Film for metal layer laminate

Abstract

To provide a film for a metal layer laminate which suppresses a variation in dielectric constant caused before and after hot press processing.SOLUTION: It is used for laminating the metal layer 5. The film for a metal layer laminated plate includes a porous resin layer 2 and a skin layer 3 in order in the thickness direction. An average pore diameter W in the whole thickness direction of the porous resin layer 2 is 7.0 μm or less. The porous resin layer 2 includes a first region 11 to a fifth region 15 arranged in order in a direction away from the skin layer 3 when the porous resin layer is divided into five equal parts in the thickness direction. The ratio (A5 / A1) of the average pore diameter A1 of the first region 11 to the average pore diameter A5 of the fifth region 15 is 0.45 or more and 1 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a film for a metal layer laminate, and more particularly to a film for a metal layer laminate used for laminating metal layers. [Background technology]

[0002] A film for a metal layer laminate is known, which has a porous resin layer and a skin layer in that order in the thickness direction (see, for example, Patent Document 1 below). A metal layer laminate is obtained by laminating the film for a metal layer laminate on a metal layer.

[0003] In the film for metal layer laminates described in Example 2 of Patent Document 1, the average pore size in the entire thickness direction of the porous resin layer is large, at approximately 8 μm (based on FIG. 4). Furthermore, when the above-mentioned porous resin layer is divided into five equal parts in the thickness direction, it includes first to fifth regions arranged in order in the direction away from the skin layer, and the ratio of the average pore size of the first region to the average pore size of the fifth region is approximately 0.8, close to 1 (based on FIG. 4). In other words, the average pore size of the first region is similar to the average pore size of the fifth region. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] WO2018 / 186486 Summary of the Invention [Problem to be solved by the invention]

[0005] When producing a metal layer laminate from a film for a metal layer laminate, and further when processing the metal layer laminate, the film for a metal layer laminate may be pressed (specifically, hot pressed) in the thickness direction.

[0006] However, if the average pore size of the entire porous resin layer in the thickness direction is large, the above-mentioned reduction rate in thickness after pressing becomes excessive, which causes a problem of large fluctuation in the dielectric constant before and after pressing.

[0007] On the other hand, if the average pore size of the entire porous resin layer in the thickness direction is reduced, the ratio of the average pore size of the first region to the average pore size of the fifth region becomes too small. Specifically, the ratio approaches 0. In this case, the average pore size of the fifth region becomes too large compared to the average pore size of the first region, resulting in a problem of large fluctuations in the dielectric constant before and after pressing. [Means for solving the problem]

[0008] The present invention provides a film for metal layer laminates used for laminating metal layers, the film comprising a porous resin layer and a skin layer in that order in the thickness direction, the porous resin layer having an average pore diameter of 7.0 μm or less throughout the entire thickness direction, the porous resin layer including a first region to a fifth region arranged in that order in the direction away from the skin layer when the porous resin layer is divided into five equal parts in the thickness direction, and the ratio of the average pore diameter of the first region to the average pore diameter of the fifth region is 0.45 or more and 1 or less. [Effects of the Invention]

[0009] In the film for metal layer laminates of the present invention, although the average pore size of the entire thickness direction of the porous resin layer is as small as 7.0 μm or less, the ratio of the average pore size of the first region to the average pore size of the fifth region is 0.45 or more, which prevents the ratio from becoming too small, and therefore fluctuations in the dielectric constant before and after pressing can be suppressed. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view of one embodiment of the film for metal layer laminates of the present invention. [Figure 2] FIG. 2 is a cross-sectional view of a modified example of the film for metal layer laminate. DETAILED DESCRIPTION OF THE INVENTION

[0011] <One embodiment of the film for metal layer laminate> One embodiment of the film for metal layer laminates of the present invention will be described with reference to FIG. 1. As shown in FIG. 1, the film for metal layer laminates 1 has a thickness and extends in a plane direction perpendicular to the thickness direction. The thickness of the film for metal layer laminates 1 is not particularly limited. The film for metal layer laminates 1 has a dielectric constant of, for example, 2.5 or less, preferably 2.0 or less, and for example, greater than 1.0 at a frequency of 10 GHz. The dielectric constant of the film for metal layer laminates 1 is measured by a dielectric resonator method. The thickness of the film for metal layer laminates 1 is, for example, 2 μm or more, preferably 5 μm or more, and for example, 1,000 μm or less, preferably 500 μm or less.

