GB1558919A - Electrolytic surface treating process for copper foil for use in printed circuit - Google Patents

Description

(54) ELECTROLYTIC SURFACE TREATING PROCESS FOR COPPER FOIL FOR USE IN PRINTED CIRCUIT (71) We, NIPPON MINING CO. LTD., a Japanese Company, of 2-10-1, Toranomon, Minato-Ku, Tokyo, Japan and formerly of 3-Akasaka Aoi-cho, Minato-Ku, Tokyo, Japan, @@ @@@@@@@ @@@ @@ @@@ted to us and ERRATA SPECIFICATION NO 1558919 Page I, heading (21) Application No. delete 19308/77 insert 22926/77 Page 1, heading (22) Filed delete 9 May 1977 insert 31 May 1977 Page 1, heading (31) Convention Application No. delete 7615166 insert 51/062384 Page I, heading (32) Filed delete 14 May 1976 in insert 31 May 1976 in Page 1, heading (33) delete France (FR) insert JAPAN (JP) Page I, heading (44) Complete Specification Published delete 9 Jan. 1980 insert 9 Jan. 1980 Page 1, heading (51) INT. CL. 3 delete B24B 19/00 insert C25D 3/38 Page l, heading (52) Index at Acceptance delete B3D 1 D3D 1 H12 2A I 5 2A 1 2A20 2A21 insert C7B 125 148 305 306 325 431 475 701 721 727 AK DE THE PATENT OFFICE 26 February 1980 Bas 74096/10 < snotClear,nuwevet,mm,uumj'mt < -'-nv-'-"j........-.--.. presence of nickel ions and copper ions. The color of a deposited layer is dark brown, and the deposited layer affords a metallic gloss. The deposited layer is not attended with powdering. In cases where the copper concentration is too high, then the deposited surface exhibits an oxidized copper color, and in cases where the copper concentration is too low, then a metallic nickel color is obtained. Meanwhile, when the thickness of an electro-deposited layer is increased by extending the duration of a cathodic treatment, then a ratio of copper to nickel contained in a deposited layer which has been washed off the copper foil in a pressurised water stream is found to be about 0. 5 to 1. As a result, the deposited layer is considered to consist of an alloy and/or an oxide which essentially comprises nickel and copper. The electro-deposited layer thus obtained according to the present invention is entirely different in its nature from an electro-deposited layer obtained (54) ELECTROLYTIC SURFACE TREATING PROCESS FOR COPPER FOIL FOR USE IN PRINTED CIRCUIT (71) We, NIPPON MINING CO. LTD., a Japanese Company, of 2-10-1, Toranomon, Minato-Ku, Tokyo, Japan and formerly of 3-Akasaka Aoi-cho, Minato-Ku, Tokyo, Japan, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a surface treating process for a copper foil for use in a printed circuit, and more particularly to a cathodic treatment using a copper foil as a cathode.

Hitherto, the surface treatment of a copper foil for use in a printed circuit suffers from the following shortcoming: poor bonding strength, insufficient chemical resistance and poor adaptability to electro-plating, More particularly the poor chemical resistance results in a side etching phenomenon during an etching process, after printing a circuit. In addition, poor adaptability to the electro-plating results in undesirable appearance of a printed circuit.

It is accordingly a principal object of the present invention to provide a surface treating process for a copper foil for use in a printed circuit, which provides desired bonding strength, high chemical resistance, and good adaptability to electro-plating.

According to the present invention, there is provided a surface treating process for a copper foil for use in a printed circuit, in which the surface of a copper foil is subjected to a cathodic treatment in an electrolytic bath of a sulfuric acid aqueous solution containing nickel and copper, with the copper foil being used as a cathode.

According to a preferred aspect of the present invention, the copper foil thus cathode treated is brought into contact with an aqueous solution containing one of sodium hexametaphosphate, a-nitroso R salt, 2-mercaptobenzothiazole rubeanic acid. anthranilic acid, benzensulfonamide, phthalic acid, and potassium dichromate.

