JP2007173676A - Circuit formation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an economical circuit formation method by means of a semi-additive method capable of keeping a cross section of a circuit rectangular, and also assuring insulation between circuits. <P>SOLUTION: The circuit formation method includes a step of forming a plated resist layer on part of the surface of an insulator substrate covered with a copper plated conductor layer, a step of thickening copper by a plating method on the copper plated conductor layer exposed on an opening of the resist layer to form a circuit region, a step of forming an organic protective film on the surface of the circuit region of copper formed by the plating method, a step of removing the resist layer, and a step of etching off the copper plated conductor layer exposed by the removing step. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a circuit forming method, and more specifically, a step of forming a plating resist layer on a part of the surface of an insulating substrate coated with a copper plating conductor layer, and a copper plating conductor exposed in the opening of the resist A circuit forming method (hereinafter referred to as semi-additive) including a step of forming a circuit portion by thickening copper on the layer by plating, a step of removing the plating resist layer, and a step of etching away the exposed copper plating conductor layer In other words, the present invention relates to an economical circuit forming method capable of maintaining the cross-sectional shape of the circuit portion in a rectangular shape and ensuring insulation between the circuits with certainty.

  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 in which a copper layer as a good conductor is adhered to a polyimide film that is a high heat resistance and high insulating resin is used, and the copper layer on the substrate is used. After fine patterning by a photolithography technique, a method of coating a desired portion with tin plating and a solder resist is taken.

  As a method for forming a metal layer on the surface of the polyimide film, first, a metal layer such as a nickel-chromium alloy is formed by a sputtering method, and then a copper layer is formed in order to impart good conductivity. At this time, generally, the thickness of the metal 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 plating layer is formed on the metal layer by electroplating or a combination of electroplating and electroless plating. The thickness of the copper plating layer is generally 8 to 12 μm. Here, as the polyimide film, commercially available products such as Kapton EN (manufactured by Toray DuPont), Upilex S (manufactured by Ube Industries) and NPI (manufactured by Kaneka) are used, and generally a thickness of 25 to 38 μm. What has the thickness is used.

  As a circuit formation method using the photolithography technique, a photoresist layer is formed on the surface of the copper plating layer, exposure is performed using a mask having a desired shape, and development processing is performed to form an etching resist layer on the surface of the circuit portion. . Thereafter, the exposed copper plating layer is removed by etching using a copper solution such as ferric chloride to form a circuit. Thereafter, the etching resist layer is removed, and a tin plating film and a solder resist layer are formed on a desired portion of the circuit by an electroless plating method to obtain a COF. Such a circuit formation method is called a so-called subtractive method.

  Further, a semi-additive method has been studied as a method for forming a finer pitch circuit. In this method, a metal layer is first formed on the surface of the polyimide film by an electroless plating method or a sputtering method, and then a copper plating layer having a copper thickness of about 1 μm is formed by an electrolytic copper plating method or the like. Next, using this copper plating layer as a conductor layer, a plating resist layer having a thickness equal to or greater than the circuit thickness is formed on the surface of the copper plating layer by a photolithography technique or the like. Next, copper is thickened to a desired thickness on the surface of the copper plating layer exposed in the resist opening by an electrolytic copper plating method. Thereafter, the plating resist layer is removed, and the exposed copper plating layer and the conductive layer such as the sputtering layer are removed by etching to form a circuit (see, for example, Patent Document 1).

  Here, the advantage of the semi-additive method is that, when the circuit is formed by the above-described subtractive method, the cross-sectional shape of the circuit portion is a mountain shape, whereas the cross-sectional shape of the formed circuit portion is photolithography. Since it is determined by the shape of the plating resist formed by the technique and is substantially rectangular, the circuit formation method is particularly suitable for fine patterning with a narrow circuit width and circuit interval. However, the biggest problem with the semi-additive method is that the circuit section, particularly the circuit bottom, is also etched when the conductor layer, etc., is removed to insulate the circuit after forming the circuit. It is difficult to form a rectangle.

  As a solution to this problem, there has been proposed a method in which after forming a circuit part by copper plating, a metal layer of a type different from the conductor layer is formed as a protective film on the surface of the circuit part. For example, after forming a circuit part by copper plating, the resist part is shrunk by exposure to a vacuum to form a gap in the circuit side wall and the resist side wall, and further, a conductor is formed on the circuit top bottom, side wall part, and resist top bottom by sputtering. A metal layer different from the layer is formed as an etching resist. Here, the conductor layer is any of copper, nickel, chromium, gold, aluminum, zinc, tin, lead, silver, and the protective film is a metal type different from the conductor layer, such as copper, nickel, chromium, gold, It is disclosed that any one of aluminum, zinc, tin, lead, and silver is formed. Specifically, copper is used as the conductor layer, tin is used as the protective film, and etching removal of the conductor layer is performed using a ferric chloride aqueous solution, aluminum as the conductive layer, nickel as the protective film, and the conductor. A method using an aqueous sodium hydroxide solution (for example, see Patent Document 2) is disclosed for etching removal of the layer.

