Resin sheet body, resin sheet body with conductor layer, multilayer circuit board, and method for manufacturing multilayer circuit board

Abstract

The present invention provides a resin sheet body with which it is possible to reduce the environmental load when a multilayer circuit board is manufactured.　A resin sheet body (10) according to the present invention has a first main surface (11) and a second main surface (12) that is opposite to the first main surface (11), and contains a wholly aromatic polyester. The resin sheet body (10) is characterized in that: in a thermally stimulated current spectrum that is obtained by performing thermally stimulated current measurement using the resin sheet body (10), there are a first relaxation temperature (A) at which the current value has a first peak, and a second relaxation temperature (B) which is higher than the first relaxation temperature (A) and at which the current value has a second peak; and the current value (AA) at the second relaxation temperature (A) is greater than the current value (AB) at the first relaxation temperature.

Description

Resin sheet body, resin sheet body with conductor layer, multilayer circuit board, and method for manufacturing multilayer circuit board

[0001] The present invention relates to a resin sheet, a resin sheet with a conductor layer, a multilayer circuit board, and a method for manufacturing a multilayer circuit board.

[0002] A resin sheet body with a conductor layer, in which a conductor layer is disposed on the surface of a resin sheet body, has been conventionally used as a material for manufacturing circuit boards such as flexible wiring boards and circuit boards for semiconductor packaging. Thermoplastic liquid crystal polymers are known to be used as a resin constituting the resin sheet body because of their low moisture absorption, heat resistance, chemical resistance, and excellent electrical properties.

[0003] Patent Document 1 discloses a metal-clad laminate as a resin sheet body with a conductor layer using a thermoplastic liquid crystal polymer, in which a metal foil is bonded to at least one surface of a thermoplastic liquid crystal polymer film, in which the surface roughness of the metal foil is less than 2.0 μm and the thickness of the skin layer of the thermoplastic liquid crystal polymer film is equal to or less than the surface roughness of the metal foil.

[0004] Patent No. 6656231

[0005] The thermoplastic liquid crystal polymer material used in the metal-clad laminate described in Patent Document 1 has a high dielectric loss tangent, and circuit boards fabricated using the metal-clad laminate described in Patent Document 1 have the problem of high transmission loss. To solve this problem, it has been considered to use a material with a low dielectric loss tangent as the thermoplastic liquid crystal polymer material. However, materials with a low dielectric loss tangent have low fluidity. Therefore, when laminating metal-clad laminates using materials with a low dielectric loss tangent, high-temperature, high-pressure, and long-term hot pressing is required to sufficiently fluidize the materials with a low dielectric loss tangent. Therefore, when laminating metal-clad laminates using materials with a low dielectric loss tangent, there have been problems of low productivity and a large environmental impact.

[0006] The present invention has been made to solve the above problems, and an object of the present invention is to provide a resin sheet body that can reduce the environmental load when manufacturing a multilayer circuit board.

[0007] The resin sheet of the present invention has a first main surface and a second main surface opposite to the first main surface, and contains a wholly aromatic polyester. In a thermally stimulated current spectrum obtained by performing thermally stimulated current measurement using the resin sheet, there is a first relaxation temperature at which the current value forms a first peak, and a second relaxation temperature at which the current value forms a second peak at a temperature higher than the first relaxation temperature, and the current value at the second relaxation temperature is larger than the current value at the first relaxation temperature.

[0008] The resin sheet body with a conductor layer of the present invention is characterized by comprising the resin sheet body of the present invention described above and a conductor layer disposed on a first main surface of the resin sheet body.

[0009] The multilayer circuit board of the present invention has a first main surface and a second main surface opposite to the first main surface, and comprises a resin sheet body with a conductor layer, the resin sheet body including a wholly aromatic polyester and a conductor layer disposed on the first main surface, and is characterized in that in a thermally stimulated current spectrum obtained by performing thermally stimulated current measurement using the resin sheet body, there is a first relaxation temperature at which the current value forms a first peak, and a second relaxation temperature at which the current value forms a second peak at a temperature higher than the first relaxation temperature, and the current value at the second relaxation temperature is larger than the current value at the first relaxation temperature.

[0010] The method for manufacturing a multilayer circuit board of the present invention is characterized by comprising a conductor layer-equipped resin sheet body preparation step of preparing the conductor layer-equipped resin sheet body of the present invention described above; an arrangement step of arranging the conductor layer-equipped resin sheet body on the substrate so that the resin sheet body of the conductor layer-equipped resin sheet body contacts the substrate; and a heating and pressurizing step of heating and pressurizing the conductor layer-equipped resin sheet body and the substrate.

[0011] According to the present invention, it is possible to provide a resin sheet body that can reduce the environmental load when manufacturing a multilayer circuit board.

[0012] FIG. 1 is a cross-sectional view schematically showing an example of a resin sheet body according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing an example of a resin sheet body with a conductor layer according to a second embodiment of the present invention. FIG. 3 is a cross-sectional view schematically showing an example of a multilayer circuit board according to a third embodiment of the present invention. FIG. 4 is a cross-sectional view schematically showing another example of a multilayer circuit board according to the third embodiment of the present invention. FIG. 5 is a cross-sectional view schematically showing another example of a multilayer circuit board according to the third embodiment of the present invention. FIG. 6 is a cross-sectional view schematically showing another example of a multilayer circuit board according to the third embodiment of the present invention. FIG. 7 is a cross-sectional view schematically showing another example of a multilayer circuit board according to the third embodiment of the present invention. FIG. 8A is a chart of a thermal stimulated current spectrum obtained by performing a thermal stimulated current measurement using a resin sheet body with a conductor layer according to Example 1. FIG. 8B is a chart of a thermal stimulated current spectrum obtained by performing a thermal stimulated current measurement using a resin sheet body with a conductor layer according to Example 2. FIG. 8C is a chart of a thermal stimulated current spectrum obtained by performing a thermal stimulated current measurement using a resin sheet body with a conductor layer according to Example 3. 9A is a chart of a thermally stimulated current spectrum obtained by performing a thermally stimulated current measurement using a resin sheet with a conductor layer according to Comparative Example 1. FIG. 9B is a chart of a thermally stimulated current spectrum obtained by performing a thermally stimulated current measurement using a resin sheet with a conductor layer according to Comparative Example 2.

