JPH11298102A - Two-layer flexible printed board and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise the dynamical property, the heat resistance, and the peel strength by constituting a printed board of the two layers of a specified structure of aromatic polyimide layer and a copper foil. SOLUTION: A two-layer flexible printed board, which consists of the two layers of an aromatic polyimide layer being shown by formula 1 (not shown) and having structure units A and B, and a copper layer and in which these two layers are directly in contact, is constituted. Then the mol ratio X/Y between the structure units A and B of the aromatic polyimide shown by formula 1 is in the range of 50/50 to 90/10, preferably, in the range of 70/30-85/15. If this mol ratio X/Y is in this range, all of the peel strength, the rupture strength of the polyimide layer, and the elasticity show favorable values. For the copper layer, it is to be desired that the face in contact with the aromatic polyimide layer should be a rough face, and using, especially, a roughened electrolytic copper foil as the copper layer will let the aromatic polyimide permeate enough to the inner part of the roughened face, and make it present higher peel strength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible printed circuit board comprising only two layers, polyimide and copper, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Polyimides are useful for applications in the electronics field, and are used as insulating films and protective coatings on semiconductor devices. In particular, wholly aromatic polyimides are widely used for flexible printed boards, integrated circuits, and the like because of their excellent heat resistance, mechanical properties, and electrical properties. As a method of manufacturing a flexible printed board, a method of manufacturing by bonding a copper foil and a polyimide film via an adhesive layer, a method of applying a polyimide precursor to a copper foil and converting it to imide, plating or sputtering on a polyimide film For example, there is a method of forming a copper layer by such a method. At present, as the density of integrated circuits increases, it is necessary to reduce the capacity of a flexible printed circuit board, and the flexible printed circuit board is mainly formed of only two layers.

A polyamic acid solution used in the production of a flexible printed board is produced by reacting an aromatic diamine and an aromatic tetracarboxylic dianhydride in a solvent. 109
No. 99, JP-A-62-275165, JP-A-64-5057, JP-B-2-38149,
JP-B-2-38150, JP-A-1-299871
JP-A-58-122920, JP-B-58-122920,
No. 34454, JP-A-58-185624,
Journal of Polymer Science, Macromolecular Reviews
Vol.11 P.199 (1976), U.S. Pat. No. 4,238,528, JP-B-3-4588, JP-B-7-3024
7, JP-A-7-41556, JP-A-7-6
JP-A-2095, JP-A-7-133349, JP-A-7-149896, JP-A-6-207014, JP-B-7-17870, JP-B7-178
No. 71, IBM Technical Disclosure Bulletin Vol.
20 No. 6, P.2041 (1977), etc., which use an aprotic polar solvent, and JP-A-6-1915.
Various solutions have been proposed, such as a solution using a mixed solvent selected from a water-soluble ether compound, a water-soluble alcohol compound, a water-soluble ketone compound and water as described in Japanese Patent Application Laid-Open No. H10-260,036.

[0004] Further, as the polyimide precursor as a solute in the polyimide precursor solution, various polymers other than polyamic acid are known. For example, Macromolecules V
ol.22 P.4477 (1989) and Polyimides and Other High Te
Mperature Polymers. P. 45 (1991) discloses a polyamic acid ester represented by the following general formula.

[0005]

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Also, Macromolecules Vol. 24 P. 3475 (19
91) discloses a trimethylsilyl polyamic acid ester represented by the following general formula.

[0007]

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[0008] Further, Journal of Polymer Science Par
t B Vol.8 P.29 (1970), Journalof Polymer Science
Part B Vol.8 P.559 (1970), Chemical Society of Japan Vol.1972
P.1992, Journal of Polymer Science Polymer Chemis
try Edition Vol.13 P.365 (1975) describes polyamic acid bis (diethylamide) represented by the following formula.

