JP2025138045A - Resin films, metal-clad laminates, circuit boards, electronic devices and electronic equipment - Google Patents

Abstract

[Problem] To provide a resin film consisting of a single polyimide layer that has excellent transparency, heat resistance, and dimensional stability, and to provide a metal clad laminate that can be used as an insulating resin layer that is directly laminated to a metal layer, even though it is a single layer, and that has excellent adhesion between the insulating resin layer and the metal layer.
[Solution] A single-layer polyimide resin film satisfies the following conditions a to c: a) a thickness within the range of 5 μm or more and 100 μm or less; b) a total light transmittance of 80% or more; and c) a yellowness index YI at a thickness of 25 μm of 30 or less, wherein the polyimide constituting the polyimide layer contains an aromatic tetracarboxylic dianhydride residue and a diamine residue, and the polyimide contains a polyimide represented by the following general formula (1) with respect to all the diamine residues:

and 1 mol % to 40 mol % of diamine residues consisting of a secondary aromatic diamine such as 1,3-bis(3-aminophenoxy)benzene.
[Selection diagram] None

Description

The present invention relates to a highly transparent resin film (insulating resin layer) that has excellent heat resistance, adhesiveness, and flexibility, a metal-clad laminate obtained by laminating the same, and circuit boards, electronic devices, and electronic equipment that utilize them.

Polyimide is a heat-resistant resin obtained by ring-closing polyamic acid, which is synthesized by a condensation reaction of tetracarboxylic acid anhydrides and diamines. Its molecular chain rigidity, resonance stabilization, and strong chemical bonds give it excellent resistance to thermal decomposition, high durability against chemical changes such as oxidation and hydrolysis, and excellent flexibility, mechanical properties, and electrical properties. Polyimide is widely used in the insulating resin layers of flexible printed circuit boards (FPCs), which are commonly used in electronic devices.

Generally, the polyimide insulating resin layer in commercially available copper clad laminate (CCL) used in FPCs is yellowish-brown, making it difficult to apply to FPCs that require transparency. However, CCL's excellent transparency allows for excellent visibility from the insulating resin layer side when mounting semiconductor elements on a wiring board. Therefore, when bonding semiconductor elements to FPCs via a photocurable resin, CCL is advantageous for light irradiation from the insulating resin layer side, making it promising for use in transparent FPCs.

Therefore, in order to make polyimides colorless and transparent, studies have been conducted to suppress the formation of intramolecular and intermolecular charge-transfer complexes by using alicyclic diamines or alicyclic acid anhydrides as diamine components. For example, Patent Document 1 proposes a colorless and transparent semi-alicyclic polyimide formed from an alicyclic diamine and an aromatic acid dianhydride, while Patent Document 2 proposes a colorless and transparent fully alicyclic polyimide composed of an alicyclic diamine and an alicyclic acid anhydride. However, the glass transition temperatures of the resulting polyimides are all approximately 280°C or below, and their heat resistance is insufficient, making them difficult to use as a major component such as an insulating layer in an FPC.

Patent Documents 3 and 4 propose a laminate of metal and polyimide using a fluorinated polyimide as an insulating resin layer. However, while the resulting laminate has excellent transparency, it lacks sufficient control of the thermal expansion coefficient and other properties of the insulating layer, and has low adhesive strength with the smooth metal layer, meaning it does not fully satisfy the properties required for a wiring board laminate suitable for FPC applications.

For this reason, in Patent Document 5, the applicant proposed a resin film with excellent heat resistance, adhesiveness, flexibility, and high transparency, which was achieved by using multiple polyimide layers, including a non-thermoplastic polyimide layer and a thermoplastic polyimide layer. However, because multiple polyimide layers are formed by sequential coating using a casting method, the manufacturing time (coating time) is long, raising concerns about reduced yield. Furthermore, in Patent Document 6, a metal-clad laminate was proposed in which a single polyimide layer made of transparent polyimide was laminated. However, because the metal layer is formed on the polyimide film by sputtering, there are concerns about adhesion to the metal layer.

Japanese Unexamined Patent Publication No. 7-10993 JP 2008-163210 A Japanese Patent Application Publication No. 4-47933 Japanese Patent Application Laid-Open No. 2000-198842 Patent No. 7222089 Japanese Patent Application Laid-Open No. 2023-20715

In order to solve the above-mentioned problems, the object of the present invention is to provide a resin film consisting of a single polyimide layer that has excellent transparency, heat resistance, and dimensional stability, and to provide a metal clad laminate that can be used as an insulating resin layer that is directly laminated to a metal layer, even though it is a single layer, and that has excellent adhesion between the insulating resin layer and the metal layer.