[0013] The resin sheet body, the resin sheet body with a conductor layer, the multilayer circuit board, and the method for manufacturing the multilayer circuit board of the present invention will be described below. However, the present invention is not limited to the following embodiments, and can be appropriately modified and applied within the scope that does not change the gist of the present invention. A combination of two or more of the individual desirable configurations of the present invention described in the following embodiments also constitutes the present invention.

[0014] The drawings shown below are schematic diagrams, and the dimensions, aspect ratio, scale, etc. may differ from those of the actual product.

[0015] Furthermore, the following embodiments are merely examples, and it goes without saying that partial substitution or combination of the configurations shown in different embodiments is possible. From the second embodiment onwards, a description of the matters common to the first embodiment will be omitted, and only the differences will be described. In particular, similar effects resulting from similar configurations will not be mentioned in each embodiment.

[0016] (First embodiment) A resin sheet according to a first embodiment of the present invention has a first main surface and a second main surface opposite the first main surface, and contains a wholly aromatic polyester. A thermally stimulated current (TSC) spectrum obtained using the resin sheet shows a first relaxation temperature at which the current value forms a first peak, and a second relaxation temperature at which the current value forms a second peak at a temperature higher than the first relaxation temperature, with the current value at the second relaxation temperature being greater than the current value at the first relaxation temperature. The resin sheet according to the first embodiment of the present invention may include other components as long as it has the above characteristics and achieves the effects of the present invention. The components of the resin sheet according to the first embodiment of the present invention are described in detail below.

[0017] Fig. 1 is a cross-sectional view schematically illustrating an example of a resin sheet body according to a first embodiment of the present invention. The resin sheet body 10 shown in Fig. 1 has a first main surface 11 and a second main surface 12 opposite to the first main surface 11. As will be described in detail later, a conductor layer is disposed on the resin sheet body 10. In this case, the conductor layer is disposed on the first main surface 11 of the resin sheet body 10.

[0018] The thickness of the resin sheet 10 can be determined appropriately, but is preferably, for example, 10 μm or more and 500 μm or less.

[0019] In the resin sheet 10, a thermally stimulated current spectrum obtained by performing thermally stimulated current measurement using the resin sheet 10 has a first relaxation temperature A at which the current value forms a first peak and a second relaxation temperature B at which the current value forms a second peak at a temperature higher than the first relaxation temperature A, with the current value at the second relaxation temperature B being greater than the current value at the first relaxation temperature A. In the resin sheet 10 having such characteristics, the molecules constituting the wholly aromatic polyester are more mobile, and the wholly aromatic polyester is more likely to flow at low temperatures and low pressures. Therefore, the environmental impact can be reduced when a multilayer circuit board is produced using the resin sheet 10. As will be described in detail later, such a resin sheet 10 can be produced by modifying the surface of a sheet-like material containing a wholly aromatic polyester by irradiating it with ultraviolet light.

[0020] The term "thermally stimulated current measurement" in this specification will be described. The resin sheet is placed in an electron trap measurement system (model name: TS-FETT, manufacturer: Rigaku Corporation), heated to a polarization temperature of 150°C, and held for 15 minutes with a voltage of 100V applied. After holding, the resin sheet is cooled to -80°C while the voltage is still applied, and polarization is performed. Next, both sides of the resin sheet are short-circuited by sandwiching them between Al plate electrodes, connected to a microammeter, and the current value flowing through the microammeter is observed when the temperature is raised to 250°C at a heating rate of 5°C / min. This allows a thermally stimulated current spectrum to be obtained. Furthermore, peak separation can be performed by fitting the current value in the obtained thermally stimulated current spectrum using a pseudo-Voigt function (a function obtained by combining a Lorentzian function and a Gaussian function). This allows the temperature at which the current value peaks in the thermally stimulated current spectrum and the current value at that temperature to be identified.

[0021] In the resin sheet body 10, the pressure at which the wholly aromatic polyester flows out at a temperature of 250°C is preferably 7.0 MPa or more and 8.0 MPa or less.

[0022] The resin sheet 10 includes a wholly aromatic polyester. The wholly aromatic polyester preferably contains a first structural unit having a naphthalene ring and a second structural unit having a benzene ring in its main chain, and the number of moles of the first structural unit is greater than the number of moles of the second structural unit. Such a wholly aromatic polyester has a naphthalene ring-rich molecular structure, thereby reducing dielectric loss. Therefore, when a multilayer circuit board is manufactured using the resin sheet 10, transmission loss can be reduced. Note that a naphthalene ring-rich molecular structure generally reduces the fluidity of the wholly aromatic polyester. However, as described above, the resin sheet 10 has the characteristic that the current value at the second relaxation temperature is greater than the current value at the first relaxation temperature in the thermally stimulated current spectrum, and therefore the fluidity of the wholly aromatic polyester is sufficiently high.

[0023] The first relaxation temperature A is preferably 130° C. or higher and 150° C. or lower. The second relaxation temperature B is preferably 160° C. or higher and 180° C. or lower.

[0024] In the resin sheet 10, the ratio of the number of moles of the first constituent units to the number of moles of the second constituent units ([number of moles of first constituent units] / [number of moles of second constituent units]) is preferably greater than 1.0 and not more than 9.0, and more preferably not less than 1.5 and not more than 4.0. With such a ratio, transmission loss can be further reduced when a multilayer circuit board is manufactured using the resin sheet 10.

