JPH0567876A - Manufacture of flexible multilayer printed circuit wiring board - Google Patents

Abstract

PURPOSE:To contrive the efficient production of a flexible multilayer printed circuit wiring board, small in the positional deviation of a base material film at the time of lamination and a dimensional change in the base material film and superior in peel strength, soldering temperature resistance and electrolytic corrosion resistance. CONSTITUTION:A flexible multilayer printed circuit wiring board has a printed circuit wiring board consisting of a base material film 2 with conductive metal layer adhered on both surfaces of the film 2 and 5 subjected to circuit processing, as a circuit for at least one layer or more of an internal layer and a base material film 2 to be adhered with a conductive metal layer 3 on one surface is superposed on the outermost layer of this printed circuit wiring board via a bonding agent layer 1, which is hardened with a radiation, in such a way that the layer 3 is located upward. After that, the high-energy radiation is emitted over the outermost layer to harden the layer 1.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method of manufacturing a flexible multilayer printed circuit wiring board.

[0002]

2. Description of the Related Art A flexible multilayer printed circuit wiring board will be described by taking a conventional four-layer flexible printed circuit wiring board as an example. In this case, a single-sided circuit processed product of double-sided MCF is multilayered through an adhesive layer. "Laminate method" or "core method" in which double-sided circuit processed products of double-sided MCF are sandwiched between and MCF composed of copper foil on one side and adhesive on the other side is laminated from both sides, and then heating / heating is performed. It has been obtained by pressing to cure the adhesive layer.

[0003]

In recent years, there has been an increasing demand for multilayered flexible printed circuit wiring boards.
However, the conventional manufacturing method requires a heating / pressurizing process, which causes dimensional changes due to misalignment between multilayered wiring boards, thermal expansion and heat shrinkage of the base film, etc. Flexible multi-layer printed circuit wiring boards that require high dimensional accuracy have been a major obstacle to multi-layering. Further, in the usual heat curing process, it takes a long time to cure, and thus the production efficiency is poor. The present invention has been made in view of the above points, and a flexible multilayer excellent in basic characteristics such as peeling strength, solder heat resistance, and electrolytic corrosion resistance, in which misalignment and dimensional change of the base material film during multilayer wiring are small. It is intended to provide a method for efficiently producing a printed circuit wiring board.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above problems by curing the adhesive layer with high energy radiation instead of the conventional thermosetting reaction. That is, the present invention has a printed circuit wiring board circuit-processed conductive metal layers that adhere to both sides of the base film as at least one inner layer circuit, via an adhesive layer that is cured by radiation, After overlaying the outermost layer with a base film on which the conductive metal layer is bonded on one side so that the conductive metal layer is on top, irradiating higher energy radiation than the outermost layer to cure the adhesive layer And a method for manufacturing a flexible multilayer printed circuit wiring board.

Next, as the substrate film used in the present invention, a plastic film such as a heat-resistant polyimide film, a polyamide film or a polyester film is preferably used. Among them, the polyimide film is particularly excellent, but its thickness is preferably 12.5 to 125 μm in view of bending resistance, strength, electron beam transparency, and the like.
25 to 50 μm is more suitable. If necessary, the surface may be sandblasted.

Next, as the conductive metal foil used in the present invention, copper foil, silver, gold, aluminum foil and the like can be mentioned. Copper foil is superior in terms of electrical conductivity, price, etc.
When used for flexible printed circuit wiring boards, its thickness is
It is preferably 50 μm or less, more preferably 10 to 40 μm. Further, a rolled copper foil is more preferable than an electrolytic copper foil because the material is desired to have bending resistance, and its surface may be plated with nickel or the like in order to improve the wettability of the adhesive.

Next, the adhesive layer used in the present invention will be described in detail. The term “adhesive layer” as used in the present invention refers to the above-mentioned base film coated with an adhesive on one side or both sides. The adhesive is a block copolymer elastomer having an unsaturated double bond in the molecule, which contains a rubber diene component such as polybutadiene or polyisoprene in the molecule, and polystyrene or polystyrene derivative is block copolymerized at both ends or one end thereof. Is a polymer. Specific examples of these polymers include poly- (styrene-butadiene), poly- (styrene-isoprene), poly- (styrene-butadiene-styrene), poly- (styrene-isoprene-styrene) and the like. These may be used alone or in a blend. In order for these polymers to be sufficiently cured by electron beams and to have heat resistance, the rubber component of butadiene or isoprene is 60 wt%
The above is preferable. Further, in order to maintain sufficient adhesive strength in the adhesive, its molecular weight is preferably 50,000 or more, but when the value exceeds 500,000, dispersibility in an organic solvent is deteriorated, which is not preferable.