[0012] The film 1 for metal layer laminates includes a porous resin layer 2 and a skin layer 3 in this order toward one side in the thickness direction.

[0013] <Porous resin layer 2> The porous resin layer 2 forms the other surface in the thickness direction of the film 1 for metal layer laminates. The porous resin layer 2 extends in the plane direction. The porous resin layer 2 is porous. The porous resin layer 2 has a closed-cell structure and / or an open-cell structure. The porosity of the porous resin layer 2 is, for example, 50% or more, preferably 60% or more, and more preferably 70% or more. The porosity of the porous resin layer 2 is, for example, less than 100%, or even 99% or less. When the porous resin layer 2 is made of polyimide, the porosity can be calculated from the following formula. Dielectric constant of porous resin layer 2=Dielectric constant of air×Porosity+Dielectric constant of polyimide×(1−Porosity)

[0014] <Average pore diameter W throughout the thickness> The average pore diameter W of the porous resin layer 2 in the entire thickness direction is 7.0 μm or less. If the average pore diameter W of the porous resin layer 2 in the entire thickness direction exceeds 7.0 μm, when the film for metal layer laminate 1 is pressed in the thickness direction (specifically, heat pressed), the fluctuation rate of the pressed thickness becomes negative and the absolute value becomes large. In other words, the rate of thickness reduction becomes excessive. This results in a large change in the dielectric constant of the film 1 for metal layer laminates before and after pressing.

[0015] The average pore diameter W of the porous resin layer 2 throughout its entire thickness is preferably 6.0 μm or less. The lower limit of the average pore diameter W of the porous resin layer 2 throughout its entire thickness is not limited. The lower limit of the average pore diameter W of the porous resin layer 2 throughout its entire thickness is, for example, 0.1 μm. A method for determining the average pore diameter W of the porous resin layer 2 throughout its entire thickness will be described later in the Examples.

[0016] <Five equal areas> When the porous resin layer 2 is divided into five equal parts in the thickness direction, the porous resin layer 2 includes a first region 11 to a fifth region 15 that are arranged in this order from one surface to the other surface in the thickness direction. Specifically, in the porous resin layer 2, the first region 11, the second region 12, the third region 13, the fourth region 14, and the fifth region 15 are arranged in this order toward the other side in the thickness direction (toward a direction away from the skin layer 3 described below). In FIG. 1, the boundaries between adjacent regions in the thickness direction are indicated by dashed dotted lines, but the above-mentioned boundaries are not observed when an actual cross-section is observed.

[0017] The first region 11 forms one surface of the porous resin layer 2 in the thickness direction. The fifth region 15 forms the other surface of the porous resin layer 2 in the thickness direction. The third region 13 is a central region in the thickness direction. The second region 12 is sandwiched between the first region 11 and the third region 13. The fourth region 14 is sandwiched between the third region 13 and the fifth region 15. The thickness of the first region 11, the thickness of the second region 12, the thickness of the third region 13, the thickness of the fourth region 14, and the thickness of the fifth region 15 are all the same.

[0018] <Average pore size ratio> The ratio (A1 / A5) of the average pore size A1 of the first region 11 to the average pore size A5 of the fifth region 15 is 0.45 or more and 1.0 or less.

[0019] If the ratio (A1 / A5) of the average pore diameter A1 of the first region 11 to the average pore diameter A5 of the fifth region 15 is less than 0.45, the average pore diameter A5 of the fifth region 15 will be excessively large compared to the average pore diameter A1 of the first region 11, resulting in a large variation in the dielectric constant of the film 1 for metal layer laminates before and after pressing.

