JPH04334088A - Manufacture of flexible printed circuit board - Google Patents

Abstract

PURPOSE:Tp improve resistance to heat by a method wherein, on a two-layered flexible board having specified composition, a polyimide insulative coat having the same composition is formed, without using adhesive agent. CONSTITUTION:Polyamic acid solution A obtained by making 3,3', 4,4'-biphenyl tetracarboxylic dianhydride react with paraphenylene diamine and polyamic acid solution B obtained by making pyromellitic dianhydride react with 4,4'- diaminophenyl ether are so mixed that solid matter ratio A/B=55/45-75/25 is obtained. The obtained varnish of polyamic acid is spread on a rolling copper foil and dried, and a polyimide film 1 is formed. Then the copper foil 2 is subjected to circuit working. After vanish is spread on a release film 4 and dried, and a polyamic film 3 is formed, said film 3 is subjected to specified working. After setting on the copper foil 2, heating, pressurizing, and preliminary bonding the release film 4 is peeled. After drying, a flexible printed circuit boad with insulative coat is obtained by baking.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a flexible printed circuit board having a polyimide insulation coating without using an adhesive and having excellent heat resistance.

0002

[Prior Art] Conventional flexible printed circuit board (hereinafter referred to as F
PC) uses a base material in which a base film and a conductor layer are bonded together with an adhesive layer, or a base material in which a polyimide layer is formed directly on the conductor, and the unnecessary portions of the conductor layer are etched away to form multiple conductor circuits. After forming an adhesive layer on an insulating film, use a mold or drill to form windows at the positions necessary for connecting multiple conductor circuits, align the positions and overlap them, and then heat them.・The circuit board is made by applying pressure and laminating and integrating the layers.

However, with this method, which is widely used, the seepage of the adhesive during processing hinders high-density wiring, and the heat resistance of the adhesive layer itself does not directly apply to the base film or conductor. Since it is significantly lower than the formed polyimide layer, it has the disadvantage that the heat resistance as an FPC is determined by the heat resistance of the adhesive layer.

0004

[Problems to be Solved by the Invention] The present invention enables high-density wiring by directly forming a polyimide insulating coating of a similar composition on a two-layer flexible substrate of a specific composition without using an adhesive. The present invention provides a method for manufacturing an FPC with extremely excellent heat resistance.

[0005]

[Means for Solving the Problems] The present invention provides 3, 3', 4
, a polyamic acid solution (A) obtained by reacting 4'-biphenyltetracarboxylic dianhydride and paraphenylenediamine, and a polyamic acid solution (A) obtained by reacting pyromellitic anhydride with 4,4'-diaminodiphenyl ether. and the polyamic acid solution (B) with a solid content molar ratio of A/B=5.
Circuit processing was performed on a two-layer flexible printed circuit board obtained by directly casting and drying a polyamic acid varnish (C) obtained by mixing in a ratio of 5/45 to 75/25 on a conductive foil. After applying, using polyamic acid varnish (C), a semi-cured amic acid film of a predetermined shape created on the release film is aligned and overlapped on the circuit, and after temporary adhesion by heating and pressure, This is a method for manufacturing a flexible printed circuit board with an insulation coating, which is characterized by performing imidization.

[0006] Polyamic acid varnish used in the present invention (
For C), it is most suitable to use the above-mentioned polyamic acid, which has film-forming ability and adhesion to metal foil. That is, polyamic acid solution (A)
and polyamic acid solution (B), the solid content molar ratio is A.
This is a polyamic acid mixed solution obtained by mixing and stirring at a ratio of /B = 55/45 to 75/25. When the ratio of (A) is less than the above-mentioned ratio, curling occurs, and on the other hand, when it is more than the above ratio, it becomes too rigid, loses flexibility, and impairs adhesion to the copper foil. The stirring temperature for synthesizing (A) and (B) and mixing them to obtain (C) is 0 to 10
The temperature is preferably 0°C. This is because if the temperature is below 0°C, the reaction rate will be slow, and if it is above 100°C, the ring-closing reaction and depolymerization reaction of the produced polyamic acid will start. Usually, stirring is performed at around 20°C.

