JP2006324474A - Method of manufacturing metal-clad polyimide substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a metal-clad polyimide substrate which uniformly adheres a sputter layer to an electroplating layer forming the metal covered polyimide substrate at a high accuracy, and suppresses the forming of pin-holes. <P>SOLUTION: After forming a copper layer of 50-500 nm thick by sputtering on the surface of a metal layer formed on a polyimide film surface, a substrate having a copper film formed by electroplating on the copper layer is heat treated at temperatures of 120-200°C. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a metal-coated polyimide substrate, and more specifically, a metal layer (hereinafter sometimes referred to as a sputter layer) formed by a sputtering method, which constitutes the metal-coated polyimide substrate, and the metal layer. A metal-coated polyimide substrate capable of uniform and high adhesion with a copper coating (hereinafter sometimes referred to as an electroplating layer) formed by electroplating on the top and suppressing the occurrence of pinholes It relates to the manufacturing method.

  A metal-coated polyimide substrate is widely used as a semiconductor mounting substrate for mounting a driving semiconductor for displaying an image on a liquid crystal screen. In recent years, COF (Chip on Film) has attracted attention as a method of mounting a driver IC chip for liquid crystal screen display. Compared with TCP (Tape Carrier Package), which is the mainstream of conventional mounting methods, COF has features that it is possible to mount fine pitch, and that it is easy to reduce the size and cost of the driver IC. is there.

  As a general method for producing COF, a metal-coated polyimide substrate is used in which a copper film that is a good conductor is adhered to a polyimide film that is a highly heat-resistant and highly insulating resin. After fine patterning by a photolithography technique, a method of coating a desired portion with tin plating and a solder resist is taken.

  Here, as the polyimide film, a commercially available product is used, and generally a film having a thickness of 25 to 38 μm is used. Moreover, as a method of forming a metal layer on the polyimide film surface, first, a first metal layer such as a nickel-chromium alloy is formed by sputtering, and then a copper layer is formed to impart good conductivity. Form. At this time, generally, the thickness of the copper layer formed by the sputtering method is about 100 to 500 nm. Furthermore, when it is necessary to increase the film thickness, generally, a copper film is formed on the metal layer by electroplating or a combination of electroplating and electroless plating (see, for example, Patent Document 1). .) The thickness of the copper coating is usually 5 to 12 μm when a circuit is formed by a subtractive method, and is usually 1 to 2 μm when a circuit is formed by a semi-additive method.

  At this time, it is important to ensure adhesion between the sputtered layer and the electroplated layer when electroplating the surface of the sputtered layer in order to increase the film thickness. As a countermeasure, it has been proposed and implemented to perform a chemical activation treatment on the surface of the sputtered layer in order to remove the oxide film (see, for example, Patent Document 2).

  By the way, with the rapid progress of recent high-definition liquid crystal display screens, miniaturization of liquid crystal driving ICs, etc., even with respect to COF obtained using the metal-coated polyimide substrate, high-definition of electronic circuits, That is, a fine pitch is strongly demanded. However, when the metal-coated polyimide substrate obtained by the conventional proposal is used for COF, the pin yield existing in the sputter layer causes the product yield to be reduced at the time of fine patterning, and in the fine circuit section. There were problems such as local peeling at the interface between the sputter layer and the electroplating layer, and the product reliability was not fully satisfactory.

JP-A-2002-252257 (first page, second page) JP 2002-150516 A (first page, second page)

  The object of the present invention is to make the adhesion between the sputter layer and the electroplating layer constituting the metal-coated polyimide substrate uniform and high in strength, and to suppress the generation of pinholes, in view of the above-mentioned problems of the prior art. An object of the present invention is to provide a method for producing a metal-coated polyimide substrate.

  In order to achieve the above object, the present inventor has conducted extensive research on a method for producing a metal-coated polyimide substrate, and as a result, a substrate formed by forming a sputter layer and an electroplating layer having a specific thickness on the surface of the polyimide film. Was subjected to heat treatment under specific conditions, and it was found that the adhesion between the sputtered layer and the electroplating layer can be made uniform and high in strength and the occurrence of pinholes can be suppressed, thereby completing the present invention.

