KR102670785B1 - Flexible substrate and manufacturing method thereof - Google Patents

Abstract

[Problem] To provide a flexible substrate capable of suppressing a decrease in heat-resistant peel strength and suppressing the overall manufacturing cost of the flexible substrate.
[Solution] The flexible substrate 10 includes a polyimide film 11, a base metal layer 12 formed on the surface of the polyimide film 11, and copper formed by overlapping the base metal layer 12. It is comprised including a conductor layer (13). The base metal layer 12 contains a chromium-containing alloy layer 14. And this chromium-containing alloy layer 14 has a first metal layer 14a in contact with the polyimide film 11 and a second metal layer 14b positioned to overlap the first metal layer 14a, and the first metal layer 14 The weight percent of chromium in (14a) is greater than the weight percent of chromium in the second metal layer (14b). With this configuration, diffusion of copper into the first metal layer 14a can be suppressed, and a decrease in heat-resistant peeling strength can be suppressed. Additionally, the manufacturing cost of the flexible substrate 10 can be suppressed.

Description

Flexible substrate and manufacturing method thereof {FLEXIBLE SUBSTRATE AND MANUFACTURING METHOD THEREOF}

The present invention relates to flexible substrates. More specifically, it relates to a flexible substrate with excellent heat resistance.

Various types of flexible wiring boards obtained by covering a heat-resistant resin film with a metal film are used in liquid crystal panels, notebook personal computers, digital cameras, mobile phones, etc. For this flexible wiring board, a resin film having a metal film formed by forming a metal film on one or both sides of a heat-resistant resin film is widely used. In this specification, the resin film having these metal films may be referred to as a “flexible substrate.”

As a manufacturing method of this type of flexible board, conventional methods include a method of manufacturing a metal foil by adhering it to a resin film with an adhesive (method of manufacturing a three-layer board), a method of manufacturing a metal foil by coating a thermosetting resin solution and drying it ( Casting method), a method of manufacturing by attaching a thermoplastic resin film to a metal foil and heat-pressing it (lamination method), and a method of manufacturing a metal film by forming a metal film on a resin film using a vacuum film forming method or a vacuum film forming method and wet plating method (metalizing method). etc. are known. Additionally, vacuum film forming methods of the metallizing method include vacuum deposition, sputtering, ion plating, and ion beam sputtering.

Here, in the vacuum film forming method, the sputtering method generally has excellent adhesion, but the peel strength (hereinafter sometimes referred to as heat-resistant peel strength) measured after heating the substrate to 150°C in the air and holding it for 168 hours decreases. It is known.

Regarding the flexible substrate that suppresses the decrease in heat-resistant peel strength, Patent Document 1 describes a metallizing method in which a chromium layer is sputtered on a polyimide insulating layer, and then copper is sputtered to form a conductor layer on the polyimide insulating layer. A method of forming is disclosed. In addition, in Patent Document 2, a flexible film formed by sequentially stacking a first metal thin film formed by sputtering with a copper nickel alloy as a target and a second metal thin film formed by sputtering with copper as a target on a polyimide film. A material for a circuit board is disclosed. Additionally, Patent Document 3 discloses a two-layer copper polyimide substrate in which the surface of a polyimide film is modified, and Patent Document 4 discloses a metal-coated polyimide resin substrate in which the surface of a polyimide resin film is modified.

Patent Document 1: Japanese Patent Publication No. 2-98994 Patent Document 2: Japanese Patent No. 3447070 Patent Document 3: Japanese Patent Publication No. 2007-318177 Patent Document 4: International Publication No. 2010/098236

In Patent Documents 1 and 2, a metal layer of chromium or nickel copper is formed on the surface of the polyimide film by sputtering in order to suppress a decrease in heat-resistant peeling strength. However, in the flexible substrates obtained according to these documents, the reduction in heat-resistant peeling strength was insufficiently suppressed. In addition, in Patent Documents 3 and 4, the decrease in heat-resistant peel strength is suppressed by modifying the surface of the polyimide film before the metal layer is formed on the polyimide film, but it can be said that the suppression of the decrease in heat-resistant peel strength is sufficient. In addition, there was a problem that processes such as plasma treatment for modifying the surface of the polyimide film were expensive.