When used as an adhesive, the polymer diluting solvent can be selected from MEK, toluene, ethyl acetate, benzene, THF, carbon tetrachloride, hexane and the like, which have excellent compatibility and dispersibility. The drying temperature of the solvent, which has a great influence on the dimensional stability, is determined by the boiling point of the solvent used and the temperature dependence of the heat shrinkage, but it is usually 200 ° C or lower, and more preferably 150 ° C or lower. Further, the adhesive used in the present invention may contain a polymerization inhibitor such as hydroquinone or benzoquinone or an antioxidant in order to maintain the stability of the unsaturated double bond.

On the other hand, there are electron beams, ultraviolet rays, X-rays, γ-rays, etc. as radiation irradiation radiation sources.
The electron beam is most preferable from the viewpoint of safety. The energy level is 500 because the electron beam needs to penetrate the copper foil.
KeV or higher is indispensable, but 1M with high penetrating power
A high energy type of eV or higher is more preferable.

The radiation dose for curing the adhesive of the present invention can be used usually in the range of 0.5 to 100 Mrad, but 1.0 to 50 Mrad is more preferable. If the dose is less than 0.5 Mrad, sufficient crosslinking may not be obtained, and if it exceeds 100 Mrad, the polymer starts to decompose. At the time of electron beam irradiation, what needs attention is deactivation of active radicals by oxygen. In order to avoid this, it is preferable that the adhesive is degassed in vacuum in advance, then the base film is coated with the solvent and the solvent is dried, and then the copper foil is immediately laminated so as not to entrap air bubbles. At this time, heat aging may be performed after the lamination depending on the case.

[0011]

The reason why the effect of the present invention is exhibited is not always clear, but the reason why the adhesive on the opposite surface of the copper foil is cured from above the copper foil, which is one of the features of this method, is explained in FIG. To be done.

That is, a high-voltage type electron beam of 1.0 MeV or more has a maximum penetrating power of 4.0 mm in a substance having a specific gravity of 1 and has a specific gravity of about 8.9 and penetrates a 35 μm-thick copper foil. To do. Therefore, it is possible to cure the adhesive on the back surface of the copper foil, which eliminates the need for the adhesive curing process by heating and pressurizing the multilayered product, thus improving the production efficiency. Further, it is clear that the product of the present invention has a small displacement because there is no high temperature heating / pressurizing process, and the reason why the dimensional change rate is smaller is devised as follows. That is, the conventional thermosetting adhesive has an internal strain due to the heat history of heating to the curing temperature and then cooling to room temperature, and the strain is released during the copper foil etching step to cause a dimensional change. Therefore, in the present invention using the electron beam reaction, it is considered that the dimensional change is small because the adhesive can be cured without undergoing a high temperature heat history. Further, the degree of polymerization shrinkage of the adhesive which causes warpage and twist of the substrate depends on the number of reaction points, but when a rubber prepolymer having a low Tg is used as a starting material like the adhesive of the present invention, It is presumed that there are few reaction points, and that the internal strain-induced relaxation mechanism of the flow works, and that / twist is suppressed. Further, the mechanism that causes electrolytic corrosion is devised as follows. In the case of a highly polar polymer such as the conventional NBR, it is inevitable that a trace amount of ionic impurities are mixed into the polymer during its synthesis. When a voltage is applied to the circuits by using these impurities as a medium, electrolysis occurs between the insulated copper and a short circuit occurs between the circuits. However, in the case of the polymer as described in claim 5, it is considered that such a phenomenon does not occur because there is no such ionic impurity.