After extensive research into resolving the above-mentioned issues, the inventors discovered that the above-mentioned issues could be resolved by using a specific polyimide in the insulating resin layer of a wiring board laminate or FPC, and by controlling the thickness and specific physical properties of the polyimide layer, leading to the completion of the present invention.

That is, the present invention provides a resin film comprising a single polyimide layer,
The following conditions a to c:
a) the thickness is in the range of 5 μm or more and 100 μm or less;
b) total light transmittance is 80% or more;
c) Yellowness index YI at a thickness of 25 μm is 30 or less;
Fulfilling
the polyimide constituting the polyimide layer contains an aromatic tetracarboxylic dianhydride residue derived from an aromatic tetracarboxylic dianhydride component and a diamine residue derived from a diamine component;
With respect to all diamine residues, the following general formula (1):
[In formula (1), each substituent X independently represents an alkyl group having 1 to 3 carbon atoms substituted with a fluorine atom, and each of m and n independently represents an integer of 1 to 4.]
and a diamine residue derived from a first aromatic diamine represented by the following general formula (2):
[In formula (2), the linking group Y independently represents a divalent group selected from -O- and -S-, and the linking group X represents a group represented by formula (x1), formula (x2), or formula (x3);
In formula (x3), Z represents a divalent group selected from —O—, —S—, —CH ₂ —, —CH(CH ₃ )—, —C(CH ₃ ) ₂ —, —CO—, —SO ₂ —, —NH—, or —NHCO—.]
The resin film is characterized by containing 1 mol % or more and 40 mol % or less of a diamine residue derived from a second aromatic diamine represented by the following formula:

In the resin film of the present invention, the polyimide is a wholly aromatic tetracarboxylic acid dianhydride residue represented by the following formula (3):
and the acid dianhydride residue derived from pyromellitic anhydride represented by the following general formula (4):
[In formula (4), X represents a divalent group selected from a single bond, —O—, or —C(CF ₃ ) ₂ —.]
The present invention is characterized in that the aromatic tetracarboxylic acid dianhydride of the present invention contains 10 mol % or more and 50 mol % or less of an acid dianhydride residue derived from an aromatic tetracarboxylic acid dianhydride represented by the following formula:

The resin film of the present invention further satisfies the following condition d in addition to the above conditions a to c:
d) a thermal expansion coefficient in the range of 10 ppm/K or more and 40 ppm/K or less;
The present invention is characterized in that:
The resin film of the present invention further satisfies the following condition e in addition to the above conditions a to c:
e) HAZE is 5% or less;
The present invention is characterized in that:

The present invention relates to a metal-clad laminate comprising an insulating resin layer and a metal layer laminated on one or both sides of the insulating resin layer, wherein the insulating resin layer is made of the resin film described above, and also to a circuit board, electronic device, or electronic equipment.

The resin film of the present invention has excellent dimensional stability, adhesiveness, and high transparency, and is therefore particularly suitable for use as an insulating material for electronic components such as FPCs, particularly for transparent FPCs that require colorless transparency. Furthermore, since it is a single layer, it can significantly reduce production time and improve yield compared to multi-layer polyimide resin films, and is also desirable from the standpoints of energy conservation and carbon dioxide emission reduction (carbon neutrality).
The resin film and metal clad laminate of the present invention can also be applied to display devices such as liquid crystal display devices, organic EL display devices, touch panels, color filters, and electronic paper, as well as their component parts.

The resin film of the present invention will be described below.
From the viewpoint of transparency, the resin film of the present invention must have a thickness in the range of 5 μm or more and 100 μm or less, a total light transmittance in the visible region of 80% or more, and a yellowness index YI at a thickness of 25 μm of 30 or less.
The resin film of the present invention is a single polyimide layer, which makes it possible to provide a resin film that is excellent not only in transparency but also in physical properties such as heat resistance and dimensional stability.

