JPH0561792B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for manufacturing a flexible printed circuit board having a two-layer structure without an adhesive layer and having strong adhesion between a metal conductive layer and a plastic film substrate. Conventional technology Demand for flexible printed circuit boards has been increasing in the electronics field in recent years, especially for TABs and liquid crystals that require high-density wiring that is thinner and more flexible than conventional circuit boards and has a line width of 100 μm or less. A usable "two-layer structure without an adhesive layer" is attracting attention. Methods for creating this two-layer structure can be broadly divided into ``coating a copper foil with polyimide varnish'' and ``forming a thin copper film on a polyimide film.'' Problem to be solved by the invention The former is “applying polyimide varnish to copper foil”
With this method, the practical application of thin products has been delayed for the following reasons. (1) Among rolled copper foils with excellent flexibility, thin ones of 10 μm or less are expensive, and moreover, they tend to wrinkle when applied with imide varnish. (2) Since polyimide varnish is modified for the purpose of improving adhesion, linear expansion coefficient, etc., the original properties of polyimide deteriorate. The latter method of ``forming a thin copper film on polyimide film'' includes a wet method and a dry method.The wet method involves electroless plating on a plastic film substrate and then electroplating using its conductivity. Although it is easy to form a thin conductive layer with a thickness of 10 μm or less, the adhesion between the conductive layer and the plastic film substrate is poor and has not been put to practical use. On the other hand, in some dry methods, conductive layers are formed by sputtering or sputtering + electrolytic plating, but since the sputtering film formation speed is very slow at around 0.001 μm/sec, the production cost is high and it is not suitable for consumer use. It was not something that could be used for any purpose. It is also possible to use vacuum evaporation, which has a faster film formation rate, instead of sputtering, but vacuum evaporation alone can only produce a film with a thickness of 3 μm.
It is not possible to obtain a film thicker than this, and if an attempt was made to make up for the lack of film thickness by wet-processing electrolytic plating, the adhesion between the vacuum-deposited film and the plastic film substrate would decrease, making it unusable. In view of the above-mentioned problems, the present invention has developed two
To provide a method for manufacturing a flexible printed circuit board which has a layered structure and has strong adhesion between a conductive layer and a plastic film substrate. Means for Solving the Problems In order to solve the above problems, the present invention uses a vacuum evaporation method to form a first conductive layer on a plastic film substrate at a deposition rate of 0.01 to 1.0 μm/sec, and then:
It is characterized in that a second conductive layer is formed on the conductive layer by electrolytic plating. Effect The present inventor has conducted intensive studies to improve the adhesion between a plastic film substrate and a thin metal film, and has found that the temperature of the substrate during vacuum evaporation, the structure and thickness of the thin metal film that forms the interface with the substrate can be improved by wet treatment. It was found that this affects the subsequent adhesion. Specifically, by blocking high-incidence components with an incident angle of 30° or more in the early stages of vapor deposition, the low-incidence components with a large amount of evaporation hit the substrate first, and their large amount of latent heat and radiant heat from the evaporation source The substrate temperature is higher, and the metal thin film forming the interface with the substrate has a denser structure. In the present invention, the film formation rate of the vacuum evaporation method for forming the first conductive layer is preferably within the range of 0.01 to 1.0 μm/sec, and if it is less than 0.01 μm/sec, the productivity is low and the cost of sputtering is low. On the other hand, at a high deposition rate exceeding 1.0 μm/sec, a deposited film with many defects may be formed, and the plastic film substrate may undergo thermal deterioration due to enormous latent heat or radiant heat from the evaporation source. As a result, the adhesion of the deposited film decreases. Further, in the present invention, the thickness of the vacuum-deposited film as the first conductive layer is preferably within the range of 0.2 to 1.0 μm,
If the thickness is less than 0.2 μm, it is difficult to form the second conductive layer efficiently using the electrolytic plating method, while if the thickness exceeds 1.0 μm, internal residual stress in the deposited film may increase when using the vacuum deposition method, which has a high film formation rate. The adhesion of the deposited film decreases as the plastic film substrate is thermally degraded due to the enormous amount of latent heat and radiant heat from the evaporation source. The type of plastic film used in the present invention is not particularly limited, but one with high heat resistance such as polyimide or a copolymer thereof is preferred. This is because a low-incidence component with a large amount of evaporation hits the substrate in the early stage of evaporation, and the surface temperature of the substrate increases due to a large amount of latent heat and radiant heat from the evaporation source.
