Thermosetting resin sheet and printed wiring board

Abstract

The present disclosure provides a thermosetting resin sheet which, when preparing an insulating layer in which a conductor is embedded, makes embedding of the conductor into the insulating layer easy and makes it unlikely that the workability thereof worsens. The thermosetting resin sheet (1) is equipped with: a prepreg layer (2) provided with a substrate (4) and an uncured or partially cured article of a first thermosetting resin composition with which the substrate (4) has been impregnated; and a resin sheet layer (3) which overlaps the prepreg layer (2). The resin sheet layer (3) is an uncured or partially cured article of a second thermosetting resin composition. The curing time of the resin sheet layer (3) is longer than the curing time of the prepreg layer (2).

Description

[Technical field]

[0001] The present disclosure relates to a thermosetting resin sheet and a printed wiring board, and more particularly to a thermosetting resin sheet that can be used to prepare an insulating layer of a printed wiring board, and a printed wiring board including an insulating layer prepared from this thermosetting resin sheet. [Background technology]

[0002] A printed wiring board is produced by stacking a resin sheet and a prepreg on a conductor and integrating them together to produce an insulating layer made of a cured product of the resin sheet and the prepreg on the conductor, and embedding the conductor in the cured product of the resin sheet.

[0003] For example, Patent Document 1 discloses a method for producing a multilayer printed wiring board by forming a laminate by disposing a heat-meltable and thermosetting resin film between the exposed via-hole surface of a substrate and a prepreg containing an inorganic filler. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2003-37362 A Summary of the Invention

[0005] An object of the present disclosure is to provide a thermosetting resin sheet that, when producing an insulating layer in which a conductor is embedded, allows a conductor to be easily embedded in the insulating layer and does not easily deteriorate in formability, and a printed wiring board including an insulating layer produced from this thermosetting resin sheet.

[0006] The thermosetting resin sheet according to the first aspect of the present disclosure includes a prepreg layer and a resin sheet layer overlapping the prepreg layer. The prepreg layer includes a base material and an uncured or semi-cured product of a first thermosetting resin composition impregnated in the base material. The resin sheet layer is an uncured or semi-cured product of a second thermosetting resin composition. The curing time of the resin sheet layer is longer than the curing time of the prepreg layer.

[0007] A printed wiring board according to a first aspect of the present disclosure includes a core material including an insulating substrate and a conductor overlapping the insulating substrate, and an insulating layer made of a cured product of the thermosetting resin sheet overlapping the core material so as to face the conductor. The insulating layer includes a first layer which is a cured product of the prepreg layer, and a second layer which is a cured product of the resin sheet layer and is located on the conductor side of the first layer. The conductor is embedded in the second layer. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1A is a schematic cross-sectional view of a thermosetting resin sheet, a core material, and a laminate composed of the thermosetting resin sheet and the core material in one embodiment of the present disclosure, and FIG. 1B is a schematic cross-sectional view of a printed wiring board in one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] According to the inventor's research, in order to manufacture a multilayer printed wiring board with a thick inner layer conductor, it is necessary to use a prepreg that has a sufficient amount of resin required to fill the spaces between the inner layer conductors, but because the prepreg contains a base material (generally glass cloth), there is a limit to the amount of resin that can be contained. Therefore, by using a resin sheet that does not contain a base material instead of the prepreg, it is possible to improve the filling property, but because the resin sheet does not contain glass cloth, the amount of resin flow during multilayer molding becomes large, resulting in a problem of insufficient resin filling between the conductors.

[0010] Therefore, the inventors conducted research and development to obtain a thermosetting resin sheet that allows conductors to be easily embedded in an insulating layer and is less likely to deteriorate in formability when producing an insulating layer in which a conductor is embedded, and have completed the present disclosure.

[0011] Hereinafter, one embodiment of the present disclosure will be described. Note that the embodiment described below is merely one of various embodiments of the present disclosure. The following embodiment can be modified in various ways depending on the design as long as the object of the present disclosure can be achieved.

[0012] As shown in Fig. 1A, the thermosetting resin sheet 1 according to this embodiment includes a prepreg layer 2 and a resin sheet layer 3 overlapping the prepreg layer 2. The prepreg layer 2 includes a base material 4 and an uncured or semi-cured product of a first thermosetting resin composition impregnated in the base material 4. The resin sheet layer 3 is an uncured or semi-cured product of a second thermosetting resin composition. The curing time of the resin sheet layer 3 is longer than the curing time of the prepreg layer 2.