The resin film of the present invention is a non-thermoplastic polyimide that does not soften even when heated, has excellent dimensional stability, and has a coefficient of thermal expansion (CTE) of preferably 1 ppm/K or more and 50 ppm/K or less, more preferably 10 ppm/K or more and 40 ppm/K or less.
From the viewpoint of transparency, the resin film of the present invention has a total light transmittance in the visible region of 80% or more. For example, it is preferable that this is satisfied when the resin film has a thickness of 25 μm. More preferably, the total light transmittance is 85% or more. By controlling the total light transmittance within this range, cloudiness due to light reflection and scattering in the resin film is suppressed, resulting in excellent transparency. In addition, the position of the metal layer can be recognized and viewed through the insulating resin layer.
The resin film of the present invention preferably has a haze (turbidity) of 5% or less, more preferably 2% or less. If the haze exceeds 5%, for example, visibility and light transmittance tend to decrease.
The resin film of the present invention has a YI (yellowness index) of 30 or less when the thickness is 25 μm, and more preferably 20 or less. By controlling the YI within such a range, the resin film can be made almost colorless.

The resin film of the present invention consists of a single polyimide layer, and the polyimide constituting the polyimide layer contains aromatic tetracarboxylic dianhydride residues derived from the aromatic tetracarboxylic dianhydride component and diamine residues derived from the diamine component.

The polyimide contains, as diamine components, an aromatic diamine residue (hereinafter also referred to as the first aromatic diamine residue) derived from a first aromatic diamine represented by general formula (1) and an aromatic diamine residue (hereinafter also referred to as the second aromatic diamine residue) derived from a second aromatic diamine represented by general formula (2).

The primary aromatic diamine residue is represented by the following general formula (1):
[In formula (1), each substituent X independently represents an alkyl group having 1 to 3 carbon atoms substituted with a fluorine atom, and each of m and n independently represents an integer of 1 to 4.]
It is a diamine residue derived from an aromatic diamine represented by the formula:
The substituent X is preferably a trifluoromethyl group, and m and n are preferably 1 or 2.
The content of primary aromatic diamine residues is in the range of 60 mol % to 99 mol %, preferably 95 mol % or less, more preferably 90 mol % or less, based on the total diamine residues.

By containing a predetermined amount of primary aromatic diamine residue, the resin film can be made colorless and transparent, an increase in the coefficient of thermal expansion (CTE) can be suppressed, and dimensional stability can be improved.
Preferred examples of the primary aromatic diamine include diamines represented by the following structural formula:

The secondary aromatic diamine residue is represented by the following general formula (2):
[In formula (2), the linking group Y independently represents a divalent group selected from -O- and -S-, and the linking group X represents a group represented by formula (x1), formula (x2), or formula (x3);
In formula (x3), Z represents a divalent group selected from —O—, —S—, —CH ₂ —, —CH(CH ₃ )—, —C(CH ₃ ) ₂ —, —CO—, —SO ₂ —, —NH—, or —NHCO—.]
is a diamine residue derived from a second aromatic diamine represented by the formula:
The secondary aromatic diamine residue is contained in an amount of 1 mol % to 40 mol % of the total diamine residues, preferably 5 mol % or more, and more preferably 10 mol % or more.

Secondary aromatic diamines are represented by general formula (2). The main backbone contains a heteroatom (-O-, -S-) as the linking group Y, allowing the molecular chain to rotate freely and providing high flexibility. The highly flexible molecular chains facilitate non-planar structures, preventing electron cloud overlap and reducing charge transfer (CT) between the aromatic tetracarboxylic acid residue and the aromatic diamine residue, allowing the polyimide to approach colorless transparency. Polyimides with highly flexible molecular chains exhibit high adhesion to substrates such as metal layers due to the entanglement of the molecular chains. In general formula (2), molecular chains containing linking groups Y or X (x1-3) in the main backbone, and molecular chains containing linking group Z in the case of the formula (x3) structure, exhibit high interaction, such as chemical bonding, with metals and metal surface treatment agents, providing excellent adhesion. For the reasons described above, by blending a predetermined amount of a secondary aromatic diamine represented by general formula (2), which is excellent in improving the transparency of polyimide and the adhesion to a support such as a metal layer, with a primary aromatic diamine represented by general formula (1), which is excellent in improving the transparency and dimensional stability of polyimide, a polyimide film excellent in transparency, high dimensional stability, and adhesion can be obtained.
Preferred examples of the secondary aromatic diamine include diamines represented by the following structural formula:
As the second aromatic diamine, those having a structure in which the amino group is linked at the m-position are particularly preferred.

The resin film of the present invention may contain diamine residues derived from other diamines, as long as the purpose of the present invention is not impaired. However, if other diamine residues are contained, the amount of such residues is preferably less than 30 mol %, more preferably less than 10 mol %, of the total diamine residues.

