JP2006310689A - Manufacturing method of double-access flexible circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a double-access flexible circuit board excellent in mechanical characteristics, chemical resistance, insulation reliability, and size stability. <P>SOLUTION: The manufacturing method of the double-access flexible circuit board comprises a step of forming a laminate by disposing a photosensitive base layer 2 on one surface of a conductor layer 1, forming a wiring pattern by subjecting the foregoing conductor layer to etching processing, disposing a coated layer 3 made of photosensitive polyimide on an exposed surface of the wiring pattern likewise the foregoing conductor layer, opening the foregoing wiring pattern by photoetching processing, and forming a connection land 4 on both surfaces of the foregoing wiring pattern. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a double access type flexible circuit board in which connection openings are formed on both sides of a conductor layer, and in particular, a flexible circuit board based on the structure of a single-sided copper-clad flexible circuit board. It relates to the manufacturing method.

  Non-Patent Document 1 discloses a pre-punching method as a method of manufacturing a double-access type printed wiring board in which a connection land is also provided on the base surface. According to this, both sides of the conductor can be obtained by using a base film with an adhesive that has been pre-perforated when producing a copper-clad laminate (three-layer material) laminated with an adhesive between the copper foil and the base film. A flexible circuit board that can be connected to the circuit board can be manufactured.

  In recent years, copper-clad laminates have a non-adhesive copper-clad laminate that does not use an adhesive between the copper foil and the polyimide layer in order to meet the requirements of heat resistance, overall circuit thickness reduction, and halogen-free and flame retardant compatibility. The range of application of plates (referred to as two-layer materials) is expanding. As a method for forming a connection land on the base film layer when manufacturing a double-access type printed wiring board using a two-layer material, there is a method of applying and drying a polyimide varnish by avoiding the connection land portion by screen printing or the like. However, there is a problem that the degree of freedom in design is low, for example, a minute opening cannot be made. In addition, there is a method of forming a connection land on the base film layer by laser processing or plasma processing, but since laser processing is a single hole process, productivity is low and a process of removing the burned foreign matter adhering to the land is required. Production costs increase. In addition, plasma processing can be performed in a batch, but the productivity is low because a masking step is required as a pretreatment.

  In order to solve these problems, a polyimide precursor varnish is applied to one side of a metal foil for a conductor circuit, dried to form a polyimide precursor layer, and a polyimide precursor is coated with a photoresist for photolithography, It is possible to manufacture a double access type flexible circuit board by providing a land access opening by exposure and development, and then manufacturing a copper pattern by an etching method and then imidizing a polyimide precursor layer at a high temperature. 1.

It is also possible to use photosensitive polyimide having a photoresist function as the base film of the two-layer material of the above method. As a specific example of a photosensitive polyimide, a negative photosensitive polyimide precursor in which a photosensitive group is introduced into a polyimide precursor via an ester bond or an ionic bond, and a positive photosensitive material having a structure having an o-nitrobenzyl ester group in a side chain. There is polyimide.
JP 2000-156555 A Nikkan Kogyo Shimbun, published in 1998 Kenji Numakura “Introduction to High Density Flexible Substrates” Toray Research Center, Inc., published on January 5, 2003 "Latest Trends in Resist for Electronics"

  In the process of sequentially forming an insulating layer using a polyimide precursor, the polyimide precursor is brittle as a coating material, and the surface layer is formed by being immersed in a weak alkaline solution for photoresist development in the wiring pattern forming process and hydrolyzed. to degrade. Therefore, in the wiring pattern forming step, it is necessary to use a weak adhesive tape as a protective film for the purpose of protecting the insulating layer from the chemical solution and protecting the conductor layer exposed from the access opening, resulting in poor productivity ( Mechanical properties, chemical resistance).

  In the wiring pattern formation process, the surface of the polyimide precursor exposed by copper etching of the conductor layer is also hydrolyzed by a strong acid to form a fragile layer, and the cover coat adhesion and insulation reliability are improved. Problems (mechanical properties, chemical resistance). Furthermore, since the development and thermosetting processes are sequentially performed one side at a time and volume shrinkage due to imidization reaction is unavoidable (dimensional stability), there is a concern that warpage may occur (dimensional stability).

  The present invention has been made in view of the above points, and an object of the present invention is to provide a double access type flexible circuit board having good mechanical properties, chemical resistance, insulation reliability, and dimensional stability.

In order to achieve the above object, in the present invention,
A laminated board is formed by arranging a coating layer of photosensitive polyimide on one surface of the conductor layer,
Forming a wiring pattern by etching the conductor layer;
Arranging a coating layer made of the same photosensitive polyimide as the conductor layer on the exposed surface of the wiring pattern,
A method of manufacturing a double-access-type flexible circuit board, comprising: opening the two coating layers by photoetching; and forming connection lands on both sides of the wiring pattern;
Is to provide.

  As described above, the present invention is a manufacturing method in which a photosensitive polyimide having excellent chemical resistance is arranged on one surface of a conductor layer to form a laminated board, and after forming a wiring pattern, a connection land is simultaneously formed on both sides. When the wiring pattern is formed, the material is not deteriorated, and the mechanical characteristics, chemical resistance and insulation reliability can be improved. Moreover, since it is a double-sided connection land formation process using polyimide, volume shrinkage and warping are improved.