  That is, according to the first aspect of the present invention, after a copper layer having a thickness of 50 to 500 nm is formed on the surface of the metal layer formed on the polyimide film surface by sputtering, electroplating is performed on the copper layer. There is provided a method for producing a metal-coated polyimide substrate, wherein a substrate formed with a copper coating is subjected to a heat treatment at a temperature of 120 to 200 ° C.

  According to a second aspect of the present invention, there is provided the method for producing a metal-coated polyimide substrate according to the first aspect, wherein the copper layer has a thickness of 50 to 200 nm.

  According to a third aspect of the present invention, there is provided the method for producing a metal-coated polyimide substrate according to the first aspect, wherein the atmosphere for the heat treatment is air or a neutral atmosphere.

  According to the method for producing a metal-coated polyimide substrate of the present invention, the adhesion between the sputtered layer and the electroplated layer can be made uniform and high in strength, and the occurrence of pinholes can be suppressed. The value is extremely great.

  Moreover, since the thickness of the sputtered copper layer can be reduced to 200 nm or less as compared with the conventional 100 to 500 nm, it is possible to achieve higher density of electronic parts such as COF and to supply economical products. It is more advantageous because a higher effect can be obtained.

Hereinafter, the manufacturing method of the metal-coated polyimide substrate of the present invention will be described in detail.
In the method for producing a metal-coated polyimide substrate of the present invention, a copper layer (sputtering layer) having a thickness of 50 to 500 nm is formed on the surface of the metal layer formed on the polyimide film surface by a sputtering method, A substrate obtained by forming a copper coating (electroplating layer) on the substrate by heat plating is subjected to heat treatment at a temperature of 120 to 200 ° C.

  In the present invention, it is important to subject a substrate formed by forming a sputter layer and an electroplating layer on the polyimide film surface to a heat treatment at a predetermined temperature. Thereby, the adhesion between the sputter layer and the electroplating layer can be made uniform and high in strength. For this reason, the conventional chemical activation treatment of the sputtered layer can be reduced or omitted, and the generation of pinholes associated with the treatment can be suppressed.

First, the adhesion strength and the generation of pinholes that are important properties required for a metal-coated polyimide substrate will be described in detail below.
In the manufacturing process of the metal-coated polyimide substrate, the chemical activation treatment of the sputter layer (hereinafter sometimes referred to as activation treatment) activates the inactive portion of the sputter layer surface as a pretreatment for electroplating. Therefore, the surface of the sputtered layer is washed with sulfuric acid or the like. That is, an inert portion exists on the surface of the sputtered layer after sputtering, though it is not oxidized or completely oxidized. Conventionally, a chemical activation process for the sputtered layer has been performed as a countermeasure. However, if an inactive portion remains locally even after the activation treatment, an electroplating layer is formed on the portion with insufficient adhesion strength. Therefore, when an external force such as bending is applied to the substrate after electroplating, the substrate may be peeled off at the interface between the sputtered layer and the electroplated layer.

  Incidentally, in order to obtain a sufficient effect by the activation treatment, it is necessary to etch the sputtered layer itself including the inactive portion. At that time, the etching amount for obtaining a uniform and sufficient high strength in the adhesion between the sputtered layer and the electroplating layer is at least 2 to 3 μm. However, the thickness of the sputtered layer of the metal-coated polyimide substrate is usually 500 nm or less. This is because the thickness is limited in order not to reveal the deformation of the polyimide film, the change of characteristics, etc. due to the excessive heat history during the sputtering process. Therefore, since the thickness of the sputtered layer itself is insufficient, it is not possible to perform an etching process that sufficiently exhibits the activation process effect. Furthermore, if the etching process is performed unevenly, the sputtered layer is locally dissolved and removed, which causes pinholes in the copper film formed by subsequent electroplating.

