JP6488170B2 - Circuit board - Google Patents

Description

  An object of the present invention is to provide a circuit board that can cope with high frequencies associated with downsizing and high performance of electronic devices.

  In recent years, the performance and miniaturization of electronic devices are rapidly progressing, and there is an increasing demand for higher density, smaller size, and thinner electronic components used in electronic devices. Along with this, further improvements in various physical properties such as heat resistance, mechanical strength, and electrical characteristics have been required for materials used for electronic components. For example, printed circuit boards on which semiconductor elements are mounted are required to have higher density, higher functionality, and higher performance.

  Under such circumstances, there is an increasing demand for flexible printed wiring boards (hereinafter referred to as FPC) capable of three-dimensional wiring and mounting in a narrow space. In general, FPC has a structure in which a circuit pattern is formed on a polyimide film having excellent heat resistance and flexibility, and an insulating resin layer having an adhesive layer, that is, a so-called coverlay film is bonded to the surface.

  In recent years, since the frequency of transmission signals in FPC has been remarkably increased, materials used for FPC are required to be able to reduce electrical signal loss in the high frequency region. As a means of reducing electric signal loss in FPC, it is necessary to use FPC material having excellent electrical characteristics (low dielectric constant, low dielectric loss tangent) in a high frequency region, copper foil with low conductor loss, and both It is necessary to design the material in consideration of the above. However, Patent Document 1 uses a coverlay film having excellent electrical characteristics (low dielectric constant, low dielectric loss tangent) in a high-frequency region, but does not consider the electrical characteristics of the insulating layer of the circuit board.

  In Patent Document 2, the electrical signal loss is reduced by using an FPC having a liquid crystal polymer film as an insulating layer of a circuit board and polytetrafluoroethylene as an adhesive layer of a coverlay film. There is room for improvement in adhesion to foils and coverlay films, and all FPC resin materials have excellent electrical characteristics (low dielectric constant, low dielectric loss tangent) in the high-frequency region, and also have excellent heat resistance, metal foil, There was no FPC excellent in adhesiveness with the coverlay film.

International publication WO2014 / 064986 JP2013-74129A

  An object of the present invention is to provide a circuit board that can cope with high frequencies associated with downsizing and high performance of electronic devices.

  In order to solve the above-mentioned problems, the present inventors paid attention to the electrical characteristics of the adhesive layer and the insulating layer in the coverlay film and the insulating layer of the substrate material, and are resin materials excellent in thickness control and electrical characteristics thereof. As a result, it has been found that a circuit board such as an FPC having excellent transmission characteristics in a high frequency region can be obtained, and the present invention has been completed.

That is, the circuit board of the present invention includes a polyimide insulating layer, a circuit wiring layer laminated on at least one surface of the polyimide insulating layer, and a coverlay film laminated on the circuit wiring layer. And the circuit board of this invention has the following structure ac:
a) The thickness La of the polyimide insulating layer is in the range of 12 to 50 μm;
b) The thickness Lc of the coverlay film is in the range of 25 to 70 μm;
c) When the dielectric constant of the polyimide insulating layer is Dka, the dielectric loss tangent is Dfa, and the thickness is La, and the dielectric constant of the coverlay film is Dkc, the dielectric loss tangent is Dfc, and the thickness is Lc,
The following formula (i);
{(√Dka) × Dfa × La + (√Dkc) × Dfc × Lc} / (La + Lc) (i)
The values calculated in the above are less than 0.014 when measured by a split post dielectric resonator (SPDR) at frequencies of 5 GHz, 10 GHz and 20 GHz;
It comprises.

In the circuit board of the present invention, the polyimide insulating layer has an adhesive polyimide layer (A1) in contact with the circuit wiring layer,
The coverlay film is composed of a base film layer (C1) and an adhesive polyimide layer (C2),
The difference between the imide group concentration in the adhesive polyimide layer (A1) and the imide group concentration in the adhesive polyimide layer (C2) (the imide group concentration of A1−the imide group concentration of C2) was within ± 7% by weight. May be.

In the circuit board of the present invention, the coverlay film may be composed of a base film layer (C1) and an adhesive polyimide layer (C2), and the base film layer (C1) is composed of polyimide. May be.

  The circuit board of the present invention may include the circuit wiring layer on one surface of the polyimide insulating layer and further include a ground conductor layer on the other surface. In this case, the maximum height roughness (Rz) of the circuit wiring layer and the ground conductor layer on the side in contact with the polyimide insulating layer may be 1.0 μm or less.

  The circuit board of the present invention can be suitably used as an electronic material that requires high-speed signal transmission by controlling the electrical characteristics of the resin layer and controlling the thickness.

Embodiments of the present invention will be described below. A circuit board according to an embodiment of the present invention includes a polyimide insulating layer, a circuit wiring layer laminated on at least one surface of the polyimide insulating layer, and a coverlay film laminated on the circuit wiring layer. Yes. And, when the dielectric constant of the polyimide insulating layer is Dka, the dielectric loss tangent is Dfa, and the thickness is La, and the dielectric constant of the coverlay film is Dkc, the dielectric loss tangent is Dfc, and the thickness is Lc,
The following formula (i);
{(√Dka) × Dfa × La + (√Dkc) × Dfc × Lc} / (La + Lc) (i)
The values calculated in (5) are all less than 0.014 when measured with a split post dielectric resonator (SPDR) at frequencies of 5 GHz, 10 GHz, and 20 GHz.
As described above, in the circuit board of the present embodiment, the entire insulating layer (polyimide insulating layer) of the circuit board is not lowered without lowering the dielectric characteristics (dielectric constant, dielectric loss tangent) of either the polyimide insulating layer or the coverlay film. The transmission loss of the circuit board in the high frequency region can be effectively reduced by reducing the dielectric characteristics of the + coverlay film.

[Polyimide insulation layer]
The thickness La of the polyimide insulating layer in the circuit board of the present embodiment is within the range of, for example, 12 μm or more and 50 μm or less from the viewpoint of improving the dielectric characteristics of the entire circuit board by setting the value of the above formula (i) to less than 0.014. Is preferred. Moreover, the polyimide insulating layer may have an adhesive polyimide layer (A1). Since the polyimide insulating layer requires control of heat resistance and thermal expansion coefficient, it is necessary to set the imide group concentration higher when compared with the adhesive polyimide layer (C2) of the coverlay film. It becomes difficult to lower the dielectric constant and dielectric loss tangent. Therefore, in order to make the value of the above formula (i) less than 0.014, it is not preferable to increase the thickness of the polyimide insulating layer more than necessary.

  From the viewpoint of improving the dielectric characteristics of the entire circuit board by setting the value of the above formula (i) to less than 0.014, the polyimide insulating layer is polyimide insulating in the measurement at frequencies of 5 GHz, 10 GHz and 20 GHz using the SPDR resonator. The dielectric constant Dka of the entire layer is preferably in the range of 2.8 to 4.0, and more preferably in the range of 3.0 to 3.5.

