JP4889194B2 - Manufacturing method of substrate for flexible printed wiring board - Google Patents

Description

  The present invention relates to a method for producing a substrate for a flexible printed wiring board obtained by continuously and directly applying a polyimide resin precursor solution onto a metal foil.

  Conventionally, a substrate for a flexible printed wiring board is manufactured by bonding a polyimide or polyester film and a metal foil through an adhesive such as an epoxy resin or an acrylic resin. However, the flexible printed wiring board substrate manufactured by such a method has a problem that heat resistance and flame retardancy are reduced due to the adhesive layer. In addition, there has been a problem that the rate of dimensional change is large when the metal foil is etched or when any heat treatment is performed, which hinders subsequent processes. In order to solve such problems, a method for manufacturing a flexible printed wiring board substrate by directly forming a polyimide resin layer on a metal foil without the presence of an adhesive layer is disclosed. . For example, Patent Document 1 proposes a method in which a polyimide resin precursor having a specific structure is directly applied and dried on a metal foil and then cured to obtain a flexible printed wiring board substrate.

  Moreover, as a drying and subsequent polyimide curing method, Patent Document 2 includes (1) a method of drying and curing in a line shape, and (2) rewinding a substrate that has only been dried in an apparatus such as a vacuum furnace. Methods such as a method of curing by heating and (3) a method of heat-treating a substrate that has only been dried in a roll state are described. Furthermore, the same document also describes that when heat treatment is performed in a roll shape, a substrate having a large surface irregularity such as a nonwoven fabric or a wire mesh is used as a spacer. A method of heat-treating a substrate that has only been dried using a spacer or the like in a roll state can efficiently produce a substrate for a flexible printed wiring board with a compact apparatus, but for a flexible printed wiring board produced by this method The substrate was not curled and dimensional stability was not sufficient.

JP-A-60-157286 JP-A-5-175634

  An object of the present invention is to provide a method capable of efficiently producing a flexible printed wiring board substrate substantially free from curling and excellent in dimensional stability with a compact apparatus.

  As a result of intensive studies to solve the above problems, the present inventors have conducted preliminary drying until the resin concentration in the coating film reaches a specific range, and then wound up and dried at a specific temperature condition. Then, the inventors have found that the above-mentioned problems can be solved by curing, and have reached the present invention.

That is, the gist of the present invention is that a polyimide resin precursor solution is continuously and directly applied on a metal foil, and pre-dried continuously until the solid content concentration in the formed coating film is 40 to 80% by mass. After that, this is a width that occupies 0.5 to 20% of the width of the solution application part, and is accompanied by a spacer having a thickness of 0.5 to 2 mm including the uneven part, whereby the polyimide resin precursor solution is obtained. It is characterized in that it is further dried with hot air at a temperature of less than 200 ° C. for 10 minutes or more in a wound state with a gap provided between the circumferences of the coated metal foil, and then the polyimide is thermally cured at a temperature of 200 ° C. or more. It is a manufacturing method of the board | substrate for flexible printed wiring boards.

  ADVANTAGE OF THE INVENTION According to this invention, the board | substrate for flexible printed wiring boards which is substantially curl-free and excellent in dimensional stability can be efficiently manufactured with a compact apparatus.

  The polyimide resin precursor referred to in the present invention is a polyimide resin having an imide bond by heat curing and having a structural unit represented by the following structural formula (1). Any compound can be used as long as it is such a compound. For example, a polyamic acid represented by the following structural formula (2) can be used as a polyimide resin precursor. The polyamic acid can be usually produced as a polyimide resin precursor solution composed of a polyamic acid and a solvent.

  In the structural formulas (1) and (2), R represents a tetravalent organic residue, and R ′ represents a divalent organic residue.

  Examples of the solvent for producing the polyimide resin precursor solution include an aprotic polar solvent, an ether compound, and a water-soluble alcohol compound.

  Examples of the aprotic polar solvent include N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoramide and the like.

  Examples of the ether compounds include 2-methoxyethanol, 2-ethoxyethanol, 2- (methoxymethoxy) ethoxyethanol, 2-isopropoxyethanol, 2-butoxyethanol, tetrahydrofurfuryl alcohol, diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol. Monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol, triethylene glycol monoethyl ether, tetraethylene glycol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, dipropylene glycol, dipropylene glycol monomethyl ether, di Propylene glycol monoethyl ether, tripropylene glycol monomethyl ether, poly Ji glycol, polypropylene glycol, tetrahydrofuran, dioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and the like.

  Examples of water-soluble alcohol compounds include methanol, ethanol, 1-propanol, 2-propanol, tert-butyl alcohol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, and 1,3-butanediol. 1,4-butadiol, 2,3-butanediol, 1,5-pentanediol, 2-butene-1,4-diol, 2-methyl-2,4-pentanediol, 1,2,6-hexanetriol And diacetone alcohol.

