Background Art Generally, a printed circuit board, which is an electronic component for use in fine control circuits of electrical devices or electronic communication equipment, is fabricated by wiring a circuit network through a copper foil on any one surface or both surfaces of a dielectric substrate, such as a synthetic resin, disposing IC or electronic parts on the substrate, and then electrically connecting them, followed by coating by use of a dielectric material.

Further, a multi-layered printed circuit board

results from laminating a copper foil on the dielectric substrate under conditions of high temperatures and high pressure, screen-printing a circuit pattern and etching it by use of a commercial copper etching solution to form a circuit network, and then mounting a semiconductor device, etc. , thereon.

As such, the copper foil for use in the printed circuit board has a maximized surface area by forming a rough surface layer composed of a copper electrodeposit in the form of a plurality of projections thereon. Thereby, adhesive strength between the copper foil and the dielectric substrate can be sufficiently maintained even during high temperature heating, wet treatment, welding, chemical treatment or the like.

Referring to FIGS. 1 and 2, there are shown copper electrodeposits 12 formed on the protrusions 11 formed on a copper foil as a means for increasing adhesive strength of the copper foil, according to conventional technique. On the other hand, if there are no cone-shaped protrusions 11 on the copper foil, the roughening-treated surface layer composed of the copper electrodeposit 12 may be formed on a smooth surface of the copper foil.

However, when the roughening-treated surface layer composed of the copper electrodeposit 12 on the protrusions 11 of the copper foil is formed by use of an electrolytic copper bath, the copper electrodeposit 12 is formed over

large ranges along peak and valley parts of the protrusion 11, as seen in FIG. 2. Therefore, an adhering surface between the copper foil and the resin substrate becomes small, and thus, the copper foil may be detached from the resin substrate, by reason of low adhesive strength with the dielectric substrate.

To form the copper electrodeposit 12 on the protrusion 11 of the copper foil, there are proposed Japanese Patent Application Examined Publication Nos. Sho.

54-38053 and 53-39327 disclosing electrolysis technique at an approximate limiting current density by use of an electrolytic bath containing the Group 6B elements on the Periodic Table, such as arsenic, antimony, bismuth, selenium or the like.

However, when arsenic is contained in the electrolytic bath, the resultant copper electrodeposit includes a predetermined amount of arsenic. Thus, upon reuse and other treatments of the copper foil or disposal of an arsenic-containing etching solution, arsenic can negatively affect environments and humans.

In addition, with the aim of formation of the copper electrodeposit 12 on the protrusion 11 of the copper foil, Japanese Patent Application Examined Publication No. Sho.

56-411196 discloses a using method of a bath containing a very small amount of benzoquinoline, and Japanese Patent Application Examined Publication No. Sho. 62-56677

discloses a using method of a bath containing any one selected from among molybdenum, vanadium and mixtures thereof. Also, in Japanese Patent Laid-open Publication Nos. Hei. 6-169169 and 8-236930, there is disclosed the use of a bath containing any one selected from among chromium, tungsten and mixtures thereof. As well, Japanese Patent Laid-open Publication Nos. Sho. 63-017597 and 58-164797 disclose a pulse plating method or the use of vanadium, zinc, iron, nickel, cobalt, chromium, etc.

These methods are advantageous in that the used bath does not contain a toxic element, such as arsenic, it does not have a negative affect on environments and humans.

However, the methods suffer from low adhesive strength of the copper foil with the dielectric substrate, due to the copper electrodeposit 12 formed widely on not only the peak part but also the valley part of the protrusion 11 of the copper foil. Consequently, the copper electrodeposit 12 may be easily detached from the substrate.

Disclosure of the Invention Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an object of the present invention is to provide a method for manufacturing a copper foil for printed circuit board, which is advantageous in that a surface area of the

copper foil increases, thereby increasing adhesive strength of the copper foil with a dielectric substrate as well as electrical properties of the printed circuit board.

To accomplish the above object, the present invention provides a method for manufacturing a copper foil for printed circuit board, including electrolyzing a copper foil set to a cathode in an acid electrolytic bath at an limitig current density to form a rough surface layer composed of a copper electrodeposit on a protrusion or a smooth surface of the copper foil, wherein an inorganic polyanion containing tungsten with a molecular weight of 2000 or more is further added to a plating solution of the electrolytic bath, or an inorganic polyanion containing tungsten and phosphorous with a molecular weight of 2000 or more is further added to a plating solution of the electrolytic bath, or an inorganic polyanion containing tungsten and silicon with a molecular weight of 2000 or more is further added to a plating solution of the electrolytic bath.

Brief Description of the Drawings The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is an electron micrograph showing protrusions of a copper foil, according to conventional techniques; FIG. 2 is an electron micrograph showing copper electrodeposited onto the protrusions of the copper foil of FIG. 1 ; and FIG. 3 is an electron micrograph showing copper electrodeposited onto protrusions of a copper foil, according to the present invention.