[0020] In the manufacturing method described below, it is impossible for the average pore size A5 of the fifth region 15 to be smaller than the average pore size A1 of the first region 11. Therefore, the ratio (A1 / A5) of the average pore size A5 of the fifth region 15 to the average pore size A1 of the first region 11 does not exceed 1.0.

[0021] The ratio (A1 / A5) of the average pore size A1 of the first region 11 to the average pore size A5 of the fifth region 15 is preferably 0.50 or more.

[0022] To set the ratio (A1 / A5) of the average pore diameter A1 of the first region 11 to the average pore diameter A5 of the fifth region 15 within the above range, the resin formulation (composition), the viscosity of the porous precursor solution, the coater gap, the thickness of the porous resin layer 2, etc., which will be described below, are adjusted.

[0023] The average pore size A1 of the first region 11 is, for example, 1.0 μm or more, preferably 2.0 μm or more, and for example, less than 4.0 μm, preferably 3.5 μm or less. The average pore size A5 of the fifth region 15 is, for example, 9.0 μm or less, preferably 8.0 μm or less, and for example, 2.0 μm or more, preferably 4.0 μm or more.

[0024] The average pore diameter A1 of the first region 11 and the average pore diameter A5 of the fifth region 15 are determined by SEM cross-sectional observation. Details of how to determine these diameters will be described in the examples below.

[0025] Examples of materials for the film 1 for metal layer laminates include thermosetting resins. Examples of thermosetting resins include polycarbonate resins, polyimide resins, fluorinated polyimide resins, epoxy resins, phenolic resins, urea resins, melamine resins, diallyl phthalate resins, silicone resins, thermosetting urethane resins, fluororesins (fluorine-containing olefin polymers (specifically, polytetrafluoroethylene (PTFE))), and liquid crystal polymers (LCPs). These can be used alone or in combination of two or more. Of the above-mentioned resins, polyimide resins are preferred from the viewpoint of mechanical strength. Details of polyimide resins, including their physical properties and production methods, are described, for example, in WO2018 / 186486.

[0026] The thickness of the porous resin layer 2 is, for example, 60 μm or less, preferably 50 μm or less, more preferably 40 μm or less, and 10 μm or more, preferably 25 μm or more. When the thickness of the porous resin layer 2 is equal to or less than the upper limit described above, the average pore size ratio (A1 / A5) can be easily set within the range described above.

[0027] <Skin layer 3> The skin layer 3 is disposed on one surface in the thickness direction of the porous resin layer 2. Therefore, the first region 11 to the fifth region 15 in the porous resin layer 2 are disposed in order in a direction away from the skin layer 3 (corresponding to the other side in the thickness direction). The skin layer 3 is in contact with the entire one surface in the thickness direction of the first region 11 of the porous resin layer 2. The skin layer 3 extends in the planar direction. The skin layer 3 forms one surface in the thickness direction of the film 1 for metal layer laminates. The skin layer 3 is substantially non-porous. The porosity of the skin layer 3 is, for example, 1% or less. The material of the skin layer 3 is not particularly limited. Preferably, the material of the skin layer 3 is the same as the material of the porous resin layer 2. In this case, the skin layer 3 is formed integrally with one surface in the thickness direction of the porous resin layer 2. The thickness of the skin layer 3 is, for example, 1 μm or more and, for example, 5 μm or less. The ratio of the thickness of the skin layer 3 to the thickness of the film for metal layer laminate 1 is, for example, not less than 0.01 and not more than 0.2.

[0028] Next, a method for producing the film for metal layer laminate 1 will be described.

[0029] Specifically, first, a substrate film 7 (indicated by parentheses and imaginary lines) made of metal is prepared. The substrate film 7 extends in the planar direction. Examples of metals include copper, iron, silver, gold, aluminum, nickel, and alloys thereof (stainless steel, bronze). A preferred example of the metal is copper. The thickness of the substrate film 7 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.