[0013] The curing time is the time required for curing when the resin sheet layer 3 and the prepreg layer 2 are heated under the same temperature conditions that allow both to cure. The curing time is the curing time at a temperature of 170°C, measured, for example, according to JIS C6521-1996, and is measured by stirring about 0.2 g of resin powder of the resin sheet layer 3 or the prepreg layer 2 on a hot plate at 170°C and measuring the time until the powder gels.

[0014] An insulating layer 8 in which a conductor 9 is embedded can be produced from this thermosetting resin sheet 1. This allows the thermosetting resin sheet 1 to be used, for example, to produce an insulating layer 8 in a printed wiring board 5. In this embodiment, when the insulating layer 8 in which a conductor 9 is embedded is produced from the thermosetting resin sheet 1, the conductor 9 can be easily embedded in the insulating layer 8, and moldability is not easily deteriorated.

[0015] The preparation of insulating layer 8 and the manufacturing of printed wiring board 5 will be described with reference to FIGS. 1A and 1B.

[0016] The method for manufacturing printed wiring board 5 includes the steps of preparing a core material 11 having an insulating substrate 10 and a conductor 9 overlapping insulating substrate 10, and a thermosetting resin sheet 1, stacking core material 11 and thermosetting resin sheet 1 so that the conductor 9 and resin sheet layer 3 face each other, and heating thermosetting resin sheet 1 to cause resin sheet layer 3 to flow and then harden to produce second layer 7, and hardening prepreg layer 2 to produce first layer 6.

[0017] Specifically, first, a core material 11 and a thermosetting resin sheet 1 are prepared. The core material 11 includes an insulating substrate 10 and a conductor 9 overlapping the insulating substrate 10. There are no particular limitations on the materials of the insulating substrate 10 and the conductor 9 as long as they are applicable as materials for printed wiring boards. The insulating substrate 10 is, for example, a resin substrate such as a glass-based epoxy resin substrate, and the conductor 9 is, for example, a copper wiring produced by an additive method, a subtractive method, or the like.

[0018] Next, the core material 11 and the thermosetting resin sheet 1 are laminated together so that the conductor 9 and the resin sheet layer 3 face each other, thereby obtaining a laminate 12 as shown in FIG. 1A.

[0019] Next, the thermosetting resin sheet 1 is heated to cause the resin sheet layer 3 to flow and then harden to produce the second layer 7, and the prepreg layer 2 is hardened to produce the first layer 6. In this way, an insulating layer 8 including the first layer 6 and the second layer 7 is produced. Specifically, for example, the laminate 12 is heat-pressed. Then, the resin sheet layer 3 in the thermosetting resin sheet 1 is first softened or melted to reduce its viscosity, and flows to follow the shape of the conductor 9. This causes the conductor 9 to be embedded in the resin sheet layer 3. Then, the resin sheet layer 3 is hardened. This causes the second layer 7, which is the hardened product of the resin sheet layer 3, to be produced, and the conductor 9 is embedded in this second layer 7. The prepreg layer 2 is also first softened or melted to reduce its viscosity and flow, and then hardened to produce the first layer 6, which is the hardened product of the prepreg layer 2. This produces the printed wiring board 5 shown in FIG. 1B.

[0020] The printed wiring board 5 comprises a core material 11 and an insulating layer 8. The core material 11 comprises an insulating substrate 10 and a conductor 9 overlapping the insulating substrate 10. The insulating layer 8 overlaps the core material 11 so as to face the conductor 9. The insulating layer 8 is made of a cured product of a thermosetting resin sheet 1. The insulating layer 8 comprises a first layer 6 which is a cured product of a prepreg layer 2, and a second layer 7 which is a cured product of a resin sheet layer 3. The second layer 7 is on the conductor 9 side of the first layer 6. The conductor 9 is embedded in the second layer 7.