In the present invention, a polyamic acid solution (
When producing A) or the polyamic acid solution (B), a small amount of other tetracarboxylic dianhydride or diamine may be added to the tetracarboxylic dianhydride component or diamine component.

[0008] As the tetracarboxylic dianhydride component,
For example, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-P-tel Phenyltetracarboxylic dianhydride, 2,3,6,7-
Naphthalenetetracarboxylic dianhydride, 4,4'-hexafluoroisopropylidene bis (phthalic anhydride), etc. can be used in combination.

As the diamine component, for example, 4,4'-
Diaminodiphenylmethane, 3,3'-dimethylbenzidine, 4,4'-diamino-P-terphenyl, 4,4
'-Diamino-P-quarterphenyl, 2,8-diaminodiphenylene oxide, etc. can be used in combination.

[0010] The reaction between the tetracarboxylic dianhydride component and the diamine component is carried out at an acid component/amine component (molar ratio) of 0.90.
-1.00 is preferable; if it is lower than 0.90, the degree of polymerization will not increase and the properties of the film after curing will be poor. If it is larger than 1.00, gas will be generated during curing, making it impossible to obtain a smooth film.

The reaction is usually carried out in an organic polar solvent that does not react with the tetracarboxylic dianhydride or diamines. This organic polar solvent is inert to the reaction system,
In addition to being a solvent for the product, it must also be a good solvent for at least one, preferably both, of the reaction components. A typical solvent of this type is N
, N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfone, dimethylsulfoxide, N
-methyl-p-2-pyrrolidone, etc., and these solvents are used alone or in combination. In addition, non-polar solvents such as benzene, dioxane, xylene, toluene, and cyclohexane are also used in combination as solvents, as dispersion media for raw materials, reaction regulators, volatilization regulators from products, film smoothing agents, etc. used.

[0012] The reaction is generally preferably carried out under anhydrous conditions. This is because the tetracarboxylic dianhydride may be ring-opened by water, inactivated, and the reaction may be stopped. Therefore, it is necessary to remove both the moisture in the raw materials and the moisture in the solvent. However, on the other hand, it regulates the progress of the reaction,
Water is sometimes intentionally added to control the degree of resin polymerization. Moreover, it is preferable that the reaction is carried out in an inert gas atmosphere. This is to prevent oxidation of diamines. Dry nitrogen gas is generally used as the inert gas.

In the present invention, a method for obtaining a flexible printed circuit board by casting a polyamic acid solution on a conductive foil is performed using a known coating means such as a rotary coater, knife coater, doctor blade, flow coater, etc. to a thickness of 50 to 1000 μm. A method is used in which the coating is cast to a uniform thickness.

[0014] When removing the solvent from a polyamic acid solution by heating, if strong heating is performed from the beginning before the polyimide film is formed, the surface will become rough or twitch.
It is preferable to gradually increase the heating from a low temperature. For example, it is heated continuously from 100°C to 350°C over 0.5 hours or more. If it is less than 0.5 hours, depending on the film thickness, the solvent removal may be insufficient or the imide ring closure may be insufficient and the properties may not be exhibited. For example, 1
00℃ for 30 minutes, then 150℃ for 30 minutes, 200℃ for 30 minutes, 250℃ for 30 minutes, 300℃ for 30 minutes, 350℃
The temperature may be increased stepwise, such as at ℃ for 30 minutes. Although the heating atmosphere may be in the air in some cases, when a metal foil that is easily oxidized such as a copper foil is used as the metal foil, it is preferable to conduct the heating under reduced pressure or under non-oxidizing conditions while flowing an inert gas. The polyimide coating layer thus formed generally has a thickness of 10 to 200 μm.

In the present invention, the method for forming a semi-cured polyamic acid film on a release film is to release the polyamic acid film onto the release film using a known coating means such as a rotary coater, knife coater, doctor blade, flow coater, etc. It can be obtained by casting the film to a uniform thickness of 1 to 100 μm from the upper end and then heating and drying it. In addition, a semi-cured polyamic acid film is formed on the release film, and then a polyamic acid film formed on another release film of the same composition or a different composition is aligned with the amic acid film surface, and if necessary during this time. It is also possible to obtain a thick polyamic acid film by inserting a predetermined number of amic acid films into the polyamic acid film and heating and pressing two or more of them at the same time.