As the other diamine, any of those known as diamine components for polyimides, particularly transparent polyimides, can be used. Specific examples include, but are not limited to, the following:

The polyimide preferably contains, as its acid dianhydride components, predetermined amounts of acid dianhydride residues derived from pyromellitic anhydride represented by formula (3) and acid dianhydride residues derived from aromatic tetracarboxylic acid anhydride represented by general formula (4).

The pyromellitic acid residue is represented by formula (3);
It is an acid dianhydride residue derived from pyromellitic acid represented by the following formula:
The content of pyromellitic acid residues is preferably in the range of 50 mol % to 95 mol % based on the total acid dianhydride residues, with the lower limit being more preferably 70 mol % or more, and even more preferably 80 mol % or more, and the upper limit being more preferably 90 mol % or less.

By containing a certain amount of pyromellitic acid residues, the heat resistance (Tg) of the single-layer polyimide can be increased, the coefficient of thermal expansion (CTE) can be appropriately controlled, and dimensional stability can be improved.

The aromatic tetracarboxylic dianhydride residue that is preferably present together with the pyromellitic acid residue is represented by the general formula (4):
[In formula (4), X represents a divalent group selected from a single bond, —O—, or —C(CF ₃ ) ₂ —.]
It is an acid dianhydride residue derived from an aromatic tetracarboxylic acid dianhydride represented by the following formula:
The aromatic tetracarboxylic dianhydride residue of formula (4) is preferably contained in an amount of 5 mol % to 50 mol %. The lower limit is more preferably 10 mol % or more, and the upper limit is more preferably 30 mol % or less, and even more preferably 20 mol % or less.

By containing a predetermined amount of the aromatic tetracarboxylic dianhydride residue of formula (4), it is possible to impart strength and flexibility to the single-layer polyimide, and it is possible to provide excellent heat resistance and transparency, and to control the CTE within an appropriate range.
Preferred examples of the aromatic tetracarboxylic dianhydride of formula (4) include acid dianhydrides of the following structural formula:

The resin film of the present invention may contain other acid anhydride residues as long as the purpose of the present invention is not impaired. However, if other acid dianhydride residues are contained, the amount of such residues is preferably less than 30 mol %, more preferably less than 10 mol %, of the total acid dianhydride residues.

As the other acid dianhydride, any of those known as an acid dianhydride component of polyimide, particularly transparent polyimide, can be used. Specific examples include, but are not limited to, the following:

In the polyimide that constitutes the resin film of the present invention, various physical properties such as transparency, heat resistance, dimensional stability, and adhesiveness can be controlled by selecting the type and molar ratio of the diamine and acid dianhydride.

Next, a method for synthesizing the polyimide constituting the resin film of the present invention (hereinafter also referred to as single-layer polyimide) will be described.
The single-layer polyimide of the present invention can be produced by reacting the diamine and acid dianhydride described above in a solvent to form a polyamic acid, followed by heating and ring-closure. For example, approximately equimolar amounts of the diamine and acid dianhydride are dissolved in an organic solvent and the resulting mixture is stirred at a temperature ranging from 0°C to 100°C for 30 minutes to 24 hours to polymerize the polyamic acid, which serves as the polyimide precursor. Examples of organic solvents used in the polymerization reaction include N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, 2-butanone, dimethyl sulfoxide, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diglyme, triglyme, and γ-butyrolactone. Two or more of these solvents can also be used in combination, and aromatic hydrocarbons such as xylene and toluene can also be used in combination.
The amount of organic solvent used is not particularly limited, but it is preferable to adjust the concentration of the polyamic acid solution (polyimide precursor solution) obtained by the polymerization reaction to about 5 to 30% by weight.
The single-layer polyimide of the present invention may contain an end-capping agent. The end-capping agent is preferably a monoamine or a dicarboxylic acid. The amount of the end-capping agent to be introduced is preferably in the range of 0.0001 mol to 0.1 mol per mol of the acid anhydride component.

The synthesized polyamic acid is usually advantageously used as a reaction solvent solution, but it can be concentrated, diluted, or substituted with another organic solvent if necessary. The method for imidizing the polyamic acid is not particularly limited; for example, it can be heat-treated in a solvent at a temperature of 80°C to 400°C for 1 to 24 hours.

