thermosetting resin composition is not particularly limited, but may be, for example, a method of adjusting the conditions for heating and pressurizing the resin film with the release film and the fiber substrate, specifically, a method of adjusting the lamination conditions. Here, when the lamination conditions are the same for the thin fiber substrate and the thick fiber substrate, the thick fiber substrate tends to be more difficult to impregnate the resin film into the fiber substrate. Therefore, even if the lamination conditions of this embodiment are the same as those of the conventional thin fiber substrate, the fiber substrate can have an unimpregnated region of the thermosetting resin composition. Specific methods for adjusting the heating and pressurizing conditions are not particularly limited, but include, for example, the following methods. First, a prepreg is prepared under a predetermined heating and pressing conditions, and then the ratio of the impregnated region of the thermosetting resin composition in the fiber base material is calculated based on the calculation method. As a result, if the impregnated region is 100%, that is, if there is no unimpregnated region, the heating temperature or the pressurizing pressure is lowered, or both the heating temperature and the pressurizing pressure are lowered, the prepreg is reprepared, and the ratio of the impregnated region is calculated again. By repeating this process as necessary, the conditions for producing a prepreg having an unimpregnated region can be easily grasped. When it is desired to adjust the proportion of unimpregnated regions to a lower value, the heating temperature or the pressing pressure may be increased, or both the heating temperature and the pressing pressure may be increased, and the prepreg may be produced again. When lamination is performed under reduced pressure, it is also possible to adjust the proportion of unimpregnated regions by adjusting the degree of vacuum.

[0046] It is preferable to laminate one or more resin films on each side of the fiber substrate. The number of resin films per side of the fiber substrate is preferably one or two, and more preferably one. After the resin film has been impregnated into the fiber base material, it is cooled as necessary, and then the release film is peeled off from the resulting prepreg with the release film, thereby producing a prepreg having a surface waviness (Wa) of 5.0 μm or less.

[0047] [Laminates, metal-clad laminates] The present disclosure also provides a laminate having one or more prepregs of the present embodiment. The laminate having a metal foil arranged thereon is particularly called a "metal-clad laminate". That is, the present disclosure also provides a metal-clad laminate having a metal foil and one or more prepregs of the present embodiment. The prepreg of the present embodiment may be used in combination with other prepregs. In the laminate and metal-clad laminate of the present embodiment, as long as the laminate and metal-clad laminate have one or more prepregs of the present embodiment, the number of prepregs may be 1 to 20, 2 to 20, 5 to 18, or 8 to 16. Examples of the metal foil in the metal-clad laminate include copper foil, aluminum foil, tin foil, tin-lead alloy (solder) foil, and nickel foil. The thickness of the metal foil can be a thickness generally used in laminates, for example, 1 to 200 μm. In addition, a three-layer composite foil having an intermediate layer of nickel, nickel-phosphorus, nickel-tin alloy, nickel-iron alloy, lead, or lead-tin alloy, and a copper layer of 0.5 to 15 μm and a copper layer of 10 to 300 μm on both sides of the intermediate layer, and a two-layer composite foil having aluminum and copper foil can be used. When the metal foil is a copper foil, the metal-clad laminate is called a copper-clad laminate.

[0048] [Metal-clad laminate manufacturing method] The present disclosure also provides a method for producing a metal-clad laminate by placing metal foil on both sides of one prepreg of the present embodiment or on both sides of a prepreg laminate including at least one prepreg of the present embodiment, and then press-molding the laminate. Specific methods for the press molding include, for example, a method of press molding in a vacuum press under conditions of a degree of vacuum of preferably 300 kPa or less, more preferably 100 kPa or less, a temperature of preferably 130 to 350°C, more preferably 150 to 300°C, and even more preferably 170 to 250°C, and a pressure of preferably 0.5 to 10 MPa, more preferably 1 to 5 MPa. The press molding allows the thermosetting resin composition to flow into the unimpregnated region of the thermosetting resin composition in the fiber base material, thereby suppressing the generation of voids. The prepreg laminate is not particularly limited, but in order to obtain a copper-clad laminate with high thickness accuracy, it is preferable that 10% by mass or more is composed of the prepreg of this embodiment, more preferably 20% by mass or more is composed of the prepreg of this embodiment, and even more preferably 50% by mass or more is composed of the prepreg of this embodiment, and it may be entirely composed of the prepreg of this embodiment. However, even if the prepreg of this embodiment constitutes less than 10% by mass of the prepreg laminate, it contributes to increasing the thickness accuracy of the copper-clad laminate. The laminate of this embodiment can be obtained by removing the metal foil from the metal-clad laminate of this embodiment by etching or the like.