such as polyethylene terephthalate (PET),
Plastic films that do not have very high heat resistance may undergo thermal deterioration or precipitate oligomers, reducing the adhesion of the deposited film. In addition, when forming the first conductive layer on a plastic film substrate by vacuum evaporation, if the plastic film substrate is heated in advance to degas it with a heater or the like, or the surface is treated with plasma treatment, etc.
The adhesion of the deposited film can be further improved. In addition, in the present invention, there are two methods for forming the second conductive layer by electrolytic plating: a method of plating the entire surface to increase the film thickness, and a method of plating only the portion used as a circuit (semi-additive method). However, the present invention is not limited to these. However, it is the latter case that makes the invention more effective. Embodiment An embodiment of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a schematic diagram of a winding type vacuum evaporation apparatus in an embodiment of the present invention. In the figure, 1 is an unwinding roll, 2 is a plastic film, 3 is a can roll, 4 is a take-up roll, 5 is a shielding plate, 6 is an evaporation source, 7 is a vacuum pump, and 8 is an evaporation source heating device. A plastic film 2 fed out from an unwinding roll 1 moves along a central can roll 3 and is wound onto a winding roll 4. During this process, an evaporation source 6 is placed on the surface of the plastic film 2.
A thin metal film is formed by the vapor flow that is not blocked by the blocking plate 5. Although the shielding plate 5 may be placed on the take-up roll 4 side to limit the incident angle in the latter stage of vapor deposition, this only reduces the adhesion efficiency of vapor deposition and does not provide the effect of the present invention. Line perpendicular to plastic film 2 and evaporation source 6
The angle formed by the vapor flow from
The angle of incidence was adjusted by moving left and right on Figure 1. In order to obtain a high film formation rate, a crucible was used as the evaporation source 6, and an electron beam device was used as the evaporation source heating device 8. Example 1 A polyimide film (manufactured by Ube Industries, Ltd., trade name: Upilex 25S) with a thickness of 25 μm was set as the plastic film 2 in the apparatus shown in FIG. =
Install it so that the angle is 30°, vacuum degree: 1×
Copper was vacuum deposited under the conditions of 10 ^-4 Torr, electron beam power: 52KW, film speed: 20m/min, and the thickness was 0.8μm.
A thick copper thin film was formed. The film formation rate at this time was 0.4μ
m/sec. Example 2 The film speed was exactly the same as Example 1 except that the film speed was changed to 80, 40, and 16 m/min, respectively.
Copper thin films with a thickness of 0.4 and 1.0 μm were formed. Example 3 A copper thin film was formed in the same manner as in Example 1, except that the blocking plate was installed so that the maximum incident angle at the initial stage of vapor deposition was 0°, and the electron beam output was increased to 58 KW. At this time, the film thickness was 0.5 μm and the film forming rate was 0.3 μm/sec. Comparative example 1 The evaporation source was brought close to the plastic film substrate,
A shield plate was installed so that the maximum incident angle at the initial stage of evaporation was 30°, and copper was vacuum evaporated under conditions of vacuum degree: 1 × 10 ^-4 Torr, electron beam output: 80 KW, and film speed: 60 m/min. A copper thin film was formed in the same manner as in Example 1. At this time, the film thickness was 0.8 μm, and the deposition rate was 1.2 μm/
It was hot in seconds. Comparative Example 2 Example 1 except that the film speed was 13 m/min.