[0009]

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Each of these polyimide precursors is a solution of a polymer having a high degree of polymerization. When obtaining a polyimide coating film from these polymer solutions, generally, this polymer solution is coated on a substrate such as copper or glass, and the solvent is removed and imidation is performed by heating to obtain a polyimide coating film. However, when coating a polymer solution having a high degree of polymerization, there is a problem that the concentration of the solute must be lowered in order to obtain a viscosity of a solution that can be applied due to the degree of polymerization. In addition, when the concentration of the solute is increased in order to increase the productivity, the viscosity of the solution becomes high, so that there is a problem that the coating cannot be performed. Also,
Even if it can be applied, it has a high viscosity, so when manufacturing a two-layer flexible printed circuit board, even if it is applied to the roughened surface of the copper foil that has been subjected to the However, there was a problem that the polyimide precursor did not penetrate into the film and the peel strength was not sufficient.

In a method of forming a two-layer flexible printed board by depositing a metal layer on a surface-roughened polyimide film as disclosed in JP-A-5-259595 and the like, Is difficult to control, there is a possibility that the reliability as an electric circuit may be problematic, and the manufacturing requires many steps and large-scale equipment. In order to overcome these problems, attempts have been made to improve the adhesiveness by introducing a functional group into polyimide as disclosed in Japanese Patent Application Laid-Open No. Hei 4-274382. However, there is a problem that heat resistance and mechanical properties of the polyimide layer are impaired. Furthermore, when a two-layer flexible printed circuit board is manufactured using a polymer solution, the polymer solution is difficult to withstand long-term storage, and it is extremely difficult to store the polymer solution for a long period of time while maintaining its degree of polymerization.

[0012]

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a two-layer flexible printed circuit board having excellent mechanical properties and heat resistance and having a high peel strength, and the efficiency of such a two-layer flexible printed circuit board. It is intended to provide a method of manufacturing well.

[0013]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that a two-layer flexible printed board having a polyimide layer having a specific structure has a high peel strength, Have also been found to be excellent in heat resistance and mechanical properties, and such a two-layer flexible printed circuit board is a solute obtained from a salt obtained from a diamine having a specific structure and a tetracarboxylic acid derivative having a specific structure. The present invention has been found that a high-concentration, low-viscosity polyimide precursor containing as a component is obtained by applying the polyimide precursor on a copper foil and converting it into imide. That is, the gist of the present invention is, first, composed of two layers of an aromatic polyimide layer represented by the following structural formula (1) having the following structural units A and B and a copper layer, and these two layers are: Are in direct contact with each other, and the molar ratio X / Y between the structural units A and B of the aromatic polyimide represented by the following structural formula (1) is 50/50.
To 90/10 in a two-layer flexible printed circuit board.

[0014]

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Second, a diamine represented by the following structural formula (2) and a tetracarboxylic acid derivative represented by the following structural formula (3), and a diamine represented by the following structural formula (2): And the molar ratio (a) / (b) of (b) is 50
/ 50 to 90/10 as a solute, a solute concentration of not less than 20% by weight and a viscosity of not more than 50 poise is applied to a polyimide precursor solution on a copper foil. This is a method for producing a two-layer flexible printed circuit board, characterized by performing imide conversion.

[0016]

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[0017]

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[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
First, terms used in the present invention will be described. (1) Polyimide An organic polymer in which 80 mol% or more of the repeating unit of the polymer chain has an imide structure. And this organic polymer shows heat resistance. (2) Polyimide precursor An organic compound which becomes a polyimide by ring closure, i.e., imide conversion by heating or chemical action. Here, ring closure means that an imide ring structure is formed. (3) Polyimide solution A polyimide solution in which a polyimide precursor is dissolved. Here, the solvent means a compound which is liquid at 25 ° C. (4) Viscosity The rotational viscosity at 20 ° C. was measured using a DVL-BII type digital viscometer (B type viscometer) manufactured by Tokimec Co., Ltd. (5) Solute concentration It is a numerical value expressing the weight ratio of the polyimide precursor in the solution in percentage. (6) Polyimide coating film This refers to a polyimide film formed on a base material such as copper, aluminum, or glass. Among these polyimide coatings, those used in close contact with the substrate are called polyimide coatings, and those used after being peeled off from the substrate are called polyimide films. (7) Peel strength Measured according to JIS C6481 (180 degree peel). (8) Tensile modulus, rupture strength, rupture elongation These values were measured at a tensile speed of 10 mm / min. At room temperature with an Intesco Precision Universal Material Testing Machine manufactured by Intesco Corporation. (9) Heat resistance Shows heat resistance means a high degree of dimensional stability at high temperatures,
Specifically, it has a coefficient of linear thermal expansion of 50 ppm or less up to 250 ° C. and does not show any chemical modification at high temperatures, specifically, heating up to 400 ° C.

