JP2008053682A - Method for manufacturing polyimide wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a polyimide wiring board by which the polyimide wiring board wherein the adhesiveness between a metal thin film and a polyimide is excellent and the metal thin film having a sufficient thickness is comprised can be manufactured without causing deformation of a substrate and a crack in the metal thin film. <P>SOLUTION: The method for manufacturing the polyimide wiring board includes: a modification process wherein, as shown in Fig.4, a polyimide substrate 1 is treated with an alkaline solution to form a polyimide modifying layer 2 whose imide ring is opened; a metal ion adsorption process wherein the polyimide substrate is treated with a metal-ion- contained solution to make the modifying layer 2 adsorb a metal ion B; a mask pattern formation process wherein a mask pattern 3 is formed on the modifying layer to selectively expose the modifying layer; and a metal ion reduction process wherein the polyimide substrate 1 is reduced in a reduction bath to reduce the metal ion adsorbed by the modifying layer, thereby the metal thin film 4 is deposited in the exposed region of the modifying layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a polyimide wiring board.

  In recent years, electronic devices typified by portable information devices such as mobile phones have been required to be smaller and lighter. In response to this requirement, flexible printed circuit boards (FPC (Flexible Printed Circuit)) and printed circuit boards that are mounted on electronic devices are rigid combinations that combine FPC with rigid substrates such as glass epoxy substrates. -The amount of flexible wiring boards used is increasing. As an FPC substrate material, a polyimide resin excellent in heat resistance, electrical insulation, and mechanical strength is widely used.

  As a method for forming a wiring on an FPC using a polyimide resin, a subtractive method is conventionally used in which a metal film attached to the entire surface of a substrate material via an adhesive is removed by etching and patterned. However, as the density of printed wiring boards is increased, a finer wiring pattern is required. It is being considered.

  On the other hand, an additive method in which a metal film is selectively formed using an electroless plating method to form a wiring is a wiring forming method that does not require an adhesive. However, the conventional additive method has a problem that the adhesion between the metal film and the polyimide substrate is poor.

  In order to solve this problem, a copper-clad two-layer substrate formed by forming a metal thin film on the surface of a polyimide substrate using a technique called a direct metallization method, and performing electrolytic Cu plating using the metal thin film as a power feeding layer. And a method for producing a flexible printed wiring board has been proposed (for example, Patent Document 1). Specifically, in the direct metallization method, first, a polyimide substrate is immersed in an alkaline solution such as KOH or NaOH, and the surface of the polyimide substrate is hydrolyzed to form a modified layer. This modified layer has a structure of a polyamic acid having a carboxyl group or a polyamic acid salt by opening the imide ring. Next, the polyimide substrate is immersed in a metal ion-containing solution to coordinate metal ions to carboxyl groups to form a metal salt, and the metal salt is reduced to obtain a metal thin film. Then, electrolytic Cu plating is performed using this metal thin film as a seed layer to produce a copper-clad two-layer substrate. This copper-clad two-layer substrate is subjected to circuit etching.

However, the above method has the following problems.
In the direct metallization method, a polyamic acid salt existing on the surface of a polyimide substrate is reduced to deposit a metal, so that fine metal particles are first reduced and grow to form a metal thin film. At this time, if the reduction time is insufficient or the amount of the polyamic acid salt is insufficient, the metal thin film becomes porous, so that the sheet resistance of the metal thin film increases and electrolytic Cu plating cannot be performed. In order to prevent the metal thin film from becoming porous, it is necessary to increase the thickness of the modified layer formed on the surface of the polyimide substrate and to sufficiently form the polyamic acid salt. However, since the polyamic acid or polyamic acid salt constituting the modified layer is softer than polyimide, when the ratio of the modified layer to the unmodified layer in the polyimide substrate is increased, the polyimide substrate is deformed and the polyimide There was a problem that difficulty in handling the substrate occurred. Furthermore, since the polyamic acid and the polyamic acid salt swell when they absorb water, the volume greatly changes during water absorption and during drying. Therefore, after forming a metal thin film by immersing it in an aqueous solution containing a reducing agent, if the polyimide substrate is dried, stress is applied to the metal thin film due to swelling / shrinkage of the modified layer. There are problems of deformation such as unevenness on the surface and deterioration of flatness, and cracks in the metal thin film.

In addition, a part of the reactive group in at least one of the resin precursor and the semi-cured resin having at least one reactive group that can be partially substituted under alkalinity is replaced with an alkali metal ion in an alkaline solution, Alkali metal ions are exchanged for ions of the conductive substance in an ion solution of the conductive substance, the conductive substance ions are reduced to precipitate the conductive substance, and then the reactive groups are reacted to form a resin. And a method for producing a surface conductive resin in which a layer made of the conductive material is formed on a part or all of the surface of the resin has been reported (Patent Document 2). As a result, the surface conductive resin can be produced safely and efficiently at low cost in a short time without damaging the polymer main chain. However, even in such a method, polyamic acid has high hygroscopicity and is softer than cured polyimide or metal thin film, so that the problem of deformation of the substrate and crack of the metal thin film (conductive material film) also occurred.
Japanese Patent Laid-Open No. 2004-6684 JP 2003-105084 A

  The present invention provides a polyimide wiring board capable of producing a polyimide wiring board having a sufficient thickness of a metal thin film with good adhesion between the metal thin film and the polyimide without causing deformation of the substrate and cracking of the metal thin film. It aims to provide a method.

The present invention
A modifying step of treating the polyimide substrate with an alkaline solution to form a polyimide modified layer in which the imide ring is opened;
A metal ion adsorption step of treating the polyimide substrate with a metal ion-containing solution to adsorb the metal ions to the modified layer;
A mask pattern forming step of forming a mask pattern on the modified layer and selectively exposing the modified layer; and reducing the polyimide substrate in a reducing bath to thereby remove metal ions adsorbed on the modified layer. A metal ion reduction step of reducing and depositing a metal thin film on the exposed region of the modified layer;
It is related with the manufacturing method of the polyimide wiring board characterized by including.

According to the method for producing a polyimide wiring board of the present invention, a direct metallization method is adopted, and a structure in which polyimide and a metal thin film are meshed at a nano level can be realized. You can get in productivity and reliability.
In the method of the present invention, a modified layer is formed on the substrate surface in the modifying step, a metal ion is adsorbed on the modified layer, a mask pattern is formed, and the mask pattern is exposed in the subsequent reducing step. The exposed area of the modified layer is reduced in a reduction bath. Therefore, since the metal ions in the modified layer directly under the mask also contribute to the formation of the metal thin film, it is possible to effectively increase the thickness of the metal thin film in a relatively short time. As a result, since the metal thin film 4 having a sufficient thickness can be formed without increasing the thickness of the modified layer, it is possible to solve the problems of substrate deformation (warping / unevenness) due to swelling / shrinkage of the modified layer and cracks in the metal thin film. .
In the method of the present invention, since the mask pattern is formed after metal ions are adsorbed to the modified layer, a material having poor alkali resistance may be used as the mask pattern.
Furthermore, by making the mask pattern different from the wiring pattern in the method of the present invention, it is possible to further obtain an effect that wiring with a finer pitch can be easily formed.

(First embodiment)
A first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is an example of a flow diagram showing a manufacturing process of a method for manufacturing a polyimide wiring board according to the first embodiment of the present invention, and FIGS. 2 to 10 show a polyimide wiring board according to the first embodiment of the present invention. It is an example of the schematic sectional drawing and schematic top view of the polyimide substrate for demonstrating the manufacturing process of this.

The manufacturing method of the polyimide wiring board which concerns on 1st Embodiment of this invention includes the process shown below;
A modifying step of treating the polyimide substrate with an alkaline solution to form a polyimide modified layer in which the imide ring is opened;
A metal ion adsorption step of treating the polyimide substrate with a metal ion-containing solution to adsorb the metal ions to the modified layer;
A mask pattern forming step of forming a mask pattern on the modified layer and selectively exposing the modified layer; and reducing the polyimide substrate in a reducing bath to thereby remove metal ions adsorbed on the modified layer. A metal ion reduction step of reducing and depositing a metal thin film on the exposed region of the modified layer.

