Low dielectric substrate material and manufacturing method thereof

Abstract

A low dielectric substrate material (1) is provided with a metal layer (2) and a porous polyimide layer (3) in this order on one side in the thickness direction. The peel strength of the low dielectric substrate material (1) in an agglomeration failure mode in which the porous polyimide layer (3) is agglomerated and broken is 0.4 N / mm or more.

Description

Technical Field

[0001] The present invention relates to a low dielectric substrate material and a method for manufacturing the same. Background Art

[0002] There is known a low dielectric substrate material having a metal layer and a porous polyimide layer (for example, refer to Patent Document 1 below).

[0003] Patent Document 1 proposes the following manufacturing method: A varnish containing a polyimide precursor, a porogen, a nucleating agent, and a solvent is applied to one surface of the metal layer and heated to dry it, thereby forming a coating film. Then, the porogen is extracted, and the polyimide precursor is heated and cured. In Examples 1 and 2 of Patent Document 1, the varnish was heated at 120°C for 30 minutes to form a coating film.

[0004] Prior Art Documents Patent Documents Patent Document 1: Japanese Unexamined Patent Application Publication No. 2019-123851 Summary of the Invention Problems to be Solved by the Invention Higher peel strength is required for the low dielectric substrate material. The peel strength is the peel strength measured in a cohesive failure mode in which the porous polyimide layer is cohesively damaged.

[0005] The present invention provides a low dielectric substrate material having high peel strength and a method for manufacturing the same.

[0006] Technical Means for Solving the Problems The present invention [1] includes a low dielectric substrate material, wherein the low dielectric substrate material sequentially includes a metal layer and a porous polyimide layer on one side in the thickness direction, and the peel strength of the low dielectric substrate material in a cohesive failure mode in which the porous polyimide layer is cohesively damaged is 0.4 N / mm or more.

[0007] The present invention [2] includes the low dielectric substrate material according to [1], wherein the porosity of the porous polyimide layer is 60% or more and 95% or less.

[0008] The present invention [3] includes the low dielectric substrate material according to [1] or [2], wherein the low dielectric substrate material further includes a non-porous polyimide layer, and the non-porous polyimide layer is disposed between the metal layer and the porous polyimide layer.

[0009] The present invention [4] includes the low dielectric substrate material according to [3], wherein the peel strength is 0.5 N / mm or more.

[0010] The present invention [5] includes a method for manufacturing a low-dielectric substrate material, which is the method for manufacturing the low-dielectric substrate material described in [1] or [2], and includes: Step (1) of coating a varnish containing a polyimide precursor, a porogen, a nucleating agent, and a solvent on one surface in the thickness direction of a metal layer and heating it to dry it, thereby forming a coating film, wherein the imidization rate of the coating film obtained by the following measurement method is 0.30 or more and 0.45 or less, and the residual ratio of the solvent is 6% by mass or more and 19% by mass or less to form the coating film; Step (2) of extracting at least a part of the porogen from the coating film; and Step (3) of heating the coating film to cure it, thereby forming a porous polyimide layer.

[0011] Measurement method: In infrared absorption spectrometry, measure the imidization intensity ratio at 1773 cm -1 and 3064 cm -1 of the coating film; measure the imidization intensity ratio of the completely cured body obtained by heating the coating film at 420 °C; calculate the ratio of the imidization intensity ratio of the coating film to the imidization intensity ratio of the completely cured body as the imidization rate.

[0012] The present invention [6] includes the method for manufacturing a low-dielectric substrate material described in [5], wherein Step (1) includes: a first heating step of heating the varnish at a first temperature; and a second heating step of heating the varnish at a second temperature higher than the first temperature after the first heating step.

[0013] The present invention [7] includes the method for manufacturing a low-dielectric substrate material described in [6], wherein Step (1) further includes a third heating step of heating the varnish at a third temperature higher than the second temperature after the second heating step, the temperature in the first heating step is 80 °C or more and less than 110 °C, the temperature in the second heating step is 110 °C or more and less than 130 °C, and the temperature in the third heating step is 130 °C or more and less than 150 °C.

[0014] The present invention [8] includes a method for manufacturing a low-dielectric substrate material, which is the method for manufacturing the low-dielectric substrate material described in [3] or [4], and includes: step (4) of coating a varnish containing a polyimide precursor and a solvent on one surface in the thickness direction of a metal layer and heating it to dry, thereby forming a first coating film, wherein the first coating film is formed such that the imidization rate of the first coating film obtained by the following measurement method is 0.60 or more; step (5) of coating a varnish containing a polyimide precursor, a pore-forming agent, a nucleating agent, and a solvent on one surface in the thickness direction of the first coating film and heating it to dry, thereby forming a second coating film; step (6) of extracting at least a part of the pore-forming agent in the second coating film; and step (7) of heating the first coating film and the second coating film to cure them, thereby forming a non-porous polyimide layer and a porous polyimide layer.

[0015] Measurement method: In infrared absorption spectrometry, measure the imidization intensity ratio of 1773 cm -1 and 3064 cm -1 of the first coating film; measure the imidization intensity ratio of the completely cured body obtained by heating the first coating film at 420 °C; calculate the ratio of the imidization intensity ratio of the first coating film to the imidization intensity ratio of the completely cured body as the imidization rate.

[0016] The present invention [9] includes the method for manufacturing a low-dielectric substrate material described in [8], wherein in the step (4), the first coating film is heated to 130 °C or higher.

