JP2003034829A - Copper alloy foil for laminate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper alloy foil for a laminate, with small surface roughness, which is used for the printed circuit board employing polyimide as a resin substrate, and can be directly bonded to the polyimide substrate without being plated beforehand for roughening. SOLUTION: The copper alloy foil for the laminate includes elements of iron, nickel, and cobalt of 1 wt.% in total, and P of 0.2 wt.% or less in total, and has tensile strength of 500 N/mm<2> or more, conductance of 60% IACS or more, surface roughness of 2 μm by ten-points average surface roughness (Rz), and peel strength of 8.0 N/cm or more by an 180 degree peel test after directly bonded to a polyimide film without being plated for roughening. The foil can include an element having a solution strengthening effect, of 2.5 wt.% or less.

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. A printed wiring board is a rigid laminated board (rigid board) that uses a glass epoxy board and a paper phenol board as constituent materials, depending on the type of resin used as the base material.
And a flexible laminated plate (flexible substrate) including a polyimide substrate and a polyester substrate as constituent materials.

Of the above printed wiring boards, the flexible board is characterized by flexibility, and is used not only for wiring the movable part but also for storing it in a bent state in electronic equipment. It is also used as a space-saving wiring material. 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. The flexible substrate is a three-layer flexible substrate formed by laminating a resin substrate and a copper foil with an adhesive, and then curing the adhesive by heating and pressing, and a resin substrate and a copper foil without using the adhesive. There is a two-layer flexible substrate in which and are directly laminated by heating and pressing. In the three-layer flexible substrate, a polyimide resin film or polyester is used as a resin substrate, and an epoxy resin or an acrylic resin is widely used as an adhesive. On the other hand, a polyimide resin is generally used for a resin substrate of the two-layer flexible substrate. In recent years, the use of lead-free solder has been widespread due to the influence on the environment. However, since the melting point is higher than that of the conventional lead solder, the demand for heat resistance of the flexible substrate has become strict.

In the printed wiring board, various wiring patterns are formed by etching the copper foil of the copper clad laminate, and electronic parts are connected by soldering and mounted. Since the material for the printed wiring board is repeatedly exposed to such a high temperature, heat resistance is required. In recent years, lead-free solders have come to be used due to consideration for the environment, but as a result, the melting point becomes higher than that of conventional lead solders, and printed wiring boards are required to have high heat resistance. For this reason,
Since the two-layer flexible substrate uses only the polyimide resin having excellent heat resistance as the organic material, it is easier to improve the heat resistance than the three-layer flexible substrate and the amount of use thereof is increasing.

Copper foil is mainly used as a conductive material for a printed wiring board, but the copper foil is classified into an electrolytic copper foil and a rolled copper foil depending on the manufacturing method thereof. The electrolytic copper foil is manufactured by electrolytically depositing copper on a titanium or stainless steel drum from a copper sulfate plating bath. Since the rolled copper foil is manufactured by plastic working with a rolling roll, the surface morphology of the rolling roll is transferred to the surface of the foil, and a smooth surface is obtained. As the copper foil used as the conductive material of the flexible substrate, rolled copper foil is mainly used because of its good flexibility. The copper foil used for the printed wiring board is subjected to a roughening plating 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. Further, in the 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 metal copper foil and the organic adhesive. However, since the pressure of the two-layer flexible substrate is 300 ° C. to 400 ° C., which is higher than the temperature of 100 to 200 ° C. of the three-layer flexible substrate, thermal decomposition of the coupling agent easily occurs and the adhesiveness is improved. Not not. The foil generally means a thin plate having a thickness of 100 μm or less.

