JP2007012940A - Copper foil for printed wiring - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface treatment copper foil which has a smooth surface and proper adhesion with polyimide, and to provide its manufacturing method. <P>SOLUTION: In the copper foil for a printed wiring, at least a surface in contact with a resin has an Fe alloy layer in a copper and copper alloy foil, whose surface roughness Rz<SB>JIS</SB>(JIS B 0601(2001)) is 2.0 μm or less, and Cr exists in the surface. The Fe alloy is an alloy with one kind or two or more kinds of Cr, Ni and Co. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a copper foil surface treatment layer having good adhesion to polyimide used for a flexible printed circuit board or the like.

Printed wiring boards are often used in electronic circuits of electronic devices. Depending on the type of resin used as the equipment, the printed wiring board is a rigid laminate (rigid substrate) composed of a glass epoxy substrate and a phenol substrate, and a flexible laminate (flexible substrate) composed of a polyimide substrate and a polyester substrate. ). Copper foil is mainly used as the conductive material of the printed wiring board.
The printed wiring board is formed by laminating a resin substrate and a copper foil using an adhesive, and then curing the adhesive by heating and pressing. Among the printed boards, polyimide films are mainly used as the resin for the flexible board.
The flexible substrate includes a three-layer type in which polyimide and copper foil are laminated through an adhesive, and a two-layer type in which lamination is performed without using an adhesive. Since the three-layer type includes an adhesive layer, the thickness of the substrate does not reach that of the two-layer type, and the two-layer type is mainly used for parts that are required to be light and thin.
A two-layer type flexible substrate is manufactured by coating a polyimide precursor varnish on a copper foil, followed by heat curing.
The three-layer type flexible substrate is manufactured as a three-layer structure with an adhesive such as an epoxy resin, an acrylic resin, or recently a thermoplastic polyimide resin between the copper foil and the polyimide.

In both rigid and flexible substrates, the adhesive strength between copper and resin is low, so there is almost no direct adhesion, a roughened layer that increases unevenness, a heat-resistant layer that prevents thermal diffusion of copper, and corrosion resistance is increased. In many cases, a four-layer structure of an organic layer that enhances adhesion to a rust-preventing layer and resin is used.
The roughening layer often uses burn-off plating that occurs when plating at a current density higher than the limit current density, and copper and copper alloy burn-off plating and Ni alloy burn-off plating that also serves as a heat-resistant layer are used. ing.
In many cases, Ni and a Ni alloy having a high copper diffusion preventing ability are used for the heat-resistant layer, and Zn and a Zn alloy are used in part.
Chromate treatment is used for the rust prevention layer.
A silane coupling agent is used for the organic layer.

  When a conventional copper foil having a roughened surface is used, copper tends to remain on the polyimide in the etching process, and it becomes difficult to form a circuit having a narrow wiring pitch. Also, when used in a high frequency region, current concentrates on the surface of the conductor due to the skin effect, so that the higher the surface roughness, the higher the resistance and the greater the signal degradation. For these reasons, a technique that does not perform roughening is required.

As a countermeasure, Patent Document 1 manufactures an electrolytic copper foil for a fine pitch circuit in which the surface roughness Rz _JIS is suppressed to 0.5 to 5 μm by applying bright copper plating while maintaining adhesion with polyimide. Although a method is shown, in recent years, Rz _JIS of 2 μm or less is required.

  In Patent Document 2, at least one of zinc, zinc-tin, zinc-nickel, zinc-cobalt, copper-zinc, copper-nickel-cobalt, and nickel-cobalt is used as the heat-resistant layer, and an olefin-based silane coupling agent is used. Although a technique for forming a layer is disclosed, a sufficient adhesive force may not be obtained.

  Patent Document 3 has an alloy layer of at least one selected from iron, nickel, molybdenum, cobalt, and tungsten for bonding a polyphenylene ether substrate and a smooth copper foil, and a chemical conversion treatment layer on the alloy, Although a technique for increasing the adhesive strength by providing a rust preventive layer for the coupling agent on the chemical conversion treatment layer is disclosed, the chemical conversion treatment layer and the coupling agent are essential, and the adhesion to the polyimide is not sufficient Met.

  These patents all have a layer structure that always includes a heat-resistant layer, a rust-preventing layer, and a coupling agent layer. Considering from this layer structure, it is considered that the coupling agent layer, which is a layer in direct contact with the resin, works dominantly in the adhesiveness. Therefore, in these techniques, it is considered important how to increase the adhesive strength between the heat-resistant layer and the chromate film or between the chromate film and the coupling agent.

