JPS61106235A - Substrate for polyimide circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is used for manufacturing flexible printed circuits, etc., which have a structure in which a polyimide insulating layer is formed on the surface of a metal foil with or without a resistor layer. This invention relates to a polyimide circuit board.

(Prior Art) Conventionally, polyimide films, polyester films, and epoxy resin-impregnated glass films have been known as insulating films used in circuit boards of this type.

(Problems to be solved by the invention) Of these, epoxy resin-impregnated glass cloth has relatively good dimensional stability and heat resistance, but has the disadvantage of poor flexibility, and polyester film has poor heat resistance. On the other hand, polyimide film has excellent heat resistance, electrical insulation, chemical resistance, radiation resistance, mechanical strength, etc. In particular, it has excellent solder heat resistance, which is an essential requirement for circuit boards. Since it satisfies both solvent resistance and bending resistance, it is attracting attention as an insulating film λ for circuit boards.

By the way, the above-mentioned polyimide film is obtained by reacting pyromellitic anhydride and aromatic diamine, and does not have adhesive properties by itself, so polyimide films based on polyacrylic acid alkyl ester, rubber-epoxy, and polyester resin are used. However, the heat resistance of these adhesives is inferior to that of polyimide film, and even though polyimide film is used, However, in the circuit board obtained, there was a regret that the excellent heat resistance of the film could not be fully demonstrated. As a result, they discovered that a specific polyimide film exhibits thermal adhesive properties and can be firmly bonded to metal foil, leading to the completion of the present invention.

That is, the present invention relates to a polyimide circuit board characterized in that a polyimide film whose main component is a repeating unit represented by the following general formula is bonded to the surface of a metal foil, with or without a resistor layer. It is something.

The polyimide film used in the present invention is mainly composed of repeating units represented by the above general formula, and contains 3.3', 4.4'-piphenyldetracarboxylic dianhydride (hereinafter referred to as , 5-BPDA) and 2.
It is obtained using 2-bis(4-(4-aminophenoxy)phenyl)propane (hereinafter referred to as BAPP) as the main raw material.

There are two preferred methods for producing the polyimide film used in the present invention: The first method involves reacting S-BPDA and BAPP in approximately equimolar organic polar solvents to produce polyamic acid, etc. A polyimide precursor is used, a polyimide precursor film is formed from a solution of this polyimide precursor, and then this film is heated to imidize it.゛The organic polar solvents include N-methyl-2-pyrrolidone, N-N-dimethylformamide, N-N-dimethylacetamide, dimethyl sulfoxide, tetramethylurea, metacresol, baracresol, metacresol, paracresol, Examples include solvents that can dissolve the polyimide precursor, such as xylenol and phenol. The amount of the organic polar solvent to be used is preferably such that the concentration of both of the above components is usually 5 to 30% by weight.

In this organic polar solvent, the above two components are mixed in approximately equal moles, usually 0 to 0.
The reaction is carried out at 80° C. for 1 to 10 hours to obtain a polyimide precursor solution. The polyimide precursor obtained at this time has a logarithmic viscosity (0.5 g/10 in N-methyl-2-pyrrolidone).
High molecular weights (measured at 30 DEG C. at a concentration of 0 ml) are preferred, usually in the range 1.5 to 6. If this value is too small, the resulting polyimide film will have a low mechanical strength, which is not preferred. Note that this logarithmic viscosity is calculated using the following formula.

Forming a polyimide precursor film from the polyimide precursor solution obtained in this manner can be performed by a known molding method. That is, a method in which a solution of a polyimide precursor is poured directly or diluted onto a smooth flat plate such as a stainless steel plate, a glass plate, an aluminum plate, a copper plate, etc. to form a film, and the solvent is gradually removed from this film by heating. , 6 or an endless stainless steel belt to form a film by pouring this solution and introducing it into a heating furnace.
There are methods to gradually remove the solvent. The film of the polyimide precursor thus obtained is usually 100 to 3
By heating at 50° C. for about 30 to 300 minutes to cause an imidization reaction, a polyimide film having thermal adhesive properties used in the present invention can be obtained. Note that when forming a film from a polyimide precursor solution, the removal of the solvent and the heating for the imidization reaction may be performed continuously, or the second half of the solvent removal and the first half of the imidization reaction may be performed simultaneously. It's okay.