The weight-average molecular weight (Mw) of the polyamic acid is preferably in the range of 10,000 to 400,000, and more preferably in the range of 50,000 to 350,000. If the weight-average molecular weight is less than 10,000, the film tends to have reduced strength and become brittle. On the other hand, if the weight-average molecular weight exceeds 400,000, the viscosity increases excessively, making the film more susceptible to defects such as uneven thickness and streaks during coating.

The monolayer polyimide resin film of the present invention may be a single insulating resin film (sheet), or may be an insulating resin film laminated on a substrate such as a resin sheet, such as a copper foil, a glass plate, a polyimide film, a polyamide film, or a polyester film.
Examples of methods for preparing the resin film of the present invention include a method in which a polyamic acid solution is applied to a support substrate, dried, and then imidized to produce a resin film, or a method in which a polyamic acid solution is applied to a support substrate, dried, and then the polyamic acid gel film is peeled off from the support substrate and imidized to produce a resin film. The method for applying the polyimide solution (or polyamic acid solution) to the substrate is not particularly limited, and it can be applied using, for example, a coater such as a comma, die, knife, or lip coater.

The metal-clad laminate of the present invention will be described below.
The metal-clad laminate of the present invention uses the resin film of the present invention as an insulating resin layer, and has a metal layer on at least one side of the insulating resin layer, i.e., on one or both sides.

The thickness of the insulating resin layer is in the range of 5 μm to 100 μm. If it is less than the lower limit, electrical insulation cannot be ensured, and there is a concern that handling may be impaired. If it exceeds the upper limit, dimensional changes before and after etching will be significant, and visibility will tend to be impaired. The preferred range is 10 μm to 50 μm.

The insulating resin layer preferably has a glass transition temperature (Tg) of 270° C. or higher, more preferably 300° C. or higher, and even more preferably 350° C. or higher. The thermal decomposition temperature (1% weight loss temperature, Td1) is preferably 500° C. or higher, and the thermal decomposition temperature (5% weight loss temperature, Td5) is preferably 550° C. or higher.
The insulating resin layer preferably has a coefficient of thermal expansion (CTE) in the range of 10 ppm/K to 50 ppm/K.
From the viewpoint of transparency and visibility, the insulating resin layer preferably has a total light transmittance (TT) in the visible region of 80% or more. For example, it is preferable that this is satisfied when the insulating resin layer has a thickness of 20 μm. More preferably, the total light transmittance is 85% or more.
The insulating resin layer preferably has a yellowness index (YI) of 30 or less. For example, it is preferable that this is satisfied when the insulating resin layer has a thickness of 25 μm.
The insulating resin layer preferably has a haze of 5% or less, more preferably 3% or less.
The insulating resin layer preferably has an elastic modulus of 10 GPa or less, a maximum strength of 130 MPa or more, and a maximum elongation of 5% or more.

In the metal-clad laminate of the present invention, methods for forming the insulating resin layer include, for example, a method (casting method) in which a polyamic acid solution is applied to a metal layer (metal foil), dried, and then imidized to produce a resin film; a method (lamination method) in which a pre-formed resin film and metal foil are thermocompression-bonded; and a method (sputtering method) in which metal is sputtered onto a pre-formed resin film. In particular, when the resin film of the present invention is used to form the insulating resin layer by a casting method, a metal-clad laminate with excellent adhesion to the metal layer can be produced.

The insulating resin layer may contain an inorganic filler as needed. Examples of inorganic fillers include silicon dioxide, aluminum oxide, magnesium oxide, beryllium oxide, boron nitride, aluminum nitride, silicon nitride, aluminum fluoride, and calcium fluoride.

In metal-clad laminates, the material of the metal layer is not particularly limited, but examples include copper, stainless steel, iron, nickel, beryllium, aluminum, zinc, indium, silver, gold, tin, zirconium, tantalum, titanium, lead, magnesium, manganese, and alloys thereof. Copper, iron, or nickel is particularly preferred.

The thickness of the metal layer is not particularly limited, but is preferably 100 μm or less, and more preferably in the range of 1 μm to 20 μm.

When manufacturing a metal-clad laminate having metal layers on both sides, it can be obtained, for example, by laminating a metal layer directly onto the insulating resin layer side of a single-sided metal-clad laminate obtained by the casting method described above, using a method such as thermocompression bonding. The heat-pressing temperature for thermocompression bonding is preferably equal to or higher than the glass transition temperature of the single-layer polyimide. The heat-pressing pressure is, for example, in the range of 1 kg/m2 to 500 kg/m2.

