JP4684983B2 - Laminated body for flexible printed wiring board and copper alloy sputtering target - Google Patents

Description

The present invention relates to a material for the flexible printed circuit board, a flexible printed wiring board laminate for a two-layer structure type obtained by forming a conductive layer without using an adhesive on the resin film (base film), the It is related with the copper alloy sputtering target used in order to form the conductor layer (copper alloy layer) of the laminated body for flexible printed wiring boards .

  In recent years, flexible printed wiring boards (flexible electronic circuit boards) that can be bent have been widely used in mobile phones, digital cameras, liquid crystal displays, and the like. Resin films (plastic films) are used for flexible printed wiring boards. Among them, polyimide films have excellent heat resistance and chemical stability, and are particularly excellent in mechanical properties. Since it is not damaged, it is used as a base film which is an electrically insulating substrate of a flexible printed wiring board which is rich in flexibility.

  The flexible printed wiring board is a laminated body for a flexible printed wiring board by forming a conductor layer on a resin film (base film) represented by the polyimide film, and the conductor layer of the laminated body is electronically etched or the like. A circuit is formed. Here, in a laminate in which a copper foil is provided as a conductor layer, generally, the adhesion between a resin film including a polyimide film and the copper foil is poor. It has been broken. Moreover, the adhesive force between the resin film and the copper foil is ensured by applying a thermosetting or ultraviolet curable resin material on the copper foil having irregularities on the surface and then curing it. Yes.

  Recently, with the progress of higher density electronic circuits, flexible printed wiring boards have been required to be finely processed. In this case, there arises a problem that non-uniform etching occurs due to unmelted adhesive in the etching process and unevenness of the copper foil. Moreover, when the thickness of the copper foil to join is thick, there exists a problem that it is difficult to produce the fine wiring of the space | interval narrower than a film thickness by an etching.

  As a method for solving these problems, the metallizing method has attracted attention. In the metalizing method, a copper seed layer is formed on a smooth resin film by vapor deposition or sputtering, and then a copper plating layer (copper plating film) having an appropriate thickness is formed thereon by electroplating. . This metallizing method is suitable for fine wiring formation because the thickness of the copper plating layer can be arbitrarily adjusted and a thin copper plating layer can be formed. Further, if a resin surface having a smooth surface is used as the substrate, the etching non-uniformity can be reduced.

  However, even with the metallizing method, the adhesion between the copper layer (copper plating layer) and the resin film (polyimide film) is not high, so that when the electronic circuit is mounted, the copper layer is easily peeled off from the resin film. There's a problem.

  In order to solve this problem, it has been proposed to form an adhesion layer between the copper layer and the resin film. For example, in Japanese Patent Publication No. 4-65558 (Patent Document 1), as a circuit material, an adhesive layer (adhesion layer) made of chromium / chromium oxide is formed on an electrically insulating support film, and a copper layer is formed thereon. Circuit materials designed to be formed have been proposed. In Japanese Patent Publication No. 57-18357 (Patent Document 2), a film of Ni, Co, Zr, Pd or an alloy containing these is formed as an adhesion layer on a plastic substrate, and a copper thin film is formed thereon. In Japanese Patent Publication No. 57-18356 (Patent Document 3), a Ni or Ni alloy film is formed as an adhesion layer on a polyimide film, and a copper film is formed thereon. A printed circuit board has been proposed.

  In JP-A-8-332697 (Patent Document 4), an alloy layer containing at least two of Ti, Co, Mo and Ni is formed as an adhesion layer on a plastic film, and a copper layer is formed thereon. A formed metal polymer film has been proposed. In JP 2001-77493 A (Patent Document 5), a tantalum carbide layer, a titanium carbide layer or an amorphous carbon layer is formed as an adhesion layer on a polyimide film, and a metal layer (copper layer) is formed thereon as a conductor layer. A flexible printed circuit board formed by forming a layer) has been proposed.

  Thus, in order to ensure the adhesiveness of a copper layer and a resin film, what has the metal or alloy layer used as an adhesion layer between a copper layer and a resin film has become mainstream now. For example, a Ni-Cr alloy is an example of an alloy that is particularly often used as the adhesion layer, but the adhesion layer is designed to prevent the copper layer from peeling off.