  These solvents can be used as a mixture of two or more. Among these solvents, particularly preferred examples include N, N-dimethylacetamide and N-methyl-2-pyrrolidone as the sole solvent, and examples of the mixed solvent include N, N-dimethylacetamide and N- Examples thereof include a combination of methyl-2-pyrrolidone, N-methyl-2-pyrrolidone and methanol, N-methyl-2-pyrrolidone and 2-methoxyethanol.

Next, the manufacturing method of a polyimide resin precursor is demonstrated.
First, a solution composed of a polyamic acid is prepared by, for example, mixing an aromatic tetracarboxylic dianhydride represented by the following structural formula (3) and an aromatic diamine represented by the following structural formula (4) with the above solvent such as aprotic polarity. It can manufacture by making it react in a solvent.

Here, R ₁ represents a tetravalent aromatic residue.

Here, R ₂ represents a divalent aromatic residue.

  In the above reaction, the ratio of the tetracarboxylic dianhydride and the diamine is preferably 1.03 to 0.97 mol of tetracarboxylic dianhydride with respect to 1 mol of diamine, more preferably 1 mol of diamine. On the other hand, tetracarboxylic dianhydride is 1.01-0.99 mol. Moreover, -30-60 degreeC is preferable and, as for reaction temperature, -20-40 degreeC is more preferable.

  In the above reaction, the mixing order of the monomer and the solvent is not particularly limited and may be any order. When a mixed solvent is used as a solvent, a solution composed of polyamic acid can also be obtained by dissolving or suspending separate monomers in each solvent, mixing them, and reacting at a predetermined temperature and time with stirring. Is obtained. Two or more kinds of polyimide resin precursor solutions may be mixed and used.

  Specific examples of the aromatic tetracarboxylic dianhydride represented by the structural formula (3) include pyromellitic acid, 3,3 ′, 4,4′-biphenyltetracarboxylic acid, 3,3 ′, 4,4. '-Benzophenone tetracarboxylic acid, 3,3', 4,4'-diphenylsulfone tetracarboxylic acid, 2,3,3 ', 4'-diphenyl ether tetracarboxylic acid, 2,3,3', 4'-benzophenone tetra Carboxylic acid, 2,3,6,7-naphthalenetetracarboxylic acid, 1,4,5,7-naphthalenetetracarboxylic acid, 1,2,5,6-naphthalenetetracarboxylic acid, 3,3 ', 4,4 '-Diphenylmethanetetracarboxylic acid, 2,2-bis (3,4-dicarboxyphenyl) propane, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane, 3, , 9,10-tetracarboxyperylene, 2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl] propane, 2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl] hexa Fluoropropane dianhydride and the like. These aromatic tetracarboxylic dianhydrides can be used in combination of two or more.

  In the present invention, pyromellitic acid or 3,3 ′, 4,4′-biphenyltetracarboxylic acid can be used as a particularly preferred aromatic tetracarboxylic dianhydride. These can be used alone or in combination.

  Specific examples of the aromatic diamine represented by the structural formula (4) include p-phenylene diamine, m-phenylene diamine, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 4,4 ' -Diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 1,2-bis (anilino) ethane, diaminodiphenylsulfone , Diaminobenzanilide, diaminobenzoate, diaminodiphenyl sulfide, 2,2-bis (p-aminophenyl) propane, 2,2-bis (p-aminophenyl) hexafluoropropane, 1,5-diaminonaphthalene, diaminotoluene, Diaminobenzotrifluoride, 1,4- (P-aminophenoxy) benzene, 4,4'-bis (p-aminophenoxy) biphenyl, diaminoanthraquinone, 4,4'-bis (3-aminophenoxyphenyl) diphenyl sulfone, 1,3-bis (anilino) Examples include hexafluoropropane, 1,4-bis (anilino) octafluorobutane, 1,5-bis (anilino) decafluoropentane, 1,7-bis (anilino) tetradecafluoroheptane. Two or more of these aromatic diamines can be mixed and used.

  In the present invention, p-phenylenediamine or 4,4′-diaminodiphenyl ether can be used as a particularly preferred aromatic diamine. These can be used alone or in combination.

  In the present invention, when a polyimide resin precursor solution is produced, an amine, diamine, dicarboxylic acid, tricarboxylic acid, or tetracarboxylic acid derivative having a polymerizable unsaturated bond is added to form a crosslinked structure during thermosetting. Can be made. As the unsaturated compound, maleic acid, nadic acid, tetrahydrophthalic acid, ethynylaniline and the like can be used.

  There is no particular problem even if a partially imidized polyimide resin precursor is present in the polyimide resin precursor due to synthesis conditions, drying conditions, and other reasons of the polyimide resin precursor.