That is, a polyamic acid solution is applied onto a release film and dried until it becomes tack-free to form a polyamic acid film. Thereafter, the polyamic acid film surfaces are overlapped, and the polyamic acid films are heated and pressed together to produce a polyamic acid film having a thickness that is an integral multiple of the thickness originally applied and dried. At this time, be sure to overlap the polyamic acid surfaces as necessary.
A thicker polyamic acid film can also be obtained by inserting a predetermined number of polyamic acid films from which the release film has been peeled off. It is also possible to peel off the release film on one side after pressure bonding and repeat the same process to obtain an even thicker product.

Appropriate conditions for drying the polyamic acid solution on the release film to form a semi-cured polyamic acid film are 80 to 200°C for 5 to 30 minutes. If the temperature is lower than this and the time is shorter, the fluidity will be greater when hot-pressing the conductor foil, and bleeding at the openings will occur.
The seepage becomes large, the variation in film thickness becomes large, and the dimensional change after imidization becomes large. In addition, if the temperature is higher than this and the time is longer, when heating and crimping the conductor foil,
The fluidity is too low, the peel strength with the conductive foil or flexible printed circuit board is reduced, and voids are often generated.

The coating thickness of one sheet of amic acid is suitably 50 μm or less after imidization. If it is thicker than this, the stress due to shrinkage due to imidization exceeds the supporting force of the release film, causing large curls during drying. Furthermore, since the film layer is thick, the evaporation rate of the solvent is slow, resulting in a significant drop in productivity.

[0019] The conditions for heating and press-bonding the polyamic acid films to the conductor foil are 70~70 in the case of press type.
200℃, 5-100kg/cm2, 5-30 minutes, 70-200℃, 1-50kg for roll laminator
/cm, 0.1 to 10 m/min.
It is desirable to carry out the reaction at a temperature lower than 0 to 30° C. without generating volatile substances.

The imidization rate in the state of the polyamic acid film is preferably 10 to 50%, preferably 20 to 40%.

[0021] To process the polyamic acid film into a predetermined shape, the polyamic acid film with the release film is processed using a conventional method, for example,
After punching, cutting, alkali etching, laser, etc., punch holes and/or process the periphery of the polyamic acid film together with the release film, and after the processing is completed,
After heating and press-bonding the flexible printed circuit board, the release film is peeled off and sufficient imidization is performed.

[0022] Materials that can be used as the conductor layer include metal foils such as copper, aluminum, constantan, and nickel.

[0023]

[Operation] First, as shown in Figure 1, a polyamic acid mixed solution is applied onto the release film (4), dried,
Producing a polyamic acid film with a release film (a
). Next, the parts necessary for surface connection of the plurality of conductor wirings are processed using a mold or drill (b), and then superimposed on the base material consisting of the polyimide film (1) and the plurality of conductor wirings (2) ( c) Temporary adhesion is performed by heating and pressurizing, and after the temporary adhesion is completed, the release film is peeled off. After this, further heating is performed to imidize the polyimide film (1) and the plurality of polyimide films without using an adhesive layer. FP characterized in that (d) a polyimide insulation coating (3) is directly formed on the conductor wiring (2).
This is the manufacturing method of C, and it is possible to easily and inexpensively obtain a flexible printed circuit board with good productivity and yield, which has a polyimide insulation coating without using an adhesive and has excellent heat resistance.

[0024]

【Example】

(Example 1) Purified anhydrous para-phenylenediamine 108 in a four-neck separable flask equipped with a thermometer, stirrer, reflux condenser, and dry nitrogen gas inlet
g, and add anhydrous N-methyl-2-pyrrolidone 9
A mixed solvent of 0% by weight and 10% by weight of toluene was added and dissolved in an amount sufficient to make the solid content ratio in the total raw materials 20% by weight. Dry nitrogen gas was allowed to flow throughout the reaction from the preparatory stage to the product removal. Next, 294 g of purified anhydrous 3,3',4,4'-biphenyltetracarboxylic dianhydride was added little by little while stirring, but since it was an exothermic reaction, cold water at about 15°C was circulated in an external water tank. This was cooled. After addition, increase internal temperature to 20℃
The mixture was stirred for 5 hours to complete the reaction and a polyamic acid solution (referred to as A) was obtained. Next, using the same apparatus and method as above, anhydrous 4,4'-diaminodiphenyl ether 20
0g and purified anhydrous pyromellitic dianhydride 218g
were reacted to obtain polyamic acid (referred to as B). Next, A and B were mixed and stirred so that the molar ratio of solid content was A/B=60/40 to obtain a polyamic acid varnish (C).

