JP2007123622A - Flexible printed circuit and method of manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible printed circuit with high reliability wherein wiring adhesion strength is high even if forming a micro patterning, and to provide a method of manufacturing the same. <P>SOLUTION: In the method, a photo resist layer is formed on a metal seed layer formed on at least one side of an insulation film, conductor plating is applied to a photo resist pattern obtained by etching the photo resist layer, and the photo resist pattern is exfoliated and removed to form a metal wiring layer, after the photo resist pattern is exfoliated and removed. The side face of the metal wiring layer is etched until an undercut is removed on a lower part of the side face of the metal wiring layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor package wiring board used for various electric devices and a method for manufacturing the same, and more particularly to a flexible wiring board in which a wiring circuit on an insulating film is formed by plating and a method for manufacturing the same.

TAB (Tape Automated Bonding) tapes and printed wiring boards, which have dramatically increased in use with the development of electronic equipment, are generally so-called copper-clad glass in which a copper film is formed on a glass epoxy board. Epoxy resin substrates are often used. The copper-clad glass epoxy resin substrate is formed by laminating an adhesive-coated copper foil with an adhesive coated on the surface in advance and a glass epoxy plate obtained by impregnating a glass cloth with an epoxy resin. They are manufactured by a method obtained by bonding them together, a method of laminating a glass epoxy resin laminate molding material and a copper foil, and thermocompression bonding.
However, as printed wiring boards are widely used in consumer equipment such as televisions and cameras, and various industrial equipment such as computers, high-density wiring has been required, so that fine circuits can be formed with high accuracy. In addition, the thickness of the copper coating layer has been further reduced.
Therefore, the development of forming a copper coating by electroless plating is progressing with the copper-clad glass epoxy resin substrate as the copper coating layer becomes thinner.

In general, a TAB tape or a flexible wiring board forms a photoresist layer on a copper foil formed on an insulating film such as a polyimide film, and forms a wiring circuit by etching the copper foil. A semi-additive method that is advantageous for forming fine wiring has been proposed because of the demand for higher density (see, for example, Patent Document 1).
In the semi-additive method, a photoresist pattern is formed on a metal seed layer formed on an insulating film, and a conductive metal plating is applied to the surface of the metal seed layer exposed along the photoresist pattern to form a metal wiring. In this method, a circuit is formed, and then the resist is removed and removed, and the remaining metal seed layer is removed by etching.
The flexible wiring board obtained in this way is superior in thermal reliability of circuit adhesive strength and electrical insulation between circuits because no adhesive is interposed on the interface between the metal coating and the glass epoxy resin. There are benefits to be gained.
Recently, a full additive method in which a metal catalyst layer is formed on an insulating film without forming a metal seed layer, a resist is formed, and a metal is plated to form a circuit has been studied.

The conventional semi-additive method will be described below with reference to FIG.
First, as shown in FIG. 4A, a nickel / chromium alloy layer as a first metal seed layer 2 and a copper sputter layer as a second metal seed layer 3 are formed on an insulating film 1 made of polyimide or the like. A photoresist layer 17 is formed on the surface of a layer CCL (Copper Clad Laminate) substrate using a dry film resist or the like.
Next, as shown in FIG. 4B, the photoresist layer 17 is exposed using a desired circuit pattern mask 18 and developed to form a photoresist pattern 7. At this time, the width W of the wiring circuit pattern is formed to be the same as the desired wiring circuit width. In the case of FIG. 4, the interval W between the metal wiring layers is the same as the wiring circuit width.
When the photoresist layer 17 is exposed and etched, it is difficult to vertically etch the deepest part of the resist layer, so that a resist overhanging part 27 is formed in the deepest part of the resist layer.
Next, as shown in FIG. 4C, the exposed portion of the photoresist pattern 7 is plated using a copper sulfate plating bath or the like to form a metal wiring layer. Thereafter, the photoresist pattern 7 is peeled and removed. At this time, the constriction 14 is generated in the metal wiring layer along the protruding portion 27 of the resist.