[0030] Next, a varnish containing the above-mentioned resin precursor, a porosifying agent, a nucleating agent, and a solvent is prepared, and then the varnish is applied to one surface in the thickness direction of the substrate film 7 to form a coating film. The types and blending ratios of the porosifying agent, nucleating agent, and solvent in the varnish are described, for example, in WO2018 / 186486.

[0031] The case where the resin is a polyimide resin will be described. The precursor of the polyimide resin is, for example, a reaction product of a diamine component and an acid dianhydride component. Examples of the diamine component include aromatic diamines, aliphatic diamines, and alicyclic diamines. A preferred example of the diamine component is an aromatic diamine.

[0032] Aromatic diamines include primary, secondary, and tertiary diamines.

[0033] The first diamine contains a single aromatic ring. Examples of the first diamine include phenylenediamine, dimethylbenzenediamine, and ethylmethylbenzenediamine. From the viewpoint of mechanical strength, phenylenediamine is preferred. Examples of the phenylenediamine include o-phenylenediamine, m-phenylenediamine, and p-phenylenediamine. Examples of the phenylenediamine include p-phenylenediamine.

[0034] The second diamine contains a plurality of aromatic rings and ether bonds disposed between them. Examples of the second diamine include oxydianiline. Examples of the oxydianiline include 3,4'-oxydianiline and 4,4'-oxydianiline. From the viewpoint of mechanical strength, 4,4'-oxydianiline is preferred.

[0035] The tertiary diamine contains a plurality of aromatic rings and ester bonds disposed between them. The tertiary diamine is a component that increases the above-mentioned ratio (A1 / A5) in the porous resin layer 2. Examples of the tertiary diamine include aminophenyl aminobenzoate, and preferably 4-aminophenyl-4-aminobenzoate.

[0036] In addition to the primary to tertiary diamines, examples of the aromatic diamine include 4,4'-methylenedianiline, 4,4'-dimethylenedianiline, 4,4'-trimethylenedianiline, and bis(4-aminophenyl)sulfone.

[0037] The diamine components described above can be used alone or in combination. A preferred diamine component is a combination of a primary diamine, a secondary diamine, and a tertiary diamine. A more preferred diamine is a combination of p-phenylenediamine, 4,4'-oxydianiline, and 4-aminophenyl-4-aminobenzoate.

[0038] p-Phenylenediamine is sometimes abbreviated as PDA, 4,4'-oxydianiline (also known as 4,4'-diaminophenyl ether) is sometimes abbreviated as ODA, and 4-aminophenyl-4-aminobenzoate is sometimes abbreviated as APAB.

[0039] The molar fraction of the first diamine in the diamine component is preferably 10 mol% or more, more preferably 20 mol% or more, and for example, 70 mol% or less, preferably 65 mol% or less. The molar fraction of the second diamine in the diamine component is preferably 5 mol% or more, more preferably 10 mol% or more, and for example, 40 mol% or less, preferably 30 mol% or less. The molar fraction of the tertiary diamine in the diamine component is preferably 5 mol% or more, more preferably 10 mol% or more, and for example, 40 mol% or less, preferably 30 mol% or less.

[0040] <Acid dianhydride component> The acid dianhydride component contains, for example, an acid dianhydride containing an aromatic ring. Examples of the acid dianhydride containing an aromatic ring include aromatic tetracarboxylic dianhydrides. Examples of the aromatic tetracarboxylic dianhydrides include benzenetetracarboxylic dianhydride, benzophenonetetracarboxylic dianhydride, biphenyltetracarboxylic dianhydride, biphenylsulfonetetracarboxylic dianhydride, and naphthalenetetracarboxylic dianhydride.