On the other hand, according to the method of the present invention, the substrate formed by forming the sputter layer and the electroplating layer on the polyimide film surface is subjected to heat treatment at a predetermined temperature, so that the sputter layer is activated or not. Regardless of this, the adhesion between the inactive portion and the electroplating layer can be improved, and the adhesion between the sputtered layer and the electroplating layer can be made uniform and high in strength.
Therefore, in the method of the present invention, since the activation process of the sputter layer is not an indispensable process, the activation process of the sputter layer can be reduced or omitted. If foreign matter adheres to the surface of the sputtered layer, that part will hinder the formation of a copper film by subsequent electroplating. Therefore, if the activation process is omitted, a separate physical removal process must be performed. It is preferably performed prior to electroplating.

Next, the configuration and operation of the method of the present invention will be described.
The metal-coated polyimide substrate according to the method of the present invention will be described with reference to the drawings. FIG. 1 shows an example of a schematic cross-sectional view of a metal-coated polyimide substrate obtained by the production method of the present invention. In FIG. 1, the cross section has a structure in which a nickel-chromium alloy layer 2, a copper layer 3, and a copper coating 4 are sequentially laminated on the surface of a polyimide film 1. Here, as a method for producing a metal-coated polyimide substrate, first, a nickel-chromium alloy layer 2 (first metal layer) is formed on the surface of the polyimide film 1 as a metal layer by a sputtering method to a predetermined thickness. Then, a copper layer 3 having a predetermined thickness is formed on the surface as a second metal layer by sputtering. Next, the copper coating 4 is formed to a predetermined thickness on it by either electroplating or a combination of electroplating and electroless plating. Thereafter, the substrate on which the sputter layer and the electroplating layer are laminated is heat-treated under predetermined conditions.

  The polyimide film used in the method of the present invention is not particularly limited, and examples thereof include commercially available products such as Kapton EN (manufactured by Toray DuPont), Upilex s (manufactured by Ube Industries), NPI (manufactured by Kaneka). The thickness is not particularly limited, and is preferably 25 to 50 μm, more preferably 30 to 40 μm in the case of a COF material that is a mounting method of a liquid crystal display driver IC. For example, Kapton 150EN (made by Toray DuPont), Upilex 35s (made by Ube Industries), etc. are mentioned.

  The thickness of the sputtered copper layer used in the method of the present invention, that is, the copper layer formed by the sputtering method is 50 to 500 nm, and 50 to 200 nm is preferably used.

  That is, when the above-described deformation of the polyimide film due to an excessive heat history does not adversely affect the product characteristics, the activation layer can be sufficiently activated by increasing the thickness of the sputter layer to 2 μm or more. Therefore, the region where the method of the present invention is effective is a region where the thickness of the sputtered layer, which normally omits the activation treatment, is less than 2 μm, and is 500 nm or less in consideration of the economy and the influence of thermal history. On the other hand, when the thickness of the sputtered layer is extremely thin, sufficient conductivity cannot be obtained, which adversely affects the subsequent deposition of electroplating. Therefore, the plating thickness becomes non-uniform, and only pinholes are generated. However, the problem that the adhesive strength of a polyimide film and a metal layer falls arises. Accordingly, the lower limit of the thickness of the sputtered copper layer that does not cause these problems is 50 nm in the current general sputtering technique.

  As the sputter layer, a first metal layer and a second metal layer are usually formed on the polyimide film surface by sputtering. The first metal layer directly formed on the polyimide film is preferably a nickel-chromium alloy layer. The first metal layer plays a role of ensuring characteristics such as adhesion strength between the polyimide film and the metal layer, heat resistance of the substrate, and stability in a humidity resistant environment.

  The alloy composition and thickness of the nickel-chromium alloy layer are not particularly limited, but the chromium concentration in the alloy layer is preferably 5 to 30% by weight and the thickness is preferably 5 to 50 nm. In other words, the alloy composition and thickness are closely related to the above characteristics, and when an electronic circuit is formed by etching a metal layer using COF or the like, the etching property is greatly different from that of a good conductor copper. This is because it is inconvenient if the alloy composition and thickness are different from each other.