  Moreover, when manufacturing the solution of these polyimide resin precursors, other heat resistant resins, such as a polyimide resin soluble in the said solvent and a polyamideimide resin, can be mixed. Furthermore, in order to improve adhesiveness (adhesiveness) and film properties, a silane coupling agent and various surfactants can be added in minute amounts.

  Examples of the metal foil in the present invention include foils of copper, aluminum, iron, silver, palladium, nickel, chromium, molybdenum, tungsten or alloys thereof, preferably copper. The surface of these metal foils is chemically or mechanically surfaced with siding, nickel plating, copper-zinc alloy plating, aluminum alcoholate, aluminum chelate, silane coupling agent, etc. for the purpose of improving adhesion. Processing may be performed. 5-50 micrometers is preferable and, as for the thickness of metal foil, 10-20 micrometers is more preferable.

  Coating can be performed using any coating machine, and examples thereof include a die coater, a lip coater, a gravure coater, a bar coater, a doctor blade coater, a comma coater, a reverse roll coater, and a bar reverse roll coater. In addition, it is also possible to apply multiple layers for the purpose of improving characteristics, and the polyimide resin precursor solutions in each layer may be the same or different.

  Any device can be used for the preliminary drying, and a hot air dryer is preferable, but infrared heating, electromagnetic induction heating, or the like may be used or used in combination.

  The preliminary drying is preferably performed immediately after coating and continuously until the solid content concentration in the coating film is in the range of 40 to 80% by mass. At this time, when the solid content concentration is less than 40% by mass, winding cannot be performed satisfactorily due to stickiness of the coated surface. On the other hand, when the solid content concentration exceeds 80% by mass, curling tends to increase after winding and drying, and dimensional stability tends to deteriorate.

  After winding, drying is performed at a temperature of less than 200 ° C. for 10 minutes or more. At this time, if the time of less than 200 ° C. is less than 10 minutes, the curl becomes large and the dimensional stability is deteriorated. During the temperature period of less than 200 ° C., the temperature may be appropriately changed, and a period during which the temperature is kept constant may be included.

  Thereafter, the polyimide is cured by further heat treatment, and the curing temperature is 200 ° C. or higher, preferably 300 ° C. or higher. Moreover, an upper limit is about 450 degreeC. The time for curing is preferably 2 hours or more, and more preferably 5 hours or more.

When drying in a wound state, it is necessary to entrain the metal foil coated with the polyimide resin precursor solution and the spacer . The spacer is in the form of a band or a string, and can be provided with a gap between the circumferences of the metal foil by accompanying winding with the metal foil coated with the polyimide resin precursor solution. The material is not particularly limited as long as it is a material that can withstand the drying process, such as metal, resin, paper, glass fiber, and preferably stainless steel, copper, aluminum, PET, nylon, and the like.

The width of the spacer needs to occupy 0.5 to 20% of the width of the solution application part , and preferably 1 to 10%. If it is less than 0.5%, it becomes difficult to handle during the accompanying winding. On the other hand, if it exceeds 20%, the area that can be effectively used as a product becomes small. In addition, in order to prevent the metal foil from wrinkling, the spacers should be positioned symmetrically with respect to the width direction of the metal foil, and are arranged in two rows near the left and right ends or three rows near the center and both left and right ends. Is preferred. When using a plurality of spacers, the total spacer width may be in the above range.

In addition, since the shape of the spacer requires air permeability for facilitating escape of gas generated at the time of drying, it is preferable to have irregularities, and shapes such as an embossed product and a corrugated product are preferable. Even if the air permeability is not sufficient, the necessary air permeability can be ensured by providing gaps in places such as intermittent use. The thickness of the spacer, including the concavo-convex portion , needs to be 0.5 to 2 mm. The same type or different types of spacers can be laminated, and in this case, the thickness of the plurality of sheets may be in the above-mentioned range, and the thickness of a single item is not particularly limited.

  The accompanying winding of the spacer is performed at the same time as the winding after the application / preliminary drying described above, or after coating / predrying / winding, the metal foil coated with the polyimide resin precursor solution is unwound and the spacer is unwound. It may be wound around another core while sandwiching.

  The polyimide may be heat-cured in a wound state with a spacer or after the spacer is removed, but the latter is preferable because it can be performed with a more compact device and has high efficiency. Since gas such as water is generated during thermosetting, it is preferably performed under reduced pressure. In addition, when using an easily oxidizable substance such as a copper foil as the metal foil, it is more preferable to carry out in an inert atmosphere.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example and a comparative example, this invention is not limited to this.