-Modification process In this process, the polyimide board | substrate is processed with an alkaline solution and the polyimide modified layer by which the imide ring was opened is formed (process (1) of FIG. 1). Specifically, by immersing a polyimide substrate 1 as shown in FIG. 2 (a) in an alkaline solution, a polyimide substrate having a modified layer 2 formed on both sides as shown in FIG. 2 (b) is obtained, and then washed with water. To do. By this process, the imide ring of the polyimide molecule on the polyimide substrate surface is opened by hydrolysis, and a carboxyl group is generated. At the same time, hydrogen ions of the carboxyl group are replaced with metal ions in the alkaline solution, thereby forming a modified layer. The For example, when a polyimide represented by the chemical formula (1) is treated with an aqueous KOH solution, potassium ions are adsorbed on the carboxyl group generated by ring opening by hydrolysis, and have a structure represented by the chemical formula (2). Become.

  The alkaline solution is not particularly limited as long as the imide ring of the polyimide can be opened. For example, an aqueous solution containing an alkali metal hydroxide such as K or Na, or a solution containing an amine such as amino alcohol can be used. It is. The metal ion that is contained in the alkaline solution and replaces the hydrogen ion in this step is hereinafter referred to as metal ion A.

  For example, when the alkaline solution concentration is 1 to 5 mol / l and the solution temperature is 30 to 60 ° C., the soaking time is preferably 3 to 30 minutes.

  The polyimide substrate is not particularly limited, and any polyimide can be used from a flexible film-like material to a rigid board-like material. However, from the viewpoint of manufacturing a flexible wiring board, the thickness is 10 A film having a flexibility of ˜200 μm is preferably used.

  A commercially available polyimide substrate can be used, for example, Apical (R) (manufactured by Kaneka), Kapton (R) (manufactured by Toray DuPont), Upilex (R) (manufactured by Ube Industries), and the like.

  If vias that electrically connect both sides of the wiring board are required, through vias may be formed in the polyimide substrate 1 by drilling such as drilling before the reforming step. Since the metal ions deposited as a metal thin film are adsorbed on the inner wall of the through via by the reforming process and the metal ion adsorption process described later, a metal thin film is formed on both sides of the polyimide substrate unless a mask is formed in the next process. At the same time as the forming process is completed, a metal thin film is also formed on the inner wall of the via, which is efficient.

  When proceeding to the next step, it is desirable to prevent the polyimide substrate from drying. When drying is performed, cracks may occur on the surface of the polyimide substrate. For this reason, the process proceeds to the next step with the polyimide substrate kept wet.

Metal ion adsorption step In this step, the polyimide substrate on which the modified layer 2 as shown in FIG. 2B is formed is treated with a metal ion-containing solution, and the metal ions contained in the solution are treated with the modified layer. (Step (2) in FIG. 1). Specifically, by immersing the polyimide substrate having the modified layer 2 in the metal ion-containing solution, the entire surface of the modified layer is treated, and the metal ions A in the modified layer are converted into the metal in the metal ion-containing solution. Replace with ions and wash with water.

The metal ions contained in the metal ion-containing solution are reduced in a process described later and are deposited as a metal film on the surface of the modified layer. Examples of the metal ion-containing solution used in this step include aqueous solutions of metal salts such as Cu, Ni, Co, Ag, Pd, and Fe. Specifically, for example, CuSO ₄ aqueous solution, NiSO ₄ aqueous solution, AgNO ₃ aqueous solution and the like can be used. However, since the modified layer 2 has characteristics as a weakly acidic cation exchange resin, even if the metal ion concentration is high, only hydrogen ions are adsorbed under strong acidity. Therefore, the metal ion-containing solution used in this step is adjusted from alkaline to weakly acidic. From the viewpoint of improving the versatility (inexpensive price) as a material and the long-term reliability of the wiring board (preventing re-dissolution in polyimide), it is preferable to use an aqueous solution containing Ni ions. The metal ions that are contained in the metal ion-containing solution and replace the metal ions A in this step are hereinafter referred to as metal ions B.

  When the metal ion B in the metal ion-containing solution forms an insoluble or hardly soluble salt in the strong alkaline aqueous solution, the surface of the polyimide substrate is subjected to a step of washing with water or immersing in a weak alkaline solution before this step. It is desirable to change from neutral to weakly alkaline.

-Mask pattern formation process In this process, mask pattern 3 is formed as shown in Drawing 3 (a) and (b) to modification layer 2 which metal ion B adsorbed on a polyimide substrate, and this modification layer 2 is selectively exposed (step (3) in FIG. 1). The schematic cross-sectional view of FIG. 3A is a cross-sectional view taken along the line AB in the center of the schematic top view of FIG. As shown in FIG. 3B, the exposed region of the modified layer 2 that is not covered with the mask pattern 3 is a region where the metal thin film 4 is formed in the metal ion reduction process described later. In the metal ion adsorption step, the mask pattern 3 is formed on the modified layer in which the metal ions B are adsorbed on the entire modified layer, and the modified layer 2 is selectively exposed. When the reduction treatment is performed, the metal thin film 4 (FIG. 4B) formed on the surface of the modified layer exposed region (FIG. 3B) is effectively thickened. Specifically, in the vicinity of the surface of the exposed region of the modified layer, the metal ions B are consumed in forming the metal thin film or eluted into the reducing bath without being reduced, so that the concentration is relatively low. On the other hand, the region covered with the mask pattern 3 and the exposed region even if it is away from the surface of the modified layer does not touch the reducing bath, and the metal ions B are neither reduced nor eluted, so that the concentration is relatively high. . When the distribution of the ion concentration occurs in this manner, the metal ions B diffuse and move from the high concentration region to the low concentration region according to the concentration gradient, so that the region where the metal thin film 4 is formed on the surface. Metal ions B are supplied to the modified layer 2 from the modified layer 2 in the region covered with the mask pattern 3. Therefore, since the supplied metal ions B contribute to the formation of the metal thin film, the thickness of the metal thin film is compared with the case of having a modified layer having the same thickness and reducing without forming the mask pattern 3. Membrane formation can be achieved effectively. As a result, since the relatively thick metal thin film 4 can be formed only in a necessary region without increasing the thickness of the modified layer 2, deformation of the substrate due to swelling / shrinkage of the modified layer and cracks in the metal thin film are prevented. Can solve the problem.

  The ratio of the covering region to the exposed region (covering region / exposed region; area ratio) by the mask pattern is not particularly limited as long as the object of the present invention is achieved, and from the viewpoint of suppressing exhaustion of the reducing bath, A smaller exposed area is preferred. Desirably, the formation area of the conductor layer 6 and the formation area of the conductor layer 6 are covered with a mask pattern except for a route necessary for supplying power in a subsequent electrolytic plating process.

  The mask pattern 3 may be formed by any method as long as the reduction of the metal ions B in the modified layer immediately below the mask pattern can be suppressed in the metal ion reduction step. For example, a printing method, a photolithography method or the like may be used, and a printing method is preferable. Alternatively, a method of forming the mask pattern 3 by thermocompression bonding a previously patterned thermoplastic resin film to the surface of the modified layer 2 may be used.

  The printing method is a method of forming a mask pattern (resist pattern) by printing on a predetermined area a heat-drying resist ink obtained by dissolving a thermosetting resin in an organic solvent, and volatilizing the organic solvent in the ink. is there. In the printing method, the mask pattern 3 can be formed without a development step using a weakly alkaline aqueous solution, so that it is possible to prevent a decrease in metal ions adsorbed on the modified layer.

  The thermosetting resin constituting the ink is not particularly limited, and for example, an acrylic resin can be used.

  The photolithography method is a method for forming a predetermined mask pattern (resist pattern) by exposing and developing a photosensitive photoresist. For example, a mask covering region of a photoresist made of a photosensitive resin that undergoes a crosslinking reaction (curing) with respect to light of a specific wavelength, that is, a region for forming a mask pattern is exposed, and an unexposed portion of the photoresist is removed by etching Thus, development can be performed to form a resist pattern.

  The photoresist material is not particularly limited, and various commercially available materials can be used. For example, a liquid resist, a film resist, or the like that contains a novolak resin as a main component and contains a solvent such as a photosensitizer, ethyl lactate, and normal butyl acetate can be used.

The liquid resist is available as, for example, commercially available OFPR (manufactured by Tokyo Ohka Kogyo Co., Ltd.).
In the case of using a liquid positive resist, first, a polyimide substrate is placed on a spin coater, and the liquid positive resist is dropped or applied, rotated, and then heated (pre-baking process) with a hot plate to have a thickness of about 3 to 4 μm. Get a membrane. Next, after exposure, it is immersed in about 3% TMAH (tetramethylammonium hydroxide) for 1 minute for development and washing with water. Thereafter, heating (post-bake process) is performed again with a hot plate to cure the resist pattern portion with resin. As a result, a resist pattern having a width of 1 μm can be formed, so that a high-definition wiring pattern can be formed.