[0017] Advantages of the Invention The method for manufacturing a low-dielectric substrate material of the present invention and the low-dielectric substrate material manufactured thereby have high peel strength. Brief Description of the Drawings

[0018] Figure 1 is a cross-sectional view of a first embodiment of the low-dielectric substrate material of the present invention.

[0019] Figure 2 is Figure 1 step (1) included in the method for manufacturing the low-dielectric substrate material shown.

[0020] Figure 3 is a cross-sectional view of a second embodiment of the low-dielectric substrate material of the present invention.

[0021] Figure 4A and Figure 4B is Figure 3 a manufacturing process diagram of the method for manufacturing the low-dielectric substrate material shown. Figure 4A is step (5). Figure 4B is step (6).

[0022] Figure 5 It is a cross-sectional view of a flexible multi-layer circuit board using the low-dielectric substrate material of the present invention. Detailed implementation manners

[0023] 1. First implementation manner Refer to Figure 1 to describe the first implementation manner of the low-dielectric substrate material of the present invention.

[0024] As Figure 1 shown, the low-dielectric substrate material 1 has a thickness. The low-dielectric substrate material 1 extends in the plane direction. The plane direction is orthogonal to the thickness direction. The low-dielectric substrate material 1 has a film shape. The low-dielectric substrate material 1 has flexibility. The thickness of the low-dielectric substrate material 1 is, for example, 5 μm or more and, for example, 2000 μm or less.

[0025] 1.1 Layer structure of the low-dielectric substrate material 1 The low-dielectric substrate material 1 sequentially includes a metal layer 2 and a porous polyimide layer 3 on one side in the thickness direction. The low-dielectric substrate material 1 may further include a polyimide surface layer 4 represented by a phantom line. In this case, the low-dielectric substrate material 1 sequentially includes a metal layer 2, a porous polyimide layer 3, and a polyimide surface layer 4 on one side in the thickness direction.

[0026] 1.2 Metal layer 2 The metal layer 2 is disposed at the other end in the thickness direction of the low-dielectric substrate material 1. The metal layer 2 has a thickness. The metal layer 2 extends in the plane direction. Specifically, the metal layer 2 is a metal foil. As the metal, for example, copper, iron, silver, gold, aluminum, nickel, and their alloys (stainless steel, bronze) can be cited. As the metal, copper is preferably cited. The thickness of the metal layer 2 is, for example, 0.1 μm or more, preferably 1 μm or more, and, for example, 100 μm or less, preferably 50 μm or less.

[0027] 1.3 Porous polyimide layer 3 The porous polyimide layer 3 is disposed on one surface of the metal layer 2 in the thickness direction. The porous polyimide layer 3 is in contact with one surface of the metal layer 2 in the thickness direction. The porous polyimide layer 3 has a thickness. The porous polyimide layer 3 extends in the plane direction. The porous polyimide layer 3 has an independent bubble structure and / or a continuous bubble structure.

[0028] The porosity of the porous polyimide layer 3 is, for example, 60% or more, preferably 70% or more, more preferably 75% or more. In addition, the porosity of the porous polyimide layer 3 is, for example, 95% or less, preferably 90% or less, more preferably 85% or less. The porosity of the porous polyimide layer 3 is obtained by the following formula.

[0029] Porosity (%) = (1 - specific gravity of the porous polyimide layer 3 / specific gravity of polyimide) × 100 The dielectric constant of the porous polyimide layer 3 at a frequency of 10 GHz is, for example, 2.10 or less, preferably 1.80 or less, and, for example, 1.55 or more. The dielectric constant of the porous polyimide layer 3 is measured by the resonator method.

[0030] The thickness of the porous polyimide layer 3 is, for example, 10 μm or more, and, for example, 500 μm or less, preferably 150 μm or less.

[0031] 1.4 Polyimide surface layer 4 The polyimide surface layer 4 is disposed on one surface of the porous polyimide layer 3 in the thickness direction. The polyimide surface layer 4 is in contact with one surface of the porous polyimide layer 3 in the thickness direction. The polyimide surface layer 4 has a thickness. The polyimide surface layer 4 extends in the plane direction. For example, the polyimide surface layer 4 is a non-porous layer (a solid dense film). The thickness of the polyimide surface layer 4 is, for example, 1 μm or more, and, for example, 50 μm or less. The porosity of the polyimide surface layer 4 is, for example, 0.1% or less, further 0%.

[0032] 1.5 Peel strength of the low-dielectric substrate material 1 The peel strength of the low-dielectric substrate material 1 in the cohesive failure mode in which the porous polyimide layer 3 is cohesively damaged is 0.4 N / mm or more.

[0033] If the peel strength of the low-dielectric substrate material 1 is less than 0.4 N / mm, the peel strength is significantly low.

[0034] The peel strength of the above-mentioned low-dielectric substrate material 1 is preferably 0.41 N / mm or more, more preferably 0.42 N / mm or more.

[0035] There is no limitation on the upper limit of the peel strength of the low-dielectric substrate material 1. The upper limit of the peel strength of the low-dielectric substrate material 1 is, for example, 5.0 N / mm, further 2.0 N / mm.

[0036] The peel strength of the low-dielectric substrate material 1 is measured by a 90-degree peel test at a peeling speed of 50 mm / minute. The detailed measurement method of the peel strength of the low-dielectric substrate material 1 is described in the following examples.