Next, as shown in FIG. 4D, the second metal seed layer 3 made of a copper sputter layer exposed between the metal wiring layers is removed by etching. For etching the second metal seed layer 3 made of a copper sputter layer, a soft etching solution made of sulfuric acid and hydrogen peroxide is often used.
Next, as shown in FIG. 4E, the nickel / chromium alloy layer, which is the first metal seed layer 2, is removed by etching with a commercially available dedicated solution.
Thereafter, as shown in FIG. 4F, an insulating protective film 5 is formed around the metal wiring layer 4 as necessary.
FIG. 5 shows an enlarged cross-sectional structure of the wiring circuit portion of the circuit board thus obtained.
Japanese Patent Application Laid-Open No. 08-064930

However, in the above-described conventional method for manufacturing a flexible wiring board, the resist bottom portion (resist overhanging portion) generated on the lower surface of the outer periphery of the formed photoresist pattern causes a lower portion of the side surface of the metal wiring layer after plating to be formed as shown in FIG. As shown in FIG. 3, a region where the metal wiring layer is not bonded to the substrate, that is, a so-called undercut 9 occurs.
Due to the undercut 9, the adhesive width w between the insulating film 1 and the metal wiring layer becomes narrower than the width W of the metal wiring layer, which causes a decrease in the adhesive strength of the metal wiring layer. For this reason, particularly in the formation of fine wiring with a metal wiring layer width W of 15 μm or less, the wiring circuit width itself becomes narrow, so the ratio of the bonding width w to the wiring circuit W width decreases, and the decrease in bonding strength becomes more serious. It was. The undercut depth D is expressed by (W−w) / 2, and when D exceeds 7.5% of W, a decrease in adhesive strength becomes a serious problem.
An object of the present invention is to solve such problems and propose a highly reliable flexible wiring board having a high metal wiring layer adhesion strength in the formation of a fine wiring circuit and a method for producing the same.

In order to solve the above-described problems, the present invention removes an undercut portion caused by a resist skirt residue by etching a side surface of a wiring after plating.
For this purpose, the width of the metal wiring layer is made thick beforehand, and a desired dimension is obtained after the side surface of the metal wiring layer is etched together with the undercut.
By doing so, undercuts can be easily reduced, and it is possible to provide a flexible wiring board with high wiring adhesive strength even in the formation of fine wiring.

That is, one of the methods for producing a flexible wiring board of the present invention is a photoresist obtained by forming a photoresist layer on a metal seed layer formed on at least one side of an insulating film and etching the photoresist layer. In a method of manufacturing a flexible wiring board in which a conductive plating is applied to a pattern and then the photoresist pattern is peeled and removed to form a metal wiring layer, the photoresist pattern is peeled and removed, and then present on the lower side of the metal wiring layer. The side surface of the metal wiring layer is etched until the undercut is removed.
Another method for producing a flexible wiring board according to the present invention is a photoresist obtained by forming a photoresist layer on a metal seed layer formed on at least one surface of an insulating film and etching the photoresist layer. In the method for manufacturing a flexible wiring board in which a conductive plating is applied to the pattern, and then the photoresist pattern is peeled and removed to form a metal wiring layer, the photoresist pattern is peeled and removed, and then the metal seed layer is etched, The side surface of the metal wiring layer is etched until the undercut existing at the lower side of the side surface of the metal wiring layer is removed.

In the method for producing a flexible wiring board of the present invention, it is preferable that the photoresist pattern is formed so that the width of the metal wiring layer after plating is 1 to 5 μm wider than the width of the desired metal wiring layer.
The metal seed layer is preferably copper or a copper alloy.
Furthermore, it is preferable that the metal seed layer comprises a first metal seed layer made of nickel, chromium or an alloy thereof and a second metal seed layer made of copper or a copper alloy.

In the method for manufacturing a flexible wiring board according to the present invention, the metal wiring layer and the undercut etching under the metal wiring layer can be removed by spray etching.
If these manufacturing methods are employed, a flexible wiring board having high wiring adhesive strength and high reliability can be reliably provided by a simple method.

Also, one of the flexible wiring boards of the present invention is a flexible wiring board obtained by the above manufacturing method, wherein the width of the metal wiring layer is in the range of 5 to 15 μm and is insulated from the metal wiring layer. The depth of the undercut existing between the films is in the range of 0.21 to 1.0 μm from the side surface of the metal wiring layer.
If the flexible wiring board having such a structure is used, a flexible wiring board having a high bonding strength of the metal wiring layer can be obtained even in a fine wiring.
Furthermore, in another flexible wiring board of the present invention, the insulating film is made of a polyimide resin, and the metal wiring layer is formed on the surface of a two-layer CCL substrate made of a nickel-chromium alloy layer and a copper sputter layer. It is characterized by.
With a flexible wiring board having such a structure, circuit wiring having excellent durability and good conductivity can be formed, so that a fine circuit can be formed and can greatly contribute to miniaturization of electronic equipment.