A film-like resist is available as Asahi Kasei SUNFORT (R) ASG-253, for example.
When using Asahi Kasei SUNFORT (R) ASG-253 as a film-like resist, a commercially available film laminator is used and affixed on a polyimide substrate at a pressure of about 0.4 MPa while heating at 110 ° C. At the time of development, an unexposed portion can be removed using an aqueous sodium carbonate solution.

  As shown in FIG. 3B, the mask pattern 3 has a shape in which a region (modified layer exposed region; opening) where the mask pattern 3 is not formed forms a continuous figure as viewed from above. Such a shape is preferable. As a result, the metal thin film formed in the metal ion reduction process forms a continuous figure as viewed from above, so when performing electroplating in the plating process described later, Installation of the power supply electrode is facilitated.

  When the mask pattern 3 is formed on both sides of the substrate, as shown in FIG. 3A, it is preferable that the mask pattern 3 has a symmetrical shape on both sides when viewed from the cross-sectional direction. That is, it is preferable that the mask pattern is formed on the back surface of the portion where the mask pattern is formed on one surface, and the mask pattern is formed so as to have symmetry in the thickness direction of the substrate. As a result, when the resist ink is cured or when a metal thin film is formed in the subsequent metal ion reduction step, the stress generated on the surface of the substrate is offset in the thickness direction, and the substrate can be more effectively prevented from warping.

  Since the mask pattern 3 is formed after the metal ions are adsorbed on the modified layer, the constituent material is not particularly limited. For example, the mask pattern 3 may be a material having poor alkali resistance, and is resistant to the reducing bath. I just need it.

  The mask pattern forming step may be performed on the modified layer on one side of the polyimide substrate, or may be performed on the modified layer on both sides in succession.

Metal ion reduction step In this step, the metal ions B are adsorbed in the modified layer and the polyimide substrate on which the mask pattern is formed is reduced in a reduction bath to reduce the metal ions B, and FIG. As shown in (a) and (b), a metal thin film 4 is deposited and formed in the exposed region of the modified layer 2 (step (4) in FIG. 1). Specifically, the polyimide substrate on which the mask pattern is formed is immersed in a reducing bath. As a result, the metal ion B is reduced at the interface where the surface of the modified layer 2 is in contact with the reducing bath, and the metal thin film 4 is formed. At this time, as described above, even the metal ions B in the modified layer such as the region covered with the mask pattern 3 diffuse and move and contribute to the formation of the metal thin film. Can be achieved simply and effectively. 4A is a cross-sectional view taken along the line AB in the center of the schematic top view of FIG. 4B.

  The reduction bath is not particularly limited as long as it is a liquid capable of reducing metal ions B by contact with the reduction bath. For example, reduction of alkylamines such as borohydride ions, hypophosphite ions, and dimethylamine borane complexes. It is an aqueous solution containing a chemical substance and a pH adjuster to be added as necessary. As a reducing agent capable of providing a reducing substance, for example, sodium borohydride, sodium hypophosphite, dimethylamine borane and the like can be used. Examples of the pH adjuster include citric acid and triethanolamine.

  The treatment conditions in the reduction bath are not particularly limited as long as the metal thin film can be thickened. Usually, in the case of a dimethylamine borane solution, the concentration of the reduction bath is 0.01 to 0.5 mol / l, and the temperature is 30. ˜50 ° C. and immersion time is preferably 5 to 40 minutes.

  A metal thin film having a thickness of 100 to 300 nm can be usually formed only by performing the above reforming step to metal ion reduction step once.

After carrying out the metal ion reduction step in the first embodiment, the following steps are usually carried out;
A mask pattern removing step for removing the mask pattern;
A cleaning treatment step of washing the polyimide substrate; and a heat treatment step of ring-closing treatment of the polyimide modified layer by heating.

Mask Pattern Removal Step In this step, the mask pattern 3 is removed from the polyimide substrate having the mask pattern 3 and the metal thin film 4 as shown in FIGS. 4A and 4B, and FIGS. As shown in b), the modified layer 2 is exposed (step (5) in FIG. 1). Specifically, for example, the mask pattern 3 may be peeled or dissolved by dipping in a stripping solution. For example, when resist ink is used as the mask pattern, the mask pattern can be removed using a stripping solution containing an organic solvent such as propylene glycol monomethyl ether acetate. For example, when the above-mentioned film resist manufactured by Asahi Kasei is used, the mask pattern can be removed using an aqueous solution of sodium hydroxide or potassium hydroxide, or an organic amine-based stripping solution. For example, in the case of a liquid resist mainly composed of a so-called novolac resin, a stripping solution containing an organic solvent such as propylene glycol methyl ether acetate or alkylbenzene sulfonic acid can be used. The schematic cross-sectional view of FIG. 5A is a cross-sectional view taken along the line AB in the center of the schematic top view of FIG.
By immersing in a stripping solution, the mask pattern removal step can be performed simultaneously on the mask patterns on both sides of the polyimide substrate.

-Cleaning treatment step In this step, the polyimide substrate is washed to replace metal ions contained in the modified layer 2 with hydrogen ions (step (6) in FIG. 1). Thereby, the ring closure process of the modified layer can be effectively performed in the heat treatment process. For example, when the subsequent heat treatment process is performed while the cleaning process is not sufficient and the metal ions B remain in the modified layer 2, the ring closing process of the modified layer 2 is not sufficiently performed. In this case, since the region that was the modified layer 2 remains in a chemically unstable state, when voltage is applied between the wirings under high temperature and high humidity, ion migration occurs and the insulating state is maintained. I can't. Further, the modified layer 2 does not have a structure in which polymer molecular chains are intricately entangled and does not have elasticity, so that a phenomenon that the modified layer 2 breaks into a shell shape with respect to tensile stress occurs. In such a case, since the modified layer 2 does not have sufficient strength, it does not have sufficient strength as a wiring board. Therefore, it is necessary to sufficiently perform the cleaning process so that the metal ions B do not remain in the modified layer 2 and to complete the ring closing process of the modified layer 2 in the heat treatment process in the subsequent process.

  The metal ion to be substituted is a metal ion contained in the metal ion-containing solution or the reduction bath. Although deionized water may be used for the cleaning liquid, from the viewpoint of substitution with hydrogen ions, an acidic solution containing a large amount of hydrogen ions is preferable, and further, a strongly acidic solution in which the carboxyl group loses ion exchange properties. An aqueous solution is desirable. However, if the cleaning process is performed for a long time with a strong acidic aqueous solution, the metal thin film 4 is excessively etched, and there is a risk of hindering the electroplating performed in the subsequent process. It is necessary to select an acidic solution. For example, when nickel is formed as the metal thin film 4, a weakly acidic aqueous solution such as dilute sulfuric acid or citric acid can be used. When copper is formed as the metal thin film 4, copper is oxidized and dissolved even with the weak oxidizing power of dilute sulfuric acid, so a weakly acidic aqueous solution such as citric acid is used. Specifically, for example, when treated with 0.2 mol / l citric acid for 15 minutes, the decrease in the metal film thickness is 60 nm, and a sufficient film thickness can be left for electrolytic plating.

  The washing treatment conditions are not particularly limited as long as the removal of metal ions from the modified layer can be achieved. For example, in the case of a citric acid solution, the concentration is 0.05 to 0.2 mol / l, the temperature is 20 to 30 ° C., The time is preferably 10 to 20 minutes.

  In the cleaning treatment step, it is preferable to dehydrate the polyimide substrate by vacuum drying after washing the polyimide substrate as described above. The moisture inside the modified layer is removed by dehydration treatment, the metal thin film deposited in the previous reduction step is prevented from being ionized again, and the ring closure treatment in the heat treatment step can be performed more sufficiently. Since the modified layer is made of polyamic acid and has the property of “acid”, the polyamic acid dissolves and ionizes the metal thin film in the presence of moisture. If metal ions are adsorbed again on the polyamic acid, it cannot be sufficiently re-imidized in the heat treatment step. Therefore, moisture taken into the modified layer 2 in the steps so far is removed by vacuum drying to prevent reionization of the metal thin film.

  As a dehydration treatment condition, the polyimide substrate is dehydrated by leaving it in a vacuum atmosphere of 200 Pa or less for 1 hour or more.

Heat treatment step In this step, the polyimide modified layer is subjected to a ring closing treatment by heating (step (7) in FIG. 1). Specifically, by heating the polyimide substrate obtained in the previous step, the polyimide-modified layer is re-imidized and has a structure as shown in FIGS. 6 (a) and 6 (b). Here, the difference between FIG. 6 and FIG. 5 is that the modified layer 2 is imidized and the boundary between the substrate and the polyimide disappears. The schematic cross-sectional view of FIG. 6A is a cross-sectional view taken along the line AB in the center of the schematic top view of FIG.