[0037] 1.6 Manufacturing method of the low-dielectric substrate material 1 Refer to Figure 1 and Figure 2 , the manufacturing method of the low-dielectric substrate material 1 of the first embodiment will be described.

[0038] The manufacturing method of the low dielectric substrate material 1 includes process (1), process (2), and process (3). Process (1), process (2), and process (3) are implemented in sequence.

[0039] 1.6.1 Process (1) As Figure 2 shown, in process (1), the varnish described below is coated on one surface of the metal layer 2 in the thickness direction and heated to dry it, thereby forming a coating film 3C. In addition, in process (1), the coating film 3C is formed such that the imidization rate of the coating film 3C is 0.30 or more and 0.45 or less, and the residual ratio of the solvent is 6% by mass or more and 19% by mass or less.

[0040] Measurement method: In infrared absorption spectrometry, the imidization intensity ratio of 1773 cm -1 and 3064 cm -1 of the coating film 3C is measured. The above imidization intensity ratio of the completely cured body obtained by heating the coating film 3C at 420 °C is measured. The ratio of the imidization intensity ratio of the coating film 3C to the imidization intensity ratio of the completely cured body is calculated as the imidization rate.

[0041] If the imidization rate of the coating film 3C is 0.30 or more and 0.45 or less, the imidization rate is controlled and the porogen becomes easy to be extracted. That is, since the polyimide resin is not cured, the remaining amount of the porogen becomes less. Therefore, a porous polyimide layer 3 with high cohesion can be formed. The imidization rate of the coating film 3C is preferably 0.35 or more.

[0042] The residual ratio of the solvent is preferably 8% by mass or more, more preferably 10% by mass or more, further preferably 12% by mass or more, and preferably 15% by mass or less. If the residual ratio of the solvent is within the above range, the remaining solvent is also extracted as the porogen does, so that a porous polyimide layer 3 with increased porosity of the porous polyimide layer 3 and given desired peel strength can be formed. The measurement method of the residual ratio of the solvent is described in the following examples.

[0043] Specifically, process (1) includes: a first heating process of heating the varnish at a first temperature; a second heating process of heating the varnish at a second temperature after the first heating process; and a third heating process of heating the varnish at a third temperature after the second heating process.

[0044] The varnish contains a polyimide precursor, a porogen, a nucleating agent, and a solvent.

[0045] The polyimide precursor is a reaction product of a diamine component and an acid dianhydride component. As the diamine component, for example, aromatic diamines can be cited. As the aromatic diamines, a first diamine, a second diamine, and a third diamine can be cited.

[0046] The first diamine contains a single aromatic ring. As the first diamine, for example, phenylenediamine, dimethylphenylenediamine, and ethylmethylphenylenediamine can be cited. Preferably, phenylenediamine can be cited. As phenylenediamine, for example, o-phenylenediamine, m-phenylenediamine, and p-phenylenediamine can be cited. As phenylenediamine, preferably, p-phenylenediamine can be cited. p-Phenylenediamine is sometimes abbreviated as PDA.

[0047] The second diamine contains multiple aromatic rings and an ether bond disposed between them. As the second diamine, for example, oxydianiline can be cited. As oxydianiline, for example, 3,4'-oxydianiline and 4,4'-oxydianiline can be cited. Preferably, 4,4'-oxydianiline (alias: 4,4-diaminodiphenyl ether) can be cited. 4,4'-oxydianiline is sometimes abbreviated as ODA.

[0048] The third diamine contains multiple aromatic rings and an ester bond disposed between them. As the third diamine, for example, p-aminophenyl p-aminobenzoate can be cited, and preferably, 4-aminobenzoic acid-4-aminophenyl ester can be cited. 4-aminobenzoic acid-4-aminophenyl ester is sometimes abbreviated as APAB.

[0049] It should be noted that as the aromatic diamines, in addition to the first diamine to the third diamine, for example, 4,4'-methylenedianiline, 4,4'-dimethylene dianiline, 4,4'-trimethylene dianiline, and bis(4-aminophenyl) sulfone can also be cited.

[0050] The above diamine components can be used alone, and in addition, they can be used in combination. As the diamine component, preferably, a combination of the first diamine, the second diamine, and the third diamine can be cited. More preferably, a combination of p-phenylenediamine (PDA), 4,4'-oxydianiline (ODA), and 4-aminobenzoic acid-4-aminophenyl ester (APAB) can be cited.

[0051] The molar fraction of the first diamine in the diamine component is, for example, 10 mol% or more, preferably 20 mol% or more, and in addition, for example, 70 mol% or less, preferably 65 mol% or less. The molar fraction of the second diamine in the diamine component is, for example, 5 mol% or more, preferably 10 mol% or more, and in addition, for example, 40 mol% or less, preferably 30 mol% or less. The molar fraction of the third diamine in the diamine component is, for example, 5 mol% or more, for example, 10 mol% or more, and in addition, for example, 40 mol% or less, preferably 30 mol% or less.

[0052] In addition, with respect to a total of 100 mol parts of the first diamine and the second diamine, the mol part of the third diamine is, for example, 5 mol parts or more, preferably 10 mol parts or more, more preferably 20 mol parts or more, and, for example, 100 mol parts or less, preferably 50 mol parts or less, more preferably 30 mol parts or less.

