JP5354443B2 - Polyimide ink composition, protective film, and flexible printed wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyimide ink composition forming a protective film that satisfies recent requirements and has a low modulus of elasticity and a small warpage even in the case in which a small amount of expensive monomer such as OPDA is used, forming a protective film hardly causing whitening on a protective film in gold plating and bad condition of plating adhesion etc., and satisfying other properties required for FPC protective film such as sufficient flame retardance etc., by printing. <P>SOLUTION: The polyimide ink composition comprises a soluble polyimide resin being a condensation product of a diamine component containing a silicone diamine and an aromatic tricarboxylic acid dianhydride, a solvent dissolving the soluble polyimide resin in which the composition ratio of the silicone diamine in the diamine component is &ge;66 wt.% and &le;80 wt.%. The protective film is formed from the polyimide ink composition. The flexible printed wiring board is equipped with the protective film. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a polyimide ink composition used for forming a protective film of a flexible printed wiring board. The present invention further relates to a protective film that is formed of the polyimide ink composition and protects the wiring of the flexible printed wiring board, and a flexible printed wiring board provided with the protective film.

  In many cases, a flexible printed wiring board (hereinafter referred to as FPC) is provided with a protective film (coverlay) for protecting wiring (copper foil pattern or the like) on its outer surface. In recent years, a protective film having higher heat resistance has been desired, and a protective film made of a polyimide resin having higher heat resistance has been proposed.

  As a method for forming a protective film made of polyimide, for example, a method of laminating a cover lay film made of polyimide film on a wiring board is widely used, but polyimide ink is printed on the wiring board (coating and drying). This method is also adopted because of the ease of production of the protective film.

  Polyimide inks are also known that contain polyamic acid and form a protective film by heat ring closure (imidization) after application to the wiring board. When this ink is used, heat ring closure imidization is also known. In order to achieve this, it is usually necessary to raise the temperature to 300 ° C. or higher, and the substrate of the wiring board may not be able to withstand this high temperature. In addition, the polyimide formed during imidation has a large shrinkage and is likely to cause a problem that the wiring board is curled. Therefore, a method of using a polyimide ink composition obtained by dissolving a solvent-soluble polyimide (soluble polyimide resin) in a solvent is proposed in WO 2005/116152 (Patent Document 1, Claim 1) and the like. .

  Patent Document 1 discloses a polycondensate of an aromatic tetracarboxylic dianhydride and a diamine component containing a silicone diamine having a siloxane group in the skeleton as a soluble polyimide resin (Claim 1). And, by using a soluble polyimide resin containing 15 to 85% by weight of silicone diamine in the diamine component, the warpage of the substrate is prevented, good flexibility (low elastic modulus), and adhesion to the substrate. Describes that a heat-resistant protective film can be obtained (paragraph 0021).

In recent years, more and more flame retardancy is desired in the fields of electrical and electronic equipment, and it is difficult for FPC to meet UL-94V-0 (US Underwriters Laboratory Standard). In many cases, flammability is required. Therefore, as the polyimide ink composition, a flame retardant added to impart flame retardancy is used. As a flame retardant, a non-halogen (halogen-free) flame retardant is desired due to environmental requirements. In order to satisfy such a requirement, Patent Document 1 discloses a polyimide ink composition comprising a solution of a soluble polyimide resin and added with an inorganic flame retardant such as a hydrated metal compound such as magnesium hydroxide. (Paragraph 0014).
WO 2005/116152 (Claim 1, paragraphs 0014 and 0021)

  However, the protective film obtained from the conventional polyimide ink composition has a problem in that it has a high elastic modulus due to the inclusion of an inorganic flame retardant, and the flexibility is lowered and warping cannot be sufficiently prevented. Therefore, it does not sufficiently satisfy the recent demands for lowering the elastic modulus and preventing warping, and improvements are desired.

  The reduction of the elastic modulus and the warpage of the protective film is achieved by using 4,4′-oxydiphthalic dianhydride (hereinafter referred to as OPDA) as an acid monomer (aromatic tetracarboxylic dianhydride or the like) constituting the polyimide. This can be achieved to some extent by using. However, OPDA is expensive, and there has been a demand for a polyimide ink composition capable of obtaining a protective film having a low elastic modulus and small warpage even when the amount of such expensive monomers used is small.

