Adhesive composition for printed wiring boards, bonding film for printed wiring boards, coverlay for printed wiring boards, and printed wiring board

Abstract

An adhesive composition for printed wiring boards according to the present disclosure contains: a siloxane-modified polyimide containing a first structural unit represented by formula (1) and a second structural unit represented by formula (2); an epoxy resin; an inorganic filler; and a compound represented by formula (3) or a phosphaphenanthrene compound. The content of the compound represented by formula (3) or the phosphaphenanthrene compound is 0.1-5.0 parts by mass per 100 parts by mass of the siloxane-modified polyimide. In formula (1) and formula (2), Ar represents a tetravalent aromatic tetracarboxylic acid residue. In formula (1), R1 represents a divalent diaminosiloxane residue. In formula (2), R2 represents a divalent aromatic diamine residue. In formula (3), R10 represents an unsubstituted monovalent hydrocarbon group having one to three carbon atoms inclusive.

Description

Adhesive composition for printed wiring boards, bonding film for printed wiring boards, coverlay for printed wiring boards, and printed wiring boards

[0001] The present disclosure relates to an adhesive composition for printed wiring boards, a bonding film for printed wiring boards, a coverlay for printed wiring boards, and a printed wiring board. This application claims priority to Japanese Application No. 2023-125877, filed August 1, 2023, and incorporates by reference all of the contents of said Japanese application.

[0002] In recent years, as automotive systems have become more sophisticated, the number of engine control units installed in automobiles has increased. Meanwhile, amid growing demand for more energy-efficient and lightweight automobiles, there has been a demand for more compact automobiles, and expectations for flexible printed wiring boards (FPCBs) have risen accordingly. Flexible printed wiring boards are formed, for example, by adhering copper foil to the surface of a polyimide base film, etching the copper foil to form a conductive pattern, and then laminating a cover film using an adhesive to cover the surface of the conductive pattern. This cover film is made of polyimide or the like and serves to prevent oxidation, insulate, and protect the conductive pattern.

[0003] However, when a flexible printed wiring board is used in an engine control unit around an automobile engine, it requires higher heat resistance than other parts. For example, heat resistance of 150°C is required around the engine. Therefore, in the prior art, a resin composition for flexible printed wiring boards containing a siloxane-containing polyimide has been proposed (see Patent Documents 1 and 2).

[0004] JP 2011-190425 A JP 2011-15740 A

[0005] The adhesive composition for printed wiring boards of the present disclosure contains a siloxane-modified polyimide including a first structural unit represented by the following formula (1) and a second structural unit represented by the following formula (2), an epoxy resin, an inorganic filler, and a compound represented by the following formula (3) or a phosphaphenanthrene compound, wherein the content of the compound represented by the following formula (3) or the phosphaphenanthrene compound is 0.1 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of the siloxane-modified polyimide. In formula (1) and formula (2), Ar is a tetravalent aromatic tetracarboxylic acid residue. In formula (1), R １ is a divalent diaminosiloxane residue. ２ is a divalent aromatic diamine residue. In the above formula (1), m represents the molar ratio of the first structural unit in all structural units of the siloxane-modified polyimide, and is 0.35 or more and 0.65 or less. In the above formula (2), n represents the molar ratio of the second structural unit in all structural units of the siloxane-modified polyimide, and is 0.35 or more and 0.65 or less, with the proviso that the sum of m and n is 1 or less. (In formula (3), R １０ is an unsubstituted monovalent hydrocarbon group having 1 to 3 carbon atoms.

[0006] FIG. 1 is a schematic cross-sectional view showing a main portion of a flexible printed wiring board according to an embodiment of the present disclosure. FIG. 2 is a schematic cross-sectional view for explaining a method for manufacturing the flexible printed wiring board of FIG. 1. FIG. 3 is a schematic cross-sectional view for explaining a method for manufacturing the flexible printed wiring board of FIG. 1. FIG. 4 is a schematic cross-sectional view for explaining a method for manufacturing the flexible printed wiring board of FIG. 1. FIG. 5 is a schematic cross-sectional view of an evaluation sample 71 used in examples of the present disclosure. FIG. 6 is a schematic cross-sectional view of an evaluation sample 72 used in examples of the present disclosure. FIG. 7 is a schematic cross-sectional view of an evaluation sample 73 used in examples of the present disclosure.

[0007] [Problem to be Solved by the Present Disclosure] In general-purpose flexible printed wiring boards, the constituent materials thereof, such as polyimide and conductive patterns, have sufficient heat resistance, but the adhesives used to laminate them have poor heat resistance. Therefore, adhesives applicable to flexible printed wiring boards used around engines have been investigated. Furthermore, adhesives containing siloxane bonds have been investigated with the aim of improving processability and minimizing deterioration of adhesiveness in high-temperature environments. However, while conventional adhesives containing siloxane bonds improve flexibility, they also have high oxygen and moisture permeability. Therefore, when the adhesive layer is press-bonded to a copper-clad laminate, conductive pattern, or the like, oxygen permeation easily oxidizes the surfaces of the copper foil, conductive pattern, and the like of the copper-clad laminate. As a result, copper oxide is formed on the surfaces of the copper foil, conductive pattern, and the like in printed wiring boards containing adhesives containing siloxane bonds. As a result, when processed with acidic treatment solutions such as etching solutions or electroless nickel plating solutions before gold plating, the copper oxide on the surfaces of the copper foil, conductive pattern, and the like is eluted, resulting in voids between the adhesive layer and the copper foil. The present inventors have found that the acidic treatment liquid seeps into these voids, causing the adhesive layer to lift.

[0008] The present disclosure aims to provide an adhesive composition for printed wiring boards that improves the heat resistance of printed wiring boards and can reduce lifting of the adhesive layer due to penetration of the acidic treatment liquid between the adhesive layer and the copper foil.

[0009] [Effects of the Present Disclosure] The adhesive composition for printed wiring boards of the present disclosure can improve the heat resistance of printed wiring boards and reduce lifting of the adhesive layer due to penetration of the acidic treatment liquid between the adhesive layer and the copper foil. Therefore, the adhesive composition for printed wiring boards can be suitably used in printed wiring board bonding films, printed wiring board coverlays, and printed wiring boards, and can be particularly suitably used in printed wiring boards used in high-temperature environments.

[0010] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described.

[0011] The adhesive composition for printed wiring boards of the present disclosure contains: [1] a siloxane-modified polyimide including a first structural unit represented by the following formula (1) and a second structural unit represented by the following formula (2), an epoxy resin, an inorganic filler, and a compound represented by the following formula (3) or a phosphaphenanthrene compound, wherein the content of the compound represented by the following formula (3) or the phosphaphenanthrene compound is 0.1 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of the siloxane-modified polyimide. In formula (1) and formula (2), Ar is a tetravalent aromatic tetracarboxylic acid residue. In formula (1), R １ is a divalent diaminosiloxane residue. ２ is a divalent aromatic diamine residue. In the above formula (1), m represents the molar ratio of the first structural unit in all structural units of the siloxane-modified polyimide, and is 0.35 or more and 0.65 or less. In the above formula (2), n represents the molar ratio of the second structural unit in all structural units of the siloxane-modified polyimide, and is 0.35 or more and 0.65 or less, with the proviso that the sum of m and n is 1 or less. (In formula (3), R １０ is an unsubstituted monovalent hydrocarbon group having 1 to 3 carbon atoms.