Next, the two-layer flexible printed circuit board of the present invention will be described. The two-layer flexible printed board according to the present invention comprises only two layers of an aromatic polyimide layer and a copper layer having the structure represented by the structural formula (1),
The copper layer is in direct contact with the aromatic polyimide layer. (1) The structural unit A of the aromatic polyimide represented by the structural formula
And the molar ratio X / Y between B and B is in the range of 50/50 to 90/10, and preferably in the range of 70/30 to 85/15. When the molar ratio X / Y is within this range,
The peel strength, the breaking strength of the polyimide layer and the breaking elongation show good values. However, if it is smaller than 50/50, the strength as a substrate is insufficient.
Peel strength and elongation at break are not significantly changed as compared with those of 00/0. The surface of the copper layer is preferably a rough surface in contact with the aromatic polyimide layer, particularly when using an electrolytic copper foil subjected to a surface roughening treatment as the copper layer, the inner part of the roughened surface The aromatic polyimide sufficiently penetrates to a higher peel strength. The layer thickness of the copper layer is preferably at least 1 micron, more preferably in the range of 2 to 100 microns.
If the layer thickness is less than 1 micron, various performances when wiring is formed may be reduced. The thickness of the polyimide layer is 1
It is preferably at least 5 microns, more preferably at least 5 microns. If the layer thickness is less than 1 micron, the strength as a substrate may be insufficient.

Next, a method for manufacturing a two-layer flexible printed board according to the present invention will be described. The solution of the polyimide precursor in the present invention is a solution in which a salt comprising a diamine represented by the structural formula (2) and a tetracarboxylic acid derivative represented by the structural formula (3) is dissolved in a solvent as a solute. In the solution of the polyimide precursor of the present invention, any solvent may be used as long as the solvent dissolves a salt composed of the diamine represented by the structural formula (2) and the tetracarboxylic acid derivative represented by the structural formula (3).

Examples of the solvent include aprotic polar solvents such as N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide,
Dimethyl sulfoxide, hexamethylphosphoramide and the like, and ether compounds such as 2-methoxyethanol, 2-ethoxyethanol, 2- (methoxymethoxy) ethoxyethanol, 2-isopropoxyethanol, 2-butoxyethanol, tetrahydro Furfuryl 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, dipropylene glycol monoethyl ether, tripropylene glycol monomethyl ether, polyethylene glycol, polypropylene glycol, tetrahydrofuran, dioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether , A water-soluble alcohol-based compound, methanol,
Ethanol, 1-propanol, 2-propanol, t
tert-butyl alcohol, ethylene glycol, 1,
2-propanediol, 1,3-propanediol,
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, diacetone alcohol and the like can be mentioned, and a mixture of two or more of these can be used. it can.

Among these solvents, particularly preferred examples include N, N dimethylacetamide as the sole solvent,
N-methyl-2-pyrrolidone, as a mixed solvent, N,
Examples include N-dimethylacetamide and N-methyl-2-pyrrolidone, N-methyl-2-pyrrolidone and methanol, and N-methyl-2-pyrrolidone and 2-methoxyethanol.

The concentration of the polyimide precursor in the solution of the polyimide precursor in the present invention is preferably 20% by weight or more. It is more preferably at least 25% by weight, even more preferably at least 30% by weight. Further, the viscosity of the polyimide precursor solution is preferably 50 poise or less, more preferably 35 poise or less, and even more preferably 20 poise or less. The solution of the polyimide precursor in the present invention can be produced by adding a tetracarboxylic acid derivative represented by the structural formula (3) to a diamine solution represented by the structural formula (2).