With the recent miniaturization, weight reduction, and high functionality of electronic equipment, there is an increasing demand for high-density mounting on printed wiring boards. Flexible substrates are also used as space-saving wiring materials, semiconductor package interposer applications, and IC tape carriers for liquid crystal displays. Especially, in these applications, the wiring width and wiring interval of electronic circuits are reduced due to the demand for high-density mounting. Fine pitching is progressing. A copper foil with a large surface roughness or a copper foil having irregularities formed by a roughening plating treatment may have an etching residue where copper remains in the resin when a circuit is formed by etching,
The etching linearity is liable to decrease and the circuit width tends to be nonuniform. Therefore, in order to make the electronic circuit fine-pitch, it is preferable that the surface roughness of the copper foil is small, and it is desirable to bond the copper foil having a small surface roughness that is not subjected to the roughening plating treatment to the resin film.

In electronic devices such as personal computers and mobile communications, electric signals have a high frequency, but when the frequency of the electric signals is 1 GHz or higher, the effect of the skin effect in which the current flows only on the surface of the conductor becomes remarkable. . The surface of the copper foil is roughened by roughening the surface of the copper foil to roughen the surface. However, at high frequencies of 1 GHz or higher, the effect of changing the transmission path due to the roughness of the surface cannot be ignored. In order to deal with this, it is necessary to secure the adhesive strength without performing the roughening plating treatment. Also in this case, it is desirable to bond a copper foil having a small surface roughness, which is not subjected to the roughening plating treatment, to the resin film.

In order to form a fine circuit by etching, it is necessary to reduce the thickness of the copper foil in addition to the surface roughness of the copper foil being small. As the copper foil becomes thinner, the difference in the circuit width in the thickness direction becomes smaller, so that a fine circuit can be formed. Fine circuits can be formed by reducing the thickness of the copper foil used for the copper-clad laminate or by reducing the thickness of the copper foil of the copper-clad laminate by etching. Copper is a material having excellent conductivity, and pure copper having a purity of 99.9% or more is generally used in the above fields where conductivity is important.
However, since the strength of copper decreases as the purity increases, the handleability deteriorates when the copper foil becomes thin. Further, reducing the thickness of the copper foil by etching has a problem of increasing the number of manufacturing processes. Therefore, it is preferable to use a copper foil, which has a conductivity suitable for a circuit material and a high strength, for the laminate. In addition, since the two-layer flexible substrate requires heat treatment at a high temperature of 300 ° C. to 400 ° C. for about 10 minutes to 1 hour when laminated, the copper foil is softened and the handling property deteriorates. 1
It is preferable that it is not softened by a heat treatment for about an hour.

Under such circumstances, a copper foil obtained by rolling high-purity oxygen-free copper suitable for a conductive material is used as a resin film as a polyimide film with a smooth surface not subjected to roughening plating. Was attempted to be bonded without using an adhesive to fabricate a two-layer flexible substrate. As a result,
It was found that the adhesion between the polyimide film and the rolled copper foil of pure copper was poor, and peeling was easy. Therefore, when a copper foil having a small surface roughness that is not subjected to roughening plating is used as the conductive material of the two-layer flexible substrate, peeling of the copper foil is likely to occur, and problems such as disconnection are likely to occur. found. Therefore, there is a demand for a copper foil having high conductivity and high strength, which has excellent surface adhesiveness with a polyimide resin and which has a small surface roughness without being subjected to a roughening plating treatment.

[0010]

The adhesive strength required for the printed wiring board varies depending on the manufacturing conditions of the electronic equipment and the operating environment, but the 180 ° peel strength is generally 8.0 N / cm.
If it is above, there is no problem in practical use. In the present invention, a copper foil having a surface roughness Rz of 2 μm or less has an adhesive strength of 1 without being subjected to a special treatment such as a roughening plating treatment.
The target was 80 N peel strength of 8.0 N / cm or more. Further, the tensile strength before heating was set to 500 N / mm ² or more in consideration of handleability, and the target value of the conductivity was set to 60% IACS or more.
An object of the present invention is to provide a copper foil for a laminated board, which has a small surface roughness and is excellent in adhesiveness with polyimide.