[0025] The number of moles of the first structural unit and the number of moles of the second structural unit in the resin sheet 10 can be measured by reactive pyrolysis-GC / MS. More specifically, the resin is decomposed using tetramethylammonium hydroxide as a reactive pyrolysis reagent, and the ratio of the number of moles can be calculated by quantifying the peaks of structural units having naphthalene tubes and structural units having benzene tubes using reactive pyrolysis-GCMS. The GC / MS analyzer can be a Multi-Shot Pyrolyzer EGA / PY-3030D manufactured by Shimadzu Corporation.

[0026] In the resin sheet 10, the proportion of the second structural unit in the structural units constituting the main chain of the wholly aromatic polyester is preferably 20% or more and less than 50%. When the surface of a resin sheet made using a wholly aromatic polyester is modified by ultraviolet irradiation, the locations where benzene rings are continuous serve as the starting points for modification. When the proportion of the second structural unit is within the above range, the main surface of the resin sheet is suitably modified by ultraviolet irradiation.

[0027] The wholly aromatic polyester is preferably a liquid crystal polymer, and more preferably a thermotropic liquid crystal polymer. The wholly aromatic polyester material is preferably a block copolymer with parahydroxybenzoic acid, 2,6-hydroxynaphthoic acid, hydroquinone, 4,4-dihydroxybiphenyl, 2,6-naphthalenedicarboxylic acid, terephthalic acid, or isophthalic acid. Note that, in terms of water absorption, the wholly aromatic polyester in the resin sheet according to the first embodiment of the present invention preferably does not have an amide bond.

[0028] The wholly aromatic polyester is preferably heated to 400°C in an inert atmosphere, cooled to room temperature at a temperature decrease rate of 40°C / min or more, and then heated again at a temperature increase rate of 40°C / min while being measured using a differential scanning calorimeter, and the endothermic peak temperature exceeds 310°C. If the endothermic peak temperature exceeds 310°C, the heat resistance of a resin sheet containing the wholly aromatic polyester is improved. Furthermore, when a circuit board is produced using the resin sheet according to the first embodiment of the present invention, the circuit board is less likely to deform during solder mounting, such as a reflow process.

[0029] For example, in the case of a combination of parahydroxybenzoic acid and 4,6-hydroxynaphthoic acid, the endothermic peak temperature of the wholly aromatic polyester exceeds 310°C when the content of 4,6-hydroxynaphthoic acid is 70% by mass or more or 20% by mass or less. However, the monomer combination is not limited to this. The endothermic peak temperature of the wholly aromatic polyester is preferably 350°C or less. From the viewpoint of molding a resin sheet, the endothermic peak temperature is preferably lower than the decomposition temperature of the wholly aromatic polyester.

[0030] Next, an example of a method for producing a resin sheet body according to the first embodiment of the present invention will be described. The example of the method for producing a resin sheet body according to the first embodiment of the present invention may include, for example, a molding step of molding a sheet-like material from a wholly aromatic polyester and an ultraviolet irradiation step of irradiating ultraviolet rays onto the surface of the sheet-like material.

[0031] <Molding step> In this step, a wholly aromatic polyester is prepared. The wholly aromatic polyester is preferably one obtained by polymerizing a monomer having a naphthalene ring and a functional group capable of forming an ester bond with a monomer having a benzene ring and a functional group capable of forming an ester bond via an ester bond. In addition, in the wholly aromatic polyester, it is preferable to blend the respective monomers so that the number of moles of the first structural unit having a naphthalene ring is greater than the number of moles of the second structural unit having a benzene ring.

[0032] Next, the wholly aromatic polyester is molded into a sheet to produce a sheet-like product. In this step, for example, a melt extrusion molding method can be used. Specifically, the melt of the wholly aromatic polyester may be directly molded into a sheet-like product by a conventionally known method such as a T-die method or an inflation method.

[0033] <Ultraviolet Light Irradiation Step> In this step, a resin sheet body is manufactured by irradiating a first main surface of a sheet-like material with ultraviolet light to modify the first main surface of the sheet-like material. Here, the ultraviolet light irradiation conditions are adjusted so that the manufactured resin sheet body has the following characteristics: In a thermally stimulated current spectrum obtained by performing a thermally stimulated current measurement using the resin sheet body, there is a first relaxation temperature at which the current value forms a first peak, and a second relaxation temperature at which the current value forms a second peak at a temperature higher than the first relaxation temperature, and ultraviolet light is irradiated so that the current value at the second relaxation temperature is larger than the current value at the first relaxation temperature.

[0034] The preferred ultraviolet irradiation conditions are as follows.

[0035] Ultraviolet rays are mainly classified into short-wavelength ultraviolet rays of 290 nm or less, medium-wavelength ultraviolet rays of 291 to 320 nm, and long-wavelength ultraviolet rays of 321 to 400 nm. In this process, at least short-wavelength ultraviolet rays are irradiated onto one main surface of the sheet-like material. This is because it is difficult to sufficiently modify one main surface of the sheet-like material with medium- and long-wavelength ultraviolet rays alone. However, as long as the ultraviolet rays to be irradiated include short-wavelength ultraviolet rays, those containing medium-wavelength ultraviolet rays or long-wavelength ultraviolet rays can also be used. Furthermore, those containing light rays other than ultraviolet rays may also be used.

[0036] The ultraviolet irradiation device to be used is not particularly limited as long as it can irradiate short wavelength ultraviolet light, but for example, a low pressure mercury lamp with a dominant wavelength of 185 nm and 254 nm, or a high pressure mercury lamp with a dominant wavelength of 254 nm and 365 nm is preferable because it is easy to handle. Also, a KrCl excimer lamp with a dominant wavelength of 222 nm, or a Xe excimer lamp with a dominant wavelength of 172 nm are preferable. ２ Excimer lamps and Kr ２ Excimer lamp, 126 nm Ar ２ An excimer lamp or the like may also be used, but since ultraviolet light of 230 nm or less is easily absorbed by oxygen and irradiation in air is inefficient, when using such a device, irradiation in a nitrogen environment or a vacuum environment is preferred.