In consideration of the above-described circumstances, the purpose of the present invention is to provide a flexible substrate capable of suppressing a decrease in heat-resistant peel strength and suppressing the overall manufacturing cost of the flexible substrate.

The flexible substrate of the first invention is comprised of a polyimide film, a base metal layer formed on the surface of the polyimide film, and a copper conductor layer formed to overlap the base metal layer, and the base metal layer is , a chromium-containing metal layer, wherein the chromium-containing metal layer has a first metal layer in contact with the polyimide film and a second metal layer positioned to overlap the first metal layer, and the chromium in the first metal layer The weight percentage is greater than the weight percentage of chromium in the second metal layer.

The flexible substrate of the second invention is characterized in that, in the first invention, the chromium-containing metal layer is a nickel chromium alloy layer.

According to the first invention, the base metal layer formed on the surface of the polyimide film includes a chromium-containing metal layer, and the weight percent of chromium in the first metal layer in contact with the polyimide film among the chromium-containing metal layers is the second. By being larger than the weight percent of chromium in the metal layer, diffusion of copper into the first metal layer can be suppressed. Since the heat-resistant peel strength decreases when the polyimide film is decomposed by copper, the decrease in heat-resistant peel strength can be suppressed by suppressing diffusion of copper into the first metal layer. In addition, it is relatively easy to make the weight percentage of chromium in the first metal layer larger than the weight percentage of chromium in the second metal layer, thereby suppressing the manufacturing cost of the flexible substrate and reducing the heat-resistant peel strength. It can be suppressed.

According to the second invention, since the chromium-containing metal layer is a nickel chromium alloy layer, the nickel chromium alloy can be easily obtained, and thus the decrease in heat-resistant peeling strength can be suppressed at a lower cost.

1 is an enlarged partial cross-sectional view of a flexible substrate according to a first embodiment of the present invention.
Figure 2 is a cross-sectional view of a flexible substrate according to the first embodiment of the present invention.
Figure 3 is a measurement diagram of elemental mapping by TEM of the flexible substrate according to the first embodiment of the present invention. (Figure A) This is a diagram showing the distribution state of Cr element after superheated steam treatment. (Figure B) This is a diagram showing the distribution state of Cr element before superheated steam treatment. (Figure C) This is a diagram showing the distribution state of Cu element after superheated steam treatment. (Figure D) This is a diagram showing the distribution state of Cu element before superheated steam treatment.

Next, embodiments of the present invention will be described based on the drawings. However, the embodiment shown below exemplifies the flexible substrate 10 for embodying the technical idea of the present invention, and the present invention does not specify the flexible substrate 10 as follows. In addition, the size or positional relationship of members shown in each drawing may be exaggerated for clarity of explanation.

(First Embodiment)

Figure 2 shows a cross-sectional view of the flexible substrate 10 according to the first embodiment of the present invention. As shown in FIG. 2, the flexible substrate 10 according to the present invention includes a polyimide film 11, a base metal layer 12 formed on the surface of the polyimide film 11, and this base metal layer ( It is configured to include a copper conductor layer 13 formed overlapping with 12). The base metal layer 12 is composed of, for example, a chromium-containing metal layer 14 and a base copper layer 15 provided on the polyimide film 11 side. In addition, in this embodiment, the base metal layer 12 and the like are formed on one side of the polyimide film 11, but this is not particularly limited, and the base metal layer 12 and the like are formed on both sides of the polyimide film 11. This also corresponds to the flexible substrate 10 according to the present invention.

Figure 1 shows an enlarged view of the portion surrounded by a circle in Figure 2. In this embodiment, the chromium-containing metal layer 14 of the base metal layer 12 includes a first metal layer 14a in contact with the polyimide film 11 and a second metal layer positioned to overlap the first metal layer 14a. It is a configuration with (14b). Additionally, the flexible substrate 10 according to the present invention is characterized in that the weight percent of chromium in the first metal layer 14a is greater than the weight percent of chromium in the second metal layer 14b.