By way of example, the process according to the present invention will now be described in more detail, hereunder. A copper foil derived according to rolling or electrolysis is subjected to a cathodic treatment in a sulfuric acid bath containing polyacrylamide (PAA), nickel ions, and copper ions, with the copper foil being used as a cathode and a copper plate as an anode. It does not have effect on the gist of the present invention to delete the polyacrylamide (PAA) from the sulfuric acid bath. However, in case of adding the polyacrylamide (PAA) thereto, the range of the permissible sulfuric acidity of the bath is relatively wide. In the process according to the invention, there may be derived an electro-deposited surface. The mechanism of the production of an electro-deposited surface is not clear. However, thin, uniform electro-deposited layer may be obtained due to the presence of nickel ions and copper ions. The color of a deposited layer is dark brown, and the deposited layer affords a metallic gloss. The deposited layer is not attended with powdering. In cases where the copper concentration is too high, then the deposited surface exhibits an oxidized copper color, and in cases where the copper concentration is too low, then a metallic nickel color is obtained. Mleanwhile, when the thickness of an electro-deposited layer is increased by extending the duration of a cathodic treatment, then a ratio of copper to nickel contained in a deposited layer which has been washed off the copper foil in a pressurised water stream is found to be about 0. 5 to 1. As a result, the deposited layer is considered to consist of an alloy andlor an oxide which essentially comprises nickel and copper. The electro-deposited layer thus obtained according to the present invention is entirely different in its nature from an electro-deposited layer obtained according to a cathodic treatment in a copper sulfate-sulfuric acid system bath which has been used hitherto.

Any soluble inorganic copper compounds may be used as a copper ion source. However, copper, sulfate is most recommendable. Preferable copper concentration depends on a' nickel concentration and a current density. A range from 3 g/liter to 15 g/liter is preferable.

A range from 3 to 6 g/liter is preferable in case a nickel concentration ranges from 20 g/liter io 70 g/liter.

The preferable molecular weight and concentration of polyacrylamide ranges from 100, 00 to 1000,000, and 0.5 liter to 15 g/liter, respectively.

Any soluble inorganic nickel compounds may be used as a nickel source. However, nickel sulfate is most recommendable. The concentration of nickel has no limitation. However, if the concentration of nickel is lower than 10 liter under a certain condition, uniform electro-deposited layer cannot be obtained. A preferable range of concentration of nickel is between 20 and 70 g/liter.

In cases where the acidity of a bath is below pH 3, then a deposited layer with the same characteristics as those stated in the above paragraph may be obtained, while a range of 5 to 200 liter of sulfuric acid is preferable. In case the polyacrylamide (PAA) is not used, the same characteristics may be obtained if the acidity of the bath is between pH 1.5 and 3.5.

Particularly the range from pH 2.2 to pH 3.0 is preferable. Adding Glauber's salt thereto is effective for increasing ionization degree of a bath.

The preferable electrolytic conditions in the aforesaid bath composition are a current density of 200 to 500 A/m and the electrolysis time of 20 to 60 seconds. The temperature of a bath is preferably a room temperature, although no limitation is imposed thereon. Also, no limitation is imposed on a cyclic flow rate of a bath, and hence a cyclic flow rate may be zero. It is preferable that an electrolytic bath according to the present invention be used after an electrolysis pretreatment using a copper plate as an anode, at a current density of 100 to 300 A/m, current concentration of 4 to 8 A/liter (electrolyte), and an amount of current of 5 to 10 A hr.

The copper foil subjected to a cathodic treatment may be used as a product, as it is. It was found that a copper foil makes a time-dependent-change in its peeling strength, surface grain and color tone, during storage, as shown in Table 1.

Table 1 Immediately after cathodic treatment After 30 days Peeling strength 1.50-1.70 1.00-1.30 (kg/cm) Surface grain Grains of less than No grain of less diameter'/u'o u are present than l/loo, u Color tone Dark brown having Reddish brown purple color * It appears that smaller grains join larger grains, presenting a smooth surface. (30,000 to 60,000 X) For the purpose of suppressing the aforesaid time-depcndent-change, a close study was given to a copper ion detecting reagent and a crystalline-growth-preventive agent. The following was found to be satisfactory for this purpose: sodium ; nitroso-R salt ; 2-mercaptobenzothiazole ; rubeanic acid; anthranilic acid; benzensulfona mide; phthalic acid; and potassium dichromate. Nitroso-R salt is the sodium salt of 1-nitroso-2-hydroxynapthalene-3, 6-disulfonic acid; it is described for example in"The Merck Index of Chemicals and Drugs", Sixth Edition, Merck & Co., Inc., Rahway, New Jersey, United States of America, 1952.

According to an embodiment of the present invention, it is preferable that a copper foil subjected to a cathodic treatment is brought into contact with an aqueous solution of one of the aforesaid reagents for 60 to 120 seconds. This treatment precludes a time-dependent change of a copper foil, when allowed to stand in a room. The table 2 summarizes the effects of suppression of a time-dependent change and the effective minimum concentration of the reagent. Meanwhile, for the treatment, a copper foil was dipped in the reagent at a room temperature for 120 seconds, followed by water rinsing.