[0053] The acid dianhydride component contains an acid dianhydride having an aromatic ring. Examples of the acid dianhydride having an aromatic ring include aromatic tetracarboxylic dianhydrides. Examples of the aromatic tetracarboxylic dianhydride include pyromellitic dianhydride, benzophenone tetracarboxylic dianhydride, biphenyltetracarboxylic dianhydride, biphenylsulfone tetracarboxylic dianhydride, and naphthalenetetracarboxylic dianhydride. They can be used alone or in combination. As the acid dianhydride having an aromatic ring, biphenyltetracarboxylic dianhydride is preferably used. Examples of the biphenyltetracarboxylic dianhydride include 3,3'-4,4'-biphenyltetracarboxylic dianhydride, 2,2'-3,3'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, and 3,3',4,4'-diphenylethertetracarboxylic dianhydride. As the biphenyltetracarboxylic dianhydride, 3,3'-4,4'-biphenyltetracarboxylic dianhydride is preferably used. It should be noted that 3,3'-4,4'-biphenyltetracarboxylic dianhydride is sometimes abbreviated as BPDA.

[0054] The ratio of the diamine component to the acid dianhydride component is adjusted so that the molar amount of the amino group (-NH2) of the diamine component and the molar amount of the acid anhydride group (-CO-O-CO-) of the acid dianhydride component are, for example, equal.

[0055] To prepare a polyimide precursor, the above-mentioned diamine component, the above-mentioned acid dianhydride component, and a solvent are mixed to prepare a raw material varnish, and the raw material varnish is heated. Then, a nucleating agent and a porogen are added to the raw material varnish. Thus, a varnish is prepared.

[0056] The proportion of the polyimide precursor solution in the varnish is, for example, 5% by mass or more, preferably 10% by mass or more, and, for example, 40% by mass or less, preferably 25% by mass or less.

[0057] The types and compounding ratios of the porogen, the nucleating agent, and the solvent are described, for example, in Japanese Patent Application Laid-Open No. 2022-165379 and WO2018 / 186486.

[0058] 1.6.1.1 First heating step The first temperature in the first heating step is, for example, 80°C or higher, preferably 90°C or higher, more preferably 95°C or higher, and, for example, less than 110°C, preferably 105°C or lower. The time in the first heating step is, for example, 1 minute or longer, preferably 3 minutes or longer, and, for example, 10 minutes or shorter, preferably 7 minutes or shorter.

[0059] 1.6.1.2 Second heating step The second temperature in the second heating process is higher than the first temperature. The temperature (temperature difference) obtained by subtracting the first temperature from the second temperature is, for example, 10 °C or more, preferably 15 °C or more, and, for example, 30 °C or less, preferably 25 °C or less. Specifically, the temperature in the second heating process is, for example, 110 °C or more, preferably 115 °C or more, and, for example, less than 130 °C, preferably 125 °C or less. The time in the second heating process is, for example, 1 minute or more, preferably 3 minutes or more, and, for example, 10 minutes or less, preferably 7 minutes or less.

[0060] 1.6.1.3 Third heating process The third temperature in the third heating process is higher than the second temperature. The temperature (temperature difference) obtained by subtracting the second temperature from the third temperature is, for example, 10 °C or more, preferably 15 °C or more, and, for example, 30 °C or less, preferably 25 °C or less. Specifically, the temperature in the third heating process is, for example, 130 °C or more, preferably 135 °C or more, and, for example, less than 150 °C, preferably 145 °C or less.

[0061] In step (1), by performing the above-described first heating process, second heating process, and third heating process, that is, by stepwise heating, the porogen can be uniformly arranged (uniformly in the thickness direction) in the coating film 3C and the solvent can be removed. Thereby, the coating film 3C is formed.

[0062] 1.6.2 Step (2) In step (2), at least a part of the porogen in the coating film 3C is extracted.

[0063] In step (2), for example, by a supercritical extraction method using supercritical carbon dioxide as a solvent, the porogen is extracted (extracted or removed) from the precursor film.

[0064] 1.6.3 Step (3) As Figure 1 shown, in step (3), the coating film 3C is heated to be cured, thereby forming the porous polyimide layer 3. The temperature in step (3) is, for example, 340 °C or more, preferably 360 °C or more, and, for example, 420 °C or less, preferably 400 °C or less.

[0065] Thereby, the porous polyimide layer 3 is formed from the coating film 3C.

[0066] 1.7 Effects of the first embodiment (1) The peel strength of the low-dielectric substrate material 1 is 0.4 N / mm or more, which is high.

[0067] (2) Even when the porosity of the porous polyimide layer 3 is as high as 60% or more and 95% or less, the low-dielectric substrate material 1 has a high peel strength.

[0068] (3) In step (1) of the manufacturing method of the low-dielectric substrate material 1, the imidization rate of the coating film 3C is 0.30 or more and 0.45 or less, and the residual ratio of the solvent is 6% by mass or more and 19% by mass or less, so that the imidization rate of the coating film 3C and the residual ratio of the solvent are appropriately maintained respectively. Thus, the low-dielectric substrate material 1 with a high peel strength can be manufactured.

[0069] (4) In addition, in step (1), a first heating step, a second heating step, and a third heating step are sequentially performed. That is, the varnish is heated step by step. Therefore, the porogen can be uniformly arranged in the coating film 3C. As a result, the shift of the pores in the porous polyimide layer 3 can be suppressed. Therefore, the low-dielectric substrate material 1 with a high peel strength can be manufactured.