  In addition, the polyimide insulating layer has a value of the above formula (i) of less than 0.014, and from the viewpoint of improving the dielectric characteristics of the entire circuit board, in the measurement at frequencies of 5 GHz, 10 GHz and 20 GHz using an SPDR resonator, The dielectric loss tangent Dfa as the entire polyimide insulating layer is preferably in the range of 0.002 to 0.007, and more preferably in the range of 0.003 to 0.005. In order to improve the dielectric characteristics of the entire circuit board, it is particularly important to control the dielectric loss tangent of the polyimide insulating layer. By setting the dielectric loss tangent within the above range, the effect of reducing transmission loss increases.

  The polyimide insulating layer in the circuit board of the present embodiment is a polyimide obtained by reacting an acid anhydride component containing an aromatic tetracarboxylic acid anhydride component and a diamine component containing an aromatic diamine. Since polyimide is generally produced by reacting an acid anhydride with a diamine, a specific example of polyimide can be understood by explaining the acid anhydride and diamine. Hereinafter, a preferable polyimide will be described using an acid anhydride and a diamine.

<Acid anhydride>
In the polyimide insulating layer of the present embodiment, pyromellitic anhydride and 1,4,5,8-naphthalenetetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyl are used as the raw acid anhydride component. Preferred examples include tetracarboxylic dianhydride, 3,3 ′, 4,4′-diphenylsulfone tetracarboxylic dianhydride, and 4,4′-oxydiphthalic anhydride. Moreover, 2,2 ', 3,3'-, 2,3,3', 4'- or 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride, 2,3 ', 3,4'-biphenyltetracarboxylic dianhydride, 2,2', 3,3'-biphenyltetracarboxylic dianhydride, 2,3 ', 3,4'-diphenyl ether tetracarboxylic dianhydride Bis (2,3-dicarboxyphenyl) ether dianhydride, 3,3``, 4,4 ''-, 2,3,3``, 4 ''-or 2,2 '', 3, 3 ''-p-terphenyltetracarboxylic dianhydride, 2,2-bis (2,3- or 3,4-dicarboxyphenyl) -propane dianhydride, bis (2,3- or 3.4-di Carboxyphenyl) methane dianhydride, bis (2,3- or 3,4-dicarboxyphenyl) sulfone dianhydride, 1,1-bis (2,3- or 3,4-dicarboxyphenyl) ethane dianhydride 1,2,7,8-, 1,2,6,7- or 1,2,9,10-phenanthrene-tetracarboxylic dianhydride, 2,3,6,7-anthracene tetracarboxylic acid Anhydride, 2,2-bis (3,4-dicarboxyphenyl) tetrafluoropropane dianhydride, 2,3,5,6-cyclohexane dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5 , 6-Naphthalenetetracarboxylic dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic dianhydride, 2, 6- or 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7- (or 1,4,5,8-) tetrachloronaphthalene-1, 4,5,8- (or 2,3,6,7-) tetracarboxylic dianhydride, 2,3,8,9-, 3,4,9,10-, 4,5,10,11- Or 5,6,11,12-perylene-tetracarboxylic dianhydride, cyclopentane-1,2,3,4-tetracarboxylic dianhydride, pyrazine-2,3,5,6-tetracarboxylic dianhydride Anhydride, pyrrolidine-2,3,4,5-tetracarboxylic dianhydride, thiophene-2,3,4,5-tetracarboxylic dianhydride, 4,4'-bis (2,3-dicarboxy Phenoxy) Examples include phenylmethane dianhydride.

<Diamine>
The polyimide insulating layer of the present embodiment is a dimer acid type diamine in which two terminal carboxylic acid groups of dimer acid are substituted with primary aminomethyl groups or amino groups as raw material diamine components. Diamino-2,2′-dimethylbiphenyl, 4,4′-diamino-3,3′-dimethylbiphenyl, 4,4′-diamino-2,2′-bis (trifluoromethyl) biphenyl, 4,4′- Diaminodiphenyl ether, 2'-methoxy-4,4'-diaminobenzanilide, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 2,2'-bis [ 4- (4-Aminophenoxy) phenyl] propane, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dihydroxy-4,4'-diaminobiphenyl, 4,4'-diaminobenzanilide 2,2-bis- [4- (3-aminophenoxy) phenyl] propane Bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, bis [4- (4-aminophenoxy)] biphenyl, bis [4- (3-aminophenoxy) ) Biphenyl, bis [1- (4-aminophenoxy)] biphenyl, bis [1- (3-aminophenoxy)] biphenyl, bis [4- (4-aminophenoxy) phenyl] methane, bis [4- (3- Aminophenoxy) phenyl] methane, bis [4- (4-aminophenoxy) phenyl] ether, bis [4- (3-aminophenoxy) phenyl] ether, bis [4- (4-aminophenoxy)] benzophenone, bis [ 4- (3-aminophenoxy)] benzophenone, bis [4,4 '-(4-aminophenoxy)] benzanilide, bis [4,4'-(3-aminophenoxy)] benzanilide, 9,9-bis [4 -(4-A Minophenoxy) phenyl] fluorene, 9,9-bis [4- (3-aminophenoxy) phenyl] fluorene, 2,2-bis- [4- (4-aminophenoxy) phenyl] hexafluoropropane, 2,2- Bis- [4- (3-aminophenoxy) phenyl] hexafluoropropane, 4,4'-methylenedi-o-toluidine, 4,4'-methylenedi-2,6-xylidine, 4,4'-methylene-2, 6-diethylaniline, 4,4'-diaminodiphenylpropane, 3,3'-diaminodiphenylpropane, 4,4'-diaminodiphenylethane, 3,3'-diaminodiphenylethane, 4,4'-diaminodiphenylmethane, 3 , 3'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl ether 3,3-diaminodi Phenyl ether, 3,4'-diaminodiphenyl ether, benzidine, 3,3'-diaminobiphenyl, 3,3'-dimethoxybenzidine, 4,4 ''-diamino-p-terphenyl, 3,3 ''-diamino- p-terphenyl, m-phenylenediamine, p-phenylenediamine, 2,6-diaminopyridine, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 4, 4 '-[1,4-phenylenebis (1-methylethylidene)] bisaniline, 4,4'-[1,3-phenylenebis (1-methylethylidene)] bisaniline, bis (p-aminocyclohexyl) methane, bis (p-β-amino-t-butylphenyl) ether, bis (p-β-methyl-δ-aminopentyl) benzene, p-bis (2-methyl-4-aminopentyl) benzene, p-bis (1, 1-dimethyl-5-aminopentyl) benzene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene 2,4-bis (β-amino-t-butyl) toluene, 2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylenediamine, Examples thereof include p-xylylenediamine, 2,6-diaminopyridine, 2,5-diaminopyridine, 2,5-diamino-1,3,4-oxadiazole, piperazine and the like.

