JP2007009286A - Copper foil for printed circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide surface treated copper foil having a smooth surface, and whose adhesion with polyimide is satisfactory, and to provide a method for producing the same. <P>SOLUTION: Regarding the copper foil for a printed circuit board, in copper and copper alloy foil whose ten point average roughness Rz<SB>JIS</SB>(JIS B 0601(2001)) is ≤2.0 μm, at least the face to be stuck with resin has an Fe or Fe alloy layer. The Fe alloy is an alloy of one or more kinds selected from Ni, Co, Mo, W, Zn and Cu. <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 via 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 any type, since the adhesive strength between copper and resin is low, there is almost no direct adhesion, a roughening treatment layer that increases unevenness, a heat-resistant layer that prevents heat diffusion of copper, a rust-proof layer that enhances corrosion resistance, In many cases, the organic layer has a four-layer structure that improves the adhesion to the resin.
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, there is a demand for a technique that does not perform roughening.

As a countermeasure, Patent Document 1 discloses a method for producing an electrolytic copper foil for a fine pitch circuit in which surface roughness Rz _JIS is suppressed to 0.5 to 5 μm by applying bright copper plating while maintaining adhesion with polyimide. 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 olefinic silane coupling agent is used. Although a technique for forming a layer is disclosed, a sufficient adhesive force may not be obtained.

In patent document 3, in order to adhere | attach a polyphenylene ether base material and smooth copper foil, it has an alloy layer of at least 1 sort (s) chosen from iron and nickel, molybdenum, cobalt, tungsten, a chemical conversion treatment layer on the alloy, Although the technique which improves adhesive strength by providing a coupling agent rust prevention layer on a chemical conversion treatment layer is disclosed, a chemical conversion treatment layer and a coupling agent are essential. The thickness of the film of iron or the like is very thin, and a very thin film of 0.01 to ² mg / dm ² with Fe. This is a thickness of 0.1 to 20 nm on the assumption that a film is formed on a completely flat surface. For this reason, it is assumed that a chemical conversion treatment and a coupling agent rust prevention layer become essential.
Also, the chromate treatment used for the rust prevention layer contains chromium, and it is preferable not to use it from the viewpoint of the environment. In the patent documents raised so far, since a chromate film is essential, it is a material containing chromium, although in a very small amount.
Furthermore, considering the layer structure, the layers such as iron and nickel have a strong meaning as heat-resistant layers, and the adhesion is considered to be dominated by the coupling agent layer that is in direct contact with the resin and the chromate layer below it. It is. Therefore, although these techniques have knowledge of the adhesion between the heat-resistant layer and the chromate layer, they do not have any information regarding the adhesion between the heat-resistant layer and the resin.

  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 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, good adhesion to a resin such as polyimide without using a chromate film, and a method for producing the same.

  As a result of studying various surface treatments, the present inventors have obtained sufficient adhesion to a resin such as polyimide by having an Fe or Fe alloy layer on at least the surface to be bonded to the resin in copper and copper alloy foils. I found out that

That is, the present invention provides (1) a copper or copper alloy foil having a 10-point average roughness Rz _JIS (JIS B 0601 (2001)) of 2.0 μm or less, and at least a Fe or Fe alloy layer is provided on the surface to be bonded to the resin. Copper foil for printed wiring, characterized by having
(2) The copper foil for printed wiring boards according to (1) above, wherein the Fe alloy is an alloy of any one or more of Ni, Co, Mo, W, Zn, and Cu.
(3) The copper foil for printed wiring boards according to claim 1 or ² , wherein the Fe or Fe alloy layer is 0.1 to 100 mg / dm2.
(4) The copper for printed wiring boards according to the above (1) to (2), wherein the Fe or Fe alloy layer is ² to 50 mg / dm ² ,
(5) The copper foil for printed wiring boards according to the above (1) to (3), wherein the Fe content of the Fe alloy is 20 to 90 mass%,
(6) The copper foil for printed wiring boards according to (1) to (4) above, wherein Fe in the surface layer is an oxide, and the ratio of Fe in the surface layer is 5 at% or more,
(7) The copper foil for printed wiring boards according to the above (1) to (5), wherein the Fe or Fe alloy layer is produced by dry plating,
(8) The copper foil for printed wiring boards according to (1) to (6) above, wherein the Fe alloy is Ni, Co, and the Fe content is 20 to 90 mass%.
(9) The copper foil for printed wiring boards according to the above (1) to (7), wherein the resin to be bonded is polyimide and a polyimide precursor.

  According to the present invention, the surface-treated copper foil has a smoother surface than conventional roughened copper foil, and has good adhesion to a resin such as polyimide even without a chromate film. 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 with polyimide is made of Fe or an alloy of Fe and Ni, Co, Mo, W, Zn, Cu, and the Fe or Fe alloy layer is 0.1 to 100 mg / dm. ² Preferably it is 2-50 mg / dm < ² >, and it is preferable that Fe content in an alloy is 20-90 mass%, Furthermore, it is preferable that it is 20-80 mass%. Furthermore, it is desirable that the surface layer Fe is an oxide and the abundance ratio on the surface is 5 at% or more.