[0070] 1.8 Modification In the following modification, the same reference numerals are given to the same components and steps as those in the above first embodiment, and their detailed descriptions are omitted. In addition, the modification can achieve the same effects as the first embodiment except as otherwise specified. Moreover, the first embodiment and its modification can be appropriately combined.

[0071] In step (4), the first heating step and the second heating step may be performed without performing the third heating step.

[0072] In step (4), in addition to performing the first heating step, the second heating step, and the third heating step, a fourth heating step may also be performed. The heating temperature (fourth temperature) in the fourth heating step is higher than the third temperature.

[0073] In step (4), instead of heating step by step, continuous heating (temperature increase) may be performed.

[0074] 2. Second Embodiment In the second embodiment, the same reference numerals are given to the same components and steps as those in the above first embodiment, and their detailed descriptions are omitted. In addition, the second embodiment can achieve the same effects as the first embodiment except as otherwise specified. Moreover, the first embodiment, its modification, and the second embodiment can be appropriately combined.

[0075] Refer to Figure 3 , and the second embodiment of the low-dielectric substrate material of the present invention will be described.

[0076] 2.1 Non-porous Polyimide Layer 5 As Figure 3 shown, the low dielectric substrate material 1 further includes a non-porous polyimide layer 5. The non-porous polyimide layer 5 is disposed between the metal layer 2 and the porous polyimide layer 3. That is, the low dielectric substrate material 1 sequentially includes the metal layer 2, the non-porous polyimide layer 5, and the porous polyimide layer 3 on one side in the thickness direction.

[0077] The non-porous polyimide layer 5 is disposed on one surface of the metal layer 2 in the thickness direction. The non-porous polyimide layer 5 is in contact with one surface of the metal layer 2 in the thickness direction. The non-porous polyimide layer 5 is disposed on the other surface of the porous polyimide layer 3 in the thickness direction. The non-porous polyimide layer 5 is in contact with the other surface of the porous polyimide layer 3 in the thickness direction.

[0078] The non-porous polyimide layer 5 has a thickness. The non-porous polyimide layer 5 extends in the plane direction. The non-porous polyimide layer 5 is a solid dense film.

[0079] The thickness of the non-porous polyimide layer 5 is, for example, 1 μm or more, preferably 2 μm or more, and, for example, 10 μm or less, preferably 7 μm or less. The ratio of the thickness of the non-porous polyimide layer 5 to the thickness of the porous polyimide layer 3 is, for example, 0.01 or more, preferably 0.05 or more, and, for example, 0.3 or less, preferably 0.2 or less. The porosity of the non-porous polyimide layer 5 is, for example, 0.1% or less, further 0%.

[0080] 2.2 Physical properties of the low dielectric substrate material 1 In the second embodiment, the peel strength of the low dielectric substrate material 1 is 0.5 N / mm or more, preferably 0.65 N / mm or more, more preferably 0.8 N / mm or more. The upper limit of the peel strength in the second embodiment is, for example, 10.0 N / mm, further 3.0 N / mm.

[0081] 2.3 Manufacturing method Refer to Figure 3 , Figure 4A , Figure 4B , the manufacturing method of the low dielectric substrate material 1 of the second embodiment will be described.

[0082] The manufacturing method of the low dielectric substrate material 1 includes process (4), process (5), process (6), and process (7). Process (4), process (5), process (6), and process (7) are sequentially implemented.

[0083] 2.3.1 Process (4) As Figure 4AAs shown, in step (4), varnish is applied to one surface in the thickness direction of the metal layer 2 and heated to dry it, thereby forming the first coating film 5C. The varnish contains the above polyimide precursor and the above solvent. The concentration (solid content concentration) of the polyimide precursor in the varnish is, for example, 10% by mass or more, preferably 40% by mass or more, and, for example, 95% by mass or less, preferably 75% by mass or less.

[0084] In step (4), the first coating film 5C is formed such that the imidization rate of the first coating film 5C determined by the following measurement method is 0.60 or more.

[0085] There is no limit to the upper limit of the imidization rate of the first coating film 5C. The upper limit of the imidization rate of the first coating film 5C is, for example, 1.0, preferably 0.9.

[0086] Measurement method: In infrared absorption spectrometry, measure the imidization intensity ratio of 1773 cm -1 and 3064 cm -1 of the first coating film 5C. Measure the above imidization intensity ratio of the completely cured body obtained by heating the first coating film 5C at 420 °C. Calculate the ratio of the imidization intensity ratio of the first coating film 5C to the imidization intensity ratio of the completely cured body as the imidization rate.

[0087] Specifically, in step (4), the varnish is heated to 130 °C or higher. If the heating temperature is lower than 130 °C, there may be a case where the imidization in the first coating film 5C becomes insufficient. Therefore, it integrates with the subsequently formed second coating film 3C1 (the film for forming the porous polyimide layer 3). As a result, there may be a case where the non-porous polyimide layer 5 cannot be formed.

[0088] There is no particular limitation on the upper limit of the heating temperature. If the implementation of step (7) is considered, the upper limit of the heating temperature is, for example, 300 °C, further 250 °C, and still further 200 °C.

[0089] The heating time in step (4) is, for example, 10 minutes or more, preferably 15 minutes or more. There is no limit to the upper limit of the heating time. The upper limit of the heating time is, for example, 30 minutes, preferably 25 minutes.

