[invention Title] ELECTROLESS PLATING METHOD AND PLATING FILM OBTAINED BY THE ELECTROLESS PLATING METHOD [Technical Field] The present invention relates to an electroless plating method, and more particularly, to an electroless plating method of forming an electroless plating film on a surface of an electro-polished workpiece using an electroless plating. [Background Art] Since fluorine resin has characteristics, such as a strong endurance capability against chemicals, a superior electrical properties, a high temperature stability, it is generally coated on surfaces of mechanical parts, electrical and electronic parts, and the like. To enhance the adhesivity of the fluorine resin to a workpiece, a surface of the workpiece is in advance roughened to have a high roughness and then the fluorine resin film is coated on the roughened surface of the workpiece. Also, a workpiece is treated using an inorganic or organic binder and then the fluorine resin film is relatively thickly coated to a total thickness of 100 - 200 jωm (see Japanese Patent Publication No. 2001-328121, Japanese Patent Publication No. 2000-328256, Japanese Patent Publication No. Pyeong 4-365875, Japanese Patent Publication No. Pyeong 1-60584, Japanese Patent Publication No. So 61- 234202, Japanese Patent Publication No. So 51-1112348) . However, like the aforementioned conventional arts, the methods of roughening the surface of the workpiece and coating a fluorine resin film on the roughened surface of the workpiece may cause the following problems. In other words, when a roughness, i.e., a height difference between a concave portion and a convex portion of the roughened surface, is about 1 μm, which is relatively low value, the plating film of the fluorine resin completely fills the concave portions, so that the height difference disappears to remarkably decrease the adhesivity of the fluorine resin and to cause delamination of the fluorine resin film. Also, since the fluorine resin is comparatively expensive, it is required in market to make thin the thickness of the fluorine resin film and decrease the use amount of the fluorine resin. However, simply making thin the fluorine resin film seriously deteriorates the adhesivity due to a low frictional coefficient between the fluorine resin and the fluorine resin coating, makes easy the occurrence of pinholes, and makes it impossible to form a thin fluorine resin coating film. Meanwhile, International Patent Publication NO. WO 2004/024985 discloses a method of forming a fluorine resin film having a good adhesivity by exposing a workpiece to a first electroless-plating solution containing at least one selected from the group consisting of a metal salt, a metal complexing agent, a reducing agent, ammonia water, thiosulfate and thiourea to form a first plating film and exposing the surface of the first plating to a second plating solution containing fluorine resin to form a second plating film. However, in the case of the above prior art, when the workpiece is of noble metal, stainless steel or molybdenum steel, the plating film may be easily delaminated. In other words, as shown in FIG. 1, since the height difference between a convex portion 12 and a concave portion 14 is so large, pinholes can be easily generated in the concave portions while the first plating film is formed. These pinholes function to increase the possibility in the delamination of the plating film. [Disclosure] [Technical Problem] Accordingly, the present invention is provided to solve the above problems, and an object of the present invention is to provide an electroless plating method that can be applied to workpieces including a noble metal, a stainless steel, and a molybdenum steel. Another object of the present invention is to provide an electroless plating method that can enhance the adhesive force of a plating film to a workpiece by suppressing the occurrence of pinholes between the plating film and the workpiece. [Technical Solution] To accomplish the above objects, there is provided an electroless plating method. The method includes: electro- polishing a surface of a workpiece; performing an electroless plating of the electro-polished workpiece in a first electroless plating solution containing a metal salt to form a plating film containing a fluorine resin. In the electro-polishing, the workpiece may be dipped in an electrolyte solution and applied a positive voltage such that the workpiece functions as an anode. The may be a nickel-plating film containing the fluorine resin when the workpiece is a stainless steel. The plating film may be a zinc layer containing the fluorine resin when the workpiece is an aluminum alloy. In another aspect of the present invention, there is provided an electroless plating method. The method includes: electro-polishing a surface of a workpiece; performing an electrical strike plating of the electro-polished workpiece to form a first plating film serving as a protecting layer; and performing an electroless plating of the workpiece having the first plating