[0013]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Example 1 (1) How to make a film with a double-sided adhesive Poly- (styrene-butadiene-styrene) block copolymer (manufactured by Shell Chemical Co., trade name TR-1150,
A butadiene component (62 wt%, weight average molecular weight: 120,000) was dissolved in toluene to form a 15 wt% solution, and handloquinone monomethyl ether was added to the polymer weight of 1,000 pp.
Added to be m. A polyimide film (Toray DuPont Co., Ltd., trade name Kapton 100H,
Both sides are sandblasted, thickness 25μm) and coated on both sides of the film so that the solid content thickness is 40μm.
The solvent was dried in a drying oven at 00 ° C for 10 minutes. (2) Preparation of double-sided MCF Rolled copper foil (Nikko Gould Co., Ltd., double-sided nickel treatment, thickness 35 μm) is defoamed on the double-sided adhesive film obtained in (1), but be careful not to mix air bubbles. Then, it was laminated on both sides of a polyimide film with an adhesive to obtain an MCF with double-sided copper foil. This double-sided MCF was irradiated with 15 Mrad of a high energy electron beam from above the copper foil. (Acceleration voltage 1.
0 MeV, current 5.0 mA). (3) How to make single-sided FPC (copper foil on the other side) A resist is attached to one side of the double-sided MCF obtained in (2), and pattern printing, development, etching and resist stripping are sequentially performed on only one side to form a circuit. did. The other surface was entirely etched. (4) Method of making double-sided FPC Resists were attached to both sides of the MCF obtained in (2), and pattern baking, development, etching, and resist stripping were sequentially performed on both sides to form a circuit on both sides. (5) How to make a 4-layer FPC With the adhesive film obtained in (1) on both sides of the double-sided FPC obtained in (4), the circuit surface of the single-sided FPC obtained in (3) should be on the outside. I put them together. This is 120 ℃, 10
After heating and pressurizing at kg / cm ² for 10 minutes, a high energy electron beam was irradiated from the outermost layer of 15 Mrad as in (2). Finally, in the same manner as in (3), a resist was attached to the copper foil on both sides of the outermost layer, and the steps of pattern baking, development, etching and resist stripping were performed to obtain a 4-layer FPC. (See FIG. 1) Each test of (1) misalignment (2) dimensional change rate (3) peel strength (4) solder heat resistance (5) electrolytic corrosion resistance was performed on this four-layer FPC. The results are shown in Table 1.

Example 2 70% by weight of poly- (styrene-butadiene-styrene) used in Example 1 instead of 62% by weight of the butadiene component (manufactured by Shell Chemical Co., trade name TR-1101, weight average molecular weight) 110,000) as an adhesive,
A four-layer FPC was obtained in the same manner as above, and the same test was performed.

Example 3 Instead of the poly- (styrene-butadiene-styrene) polymer used in Example 1, a poly- (styrene-isoprene-styrene) polymer (manufactured by Nippon Zeon Co., Ltd., trade name SIS-5000, weight) was used. A four-layer FPC was obtained in the same manner as in Example 1 using an average molecular weight of 100,000) as an adhesive, and the same test was performed.

Example 4 The poly- (styrene-butadiene-styrene) polymer used in Example 1 was replaced by 53.5 wt% of butadiene component.
% Poly- (styrene-butadiene) polymer (manufactured by Nippon Zeon Co., Ltd., trade name Nipol, NS-220, weight average molecular weight about 100,000) was used as an adhesive, and Example 1 was used.
A four-layer FPC was obtained in the same manner as above, and the same test was performed.

Comparative Example 1 In place of the high energy electron beam irradiation apparatus used in Example 1, a low energy electron beam irradiation apparatus having an accelerating voltage of 200 keV was used in the same manner as in Example 1 to obtain a four-layer FPC. A similar test was conducted.

Comparative Example 2 Instead of the poly- (styrene-butadiene-styrene) polymer used in Example 1, poly-acrylonitrile-
Butadiene (trade name Nipol, N manufactured by Nippon Zeon Co., Ltd.)
-1032) / phenol (trade name H-2400 manufactured by Hitachi Chemical Co., Ltd.) / Epoxy (brand name BREN-S manufactured by Nippon Kayaku Co., Ltd.) curing agent (trade name BF ₃ manufactured by Hashimoto Kasei Co., Ltd.)
-MEA) / filler (Higelite 42M, trade name, manufactured by Showa Denko KK) was blended at a weight ratio of 50/30/20/5/70 and used as an adhesive. The adhesive is cured at 170 ° C and 30 kg / cm ² instead of 60 times at 60
Heat and pressure were used for minutes.

