Abstract:
A method for manufacturing an EMI shielding element from a sheet of polymer material includes forming the shielding element by vacuum- or pressure-molding. The formed element is then chemically etched to roughen its surface on a microscopic scale. The surface is subsequently treated with a catalyzing solution to enable the shielding element to be plated by electroless plating. A first metallic layer is deposited on the etched and catalyzed surface by electroless plating, and a second metallic layer is deposited on the first by electrolytic plating.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to shielding elements for electronic equipment, such as telecommunications, fiberoptic and computer equipment and the like. The shielding elements are required to shield components of such equipment and connections thereto from electromagnetic fields which may interfere with their operation. 
         [0002]    In the prior art, shielding elements of this type have been formed from metallic sheets by cutting and bending them into a desired cover-like shape. In addition, shielding elements have been formed from plastic by injection molding, and subsequently plated with metallic layers which provide the required shielding. 
         [0003]    The present invention is an improvement over these prior-art methods by providing a more economical method for manufacturing shielding elements of this type. 
       SUMMARY OF THE INVENTION 
       [0004]    Accordingly, the present invention is a method for manufacturing a shielding element for use in providing EMI (electromagnetic interference) shielding for electronic equipment by catalyzing and plating a sheet of polymer material formed by pressure or vacuum into the shape of the shielding element. 
         [0005]    The method includes the step of etching the part, as the shielding element is known during the manufacturing process, the part being formed from the sheet of polymer material to roughen its surface on a microscopic level to enable it to be catalyzed and to enable a metallic layer to adhere to it. The etched surface is then catalyzed with a catalyzing solution to enable it to be plated by electroless plating. 
         [0006]    Electroless plating is used to deposit a first metallic layer on the surface of the part. The first metallic layer may be of any conductive metal, including copper, nickel, cobalt, silver, gold or tin, and renders the part electrically conductive, so that it may function as a cathode in a subsequent electrolytic plating step. 
         [0007]    Finally, electrolytic plating is used to deposit a second metallic layer on the surface of the part over the first metallic layer. The second metallic layer may be of any electrolytic metal including nickel, tin, copper, zinc or chromium. 
         [0008]    The present invention will now be described in greater detail in the discussion that follows. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0009]    The shielding elements which are manufactured in accordance with the method of the present invention have a wide variety of uses in the electronics industry, where they are generally used for EMI shielding. As such, they have a wide variety of shapes and configurations to enable them to carry out a desired shielding function for a particular application. For example, a shielding element may be a cover for a chip on a circuit board within a piece of electronic equipment, or it may be a cover or housing for an entire component within a piece of electronic equipment, such as a personal computer. In addition, the shielding element may be an enclosure for a cable connection to a piece of electronic equipment. In short, the present invention is not limited to a shielding element of any one of these specific varieties, but is intended to cover all of these as well as others not explicitly identified here. 
         [0010]    In accordance with the present invention, the shielding elements are pressure- or vacuum-molded from sheets of polymer material, rather than injection-molded following the established procedures of the prior art. The polymer material, in sheet form, may be of any variety, including TEFLON® (polytetrafluoroethylene), polyester or polypropylene, but is preferably of ABS (acrylonitrile-butadiene-styrene copolymer), HIPS (high-impact polystyrene) or PC-ABS (polycarbonate ABS), which are preferred as they are readily susceptible to standard catalyzation and plating procedures. A suitable ABS plastic is available from Bayer Corporation of Elkhart, Ind., USA as Lustran 752, which is a high-impact, high-gloss, black ABS plastic provided in sheet form having a thickness of 17 mils (0.017 inch; 0.43 mm). LUSTRAN® is a registered trademark (U.S. Registration No. 720,161) owned by Bayer Corporation. 
         [0011]    In order to be formed into a shielding element of a desired three-dimensional geometry, the sheet of polymer material is cut into a size that will fit into the forming apparatus to be used, that is, either a pressure- or vacuum-molding apparatus. The sheet is heated slightly, so that it may be softened and readily deformable, and placed between the two dies of the mold in the forming apparatus. The mold is then closed and either pressure or vacuum is used to make the polymer sheet conform to the shape of the mold. The “part” thereby obtained retains that shape upon removal from the mold. It will be appreciated that the “part” will have both formed portions, which will eventually become the shielding element being manufactured, and unformed portions, these being areas of the sheet not deformed in the molding apparatus. These latter portions may be trimmed from the shielding element as necessary, perhaps at the end of the plating process. 