A copper thin film was formed in the same manner as above. At this time, the film thickness is 1.2μ
m, and the film-forming speed was 0.4 μm/sec. Comparative Example 3 A copper thin film was formed in the same manner as in Example 1, except that the blocking plate was installed so that the maximum incident angle at the initial stage of vapor deposition was 60°, and the electron beam output was weakened to 42 KW. At this time, the film thickness was 0.7 μm and the film formation rate was 0.3 μm/sec. Comparative Example 4 A copper thin film was formed in the same manner as in Example 1, except that the blocking plate was removed and the electron beam output was weakened to 40 KW. At this time, the film thickness was 0.8 μm and the film forming rate was 0.3 μm/sec. Comparative Example 5 A 0.8 μm thick copper thin film was formed in the same manner as in Example 1 except that a PET film was used instead of the polyimide film. The copper vapor-deposited films obtained in the Examples and Comparative Examples were subjected to a boiling test, copper electrolytic plating, and peel strength measurement after plating, and the results are shown in Table 1. In addition, the peel strength after plating and the deposited film thickness,
The relationship with the deposition incident angle is shown in FIGS. 2 and 3, respectively. The boiling test is a test in which copper-deposited film is placed in boiling water.
Boil for 30 minutes and check for peeling of the deposited film, and if it has not peeled off, let it air dry at room temperature for 16 to 24 hours, then perform a tape peeling test (Nippon Denko adhesive tape No.
315) was used to examine the peeling of the deposited film. Copper electrolytic plating used a copper sulfate bath. The peel strength measurement was performed in accordance with the JPCA standard (JPCA-FCO ₁ ) after performing copper electrolytic plating on the copper vapor deposited film to make the total copper thickness 35 μm.

【table】

[Table] As is clear from Table 1, FIG. 2, and FIG. By setting the film thickness to 0.2 to 1.0 μm and blocking high-incidence components with an incident angle of 30° or more in the early stage of vapor deposition, strong adhesion is maintained even when wet electrolytic plating is performed on the vapor-deposited film. be able to.
In addition, this example using polyimide film
Stronger adhesion can be obtained compared to Comparative Example 5 using PET film. In addition, in each example, the copper for forming the copper vapor deposition film may be a copper alloy. Effects of the Invention As described above, the present invention makes it possible to form a metal thin film that can withstand wet electrolytic plating using a highly productive vacuum evaporation method.
A flexible printed circuit board having a layered structure and strong adhesion between a conductive layer and a plastic film substrate can be provided at low cost.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of a winding type vacuum evaporation apparatus in an embodiment of the present invention, Fig. 2 is a correlation diagram between peel strength after plating and deposited film thickness, and Fig. 3 is a correlation diagram between peel strength after plating and deposited film thickness. It is a correlation diagram with the vapor deposition incident angle. DESCRIPTION OF SYMBOLS 1... Unwinding roll, 2... Plastic film, 3... Can roll, 4... Winding roll, 5... Shield plate, 6... Evaporation source, 7... Vacuum pump, 8... Evaporation source heating device .

Claims (1)

[Claims] 1. A film formation rate on a plastic film substrate is
A flexible printed circuit board characterized in that a first conductive layer is formed by a vacuum deposition method at a rate of 0.01 to 1.0 μm/sec, and then a second conductive layer is formed on the conductive layer by an electrolytic plating method. Production method. 2. The method for manufacturing a flexible printed circuit board according to claim 1, wherein the first conductive layer has a thickness of 0.2 to 1.0 μm. 3 When forming the first conductive layer by vacuum evaporation, the angle of incidence of the metal vapor flow on the side where the direction of the metal vapor flow from the evaporation source and the direction of movement of the plastic film are opposite to each other is 30° or more. 2. The method of manufacturing a flexible printed circuit board according to claim 1, further comprising blocking an incident component.