[0037] The cumulative light amount of the short-wavelength ultraviolet light irradiated in this step is 500 to 2000 mJ / cm ２The cumulative light amount of short-wavelength ultraviolet light is preferably 500 mJ / cm ２ If the total amount of short-wavelength ultraviolet light is less than 2000 mJ / cm, sufficient effect may not be obtained. ２ If the amount of light exceeds this limit, the sheet-like material may be deformed or its strength may be reduced. ２ Since the integrated light quantity is the product of the UV radiation intensity and the irradiation time (seconds), the integrated light quantity can be adjusted by adjusting the intensity of the UV radiation used and the irradiation time.

[0038] Furthermore, when irradiating ultraviolet rays, it is necessary to control the temperature of the sheet-like material. For example, if the temperature of the sheet-like material becomes too high, the sheet-like material may deform and wrinkle. The temperature of the sheet-like material depends on the amount of ultraviolet light irradiated and the distance (mm) between the UV tube and the sheet-like material, so these also need to be controlled. The temperature of the sheet-like material can be appropriately determined depending on the type of wholly aromatic polyester, but it is preferable to set the temperature of the sheet-like material at a temperature of 80°C or higher and 180°C or lower, for example.

[0039] Through the above steps, the resin sheet body according to the first embodiment of the present invention can be manufactured.

[0040] Second Embodiment Next, a resin sheet body with a conductor layer according to a second embodiment of the present invention will be described. Fig. 2 is a cross-sectional view schematically showing one example of a resin sheet body with a conductor layer according to the second embodiment of the present invention. The resin sheet body with a conductor layer 1 according to the second embodiment of the present invention shown in Fig. 2 includes the resin sheet body 10 according to the first embodiment of the present invention and a conductor layer 20 arranged on a first main surface 11 of the resin sheet body 10.

[0041] As described above, the resin sheet body 10 is modified by ultraviolet irradiation in the vicinity of the first main surface 11. Therefore, when the conductor layer 20 is disposed on the first main surface 11 of the resin sheet body 10, peeling of the conductor layer 20 can be prevented.

[0042] In the resin sheet body with a conductor layer according to the second embodiment of the present invention, the conductor layer is preferably a metal foil. Furthermore, the metal foil may be copper foil, copper alloy foil, silver foil, aluminum foil, or the like. Among these, copper foil is preferred. When the conductor layer is a metal foil, the resin sheet body and the metal foil can be bonded by placing the metal foil on the first main surface of the resin sheet body according to the first embodiment of the present invention and applying heat and pressure, thereby manufacturing the resin sheet body with a conductor layer according to the second embodiment of the present invention.

[0043] The conditions for the heating and pressing are not particularly limited, but may be, for example, 250° C. or higher and 350° C. or lower, 1.0 MPa or higher and 10.0 MPa or lower, and 1 second or higher and 20 minutes or shorter.

[0044] Even if such heating and pressurization are performed, the thermally stimulated current spectrum in the thermally stimulated current measurement of the resin sheet body remains unchanged. Therefore, whether or not a certain resin sheet body with a conductor layer is the resin sheet body with a conductor layer according to the second embodiment of the present invention can be determined, for example, by the following method.

[0045] That is, the conductor layer of a certain conductor-layer-equipped resin sheet body is removed by etching or the like. Next, the remaining resin sheet body is used to measure the thermally stimulated current spectrum by performing the above-mentioned thermally stimulated current measurement. In the thermally stimulated current spectrum, there is a first relaxation temperature at which the current value forms a first peak, and a second relaxation temperature at which the current value forms a second peak at a temperature higher than the first relaxation temperature. If the current value at the second relaxation temperature is greater than the current value at the first relaxation temperature, the conductor-layer-equipped resin sheet body can be determined to be a conductor-layer-equipped resin sheet body according to the second embodiment of the present invention. Furthermore, when the conductor-layer-equipped resin sheet body is part of a multilayer circuit board, the resist material or coverlay material on the surface of the board can be removed by solvent or mechanical removal to expose the conductor layer, and then the conductor layer (conductor circuit pattern) can be etched away using a conventional etching solution such as a ferric chloride aqueous solution.

[0046] In the resin sheet body with a conductor layer according to the second embodiment of the present invention, the thickness of the conductor layer is not particularly limited, but is preferably 1 μm or more and 70 μm or less.

[0047] In the conductor layer-equipped resin sheet body according to the second embodiment of the present invention, the ten-point mean roughness (Rzjis) of the main surface of the conductor layer on the side disposed on the first main surface of the resin sheet body is preferably 2.0 μm or less, and more preferably 0.1 μm or more and 1.5 μm or less. When the ten-point mean roughness (Rzjis) of the main surface of the conductor layer is 2.0 μm or less, the conductor skin loss can be reduced, thereby reducing the transmission loss in a multilayer circuit board manufactured using the conductor layer-equipped resin sheet body according to the second embodiment of the present invention. Furthermore, a roughened surface having a ten-point mean roughness (Rzjis) of 2.0 μm or less can be easily formed. Furthermore, when the ten-point mean roughness (Rzjis) of the main surface of the conductor layer is 2.0 μm or less, residue is less likely to be left behind when removing a portion of the conductive layer by etching or the like. Note that the ten-point mean roughness (Rzjis) refers to the ten-point mean roughness defined in JIS B 0601-2001.

[0048] Generally, if the ten-point average roughness (Rzjis) of the main surface of the conductor layer is low, the adhesive strength (peel strength) between the conductor layer and the resin sheet body is reduced. However, as described above, in the conductor layer-equipped resin sheet body according to the second embodiment of the present invention, the first main surface of the resin sheet body is modified by ultraviolet light. Therefore, in the conductor layer-equipped resin sheet body according to the second embodiment of the present invention, even if the ten-point average roughness (Rzjis) of the main surface of the conductor layer is 2.0 μm or less, the adhesive strength (peel strength) between the conductor layer and the resin sheet body is sufficiently high.