[0041] Examples of benzenetetracarboxylic dianhydrides include benzene-1,2,4,5-tetracarboxylic dianhydride (also known as pyromelotic dianhydride). Examples of benzophenonetetracarboxylic dianhydrides include 3,3'-4,4'-benzophenonetetracarboxylic dianhydride. Examples of biphenyltetracarboxylic dianhydrides 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. Examples of biphenylsulfonetetracarboxylic dianhydrides include 3,3',4,4'-biphenylsulfonetetracarboxylic dianhydride. Examples of naphthalenetetracarboxylic dianhydrides include 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,2,4,5-naphthalenetetracarboxylic dianhydride, and 1,4,5,8-naphthalenetetracarboxylic dianhydride. These can be used alone or in combination. From the viewpoint of mechanical strength, the dianhydride component is preferably biphenyltetracarboxylic dianhydride, and more preferably 3,3'-4,4'-biphenyltetracarboxylic dianhydride. 3,3'-4,4'-biphenyltetracarboxylic dianhydride is sometimes abbreviated as BPDA.

[0042] 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.

[0043] To prepare a polyimide resin precursor, the diamine component, the acid dianhydride component, and a solvent are mixed to prepare a varnish, and the varnish is heated to prepare a precursor solution. Subsequently, a nucleating agent and a porosifying agent are mixed with the precursor solution to prepare a porous precursor solution.

[0044] The viscosity of the porous precursor solution at 25°C is appropriately set depending on the coater conditions and the thickness of the precursor film, which will be described below. Specifically, the viscosity of the porous precursor solution at 25°C is, for example, 5 Pa·s or more, preferably 10 Pa·s or more, and for example, 100 Pa·s or less, preferably 50 Pa·s or less. The viscosity of the porous precursor solution at 25°C is measured using an E-type viscometer.

[0045] The porous precursor solution is then applied to one surface of the substrate film 7 in the thickness direction to form a coating film. A coater is used to form the coating film. The coater is not particularly limited. Examples of coaters include gravure roll coaters, reverse roll coaters, kiss roll coaters, dip roll coaters, bar coaters, knife coaters, spray coaters, comma coaters, direct coaters, and die coaters. Comma coaters and die coaters are preferred. On the other hand, methods using a die may result in an excessively thick coating film, making them unsuitable.

[0046] The coating is then dried by heating to form a precursor film. As the heating proceeds, the solvent is removed, resulting in a precursor film having a phase-separated structure of the polyimide resin precursor and the porosifying agent, with the nucleating agent as the core. The drying temperature by heating is low, and the drying time is short. Specifically, the drying temperature is, for example, 160°C or less. The drying time is, for example, 1000 seconds or less. The drying by heating forms a skin layer 3 on one surface of the precursor film in the thickness direction.

[0047] Thereafter, the porosifying agent is extracted (pulled out or removed) from the precursor film by, for example, supercritical extraction using supercritical carbon dioxide as a solvent.

[0048] The precursor film is then cured by heating to form a film for metal layer laminates 1 made of polyimide resin. This film for metal layer laminates 1 includes a skin layer 3 and a porous resin layer 2 in this order toward the other side in the thickness direction. One surface in the thickness direction of the skin layer 3 is in contact with the base film 7.

[0049] Thereafter, as necessary, the substrate film 7 is removed as shown by the solid line in FIG. 1. For example, the substrate film 7 is dissolved using a stripping solution. Examples of the stripping solution include FeCl3. In this way, the film 1 for metal layer laminate is obtained. When producing the metal layer laminate 10 described below, the substrate film 7 is not removed but remains as the first metal layer 5.

[0050] <Application> Next, a metal layer laminate 10 including a film 1 for a metal layer laminate will be described, as shown by the imaginary lines in Fig. 1. The metal layer laminate 10 includes the film 1 for a metal layer laminate and two metal layers 5 and 6 shown by the imaginary lines.

[0051] The film 1 for a metal layer laminate is provided on a metal layer laminate 10. That is, the film 1 for a metal layer laminate is used to laminate two metal layers 5 and 6, which will be described next.

[0052] The two metal layers 5, 6 include a first metal layer 5 and a second metal layer 6. The first metal layer 5 is disposed on one surface in the thickness direction of the film 1 for metal layer laminates. Specifically, the first metal layer 5 is in contact with the entire one surface in the thickness direction of the skin layer 3. Examples of materials for the first metal layer 5 include the metals exemplified for the base film 7. Preferably, copper is used. The thickness of the first metal layer 5 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.