  Each of the acid anhydrides and diamines may be used alone or in combination of two or more. Also, diamines and acid anhydrides other than those described above can be used together with the above acid anhydrides or diamines. By selecting the types of acid anhydrides and diamines, and the respective molar ratios when using two or more acid anhydrides or diamines, the thermal expansibility, adhesiveness, glass transition temperature, etc. can be controlled. .

The polyimide insulating layer used in this embodiment preferably has an imide group concentration of 33% or less, and more preferably 32% or less. Here, the “imide group concentration” means a value obtained by dividing the molecular weight of the imide group (— (CO) ₂ —N—) in the polyimide by the molecular weight of the entire structure of the polyimide. When the imide group concentration exceeds 33%, the flame retardancy of the polyimide is lowered and the dielectric properties are also deteriorated due to the increase in polar groups.

  The polyimide insulating layer used in the present embodiment can be produced by reacting a dianhydride component and a diamine component in a solvent to form a precursor resin and then ring-closing with heating. For example, it is a polyimide precursor by dissolving an acid anhydride component and a diamine component in an approximately equimolar amount in an organic solvent and stirring and polymerizing at a temperature in the range of 0 to 100 ° C. for 30 minutes to 24 hours. A polyamic acid is obtained. In the reaction, the reaction components are dissolved so that the precursor to be produced is in the range of 5 to 30% by weight, preferably in the range of 10 to 20% by weight in the organic solvent. Examples of the organic solvent used for the polymerization reaction include N, N-dimethylformamide, N, N-dimethylacetamide (DMAC), N-methyl-2-pyrrolidone, 2-butanone, dimethyl sulfoxide, dimethyl sulfate, cyclohexanone, and dioxane. , Tetrahydrofuran, diglyme, triglyme and the like. Two or more of these solvents can be used in combination, and further, aromatic hydrocarbons such as xylene and toluene can be used in combination. The amount of such organic solvent used is not particularly limited, but the amount used is such that the concentration of the polyamic acid solution (polyimide precursor solution) obtained by the polymerization reaction is about 5 to 30% by weight. It is preferable to adjust and use.

  The synthesized precursor is usually advantageously used as a reaction solvent solution, but can be concentrated, diluted, or replaced with another organic solvent if necessary. Moreover, since a precursor is generally excellent in solvent solubility, it is advantageously used. The method for imidizing the precursor is not particularly limited, and for example, heat treatment such as heating in the solvent at a temperature within the range of 80 to 400 ° C. for 1 to 24 hours is suitably employed.

Since the polyimide insulating layer used in this embodiment has low adhesiveness and low thermal expansion, application as a base resin layer (main layer of an insulating resin layer) in a resin film is suitable. Specifically, the polyimide insulating layer of the present embodiment has a thermal linear expansion coefficient in the range of 1 × 10 ⁻⁶ to 30 × 10 ⁻⁶ (1 / K), preferably 1 × 10 ^{−6 to} 25 × 10. ^{It is in} the range of ⁻⁶ (1 / K), more preferably in the range of 15 × 10 ^{−6 to} 25 × 10 ⁻⁶ (1 / K). Therefore, when the polyimide insulating layer used in this embodiment is applied to the base resin layer, excellent dimensional stability can be obtained.

  On the other hand, the adhesive polyimide layer (A1) used in the present embodiment can contain a thermoplastic polyimide layer exceeding the thermal linear expansion coefficient. Such a polyimide layer is preferably applied as an adhesive layer with a base material such as a metal layer or another resin layer. As the thermoplastic polyimide that can be suitably used as such an adhesive polyimide layer (A1), those having a glass transition temperature of, for example, 330 ° C. or lower are preferable, and those in the range of 200 to 320 ° C. More preferred. By setting the glass transition temperature within such a range, it is possible to suppress a decrease in solder heat resistance, and to secure a sufficient adhesive force even in thermocompression bonding (lamination) with a copper foil, for example.

  Examples of the acid anhydride suitably used for forming the thermoplastic polyimide include pyromellitic anhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4 Examples include '-diphenylsulfonetetracarboxylic dianhydride and 4,4'-oxydiphthalic anhydride. In addition, the acid anhydride mentioned in description of the said polyimide insulating layer can be mentioned. Among these, particularly preferred acid anhydrides include pyromellitic anhydride (PMDA), 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride (BPDA), 3,3', 4,4'- One or more acid anhydrides selected from benzophenone tetracarboxylic dianhydride (BTDA) and 3,3 ′, 4,4′-diphenylsulfone tetracarboxylic dianhydride (DSDA) may be mentioned.

  As an aromatic diamine preferably used for forming a thermoplastic polyimide, from the viewpoint of heat resistance and adhesiveness, those having a phenylene group or a biphenylene group in the molecule, or containing an oxygen element or a sulfur element in the molecule Those having a divalent linking group are preferred, for example, 4,4′-diaminodiphenyl ether, 2′-methoxy-4,4′-diaminobenzanilide, 1,4-bis (4-aminophenoxy) benzene, 1, 3-bis (4-aminophenoxy) benzene, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dihydroxy -4,4'-diaminobiphenyl, 4,4'-diaminobenzanilide and the like. In addition, the diamine mentioned by description of said polyimide insulating layer can be mentioned. Among these, particularly preferred diamine components include aliphatic amines such as dimer acid diamines in which two terminal carboxylic acid groups of dimer acid are substituted with primary aminomethyl groups or amino groups, 1,3-bis ( 4-aminophenoxy) -2,2-dimethylpropane (DANPG), 2,2-bis [4- (4-aminophenoxy) phenyl] propane (BAPP), 1,3-bis (3-aminophenoxy) benzene ( One or more diamines selected from (APB), paraphenylenediamine (p-PDA), 3,4′-diaminodiphenyl ether (DAPE34), and 4,4′-diaminodiphenylether (DAPE44) can be mentioned.

  The polyimide insulating layer including the adhesive polyimide layer (A1) used in this embodiment preferably has a dielectric constant of 2.5 to 3 in measurement at frequencies of 5 GHz, 10 GHz, and 20 GHz using an SPDR resonator. In the range of .8, more preferably in the range of 3.0 to 3.5. The dielectric loss tangent of the polyimide insulating layer is preferably in the range of 0.002 to 0.007, more preferably in the range of 0.003 to 0.005 at any frequency in the above measurement. Is preferred. When the dielectric constant and dielectric loss tangent value of the polyimide insulating layer including the adhesive polyimide layer (A1) exceed the upper limit values, the dielectric characteristics of the entire circuit board are also deteriorated.

  The polyimide insulating layer including the adhesive polyimide layer (A1) may contain an inorganic filler in the polyimide layer as necessary. Specific examples include silicon dioxide, aluminum oxide, magnesium oxide, beryllium oxide, boron nitride, aluminum nitride, silicon nitride, aluminum fluoride, and calcium fluoride. These may be used alone or in combination of two or more.