[0021] When the printed wiring board 5 is manufactured in this manner, the softened or melted resin sheet layer 3 is caused to flow, thereby allowing the conductor 9 to be embedded in the insulating layer 8, and the conductor 9 is less likely to come into contact with the base material 4 in the prepreg layer 2 within the insulating layer 8, which tends to improve the reliability of the printed wiring board 5 in a high temperature environment. Furthermore, within the insulating layer 8, the base material 4 is not present in the second layer 7, but is present in the first layer 6, so that the number of base materials 4 used can be reduced, and the thickness of the insulating layer 8 can be easily reduced.

[0022] In this embodiment, as described above, the curing time of the resin sheet layer 3 is longer than the curing time of the prepreg layer 2. That is, when the resin sheet layer 3 and the prepreg layer 2 are heated simultaneously under the same conditions, the prepreg layer 2 cures before the resin sheet layer 3. Therefore, in the process of producing the insulating layer 8 from the thermosetting resin sheet 1, the hardness of the prepreg layer 2 increases while the softened or molten resin sheet layer 3 is flowing. Therefore, even if the resin sheet layer 3 flows, the prepreg layer 2 can prevent the overall shape of the thermosetting resin sheet 1 from changing. Furthermore, the resin sheet layer 3 can easily apply an appropriate pressure to the resin sheet layer 3 uniformly, and therefore can promote the flow of the resin sheet layer 3 that follows the shape of the conductor 9. In addition, even if the resin sheet layer 3 is sufficiently flowed, the prepreg layer 2 is unlikely to flow, so that the outflow of the resin from the thermosetting resin sheet 1 is suppressed.

[0023] Therefore, even if the conductor 9 is thick, the gap between the insulating layer 8 and the conductor 9 is unlikely to be left unfilled, and the insulating layer 8 is unlikely to have shape defects such as uneven thickness.

[0024] The thermosetting resin sheet 1 will now be described in more detail.

[0025] As described above, the thermosetting resin sheet 1 includes the prepreg layer 2 and the resin sheet layer 3.

[0026] The prepreg layer 2 includes a base material 4 and an uncured or semi-cured product of a first thermosetting resin composition impregnated into the base material 4.

[0027] The substrate 4 is, for example, an inorganic fiber woven fabric, an inorganic fiber nonwoven fabric, an organic fiber woven fabric, or an organic fiber nonwoven fabric. The inorganic fiber is, for example, glass fiber or a fiber of an inorganic material other than glass. The glass constituting the glass fiber is, for example, E glass, D glass, S glass, NE glass, T glass, quartz, or the like. The organic fiber is, for example, aramid fiber, polyparaphenylene benzobisoxazole (PBO) fiber, polybenzimidazole (PBI) fiber, polytetrafluoroethylene (PTFE) fiber, polyparaphenylene benzobisthiazole (PBZT) fiber, or wholly aromatic polyester fiber, or the like.

[0028] The first thermosetting resin composition is not particularly limited as long as it can be used to produce insulating layer 8 of printed wiring board 5 .

[0029] The prepreg layer 2 is produced by impregnating the base material 4 with the first thermosetting resin composition and then drying or semi-curing the first thermosetting resin composition by heating. The conditions for heating the first thermosetting resin composition are appropriately adjusted depending on the composition of the first thermosetting resin composition and the physical properties to be imparted to the prepreg layer 2.

[0030] The thickness of the prepreg layer 2 is, for example, 40 μm or more and 200 μm or less. In the example shown in Fig. 1A, the prepreg layer 2 is composed of one prepreg. However, the prepreg layer 2 may be composed of a plurality of laminated prepregs.

[0031] On the other hand, the resin sheet layer 3 is an uncured or semi-cured product of the second thermosetting resin composition.

[0032] The second thermosetting resin composition is not particularly limited as long as it can be applied to producing insulating layer 8 of printed wiring board 5.

[0033] The second thermosetting resin composition may have the same composition as the first thermosetting resin composition or may have a different composition. That is, the components and their blending ratios contained in the second thermosetting resin composition may be the same as or different from the components and their blending ratios contained in the first thermosetting resin composition.

[0034] When producing the resin sheet layer 3, for example, the second thermosetting resin composition is formed into a sheet by a coating method or the like. The coating method is, for example, a dipping method, a spray method, a spin coating method, a roll coating method, a curtain coating method, a screen printing method, or the like. Then, the second thermosetting resin composition is dried or semi-cured by heating to produce the resin sheet layer 3. The conditions for heating the second thermosetting resin composition are appropriately adjusted depending on the composition of the second thermosetting resin composition and the physical properties to be imparted to the resin sheet layer 3.

