JP2003055723A - Copper alloy foil for laminate sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide copper alloy foil with a small surface roughness which has satisfactory adhesiveness with an adhesive containing an epoxy resin even without undergoing roughening treatment, and can be laminated on a copper- covered laminate sheet, and has high electric conductivity and strength in a three layer flexible board. SOLUTION: The copper alloy foil for a laminate sheet contains additional element components of, by mass, 0.01 to 0.5% Sn, and the balance copper with inevitable impurities. By controlling the thickness of a rust preventive film to <=3 nm from the surface, the foil has the surface roughness of <=2 μm by a ten point surface roughness (Rz), an electric conductivity of >=70%IACS, and requires no roughening treatment, and has >=8.0 N/cm 180 deg. peel strength with an adhesive containing an epoxy resin when the adhesive is joined with a board resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copper alloy foil used for a laminated board for a printed wiring board.

[0002]

2. Description of the Related Art Printed wiring boards are often used in electronic circuits of electronic equipment. The printed wiring board is roughly classified into a hard laminated board (rigid board) and a flexible laminated board (flexible board) depending on the type of resin as a base material. The flexible substrate is characterized by its flexibility, and besides being used for the wiring of movable parts, it can also be stored in a bent state in electronic devices, so it is also used as a space-saving wiring material. There is. Since the substrate itself is thin, it is also used as an interposer for semiconductor packages or as an IC tape carrier for liquid crystal displays. A polyimide resin film or a polyester resin film is used as the base material of the flexible substrate, but currently polyimide is often used from the viewpoint of heat resistance. Copper is generally used as the conductive material of the flexible substrate from the viewpoint of conductivity. The printed wiring board is formed by etching the copper foil of the copper clad laminate to form various wiring patterns and connecting electronic components with solder to mount them.

Flexible substrates include two-layer flexible substrates and three-layer flexible substrates due to their structure. The two-layer flexible substrate has a structure in which a resin such as polyimide and copper serving as a conductive material are directly bonded. On the other hand, the three-layer flexible substrate has a structure in which a resin film such as polyimide and a copper foil serving as a conductive material are bonded with an adhesive containing an epoxy resin, an acrylic resin, or the like, but the adhesiveness is good. It is widely used because it is inexpensive. Due to such a difference in structure, the resin bonded to copper in the flexible substrate is the resin contained in the adhesive in the three-layer flexible substrate, whereas the two-layer flexible substrate is polyimide.

Since the adhesive used for the three-layer flexible substrate needs characteristics such as heat resistance, durability and flexibility, various resins are mixed to adjust the strength and the glass transition temperature. However, those containing an epoxy resin as a main component are generally used. The adhesive used for this purpose is a solvent-like or sheet-like adhesive containing an epoxy resin (for example, bisphenol A type glycidyl ether or glycidyl ester type epoxy resin) as a curing agent such as amine, and nitrile rubber or elastomer for imparting flexibility. To be The method for producing a copper-clad laminate is generally a method in which a solvent-like adhesive is applied onto a polyimide film and then a copper foil is laid over it where it is dried, or the adhesive is formed into a sheet between the polyimide film and the copper foil. It is sandwiched between objects and temporarily adhered by a roll press machine or a plane heating press machine, and then heat cured at 100 to 200 ° C. for several tens of minutes to several hours to adhere.

When a printed wiring board is mounted by connecting electronic components with solder, thermal stress is applied due to the difference in thermal expansion coefficient between the copper foil and the resin, so that the adhesiveness between the copper foil and the resin is poor. The problem of peeling occurs. For this reason, the copper foil used in the copper-clad laminate has been subjected to a roughening treatment in which copper particles are formed on the surface of the copper foil by electroplating in order to improve the adhesion with the resin. This is to improve the adhesiveness by a so-called anchor effect, in which unevenness is formed on the surface of the copper foil and the copper foil is made to dig into the resin to obtain mechanical adhesive strength. On the other hand, as electronic devices have become smaller, lighter and more sophisticated in recent years, the demand for high-density mounting on printed wiring boards has increased,
Fine pitches are being made by reducing the wiring width and spacing of electronic circuits. When a copper foil with a large surface roughness or a copper foil that has been roughened by a roughening treatment is used as the conductive material, etching residue may remain in the resin when etching the circuit, or the etching linearity may deteriorate. Then, the circuit width tends to be uneven. Therefore, in order to make the electronic circuit finer, it is preferable that the surface roughness of the copper foil is small. In electronic devices such as personal computers and mobile communications, the frequency of electric signals is high, but the frequency of electric signals is 1G.
When the frequency is higher than Hz, the effect of the skin effect in which the current flows only on the surface of the conductor becomes remarkable, and the effect of changing the transmission path due to the unevenness of the surface cannot be ignored. Therefore, attempts have been made to reduce the surface roughness of the copper foil due to the high frequency characteristics.