[0012] The adhesive composition for printed wiring boards contains a siloxane-modified polyimide having a first structural unit represented by formula (1) containing a diaminosiloxane residue and a second structural unit represented by formula (2) containing an aromatic diamine. In this siloxane-modified polyimide, the molar ratios of the structural units represented by formula (1) and formula (2) are 0.35 or more and 0.65 or less, respectively, i.e., the number of siloxane residues in the molecule is approximately the same as that of aromatic diamine residues. Thus, the siloxane-modified polyimide used in the adhesive composition does not contain excessive siloxane residues, which can reduce short-term heat resistance. As a result, the adhesive composition for printed wiring boards can minimize a decrease in the heat resistance of the adhesive layer. Furthermore, the adhesive composition for printed wiring boards contains a compound represented by formula (3) or a phosphaphenanthrene compound, which effectively induces interactions between nitrogen atoms or phosphorus atoms and copper atoms at the interface of copper foil, conductive patterns, etc. As a result, in the printed wiring board, bonding between copper and oxygen is inhibited, improving copper stability and reducing penetration of the acidic treatment solution between the adhesive layer and the copper foil due to elution of copper(II) oxide. Furthermore, by having the content of the compound represented by formula (3) or the phosphaphenanthrene compound be 0.1 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of the siloxane-modified polyimide, the effect of reducing penetration of the acidic treatment solution between the adhesive layer and the copper foil and improving the peel strength of the insulating layer of the printed wiring board at high temperatures can be achieved. By including an epoxy resin in the printed wiring board adhesive composition, it is believed that it can act as a crosslinking agent for the siloxane-modified polyimide. Therefore, by crosslinking the siloxane-modified polyimide with the epoxy resin, it is believed that the heat resistance, moisture resistance, and strength of the adhesive layer formed by the printed wiring board adhesive composition can be improved. Furthermore, by including an inorganic filler in the printed wiring board adhesive composition, it is possible to improve the mechanical strength of the adhesive layer of the printed wiring board and also improve the peel strength.Therefore, the adhesive composition for printed wiring boards can improve the heat resistance of printed wiring boards and reduce lifting of the adhesive layer due to penetration of the acidic treatment liquid between the adhesive layer and the copper foil.

[0013] [2] In the above [1], the weight-average molecular weight Mw of the siloxane-modified polyimide may be 25,000 or more and 150,000 or less. When the weight-average molecular weight Mw of the siloxane-modified polyimide is 25,000 or more and 150,000 or less, aggregation of the siloxane-modified polyimide can be inhibited. Therefore, by including such a siloxane-modified polyimide, the adhesive composition for printed wiring boards can further reduce a decrease in peel strength due to aggregation of the siloxane-modified polyimide.

[0014] Here, the "weight average molecular weight Mw" is the weight average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC). The weight average molecular weight Mw in the present disclosure is a value measured under the following measurement conditions. Measurement device: Tosoh Corporation's "HLC-8220GPC" Column: GMH-HR-H Mobile phase: n-methyl-2-pyrrolidone Column temperature: 40°C Flow rate: 0.5 mL / min Sample concentration: 1.0% by mass Sample injection amount: 10 μL Detector: differential refractometer Standard material: monodisperse polystyrene

[0015] [3] In the above [1] or [2], the epoxy resin may be a cresol novolac epoxy resin. When the epoxy resin is a cresol novolac epoxy resin, the epoxy resin has good heat resistance and low moisture absorption.

[0016] [4] In any one of the above [1] to [3], the content of the inorganic filler may be 10 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the siloxane-modified polyimide. By having the content of the inorganic filler be 10 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the siloxane-modified polyimide, the peel strength of the adhesive layer of the printed wiring board can be further improved.

[0017] [5] In any one of the above [1] to [4], the phosphaphenanthrene compound may be 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide. When the phosphaphenanthrene compound is 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, the effect of reducing penetration of the acidic treatment solution between the adhesive layer and the copper foil can be further improved.

[0018] [6] The printed wiring board bonding film of the present disclosure is formed from the printed wiring board adhesive composition according to any one of [1] to [5] above. Because the printed wiring board bonding film is formed from the printed wiring board adhesive composition, it is possible to improve the heat resistance of the printed wiring board and reduce lifting of the adhesive layer due to penetration of the acidic treatment liquid between the adhesive layer and the copper foil.

[0019] [7] The present disclosure also provides a cover lay for a printed wiring board, comprising a cover film and an adhesive layer laminated on one side of the cover film and formed from the adhesive composition for a printed wiring board according to any one of [1] to [5]. By providing the adhesive layer formed from the adhesive composition for a printed wiring board, the cover lay for a printed wiring board can improve the heat resistance of the printed wiring board and reduce lifting of the adhesive layer due to penetration of the acidic treatment liquid between the adhesive layer and the copper foil.

[0020] [8] The printed wiring board of the present disclosure includes a base film, a conductive pattern laminated to the base film directly or via another layer, and the coverlay for printed wiring boards described in [7] laminated to the base film and the conductive pattern. By including the coverlay for printed wiring boards, the printed wiring board can improve the heat resistance of the printed wiring board and reduce lifting of the adhesive layer due to penetration of the acidic treatment solution between the adhesive layer and the copper foil.

[0021] [Details of Embodiments of the Present Disclosure] Hereinafter, an adhesive composition for printed wiring boards, a bonding film for printed wiring boards, a coverlay for printed wiring boards, and a printed wiring board according to embodiments of the present disclosure will be described in detail with reference to the drawings.

[0022] <Adhesive Composition for Printed Wiring Boards> The adhesive composition for printed wiring boards (hereinafter also referred to as "the adhesive composition") contains a siloxane-modified polyimide including a first structural unit represented by the following formula (1) and a second structural unit represented by the following formula (2), an epoxy resin, an inorganic filler, and a compound represented by the following formula (3) or a phosphaphenanthrene compound. The adhesive composition may contain a curing agent as a suitable component. In addition, it may contain other optional components as long as the effects of the present disclosure are not impaired.

[0023] [Siloxane-modified polyimide] The siloxane-modified polyimide is the main adhesive component in the adhesive composition. This siloxane-modified polyimide contains a first structural unit represented by the following formula (1) and a second structural unit represented by the following formula (2).

[0024]

[0025] In formula (1) and formula (2), Ar is a tetravalent aromatic tetracarboxylic acid residue. １ is a divalent diaminosiloxane residue. ２ is a divalent aromatic diamine residue.

[0026] Examples of the tetravalent aromatic tetracarboxylic acid residue represented by Ar include tetravalent groups represented by the following formula (4) or (5).

[0027]

[0028] In formula (5), W is a single bond, a divalent hydrocarbon group having from 1 to 15 carbon atoms, -O-, -S-, -CO-, -SO2-, -NH-, or -CONH-. Among these, W may be a divalent hydrocarbon group having from 1 to 15 carbon atoms, a single bond, or -O-.

[0029] ​Examples of the divalent hydrocarbon group having 1 to 15 carbon atoms represented by W include a linear or branched divalent chain hydrocarbon group having 1 to 15 carbon atoms, a divalent alicyclic hydrocarbon group having 3 to 15 carbon atoms, a divalent aromatic hydrocarbon group having 6 to 10 carbon atoms, or a divalent group that is a combination of these groups.

[0030] The above R １ The divalent diaminosiloxane residue represented by the formula (6) is a group having a siloxane bond (—Si—O—Si—). By increasing the proportion of this siloxane bond, it is possible to impart sufficient flexibility to the adhesive layer formed from the adhesive composition even if the plasticizer content is reduced. Examples of the divalent diaminosiloxane residue include a divalent group represented by the following formula (6):

[0031]

[0032] In formula (6), R ３ and R ４ R are each independently a single bond or a divalent organic group which may contain an oxygen atom. ５ From R ８ are each independently a hydrocarbon group having 1 to 6 carbon atoms; a is a siloxane unit (—SiR ５ R ６ represents the average number of repeating units of the formula (-O-) and is an integer of 1 or more and 20 or less. If a is smaller than 1, the flexibility of the adhesive layer formed from the adhesive composition may decrease. On the other hand, if a exceeds 20, the adhesiveness of the adhesive layer may decrease. From this point of view, a may be an integer of 5 or more and 15 or less.

[0033] The above R ２ Examples of the divalent aromatic diamine residue represented by the formula (7) include divalent groups represented by the formula (9) below.

[0034]

[0035] In formulas (7) to (9), R ９are each independently a monovalent hydrocarbon group or alkoxy group having 1 to 6 carbon atoms; Z is a single bond, a divalent hydrocarbon group having 1 to 15 carbon atoms, —O—, —S—, —CO—, or —SO ２ -, -NH-, or -CONH-, and b is an integer of 0 to 4.

[0036] In the formula (1), m represents the molar ratio of the first structural unit to all structural units of the siloxane-modified polyimide. In the formula (2), n represents the molar ratio of the second structural unit to all structural units of the siloxane-modified polyimide. m and n are each independently 0.35 or more and 0.65 or less, provided that the sum of m and n is 1 or less. When m exceeds 0.65 (when n is less than 0.35), the short-term heat resistance of the adhesive layer formed from the adhesive composition may be reduced in a printed wiring board bonding film, a printed wiring board coverlay, and a printed wiring board. In addition, due to the high fluidity of the adhesive composition at about 150°C, oil at about 150°C may easily penetrate into the adhesive layer formed from the adhesive composition. In addition, due to the increased moisture permeability of the adhesive layer, the peel strength may be easily reduced under high temperature and high humidity conditions. On the other hand, if m is less than 0.35 (n is greater than 0.65), the proportion of siloxane bonds in the siloxane-modified polyimide is reduced, which may prevent the adhesive layer formed from the adhesive composition from being sufficiently flexible. Furthermore, the fluidity of the adhesive composition at low temperatures may be reduced, resulting in insufficient peel strength when the adhesive composition is bonded at temperatures below 200°C. Bonding at temperatures above 200°C may result in a decrease in properties due to oxidation of the conductive pattern, residual stress caused by thermal expansion / contraction, and other factors. Furthermore, the need to use special heat-resistant auxiliary materials for the bonding process, such as auxiliary materials for uniformly transmitting pressure during heat pressing, increases manufacturing costs. Furthermore, if m is less than 0.35 (n is greater than 0.65), the thermal expansion coefficient of the adhesive layer increases, resulting in a large difference in the thermal expansion coefficient with the base film. This may lead to warping of the printed wiring board coverlay during coating and drying of the adhesive composition due to the difference in thermal expansion coefficient, potentially reducing workability.

[0037] The lower limit of the weight average molecular weight Mw of the siloxane-modified polyimide may be 25,000, 40,000, or 50,000. The upper limit of the weight average molecular weight Mw may be 150,000, 125,000, or 90,000. When the weight average molecular weight Mw of the siloxane-modified polyimide is 25,000 or more, cohesive force can be maintained and sufficient peel strength can be ensured. On the other hand, when the weight average molecular weight Mw of the siloxane-modified polyimide is 150,000 or less, aggregation of the molecular chains of the siloxane-modified polyimide is inhibited and peel strength can be maintained.

[0038] [Method for Preparing Siloxane-Modified Polyimide] The siloxane-modified polyimide can be prepared as a polymer solution by, for example, generating a polyamic acid solution using a reaction solution in which an acid anhydride component and a diamine component are added to an organic solvent, and then heating the reaction solution to cause ring closure (imidization).

[0039] As the acid anhydride component, an aromatic tetracarboxylic acid anhydride is used.

[0040] An example of the aromatic tetracarboxylic acid anhydride is oxydiphthalic anhydride. Examples of the oxydiphthalic acid anhydride include 4,4'-oxydiphthalic anhydride (also known as 5,5'-oxybis-1,3-isobenzofurandione) (ODPA), 3,3'-oxydiphthalic anhydride, and 3,4'-oxydiphthalic anhydride. Among these, 4,4'-oxydiphthalic anhydride may be used. The aromatic tetracarboxylic acid anhydrides exemplified above may be used alone or in combination of two or more.

[0041] When an acid anhydride component containing 4,4'-oxydiphthalic anhydride is used, the molar ratio of 4,4'-oxydiphthalic anhydride in the acid anhydride may be 50% or more, 80% or more, or even 100%.

[0042] Further examples of aromatic tetracarboxylic acid anhydrides include 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA), 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride (BTDA), 3,3',4,4'-diphenylsulfonetetracarboxylic acid dianhydride (DSDA), pyromellitic acid dianhydride (PMDA), etc. These may be used alone or in combination of two or more, or may be used in combination with 4,4'-oxydiphthalic acid anhydride (ODPA).

[0043] As the diamine component, a diaminosiloxane or an aromatic diamine is used.

[0044] Examples of diaminosiloxanes include those in which amino groups are bonded to two terminals of the diaminosiloxane residue represented by the above formula (6). By using diaminosiloxane as the diamine, a siloxane skeleton can be introduced into the siloxane-modified polyimide. This gives the adhesive composition fluidity during thermocompression bonding, and improves the ability of the adhesive composition to fill between the cover film and the base film of a printed wiring board.

[0045] The diaminosiloxane may be any of those represented by the following formulas (10) to (14), and among these, the diaminosiloxane represented by formula (10) may be used. The diaminosiloxanes represented by the following formulas (10) to (14) may be used alone or in combination of two or more.

[0046]

[0047] In the formulas (10) to (14), a has the same meaning as in the above formula (6).

[0048] Examples of the aromatic diamine include 2,2-bis(4-aminophenoxyphenyl)propane (BAPP), 2,2'-divinyl-4,4'-diaminobiphenyl (VAB), 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB), 2,2'-diethyl-4,4'-diaminobiphenyl, 2,2',6,6'-tetramethyl-4,4'-diaminobiphenyl, 2,2'-diphenyl-4,4'-diaminobiphenyl, and 9,9-bis(4-aminophenyl)fluorene. Among these, the aromatic diamine may be 2,2-bis(4-aminophenoxyphenyl)propane (BAPP), 2,2'-divinyl-4,4'-diaminobiphenyl (VAB), or 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB). The exemplified aromatic diamines may be used alone or in combination of two or more.

[0049] The compounding ratio of the aromatic tetracarboxylic acid anhydride to the diamine component (diaminosiloxane and aromatic diamine) in the reaction solution is approximately equimolar, for example, 45:55 or more and 55:45 or less. The compounding ratio (molar ratio) of the diaminosiloxane to the aromatic diamine is 35:65 or more and 65:35 or less. By setting the compounding ratio (molar ratio) of the diaminosiloxane to the aromatic diamine within the above range, the number of siloxane residues in the siloxane-modified polyimide is approximately the same as that of the aromatic diamine residues. Therefore, the siloxane-modified polyimide prevents an excessive number of siloxane residues, which can reduce short-term heat resistance. As a result, the adhesive composition can improve the short-term heat resistance of the adhesive layer.

[0050] Examples of the organic solvent include N,N-dimethylformamide, N,N-dimethylacetamide (DMAC), N-methyl-2-pyrrolidone, 2-butanone, dimethyl sulfoxide, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diglyme, triglyme, xylene, and toluene. These solvents may be used alone or in combination of two or more.

[0051] The content of the organic solvent in the reaction solution may be in a range such that the content of polyamic acid in the polyamic acid solution produced from this reaction solution is 5% by mass or more and 50% by mass or less, or may be in a range such that the content of polyamic acid is 10% by mass or more and 40% by mass or less.

[0052] The conditions for the polyamic acid production reaction are that the temperature of the reaction solution is 0° C. or higher and 100° C. or lower, and the reaction time is 30 minutes or higher and 24 hours or lower.

[0053] The polyamic acid solution can usually be used as it is, but may be concentrated, diluted, or substituted with another organic solvent as required.

[0054] The imidization of polyamic acid is carried out, for example, by heating a polyamic acid solution at a temperature of 80° C. or higher and 400° C. or lower for 1 hour or higher and 24 hours or lower.

