JP2007208251A - Substrate for flexible board, flexible board using it, and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate for a flexible board that has excellent adhesiveness between a polyimide film and a conductive metal layer, and a flexible board using the substrate. <P>SOLUTION: A surface of a polyimide film is activated by lightly etching the surface so that the degree of surface roughness becomes as small as possible, and then an Ni-B alloy layer and a Cu layer are formed by using a vacuum film forming method to obtain a substrate for a flexible board, and thereafter a second Cu layer that is a conductive metal layer is formed on the substrate for the flexible board by using a wet plating method to obtain the flexible board of the present invention. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a substrate for a flexible substrate used for a printed circuit board or the like, a flexible substrate using the substrate, and a method for producing them.

  TAB is a lightweight, deformable, and flexible TAB that can be mounted at high density as a printed circuit board for use in energization circuits of electronic devices that are required to be small and lightweight, such as notebook computers, printers, digital cameras, and liquid crystal displays. (Tape Automated Bonding) There is an increasing demand for tapes and flexible substrates. As a conventional printed circuit board, a heat-resistant and flexible plastic substrate that can withstand a temperature rise due to continuous use, for example, a conductive metal layer using an adhesive made of a thermosetting resin such as an epoxy resin on a polyimide film What stuck the copper foil was used. However, the current-carrying circuit using a printed circuit board using an adhesive is easily deformed and has poor dimensional stability, and the heat resistance of the thermosetting adhesive is inferior to that of the substrate material, so that the heat stability is not sufficient. . Furthermore, in a printed board using copper foil, the thickness of the copper foil is large, and it has not been possible to sufficiently cope with high-density mounting, that is, reduction in circuit weight and size.

In order to solve these problems, as a technology to form a metal layer on the polyimide film without using an adhesive,
(1) Casting method in which polyamic acid is applied on a copper foil using a casting method, dried and cured (2) Laminating method in which a polyimide film is thermocompression-bonded on a copper foil (3) Electroless plating on the polyimide film surface An electroless plating method in which a metal thin film is formed and a metal layer having a predetermined thickness is formed thereon by electroplating. (4) A metal thin film is formed on a polyimide film surface by using a vacuum film forming method, and a metal thin film is formed thereon. Various methods such as a vacuum film forming method in which a metal layer having a predetermined thickness is formed by electroplating have been tried.

  Circuit boards formed by using the casting method (1) and the laminating method (2) are superior to conventional printed boards using adhesives in terms of thermal stability and dimensional stability, and are widely used. . However, these methods using a thick copper foil by rolling or electroforming for a high-density mounting substrate of a next-generation electronic device that is required to use a conductive layer having a thickness of 10 μm or less are light in weight and cost. There is a problem.

  According to the electroless plating method (3), it is possible to form a thin conductive layer, which is suitable for a lightweight high-density mounting substrate. However, in the electroless plating method, the surface of the polyimide film, which is implemented to improve the adhesion of the plating layer, is activated with chemicals. However, the manufacturing cost increases due to chemical post-treatment and environmental pollution due to post-treatment operations. There is a problem from the point of view.

  In the case of using the vacuum film forming method (4), there is no problem of environmental pollution, but it has a drawback that the adhesive strength between the polyimide film and the metal thin film formed thereon is small and it is easy to peel off. In order to overcome this drawback, the following various methods have been proposed.

  For example, Patent Document 1 proposes a conductive film formed by sequentially forming a nickel layer, a copper layer, and a nickel layer in a vacuum on a plastic film substrate. Further, in Patent Document 2, a vapor-deposited layer of a highly conductive metal such as Cu or Al is provided on one side of a heat-resistant base film via a vapor-deposited layer of corrosion resistant metal such as Ni or Ni-Cr, and Proposed a film material for flexible printed circuits in which a vapor-deposited layer of Ni or Ni-Cr corrosion-resistant metal is provided on the vapor-deposited layer, and a metal vapor-deposited film or an organic or inorganic polymer coating layer is provided on the other side of the base film. ing. In Patent Document 3, at least one first metal of Cu, Ni, Cr, Ti, V, W, and Mo is attached to the surface of a polymer film such as polyimide by a vacuum film forming means, and then the first Proposed a method of forming a metal layer on a polymer film by thermally diffusing the metal in the polymer film and subsequently forming Cu, Ni, Al, etc. using an electroless plating method or an electroplating method. ing. Further, in Patent Document 4, the surface of the polyimide resin film is hydrophilized to give a catalyst, and then nickel, cobalt, or one of their alloys is applied by electroless plating, and then electroless copper plating or electrolytic copper plating is performed. Proposes a method for producing a copper polyimide substrate.