Other methods for producing the polyimide film used in the present invention include:
While the present inventors were studying to obtain a polyimide film having thermal adhesive properties, they learned that polyimide whose main component is a repeating unit represented by the above general formula is soluble in solvents. It is something that

That is, in this manufacturing method, the above-mentioned 5-BPDA and B
Approximately equimolar amounts of APP are reacted in a phenolic solvent to obtain a solvent-soluble polyimide, and a polyimide film is formed from this polyimide solution. A film of good quality can be obtained since no processing steps are required and no voids are generated in the film due to dehydration during the imidization reaction.

The reaction in a phenolic solvent in this production method is
It is a polycondensation reaction consisting of a reaction to produce a polyimide precursor, such as an amidation reaction, and a subsequent imidization reaction, and is usually carried out at a temperature of 80 to 220°C for 1 to 7 hours. When the polyimide precursor is polyamic acid, water is produced as a by-product during the imidization reaction, and this water is removed by distillation out of the reaction system. Removal of water increases the reaction rate and gives good results for the production of high molecular weight polyimide. Phenolic solvents are difficult to miscible with water, making it easy to distill off the by-product water, and it is economical and easy to use during film formation. Polar solvents such as pyrrolidone, which easily volatilize, are unsuitable for this reaction from the above point of view.Phenolic solvents include metacresol, paracresol, xylenol,
Phenol and mixed solvents thereof are used.

It is a preferable method to use an aromatic solvent such as xylene or toluene, which is azeotropic with water, in combination with these phenolic solvents to facilitate distillation of water.The polymerization reaction product obtained in this way is , almost completely imidized and 0.5 g/100 in N-methyl-2-pyrrolidone
The logarithmic viscosity measured at 30°C at a concentration of about 1.
This polyimide has a high molecular weight in the range of 5 to 6.0 This polyimide can be used as it is as a solution in the phenolic solvent used during the polymerization reaction, or if necessary, it can be precipitated in acetone or methanol. After purification by filtering and drying, it can be used by dissolving it in various organic solvents such as cresol and other phenolic solvents, N-methyl-2-pyrrolidone, dimethylacetamide, dimethylformamide, and hexamethylene phosphoramide. can.

The solid content concentration during use is not particularly specified;
It can be selected as appropriate depending on the purpose of use, but it is usually preferably 25% by weight or less. If the solid fraction is too high, the polyimide may become insolubilized or it may become bitter during storage, which is not preferable. Note that this polyimide solution has good storage stability and is normally stored stably for 6 to 12 months.To form a polyimide film from this solvent-soluble polyimide solution, a smooth flat plate such as a glass plate is used. This is carried out by pouring this solution on top to form a film and gradually removing the solvent by heating.

The polyimide film obtained in this manner is mainly composed of repeating units represented by the above general formula, and is different from conventionally used films, such as films obtained by reacting pyromellitic acid and aromatic diamine. Unlike,
Surprisingly, it shows good thermal adhesion.

In the present invention, the metal foil is bonded to the polyimide film with or without a resistor layer. The bonding between the two can be easily carried out because the polyimide film exhibits thermal adhesive properties, and its adhesive strength is great as shown in the following examples.

The heating and pressing conditions when thermally bonding the metal foil and the polyimide film are such that the temperature is above the glass transition point of the polyimide film and below the thermal decomposition temperature, preferably 300 to 400°C, and the pressure is preferably 3 kQ/lx" or above. is 5-50
#/Bacteria! 〇 Figure 1 shows a flexible printed circuit board according to the present invention, which is made of copper, aluminum, etc. and has a thickness of approximately 15 to 7 mm.
A conductive metal foil 1 with a thickness of about 5 to 250 μm is coated on one side of the conductive metal foil 1 of 0 μm.
A μm polyimide film 2 is thermally bonded.

Further, in the present invention, as shown in FIG. 2, nickel, tin, etc.
A resistor layer 3 of about 0.01 to 10 μm thick made of nickel, tin-nickel-sulfur, tin-nickel-steel-sulfur, etc. is provided, and a polyimide film 1 is thermally bonded through this resistor layer 3. You can also.

Such a polyimide circuit board according to the present invention can be produced by, for example, etching a metal foil to form a pattern.
A desired printed circuit can be obtained.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 282 g of N-methyl-2-pyrrolidone and 41 g (0.1 mol) of BAPP are placed in a 11 separable flask and mixed well at room temperature until BAPP is dissolved.

Next, while stirring, 29.49 (0.1 mol) of 5-
BPDA is slowly added into the flask over about 10 minutes. At this time, the flask is cooled with water to suppress the temperature rise. During this time, the viscosity of the solution gradually increased.