[0055] [Epoxy Resin] The epoxy resin improves the heat resistance and mechanical strength of the adhesive layer formed from the adhesive composition. From this, it is speculated that the epoxy resin can act as a crosslinking agent for the siloxane-modified polyimide. Crosslinking the siloxane-modified polyimide with this epoxy resin increases the cohesive strength of the adhesive composition, which is thought to improve the heat resistance and mechanical strength of the adhesive layer formed from the adhesive composition. Similarly, the peel strength retention under high temperature and high humidity conditions is also improved, which is thought to be due to factors such as the inhibition of moisture permeation due to the improved cohesive strength and the lower water absorption rate compared to polyimide. There are no particular restrictions on such epoxy resins, as long as they have two or more epoxy groups per molecule. Examples of epoxy resins include bisphenol A epoxy resins, bisphenol F epoxy resins, phenol novolac epoxy resins, cresol novolac epoxy resins, alicyclic epoxy resins, glycidyl ester epoxy resins, glycidyl amine epoxy resins, hydantoin epoxy resins, isocyanurate epoxy resins, acrylic acid-modified epoxy resins (epoxy acrylates), phosphorus-containing epoxy resins, halides thereof (brominated epoxy resins, etc.), and hydrogenated versions thereof. Among these, cresol novolac epoxy resins are preferred from the viewpoint of heat resistance and low moisture absorption. The exemplified epoxy resins may be used alone or in combination of two or more.

[0056] The lower limit of the epoxy resin content may be 1 part by mass or 2 parts by mass per 100 parts by mass of the siloxane-modified polyimide. The upper limit of the epoxy resin content may be 20 parts by mass, 15 parts by mass, or 10 parts by mass per 100 parts by mass of the siloxane-modified polyimide. It is believed that by setting the epoxy resin content within the above range, the siloxane-modified polyimide can be suitably crosslinked by the epoxy resin, and the heat resistance and strength of the adhesive layer formed from the adhesive composition can be further improved.

[0057] The adhesive composition may contain a curing agent for the epoxy resin.

[0058] [Curing Agent] Known curing agents can be used, including phenolic resins, polyamine-based curing agents, acid anhydride-based curing agents, imidazole-based curing agents, boron trifluoride amine complex salts, aromatic diamine-based curing agents, and carboxylic acid-based curing agents. Among these, phenolic resins are preferred. When the adhesive composition contains a phenolic resin as a curing agent, the epoxy resin can be cured by crosslinking or the like. Furthermore, in combination with the improved heat resistance and strength achieved by crosslinking the siloxane-modified polyimide with the epoxy resin, the heat resistance and strength of the siloxane-modified polyimide can be further improved. These curing agents may be used alone or in combination of two or more.

[0059] Phenolic resins include phenol-formaldehyde resins, as well as xylene resins, resorcinol resins, resorcinol-modified phenolic resins, cresol-modified phenolic resins, alkylphenol-modified resins, etc. These phenolic resins can be synthesized, for example, from a phenol component and an aldehyde component.

[0060] Examples of polyamine-based curing agents include aliphatic amine-based curing agents such as diethylenetriamine and tetraethylenetetramine, alicyclic amine-based curing agents such as isophoronediamine, aromatic amine-based curing agents such as diaminodiphenylmethane and phenylenediamine, and dicyandiamide.

[0061] Examples of the acid anhydride curing agent include phthalic anhydride, pyromellitic anhydride, trimellitic anhydride, and hexahydrophthalic anhydride.

[0062] Examples of imidazole-based curing agents include methylimidazole, phenylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, and 1-cyanoethyl-2-undecylimidazole.

[0063] The content of the curing agent in the adhesive composition may be determined depending on the desired degree of curing, etc. The lower limit of the curing agent content may be 1 part by mass, 5 parts by mass, or 10 parts by mass per 100 parts by mass of epoxy resin. The upper limit of the curing agent content may be 100 parts by mass or less, or 90 parts by mass or less per 100 parts by mass of epoxy resin. When the content of the curing agent is within the above range, the effect of improving heat resistance can be obtained.

[0064] [Inorganic Filler] The inorganic filler improves the peel strength and mechanical strength of the adhesive layer formed from the adhesive composition relative to a base film or the like.

[0065] Examples of inorganic fillers include talc, silica, alumina, silicon carbide, boron carbide, titanium carbide, tungsten carbide, silicon nitride, boron nitride, aluminum nitride, mica, potassium titanate, barium titanate, calcium carbonate, magnesium oxide, and zirconium oxide.

[0066] The inorganic filler may have, for example, a plate-like, spherical, needle-like, fibrous or amorphous form, and may be in the form of a plate.

[0067] The lower limit of the average particle size of the inorganic filler may be 2 μm or 3 μm. The upper limit of the average particle size may be 20 μm, 15 μm, or 10 μm. When the average particle size is within the above range, the peel strength of the adhesive layer can be sufficiently improved. Here, the "average particle size" is the median diameter (d50) calculated from the cumulative distribution measured by a laser diffraction method or the manufacturer's nominal value.

[0068] The lower limit of the inorganic filler content may be 8 parts by mass or 10 parts by mass per 100 parts by mass of the siloxane-modified polyimide. The upper limit of the inorganic filler content may be 70 parts by mass or 60 parts by mass per 100 parts by mass of the siloxane-modified polyimide. When the inorganic filler content is within the above range, the peel strength of the adhesive layer can be sufficiently improved.

[0069] [Compound Represented by Formula (3)] The adhesive composition contains a compound represented by Formula (3) below, which has an oxygen blocking effect on copper foil, conductive patterns, etc. The adhesive composition effectively induces interactions between nitrogen atoms and copper atoms at the interface between the copper foil, conductive patterns, etc., thereby inhibiting bonding between copper and oxygen and improving copper stability. It is therefore believed that this can reduce penetration of the treatment solution between the adhesive layer and the copper foil due to elution of copper(II) oxide.

[0070]

[0071] In the above formula (3), R １０ is an unsubstituted monovalent hydrocarbon group having 1 to 3 carbon atoms.

[0072] The above R １０ Examples of the unsubstituted monovalent hydrocarbon group having 1 to 3 carbon atoms represented by the formula (I) include linear or branched monovalent hydrocarbon groups having 1 to 3 carbon atoms. Among these, from the viewpoint of improving the effect of reducing penetration of the treatment liquid between the adhesive layer and the copper foil, R １０ may be a methyl group. That is, the compound represented by the formula (3) may be tolyltriazole.

[0073] [Phosphaphenanthrene Compound] The adhesive composition contains a phosphaphenanthrene compound, which effectively induces an interaction between phosphorus atoms and copper atoms at the interface between the copper foil, conductive pattern, etc. As a result, it is believed that bonding between copper and oxygen at the interface between the copper foil, conductive pattern, etc. is inhibited, the stability of copper is improved, and penetration of a treatment solution between the adhesive layer and the copper foil, conductive pattern, etc., due to elution of copper(II) oxide, can be reduced.

[0074] The phosphaphenanthrene compound refers to a compound having at least one phosphaphenanthrene skeleton in the molecule. Examples of the phosphaphenanthrene compound include 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10-(2,5-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and 10-benzyl-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide. Among these, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide may be used from the viewpoint of improving the effect of reducing penetration of the treatment liquid between the adhesive layer and the copper foil.

[0075] The lower limit of the content of the compound represented by formula (3) or the phosphaphenanthrene compound is 0.1 parts by mass or may be 0.2 parts by mass per 100 parts by mass of the siloxane-modified polyimide. On the other hand, the upper limit of the content of the compound represented by formula (3) or the phosphaphenanthrene compound is 5.0 parts by mass, or may be 4.0 parts by mass, or may be 3.5 parts by mass. If the content is less than 0.1 parts by mass, the effect of reducing penetration of the treatment liquid between the adhesive layer and the copper foil may be insufficient. On the other hand, if the content exceeds 5.0 parts by mass, the peel strength of the insulating layer of the printed wiring board at high temperatures may not be sufficiently improved. By having the content of the compound represented by formula (3) or the phosphaphenanthrene compound within the above range, the effect of reducing penetration of the treatment liquid between the adhesive layer and the copper foil and the peel strength of the insulating layer of the printed wiring board at high temperatures may be improved.