Copper foil which is a conductive material of a printed wiring board is classified into electrolytic copper foil and rolled copper foil depending on the manufacturing method. Electrolytic copper foil is generally manufactured by electrolytically depositing copper from a sulfuric acid-acidified copper sulfate plating bath on a titanium or stainless steel drum. When electrolytically depositing, irregularities are formed on the copper foil and the surface roughness increases. Recently, adding additives to the plating bath,
A copper foil, a so-called low profile foil, whose surface roughness is reduced by adjusting electrolytic deposition conditions has come to be manufactured. Since the rolled copper foil is manufactured by plastic working with a rolling roll, a smooth surface in which the surface morphology of the rolling roll is transferred to the surface of the foil can be obtained. The foil is generally 100μ.
A thin plate having a thickness of m or less.

As described above, the copper foil currently used in the copper-clad laminate is currently subjected to a roughening treatment in order to improve the adhesiveness with the resin. For the above reasons, the roughening treatment is performed. It is desirable to bond a copper foil having a small surface roughness that is not applied to the resin film, and it is necessary to secure adhesive strength without performing a roughening treatment. Further, in a three-layer flexible substrate, an attempt has been made to apply a silane coupling agent or the like to the copper foil in order to improve the adhesive strength between the copper foil that is a metal and the adhesive that is an organic substance, but sufficient adhesiveness is not obtained. Has not been done.

The material of the copper foil used as the conductive material is
Pure copper or a copper alloy containing a small amount of additional elements is used. Copper foil, which is a conductor, has become thinner and the circuit width has become narrower as the pitch of electronic circuits has become finer. ing. Copper is a material with excellent conductivity,
In the above fields where conductivity is important, pure copper having a purity of 99.9% or more is generally used. However, since the strength of copper decreases as the purity increases, the handling property deteriorates when the copper foil becomes thin. Therefore, the strength of the copper foil is preferably high.

Under these circumstances, an attempt was made to bond the polyimide film to the polyimide film using an adhesive containing an epoxy resin, without subjecting the copper foil as a conductive material to roughening treatment. However, it has been found that the polyimide film and the rolled copper foil of pure copper are easily separated, and the interface between the adhesive containing the epoxy resin and the copper is easily separated. For this reason, using a copper foil as a conductive material without subjecting it to roughening treatment tends to cause peeling of the copper foil from the epoxy resin, which is the main component of the adhesive, resulting in a problem such as disconnection. , Has not been put to practical use.

[0010]

To improve the adhesiveness when a three-layer printed wiring board is manufactured by bonding a polyimide resin film as a base material and a copper foil as a conductive material with an adhesive containing an epoxy resin. A copper alloy for a laminated plate, which can obtain a surface roughness of a copper foil of 2 μm or less in Rz and a bonding strength of 8.0 N / cm or more in a 180 ° peel strength without performing a special treatment such as a roughening treatment. Is to provide foil.