[0090] 2.3.2. Step (5) As Figure 4BAs shown, in step (5), varnish is applied to one surface in the thickness direction of the first coating film 5C and heated to dry it, thereby forming the second coating film 3C1. The varnish contains a polyimide precursor, a porogen, a nucleating agent, and a solvent. The imidization rate of the second coating film 3C1 in the second embodiment is different from that of the coating film 3C in the first embodiment (0.30 or more and 0.45 or less), and is not limited.

[0091] In the second embodiment, the heating method of the varnish is not limited. In step (5), for example, the first heating step, the second heating step, and the third heating step of the first embodiment are implemented.

[0092] In step (6), at least a part of the porogen in the second coating film 3C is extracted. Step (5) is the same as step (2) in the first embodiment.

[0093] As Figure 3 shown, in step (7), the first coating film 5C and the second coating film 3C1 are heated to cure them, thereby forming the non-porous polyimide layer 5 and the porous polyimide layer 3. Step (7) is the same as step (3) in the first embodiment.

[0094] 2.4 Effects of the second embodiment (5) The peel strength of the low-dielectric substrate material 1 is 0.5 N / mm or more, which is high.

[0095] In the second embodiment, the low-dielectric substrate material 1 further includes a non-porous polyimide layer 5 disposed between the metal layer 2 and the porous polyimide layer 3. Therefore, compared with the first embodiment, the peel strength can be improved.

[0096] (6) In step (4), the first coating film 5C is formed such that the imidization rate of the first coating film 5C becomes 0.60 or more. Therefore, it is possible to suppress the formation defect of the non-porous polyimide layer 5 caused by insufficient imidization.

[0097] (7) In step (4), the first coating film 5C is heated to 130°C or more. Therefore, it is possible to more reliably suppress the formation defect of the non-porous polyimide layer 5 caused by insufficient imidization.

[0098] 3.1 Use The above-described low-dielectric substrate material 1 has high peel strength. Therefore, the above-described low-dielectric substrate material 1 is suitable for use in flexible multilayer circuit boards. When the above-described low-dielectric substrate material 1 is used in a flexible multilayer circuit board, peeling at the bent portion in the flexible multilayer circuit board can be suppressed due to the high peel strength. Further, the above-described low-dielectric substrate material 1 is also suitable for use in a flexible multilayer circuit board assembly in which a connector is mounted on a flexible multilayer circuit board. When the above-described low-dielectric substrate material 1 is used in a flexible multilayer circuit board assembly, peeling during connector insertion and removal can be suppressed.

[0099] 3.2 Flexible Multilayer Circuit Board Refer to Figure 5 and a flexible multilayer circuit board using the above-described low-dielectric substrate material 1 will be described.

[0100] As Figure 5 shown, the flexible multilayer circuit board 10 includes the above-described low-dielectric substrate material 1. Specifically, the flexible multilayer circuit board 10 includes, for example, a first low-dielectric substrate material 11, a bonding layer 60, and a second low-dielectric substrate material 12 in this order in the thickness direction. That is, the first low-dielectric substrate material 11 and the second low-dielectric substrate material 12 are in contact with the bonding layer 6. Specifically, the exposed surface of the porous polyimide layer (first porous polyimide layer 31) of the first low-dielectric substrate material 11 is in contact with the bonding layer 6, and the exposed surface of the porous polyimide layer (second porous polyimide layer 32) of the second low-dielectric substrate material 12 is in contact with the bonding layer 6.

[0101] More specifically, the flexible multilayer circuit board 10 includes, in this order in the thickness direction, a first metal layer 21, a first non-porous polyimide layer 51, a first porous polyimide layer 31, a bonding layer 6, a second porous polyimide layer 32, a second non-porous polyimide layer 52, and a second metal layer 22. Further, the flexible multilayer circuit board 10 may have a metal wiring 23 represented by a phantom line embedded in the bonding layer 6.

[0102] Further, the flexible multilayer circuit board 10 may have a via connection portion 60 as shown by a phantom line, which penetrates the first non-porous polyimide layer 51, the first porous polyimide layer 31, the bonding layer 6, the second porous polyimide layer 32, and the second non-porous polyimide layer 52 and connects the first metal layer 21 and the second metal layer 22. Although not shown, the flexible multilayer circuit board 10 may have covering insulating layers on the opposite sides of the first low-dielectric substrate material 11 and the second low-dielectric substrate material 12 that are in contact with the bonding layer 60.

[0103] In addition, although not shown, in the flexible multilayer circuit board 10, the first metal layer 21 and the second metal layer 22 can have terminals connected to the metal wiring 23 at both ends in the length direction. By connecting a connector to the terminals, a flexible multilayer circuit board assembly can be obtained.

[0104] [Embodiment] Examples and comparative examples are shown below to further specifically illustrate the present invention. It should be noted that the present invention is not limited to any examples and comparative examples. In addition, the specific numerical values such as the mixing ratio (content ratio), physical property values, parameters, etc. used in the following descriptions can replace the upper limits (values defined as "below", "less than") or lower limits (values defined as "above", "exceeding") of the corresponding mixing ratios (content ratios), physical property values, parameters, etc. described in the above "Detailed Description".

