JPH04285192A - Copper foil for printed circuit and its manufacture - Google Patents

Abstract

PURPOSE:To obtain copper foil for a printed circuit having a thermal decoloration resistant film by forming an indiumzinc layer on the surface of copper foil for a printed circuit. CONSTITUTION:An In-Zn layer constituted of, by weight, 25 to 75% In and the balance Zn is formed at least on one side of copper foil for a printed by an electroplating method. Copper foil for a printed circuit free from any decoloration on the surface even if subjected to heating history of >=200 deg.C high temp. and excellent in solder expansibility, adhesion with a resist ink or the like required for copper foil for a printed circuit can be obtd. This copper foil is heated and press-fixed to a resin substrate into a copper-plated laminate for a printed circuit.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a copper foil for printed circuits and a method for producing the same, and more particularly to a copper foil for printed circuits having an excellent heat-resistant discoloration coating on the surface of the copper foil and a method for producing the same. It is.

0002

BACKGROUND OF THE INVENTION Generally, as is well known, the surface of copper is gradually oxidized in the atmosphere, and as time passes, it loses its original copper luster and turns brown. In a heated atmosphere, the oxidation is further promoted and becomes blackish brown copper oxide. Therefore, for copper products, a discolored copper surface that loses its original copper color means a significant decrease in its commercial value. In particular, the presence of a copper oxide layer on the surface of copper foil for printed circuits, which is often used as a conductor material for printed wiring boards, not only impairs the quality of the appearance, but also reduces the quality of the copper foil required for printed circuits. This is a factor that deteriorates properties such as solder spreading and adhesion with resist ink. In particular, heat discoloration resistance of the copper foil surface in a high-temperature atmosphere is considered to be one of the important characteristics required for copper foil for printed circuits.

Conventionally, various methods have been proposed as methods for imparting thermal discoloration resistance, that is, antioxidation ability, to the surface of copper foil. For example, Japanese Patent Publication No. 51-42575 proposes a method in which a copper foil is immersed in an aqueous solution containing hexavalent chromium ions, and the foil surface is subjected to cathode treatment to form a so-called chromate layer. However, when copper foil with a chromate layer is used to heat and press a resin base material to produce a copper-clad laminate, the chromate layer is destroyed by the heat and the copper foil surface is oxidized. , turns brown. Therefore, it is difficult to expect good thermal discoloration properties from the formation of a chromate layer.

[0004] Furthermore, it is generally well known that a zinc coating is formed on a copper surface using a plating solution containing zinc ions. For example, in Japanese Patent Publication No. 54-29187,
Immerse the copper in an alkaline aqueous solution containing zinc ions, or
Alternatively, a method has been proposed in which a dense oxide layer containing Zn and Cu is formed on the copper surface by energizing copper as an anode in this alkaline aqueous solution. The zinc-coated copper foil obtained in this way can maintain heat discoloration resistance much better than copper foil coated with a chromate layer. However, even with this copper foil having a zinc coating, if the thickness of the zinc coating is relatively thin, sufficient heat discoloration resistance cannot be obtained in an atmosphere exceeding 200°C.On the other hand, if the thickness of the zinc coating is increased, Due to mutual thermal diffusion between zinc and copper, a brass layer is formed which is an alloy of the two, and a strong yellow hue appears on the copper foil surface, resulting in an undesirable appearance.

[0005] JP-A-52-735 discloses that zinc is electroplated on the smooth shiny surface of copper foil, and then heat treated under conditions that form a brass layer by mutual diffusion of zinc and copper. It has been proposed to form a brass layer on. In this method as well, as described above, the brass layer develops a strong yellowish tinge on the copper foil surface, causing problems in terms of appearance.

[0006] Furthermore, Japanese Patent Publication No. 33906/1983 describes a method in which a zinc coating is formed on both sides of a copper foil, and then a chromium oxide coating is formed on each zinc coating. However, the copper foil obtained by this method also
When exposed to a high-temperature atmosphere that exceeds 100%, the heat discoloration resistance significantly decreases and the color changes, which is a practical problem.

Japanese Patent Publication No. 58-7077 discloses a method of forming a layer of a mixture of zinc or zinc oxide and chromium oxide on at least one surface of a copper foil. When exposed to a high temperature atmosphere exceeding .degree. C., the degree of discoloration increases significantly, which is a practical problem.

Japanese Patent Publication No. 51-35711 proposes a method of forming an electrodeposited metal layer of a metal selected from the group consisting of zinc, indium and brass on one side of a copper foil layer. However, copper foil coated with an electrodeposited indium layer has a low resistance to heat discoloration, and also has the disadvantage that when the amount of indium deposited is increased, the indium layer itself takes on a grayish-white color. Copper foil coated with an electrodeposited zinc layer or an electrodeposited brass layer has the same problem of low heat discoloration resistance.