  As described above, according to the present invention, it is possible to reduce the undercut at the lower side of the metal wiring layer, and it is possible to provide a flexible wiring board with high wiring adhesion strength and high reliability in the formation of fine wiring.

First, the flexible wiring board of the present invention will be described.
FIG. 1 is a cross-sectional view showing a structure in the vicinity of a metal wiring layer of a flexible wiring board according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view showing the structure in the vicinity of the metal wiring layer of the flexible wiring board according to the second embodiment of the present invention.
The flexible wiring board according to the first embodiment of the present invention shown in FIG. 1 is a wiring board in which a metal wiring layer 4 is formed by plating on one side of an insulating film 1, and the metal wiring layer 4 is insulated over its entire width. A flexible wiring board bonded to the film 1.
Since this flexible wiring board has a large contact area between the metal wiring layer 4 and the insulating film 1, it is a flexible wiring board having high bonding strength and high reliability even if it becomes a fine wiring.

The flexible wiring board according to the second embodiment of the present invention shown in FIG. 2 is a flexible wiring board in which the metal wiring layer 4 is formed by plating on one side of the insulating film 1, and the entire width of the metal wiring layer 4 is 85. ˜95% is a flexible wiring board bonded to the insulating film 1. That is, the width w at which the metal wiring layer 4 is bonded to the insulating film 1 is 85 to 95% of the width W of the metal wiring layer 4 (w / W = 0.85 to 0.95). The width d of the undercut 9 of the metal wiring layer 4 has a relationship of d = (W−w) / 2. In other words, if the width d of the undercut 9 is in the range of d = [1- (0.85 to 0.95)] W / 2, the bonding strength does not fall short, and the highly reliable flexible wiring board. It becomes.
In forming the flexible wiring board, it is quite difficult from the viewpoint of manufacturing yield to completely eliminate the undercut of the metal wiring layer, so that even if some undercut remains, it can contribute to the improvement of the bonding strength.

Next, an example of a method for manufacturing a flexible wiring board according to the present invention will be described with reference to the drawings.
FIG. 3 is a cross-sectional process diagram illustrating a method for manufacturing a flexible wiring board according to the present invention.
First, as shown in FIG. 3A, two layers in which a first metal seed layer 2 made of nickel / chromium alloy and a second metal seed layer 3 made of a sputtered copper film are formed on one surface of an insulating resin film 1. A photoresist layer 17 made of a dry film is formed on a surface of a copper sputter layer forming the second metal seed layer 3 of a CCL (Copper Clad Laminate) substrate by a laminating method.
Next, as shown in FIG. 3B, the photoresist layer 17 is exposed using a desired circuit pattern mask 18 and developed to form a photoresist pattern 7. The circuit pattern mask 18 at this time is corrected so that the circuit wiring width is widened in advance because the circuit wiring width is reduced by etching in a later process. That is, the width W ′ of the circuit pattern mask 18 for circuit wiring is set wider than the width W of the desired metal wiring layer in anticipation of the width to be etched in the etching process. On the contrary, the interval W ″ between the metal wiring layers is made narrower than the desired width W of the metal wiring layer. That is, the relationship W ″ <W <W ′ is established in FIG. The ratio of widening (W′−W) is set to be 0.5 to 3 times, preferably 1 to 3 times wider than the undercut width that will be generated due to the etching process. Although the undercut width depends on the resist, for example, RY3215 manufactured by Hitachi Chemical Co., Ltd. may generate approximately 0.5 to 1.5 μm. In this case, the width of the metal wiring layer is desirably corrected by 1 to 5 μm wider in the resist pattern than the target metal wiring layer width.