[0076] (Optional Components) Examples of optional components include plasticizers, flame retardants, flame retardant assistants, pigments, antioxidants, opacifying agents, lubricants, processing stabilizers, foaming agents, and coupling agents.

[0077] Examples of the plasticizer include phosphate ester plasticizers such as trimethyl phosphate, triethyl phosphate, tributyl phosphate, tri-2-ethylhexyl phosphate, tributoxyethyl phosphate, trioleyl phosphate, triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, cresyl diphenyl phosphate, xylenyl diphenyl phosphate, and 2-ethylhexyl diphenyl phosphate; polyester plasticizers such as 1,3-butylene glycol adipate; phthalate ester plasticizers such as dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diheptyl phthalate, di-2-ethylhexyl phthalate, di-n-octyl phthalate, diisodecyl phthalate, butyl benzyl phthalate, diisononyl phthalate, and ethyl phthalyl ethyl glycolate; Examples of the plasticizer include fatty acid ester-based plasticizers such as dimethyl adipate, diisobutyl adipate, dibutyl adipate, di-2-ethylhexyl adipate, diisodecyl adipate, dibutyl diglycol adipate, di-2-ethylhexyl azelate, dimethyl sebacate, dibutyl sebacate, di-2-ethylhexyl sebacate, and methyl acetylricinoleate. These plasticizers may be used alone or in combination of two or more.

[0078] The flame retardant imparts flame retardancy to the adhesive or the like formed from the adhesive composition.Examples of the flame retardant include chlorine-based flame retardants such as chlorinated paraffin, chlorinated polyethylene, chlorinated polyphenyl, and perchloropentacyclodecane; bromine-based flame retardants such as ethylenebispentabromobenzene, ethylenebispentabromodiphenyl, tetrabromoethane, tetrabromobisphenol A, hexabromobenzene, decabromobiphenyl ether, tetrabromophthalic anhydride, polydibromophenylene oxide, hexabromocyclodecane, and ammonium bromide; Phosphate esters or phosphorus compounds such as triallyl phosphate, alkyl allyl phosphate, alkyl phosphate, dimethyl phosphate, phospholinate, halogenated phospholinate ester, trimethyl phosphate, tributyl phosphate, trioctyl phosphate, tributoxyethyl phosphate, octyl diphenyl phosphate, tricresyl phosphate, cresyl phenyl phosphate, triphenyl phosphate, tris(chloroethyl)phosphate, tris(2-chloropropyl)phosphate, tris(2,3-dichloropropyl)phosphate, tris(2,3-dibromopropyl)phosphate, tris(bromochloropropyl)phosphate, bis(2,3-dibromopropyl)2,3-dichloropropyl phosphate, bis(chloropropyl)monoctyl phosphate, polyphosphonate, polyphosphate, aromatic polyphosphate, dibromoneopentyl glycol, and aluminum tris(diethylphosphinate); Examples of suitable inorganic compounds include: polyols such as phosphonate-type polyols, phosphate-type polyols, and halogen-containing polyols; metal powders or inorganic compounds such as aluminum hydroxide, magnesium hydroxide, magnesium carbonate, antimony trioxide, antimony trichloride, zinc borate, antimony borate, boric acid, antimony molybdate, molybdenum oxide, phosphorus-nitrogen compounds, calcium-aluminum silicate, zirconium compounds, tin compounds, dawsonite, calcium aluminate hydrate, copper oxide, metallic copper powder, calcium carbonate, and barium metaborate; nitrogen compounds such as triazine, isocyanurate, urea, and guanidine; and other compounds such as silicone-based polymers, ferrocene, fumaric acid, and maleic acid.Among these, halogen-based flame retardants such as bromine-based flame retardants and chlorine-based flame retardants may be used. The bromine-based flame retardants and chlorine-based flame retardants may be used alone or in combination of two or more kinds.

[0079] The flame retardant aid further improves the flame retardancy of the adhesive layer formed from the adhesive composition. Examples of the flame retardant aid include antimony trioxide.

[0080] The pigment is used to color the adhesive layer formed from the adhesive composition. As the pigment, various known pigments can be used, for example, titanium oxide.

[0081] The antioxidant prevents oxidation of the adhesive layer formed from the adhesive composition. Various known antioxidants can be used, such as phenolic antioxidants.

[0082] When optional components are blended into the adhesive composition, the lower limit of the total content of the optional components may be 1 part by mass or 2 parts by mass relative to 100 parts by mass of the siloxane-modified polyimide, and the upper limit of the total content may be 10 parts by mass or 7 parts by mass.

[0083] [Preparation of Adhesive Composition] The adhesive composition can be prepared by mixing a siloxane-modified polyimide, an epoxy resin, an inorganic filler, the compound represented by formula (3) or a phosphaphenanthrene compound, and, if necessary, other optional components such as a curing agent such as a phenolic resin. The adhesive composition may be prepared by dissolving or dispersing the above components in a solvent.

[0084] The solvent used is preferably one that uniformly dissolves or disperses the other components in the adhesive composition and does not react with the other components. Examples of such solvents include the same solvents used in preparing the siloxane-modified polyimide, and the solvents exemplified above may be used alone or in combination of two or more.

[0085] The adhesive composition contains a siloxane-modified polyimide having a structural unit represented by formula (1) containing a diaminosiloxane residue and a structural unit represented by formula (2) containing an aromatic diamine. This siloxane-modified polyimide has a molar ratio of the structural units represented by formula (1) and formula (2) of 0.35 or more and 0.65 or less, respectively, i.e., the number of siloxane residues in the molecule is approximately the same as that of the aromatic diamine residues. This allows the adhesive composition to minimize a decrease in the short-term heat resistance of the adhesive layer. Furthermore, the adhesive composition contains an epoxy resin, which is thought to crosslink the siloxane-modified polyimide with the epoxy resin, thereby improving the heat resistance and strength of the adhesive layer formed by the adhesive composition. Additionally, the adhesive composition contains an inorganic filler, which can improve the mechanical strength of the adhesive composition and also improve peel strength.

[0086] Furthermore, it is believed that the adhesive composition for printed wiring boards containing the compound represented by formula (3) or the phosphaphenanthrene compound can reduce penetration of the treatment liquid between the adhesive layer and the copper foil, the conductive pattern, etc.

[0087] Therefore, the adhesive composition for printed wiring boards can improve the heat resistance of printed wiring boards and reduce lifting of the adhesive layer due to penetration of a treatment liquid between the adhesive layer and copper foil, conductive pattern, or the like.

[0088] <Bonding Film for Printed Wiring Boards> The bonding film for printed wiring boards (hereinafter also referred to as the bonding film) is formed from the adhesive composition and serves as an adhesive layer for arranging a conductive pattern on a base film in a printed wiring board and for mounting electronic components, etc. on the lands, etc. of the conductive pattern. The bonding film can be formed by a known method, for example, a melt extrusion method, a solution casting method, or a calendar method.

[0089] The printed wiring board bonding film can also be configured as a conductive film. In this case, a conductive material such as conductive particles can be blended into the adhesive composition to form a conductive material dispersed in the printed wiring board bonding film. Examples of conductive materials include metal particles, metal-plated resin beads, carbon, carbon nanotubes, and graphite. The shape of the conductive material is not limited to spherical, but may also be a shape with a high aspect ratio, such as a needle shape.

[0090] The printed wiring board bonding film formed from the printed wiring board adhesive composition can improve the heat resistance of the printed wiring board and reduce lifting of the adhesive layer due to penetration of a treatment liquid between the adhesive layer and the copper foil, conductive pattern, or the like.

[0091] <Coverlay for printed wiring board> The coverlay for printed wiring board (hereinafter also referred to as the coverlay) protects conductive patterns and the like on a printed wiring board. The coverlay includes a cover film and an adhesive layer laminated on one side of the cover film and made of the adhesive composition.