[0011]

The inventors of the present invention have found that the adhesiveness with polyimide is based on pure copper having excellent conductivity.
It was found to be improved by a copper alloy with a small amount of additive element added. Specifically, adhesiveness with polyimide,
As a result of repeated studies on the influence of various additive elements on the strength and conductivity, the present invention shows that (1) Fe is 0.02 mass% to 0.5 mass% and Ni is a mass ratio of the additive element components. 0.04% by mass to 1.0% by mass, and one or more of 0.04% by mass to 1.0% by mass of Co is contained in a range not exceeding 1.0% by mass, and Fe and Ni are contained. And 0.05 to the total amount of Co
A tensile strength of 500 N / mm ² or more is obtained by containing 0.2 times the weight of P and making the balance copper and inevitable impurities.
Conductivity is 60% IACS or more, surface roughness is 10 μm average surface roughness (Rz) of 2 μm or less, and 180 ° peel when directly bonded to a polyimide film without roughening treatment. A copper alloy foil for a laminate, characterized by having a strength of 8.0 N / cm or more (2) The tensile strength when heated for 1 hour is the tensile strength before heating and the tensile strength when softened. The copper alloy foil for laminated plate according to (1) is characterized in that the intermediate temperature of the strength is 300 ° C. or higher.

The present invention also provides Ag, Al, Be, M
All of g, Mn, Pb, Sn, Ti and Zn have an effect of enhancing the strength of the copper alloy mainly by solid solution strengthening, and it is possible to add one or more elements as necessary. 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. Ag, Al, B
The total content of e, Mg, Mn, Pb, Sn, Ti and Zn is preferably 0.005 to 2.5 mass%.
In the present invention, the surface roughness of a copper alloy foil is defined by a ten-point average surface roughness (R
It is also a foil having z) of 2 μm or less.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The reason why the alloy composition and the like are limited to the above in the present invention will be described. (1) Fe, Ni, Co, P: Fe, Ni, and Co are known to act as a catalyst for promoting polymerization when a resin is produced. Therefore, Fe, Ni, Co
It has been found that the addition of copper to copper to form an alloy foil improves the adhesion to polyimide. The reason is F
It is considered that e, Ni, and Co promoted the bond between the metal and the resin, and the bond at the interface was strengthened. If the content of these components is too small, they do not act sufficiently as a catalyst, so that the metal and resin are not sufficiently bonded and the effect of improving the adhesiveness is small. Further, it was found that Fe, Ni, and Co exhibit the action of improving the adhesion between the metal and the polyimide resin by forming a solid solution in copper as a simple element in the copper alloy, and the action is reduced when the compound is formed. . F dissolved in copper
If the amounts of e, Ni, and Co increase, the conductivity decreases and it becomes unsuitable as a conductive material for circuits. On the other hand, P is Fe,
Compounds of Fe ₂ P, Ni ₃ P, and Co ₂ P are formed with Ni and Co, respectively, and deposited as fine particles. These fine precipitates suppress the movement of dislocations and grain boundaries to increase the strength and improve the softening resistance at the time of heating, but if the amount of formation is small, the improvement effect is small. Therefore, in order to enhance the strength and simultaneously exhibit the effect of improving the softening resistance at the time of heating and the effect of improving the adhesion between the metal and the polyimide resin, Fe, Ni, and Co are added to P in the copper alloy foil. It is necessary for Fe, Ni, and Co to form a solid solution as a simple element while forming a compound. P for Fe, Ni, Co
Although the compound increases as the addition ratio of is increased, Fe, Ni, and Co that form a solid solution decrease, and the effect of improving the adhesiveness between the metal and the polyimide resin decreases. Further, if the amount of precipitates increases, there is a problem that the plastic workability of the copper alloy is impaired. As a result of investigating an appropriate composition from these characteristics, as a copper alloy foil for a laminated board of a printed wiring board, an appropriate content range of alloy components is 0.02 to 0.5 mass% of Fe in weight ratio,
More preferably 0.05 to 0.3 mass%, Ni is 0.0
4 to 1.0% by mass, more preferably 0.1 to 0.5% by mass, Co is 0.04 to 1.0% by mass, and more preferably 0.1 to 0.5% by mass. Choose and Fe,
The total amount of Ni and Co does not exceed 1.0% by mass, and P is 0.05 with respect to the total weight of Fe, Ni, and Co.
~ 0.2 times the weight, more preferably 0.07 to 0.15
Determined to be twice as heavy.