Next, as shown in FIG. 3C, the metal wiring layer 4 is formed by performing copper plating on the surface of the copper sputter layer exposed at the opening of the photoresist pattern 7. For the copper plating, a commercially available copper sulfate plating bath can be used. Thereafter, the photoresist pattern 7 is peeled off using a sodium hydroxide aqueous solution or the like.
Next, as shown in FIG. 3D, the copper sputter layer exposed between the circuit wirings is removed by etching using a commercially available soft etching solution to expose the nickel / chromium alloy layer. At this time, the side surface 4a of the metal wiring layer 4 is also etched at the same time or thereafter, so that the etching is performed in excess of the conventional copper sputtering only. Further, it is preferable to use spray etching in order to provide selectivity of the etching rate between the upper surface of the circuit metal wiring and the side surface of the metal wiring layer, and to facilitate the etching of the side surface of the metal wiring layer.
Further, at this time, the metal wiring layer is thinned by etching the side surface of the metal wiring layer, but a desired metal wiring layer width W is obtained here.

Next, as shown in FIG. 3E, the exposed nickel / chromium alloy layer is removed using a commercially available nickel / chromium selective etching solution or the like.
Thereafter, as shown in FIG. 3F, an insulating protective film 5 is formed around the metal wiring layer 4 as necessary, as in the conventional technique.

According to the above process, the etching is difficult to proceed in the undercut portion where the gap is narrow, and the side surface of the metal wiring layer where the circulation of the etching solution is good is likely to proceed. For this purpose, it is possible to reduce the undercut by forming a large metal wiring layer width in advance and performing excessive etching in the step of FIG.
Further, the same effect can be obtained by performing only the conventional copper sputter etching in the step 3 (d) and then etching the side surfaces of the circuit wiring after the step of FIG. 3 (e).
[Examples and Comparative Examples]
Hereinafter, examples and comparative examples according to the present invention will be described.

A flexible circuit board was produced according to the process diagram shown in FIG.
In this example, a two-layer CCL substrate in which a nickel / chrome layer having a thickness of 170 mm and a copper sputter layer having a thickness of 0.1 μm formed on a polyimide film having a thickness of 38 μm by a sputtering method was used.
First, as shown in FIG. 3A, a dry film resist (product name RY-3215: manufactured by Hitachi Chemical Co., Ltd.) was laminated on the surface of the copper sputter layer.
Next, as shown in FIG. 3B, exposure was performed at an illuminance of 40 mJ, a resist film was brought into contact with a 1% sodium carbonate aqueous solution at a temperature of 30 ° C., and development was performed to form a resist circuit pattern. At this time, the exposure pattern mask had a final line / space width of 10 μm / 10 μm, and the width of the circuit wiring pattern was increased by 3 μm to 13 μm / 7 μm.

Next, as shown in FIG.3 (c), about 9 micrometers thick copper plating was performed using the commercially available copper sulfate plating bath. Thereafter, the dry film resist was peeled and removed using an aqueous sodium hydroxide solution having a concentration of 5%.
Next, as shown in FIG. 3 (d), using a soft etching solution (product name: CPE800: manufactured by Hishie Chemical Co., Ltd.) whose main components are sulfuric acid and hydrogen peroxide, a temperature of 30 ° C. and a pressure of 0.1 MPa. For about 30 seconds.

Next, as shown in FIG. 3 (e), the exposed nickel / chromium alloy layer was immersed for 2 seconds at a temperature of 40 ° C. using a commercially available nickel / chromium selective etching solution (product name CH1920: manufactured by MEC Co., Ltd.). The nickel / chromium alloy layer was removed.
The results of Table 1 were obtained by measuring the wiring peel strength of the obtained flexible wiring board and measuring the circuit wiring dimensions by the cross section.

(Comparative Example 1)
A flexible circuit board was produced based on the process diagram of FIG.
In this comparative example, two layers in which a nickel / chromium layer having a thickness of 170 mm and a copper sputter layer having a thickness of 0.1 μm formed on a polyimide film having a thickness of 38 μm and a copper sputtering layer having a thickness of 0.1 μm were formed on a polyimide film having a thickness of 38 μm. A CCL substrate was used.
First, as shown in FIG. 4A, a dry film resist (product name RY-3215: manufactured by Hitachi Chemical Co., Ltd.) was formed on the surface of the copper sputter layer by the laminating method as in Example 1 of the present invention.
Next, as shown in FIG. 4B, exposure was performed at an illuminance of 40 mJ, and the resist film was brought into contact with a 1% sodium carbonate aqueous solution at a temperature of 30 ° C. for development. At this time, the exposure pattern mask had a line / space width of 10 μm / 10 μm as the final target.