Since the resin film of the present invention has excellent adhesion to a metal layer, the metal layer does not necessarily require surface roughening treatment. However, if the surface is roughened, it is preferable that the ten-point average roughness Rzjis of the surface is 0.5 μm or less.
In the metal-clad laminate of the present invention, the peel strength between the insulating resin layer and the metal layer is preferably 0.5 kN/m or more.

The metal-clad laminate of the present invention can be suitably used as a circuit board material such as an FPC. For example, it is useful as a circuit board such as an FPC, an electronic circuit including active elements such as transistors and diodes, and passive devices such as resistors, capacitors, and inductors, as well as a sensor element for sensing pressure, temperature, light, humidity, etc., a light-emitting element, an image display element such as a liquid crystal display, an electrophoretic display, or a self-luminous display, a wireless or wired communication element, an arithmetic element, a memory element, a MEMS element, a solar cell, a thin-film transistor, etc.

[Electronic Devices and Electronic Equipment]
The electronic devices and electronic equipment according to the embodiments of the present invention include the circuit board. Examples of the electronic devices according to the present embodiments include display devices such as liquid crystal displays, organic EL displays, and electronic paper, as well as organic EL lighting, solar cells, touch panels, camera modules, inverters, converters, and components thereof. Examples of the electronic equipment include HDDs, DVDs, mobile phones, smartphones, tablet devices, automotive electronic control units (ECUs), power control units (PCUs), and the like. In these electronic devices and electronic equipment, the circuit board is preferably used as a component, such as wiring for moving parts, cables, and connectors.

The present invention will be explained in detail below based on examples, but the present invention is not limited to these examples. Physical properties were measured and evaluated as follows:

[Viscosity of Polyamic Acid]
The polyamic acid solutions obtained in the synthesis examples were measured at 25° C. using a cone-plate viscometer equipped with a thermostatic water bath (manufactured by Tokimec Co., Ltd.).
[Number average molecular weight (Mn) Weight average molecular weight (Mw)]
Measurement was performed by gel permeation chromatography (manufactured by Tosoh Corporation, trade name: HLC-8220GPC). Polystyrene was used as a standard substance, and N,N-dimethylacetamide was used as a developing solvent.

[Calculation of Yellowness Index (YI)]
The yellowness index (YI) of a polyimide film (50 mm x 50 mm) was measured using a UV-3600 spectrophotometer manufactured by Shimadzu Corporation. Here, YI was calculated based on the following formula (1) in accordance with JIS Z 8722.
YI=100×(1.2879X-1.0592Z)/Y...(1)
X, Y, and Z: Tristimulus values of test piece The YI(25) of a polyimide film having a thickness of 20 μm was calculated by substituting the YI value calculated by the above formula (1) into the following formula (2).
YI(25)=YI/L×25...(2)
L: Thickness of polyimide film (μm)
[Measurement of haze (turbidity) and total light transmittance (T.T.)]
The haze (turbidity) and total light transmittance (TT) of the polyimide film (50 mm x 50 mm) were measured using a HAZE METER NDH5000 manufactured by Nippon Denshoku Industries Co., Ltd. in accordance with JIS K7136.

[Measurement of coefficient of thermal expansion (CTE)]
A polyimide film (3 mm × 15 mm) was heated from 30°C to 280°C at a heating rate of 10°C/min while applying a load of 5.0 g in a thermomechanical analysis (TMA) device, and then cooled from 250°C to 100°C. The thermal expansion coefficient was measured from the elongation (linear expansion) of the polyimide film during cooling.
[Measurement of Glass Transition Temperature (Tg)]
The polyimide layer (5 mm x 22.6 mm) was heated from 30°C to 400°C at a rate of 10°C/min using a dynamic thermomechanical analyzer, and the dynamic viscoelasticity was measured to determine the glass transition temperature (Tan δ maximum value: °C).
[Calculation of thermal decomposition temperatures (Td1, Td5)]
A polyimide film weighing 10 to 20 mg was heated at a constant rate from 30°C to 550°C in a nitrogen atmosphere using a thermogravimetric analyzer (TG) TG/DTASTA200 manufactured by Seiko Corporation, and the change in weight was measured. The weight at 200°C was set to zero, and the temperature at which the weight loss rate was 1% was defined as the thermal decomposition temperature (Td1), and the temperature at which the weight loss rate was 5% was defined as the thermal decomposition temperature (Td5).