[0025] This polyamic acid solution was cast onto a 35μ rolled copper foil so that the film thickness after drying would be 25μ, then placed in a dryer and heated continuously from 100°C to 200°C for 1 hour. After raising the temperature, put it in a dryer for 20 minutes.
The temperature was raised continuously from 0° C. to 380° C. over 1 hour to obtain a flexible printed circuit board having a thickness of 25 μm for the film (1), and further circuit processing was performed on the copper foil (2).

Next, the polyamic acid varnish was applied onto the release film (4) and dried with hot air at 80°C for 30 minutes to form a polyamic acid film (3) (a). After performing the necessary processing (b) on this polyamic acid film, it was set on a flexible printed circuit board that had been subjected to circuit processing, and was pressed in a press heated to 85°C to produce a film of approximately 40 kg/cm2.
Pressure was applied for 15 minutes at a pressure of
A flexible printed circuit board (d) with an insulating coating was produced by raising the temperature and firing stepwise at 300° C. for 15 minutes and 300° C. for 30 minutes.

Regarding the circuit board thus obtained,
The peel strength with the copper foil (based on the part provided for measurement), solder heat resistance, and the amount of seepage at the surface connection of the copper foil were investigated. The peel strength with copper foil was determined by a method based on JIS C 5016, and the solder heat resistance was determined by floating it in a solder bath heated to 300°C for a certain period of time, and determining whether or not the cover film peeled off.
The folding durability was determined by the number of times the copper foil was broken in the MIT folding test 0.8R, and the amount of seepage was determined by the amount of decrease in the diameter of the surface connection hole, which should have a diameter of 5 mm. These results are shown in Table 1.

(Example 2) A polyamic acid varnish prepared in the same manner as in Example 1 was applied onto a release film.
A circuit board was prepared in the same manner as in Example 1, except that it was dried with hot air at 0°C for 10 minutes, and the peel strength with copper foil, solder heat resistance, bending durability, and surface connection of copper foil were evaluated in the same manner as in Example 1. The amount of seepage in the area was investigated. The results are shown in Table 1.

[0029]

[Table 1]

[0030]

Effects of the Invention The FPC manufacturing method according to the present invention, in which a specific polyimide insulating coating is directly formed on a plurality of conductor wirings without using an adhesive, enables high-density wiring. Furthermore, by directly forming a polyimide insulation coating with the same composition as the base film on the base film and multiple conductor wiring without using adhesives, we manufacture FPCs with extremely excellent heat resistance and bending durability. can do.

[Brief explanation of the drawing]

[Figure 1] Cross-sectional view showing an embodiment of the present invention

[Explanation of symbols]

1 Polyimide film 2 Copper foil 3 Polyimide insulation coating 4 Release film

Claims (1)

[Claims] Claim 1: A polyamic acid solution (A) obtained by reacting 3,3',4,4'-biphenyltetracarboxylic dianhydride and paraphenylene diamine, pyromellitic dianhydride, and 4 , 4'-diaminodiphenyl ether and the polyamic acid solution (B) obtained by reacting the polyamic acid solution (B) with a solid content molar ratio of A/B = 55/45 to 75/25.
Polyamic acid varnish (C
) was directly cast on a conductive foil, dried, and imidized to form a two-layer flexible printed circuit board. After circuit processing was performed, a polyamic acid varnish (C) was used to create the circuit board on a release film. A method for producing a flexible printed circuit board with an insulating coating, which comprises aligning and overlapping a semi-cured amic acid film in a predetermined shape on a circuit, temporarily adhering it by heat and pressure, and then imidizing it. .