[0011]

The inventors of the present invention have investigated the adhesiveness when a polyimide resin film and a copper foil of a conductive material are bonded together with an adhesive containing an epoxy resin, and as a result, the adhesiveness is conductive. It has been found that the improvement is achieved by a copper alloy with a small amount of additional elements based on pure copper having excellent properties, and that it is reduced as the rustproof coating of the copper alloy foil becomes thicker.
Specifically, as a result of repeated studies on the influence of various additive elements on the adhesiveness with an adhesive containing an epoxy resin and the relationship between the thickness of the rust-preventive coating and the adhesiveness, the present invention was The weight ratio of Sn component is 0.01
% To 0.5% by mass, with the balance consisting of copper and unavoidable impurities, and the thickness of the rust-preventive coating being 3 nm or less from the surface, the surface roughness in terms of ten-point average surface roughness (Rz). 180μ peel strength between the adhesive containing epoxy resin and the copper alloy foil when it is bonded to the substrate resin with the adhesive containing epoxy resin, the roughness is not more than 2μm, the conductivity is 70% IACS or more. Is 8.0 N / cm or more, a copper alloy foil for a laminate. (2) Sn contains 0.01% by mass to 0.5% by mass of the component of the additional element, and further contains Al, Be, Co, F.
e, Mg, Mn, Ni, P, Pb, Si, Ti and Z
The total amount of one or more of the n components is 0.005% by mass to
The surface roughness is 2 μm in terms of ten-point average surface roughness (Rz) by containing 2.5% by mass, the balance consisting of copper and unavoidable impurities, and the thickness of the rust preventive film being 3 nm or less from the surface.
Below, tensile strength is 500 N / mm ² or more, conductivity is 60
% IACS or more, no roughening treatment is required, and the 180 ° peel strength between the adhesive containing the epoxy resin and the copper alloy foil is 8.0 N / cm or more when bonded to the substrate resin with the adhesive containing the epoxy resin. The copper alloy foil for laminated boards, characterized in that

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The reason why the surface condition and alloy composition are limited to the above in the present invention will be described. (1) Anticorrosion coating: To prevent discoloration of pure copper and copper alloys, organic substances containing nitrogen such as benzotriazole and imidazole are widely used to form a chelate with copper on the surface to form an anticorrosion coating. It is being appreciated. On the other hand, these rust-proof coatings have water repellency and have an effect of impairing the bonding of the epoxy resin to deteriorate the adhesiveness. Therefore, by limiting the thickness of the rust-preventive coating to 3 nm or less from the surface, it becomes possible to firmly bond the copper alloy foil and the polyimide film using an adhesive containing an epoxy resin. In order to reduce the thickness of the rust preventive film, for example, there is a method of reducing the concentration of the rust preventive agent. When benzotriazole is used as the rust preventive agent, the concentration is preferably 3000 ppm or less. The thickness of the anticorrosion coating from the surface can be quantified by measuring by Auger electron spectroscopy. That is, by Auger electron spectroscopy analysis, analysis is performed in the depth direction, and the depth from the surface until the detected intensity of nitrogen, which is an element constituting the rust preventive agent, becomes the same as the background, is measured in terms of SiO _2. Required by

(2) Sn: Sn is known to act as a catalyst for promoting polymerization when producing a resin. Therefore, it is considered that by adding Sn to copper to form an alloy foil, the bonding between the metal and the epoxy resin which is the main component of the adhesive is promoted, and the bonding at the interface is strengthened. However, if the added amount of Sn is too small, it does not sufficiently act as a catalyst, so that the metal and the resin are not sufficiently bonded and the effect of improving the adhesiveness is small. As a printed wiring board, it is necessary to provide a 180 ° peel strength of 8.0 N / cm or more, which does not hinder practical use.
In order to obtain this characteristic, the addition amount of Sn is 0.
It was found to be 01 mass% or more. On the other hand, when the amount of Sn added to copper increases, the conductivity decreases and it becomes unsuitable as a conductive material for circuits. Therefore, as a result of studying a suitable composition as a copper alloy foil for a laminated board of a printed wiring board, Sn is 0.01 to 0.5 mass% by weight, more preferably 0.02 to 0.2 mass%. It turned out to be.

(3) Al, Be, Co, Fe, Mg,
Mn, Ni, P, Pb, Si, Ti and Zn all have the effect of mainly increasing the strength of the copper alloy,
If necessary, one or more kinds are added. If the total content is less than 0.005 mass%, the desired effects cannot be obtained, while if the total content exceeds 2.5 mass%, the conductivity, solderability, and workability are not obtained. Significantly deteriorates. Therefore, Al, Be, Co, Fe, Mg, M
The total content range of n, Ni, P, Pb, Si, Ti and Zn was set to 0.005% by mass to 2.5% by mass.