  The heating conditions are not particularly limited as long as reimidation of the modified layer can be achieved. For example, the temperature is preferably 250 ° C. to 350 ° C., and the treatment time is preferably 30 minutes to 1 hour. In order to suppress the surface oxidation of the metal thin film 4, it is preferable to use an oven in which the oxygen concentration is lowered by introducing nitrogen.

  Although the metal thin film 4 obtained by carrying out the above steps may be used as a wiring layer in a single layer, another metal thin film (conductor layer) is formed on the metal thin film, and the laminate is wired. It may be used as a part. When a metal thin film is used as a wiring part in a single layer, the mask pattern formed in the mask pattern forming step may be a predetermined wiring shape.

In the case of forming a wiring portion by laminating a conductor layer on the metal thin film 4, the following steps are performed after the heat treatment step is performed;
Forming a plating resist on the polyimide substrate surface, and selectively exposing the metal thin film;
A plating step of forming a conductor layer on the exposed region of the metal thin film by plating;
A plating resist removing step of exposing the metal thin film by removing the plating resist; and an etching step of etching away the metal thin film exposed in the plating resist removing step using the conductor layer as a mask.

-Plating resist formation step In this step, as shown in FIGS. 7A and 7B, a plating resist 5 is formed on the surface of the polyimide substrate to selectively expose the metal thin film 4 (FIG. 1). Step (8)). All openings of the plating resist 5 are formed on the metal thin film 4. The plating resist pattern has a predetermined wiring shape. The schematic cross-sectional view of FIG. 7A is a cross-sectional view taken along the line AB in the center of the schematic top view of FIG.

  The plating resist 5 may be formed in a predetermined pattern shape by exposing and developing a photosensitive liquid or film resist by a photolithography method that can be employed in the mask pattern forming step.

-Plating process In this process, as shown to Fig.8 (a) and (b), the conductor layer 6 is formed in the exposed area | region of the said metal thin film 4 by a plating process (process (9) of FIG. 1). The schematic cross-sectional view of FIG. 8A is a cross-sectional view taken along the line AB in the center of the schematic top view of FIG. The plating method is not particularly limited as long as a predetermined conductor layer is formed, and may be, for example, an electrolytic plating method, an electroless plating method, or a combination thereof. From the viewpoint of the formation efficiency of the conductor layer, it is preferable to employ an electrolytic plating method.

  When the electrolytic plating method is adopted, the polyimide thin film is immersed in an electrolytic plating bath, and electrolytic plating is performed using the metal thin film 4 as a power feeding layer. As shown in FIGS. 8A and 8B, the metal thin film is obtained. A conductor layer (plating film) 6 is deposited on the exposed areas 4. Since the metal thin film 4 is used as the power feeding layer and the resist 5 exists in the non-wiring region on the metal thin film 4, the conductor layer 6 is selectively deposited only in the exposed region as the wiring region. The electrolytic plating process can be performed simultaneously on the metal thin film exposed regions on both sides of the polyimide substrate. When the metal thin film 4 is formed continuously rather than intermittently when viewed from above, it is not necessary to install a power supply electrode for electroplating for each metal thin film, so that the processing is simple.

  The metal ions contained in the electrolytic plating bath are deposited as a conductor layer 6 in the exposed region of the metal thin film 4 in this step, and are not particularly limited as long as the conductor layer has conductivity. Any plating metal can be used, but from the viewpoint of reducing plating residual stress, it is desirable that the crystal lattice spacing of the metal constituting the metal thin film 4 and the conductor layer 6 is close. Therefore, the plating metal needs to be the same metal as the metal thin film 4 or a metal whose crystal lattice spacing between the metal thin film 4 and the metal is close. Moreover, when using as a wiring of a printed wiring board, Cu is preferable from a viewpoint of resistance reduction and migration tolerance. In order to use the difference in etching rate, a metal thin film of a different metal is preferable. Examples of the electrolytic plating bath include a sulfate bath and a sulfamine bath when Cu is plated. In the case of plating Ag, Au or an alloy thereof, a cyan bath may be used.

  When the electroless plating method is adopted, the polyimide substrate is immersed in an electroless plating bath, electroless plating is performed using the metal thin film 4 as a catalyst nucleus, and as shown in FIGS. 8A and 8B, A conductor layer (plating film) 6 is deposited on the exposed region of the metal thin film 4. As the electroless plating bath, those conventionally used in the field of electroless plating can be used. For example, those containing copper sulfate, a reducing agent, sodium ethylenediaminetetraacetate and a pH adjusting agent are used. As the reducing agent, formaldehyde, dimethylamine borane, cobalt sulfate or the like is used, and a pH adjusting agent is used in order to adjust to a pH suitable for the reducing agent.

  Electrolytic plating conditions and electroless plating conditions are not particularly limited, and arbitrary conditions may be selected and used.

After the conductor layer 6 having a required thickness is deposited, the polyimide substrate is taken out of the plating bath and washed with water. The conductor layer 6 is usually formed with a thickness of about 5 to 25 μm.
The metal ions contained in the electrolytic plating bath or the electroless plating bath and deposited as a conductor layer in this step will be referred to as metal ions C hereinafter.

-Plating resist removal step In this step, the plating resist 5 is removed from the polyimide substrate having the plating resist 5 and the conductor layer 6 as shown in FIGS. ) And (b), the metal thin film 4 is exposed (step (10) in FIG. 1). The schematic cross-sectional view of FIG. 9A is a cross section taken along the line AB in the center of the schematic top view of FIG. 9B.

  The resist may be removed by dipping in a stripping solution and stripping or dissolving the resist. Specifically, a method similar to that used for removing the liquid or film resist in the mask pattern removing step may be employed.

Etching Step In this step, the conductive layer 6 is used as a mask, and the metal thin film 4 exposed in the plating resist removing step is etched away as shown in FIGS. 9A and 9B (step of FIG. 11)). Specifically, the polyimide substrate is immersed in an etching solution to remove the exposed region of the metal thin film 4, and the metal film 4 and the conductor layer 6 are left only in the wiring region as shown in FIGS. 10 (a) and 10 (b). As a result, an arbitrary fine pitch wiring pattern 7 can be formed on both surfaces of the polyimide substrate. The schematic cross-sectional view of FIG. 10A is a cross-sectional view taken along the line AB in the center of the schematic top view of FIG.

  The etching solution is determined depending on the metal of the metal thin film 4 and the metal of the conductor layer 6, and it is preferable to use an etching solution having selectivity that removes the metal thin film 4 but does not remove the conductor layer 6. As long as the thin film 4 can be removed by etching, there is no need to have selectivity with the conductor layer 6. Since there is a thickness difference of about one digit between the metal thin film 4 and the conductor layer 6, the metal thin film 4 can be completely removed by adjusting the etching time without completely removing the conductor layer 6. Because is possible.

For example, when the metal thin film 4 is made of Ni and the conductor layer 6 is made of Cu, the etching solution can be an FeCl ₃ aqueous solution, HNO ₃ , or a mixed acid containing HNO ₃ .
For example, when the metal thin film 4 is made of Cu and the conductor layer 6 is also made of Cu, an aqueous solution of FeCl ₃ , CuCl ₂ , (NH ₄ ) ₂ S ₂ O _8, or the like can be used.
For example, when the metal thin film 4 is made of Ag, the etching solution can be HNO ₃ , a mixed solution of H ₂ SO ₄ and H ₂ O ₂ , an Fe (NO ₃ ) ₃ aqueous solution, or the like.
Further, for example, when the metal thin film 4 is made of Pd, an NH ₃ I aqueous solution or the like can be used as the etching solution.

  In the first embodiment of the present invention, in the above, after performing the reforming process, the metal ion adsorption process, the mask pattern forming process, and the metal ion reduction process, the mask pattern removing process, the cleaning process process, and the heat treatment process are performed. Although the conductor layer is formed, the cleaning treatment step and the heat treatment step, particularly the heat treatment step, may be performed after the formation of the conductor layer. That is, the following process sequence (1) or (2) may be adopted.

(1) Modification step-Metal ion adsorption step-Mask pattern formation step-Metal ion reduction step-Mask pattern removal step-Plating resist formation step-Plating step-Plating resist removal step-Etching step-Cleaning treatment step-Heat treatment Process.
(2) Modification step-Metal ion adsorption step-Mask pattern formation step-Metal ion reduction step-Mask pattern removal step-Cleaning treatment step-Plating resist formation step-Plating step-Plating resist removal step-Etching step-Heat treatment Process.