  Further, in the manufacture of FPC, a polyimide ink composition may be printed and dried to form a protective film, and then gold plating may be performed. In this case, acid cleaning may be performed as a pretreatment. However, when magnesium hydroxide, an inorganic flame retardant, is contained in the protective film, magnesium hydroxide is soluble in the acid treatment agent used for acid cleaning, so it elutes from the surface of the protective film during acid cleaning, There was a problem that the surface deteriorated and whitening on the protective film or defects of plating adhesion occurred. In particular, this problem becomes more prominent as plating conditions are severe.

  The present invention has been made in view of the above problems, and forms a protective film with a low elastic modulus and a small warp that satisfies recent requirements even when the amount of expensive monomers such as OPDA used is small. In addition, a protective film satisfying other characteristics required for an FPC protective film, such as whitening on the protective film at the time of gold plating and difficulty in plating adhesion, and sufficient flame resistance, etc. It is an object of the present invention to provide a polyimide ink composition that can be formed by printing.

  Further, the present invention is a protective film formed from this polyimide ink composition, has a low elastic modulus and a small warp, is less prone to whitening on the protective film during gold plating treatment, defects in plating adhesion, etc. The present invention provides an FPC protective film satisfying other properties required for an FPC protective film such as flame retardancy, and an FPC having the protective film.

  As a result of intensive studies, the inventor is a polyimide ink composition containing a soluble polyimide resin, characterized in that the diamine component constituting the soluble polyimide resin contains silicone diamine in a specific range of composition. By using the polyimide ink composition, a protective film having flame retardancy suitable for UL-94V-0 or VTM-0 can be obtained without blending an inorganic flame retardant such as magnesium hydroxide. In addition, by not blending an inorganic flame retardant, this protective film has a low elastic modulus and a small warp, and it has been found that whitening on the protective film during gold plating treatment and defects in plating adhesion are unlikely to occur. completed.

  The present invention includes, as claim 1 thereof, a soluble polyimide resin that is a condensate of a diamine component containing a silicone diamine and an aromatic tetracarboxylic dianhydride, and a solvent that dissolves the soluble polyimide resin, Provided is a polyimide ink composition, wherein the composition ratio of silicone diamine in the diamine component is 66% or more and 80% or less by weight.

  Here, the soluble polyimide resin means a polyimide soluble in a solvent. A polyimide can be obtained by subjecting a diamine component and an aromatic tetracarboxylic dianhydride to a condensation reaction. Specifically, it can be produced by dissolving a diamine component and an aromatic tetracarboxylic dianhydride in an equimolar amount of about 1: 1 in a solvent and heating to cause a condensation reaction. The molar ratio is preferably in the range of 0.95 to 1.05, more preferably in the range of 0.98 to 1.02.

  It is preferable to use the same solvent as the solvent for the polyimide ink composition as the solvent used in this condensation reaction, because the operation for replacing the solvent becomes unnecessary during the production of the polyimide ink composition. Therefore, as this solvent, what is illustrated as a solvent which melt | dissolves the polyimide resin mentioned later is used preferably.

  The present invention is characterized in that the diamine component constituting the soluble polyimide resin contains a silicone diamine, and the composition ratio thereof is 66% by weight or more and 80% by weight or less in the total diamine component. The addition of solubility to the polyimide can be performed by introducing a group having a high affinity with the solvent into the polymer chain. In the present invention, the diamine component has a specific amount of a silicone diamine having a high affinity with the solvent. Since it contains, solubility is provided by this silicone diamine. Moreover, adhesiveness with a board | substrate improves by containing silicone diamine.

  Furthermore, by setting the composition ratio of silicone diamine within the above range, flame retardancy suitable for UL-94V-0 (or VTM-0) can be achieved without blending an inorganic flame retardant such as magnesium hydroxide. A polyimide ink composition is obtained that forms a protective film that is flexible (low elastic modulus) and hardly warps.

  That is, when the composition ratio of the silicone diamine is less than 66% by weight, the elastic modulus of the protective film formed from the polyimide ink composition made of this soluble polyimide resin is increased, and warpage tends to occur. On the other hand, when it exceeds 80% by weight, the flame retardancy of the protective film is lowered, and when an inorganic flame retardant such as magnesium hydroxide is not blended, the flame retardancy conforming to UL-94V-0 cannot be obtained. Moreover, when the composition ratio of silicone diamine is increased, the glass transition temperature of the protective film tends to be lowered, and the problem of heat resistance tends to occur.

  Here, the silicone diamine is a compound having a siloxane group in the skeleton and two primary amino groups at its ends, and for example, those represented by the following structural formula (I) can be used.