  However, in the case of having an adhesion layer made of a metal or alloy as described above, the etching characteristics of the copper layer and the etching characteristics of the adhesion layer are considerably different, and thus special etching is required. For example, in the case of having an adhesion layer made of Cr, the adhesion between the resin film and the copper layer is enhanced through the Cr adhesion layer, but on the other hand, etching of the Cr adhesion layer itself is difficult. For this reason, an adhesion layer made of the above-described Ni—Cr alloy has been proposed to solve this problem, and is currently mainstream. In the case of the adhesion layer made of this Ni—Cr alloy, etching can be performed with the same ferric chloride solution that etches the copper layer, but the etching rate is different from the etching rate of the copper layer, resulting in a speed difference. Therefore, non-uniform etching and residue are likely to occur.

  In addition, in the case of having an adhesion layer made of a metal or an alloy as described above, the etching characteristics in the vicinity of the interface due to the generation of an electrical contact potential at the junction between the copper layer and an adhesion layer made of a different metal. Changes drastically, and an adhesive layer with a width of several μm near the copper layer remains as a portion that cannot be etched. These undissolved residues did not pose a problem when the wiring pitch is wide, but cannot be overlooked when the wiring pitch is about 20 μm or less.

  In this way, as electronic circuits become more dense (miniaturized) in the future, etching itself becomes a more difficult process than ever, making it difficult to perform two-stage etching that requires delicate control, Residue is a problem, and a slight undissolved portion of the adhesion layer around the copper layer becomes a serious problem that leads to a short circuit of the wiring.

  Therefore, there is a demand for a laminate for a flexible printed wiring board that has good adhesion between a resin film and a conductor layer, is easy to etch when providing an electronic circuit, and has few etching residues. Yes.

  From such a viewpoint, proposals such as those described in JP-A-2005-158887 (Patent Document 6) and JP-A-2005-203581 (Patent Document 7) have been made. In these proposals, since a trace metal element is added to Cu and used as an adhesion layer, the above-described problem due to generation of residues does not occur.

  However, although the adhesion layer technology as described above has been successful for some time, the adhesion is remarkably observed when a severe durability test (for example, a durability test at 150 ° C. for 168 hours in an air atmosphere) is performed. It is known that the sex decreases. Even if it has a Ni-Cr alloy layer which is a frequently used adhesion layer, the adhesion will be reduced to half or less after the durability test. Although the cause of such a decrease in the adhesion strength after the test has not been clarified, it is considered that the oxidation reaction of the conductor layer Cu or the adhesion layer itself and the alteration of the resin film may have an influence. Therefore, the development of materials and processes that ensure adhesion after the durability test is urgent as a major technical problem in the technical field.

That is, in order to realize a flexible circuit board with high reliability and capable of forming a high-density circuit, there is no decrease in the adhesion between the resin film and the conductor layer even after the durability test, and the conductor layer In the process of forming the wiring, it is important that there is no residue between the wirings and that there is no undissolved residue around the wiring.
Japanese Examined Patent Publication No. 4-65558 Japanese Patent Publication No.57-18357 Japanese Patent Publication No.57-18356 JP-A-8-332697 JP 2001-77493 A JP 2005-158887 A JP 2005-203581 A

The present invention has been invented as a solution to the above-described conventional problems, and in a laminate for a flexible printed wiring board formed with a conductor layer on a resin film, has excellent etching properties, and has a resin film and a conductor layer. The laminate for flexible printed wiring boards that exhibits excellent reliability, and that is retained even after a durability test, and the conductor layer (copper alloy layer) of the laminate for flexible printed wiring boards are formed. An object of the present invention is to provide a copper alloy sputtering target used for the purpose .

The invention according to claim 1 is a laminate for a flexible printed wiring board, wherein a copper alloy layer containing 0.1 to 10.0 atomic% of Mg or Si is formed on a resin film. .

According to the invention of claim 2, a copper alloy layer containing 0.1 to 10.0 atomic% of Mg or Si is formed on a resin film, and a copper sputter layer and / or a copper plating layer is formed on the copper alloy layer. It is the laminated body for flexible printed wiring boards characterized by forming. The invention according to claim 3 is a copper alloy sputtering target for forming the copper alloy layer according to claim 1 or 2, characterized by containing 0.1 to 10.0 atomic% of Mg or Si. This is a copper alloy sputtering target.