  By the way, in an electronic component such as COF, in practice, copper is generally used as a metal species of a circuit portion from the viewpoint of conductivity, reliability, economy, etc. In this case, tin is used as a protective film. However, when a tin film is formed by electroless plating, the resist layer is peeled off because a strong corrosive solution such as borofluoric acid is usually used as a plating solution at a high temperature of 60 ° C. or higher. This causes the problem of tin plating film deposition on the surface of the conductor layer. In such a case, the portion of the conductor layer where the tin is deposited tends to remain when the conductor layer is etched, and may cause a problem such as a short circuit between circuits. Moreover, as a case where a metal other than tin is formed as the protective film, gold is listed as a candidate, but there is a problem in economical efficiency. When forming a metal other than this as a protective film, it is necessary to use a vacuum film forming process such as a sputtering method. In this case, since the film is formed not only on the circuit bottom but also on the resist surface, Not only does subsequent resist removal be difficult, but there is also a problem in economic efficiency.

From the above situation, there is a need for a circuit forming method that can ensure the insulation between the circuits while keeping the cross-sectional shape of the circuit part rectangular in an economical manner in the circuit forming method by the semi-additive method. Yes.
JP 05-037104 (first page, second page) JP 2004-63643 A (first page, second page)

  In view of the above-described problems of the prior art, an object of the present invention is to economically ensure that the cross-sectional shape of a circuit portion is rectangular and that insulation between circuits is reliably ensured in a circuit forming method by a semi-additive method. Is to provide a simple circuit forming method.

  In order to achieve the above object, the present inventor conducted extensive research on the circuit forming method by the semi-additive method, and as a result, a plating resist layer was formed on a part of the surface of the insulator substrate covered with the copper plating conductor layer. A step of forming, a step of forming a circuit portion by thickening copper by plating on the copper plating conductor layer exposed in the opening of the resist, a step of removing the plating resist layer, and a copper plating conductor exposed thereby In the circuit formation method including the step of removing the layer by etching, the step of forming the organic protective film on the copper surface of the circuit portion is performed prior to the step of removing the plating resist layer. It was found that the insulation between the circuits can be ensured with certainty, and the present invention has been completed.

  That is, according to the first invention of the present invention, the step of forming a plating resist layer on a part of the surface of the insulating substrate coated with the copper plating conductor layer, and the copper plating exposed at the opening of the resist layer A step of thickening copper on the conductor layer by a plating method to form a circuit portion, a step of forming an organic protective film on the surface of the copper circuit portion formed by the plating method, and a step of removing the resist layer And a step of etching away the copper-plated conductor layer exposed thereby, to provide a circuit forming method.

  According to a second aspect of the present invention, there is provided a circuit formation method according to the first aspect, wherein the organic protective film is an alkylimidazole film.

  According to a third aspect of the present invention, there is provided the circuit forming method according to the second aspect, further comprising a step of removing the organic protective film remaining on the surface of the circuit portion with a dilute sulfuric acid solution. Provided.

  According to a fourth invention of the present invention, in any one of the first to third inventions, the step of removing the resist layer and the step of etching away are performed using an alkaline etching solution. A circuit forming method is provided.

  According to a fifth invention of the present invention, in any one of the first to fourth inventions, the insulator substrate coated with the copper-plated conductor layer is a copper-coated polyimide substrate. Law is provided.

  According to a sixth invention of the present invention, in the fifth invention, the copper-coated polyimide substrate is formed by forming a nickel chromium alloy layer and a copper film on a polyimide film by a sputtering method, and then a copper plating conductor layer. A circuit forming method is provided, which is characterized by being formed.

  The circuit forming method of the present invention is a copper-plated conductor layer exposed by removing the resist layer by forming an organic protective film as an etching protective film on the copper-plated surface at the bottom of the circuit in the circuit forming method by the semi-additive method When etching is removed, the cross-sectional shape of the circuit portion can be kept rectangular and insulation between the circuits can be reliably ensured, so that its industrial value is extremely high.