  In addition to this, compounds having an amino group attached via a phenylene group, for example, a compound represented by the following structural formula (II) can also be mentioned as examples of silicone diamine.

  The weight average molecular weight of the silicone diamine is preferably 4000 or less. Accordingly, a in formula (I) and formula (II) is preferably about 36 or less. In particular, when it is desired to increase the adhesive strength with the copper foil, the average molecular weight is 1000 or less, and a is preferably 1-9. Here, the weight average molecular weight is a value measured by GPC and obtained by calculation using standard polystyrene.

  In the production of the polyimide ink composition of the present invention, a commercially available silicone diamine can be used. X-22-1660B-3, KF-8010, X-22-161A, etc. manufactured by the company can be mentioned. Silicone diamines can be used alone or in combination of two or more.

  Examples of the diamine other than the silicone diamine contained in the diamine component used in the production of the polyimide ink composition of the present invention include bis (3-aminopropyl) ether ethane and 3,3′-diamino-4,4. 'Dihydroxydiphenylsulfone, 4,4'diamino-3,3'dihydroxybiphenyl, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, siloxane diamine, bis (3-aminopropyl) ether ethane N, N-bis (3-aminopropyl) ether, 1,4-bis (3-aminopropyl) piperazine, isophoronediamine, 1,3′-bis (aminomethyl) cyclohexane, 3,3′-dimethyl-4 , 4′-diaminodicyclohexylmethane, 4,4′-methylenebis (cyclohexyl Silamine), 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 4,4'-diamino-diphenyl sulfone, 3,4'-diamino-diphenyl sulfone, 3,3 '-Diamino-diphenyl sulfone, 2,4'-diaminodiphenyl ether, 1,3-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene (hereinafter referred to as “APB”) 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, bis [4- (4-aminophenoxy) phenyl ] Sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone (hereinafter referred to as “ APSM "), 4,4'bis (4-aminophenoxy) biphenyl, 1,4-bis (4-aminophenoxy) benzene, 4,4'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide 3,3′-diaminodiphenyl sulfide, 3,3′diamino-4,4′dihydroxydiphenyl sulfone, 2,4-diaminotoluene, 2,5-diaminotoluene, 3,5-diaminobenzoic acid, 2,6- Examples include diaminopyridine, 4,4′diamino-3,3′dimethoxybiphenyl, 4,4′diamino-3,3′dimethylbiphenyl, 9,9′-bis (4-aminophenyl) fluorene and the like. APB and BAPSM represented by the structural formula (III) can be preferably used. These can be used individually by 1 type or in combination of 2 or more types.

  By containing a diamine having a hydroxyl group in the molecule in another diamine component, alkali solubility can be imparted to the film formed from the polyimide ink composition. And photosensitivity can also be provided by mix | blending positive type photosensitizers, such as a naphthoquinone diazide sulfonyl ester of an aromatic polyhydroxy compound, with this alkali-soluble polyimide ink composition. The protective film of the FPC covers the wiring, the element portion, and the like, but sometimes the pad portion and the like are exposed. After using the polyimide ink composition to which photosensitivity is imparted as described above, the polyimide ink composition is first applied to the entire surface of the FPC substrate on which wirings, elements, and the like are formed to form a polyimide film. Then, only a predetermined portion is exposed to ultraviolet rays through a mask or the like, developed, and patterned to remove a part of the film, thereby exposing the predetermined portion.

  As aromatic tetracarboxylic dianhydride constituting the soluble polyimide resin, OPDA (represented by the following structural formula (IV)), 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride (hereinafter referred to as “BTDA”) represented by the structural formula (V), 3,3 ′, 4,4′-diphenyl sulfonetetra Carboxylic dianhydride, bicyclo (2,2,2) -oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride , Pyromellitic dianhydride, 2,2-bis (3,4-dicarbonoxyphenyl) hexafluoropropane dianhydride, 5- (2,5-dioxotetrahydrofuryl) -3-methyl-3-cyclohexene -1 , 2-dicarboxylic acid anhydride and the like. These can be used individually by 1 type or in combination of 2 or more types.

  Among these, if OPDA is used, a more flexible protective film can be obtained and warpage can be suppressed. However, in the present invention, by setting the composition ratio of silicone diamine within a specific range, the protective film can be made flexible (low elastic modulus) and hardly warped. Even if the ratio of OPDA in the product is lowered, a protective film that is flexible (low elastic modulus) and hardly warps can be obtained. Therefore, the amount of expensive OPDA used can be reduced, and the cost can be reduced.

