JP2006303207A - Substrate for flexible print circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a fine pattern, exhibiting superior adhesion between an aromatic polyamide film and a metal layer, while facilitating etching in a two-layer substrate for flexible print circuit that employs an aromatic polyamide film. <P>SOLUTION: In the substrate for flexible print circuit, having a copper layer on a sheet-like substrate composed of aromatic polyamide, impurities in the copper layer is 0.5 wt.% or lower. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a flexible printed circuit board, and more particularly to a flexible printed circuit board using a sheet made of aromatic polyamide as a base material and having a copper layer.

  Conventionally, as a substrate for a flexible printed circuit, a substrate having a three-layer structure in which a copper foil as a conductive metal layer is bonded to a plastic film base via an organic adhesive layer is known. This type of flexible printed circuit board has a problem that the dimensional accuracy after processing is lowered because the heat resistance of a commonly used organic adhesive is lower than that of a plastic film substrate. Moreover, since the thickness of the copper foil used is usually 10 μm or more, it has been pointed out that it is difficult to perform etching for patterning for high-density wiring with a narrow pitch.

  On the other hand, a conductive metal layer is formed on a plastic film substrate by a wet plating method or a dry plating method (for example, a vacuum deposition method, a sputtering film forming method, an ion plating method, etc.) without using an organic adhesive. A two-layer structure type flexible printed circuit board substrate has been proposed.

  For example, Patent Document 1 describes that an adhesion layer made of a nickel-chromium alloy is used between a sheet-like substrate and a copper thin film layer. Patent Document 2 describes the use of chromium-based ceramics as such an adhesion layer.

  However, in the case of such a two-layer structure type, since the conductive metal layer can be made thinner than 10 μm, high-density wiring is possible, but a severe thermal load test is performed, tin, nickel, solder, or gold When the electroless plating process such as the above is performed, there is a problem that the adhesion between the plastic film substrate and the conductive metal layer is reduced.

  On the other hand, Patent Document 3 proposes the use of an aromatic polyamide as a sheet base material. However, aromatic polyamide sheet base materials generally have difficulty in adhesion to a metal layer made of copper.

JP-A-9-83134 Japanese Patent Publication No.8-8400 Japanese Patent No. 2626049

  The objective of this invention is providing the board | substrate for flexible printed circuits which is excellent in the adhesiveness and is excellent in the etching property in which fine wiring is possible.

  The present inventors diligently studied to achieve the above object, and in the case of using an aromatic polyamide film as a base material, when focusing attention on impurities in the copper layer, surprisingly, impurities were introduced into the copper layer. It was found that a flexible printed circuit board having excellent adhesion between the aromatic polyamide film and the copper layer and having excellent etching properties can be obtained by including 0.5% by weight or less, thereby completing the present invention. .

That is, the present invention is as follows.
[1] A flexible printed circuit board having a copper layer on a sheet-like substrate made of an aromatic polyamide, wherein impurities in the copper layer are 0.5% by weight or less. Substrate.
[2] The flexible printed circuit board as described above, wherein the copper layer is a copper plating layer formed by a plating method.
[3] The flexible printed circuit board as described above, wherein the copper layer is a copper thin film layer formed by a sputtering method.
[4] The flexible printed circuit board as described above, which has a copper thin film layer and a copper plating layer in this order on a sheet-like substrate made of aromatic polyamide.
[5] The flexible printed circuit board described above, wherein a metal thin film layer mainly composed of an alloy of nickel and chromium is provided between a sheet-like base material made of aromatic polyamide and a copper thin film layer.

  According to the present invention, in a flexible printed circuit board using an aromatic polyamide sheet-like substrate, the adhesion between the thin metal layer containing copper and the sheet-like substrate is excellent, and the etching property of the thin metal layer is improved. It is possible to provide a flexible printed circuit board in which an excellent fine pattern can be easily formed.

The flexible printed circuit board of the present invention is formed by laminating a copper layer containing impurities at a ratio of 0.5% by weight or less on a sheet-like base material made of aromatic polyamide.
In this flexible printed circuit board, the sheet-like base material made of aromatic polyamide may have a metal thin film layer mainly composed of an alloy made of nickel and chromium between the copper layer containing impurities.