[0049] [Printed wiring board] The present disclosure also provides a printed wiring board comprising the laminate of the present embodiment or the metal-clad laminate of the present embodiment. In other words, the present disclosure also provides a printed wiring board obtained by forming a wiring pattern on the laminate of the present embodiment or the metal-clad laminate of the present embodiment. The printed wiring board of the present embodiment can be manufactured by forming a wiring pattern on the laminate of the present embodiment or the metal-clad laminate of the present embodiment. Methods for forming the wiring pattern include known methods such as the subtractive method, the full additive method, the semi-additive method (SAP: Semi Additive Process), and the modified semi-additive method (m-SAP: modified Semi Additive Process).

[0050] [Semiconductor package] The present disclosure also provides a semiconductor package including the printed wiring board of the present embodiment and a semiconductor element. The semiconductor package of the present embodiment can be manufactured, for example, by mounting a semiconductor element such as a semiconductor chip or memory at a predetermined position of the printed wiring board of the present embodiment by a known method, and then sealing the semiconductor element with a sealing resin or the like. EXAMPLES

[0051] The present embodiment will now be described in more detail with reference to the following examples, but these examples are not intended to limit the present embodiment. The prepregs and copper-clad laminates produced in each example were evaluated according to the following methods.

[0052] [1. Surface waviness (Wa)] The surface waviness (Wa) was measured using the prepregs produced in each example. Using a shape analysis laser microscope "VK-X100" (manufactured by Keyence Corporation), shape measurements were automatically performed using an observation application to obtain a waviness curve conforming to ISO 4287 (1997). For the obtained waviness curve, a surface roughness analysis was performed using an analysis application to calculate the surface waviness (Wa). Here, the waviness curve is a curve obtained by applying a phase compensation high-pass filter λc (λc = 80 μm) to a 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.

[0053] [2. Surface roughness (Ra)] The surface roughness (Ra) was measured using the prepregs produced in each example. Using a shape analysis laser microscope "VK-X100" (manufactured by Keyence Corporation), shape measurements were automatically performed using an observation application to obtain a roughness curve conforming to ISO 4287 (1997). The obtained roughness curve was subjected to surface roughness analysis using an analysis application to calculate the surface roughness (Ra). Here, the roughness curve is a curve obtained by applying a phase compensation high-pass filter λc (λc = 80 μm) to the cross-sectional curve and removing wavelengths of 80 μm or more from the cross-sectional curve. The analysis range was 1,000 μm x 1,000 μm. The surface roughness (Ra) was measured on both sides of the prepreg, and the larger value was used.

[0054] [3. Ratio of impregnated regions] The ratio (%) of the region impregnated with the thermosetting resin composition in the fiber base material was calculated based on the following calculation method. -Calculation method- The surface of the prepreg was observed under the following conditions using an optical microscope (manufactured by Olympus Corporation, product name: MX61L-F) to obtain a surface observation image. <Observation conditions> ·Magnification: 50x Observation mode: dark field Sensitivity: ISO400 Exposure time for surface photography: 60-100ms - Brightness of the observation environment: Two 35W fluorescent lamps were installed 2m 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 parts (RGB value = 255) and white parts (RGB value = 0) were calculated. From these values, the area ratio of the black parts to the total of the black and white parts was calculated. The area ratio of the black parts thus obtained was taken as the presence ratio (%) of the impregnated region. Here, when photographing the surface observation image, the image was photographed at an appropriate brightness by adjusting the exposure time during surface photographing between 60 and 100 ms as described above so that the impregnated and non-impregnated areas could be adequately reflected. The image editing software used was "Microsoft Paint" (manufactured by Microsoft Corporation), and the image conversion software used was "bmp2csv," which is free software.