Patent Document 4 shows that high adhesion to thermoplastic polyimide can be obtained by adhering 0.17 mg / dm ² or more of nickel to the surface of the copper foil. In this technique, nickel and thermoplastic polyimide are directly bonded, and the chromate and coupling layers of the corrosion resistant layer can be omitted. That is, a conventional chromate or coupling agent is not required, and the resin and the copper foil can be easily bonded. However, in this method, adhesive strength can be obtained with thermoplastic polyimide, but sufficient adhesion cannot be obtained with a method using a polyimide precursor or a method using another adhesive.

JP-A-5-29740 JP 2003-201585 A JP-A-8-74090 JP 2002-307609 A

  An object of the present invention is to provide a surface-treated copper foil having a smooth surface and good adhesion to polyimide, and a method for producing the same.

  As a result of studying various surface treatments, the present inventors have found that copper and copper alloy foils have an Fe alloy layer on at least the surface to be bonded to the resin, and that Cr is sufficiently present so that the resin is sufficient with a resin such as polyimide. It was found that excellent adhesion can be obtained.

That is, the present invention has (1) a surface roughness Rz _JIS (JIS B 0601 (2001)) of 2.0 μm or less of copper and copper alloy foil, and has an Fe alloy layer on at least the surface to be bonded to the resin, and further Cr Copper foil for printed wiring, characterized in that is present on the surface,
(2) The copper foil for printed wiring board according to (1) above, wherein the Fe alloy is an alloy of one or more of Cr, Ni and Co.
(3) The copper foil for printed wiring boards according to the above (1) to (2), wherein the Fe alloy layer is 0.1 to 100 mg / dm ² ,
(4) The copper foil for printed wiring boards according to the above (1) to (2), wherein the Fe alloy layer is ² to 50 mg / dm ² ,
(5) The copper foil for printed wiring boards according to the above (1) to (4), wherein the Fe content of the Fe alloy is 20 to 90 mass%,
(6) The copper foil for printed wiring boards according to the above (1) to (5), wherein the Fe alloy layer is produced using dry plating,
(7) The copper foil for printed wiring boards according to the above (1) to (6), wherein a chromate treatment is performed on the Fe alloy layer,
(8) The copper foil for printed wiring boards according to the above (1) to (7), wherein Cr is present in the surface layer at 1.0 at% or more,
(9) The copper foil for printed wiring boards according to the above (1) to (8), wherein the resin to be bonded is polyimide and a polyimide precursor.

  According to the present invention, the surface-treated copper foil is smoother than the conventional roughened copper foil and has good adhesion to a resin such as polyimide. Thereby, the copper foil corresponding to fine pitch and high frequency can be provided.

Hereinafter, embodiments of the surface treatment according to the present invention will be described. The copper foil used in the present invention may be either an electrolytic copper foil or a rolled copper foil.
A thin film is formed on the surface of the copper foil by a surface treatment, and the surface roughness of the thin film is greatly affected by the surface roughness of the copper foil. If the surface roughness of the copper foil is rough, copper tends to remain when a circuit is formed by etching, which is not preferable as a copper foil for a wiring board. Accordingly, the surface roughness of the copper foil used in the present invention is one having a 10-point average roughness Rz _JIS specified by JIS B 0601 (2001) of 2.0 μm or less, more preferably Rz _JIS of 1.5 μm or less. It is preferable to select and use.

The surface treatment layer capable of improving the adhesion to polyimide is made of an alloy of Fe and Cr, Ni, Co, and the Fe or Fe alloy layer is 0.1 to 100 mg / dm ^2, preferably ² to 50 mg / dm. ² , the Fe content in the alloy is preferably 20 to 90 mass%, more preferably 20 to 80 mass%. Furthermore, higher adhesion can be obtained when Cr is present at 1.0 at% or more in the surface layer. This surface Cr can be obtained by forming an Fe-Cr alloy layer, but even when using an Fe-Ni or Fe-Co alloy layer, it can be realized by carrying out a conventional chromate treatment. is there.
Due to the presence of Fe oxide and Cr, chemical bonds with organic substances such as resins and adhesives are promoted, and a strong adhesive force can be obtained. In addition, it has been found that the adhesive force is increased when the oxide is a composite with a metal such as Cr, Ni, and Co, rather than when the oxide is Fe alone. In particular, in the case of a combination of Fe and Cr, the adhesive force is remarkably improved. Specifically, very high adhesive strength can be exhibited when Cr is present at 1.0 at% or more in the surface layer.

  Patent Document 3 discloses a mutual effect between Ni and a thermoplastic polyimide similar to the present invention, but Fe can obtain a higher adhesive force than Ni, and Cr is present. Therefore, it is effective not only in thermoplastic polyimide but also in a method using a polyimide precursor or a method of bonding via an adhesive such as epoxy or acrylic.