Hereinafter, the circuit forming method of the present invention will be described in detail.
The circuit forming method of the present invention includes a step of forming a plating resist layer on a part of the surface of an insulating substrate coated with a copper plating conductor layer, and plating on the copper plating conductor layer exposed in the opening of the resist layer. A step of thickening copper by a method to form a circuit portion, a step of forming an organic protective film on the surface of the copper circuit portion formed by a plating method, a step of removing the resist layer, and an exposure thereby And a step of etching away the copper-plated conductor layer.

  In the method of the present invention, it is important to form an organic protective film on the surface of copper forming the circuit portion. As a result, when the copper plating conductor layer exposed by removing the resist layer is removed by etching, it acts as a protective film for etching, keeps the cross-sectional shape of the circuit portion rectangular, and ensures insulation between circuits reliably. be able to. That is, as described above, a circuit of an electronic component such as COF is generally formed of copper. In the semi-additive method, since the circuit is usually formed by electroplating, the conductive layer for electroplating is preferably a highly conductive metal, and it is also desirable to use copper. Therefore, as an etching protective film used in the present invention, a film can be selectively formed only on the copper surface without forming a film on the surface of the resist layer, and when the copper plating conductor layer is removed by etching. An organic protective film having a characteristic resistant to rust is used. As a result, the above-described problems of the metal protective film are eliminated.

  The organic protective film used in the method of the present invention is not particularly limited, and can form a film selectively on the copper surface, and has a characteristic that is resistant when the copper plating conductor layer is removed by etching. Examples thereof include films of azoles, thiazoles, pyridinium compounds, and the like, among which alkyl imidazole films having particularly excellent characteristics are preferable. That is, the alkylimidazole film has a characteristic that it is selectively adsorbed only on the copper surface, while being resistant to an alkaline solution and easily dissolved in an acidic solution. In general, alkylimidazole has a thickness at the molecular film level when bonded to copper. Therefore, when an alkylimidazole film is used as a protective film, an alkaline solution is used when the copper plating conductor layer is removed by etching, and further, as in the case of an electronic component that partially forms a tin film on the circuit surface, Thereafter, when it is necessary to peel off the alkylimidazole film, an acidic solution may be used within a range not involving dissolution of copper in the circuit portion.

  The insulator substrate coated with the copper plating conductor layer used in the above method is not particularly limited, and polyimide, polyethylene terephthalate, polypropylene, polycarbonate, polyethylene naphthalate, polyetheretherketone, polyphenylene sulfide, aramid, liquid crystal Polymer film or glass cloth base epoxy resin, glass cloth base bismaleimide triazine resin and other resin plates are used. Among them, the surface of polyimide film, which is highly heat resistant and highly insulating resin, has good conductivity. A copper-coated polyimide substrate formed by closely attaching a copper layer as a body is preferable.

  As the copper-coated polyimide substrate, a copper-coated polyimide substrate composed of three layers obtained by bonding a polyimide film and a copper foil via an adhesive, and a copper-coated polyimide substrate composed of two layers in which a metal layer is directly formed on the polyimide film ( Hereinafter, the two-layer substrate may be referred to as a two-layer substrate. Further, as the two-layer substrate, a direct-sputtering method on a casting substrate obtained by forming a polyimide film on a commercially available copper foil and a commercially available polyimide film. A two-layer plating substrate manufactured by laminating copper by forming a seed layer such as a nickel-chromium alloy layer by electroplating or electroless plating, or a method using a combination of both is provided. Of these, a two-layer plated substrate is preferred. As a result, a fine pitch circuit such as COF can be formed.

  Although it does not specifically limit as said polyimide film, When using as a raw material of COF which is the mounting method of the driver IC for liquid crystal displays, as thickness, 25-50 micrometers is preferable and 30-40 micrometers is more preferable. . For example, Kapton 150EN (made by Toray DuPont), Upilex 35S (made by Ube Industries), etc. are suitable.

  The alloy composition and thickness of the nickel chrome alloy layer are not particularly limited, but the copper conductor layer and the etching together with adhesion to the polyimide film, insulation reliability between circuits, and long-term stability of various characteristics. Considering that the etching can be economically performed if the properties are similar, it is preferable that the chromium concentration in the alloy layer is 5 to 30% by weight and the thickness of the alloy layer is 5 to 50 nm.