[0055] [4. Handling of prepreg] The prepreg obtained in each example was cut into a 250 mm square size and used as an evaluation sample. The evaluation sample was folded 180° around one diagonal line and then returned to its original position. In this procedure, samples in which no resin powder was observed to fall off were rated as "A," and samples in which resin powder was observed to fall off were rated as "B." A indicates excellent handleability.

[0056] [5. Difference in thickness of resin protruding from the fiber base material on the front and back of the prepreg (difference in resin thickness on the front and back)] The prepreg obtained in each example was dried in an explosion-proof dryer at 170°C for 1 hour, and then further dried at 200°C for 1 hour. After the dried prepreg was cast with epoxy resin, the cross section was observed with a metallurgical microscope and the difference in thickness of the resin protruding from the fiber base material on the front and back of the prepreg was measured. As shown in Figure 3, the shortest distance from the edge of the resin on the front side of the prepreg to the glass cloth was defined as T1, and the shortest distance from the edge of the resin on the back side of the prepreg to the glass cloth was defined as T2. The absolute value of the difference between T1 and T2 was defined as the difference in resin thickness.

[0057] [6. Variation in thickness of copper-clad laminate] The thickness of the copper-clad laminate obtained in each example was measured at 10 points in the width direction at 50 mm intervals from the width center, and at 10 points in the length direction at 50 mm intervals starting from each of the 10 points (however, each of the 10 points includes the starting point. In other words, the measurement points were 10 points x 10 points = 100 points in total). Specifically, measurements were made in 0.001 mm increments using a base adjusted to a horizontal position and a digital indicator "ID-C112P" (manufactured by Mitutoyo Corporation). The value calculated from the following formula was used as an index of thickness variation. A smaller value indicates less thickness variation and therefore better thickness precision. Thickness variation (%) = 100 x (maximum thickness - average thickness) / average thickness

[0058] [7. Copper solder heat resistance] The copper-clad laminate obtained in each example was cut into 25 mm squares to prepare evaluation boards. The evaluation boards were floated in a solder bath at 288°C for a maximum of 60 minutes, while visually observing the appearance, to measure the time until blistering occurred. If no blistering was observed after 60 minutes of floating, it was recorded as ">60". The longer the time until blistering occurred, the better the copper-plated solder heat resistance.

[0059] [8. Warpage of copper-clad laminate] The copper-clad laminate obtained in each example for evaluating the amount of warping was cut into a 250 mm square to prepare an evaluation board. The evaluation board was placed flat on a measuring table to measure the amount of warping. The height from the measuring table to the corner that was curled the most among the four corners of the evaluation board was used as the amount of warping. The copper-clad laminate was rated as A when the warp was 10 mm or less, and as B when it exceeded 10 mm.

[0060] Reference example 1 The surface waviness (Wa) of the following glass cloths was measured in the same manner as in [1. Surface waviness (Wa)] above, and then the surface waviness (Wa) of glass cloths of different thicknesses was compared. Note that the thickness of each glass cloth below is the average value of the values ​​obtained by measuring five arbitrary points with a micrometer "MDC-25MX" (manufactured by Mitutoyo Corporation). <Glass cloth with a thickness of 40 μm or more> (i) Glass cloth "IPC#2116" (manufactured by Nitto Boseki Co., Ltd., basis weight: 104 g / m 2 , substrate width: 530mm, thickness: 91μm) (ii) Glass cloth "IPC#3313" (manufactured by Nitto Boseki Co., Ltd., basis weight: 82 g / m 2 , substrate width: 530mm, thickness: 73μm) (iii) Glass cloth "IPC#1078" (manufactured by Nitto Boseki Co., Ltd., basis weight: 47 g / m 2 , substrate width: 530mm, thickness: 44μm) <Glass cloth with a thickness of less than 40 μm> (iv) Glass cloth "IPC#1037" (manufactured by Nitto Boseki Co., Ltd., basis weight: 24 g / m 2, substrate width: 530mm, thickness: 24μm) (v) Glass cloth "IPC#1027" (manufactured by Nitto Boseki Co., Ltd., basis weight: 20 g / m 2 , substrate width: 530mm, thickness: 21μm) The surface waviness (Wa) of the above glass cloths "IPC#2116", "IPC#3313", and "IPC#1078" was 21.9 μm, 13.4 μm, and 7.3 μm, respectively. Moreover, the surface waviness (Wa) of the above glass cloths "IPC#1037" and "IPC#1027" was 4.7 μm and 4.5 μm, respectively. It can be seen that the glass cloth having a thickness of 40 μm or more has a larger surface waviness (Wa) than the glass cloth having a thickness of less than 40 μm.