(Second Embodiment)
In the first embodiment, since the mask pattern removing step is performed before the formation of the conductor layer, a plating resist forming step for forming the conductor layer is required. However, in the second embodiment, before the mask pattern removing step, A conductor layer is formed. Therefore, since the mask pattern can be used for forming the conductor layer, the plating resist forming process, the plating resist removing process, and the etching process are not required when the mask pattern has a predetermined wiring shape.

A second embodiment of the present invention will be described with reference to FIGS.
FIG. 11 is an example of a flow diagram illustrating a manufacturing process of a method for manufacturing a polyimide wiring board according to the second embodiment of the present invention, and FIGS. 12 to 19 illustrate a polyimide wiring board according to the second embodiment of the present invention. It is an example of the schematic sectional drawing and schematic top view of the polyimide substrate for demonstrating the manufacturing process of this.

The manufacturing method of the polyimide wiring board which concerns on 2nd Embodiment of this invention includes the process shown below;
A modifying step of treating the polyimide substrate with an alkaline solution to form a polyimide modified layer in which the imide ring is opened;
A metal ion adsorption step of treating the polyimide substrate with a metal ion-containing solution to adsorb the metal ions to the modified layer;
A mask pattern forming step of forming a mask pattern on the modified layer and selectively exposing the modified layer;
A metal ion reduction step of reducing the metal ions adsorbed on the modified layer by depositing the polyimide substrate in a reducing bath and depositing a metal thin film on the exposed region of the modified layer;
A plating step of forming a conductor layer on the metal thin film by plating;
A mask pattern removing step for removing the mask pattern;
A cleaning treatment step of washing the polyimide substrate; and a heat treatment step of ring-closing treatment of the polyimide modified layer by heating.

-Modification process In this process, by the method similar to the modification process of 1st Embodiment, the polyimide board | substrate 1 is processed with an alkaline solution, and the polyimide modified layer 2 by which the imide ring was opened is formed (FIG. 11). Step (1)).

Metal ion adsorption step In this step, the polyimide substrate is treated with a metal ion-containing solution by the same method as the metal ion adsorption step of the first embodiment, and the metal ions are adsorbed to the modified layer 2 ( Step (2) in FIG.

Mask pattern forming step In this step, the modified layer 2 is formed in the same manner as in the mask pattern forming step of the first embodiment except that the mask pattern has a predetermined wiring shape. And the mask pattern 103 is formed as shown to (b), and this modified layer 2 is selectively exposed (process (3) of FIG. 11). The schematic cross-sectional view of FIG. 12A is a cross-sectional view taken along the line AB in the center of the schematic top view of FIG. As shown in FIG. 12B, the exposed region of the modified layer 2 that is not covered with the mask pattern 103 is a region where the metal thin film 104 is formed in a metal ion reduction process described later. By forming the mask pattern in this way, as in the first embodiment, even the metal ions B in the modified layer such as the region covered with the mask pattern 103 diffuse and move, and the metal thin film Since it contributes to formation, thickening of the metal thin film can be achieved easily and effectively.

  The mask pattern 103 is the same as the mask pattern 3 of the first embodiment except that the wiring shape is different. Preferably, it is formed by a printing method. When the opening of the mask pattern 103 is a fine pattern and the distance between the covered region and the exposed region by the mask pattern is sufficiently small, for example, 20 μm or less, the ion diffused in the modified layer 2 Therefore, it is preferable to provide the mask pattern 103 through the steps of exposure and development after applying the photosensitive film resist, giving priority to ensuring the dimensional accuracy.

  The shape of the mask pattern 103 is preferably such that a region where the mask pattern 103 is not formed (modified layer exposed region; opening) forms one continuous figure as viewed from above. As a result, the metal thin film formed in the metal ion reduction process forms a continuous figure as viewed from above, so when performing electroplating in the plating process described later, Installation of the power supply electrode is facilitated.

-Metal ion reduction step In this step, the polyimide substrate is reduced in a reduction bath by the same method as the metal ion reduction step of the first embodiment to reduce the metal ions B adsorbed on the modified layer. 13 (a) and 13 (b), a metal thin film 104 is deposited and formed on the exposed region of the modified layer 2 (step (4) in FIG. 11). The schematic cross-sectional view of FIG. 13A is a cross-sectional view taken along the line AB in the center of the schematic top view of FIG. The metal thin film 104 is the same as the metal thin film 4 in the metal ion reduction process of the first embodiment except that it has a predetermined wiring shape.

  In this step, the reducing bath can be the electroless plating bath used in the plating step of the first embodiment, in addition to the reducing bath used in the metal ion reduction step of the first embodiment. When an electroless plating bath is used as the reducing bath, when the metal ions B adsorbed on the modified layer 2 are reduced by the reducing agent in the electroless plating bath to form metal particles, the metal particles are used as catalyst nuclei. The metal ions B contained in the modified layer 102 and the metal complex in the reduction bath are continuously reduced, and the metal thin film 104 and the conductor layer 106 are continuously formed. In this case, after that, the mask pattern removing process may be performed without performing the plating process.

-Plating step In this step, the conductive layer 106 is formed on the metal thin film 104 by plating as shown in FIGS. 14A and 14B by the same method as the plating step of the first embodiment. (Step (5) in FIG. 11). The plating method is not particularly limited as long as a predetermined conductor layer is formed, and may be, for example, an electrolytic plating method, an electroless plating method, or a combination thereof. From the viewpoint of the formation efficiency of the conductor layer, it is preferable to employ an electrolytic plating method. 14A is a cross-sectional view taken along the line AB in the center of the schematic top view of FIG. 14B. The conductor layer 106 is the same as the conductor layer 6 in the plating step of the first embodiment except that it has a predetermined wiring shape.

Mask pattern removing step In this step, the mask pattern 103 is removed from the polyimide substrate having the mask pattern 103 as shown in FIGS. 14A and 14B by the same method as the mask pattern removing step of the first embodiment. By removing, the modified layer 2 is exposed as shown in FIGS. 15A and 15B (step (6) in FIG. 11). The schematic cross-sectional view of FIG. 15A is a cross-sectional view taken along the line AB in the center of the schematic top view of FIG.

Cleaning process In this process, the polyimide substrate is cleaned by the same method as the cleaning process of the first embodiment, and the metal ions contained in the modified layer 2 are replaced with hydrogen ions (the process of FIG. 11). (7)). Preferably, the dehydration process is performed after washing as in the first embodiment. In this embodiment, since the conductor layer is formed before the mask pattern removing step and the metal thin film is not exposed, it is not necessary to select an acidic solution according to the metal material of the metal thin film in this step.

Heat treatment step In this step, the polyimide-modified layer is subjected to ring-closing treatment by heating in the same manner as the heat treatment step of the first embodiment (step (8) in FIG. 11). As a result, the polyimide-modified layer 2 is re-imidized, and a structure in which the wiring pattern 107 is formed on the substrate 1 made of only polyimide as shown in FIGS. 16A and 16B can be obtained. Here, the difference between FIG. 16 and FIG. 15 is that the modified layer 2 is imidized and the boundary between the substrate and the polyimide is eliminated. The schematic cross-sectional view of FIG. 16A is a cross-sectional view taken along the line AB in the center of the schematic top view of FIG.

  In both the first embodiment and the second embodiment, after the wiring pattern is formed, a cover lay forming process for forming a cover lay on the polyimide substrate on which the wiring pattern is formed is generally performed. Complete the polyimide wiring board by carrying out the terminal part surface treatment process that performs surface treatment such as Au plating on the terminal part and the substrate division process that divides the large-area sheet-like substrate into predetermined dimensions as desired Let

Coverlay forming step The coverlay is intended to mechanically protect the wiring pattern formed in the above steps and to insulate it from the outside. When soldering is performed for connection between the wiring pattern and the outside, it is also called a solder resist because it is formed to define a region where the solder should not get wet.

The materials and methods used in the coverlay forming step are not particularly limited, and commercially available materials and methods can be used. There are a film-like thing and a liquid thing, and what is necessary is just to use them.
For example, Hitachi Chemical's Raytec FR-5638 can be used. This film is attached to the entire surface of the polyimide substrate, and unnecessary portions are removed by photolithography. At this time, the portion from which the coverlay has been removed becomes the terminal portion. This operation is performed on both sides.

・ Terminal surface treatment process Next, surface treatment of the terminals is performed for the locations that will be the external terminals of the wiring pattern. For example, when forming a soldering terminal, the Ni film and the Au film are subsequently formed. A Ni film having a thickness of about 5 μm is formed by dipping in a commercially available electroless Ni plating bath, and then an Au film having a thickness of about 0.5 μm is formed by dipping in a commercially available electroless Au plating bath.