  The polyimide ink composition of the present invention can be obtained by adding and mixing the above soluble polyimide resin and a solvent.

  As a solvent for the polyimide ink composition, that is, a solvent for dissolving the soluble polyimide resin, a polar solvent is preferable, and N-methyl-2-pyrrolidone, N, N′-dimethylacetamide, dimethylformamide, dimethyl sulfoxide, acetonitrile, diglyme, γ -Butyrolactone, methyl benzoate, ethyl benzoate, γ-valerolactone, phenol, toluene, dioxane, tetrahydrofuran, sulfolane, hexamethylphosphoramide and the like. Of these, methyl benzoate and γ-butyrolactone are preferably used from the viewpoints of solubility, volatility, water absorption, odor, and the like. The amount used is preferably equal to or greater than the amount that completely dissolves the soluble polyimide resin.

  By using the polyimide ink composition of the present invention, a protective film having excellent flame retardancy can be obtained without blending an inorganic flame retardant such as magnesium hydroxide, so that the addition of an inorganic flame retardant is possible. As a result, it is possible to prevent the protective film from warping and to prevent whitening on the protective film during plating and the occurrence of defects in plating adhesion.

  The invention according to claim 2 is the polyimide ink composition according to claim 1, further comprising a melamine compound such as hexamethylmethoxymelamine (hereinafter referred to as HMMM). When the polyimide ink composition contains a melamine compound such as HMMM, the polyimide ink composition is applied onto a substrate to form a polyimide film, and then heated to cause cross-linking between the polyimides and cure the film. Thus, the solvent resistance of the protective film to solvents such as acetone, methyl ethyl ketone and alcohol can be improved.

  Here, the addition amount of a melamine compound such as HMMM is preferably 0.1% to 10%. The heating conditions for curing the film are preferably 180 ° C. to 200 ° C. for 10 to 60 minutes.

  The invention according to claim 3 is characterized in that the aromatic tetracarboxylic dianhydride is a mixture of OPDA and BTDA in a ratio of 4: 6 to 6: 4 (molar ratio). 2. The polyimide ink composition according to 2. Among the aromatic tetracarboxylic dianhydrides exemplified above, BTDA is preferable because it is inexpensive and has a certain degree of flexibility. In addition, as described above, in the present invention, even when the amount of OPDA used is reduced, flexibility can be imparted to the protective film and the problem of warpage can be suppressed.

  In addition to the polyimide ink composition, the present invention provides an FPC protective film (Claim 4) that can be obtained by applying the composition onto a wiring board and drying it. The present invention further provides an FPC (Claim 5) comprising the protective film.

  The protective film of the present invention is provided on the outer surface of the FPC and covers these in order to protect the wiring, the element portion, and the like. The protective film of the present invention and the FPC of the present invention are obtained by applying the polyimide ink composition to the outer surface of an FPC (substrate) and drying it. Therefore, the protective film of the present invention has a low elastic modulus and a small warpage, is less likely to cause whitening on the protective film during gold plating treatment, defects in plating adhesion, and the like, and exhibits sufficient flame retardancy.

  The soluble polyimide resin used in the present invention is already imidized. Therefore, heating at a high temperature necessary for forming an imide ring is not necessary when forming a coating film. However, when the raw material polyimide ink composition contains a curing agent such as HMMM, it is cured by heating after coating and drying. Post-curing can cause cross-linking between polyimides and improve the solvent resistance of the protective film.

  By using the polyimide ink composition of the present invention, a protective film having flame retardancy suitable for UL-94V-0 can be obtained without blending an inorganic flame retardant such as magnesium hydroxide. And by not mix | blending an inorganic flame retardant, while being able to make a protective film lower elastic modulus and suppressing curvature, it can make it difficult to produce the whitening on a protective film at the time of a gold plating process, the malfunction of plating adhesion, etc. ( Excellent plating resistance is obtained.) In addition, even when the content of OPDA in the aromatic tetracarboxylic dianhydride is small, a protective film with low elastic modulus and low warpage can be obtained, so the amount of expensive OPDA used can be reduced and the cost can be reduced Can be achieved.

  Therefore, the protective film of the present invention has a low elastic modulus and a small warp, is not prone to whitening on the protective film at the time of the gold plating process, plating adhesion failure, etc., and exhibits sufficient flame retardancy. The FPC of the present invention including a film has high flame retardancy, hardly warps, and is non-halogen. Therefore, the FPC is suitably used for an electronic component that requires these characteristics.