film in a first electroless plating solution containing a metal salt to form a second plating film containing a fluorine resin. In another aspect of the present invention, there is provided an electroless plating method. The method includes: electro-polishing a surface of a workpiece; performing an electrical strike plating of the electro-polished workpiece to form a first plating film serving as a protecting layer; performing a first electroless plating of the workpiece including the first plating film in a first electroless plating solution containing a metal salt to form a second plating film on the first plating film; and performing a second electroless plating of the workpiece including the first and second plating films in a second electroless plating solution to form a third plating film containing a fluorine resin on the second plating film. In another aspect of the present invention, there is provided a plated workpiece obtained by any of the above methods. [Advantageous Effects] According to the inventive electroless plating method and electroless plating workpiece, it is possible to form an electroless plating film having a very high flatness and adhesivity to a workpiece shaped in a pipe made of a noble metal, a stainless steel or a molybdenum steel by suppressing the occurrence of pinholes between the workpiece and the plating film. [Description of Drawings] FIG. 1 is a sectional view showing a surface state of a workpiece according to the conventional art. FIG. 2 is a schematic view showing an electro polishing in an electroless plating method according to an embodiment of the present invention. FIG. 3 is a sectional view showing a surface state of a workpiece according to an embodiment of the present invention. FIG. 4 is a sectional view showing that an electroless plating film is coated on a workpiece according to an embodiment of the present invention. [Best Mode] Hereinafter, preferred embodiments of an electroless plating method and electroless plating workpiece according to the present invention will be described in detail with reference to the accompanying drawings. An electroless plating method according to an embodiment of the present invention includes: electro- polishing a surface of a workpiece; performing an electrical strike plating of the electro-polished workpiece using a metal having a high surface adhesive force to the workpiece to form a first plating film; performing an electroless plating of the workpiece including the first plating film in a first electroless plating solution containing a metal salt to form a second plating film on the first plating film; and performing an electroless plating of the workpiece including the first and second plating films in a second electroless plating solution containing a fluorine resin to form a third plating film on the second plating film. The electro polishing that is a first process of the electroless plating method according to the present invention will be first described. As shown in FIG. 2, in the electro polishing, a first electrode 20, a second electrode 30 and an electrolyte are prepared. A positive voltage is applied to the workpiece serving as the first electrode 20, i.e., such that the workpiece serves as an anode, and a negative voltage is applied to the second electrode 30 such that the second electrode 30 serves as a cathode. As the negative voltage and the positive voltage are applied to the respective electrodes, a surface of the workpiece 20 serving as the anode is electrically polished. Specifically, before the electro polishing is performed, the surface of the workpiece has a structure that convex portions and concave portions are alternatively formed as indicated by a dotted line in FIG. 3. As aforementioned, the concave portions are very deep, but while the electro polishing is performed, protruded portions 22 of the surface of the workpiece are concentratively polished and the sharply protruded portions are polished into smooth forms as indicated by a solid line in FIG. 3. As a result, a height difference between the uppermost location of the protruded portions 22 and the lowest bottom of a concave portion 24 decreases. Accordingly, the occurrence possibility of pinholes in the concave portions decreases and the adhesive force between the surface of the workpiece and the plating film increases. Finally, the delamination possibility of the plating film is remarkably lowered. In other words, the surface roughness of the workpiece when the electro polishing has been completed decreases and the gloss increases remarkably. After the electro polishing is completed, it is preferable that the workpiece is plated three times. In other words, once electric plating and two times of electroless platings are performed. Alternatively, after the electro polishing is completed, only once electroless plating for forming a coating film containing a fluorine resin may be performed. Also, after the electro polishing is completed, once electroless plating for forming a plating film not containing a