[0105] Example 1 <Step (1)> 0.66 mol of p-phenylenediamine (PDA) (the first diamine), 0.22 mol of 4,4'-oxydianiline (ODA) (the second diamine), and 0.22 mol of 4-aminobenzoic acid 4-aminophenyl ester (APAB) (the third diamine) were dissolved in N-methyl-2-pyrrolidone (NMP) to prepare a diamine component solution. Then, 1.00 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added to the diamine component solution and stirred at 80 °C. Stirring was stopped and it was allowed to cool naturally to prepare a raw material varnish. The solid content concentration of the raw material varnish was 13% by mass.

[0106] To 100 parts by mass of the raw material varnish, 150 parts by mass of polyoxyethylene dimethyl ether with a weight average molecular weight of 400 (manufactured by NOF Corporation, grade: MM400) as a pore-forming agent and 3 parts by mass of PTFE powder with a particle size of 1 μm or less as a nucleating agent were added, and they were stirred to obtain a transparent and uniform solution. 4 parts by mass of 2-methylimidazole was added to the obtained solution as an imidization catalyst to prepare a varnish. As Figure 2 shown, the varnish was coated on one surface of the metal layer 2 including a copper film and heated to dry it, thereby forming a coating film 3C with a thickness of 50 μm. In step (1), a first heating step, a second heating step, and a third heating step were sequentially performed to form the coating film 3C.

[0107] The temperature of the first heating step was 100 °C and the time was 5 minutes. The temperature of the second heating step was 120 °C and the time was 5 minutes. The temperature of the third heating step was 140 °C and the time was 15 minutes.

[0108] <Step (2)> After step (1), by supercritical extraction using supercritical carbon dioxide, in the coating film 3C, the extraction and removal of the porogen and the formation of pores were promoted.

[0109] <Step (3)> After step (2), the coating film 3C was heated at 360 °C to perform imidization. As a result, Figure 1 as shown, a porous polyimide layer 3 was formed. Thus, the low dielectric substrate material 1 having the metal layer 2 and the non-porous polyimide layer 5 with a thickness of 50 μm was manufactured.

[0110] Example 2, Comparative Examples 1 to 4 The low dielectric substrate material 1 was manufactured in the same manner as in Example 1. However, the temperature and time of heating in step (1) were changed as described in Table 1.

[0111] Example 3 <Step (4)> The same raw material varnish as in step (1) of Example 1 was prepared. However, the solid content concentration of the raw material varnish was 50% by mass.

[0112] As Figure 4A shown, the raw material varnish was coated on one surface of the metal layer 2 including the copper film and heated to dry it, thereby forming the first coating film 5C. In step (4), by heating at 140 °C for 20 minutes, the first coating film 5C with a thickness of 5 μm was formed.

[0113] <Step (5)> After step (4), the varnish used in step (1) of Example 1 was coated on one surface of the first coating film 5C and heated to dry it, thereby forming the second coating film 3C1. In step (5), the first heating step, the second heating step, and the third heating step were sequentially performed. The temperature of the first heating step was 100 °C and the time was 5 minutes. The temperature of the second heating step was 120 °C and the time was 5 minutes. The temperature of the third heating step was 140 °C and the time was 15 minutes. By step (5), NMP was removed.

[0114] <Step (6)> By supercritical extraction using supercritical carbon dioxide, in the second coating film 3C1, the extraction and removal of the porogen and the formation of pores were promoted.

[0115] <Step (7)> The first coating film 5C and the second coating film 3C1 were heated at 360 °C for imidization. Thereby, a non-porous polyimide layer 5 and a porous polyimide layer 3 with a thickness of 31 μm were formed. Thereby, a low dielectric substrate material 1 having a metal layer 2, a non-porous polyimide layer 5, and a porous polyimide layer 3 was manufactured.

[0116] Example 4, Example 5, Comparative Example 5 A low dielectric substrate material 1 was manufactured in the same manner as in Example 3. Among them, the temperature and time of heating in step (1) were changed as described in Table 1.

[0117] It should be noted that in Comparative Example 5, the first coating film 5C was formed in step (4). However, in step (5), the non-porous polyimide layer 5 was not formed, and the porous polyimide layer 3 was formed from the first coating film 5C and the second coating film 3C1.

[0118] (Evaluation) Regarding each example and each comparative example, the following items were evaluated. These results are shown in Table 1 and Table 2.

[0119] (Peel strength of the low dielectric substrate material 1) The low dielectric substrate material 1 was machined into a shape of 110 mm in length × 10 mm in width to prepare a sample. The sample was placed on a tensile testing machine (TG series, manufactured by Minebea Co., Ltd.) and a 90-degree peel test was performed. Specifically, the other surface of the metal layer 2 of the sample was fixed to the plane of the stage of the tensile testing machine. And, adhesive tape No. 5000NS (manufactured by Nitto Denko Corporation) was attached to one surface of the porous polyimide layer 3. Then, the adhesive tape was stretched relative to the plane of the stage in a 90-degree direction using a chuck.

[0120] In any of the examples and comparative examples, the mode of cohesive failure of the porous polyimide layer 3 was observed.

[0121] (Imidization rate of the coating film 3C, the first coating film 5C, and the second coating film 3C1) Measurement method: In infrared absorption spectrometry, the imidization intensity ratio at 1773 cm -1 and 3064 cm -1 of the coating film 3C of Example 1, Example 2, and Comparative Examples 1 to 4 was measured. In addition, the imidization intensity ratio of the fully cured body obtained by heating the coating film 3C at 420 °C was measured. The ratio of the imidization intensity ratio of the coating film 3C to the imidization intensity ratio of the fully cured body was calculated as the imidization rate.