<Circuit wiring layer>
The circuit wiring layer that is the material of the circuit board of the present embodiment is, for example, a metal laminated on a polyimide insulating layer having an adhesive polyimide layer (A1) on one side or both sides and an adhesive polyimide layer on one side or both sides And a metal-clad laminate having a layer. Preferable specific examples of the metal-clad laminate include, for example, a copper-clad laminate (CCL) in which a copper foil and a polyimide insulating layer are laminated. The material of the copper foil may be a copper alloy.

  From the viewpoint of reducing transmission loss in high-frequency transmission, the surface of the circuit wiring layer that is in contact with the adhesive polyimide layer (A1) is roughened, and the maximum height roughness (Rz) is 1.0 μm or less. It is preferable. The transmission loss is composed of the sum of the conductor loss and the dielectric loss, but if the roughening roughness of the copper foil is large, the conductor loss increases. That is, since the transmission loss is adversely affected, it is necessary to control the roughening roughness.

[Coverlay film]
The coverlay film of the present embodiment includes a base film layer (C1) and an adhesive layer laminated on the base film layer (C1). The total thickness Lc of the coverlay film is preferably 25 μm or more and 70 μm or less, for example, from the viewpoint of improving the dielectric characteristics of the entire circuit board by setting the value of the above formula (i) to less than 0.014. Further, the thickness of the adhesive layer with respect to the thickness Lc of the entire coverlay film is preferably 40% or more in order to develop more excellent dielectric properties. Furthermore, in order to suppress warping of the coverlay film, it is desirable that the elastic modulus of the base film layer (C1) is higher than the elastic modulus of the adhesive layer. Since the adhesive layer has fewer restrictions on the glass transition temperature and the linear thermal expansion coefficient than the base film (C1), it is relatively easy to improve the dielectric properties. For this reason, the adhesive layer exhibits superior dielectric properties compared to the base film layer. Therefore, in order to develop more excellent dielectric properties as a coverlay film, it is necessary to ensure the thickness ratio of the adhesive layer to a certain thickness or more. Further, when the elastic modulus of the base film is lower than the elastic modulus of the adhesive layer, the coverlay film warps due to the influence of the adhesive layer having a large linear thermal expansion coefficient.

  From the viewpoint of improving the dielectric characteristics of the entire circuit board, the coverlay film of the present embodiment has a value of the above formula (i) of less than 0.014, and at frequencies of 5 GHz, 10 GHz, and 20 GHz using an SPDR resonator. In the measurement, the dielectric constant Dkc of the entire coverlay film is preferably in the range of 2.5 to 3.8, more preferably in the range of 2.8 to 3.6, and still more preferably. Is preferably in the range of 2.8 to 3.2.

  Further, the coverlay film of the present embodiment has a value of the above formula (i) less than 0.014, and from the viewpoint of improving the dielectric characteristics of the entire circuit board, 5 GHz, 10 GHz, and 20 GHz using SPDR resonators. In the measurement at frequency, the dielectric loss tangent Dfc as the whole coverlay film is preferably in the range of 0.001 to 0.015, more preferably in the range of 0.002 to 0.005, More preferably, it is in the range of 0.003 to 0.005. In order to improve the dielectric characteristics of the entire circuit board, it is particularly important to control the dielectric loss tangent of the coverlay film. By making the dielectric loss tangent within the above range, the effect of reducing transmission loss increases.

[Base film layer (C1)]
The base film layer (C1) of the coverlay film is preferably excellent in electrical characteristics in a high frequency region, that is, has a low dielectric constant and a low dielectric loss tangent. Specific examples of such a resin material include a resin substrate mainly composed of a liquid crystal polymer (LCP), polytetrafluoroethylene (PTFE), polyimide (PI), polyethylene naphthalate (PEN), and the like. It is done. Moreover, as a base film layer (C1), the thermal expansion coefficient is in the range of 1 × 10 ⁻⁶ to 30 × 10 ⁻⁶ (1 / K), preferably from the viewpoint of suppressing warpage when bonded to FPC. It is preferable to be in the range of 1 × 10 ^{−6 to} 25 × 10 ⁻⁶ (1 / K), more preferably in the range of 15 × 10 ^{−6 to} 25 × 10 ⁻⁶ (1 / K).

  In addition, the base film layer (C1) has a value of the above formula (i) less than 0.014, and from the viewpoint of improving the dielectric characteristics of the entire circuit board, at a frequency of 5 GHz, 10 GHz, and 20 GHz using an SPDR resonator. In the measurement, the dielectric constant is preferably in the range of 2.0 to 4.0, more preferably in the range of 2.5 to 3.8. More preferably, it is in the range of 3.0 to 3.4. The dielectric loss tangent is preferably in the range of 0.015 to 0.015, more preferably in the range of 0.002 to 0.012. More preferably, it is in the range of 0.003 to 0.005. Furthermore, using a base film layer in a more preferable range is the most effective means for improving the dielectric characteristics of the entire circuit board in the present invention.

  Moreover, when using a polyimide resin as a base film layer (C1), you may use the material similar to the said polyimide insulating layer.

  Moreover, a base film layer (C1) may contain an inorganic filler as needed. Specific examples include silicon dioxide, aluminum oxide, magnesium oxide, beryllium oxide, boron nitride, aluminum nitride, silicon nitride, aluminum fluoride, and calcium fluoride. These may be used alone or in combination of two or more.

[Adhesive layer]
The adhesive layer of the coverlay film is preferably excellent in electrical characteristics in the high frequency region, that is, has a low dielectric constant and a low dielectric loss tangent. Specific examples of such a resin material include resin materials mainly composed of liquid crystal polymer (LCP), polytetrafluoroethylene (PTFE), polyimide (PI), polyethylene naphthalate (PEN), and the like. It is done.

  In addition, when polyimide is used as the adhesive layer and the adhesive polyimide layer (C2) is formed, the acid anhydride component and the diamine component are reacted in a solvent to form a precursor resin and then ring-closed by heating. Can be manufactured. For example, a polyimide solution can be obtained by dissolving an acid anhydride component and a diamine component in an organic solvent in an approximately equimolar amount and stirring for 30 minutes to 24 hours at a temperature within a range of 0 to 200 ° C. . In the reaction, the reaction components are dissolved so that the resulting polyimide is in the range of 5 to 50% by weight, preferably in the range of 20 to 40% by weight, in the organic solvent. Examples of the organic solvent used for the polymerization reaction include N, N-dimethylformamide, N, N-dimethylacetamide (DMAC), N-methyl-2-pyrrolidone, 2-butanone, dimethyl sulfoxide, dimethyl sulfate, cyclohexanone, and dioxane. , Tetrahydrofuran, diglyme, triglyme and the like. Two or more of these solvents can be used in combination, and a solvent azeotropic with water such as xylene and toluene may be used.

  3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride (BTDA), 4,4′-oxydiphthalic anhydride (ODPA, also known as an acid anhydride) as a raw acid anhydride for the adhesive polyimide layer (C2) 5,5′-oxybis-1,3-isobenzofurandion), 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA), 3,3 ′, 4,4′-diphenylsulfonetetra Carboxylic dianhydride (DSDA), pyromellitic dianhydride (PMDA), 5,5 '-[1-methyl-1,1-ethanediylbis (1,4-phenylene) bisoxy] bis (isobenzofuran-1, 3-dione) (BISDA), 4,4′-diaminodicyclohexylmethane, and the like can be used. These can be used alone or in combination of two or more.