[0035] The minimum melt viscosity of the resin sheet layer 3 is, for example, 500 Pa·s or more and 50,000 Pa·s or less.

[0036] The thickness of the resin sheet layer 3 is, for example, 30 μm or more and 400 μm or less, and preferably 50 μm or more and 200 μm or less. In the example shown in Fig. 1A, the resin sheet layer 3 is composed of one resin sheet. However, the resin sheet layer 3 may be composed of multiple laminated resin sheets.

[0037] Each of the first thermosetting resin composition and the second thermosetting resin composition contains a thermosetting resin. The thermosetting resin contains at least one selected from the group consisting of, for example, epoxy resin, polyimide resin, phenol resin, bismaleimide triazine resin, and thermosetting polyphenylene ether resin. The epoxy resin contains at least one component selected from the group consisting of, for example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, cresol novolac type epoxy resin, bisphenol A novolac type epoxy resin, bisphenol F novolac type epoxy resin, naphthalene type epoxy resin, biphenyl type epoxy resin, dicyclopentadiene type epoxy resin, and polyfunctional epoxy resin. Note that the components that the thermosetting resin may contain are not limited to the above.

[0038] Each of the first thermosetting resin composition and the second thermosetting resin composition may further contain an appropriate additive selected from the group consisting of a curing agent, a curing accelerator, a flame retardant, and an inorganic filler. The second thermosetting resin composition may further contain a solvent. The curing agent contains at least one selected from the group consisting of, for example, a diamine-based curing agent, a bifunctional or higher phenol-based curing agent, an acid anhydride-based curing agent, dicyandiamide, and a low molecular weight polyphenylene ether compound. The curing accelerator contains at least one selected from the group consisting of, for example, an imidazole-based compound, a tertiary amine-based compound, an organic phosphine compound, and a metal soap. The flame retardant contains at least one selected from the group consisting of, for example, a halogen-based flame retardant and a non-halogen-based flame retardant. The inorganic filler contains at least one selected from the group consisting of, for example, silica, aluminum hydroxide, magnesium hydroxide, aluminum silicate, magnesium silicate, talc, clay, mica, and a molybdenum compound. The solvent contains at least one selected from the group consisting of, for example, an appropriate organic solvent and water. The components that each of the first thermosetting resin composition and the second thermosetting resin composition can contain are not limited to those mentioned above.

[0039] As described above, the curing time of the resin sheet layer 3 is longer than the curing time of the prepreg layer 2. In order to realize such a difference in curing time, appropriate means can be adopted. For example, if the time for heating the first thermosetting resin composition when preparing the prepreg layer 2 is longer than the time for heating the second thermosetting resin composition when preparing the resin sheet layer 3, the degree of curing of the uncured or semi-cured product of the first thermosetting resin composition in the prepreg layer 2 is more advanced than the degree of curing of the uncured or semi-cured product of the second thermosetting resin composition in the resin sheet layer 3, so that the curing time of the resin sheet layer 3 can be longer than the curing time of the prepreg layer 2. In addition, by selecting a combination of the thermosetting resin and the curing agent in each of the first thermosetting resin composition and the second thermosetting resin composition so that the reactivity of the thermosetting resin and the curing agent in the second thermosetting resin composition is higher than the reactivity of the thermosetting resin and the curing agent in the first thermosetting resin composition, the curing time of the resin sheet layer 3 can be longer than the curing time of the prepreg layer 2. Furthermore, by selecting the type and amount of the curing accelerator in the first thermosetting resin composition and the type and amount of the curing accelerator in the second thermosetting resin composition such that the curing reaction in the second thermosetting resin composition is promoted more than the curing reaction in the first thermosetting resin composition, the curing time of the resin sheet layer 3 can be made longer than the curing time of the prepreg layer 2. The curing time of the resin sheet layer 3 can also be made longer than the curing time of the prepreg layer 2 by combining a plurality of means.