[0053] The second metal layer 6 is disposed on the other surface in the thickness direction of the film 1 for metal layer laminates. Specifically, the second metal layer 6 is in contact with the entire other surface in the thickness direction of the porous resin layer 2 (fifth region 15). The second metal layer 6 may be disposed on the other surface in the thickness direction of the porous resin layer 2 via an adhesive layer (not shown). Examples of materials for the second metal layer 6 include the metals exemplified for the base film 7. The thickness of the second metal layer 6 is the same as that of the first metal layer 5.

[0054] The method for manufacturing the metal layer laminate 10 will be described. First, during manufacturing, a second metal layer 6 is disposed on the other surface in the thickness direction of a laminate comprising a base film 7 and a film 1 for a metal layer laminate. On the other hand, since the base film 7 is made of metal, it is left as it is as the first metal layer 5 (it is diverted to the first metal layer 5). In this way, a metal layer laminate 10 is obtained, comprising the film 1 for a metal layer laminate, and the first metal layer 5 and the second metal layer 6 disposed on one and the other surfaces in the thickness direction thereof.

[0055] Thereafter, the first metal layer 5 and the second metal layer 6 are patterned by, for example, etching.

[0056] Depending on the application and purpose, the metal layer laminate 10 is pressed before, during, and / or after the formation of the above-mentioned pattern. Specifically, the metal layer laminate 10 is heat-pressed.

[0057] This metal layer laminate 10 is used, for example, in fifth-generation (5G) standard wireless communications and high-speed flexible printed circuit boards (FPCs).

[0058] (Effects of one embodiment)

[0059] In this film 1 for metal layer laminates, although the average pore diameter W of the entire porous resin layer 3 in the thickness direction is as small as 7.0 μm or less, the ratio (A1 / A5) of the average pore diameter A1 of the first region 11 to the average pore diameter A5 of the fifth region 15 is 0.45 or more, preventing it from becoming too small. Therefore, fluctuations in the dielectric constant of the film 1 for metal layer laminates before and after pressing can be suppressed.

[0060] (Variation) In the following modifications, the same components and steps as those in the above-described embodiment are denoted by the same reference numerals, and detailed descriptions thereof will be omitted. Furthermore, the modifications can achieve the same effects as those in the above-described embodiment, unless otherwise specified. Furthermore, the embodiment and its modifications can be combined as appropriate.

[0061] The material of the base film 7 may be resin. In that case, after producing the film 1 for metal layer laminates, the base film 7 is removed, and then the first metal layer 5 is attached to one surface in the thickness direction of the skin layer 3, using an adhesive layer as necessary. At this time, pressing (specifically, heat pressing) is used.

[0062] As shown in Fig. 2, the film 1 for metal layer laminates of the modified example includes two skin layers 3 and 4. The two skin layers 3 and 4 include the above-mentioned skin layer 3 and a second skin layer 4. The second skin layer 4 is disposed on the other surface in the thickness direction of the porous resin layer 2. Specifically, the second skin layer 4 is in contact with the entire other surface in the thickness direction of the porous resin layer 2 (fifth region 15). The material and thickness of the second skin layer 4 are the same as those of the skin layer 3 described above. [Example]

[0063] The present invention will be described in more detail below with reference to examples and comparative examples. It should be noted that the present invention is not limited to these examples and comparative examples. The specific numerical values ​​of the blending ratios (content ratios), physical property values, parameters, etc. used in the following description can be substituted with the upper limit (a numerical value defined as "equal to or less than") or lower limit (a numerical value defined as "equal to or more than" or "exceeding") of the corresponding blending ratios (content ratios), physical property values, parameters, etc. described in the "Description of the Invention" above.

[0064] Example 1 A reactor equipped with a stirrer and a thermometer was charged with 71.37 g (0.66 mol) of PDA, 44.05 g (0.22 mol) of ODA, and 50.22 g (0.22 mol) of APAB, and 2300 g of N-methyl-2-pyrrolidone (NMP) was added as a solvent and stirred to prepare an NMP solution of PDA, ODA, and APAB. The NMP solution contained 1.10 mol of the diamine component.