[Measurement of tensile strength]
Using a tensile tester Strograph VG1F (manufactured by TOYOSEIKI), a tensile test was performed on a test sample of the protective film (size 10 mm x 110 mm) at a speed of 10 mm/min under a load of 100 N to determine the elastic modulus, maximum point strength, and maximum point elongation.

[Peel strength measurement] (copper clad laminate)
Using a tension tester, the polyimide layer side of a test sample having a 1 mm-wide circuit obtained from a laminate (copper-clad laminate) of copper foil and a polyimide layer serving as a support was fixed to an aluminum plate with double-sided tape, and the copper was peeled off in a 180° direction at a rate of 50 mm/min to determine the peel strength between the copper foil and the polyimide layer.

The abbreviations used in the examples represent the following compounds.
PMDA: pyromellitic dianhydride
6FDA: 2,2-bis(3,4-dicarboxyphenyl)-hexafluoropropanoic dianhydride
TFMB: 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl
APB: 1,3-bis(3-aminophenoxy)benzene
M-BAPS: bis[4-(3-aminophenoxy)phenyl]sulfone
DMAc: N,N-dimethylacetamide

Synthesis Example 1
To synthesize polyamic acid solution A, DMAc solvent was added to a 500 ml separable flask under a nitrogen stream to a solids concentration of 15 wt %, and the diamine and acid anhydride components shown in Table 1 were added and dissolved with stirring at 40°C. The solution was then stirred at room temperature for one day to carry out a polymerization reaction, producing a viscous polyamic acid solution A. The viscosity was 27,940 cP.

Synthesis Example 2
To synthesize polyamic acid solution B, DMAc solvent was added to a 300 ml separable flask under a nitrogen stream to a solids concentration of 15 wt %, and the diamine component and acid anhydride component shown in Table 1 were added and dissolved with stirring at 40°C. The solution was then stirred at room temperature for two days to carry out a polymerization reaction, producing a viscous polyamic acid solution B. The viscosity was 4310 cP.

Synthesis Example 3
To synthesize polyamic acid solution C, DMAc solvent was added to a 300 ml separable flask under a nitrogen stream to a solids concentration of 15 wt %, and the diamine component and acid anhydride component shown in Table 1 were added and dissolved with stirring at 40°C. The solution was then stirred at room temperature for one day to carry out a polymerization reaction, producing a viscous polyamic acid solution C. The viscosity was 6279 cP.

Synthesis Example 4
Polyamic acid solution D was prepared by changing the type of monomer as shown in Table 1 and carrying out polymerization in the same manner as in Synthesis Example 3. A viscous polyamic acid solution D was prepared. The viscosity was 2913 cP.

Synthesis Example 5
Polyamic acid solution E was prepared by changing the type of monomer as shown in Table 1 and carrying out polymerization in the same manner as in Synthesis Example 3. A viscous polyamic acid solution E was prepared. The viscosity was 1945 cP.

Synthesis Example 6
Polyamic acid solution F was prepared by changing the type of monomer as shown in Table 1 and carrying out polymerization in the same manner as in Synthesis Example 1. A viscous polyamic acid solution F was prepared. The viscosity was 32,385 cP.

Synthesis Example 7
Polyamic acid solution G was prepared by changing the type of monomer as shown in Table 1 and carrying out polymerization in the same manner as in Synthesis Example 2. A viscous polyamic acid solution G was prepared. The viscosity was 3802 cP.

Synthesis Example 8
To synthesize polyamic acid solution H, DMAc solvent was added to a 500 ml separable flask under a nitrogen stream to a solids concentration of 15 wt %, and the diamine and acid anhydride components shown in Table 1 were added and dissolved with stirring at 40°C. The solution was then stirred at room temperature for two days to carry out a polymerization reaction, producing a viscous polyamic acid solution H. The viscosity was 26,950 cP.