<Aliphatic diamine>
As the diamine component of the raw material of the adhesive polyimide layer (C2), dimer acid type diamine in which two terminal carboxylic acid groups of dimer acid are substituted with primary aminomethyl group or amino group, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 2-methyl-1,5-diaminopentane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,3-bis (aminomethyl) cyclohexane, Diamino such as 1,4-bis (aminomethyl) cyclohexane, 1,9-diaminononane, 1,10-diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane, 4,4′-methylenebiscyclohexylamine Alkanes, tris (2-aminoethyl) amine, N, N′-bis (2-aminoethyl) -1,3-propanediamine, (3-aminopropyl) ethylenediamine, 1,4-bis (3-aminopropyl) piperazine, diethylenetriamine, N-methyl-2,2′-diaminodiethylamine, 3,3′-diaminodipropylamine, N, N— Amines containing nitrogen atoms such as bis (3-aminopropyl) methylamine, bis (3-aminopropyl) ether, 1,2-bis (2-aminoethoxy) ethane, 3,9-bis (3-amino) Propyl) -2,4,8,10-tetraoxaspiro [5.5] -undecane-containing amines, amines having a sulfur atom such as 2,2′-thiobis (ethylamine), etc. Desirably, the main component is an aliphatic diamine, and these can be used alone or in combination of two or more. Moreover, since the adhesive polyimide layer (C2) has a low dielectric constant and a low dielectric loss tangent and needs to be soluble, the aliphatic diamine is preferably 60 mol% or more based on the total diamine, Preferably it is 80 mol% or more.

<Aromatic diamine>
As a diamine component of the raw material of the adhesive polyimide layer (C2), 4,4′-diamino-2,2′-dimethylbiphenyl, 4,4′-diamino-3,3′-dimethylbiphenyl, 4,4′-diamino -2,2'-bis (trifluoromethyl) biphenyl, 4,4'-diaminodiphenyl ether, 2'-methoxy-4,4'-diaminobenzanilide, 1,4-bis (4-aminophenoxy) benzene, 1 , 3-Bis (4-aminophenoxy) benzene, 2,2'-bis [4- (4-aminophenoxy) phenyl] propane, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3 '-Dihydroxy-4,4'-diaminobiphenyl,4,4'-diaminobenzanilide, 2,2-bis- [4- (3-aminophenoxy) phenyl] propane, bis [4- (4-aminophenoxy) phenyl ] Sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, bis [4- (4-amido] Nophenoxy)] biphenyl, bis [4- (3-aminophenoxy) biphenyl, bis [1- (4-aminophenoxy)] biphenyl, bis [1- (3-aminophenoxy)] biphenyl, bis [4- (4 -Aminophenoxy) phenyl] methane, bis [4- (3-aminophenoxy) phenyl] methane, bis [4- (4-aminophenoxy) phenyl] ether, bis [4- (3-aminophenoxy) phenyl] ether, Bis [4- (4-aminophenoxy)] benzophenone, bis [4- (3-aminophenoxy)] benzophenone, bis [4,4 ′-(4-aminophenoxy)] benzanilide, bis [4,4 ′-( 3-aminophenoxy)] benzanilide, 9,9-bis [4- (4-aminophenoxy) phenyl] fluorene, 9,9-bis [4- (3-aminophenoxy) phenyl] fluorene, 2,2-bis- [4- (4-aminophen Noxy) phenyl] hexafluoropropane, 2,2-bis- [4- (3-aminophenoxy) phenyl] hexafluoropropane, 4,4'-methylenedi-o-toluidine, 4,4'-methylenedi-2,6 -Xylidine, 4,4'-methylene-2,6-diethylaniline, 4,4'-diaminodiphenylpropane, 3,3'-diaminodiphenylpropane, 4,4'-diaminodiphenylethane, 3,3'-diamino Diphenylethane, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,3 ' -Diaminodiphenyl sulfone, 4,4'-diaminodiphenyl ether, 3,3-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, benzidine, 3,3'-diaminobiphenyl, 3,3'-dimethoxybenzidine, 4,4 ''- Amino-p-terphenyl, 3,3 ″ -diamino-p-terphenyl, m-phenylenediamine, p-phenylenediamine, 2,6-diaminopyridine, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 4,4 '-[1,4-phenylenebis (1-methylethylidene)] bisaniline, 4,4'-[1,3-phenylenebis (1-methyl) Ethylidene)] bisaniline, bis (p-aminocyclohexyl) methane, bis (p-β-amino-t-butylphenyl) ether, bis (p-β-methyl-δ-aminopentyl) benzene, p-bis (2- Methyl-4-aminopentyl) benzene, p-bis (1,1-dimethyl-5-aminopentyl) benzene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,4-bis (β-amino- t-butyl) toluene, 2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylene diene Aromatic diamines such as amines, p-xylylenediamine, 2,6-diaminopyridine, 2,5-diaminopyridine, 2,5-diamino-1,3,4-oxadiazole, piperazine, etc. Can be used alone or in combination of two or more. Moreover, you may combine with aliphatic diamine. Moreover, since the polyimide which comprises an adhesive polyimide layer (C2) has a low dielectric constant and a low dielectric loss tangent and needs to be soluble, it is not preferable that the aromatic diamine ratio becomes high. For this reason, the aliphatic diamine is preferably less than 40 mol%, more preferably less than 20 mol%, based on the total diamine.

  The resin constituting the adhesive polyimide layer (C2) has a value of the above formula (i) of less than 0.014, and from the viewpoint of improving the dielectric characteristics of the entire circuit board, 5 GHz, 10 GHz and 20 GHz using an SPDR resonator. In the measurement at the frequency, the dielectric constant is preferably in the range of 2.0 to 3.0, more preferably in the range of 2.3 to 2.8.

  The resin constituting the adhesive polyimide layer (C2) is 5 GHz, 10 GHz using an SPDR resonator from the viewpoint of improving the dielectric characteristics of the entire circuit board by setting the value of the above formula (i) to less than 0.014. And the measurement at a frequency of 20 GHz, the dielectric loss tangent is preferably in the range of 0.001 to 0.005, and more preferably in the range of 0.002 to 0.004. In order to improve the dielectric characteristics of the entire circuit board, it is particularly important to control the dielectric loss tangent of the adhesive polyimide layer (C2). By setting the dielectric loss tangent within the above range, the effect of reducing transmission loss can be obtained. Increase.

  In addition to the polyimide resin, the resin constituting the adhesive polyimide layer (C2) includes, as an optional component, other curing resin components such as a plasticizer and an epoxy resin, a curing agent, a curing accelerator, an inorganic filler, and a coupling agent. In addition, fillers, pigments, solvents, flame retardants, and the like can be appropriately blended. However, some plasticizers contain a large number of polar groups, and there is a concern that this may promote the diffusion of copper from the copper wiring. Therefore, it is preferable not to use the plasticizer as much as possible.