・ Substrate dividing process The substrate dividing process is continued. This is necessary when the substrate size as a product is different from the work size to be processed. For example, an extra area is provided in the peripheral part of the work to be processed for handling. This part is removed.
Specifically, the polyimide substrate that has undergone the above steps is placed in a mold, and punching is performed. By doing so, a double-sided polyimide wiring board can be formed.

  In the second embodiment, as shown in FIGS. 12A and 12B, the openings (modified layer exposed regions) of the mask pattern 103 are formed intermittently when viewed from above, so that the metal thin film is continuous. When the electroplating is not performed in the plating process and the power supply electrode needs to be installed on each metal thin film, the processing is complicated. However, such a problem can be solved by devising the shape of the opening of the mask pattern and performing a substrate dividing step. Specifically, the shape of the opening of the mask pattern is a composite continuous shape including openings for intermittent wiring portions and openings for connecting the individual intermittent wiring portions. Thereby, even a wiring board having a wiring portion intermittently can be manufactured by a simple electrolytic plating process.

  For example, except for using a mask pattern 203 having a composite continuous shape opening as shown in FIGS. 17A and 17B, the modification step, the metal ion adsorption step, and the second embodiment, By performing the mask pattern forming step, a polyimide substrate having the mask pattern 203 formed on the modified layer 2 is obtained as shown in FIGS. The schematic cross-sectional view of FIG. 17A is a cross-sectional view taken along the line AB in the center of the schematic top view of FIG. With respect to the composite continuous shape opening (corresponding to 2) included in the mask pattern 203 shown in FIG. 17B, the opening for the intermittent wiring is an opening in dotted brackets, and the wiring The opening for connecting the parts is an opening outside the dotted brackets. The mask pattern 203 is the same as the mask pattern 103 of the second embodiment except that the shape when viewed from above is different.

  Next, by performing the same metal ion reduction process, plating process, mask pattern removal process, cleaning process and heat treatment process as in the second embodiment, except that electrolytic plating is performed in the plating process, FIG. As shown in (b), a polyimide substrate is obtained on which a wiring portion 207 comprising a metal thin film 204 and a conductor layer 206 having the same shape as the composite continuous shape is formed. The schematic cross-sectional view of FIG. 18A is a cross-sectional view taken along the line AB in the center of the schematic top view of FIG. The metal thin film 204 forms a continuous figure as viewed from above, and the power supply electrode need only be installed on one metal thin film in the plating process, so the processing is simple. The metal thin film 204 is the same as the metal thin film 104 of the second embodiment except that the shape when viewed from the top is different.

  Thereafter, by performing the same coverlay forming process and substrate dividing process as in the second embodiment, as shown in FIG. 19, a wiring board having a wiring portion having a conductor layer 206 on the surface is obtained. be able to. Reference numeral 208 denotes a coverlay.

  Although the manufacturing method of the polyimide wiring board of this invention is demonstrated in detail by an Example, this invention is not limited to these Examples.

[Example 1]
Example 1 corresponds to the first embodiment.
In this example, a polyimide wiring board was manufactured by the steps described below.
As an object to be plated, a polyimide substrate 1 made of polyimide (apical NPI manufactured by Kaneka Corporation) having a size of 200 mm × 200 mm × 50 μm was used.

(Reforming process)
Next, the polyimide substrate 1 (FIG. 2A) was immersed in a 5 mol / L, 50 ° C. aqueous KOH solution for 3 minutes and washed with water for 2 minutes. On the surface of the polyimide substrate 1, hydrolysis of the imide ring was performed, and the formed polyamic acid potassium salt in which potassium ions were coordinated to the carboxyl group was formed in the formed modified layer 2 (FIG. 2 (b)). .

(Metal ion adsorption process)
Next, the polyimide substrate 1 was immersed for 10 minutes in a 0.05 mol / L CuSO ₄ aqueous solution at 30 ° C., and the potassium ions in the modified layer 2 were exchanged with copper ions to form a polyamic acid copper salt. Thereafter, it was washed with water for 2 minutes and dried.

(Mask pattern forming process)
Next, a resist ink containing a thermoplastic resin and an organic solvent as a solvent was printed on one surface of the polyimide substrate 1. Next, the polyimide substrate 1 was heated with a hot plate at 150 ° C. to volatilize the solvent in the resist ink, thereby forming a mask pattern 3. Next, the mask pattern 3 was similarly formed on the remaining one surface of the polyimide substrate 1 (FIGS. 3A and 3B). The ratio (covered area / exposed area; area ratio) between the covered area and the exposed area by the mask pattern was 2/1 on both surfaces.

(Metal ion reduction process)
Next, the polyimide substrate 1 is immersed in a 0.005 mol / L, 30 ° C. NaBH ₄ aqueous solution for 5 minutes to form a metal thin film 4 made of copper on the exposed surface of the modified layer 2, and further washed with water for 2 minutes. This was done (FIGS. 4 (a) and (b)). This NaBH ₄ aqueous solution was adjusted to pH 8 or lower using citric acid and sodium citrate in order to suppress the generation of copper oxide. Although the thickness of the formed metal thin film 4 varied from 100 to 300 nm, the average film thickness was 150 nm.

(Mask pattern removal process)
Next, the mask pattern 3 was peeled off using propylene glycol monomethyl ether acetate, rinsed with isopropyl alcohol, and further washed with water (FIGS. 5A and 5B).
(Washing process)
Next, the polyimide substrate 1 was immersed in 0.1 mol / l citric acid at 25 ° C. for 15 minutes, washed with water for 2 minutes, and dried by N ₂ blow. The results of elemental analysis before and after cleaning are shown in FIGS. 20 (a) and 20 (b). The measurement location is inside the modified layer 1 μm inside from the metal thin film in the cross section. In FIG. 20 (b) showing the chart after cleaning, the peak intensity of Cu-La is reduced from that in FIG. 20 (a) showing the chart before cleaning, and the Cu in the modified layer is obtained by performing acid cleaning. It can be seen that the ions have been removed. As a result of cross-sectional observation, the metal film thickness was reduced by 60 nm. Even so, the average film thickness was 90 nm, and even the thinnest film was 40 nm. The state where the metal thin film covered the polyimide surface was maintained. Further, the decrease in sheet resistance value was within 10%, and there was no problem in carrying out the electrolytic plating.
Next, after putting the polyimide substrate 1 in a vacuum oven, the pressure was reduced to 50 Pa and dehydration was performed for 3 hours. As a result, it is possible to prevent the metal thin film on the polyimide from being reionized in the modified layer, and to form a structure in which the metal thin film is arranged on the polyimide. FIG. 21 shows the result of elemental analysis of the polyimide substrate left for 3 hours in the drying room (temperature 25 ° C., humidity 0%) after the dehydration treatment. In FIG. 21, the peak intensity of Cu—La is similar to that in FIG. 20B showing the chart after cleaning, and it can be seen that reionization of the metal thin film is prevented.

(Heat treatment process)
Thereafter, the polyimide substrate 1 was put into an oven, and after the oxygen concentration was reduced to 200 ppm or less by nitrogen substitution, the temperature increase was started, held at 120 ° C. for 1 hour, further heated to 250 ° C., and held for 1 hour ( 6 (a) and (b)). When the depth in the substrate exposed region after heating is completed and analyzed polyimide sites 2~4μm in FT-IR, ring-opening amide appearing near 1647cm ^-1 (C = O) absorption spectrum, 1539Cm around ^-1 The ring-opening amide (C—N) absorption spectrum shown in FIG. Therefore, it was found that the imide ring was completely closed by heat treatment.

(Plating resist formation process)
Next, a negative photosensitive film resist having a thickness of 25 μm was attached to both surfaces of the polyimide substrate 1. After the exposure, development was performed using a 1% by weight, 30 ° C. aqueous sodium carbonate solution to form a resist 5 for plating as shown in FIGS. 7 (a) and (b). The width of the exposed region of the metal thin film 4 by the resist 5 was 20 μm.

(Plating process)
Next, the polyimide substrate 1 is immersed in 1 vol% sulfuric acid for 20 seconds to remove the oxide film of the metal thin film 4, and then an electrolytic copper plating solution (Microfab Cu200 (trademark (R)) manufactured by Nippon Electroplating Engineers Co., Ltd.) Then, electrolytic copper plating was performed using the metal thin film 4 as a power feeding layer, and a plating temperature of 28 ° C., a current density of 2 A / dm ² , and electroplating for 50 minutes to form a conductor layer 6 having a thickness of about 20 μm. (FIGS. 8A and 8B).

