JP2010114177A - Method of forming printed circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of forming a printed circuit board capable of reliably removing dummy wiring formed together with wiring. <P>SOLUTION: In the method of forming the printed circuit board, the printed circuit board for which a conductive layer is formed on a resin layer is prepared, conductor wiring and the dummy wiring are formed by metal-etching the conductive layer, and the dummy wiring is removed by resin etching. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a printed wiring board by a semi-additive method.

  Conventionally, for example, a printed wiring board formed by laminating a conductive wiring layer on an organic resin insulating layer is known. When the wiring layer is formed on the surface of the insulating layer, a method of forming the wiring layer by pattern plating on the surface of the insulating layer, a so-called semi-additive method is common.

  A method for forming a wiring layer by a semi-additive method mainly includes the following steps. First, a plating seed layer which is a conductive layer necessary for performing subsequent electrolytic plating is formed on the surface of the organic resin insulating layer. A plating resist layer having a predetermined pattern of openings is formed on the plating seed layer.

  A wiring layer is formed in the opening of this pattern by electrolytic plating. Subsequently, the plating resist is removed. Next, a wiring pattern is formed by etching away an excess seed layer corresponding to the portion from which the plating resist has been removed.

  By the way, in a general printed wiring board product, places where patterns are densely populated and places where the patterns are relatively sparse are mixed in the plane of the wiring board. Then, a current concentrates locally at the pattern end portion where the dense pattern is interrupted and becomes a region without a pattern, and the phenomenon that the plating thickness becomes thicker than other wiring portions occurs.

As means for avoiding current concentration, a method of providing an insulating current shield between the anode and the cathode, a method of using an auxiliary electrode, and a method of providing a dummy pattern in a sparse pattern density (Patent Document 1, In addition to these, in recent years, there has been a demand for the development of a method that can deal with finer uniformization as the wiring density becomes higher and finer.
JP 55-85691 A Japanese Utility Model Publication No. 61-34771 Japanese Patent Laid-Open No. 03-1204090

Conventionally, the dummy wiring is left in the product together with the necessary wiring. This is because the dummy wiring is electrically isolated and is considered to have no functional problem. However, in recent years, with the increase in density and miniaturization of wiring, for example, the following points are problematic because the dummy wiring is left in the vicinity of the necessary wiring.
1) When mounting functional parts such as other resistors and ICs on the wiring board, there may be a case where the mounting position is erroneously recognized due to the dummy wiring. This is because disturbance may occur in image recognition of so-called “recognition marks” provided to assist position recognition in addition to erroneously recognizing dummy wirings as necessary wirings during positioning by image recognition.
2) When mounting functional components, the dummy wiring may come in contact with the mounting position, which may cause a functional error problem although it is not fatal to the electrical function. In many cases, it is regarded as a defect in the mounting process.
3) In addition, disturbance may occur in product inspection using image recognition and electrical product inspection.

  Further, in order to avoid the above problem, there is a method of moving the dummy wiring away from the necessary wiring, but there is a problem that the effect of providing the dummy wiring and making the wiring thickness uniform is reduced.

  By the way, as a method of removing dummy wiring unnecessary in terms of function, a method of attaching a conductive tape in the vicinity of the wiring pattern, or a method of previously printing a conductive paste in a resist film shape on the resist opening near the required wiring pattern In addition, a method of removing the resist together with the resist film is known (see Patent Document 3).

  These are effective means in order not to leave dummy wirings that are not functionally necessary in the final product. However, with these methods, there is a limit to the distance at which the dummy wiring is brought close to the necessary wiring, and the current concentration reduction effect is low. In addition, the dummy wiring must be formed in a separate process from the necessary wiring formation. There is a practical problem that it is necessary to perform precise positioning when placing the wiring near the necessary wiring with high accuracy.

  The present invention has been made in consideration of the above-described points, and an object of the present invention is to provide a method for forming a printed circuit board that can reliably remove the dummy wiring formed together with the wiring.

In order to achieve the above object, in the present invention,
Prepare a printed wiring board with a conductive layer formed on the resin layer,
Conductor wiring and dummy wiring are formed by metal etching the conductive layer,
A method of forming a printed wiring board, wherein the dummy wiring is removed by resin etching;
Is to provide.