Best Mode for Carrying Out the Invention Reference should now be made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components.

FIG. 3 is an electron micrograph showing copper electrodeposits formed on protrusions of a copper foil, according to the present invention. As for a manufacturing method of a copper foil for printed circuit board of the present invention, a copper foil set to a cathode in an acid electrolytic bath is electrolyzed at a critical current density, thereby forming a rough surface layer composed of a copper electrodeposit 12 on protrusions 11 or a smooth surface of the copper foil. At this time, an inorganic polyanion containing tungsten with a molecular weight of 2000 or more is further added to a plating

solution of the electrolytic bath, or an inorganic polyanion containing tungsten and phosphorous with a molecular weight of 2000 or more is further added to the plating solution of the electrolytic bath. Otherwise, an inorganic polyanion containing tungsten and silicon with a molecular weight of 2000 or more is additionally added to the plating solution of the electrolytic bath.

Compositions of the plating solution of the acid electrolytic bath are given along with plating conditions in Table 1, below, in which an environmentally friendly inorganic polyanion having a molecular weight of 2000 or more is used, instead of arsenic added conventionally to the plating solution.

TABLE 1 Plating Solution Compositions and Plating Conditions Copper Sulfuric Inorganic Plating Current Plating Ion Acid Polyanion Temp. Density Time 5-150 g/1 10-200 g/1 0. 001-5 g/l 20-50°C 5-100 AI (le 1-30 sec The rough surface layer is formed by use of the acid electrolytic bath further containing the inorganic polyanion, whereby generation of nucleus as well as growth of dendrite structures are prevented upon the formation of the copper electrodeposit 12 on the protrusion 11 of the copper foil. Hence, the copper electrodeposit 12 is formed to be round, as shown in FIG. 3.

In such cases, a supply source of the inorganic

polyanion is exemplified by para-tungstic acid, meta- tungstic acid, 12-phosphotungstic acid, 12-molybdotungstic acid, or sodium salts or ammonium salts thereof. The inorganic polyanion is added in a concentration of 0.001-5 g/1, and preferably, 0.01-2 g/1, to the plating solution of the copper electrolytic bath.

In addition, the method of the present invention can be applied to not only the copper foil having the protrusions 11 thereon, but also a copper foil having no protrusion 11 thereon, such as an electrolyzed copper foil or rolled copper foil.

A better understanding of the present invention may be obtained through the following examples and comparative examples which are set forth to illustrate, but are not to be construed as the limit of the present invention.

EXAMPLE 1 In an acid plating bath of a 30°C aqueous solution containing 100 g/1 of copper sulfate pentahydrate, 200 g/l of sulfuric acid, and 0.001-5 g/1 of sodium meta-tungstate, a surface of a copper foil to be stuck having a thickness of 35 pm was plated at a current density of 20 A/dm2 for 6 sec. Thereafter, a plating process was further performed at a current density of 20 A/dm2 for 10 sec by use of a 45°C electrolyte containing 50 g/1 of a copper ion and 100 g/l of sulfuric acid.

The thus obtained copper foil was laminated on an epoxy resin (not shown), to fabricate a copper-clad laminate, which was then measured for adhesive strength between the copper foil and the resin by use of UTM. In addition, the resin surface after etching was observed by means of an optical microscope to confirm generation of copper debris. The results are given in Table 2, later.

The adhesive strength between the copper foil and the resin after ten measurements had an average value of about 2.25 kgf/cm, which was regarded to be very high. Also, there was no copper debris. From this, the resultant copper electrodeposits were found to have very high electrodeposition efficiencies.

That is, as apparent from FIG. 3, it can be found that adhesive strength of the copper foil laminated on the resin substrate can be increased, resulting from a largely increased adhering area with the epoxy resin, compared to FIG. 2, due to copper electrodeposits 12 having uniform sizes mainly formed to peak parts of protrusions 11 of the copper foil.

Further, the addition of sodium meta-tungstate less than 0.001 g/l to the acid electrolytic copper bath resulted in no increase in adhesive strength, and generation of copper debris after etching. Whereas, if sodium meta-tungstate was used in the concentration exceeding 5.0 g/1, economical burdens became high.

EXAMPLE 2 In an acid plating bath of a 30°C aqueous solution containing 100 g/l of copper sulfate pentahydrate, 200 g/l of sulfuric acid, and 0.001-5 g/1 of 12-silicotungstic acid, a surface of a copper foil to be stuck having a thickness of 35 pm was plated at a current density of 20 A/dm2 for 6 sec. Thereafter, a plating process was additionally performed at a current density of 20 A/dm2 for 10 sec by use of a 45°C electrolyte containing 50 g/1 of a copper ion and 100 g/l of sulfuric acid.