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

  Hereinafter, in the present invention, the case where positive photosensitive polyimide is used as the material of the base film will be described. The positive photosensitive polyimide used here can be variously selected and used depending on the intended characteristics.

  1 (a) to 1 (e) show the steps in one embodiment of the present invention in order. FIG. 1A shows the first step in the method according to the present invention, in which a photosensitive polyimide base layer 2 is formed on one surface of a conductor layer 1.

  Subsequently, the conductor layer 1 is etched to form a wiring pattern (FIG. 1B). Thereafter, a photosensitive polyimide cover layer 3 is formed on the exposed surface of the wiring pattern using the same photosensitive polyimide as the photosensitive polyimide base layer 2 (FIG. 1C). A double-access type flexible circuit board having connection lands formed on both sides of the wiring pattern can be manufactured by photoetching the openings on both sides of the photosensitive polyimide layer (FIG. 1 (d)) (FIG. 1 (e)). )).

  The photosensitive polyimide base layer 2 and the photosensitive polyimide cover layer 3 can be roughly classified into two types, a negative type for organic solvent development and a positive type for alkali development. The photosensitive polyimide base layer 2 and the photosensitive polyimide cover layer 3 do not contain cross-linking components such as acrylic and epoxy, which are inferior in chemical properties and mechanical properties than polyimide, in the chemical components of the insulating film. Has excellent properties.

  For example, as a specific example of photosensitive polyimide, there is a reaction phenomenon type resist in which a non-photosensitive solvent-soluble polyimide hequinonediazide compound is mixed to form a positive photosensitive polyimide (Non-patent Document 2).

  Among the photosensitive polyimides, it is preferable to use a positive photosensitive polyimide obtained by mixing a quinonediazide compound with polyimide. This positive photosensitive polyimide may be a commercially available general one, or a commercially available solvent-soluble quinonediazide compound mixed to impart photosensitivity. For example, RN-902 manufactured by Nissan Chemical Co., Ltd. can be used as the alkaline phenomenon type positive photosensitive polyimide.

  Next, each step of the manufacturing method according to the present invention shown in FIGS. 1 (a) to (e) will be described.

  First, a positive photosensitive polyimide 2 is provided on one surface of the copper foil 1 (FIG. 1 (a)). This is performed by applying positive photosensitive polyimide to one surface of the copper foil 1 by screen printing and then drying. Thereby, the photosensitive base layer 2 of the copper foil 1 which is a conductor layer is formed.

  Next, a photoresist film is laminated on the other surface of the copper foil 1, and an etching resist pattern corresponding to the conductor circuit pattern is formed by photolithography. Then, a wiring pattern is formed by etching the other surface of the copper foil 1, and a conductor circuit is formed by removing the etching resist (FIG. 1 (b)).

  Subsequently, when the positive photosensitive polyimide layer 3 is applied on the wiring pattern by a screen printing method and dried, the photosensitive cover layer 3 is formed (FIG. 1C).

  Thereafter, the photosensitive base layer 2 and the photosensitive cover layer 3 are exposed from both sides of the copper foil 1 through an exposure mask (not shown) using a high-pressure mercury lamp or the like, and then developed with an alkali solution such as sodium hydroxide. Then, the exposed portion is removed by rinsing with an aqueous solution containing an organic solvent such as alcohol or warm water. As a result, the connection land portion 4 is simultaneously formed for the photosensitive base layer 2 and the photosensitive cover layer 3 (FIG. 1 (d)).

  Finally, the polyimide of the photosensitive base layer 2 and the photosensitive cover layer 3 is collectively heated in an air atmosphere or a nitrogen atmosphere to volatilize and remove the solvent and the photosensitive agent.

  In this way, a double-access type single-sided flexible circuit board that can be accessed from the base layer 2 and the cover layer 3 is completed (FIG. 1 (e)).

Other examples

  In the above embodiment, positive photosensitive polyimide was used, but it can be selected and used depending on the intended characteristics as long as it is resistant to acids and alkalis. Photosensitive polyimide may be used. For example, Durimide 7000 series manufactured by FUJIFILM Electronics Materials Co., Ltd. can be used as an organic solvent developing type value photosensitive polyimide.

1 (a) to 1 (e) are explanatory views showing steps of an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Conductor layer 2 Photosensitive polyimide base layer 3 Photosensitive polyimide cover layer 4 Connection land

Claims (4)

A laminated board is formed by arranging a coating layer of photosensitive polyimide on one surface of the conductor layer,
Forming a wiring pattern by etching the conductor layer;
Arranging a coating layer made of the same photosensitive polyimide as the conductor layer on the exposed surface of the wiring pattern,
A method of manufacturing a double access type flexible circuit board, wherein both the covering layers are opened by photoetching, and connection lands are formed on both sides of the wiring pattern. In the manufacturing method of the double access type flexible circuit board according to claim 1,
The method for producing a double access flexible circuit board, wherein the photosensitive polyimide is an alkali developing type positive photosensitive polyimide. In the manufacturing method of the double access type flexible circuit board according to claim 2,
The method for producing a double access flexible circuit board, wherein the alkali developing type positive photosensitive polyimide is obtained by mixing a quinonediazide compound with an organic solvent soluble polyimide. In the manufacturing method of the double access type flexible circuit board according to claim 1,
The photosensitive polyimide is a negative photosensitive polyimide of an organic solvent development type. A method for producing a double access flexible circuit board.

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