Here, as a preferred example, a solution of a diamine represented by the structural formula (2) is prepared by reacting a tetracarboxylic dianhydride with a diamine in an aprotic polar compound. A method for producing a solution of a polyimide precursor by adding a tetracarboxylic acid derivative represented by the formula (3) will be described. First, an aromatic tetracarboxylic dianhydride represented by Structural Formula (4) is reacted with an aromatic diamine represented by Structural Formula (5) in an aprotic polar compound, and represented by Structural Formula (2). To produce a solution of the diamine.

[0025]

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[0026]

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The reaction temperature is preferably from -30 to 60 ° C, more preferably from -20 to 40 ° C. In the reaction between the tetracarboxylic dianhydride and the diamine to obtain the diamine represented by the structural formula (2), 0.60 to 0.95 mol of the tetracarboxylic dianhydride is preferably based on 1 mol of the diamine,
More preferably, the amount of the tetracarboxylic dianhydride is 0.75 to 0.90 mol per 1 mol of the diamine. Diamine 1
If the amount of tetracarboxylic dianhydride is less than 0.60 per mole, the strength as a substrate may be insufficient. Next, an aromatic tetracarboxylic acid derivative represented by the structural formula (3) is added to a solution of the diamine represented by the structural formula (2). The addition ratio of the aromatic tetracarboxylic acid derivative represented by the structural formula (3) is preferably 0.95 to 1.05 mol, more preferably 0.97 to 1 mol, per 1 mol of the diamine represented by the structural formula (2). 0.03 mol. The addition ratio of the aromatic tetracarboxylic acid derivative of the structural formula (3) is 0.95 to 1.
If the amount is out of the range, the desired salt tends to be hardly obtained.

In preparing the solution of the diamine represented by the structural formula (2), the order of mixing the monomer and the solvent is not particularly limited and may be any order. When a mixed solvent is used as the solvent, the monomer represented by the structural formula (2) can also be prepared by dissolving or suspending different monomers in each solvent, mixing them, and reacting them under stirring at a predetermined temperature and time. Is obtained. The method of adding the tetracarboxylic acid derivative represented by the structural formula (3) is to add the diamine solution to the diamine solution while stirring, either as a solid or as a solution. Alternatively, when the diamine represented by the structural formula (2) is produced, it may be added simultaneously with the tetracarboxylic dianhydride.

The solution of the polyimide precursor obtained by the above method is applied to a rough surface of a copper foil using a bar coater or the like, dried, and the solvent is removed. A two-layer flexible substrate is obtained by subjecting the body to imide conversion. The preferred thickness of the polyimide precursor solution varies depending on the concentration and viscosity of the solution. Further, the preferable drying temperature after application varies depending on the solvent and the solute concentration. The firing temperature is preferably 250 ° C. or higher, more preferably 300 ° C. or higher, and even more preferably 350 ° C. or higher. If the temperature is lower than 250 ° C., the imide conversion becomes insufficient, and various properties may be deteriorated. Coating, drying,
The operation of the imide conversion may be repeated twice or more, and in that case, a solution of a polyimide precursor having another composition may be used.

[0030]