[0065] Next, 323.64 g (1.10 mol) of 3,3'-4,4'-biphenyltetracarboxylic dianhydride (3,3'-4,4'-BPDA) was gradually added to the NMP solution of PDA, ODA, and APAB, and 331 g of N-methyl-2-pyrrolidone (NMP) was added. The mixture was heated to 80°C and stirred for 10 hours to obtain a polyimide precursor solution.

[0066] To 100 parts by mass of the solids content of the polyimide precursor solution, 3 parts by mass of PTFE powder with a median diameter of 1 μm or less was added as a nucleating agent, 200 parts by mass of polyoxyethylene dimethyl ether (grade: MM400, manufactured by NOF Corporation) with a weight-average molecular weight of 400 as a porosifying agent, and 4 parts by mass of 2-methylimidazole (2Mz-H, manufactured by Shikoku Chemical Industries Co., Ltd.) to obtain a porous precursor solution. The viscosity of the porous precursor solution at 25 °C was 50 Pa·s. This porous precursor solution was applied to a copper substrate film 7 (second metal layer 6) using a comma coater to form a coating. The comma coater has two rolls arranged opposite each other with a gap between them. The substrate film 7 was brought into contact with one roll, and the closest distance (gap) between the substrate film 7 and the other roll was set to 225 μm.

[0067] Thereafter, the coating was dried at 120 to 160°C for 540 seconds to prepare a precursor film with a thickness of approximately 50 µm.

[0068] This precursor film was immersed in carbon dioxide pressurized to 30 MPa at 60°C and passed through for 8 hours to promote the extraction and removal of the porosifying agent, phase separation of the remaining NMP, and the formation of pores.The carbon dioxide pressure was then reduced.

[0069] The precursor film was then heat-treated under vacuum at a temperature of 300°C to 400°C for approximately 5 hours to remove remaining components and promote imidization, thereby obtaining a film 1 for metal layer laminates arranged on one surface in the thickness direction of the base film 7. The base film 7 and the film 1 for metal layer laminates were then immersed in an FeCl3 solution to dissolve and remove the base film 7. In this way, a film 1 for metal layer laminates comprising a porous resin layer 2 and a skin layer 3 was produced.

[0070] The thicknesses of the porous resin layer 2, skin layer 3, and film for metal layer laminates 1 in Example 1 were 40.7 μm, 3.0 μm, and 43.7 μm, respectively. The thickness of the film for metal layer laminates 1 was measured using a film thickness measuring device (HKT-1200, manufactured by Fujiwork Co., Ltd.). The thickness of the skin layer 3 was determined by SEM observation, which will be described later. The thickness of the porous resin layer 2 was determined by subtracting the thickness of the skin layer 3 from the thickness of the film for metal layer laminates 1. The thicknesses in the following examples were also determined in the same manner as above.

[0071] The dielectric constant of film 1 for metal layer laminates at a frequency of 10 GHz was 1.62. The dielectric constant was determined by the Split Post Dielectric Resonator (SPDR) method using a PNA network analyzer (Agilent Technologies). The dielectric constants of the following examples were determined in the same manner as above.

[0072] Example 2 A film 1 for metal layer laminates was produced in the same manner as in Example 1. However, the gap was changed to 250 μm and the drying time was changed to 900 seconds. The thicknesses of the porous resin layer 2, skin layer 3, and film 1 for metal layer laminates in Example 2 were 44.9 μm, 3.9 μm, and 48.8 μm, respectively. The dielectric constant of the film 1 for metal layer laminates in Example 2 at a frequency of 10 GHz was 1.61.

[0073] Example 3 A film 1 for metal layer laminates was produced in the same manner as in Example 2. However, the viscosity of the porous precursor solution at 25°C was changed to 10 Pa·s by changing the stirring time from 10 hours after heating to 80°C during preparation of the polyimide precursor solution to 15 hours. The thicknesses of the porous resin layer 2, skin layer 3, and film 1 for metal layer laminates in Example 3 were 42.0 μm, 3.0 μm, and 45.0 μm, respectively. The dielectric constant of the film 1 for metal layer laminates in Example 3 at a frequency of 10 GHz was 1.63.