The sheet-like substrate used in the present invention is made of an aromatic polyamide. As this aromatic polyamide, it is comprised by the unit selected from the group which consists of the following structural unit, for example.
—NH—Ar ¹ —NH— (1)
—CO—Ar ² —CO— (2)
—NH—Ar ³ —CO— (3)

Here, Ar ¹ , Ar ² , and Ar ³ may be the same or different, and each includes at least one aromatic ring. Such an aromatic ring includes a divalent hydrocarbon group having 6 to 12 carbon atoms and optionally having a sulfonyl bond or an ether bond, such as a p-phenylene group, an m-phenylene group, an o-phenylene group, 2, Examples include 6-naphthylene group, biphenylene group, 4,4′-diphenylene ether, 3,4′-diphenylene ether, and the like. The aromatic ring of these groups may have a substituent such as a halogen group, a nitro group, an alkyl group, or an alkoxy group. Typical examples of these include those shown below which are composed of units represented by the above formulas (1) and (2). That is, substantially the following formula (4)
— (— CO—Ar ¹¹ —CONH—Ar ²¹ —NH —) — (4)
An aromatic polyamide comprising a repeating unit represented by Particularly preferred is para-oriented aromatic polyamide (polyphenylene terephthalamide, hereinafter may be referred to as PPTA). Here, both Ar ¹¹ and Ar ²¹ are p-phenylene groups. PPTA is a sheet (film) with excellent dimensional stability against heat, humidity, and external force. Since this film has a very small coefficient of thermal expansion, its dimensional change is small and all layers are laminated. It has an excellent characteristic that it is difficult to cause deformation such as curling when heated. In particular, the thermal expansion coefficient from 25 ° C. to 250 ° C. is (0-15) ppm / ° C., the thermal shrinkage at 250 ° C. is 0.1% or less, and the hygroscopic expansion coefficient at 25 ° C. is 30 ppm / ° C. Those having a moisture absorption rate of 2.5% by weight or less at 25 ° C. and 50% RH are extremely useful as a sheet-like base material for flexible printed circuit boards. It goes without saying that a plurality of these characteristics may be provided.

  In the aromatic polyamide used in the present invention, as long as the physical properties of the laminate are not impaired or the object of the present invention is not violated, a lubricant, a coloring agent such as a dye or a pigment, a flame retardant, an antistatic agent, an antioxidant, Other additives, modifiers, and other polymers may be included.

  If the degree of polymerization of the aromatic polyamide used in the present invention is too low, a film having good mechanical properties cannot be obtained. Therefore, a logarithmic viscosity ηinh of 3.5 or more, preferably 4.5 or more (polymer 0.1. A polymer having a degree of polymerization that gives a value obtained by dissolving 5 g and measuring at 30 ° C. is selected.

  As a method for producing a sheet-like substrate made of an aromatic polyamide, in the case where the aromatic polyamide is soluble in an organic solvent, the solution is obtained by directly polymerizing in a solvent, or once isolating the polymer and then re-dissolving it. Then, the film can be formed by a dry method or a wet method. In addition, those which are hardly soluble in an organic solvent such as PPTA can be dissolved in concentrated sulfuric acid to form a solution, and then formed into a film by a dry-wet method or a wet method. In the wet method, the solution is extruded directly from a die into a coagulating liquid, or cast onto a metal drum or an endless belt in the same manner as in the dry process, and then guided into the coagulating liquid and coagulated. Subsequently, these films are washed with a solvent, an inorganic salt, or the like in the film and subjected to treatment such as stretching, drying, and heat treatment.

For example, a method described in Japanese Patent No. 2664959 can be used as a method for producing a sheet-like substrate made of PPTA.
The thickness of the sheet-like base material made of aromatic polyamide in the present invention is usually 3 to 25 μm, preferably 4 to 12 μm. In the case of a PPTA sheet base material, a particularly thin one can be produced. It is suitable for the use of the substrate, and 4 to 12 μm is preferable.

  In the flexible printed circuit board of the present invention, a metal thin film layer preferably made of an alloy of nickel and chromium is formed on a sheet-like base material made of the above aromatic polyamide. The surface of the material may be subjected to primary pretreatment for degreasing, removing dust and the like. Further, if necessary, secondary treatment such as plasma treatment, corona discharge treatment, ozone treatment, dehumidification treatment, and heat treatment may be performed. Moreover, you may perform the surface treatment by aqueous alkali solution.

  As a surface treatment method of the sheet-like substrate made of aromatic polyamide with the above alkaline aqueous solution, for example, a method of immersing in an aqueous solution at 0 to 90 ° C. for 1 to 100 minutes is used. The treatment with the alkaline aqueous solution may be a method such as spraying or nozzle spraying.