[0049] Third Embodiment Next, a multilayer circuit board according to a third embodiment of the present invention will be described. The multilayer circuit board according to the third embodiment of the present invention is a multilayer circuit board including the resin sheet body with a conductor layer according to the second embodiment of the present invention.

[0050] That is, the multilayer circuit board according to the third embodiment of the present invention has a first main surface and a second main surface opposite to the first main surface, and comprises a resin sheet body with a conductor layer, the resin sheet body including a wholly aromatic polyester and a conductor layer disposed on the first main surface, and is characterized in that in a thermally stimulated current spectrum obtained by performing thermally stimulated current measurement using the resin sheet body, there is a first relaxation temperature at which the current value forms a first peak, and a second relaxation temperature at which the current value forms a second peak at a temperature higher than the first relaxation temperature, and the current value at the second relaxation temperature is greater than the current value at the first relaxation temperature.

[0051] The multilayer circuit board according to the third embodiment of the present invention may include any other substrates as long as it includes at least one resin sheet body with a conductor layer according to the second embodiment of the present invention.

[0052] The multilayer circuit board according to the third embodiment of the present invention is preferably a multilayer circuit board in which a plurality of conductor layer-equipped resin sheets according to the second embodiment of the present invention are stacked.

[0053] The multilayer circuit board according to the third embodiment of the present invention can be manufactured by a method for manufacturing a multilayer circuit board, including a conductor layer-equipped resin sheet body preparation step of preparing a conductor layer-equipped resin sheet body according to the second embodiment of the present invention, an arrangement step of arranging the conductor layer-equipped resin sheet body on a substrate so that the resin sheet body of the conductor layer-equipped resin sheet body contacts the substrate, and a heating and pressurizing step of heating and pressurizing the conductor layer-equipped resin sheet body and the substrate.

[0054] The method for manufacturing a multilayer circuit board according to the third embodiment of the present invention is also the method for manufacturing a multilayer circuit board according to the present invention.

[0055] The method for producing a multilayer circuit board of the present invention uses a resin sheet with a conductor layer according to the second embodiment of the present invention. As described above, the resin sheet of the resin sheet with a conductor layer according to the second embodiment is modified by ultraviolet irradiation, which increases the fluidity of the wholly aromatic polyester at low temperature and low pressure. Therefore, even at low temperature and low pressure, the layers can be firmly laminated, and the heating and pressurizing time can be shortened. As a result, the environmental impact of producing a multilayer circuit board can be reduced.

[0056] Furthermore, in the resin sheet body, the wholly aromatic polyester exhibits high fluidity at low temperatures and low pressures. Therefore, when the resin sheet body with a conductor layer is placed on a substrate in the placement step, even if a conductor circuit pattern or via conductors are formed on the substrate, the resin sheet body can cover these structures. Therefore, in the method for manufacturing a multilayer circuit board according to the third embodiment of the present invention, the resin sheet body with a conductor layer and the substrate can be laminated without any gaps.

[0057] In the manufacturing method of the multilayer circuit board according to the third embodiment of the present invention, in the heating and pressing step, it is preferable to heat and pressurize at a temperature equal to or higher than the second relaxation temperature of the resin sheet body and at a pressure of 1.0 MPa or more and 15.0 MPa or less, and it is more preferable to heat and pressurize at a temperature of 200°C or more and 350°C or less and at a pressure of 1.0 MPa or more and 15.0 MPa or less.

[0058] Hereinafter, an example of a multilayer circuit board according to a third embodiment of the present invention in which a plurality of conductor layer-equipped resin sheet bodies according to the second embodiment of the present invention are stacked will be described with reference to the drawings.

[0059] Fig. 3 is a cross-sectional view schematically showing an example of a multilayer circuit board according to a third embodiment of the present invention. The multilayer circuit board 2a shown in Fig. 3 includes a conductor layer-equipped resin sheet body 1a in which a conductor layer 20a is arranged on a first main surface 11a of a resin sheet body 10a, and a conductor layer-equipped resin sheet body 1b in which a conductor layer 20b is arranged on a first main surface 11b of a resin sheet body 10b. Both the conductor layer-equipped resin sheet body 1a and the conductor layer-equipped resin sheet body 1b are conductor layer-equipped resin sheets according to the second embodiment of the present invention.

[0060] As shown in FIG. 3, in the multilayer circuit board 2a, the resin sheet body 10a and the resin sheet body 10b are stacked so that the second main surface 12a and the second main surface 12b thereof are in contact with each other.

[0061] The multilayer circuit board 2a can be produced by stacking the conductor layer-equipped resin sheet body 1a and the conductor layer-equipped resin sheet body 1b in the above-mentioned arrangement, and heating and pressurizing them using a vacuum hot press.

[0062] Fig. 4 is a cross-sectional view schematically showing another example of a multilayer circuit board according to the third embodiment of the present invention. A multilayer circuit board 2b shown in Fig. 4 includes a conductor layer-equipped resin sheet body 1a in which a conductor layer 20a is arranged on the first main surface 11a of a resin sheet body 10a, a conductor layer-equipped resin sheet body 1b in which a conductor layer 20b is arranged on the first main surface 11b of a resin sheet body 10b, and a conductor layer-equipped resin sheet body 1c in which a conductor layer 20c is arranged on the first main surface 11c of a resin sheet body 10c. The conductor layer-equipped resin sheet body 1a, the conductor layer-equipped resin sheet body 1b, and the conductor layer-equipped resin sheet body 1c are all conductor layer-equipped resin sheets according to the second embodiment of the present invention.

