JP2680816B2 - Flexible printed circuit board - Google Patents

Description

TECHNICAL FIELD The present invention relates to a flexible printed circuit board that is free from curling, twisting, warping, etc. with respect to temperature changes and has excellent heat resistance and dimensional stability. [Prior Art] Conventionally, a flexible printed circuit board (also referred to as a flat cable) generally has a dimensional change in an etching and drying treatment step after patterning. Had to design. The amount of change in this dimension varies depending on the type of pattern of the flexible printed circuit board, which complicates the manufacturing process of the flexible printed circuit board and is a major factor in reducing the product yield. Various attempts have been made to improve this dimensional change. For example, as disclosed in JP-A-60-243120, by reducing the linear expansion coefficient of the insulating material,
We are trying to improve this. However, this JP-A-60-
Although the one disclosed in Japanese Patent No. 243120 has succeeded in lowering the linear expansion coefficient of the insulating material, at the same time, the toughness of the insulating material is lost, and as a result, the insulating material becomes very fragile and flexible. This kind of improvement has not been put to practical use because the flexibility and bending resistance peculiar to the printed circuit board deteriorate. On the other hand, there is also an attempt to realize the above-mentioned low linear expansion coefficient by stretching an insulating material as disclosed in, for example, JP-A-61-296034, but in this case, the same as the former case. The flexibility of the insulating material is impaired, and as a result, there is a defect in towability such as bending resistance, which is an essential condition of the flexible printed circuit board. [Problems to be Solved by the Invention] As described above, the present invention provides the dimensional stability of a conventional flexible printed circuit board that has undergone a large dimensional change in the steps of patterning, etching and drying. Is to improve without sacrificing flexibility. [Means for Solving Problems] That is, according to the present invention, in a flexible printed circuit board including at least a conductor and an insulating material, the linear expansion coefficient of the insulating material is 2.0 × 10 ⁻⁵ / ° C. or less, and The flexible printed circuit board is characterized by having an elongation at break of 30% or more. The flexible printed circuit board according to the present invention has both the conventional good flexibility and the unprecedented dimensional stability. The above-mentioned flexible printed board refers to one in which an insulating layer and a conductor are bonded together via an adhesive agent, and one to which this is subjected to patterning, etching treatment, etc. It is possible to use adhesives used in the manufacture of printed circuit boards. The conductor referred to in the present invention, metal such as copper, iron, aluminum,
Alternatively, it is represented by a metal foil, but other materials may be used. The insulating material, which is an important material used in the present invention, has a linear expansion coefficient of 2.0 × 10 ⁻⁵ / ° C. or less and an elongation at break of 30.
% Or more, it can be used, but synthetic resin, particularly polyimide is preferable. Within the polyimide and [R ₁ and R ₂ are tetravalent aromatic groups, R ₃ is a hydrogen atom, a hydroxyl group, and one or more groups selected from a methyl group and a methoxy group, and n is an integer of 1, 2, or 3. ] The aromatic polyimide copolymer represented by Examples of R ₁ and R ₂ are Examples include one or two or more groups selected from
Among these Is particularly preferred. In general formula (B) Examples of And one or more kinds of groups such as Is particularly effective. The aromatic polyimide copolymer used in the present invention has the same structure as R ₁ , R _{2 in the} general formulas (A) and (B).
Is a tetravalent aromatic group derived from benzene, biphenyl, benzophenone or naphthalene, R ₃ is one or more groups selected from hydrogen atom, chlorine atom, methyl group and methoxy group, and n is 1 or 2 Or an aromatic polyimide copolymer which is an integer of 3, by setting the molar ratio of (A) / (B) of the repeating units represented by the general formulas (A) and (B) to a range greater than 1. The effect of the present invention can be obtained. The insulating material may be compounded with various organic additives, inorganic fillers, or various reinforcing materials. The polyimide insulating material can be obtained from a polyamic acid solution which is a precursor thereof, and a known method can be used as a method for producing the polyamic acid. In the case of an aromatic copolymer, it can be obtained by the following method. (1) Aromatic tetracarboxylic acid dianhydride (a) and an aromatic diamine compound (b) in a small amount relative thereto are reacted in an organic polar solvent to prepare a prepolymer having an acid anhydride group at both ends. Obtain the polymer. Then, the aromatic diamine compound (c) is added and reacted so that the wholly aromatic diamine ((b) + (c)) is substantially equimolar to the aromatic tetracarboxylic dianhydride (a). Method by copolymerization method. (2) Aromatic tetracarboxylic dianhydride (a) is reacted with an excess molar amount of aromatic diamine compound (b) in an organic polar solvent to give a prepolymer having amino groups at both ends. obtain. Then, after the aromatic diamine compound (c) is additionally reacted here, all diamine components ((b) +