  In the present invention, it is preferable that an alloy metal thin film layer mainly composed of nickel and chromium is formed on at least one surface of a sheet-like base material made of aromatic polyamide, since adhesion is improved. In this case, it is more preferable to form the metal thin film layer after treating the surface of the sheet-like base material made of aromatic polyamide with the alkaline aqueous solution. Such a metal thin film layer can be formed using, for example, a vapor deposition method, a DC magnetron sputtering method, an RF magnetron sputtering method, an ion plating method, an ion beam sputtering method, or a CVD method. The DC magnetron sputtering method is preferable from the viewpoint of forming the film.

  In the DC magnetron sputtering method, for example, a film can be formed using a target made of nickel and chromium having a composition substantially corresponding to a target metal thin film layer. For example, when forming an alloy thin film layer made of nickel and chromium containing 1 to 10% by weight of chromium, it is preferable to use a target to which 1 to 10% by weight of chromium is added.

  In the present invention, a copper thin film layer is usually formed on the metal thin film layer made of the nickel chromium alloy. As a method for forming this copper thin film layer, it is preferable to use a sputtering method because it is possible to stably produce a dense and homogeneous thin film. In spite of the vacuum thermal evaporation method or ion plating method, the sputtering film forming method in this method irradiates the target with charged particles accelerated in a low-pressure gas and recoils atoms and molecules on the target surface to form a sheet. This is a method of depositing a thin film on the substrate surface, and there are two to three-pole DC sputtering, two-pole RF sputtering, ion beam sputtering, and magnetron sputtering depending on the method of generating charged particles. In the case of a nickel-chromium alloy, any method can be used. However, for a nickel-chromium alloy, it is desirable to use a direct current magnetron sputtering method capable of high-speed sputter evaporation at a low temperature. In addition, as a method of minimizing the influence of abnormal discharge on the target, a method of applying a voltage of several kHz to several tens of kHz and a voltage of several tens% of the power supply voltage of the target at the time of sputtering with an AC power supply may be used in combination. Useful.

  The thickness of the copper thin film layer may be determined in consideration of the conductivity necessary for the subsequent step (electrolytic copper plating or the like), but is generally 50 to 600 nm, preferably 100 to 400 nm. If the thickness is less than 50 nm, sufficient conductivity necessary for electrolytic plating for forming a copper layer on the copper thin film layer later by a plating method cannot be obtained. Further, if it is thicker than 600 nm, the stress at the time of film formation is greatly applied to the base film, which may impair the ease of handling, and it is productivity to form a copper thin film by sputtering with such a thickness. This is not advantageous.

  The formation of the metal thin film layer mainly composed of nickel chrome and the copper thin film layer described above can be similarly performed on both sides of the sheet-like base material. In this case, as a double-sided flexible printed circuit board, can get. The finally obtained sheet-like substrate on which the copper layer is formed is particularly effectively used as a flexible printed circuit board, but the printed circuit production method therefor is particularly different from the case of a general copper foil-clad FPC. There is no. In other words, an etching resist film is produced by a printing method, a dry film method, etc., and an unnecessary copper film and a nickel chromium alloy film are removed by etching with ferric chloride and the obtained copper circuit is formed with an insulating film. The masking process, the soldering process for the terminals, and the drilling process are performed in the same manner. However, unlike the copper foil, the copper layer is thin, so that the etching is fast and the smoothness is excellent. Therefore, there is a great merit that the reproducibility of the circuit pattern is extremely excellent and a finer circuit can be manufactured.

  As described above, the flexible printed circuit board of the present invention is formed by sequentially laminating a metal thin film layer mainly containing nickel and chromium and a thin film layer made of copper on a sheet-like base material made of aromatic polyamide. . In such a flexible printed circuit board, a copper plated layer is preferably formed on a thin film layer made of copper by an electrolytic plating method or an electroless plating method, thereby providing a printed circuit board.

  The copper plating layer has good etching properties when impurities are contained at 0.5 wt% or less. If the impurity concentration is greater than 0.5% by weight, the etching property cannot be said to be sufficient, and the electrical characteristics of copper are impaired, making circuit design difficult. Further, the lower limit of the impurity concentration is not particularly limited, but if it is less than 0.1 ppm, there is no problem as a characteristic, but it is difficult to control in the manufacturing process and is not advantageous for industrial production. . There may be one type of impurity, but it also includes cases where two or more types are mixed. When mixed, the total concentration of the plurality of impurities is 0.5% by weight or less.