  As the second metal layer, after forming the first metal layer by sputtering and before electroplating, a copper layer is subsequently formed by sputtering in order to ensure the conductivity of the sputtered layer. The thickness of the copper layer is not particularly limited, but is preferably 50 to 500 nm in order to impart conductivity to the sputtered layer so that deposition by electroplating can be performed uniformly and smoothly. That is, if the thickness is less than 50 nm, sufficient conductivity cannot be obtained, and the uniformity of copper deposition by subsequent electroplating is adversely affected. On the other hand, if the thickness exceeds 500 nm, it is advantageous in terms of imparting conductivity, but as described above, due to the influence of substrate dimensional change, deformation, etc. due to an increase in the thermal history of the polyimide film by sputtering, COF There are concerns about adverse effects on the resulting products.

  The apparatus used for the sputtering is not particularly limited, and a magnetron sputtering apparatus or the like is used.

  In the present invention, if necessary, when the electroplating is performed on the sputtered layer after the sputtering treatment, the surface of the sputtered layer can be activated. However, as described above, since the activation process causes the copper film to be thin, the sputter layer is dissolved and removed, that is, pinholes are generated. This increases the product yield of electronic circuits such as COF that require fine patterning. It becomes a factor to make it worse. Therefore, in performing the activation process, it is necessary to optimize the conditions so that a uniform process state can be realized.

  As electroplating used in the present invention, either electroplating or a combination of electroplating and electroless plating is used. Here, electroless plating can be performed prior to electroplating or alternately with electroplating as a countermeasure against pinholes in the sputtered layer.

  The thickness of the copper coating formed by the electroplating is 8 to 12 μm. The thickness of the copper coating is selected from the characteristics of the product such as COF, but about 5 μm is more preferable in order to realize fine patterning. Furthermore, in the case of circuit formation by the semi-additive method, the copper thickness as the conductive layer including the copper layer formed by sputtering is about 1 to 2 μm. Formation of the copper film by electroplating is carried out by using an acidic plating solution mainly composed of sulfuric acid and copper sulfate.

  The temperature of the heat treatment used in the method of the present invention is 120 to 200 ° C. That is, when the temperature of the heat treatment is less than 120 ° C., the effect of improving the adhesion between the sputtered layer and the electroplated layer is insufficient, and the problem of peeling is partially included. On the other hand, when the temperature exceeds 200 ° C., the effect of improving the adhesion can be obtained, but the dimensional change, characteristic change, etc. due to the heat of the substrate become obvious. The value deviates from the original design value, or the variation becomes large, which adversely affects reliability.

  The atmosphere of the heat treatment used in the method of the present invention is not particularly limited, but can be carried out in a normal atmospheric environment, but when there is a concern about the adverse effect on product quality due to copper oxidation, An inert gas atmosphere is desirable.

The heat treatment time used in the method of the present invention is not particularly limited and is not specified because it is closely related to the heat treatment temperature and the like, but it is preferably about 10 to 60 minutes.
The heat treatment equipment used in the method of the present invention is not particularly limited, and a continuous or batch heating furnace is used.

  The metal-coated polyimide substrate obtained by the method of the present invention has a high adhesion strength at the interface between the sputtered layer and the electroplated layer, and adversely affects the product yield when an electronic circuit such as a pinhole is formed in the metal layer. Since the occurrence of defective portions is suppressed, sufficient characteristic and dimensional reliability as a precise electronic component can be obtained. In addition, since the thickness of the sputter layer can be reduced, it is possible to achieve higher density of electronic parts such as COF, and to supply economical products.

  Hereinafter, the present invention will be described in more detail by way of examples and comparative examples of the present invention, but the present invention is not limited to these examples. In addition, the evaluation method of the adhesiveness of the sputter | spatter layer and electroplating layer of a metal coating polyimide substrate used by the Example and the comparative example is as follows.