Among the base metal layers 12 formed on the surface of the polyimide film 11, the weight percent of chromium in the first metal layer 14a in contact with the polyimide film 11 is the weight percent of chromium in the second metal layer 14b. By being larger than the weight percent of chromium, diffusion of copper into the first metal layer 14a can be suppressed, as will be described later.

One of the causes of the decrease in heat-resistant peeling strength of the flexible substrate 10 is that the polyimide film 11 is decomposed by copper. In other words, if highly conductive copper can be prevented from directly contacting the polyimide film 11, the heat-resistant peeling strength increases. At least a part of the underlying metal layer 12 is the chromium-containing metal layer 14 in this embodiment, specifically a nickel-chromium alloy layer, so that copper can be prevented from contacting the polyimide film 11. However, even if the chromium-containing metal layer 14 is formed, as the temperature of the flexible substrate 10 increases, copper gradually diffuses into the chromium-containing metal layer 14 and comes into contact with the polyimide film 11.

Therefore, a chromium-rich layer, that is, the first metal layer 14a, is present in a part of the chromium-containing metal layer 14. When the flexible substrate 10 becomes hot, copper diffuses into the chromium-containing metal layer 14 by combining with oxygen in the chromium-containing metal layer 14 . If the layer in which this oxygen is bound to chromium, that is, the first metal layer 14a rich in chromium, exists, diffusion of copper is suppressed even if the temperature of the flexible substrate 10 increases due to the first metal layer 14a, The decline in heat-resistant peeling strength can be suppressed.

In addition, a method of increasing the weight percent of chromium in the first metal layer 14a than the weight percent of chromium in the second metal layer 14b will be described later. Since this method can be carried out relatively easily, A decrease in heat-resistant peel strength can be suppressed while suppressing the manufacturing cost of the flexible substrate 10.

In addition, in the flexible substrate 10 according to the present invention, the base metal layer 12 includes a chromium-containing metal layer 14, that is, a nickel chromium alloy layer, and this nickel chromium alloy layer includes the first metal layer 14a and It is preferably comprised of the second metal layer 14b. Since nickel chromium alloys are readily available, the decrease in heat-resistant peeling strength can be suppressed at a lower cost.

(polyimide film (11))

The polyimide film 11 used in the flexible substrate 10 according to this embodiment is a film-type insulator. For example, Kapton (registered trademark) 100EN film manufactured by Toray and Dupont, or Upilex (registered trademark) 25SGA manufactured by Ube Kosan, etc.

(Underlying metal layer 12)

The base metal layer 12 constituting the flexible substrate 10 according to this embodiment is formed directly on the surface of the polyimide film 11. The base metal layer 12 is preferably formed to include a chromium-containing metal layer 14 and a base copper layer 15. The chromium-containing metal layer 14 is a nickel-chromium alloy in the present embodiment, but at least one selected from chromium and chromium oxide can be used. These base metal layers 12 are preferably formed by sputtering, which is dry plating. In addition, the formation of the base metal layer 12 is not problematic even if it is vacuum deposition or ion plating.

The chromium-containing metal layer 14 has relatively good adhesion to the synthetic resin that is the constituent material of the polyimide film 11. Additionally, the underlying copper layer 15 has high conductivity. Since the base metal layer 12 is composed of two layers in this way, the adhesion between the base metal layer 12 and the polyimide film 11 is improved and the conductivity is increased, and the copper conductor layer provided overlapping the base metal layer 12 The wet plating of (13) is easily performed.

The thickness of the chromium-containing metal layer 14 is preferably 50 angstroms or more and 500 angstroms or less, and the underlying copper layer 15 is preferably 500 angstroms or more and 5000 angstroms or less.

If the thickness of the chromium-containing metal layer 14 is less than 50 angstroms, problems with adhesion are likely to occur during each subsequent treatment process. In addition, when it is thicker than 500 angstroms, it becomes difficult to remove nickel or chromium during wiring processing, and cracks or warping are likely to occur in the chromium-containing metal layer 14. In this regard, the polyimide film 11 and the base Problems with the adhesion of the metal layer 12 are likely to occur. In addition, when the thickness of the underlying copper layer 15 is less than 500 angstroms, the effect of reducing defects caused by pinholes is reduced, and there is a possibility of causing conduction failure during wet plating performed thereafter. Additionally, if it exceeds 5000 angstroms, cracks or warping are likely to occur in the underlying copper layer 15, and in this regard, problems with adhesion between the polyimide film 11 and the underlying metal layer 12 are likely to occur.