The Fe alloy composition in the film can be known by instrumental analysis such as fluorescent X-ray method or EPMA. However, if the film is thin, sufficient characteristic X-rays cannot be obtained and measurement may be difficult. In that case, it is possible to measure the weight and concentration by dissolving the film in the solution and performing wet analysis such as ICP method or titration method on the amount of metal ions in the solution.
On the other hand, the composition of the surface layer greatly affects the adhesion, but cannot be measured by the method of measuring the film composition described above. Therefore, it is necessary to perform measurement using a method such as XPS, AES, or SIMS that can analyze only the surface layer. In this patent, evaluation was performed using XPS as surface analysis. This is because the excitation source is X-ray and average surface information in a relatively wide area can be obtained, and it is easy to know the chemical state such as the oxidation number.

This surface treatment can be performed using a known electroplating method, but is not limited to electroplating, and any other dry plating method such as vapor deposition, sputtering, ion plating, etc. may be used. Conversely, the use of the dry plating method has an advantage that the composition of the Fe alloy can be adjusted more easily than the wet method. In general, since the film formation speed of the dry plating method is slower than that of the wet plating method, when the plating thickness is on the order of 100 mg / dm ² , the dry plating method is disadvantageous from the viewpoint of productivity. However, in the case of the present invention, the thickness of the Fe alloy layer is 0.1 to 100 mg / dm ² , and in the region at the lower limit of the range, it is a thickness that can be manufactured by a dry method. Often it is advantageous to use the method.

There is no problem even if rolling is performed after the film is formed, and it is important that the surface state of the claims is reached at the time of joining with the resin.
Further, after the surface treatment layer is provided, silane coupling treatment, titanium coupling treatment, or the like may be performed.

EXAMPLES Next, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these. In addition, the surface treatment adhesion amount to the copper foil shown in the Example, the surface roughness Rz _{JIS of} the surface-treated copper foil, and the peel strength between the surface-treated copper foil and polyimide were measured by the following methods.

(1) Amount of coating and concentration on surface A sample of a certain area was dissolved with acid, and the amount of coating and the metal composition of the coating were measured by ICP analysis for the metal concentration in the solution.
Moreover, the density | concentration in the surface was measured on condition of the following using the XPS measuring apparatus (ULVAC-PHI Co., Ltd. 5600MC).
Ultimate vacuum 5 × 10 ⁻¹⁰ Torr
X-ray monochromatization: Al Kα
Output: 300W
Detection area: 800μmφ
Angle between sample and detector: 45 degrees

(2) Surface roughness Rz _JIS
Using a stylus type surface roughness measuring instrument (Surf coder SE-3400 manufactured by Kosaka Laboratories), measurement was performed at a cut-off value of 0.25 mm and a measurement length of 1.25 mm according to the method defined in JIS B 0601.

(3) Peel strength A sample was cut into a size having a length of 100 mm and a width of 5 mm, and the copper foil was peeled from the end of the short side according to the method defined in JIS C 6471, and the stress was measured. The peeling angle was 90 ° and the peeling speed was 50 mm / min.

(4) Corrosion resistance When copper dissolves in the polyamic acid contained in the polyimide precursor varnish, it oxidizes during heating and discolors the polyimide. That is, if there are pits in the surface treatment layer, copper diffuses from there and discolors the polyimide, and if there is a layer without pits, no discoloration of the polyimide occurs. Using this property, the corrosion resistance of the surface treatment layer was evaluated by the presence or absence of discoloration.
<Production of sample>
Cold rolling and annealing of a tough pitch copper ingot were repeated to produce a 18 μm rolled copper foil. At that time, the roughness of the rolling roll and the rolling conditions were adjusted to prepare a material having Rz of 0.7 to 3.0 μm.

<Surface treatment>
"Fe-Cr"
It was produced using a dry plating method. Specifically, the film was formed using an ion plating apparatus.
Device name: Ion plating device (made by Showa Vacuum, SIP-700 (special))
Degree of vacuum: 3 × 10 ⁻⁴ Pa
High frequency power 50W, 0.04Pa (Ar gas)
Deposition rate: about 1 A / s

"Fe-Ni"
The copper foil was subjected to general electrolytic degreasing and pickling, and an Fe—Ni plating layer was formed under the following conditions.
Ferrous chloride (FeCl ₂ · 4H ₂ O) 280-330 g / L
Nickel chloride _{(NiCl 2 · 6H 2 O)} 40~50g / L
Calcium chloride (CaCl ₂ · 2H ₂ O) 150-200 g / L
pH 2.5-3.0
Bath temperature 60-70 ° C
Current density 1-10 A / dm ₂
Time 1-10 seconds