  Evaluation method of adhesion: First, using the obtained metal-coated polyimide substrate, an electronic circuit having a circuit width of 12 μm and a circuit interval of 13 μm was formed using a photolithography technique. Next, the electronic circuit part was folded 180 degrees with the circuit side inside, and the operation of opening the electronic circuit part to the original state was repeated three times, and then the presence or absence of abnormality such as peeling of the bent part was observed with a microscope.

Example 1
Kapton 150EN (manufactured by Toray DuPont) was used as the polyimide film. First, the said polyimide film was inserted into the sputtering device, and the heat processing for 1 minute were performed at 150 degreeC within the chamber hold | maintained at 0.01-0.1Pa of vacuum degree. Subsequently, a nickel-chromium alloy target containing 20% by weight of chromium was used as a sputtering target, and a nickel-chromium alloy layer having a thickness of 20 nm was formed on the polyimide film surface. A 100 nm thick copper layer was formed, and a sputter substrate on which a metal layer was laminated was obtained.
Next, this board | substrate was inserted into the electroplating apparatus, copper plating was performed to thickness 8 micrometers, and the copper film was formed. The obtained copper plating board was washed with water. The composition of the plating solution was a sulfuric acid concentration of 180 g / L and a copper sulfate concentration of 80 g / L, and the plating temperature was adjusted to 40 ° C. Subsequently, the substrate after copper plating was placed in an air drying furnace, and heat treatment was performed at 180 ° C. for 30 minutes to obtain a metal-coated polyimide substrate.
Thereafter, the adhesion of the obtained metal-coated polyimide substrate was evaluated. As a result, no abnormality such as peeling was observed in the electronic circuit section. That is, the adhesion between the sputter layer and the electroplating layer was made uniform and high in strength. Furthermore, various characteristics such as suppression of occurrence of pinholes required when this was used as an electronic component such as COF were satisfied.

(Example 2)
Prior to copper plating, a metal-coated polyimide substrate was obtained in the same manner as in Example 1 except that the surface of the sputter substrate was activated. The activation treatment was performed using sulfuric acid having a concentration of 5% by weight at 25 ° C. for 30 seconds.
Thereafter, the adhesion of the obtained metal-coated polyimide substrate was evaluated. As a result, no abnormality such as peeling was observed in the electronic circuit section. That is, the adhesion between the sputter layer and the electroplating layer was made uniform and high in strength. Furthermore, various characteristics such as suppression of occurrence of pinholes required when this was used as an electronic component such as COF were satisfied.

(Example 3)
A metal-coated polyimide substrate was obtained in the same manner as in Example 1 except that the heat treatment was performed at 200 ° C. for 10 minutes under a nitrogen atmosphere (oxygen concentration: 3 ppm).
Thereafter, the adhesion of the obtained metal-coated polyimide substrate was evaluated. As a result, no abnormality such as peeling was observed in the electronic circuit section. That is, the adhesion between the sputter layer and the electroplating layer was made uniform and high in strength. Furthermore, various characteristics such as suppression of occurrence of pinholes required when this was used as an electronic component such as COF were satisfied.

Example 4
A metal-coated polyimide substrate was obtained in the same manner as in Example 1 except that the heat treatment was performed at 120 ° C. for 60 minutes.
Thereafter, the adhesion of the obtained metal-coated polyimide substrate was evaluated. As a result, no abnormality such as peeling was observed in the electronic circuit section. That is, the adhesion between the sputter layer and the electroplating layer was made uniform and high in strength. Furthermore, various characteristics such as suppression of occurrence of pinholes required when this was used as an electronic component such as COF were satisfied.

(Example 5)
A metal-coated polyimide substrate was obtained in the same manner as in Example 1 except that the thickness of the copper layer was changed to 50 nm in sputtering.
Thereafter, the adhesion of the obtained metal-coated polyimide substrate was evaluated. As a result, no abnormality such as peeling was observed in the electronic circuit section. That is, the adhesion between the sputter layer and the electroplating layer was made uniform and high in strength. Furthermore, various characteristics such as suppression of occurrence of pinholes required when this was used as an electronic component such as COF were satisfied.