The weight percentage of chromium in the chromium-containing metal layer 14 is preferably 12 percent or more and 50 percent or less. With this configuration, the certainty of suppressing diffusion of copper into the first metal layer 14a can be increased.

When the weight percentage of chromium is less than 12 percent, chromium does not sufficiently move to the first metal layer 14a, and the movement of copper is not sufficiently suppressed. Additionally, when the weight percentage of chromium is greater than 50%, the cost of sputtering increases.

(Copper conductor layer (13))

The copper conductor layer 13 constituting this flexible substrate 10 in this embodiment is formed directly on the surface of the base metal layer 12. When the flexible substrate 10 according to this embodiment is turned into a flexible wiring substrate by the semi-additive method, the thickness of the copper conductor layer 13 is about 2 μm. This is because the handling properties of the flexible substrate 10 become better. Additionally, when the flexible substrate 10 according to the present embodiment is turned into a flexible wiring substrate by the subtractive method, the thickness of the copper conductor layer 13 is around 8 μm. Additionally, the flexible substrate 10 according to the present invention is not limited to these thicknesses. The wet plating performed by the manufacturing method of the flexible substrate 10 according to this embodiment is known electroplating.

(Superheated steam treatment)

After the copper conductor layer 13 is formed on the flexible substrate 10 according to this embodiment, superheated steam treatment is performed by irradiating superheated steam. By performing this superheated steam treatment, the chromium-containing metal layer 14 constituting the base metal layer 12 is configured to have a first metal layer 14a in which the weight percentage of chromium is greater than that of the second metal layer 14b. In addition, in the present embodiment, the chromium-containing metal layer 14 is configured to have a first metal layer 14a in which chromium increases due to superheated steam treatment, but the first metal layer 14a in which oxygen increases, for example, by heating in a vacuum furnace. It is also possible to have a structure having the metal layer 14a.

The temperature of the superheated steam is preferably 200°C or higher and 450°C or lower. If the temperature is lower than 200°C, the chromium concentration of the two metal layers of the chromium-containing metal layer 14 does not change, and a decrease in heat-resistant peeling strength cannot be suppressed. Additionally, superheated steam with a temperature higher than 450°C is difficult to handle, and excessive effort is required to treat the superheated steam.

The time for irradiating superheated steam is preferably 60 seconds or more and 180 seconds or less. This is because if the time is shorter than 60 seconds, the chromium concentration of the two metal layers of the chromium-containing metal layer 14 does not change, and a decrease in heat-resistant peeling strength cannot be suppressed. Additionally, if the time is longer than 180 seconds, the productivity of the flexible substrate 10 decreases.

FIG. 3 shows element mapping measurements by TEM of the flexible substrate 10 before and after superheated steam treatment. The picture inside the circle in each figure shows the inside of the circle shown in FIG. 2, and the width of the hatched line indicates the amount or amount of each element. In other words, the narrow portion of the hatching line indicates that there are more elements, that is, the volume percentage of the element is higher than the portion where the hatching line is wide. Figure 3(A) and Figure 3(B) show the distribution state of chromium element before and after superheated steam treatment, and Figure 3(C) and Figure 3(D) show the copper element before and after superheated steam treatment. It shows the distribution state of .

As shown in FIG. 3(B), in the shear layer of the superheated steam treatment, the chromium element exists uniformly distributed within the chromium-containing metal layer 14. In the later stage of superheated steam treatment, a large amount of chromium element exists in the first metal layer 14a of the chromium-containing metal layer 14, and less chromium element exists in the second metal layer 14b than in the first metal layer 14a. .