[0063] 4, in the multilayer circuit board 2b, the resin sheet bodies 10a and 10c are stacked so that the second main surface 12a of the resin sheet body 10a and the second main surface 12b of the resin sheet body 10b are in contact with each other, and the conductor layer 20a of the resin sheet body 10a and the second main surface 12c of the resin sheet body 10c are stacked so that they are in contact with each other.

[0064] The multilayer circuit board 2b can be manufactured by stacking the conductor layer-equipped resin sheet body 1a, the conductor layer-equipped resin sheet body 1b, and the conductor layer-equipped resin sheet body 1c in the above-mentioned arrangement, and then heating and pressurizing them using a vacuum hot press.

[0065] Fig. 5 is a cross-sectional view schematically illustrating another example of a multilayer circuit board according to the third embodiment of the present invention. The multilayer circuit board 2c shown in Fig. 5 differs from the multilayer circuit board 2a in that a conductor circuit pattern 30 is disposed between the second main surface 12a of the resin sheet body 10a and the second main surface 12b of the resin sheet body 10b. Note that a conventionally known conductor circuit pattern 30 can be used as the conductor circuit pattern 30.

[0066] Such a multilayer circuit board 2c can be manufactured by arranging a conductor circuit pattern 30 on the second main surface 12a of the resin sheet body 10a or the second main surface 12b of the resin sheet body 10b, stacking the resin sheet body 1a with a conductor layer and the resin sheet body 1b with a conductor layer in the above-mentioned arrangement, and heating and pressurizing them using a vacuum hot press.

[0067] Since the resin sheet body 10a and the resin sheet body 10b are the resin sheet body according to the first embodiment of the present invention, they have high fluidity at low temperature and low pressure, and therefore, even if such a conductor circuit pattern 30 is present, the resin sheet body 1a with a conductor layer and the resin sheet body 1b with a conductor layer can be laminated without gaps by heating and pressing at low temperature and low pressure.

[0068] Fig. 6 is a cross-sectional view schematically illustrating another example of a multilayer circuit board according to the third embodiment of the present invention. The multilayer circuit board 2d shown in Fig. 6 differs from the multilayer circuit board 2c in that via conductors 40 connecting the conductor layer 20a and the conductor circuit pattern 30 are arranged so as to penetrate the resin sheet body 10a. Conventionally known via conductors 40 may be used.

[0069] Such a multilayer circuit board 2d can be manufactured by the following method. First, via conductors 40 are formed in the conductor-layer-equipped resin sheet body 1a so as to penetrate the resin sheet body 10a and connect to the conductor layer 20a. A conductor circuit pattern 30 is also arranged on the second main surface 12b of the resin sheet body 10b. The conductor-layer-equipped resin sheet body 1a and the conductor-layer-equipped resin sheet body 1b are then stacked on top of each other so that the conductor circuit pattern 30 and the via conductors 40 are in contact with each other, and the resulting stack is heated and pressurized by a vacuum hot press. This allows the multilayer circuit board 2d to be manufactured.

[0070] Since the resin sheet body 10a and the resin sheet body 10b are the resin sheet body according to the first embodiment of the present invention, they have high fluidity at low temperature and low pressure, and therefore, even if such a conductor circuit pattern 30 and via conductors 40 are present, the conductor layer-equipped resin sheet body 1a and the conductor layer-equipped resin sheet body 1b can be laminated without gaps by heating and pressing at low temperature and low pressure.

[0071] 7 is a cross-sectional view schematically illustrating another example of a multilayer circuit board according to the third embodiment of the present invention. The multilayer circuit board 2e shown in FIG. 7 differs from the multilayer circuit board 2a in that via conductors 40 connecting the conductor layers 20a and 20b are arranged to penetrate the resin sheet bodies 10a and 10b. Conventionally known via conductors 40 may be used.

[0072] Such a multilayer circuit board 2e can be manufactured by the following method. First, via conductors 40 are formed in the conductor-layer-equipped resin sheet body 1a so as to penetrate the resin sheet body 10a and connect to the conductor layer 20a. At this time, the length of the via conductors 40 protruding from the second main surface 12a of the resin sheet body 10a is set to a length that allows them to penetrate the resin sheet body 10b and contact the conductor layer 20b. The conductor-layer-equipped resin sheet body 1a and the conductor-layer-equipped resin sheet body 1b are then stacked on top of each other, and heated and pressurized by a vacuum hot press so that the via conductors 40 penetrate the resin sheet body 10b and contact the conductor layer 20b. This completes the manufacture of the multilayer circuit board 2e.

[0073] Since the resin sheet body 10a and the resin sheet body 10b are the resin sheet body according to the first embodiment of the present invention, they have high fluidity at low temperature and low pressure, and therefore, even if such via conductors 40 are present, the resin sheet body 1a with a conductor layer and the resin sheet body 1b with a conductor layer can be laminated without gaps by heating and pressing at low temperature and low pressure.

[0074] This specification describes the following:

[0075] The present invention (1) is a resin sheet body having a first main surface and a second main surface opposite to the first main surface, and containing a wholly aromatic polyester, wherein a thermally stimulated current spectrum obtained by performing thermally stimulated current measurement using the resin sheet body has a first relaxation temperature at which the current value forms a first peak, and a second relaxation temperature at which the current value forms a second peak at a temperature higher than the first relaxation temperature, and the current value at the second relaxation temperature is larger than the current value at the first relaxation temperature.

[0076] The present invention (2) is the resin sheet according to the present invention (1), wherein the wholly aromatic polyester contains a first structural unit having a naphthalene ring and a second structural unit having a benzene ring in the main chain, and the number of moles of the first structural unit is greater than the number of moles of the second structural unit.

[0077] The present invention (3) is a resin sheet body with a conductor layer, characterized by including the resin sheet body according to the present invention (1) or (2) and a conductor layer disposed on the first main surface of the resin sheet body.