  Further, Patent Document 5 discloses a polymer film such as a polyimide resin having a plasma-treated surface and nickel or Cu, Cr, Fe, V, Ti, Al, Si, Pd, and the like attached to the plasma-treated surface. A nickel tight coat layer containing a nickel alloy having a metal selected from the group consisting of Ta, W, Zn, In, Sn, Mn, Co and a mixture of two or more thereof as a metal for the alloy, and the nickel tight coat layer An adhesive-free flexible laminate is proposed that includes a copper seed coat layer adhered to the substrate.

  However, the techniques proposed by these documents cannot eliminate the phenomenon that the Cu layer peels off from the polyimide film. In addition, there is a need to suppress a decrease in adhesive strength when aged for a long time at a high temperature due to a temperature increase due to continuous use.

Japanese Patent Laid-Open No. 62-047908 JP 62-181488 A Japanese Patent Laid-Open No. 03-274261 JP 05-090737 A JP 2000-508265 A

  Therefore, the present invention provides a flexible substrate that is excellent in adhesion between the polyimide film and the conductive metal layer and can suppress a decrease in adhesive strength when aged for a long time at a high temperature, and a flexible substrate for obtaining the same. It aims at providing a base material and those manufacturing methods.

In order to achieve the above object, the substrate for flexible substrate of the present invention comprises Ni-- in order from the bottom on at least one surface of a polyimide film having a surface roughness Ra (JIS B0601) after activation treatment of 1.5 to 10 nm. A B alloy layer and a Cu layer are formed.
According to a second aspect of the present invention, in the flexible substrate substrate according to the first aspect, the Ni-B alloy layer has a thickness of 5 to 100 nm. According to a third aspect of the present invention, in the flexible substrate base material according to the first or second aspect, the thickness of the Cu layer is 50 to 300 nm. Furthermore, invention of Claim 4 is a base material for flexible substrates in any one of Claims 1-3, B content rate of the said Ni-B alloy layer is 0.1-22 weight%, It is characterized by the above-mentioned. And
Moreover, the flexible substrate of this invention which concerns on Claim 5 provides the 2nd Cu layer of thickness of 1-100 micrometers on the Cu layer of the base material for flexible substrates in any one of Claims 1-4. It is characterized by.

  And the manufacturing method of the base material for flexible substrates of this invention of Claim 6 for achieving the said objective is activated by the surface roughness Ra (JIS B0601) 1.5-10nm by the plasma processing of the surface of a polyimide film. A step of forming a Ni-B alloy layer having a thickness of 5 to 100 nm on the surface of the activated polyimide film by a vacuum film-forming method, and a conductive layer on the Ni-B alloy layer. It comprises a step of forming a Cu layer having a thickness of 50 to 300 nm by a vacuum film forming method as an underlayer.

  Furthermore, the manufacturing method of the flexible substrate of this invention of Claim 7 for achieving the said objective creates the base material for flexible substrates using the manufacturing method of the base material for flexible substrates of Claim 6, Next, a second Cu layer having a thickness of 1 to 100 μm is formed on the Cu layer of the substrate for flexible substrate by electroplating.

  The flexible substrate of the present invention is activated by lightly etching the surface of the polyimide film while suppressing the degree of roughening as much as possible, and then using a vacuum film forming method to form a Ni-B alloy layer and a Cu layer thereon. A flexible substrate and a second Cu layer are obtained by forming a second Cu layer, which is a conductive metal layer, by a wet plating method. Excellent adhesive strength can be obtained, and good adhesive strength can be maintained even after aging at high temperatures for a long time, and the thermal stability is excellent. As a result, it is possible to obtain a flexible substrate that can be suitably used as a printed circuit board used in an energization circuit that requires high-density mounting of electronic devices.

  Hereinafter, the present invention will be described in detail. FIG. 1 is a schematic cross-sectional view of the substrate for flexible substrate of the present invention. The substrate 10 for flexible substrate is configured by forming a Ni—B alloy layer 2 on one surface of a polyimide film 1 and forming a Cu layer 3 on the Ni—B alloy layer 2. Although FIG. 1 shows the case where the Ni-B alloy layer 2 and the Cu layer 3 are formed on one side of the polyimide film 1, the Ni-B alloy layer 2 and the Cu layer 3 are similarly formed on the other side of the polyimide film 1. May be formed.