[0040] The curing time of the prepreg layer 2 and the curing time of the resin sheet layer 3 are appropriately set. For example, the curing time of the prepreg layer 2 is preferably 30 seconds or more and less than 360 seconds. The curing time of the resin sheet layer 3 is preferably more than 30 seconds and less than 360 seconds. In this case, when the insulating layer 8 is produced from the thermosetting resin sheet 1 by heat pressing, the softened or molten resin sheet layer 3 is sufficiently fluidized to easily embed the conductor 9 in the resin sheet layer 3 without any unfilled portions, and excessive fluidization of the resin sheet layer 3 can be suppressed, so that the moldability is not particularly deteriorated. The curing time of the prepreg layer 2 is more preferably 50 seconds or more and 240 seconds or less, and even more preferably 60 seconds or more and 180 seconds or less. The curing time of the resin sheet layer 3 is more preferably 60 seconds or more and 270 seconds or less, and even more preferably 75 seconds or more and 240 seconds or less.

[0041] The difference between the curing time of the resin sheet layer 3 and the curing time of the prepreg layer 2 is preferably 1 second or more and 180 seconds or less. In this case, when the insulating layer 8 is produced from the thermosetting resin sheet 1 by hot pressing, the prepreg layer 2, which starts curing before the resin sheet layer 3, can particularly effectively suppress excessive deformation of the thermosetting resin sheet 1 and outflow of the resin during molding. Therefore, the moldability is particularly unlikely to deteriorate. This difference in curing time is more preferably 5 seconds or more and 120 seconds or less, and even more preferably 10 seconds or more and 90 seconds or less.

[0042] The resin sheet layer 3 and the prepreg layer 2 are, for example, in direct contact with each other and bonded together. To achieve this, when manufacturing the thermosetting resin sheet 1, for example, the substrate 4 is first impregnated with the first thermosetting resin and then the first thermosetting resin is heated to produce an intermediate product. The second thermosetting resin composition is applied onto this intermediate product, and then the first thermosetting resin composition and the second thermosetting resin composition are heated. This allows the resin sheet layer 3 and the prepreg layer 2 to be produced, and the resin sheet layer 3 and the prepreg layer 2 to be bonded together to produce the thermosetting resin sheet 1. In this method, the time for heating the first thermosetting resin composition is longer than the time for heating the second thermosetting resin composition, and the curing time of the resin sheet layer 3 can be adjusted to be longer than the curing time of the prepreg layer 2.

[0043] Alternatively, the resin sheet layer 3 and the prepreg layer 2 may be separately produced, and then the two may be laminated together by an appropriate method to produce the thermosetting resin sheet 1.

[0044] Alternatively, the thermosetting resin sheet 1 can be produced by producing the resin sheet layer 3 and the prepreg layer 2 separately and then simply stacking them together without bonding them together.

[0045] As described above, the insulating layer 8 can be made from the thermosetting resin sheet 1, and the printed wiring board 5 having the insulating layer 8 can be manufactured.

[0046] In manufacturing the printed wiring board 5, the thickness of the conductor 9 embedded in the insulating layer 8 is, for example, 100 μm or more and 500 μm or less. In this embodiment, even if the thickness of the conductor 9 is so large, the conductor 9 can be easily embedded in the insulating layer 8 and the moldability is not easily deteriorated. Furthermore, if the thickness of the conductor 9 is so large, the current value that can be passed through the conductor 9 can be increased accordingly. Therefore, the printed wiring board 5 can be applied to industrial equipment and in-vehicle board applications that require large currents. The thickness of the conductor 9 is more preferably 140 μm or more and 450 μm or less, and even more preferably 175 μm or more and 400 μm or less. The thickness of the conductor 9 is not limited to the above.

[0047] When the printed wiring board 5 is manufactured by hot pressing the laminate 12 as described above, the laminate 12 may further include a metal foil. That is, the core material 11 and the thermosetting resin sheet 1 are stacked so that the conductor 9 and the resin sheet layer 3 face each other, and further a metal foil is stacked on the thermosetting resin sheet 1 so that it faces the prepreg layer 2 to produce the laminate 12, and the laminate 12 may be hot pressed. In this case, the printed wiring board 5 having the metal foil overlapping the insulating layer 8 is obtained. The metal foil may be patterned by etching or the like to produce a conductor wiring. In this case, the printed wiring board 5 having the conductor wiring overlapping the insulating layer 8 is obtained.