As shown in FIG. 3(D), the copper element is consistently present in the underlying copper layer 15 and the copper conductor layer 13 in the previous stage of the superheated steam treatment. In the subsequent stage of superheated steam treatment, copper element was diffused into the second metal layer 14b, but copper was not diffused into the first metal layer 14a.

By performing the superheated steam treatment, the weight percentage of chromium in the first metal layer 14a is higher than that of the second metal layer 14b as described above, thereby suppressing diffusion of the copper element and reducing the heat-resistant peeling strength. is suppressed.

The thickness of the first metal layer 14a (distance above and below on the paper in FIG. 1) is determined depending on the temperature and time of the superheated steam treatment. For example, if it is 20 angstroms or more, diffusion of copper elements can be suppressed.

(Example)

Hereinafter, the present invention will be described by showing examples and comparative examples. Additionally, the flexible substrate 10 according to the present invention is not limited in any way to the following examples.

(Example 1)

As the polyimide film 11, Kapton (registered trademark) 100EN film manufactured by Toray DuPont was used. A chromium-containing metal layer 14 of 150 angstroms was formed on both sides of the polyimide film 11 by sputtering, and a 200 nm thick underlying copper layer 15 was formed overlapping the chromium-containing metal layer 14. . These chromium-containing metal layers 14 and the underlying copper layer 15 form the underlying metal layer 12 . Additionally, in Example 1, the proportion of chromium in the chromium-containing metal was 20 weight percent, and most of the other metals were nickel. Overlapping this base metal layer 12, an 8 µm-thick copper conductor layer 13 was formed by electrical copper plating. Afterwards, superheated water vapor at 300°C was irradiated for about 120 seconds, and then the substrate was cooled to room temperature, thereby obtaining the flexible substrate 10.

The thickness of the first metal layer 14a in this flexible substrate 10 was measured. Additionally, a 1 mm wide pattern for peeling strength measurement was created from this flexible substrate 10 using a ferric chloride etching solution. And the initial peel strength of the flexible substrate 10 was measured. In addition, the flexible substrate 10 was heated and held in the air at 150°C for 168 hours, and then its heat-resistant peeling strength was measured. Regarding the heat-resistant peel strength, it was judged to be good if it was 75% of the initial peel strength. The results are shown in Table 1.

In Example 1, the initial peel strength was 510 N/m, the heat-resistant peel strength was 500 N/m, and the strength retention rate was 98.0%. In other words, good results were obtained with the heat-resistant peel strength remaining almost unchanged from the initial peel strength.

(Example 2)

The same conditions as Example 1 were used, except that the chromium in the chromium-containing metal layer 14 was 40 weight percent. The measurement results are shown in Table 1.

In Example 2, the initial peel strength was 510 N/m, the heat-resistant peel strength was 500 N/m, and the strength retention rate was 98.0%. In other words, good results were obtained with the heat-resistant peel strength remaining almost unchanged from the initial peel strength.

(Example 3)

The same conditions as Example 1 were used, except that the chromium in the chromium-containing metal layer 14 was 100 weight percent. The measurement results are shown in Table 1.

In Example 3, the initial peel strength was 510 N/m, the heat-resistant peel strength was 500 N/m, and the strength retention rate was 98.0%. In other words, good results were obtained with the heat-resistant peel strength remaining almost unchanged from the initial peel strength.

(Example 4)

The same conditions as Example 1 were used, except that the film thickness of the chromium-containing metal layer 14 was 75 angstroms. The measurement results are shown in Table 1.

In Example 4, the initial peel strength was 510 N/m, the heat-resistant peel strength was 500 N/m, and the strength retention rate was 98.0%. In other words, good results were obtained with the heat-resistant peel strength remaining almost unchanged from the initial peel strength.

(Example 5)

The same conditions as Example 1 were used, except that the film thickness of the chromium-containing metal layer 14 was 300 angstroms. The measurement results are shown in Table 1.

In Example 5, the initial peel strength was 510 N/m, the heat-resistant peel strength was 500 N/m, and the strength retention rate was 98.0%. The heat-resistant peel strength was almost unchanged from the initial peel strength, and good results were obtained.

(Example 6)

The same conditions as in Example 1 were used, except that the temperature of the superheated steam was 200°C. The measurement results are shown in Table 1.