  According to the present invention, dummy wiring for suppressing variation in the thickness of necessary wiring can be accurately arranged by photomask exposure without being performed in another process such as mask printing, and further, unnecessary dummy wiring can be removed. And solve functional problems.

<Elemental technology of the invention>
The method for forming a printed circuit board according to the present invention uses several elemental technologies to selectively remove only dummy wirings while forming dummy wirings by a known semi-additive method in which copper wiring is formed simultaneously with necessary wirings. .

  (1) Resin etching, (2) Dummy wiring configuration, (3) Insulating base material, (4) Resin etchant, and (5) Post-treatment will be described as each treatment in the present invention.

(1) Resin Etching The insulating resin disposed under the conductor wiring of the wiring board can be etched by an alkaline resin etching method or a plasma resin etching method. This resin etching is a method widely used to remove unnecessary burrs and smears around the hole and the inner wall, especially after drilling with a laser, drill, etc. in a multilayer wiring board or double-sided wiring board, A plurality of methods may be used alone or in combination depending on the type of resin and the required amount of treatment.

  By the way, when these resin etchings are performed on the wiring pattern, the etching effect does not stop only on the resin surface of the wiring gap but progresses to the conductor wiring-resin interface depending on the degree of processing. If excessive treatment is performed, the adhesion between the conductor wiring and the underlying resin is reduced, and eventually the conductor wiring is peeled off from the underlying resin.

  The stripping time of the conductor wiring from the base resin depends on the wiring-underground resin remaining adhesion width as the resin etching progresses. However, the thick wiring of the original wiring-resin adhesion width peels off later.

  The inventor of the present invention appropriately selects a wiring pattern (for example, dummy wiring) to be peeled and removed and a line width of a necessary wiring that is not to be peeled and removed, and further appropriately selects a resin etching amount, thereby performing resin etching. It has been found that only unnecessary conductor wiring can be selectively removed to leave necessary wiring.

  Actually, various conditions can be selected depending on the wiring width and shape of the conductor wiring, and the distance and shape of the conductor wiring gap serving as the resin etching resist. However, in general, the line width of an unnecessary wiring pattern is reduced to about 50% of the minimum line width of the necessary wiring patterns, and resin is removed immediately after the unnecessary wiring is peeled off. By controlling the process so that the etching process is stopped and the necessary wiring is not peeled and removed, only unnecessary wiring can be selectively removed.

  More preferably, the removal time of unnecessary wiring can be shortened by reducing the line width of unnecessary wiring to 10 to 25% with respect to the minimum line width of necessary wiring. Furthermore, it is possible to suppress a decrease in the adhesion strength between the necessary wiring and the base insulating resin.

(2) It is also more useful to reduce the wiring width that does not require the dummy wiring configuration in terms of relaxing the resin etching process conditions (conditions and time) and suppressing the decrease in adhesion strength of the necessary wiring to the underlying resin. . However, it is disadvantageous in that the line width is narrow and the area of the dummy wiring is reduced, and the dummy effect is reduced.

  This disadvantage can be solved to some extent by arranging a large number of dummy wirings. In addition, in the case of fine wiring, since there is a limit in creating a thin wiring depending on the resolution of the copper plating resist, in the currently available copper plating resist, it is considered that the lower limit of the dummy wiring is about 10% of the necessary wiring. However, it is thought that the minimum resolution will be improved by improving the resist in the future, and even thinner dummy wirings can be created.

  A dummy wiring pattern image thinner than the necessary wiring pattern as described above is provided in advance in the vicinity of the necessary wiring pattern image on the photomask used when exposing the image of the necessary wiring pattern. If the necessary wiring image and the dummy wiring image are made to coexist on one photomask by this method, the gap between the dummy wiring and the necessary wiring, which is a practical disadvantage of the method in which the conductive paste or the like is performed in a separate process. Precise placement can be easily achieved.

  The pattern image of the dummy wiring is necessary to reduce the local current concentration of the pattern at the end of the necessary wiring, effectively suppress the wiring thickness variation, and perform the resin etching effectively It is effective to install in the vicinity of the end wiring of the necessary wiring at the same distance as the gap between the wiring groups. Further, in terms of arrangement, it is more effective to arrange a large number of dummy wirings in order to further reduce local current concentration if possible and suppress variations in wiring thickness.