(4) Surface roughness: When the surface roughness of the copper foil increases, the impedance increases due to the skin effect in which the frequency of the electric signal is 1 GHz or more and the current flows only on the surface of the conductor, so that high-frequency signals can be transmitted. Affect. Therefore, it is necessary to reduce the surface roughness in the use of conductive materials for high-frequency circuits.As a result of studying the relationship between surface roughness and high-frequency characteristics, the surface roughness of copper alloy foil for laminated boards of printed wiring boards It was found that the ten-point average surface roughness (Rz) should be 2 μm or less. As a method for reducing the surface roughness, there are methods such as optimizing the manufacturing conditions of rolled copper foil and electrolytic copper foil, and chemically polishing or electrolytic polishing the surface of the copper foil. In general, rolled copper foil can easily reduce the surface roughness, and it is possible to reduce the surface roughness of the work roll of the rolling mill to reduce the profile of the work roll transferred to the copper foil. it can.

The copper alloy foil of the present invention is not limited to a manufacturing method, and can be manufactured by a method such as electrolytic copper foil by an alloy plating method or a rolled copper foil in which an alloy is melt cast and rolled. The rolling method will be described below as an example. A predetermined amount of alloying element is added to molten pure copper and cast in a mold to form an ingot. The melting and casting of the copper alloy is preferably performed in a vacuum or in an inert gas atmosphere in order to suppress the formation of oxides and the like. It is desirable to use electrolytic copper or oxygen-free copper having a low oxygen content as the raw material. The ingot is thinned to a certain thickness by hot rolling, then cut, then repeatedly cold-rolled and annealed, and finally cold-rolled to obtain a foil. Rolling oil adheres to the material after rolling, so
Degrease with acetone or petroleum solvent.

If an oxide layer is formed by annealing, it will interfere with the subsequent steps. Therefore, it is necessary to perform the annealing in vacuum or in an inert gas atmosphere, or to remove the oxide layer after annealing.
For example, in order to remove the oxide layer by pickling, it is preferable to use sulfuric acid + hydrogen peroxide, nitric acid + hydrogen peroxide, or sulfuric acid + hydrogen peroxide + fluoride.

[0018]

EXAMPLES Examples of the present invention will be described below. The copper alloy was prepared by melting oxygen-free copper as a main raw material in a high-purity graphite crucible in an Ar atmosphere using a high-frequency vacuum induction melting furnace, and tin, aluminum, a copper beryllium master alloy as a sub-raw material, After adding an additive element selected from cobalt, copper-iron master alloy, magnesium, manganese, nickel, copper-phosphorus master alloy, lead, copper-silicon master alloy, titanium and zinc, it was cast in a cast iron mold. With this method, thickness 30mm, width 50mm, length 150mm, weight about 2kg.
To obtain a copper alloy ingot. 900 this ingot
After heating to 0 ° C. and hot rolling to a thickness of 8 mm to remove oxide scale, cold rolling and heat treatment were repeated to obtain a rolled copper alloy foil having a thickness of 35 μm.

Since the rolling oil adhered to the copper alloy foil having a thickness of 35 μm obtained by the above method, it was immersed in acetone to remove the oil. This was immersed in an aqueous solution containing 10% by weight of sulfuric acid and 1% by weight of hydrogen peroxide to remove the oxide layer and the rust preventive film on the surface. For the purpose of investigating the influence of the thickness of the rust preventive film, the film was immersed in an aqueous solution in which the concentration of benzotriazole was adjusted and immediately dried. Other than this, no special surface treatment such as roughening treatment or silane coupling treatment for improving adhesiveness is carried out. The copper alloy foil thus prepared was bonded to a polyimide film with an adhesive containing an epoxy resin to prepare a copper clad laminate. The copper-clad laminate is prepared by coating a solvent-type adhesive, which is a mixture of an epoxy resin and a curing agent, on a polyimide film having a thickness of 25 μm with an applicator having a gap amount of 100 μm, and the temperature is 130 ° C. in a dryer. After drying for 4 minutes, the above-mentioned copper alloy foils were overlaid and held for 30 minutes under the conditions of a temperature of 170 ° C. and a pressure of 30 kgf / cm ² using a flat heating press to obtain a copper-clad laminate. Here, the thickness of the adhesive after drying is 20 μm.
Met.