In Example 6, the initial peel strength was 510 N/m, the heat-resistant peel strength was 400 N/m, and the strength retention rate was 78.4%. That is, although the heat-resistant peel strength was lowered, it was about 78% of the initial peel strength, so good results were obtained.

(Example 7)

The same conditions as in Example 1 were used, except that the temperature of the superheated steam was 350°C. The measurement results are shown in Table 1.

In Example 7, the initial peel strength was 510 N/m, the heat-resistant peel strength was 500 N/m, and the strength retention rate was 98.0%. In other words, good results were obtained with the heat-resistant peel strength remaining almost unchanged from the initial peel strength.

(Example 8)

The same conditions as in Example 1 were used, except that the temperature of the superheated steam was 450°C. The measurement results are shown in Table 1.

In Example 8, the initial peel strength was 510 N/m, the heat-resistant peel strength was 510 N/m, and the strength retention rate was 100.0%. In other words, the heat-resistant peel strength did not change from the initial peel strength and good results were obtained.

(Example 9)

The same conditions as in Example 1 were used except that the polyimide film 11 was Upilex (registered trademark) 25SGA manufactured by Ube Kosan. The measurement results are shown in Table 1.

In Example 9, the initial peel strength was 550 N/m, the heat-resistant peel strength was 450 N/m, and the strength retention rate was 81.8%. In other words, good results were obtained with the heat-resistant peel strength remaining almost unchanged from the initial peel strength.

(Comparative Example 1)

The same conditions as Example 1 were used except that superheated steam treatment was not performed. The measurement results are shown in Table 1.

In Comparative Example 1, the initial peel strength was 510 N/m, the heat-resistant peel strength was 350 N/m, and the strength retention rate was 68.6%. That is, the heat-resistant peeling strength was low compared to the initial peeling strength.

(Comparative Example 2)

The same conditions as Example 1 were used, except that the chromium content of the chromium-containing metal layer 14 was 7 weight percent. The measurement results are shown in Table 1.

In Comparative Example 2, the initial peel strength was 510 N/m, the heat-resistant peel strength was 300 N/m, and the strength retention rate was 58.8%. That is, the heat-resistant peeling strength was low compared to the initial peeling strength.

(Comparative Example 3)

The same conditions as Example 1 were used, except that the film thickness of the chromium-containing metal layer 14 was 30 angstroms. The measurement results are shown in Table 1.

In Comparative Example 3, the initial peel strength was 510 N/m, the heat-resistant peel strength was 200 N/m, and the strength retention rate was 39.2%. That is, the heat-resistant peeling strength was low compared to the initial peeling strength.

(Comparative Example 4)

The same conditions as in Example 1 were used except that the polyimide film 11 was Upilex (registered trademark) 25SGA manufactured by Ube Kosan and that superheated steam treatment was not performed. The measurement results are shown in Table 1.

In Comparative Example 4, the initial peel strength was 600 N/m, the heat-resistant peel strength was 300 N/m, and the strength retention rate was 50.0%. That is, the heat-resistant peeling strength was low compared to the initial peeling strength.

10 Flexible substrate
11 Polyimide film
12 Base metal layer
13 copper conductor layer
14 Chromium-containing metal layer
14a first metal layer
14b second metal layer

Claims (4)

delete delete A step of forming a base metal layer on the surface of a polyimide film, including a chromium-containing metal layer in contact with the polyimide film;
A process of forming a copper conductor layer by overlapping the base metal layer;
Heat is applied to the polyimide film, the base metal layer, and the copper conductor layer by a predetermined heating method to suppress a decrease in heat-resistant peeling strength, and the chromium-containing metal layer is applied to a first metal layer in contact with the polyimide film. and a second metal layer positioned to overlap the first metal layer,
A method of manufacturing a flexible substrate, wherein the weight percent of chromium in the first metal layer is greater than the weight percent of chromium in the second metal layer. The method of manufacturing a flexible substrate according to claim 3, wherein the heating method is a superheated steam treatment in which superheated steam is irradiated to the polyimide film, the base metal layer, and the copper conductor layer.