(3) Insulating Base Material Examples of the resin material for the insulating base material include polyimide resins and aromatic liquid crystal polyester resins. Typical examples of the imide resin film include Kapton (trade name, manufactured by DuPont, USA), Iupilex (trade name, manufactured by Ube Industries), and Apical (trade name, Kaneka Chemical Co., Ltd.). Examples of the liquid crystal polyester resin include Bexter (trade name, manufactured by Kuraray Co., Ltd.), BIAC (trade name, manufactured by Japan Gore-Tex Co., Ltd.), and the like.

(4) Resin Etching Solution As the resin etching, it is necessary to select means according to the type of resin base material to be used. As imide resin etching means, wet-etching with a chemical solution includes urea-alkali metal compound (Japanese Patent Publication No. 60-14776), alkali hydrazine-based etching liquid (Japanese Patent Laid-Open No. 3-101228), oxyalkylamine-alkali metal compound. (Japanese Patent Laid-Open No. 10-97081), an alkaline permanganate-based oxidizing chemical solution, and a plasma method as a dry etching method are known.

  As a liquid crystal polyester resin etching means, an aliphatic alcohol-based alkaline etching solution (Japanese Patent Laid-Open No. 2003-261699) is known. As for the degree of resin etching, the dummy pattern wiring can be completely removed, and the influence of etching affects the interface between the metal layer of the wiring pattern conductor and the underlying insulating resin, which is originally required, and the adhesion strength between the conductor and the resin. It is necessary to select the optimum conditions so that the decrease in the temperature can be suppressed.

(5) Post- processing Depending on the type of etching process, it is also necessary to add post-processing. For example, in the case of strong alkaline solution treatment or plasma treatment, the surface of the conductor metal is oxidized, which may affect the appearance problem due to discoloration, or affect the conductor protective cover / adhesion of the laminated material / surface protection plating. It is desirable to perform layer removal.

  Further, when the metal oxide film is too thick to be removed by acid treatment, soft etching can be performed. Alternatively, in order to strengthen the adhesion strength between the conductor protective covers and the laminated material, a post-treatment for roughening the conductor surface by metal etching solution treatment or blast treatment can be added. Furthermore, the surface of the conductor can be protected by performing a metal rust prevention treatment represented by benzotriazoles.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 shows a process of forming a conductive seed layer as an initial process for manufacturing a printed wiring board according to the present invention. As the insulating resin substrate 1, a polyimide film “Kapton 100EN” (trade name, manufactured by Toray DuPont Co., Ltd., 25 μm thickness) was used. A conductive seed layer 2 was formed on the insulating resin substrate 1 by sputtering using a decompression device. The conductive seed layer 2 has a thickness of 0.5 to 1 μm and is made of a copper-nickel-chromium alloy.

  FIG. 2 shows a process for forming a plating resist layer. A dry film resist (manufactured by Hitachi Chemical Co., Ltd., 15 μm thickness) is laminated as a plating resist on the conductive seed layer 2 formed on the insulating resin base material 1 by heating and pressing with a roll laminator. Layer 3 was formed.

  FIG. 3 shows a dummy wiring pattern forming process. Using a photomask having a predetermined pattern, mask contact exposure was performed with parallel light using an ultrahigh pressure mercury lamp as a light source. On the photomask, a dummy wiring pattern image is printed in the vicinity of the circuit pattern together with the necessary wiring pattern image.

  Specifically, as shown in FIG. 3, adjacent to the endmost wiring of the linear circuit pattern image (4C ′) having a wiring length of 20 mm, a wiring width of 22 μm, a gap of 18 μm, and 30 (per block). A gap (4E) having a width of 18 μm was provided, and a dummy pattern (4D ′) having a width of 7 μm was further provided across the gap.

  FIG. 4 shows a process for forming a circuit pattern intermediate. After developing with a 1% aqueous sodium carbonate solution to remove the unexposed portion of the resist layer and forming an opening, a conductive seed is formed by a copper sulfate plating bath (Meltex Co., Ltd., copper sulfate concentration 80 g / L). Electrolytic copper was deposited on the portion of the layer 2 where the resist layer was removed to form a circuit pattern intermediate 4A. The average plating thickness in the wiring board was 10 μm as a target value.