         [0012]    The next step in the manufacturing process is to clean the part to be plated to remove any oil, grease or other contaminant it may have acquired during forming. For example, the part may be cleaned by dipping it into 1-propanol (propyl alcohol) at room temperature for thirty seconds, and then rinsed in running DI (deionized) water to remove any alcohol film remaining on the part after dipping. More generally, any commercially available solvent, such as an alcohol, may be used in the cleaning step. 
         [0013]    The manufacturing process proceeds with an etching step, in which the surface of the part is roughened on a microscopic level to prepare it for catalyzation and plating. A chrome/sulfuric acid etching solution may be used for this purpose. 
         [0014]    Such a solution may be prepared by dissolving 380 grams of chromic acid in DI water sufficient to produce a solution having a volume of 830 ml. Then, 170 ml of concentrated sulfuric acid are added to bring the volume to 1 liter. 
         [0015]    The resulting solution is heated to 70° C., and mechanically stirred while the part is immersed for approximately seven minutes. The part is then removed and rinsed under running DI water until chromium is no longer visibly present on its surface. 
         [0016]    In the next step, namely, the catalyzing step, the etched surface of the part is catalyzed to enable it to be plated by electroless plating. A commercially available catalyzer may be used for this purpose. For example, Shipley Cataposit 44, available from the Shipley Company of Marlboro, Mass., USA, may be used. CATAPOSIT® is a registered trademark (U.S. Registration No. 1,031,891) owned by Rohm and Haas Company of Philadelphia, Pa., USA. 
         [0017]    A catalyzing solution for the present manufacturing process is prepared by diluting 50 ml of Shipley Cataposit 44 with sufficient DI water to produce a volume of 300 ml. The resulting catalyzing solution is then heated to 40° C., and mechanically stirred while the part is immersed therein for one minute. The part is then removed and immersed sequentially in three containers of DI water, the part being left in the third container until the next step in the manufacturing process is to be performed. 
         [0018]    Shipley Cataposit 44 uses a tin and palladium mixture as the catalyzer. Other catalysts employing palladium, gold, silver or platinum may also be used in the practice of the present invention. 
         [0019]    The next step is an electroless plating step. A commercially available electroless plating solution may be used for this purpose. For example, MacDermid Ultra Dep 1000 electroless copper, available from MacDermid Incorporated of Waterbury, Conn., USA, may be used. To carry out the electroless plating step, a suitable amount of MacDermid Ultra Dep 1000 electroless copper solution is prepared, heated to 50° C., and mechanically stirred while spare catalyzed material is plated for 15 to 20 minutes to activate the solution. The spare material is then removed, and the part to be plated is then immersed in the solution, which is still being mechanically stirred, and plated for approximately seven minutes. The part is then removed and rinsed under running DI water. 
         [0020]    Alternatively, the electroless plating step may be performed with electroless plating solutions based on nickel, cobalt, silver, gold or tin without departing from the scope of the present invention. 
         [0021]    The final step in the manufacturing process of the present invention is an electrolytic plating step. A commercially available electrolytic plating solution may be used for this purpose. For example, MacDermid Barrett SN (electrolytic sulfamate nickel), also available from MacDermid Incorporated of Waterbury, Conn., USA, may be used. To carry out the electrolytic plating step, a suitable amount of MacDermid Barrett SN is prepared, heated to 50° C., and, adjusted to have a pH of 4.0. A standard Hull-cell nickel anode is then mounted in the electrolytic plating solution, which is mechanically stirred. The part is then plated at 2.0 amps for approximately 2 minutes, rotated by 180°, and plated for an additional approximately 2 minutes at 2.0 amps. The part is then removed from the solution, rinsed in running DI water, and dried at 80° C. for 30 minutes. 
         [0022]    While nickel is most commonly used in electroplating because of its corrosion resistance, the electrolytic plating step could alternatively be used to apply a layer of tin, copper, zinc or chromium onto the part. All of these metals are useful in providing EMI shielding. 
         [0023]    Modifications to the above would be obvious to those of ordinary skill in the art, but would not bring the invention so modified beyond the scope of the appended claims.