[0078] The present invention (4) is the resin sheet body with a conductor layer according to the present invention (3), wherein the conductor layer is a metal foil.

[0079] The present invention (5) is the resin sheet body with a conductor layer according to the present invention (4), wherein the metal foil is a copper foil.

[0080] The present invention (6) is the resin sheet body with a conductor layer according to any one of the present inventions (3) to (5), wherein the ten-point average roughness (Rzjis) of the main surface of the conductor layer on the side arranged on the first main surface is 2.0 μm or less.

[0081] The present invention (7) is a multilayer circuit board comprising a resin sheet body with a conductor layer, the resin sheet body having a first main surface and a second main surface opposite the first main surface, the resin sheet body including a wholly aromatic polyester, and a conductor layer disposed on the first main surface, wherein a thermally stimulated current spectrum obtained by performing thermally stimulated current measurement using the resin sheet body has a first relaxation temperature at which the current value forms a first peak, and a second relaxation temperature at which the current value forms a second peak at a temperature higher than the first relaxation temperature, and the current value at the second relaxation temperature is larger than the current value at the first relaxation temperature.

[0082] The present invention (8) is a method for manufacturing a multilayer circuit board, comprising: a conductor layer-equipped resin sheet body preparation step of preparing a conductor layer-equipped resin sheet body according to any one of the present inventions (3) to (6); an arrangement step of arranging the conductor layer-equipped resin sheet body on a substrate so that the resin sheet body of the conductor layer-equipped resin sheet body contacts the substrate; and a heating and pressurizing step of heating and pressurizing the conductor layer-equipped resin sheet body and the substrate.

[0083] The present invention (9) is a method for producing a multilayer circuit board according to the present invention (8), wherein a thermally stimulated current spectrum obtained by performing thermally stimulated current measurement using the resin sheet has a first relaxation temperature at which the current value forms a first peak and a second relaxation temperature at which the current value forms a second peak at a temperature higher than the first relaxation temperature, and the heating and pressurizing step involves heating and pressurizing at a temperature equal to or higher than the second relaxation temperature and at a pressure of 15.0 MPa or less.

[0084] The present invention (10) is the method for producing a multilayer circuit board according to the present invention (8) or (9), wherein the heating and pressing step involves heating and pressing at 200° C. or higher and 350° C. or lower and at 1.0 MPa or higher and 15.0 MPa or lower.

[0085] EXAMPLES Hereinafter, examples will be shown that more specifically disclose the resin sheet body of the present invention and the resin sheet body with a conductor layer of the present invention, but the present invention is not limited to the following examples.

[0086] Example 1 A wholly aromatic polyester with a high HNA ratio (Tm = 330°C) was produced by melt-polymerizing a monomer ratio of p-hydroxybenzoic acid (HBA):6-hydroxy-2-naphthoic acid (HNA) = 3:7 at 340°C. This wholly aromatic polyester was melt-extruded into a sheet and then transversely stretched to produce a sheet-like product (thickness 50 μm) that was equi-oriented in the in-plane direction.

[0087] Next, the first main surface of the sheet-like material was irradiated with ultraviolet light using a high-pressure UV treatment device. At this time, the distance between the high-pressure UV tube and the sheet-like material was kept at 170 mm, and the integrated light amount of ultraviolet light having a wavelength of 250 to 270 nm was 1185 mJ / cm. ２ The temperature of the first main surface of the sheet-like material during irradiation was 103°C.

[0088] Through the above steps, a resin sheet according to Example 1 was produced.

[0089] Next, an electrolytic copper foil having a thickness of 12 μm was prepared, and one main surface of the electrolytic copper foil was roughened so that the ten-point average roughness (Rzjis) was 1.8 μm. Then, the resin sheet body according to Example 1 and the electrolytic copper foil were superposed on each other so that the first main surface of the resin sheet body according to Example 1 faced the roughened main surface of the electrolytic copper foil, and the resin sheet body according to Example 1 and the electrolytic copper foil were heated and pressed at 300° C. and 3 MPa using a pair of roll laminators to bond the resin sheet body according to Example 1 and the electrolytic copper foil to form a laminate, thereby producing a resin sheet body with a conductor layer according to Example 1.

[0090] (Example 2) and (Example 3) Resin sheet bodies and resin sheet bodies with conductor layers according to Examples 2 and 3 were prepared in the same manner as Example 1, except that the conditions for irradiating ultraviolet light onto the first main surface of the sheet-like material were changed as shown in Table 1.

[0091] Comparative Example 1 A resin sheet body and a resin sheet body with a conductor layer according to Comparative Example 1 were produced in the same manner as in Example 1, except that the first main surface of the sheet-like material was not irradiated with ultraviolet light.

[0092] (Comparative Example 2) A resin sheet body and a resin sheet body with a conductor layer according to Comparative Example 2 were prepared in the same manner as in Example 1, except that the conditions for irradiating ultraviolet light onto the first main surface of the sheet-like material were changed as shown in Table 1.

[0093]

[0094] (Thermal Stimulation Current Measurement) The conductor layer of each resin sheet with a conductor layer according to each example and comparative example was removed by etching with ferric chloride. After etching, the conductor layer was washed with water and dried to obtain a resin sheet. The resulting resin sheet was placed in an electron trap measurement system (model name: TS-FETT, manufacturer: Rigaku Corporation), heated to a polarization temperature of 150°C, and held for 15 minutes with a voltage of 100V applied. After holding, the resin sheet was cooled to -80°C with the voltage still applied, and polarization treatment was performed. Next, both sides of the resin sheet were short-circuited by sandwiching them between Al plate electrodes and connected to a microcurrent meter. The current flowing through the microcurrent meter was observed as the temperature was raised to 250°C at a heating rate of 5°C / min. The results are shown in Table 1, Figures 8A to 8C, and Figures 9A to 9B.