  5A and 5B show a process for forming a circuit pattern intermediate. The plating resist layer 3 was removed using a 3% aqueous sodium hydroxide solution.

  Subsequent to the step of FIG. 4, the conductive seed layer 2 was etched away for 60 seconds using sulfuric acid-acidic hydrogen peroxide as a metal etchant to form a circuit pattern intermediate 4B. FIG. 4A is a sectional view taken along the line a-a ′ of FIG. 4B which is a plan view.

  In the circuit pattern intermediate 4B at this stage, there exist a wiring 4C having a width of 20 μm which should be finally left as a circuit pattern, and a dummy pattern 4D having a width of 5 μm which is finally unnecessary as a circuit.

  FIG. 6 shows a dummy pattern removing process. After treating the base with 3% sodium hydroxide alkalinity sodium permanganate (trade name: Macudizer 9275, manufactured by Nihon McDermid Co., Ltd.), sulfuric acid amine-based reducing solution (trade name: Macudizer 9279) And then rinsed with pure water and dried with warm air to remove only the unnecessary dummy pattern 4D and finally complete the circuit pattern 4C wiring board.

  At the time of exposure, the photomask of the first embodiment is used in place of the photomask having a reduced circuit pattern width of the necessary wiring and the same other design such as the dummy pattern width. Others were the same as in Example 1, and required wiring 4C having a wiring width of 10 μm and dummy pattern 4D having a width of 5 μm were obtained. Subsequent steps were the same as those in Example 1, and the circuit pattern 4C was finally completed.

Comparative Example 1

  At the time of exposure, exposure is performed using a photomask different from that of the first embodiment in which only the linear circuit pattern image 4C ′ having a width of 20 μm is provided and the dummy pattern image 4D ′ is not provided. Pattern 4C was obtained.

Comparative Example 2

  Exposure was performed using the same photomask as in Example 1 to form a circuit pattern intermediate 4B. However, the wiring board in which the dummy pattern 4D adjacent to the circuit pattern 4C was left as it was without performing the resin etching process in Example 1 or 2 was obtained.

Confirmation of effect

  FIG. 7 is a chart showing product inspection results of the above-described examples and comparative examples. The thickness of the finally obtained circuit pattern 4C: maximum thickness of end wiring, frequency of occurrence of image recognition product inspection error, frequency of occurrence of image recognition error when mounting components on a wiring board: production loss due to error occurrence and re-inspection A comparative evaluation of the effect was performed in terms of time and error occurrence frequency in the function check after component mounting.

  In addition, the thickness of the circuit pattern was measured with a laser microscope (model name: VK-9500, manufactured by Keyence Corporation). In any evaluation item, it was confirmed that Example 1 and Example 2 were superior to Comparative Example 1 and Comparative Example 2, and the effect was remarkable.

Sectional drawing which shows the formation process of the electroconductive seed layer for manufacturing the printed wiring board by this invention. FIG. 2 is a cross-sectional view showing a plating resist layer forming step. FIG. 3 is a cross-sectional view showing a dummy wiring pattern forming process. FIG. 4A is a cross-sectional view showing a step of forming a circuit pattern intermediate along the a-a ′ line in FIG. FIG. 5 is a cross-sectional view showing a process of forming a circuit pattern intermediate. FIG. 6 is a cross-sectional view showing a dummy pattern removing step. FIG. 7 is a chart showing product inspection results of Examples and Comparative Examples.

Explanation of symbols

1 insulating resin base material, 2 conductive seed layer, 3 plating resist layer,
4A circuit pattern intermediate, 4B circuit pattern intermediate, 4C wiring,
4D dummy pattern.

Claims (3)

Prepare a printed wiring board with a conductive layer formed on the resin layer,
Conductor wiring and dummy wiring are formed by metal etching the conductive layer,
A method for forming a printed wiring board, wherein the dummy wiring is removed by resin etching. In the formation method of the printed wiring board according to claim 1,
The printed wiring board, wherein a line width before the resin etching of the dummy wiring removed by resin etching is 10 to 50% with respect to a line width of the wiring that is the minimum line width among the conductor wirings. Forming method. In the formation method of the printed wiring board shown in claim 1,
The method for forming a printed wiring board, wherein the resin etching uses an alkaline resin etching chemical.

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