Example 1
A solution of polyamic acid solution A was uniformly applied onto copper foil (electrolytic copper foil, manufactured by Fukuda Metal Foil & Powder Co., Ltd., product name: CF-T9DA-SV18, thickness: 18 μm) so that the thickness after curing would be 19 μm, and then the solution was dried by stepwise heating in a temperature range up to 120° C. to remove the solvent. After forming a single-layer polyamic acid layer in this way, stepwise heat treatment was performed from 130° C. to 360° C. to complete imidization, forming an insulating resin layer composed of a single layer of polyimide A and having a thickness of 19 μm, and a metal-clad laminate 1A was prepared.
The copper foil was removed from the resulting single-sided metal-clad laminate 1A by etching using an aqueous ferric chloride solution to prepare a single-layer polyimide resin film 1a. The single-layer polyimide resin film 1a was measured for YI, T.T., haze, CTE, Td1, Td5, modulus of elasticity, maximum strength, and maximum elongation. The results are shown in Table 2.
Table 3 also shows the results of measuring the peel strength of the polyamic acid-coated surface of the obtained single-sided metal-clad laminate 1A when wiring was processed to 1 mm.

Examples 2 to 10
In the same manner as in Example 1, single-sided metal-clad laminates 2A to 10G were prepared by applying resins A to G listed in Table 1 to copper foil (same as above), and polyimide films 2a to 10g were prepared. Polyimide films 2a to 10g were measured for YI, T.T., haze, CTE, Td1, Td5, modulus of elasticity, maximum strength, and maximum elongation. The results are shown in Table 2.
Furthermore, the peel strength of the single-sided metal-clad laminates 2A to 10G was measured in the same manner as in Example 1, and the results are shown in Table 3.

Comparative Examples 1 and 2
Single-sided metal-clad laminates 1H and 2H and single-layer polyimide resin films 1h and 2h were prepared in the same manner as in Example 1, except that single-layer polyimide H shown in Table 1 was used. These single-layer polyimide resin films 1h and 2h and single-sided metal-clad laminates 1H and 2H were evaluated in the same manner as in Examples 1 and 2. The measurement results are also shown in Tables 2 and 3.

Claims (9)

A resin film consisting of a single polyimide layer,
The following conditions a to c:
a) the thickness is in the range of 5 μm or more and 100 μm or less;
b) total light transmittance is 80% or more;
c) Yellowness index YI at a thickness of 25 μm is 30 or less;
Fulfilling
the polyimide constituting the polyimide layer contains an aromatic tetracarboxylic dianhydride residue derived from an aromatic tetracarboxylic dianhydride component and a diamine residue derived from a diamine component;
With respect to all diamine residues, the following general formula (1):
[In formula (1), each substituent X independently represents an alkyl group having 1 to 3 carbon atoms substituted with a fluorine atom, and each of m and n independently represents an integer of 1 to 4.]
and a diamine residue derived from a first aromatic diamine represented by the following general formula (2):
[In formula (2), the linking group Y independently represents a divalent group selected from -O- and -S-, and the linking group X represents a group represented by formula (x1), formula (x2), or formula (x3);
In formula (x3), Z represents a divalent group selected from —O—, —S—, —CH ₂ —, —CH(CH ₃ )—, —C(CH ₃ ) ₂ —, —CO—, —SO ₂ —, —NH—, or —NHCO—.]
A resin film characterized by containing 1 mol % or more and 40 mol % or less of a diamine residue derived from a second aromatic diamine represented by the following formula: The polyimide is a compound represented by the following formula (3):
and the acid dianhydride residue derived from pyromellitic anhydride represented by the following general formula (4):
[In formula (4), X represents a divalent group selected from a single bond, —O—, or —C(CF ₃ ) ₂ —.]
2. The resin film according to claim 1, wherein the resin film contains 10 mol % or more and 50 mol % or less of an acid dianhydride residue derived from an aromatic tetracarboxylic dianhydride represented by the following formula: In addition to the above conditions a to c, the following condition d is further met:
d) a thermal expansion coefficient in the range of 10 ppm/K or more and 40 ppm/K or less;
2. The resin film according to claim 1, wherein the above formula (1) is satisfied. In addition to the above conditions a to c, the following condition e is further satisfied:
e) HAZE is 5% or less;
2. The resin film according to claim 1, wherein the above formula (1) is satisfied. A metal-clad laminate comprising an insulating resin layer and a metal layer laminated on one or both sides of the insulating resin layer, wherein the insulating resin layer is made of the resin film described in claim 1. The metal-clad laminate according to claim 5, characterized in that the 180° peel strength between the insulating resin layer and the metal layer is 0.5 kN/m or more. A circuit board comprising an insulating resin layer and a conductor circuit layer laminated on one or both sides of the insulating resin layer, wherein the insulating resin layer is made of the resin film described in claim 1. An electronic device comprising the circuit board described in claim 7. An electronic device comprising the electronic device according to claim 8.