The "tensile strength", "electrical conductivity", "thickness of rust preventive film", "surface roughness", "high frequency characteristics" and "adhesive strength" of the copper alloy foil thus obtained are as follows. It evaluated by the method. (1) Tensile strength: Tensile strength was measured by measuring the tensile strength at room temperature by a tensile test. The measurement sample is a copper foil processed to have a thickness of 35 μm and a width of 12.7 mm using a precision cutter.
It was cut into a strip having a length of 150 mm. This was measured at a distance between scores of 50 mm and a tensile speed of 50 mm / min. (2) Conductivity: The conductivity was obtained by measuring the electric resistance at 20 ° C. by a DC four-terminal method using a double bridge. As the measurement sample, a copper foil processed into a foil having a thickness of 35 μm was cut into a width of 12.7 mm. The electrical resistance was measured by measuring the electrical resistance of this for a measurement length of 50 mm. (3) Thickness of rust preventive film: As described above, the depth direction analysis of Auger electron spectroscopic analysis was performed, and from the surface until the detected intensity of nitrogen, which is an element that constitutes the rust preventive agent, became the same as the background. Was measured in terms of SiO ₂ . (4) Surface roughness: The surface roughness was measured in the direction perpendicular to the rolling direction using a stylus type surface roughness meter. Measurement conditions are JI
The ten-point average surface roughness (Rz) was evaluated according to the method described in S B 0601. (5) High frequency characteristics: The high frequency characteristics were evaluated by the impedance when a high frequency current was applied. For impedance, copper foil processed to a thickness of 35 μm was processed to a width of 1 mm, and 1
The voltage drop when a high frequency current of 0 MHz and 20 mA was applied was measured for a length of 100 mm. (6) Adhesive strength: Adhesive strength is 180 ° peel strength JI
It was carried out according to the method described in S C 5016. The width of the peeling conductor is 5.0 mm, the polyimide film side is fixed to the tensile tester side, the copper alloy foil that is the conductor is bent in the 180 ° direction, and the pulling speed is 50 mm.
It was peeled off at the speed of / min.

An embodiment according to claim 1 of the present invention will be shown.
Table 1 shows the composition of the copper alloy foil, and Table 4 shows the results of the characteristic evaluation. In addition, the part shown by "-" in the table indicates that the measurement is not performed. No. of the embodiment. 1 to N
o. 4 is an example of the copper alloy foil according to claim 1 of the present invention. The copper alloy foil of the present invention had an electrical conductivity of 70% IACS or more, and a 180 ° peel strength of 8.0 N / cm or more when the copper alloy foil was bonded to a polyimide film with an adhesive containing an epoxy resin. It can be seen that it has excellent conductivity and high adhesive strength.

[0022]

[Table 1]

[0023]

[Table 2]

Next, an embodiment according to claim 2 of the present invention will be described. Table 3 shows the composition of the copper alloy foil, and Table 4 shows the characteristic evaluation results. No. of the embodiment. 5 to No. 9 is an example of the copper alloy foil according to claim 2 of the present invention. As shown in Table 4, the copper alloy foil of the present invention has an electrical conductivity of 60% IACS or more, a tensile strength of 500 N / mm ² or more, and a copper alloy foil bonded to a polyimide film with an adhesive containing an epoxy resin. The 180 ° peel strength was 8.0 N / cm or more. It has excellent conductivity and handling,
It can be seen that it also has high adhesive strength.

[0025]

[Table 3]

[0026]

[Table 4]

Table 5 shows the composition of the copper alloy foil of Comparative Example and Table 6
Is the characteristic evaluation result. No. 10 to 12 are comparative examples relating to claim 1 of the present invention. No. 10 is a rolled copper foil to which the alloy component of the present invention is not added. An ingot obtained by melting and casting oxygen-free copper in an Ar atmosphere was processed into a foil, and the foil was bonded under the same conditions as the polyimide film using the same adhesive as in the example. Since the material is pure copper, it has high conductivity, but 180 ° peel strength is 7.5 N / cm
Since it is small and sufficient adhesive strength is not obtained, peeling may occur when a printed wiring board is formed.