[0092] [Cover Film] The cover film may be flexible and insulating. Examples of the main component of the cover film include polyimide, epoxy resin, phenolic resin, acrylic resin, polyester, thermoplastic polyimide, polyethylene terephthalate, fluororesin, and liquid crystal polymer. In particular, polyimide may be used from the viewpoint of heat resistance. The cover film may contain other resins, weatherproofing agents, antistatic agents, etc., besides the main component. The term "main component" refers to the component with the highest content, e.g., a component with a content of more than 50% by mass.

[0093] The lower limit of the average thickness of the cover film is not particularly limited, but may be 3 μm or 10 μm. The upper limit of the average thickness of the cover film is not particularly limited, but may be 500 μm or 150 μm. By having the average thickness of the cover film within the above range, sufficient protection and flexibility for the conductive pattern and the like can be obtained, and sufficient insulation can be obtained when insulation is required for the cover film. Here, "average thickness" refers to the average value of thicknesses measured at any ten points. Note that the same definition is used below when referring to "average thickness" for other components, etc.

[0094] [Adhesive Layer] The adhesive layer is laminated on one side of the cover film and serves to adhere this cover film to the base film of a printed wiring board, etc. This adhesive layer is formed from the adhesive composition described above.

[0095] The adhesive layer can be formed on the cover film by applying the adhesive composition for printed wiring boards to the cover film and then drying it, or by forming a film in the same manner as a bonding film and then laminating this film on one side of the cover film.

[0096] According to the coverlay for printed wiring boards, by providing an adhesive layer formed from the adhesive composition for printed wiring boards, the heat resistance of the printed wiring board can be improved and lifting of the adhesive layer due to penetration of a treatment liquid between the adhesive layer and the copper foil can be reduced.

[0097] <Printed Wiring Board> The printed wiring board comprises a base film, a conductive pattern primarily composed of copper and directly or indirectly laminated on the base film, and the above-mentioned coverlay laminated on the base film and the conductive pattern. The printed wiring board 1 shown in Figure 1 is configured as a flexible printed wiring board. The printed wiring board 1 comprises a base film 2, a conductive pattern 3, and a coverlay 4. The coverlay 4 also comprises a cover film 42 and an adhesive layer 41 composed of the adhesive composition.

[0098] [Base Film] The base film 2 has insulating properties and flexibility. Examples of the main component of the base film 2 include polyimide, polyethylene terephthalate, fluororesin, and liquid crystal polymer, and polyimide may be used from the viewpoint of flexibility and strength. Note that the base film 2 may contain other resins, weathering agents, antistatic agents, etc. in addition to the main components.

[0099] The lower limit of the average thickness of the base film 2 is not particularly limited, but may be 3 μm, 5 μm, or 10 μm. The upper limit of the average thickness of the base film 2 is not particularly limited, but may be 200 μm, 150 μm, or 100 μm. When the average thickness of the base film 2 is within the above range, sufficient insulation properties, mechanical strength, and flexibility can be obtained.

[0100] [Conductive Pattern] A conductive pattern 3 mainly composed of copper is laminated on the surface of the base film 2. This conductive pattern 3 is composed of a base conductor. The base conductor is formed into a desired pattern by etching copper foil. There is no particular limit to the lower limit of the average thickness of this base conductor, but it may be 2 μm or 5 μm. There is no particular limit to the upper limit of the average thickness of the base conductor, but it may be 100 μm or 75 μm. By keeping the average thickness of the base conductor within the above range, it is possible to improve conductivity and flexibility and meet the demand for thinness.

[0101] 2 to 4, an example of a method for manufacturing the printed wiring board 1 will be described. The method for manufacturing the printed wiring board 1 includes a step of using an insulating and flexible base film 2, forming a conductive pattern 3 made mainly of copper and laminated on the surface of the base film 2, and laminating a coverlay 4 on the surfaces of the base film 2 and the conductive pattern 3.

[0102] 2, copper foil 30 is first laminated on base film 2. Examples of methods for laminating copper foil 30 on base film 2 include an adhesive method in which copper foil 30 is bonded to base film 2 using an adhesive, a casting method in which a resin composition, which is the material of base film 2, is applied onto copper foil 30, a sputtering method in which a thin conductive layer (seed layer) having a thickness of several nanometers is formed on base film 2 by sputtering, vapor deposition, or the like, and then a copper layer is formed on this seed layer by electrolytic plating, and a lamination method in which copper foil 30 is bonded by hot pressing.

[0103] 3, the copper foil 30 can be patterned by a known method, such as photoetching. Photoetching is performed by forming a resist film having a predetermined pattern on the surface of the copper foil 30, and then dissolving the copper foil 30 exposed from the resist film with an etching solution to remove the resist film.

[0104] (Coverlay Laminating Process) As shown in FIG. 4 , in the coverlay laminating process, first, the coverlay 4, in which an adhesive layer 41 is laminated on one side of a cover film 42, is placed so that the adhesive layer 41 faces the base film 2. Note that, in the areas corresponding to the lands of the conductive pattern 3, the coverlay 4 is not placed or a notch is provided in the coverlay 4 to expose the areas. Next, the coverlay 4 is heated together with the base film 2 and the conductive pattern 3 to harden the adhesive layer 41. The heating temperature may be 120° C. or higher and 200° C. or lower. The heating time may be 1 minute or higher and 60 minutes or lower. By setting the heating temperature and heating time within the above ranges, the adhesive properties of the adhesive layer 41 can be effectively exhibited and deterioration of the base film 2 and the like can be reduced. The heating method is not particularly limited, and examples thereof include heating using a heating means such as a heat press, an oven, or a hot plate, and pressure heating using a heat press may also be used.

[0105] According to the printed wiring board, by providing the coverlay for the printed wiring board, the heat resistance of the printed wiring board can be improved and lifting of the adhesive layer due to seepage of a treatment liquid between the adhesive layer and the copper foil can be reduced.

[0106] In the above embodiment, a flexible printed wiring board has been described as an example of the printed wiring board, but the printed wiring board does not necessarily have to be flexible.

[0107] [Other Embodiments] The printed wiring board is not limited to a single-sided printed wiring board in which a conductive pattern is formed on one side, but may be a double-sided printed wiring board in which a conductive pattern is formed on both sides, or may be a multilayer printed wiring board in which multiple layers of conductive patterns are formed.

[0108] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is not limited to the configurations of the above-described embodiments, but is defined by the scope of the claims, and is intended to include meanings equivalent to the scope of the claims and all modifications within the scope of the claims.

[0109] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to the following examples.

[0110] <Synthesis of Siloxane-Modified Polyimides> The types and compounding ratios of the acid anhydride component and diamine component were as shown in Table 1, and siloxane-modified polyimides (A1) to (A5) were synthesized by the method described below.

[0111] Synthesis Example 1 Synthesis of Siloxane-Modified Polyimide (A1) A reaction solution was obtained by adding 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) as the acid anhydride, 2,2-bis(4-aminophenoxyphenyl)propane (BAPP) as the aromatic diamine, and a compound having an amine equivalent of 420 g / eq represented by the above formula (10) as the siloxane diamine in a molar ratio of 1.0:0.4:0.6 to a 1:1 mixed solvent (mass ratio) of N-methyl-2-pyrrolidone and xylene as the organic solvent. The amount of organic solvent in the reaction solution was set so that the polyamide resin content in the siloxane-modified polyimide precursor solution was 30% by mass.

[0112] The temperature of the reaction solution was raised to 180° C. and the reaction was carried out for 16 hours to imidize the siloxane-modified polyimide precursor, thereby obtaining a siloxane-modified polyimide solution containing a siloxane-modified polyimide (A1).

[0113] The weight-average molecular weight Mw of the siloxane-modified polyimide in the resulting siloxane-modified polyimide solution was 92,000. The definition and measurement method of the weight-average molecular weight Mw are as described above.

[0114] Synthesis Example 2 (Synthesis of Siloxane-Modified Polyimide (A2)) A polymer solution containing siloxane-modified polyimide (A2) was obtained in the same manner as in Synthesis Example 1, except that the reaction solution was heated to 180°C for 14 hours to generate polyamic acid, thereby obtaining a siloxane-modified polyimide precursor solution. The weight-average molecular weight Mw of the siloxane-modified polyimide (A2) was 75,000.