[0122] By the same method as described above, the imidization rates of the first coating film 5C and the second coating film 3C1 of Examples 3 to 5 and Comparative Example 2 were measured.

[0123] (Porosity of the porous polyimide layer 3) The porosity of the porous polyimide layer 3 was calculated based on the following formula.

[0124] Porosity (%) = (1 - specific gravity of the porous polyimide layer 3 / specific gravity of polyimide) × 100 It should be noted that the specific gravity of the porous polyimide layer 3 was measured using an electronic specific gravity meter.

[0125] (Dielectric constant of the porous polyimide layer 3) Using a PNA network analyzer (manufactured by Agilent Technologies) and an SPDR resonator, the dielectric constant of the porous polyimide layer 3 at a frequency of 10 GHz was measured.

[0126] [Table 1] [Table 2] It should be noted that the above invention is provided as an exemplary embodiment of the present invention, but this is merely an example and should not be construed in a limiting sense. Modification examples of the present invention that are obvious to those skilled in the art are included within the scope of protection of the claims described below.

[0127] Industrial Applicability The low dielectric substrate material of the present invention is suitable for use in flexible multi-layer circuit boards. In addition, the low dielectric substrate material 1 of the present invention is also suitable for use in a flexible multi-layer circuit board assembly in which a connector is mounted on a flexible multi-layer circuit board.

[0128] Explanation of Reference Numerals 1: Low dielectric substrate material 2: Metal layer 3: Porous polyimide layer 3C: Coating film 3C1: Second coating film 5: Non-porous polyimide layer 5C: First coating film.

Claims

1. A low dielectric substrate material, wherein, The low-dielectric substrate material sequentially includes a metal layer and a porous polyimide layer on one side in the thickness direction. In the cohesive failure mode where the porous polyimide layer is cohesively damaged, the peel strength of the low-dielectric substrate material is 0.4 N / mm or more.

2. The low dielectric substrate material according to claim 1, wherein The porosity of the porous polyimide layer is 60% or more and 95% or less.

3. The low dielectric substrate material according to claim 1, wherein The low-dielectric substrate material further includes a non-porous polyimide layer, and the non-porous polyimide layer is disposed between the metal layer and the porous polyimide layer.

4. The low dielectric substrate material according to claim 3, wherein The peel strength is 0.5 N / mm or more.

5. A method for manufacturing a low-dielectric substrate material, which is a method for manufacturing the low-dielectric substrate material according to claim 1 or 2, and includes: Process 1, in the said Process 1, a varnish containing a polyimide precursor, a porogen, a nucleating agent, and a solvent is coated on one surface in the thickness direction of a metal layer and heated to dry it, thereby forming a coating film, wherein, forming a coating film such that the imidization rate of the coating film obtained by the following measurement method is 0.30 or more and 0.45 or less, and the residual ratio of the solvent is 6% by mass or more and 19% by mass or less; Step 2, in which at least a part of the porogen in the coating film is extracted; and Step 3, in which the coating film is heated and cured to form a porous polyimide layer. The measurement method measures the imidization intensity ratio at 1773 cm of the coating film in infrared absorption spectrometry -1 and 3064 cm -1 of the imidization intensity ratio, measures the imidization intensity ratio of the completely cured body obtained by heating the coating film at 420 °C, and calculates the ratio of the imidization intensity ratio of the coating film to the imidization intensity ratio of the completely cured body as the imidization rate.

6. The manufacturing method of the low dielectric substrate material according to claim 5, wherein, Step 1 includes: a first heating step of heating the varnish at a first temperature; and a second heating step of heating the varnish at a second temperature higher than the first temperature after the first heating step.

7. The manufacturing method of the low dielectric substrate material according to claim 6, wherein, After the second heating step, Step 1 further includes a third heating step of heating the varnish at a third temperature higher than the second temperature. The temperature in the first heating step is 80°C or more and less than 110°C. The temperature in the second heating step is 110°C or more and less than 130°C. The temperature in the third heating step is 130°C or more and less than 150°C.

8. A method for manufacturing a low-dielectric substrate material, which is a method for manufacturing the low-dielectric substrate material according to claim 3 or 4, and includes: Step 4, in which a varnish containing a polyimide precursor and a solvent is applied to one surface in the thickness direction of the metal layer and heated to dry it, thereby forming a first coating film, wherein, forming a first coating film such that the imidization rate of the first coating film obtained by the following measurement method is 0.60 or more; Step 5, in which a varnish containing a polyimide precursor, a porogen, a nucleating agent, and a solvent is coated on one surface in the thickness direction of the first coating film and heated and dried to form a second coating film; Step 6, in which at least a part of the porogen in the second coating film is extracted; and Step 7, in which the first coating film and the second coating film are heated and cured to form a non-porous polyimide layer and a porous polyimide layer. The measurement method measures the imidization intensity ratio at 1773 cm -1 and 3064 cm -1 of the first coating film in the infrared absorption spectrometry, measures the imidization intensity ratio of the completely cured body obtained by heating the first coating film at 420°C, and calculates the ratio of the imidization intensity ratio of the first coating film to the imidization intensity ratio of the completely cured body as the imidization rate.

9. The manufacturing method of the low dielectric substrate material according to claim 8, wherein, In Step 4, the first coating film is heated to 130°C or more.

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