1. Field of the Invention
The present invention relates to a method for manufacturing a low roughness copper foil for a printed circuit board (PCB) of a fine pattern, and more particularly to a method for manufacturing a copper foil having very low roughness and gloss surface by treating the copper foil manufactured by an electrodeposition or a mechanical rolling and an apparatus for manufacturing the copper foil.
2. Description of the Background Art
Recently, as an electronic device is manufactured relatively smaller and lighter, an integrated chip (IC) adopted to the device is designed to have its wiring width fine. To implement the desired wiring width, IC wiring requests a copper foil rendering its width to be finely formed as the scale of several tens of microns. For example, if a circuit pattern is designed with a wiring width of about 100 μm, a thickness of the copper foil should be about 15 to 35 μm. Also, if a circuit pattern is designed with a wiring width of several tens of micrometers, a thickness of the copper foil should be thinner than the thickness of 15 to 35 μm.
Generally, the copper foil for a microcircuit is manufactured by a method such as an electrodeposition, a mechanical rolling, etc.
The electrodeposition manufactures a copper using a rotating drum and an anode plate apart from the surface of the rotating drum with a predetermined distance in an electrolytic cell. When a negative current is applied to the drum and a positive current is applied to the anode plate, a copper ion is electrochemically precipitated between the drum and the anode plate during the drum is rotated, and then the copper ion is electrodeposited on a surface of the drum. The electrodeposited copper foil is led by the drum, and then is rolled up to the outside from the electrolytic cell.
Here, the electrodeposited copper foil has a shiny side contacting the surface of the drum and a matte side as the opposite side of the shiny side. The roughness of the shiny side is formed to be similar to that of the drum. The roughness of the matt side depends on the electrodeposition status of the copper foil and the thickness thereof. Here, the roughness of the matt side is larger than that of the shiny side.
Generally, a roughness of the matt side is about 2.0 to 10 μm. If the roughness of the matt side is excessively high, when a wiring pattern is formed at a PCB, copper may remain on the wiring pattern after etching. Therefore, to get rid of the remaining copper from the wiring pattern, the electrodeposited copper foil surface is further processed by mechanical or chemical polishing.
For example, the mechanical polishing method is to manufacture a planar surface of a copper foil using a buff, etc., and is used to treat a surface of a relatively thick copper foil. However, the method may not be used to treat a thin copper foil because the thin copper foil can be damaged by a mechanical stress thereof.
Meanwhile, a mechanical polishing method manufactures an electrodeposited copper foil for PCB as a matt side of the copper foil is treated such that its roughness is below 1.5 μm before nodulating treatment of the electrodeposited copper foil. But the mechanically polishing method may generate a residual stress on the copper foil and also may generate a striped polishing scar on the surface. In case of forming a circuit pattern on PCB using a relatively thick copper foil, the polishing scar does not affect largely the circuit wiring pattern. However, in case of forming a circuit pattern on PCB using a thin copper foil, the polishing scar results in a short-circuit.
The chemical polishing method is to polish a copper foil by a chemical reaction. Since the chemical polishing method does not damage the copper foil and leave a scar on the surface the copper foil, neither, the method is proper for a relatively thin copper foil. For example, the chemical polishing method is used for the electrodeposited copper foil such that its the matt side has a roughness of 1 to 2 μm, which can be formed a lead pattern of 60 to 80 μm pitch. Here, the electrodeposited copper foil has a thickness of 18 to 30 μm after the chemical polishing.
However, even though the relatively protruded portions on the matte side are polished higher rate than a portion concaved, the chemical polishing method chemically polishes the entire surface of the matte side regardless of whether it is protruded or not on the surface. For example, if the copper foil with a thickness of 18 μm or less is processed by the chemical polishing method, the thickness can be rather partially thinner. Therefore, in case of forming a wiring pattern or a lead on the PCB with the copper foil generating by the chemical polishing method, the circuits in the PCB must have serious defects such that it does not operate. Accordingly, the prior art mechanical or chemical polishing method can not be used for producing a copper foil for a fine circuit of which wiring width is several tens of micrometers or less.