[0074] Example 4 A film 1 for metal layer laminates was produced in the same manner as in Example 1. However, the gap was changed to 260 μm and the drying time was changed to 900 seconds. The thicknesses of the porous resin layer 2, skin layer 3, and film 1 for metal layer laminates in Example 4 were 49.1 μm, 3.7 μm, and 52.8 μm, respectively. The dielectric constant of the film 1 for metal layer laminates in Example 4 at a frequency of 10 GHz was 1.65.

[0075] (Comparative Example 1) A film 1 for metal layer laminates was produced in the same manner as in Example 1. However, the gap was changed to 275 μm and the drying time was changed to 900 seconds. The film 1 for metal layer laminates in Comparative Example 1 had a thickness of 58.3 μm and a dielectric constant at a frequency of 10 GHz of 1.54.

[0076] (Comparative Example 2) A film 1 for metal layer laminates was produced according to the formulation of Example 2 of Patent Document 1. The thicknesses of the porous resin layer 2, skin layer 3, and film 1 for metal layer laminates in Example 2 were 94 μm, 6 μm, and 100 μm, respectively, and the dielectric constant at a frequency of 10 GHz was 1.48.

[0077] <Evaluation> The films 1 for metal layer laminates of the respective Examples and Comparative Examples were evaluated for the following items. The results are shown in Table 1.

[0078] <Average pore diameter> A secondary electron image of the cross section of the film 1 for metal layer laminates was observed using an SEM (SU8020, manufactured by Hitachi, Ltd.) at an accelerating voltage of 2.0 kV to obtain an SEM image. The first region 11 to the fifth region 15 were identified from this SEM image, and the average pore diameter A1 of the first region 11, the pore diameter A5 of the fifth region 15, and the average pore diameter W of the entire thickness direction were each measured twice. Each pore diameter was determined by measuring the maximum pore diameter using the scale bar on the SEM image as a reference. The average values ​​of the two measurements were then obtained as the average pore diameter A1 of the first region 11, the pore diameter A5 of the fifth region 15, and the average pore diameter W of the entire thickness direction, respectively. The ratio (A1 / A5) of the average pore diameter A1 of the first region 11 to the average pore diameter A5 of the fifth region 15 obtained above was also calculated.

[0079] <Heat pressability> A sample measuring 40 mm x 40 mm was prepared from the film 1 for metal layer laminates. This sample was placed in an instantaneous vacuum lamination device VS008-1515 (manufactured by Mikado Technos Co., Ltd.) and pressed at 160°C and 5 MPa for 300 seconds. The thickness and dielectric constant after pressing were determined. The variation rates of thickness and dielectric constant before and after pressing were then calculated based on the following equations.

[0080] Thickness variation rate before and after pressing (%) = (thickness after pressing - thickness before pressing) / thickness before pressing × 100

[0081] Percentage of change in dielectric constant before and after pressing (%) = (Dielectric constant after pressing - Dielectric constant before pressing) / Dielectric constant before pressing × 100

[0082] [Table 1] [Explanation of symbols]

[0083] 1. Film for metal layer laminates 2 Porous resin layer 3 Skin Layer 4 Second Skin Layer 5 1st metal layer 6 Second metal layer 10 Metal layer laminate 11 First area 15 5th area

Claims

[Claim 1] A film for metal layer laminates used for laminating metal layers, a porous resin layer and a skin layer in that order in the thickness direction; the porous resin layer has an average pore size of 7.0 μm or less in the entire thickness direction; the porous resin layer includes first to fifth regions that are arranged in order in a direction away from the skin layer when the porous resin layer is divided into five equal parts in a thickness direction, A film for metal layer laminates, wherein the ratio of the average pore size of the first region to the average pore size of the fifth region is 0.45 or more and 1 or less.

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