  According to the laminate for a flexible printed wiring board of the present invention, in the laminate for a flexible printed wiring board of a two-layer structure type in which a conductor layer is formed on a resin film without using an adhesive, the resin film and the conductor layer A laminate for a flexible printed wiring board that has a small decrease in adhesion, particularly after durability testing, is excellent in reliability as a substrate, has excellent etching properties, and can sufficiently cope with high density of electronic circuits. Can be provided.

  Hereinafter, the present invention will be described in more detail based on embodiments shown in the accompanying drawings.

  As shown in FIG. 1, the first laminate for a flexible printed wiring board according to the present invention comprises Mg and / or Si as a conductor layer on a resin film as a base film, for example, a polyimide film as a representative film. A copper alloy layer containing Cu and inevitable impurities is formed.

  The present inventor has investigated in detail the relationship between the type and amount of additive elements constituting the copper alloy layer and the adhesion between the copper alloy layer and the polyimide film, and using an aqueous ferric chloride solution. The state of residue generation near the wiring side in the etching process of the copper alloy layer was investigated in detail. For adhesion, initial adhesion and evaluation after a durability test were performed. As a result, high adhesion was shown, and in the adhesion after the endurance test, it was possible to obtain higher adhesion than when the conventional adhesion layer was a Ni—Cr alloy layer.

  In addition, when an electronic circuit is provided on the copper alloy layer, etching can be performed without generating an etching residue in an insulating portion between the wirings by using the same ferric chloride aqueous solution as that for etching copper. Unlike the conventional method of forming the adhesion layer, there is no dissimilar metal, so there is no occurrence of undissolved residue that remains without being removed near the side surface of the wiring.

  The reason why the copper alloy layer is specified to contain 0.01 to 10.0 atomic% of Mg and / or Si as additive elements will be described. In a sample in which a copper alloy layer is formed to a thickness of 100 nm on a polyimide film by a sputtering method, and a Cu film 100 nm in the sputtering method is formed thereon as a plating seed layer, and a Cu film 8 μm is further formed by the plating method, (Beer strength) was measured. As a result, a sample having a Mg and / or Si content of 0.1 atomic% or less exhibited a remarkable effect with respect to adhesion after the durability test. Further, when the content of Mg and / or Si was 10.0 atomic% or more, the initial adhesive strength was lowered, and the result was completely peeled after the environmental test. Therefore, the total content of the additive elements is in the range of 0.1 to 10.0 atomic% as a range in which the effect of the element addition of the present invention can be exhibited. Moreover, when the content of Mg and / or Si increased, the etching rate tended to change slightly. From the point which suppresses generation | occurrence | production of an etching residue more, More preferably, the range of 0.1-5.0 atomic% is good, More preferably, the range of 0.1-3.0 atomic% is good.

  The thickness of the copper alloy layer is preferably in the range of 10 nm to 10 μm. If the copper alloy layer has a thickness of less than 10 nm, when a copper layer is further formed on the copper alloy layer, a pinhole is formed in the copper alloy layer. On the other hand, if it exceeds 10 μm, the resin film warps due to stress. Because it is not good.

  As shown in FIG. 2, the second laminate for a flexible printed wiring board according to the present invention comprises Mg and / or Si as an adhesion layer on a resin film that is a base film, for example, a polyimide film that is representative of the base film. A copper alloy layer containing Cu and unavoidable impurities is formed, and a copper sputter layer and / or a copper plating layer made of Cu and unavoidable impurities is formed thereon as a conductor layer. is there.

  Thus, even if it is the structure which formed the copper alloy layer on the resin film, and also formed the copper sputter layer and / or the copper plating layer on it, it is the same as that of the 1st above-mentioned layered product for flexible printed wiring boards. A laminate for a flexible printed wiring board having excellent adhesion and etching properties can be obtained. Adhesion is a problem at the joint between the resin film and the conductor layer. In this case, a copper alloy layer is formed on the resin film, and the etching characteristics of the copper alloy layer and the copper sputter layer or copper Since there is almost no difference from the etching characteristics of the plating layer, even with a structure in which a copper sputter layer and / or a copper plating layer is further formed on the copper alloy layer, the adhesion and etching properties are excellent. .