[0009]

[Problems to be Solved by the Invention] The objects of the present invention are 20
The copper foil surface remains undiscolored even after being subjected to heat history at temperatures exceeding 0°C, and has excellent thermal discoloration resistance, and also has excellent solder spreadability and adhesion with resist ink, which are required for copper foil for printed circuits. An object of the present invention is to provide a copper foil for printed circuits that can maintain good characteristics and a manufacturing method that can continuously mass-produce the same.

0010

[Means for Solving the Problem] As a result of intensive research to solve the above problems, the present inventors have found that in a film containing both indium and zinc, the anti-oxidation ability of the copper foil surface is synergistic. The present inventors have discovered that the present invention can be improved in terms of performance, and have completed the present invention. That is, the present invention provides a copper foil for printed circuits characterized by having an indium-zinc layer on at least one side of the copper foil. The copper foil for printed circuits of the present invention can be easily manufactured by the manufacturing method of the present invention described below.

The indium-zinc layer in the copper foil for printed circuits of the present invention is a thin alloy film mainly composed of indium and zinc metals, and is tightly adhered to the base copper foil surface. A small amount of indium and zinc oxides and hydroxides may be mixed in the vicinity of the surface layer of this indium-zinc layer. This indium-zinc layer itself is a colorless and transparent dense film, and does not impair the copper color of the base material. Moreover, even in a high-temperature heating atmosphere, the copper foil does not change color and exhibits an extremely excellent anti-oxidation function while maintaining the copper color of the copper foil surface.

[0012] To explain the amounts of indium and zinc that compose this indium-zinc layer converted into metal amounts and their ratio, the amounts of each of indium and zinc are both in the range of 20 to 150 μg/dm2. is preferred. If each is less than 20 μg/dm2, the film thickness may be thin and the heat discoloration resistance may decrease;
If it exceeds 150 μg/dm2, the indium-zinc layer may take on a dull grayish-white color, although it depends on the ratio of both. Particularly preferably, the amount of each coating is 40 to 130 μg/dm 2 .

[0013] Furthermore, the ratio of the metal amounts of indium and zinc in the indium-zinc layer is preferably such that the indium content is 25 to 75% by weight with respect to the total metal amount of indium and zinc. Outside this range, the synergistic effect of heat discoloration resistance at high temperatures provided by both may be attenuated. Particularly preferred is a range of 35 to 70% by weight. In addition, the thickness of this indium-zinc layer is usually about 0.000 when converted using the specific gravity of zinc of 7.12.
It is 5 to 0.004 μm.

Means for producing the copper foil for printed circuits of the present invention by forming an indium-zinc layer on the copper foil surface is as follows:
Known electroplating methods, chemical plating methods, vacuum evaporation methods, sputtering methods, metallicon methods, etc. can be used. Among these, it is practically preferable to carry out cathodic electrolytic treatment using electroplating method from the viewpoint of mass production and economy. The manufacturing method of the present invention uses this electroplating method, in which a plating bath containing indium ions and zinc ions is used, a copper foil is cathodically treated in the plating bath, and at least one side of the copper foil is coated with indium- It is characterized by forming a zinc layer.

[0015] The copper foil used in the method of the present invention is
Representative examples include electrolytic copper foil and rolled copper foil, but they are not particularly limited. The thickness of the copper foil is also not particularly limited as long as it has a thickness that can be used as a copper foil for printed circuits. In the present invention, in order to increase the peel strength after lamination of the surface to be adhered to the resin base material, it is preferable to use a copper foil whose at least one side has been roughened.

Next, regarding the plating bath used in the method of the present invention, the metal ions contained in the plating bath are indium ions and zinc ions. Examples of indium ion sources include In2(SO4)3,
InCl3, In(SO3NH2)3, In(BF4)
3 or their hydrates are suitable. ZnSO4, ZnCl2, Zn(CH
3COO)2 or hydrates thereof are preferred. In addition, a small amount of other metal ions may be included within a range that does not interfere with achieving the object of the present invention.

A plating bath is prepared by dissolving at least one source of indium ions and at least one source of zinc ions in water. When setting the content of both metal ions in the plating bath, it is determined by taking into consideration the amount of plating metal deposited, current density, current application time, etc., but usually from a range of 0.1 to 50 g/l for each. You can choose. Preferably, each amount is 0.5 to 10 g/l. For example, the indium ion source is In2(SO
4) Using ZnSO4.7H as the zinc ion source using 3.
When 2O is used, it is particularly preferable to use it in a range of 0.1 to 10 g/l.