Thereafter, stirring was continued for 5 hours at room temperature to obtain a polyimide precursor solution containing polyamic acid as a main component and having a logarithmic viscosity of 1.5.

Next, this solution was poured onto a glass plate to form a film, placed in a hot air dryer, dried at temperatures of 120°C and 180°C for 30 minutes each, and further heated at 250°C for 3 hours to imidize. A polyimide film with a thickness of 50 μm is obtained. The glass transition point and thermal decomposition temperature of this polyimide film were 242°C and 450°C.

Next, this polyimide film was coated with 20 cI each in the vertical and horizontal directions.
Cut to size I, thickness 35 μm 1, length and width 20 each
11 on the electrolytic surface of electrolytic steel foil (manufactured by Fukuda Kinzoku Co., Ltd.) under the conditions of a temperature of 300°C and a pressure of 30#/(x'').
By applying heat and pressure for 0 minutes, the two are thermally bonded,
Polyimide circuit board with the same structure as in Figure 1 (sample number 1)
I got it.

Furthermore, apart from this, except for setting the conditions for thermally bonding the copper foil and polyimide film as shown in Table 1 below, all operations were performed in the same manner as in the case of sample number 1, and sample numbers 2 and 2 were prepared. A circuit board of No. 3 was obtained.

Table 1 shows the results obtained by measuring the adhesive strength between the copper foil and the polyimide film in these circuit boards according to ASTM-D-1876.

Example 2 Metacresol 2269 was placed in 11 separable flasks.
para-cresol 46q1 xylene 10g, 5-BPDA
29.49 (0.1 mol) $- and BAPP 41
g (0.1 mol) is added.

The mixture is heated with stirring and the temperature is increased to 150° C. in 60 minutes. During this heating up, the temperature was 140~1
A dehydration reaction occurs at 45°C, and an azeotropic mixture of water and xylene is distilled out of the system.

The temperature was maintained at 150°C and the reaction was continued for 3 hours with stirring to obtain a dark brown polyimide precursor solution containing polyamic acid as the main component and having a logarithmic viscosity of 1.7.Next, this solution was poured onto a glass plate. A polyimide film with a thickness of 50 μm is obtained by sequentially heating the film at 120° C. and 200° C. for 30 minutes each in a hot air dryer. The glass transition point and thermal decomposition temperature of this polyimide film were 242°C and 450°C.

Next, using this polyimide film, all operations were carried out in the same manner as in the case of sample number 1, except that the heating and pressurizing conditions were set as shown in Table 1, to obtain polyimide circuit boards of sample numbers 4 to 6. Ta.

Table 1 shows the adhesive strength between the copper foil and the polyimide film in these circuit boards.

Example 3 All sample numbers were the same except that aluminum foil with a thickness of 50 μm was used and the pressure was 20 kq/am”.
A polyimide circuit board (sample number 7) was obtained by working in the same manner as in the case of .

Table 1 shows the adhesive strength between the aluminum foil and the polyimide film in this circuit board.

Example 4 A nickel resistor layer with a thickness of 0.5 μm was provided on one side of the copper foil using a metal foil, and a polyimide film was overlaid on this resistor layer. Table 1 shows the adhesive strength between the resistor layer and the polyimide film on the polyimide circuit board (sample number 8) obtained from the polyimide circuit board (sample number 8). Comparative Example Pyromellitic anhydride and 4,4'- A commercially available polyimide film with a thickness of 50 μm obtained by reacting diaminodiphenyl ether and the electrolytic steel foil used in the example were bonded together using an acrylic adhesive at a temperature of 170” C1 pressure IQ & g/cm.
The circuit board (sample number 9) was obtained by bonding by heating for 30 minutes.

Table 1 shows the adhesive strength between the copper foil and the polyimide film in this circuit board.

Table 1 (Effects of the Invention) In the present invention, the polyimide film and the copper foil are thermally bonded with or without a resistor layer, and unlike conventional products, an adhesive is not used. Furthermore, as can be seen from the examples, the polyimide film and the copper foil or the resistor layer have a high bonding strength due to thermal adhesion.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are both side views showing an example of a flexible printed circuit board according to the present invention. 1...Metal foil 2...Polyimide film 3...
・Resistor layer

Claims (1)

[Claims] A polyimide film whose main component is a repeating unit represented by the following general formula ▲Mathematical formula, chemical formula, table, etc.▼ is bonded to the surface of a metal foil with or without a resistor layer. A polyimide circuit board characterized by: