JP4350112B2 - Laminated body for flexible circuit board and flexible circuit board using the laminated body for flexible circuit board - Google Patents

Description

  The present invention relates to a flexible circuit board used in, for example, an electronic device or the like, or a laminate usable as a part thereof, and particularly relates to a laminate using a polyimide film as a base material.

  Conventionally, an electric circuit board using a laminate obtained by laminating a conductive layer on a base material is, for example, a flexible circuit board (hereinafter also referred to as “FPC”), tape automatic bonding (hereinafter referred to as “TAB”). It is also widely used as a chip-on film (hereinafter also referred to as “COF”). And as a raw material of the base material used for this substrate, polyimide resin or polyimide film is often used because it has excellent mechanical properties, electrical properties, and excellent heat resistance. In order to form a layer having properties, copper (copper foil) is often used from the viewpoints of availability, handling, ease of processing, and the like.

  As a laminate using this polyimide resin or polyimide film as a raw material for a base material, a three-layer structure type (hereinafter also referred to as “three-layer type”) in which a polyimide film and a copper foil are laminated via an adhesive. And a two-layer structure type (hereinafter also referred to as “two-layer type”) in which a polyimide resin layer or polyimide film and a copper foil or copper layer are directly laminated without using an adhesive. I can do it.

  Now, there are three-layer type laminates and two-layer type laminates in this way, but with the demand for miniaturization of electronic equipment, the wiring pattern density of FPC, TAB, COF, etc. has increased. In recent years, which have been strongly demanded, there is a situation in which a three-layer type laminate cannot sufficiently cope. In other words, if the laminate is a three-layer type, the heat resistance of the adhesive used is inferior to that of the polyimide film as the base material, so it cannot withstand heating during processing, resulting in a significant reduction in dimensional accuracy. There is a problem that it will. In addition, since the thickness of the copper foil used for the three-layer type laminate is 10 tens of μm, it is difficult to miniaturize the circuit and reduce the thickness of the substrate even when trying to meet the above-mentioned demands for lightness and thinness. I was sorry.

  Therefore, the use of a two-layer type laminate for the purpose of making it thinner and forming a high-density circuit is increasing. As a lamination method for producing this two-layer type laminate, a casting method by casting a polyimide resin on a copper foil, a lamination method in which the copper foil and a non-thermoplastic polyimide resin are bonded via a thermoplastic polyimide resin There is a plating method in which a copper layer is formed by electrolytic plating after dry plating or wet plating on a polyimide film. Further, in order to form a high-density circuit, a wiring forming resist is applied and etched on a conductive layer (seed layer) formed by dry plating, and then copper is laminated as a conductive layer by wet plating. Thereafter, a semi-additive method for removing the resist may be employed.

  However, when the two-layer type is used as a structure in which polyimide and copper are directly laminated, there has always been a problem in terms of adhesion. That is, in the case of a laminate obtained by laminating these, there is a problem that the adhesion is low particularly in the case of the plating method and the semi-additive method.

  Therefore, in order to solve such a problem, a method of forming a second metal layer between a polyimide film and a copper layer has been proposed as described in Patent Document 1, for example.

Japanese Examined Patent Publication No. 2-98994

  In the case of the invention described in Patent Document 1 described above, a chromium layer is formed in advance on the surface of the polyimide insulating layer by sputtering, and then a copper layer is formed on the surface by sputtering. As a result, it is said that there is an effect that adhesion between copper and the polyimide insulating layer is ensured.

  However, with this disclosed technology, it may be possible to satisfy a certain level. However, when trying to meet the recent demands for reducing the size of electronic devices, for example, heat resistance That is insufficient. In addition, when trying to increase the density further, the lack of adhesion force surfaced, and eventually this technology could not be adequately handled, which was a problem.

  The present invention has been made in view of such problems, and the object thereof is to realize further improvement in heat resistance and adhesion, that is, polyimide layer and conductor after circuit formation. An object of the present invention is to provide a laminate that can be used as, for example, a flexible circuit board, which can provide a sufficient adhesion between the layers and prevent a decrease in adhesion after thermal load.

In order to solve the above problems, the invention according to claim 1 of the present invention is a laminate for a flexible circuit board, in which a silicon layer made of silicon carbonitride is laminated on the surface of a base film made of a polymer resin. The nitrogen atom concentration in the silicon layer is 30% or less, the thickness thereof is 0.5 nm or more and 100 nm or less, and the surface resistance value of the laminate for a flexible circuit board is 1 × 10 ¹¹ Ω or more, It is characterized by.

  The invention according to claim 2 of the present invention is characterized in that, in the laminate for flexible circuit board according to claim 1, a metal layer made of metal is laminated on the surface of the silicon layer.

  The invention according to claim 3 of the present invention is characterized in that, in the laminate for flexible circuit board according to claim 2, a copper conductive layer is further laminated on the surface of the metal layer.

  A flexible circuit board according to a fourth aspect of the present invention is obtained by using the laminate for a flexible circuit board according to any one of the first to third aspects.

  As described above, in the laminated body according to the present invention, a silicon layer made of silicon or a silicon compound is formed in advance on the surface of a plastic film such as a polyimide film, so that it can be used as a conventional flexible circuit board. Compared to the type, there is no decrease in adhesion after heat load, and the interlayer adhesion is improved, so it is easy for modern electronic circuits that require high density by using the laminate according to the present invention. A flexible circuit board applicable to the above can be obtained. In particular, when silicon carbonitride is laminated on the surface of the polyimide film, it becomes easier to obtain the desired performance, and the allowable range of the film thickness at which the silicon layer formed of silicon carbonitride can exhibit the desired performance is very wide. In other words, the allowable range in design is widened, and a laminate that can be easily designed as a flexible circuit board can be obtained.

  Embodiments of the present invention will be described below. The embodiment shown here is merely an example, and is not necessarily limited to this embodiment.

(Embodiment 1)
The laminated body according to the present invention will be described as a first embodiment.
The laminate according to the present embodiment is formed by laminating a silicon layer made of silicon or a silicon compound on the surface of a base film made of a polymer resin, and can be used as, for example, an FPC (or a part thereof). In the following description, the laminate according to the present invention will be described with the use of FPC (or a part thereof) in mind.

Hereinafter, description will be made sequentially.
First, a polymer resin film as a base material is not particularly limited, but if the use of the laminate according to the present embodiment is FPC, this polymer resin film is Since it becomes the base material which finally comprises FPC, it is desirable that it is suitable in insulation, heat resistance, etc., and it can be said that it is suitable, for example from a viewpoint, as a polyimide film. In this embodiment, a polyimide film is used as a base material, but the present invention is not necessarily limited to this.

  The thickness of the polyimide film in the present embodiment is preferably 9 μm or more and 125 μm or less. If this thickness is too thin, the strength is weakened, wrinkles are generated, and the laminate obtained in this embodiment is easily broken, so that it cannot be used as an FPC. Therefore, if the thickness is 9 μm or more, even if wrinkles are generated, they are within an allowable range, and if the thickness is 17 μm or more, the generation of wrinkles can be almost eliminated. Moreover, when this thickness is too thick, the flexibility of the obtained FPC, that is, flexibility is lost, and the thickness of the FPC itself increases. For this reason, if the thickness is 125 μm or less, an almost allowable range of flexibility can be obtained, and the thickness of the entire FPC can be within the allowable range. If the thickness is 50 μm or less, sufficient flexibility can be obtained. The thickness of can also be set to a desired thickness.

Next, the silicon layer laminated on the surface of the base film will be described.
A silicon layer is laminated on the surface of a polyimide film as a base material. This silicon layer may be made of silicon or a silicon compound. When a silicon compound is used to form the silicon layer, the silicon compound includes silicon-containing alloys (eg, Si—Ni, Si—Co), silicon or oxides of silicon-containing alloys (eg, oxidation). Any one or more of silicon), nitride (eg, silicon nitride), and carbide (eg, silicon carbide) may be used. In this embodiment, the silicon layer is any of silicon, silicon carbide, or silicon carbonitride. It shall be due to

  Such a silicon layer stacking method may be a conventionally known method known as a dry plating method, for example, a vacuum evaporation method, an electron beam evaporation method, a sputtering method, etc., but in this embodiment, a dry plating method is used. Of these, the sputtering method is used. By using a dry plating method, particularly a sputtering method, it is possible to continuously form a metal layer and a copper conductive layer to be laminated next in the same vacuum chamber, so that productivity can be improved. It becomes possible.

  Now, in the sputtering method performed when laminating the silicon layer in the present embodiment, all the sputtering conditions may be as conventionally known, and a generally known argon gas may be used as the sputtering gas. In this embodiment, nitrogen gas is used in addition to argon gas as the sputtering gas.

By using nitrogen gas simultaneously with argon gas at the time of sputtering, the surface resistance value of the FPC obtained by finally etching, for example, the laminate according to this embodiment can be easily set to a desired degree, for example, 2 × 10 ¹¹ Ω. This is possible. The desirable surface resistance value for the FPC is 1 × 10 ¹¹ Ω or more. However, if the surface resistance value is 1 × 10 ¹¹ Ω or less, sufficient insulation resistance between the wirings cannot be obtained. This is because it is difficult to use a laminated body having only such a surface resistance value as an electric circuit.