Examples of the impurities in the present invention include oxygen, nitrogen, sulfur, phosphorus, chlorine, hydrogen, argon, carbon, iron, nickel, cobalt, palladium, or a compound thereof or a compound of these elements and copper (for example, an oxide or a nitride). , Chloride) and the like. Further, the impurities are not limited to these.
The copper thin film layer preferably also contains impurities in the range of 0.5 wt% or less in the same manner as the copper plating layer. The reason is the same as described above.

  These impurities include target impurities in the sputtering process for forming the copper thin film layer, impurities such as atmospheric gas and moisture, various compounds necessary for the electroplating electroless plating process, copper oxidation and copper oxidation. Including those formed after the copper thin layer is formed by prevention treatment or the like. Impurities are considered to be caused by various substances used in these layer forming steps.

Examples of the present invention will be described below, but the present invention is not limited to these examples.
[Etching characteristics]
Masking the printed circuit board produced in the example to the shape of the test pattern created based on JIS C-5016, and stirring the 40% strength by weight iron chloride aqueous solution at 40 ° C. Etching was performed. After confirming removal of the copper layer of the non-masking portion by visual inspection, etching is further performed for 30 seconds. After removing the mask and cleaning, a DC voltage of 500 V is applied between the two electrodes, and there is no flashover. did.

[Measurement of adhesion]
Based on JIS C-5016 (1994), the peel strength was measured by a 90-degree peeling method at a speed of 50 mm / min. The peel strength shown in this rule is the adhesion.

[Measurement of impurities]
Impurity analysis was performed in the depth direction using a dynamic SIMS “SC-Ultra” manufactured by Kameka Instruments Co., Ltd.

[Example 1]
As the aromatic polyamide sheet base material, a 9 μm thick polyamide film “Aramika” (manufactured by Teijin Advanced Films Ltd .: polyparaphenylene terephthalamide) was used, and the surface of the polyamide film was placed under an argon gas 1 × 10 ⁻¹ Pa atmosphere. Plasma treatment was performed by irradiating glow discharge plasma generated at 56 MHz with 50 W · min / m ² .

Subsequently, in the same system, a metal thin film layer made of a nickel chromium alloy having a chromium concentration of 7% with a thickness of 20 nm was laminated as a metal thin film layer by a high frequency sputtering sputtering film forming method of argon gas 1 × 10 ⁻¹ Pa and 13 MHz Next, a copper thin film layer having a thickness of 200 nm was laminated on the metal thin film layer by a sputtering method. Further, this film was electrolytically plated under an aqueous copper sulfate solution, and a copper layer having a thickness of 8 μm was laminated on the copper thin film layer.

For this electroplating, an aqueous copper sulfate solution having a copper content of 70 g / liter and a sulfuric acid content of 200 g / liter as a plating solution and a chloride ion content equivalent to 50 mg / liter as an additive, “Okuno Pharmaceutical Co., Ltd.” "Top Lucina" SF-M added to the standard specified amount, using a precision plating device for 4-inch wafers manufactured by Yamamoto Kakin Tester Co., Ltd. as the plating device, and stirring at 25 ° C, the current density Electrolytic plating was performed at 2 A / dm ² , and copper was laminated until the thickness became 8 μm.
The copper impurities were measured and found to be 2 ppm in total. Copper oxide and copper chloride were detected as copper impurities.

  The 90 ° peel force (adhesion force) between the base material and the metal thin film layer of the substrate thus obtained was 0.45 N / mm, and no bottom spread was observed even after etching. In the migration test in which a DC voltage of 500 V was applied between the two electrodes, it was confirmed that there was no flashover and the etching property was good.

  The flexible printed circuit board of the present invention has high reliability because it is easy to form a fine pattern and has excellent durability. Therefore, the flexible print circuit is required to be miniaturized for mobile phones and liquid crystal applications. It is extremely useful as a material for circuit boards.

Claims (5)

  A flexible printed circuit board having a copper layer on a sheet-like substrate made of an aromatic polyamide, wherein impurities in the copper layer are 0.5% by weight or less.   The flexible printed circuit board according to claim 1, wherein the copper layer is a copper plating layer formed by a plating method.   The flexible printed circuit board according to claim 1, wherein the copper layer is a copper thin film layer formed by a sputtering method.   The board | substrate for flexible printed circuits in any one of Claims 1-3 which has a copper thin film layer and a copper plating layer in order on the sheet-like base material which consists of aromatic polyamide. 5. The flexible printed circuit according to claim 3, further comprising a metal thin film layer mainly composed of an alloy of nickel and chromium between the sheet-like base material made of aromatic polyamide and the copper thin film layer. substrate.