[0061] Manufacturing Example 1 (Preparation of Resin Varnish A) 60 parts by mass of phenol novolac type epoxy resin "EPICLON (registered trademark) N-770" (manufactured by DIC Corporation, epoxy equivalent: 188 g / eq), 40 parts by mass of biphenyl aralkyl type phenol resin (manufactured by Meiwa Kasei Co., Ltd., product name: MEH-7700), 17.5 parts by mass of aluminum hydroxide, 86 parts by mass of fused silica, 0.5 parts by mass of 2-methylimidazole, 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: 32% by volume).

[0062] Manufacturing Example 2 (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 meter with a reflux condenser, and the mixture was allowed to react for 5 hours under reflux to obtain a solution of a modified maleimide resin. (2. Preparation of Resin Varnish B) 107 parts by mass of the modified maleimide resin solution, 30 parts by mass of tetrafunctional naphthalene-type epoxy resin "EXA-4710" (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 B with a solids concentration of 65% by mass (aluminum hydroxide content: 8% by volume, fused silica content: 41.5% by volume).

[0063] Example 1 (1. Preparation of resin film) The resin varnish A obtained in Production Example 1 was applied onto a PET film (Toyobo Film Solutions Co., Ltd., thickness: 50 μm, release film, product name: G2) 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 produced by heating and drying at 130° C. for 2 minutes. (2. Preparation of prepreg) Next, glass cloth "IPC#2116" (manufactured by Nitto Boseki Co., Ltd., basis weight: 104 g / m 2 The resin film with the PET film was placed on both sides of a glass cloth (substrate width: 530 mm, thickness: 91 μm) so that the resin layer surface of the resin film with the PET film was in contact with the glass cloth. This laminate of "PET film / resin film / glass cloth / resin film / PET film" was heated and pressed under vacuum using a vacuum laminating device. In this way, a prepreg with a PET film was obtained in which the glass cloth was impregnated with the thermosetting resin composition of the resin film. The conditions for the vacuum lamination were a hot plate temperature of 100° C., a pressure of 0.3 MPa, a degree of vacuum of 100 kPa or less, and a vacuum time of 20 seconds. The PET film was peeled off from the obtained prepreg with the PET film to obtain prepreg 1 with a thickness of 130 μm. The thickness of the prepreg 1 was determined as the average value of values ​​measured at any five points using a horizontally adjusted base and a Digimatic Indicator (manufactured by Mitutoyo Corporation). The content ratio 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 thermosetting resin composition=(w r / w p ) x 100 Moreover, the above-mentioned evaluations were carried out on the obtained prepreg 1. The results are shown in Table 1. (3. Preparation of copper-clad laminate) Twelve sheets of the obtained prepreg 1 were stacked, and 12 μm thick copper foil "GTS-12" (manufactured by Furukawa Electric Co., Ltd.) was placed on top and bottom of them. Then, pressing was performed under the following conditions to produce a copper-clad laminate 1. The obtained copper-clad laminate 1 was subjected to the above-mentioned evaluations. The results are shown in Table 1. In addition, a copper-clad laminate for evaluating the amount of warping was separately prepared as follows. One sheet of prepreg 1 was arranged, and 12 μm-thick copper foil "GTS-12" (manufactured by Furukawa Electric Co., Ltd.) was arranged on the top and bottom of the prepreg. Then, pressing was performed under the following conditions to prepare a copper-clad laminate 1 for evaluating the amount of warping. -Press conditions- Heating conditions (resin varnish A): The temperature was raised from 25° C. to 185° C. at a rate of 3° C. / min, and the temperature was maintained at 185° C. for 90 minutes, followed by cooling for 30 minutes. Pressure conditions (pressure applied to 12 prepregs sandwiched between copper foils): 4MPa (from the start of heating to the end of cooling)