(2) Tensile strength and conductivity: Generally strength and conductivity
The electrical properties are in conflict with each other.
Tends to decline. Tensile strength is 500 N / mm^TwoThan
If it is small, wrinkles may occur during handling, etc.
Easy, and if the conductivity is 60% IACS or less, the laminated board
It is not preferable as a conductive material. High strength and handling
As a condition suitable for copper alloy foil for laminates with excellent ruggedness,
Tensile strength is 500 N / mm ^TwoAbove, conductivity is 60% IAC
It was defined as S or higher. (3) 180 ° peel strength: 180 ° peel strength is small
If not, peeling may occur from the laminated plate, so 8.
An adhesive strength of 0 N / cm or more is required.

(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 electrical 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,
In the use of conductive materials for high frequency circuits, it is necessary to have a small surface roughness, and as a result of examining the relationship between surface roughness and high frequency characteristics, as a 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. The method of reducing the surface roughness is to optimize the production conditions of rolled copper foil and electrolytic copper foil,
There is a method of chemically polishing or electrolytically polishing the surface of the copper foil. Generally, rolled copper foil can easily reduce the surface roughness, and the work roll surface of the rolling mill can be reduced to reduce the profile of the work roll transferred to the copper foil. .

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 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. Since the rolling oil adheres to the material after rolling, it is degreased with acetone or a 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 a copper-iron master alloy, nickel, and cobalt as auxiliary raw materials. After adding an additive element selected from a copper phosphorus master alloy, silver, aluminum, a copper beryllium master alloy, magnesium, manganese, lead, tin, titanium and zinc, it was cast in a cast iron mold. This method has a thickness of 30 mm and a width of 50 m.
A copper alloy ingot having a length of m, a length of 150 mm and a weight of about 2 kg was obtained. This ingot is heated to 900 ° C. and hot rolled to a thickness of 8 mm to remove oxide scale, and then cold rolling and heat treatment are repeated to obtain a thickness of 35 μm.
A rolled copper alloy foil was obtained.

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. Other than this, no special surface treatment such as roughening plating treatment or silane coupling treatment for improving adhesion is carried out. The copper alloy foil thus produced was bonded to a polyimide film by using a plane heating press. The adhesion conditions are such that a copper alloy foil and a polyimide film are overlapped with each other, preheated for 5 minutes on a flat heating press held at a temperature of 330 ° C., then pressurized to a pressure of 490 N / cm ² and held for 5 minutes and then unloaded, Cooled. There are various types of polyimide films such as pyromellitic acid type, biphenyl tetracarboxylic acid type, and benzophenone tetracarboxylic acid type, and flexible substrates having a thickness of 10 to 60 μm are often used. The embodiment of the present invention has a thickness of 25.
Although a biphenyltetracarboxylic acid type having a structural formula of μm shown in FIG. 1 was used, the present invention is not limited to this.

The "tensile strength", "conductivity", "heat resistance", "surface roughness", "high frequency characteristics" of the copper alloy foil thus obtained, and after the copper alloy foil was bonded to polyimide "Adhesive strength" was evaluated by the following 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) Heat resistance: Heat resistance is measured by measuring the tensile strength at room temperature when heating for 1 hour, and softening the heating temperature so that it is between the tensile strength before heating and the tensile strength when softening. It was evaluated as temperature. (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. Since the strength varies depending on the composition of the copper alloy foil, the measurement was carried out by fixing the copper alloy foil to the tensile tester side using a double-sided tape, bending the polyimide in the direction of 180 ° and peeling it off.
Peeling width is 5.0mm, pulling speed is 50mm
It was measured in minutes.