  In this case, the copper sputter layer is generally formed as a seed layer for enabling high-speed electroplating when a copper plating layer is formed on the copper sputter layer, and is formed by a sputtering method. Made of pure copper having a purity of about 99.9%. And the thickness of this copper sputter layer has the good range of 50 nm-20 micrometers. If the copper sputter layer has a thickness of less than 50 nm, when a copper plating layer is further formed on the copper sputter layer, pinholes are formed in the copper plating layer. On the other hand, if the thickness exceeds 20 μm, the resin film as the base film is stressed. This is because it is not good. The sputtered copper layer also serves to improve the adhesion between the copper alloy layer and the copper plating layer. That is, when copper plating is directly performed on the copper alloy layer, the adhesion between the copper alloy layer and the copper plating layer may be low. Such a problem can be solved by interposing a copper sputter layer between the copper alloy layer and the copper plating layer.

  The copper plating layer is formed by electroplating to increase the thickness of the conductor layer including the copper alloy layer when it is required to allow more current to flow in the electronic circuit. It is. And the thickness of this copper plating layer has the good range of 1-20 micrometers. If the thickness of the copper plating layer is less than 1 μm, the current that can be passed through the electronic circuit is not sufficient, whereas if it exceeds 20 μm, the resin film is warped by stress, which is not good.

(Example of Claim 1)
Using a 25 μm thick polyimide film (trade name Kapton (registered trademark of DuPont)) manufactured by Toray DuPont as a base film, a copper alloy layer having a thickness of 5 μm having a conductor layer composition shown in Table 1 on one side, It formed by the sputtering method by Ar gas using the copper alloy target which consists of a predetermined composition. The sputtering conditions were Ar gas pressure: 2 mTorr (0.27 Pa) and supply power: 3.3 W / cm ² . However, in Comparative Example 2, after a NiCr layer having a thickness of 20 nm was laminated, a pure Cu layer was subsequently laminated to a thickness of 5 μm as described above. For sputtering, a copper alloy target having a predetermined composition or a metal chip appropriately disposed on the copper alloy target was used. In these samples, the additive element composition of the copper alloy layer was adjusted to 2 atomic%.

  For each of the obtained laminates for flexible printed wiring boards of these samples, a copper alloy layer (wherein Comparative Example 1 is a Cu layer and Comparative Example 2 is a NiCr layer) by a wet etching method and using a ferric chloride aqueous solution. Etching was performed in a stripe shape having a width of 10 mm and a length of 90 mm. And about these samples, beer strength was measured according to the beer test method of JIS6481. In addition, the same sample was subjected to heat treatment at 150 ° C. in air for 168 hours (however, Comparative Example 1 was a half of 84 hours), that is, one week as a durability test, and the beer strength thereafter was the same as above. It was measured by the test method. Table 1 shows the measurement results of beer strength before the durability test (initial stage) and after the durability test.

  As shown in Table 1, in Examples 1 and 2, which satisfy the requirements of claim 1 of the present invention, as compared to Comparative Example 1, Cu was directly formed on the resin, compared to the polyimide film. Excellent adhesion. Further, even after a severe durability test, the adhesion is maintained at a high level of 200 N / m or more, and the adhesion strength exceeding 30% is maintained even with respect to the initial adhesion strength. It can be seen that even when compared with a typical example of the prior art using the NiCr adhesion layer of Comparative Example 2, it shows a significant advantage. Although Comparative Example 2 is more effective for improving the adhesion than Comparative Example 1, the adhesion is less than 200 N / m after the durability test, and the adhesion is less than 30% with respect to the initial adhesion. To stay. Further, in Comparative Example 2, generation of residue was confirmed in the wet etching, but Examples 1 and 2 were excellent in that no etching residue was generated.