Comparative Example 3 Instead of the polymer used in Example 1, 15 wt% of poly- (acrylonitrile-butadiene) polymer (manufactured by Nippon Zeon Co., Ltd., trade name Nipol, DN-401) was used.
% MEK solution, a four-layer FPC was obtained in the same manner as in Example 1, and the same test was performed.

The tests in the above Examples and Comparative Examples were conducted as follows. (1) Positional deviation In the circuit pattern for four layers in which about 70% of the copper foil was removed by etching, the positional deviation between the outermost layer circuit and the inner layer circuit was visually observed. (2) Dimensional change rate All the copper of the polyimide film with a copper foil was removed by etching, and the dimensional change of the polyimide film before and after etching was measured by a three-dimensional dimension measuring device. (3) Peel Strength The polyimide film with copper foil was stored in a constant temperature and humidity chamber at 40 ° C. and 90% RH for 96 hours, and immediately after that, the peeling strength of the copper foil was measured. Peeling angle 180 °, peeling speed 50 mm / min
.. (4) Soldering Heat Resistance The polyimide film with copper foil was treated for 96 hours in a thermo-hygrostat at 40 ° C. and 90% RH, and immediately after that, it was immersed in a solder bath for 1 minute and observed for any abnormality. The value indicates the maximum temperature at which no abnormality occurs. (5) Electrolytic corrosion resistance A circuit with a line width of 0.2 mm and a line interval of 0.2 mm was made on the samples prepared in each of the examples, and this was subjected to 85 ° C./85% R
A voltage of 100 V was applied in H, the presence or absence of a short circuit in the circuit was observed by a leakage current, and the time required for occurrence of abnormality was noted.

[0022]

[Table 1]

[0023]

As is clear from the examples, the manufacturing method according to the present invention has a simple manufacturing process, so that the production efficiency of a wiring board, which was conventionally complicated, is improved. Furthermore, the multilayered wiring obtained by this manufacturing method has a small positional deviation and a small dimensional change rate, and has excellent basic characteristics such as peel strength, solder heat resistance, and electrolytic corrosion resistance.

[Brief description of drawings]

FIG. 1 is a sectional view for explaining a process of an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of the present invention, which is a graph showing the penetrating ability of high-energy electron beams,
Up to an energy level of 1000 KV, (b) is 1.
It shows a penetrating ability of an electron beam of 5 MV or more.

[Explanation of symbols]

 1 Adhesive 2 Base film 3 Metal foil 4 Circuit

Claims (7)

[Claims] 1. A printed circuit wiring board having a circuit-processed conductive metal layer that adheres to both sides of a base film, has at least one or more layers as a circuit for an inner layer, and an adhesive layer that is cured by radiation is provided on the printed circuit wiring board. The outermost layer, a conductive metal layer is adhered to one side of the base film, the conductive metal layer is placed on top, then the outermost layer is irradiated with high-energy radiation to cure the adhesive layer. And a method for manufacturing a flexible multilayer printed circuit wiring board. 2. The method for producing a flexible multilayer printed circuit wiring board according to claim 1, wherein the base film is a polyimide film or a polyester film. 3. The method for manufacturing a flexible multilayer printed circuit wiring board according to claim 1, wherein the conductive metal layer is a copper foil. 4. The method for producing a flexible multilayer printed circuit wiring board according to claim 1, wherein the adhesive layer is composed of a base film and a block copolymer elastomer having an unsaturated double bond in the molecule. 5. The block copolymer elastomer having an unsaturated double bond in the molecule is poly- (styrene-butadiene-styrene) or poly- (styrene-isoprene-styrene), or poly- (styrene-butadiene), The method for producing a flexible multilayer printed circuit wiring board according to claim 4, wherein the content of the rubber component such as butadiene or isoprene is 60 to 90% by weight. 6. The block copolymer elastomer having an unsaturated double bond in the molecule has a weight average molecular weight of 50,000.
1 or 4 or 5 within the range of 500,000 to 500,000.
A method for manufacturing the flexible multilayer printed circuit wiring board described. 7. The method for manufacturing a flexible multilayer printed circuit wiring board according to claim 1, wherein the radiation source of high-energy radiation is an electron beam.