  The two-layer plating substrate is preferably a substrate in which a copper-plated conductor layer is formed on a polyimide film after a nickel chromium alloy layer and a copper coating are formed by a sputtering method. That is, after forming the nickel chromium alloy layer by sputtering and before electroplating, a copper film can be subsequently formed by sputtering in order to ensure the conductivity of the sputtering layer. This copper film is formed for imparting conductivity to the seed layer in order to uniformly and smoothly deposit by electroplating, and the thickness is preferably 50 to 500 nm. That is, if the thickness is less than 50 nm, sufficient conductivity cannot be obtained, and there is a possibility of adversely affecting the copper deposition uniformity by the subsequent electroplating. On the other hand, if the thickness exceeds 500 nm, it is convenient in terms of imparting conductivity, but COF and the like can be obtained due to the influence of substrate dimensional change, deformation, etc. due to the increase of thermal history strength to the polyimide film by sputtering. There are concerns about adverse effects on the product.

  In addition, the thickness of the copper conductor layer including the copper coating and the copper plating conductor layer is preferably 100 nm to 2000 nm in consideration of circuit conductivity, etching property, and the like. That is, if the thickness is less than 100 nm, the thickness of the circuit portion formed by plating in the opening of the resist in the subsequent process is likely to vary, and further, bonding failure may occur in the subsequent ILB or OLB process. There is. On the other hand, if the thickness exceeds 2000 nm, it is convenient in terms of conductivity, but it is necessary to enhance the strength of the etching process when the copper plating conductor layer is removed by etching, so that the rectangular shape of the circuit cross section must be maintained. Can be difficult.

  Below, the circuit formation method by the semi-additive method used for the method of this invention is demonstrated. The circuit forming method includes a step of forming a plating resist layer on a part of the surface of an insulating substrate covered with a copper plating conductor layer, and a plating method on the copper plating conductor layer exposed in the opening of the resist. A step of forming a circuit portion by thickening copper, a step of forming an organic protective film on the copper surface of the circuit portion, a step of removing the plating resist layer, and a step of etching away the exposed copper plating conductor layer For example, each process is performed as follows.

  In the step of forming the plating resist layer, a photosensitive resin layer is formed on the surface of the copper conductor film, and a part of the photosensitive resin layer is polymerized by ultraviolet light transmitted through a mask having a desired shape, and then a weak alkaline solution or the like. , The unexposed portion is dissolved and removed, and the remaining resin portion is cured by baking to obtain a plating resist. Here, the thickness of the resist layer may be a thickness necessary to obtain a desired circuit thickness. For example, when the thickness of the conductor layer is 1 μm and the total thickness of the circuit is 8 μm, The resist thickness may be 7 μm or more. Here, the photosensitive resin layer is not particularly limited, and is selected from a liquid type, a film type, and the like.

The step of forming a circuit portion by thickening copper in the opening of the resist is performed by a general copper plating method using a copper sulfate bath.
In the step of forming an organic protective film on the copper surface of the circuit part, for example, when an alkylimidazole film is used, the alkylimidazole is adsorbed only on the copper surface by treating the copper surface with a solution containing the alkylimidazole. Thereafter, the film strength is increased by heat treatment as necessary.

The step of removing the plating resist layer is generally performed by dissolving or swelling and peeling with a strong alkaline solution.
In the step of removing the exposed copper-plated conductor layer by etching, an alkaline solution may be used as described above, and for example, it can be removed by etching with an ammoniacal solution.

  Thereafter, when the nickel chromium alloy layer remains on the polyimide film surface after the copper conductor layer is removed by etching, the copper conductor layer is treated with a solution capable of selectively dissolving the nickel chromium alloy layer in the presence of copper. If necessary, the organic protective film may be peeled and removed. If an alkylimidazole film is used, the copper can be peeled and removed with a dilute sulfuric acid solution without substantially dissolving it.

  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 analysis of the plating solution used by the Example and the comparative example was performed by the ICP emission analysis method.

Example 1
A circuit formation method based on the semi-additive method of the present invention will be described in accordance with the steps of FIG. FIG. 1 shows steps (1) to (8) of the circuit forming method of the present invention.
In step (1) of FIG. 1, Kapton 150EN (manufactured by Toray DuPont) is used as the polyimide film 1 and heat treatment is performed at 150 ° C. for 1 minute in a chamber maintained at a vacuum degree of 0.01 to 0.1 Pa. It was. Subsequently, a nickel chromium alloy layer 2 having a thickness of 20 nm and a copper film 3 having a thickness of 100 nm were formed on the surface of the polyimide film by sputtering using a nickel chromium alloy target containing 20% by weight of chromium and a copper target. Thereafter, a plating solution containing 180 g / L of sulfuric acid, 80 g / L of copper sulfate, 50 mg / L of chloride ions, and an organic additive having an action of smoothing the plating surface on the surface of the copper coating 3, A copper-coated polyimide substrate covered with a copper conductor layer was obtained by forming a copper-plated conductor layer 4 having a thickness of 1 μm by electroplating.