A method according to a copolymerization method in which an insufficient amount of aromatic tetracarboxylic acid dianhydride (a) is added and reacted so as to be substantially equimolar to (c)). (3) A mixture of aromatic diamine compounds (b) and (c) is dissolved in an organic polar solvent, and the total amount ((b) +
A method by a copolymerization method in which (c)) is reacted with a substantially equimolar amount of aromatic tetracarboxylic dianhydride (a). (4) to (6) In the method of (1) to (3), an aromatic tetracarboxylic dianhydride is added to the aromatic diamine compound,
A method by a copolymerization method in which an aromatic diamine compound is replaced with an aromatic tetracarboxylic dianhydride. (7) A method for producing by mixing two or more polyamic acid solutions obtained by the methods (1) to (6). And the like, and the method (1) is particularly preferable. Examples of the aromatic tetracarboxylic dianhydride, which is a raw material used to obtain the above polyamic acid solution,
Pyromellitic dianhydride, 3,3 ', 4,4'-biphenyltetracarboxylic acid, 2', 3,3 ', 4-biphenyltetracarboxylic dianhydride, 3,3', 4,4'- Examples thereof include benzophenone tetracarboxylic dianhydride and naphthalene-1,2,5,6-tetracarboxylic dianhydride. These compounds may be used alone or in combination of two or more. As the aromatic diamine component, 4,4'-diaminodiphenyl ether and the general formula An aromatic diamine compound represented by [n and R ₃ are the same as above] is preferably used as the above-mentioned components (b) and (c). As the aromatic diamine compound represented by this general formula, paraphenylenediamine, 3,3'-dimethoxy-4,
4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-
Examples thereof include diaminobiphenyl, 3,3'-dichloro-4,4'-diaminobiphenyl, 4,4 "-diamino-paraterphenyl, and other aromatic diamine compounds such as 4,4. ′ -Bis (4-aminophenoxy) biphenyl, 4,4′-diaminodiphenyl sulfone, 3,3′-diaminodiphenyl sulfone, bis [4
-(4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone,
Bis [4- (2-aminophenoxy) phenyl] sulfone, 1,4-bis (4-aminophenoxy) benzene, 1,3
-Bis (4-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene, 1,4-bis (4-
Aminophenyl) benzene, bis [4- (4-aminophenoxy) phenyl] ether, 4,4'-diaminodiphenylmethane, bis (3-ethyl-4-aminophenyl) methane, bis (3-methyl-4-aminophenyl) )
Methane, bis (3-chloro-4-aminophenyl) methane, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 2,2 ', 5,5'-tetrachloro-4,4' -Diaminobiphenyl, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diaminobiphenyl,
4,4'-diaminooctafluorobiphenyl, 2,4-diaminotoluene, metaphenylenediamine, 2,2'-bis [4- (4-aminophenoxy) phenyl] propane,
2,2-bis [4- (4-aminophenoxy) phenyl]
Hexafluoropropane, 2,2-bis (4-aminophenyl) propane, 2,2'-bis (4-aminophenyl)
Hexafluoropropane, 2,2-bis (3-hydroxy-4-aminophenyl) propane, 2,2-bis (3-hydroxy-4-aminophenyl) hexafluoropropane, 9,9-bis (4-aminophenyl) ) -10-hydro-
Anthracene, orthotolidine sulfone, and more
It is also possible to partially use a polyvalent amine compound such as 3,3 ′, 4,4′-biphenyltetramine and 3,3 ′, 4,4′-tetraaminodiphenyl ether. Here, as the organic polar solvent used in the reaction for producing the polyamic acid solution, for example, dimethyl sulfoxide, sulfoxide-based solvent such as diethyl sulfoxide, N, N-
Formamide solvents such as dimethylformamide and N, N-diethylformamide, acetamide solvents such as N, N-dimethylacetamide and N, N-diethylacetamide, N-methyl-2-pyrrolidone, N-vinyl-2-
Pyrrolidone-based solvents such as pyrrolidone, phenol, o
Examples thereof include phenol solvents such as-, m- or p-cresol, xylenol, halogenated phenol, and catechol, or hexamethylphosformamide, γ-butyrolactan, 1,4-dioxane, tetrahydrofuran, and the like. It is preferable to use them alone or as a mixture, but it is also possible to use aromatic hydrocarbons such as xylene and toluene. Further, it is desirable from the viewpoint of handling that the polyamic acid solution is dissolved in the organic polar solvent in an amount of 5 to 40% by weight, preferably 10 to 30% by weight. Then, as a method for producing an organic insulating film made of polyimide from this polyamic acid solution, a conventionally known method can be used. That is, a method of i) thermally converting into polyimide and ii) chemically converting into polyimide using a dehydrating agent and a catalyst are adopted. Examples of the dehydrating agent here include aliphatic acid anhydrides such as acetic anhydride and aromatic acid anhydrides such as phthalic anhydride. Examples of the catalyst include aliphatic tertiary amines such as triethylamine, aromatic tertiary amines such as N, N-dimethylaniline, and heterocyclic tertiary amines such as pyridine, picoline, isoquinoline, and quinoline. And so on. In this way, it is possible to obtain an insulating material having a linear expansion coefficient of 2.0 × 10 ⁻⁵ / ° C. or less and an elongation at break of 30% or more. The thickness of the insulating material is preferably 7 μm to 125 μm. The flexible printed circuit board of the present invention is obtained by laminating a conductor on the above insulating material. A typical example will be described below, but the method is not limited to this. First, apply an adhesive to the insulating material, and after drying, approx.