The thus obtained copper foil was laminated on an epoxy resin, to fabricate a copper-clad laminate, which was then measured for adhesive strength between the copper foil and the resin by use of UTM. In addition, the resin surface after etching of the copper foil was observed by means of an optical microscope to confirm generation of copper debris. The results are shown in Table 2, later.

The adhesive strength between the copper foil and the resin after ten measurements had an average value of about 2.20 kgf/cm, which was regarded to be very high. Further, copper debris was not observed, from which the electrodeposition efficiencies of the copper electrodeposits were found to be high.

That is, it can be found that adhesive strength of the copper foil laminated on the resin substrate can be

increased, resulting from a largely increased adhering area with the epoxy resin, compared to FIG. 2, by uniformly forming the copper electrodeposits 12 having sizes smaller slightly than those of Example 1 to the peak parts of the protrusions 11 of the copper foil.

Moreover, when 12-silicotungstic acid was added in the concentration less than 0.001 g/1 to the acid electrolytic copper bath, there was no increase in adhesive strength, and copper debris after etching occurred. On the other hand, when 12-silicotungstic acid was used in the concentration exceeding 5.0 g/1, economical burdens became high.

COMPARATIVE EXAMPLE 1 A surface of a copper foil to be stuck having a thickness of 35 Fm was plated at a current density of 20 A/dm2 for 6 sec by using an electrolytic bath of a 30°C aqueous solution containing 100 g/1 of copper sulfate pentahydrate and 200 g/l of sulfuric acid without additive. Subsequently, a plating process was additionally performed at a current density of 20 A/dm for 10 sec by use of a 45°C electrolyte containing 50 g/1 of a copper ion and 100 g/l of sulfuric acid.

The thus obtained copper foil was laminated on an epoxy resin, to obtain a copper-clad laminate, which was then measured for adhesive strength between the copper foil

and the resin by use of UTM. Also, the resin surface after etching was observed by means of an optical microscope to confirm generation of copper debris. The results are given in Table 2, later.

The adhesive strength between the copper foil and the resin after ten measurements had an average value of about 1.93 kgf/cm, which was drastically decreased compared to Examples 1 and 2. Further, the copper electrodeposits on the protrusions of the copper foil were formed to be not round shaped, but rather needle shaped. Thereby, it appeared that the generation of the copper debris resulted in lowered electrodeposition efficiencies.

COMPARATIVE EXAMPLE 2 A surface of a copper foil to be stuck having a thickness of 35 Hm was plated at a current density of 20 A/dm2 for 6 sec by using an electrolytic bath of a 30°C aqueous solution containing 100 g/1 of copper sulfate pentahydrate, 200 g/1 of sulfuric acid and 3 g/1 of arsenic acid. Then, a plating process was additionally performed at a current density of 20 A/dm2 for 10 sec by use of a 45°C electrolyte containing 50 g/l of a copper ion and 100 g/l of sulfuric acid.

The thus obtained copper foil was laminated on an epoxy resin, to obtain a copper-clad laminate. Subsequently, adhesive strength between the copper foil and

the resin of the copper foil-layered substrate was measured by use of UTM. Also, the resin surface after etching was observed by means of an optical microscope to confirm generation of copper debris. The results are given in Table 2, below.

The adhesive strength between the copper foil and the resin after ten measurements had an average value of about 2.21 kgf/cm, which was similar as Examples 1 and 2.

Although the copper electrodeposits had better electrodeposition efficiencies because of no copper debris, about 100 ppm of arsenic contained therein negatively affected environments and humans.

Consequently, an inorganic polyanion with a molecular weight of 2000 or more was further added to the acid electrolytic bath, whereby a rough surface layer composed of the copper electrodeposit was formed. At this time, since the copper electrodeposit 12 formed on the copper foil was roundly shaped as shown in FIG. 3, a surface area of the copper foil was relatively increased.

TABLE 2 Properties Of Copper Foil Additive In Adhesive Strength No. Copper Debris Electrolyte (kgf/cm) Ex. 1 Sodium Meta-tungstate 2. 25 No Ex. 2 12-silicotungstic acid 2. 20 No C. Ex. 1 No 1. 93 Yes C. Ex. 2 Arsenic Acid 2. 21 No

Industrial Applicability As described above, the present invention provides a manufacturing method of a copper foil for printed circuit board, characterized in that a rough surface layer composed of a copper electrodeposit having a round shape is formed on the copper foil, whereby a contact area of the copper foil becomes relatively larger. Thus, the copper foil can be increased in adhesive strength with a dielectric substrate and heat resistance. As well, the adhesive strength between the copper foil and the resin substrate is constantly maintained, and hence, electrical properties and acid resistance are increased while minimizing copper debris.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.