Abstract:
An electroplating method includes steps of: providing a substrate having a first portion and a second portion connected to the first portion; forming a metallic layer on a surface of the second portion; immersing the first portion of the substrate in an electrolyte solution, applying a current to the metallic layer to electroplate the first portion of the substrate with a metal layer; and moving the substrate in a direction away from the electrolyte solution during electroplating the first portion of the substrate. The method can improve a uniformity of the obtained plating layer.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present invention generally relates to an electroplating method, and particularly, relates to an electroplating method for an insulative substrate. 
         [0003]    2. Discussion of Related Art 
         [0004]    Properties of carbon fibers such as high tensile strength, low weight, low thermal expansion, high electrical conductivity and heat conductivity make it very popular in many fields such as aerospace and motorsports. Generally, carbon fibers are widely employed in composite materials to improve performance thereof. For example, a copper-carbon fiber composite is disclosed in Keiidhi Kuniya et al. Development of Copper-Carbon Fiber Composite for Electrodes of Power Semiconductor Devices, IEEE Transactions on Components, Hybrids, and Manufacturing Technology, vol. 6, No. 4, pp. 467-472, Dec. 1983. 
         [0005]    It is to be understood that in metal-carbon fiber composite, carbon fibers and metal cannot thoroughly soaked with each other due to the differences of surface properties. In order to improve a bonding between metal and carbon fibers, carbon fibers are usually pre-processed using electroless plating, electroplating, physical vapor deposition, or chemical vapor deposition. Electroplating is highly preferred for its simple process, low cost and high level plating layer. 
         [0006]    Currently, carbon fibers are immersed in a plating bath and connected to an electrode during a plating process, a redox reaction occurs on surfaces of carbon fibers and plating layer is thereby deposited. However, a current distribution density is non-uniform on surfaces of carbon fibers; as a result, deposition speed of metal particles is also non-uniform. Specifically, the closer the carbon fibers are to the electrode, the higher the particles deposition speed. Therefore, the obtained plating layer is non-uniform, metal-carbon fiber composite made from such carbon fibers can&#39;t reach its expected performance. Therefore, there is a desire to develop a method of forming a uniform plating layer. 
       SUMMARY 
       [0007]    An electroplating method includes steps of: providing a substrate having a first portion and a second portion connected to the first portion; forming a metallic layer on a surface of the second portion; immersing the first portion of the substrate in an electrolyte solution, applying a current to the metallic layer to electroplate the first portion of the substrate with a metal layer; and moving the substrate in a direction away from the electrolyte solution during electroplating the first portion of the substrate. 
         [0008]    This and other features and advantages of the present invention as well as the preferred embodiments thereof and an electroplating method in accordance with the invention will become apparent from the following detailed description and the descriptions of the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Many aspects of the present invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present invention. 
           [0010]      FIG. 1  is flow chart of a method of forming a plating layer on a substrate. 
           [0011]      FIG. 2  is a schematic view showing a substrate including a first portion and a second portion. 
           [0012]      FIG. 3  is cross sectional view of  FIG. 1  along a line II-II. 
           [0013]      FIG. 4  is a schematic view showing an metallic layer is formed on the second portion of the substrate of  FIG. 1 . 
           [0014]      FIG. 5  is a cross sectional view of  FIG. 3  along a line IV-IV. 
           [0015]      FIG. 6  is a schematic view showing the substrate is plated in a plating system. 
           [0016]      FIG. 7  is a schematic view showing a uniform plating layer is formed on the substrate of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]      FIG. 1  illustrates a method of forming a plating layer on a substrate, the method will be described in detail accompany with reference to  FIGS. 2 to 7 . 
         [0018]    In step  1 , as shown in  FIG. 2 , a rectangular substrate  100  to be electroplated is provided, the substrate  100  includes a first portion  110  and a second portion  120  connected to the first portion  110 . Referring to  FIG. 3 , the first portion  110  has a surface  111 . The second portion  120  has a surface  121 . 
         [0019]    The substrate  100  is made of an dielectric material, for example, carbon fiber or plastic. Examples of plastic include polypropylene, polycarbonate, and copolymer of propylene, butadiene and styrene. Silks can be spun from above materials and the substrate  100  can be woven from the plastic silks. In the present embodiment, the substrate  100  is made of carbon fiber, and a thickness of the substrate  100  is in a range from about 1 micrometer to 100 micrometers. The substrate  100  is a rectangular shaped sheet. However, it is understood that the substrate  100  can also be threadlike or club-shaped. In order to remove dust and smear attached on the substrate  100 , the substrate is processed using plasma or an acid solution. 