fluorine resin and once electroless plating for forming a plating film containing a fluorine resin may be performed. An electroless plating solution (first and second electroless plating solutions) according to the present invention includes a metal salt, a metal complexing agent, a reducing agent, a composition solution containing ammonia water and thiosulfate. The electroless plating employed in the present invention is a plating method for plating a film on a workpiece without flowing a current. As the workpiece, a base substrate made of one selected from various materials, such as metal, aluminum, rubber, synthetic resin, may be used, but it is preferable to use products made of a material such as a noble metal, a stainless steel, a molybdenum. The metal salt contained in the electroless plating solution, includes, but limited to a nickel salt, a zinc salt, a cobalt salt, a chromium salt, a titanium salt, a hypophosphite salt, and a combination thereof. Preferably, the metal salt is at least one selected from the group consisting of a nickel salt and a zinc salt. The metal complexing agent contained in the electroless plating solution of the present invention is an organic material forming a complex with a metal salt, and preferably includes malic acid, succine acid and lactic acid. The fluorine resin includes resins containing fluorine radical, such as polytetra fluore ethylene (PTFE) or the like. The concentration of fluorine resin contained in the third electroless plating solution can be optionally selected according to its usage. The surfactant functions to prevent a compounded material from being precipitated and also serves as a dispersant of the fluorine resin. It is preferable that the surfactant uses at least one selected from the group consisting of a cationic surfactant and a non-ionic surfactant. The cationic surfactant includes fourth ammonia salt, second ammonia, third amine, indazoline, and the non- ionic surfactant includes, but limited to polyoxyethylene, polyethylene, carbonic acid, sulfonic non-ionic surfactant. In addition, it is preferable to use a fluorine surfactant having a bond of carbon atom or fluorine atom in a molecule. Optionally, the third electroless plating solution preferably contains a dispersion auxiliary agent for enhancing a dispersion of the fluorine resin into the second plating film. The dispersion auxiliary agent includes, but limited to cerium oxide and silicon carbide. The inventive electroless plating method can be performed by the same method as that generally performed in the plating industries. Next, a plated workpiece obtained by the electroless plating method of the present invention will be described. The plated workpiece includes a first plating film, a second plating film and a third plating film. The first plating film is selected at a proper thickness for the adhesivity to the workpiece. Also, the second and third plating films are selected at proper thicknesses considering the hardness and costs thereof. The plated workpiece obtained by the above method has an excellent adhesivity compared with non-plated workpiece 20 due to the electro polishing and the presence of a protecting layer, as shown in FIG. 4. Hereinafter, the inventive electroless plating methods and the plated workpiece will be exemplarily described. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. [Mode for Invention] Example 1 A stainless steel plate and a metal plate are dipped in a prepared electrolyte solution for electro polishing. At this time, the stainless steel plate is applied a positive voltage to serve as an anode, and the metal plate is applied a negative voltage to serve as a cathode. After the elapse of a predetermined time, the stainless steel plate is taken out of the electro polishing solution, is rinsed, and is dried under the room temperature environment. While the electro polishing is completed, the protruded portions of the surface of the stainless steel plate are concentratively polished, so that a height difference between the concave portion and the convex portion is decreased compared with that before the electro polishing is performed. Thereafter, the stainless steel plate is dipped in an electroless plating solution kept at 86 °C for a predetermined time, is then taken out of the electroless plating solution, rinsed in water and dried under the room temperature environment. The electroless plating solution contains nickel sulfate as a metal salt, sodium hypophosphite as a reducing agent, PTEF as a fluorine resin. A predetermined thickness of plating film is formed on the stainless steel plate, and the surface of the plating film is planarized by the PTFE. The stainless steel plate coated with the above plating film is loaded in a furnace whose inner temperature is kept at 300 "C or more and is baked for 60 minutes to thereby obtain a final plated workpiece coated with the electroless plating film. The final plated workpiece has a very high flatness and an adhesivity compared with the products disclosed in the prior art.