  Next, the best mode for carrying out the present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Synthesis Example 1 (Synthesis of soluble polyimide resin)
1. In a 1 L separate flask equipped with a cooler, a moisture measuring receiver, a mechanical stirrer, and a nitrogen introduction tube, in a nitrogen atmosphere, 60 g of γ-butyrolactone and 40 g of methyl benzoate were mixed with the structural formula ( I) is represented by a silicone diamine (manufactured by Shin-Etsu Chemical Co., Ltd., KF-8010: represented by formula (I), wherein a = 8 to 9, average molecular weight: about 1000, and in Table 1, it is described as SiOn. ) 30 g (0.03 mol: 50 mol% with respect to the total diamine) is added and dissolved. Further, 0.5 g of pyridine as a catalyst and 20 g of toluene as an azeotropic solvent are added.

2. As acid dianhydride, 9.67 g (0.03 mol) of BTDA (molecular weight: 322.2) and 9.31 g (0.03 mol) of OPDA (molecular weight: 310.2) were gradually added, and the whole amount was added and then 15 minutes. After stirring, the mixture is heated to 160 ° C. with a mantle heater and allowed to react for 1 hour. During this time, the cooling water is poured and toluene is circulated. After confirming that a specified amount of water has come out of the moisture measuring receiver, the heating is stopped and it is naturally cooled to around room temperature (50 ° C. or lower).

3. Next, 8.77 g (0.03 mol: 50 mol% with respect to the total diamine) of APB (molecular weight: 292.3) is added as a diamine, and further 40 g of a solvent γ-butyrolactone so as to have a solid content of about 30%. Add The mixture is stirred for 15 minutes, and then heated to 160 ° C. in an oil bath and reacted for 3 hours to obtain a reaction solution. After confirming that a specified amount of water had come out, the pressure was reduced and toluene and pyridine were removed from the reaction solution to obtain varnish 1.

Synthesis Examples 2 to 4 (Synthesis of base polymer varnish)
Varnish 2 (Synthesis Example 2), Varnish 3 (Synthesis Example) except that the molar ratio of silicone diamine (indicated as SiOn in Table 1) and APB was changed as shown in Table 1, as in Synthesis Example 1. 3) Varnish 4 (Synthesis Example 4) was obtained.

Example 1, Comparative Examples 1 and 2
Blue pigment (pigment blue (copper phthalocyanine) 0.8 part by weight, anti-foaming agent (KS-603 manufactured by Shin-Etsu Chemical Co., Ltd.) 0.8 part by weight for each 100 parts by weight of varnish 1, varnish 2 and varnish 3 Were dissolved to obtain polyimide ink compositions (inks).

Example 2 and Comparative Example 3
2.5 parts by weight of HMMM, 0.8 parts by weight of blue pigment (pigment blue (copper phthalocyanine), defoaming agent (KS-603 manufactured by Shin-Etsu Chemical Co., Ltd.) for 100 parts by weight of varnish 1 and varnish 3 0.8 parts by weight was added and dissolved to obtain a polyimide ink composition (ink).

Comparative Example 4
With respect to 100 parts by weight of varnish 4, 2.5 parts by weight of HMMM, 4.0 parts by weight of magnesium hydroxide (MgOH), 0.8 parts by weight of blue pigment (pigment blue (copper phthalocyanine), defoaming agent ( Shin-Etsu Chemical Co., Ltd. KS-603) 0.8 parts by weight was added and dissolved to obtain a polyimide ink composition (ink).

  For each of the polyimide ink compositions (inks) obtained in Examples 1 and 2 and Comparative Examples 1 to 4, a warp test, an adhesion test (adhesiveness to copper foil), and flame retardancy were performed by the following methods. Table 1 shows the results of a property test, dynamic viscoelasticity measurement, solvent resistance test and the like.

[Curve test]
Each of the polyimide ink compositions (inks) obtained in the examples or comparative examples was applied and formed on a copper foil having a thickness of 13 μm so that the film thickness after drying was 10 μm. Then, it cut | disconnected to the 50 square mm, dried for 60 minutes at 120 degreeC, and also calculated | required the average value of the curvature amount of four corners after performing post-curing for 30 minutes at 180 degreeC.

[Adhesion test (adhesion to copper foil)]
A sample prepared in the same manner as in the warp test was cut to a width of 5 mm, and the adhesive strength between the copper foil and the formed polyimide was evaluated by a 180 ° peel test.