Next, as shown in FIG.4 (c), about 8 micrometers thick copper plating was performed using the commercially available copper sulfate plating bath. Thereafter, the dry film resist was peeled and removed using an aqueous sodium hydroxide solution having a concentration of 5%.
Next, as shown in FIG. 2 (d), using a soft etching solution (product name: CPE800: manufactured by Hishie Chemical Co., Ltd.) whose main components are sulfuric acid and hydrogen peroxide, immersion is performed for about 15 seconds at a temperature of 30 ° C. Processed.
Finally, as shown in FIG. 2 (e), the exposed nickel / chromium alloy layer is immersed in a commercially available nickel / chromium selective etching solution (product name CH1920: manufactured by MEC Co., Ltd.) for 2 minutes at a temperature of 40 ° C. / The chromium alloy layer was removed.

  Measurement of the wiring peel strength of the obtained flexible wiring board and measurement of the circuit wiring dimensions by the cross section were performed, and the results shown in Table 2 were obtained.

  Comparing Table 1 and Table 2, it was confirmed that in Comparative Example 1, the undercut depth was larger than that in Example 1 and the joining ratio was low, so the peel strength was low.

It is sectional drawing which shows the structure of the flexible wiring board which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the structure of the flexible wiring board which concerns on the 2nd Embodiment of this invention. It is sectional process drawing explaining the manufacturing method of the flexible wiring board of this invention. It is sectional process drawing explaining the manufacturing method of the conventional flexible wiring board. It is sectional drawing explaining the structure of the conventional flexible wiring board.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Insulating film 2 1st metal seed layer 3 2nd metal seed layer 4 Metal wiring layer 5 Insulating film 7 Photoresist pattern 9 Undercut 14 Constriction 17 Photoresist layer 18 Pattern mask 27 Overhang | projection part

Claims (8)

A photoresist layer is formed on the metal seed layer formed on at least one surface of the insulating film, the photoresist pattern obtained by etching the photoresist layer is subjected to conductor plating, and then the photoresist pattern is peeled and removed. In the manufacturing method of the flexible wiring board formed with the metal wiring layer,
A method of manufacturing a flexible wiring board, comprising: removing the photoresist pattern and etching the side surface of the metal wiring layer until an undercut existing at a lower portion of the side surface of the metal wiring layer is removed. A photoresist layer is formed on the metal seed layer formed on at least one surface of the insulating film, the photoresist pattern obtained by etching the photoresist layer is subjected to conductor plating, and then the photoresist pattern is peeled and removed. In the manufacturing method of the flexible wiring board formed with the metal wiring layer,
After peeling off the photoresist pattern, the metal seed layer is etched, and at the same time, the side surface of the metal wiring layer is etched until the undercut existing at the lower side of the side surface of the metal wiring layer is removed. Manufacturing method of flexible wiring board.   3. The flexible wiring according to claim 1, wherein the photoresist pattern is formed so that a width of the metal wiring layer after plating is 1 to 5 [mu] m wider than a width of a desired metal wiring layer. A method for manufacturing a substrate.   The method of manufacturing a flexible wiring board according to claim 1, wherein the metal seed layer is copper or a copper alloy.   The said metal seed layer consists of a 1st metal seed layer which consists of nickel, chromium, or these alloys, and a 2nd metal seed layer which consists of copper or a copper alloy, The any one of Claims 1-4 characterized by the above-mentioned. The manufacturing method of the flexible wiring board as described in a term.   6. The method for manufacturing a flexible wiring board according to claim 1, wherein undercut etching removal of the lower surface of the metal wiring layer and / or the metal wiring layer is performed by spray etching.   It is a flexible wiring board obtained by the manufacturing method of any one of Claims 1-6, Comprising: The width | variety of the said metal wiring layer exists in the range of 5-15 micrometers, and between this metal wiring layer and an insulating film. A flexible wiring board having an undercut depth in the range of 0.21 to 1.0 μm from the side surface of the metal wiring layer. 8. The flexible wiring board according to claim 7, wherein the insulating film is made of a polyimide resin, and the metal wiring layer is formed on the surface of a two-layer CCL base material made of a nickel-chromium alloy layer and a copper sputter layer. .

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