  This will be further described. In this embodiment, the silicon layer is made of silicon, silicon carbide, or silicon carbonitride, but in the case of laminating silicon, an ingot-like target is used when performing sputtering. In the case of laminating silicon and silicon carbide, a silicon carbide ingot may be used as a target. When silicon carbide nitride is laminated, sputtering may be performed using a silicon carbide ingot or a silicon carbide ingot as a target. In this embodiment, a silicon carbide ingot is used as a target, and nitrogen gas is used in addition to argon gas as a sputtering gas. Therefore, the nitrogen gas reacts with silicon carbide, and finally the surface of the base film (PI film) In addition, the silicon carbonitride layer is formed as a silicon layer. Then, by laminating the silicon carbonitride layer as a silicon layer, a stronger adhesion strength and a sufficient surface resistance value can be obtained as compared with the prior art.

  Thus, as thickness of the silicon layer laminated | stacked on the polyimide film surface, it is preferable that they are 0.5 nm or more and 100 nm or less, More preferably, it is 50 nm or less. This is because when the thickness of the silicon layer is less than 0.5 nm, the heat resistance sufficient to withstand the heat treatment in manufacturing the laminate according to the present embodiment cannot be obtained, and the thickness exceeds 100 nm. This is because the productivity of the laminate according to the present embodiment is reduced, and if it is made to be less than 50 nm, an effective resistance value can be obtained in an FPC using this as described later. Is possible. In this respect, it is preferable that the thickness of the silicon layer is 30 nm or less because an even more effective resistance value can be obtained in the FPC using the silicon layer.

  By the way, if the laminate according to the present embodiment is used as an FPC, the number of layers is increased because an extra silicon layer is inserted compared to the conventional configuration of PI / metal layer. However, if only this is seen, the overall thickness seems to increase, but in the case of the laminate according to the present embodiment, the thickness of the metal layer and the thickness of the silicon layer are as described above. Even if laminated, it is possible to make it thinner than the required thickness of the metal layer in the conventional configuration, and at the same time, it becomes possible to obtain a higher surface resistance value than that of the conventional configuration. .

  This is possible because of the provision of a silicon layer. Furthermore, if silicon carbide is used as this silicon layer, it becomes possible to obtain a higher surface resistance with a thinner film thickness. It has been found that if the silicon layer is made of silicon carbonitride, a higher surface resistance value can be obtained with a thinner film thickness, or even if the film thickness is the same, the surface resistance value becomes higher. And the range of the thickness which can clear these above-mentioned conditions is 0.5 nm or more and 100 nm or less as above-mentioned, and if it is going to obtain a more suitable value, it is good to set the upper limit of thickness to 50 nm or less.

  It is also conceivable to laminate a metal layer on the surface of each layer described above. Although it does not specifically limit as a metal which comprises this metal layer, For example, it can be said that it is suitable to use any one or more of nickel, chromium, copper, or aluminum. As a method for laminating the metal layer, in this embodiment, the nickel-chromium alloy is laminated by the sputtering method, but this is not particularly limited to this, and the laminate is as described above. In addition, the technique may be a conventionally known technique, for example, a lamination method using a so-called dry plating method such as an ion plating method or a vacuum deposition method.

  In this way, by laminating silicon or a silicon compound on the surface of a base film made of a polymer resin, conventionally, after forming a metal layer on the base film made of a polymer resin to increase the adhesive force, Compared to the case where layers or the like are laminated, a strong adhesion force is generated between silicon or silicon compound and the base film, silicon or silicon compound and the metal layer, and the adhesion force between the base film and the metal layer. As a result, the same effect can be obtained. And even after applying the heat load which arises when manufacturing FPC concerning this embodiment, the fall of adhesion power can be controlled.

  When a copper conductive layer is formed as a conductive layer on the surface of the metal layer, the copper conductive layer is laminated by a sputtering method in the present embodiment, but is not limited to this and is a conventionally known method. For example, it is conceivable to use a dry plating method such as ion plating or vacuum deposition. The thickness of the copper conductive layer may be appropriately selected as appropriate, but detailed description thereof is omitted here.

  By sequentially laminating the polyimide film as described above, a laminate based on the polyimide film according to the present embodiment is obtained. In order to form a high-density circuit using this laminate, After applying and etching a wiring formation resist on the conductive layer (seed layer) formed by dry plating, copper is deposited as a conductive layer by wet plating, and then the semi-additive method is performed to remove the resist By doing so, it is possible to prevent the phenomenon of lowering the adhesion between the base material and the metal layer after a thermal load, which was a problem in the past, so that the electrons that have evolved more than ever This will greatly contribute to the realization of lighter, thinner and smaller devices. This etching may be performed by a conventionally known method.