"Fe-Co"
The copper foil was subjected to general electrolytic degreasing and pickling, and an Fe—Co plating layer was formed under the following conditions.
Ferrous chloride 330-380 g / L
Cobalt chloride 15-25g / L
Calcium chloride 150-200g / L
pH 1.0-2.0
Bath temperature 80-90 ° C
Current density 10-30 A / dm ²
Time 1-3 seconds

"Fe"
The copper foil was subjected to general electrolytic degreasing and pickling, and an Fe plating layer was formed under the following conditions.
Ferrous chloride (FeCl ₂ · 4H ₂ O) 280-330 g / L
Calcium chloride (CaCl ₂ · 2H ₂ O) 150-200 g / L
pH 2.5-3.0
Bath temperature 60-70 ° C
Current density 1-10 A / dm ²
Time 1-10 seconds

"Ni"
The copper foil was subjected to general electrolytic degreasing and pickling, and a Ni plating layer was formed under the following conditions.
Nickel sulfate 220-280g / L
Nickel chloride 40-50g / L
Boric acid 25-35g / L
pH 3.0-4.0
Bath temperature 40-50 ° C
Current density 1-5A / dm ²
Time 10-30 seconds

<Polyimide film>
The polyimide laminated with the copper foil was formed into a film under the following conditions using a commercially available polyimide precursor varnish (trade name U-varnish-A, manufactured by Ube Industries, Ltd.).
Polyimide coating thickness: 30 μm
Solvent drying: 130 ° C for 30 minutes under air Resin curing: 350 ° C for 15 minutes under Ar atmosphere

<Evaluation of surface treatment film>
Table 1 shows the evaluation results of the peel strength of polyimide and copper foil and the corrosion resistance to polyimide.
Table 1 shows the surface treatment adhesion amount and the surface roughness Rz _JIS .

Inventive Examples 1 to 3 are examples in which the Fe concentration in the film of the Fe—Cr alloy is 90, 50, and 25 wt%, Fe oxide is present on the surface, and the Cr concentration on the surface is also claimed in the claims. Since it was within the range, it had high peel strength and high corrosion resistance.
Inventive Examples 4 to 5 are examples in which the thickness of the Fe—Cr alloy is set to 1, 80 mg / dm ² , but are within the scope of the claims, and thus have high peel strength and high corrosion resistance.
Invention Example 6 is an example in which the surface roughness was reduced to 0.7, but it had high peel strength and high corrosion resistance without any problem.
Inventive Examples 7 to 8 are obtained by subjecting Fe-Ni and Fe-Co to chromate treatment, but Cr is present on the surface by chromate treatment, and since it is an Fe alloy, it has high peel strength and high corrosion resistance. Met.

Comparative Example 9 is a case of Fe plating, and neither peel strength nor corrosion resistance was sufficient.
Although Comparative Example 10 was an Fe—Ni alloy, it was a case where the Fe concentration in the film was low, and although there was corrosion resistance, the peel strength was insufficient.
Comparative Example 11 is an example of Ni plating, which has corrosion resistance but has insufficient peel strength.
Comparative Example 12 is an Fe—Cr alloy with a surface roughness of 3.0 μm. Although there is no problem in peel strength and corrosion resistance, a fine pitch circuit cannot be formed due to the roughness, and high frequency. The characteristics were also inferior.

Claims (9)

In copper and copper alloy foils with a surface roughness Rz _JIS (JIS B 0601 (2001)) of 2.0 μm or less, at least the surface to be bonded to the resin has an Fe alloy layer, and Cr is present on the surface. Characteristic copper foil for printed wiring.   2. The copper foil for printed wiring board according to claim 1, wherein the Fe alloy is an alloy of one or more of Cr, Ni and Co. The copper foil for printed wiring boards according to claim 1 or ² , wherein the Fe alloy layer is 0.1 to 100 mg / dm2. The copper foil for printed wiring boards according to claim 1 or ² , wherein the Fe alloy layer is ² to 50 mg / dm2.   The copper foil for printed wiring boards according to claim 1, wherein the Fe content of the Fe alloy is 20 to 90 mass%. The copper foil for printed wiring boards according to claim 1, wherein the Fe alloy layer is produced by dry plating. The copper foil for printed wiring boards according to claim 1, wherein a chromate treatment is performed on the Fe alloy layer.   The copper foil for printed wiring boards according to claim 1, wherein Cr is present in the surface layer at 1.0 at% or more. The copper foil for printed wiring boards according to claim 1, wherein the resin to be bonded is polyimide and a polyimide precursor.