  Examples of the polyimide film 1 that is a base on which the Ni-B alloy layer 2 and the Cu layer 3 of the substrate 10 for flexible substrate are formed include BPDA (biphenyltetracarboxylic acid) -based polyimide resin and PMDA (pyromellitic dianhydride). A film made of any polyimide resin such as a) polyimide resin can be used. The surfaces of these polyimide films 1 are activated to form the Ni—B alloy layer 2 and the Cu layer 3.

  In the activation treatment, light etching is performed so that the surface of the polyimide film is not roughened as much as possible. Etching includes dry etching such as wet etching with an alkaline aqueous solution and etching by plasma irradiation in a vacuum. In the present invention, plasma treatment in a vacuum is preferable. As a gas used for the plasma treatment, an inert gas such as He, Ne, or Ar is used alone, or two or more of these inert gases are mixed and used. As an energy supply source for generating plasma, generally used energy sources such as direct current (DC), alternating current (AC), high frequency (RF), and microwave are used. The surface roughness Ra (JIS B0601) after performing the plasma treatment in this manner is preferably 1.5 to 10 nm, and more preferably 2 to 5 nm. Since the surface roughness Ra (JIS B0601) of a normal polyimide film is 1 to 5 nm, it is slightly etched so as not to increase the surface roughness as much as possible. When the surface roughness Ra (JIS B0601) is less than 1.5 nm, good adhesive strength with the metal layer formed on the polyimide film cannot be obtained. On the other hand, when the thickness exceeds 10 nm, it is difficult to obtain a good pattern when a fine pattern is formed by etching the plating layer after forming the plating layer on the polyimide film. The surface roughness Ra of a normal polyimide film is 1 to 5 nm as described above, and partially overlaps with the surface roughness Ra when the plasma treatment in the present invention is performed, but according to the study of the present inventors, As shown in the examples described later, the adhesive strength between the polyimide film and the conductive metal layer is not only influenced by the surface roughness of the polyimide film, but is affected by the surface activation by the plasma treatment. I understood it.

  After activating the surface in this way, a metal layer that increases the adhesive force between the Cu film, which is a conductive layer formed on the polyimide film, and the polyimide film is formed. The metal layer is preferably a Ni-based alloy such as Ni, Ni—Cr, Ni—Cu, Ni—P, or Ni—B, but more preferably a Ni—B alloy layer is formed. As a result of intensive research on a layer capable of increasing the adhesive strength with a polyimide film and maintaining good adhesive strength when aged for a long time at a high temperature, the inventors used a vacuum film-forming method. It has been found that by forming a Ni-B alloy layer, better adhesion between the polyimide film and the uppermost Cu layer can be obtained than when forming a Ni alloy layer alone or a Ni alloy layer with another metal. It was. Further, as the vacuum film forming method, there are a sputtering method and a vapor deposition method, but it has been found that it is preferable to use the sputtering method.

  In the Ni—B alloy layer 2 described above, the B content is preferably 0.1 to 22% by weight. When the B content is less than 0.1% by weight, the adhesive strength with the polyimide film is lowered when the B content is aged for a long time at a high temperature. When the B content exceeds 22% by weight, a Cu layer to be described later on this Ni-B alloy layer and a second Cu layer are formed thereon, and then the metal layer is removed by etching to form a circuit. In this case, the Ni-B alloy layer remains without being completely removed, resulting in poor insulation between circuits.

  Moreover, it is preferable that the thickness of the Ni-B alloy layer 2 is 5 to 100 nm. When the thickness of the Ni-B alloy layer 2 is less than 5 nm, good adhesion with the polyimide film cannot be obtained. Even if the thickness exceeds 100 nm, the effect of improving the adhesive strength is saturated, which is not advantageous in terms of cost.

  Thus, after forming said Ni-B alloy layer 2 on a polyimide film, the thin film of Cu layer 3 is formed on it. The Cu layer 3 is formed as a conductive underlayer for forming the second Cu layer 4 using an electroplating method. As a film formation method for the Cu layer 3 on the polyimide film, it is preferable to use a vacuum film formation method such as a sputtering method or a vapor deposition method, but it is more preferable to use a sputtering method. The thickness of the Cu layer 3 is preferably 50 to 300 nm. If the thickness is less than 50 nm, the Ni-based alloy layer and the Cu layer 3 may be dissolved and lost when the second Cu layer 4 is formed by electroplating, which is not preferable. On the other hand, if it exceeds 300 nm, sufficient conductivity can be obtained, but it is not advantageous in terms of cost. As described above, after the polyimide film surface is slightly etched, a Ni-B alloy layer 2 and a Cu layer 3 are formed on the Ni-B alloy layer 2 by using a vacuum film forming method, so that a book with a uniform surface without a pinhole is formed. The base material for flexible substrates of the invention is obtained.