(Plating resist removal process)
Next, a 2% by weight, 50 ° C. NaOH aqueous solution was spray-coated on the surface of the polyimide substrate 1 to peel off the plating resist 5 and then washed with water for 5 minutes. This process was repeated twice, and the plating resist on both sides of the polyimide substrate 1 was peeled off (FIGS. 9A and 9B).

(Etching process)
Next, the polyimide substrate 1 was immersed in an etching solution for 1 minute, and the metal thin film 4 in the region covered with the plating resist 5 was removed (FIGS. 10A and 10B). As an etching solution, an aqueous solution of iron (III) [second] (FeCl ₃ ) at 35 g / L and 60 ° C. was used. This was followed by 2 minutes of water washing.

(Evaluation)
-Deformation and cracks The polyimide substrate immediately after the etching process was placed on a horizontal surface and visually observed. As a result, no warp deformation of the substrate occurred.
When the polyimide substrate immediately after the metal ion reduction step was dried, the metal thin film did not crack.

In the following evaluation, a polyimide substrate immediately after the etching process was used.
-Adhesiveness About the polyimide substrate, the 90 degree direction peeling test of Cu film | membrane (conductor layer) was implemented according to the method of JISC6471. A value of 1.1 kN / m or more was exhibited at 25 ° C., and good results were obtained.

-Fine pattern wiring The polyimide substrate was observed with the electron microscope.
A wiring pattern similar to the plating resist pattern formed in the plating resist formation step was formed.

[Example 2]
Example 2 corresponds to the second embodiment.
In this example, a polyimide wiring board was manufactured by the steps described below.
As an object to be plated, a polyimide substrate 1 made of polyimide (apical NPI manufactured by Kaneka Corporation) having a size of 200 mm × 200 mm × 25 μm in thickness was used.

(Reforming process)
The polyimide substrate 1 was immersed in a 5 mol / L, 50 ° C. aqueous KOH solution for 3 minutes and washed with water for 2 minutes.
(Metal ion adsorption process)
Next, the polyimide substrate 1 was immersed in an aqueous 0.05 mol / L CuSO ₄ solution at 30 ° C. for 10 minutes, and then washed with water for 2 minutes and dried.

(Mask pattern forming process)
Next, a negative photosensitive film resist having a thickness of 25 μm was attached to both surfaces of the polyimide substrate 1. After the exposure, development was performed using a 1% by weight, 30 ° C. aqueous sodium carbonate solution to form a mask pattern 103 as shown in FIGS. 12 (a) and 12 (b). The width of the exposed region of the modified layer 2 by the mask pattern 103 was 40 μm.

(Metal ion reduction process)
Next, the polyimide substrate 1 was immersed in a 0.05 mol / L dimethylamine borane solution at 30 ° C. for 40 minutes to form a metal thin film 104 made of copper (FIGS. 13A and 13B). Although the thickness of the formed metal thin film 104 varied from 100 to 200 nm, the average film thickness was 150 nm, and a part of the metal thin film 104 was also formed inside the polyimide substrate 1.

(Plating process)
Furthermore, the polyimide substrate 1 was immersed in an electroless copper plating solution to form a conductor layer 106 having a thickness of 5 μm on the metal thin film 104 (FIGS. 14A and 14B). The electroless copper plating solution contained copper sulfate, formaldehyde, sodium ethylenediaminetetraacetate and a pH adjuster, and was plated at a solution temperature of 70 ° C. for 4 hours.

(Mask pattern removal process)
Next, a 1% by weight NaOH aqueous solution was spray-coated on the surface of the polyimide substrate 1 to peel off the mask pattern 103, and then washed with water for 5 minutes. This process was repeated twice, and the mask pattern 103 on both surfaces of the polyimide substrate 1 was peeled off (FIGS. 15A and 15B).
(Washing process)
Next, the polyimide substrate 1 is immersed in a citric acid solution having a concentration of 0.1 mol / l and 25 ° C. for 15 minutes, washed with water for 2 minutes, and then blown with N ₂ . Dried. Next, after putting the polyimide substrate 1 in a vacuum oven, the pressure was reduced to 50 Pa and dehydration was performed for 3 hours.

(Heat treatment process)
Thereafter, the polyimide substrate 1 was placed in an oven, and with the oxygen concentration reduced to 200 ppm or less by nitrogen substitution, the temperature increase was started, held at 120 ° C. for 1 hour, further heated to 250 ° C. and held for 1 hour. (FIG. 16 (a) and (b)). When the depth in the substrate exposed region after heating is completed and analyzed polyimide sites 2~4μm in FT-IR, ring-opening amide appearing near 1647cm ^-1 (C = O) absorption spectrum, 1539Cm around ^-1 The ring-opening amide (C—N) absorption spectrum shown in FIG. Therefore, it was found that the imide ring was completely closed by heat treatment.

(Evaluation)
-Deformation and cracking When the polyimide substrate immediately after the heat treatment step was placed on a horizontal surface and observed visually, no warp deformation of the substrate occurred.
When the polyimide substrate immediately after the metal ion reduction step was dried, the metal thin film did not crack.

The following evaluation was performed by the same method as in Example 1 except that the polyimide substrate immediately after the heat treatment step was used.
-Adhesion A value of 1.1 kN / m or more was exhibited at 25 ° C., and good results were obtained.
-Fine pattern wiring A wiring pattern similar to the plating mask pattern formed in the mask pattern forming process was formed.

[Example 3]
Example 3 corresponds to the second embodiment.
In this example, a polyimide wiring board was manufactured by the steps described below.
As an object to be plated, a polyimide substrate 1 made of polyimide (apical NPI manufactured by Kaneka Corporation) having a size of 200 mm × 200 mm × 50 μm was used.

(Reforming process)
The polyimide substrate 1 was immersed in a 5 mol / L, 50 ° C. aqueous KOH solution for 3 minutes and washed with water for 2 minutes. On the surface of the polyimide substrate 1, the imide ring was hydrolyzed, and in the formed modified layer 2, potassium polyamic acid in which potassium ions were coordinated to the carboxyl group was formed.
(Metal ion adsorption process)
Next, the polyimide substrate 1 was immersed in a 0.05 mol / L CuSO ₄ SO ₄ aqueous solution at 30 ° C. for 10 minutes, and the potassium ions in the modified layer 2 were exchanged with copper ions to form a polyamic acid copper salt. Thereafter, it was washed with water for 2 minutes and dried.

(Mask pattern forming process)
Next, a negative photosensitive film resist having a thickness of 25 μm was attached to both surfaces of the polyimide substrate 1. After the exposure, development was performed using a 1% by weight, 30 ° C. aqueous sodium carbonate solution to form a mask pattern 203. The mask pattern 203 formed on one surface of the polyimide substrate 1 has openings as shown in FIGS. 17A and 17B, but the mask pattern 203 formed on the remaining surface has no openings. . The minimum width of the exposed region of the modified layer 2 by the mask pattern 203 was 20 μm. The ratio (covered area: exposed area, area ratio) of the covered area and the exposed area by the mask pattern on the upper surface was 3: 1.

(Metal ion reduction process)
Next, the polyimide substrate 1 was immersed in a 0.05 mol / L dimethylamine borane solution at 50 ° C. for 10 minutes to form a metal thin film 204 made of copper, and further washed with water for 2 minutes. The thickness of the formed metal thin film 204 varied from 100 to 300 nm, the average film thickness was 150 nm, and a part thereof was formed inside the polyimide substrate 1.

(Plating process)
Next, the polyimide substrate 1 was immersed in an electrolytic copper plating solution (Microfab Cu200 manufactured by Nippon Electroplating Engineering Co., Ltd.), and electrolytic copper plating was performed using the metal thin film 204 as a power feeding layer. Electrolytic plating was performed at a plating temperature of 28 ° C. and a current density of 2 A / dm ² for 50 minutes to form a conductor layer 206 having a thickness of about 20 μm.

(Mask pattern removal process)
Next, a 2% by weight, 50 ° C. aqueous NaOH solution was spray applied onto the surface of the polyimide substrate 1 to peel off the mask pattern 203, and then washed with water for 5 minutes. This process was repeated twice, and the mask pattern 203 on both sides of the polyimide substrate 1 was peeled off.
(Washing process)
Next, the polyimide substrate 1 was immersed in sulfuric acid having a concentration of 1 vol% and 25 ° C. for 5 minutes, washed with water for 2 minutes, and then dried by N ₂ blow. Next, after putting the polyimide substrate 1 in a vacuum oven, the pressure was reduced to 50 Pa and dehydration was performed for 3 hours.