  The polyimide obtained as described above has excellent flexibility and thermoplasticity when the adhesive polyimide layer (C2) is formed using the polyimide. For example, a wiring portion such as an FPC or a rigid flex circuit board. It has preferable characteristics as an adhesive layer for a coverlay film that protects the film. When used as an adhesive layer of a cover lay film, the adhesive resin composition is applied to one side of the base film layer (C1) in a solution state (for example, a varnish containing a solvent), and then, for example, 60 to 220 ° C. A coverlay film having a base film layer (C1) and an adhesive polyimide layer (C2) can be formed by thermocompression bonding at a temperature of. When a resin component such as a crosslinking agent or an epoxy resin is contained, the crosslinking reaction or the curing reaction of the thermosetting resin can be advanced using the heat during thermocompression bonding. Moreover, even when heat condensation at the time of thermocompression bonding is not sufficient, heat treatment can be further performed after thermocompression bonding for heat condensation. When heat treatment is performed after thermocompression bonding, the heat treatment temperature is preferably, for example, 60 to 220 ° C, and more preferably 80 to 200 ° C. Further, the adhesive resin composition is applied on an arbitrary substrate in a solution state (for example, a varnish containing a solvent), dried at a temperature of, for example, 80 to 180 ° C., and then peeled to adhere. A base film layer (C1) and an adhesive polyimide layer are also formed by forming an adhesive film and thermocompression bonding the adhesive film with the film material to be the base film layer (C1) at a temperature of, for example, 60 to 220 ° C. (C2) can be formed. The adhesive resin layer resin can also be used by forming a coating film in a solution state by screen printing on an arbitrary substrate and drying it at a temperature of 80 to 180 ° C., for example. Preferably, a cured product can be formed by further heat-treating at a temperature of 130 to 220 ° C. for a predetermined time to completely cure the coating film.

  Moreover, a coverlay film is good also as a form which pastes a release material on the adhesive surface and has a release material layer. The material of the release material is not particularly limited as long as it can be peeled without impairing the shape of the coverlay film. For example, resin films such as polyethylene terephthalate, polyethylene, and polypropylene, and these resin films on paper A laminate or the like can be used.

  Since the coverlay film of the present embodiment has excellent flexibility and thermoplasticity, for example, when used as an FPC coverlay film, the adhesive layer is filled between the wirings, and the coverlay film and the wiring layer High adhesion is obtained.

<Printed wiring board>
The printed wiring board used for the circuit board of the present invention can be manufactured, for example, by forming a wiring layer by processing a copper foil of a copper-clad laminate into a pattern by a conventional method.

  Hereinafter, a preferred method for producing a printed wiring board will be specifically described by taking the case of a cast method as an example.

  First, the manufacturing method of a copper clad laminated board can include the following processes (1)-(3).

Step (1):
Step (1) is a step of obtaining a polyamic acid resin solution which is a polyimide precursor.

Step (2):
Step (2) is a step of applying a polyamic acid resin solution on the copper foil to form a coating film. The copper foil can be used in the form of a cut sheet, a roll, or an endless belt. In order to obtain productivity, it is efficient to use a roll-like or endless belt-like form so that continuous production is possible. Furthermore, the copper foil is preferably in the form of a roll that is formed in a long length from the viewpoint of more greatly improving the effect of improving the wiring pattern accuracy in the printed wiring board.

  The coating film can be formed by applying a polyamic acid resin solution directly on a copper foil and then drying. The method of applying is not particularly limited, and it is possible to apply with a coater such as a comma, die, knife, lip or the like.

  The polyimide insulating layer may be a single layer or a plurality of layers. In the case where a plurality of polyimide insulating layers are used, other precursors can be sequentially formed on the precursor layers made of different components. When the precursor layer is composed of three or more layers, the precursor having the same configuration may be used twice or more. A two-layer or a single layer having a simple layer structure is preferable because it can be advantageously obtained industrially. The thickness of the precursor layer (after drying) is, for example, in the range of 30 to 120 μm, preferably in the range of 20 to 85 μm.

  When making a polyimide insulating layer into multiple layers, it is preferable to form a layer of a precursor so that the polyimide insulating layer which touches copper foil may become the adhesive polyimide layer (A1) which consists of thermoplastic polyimide. By using thermoplastic polyimide, the adhesion to the copper foil can be improved. Such a thermoplastic polyimide preferably has a glass transition temperature (Tg) of 330 ° C. or lower, more preferably 200 to 320 ° C.

  It is also possible to imidize a single layer or a plurality of precursor layers once to form a single layer or a plurality of polyimide insulating layers, and further form a precursor layer thereon.

Step (3):
Step (3) is a step of forming a polyimide insulating layer having the above-mentioned dielectric characteristics by heat-treating the coating film to imidize. The imidization method is not particularly limited, and for example, heat treatment such as heating for 1 to 60 minutes under a temperature condition in the range of 80 to 400 ° C. is suitably employed. In order to suppress the oxidation of the metal layer, heat treatment in a low oxygen atmosphere is preferable. Specifically, the heat treatment is performed in an inert gas atmosphere such as nitrogen or a rare gas, in a reducing gas atmosphere such as hydrogen, or in a vacuum. Is preferred. By the heat treatment, the polyamic acid in the coating film is imidized to form polyimide.

  As described above, a copper-clad laminate having the above polyimide insulating layer and copper foil can be produced.

  Moreover, the manufacturing method of a printed wiring board can include the following processes (4) in addition to the processes (1) to (3).

Step (4):
Step (4) is a step of forming a wiring layer by patterning the copper foil of the copper clad laminate. In this step, a copper foil is etched into a predetermined shape to form a pattern, and a printed wiring board is obtained by processing into a wiring layer. Etching can be performed by any method using, for example, photolithography.

  In the above description, only the characteristic steps of the printed wiring board manufacturing method have been described. That is, when manufacturing a printed wiring board, processes other than the above normally performed, for example, processes such as through-hole processing in the previous process, terminal plating in the subsequent process, and external processing can be performed according to a conventional method.

  As described above, a copper-clad laminate having excellent impedance matching can be formed by using the polyimide insulating layer and copper foil described above. In addition, by using the above-described polyimide insulating layer and copper foil, it is possible to improve electrical signal transmission characteristics and improve reliability in a circuit board typified by FPC.

<Circuit board>
The circuit board is manufactured by bonding the circuit wiring layer of the printed wiring board and the coverlay film by thermocompression bonding. Although it does not specifically limit about heating temperature and the pressure at the time of crimping | compression, From a viewpoint of the filling property and adhesiveness of the adhesive layer of the coverlay film to wiring, 150 to 200 degreeC is preferable, and heating temperature is 160 to 180 degreeC. It is more preferable that If the temperature of thermocompression bonding is below the above range, the filling property and adhesion may be reduced, and if it exceeds the above temperature, the production equipment is limited. Moreover, about the pressure at the time of thermocompression bonding, it is preferable to exist in the range of 0.5 Mpa-3.0 MPa, for example, and the inside of the range of 1.0 MPa-2.0 MPa is more preferable.