This is because the presence of the Fe oxide promotes chemical bonding with an organic substance such as a resin or an adhesive, thereby obtaining a strong adhesive force. Moreover, it has been found that the adhesive force is increased when the oxide is a composite with a metal such as Ni, Co, Mo, Zn, or Cu rather than when the oxide is Fe alone. In particular, in the case of a combination of Fe, Ni and Co, the adhesive force is remarkably improved.
In the conventional technology, chromate treatment and silane coupling treatment were essentially performed on such a metal film, but in the present invention, chromate treatment and silane coupling treatment are not essential. It is.

  Patent Document 3 discloses an effect of a film containing Fe and a polyphenylene ether base similar to the present invention, but chemical conversion treatment such as chromate treatment and silane coupling treatment are essential. Therefore, it was possible to increase the adhesive force by combining the two effects of chromate treatment and silane coupling treatment without specifying the thickness, composition and surface state of the film containing Fe. However, in the present invention, by specifying the thickness, composition, and surface state of the film containing Fe, not only the polyphenylene ether substrate but also polyimide resin, epoxy, acrylic, etc., without using the chromate film and silane coupling treatment. It is characterized by high adhesiveness with the adhesive.

Patent Document 4 discloses a mutual effect between Ni and a thermoplastic polyimide similar to the present invention. However, in the present invention, it is possible to obtain a higher adhesive force than Fe than Ni, and not only thermoplastic polyimide, but also a method using a polyimide precursor or an adhesive such as epoxy or acrylic. It is also effective in the method of bonding.
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 means that the average surface information of a relatively wide area can be obtained with an X-ray excitation source,
This is because it is easy to know the chemical state such as the oxidation number. In the case of Fe, an XPS peak appears at a position of 706 eV in the metal state and 710 eV in the oxidized state. Therefore, the presence of Fe oxide is a case where a peak of 710 eV exists and an XPS peak of oxygen coexists.

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 rate of the dry plating method is slower than that of the wet plating method, the dry plating method is disadvantageous from the viewpoint of productivity when the plating thickness is on the order of 100 mg / dm ² . 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.
Moreover, it is important that the surface state of the claims is obtained when the film is joined to the resin without any problem even if rolling is performed after the film is formed.
Moreover, after providing a surface treatment layer according to a use, a silane coupling process, a titanium coupling process, etc. may be given. This is because the surface on which Fe of the present invention is present is also suitable for the coupling treatment as well as the chromate treatment, so that the effect of the coupling treatment can be utilized.

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 monochromization: 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 defects such as pits in the surface treatment layer, copper diffuses from there and discolors the polyimide, and if there is a layer without defects such as 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-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-Zn"
The copper foil was subjected to general electrolytic degreasing and pickling, and an Fe—Zn plating layer was formed under the following conditions.
Ferric chloride 35-45 g / L
Zinc pyrophosphate 35-45 g / L
Potassium pyrophosphate 150-200g / L
pH 8.0-9.0
Bath temperature 50-70 ° C
Current density 1-5A / dm ²
Time 1-3 seconds

"Fe-Ni, Fe-W, Fe-Mo, Fe-Cu"
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

"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—Ni alloy was 90, 50, and 25 mass%, but Fe oxide was present on the surface, and the Fe concentration on the surface was also in the scope of the claims. Therefore, it has high peel strength and high corrosion resistance.
Inventive Examples 4 to 5 are examples in which the thickness of the Fe—Ni 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 Examples 6 to 7 are examples in which the surface roughness was reduced to 1.2 and 0.7, but had high peel strength and high corrosion resistance without any problem.
Invention Example 8 is a case where Fe was used, but it had a practical peel strength and high corrosion resistance, although the peel strength tended to be slightly lower than that of the Fe alloy example.
Invention Examples 9 to 13 are examples of various Fe alloys, but are within the scope of the claims, and thus have high peel strength and high corrosion resistance.

Although Comparative Example 14 was an Fe—Ni alloy, the film thickness was thin, and neither the peel strength nor the corrosion resistance was sufficient.
Although Comparative Example 15 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 16 is an example of Ni plating, but the peel strength was obtained, but the corrosion resistance was insufficient.
Comparative Example 17 is an Fe—Ni alloy having 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.
Comparative Example 18 is an example of Ni plating, but has a low peel strength.

Claims (9)

Copper and copper alloy foil having a ten-point average roughness Rz _JIS (JIS B 0601 (2001)) of 2.0 μm or less has a Fe or Fe alloy layer at least on the surface to be bonded to the resin. Copper foil.   2. The copper foil for printed wiring boards according to claim 1, wherein the Fe alloy is an alloy of any one or more of Ni, Co, Mo, W, Zn, and Cu. The copper foil for printed wiring boards according to claim 1 or ² , wherein the Fe or 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 or Fe alloy layer is ² to 50 mg / dm2.   The copper foil for printed wiring boards according to claim 1, wherein the Fe alloy has an Fe content of 20 to 90 mass%.   The copper foil for printed wiring boards according to claim 1, wherein Fe in the surface layer is an oxide, and a ratio of Fe in the surface layer is 5 at% or more. The copper foil for printed wiring boards according to claim 1, wherein the Fe or Fe alloy layer is prepared by dry plating. The copper foil for printed wiring boards according to claim 1, wherein the Fe alloy is Ni or Co, and the Fe content is 20 to 90 mass%. The copper foil for printed wiring boards according to claim 1, wherein the resin to be bonded is polyimide or a polyimide precursor.