Example 2 A stainless steel plate and a metal plate are dipped in a prepared electrolyte solution for electro polishing. At this time, the stainless steel plate is applied a positive voltage to serve as an anode, and the metal plate is applied a negative voltage to serve as a cathode. After the elapse of a predetermined time, the stainless steel plate is taken out of the electro polishing solution, is rinsed, and is dried under the room temperature environment. While the electro polishing is completed, the protruded portions of the surface of the stainless steel plate are concentratively polished, so that a height difference between the concave portion and the convex portion is decreased compared with that before the electro polishing is performed. Thereafter, the stainless steel plate is dipped in an electric plating solution containing 220 - 250 g/L of nickel chloride, 110 - 140 ml/L of hydrochloric acid (specific gravity: 1.18) and having a current density of 5 - 10 A/dm2 at room temperature for 1 - 10 minutes and, is then taken out of the electric plating solution, rinsed in water and dried under the room temperature environment. As a result, a first nickel-plating film serving as a protecting layer is formed on an upper surface of the stainless steel plate at a predetermined thickness. Next, the stainless steel plate having the first plating film is dipped in an electroless plating solution kept at 86 °C for a predetermined time, is taken out of the electroless plating solution, is rinsed in water, and is dried under the room temperature. The electroless plating solution contains nickel sulfate as a metal salt, sodium hypophosphite as a reducing agent, PTEF as a fluorine resin. A second nickel-plating film is formed on the stainless steel plate at a predetermined thickness, and the surface of the second nickel-plating film is planarized by the PTFE. The stainless steel plate coated with the above first and second nickel-plating films is loaded in a furnace whose inner temperature is kept at 300 °C or more and is baked for 60 minutes to thereby obtain a final plated workpiece coated with the electroless plating film. The final plated workpiece has a very high flatness and an adhesivity compared with the products disclosed in the prior art.

Example 3 A stainless steel plate and a metal plate are dipped in a prepared electrolyte solution for electro polishing. At this time, the stainless steel plate is applied a positive voltage to serve as an anode, and the metal plate is applied a negative voltage to serve as a cathode. After the elapse of a predetermined time, the stainless steel plate is taken out of the electro polishing solution, is rinsed, and is dried under the room temperature environment. While the electro polishing is completed, the protruded portions of the surface of the stainless steel plate are concentratively polished, so that a height difference between the concave portion and the convex portion is decreased compared with that before the electro polishing is performed. Thereafter, the stainless steel plate is dipped in an electric plating solution containing 220 - 250 g/L of nickel chloride, 110 - 140 ml/L of hydrochloric acid (specific gravity: 1.18) and having a current density of 5 - 10 A/dm2 at room temperature for 1 - 10 minutes and, is then taken out of the electric plating solution, rinsed in water and dried under the room temperature environment. As a result, a first nickel-plating film serving as a protecting layer is formed on an upper surface of the stainless steel plate at a predetermined thickness. Next, the stainless steel plate having the first nickel-plating film is dipped in a first electroless plating solution containing nickel sulfate as a metal salt, a sodium hypophosphite as a reducing agent, malic acid, succine acid or lactic acid as a complexing agent, conditioner, pH conditioner, and the like, for a predetermined time, is then taken out of the first electroless plating solution, rinsed in water, and dried under the room temperature environment. As a result, a second nickel-plating film is formed on the first nickel-plating film at a predetermined thickness. Next, the stainless steel plate having the first and second nickel-plating films is dipped in a second electroless plating solution kept at 86 °C for a predetermined time, is taken out of the electroless plating solution, is rinsed in water, and is dried under the room temperature. The second electroless plating solution contains nickel sulfate as a metal salt, sodium hypophosphite as a reducing agent, PTEF as a fluorine resin. A third nickel-plating film is formed on the second nickel-plating film at a predetermined thickness, and the surface of the third nickel-plating film is planarized by the PTFE. The stainless steel plate coated with the above first to third nickel-plating films is loaded in a furnace whose inner temperature is kept at 300 °C or more and is baked for 60 minutes to thereby obtain a final plated workpiece coated with the electroless plating film. [industrial .Applicability] The final plated workpiece has a very high flatness and an adhesivity compared with the products disclosed in the prior art. While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.