Table 2 Effective After 30 Reagent minimum con-Peeling-Grains of Change in centration strength less than color tone reduction (%) 0. 001 u Sodium Some amount hexametaphos-1. 0 gle 2-3 present None phate nitroso-R salt 0.05 gle 2-3 Some amount-None present 2-Mercapto-3-5 Almost none None benzothiazole Rubeanic acid 0.05 gle-5-10 Almost none Somewhat reddish Anthranilic-0. 05 gle 5-10 Almost none Somewhat acid reddish Benzensulfon-0. 05 g/p 3-5 Some amount Noneamide Phthalic acid 1.0 gle 5-10 None Somewhat reddish Potassium 0.05 gle 2-3 Some amount None dichromate present In case a pretreatment for a rolled copper foil as later described is carried out, prior to the surface treatment of an ordinary rolled copper foil, than there may be achieved an activated copper foil adapted for use in a printed circuit, which affords good adhesion, excellent electrical characteristic after etching, and freedom of uneven color or powdering. In addition, the process according to the present invention provides a copper foil affording an increased bonding strength and high chemical resistance and adaptability to electro-plating.

In the case of poor chemical resistance, when etching is applied to a copper-laminated plate, after a circuit-printing process so called"side etching"troubles arise, that is, the side edge of a non-removed portion is etched. In addition, in the case of poor adaptability to electro-plating results in an unsatisfactory appearance. Thus, these factors are of supreme importance in the field of a printed circuit.

The above mentioned pretreatment will now be described. Firstly, a rolled copper foil is subjected to a cleaning process such as degreasing, and then copper ions are deposited in a known bath and operational conditions, with the aforesaid copper foil being used as a cathode, at a current density below a limit current density which is known as an upper limit of current density for metallic ions in a solution to be deposited as a metal or an alloy. In this case, any well-known electrolytic bath may be used, as far as copper ions are deposited.

For instance, there may be used an acid bath such as a copper sulfate bath or a cupric borofluoride bath, a neutral bath such as a copper pyrophosphate bath and an alkaline bath such as a copper cynanide bath, which are all well known. The electrolytic conidition may be suitable selected commensurate with a specific bath used, so as to achieve a copper deposit on the surface of a rolled copper foil. The degree of the copper deposition may be such as to be visually recognizable as a copper deposited layer on the entire surface of a copper foil.

According to the above-mentioned pretreatment, the entire surface of a rolled copper foil may be activated uniformly, so that there may be obtained a copper foil having an excellent characteristic for a printed circuit.

The rolled copper foil thus subjected to the ordinary electro-depositing treatment according to the aforesaid pretreatment is then subjected to a cathodic treatment process of the present invention, with a copper plate being used as an anode, so that an electro-deposited layer may be formed on the surface of a copper foil.

The following Examples are illustrative of the features of the process according to the present invention.

Example 1 An electrolytic treatment was applied to a rolled and electrolytic copper foil of 35 11 in thickness in a electrolytic bath containing 16 glliter of CuS04-5H20, 225 g/liter of NiS04-6H20, and pH 2.3 at a bath temperature of 30 C, a current density of 360 A/m2, and electrolysis time of 60 seconds, thereby providing an electro-deposited surface or layer. The electro-deposited surface after water rinsing and drying exhibited dark-brown, clean appearance free of powdering or uneven color.

Example 2 An electrolytic treatment was applied to a rolled and electrolytic copper foil of 35 u in thickness in an electrolytic bath containing 16 g/liter of CuSOHO, 225 g/liter of NiS04-6H20, 1 g/liter of polyacrylamide (700,000 molecular weight), 5 g/liter of H2SO4 and 50 g/liter of Na2SO4 at a bath temperature of 30 C, a current density of 250 A/m2, and electrolysis time of 60 seconds, thereby providing an electro-deposited surface or layer. The electro-deposited surface after water rinsing and drying exhibited dark-brown, clean appearance free of powdering or uneven color.

Example 3 Copper foils obtained in Examples 1 and 2 were subjected to water rinsing and drying, after which the copper foils were superposed on substrate films consisting of a polyimide (Trade Name Kapton) film coated with an epoxy adhesive, and then heated under pressure, so that a copper-bonded film for use in a printed circuit was prepared. The table 3 represents the results of peeling strength and presence of residual matter thereof after etching. In this table, the surface condition of a copper foil prior to the bonding is shown, as well.

Table 3 Rolled copper Electrolytic foil copper foil Example I Peeling strength 1.45 1.90 Residual matter None None after etching Powdering of copper None None foil surface prior to bonding Uneven color on surface None None of copper foil prior to bonding Example 2 Peeling strength 1.50 1.70 Residual matter None None after etching Powdering of copper None None foil surface prior to bonding Uneven color on surface None None copper foil prior to bonding Note: 1) The peeling test in the above table was subjected according to a process in which the copper foil was peeled along with the polyimide film surface, i. e., in the direction of 180 .

2) The powdering test was given by bonding a commercially available scotch tape (Trade mark), followed by peeling. Then. particles adhering to the tape was observe.