  Next, the second Cu layer 4 is formed as a conductive layer on the Cu layer 3 of the flexible substrate 10 shown in FIG. 1 obtained as described above, as shown in FIG. And The second Cu layer 4 may be formed using any one of a dry film forming method such as a sputtering method and a vapor deposition method, and a wet plating method such as an electroless plating method and an electroplating method. It is preferable to use an electroplating method that can form a film in a short time. The thickness of the second Cu layer 4 is preferably 1 to 100 μm. When the thickness is less than 1 μm, sufficient conductivity cannot be obtained when used as an energization circuit. On the other hand, if it exceeds 100 μm, it becomes difficult to form a fine pattern circuit required for a high-density mounting substrate, which is not preferable. In this way, the flexible substrate of the present invention is obtained.

Hereinafter, the present invention will be described in detail with reference to examples.
[Polyimide film etching]
In order to form a substrate for a flexible substrate indicated by substrate symbols A to D by applying etching treatment by plasma irradiation on one side of a polyimide film having a thickness of 50 μm under the conditions shown in Table 1 using a plasma processing apparatus. A polyimide film substrate was obtained. For comparison, an untreated substrate (substrate symbol E) and a substrate (substrate symbol F) in which an electroless Ni—B alloy plating layer is formed on a polyimide film with a thickness of 0.2 μm are used. Got ready. Further, for comparison, a plasma treatment (base symbol G) having a high output and a roughened surface with a long treatment time was prepared.
A part of these substrates was cut out and the surface roughness Ra (JIS B0601) was measured using a scanning probe microscope. The measurement results are shown in Table 1.

[Formation of Ni-based alloy layer]
A Ni-B alloy layer having the B content and thickness shown in Table 2 is formed on the activation surface of the polyimide film substrate that has been activated on one side as described above using a DC magnetron sputtering apparatus. It was. For comparison, a Ni layer and a Ni—Cr layer were each formed using a DC magnetron sputtering apparatus. For comparison, a Ni-B layer formed by electroless plating (Sample No. 19) was used.

[Formation of Cu layer]
Next, a Cu layer having the thickness shown in Table 2 was formed on the metal layer using a DC magnetron sputtering apparatus.

[Formation of second Cu layer]
Subsequently, a second Cu layer having a thickness shown in Table 2 as a conductive layer was formed on the above Cu layer by electroplating under the following conditions using the following plating bath. In this way, specimens for property evaluation of sample numbers 1 to 21 were prepared.
<Plating bath>
Copper sulfate 200g / L
Sulfuric acid 50g / L
Brightener (trade name: SF-M, manufactured by Okuno Pharmaceutical Co., Ltd.) 5ml / L
<Bath temperature> 30 ° C
<Squeezing> Air bubbling <Current density> 3 A / dm ²

[Characteristic evaluation]
Samples having a size of 100 mm × 100 mm were cut out from the specimens of sample numbers 1 to 21, and a part of them was immediately measured for 90 ° peel strength as follows, and the other part was in an oven at 150 ° C. After aging for one week, the 90 ° peel strength was measured as follows as the adhesive force between the polyimide film and the metal layer. That is, after a protective tape having a width of 2 mm was applied to the surface of each test material on which the metal layer was formed, the exposed portion of the metal layer was removed by etching with a ferric chloride aqueous solution. Next, a 2 mm portion where the metal layer remained was cut into a strip shape, and then forcedly peeled between the polyimide film and the Ni layer of the metal layer or various Ni-based alloy layers, and the peeled polyimide film and these metal layers were separated from Tensilon. The 90 ° peel strength was measured between the two chucks. The 90 ° peel strength was converted to kg / cm (width). These results are shown in Table 2.

  As shown in Table 2, after activating the substrates A to D, which were activated by slightly etching the surface roughness Ra of the polyimide film within a range of 1.5 to 10 nm, respectively, a vacuum film formation method (sputtering) Method) to form a Ni-B alloy layer having a thickness of 5 to 100 nm and a B content of 0.1 to 22% by weight, and then forming a Cu layer by vacuum film formation (sputtering). Formed to have a thickness in the range of 50 to 300 nm to form a substrate for a flexible substrate, and subsequently formed a second Cu layer on the substrate by electroplating to a thickness of 1 to 10 μm Each of the flexible substrates of Sample Nos. 1 to 15 according to the examples of the present invention has a 90 ° peel strength of 0.9 kg / cm or more at the initial stage, and 0.7 to 0 even after aging for 1 week in a 150 ° C. atmosphere. .95kg / cm strength is obtained Cage, it was confirmed that both the initial and after aging are sufficient adhesion strength is obtained. In the present invention, the 90 ° peel strength is 0.9 kg / cm or more at the initial stage, and 0.7 kg / cm or more after 150 ° C. × 7 days has passed.