(Example of Claim 2)
Using a polyimide film with a thickness of 25 μm (trade name Kapton (registered trademark of DuPont)) manufactured by Toray DuPont Co., Ltd., a copper alloy layer with a thickness of 100 nm of the adhesion layer composition shown in Table 2 is formed on one side from a predetermined composition. It formed by the sputtering method by Ar gas using the copper alloy target which becomes. (However, Comparative Example 3 does not have a copper alloy layer as an adhesion layer.) Next, a copper sputter layer having a thickness of 100 nm made of Cu was formed thereon by a sputtering method. This layer made of Cu serves as a plating seed layer. Next, a copper plating layer having a thickness of 7.8 μm was formed on the copper sputtered layer by electroplating Cu to obtain a laminate for a flexible printed wiring board. The sputtering conditions were Ar gas pressure: 2 mTorr (0.27 Pa), power supply: 3.3 W / cm ^2, and copper plating was performed using an aqueous copper sulfate solution at a temperature of 25 ° C. and a current density of 0.3 mA. Film formation was performed under the conditions of / cm ² . In these samples, the additive element composition of the copper alloy layer was adjusted to 2 atomic%. However, only Cu (Cr) of Comparative Example 5 was adjusted to 1 atomic%.

  With respect to each of the obtained laminates for flexible printed wiring boards, the conductor layer was etched into a stripe shape having a width of 10 mm and a length of 90 mm using a ferric chloride aqueous solution by a wet etching method. And about this each laminated body for flexible printed wiring boards, the beer strength was measured according to the beer test method of JIS6481. In addition, the same sample was subjected to heat treatment at 150 ° C. in air for 168 hours (however, Comparative Example 3 was half 84 hours), that is, one week as a durability test, and the beer strength thereafter was the same as above. It was measured by the test method. Table 2 shows the beer strength measurement results before (initial stage) the durability test and after the durability test.

  As shown in Table 2, in Examples 3 and 4 that satisfy the requirements of claim 2 of the present invention, compared to the case where Cu was directly formed on the resin as in Comparative Example 3, it was in close contact with the polyimide film. In addition to excellent durability, the adhesiveness is high even after severe durability tests, and shows a significant advantage compared to the one using the NiCr adhesion layer of Comparative Example 4 which is a typical prior art example. there were. Although Comparative Example 4 is effective in improving the adhesion strength as compared with Comparative Example 3, the adhesion strength is greatly reduced after the durability test. Further, in Comparative Example 4, generation of a residue was confirmed in the wet etching, but Examples 3 and 4 were excellent in that no etching residue was generated. In the alloys shown in Comparative Examples 5 to 12, it is clear that the initial adhesion force is not obtained, or that the adhesion force is remarkably reduced after the environmental test, and that the additive element according to the present invention provides a specific effect. It was.

  In Examples 3 and 4 shown this time, the sputtering method was used to form the alloy layer, but the effect exhibited by the present invention is an effect obtained by adding an additive element. It doesn't ask how. For example, it is considered that the same effect can be obtained by a method using vacuum deposition. Moreover, although the said Example assumes the flexible substrate based on a polyimide film, the laminated body for flexible printed wiring boards of this invention does not limit the resin film made into the object to a polyimide-type resin. . Such wiring reliability after the durability test is a performance required for various circuit boards, such as other resin plates such as liquid crystal polymer and Teflon (registered trademark of Polytetrafluoroethylene, US DuPont), epoxy type The same applies to the printed circuit board. Although the effect of the additive element according to the present invention has not been sufficiently elucidated yet, it is considered that there is an effect of suppressing mechanical strength deterioration at the Cu-resin interface by suppressing diffusion and oxidation of Cu into the resin. This is because it is considered that the same effect is exhibited also in the above-mentioned other resin substrates, for example, liquid crystal polymer, Teflon (registered trademark of Polytetrafluoroethylene, DuPont, USA), and epoxy type printed circuit board.

It is a side view for demonstrating embodiment which concerns on Claim 1 of this invention. It is a side view for demonstrating embodiment which concerns on Claim 2 of this invention.

Claims (3)

A laminate for a flexible printed wiring board, wherein a copper alloy layer containing 0.1 to 10.0 atomic% of Mg or Si is formed on a resin film. A copper alloy layer containing 0.1 to 10.0 atomic% of Mg or Si is formed on a resin film, and a copper sputter layer and / or a copper plating layer is formed on the copper alloy layer. A laminate for a flexible printed wiring board. It is a copper alloy sputtering target for forming the copper alloy layer according to claim 1 or 2, and contains 0.1 to 10.0 atomic% of Mg or Si.

Images