Table 1 shows the composition of the copper alloy foil, and Table 2 shows the evaluation results of the characteristics of the copper alloy foil. The portion indicated by "-" in the table indicates that the measurement was not performed. No. of the embodiment.
1-No. 9 is an example of the copper alloy foil of the present invention. As shown in Table 1, the copper alloy foil of the present invention has an electric conductivity of 60% I
The tensile strength was ACS or more, the tensile strength was 500 N / mm ² or more, and the 180 ° peel strength when polyimide was adhered was 8.0 N / cm or more. It can be seen that it has excellent conductivity and heat resistance, and has high adhesive strength.

[0022]

[Table 1]

[0023]

[Table 2]

On the other hand, in Comparative Example No. 1 shown in Table 1. 10 is a book
It is a rolled copper foil to which the alloy component of the invention is not added. Acid free
Ingot made by melting and casting copper in Ar atmosphere as foil
Processed and bonded with polyimide. The material is pure copper
Because of its high conductivity, 180 ° peel strength is 7.3N
/ Cm is not enough adhesive strength, so pudding
When used as a wiring board, peeling may occur. Again
Strength is 500 N / mm ^TwoBecause it is less than less than
Ringing is bad.

No. of the comparative example. 11-No. 14 is Fe
And P were added to form a foil in the same manner as in the example.
It was No. No. 11 has less P concentration than Fe concentration
For Fe_TwoPrecipitation amount of P decreases, heat resistance and tensile strength
The strength is small. On the other hand, No. 12 is P for Fe concentration
Due to the high concentration, Fe_TwoIn the copper, the precipitation amount of P increases.
The proportion of Fe that is solid-dissolved in is reduced. For this reason,
Tensile strength of 630 N / mm ^TwoAnd a big 180 degree peel
The strength is low and there is a risk of peeling when processed into a laminated board.
is there. In addition, No. No. 13 has a Fe concentration of 0.01% by mass
The conductivity was high because it was full, but the tensile strength and heat resistance
And the effect of improving the adhesiveness is not sufficient. No. 14 is
The Fe concentration was added in an amount of more than 0.5% by weight.
Therefore, the conductivity of the printed wiring board becomes low,
Is not suitable.

No. of the comparative example. In No. 15, Fe, Ni, Co and P were added to form a foil in the same manner as in the example.
Since the total concentration of Fe, Ni, and Co is more than 1.0 mass% in terms of weight ratio, the conductivity is low and it is not suitable as a conductive material for a printed wiring board.

No. of the comparative example. In the case of No. 16, Ti was added in addition to Fe and P, but since the concentration of Ti was more than 2.5% by mass in weight ratio, the electric conductivity was small and it was not suitable as a conductive material for a printed wiring board.

No. of the comparative example. No. 17 of the example. Three
The surface of the alloy foil of No. 3 was lightly shaved 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.

[0029]

EFFECT OF THE INVENTION The copper alloy foil used for a laminate of a printed wiring board having a polyimide as a base material of the present invention has excellent adhesiveness to a base resin and has high conductivity and strength. Further, since the strength is high and the heat resistance is good, the handleability of the foil is excellent. This makes it suitable for use as a conductive material for electronic circuits that require fine wiring.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a structural formula of polyimide used in Examples and Comparative Examples.

Claims (2)

[Claims] 1. Fe is 0.02% by mass to 0.5% by mass and Ni is 0.04% by mass in terms of a weight ratio of the additive element components.
~ 1.0% by mass, Co 0.04% by mass to 1.0% by mass
One or more of them are added in a range not exceeding 1.0 mass% in total, and P is contained in an amount of 0.05 to 0.2 times the weight of the total amount of Fe, Ni and Co, and the balance is Tensile strength of 500 N / m due to copper and unavoidable impurities
m ² or more, the conductivity is 60% IACS or more, and the surface roughness is 2 μm or less in terms of ten-point average surface roughness (Rz),
A copper alloy foil for a laminate, which has a 180 ° peel strength of 8.0 N / cm or more when directly bonded to a polyimide film without being subjected to a roughening plating treatment. 2. The temperature at which the tensile strength when heated for 1 hour is intermediate between the tensile strength before heating and the tensile strength when softened is 300 ° C. or higher. 1. The copper alloy foil for laminated plate according to 1.