[0095] Fig. 8A is a chart of a thermally stimulated current spectrum obtained by performing a thermally stimulated current measurement using a resin sheet with a conductor layer according to Example 1. Fig. 8B is a chart of a thermally stimulated current spectrum obtained by performing a thermally stimulated current measurement using a resin sheet with a conductor layer according to Example 2. Fig. 8C is a chart of a thermally stimulated current spectrum obtained by performing a thermally stimulated current measurement using a resin sheet with a conductor layer according to Example 3. Fig. 9A is a chart of a thermally stimulated current spectrum obtained by performing a thermally stimulated current measurement using a resin sheet with a conductor layer according to Comparative Example 1. Fig. 9B is a chart of a thermally stimulated current spectrum obtained by performing a thermally stimulated current measurement using a resin sheet with a conductor layer according to Comparative Example 2.

[0096] As shown in Table 1, FIGS. 8A to 8C, and 9A to 9B, in the resin sheet body with a conductor layer according to each example, the current value A Ｂ The current value A at the first relaxation temperature (the temperature indicated by the symbol A in each chart) at which the first peak is formed is Ａ In addition, in the resin sheet bodies with conductor layers according to each comparative example, the current value at the second relaxation temperature (the temperature indicated by the symbol B in each chart) was smaller than the current value at the first relaxation temperature (the temperature indicated by the symbol A in each chart).

[0097] (Measurement of pressure exhibiting fluidity at 250°C) The conductor layer of the conductor-layered resin sheet body of each Example and Comparative Example was removed by etching with ferric chloride. Next, the resin sheet body was placed in a press and heated to 250°C. The pressure was increased in 0.25 MPa increments to measure the pressure at which the wholly aromatic polyester constituting the resin sheet body began to flow. When the pressure at which the wholly aromatic polyester began to flow was 8.00 MPa or less, the moldability of the interlayer connection vias and the coverage of the inner layer pattern were good, and therefore the ease of multilayering was judged to be high (indicated by "O" in Table 1). When the pressure at which the wholly aromatic polyester began to flow exceeded 8.00 MPa, the moldability of the interlayer connection vias and the coverage of the inner layer pattern were not good, and therefore the ease of multilayering was judged to be low (indicated by "X" in Table 1). The results are shown in Table 1.

[0098] As shown in Table 1, the resin sheets with conductor layers according to Examples 1 to 3 were judged to have a low pressure at 250° C. that showed fluidity, and were therefore highly easily multi-layered.

[0099] DESCRIPTION OF SYMBOLS 1, 1a, 1b, 1c Resin sheet body with conductor layer 2a, 2b, 2c, 2d, 2e Multilayer circuit board 10, 10a, 10b, 10c Resin sheet body 11, 11a, 11b, 11c First main surface 12, 12a, 12b, 12c Second main surface 20, 20a, 20b, 20c Conductor layer 30 Conductive circuit pattern 40 Via conductor

Claims

1. A resin sheet having a first main surface and a second main surface opposite the first main surface, the resin sheet comprising a wholly aromatic polyester, wherein a thermally stimulated current spectrum obtained by thermally stimulated current measurement using the resin sheet has a first relaxation temperature at which the current value forms a first peak, and a second relaxation temperature at which the current value forms a second peak at a temperature higher than the first relaxation temperature, and the current value at the second relaxation temperature is greater than the current value at the first relaxation temperature.

2. The resin sheet body according to claim 1, wherein the wholly aromatic polyester contains a first structural unit having a naphthalene ring and a second structural unit having a benzene ring in its main chain, and the number of moles of the first structural unit is greater than the number of moles of the second structural unit.

3. A resin sheet body with a conductor layer, comprising: the resin sheet body according to claim 1 or 2; and a conductor layer disposed on the first main surface of the resin sheet body.

4. The resin sheet with a conductor layer according to claim 3, wherein the conductor layer is a metal foil.

5. A resin sheet with a conductor layer according to claim 4, wherein the metal foil is copper foil.

6. A resin sheet body with a conductor layer according to any one of claims 3 to 5, wherein the ten-point average roughness (Rzjis) of the main surface of said conductor layer on the side arranged on said first main surface is 2.0 µm or less.

7. A multilayer circuit board comprising a resin sheet body with a conductor layer, the resin sheet body having a first main surface and a second main surface opposite the first main surface, the resin sheet body containing a wholly aromatic polyester, and a conductor layer disposed on the first main surface, wherein a thermally stimulated current spectrum obtained by thermally stimulated current measurement using the resin sheet body has a first relaxation temperature at which the current value forms a first peak, and a second relaxation temperature at which the current value forms a second peak at a temperature higher than the first relaxation temperature, and the current value at the second relaxation temperature is greater than the current value at the first relaxation temperature.

8. A method for manufacturing a multilayer circuit board, comprising: a conductor layer-attached resin sheet body preparation step of preparing a conductor layer-attached resin sheet body according to any one of claims 3 to 6; an arrangement step of arranging the conductor layer-attached resin sheet body on a substrate so that the resin sheet body of the conductor layer-attached resin sheet body contacts the substrate; and a heating and pressurizing step of heating and pressurizing the conductor layer-attached resin sheet body and the substrate.

9. A method for manufacturing a multilayer circuit board as described in claim 8, wherein a thermally stimulated current spectrum obtained by performing thermally stimulated current measurement using the resin sheet has a first relaxation temperature at which the current value forms a first peak and a second relaxation temperature at which the current value forms a second peak at a temperature higher than the first relaxation temperature, and wherein the heating and pressurizing step involves heating and pressurizing at a temperature equal to or higher than the second relaxation temperature, and at a temperature of 1.0 MPa or more and 15.0 MPa or less.

10. The method for manufacturing a multilayer circuit board according to claim 8 or 9, wherein the heating and pressing step involves heating and pressing at 200° C. or higher and 350° C. or lower and at 1.0 MPa or higher and 15.0 MPa or lower.

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