(Example 6)
A metal-coated polyimide substrate was obtained in the same manner as in Example 1 except that the thickness of the copper layer was changed to 500 nm in sputtering.
Thereafter, the adhesion of the obtained metal-coated polyimide substrate was evaluated. As a result, no abnormality such as peeling was observed in the electronic circuit section. That is, the adhesion between the sputter layer and the electroplating layer was made uniform and high in strength. Furthermore, various characteristics such as suppression of occurrence of pinholes required when this was used as an electronic component such as COF were satisfied.

(Comparative Example 1)
A metal-coated polyimide substrate was obtained in the same manner as in Example 1 except that the heat treatment was performed at 100 ° C. for 120 minutes in the same manner as in Example 1.
Thereafter, the adhesion of the obtained metal-coated polyimide substrate was evaluated. As a result, peeling was observed at the interface between the copper layer formed by sputtering of the electronic circuit portion and the copper coating formed by electroplating.

(Comparative Example 2)
A metal-coated polyimide substrate was obtained in the same manner as in Example 1 except that the heat treatment was performed at 220 ° C. for 5 minutes under a nitrogen atmosphere (oxygen concentration: 3 ppm).
Thereafter, the adhesion of the obtained metal-coated polyimide substrate was evaluated. As a result, no abnormality such as peeling was observed in the electronic circuit section. However, the obtained circuit dimensions differed by 0.05% compared to the dimensions set when forming the electronic circuit by photolithography technique, so that subsequent processing and bonding with the driver IC chip is impossible. became.

(Comparative Example 3)
A metal-coated polyimide substrate was obtained in the same manner as in Example 1 except that the thickness of the copper layer was 40 nm in sputtering.
Thereafter, the adhesion of the obtained metal-coated polyimide substrate was evaluated. As a result, no abnormality such as peeling was observed in the electronic circuit section. However, since the thickness of the circuit portion of the obtained electronic circuit has a difference of 4 μm between the maximum portion and the minimum portion, subsequent processing and bonding to the driver IC chip are impossible.

(Comparative Example 4)
Example 2 except that the activation treatment was performed using an aqueous solution having a sulfuric acid concentration of 5% by weight and an ammonium persulfate concentration of 5% by weight, the treatment conditions were 25 ° C. for 10 seconds, and no heat treatment was performed. Then, a metal-coated polyimide substrate was obtained.
Thereafter, the adhesion of the obtained metal-coated polyimide substrate was evaluated. As a result, peeling was observed at the interface between the copper layer formed by sputtering of the electronic circuit portion and the copper coating formed by electroplating. In addition, a number of disconnections due to pinholes that were thought to exist in the metal layer in the circuit portion were observed.

  As is clear from the above, the method for producing a metal-coated polyimide substrate of the present invention is a liquid crystal screen display driver, particularly as a semiconductor mounting substrate for mounting a driving semiconductor for displaying an image on a liquid crystal screen. It is suitable as a substrate for COF used as a technique for mounting an IC chip. Further, since the thickness of the sputter layer can be reduced, it is possible to realize further higher density of electronic parts such as COF, which is useful for supplying economical products.

It is a figure showing an example of the schematic cross section of the metal coating polyimide substrate obtained by the manufacturing method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polyimide film 2 Nickel-chromium alloy layer 3 Copper layer 4 Copper coating

Claims (3)

  After forming a copper layer having a thickness of 50 to 500 nm on the surface of the metal layer formed on the polyimide film surface by a sputtering method, a substrate formed by forming a copper film on the copper layer by electroplating is used for 120 to 200. A method for producing a metal-coated polyimide substrate, which is subjected to a heat treatment at a temperature of ° C.   The method of manufacturing a metal-coated polyimide substrate according to claim 1, wherein the copper layer has a thickness of 50 to 200 nm.   The method for producing a metal-coated polyimide substrate according to claim 1, wherein the gas atmosphere of the heat treatment is air or neutral atmosphere.

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