  Since the circuit board of the present invention enhances the adhesion between the polyimide insulating layer and the coverlay film, the difference between the imide group concentration in the adhesive polyimide layer (A1) and the imide group concentration in the adhesive polyimide layer (C2) ( (A1 imide group concentration-C2 imide group concentration) is preferably small, and is preferably within 7% by weight.

  The circuit board of the present embodiment may include a circuit wiring layer on one surface of the polyimide insulating layer of the circuit wiring layer, and further include a ground conductor layer on the other surface. In this case, from the viewpoint of reducing transmission loss in high-frequency transmission, the surface of the ground conductor layer in contact with the adhesive polyimide layer (A1) is roughened, and the maximum height roughness (Rz) is 1. It is preferably 0 μm or less.

  The features of the present invention will be described more specifically with reference to examples. However, the scope of the present invention is not limited to the examples. In the following examples, various measurements and evaluations are as follows unless otherwise specified.

[Calculation of imide group concentration]
The imide group concentration was a value obtained by dividing the molecular weight of the imide group part (— (CO) ₂ —N—) by the molecular weight of the entire structure of the polyimide.

[Measurement of peel strength]
Peel strength was measured using a Tensilon tester (trade name: Strograph VE-10, manufactured by Toyo Seiki Seisakusho Co., Ltd.) and a 1 mm wide sample (a laminate comprising a coverlay film / insulating resin layer / copper foil). The layer side is fixed to an aluminum plate with double-sided tape, and the force required to peel the insulating resin layer / copper foil from the coverlay film and the insulating resin layer / copper foil at a speed of 50 mm / min in the 180 ° direction is obtained. It was.

[Measurement of dielectric constant and dissipation factor]
The dielectric constant and dielectric loss tangent are measured using a cavity resonator perturbation method dielectric constant evaluation apparatus (manufactured by Agilent, trade name: Vector Network Analyzer E8363C) and an SPDR resonator, and a resin sheet (cured resin sheet) at a predetermined frequency. The dielectric constant and dielectric loss tangent of were measured. In addition, the resin sheet used for the measurement was left for 24 hours under the conditions of temperature; 24-26 ° C., humidity: 45-55%.

[Measurement of surface roughness of copper foil]
Using a stylus type surface roughness meter (trade name: Surfcorder ET-3000, manufactured by Kosaka Laboratory Ltd.), the measurement was performed under the following measurement conditions: Force: 100 μN, Speed: 20 μm, Range: 800 μm. The surface roughness was calculated by a method based on JIS-B0601-2001.

[Measurement of transmission loss]
The transmission characteristics are evaluated by using a sample of a microstrip line that has been processed with a copper-clad laminate and a characteristic impedance of 50Ω, and a coverlay is thermocompression bonded to the circuit processed side (transmission line side). A sample was used. Evaluation was performed at S21 (insertion loss) by measuring S parameters in a predetermined frequency region with a vector network analyzer calibrated by the SOLT method (SHORT-OPEN-LOOD-Thru). In addition, the evaluation sample used for the measurement was left for 24 hours under the conditions of temperature; 24-26 ° C., humidity: 45-55%.

Abbreviations used in Examples and Comparative Examples indicate the following compounds.
(A) Polyimide insulating layer raw material BTDA: 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride BPDA: 3,3 ′, 4,4′-diphenyltetracarboxylic dianhydride PMDA: pyromerit Acid dianhydride m-TB: 2,2′-dimethyl-4,4′-diaminobiphenyl BAPP: 2,2-bis [4- (4-aminophenoxy) phenyl] propane DDA: aliphatic diamine having 36 carbon atoms (Croda Japan Co., Ltd., trade name: PRIAMINE 1074, amine value: 210 mg KOH / g, mixture of cyclic and chain-structured dimer diamine, content of dimer component: 95% by weight or more)
N-12: dodecanedioic acid dihydrazide DMAc: N, N-dimethylacetamide K-1: talc, manufactured by Nippon Talc Co., Ltd., shape; scaly, average particle size: 6.6 μm

(B) Copper foil Copper foil (1): Electrolytic copper foil, thickness: 12 μm, surface roughness Rz on the polyimide insulating layer side: 0.9 μm

(C) Coverlay film Coverlay film (1): material: polyimide, thickness: 12.5 μm, adhesive layer (material: epoxy resin, thickness: 15 μm)
Coverlay film (2): material: polyimide, thickness: 12.5 μm, adhesive layer (material: epoxy resin, thickness: 25 μm)

<Resin synthesis for polyimide insulation layer>
In forming the polyimide insulating layer used in the examples, the synthesis of the polyamic acid used is based on the following synthesis examples 1 to 6.

Synthesis example 1
Under a nitrogen stream, a 500 ml separable flask was charged with 5.06 g DDA (0.0095 mol), 18.12 g m-TB (0.085 mol) and 255 g DMAc and stirred at room temperature. Dissolved. Next, 5.50 g of BPDA (0.019 mol) and 16.31 g of PMDA (0.075 mol) were added, and the polymerization reaction was continued for 3 hours at room temperature to obtain a polyamic acid solution a. It was. The polyamic acid solution a had a solid content concentration of 15% by weight and a solution viscosity of 29,600 cps.

Synthesis Examples 2-6
Polyamic acid solutions b to f were prepared in the same manner as in Synthesis Example 1 except that the raw material composition shown in Table 1 was used.

<Resin synthesis for adhesive layer of coverlay film>
In the formation of the adhesive polyimide layer of the coverlay film used in the examples, the synthesis of the polyamic acid used is based on the following Synthesis Examples 7-9.

Synthesis example 7
Under a nitrogen stream, a 500 ml separable flask was charged with 44.98 g BTDA (0.139 mol), 75.02 g DDA (0.140 mol), 168 g N-methyl-2-pyrrolidone and 112 g xylene. The mixture was charged and mixed well at 40 ° C. for 30 minutes to obtain a polyamic acid solution. This polyamic acid solution was heated to 190 ° C., heated and stirred for 4.5 hours, and 112 g of xylene was added to obtain a polyimide adhesive solution g in which imidization was completed. The obtained polyimide adhesive solution g had a solid content of 29.1% by weight and a viscosity of 7,800 cps. Moreover, the weight average molecular weight (Mw) of the polyimide adhesive solution g was 87,700.

Synthesis Example 8
34.4 g (10 g as a solid content) of the polyimide adhesive solution b obtained in Synthesis Example 7, 0.7 g of N-12 and 5.0 g of K-1 were blended, and 1.297 g of N-methyl- 2-Pyrrolidone and 3.869 g of xylene were added and diluted to obtain a polyimide adhesive solution h.