[0028]

[Table 5]

[0029]

[Table 6]

No. 11 and No. In No. 12, Sn was added and processed into a foil in the same manner as in the example. No. 1
Since No. 1 has a large Sn concentration, the conductivity is large, but the effect of improving heat resistance and adhesiveness is not sufficient. 180
° Peel strength is low and may peel off when processed into a laminate. On the other hand, No. Since No. 12 has a Sn concentration of more than 0.5 mass% by weight, the 180 ° peel strength is high, but the conductivity is low at less than 70% IACS, and the conductivity of a printed wiring board requiring high conductivity is low. Not suitable as a material.

No. 13 and No. 14 is a comparative example relating to claim 2 of the present invention. In addition to Sn, the No. No. 13 is Fe, and No. 14 was processed into a foil by adding Ti in the same manner as in the example. Since the addition amount of Fe or Ti exceeds 2.5 mass% by weight, the tensile strength and the peel strength are high, but the conductivity is lower than 60% IACS, and it is used as a conductive material for printed wiring boards. Is not suitable.

No. of the comparative example. No. 15 of the embodiment shown in Table 1 The alloy foil of No. 2 was used to lightly scrape the surface with emery paper to roughen the surface. As a result, when the surface roughness becomes large, the impedance increases due to the skin effect when energized at a high frequency, which is not suitable as a conductive material for a high frequency circuit.

No. of the comparative example. No. 16 of the embodiment shown in Table 1 Using the alloy foil of No. 2, a treatment of immersing it in an aqueous solution in which the concentration of benzotriazole as a rust preventive was adjusted to 0.5% (5000 ppm) was performed. Due to the high concentration of the rust preventive agent, the thickness of the rust preventive film becomes as thick as 5 nm
The 80 ° peel strength is as low as 4.5 N / cm.

[0034]

When the copper alloy foil of the present invention is used for a printed wiring board laminate by adhering it to a polyimide resin film using an adhesive containing an epoxy resin, it has excellent adhesion to the resin even if the surface roughness is small. And has high conductivity and strength. This makes it suitable for use as a conductive material for electronic circuits that require fine wiring.

Continued front page    F-term (reference) 4E351 AA01 BB01 BB30 CC18 DD04                       DD08 DD10 DD11 DD12 DD18                       DD19 DD54 DD56 GG01                 4F100 AB02A AB09A AB10A AB11A                       AB12A AB14A AB15A AB16A                       AB17A AB18A AB23A AB31A                       AB33A BA02 GB43 JG05A                       JK06 JK06A JL05 JL11                       YY00A

Claims (2)

[Claims] 1. Sn in an amount of 0.01% by mass to 0.5% by mass of a component of an additive element, the balance consisting of copper and unavoidable impurities, and a rust preventive film having a thickness of 3 nm from the surface.
By the following, the surface roughness is 2 μm or less in ten-point average surface roughness (Rz), the conductivity is 70% IACS or more, the roughening treatment is unnecessary, and the adhesive including the epoxy resin is used as the substrate resin. A copper alloy foil for a laminate, wherein a 180 ° peel strength between an adhesive containing an epoxy resin and a copper alloy foil when joined is 8.0 N / cm or more. 2. The weight ratio of the additive element component to Sn is 0.
01% by mass to 0.5% by mass, further containing Al, Be, C
O, Fe, Mg, Mn, Ni, P, Pb, Si, Ti, and Zn, each containing one or more components in a total amount of 0.005% by mass to 2.5% by mass, and the balance copper and unavoidable impurities. When the thickness of the rust preventive film is 3 nm or less from the surface, the surface roughness is 10-point average surface roughness (Rz) of 2
μm or less, tensile strength of 500 N / mm ² or more, conductivity of 60% IACS or more, no roughening treatment is required, and an adhesive containing an epoxy resin when bonded to a substrate resin with an adhesive containing an epoxy resin And a copper alloy foil having a 180 ° peel strength of 8.0 N / cm or more.