The evaluation method of the board | substrate obtained by the Example and the comparative example is as follows.
(1) Curling characteristics Using a sample with a size of 100 mm in length and 100 mm in width, the radius of curvature after being left for 24 hours in a temperature of 23 ° C. and a humidity of 60% RH is measured. 20 mm or more and less than 50 mm is represented by Δ, and less than 20 mm is represented by x.
(2) Dimensional change rate A sample having a width of 10 mm and a length of 200 mm was immersed in an aqueous ferric chloride solution, and the copper foil was entirely etched with the aqueous ferric chloride solution to remove all the copper foil from the sample. did. Measure the dimensions after etching and after heat treatment at 150 ° C for 30 minutes after etching using a digital reading microscope (NRM-D-2XZ type, manufactured by Nihon Koki Co., Ltd.). The direction and TD direction were calculated respectively.

Reference example 1
(Synthesis example of polyimide resin precursor solution)
0.15 mol of ODA, 0.85 mol of PDA, and 3329 g of NMP were placed in a three-necked flask and stirred in ice water for 30 minutes. Then, 1.00 mol of BPDA was added and stirred in a 40 ° C. water bath for 1 hour. A uniform polyimide resin precursor solution containing an acid was obtained. The solid content concentration of this solution was 20% by mass. This is solution a.
(The meaning of each abbreviation is as follows)
BPDA: 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride
ODA: 4,4'-oxydianiline
PDA: Paraphenylenediamine
NMP: N-methyl-2-pyrrolidone

Example 1
Solution A was continuously applied onto an electrolytic copper foil having a thickness of 18 μm using a lip coater so that the coating thickness after curing was 25 μm, and pre-dried at 130 ° C. for 5 minutes. The solid content concentration in the coating film at this time was 50% by mass. The obtained substrate having a width of 50 cm and a length of 100 m was wound around an aluminum core while being accompanied by a spacer having a corrugation process on a stainless steel foil having a width of 20 mm and a thickness of 100 μm to a thickness of 1.5 mm. Two spacers were used and were wound around the left and right ends of the substrate.
Then, it put in the hot-air oven, and it heated up to 180 degreeC over 10 minutes from room temperature, and also dried, heating up to 200 degreeC over 5 minutes. Then, it is taken out from the oven, the spacer is removed, it is wound around another aluminum core, heated in a hot air inert oven under a nitrogen atmosphere from room temperature to 360 ° C. over 120 minutes, and further heated at 360 ° C. for 6 hours. Then, a curing reaction was carried out to obtain a flexible printed wiring board substrate.

Example 2
The same operation as in Example 1 was performed except that the drying conditions after preliminary drying and winding were increased from room temperature to 180 ° C. over 30 minutes and further increased to 200 ° C. over 5 minutes. To obtain a substrate for a flexible printed wiring board.

Example 3
The same operation as in Example 1 was performed except that the drying conditions after pre-drying and winding were increased from room temperature to 180 ° C. over 60 minutes and further increased to 200 ° C. over 5 minutes. To obtain a substrate for a flexible printed wiring board.

Example 4
A substrate for a flexible printed wiring board was obtained by performing the same operation as in Example 1 except that preliminary drying was performed at 140 ° C. for 5 minutes and the solid content concentration of the coating film was changed to 60% by mass.

Comparative Example 1
A substrate for a flexible printed wiring board was obtained by performing the same operation as in Example 1 except that the drying conditions after the preliminary drying and winding were increased from room temperature to 200 ° C. over 5 minutes.

Comparative Example 2
A substrate for a flexible printed wiring board was obtained by performing the same operation as in Example 1 except that the drying conditions after the preliminary drying and winding were increased from room temperature to 200 ° C. over 8 minutes.

Comparative Example 3
In Example 4, a flexible printed wiring board substrate was obtained in the same manner as in Example 4 except that drying conditions after preliminary drying and winding were increased from room temperature to 200 ° C. over 8 minutes.

  Table 1 shows the results of measuring the curl characteristics and the dimensional change rate of the flexible printed wiring board substrates obtained in Examples 1 to 4 and Comparative Examples 1 to 3.

  As shown in Table 1, the flexible printed wiring board substrates obtained in Examples 1 to 4 have good curl characteristics and dimensional stability, and can withstand a high mounting density. Met.

On the other hand, the flexible printed wiring board substrates obtained in Comparative Examples 1 to 3 were inferior in curl characteristics and dimensional stability because the drying conditions were outside the scope of the present invention.

Claims (1)

The polyimide resin precursor solution is continuously applied directly onto the metal foil, and after continuous drying until the solid content concentration in the formed coating film is 40 to 80% by mass, this is applied as a solution. The width of the metal foil to which the polyimide resin precursor solution is applied by wrapping with a spacer having a thickness of 0.5 to 2 mm including the concavo-convex portion, which occupies 0.5 to 20% of the part width. A substrate for a flexible printed wiring board characterized by further performing hot air drying at a temperature of less than 200 ° C. for 10 minutes or more in a wound state with a gap in between, and then thermosetting polyimide at a temperature of 200 ° C. or more. Production method.