Synthesis Example 9
34.4 g (10 g as a solid content) of the polyimide adhesive solution g obtained in Synthesis Example 7 and 1.25 g of N-12 and 2.5 g of Exolit OP935 (manufactured by Clariant Japan Co., Ltd.) are blended. 297 g of N-methyl-2-pyrrolidone and 3.869 g of xylene were added and diluted to obtain a polyimide adhesive solution i.

<Production of circuit board>
The circuit boards used in Examples and Comparative Examples are manufactured according to the following Preparation Examples 1 to 3.

[Production Example 1]
The polyamic acid solution d was uniformly applied to the copper foil (1) so that the thickness after curing was about 2 to 4 μm, and then the solvent was removed by stepwise heat treatment from 85 ° C. to 110 ° C. Next, the polyamic acid solution a was uniformly applied thereon so that the thickness after curing was about 42 to 46 μm, and the solvent was removed by stepwise heat treatment from 85 ° C. to 110 ° C. Furthermore, after the polyamic acid composition d was uniformly applied thereon so that the thickness after curing was about 2 to 4 μm, the solvent was removed by a stepwise heat treatment from 85 ° C. to 110 ° C. After forming the three polyamic acid layers in this way, stepwise heat treatment was performed from 120 ° C. to 360 ° C. to complete imidization, and a metal-clad laminate 1 ′ was obtained. Copper foil (1) was superimposed on the resin layer side of the obtained metal-clad laminate 1 ′, and thermocompression bonded for 15 minutes under the conditions of a temperature of 340 ° C. and a pressure of 6.7 MPa, to obtain a metal-clad laminate 1 . About the obtained metal-clad laminated body 1, the wiring process of the predetermined pattern was formed with respect to the single side | surface of copper foil using the ferric chloride aqueous solution, and the circuit wiring board 1 was obtained.

[Production Example 2]
A circuit wiring board 2 is obtained in the same manner as in Production Example 1, except that the polyamic acid solution e is used instead of the polyamic acid solution d, and the polyamic acid solution b is used instead of the polyamic acid solution a. It was.

[Production Example 3]
A circuit wiring board 3 is obtained in the same manner as in Production Example 1 except that the polyamic acid solution f is used instead of the polyamic acid solution d and the polyamic acid solution c is used instead of the polyamic acid solution a. It was.

<Production of coverlay film>
The production of the coverlay film used in the examples is based on the following Production Examples 4 to 6.

[Production Example 4]
Polyimide film (manufactured by Toray DuPont, trade name; Kapton 100 ENS, length × width × thickness = 320 mm × 240 mm ×) so that the thickness after drying the polyimide adhesive solution h obtained in Synthesis Example 8 is about 25 μm 25 μm) and then dried by heating at 80 ° C. for 15 minutes. Furthermore, the coverlay film 1 was obtained by performing a heat treatment at 180 ° C. for 2 hours to completely remove the solvent.

[Production Example 5]
A coverlay film 2 was obtained in the same manner as in Production Example 4 except that the polyimide adhesive solution i obtained in Synthesis Example 9 was used and that the thickness after drying was about 30 μm.

[Production Example 6]
A coverlay film 3 was obtained in the same manner as in Production Example 4 except that the polyimide adhesive solution i obtained in Synthesis Example 9 was used.

  After uniformly applying the polyamic acid solution b obtained in Synthesis Example 2 to one surface (surface roughness Rz; 0.9 μm) of an electrolytic copper foil having a thickness of 12 μm so that the thickness after curing is about 25 μm, The solvent was removed by heat drying at 120 ° C. Furthermore, stepwise heat treatment was performed from 120 ° C. to 360 ° C. to complete imidization. About the obtained metal-clad laminate, the thickness after drying the polyimide adhesive solution i obtained in Synthesis Example 9 was about 25 μm on the film where the copper foil was etched away using an aqueous ferric chloride solution. Then, the coating was dried at 80 ° C. for 15 minutes. Further, a heat treatment was performed at 180 ° C. for 2 hours to completely remove the solvent, thereby obtaining a coverlay film 4.

[Example 1]
After being laminated so that the adhesive polyimide layer of the coverlay film 1 was in contact with the wiring of the circuit wiring board 1, the circuit board 1 was produced by pressure-bonding at 180 ° C. for 2 hours under a pressure of 2 MPa.

[Examples 2-4] and [Comparative Examples 1-2]
Circuit boards 2 to 6 were produced in the same manner as in Example 1 except that the types of the circuit wiring board and the coverlay film were combinations shown in Tables 2 and 4. In addition, the coverlay film 5 in Table 4 means a coverlay film (1), and the coverlay film 6 means a coverlay film (2).

  The results of Examples 1 to 4 and Comparative Examples 1 and 2 are collectively shown in Tables 2 to 5, respectively. The “difference in imide group concentration” in the table means the difference between the imide group concentration in the adhesive polyimide layer (A1) and the imide group concentration in the adhesive polyimide layer (C2).

  As mentioned above, although embodiment of this invention was described in detail for the purpose of illustration, this invention is not restrict | limited to the said embodiment.

Claims (5)

A polyimide insulation layer;
A circuit wiring layer laminated on at least one surface of the polyimide insulating layer;
A coverlay film laminated on the circuit wiring layer;
A circuit board comprising:
Configurations a to c below:
a) The thickness La of the polyimide insulating layer is in the range of 12 to 50 μm;
b) The thickness Lc of the coverlay film is in the range of 25 to 70 μm;
c) When the dielectric constant of the polyimide insulating layer is Dka, the dielectric loss tangent is Dfa, and the thickness is La, and the dielectric constant of the coverlay film is Dkc, the dielectric loss tangent is Dfc, and the thickness is Lc,
The following formula (i);
{(√Dka) × Dfa × La + (√Dkc) × Dfc × Lc} / (La + Lc) (i)
When the value calculated by the split post dielectric resonator (SPDR) is measured at a frequency of 5 GHz, 10 GHz, and 20 GHz, both are less than 0.014 (however, any of 5 GHz, 10 GHz, and 20 GHz) Also at a frequency of Dka within the range of 3.0 to 3.5) ;
A circuit board comprising: The polyimide insulating layer has an adhesive polyimide layer (A1) in contact with the circuit wiring layer,
The coverlay film is composed of a base film layer (C1) and an adhesive polyimide layer (C2),
The difference between the imide group concentration in the adhesive polyimide layer (A1) and the imide group concentration in the adhesive polyimide layer (C2) (the imide group concentration of A1−the imide group concentration of C2) is within ± 7% by weight. The circuit board according to claim 1. The circuit board according to claim 1 or 2, wherein the coverlay film is composed of a base film layer (C1) and an adhesive polyimide layer (C2), and the base film layer (C1) is composed of polyimide.   The circuit board according to claim 1, wherein the circuit wiring layer is provided on one surface of the polyimide insulating layer, and a ground conductor layer is further provided on the other surface. The circuit board according to claim 4, wherein the maximum height roughness (Rz) of the circuit wiring layer and the ground conductor layer on the side in contact with the polyimide insulating layer is 1.0 μm or less.