[Flame retardance test]
On the polyimide film Kapton 100EN (25 μm thickness), each of the polyimide ink compositions (inks) obtained in the examples or comparative examples was applied and formed so that the film thickness after drying was 10 μm. The film was dried at 60 ° C. for 60 minutes, and further post-cured at 180 ° C. for 30 minutes. About the sample obtained in this way, the flame retardance was measured based on the vertical flammability test (VTM) of UL94 film material. The results are shown in Table 1.

[Dynamic viscoelasticity measurement]
Each of the polyimide ink compositions (inks) obtained in the examples or comparative examples was formed so that the film thickness after drying was 25 μm, dried at 120 ° C. for 60 minutes, and further at 180 ° C. for 30 minutes. About the sample which performed postcure, Tg, tan-delta peak temperature (degreeC), and the elasticity modulus (25 degreeC) were measured using the dynamic viscoelasticity measuring apparatus (DMS). The results are shown in Table 1.

[Plating resistance test]
Each of the polyimide ink compositions (inks) obtained in the examples or comparative examples was applied and formed on a 13 μm thick copper foil, dried at 120 ° C. for 60 minutes, and further at 180 ° C. for 30 minutes. About the sample which performed postcure, the electroless gold plating process shown below was given, and the test body was obtained.

(Electroless gold plating process)
The following steps were performed in the order shown below. Specifically, the sample was dipped in a tank in each step in sequence and then dried.
Degreasing treatment (acid degreasing = acid treatment), water washing, soft etching, water washing, desmear treatment,
Palladium chloride catalyzed, nickel (nickel nitrate) plating,
Gold (potassium cyanide) plating, water washing, drying

About the obtained test body, the surface state after an electroless gold plating process was observed visually.
Evaluation criteria:
Y: No change
Δ: Damage near the edge
×: Plating adheres to the surface in granular form

[Solvent resistance test]
Each of the samples used in the warpage test was immersed in each of the solvents shown in Table 1 for 5 minutes at room temperature, and the surface state was observed visually.
Evaluation criteria:
◎: No change (with surface gloss)
○: Some roughness on the surface
Δ: Partial dissolution
×: dissolution

  As is clear from the results in Table 1, when the polyimide ink compositions of Examples 1 and 2 as examples of the present invention were used, a polyimide resin film having excellent flame retardancy (VTM-0) (protection) Film), and this protective film hardly causes warping. In addition, this protective film has a sufficient value at a practical level in terms of adhesive strength with copper foil, plating resistance, and solvent resistance.

  On the other hand, when the polyimide ink composition of Comparative Example 1 synthesized using a diamine component having a silicone diamine content smaller than the range of the present invention (less than 66% by weight) is used, excellent flame retardancy (VTM −0), the protective film has a high elastic modulus and generates a large warp. Moreover, the protective film obtained from the polyimide ink composition of Comparative Examples 2 and 3 synthesized using a diamine component having a silicone diamine content larger than the range of the present invention (when exceeding 80% by weight) The flame retardancy is insufficient and the flame retardancy of VTM-0 cannot be obtained.

  Comparative Example 4 is an example in which magnesium hydroxide as an inorganic flame retardant is contained, and is VTM-0. However, Comparative Example 4 has a problem that it is inferior in plating resistance. Furthermore, there is also a problem that warpage is large despite using OPDA alone as the aromatic tetracarboxylic dianhydride.

  Example 2 and Comparative Example 3 are examples in which HMMM is added. As is clear from the comparison between Example 1 and Example 2, the solvent resistance to acetone is improved by the addition of HMMM.

Claims (5)

It contains a soluble polyimide resin that is a condensate of a diamine component containing a silicone diamine and an aromatic tetracarboxylic dianhydride , a solvent that dissolves the soluble polyimide resin, and a melamine compound that is a crosslinking agent for the soluble polyimide resin. The composition ratio of silicone diamine in the diamine component is 66 wt% or more and 80 wt% or less. Content of the said melamine compound is 0.1 mass%-10 mass%, The polyimide ink composition of Claim 1 characterized by the above-mentioned.   The aromatic tetracarboxylic dianhydride is a 4: 6-6: 4 (molar ratio) of 4,4′-oxydiphthalic dianhydride and 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride. The polyimide ink composition according to claim 1, wherein the polyimide ink composition is a mixture of   A protective film for covering wiring of a flexible printed wiring board, comprising a cured product of the polyimide ink composition according to any one of claims 1 to 3.   A flexible printed wiring board comprising the protective film according to claim 4.