[0064] Example 2 In the preparation of the prepreg of Example 1, the conditions of vacuum lamination were changed to a hot plate temperature of 130° C., a pressure bonding pressure of 0.5 MPa, a degree of vacuum of 100 kPa or less, and a vacuum time of 30 seconds, but the same operation as in Example 1 was carried out to prepare prepreg 2 (thickness 125 μm). In addition, in the production of the copper-clad laminate of Example 1, the same operation as in Example 1 was carried out to prepare copper-clad laminate 2, but .... The evaluation results are shown in Table 1. The surface observation image of the prepreg converted to black and white mode used in calculating the abundance ratio of the impregnated region is shown in Figure 4. The observation conditions for the prepreg surface were as described above, but the exposure time for photographing the surface was 85 ms.

[0065] Example 3 Prepreg 3 (thickness 125 μm) was produced by carrying out the same operation as in Example 2, except that in the production of the prepreg of Example 2, resin varnish B was used instead of resin varnish A. Also, in the production of the copper-clad laminate of Example 2, prepreg 3 was used instead of prepreg 2, and copper-clad laminate 3 was produced by carrying out the same operation as in Example 2, except that the pressing conditions were changed as follows. The evaluation results are shown in Table 1. -Press conditions- Heating conditions (resin varnish B): The temperature was raised from 25° C. to 230° C. at a rate of 3° C. / min, and the temperature was kept at 230° C. for 90 minutes, followed by cooling for 30 minutes.

[0066] Example 4 In the preparation of the prepreg of Example 1, the conditions of vacuum lamination were changed to a hot plate temperature of 150°C, a pressure bonding pressure of 0.5 MPa, a degree of vacuum of 100 kPa or less, and a vacuum time of 30 seconds, but the same operation as in Example 1 was carried out to prepare prepreg 4 (thickness 115 μm). In addition, in the production of the copper-clad laminate of Example 1, the same operation as in Example 1 was carried out to prepare copper-clad laminate 4, but .... The evaluation results are shown in Table 1.

[0067] Example 5 In the preparation of the prepreg of Example 1, the conditions of vacuum lamination were changed to a hot plate temperature of 150°C, a pressure bonding pressure of 0.5 MPa, a degree of vacuum of 100 kPa or less, and a vacuum time of 60 seconds, but the same operation as in Example 1 was carried out to prepare prepreg 5 (thickness 110 μm). In addition, in the production of the copper-clad laminate of Example 1, the same operation as in Example 1 was carried out to prepare copper-clad laminate 5, but the same operation as in Example 1 was carried out to prepare copper-clad laminate 5. The evaluation results are shown in Table 1.

[0068] Example 6 In the preparation of the resin film of Example 1, the PET film was changed to (Toray Industries, Inc., thickness: 50 μm, release film, product name: Lumirror (registered trademark) #50-X44), and in the preparation of the prepreg, the conditions of vacuum lamination were changed to a hot plate temperature of 140° C., a pressure bonding pressure of 0.5 MPa, a vacuum degree of 100 kPa or less, and a vacuum time of 40 seconds. Except for this, prepreg 6 (thickness 125 μm) was prepared by carrying out the same operations as in Example 1. In addition, in the manufacture of the copper-clad laminate of Example 1, prepreg 6 was used instead of prepreg 1. The evaluation results are shown in Table 1.

[0069] Example 7 In the preparation of the prepreg of Example 2, the glass cloth "IPC#2116" was replaced with the glass cloth "IPC#3313" (manufactured by Nitto Boseki Co., Ltd., basis weight: 82 g / m 2 Prepreg 7 (thickness: 105 μm) was produced by carrying out the same operations as in Example 2, except that prepreg 7 was used instead of prepreg 2 in the production of the copper-clad laminate of Example 2. The evaluation results are shown in Table 1.