It is possible to obtain a flexible substrate by thermally laminating a metal foil of copper or the like of m under pressure and performing a predetermined post cure. Further, a desired circuit can be patterned on the metal surface, and then, after undergoing etching and washing and drying steps, a patterned flexible substrate can be obtained. As the adhesive, an adhesive such as an epoxy / nylon-based adhesive which is usually used for manufacturing a flexible substrate can be used. The dimensional change of the flexible printed circuit board referred to in the present invention means a dimensional change in the process of reaching the flexible printed circuit board after the above patterning. (Examples) Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to only these examples. In the examples, ODA is 4,4'-diaminodiphenyl ether, p-PDA is paraphenylenediamine, PMDA is pyromellitic dianhydride, and BPDA is 3,3 ', 4,4'-biphenyltetracarboxylic acid. The dianhydride and DMAc represent dimethylacetamide. Comparative Example 1 ODA and PMDA were polymerized in DMAc to obtain a 15.0% by weight polyamic acid solution. This polyamic acid solution was cast-coated on a glass plate and dried at about 100 ° C. for about 60 minutes, and then the generated polyamic acid coating film was peeled off from the glass plate and fixed on a support frame. After that, at about 100 ℃ for about 30 minutes, then about 200
After heating at 60 ° C. for about 60 minutes, then at about 300 ° C. for about 60 minutes, dehydration ring closure, drying, and removal from the support frame, a polyimide film insulating material having a thickness of about 20 μm was obtained. The coefficient of linear expansion of this insulating material is 2.5 × 10 ^-5 / ℃, the elongation at tensile rupture is
55%. Next, a nylon / epoxy adhesive was applied to this insulating material and dried, and then a copper foil was heat-laminated under pressure and post-cured to obtain a flexible copper clad board. Subsequently, the flexible copper-clad laminate A on an insulating material, engraved with two points B, the distance A, to measure the length of B, which l ₀
And Further, according to a standard method, patterning is performed on this flexible copper clad plate, followed by etching water washing and drying treatment,
A flexible printed circuit board was obtained. The distance between A and B was measured on this flexible printed circuit board, and this was defined as l ₁ . The dimensional change rate was calculated using the following formula. As a result, the dimensional change rate of this flexible printed circuit board was 0.4%. The folding endurance of the obtained flexible printed circuit board was about 2500 times. Comparative Example 2 p-PDA and BPDA were polymerized in DMAc to obtain a 15.0% by weight polyamic acid solution. Then, the same operation as in Comparative Example 1 was performed to obtain a polyimide film insulating material having a thickness of about 20 μm.
The coefficient of linear expansion of this insulating material was 1.7 × 10 ⁻⁵ / ° C., and the elongation at tensile rupture was 20%. Next, the same operation as in Comparative Example-1 was performed on this insulating material,
As a result of obtaining the dimensional change rate, it was 0.2%. The bending resistance of the obtained flexible printed circuit board was about 400 times. Example 1 ODA and p-PDA were used in DMAc at a molar ratio of 67/33,
This was polymerized with PMDA to obtain a 15% by weight polyamic acid copolymer solution. Then, the same operation as in Comparative Example-1 was performed to obtain about 20
A polyimide film insulating material having a thickness of μm was obtained. The coefficient of linear expansion of this insulating material was 1.5 × 10 ⁻⁵ / ° C., and the elongation at specific rupture was 45%. Next, the same operation as in Comparative Example-1 was performed on this insulating material, and the dimensional change rate was obtained. The result was 0.1%. The folding endurance of the obtained flexible printed circuit board was about 2200 times. Table 1 shows the above results. (Effects of the Invention) A flexible printed circuit board made of an insulating material having a coefficient of linear expansion of 2.0 × 10 ⁻⁵ / ° C. or less and an elongation at tensile break of 30% or more according to the present invention has sufficient flexibility. It also has improved dimensional stability.

   ────────────────────────────────────────────────── ─── Continuation of front page    (56) References JP-A-60-243120 (JP, A)                 JP-A-60-210894 (JP, A)                 JP-A-61-296034 (JP, A)                 JP 57-6757 (JP, A)                 JP-A-56-23791 (JP, A)

Claims (1)

(57) [Claims] In a flexible printed circuit board including at least a conductor, an adhesive layer and an insulating material, the insulating material is as well as [R ₁ and R ₂ are tetravalent aromatic groups derived from benzene, biphenyl, benzophenone and naphthalene, R ₃ is selected from hydrogen atom, chlorine atom, methyl group and methoxy group 1
Or a combination of two or more groups, n is an integer of 1, 2 or 3] in an aromatic polyimide copolymer containing a repeating unit represented by the formula (A) / (B) in a molar ratio of more than 1. A flexible printed circuit board, which is a united body and has a coefficient of linear expansion of 2.0 × 10 ⁻⁵ / ° C. or less and an elongation at break of 30% or more.