Although the pH of the plating bath can be adjusted over a wide range from acidic to alkaline, it is usually preferable to use it as acidic. When making it alkaline, add a complexing agent such as sulfamic acid,
It is desirable to prevent precipitation of metal ions. Furthermore, salts such as sodium sulfate and ammonium chloride may be added to the plating bath for the purpose of imparting conductivity. The liquid temperature of the plating bath may be normally room temperature, or may be heated to, for example, about 80°C.

By immersing the copper foil in this plating bath and applying electricity using the copper foil as a cathode, an indium-zinc layer is formed on the surface of the copper foil. Although the current density and the current application time cannot be specified in general because they are related to other conditions such as the amount of metal ions, the amount of plating metal deposited and their ratio, the current density is usually 0.1 to 10 A/dm2, preferably 0.2~2
A/dm2, current application time 1 to 60 seconds, preferably 1 to 30
It is desirable to select an appropriate value from the range of seconds.

[0020] Copper foil, which has been roughened on at least one side if necessary, is subjected to a water washing process, and then placed facing each other on one or both sides of the copper foil in a plating bath containing indium ions and zinc ions prepared as described above. An insoluble anode is provided, and one side, preferably the shiny side, or both sides of the copper foil is subjected to cathode treatment under the above electrolytic conditions to form an indium-zinc layer, thereby producing the copper foil for printed circuits of the present invention.

[0021] In carrying out the manufacturing method of the present invention, for example, a copper foil wound into a coil having a predetermined thickness and width is placed in a degreasing tank, a pickling tank,
Running at a constant speed in a copper foil processing equipment consisting of a washing tank, a copper plating tank for surface roughening treatment, a washing tank, followed by a plating tank for forming an indium-zinc layer, a washing tank, a drying device, etc. It is preferable to manufacture the film by continuously winding it up.

The copper foil for printed circuits of the present invention thus obtained is made into a printed circuit copper-clad laminate by heat-pressing it to a resin substrate made of phenol resin, epoxy resin, polyimide resin, etc., and then subjected to predetermined processing operations. After that, it is used as a printed circuit board.

[0023]

EXAMPLES The present invention will be explained in detail below based on Examples, but the present invention is not limited thereto. Example 1 In2(SO4)3 0.5g/l and ZnSO4.
Dissolve 2.0 g/l of 7H2O in water and adjust the pH to 3.0.
A plating bath was prepared at a liquid temperature of 30°C. Using this plating bath, an electrolytic copper foil (thickness: 35 μm), one side of which had been roughened in advance, was immersed, and the shiny side of the copper foil was immersed at a current density of 0.
A cathode treatment was performed at 5 A/dm2 for 2 seconds to form an indium-zinc layer. Immediately after the cathode treatment, the copper foil was taken out of the plating solution, washed with water, and then dried in a dryer maintained at a temperature of 100°C. The color tone of the copper foil surface on which the indium-zinc layer was formed was the same copper color as before the electrolytic treatment. Further, when the amount of plating metal deposited on this indium-zinc layer was analyzed using an IPC analyzer, the amount of indium metal was 75 μg/dm 2 and the amount of zinc metal was 55 μg/dm 2 .

Next, in order to conduct the following characteristic test, the obtained indium-zinc layered copper foil was laminated on an FR-4 grade epoxy resin-impregnated glass cloth base material with its rough surface in contact with the base material surface. Heat and pressure treated under conditions of temperature 168℃, pressure 80kg/cm2, time 60 minutes, length 250mm, width 250m
A required amount of copper-clad laminates having a thickness of 1.6 mm and a thickness of 1.6 mm were produced to be used as test pieces. The results of the following characteristic tests are summarized in Tables 1 and 2.
It was shown to.

(1) Heat discoloration resistance Degree of discoloration on the copper foil surface of the test piece immediately after lamination and 180°C
1 hour, 200℃ 1 hour, 250℃ 1 hour, 300℃ 1 hour
Visually observe the degree of discoloration of the copper foil surface when heat treated in a constant temperature bath maintained at 0 minute conditions, ○...no discoloration, △
Evaluation was made as: slight discoloration, x: marked discoloration. (2) Solder spreadability test 60Sn (as specified in JIS Z 3282)
Using solder with symbol H60B), JIS Z 319
The solder spreading rate was measured for each test piece after lamination in accordance with the spreading test method specified in 7.4-11. Spreading rate (%) = {(D-H)/D} x 100 (H; Height of spread solder (mm) D; Diameter when the solder used in the test is regarded as a sphere (mm)
), and the value calculated from D=1.24V1/3, where V=solder mass/specific gravity) The spreading rate obtained by the above formula is ○...spreading rate 90-95% △...spreading Rate: 85-89% x... Spread rate: 84% or less. (3) Resist ink adhesion test After cleaning the test piece with trichlene, apply UV ink (UR-450B, manufactured by Tamura Seisakusho) on the indium-zinc layer.
A circuit-shaped UV ink film was formed by screen printing (screen used: made of nylon, mesh 200-300 mesh), and this UV ink film was coated with a UV device (model HMW-713, manufactured by Oak Seisakusho). After being irradiated and cured, it was immersed in a 10% HCl aqueous solution at a temperature of 50°C for 5 minutes, washed with water and air-dried, and the hardness of the cured coating on the test piece was determined by JI.
It was measured in accordance with the pencil method specified in SC 3002. ○...Pencil hardness 2H or more △...Pencil hardness F~H ×...Pencil hardness B or less