  In the above description, a silicon layer, a metal layer, and a copper conductive layer were sequentially laminated on the surface of the polyimide film. However, it is also conceivable that the polyimide film is sequentially laminated on both sides instead of one side, Furthermore, it is conceivable to form a laminate having some purpose on the surface of the copper conductive layer, but the detailed description thereof is omitted here.

  In addition, if it is a laminated body which laminated | stacked only the silicon layer on the surface of the polyimide film which concerns on this Embodiment, even after applying a thermal load with respect to this laminated body, an interlayer contact | adhesion force does not fall and it is highly precise. Even if it is used for a recent electronic circuit which is required to be made, it becomes a suitable laminate. That is, in a laminate in which a silicon layer is laminated on a polymer resin substrate, when a metal layer is formed on the laminate, it can be used as an underlayer for obtaining strong adhesion.

  Hereinafter, the laminated film according to the present invention will be further described with reference to examples.

  In the examples described below, a PI film (product name “Kapton EN” manufactured by Toray DuPont Co., Ltd.) is used as the base film. The metal layer is formed by laminating a nickel-chromium alloy. In the following description, each layer is formed by a sputtering method based on a conventionally known method and conditions unless otherwise specified. Each surface resistance value was measured by a method defined in JIS C 6471.

(Example 1)
A silicon layer is laminated on the surface of the PI film so that the thickness is 1 nm, and then a metal layer is laminated on the surface so that the thickness is 10 nm, and copper is further formed on the surface so that the thickness is 100 nm. Lamination was performed to obtain a laminate. In addition, in the sputtering method performed when laminating silicon carbide, argon gas and nitrogen gas were used as the sputtering gas, and the silicon layer was formed so that the nitrogen concentration was 21%. It is silicon carbonitride that constitutes the silicon layer in the obtained laminate.

(Example 2)
Although the laminated body was formed similarly to Example 1, the thickness of the silicon layer was 10 nm.

(Example 3)
A laminate was formed in the same manner as in Example 1, but the silicon layer was formed so that the nitrogen atom concentration was 10%. It is silicon carbide that constitutes the silicon layer in the obtained laminate.

(Example 4)
A laminate was formed in the same manner as in Example 1, but the silicon layer was formed so that the nitrogen atom concentration in the silicon layer was 27%. It is silicon carbide that constitutes the silicon layer in the obtained laminate.

(Example 5)
A laminated body was formed in the same manner as in Example 1. However, since only argon gas was used as the sputtering gas, silicon carbide constitutes the silicon layer in the obtained laminated body.

(Comparative Example 1)
Lamination was performed in the same manner as in Example 1, but no silicon layer was laminated.

(Comparative Example 2)
The layers were laminated in the same manner as in Example 1, but the silicon layers were laminated so that the nitrogen atom concentration was 35%.

(Comparative Example 3)
The layers were laminated in the same manner as in Example 1, but the silicon layers were laminated so that the nitrogen atom concentration was 42%.

  The surface resistance value and initial adhesion after removal of the metal layers and copper layers of Examples 1 to 4 and Comparative Examples 1 and 2 obtained above and the adhesion after heat load were as follows.

The range of the surface resistance value suitable for the FPC is 1 × 10 ¹¹ or more, and the reason is as described above. As can be seen from this example, when the silicon layer is laminated and the material constituting the silicon layer is silicon carbonitride by using argon gas and nitrogen gas as the sputtering gas, a good surface resistance value is obtained. And a laminate having excellent initial adhesion and little decrease in adhesion after heat load. In addition, even when only argon gas is used as the sputtering gas, a laminated body having excellent surface resistance value and initial adhesion force by using silicon carbide as the silicon layer, and less reduction in adhesion force after thermal load. It can be seen that

Claims (4)

A laminate for a flexible circuit board, in which a silicon layer made of silicon carbonitride is laminated on the surface of a base film made of a polymer resin,
The nitrogen atom concentration in the silicon layer is 30% or less, and the thickness is 0.5 nm or more and 100 nm or less,
The surface resistance value of the laminate for a flexible circuit board is 1 × 10 ¹¹ Ω or more,
A laminate for a flexible circuit board. The laminate for a flexible circuit board according to claim 1,
A metal layer made of metal is laminated on the surface of the silicon layer;
A laminate for a flexible circuit board. In the laminated body for flexible circuit boards according to claim 2,
A copper conductive layer is further laminated on the surface of the metal layer;
A laminate for a flexible circuit board. It is obtained using the laminated body for flexible circuit boards according to any one of claims 1 to 3.
A flexible circuit board.