Next, the present invention will be described specifically with reference to examples. Example 1 4.65 g of 4,4'-oxydianiline, 7.53 g of paraphenylenediamine, 84 g of dimethylacetamide and 36 g of N-methyl-2-pyrrolidone were placed in a three-necked flask and stirred in ice water for 30 minutes. Thereafter, 23.22 g of biphenyltetracarboxylic dianhydride was added, and 40 ° C was added.
The mixture was stirred for 1 hour in a hot water bath. Then, 4.60 g of biphenyltetracarboxylic acid was added, and the mixture was stirred in a water bath at 40 ° C. for 2 hours, and then stirred in a water bath at 60 ° C. for 3 hours to obtain a uniform polyimide precursor solution. The concentration of the obtained solution of the polyimide precursor was 25% by weight. The solution of the above polyimide precursor was applied to the rough side of electrolytic copper foil CF-T9 manufactured by Fukuda Metal Foil & Powder Co., Ltd., and this was heat-treated at 80 ° C. for 60 minutes in a nitrogen atmosphere, and then heated at 380 ° C. for 120 minutes.
Heat treatment for a minute, to imidize the polyimide precursor,
A two-layer flexible printed board was obtained. The obtained two-layer flexible printed board was subjected to an etching treatment using an aqueous solution of iron chloride (■) to remove the copper layer, thereby obtaining a polyimide film. Structural unit A of the obtained polyimide
Table 1 shows the molar ratio X / Y of B and B, the viscosity of the polyimide precursor solution, the peel strength between the copper foil and the polyimide film of the obtained two-layer flexible printed circuit board, the breaking strength and the breaking elongation of the polyimide film. Show.

Comparative Example 1 Except that 10.38 g of 4,4'-oxydianiline, 3.74 g of paraphenylenediamine, 21.60 g of biphenyltetracarboxylic dianhydride and 4.28 g of biphenyltetracarboxylic acid were used. Is the same as in Example 1,
A polyimide precursor solution, a two-layer flexible printed board and a polyimide film were obtained. The concentration of the polyimide precursor solution was 25% by weight. The molar ratio X / Y of the structural units A and B of the obtained polyimide, the viscosity of the solution of the polyimide precursor, the peel strength between the copper foil and the polyimide film of the obtained two-layer flexible printed circuit board, and the breaking strength of the polyimide film Table 1 shows the breaking elongation.

Comparative Example 2 Except for using 10.61 g of paraphenylenediamine, 24.53 g of biphenyltetracarboxylic dianhydride, and 4.86 g of biphenyltetracarboxylic acid without using 4,4'-oxydianiline. In the same manner as in Example, a solution of the polyimide precursor, a two-layer flexible printed board and a polyimide film were obtained. The concentration of the polyimide precursor solution was 25% by weight. The molar ratio X / Y of the structural units A and B of the obtained polyimide, the viscosity of the solution of the polyimide precursor, the peel strength between the copper foil and the polyimide film of the obtained two-layer flexible printed circuit board, and the breaking strength of the polyimide film Table 1 shows the breaking elongation.

[0033]

[Table 1]

As is clear from Table 1, it can be seen that the two-layer flexible printed circuit board of the present invention has particularly excellent peel strength.

[0035]

The two-layer flexible printed circuit board of the present invention has excellent mechanical properties and heat resistance, and has high peel strength. Further, according to the production method of the present invention, since a high-concentration and low-viscosity solution of the polyimide precursor is used, a two-layer flexible printed board having a large peel strength can be efficiently produced.

Claims (4)

[Claims] 1. An aromatic polyimide layer represented by the following structural formula (1) having the following structural units A and B, and a copper layer, and the two layers are in direct contact with each other. Structural units A and B of the aromatic polyimide represented by the structural formula (1)
Wherein the molar ratio X / Y of the two-layer flexible printed circuit board is in the range of 50/50 to 90/10. Embedded image 2. The two-layer flexible printed circuit board according to claim 1, wherein the copper layer is made of electrolytic copper foil. 3. A diamine represented by the following structural formula (2) and a tetracarboxylic acid derivative represented by the following structural formula (3), and the following diamines represented by the following structural formula (2): The molar ratio (a) / (b) with b) is 50/50.
From 90 to 10/10 as a solute, a polyimide precursor solution having a solute concentration of 20% by weight or more and a viscosity of 50 poise or less is applied on a copper foil, and the polyimide precursor is imidized. A method for manufacturing a two-layer flexible printed circuit board. Embedded image Embedded image 4. The method according to claim 1, wherein the solvent of the polyimide precursor solution is N, N-
The method for producing a two-layer flexible printed circuit board according to claim 3, wherein the solvent is dimethylacetamide, N-methyl-2-pyrrolidone or a mixed solvent of both.