[0070] Example 8 In the preparation of the prepreg of Example 3, the glass cloth "IPC#2116" was replaced with the glass cloth "IPC#3313" (manufactured by Nitto Boseki Co., Ltd., basis weight: 82 g / m 2Prepreg 8 (thickness: 105 μm) was produced by carrying out the same operations as in Example 3, except that in the production of the copper-clad laminate of Example 3, prepreg 8 was used instead of prepreg 3. The evaluation results are shown in Table 1.

[0071] Example 9 In the preparation of the resin film in Example 2, the thickness after drying was changed to 24 μm, and in the preparation of the prepreg, the glass cloth “IPC#2116” was replaced with the glass cloth “IPC#1078” (manufactured by Nitto Boseki Co., Ltd., basis weight: 47 g / m 2 Prepreg 9 (thickness 70 μm) was produced by carrying out the same operations as in Example 2, except that prepreg 9 was used instead of prepreg 2 in the production of the copper-clad laminate of Example 2. The evaluation results are shown in Table 1.

[0072] Example 10 In the preparation of the prepreg of Example 1, the conditions of vacuum lamination were changed to a hot plate temperature of 90° C., a pressure bonding pressure of 0.1 MPa, a degree of vacuum of 100 kPa or less, and a vacuum time of 20 seconds, but the same operation as in Example 1 was carried out to prepare a prepreg 10 (thickness 140 μm). In addition, in the production of the copper-clad laminate of Example 1, the same operation as in Example 1 was carried out to prepare a copper-clad laminate 10, but .... The evaluation results are shown in Table 1.

[0073] Example 11 In the preparation of the resin film in Example 1, the thickness after drying was changed to 24 μm, and in the preparation of the prepreg, the glass cloth “IPC#2116” was replaced with the glass cloth “IPC#1078” (manufactured by Nitto Boseki Co., Ltd., basis weight: 47 g / m 2Prepreg 11 (thickness 65 μm) was produced by carrying out the same operations as in Example 1, except that the platen temperature was changed to 150° C., compression pressure to 0.8 MPa, degree of vacuum to 100 kPa or less, and vacuum time to 120 seconds, and prepreg 12 (thickness 65 μm) was produced. Furthermore, in the production of the copper-clad laminate of Example 1, prepreg 11 was used instead of prepreg 1, and prepreg 12 was produced by carrying out the same operations as in Example 1. The evaluation results are shown in Table 1.

[0074] Comparative Example 1 Glass cloth "IPC#2116" (manufactured by Nitto Boseki Co., Ltd., basis weight: 104g / m 2 A copper-clad laminate X (thickness: 180 μm) was produced by immersing a copper-clad laminate (substrate width: 530 mm, thickness: 91 μm) in the resin varnish A prepared in Production Example 1, removing it, and drying it by heating at 140° C. for 3.5 minutes. The copper-clad laminate X was produced by carrying out the same operations as in Example 1, except that prepreg X was used instead of prepreg 1 in the production of the copper-clad laminate of Example 1. The evaluation results are shown in Table 1. It can be seen that prepreg X has a larger surface waviness than prepregs 1 to 11 produced in the examples, and that the thickness of copper-clad laminate X produced using prepreg X varies widely. Note that, because prepreg X has a larger surface waviness, the prepreg surface was out of focus in optical microscope observation, and the proportion of impregnated regions could not be determined.

[0075] Example 12 In the manufacture of the copper-clad laminate of Example 2, a copper-clad laminate 12 was manufactured by carrying out the same operation as in Example 2, except that, instead of laminating 12 sheets of prepreg 2, "two sheets of prepreg 2" and "ten sheets of prepreg X manufactured in Comparative Example 1" were laminated. The lamination order of the prepregs was "(one sheet of prepreg 2) / (ten sheets of prepreg X) / (one sheet of prepreg 2)". The evaluation results are shown in Table 1.