(Heat treatment)
Thereafter, the polyimide substrate 1 was placed in an oven, and with the oxygen concentration reduced to 200 ppm or less by nitrogen substitution, the temperature increase was started, held at 120 ° C. for 1 hour, further heated to 250 ° C. and held for 1 hour. (FIGS. 18A and 18B). When the depth in the substrate exposed region after heating is completed and analyzed polyimide sites 2~4μm in FT-IR, ring-opening amide appearing near 1647cm ^-1 (C = O) absorption spectrum, 1539Cm around ^-1 The ring-opening amide (C—N) absorption spectrum shown in FIG. Therefore, it was found that the imide ring was completely closed by heat treatment.

(Evaluation)
-Deformation and cracking When the polyimide substrate immediately after the heat treatment step was placed on a horizontal surface and observed visually, no warp deformation of the substrate occurred.
When the polyimide substrate immediately after the metal ion reduction step was dried, the metal thin film did not crack.

The following evaluation was performed by the same method as in Example 1 except that the polyimide substrate immediately after the heat treatment step was used.
-Adhesion A value of 1.1 kN / m or more was exhibited at 25 ° C., and good results were obtained.
-Fine pattern wiring A wiring pattern similar to the plating mask pattern formed in the mask pattern forming process was formed.

[Comparative Example 1]
Without performing mask pattern formation process and mask pattern removal process, reforming process, metal ion adsorption process, metal ion reduction process, plating resist formation process, plating process, plating resist removal process, etching process, cleaning process process And the polyimide wiring board was manufactured by the method similar to Example 1 except having implemented the heat processing process sequentially.
Although the thickness of the metal thin film 4 formed in the metal ion reduction process was 100 to 200 nm, only about 50% of the surface of the polyimide substrate 1 was covered with the metal thin film 4 and used as a power feeding layer for electrolytic plating. I couldn't.

[Comparative Example 2]
(Reforming process)
Next, the polyimide substrate 1 was immersed in a 5 mol / L, 50 ° C. KOH aqueous solution for 5 minutes and washed with water for 2 minutes. On the surface of the polyimide substrate 1, the imide ring was hydrolyzed, and in the formed modified layer 2, potassium polyamic acid in which potassium ions were coordinated to the carboxyl group was formed.
(Metal ion adsorption process)
Next, the polyimide substrate 1 was immersed for 10 minutes in a 0.05 mol / L CuSO ₄ aqueous solution at 30 ° C., and the potassium ions in the modified layer 2 were exchanged with copper ions to form a polyamic acid copper salt. Thereafter, it was washed with water for 2 minutes and dried.
(Metal ion reduction process)
Next, the polyimide substrate 1 is immersed in a 0.005 mol / L, 30 ° C. NaBH ₄ aqueous solution for 5 minutes to form a metal thin film 4 made of copper on the exposed surface of the modified layer 2, and further washed with water for 2 minutes. went. This NaBH ₄ aqueous solution was adjusted to pH 8 or lower using citric acid and sodium citrate in order to suppress the generation of copper oxide. Although there was a variation of 100 to 200 nm, the average film thickness was 150 nm.
Next, when the polyimide substrate 1 was dried to form a plating resist, the metal thin film 4 was cracked. Along with the cracks in the metal thin film 4, the modified layer 2 is also cracked and could not be used as a substrate for a wiring board.

  INDUSTRIAL APPLICABILITY The present invention can be widely used in the manufacture of circuit boards such as flexible wiring boards, and the manufacture of circuit boards incorporated in electronic devices typified by portable information devices such as mobile phones that are required to be reduced in size and weight. Useful as a method.

It is a flowchart which shows the manufacturing process by 1st Embodiment of the manufacturing method of the polyimide wiring board of this invention. (A) And (b) is a schematic sectional drawing explaining one manufacturing process of the said 1st Embodiment. (A) is a schematic sectional drawing explaining one manufacturing process of the said 1st Embodiment, (b) is a schematic top view of (a). (A) is a schematic sectional drawing explaining one manufacturing process of the said 1st Embodiment, (b) is a schematic top view of (a). (A) is a schematic sectional drawing explaining one manufacturing process of the said 1st Embodiment, (b) is a schematic top view of (a). (A) is a schematic sectional drawing explaining one manufacturing process of the said 1st Embodiment, (b) is a schematic top view of (a). (A) is a schematic sectional drawing explaining one manufacturing process of the said 1st Embodiment, (b) is a schematic top view of (a). (A) is a schematic sectional drawing explaining one manufacturing process of the said 1st Embodiment, (b) is a schematic top view of (a). (A) is a schematic sectional drawing explaining one manufacturing process of the said 1st Embodiment, (b) is a schematic top view of (a). (A) is a schematic sectional drawing explaining one manufacturing process of the said 1st Embodiment, (b) is a schematic top view of (a). It is a flowchart which shows the manufacturing process by 2nd Embodiment of the manufacturing method of the polyimide wiring board of this invention. (A) is a schematic sectional drawing explaining one manufacturing process of the said 2nd Embodiment, (b) is a schematic top view of (a). (A) is a schematic sectional drawing explaining one manufacturing process of the said 2nd Embodiment, (b) is a schematic top view of (a). (A) is a schematic sectional drawing explaining one manufacturing process of the said 2nd Embodiment, (b) is a schematic top view of (a). (A) is a schematic sectional drawing explaining one manufacturing process of the said 2nd Embodiment, (b) is a schematic top view of (a). (A) is a schematic sectional drawing explaining one manufacturing process of the said 2nd Embodiment, (b) is a schematic top view of (a). (A) is a schematic sectional drawing explaining the one manufacturing process in another specific example of the said 2nd Embodiment, (b) is a schematic top view of (a). (A) is a schematic sectional drawing explaining the one manufacturing process in another specific example of the said 2nd Embodiment, (b) is a schematic top view of (a). It is a schematic top view explaining one manufacturing process in another specific example of the second embodiment. (A) And (b) is the experimental result regarding the elemental analysis of Example 1. FIG. 3 is an experimental result regarding elemental analysis of Example 1. FIG.

Explanation of symbols

  1: polyimide substrate, 2: modified layer, 3: 103: mask, 4: 104: 204: metal thin film, 5: resist for plating, 6: 106: 206: conductor layer, 7: 107: 207: wiring.

Claims (8)

A modifying step of treating the polyimide substrate with an alkaline solution to form a polyimide modified layer in which the imide ring is opened;
A metal ion adsorption step of treating the polyimide substrate with a metal ion-containing solution to adsorb the metal ions to the modified layer;
A mask pattern forming step of forming a mask pattern on the modified layer and selectively exposing the modified layer; and reducing the polyimide substrate in a reducing bath to thereby remove metal ions adsorbed on the modified layer. A metal ion reduction step of reducing and depositing a metal thin film on the exposed region of the modified layer;
The manufacturing method of the polyimide wiring board characterized by including. A mask pattern removing step for removing the mask pattern;
A cleaning process for cleaning the polyimide substrate; and a heat treatment process for ring-closing the polyimide-modified layer by heating;
The method for producing a polyimide wiring board according to claim 1, further comprising:   3. The method for manufacturing a polyimide wiring board according to claim 2, wherein, in the cleaning treatment step, after the polyimide substrate is washed, the polyimide substrate is dehydrated by vacuum drying. 4. The method for manufacturing a polyimide wiring board according to claim 2, wherein after the mask pattern removal step, the cleaning treatment step, and the heat treatment step are performed, the following steps are further performed.
Forming a plating resist on the polyimide substrate surface, and selectively exposing the metal thin film;
A plating step of forming a conductor layer on the exposed region of the metal thin film by plating;
A plating resist removing step of exposing the metal thin film by removing the plating resist; and an etching step of etching away the metal thin film exposed in the plating resist removing step using the conductor layer as a mask.   4. The method according to claim 2, wherein the mask pattern removing step, the cleaning treatment step, and the heat treatment step are performed after performing a plating step of forming a conductor layer on the metal thin film by a plating treatment. The manufacturing method of the polyimide wiring board of description.   The method for producing a polyimide wiring board according to claim 1, wherein the metal thin film formed in the metal ion reduction step forms one continuous figure.   The method for producing a polyimide wiring board according to claim 1, wherein the mask pattern is formed by a printing method in the mask pattern forming step.   The method for producing a polyimide wiring board according to claim 1, wherein the mask pattern formed in the mask pattern forming step has a symmetrical shape on both surfaces of the polyimide substrate.

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