Examples 2 to 6 The same operations as in Example 1 were carried out except that the same copper foil as used in Example 1 was used, and the plating bath with the composition concentration shown in Table 1 and the electrolytic conditions were used. A copper foil with a zinc layer formed thereon was manufactured. As in Example 1, these copper foils were analyzed for the amount of plating metal deposited and various characteristic tests were carried out, and the results are collectively shown in Tables 1 and 2.

Comparative Examples 1 to 5 The same operations as in Example 1 were carried out except that the same copper foil as used in Example 1 was used and the plating bath with the composition concentration shown in Table 1 and the electrolytic conditions were used to form an indium layer. Copper foil with zinc layer formed (Comparative Examples 1 and 2), Copper foil with zinc layer formed (Comparative Examples 3 and 4)
And a copper foil with a zinc/chromium layer formed thereon (Comparative Example 5) was manufactured. As in Example 1, these copper foils were analyzed for the amount of plating metal deposited and various characteristic tests were carried out, and the results are collectively shown in Tables 1 and 2.

Examples 1 to 6 are copper foils on which the indium-zinc layer of the present invention is formed, and by keeping the amounts of indium and zinc plating within a suitable range, the color tone of the copper foil surface after cathodic treatment is improved. It exhibits the same copper color as before treatment, and also exhibits excellent heat resistance to discoloration under various temperature conditions without discoloration as indicated. In particular, 300
It has been found that it does not discolor even under high temperature heat history, and exhibits excellent heat discoloration resistance even in an extremely high temperature atmosphere. It also shows good results in terms of solder spreadability and resist ink adhesion. On the other hand, Comparative Example 1
and Comparative Example 2 is a copper foil with an indium layer formed,
No effect on heat discoloration resistance was obtained. Comparative Example 2 is an example in which an indium layer with a larger amount of indium deposited than Comparative Example 1 was formed, but the copper foil surface after plating had a grayish white color.
When heated, it turned black. Comparative Example 3 and Comparative Example 4 are copper foils with a zinc layer formed thereon. In Comparative Example 3, the heat discoloration resistance began to decrease at around 200° C., and the color changed to brownish brown. Moreover, Comparative Example 4 is a case in which a zinc layer with a larger amount of zinc coating than Comparative Example 3 is formed, and when heated, it takes on a brass color, and in both cases practical problems cannot be avoided. Comparative Example 5 is a copper foil with a chromium-zinc layer formed, but 2
The degree of discoloration tended to increase from around 00°C.

Therefore, the above-mentioned indium-
The copper foil with a zinc layer was found to be superior in the results of each property test. This indicates that due to the synergistic effect of both indium and zinc, properties that are completely different from those obtained when a layer of indium alone or a layer of zinc alone is formed are developed, and this is particularly beneficial in heat discoloration resistance. Conceivable. A chromate layer (Cr
When formed by dipping treatment or electrolytic treatment at an amount of 5 to 80 μg/dm2), the effect of suppressing the occurrence of rust and discoloration after humidification (40° C., 90% for 3 days) can be obtained.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

Effects of the Invention As is clear from the above description, the copper foil for printed circuits of the present invention maintains an extremely beautiful appearance, and has heat resistance and discoloration without any discoloration even when exposed to high temperature atmosphere. Furthermore, it has good bonding properties with solder and adhesion with resist ink, which are essential for copper foil for printed circuits. Furthermore, since the method of the present invention does not use harmful hexavalent chromium compounds during the manufacturing process, there is no risk of contaminating the working environment. In addition, there are no problems in terms of manufacturing control, and its industrial value is extremely large.

Claims (2)

[Claims] [Claim 1] At least one side of the copper foil is indium-
Copper foil for printed circuits with a zinc layer. 2. Manufacturing a copper foil for printed circuits, using a plating bath containing indium ions and zinc ions, cathodizing the copper foil in the plating bath to form an indium-zinc layer on at least one side of the copper foil. Method.