[0048] The conditions for hot pressing the laminate 12 are appropriately set depending on the composition of each of the first thermosetting resin composition and the second thermosetting resin composition, but for example, the heating temperature is 120°C or more and 250°C or less, the pressing pressure is 0.5 MPa or more and 5 MPa or less, and the treatment time is 30 minutes or more and 180 minutes or less. EXAMPLES

[0049] More specific examples of the present embodiment will be presented below. Note that the present embodiment is not limited to only the following examples.

[0050] 1. Preparation of Thermosetting Resin Sheet A first thermosetting resin composition was prepared by mixing the components shown in the column for the composition of the prepreg layer in Tables 1 and 2. A second thermosetting resin composition was prepared by mixing the components shown in the column for the composition of the resin sheet layer in Tables 1 and 2. Details of the components shown in Tables 1 and 2 are as follows. -Bisphenol A type epoxy resin: Nippon Steel Chemical & Material Co., Ltd. Part number YD-128. -Brominated epoxy resin: Nippon Steel Chemical & Material Co., Ltd. Part number YDB-500. -Novolac type epoxy resin: Manufactured by Nippon Steel Chemical & Material Co., Ltd. Part number YDCN-220. -Phenoxy resin: Manufactured by Nippon Steel Chemical & Material Co., Ltd. Part number YP-50. - Hardener: Dicyandiamide. Manufactured by Nippon Carbide Corporation. -Cure accelerator: 2-ethyl-4-methylimidazole, manufactured by Shikoku Kasei Co., Ltd., product number 2E4MZ. -Silica: Admatechs Co., Ltd., product number SO25R. -Aluminum hydroxide: manufactured by Sumitomo Chemical Co., Ltd. Product number CL-303.

[0051] A glass cloth having an IPC specification shown in Tables 1 and 2 was impregnated with a first thermosetting resin composition, and then the first thermosetting resin composition was heated under the conditions shown in the first heat treatment column in Tables 1 and 2 to produce an intermediate product. In this way, in the cases of Comparative Examples 3 to 5, a prepreg was produced. In the cases of Examples 1 to 6 and Comparative Examples 1 and 2, a second thermosetting resin composition was applied onto the intermediate product produced by the first heat treatment, and then the first thermosetting resin composition and the second thermosetting resin composition were heated under the conditions shown in the second heat treatment column in Tables 1 and 2. In this way, a thermosetting resin sheet having a prepreg layer and a resin sheet layer was produced.

[0052] The resin content, thickness, and curing time at 170°C measured according to JIS C6521-1996 of the prepreg layer in the thermosetting resin sheet, as well as the thickness and curing time at 170°C measured according to JIS C6521-1996 of the resin sheet layer, are shown in Tables 1 and 2.

[0053] 2. Manufacturing of printed wiring boards A core material having an insulating substrate and copper wiring on the insulating substrate was prepared. The thickness of the wiring and the residual copper ratio are shown in Tables 1 and 2.

[0054] In the cases of Examples 1 to 6 and Comparative Examples 1 and 2, a laminate was formed by stacking a thermosetting resin sheet and a core material so that the resin sheet layer and the wiring (conductor) faced each other. The laminate was heat-pressed under the conditions of a maximum heating temperature of 170°C, a press pressure of 3 MPa, and a treatment time of 60 minutes.

[0055] In the cases of Comparative Examples 3 and 4, a laminate was formed by stacking two sheets of prepreg and a core material. The laminate was hot-pressed under the conditions of a maximum heating temperature of 170° C., a press pressure of 3 MPa, and a treatment time of 60 minutes.

[0056] In the case of Comparative Example 5, a laminate was formed by stacking one prepreg and a core material. The laminate was hot-pressed under the conditions of a maximum heating temperature of 170° C., a press pressure of 4 MPa, and a treatment time of 60 minutes.

[0057] In this way, a printed wiring board was manufactured.

[0058] 3. Evaluation (1) Fillability The insulating layer of the printed wiring board was visually inspected, and if no voids were found in the insulating layer, it was rated as "good", and if voids were found, it was rated as "poor".

[0059] (2) Solder heat resistance after boiling The printed wiring board was immersed in water, the water was heated to 100°C, and the board was left for 2 hours, after which the board was removed from the water. The water was wiped off from the surface of the printed wiring board, and the board was then immersed in a solder bath at 288°C in an autoclave for 20 seconds. The printed wiring board was then visually inspected, and rated as "good" if no blistering was observed in the insulating layer, and "poor" if blistering was observed in the insulating layer.