On the other hand, the comparative example of sample number 16 in which the Cu layer and the second Cu layer were formed on the Ni single layer without containing B was inferior to the above example in the 90 ° peel strength both at the initial stage and after the lapse of time. Yes. Moreover, although the comparative example of the sample number 17 which contains Cr instead of B has the adhesive strength raised rather than the sample number 16, it is inferior in each initial stage and after time compared with each Example. The comparative example of sample number 18 is the case where the Ni-B alloy layer is formed without performing the activation treatment on the surface of the polyimide film. In this case, a protective tape is applied to the test material and the second chloride is added. Etching with an aqueous iron solution removed the exposed portion of the metal layer, and the portion where the metal layer remained was cut into a strip shape, resulting in peeling, and adhesive strength could not be obtained. Furthermore, sample number 19 is a commercially available film in which an electroless plating layer is formed on the surface of a polyimide film, and a Cu layer and a second Cu layer are formed by the same method as in the present invention. Similar to 18, no adhesive strength was obtained. On the other hand, Sample No. 20 is a case where the B content of the Ni-B alloy layer is 25%. In this case, the initial strength is somewhat close, but the strength after aging is inferior. Furthermore, Sample No. 21 is a case where the surface roughness Ra in the activation treatment of the surface of the polyimide film is roughened to 11 nm. In this case, even if other treatment conditions are satisfied, the adhesive strength is considerably inferior. It was. Accordingly, in the present invention, the surface roughness Ra is set to 10 nm or less.
From the above results, the flexible substrate of the present invention is excellent in the adhesive strength between the polyimide film and the metal layer by performing under the above processing conditions, and can retain the excellent adhesive strength even after being heated at a high temperature for a long time. It was confirmed that it was possible.

  The substrate for a flexible substrate of the present invention is excellent in adhesive strength after a long period of time at a constant temperature and high temperature with a Ni-B alloy layer and a Cu layer as a base of a conductive layer formed using a vacuum film formation method. Yes. Therefore, the flexible substrate of the present invention in which the second Cu layer is formed on the substrate for the flexible substrate by using an electroplating method is small and lightweight such as a notebook computer, a printer, a digital camera, and a liquid crystal display. The present invention can be suitably applied as a printed circuit board used in an energization circuit that requires high-density mounting of electronic devices that are required to exist.

Sectional drawing of the base material for flexible substrates of this invention. Sectional drawing of the flexible substrate of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polyimide film 2 Ni-B alloy layer 3 Cu layer 4 Second Cu layer 10 Base material for flexible substrates 20 Flexible substrate

Claims (7)

  A Ni-B alloy layer and a Cu layer are formed in order from the bottom on at least one surface of a polyimide film having a surface roughness Ra (JIS B0601) after activation treatment of 1.5 to 10 nm. Base material for flexible substrates.   The base material for flexible substrates of Claim 1 whose thickness of the said Ni-B alloy layer is 5-100 nm.   The base material for flexible substrates of Claim 1 or 2 whose thickness of the said Cu layer is 50-300 nm.   The base material for flexible substrates in any one of Claims 1-3 whose B content rate of the said Ni-B alloy layer is 0.1-22 weight%.   5. A flexible substrate comprising a second Cu layer having a thickness of 1 to 100 [mu] m formed on the Cu layer of the substrate for flexible substrate according to any one of claims 1 to 4.   The surface of the polyimide film is activated by plasma treatment to a surface roughness Ra (JIS B0601) of 1.5 to 10 nm. The surface of the activated polyimide film is 5 to 100 nm thick by vacuum film formation. The method includes a step of forming a Ni-B alloy layer, and a step of forming a Cu layer having a thickness of 50 to 300 nm as a conductive underlayer on the Ni-B alloy layer by a vacuum film forming method. The manufacturing method of the base material for flexible substrates.   A base material for a flexible substrate is prepared using the method for manufacturing a base material for a flexible substrate according to claim 6, and then a second layer having a thickness of 1 to 100 μm is formed on the Cu layer of the base material for a flexible substrate by electroplating. A method for producing a flexible substrate, comprising forming a Cu layer.

Images