  In step (2), an alkali development type photoresist PMER manufactured by Tokyo Ohka Kogyo Co., Ltd. was applied to the copper surface of the copper-coated polyimide substrate and prebaked, and then a resist layer having a thickness of 8 μm was formed. Thereafter, the resist layer is irradiated with ultraviolet rays through an ultraviolet irradiation mask having a pitch of 15 μm at the inner lead portion, and then the ultraviolet unirradiated portion is dissolved and removed using an alkaline solution, followed by post-baking and a plating resist layer. 5 was formed.

In the step (3), the surface of the copper plating conductor layer 4 exposed in the resist opening formed in the step (2) is thickened with a thickness of 8 μm using the above plating solution, and the circuit portion 6 Formed.
In step (4), after treating the copper plating surface for 20 seconds at 30 ° C. using Glycoat T made of Shikoku Kasei Co., which contains alkylimidazole, the surface of the circuit part 6 is dried on the surface of the circuit part 6 by drying for 10 minutes at 80 ° C. A film 7 was formed.
In step (5), the plating resist layer 5 was dissolved and removed using an aqueous sodium hydroxide solution.

In the step (6), the copper plating conductor layer 4 exposed in the step (5) is made of cupric chloride at 100 g / L, ammonium chloride at 100 g / L, 29% ammonia water at 400 mL / L, and ammonium carbonate at 10 g. The copper plating layer 4 and the copper coating 3 were removed by etching using a solution containing / L at 25 ° C. for 1 minute.
In step (7), the top lip BT manufactured by Okuno Pharmaceutical Co., Ltd. was used, and the nickel chromium alloy sputtered layer 2 remaining between the circuits was removed by treatment at 25 ° C. for 2 minutes.
In step (8), the alkylimidazole film 7 was removed by etching to obtain a substrate on which a circuit was formed.

  A circuit having an inner lead pitch of 15 μm was formed by the above process. As a result of measuring the cross section of the inner lead portion of the obtained circuit, it was a rectangular shape having a height of 8 μm, an upper base of 12 μm, and a lower base of 12 μm. In addition, insulation between circuits could be secured.

(Comparative Example 1)
Except that the formation of the alkylimidazole film in the step (4) shown in FIG. 1 was omitted, a circuit having an inner lead portion 15 μm pitch was formed in the same manner as in Example 1. As a result of measuring the cross section of the inner lead part of the obtained circuit, the height was 7 μm, the upper base was 7 μm, and the lower base was 12 μm, which was compared with the circuit obtained in Example 1. Inferior in conductivity.

  As described above, in Example 1, since the alkyl imidazole film was formed as the organic protective film in the circuit forming method by the semi-additive method and performed according to the method of the present invention, the rectangular shape of the circuit portion was maintained and It can be seen that the insulation can be secured. On the other hand, in Comparative Example 1, since the organic protective film was not formed, the rectangular shape of the circuit portion is not maintained.

  As described above, a semiconductor package such as a COF having a circuit portion obtained by the method of the present invention can obtain a circuit having a rectangular cross-sectional shape, which is an advantage inherent in the semi-additive method. It can fully contribute to density packaging.

It is a figure explaining the process of the circuit formation method of this invention. Example 1

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polyimide film 2 Nickel chromium alloy layer 3 Copper coating 4 Copper plating conductor layer 5 Plating resist layer 6 Circuit part 7 Alkyl imidazole film

Claims (6)

  Forming a plating resist layer on a part of the surface of the insulating substrate coated with the copper plating conductor layer, and thickening copper by a plating method on the copper plating conductor layer exposed in the opening of the resist layer; The step of forming the circuit portion, the step of forming an organic protective film on the surface of the copper circuit portion formed by plating, the step of removing the resist layer, and the copper plating conductor layer exposed thereby are removed by etching. A circuit forming method comprising the steps of:   The circuit forming method according to claim 1, wherein the organic protective film is an alkylimidazole film.   The circuit forming method according to claim 2, further comprising a step of removing the organic protective film remaining on the surface of the circuit portion with a dilute sulfuric acid solution.   The circuit forming method according to claim 1, wherein the step of removing the resist layer and the step of removing the resist layer are performed using an alkaline etching solution.   The circuit forming method according to claim 1, wherein the insulating substrate covered with the copper plating conductor layer is a copper-coated polyimide substrate.   6. The circuit formation according to claim 5, wherein the copper-coated polyimide substrate is obtained by forming a copper-plated conductor layer on a polyimide film after forming a nickel chromium alloy layer and a copper film by a sputtering method. Law.

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