As is clear from the above table, the copper foil for use in a printed circuit which has been prepared according to the process of the invention is superior in adhesion to an organic adhesive and free of residual matter and hence excellent electrical characteristic,. after etching. In addition, the copper foil according to the present invention is free of uneven color and powdering, presenting good appearance.

Example 4 A rolled copper foil having a thickness of 35 u was dipped for 30 seconds in a cleaning solution obtained by diluting a scale or bright dip solution (385 volume parts of H2SO4, 165 parts of HNO3, 55 volume parts of HCt, and 440 volume parts of H20 with pure water of three times the volume of the aforesaid scale or bright dip solution. After dipping, the surface of the copper foil was subjected to electro-deposition in an electrolytic bath containing 180 g/liter of CuSO4 5H2O and 200 glliter of H2SO4, and maintained at 60 + 2 C, with the aforesaid copper foil being used as a cathode, at a current density of 500 A/m2 and a bath cyclic flow rate of 0.8 cm/second for the duration of 60 seconds. Then, the copper foil was subjected to the treatment as described with reference to Example 2. No uneven color and powdering was observed on the surface of the copper foil. As in the preceding examples, the copper foil was bonded to a polyimide film to prepare a copper bonded fill, and tested on the property of the copper-bonded laminated film. This copper-bonded film presented peeling strength as high as 1. 90 kg/cm.

Then, tests were made for the chemical resistance and adaptability to electroplating. For this purpose, the copper-bonded film was subjected to resist-etching, thereby preparing a circuit. For the test of chemical resistance, 10% solutions of HCt, H2SO4 and NaOH were used and the copper-bonded films were dipped therein for 15 minutes at a room temperature. Thereafter, the presence or absence of the side etching and an etched width due to etching were measured at the magnification of 20. Varying tests for the adaptability to plating, soldering, tin-plating, gold-plating may be used. However, the gold-plating is most severe for the test. Ordinary gold cyanide plating was applied to find a blister, change in color, and side etching.

Table 4 shows the results of these tests. For comparison purpose, a copper-bonded film for use in a printed circuit, which has been prepared according to Example 2 was tested.

Table 4 Chemical resisting') Adaptability to2 property electro-plating HCI HSO NaOH Copper foil according A A A A to Example 4 Copper foil according B A A B to Example 2 Note: 1)"A"represents freedom of side etching, and"B"represents presence of side etching.

2)"A"represents absence of blister, change in color, side etching.'B"represents presence of one of these defects.

Claims (10)

Although the present invention has been described with respect to specific details of certain embodiments thereof, it is not intended that such details be limitations upon the scope of the invention except insofar as set forth in the following claims. WHAT WE CLAIM IS:

1. A surface treating process for a copper foil for use in a printed circuit, comprising the steps of subjecting a copper foil to a cathodic treatment in an electrolytic bath containing a sulfuric-acid-aqueous solution containing nickel and copper, with said copper foil being used as a cathode.

2. A surface treating process as set forth in claim 1, wherein said aqueous solution also contains polyacrylamide.

3. A surface treating process as set forth in claim 1 or claim 2, wherein said copper foil thus subjected to said cathodic treatment is then brought into contact with an aqueous solution containing one of sodium hexametaphosphate, nitroso-R salt, 2 mercaptobenzothiazole, rubeanic acid, anthranilic acid, benzensulfonamide, phthalic acid, and potassium dichromate.

4. A surface treating process as set forth in claim 1 or claim 2, wherein said copper foil is a rolled copper foil, and said rolled copper foil is subjected to an electro-depositing pretreatment at a current density less than the limit current density, prior to said cathodic treatment.

5. A surface treating process for a copper foil for use in a printed circuit, comprising the steps of subjecting a copper foil to a cathodic treatment in an electrolytic bath containing a sulfuric-acid-aqueous solution containing nickel and copper, with said copper foil being used as a cathode, and forming an electro-deposited layer on the surface of said copper foil, the color of said layer being dark brown, and said layer affording a metallic gloss.

6. A surface treating process as set forth in claim 5, wherein said layer inclues an alloy and/or an oxide which essentially comprises nickel and copper.

7. A surface treating process for a copper foil for use in a printed circuit, said process comprising the step of subjecting a copper foil to a cathodic treatment in an electrolytic bath comprising a sulfuric-acid-aqueous solution containing from 20 to 70 gms/liter of nickel and from 3 to 6 gms/liter of copper, with said copper foil being used as a cathode, and forming an electro-deposited layer on the surface of said copper foil.

8. A surface treating process for a copper foil substantially as hereinbefore described with reference to any one of the Examples.

9. A copper foil treated by a process as defined in any one of the preceding claims.

10. A printed circuit assembly comprising a copper foil as set forth in claim 9.