[0115] Synthesis Example 3 (Synthesis of Siloxane-Modified Polyimide (A3)) To a 1:1 mixed solvent (mass ratio) of N-methyl-2-pyrrolidone and xylene as the organic solvent, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) as the acid anhydride, 2,2-bis(4-aminophenoxyphenyl)propane (BAPP) as the aromatic diamine, and a compound having an amine equivalent of 420 g / eq represented by the above formula (10) as the siloxane diamine were added in a molar ratio of 1.0:0.6:0.4 to obtain a reaction solution. The amount of organic solvent in the reaction solution was set so that the content of the siloxane-modified polyamide resin was 30% by mass.

[0116] The reaction solution was heated to 180° C. and reacted for 10 hours to imidize the siloxane-modified polyimide precursor, thereby obtaining a polymer solution containing siloxane-modified polyimide (A3). The weight-average molecular weight Mw of the siloxane-modified polyimide (A3) was 42,000.

[0117] Synthesis Example 4 (Synthesis of Siloxane-Modified Polyimide (A4)) To a 1:1 mixed solvent (mass ratio) of N-methyl-2-pyrrolidone and xylene as an organic solvent, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) as an acid anhydride, 2,2-bis(4-aminophenoxyphenyl)propane (BAPP) as an aromatic diamine, and a compound represented by the above formula (10) with an amine equivalent of 420 g / eq as a siloxane diamine were added in a molar ratio of 1.0:0.2:0.8 to obtain a reaction solution. The amount of organic solvent in the reaction solution was set so that the content of polyamic acid in the siloxane-modified polyimide precursor solution would be 30% by mass.

[0118] The reaction solution was heated to 180° C. and reacted for 16 hours to obtain a polymer solution containing siloxane-modified polyimide. The weight average molecular weight Mw of the siloxane-modified polyimide (A4) was 77,000.

[0119] Synthesis Example 5 (Synthesis of Siloxane-Modified Polyimide (A5)) To a 1:1 mixed solvent (mass ratio) of N-methyl-2-pyrrolidone and xylene as an organic solvent, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) as an acid anhydride, 2,2-bis(4-aminophenoxyphenyl)propane (BAPP) as an aromatic diamine, and a compound represented by the above formula (10) with an amine equivalent of 420 g / eq as a siloxane diamine were added in a molar ratio of 1.0:0.1:0.9 to obtain a reaction solution. The amount of organic solvent in the reaction solution was set so that the content of polyamic acid in the siloxane-modified polyimide precursor solution would be 30% by mass.

[0120] The reaction solution was heated to 180° C. and reacted for 10 hours to obtain a polymer solution containing siloxane-modified polyimide. The weight average molecular weight Mw of the siloxane-modified polyimide (A5) was 37,000.

[0121]

[0122] <Preparation of Printed Wiring Board Adhesive Composition Test No. 1 to Test No. 20> (Adhesive Composition Test No. 1) First, an adhesive composition was obtained by mixing 100 parts by mass (solids content equivalent) of siloxane-modified polyimide (A2) dissolved in a 1:1 mixed solvent (mass ratio) of N-methyl-2-pyrrolidone and xylene as a solvent, 45 parts by mass of talc (average particle size 8 μm) as an inorganic filler, 4 parts by mass of cresol novolac epoxy resin (softening point 90° C. or higher and 100° C. or lower, epoxy equivalent 209 g / eq or higher and 219 g / eq or lower) as an epoxy resin, and 3 parts by mass of a phenolic resin as a curing agent.

[0123] (Adhesive Composition Test No. 2 to Test No. 20) Adhesive compositions were prepared in the same manner as in Example 1, except that the types and amounts of components shown in Table 2 below were used. Note that "-" in Table 2 indicates that the corresponding component was not blended.

[0124] The following materials were used for the adhesive composition: (1) Cresol novolac epoxy resin: "EPICLON N695" manufactured by DIC Corporation (2) Phenol resin: "GPH-65" manufactured by Nippon Kayaku Co., Ltd. (3) Talc: "MICROACE P8" manufactured by Nippon Talc Co., Ltd. (4) Tolyltriazole: "VERZONE TTA" manufactured by Daiwa Kasei Co., Ltd. (5) 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide: "HCA" manufactured by Sankosha Co., Ltd. (6) Benzotriazole: "VERZONE Crystal #120" manufactured by Daiwa Kasei Co., Ltd. (7) Carboxybenzotriazole: "VERZONE C-BTA" manufactured by Daiwa Kasei Co., Ltd. (8) 5-amino-1H-tetrazole: manufactured by Tokasei Kogyo Co., Ltd.

[0125]

[0126] [Preparation of Evaluation Samples] As evaluation samples, a double-sided copper-clad laminate shown in FIG. 5 (evaluation sample 71), a copper-clad laminate with a coverlay shown in FIG. 6 (evaluation sample 72), and a single-sided copper-clad laminate with a rectangular hole in plan view shown in FIG. 7 (evaluation sample 73) were prepared according to the following method.

[0127] (Evaluation Sample 71) Evaluation sample 71 of Figure 5 was produced by thermocompression bonding a polyimide film 52 ("Kapton 100H" from DuPont Toray Co., Ltd.; thickness 25 µm) between two sheets of copper foil 53 (thickness 35 µm) coated with an adhesive composition to a thickness of 45 µm or more and 55 µm or less, at a pressure of 3 MPa, a heating temperature of 180°C, and a pressing time of 45 minutes. The copper foil 53 was coated with the adhesive composition to a thickness of 45 µm or more and 55 µm or less. The adhesive composition of the two adhesive layers 51 was the same.

[0128] (Evaluation Sample 72) The evaluation sample 72 of FIG. 6 was produced by bonding a coverlay 65 prepared by coating a polyimide cover film 52 ("Kapton 100H" by DuPont Toray Co.) with an adhesive composition so that the average thickness of the adhesive layer 51 was 45 μm or more and 55 μm or less, to a copper-clad laminate 60 having a copper foil 53. The coverlay 65 was bonded by thermocompression bonding at a pressure of 3 MPa, a heating temperature of 180°C, and a pressing time of 45 minutes. The copper-clad laminate 60 used was one in which a copper foil 53 having an average thickness of 35 μm and a polyimide base film 55 ("Kapton 100H" by DuPont Toray Co.) having an average thickness of 25 μm were bonded together with an epoxy resin-based adhesive layer 54.

[0129] 7 was produced by first coating a polyimide cover film 52 ("Kapton 100H" by DuPont-Toray Co., Ltd.) with an adhesive composition so that the average thickness of the adhesive layer 51 was 45 μm or more and 55 μm or less to form a coverlay 65. Next, the produced coverlay 65 was punched out into a rectangular shape measuring 4 mm × 10 mm in plan view, and thermocompression bonded to copper foil 53 at a pressure of 3 MPa, a heating temperature of 180°C, and a pressure time of 45 minutes, thereby producing evaluation sample 73.

[0130] [Evaluation] Evaluation samples 71 to 73 using the adhesive compositions of test No. 1 to test No. 20 were evaluated for peel strength and reflow solder heat resistance according to the following methods. The evaluation results are shown in Table 2.

[0131] (Peel Strength) Peel strength was measured in accordance with JIS-K-6854-2:1999 "Adhesives - Test Method for Peel Adhesion Strength - Part 2: 180-Degree Peel." This peel strength was measured using a Shimadzu Corporation tensile tester, "Autograph AG-IS." The peel strength was measured by fixing the polyimide cover film 52 of the coverlay 65 of evaluation sample 72, sandwiching the entire edge of the copper-clad laminate 60, and applying a peel force. Peel strength was measured under the following three conditions: (1) Initial peel strength of evaluation sample 72 at room temperature; (2) Peel strength of evaluation sample 72 at room temperature after leaving it at 150°C for 1,000 hours; and (3) Peel strength of evaluation sample 71 at room temperature after leaving it at 85°C and 85% humidity for 1,000 hours. The obtained measurements were evaluated using the following four-point scale. A, B, or C was considered good. A: 3.4 N / cm or more (passes JPCA standards) B: 2 N / cm or more but less than 3.4 N / cm C: 0.5 N / cm or more but less than 2 N / cm D: Peeling occurred immediately Note that "normal temperature" is used to mean the same as room temperature, and generally refers to a temperature between 20°C and 25°C.