[0060] [Table 1]

[0061] [Table 2]

[0062] According to the above results, it is recognized that in Example 1, the curing time of the resin sheet layer is longer than the curing time of the prepreg layer, so that the filling property is good and therefore the solder heat resistance after boiling is good.

[0063] In Examples 2 and 3, the thickness of the prepreg layer was made different from that of Example 1 by changing the glass cloth in the prepreg layer. However, as in Example 1, the curing time of the resin sheet layer was longer than the curing time of the prepreg layer, which resulted in good filling properties and therefore good solder heat resistance after boiling.

[0064] In Example 4, the thickness of the resin sheet layer was made thicker than that of Example 1, but as in Example 1, the curing time of the resin sheet layer was longer than the curing time of the prepreg layer, and therefore it was found that the filling property was good and that the solder heat resistance after boiling was therefore good. In addition, it is expected that a higher filling property than that of Example 1 can be obtained by making the resin sheet layer thicker.

[0065] In Example 5, the amount of the curing accelerator in the first thermosetting resin composition was reduced compared to Example 1, and the heating temperature in the first heat treatment was lower than that in Example 1, thereby making the difference between the curing time of the resin sheet layer and the curing time of the prepreg layer smaller than that in Example 1. However, since the curing time of the resin sheet layer is longer than the curing time of the prepreg layer, it was found that the filling property was good and therefore the solder heat resistance after boiling was good.

[0066] In Example 6, the thickness of the resin sheet layer is even greater than that of Example 4, and therefore even though the thickness of the wiring of the core material is as large as 420 μm, it is found to have good solder heat resistance after boiling.

[0067] In Comparative Examples 1 and 2, the amount of the curing accelerator in the first thermosetting resin composition was further reduced compared to Example 5, and the heating temperature in the first heat treatment was lowered, so that the curing time of the resin sheet layer was shorter than the curing time of the prepreg layer. In this case, both the filling property and the solder heat resistance after boiling were deteriorated in Comparative Example 1. In Comparative Example 2, the thickness of the resin sheet layer was larger than that of Comparative Example 1, so the filling property was good, but the solder heat resistance after boiling was deteriorated. This is presumably because there were places where the glass cloth in the insulating layer was close to the wiring, and swelling occurred starting from these places.

[0068] In Comparative Example 3, since a resin sheet layer was not used, both the filling property and the solder heat resistance after boiling were deteriorated. In Comparative Examples 4 and 5, since the thickness of the prepreg layer was larger than that of Comparative Example 3, the filling property was good, but the solder heat resistance after boiling was deteriorated. This is presumably because the proportion of glass cloth in the insulating layer was high, and therefore there were places where the glass cloth was close to the wiring, and the swelling started from these places. [Explanation of symbols]

[0069] 1 Thermosetting resin sheet 2 Prepreg layers 3 Resin sheet layer 4 Base material 5. Printed Wiring Boards 6 First layer 7 Second layer 8 Insulating Layer 9 Conductors

Claims

1. A prepreg layer including a substrate and an uncured or semi-cured product of a first thermosetting resin composition impregnated in the substrate; and a resin sheet layer overlapping the prepreg layer; the resin sheet layer is an uncured or semi-cured product of a second thermosetting resin composition, The curing time of the resin sheet layer is longer than the curing time of the prepreg layer, The difference between the curing time of the resin sheet layer and the curing time of the prepreg layer is 5 seconds or more and 15 seconds or less. Thermosetting resin sheet.

2. The curing time of the prepreg layer is 30 seconds or more and less than 360 seconds, The curing time of the resin sheet layer is more than 30 seconds and not more than 360 seconds. The thermosetting resin sheet according to claim 1 .

3. A core material including an insulating substrate and a conductor overlapping the insulating substrate; and an insulating layer made of the cured product of the thermosetting resin sheet according to claim 1 or 2, the insulating layer being overlapped on the core material so as to face the conductor; the insulating layer includes a first layer which is a cured product of the prepreg layer, and a second layer which is a cured product of the resin sheet layer and is located on the conductor side with respect to the first layer, The conductor is embedded in the second layer. Printed wiring board.

4. The thickness of the conductor is 100 μm or more and 500 μm or less. The printed wiring board according to claim 3 .

Images