[0076] Example 13 In the manufacture of the copper-clad laminate of Example 2, instead of laminating 12 sheets of prepreg 2, "4 sheets of prepreg 2" and "8 sheets of prepreg X produced in Comparative Example 1" were laminated, and the same operation as in Example 2 was carried out to produce a copper-clad laminate 13. The prepregs were laminated in the following order: (2 sheets of prepreg 2) / (8 sheets of prepreg X) / (2 sheets of prepreg 2). The evaluation results are shown in Table 1.

[0077] [Table 1]

[0078] From Table 1, it can be seen that when the prepreg of this embodiment is used, the thickness precision of the copper-clad laminate is high, even though a fiber base material with a relatively large waviness, that is, a fiber base material with a thickness of 40 μm or more, is used (see Examples 1 to 13). In addition, it can be said that the copper-clad laminates of Examples 1 to 13 have excellent copper solder heat resistance, and the occurrence of voids is sufficiently suppressed. Furthermore, it can be seen that the difference in the thickness of the resin protruding from the fiber base material on the front and back of the prepreg is small, and as a result, the amount of warping of the copper-clad laminate is suppressed to a small amount. On the other hand, as shown in Comparative Example 1, the prepreg produced by immersing the glass cloth in a resin varnish and then drying it had a large surface waviness (Wa), and the thickness of the copper-clad laminate varied greatly.

Claims

1. A prepreg obtained by impregnating a fiber base material having a thickness of 40 μm or more with a thermosetting resin composition, wherein the fiber base material has regions impregnated with the thermosetting resin composition and regions not impregnated, the prepreg having a surface waviness (Wa) of 5.0 μm or less, and the proportion of the impregnated regions calculated based on the following calculation method is 25 to 98%. Calculation method: A surface observation image is obtained by observing the surface of the prepreg at 50x magnification using an optical microscope. 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 saved in CSV (comma-separated values) format. The RGB data saved in CSV format is pasted into Microsoft Excel (manufactured by Microsoft Corporation), and the areas of the black parts (RGB value = 255) and white parts (RGB value = 0) are calculated. From these values, the area ratio of the black parts to the total of the black and white parts is calculated. The area ratio of the black parts thus obtained is taken as the abundance ratio of the impregnated region.

2. A prepreg as described in claim 1, having a surface waviness (Wa) of 0.01 to 3.0 μm.

3. The prepreg according to claim 1 or 2, wherein the ratio of the impregnated regions is 35 to 90%.

4. The prepreg according to any one of claims 1 to 3, having a surface roughness (Ra) of 0.1 to 5 µm.

5. The prepreg according to any one of claims 1 to 4, wherein the thickness of the fiber base material is 70 to 120 µm.

6. A laminate comprising one or more prepregs according to any one of claims 1 to 5.

7. A metal-clad laminate comprising a metal foil and one or more prepregs according to any one of claims 1 to 5.

8. A printed wiring board comprising the laminate according to claim 6 or the metal-clad laminate according to claim 7.

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

10. A method for producing a prepreg by impregnating a fiber substrate having a thickness of 40 μm or more with a film of a thermosetting resin composition by lamination, wherein regions impregnated with the thermosetting resin composition and unimpregnated regions are provided in the fiber substrate so that the abundance ratio of the impregnated regions is 25 to 98% as determined based on the following calculation method, thereby producing a prepreg having a surface waviness (Wa) of 5.0 μm or less. Calculation method: A surface observation image is obtained by observing the surface of the prepreg at 50x magnification using an optical microscope. 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 saved in CSV (comma-separated values) format. The RGB data saved in CSV format is pasted into Microsoft Excel (manufactured by Microsoft Corporation), and the areas of the black parts (RGB value = 255) and white parts (RGB value = 0) are calculated. From these values, the area ratio of the black parts to the total of the black and white parts is calculated. The area ratio of the black parts thus obtained is taken as the abundance ratio of the impregnated region.

11. A method for producing a prepreg as described in claim 10, wherein the surface waviness (Wa) of the obtained prepreg is 0.01 to 3.0 μm.

12. A method for producing a metal-clad laminate by placing metal foil on both sides of a single prepreg obtained by the production method according to claim 10 or 11 or on both sides of a prepreg laminate containing at least one prepreg, and then press-molding.

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