[0132] (Reflow solder heat resistance) The reflow solder heat resistance was evaluated by checking whether or not the adhesive layer bulged after leaving the evaluation sample 72 in a thermostatic chamber at 260° C. for 1 minute. If the adhesive layer did not bulge, the sample passed.

[0133] (Evaluation of Penetration of Plating Solution) The penetration of the plating solution was evaluated using an evaluation sample 73 shown in FIG. 7 . The evaluation sample 73 was prepared as follows. First, a copper-clad laminate 60 was prepared by bonding a copper foil 53 having an average thickness of 35 μm and a polyimide base film 55 having an average thickness of 25 μm with an epoxy resin-based adhesive layer 54. A 12 μm copper plating was applied to the surface of the copper foil 53 to form a copper plating layer 57. Next, a coverlay 65 was thermocompression-bonded to the substrate 70. The coverlay 65 was formed by applying an adhesive composition to a polyimide cover film 52 having an average thickness of 25 μm so that the adhesive layer 51 had an average thickness of 35 μm. The thermocompression bonding was performed under conditions of a pressure of 3 MPa, a heating temperature of 180°C, and a pressure time of 45 minutes. The coverlay 65 was then punched to form a rectangular hole in a plan view for observing the penetration of the nickel plating solution, thereby preparing the evaluation sample 73. To evaluate the penetration of the plating solution, first, the evaluation sample 73 was nickel plated using the following process. Then, the penetration of the nickel plating solution between the adhesive layer 51 and the substrate 70 was observed under a microscope. After each process, the sample was washed with water. (1) Degreasing at 40°C for 5 minutes (2) Soft etching at 30°C for 1 minute (3) Sulfuric acid treatment at 25°C for 1 minute (4) Hydrochloric acid treatment at 25°C for 0.5 minutes (5) Adding Pd catalyst at 30°C for 1 minute (6) Sulfuric acid treatment at 25°C for 1 minute (7) Electroless nickel-phosphorus plating at 84°C for 20 minutes

[0134] Table 2 shows the evaluation results of peel strength and plating solution penetration for adhesive compositions of Test Nos. 1 to 20.

[0135] As shown in Table 2, adhesive compositions No. 1 to No. 9, which contained a siloxane-modified polyimide containing a first structural unit represented by formula (1) and a second structural unit represented by formula (2), an epoxy resin, an inorganic filler, and a compound represented by formula (3) or a phosphaphenanthrene compound, in which the content of the compound represented by formula (3) or the phosphaphenanthrene compound was 0.1 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of siloxane-modified polyimide, obtained good results in all of the peel strength tests, including the initial peel strength, the peel strength after standing at 150°C for 1,000 hours, and the peel strength after standing at 85°C and 85% humidity for 1,000 hours, and showed reduced swelling of the adhesive layer and reduced penetration of the plating solution between the adhesive layer and the copper foil under reflow soldering conditions. 5, evaluation sample 71 used in the reflow solder heat resistance evaluation had a structure in which copper foil 53 was laminated on both sides of polyimide film 52 via adhesive layer 51. Therefore, evaluation sample 71 has a structure in which when the solvent contained in the adhesive layer composition turns into gas during reflow, this gas is difficult to discharge from adhesive layer 51, and the gas remains in adhesive layer 51, which is a so-called popcorn phenomenon, and the peel strength is likely to decrease. Therefore, evaluation sample 71, which used the adhesive compositions of Tests No. 1 to No. 9, is considered to have excellent peel strength as a result of suppressing the occurrence of the popcorn phenomenon during reflow.

[0136] On the other hand, in the adhesive compositions of Tests No. 10 to No. 14, which did not contain the compound represented by Formula (3) or the phosphaphenanthrene compound, penetration of the plating solution between the adhesive layer and the copper foil was observed. Furthermore, in the adhesive compositions of Nos. 13 and 14, in which the molar ratio of the first structural unit to all structural units of the siloxane-modified polyimide was less than 0.35 and the molar ratio of the second structural unit to all structural units exceeded 0.65, swelling of the adhesive layer was observed under reflow soldering conditions. Despite being the same azole compound, penetration of the plating solution between the adhesive layer and the copper foil was observed in Tests No. 15 and No. 16, which contained 5-amino-1H-tetrazole, Test No. 18, which contained benzotriazole, and Test Nos. 19 and 20, which contained carboxybenzotriazole. Furthermore, Test No. 17, in which the content of tolyltriazole, which is the compound represented by formula (3), exceeded 5.0 parts by mass per 100 parts by mass of siloxane-modified polyimide, exhibited poor peel strength after being left standing at 150°C for 1,000 hours, and penetration of the plating solution between the adhesive layer and the copper foil was observed.

[0137] The above results show that the adhesive composition for printed wiring boards has good peel strength and reflow solder heat resistance under high heat, and can reduce penetration of the treatment liquid between the adhesive layer and the copper foil.

[0138] REFERENCE SIGNS LIST 1 Printed wiring board 2, 55 Base film 3 Conductive pattern 4, 65 Cover lay 30, 53 Copper foil 41, 51 Adhesive layer 42, 52 Cover film 54 Epoxy resin adhesive layer 57 Copper plating layer 60 Copper clad laminate 70 Substrate 71 Evaluation sample 72 Evaluation sample 73 Evaluation sample

Claims

1. An adhesive composition for printed wiring boards, comprising: a siloxane-modified polyimide containing a first structural unit represented by formula (1) and a second structural unit represented by formula (2); an epoxy resin; an inorganic filler; and a compound represented by formula (3) or a phosphaphenanthrene compound, wherein the content of the compound represented by formula (3) or the phosphaphenanthrene compound is 0.1 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of the siloxane-modified polyimide. In formula (1) and formula (2), Ar is a tetravalent aromatic tetracarboxylic acid residue. In formula (1), R １ is a divalent diaminosiloxane residue. ２ is a divalent aromatic diamine residue. In the above formula (1), m represents the molar ratio of the first structural unit in all structural units of the siloxane-modified polyimide, and is 0.35 or more and 0.65 or less. In the above formula (2), n represents the molar ratio of the second structural unit in all structural units of the siloxane-modified polyimide, and is 0.35 or more and 0.65 or less. However, the sum of m and n is 1 or less.) (In formula (3), R １０ is an unsubstituted monovalent hydrocarbon group having 1 to 3 carbon atoms.

2. The adhesive composition for printed wiring boards according to claim 1, wherein the weight average molecular weight Mw of said siloxane-modified polyimide is from 25,000 to 150,000.

3. An adhesive composition for printed wiring boards according to claim 1 or 2, wherein the epoxy resin is a cresol novolac type epoxy resin.

4. An adhesive composition for printed wiring boards according to any one of claims 1 to 3, wherein the content of the inorganic filler is 10 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the siloxane-modified polyimide.

5. The adhesive composition for printed wiring boards according to any one of claims 1 to 4, wherein the phosphaphenanthrene compound is 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

6. A bonding film for printed wiring boards formed from the adhesive composition for printed wiring boards according to any one of claims 1 to 5.

7. A coverlay for printed wiring boards comprising: a cover film; and an adhesive layer laminated on one side of the cover film and composed of the adhesive composition for printed wiring boards according to any one of claims 1 to 5.

8. A printed wiring board comprising: a base film; a conductive pattern containing copper as a main component and laminated directly or indirectly on said base film; and the coverlay for printed wiring boards according to claim 7 laminated on said base film and said conductive pattern.

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