         [0020]    In step  2 , an metallic layer  200  is formed or disposed on a surface of the second portion  120 . Referring to  FIGS. 4 and 5 , the metallic layer  200  is connected to the first portion  110  and is configured for improving distribution uniformity of an electroplated layer formed on the surface of the first portion  110 . During a sequential process for electroplating the electroplated layer on the surface of the first portion  110 , the metallic layer  200  formed on the surface of the second portion  120  is functioned as an electrode. Thus, the electroplated layer with high distribution uniformity is formed in a width direction on a surface of the first portion  110  near to the metallic layer  200 . Generally, in order to ensure a current distribution density in a width direction of the first portion  110 , a width of the metallic layer  200  is equal to or larger than that of the first portion  110  and the second portion  120 . 
         [0021]    In this embodiment, the substrate  100  is a carbon fiber cloth. The first portion  110  and the second portion  120  have a same width. Electrically conductive silver pastes are coated on entire surfaces  121 ,  122  and then cured, thereby forming the metallic layer  200 . It is understood that other metals such as aurum, copper, nickel and aluminum can also be used to make electrically conductive pastes for the metallic layer  200 . In addition, the metallic layer  200  can also be formed by laminating a layer of electrically conductive metal powder on the two surfaces  121 ,  122  or disposing sheet metals on the two surfaces  121 ,  122 . Sheet metals are especially convenient when substrate  100  is threadlike shaped. In such condition, the substrate  100  can be clamped between two sheet metals. 
         [0022]    In step  3 , referring to  FIG. 6 , the first portion  110  of the substrate  100  is immersed into an electrolyte solution, and then in step  4  a current is applied to the metallic layer  200  on the second portion  120  for depositing a plating layer  300  on two opposite surfaces  111 ,  112  of the first portion  110 . These steps are performed in an electroplating apparatus  400 , which includes a cathode  410 , an anode (not show), a plating bath  420 , and an elevating system  430  disposed on an operating table (not shown). The cathode  410  and the anode are electrically connected to a cathode and an anode of a power supply (not shown) respectively. The elevating system  430  includes an elevating means  431  and a controller  432  connected to the elevating means  431 . The elevating means  431  includes a first guide rail  4311  and a second guide rail  4312  slidably disposed on the first guiding rail  4311 . The second guide rail  4312  is capable of sliding along a lengthwise direction of the first guide rail  4311 . The cathode  410  is fixed to the second guide rail  4312 ; therefore the cathode  410  can move along with the second guide rail  4312 . The substrate  100  is hanged on the cathode  410  during plating; as a result, the substrate  100  can be elevated or lowered by driving the elevating system  430 . The controller  432  is configured for controlling moving speed of the second guide rail  4312 . 
         [0023]    It is understood that pneumatic, fluid drive, or electric drive elevating apparatus can also be employed as the elevating means  431 . In addition, both the cathode  410  and the substrate  100  can be connected to the elevating system  430 . The elevating system  430  can directly control the movement of the substrate  100 . 
         [0024]    The process of depositing the plating layer  300  will be described in detail in the following context. Firstly, the metallic layer  200  is electrically connected to the cathode  410 ; secondly, the controller  432  controls the elevating means  431  to lower the second guide rail  4312  such that the first portion  110  of the substrate  100  is immersed in the plating bath  420 ; finally, the power supply is switched on, a redox reaction occurs on the two opposite surfaces  111 ,  112 , and the plating layer  300  is thereby deposited. It is to be understood that side surfaces of the first portion  110  can also have plating layer  300  deposited thereon. 
         [0025]    During the electroplating process, the controller  432  controls the elevating means  431  to elevate the second guide rail  4312  and the cathode  410 , as a result, the substrate  100  is gradually pulled out of the plating bath  420 . Therefore, plating time in different areas of the two opposite surfaces  111 ,  112  is different, specifically, plating time gradually increases from an end of the first portion  110  that adjacent to the second portion  120  (hereinafter as proximal end) to the opposite end (hereinafter as distal end). In contrast, a current distribution density gradually decreases from the proximal end to the distal end. The plating time and the current distribution density establish an equilibrium, and a uniform plating layer  300  can be obtained. In the present embodiment, the substrate  100  is elevated in a uniform motion. However, it is to be understood that the substrate  100  can be also elevated in a non-uniform motion. 
         [0026]    When metal particles are deposited on the two opposite surfaces  111  and  112 , the metal particles act as an assistant electrode which can accelerate the electroplating process and improve a uniformity of current distribution density. As a result, when the substrate  100  is pulled out of the plating bath  420 , the controller  432  stops the second guide rail  4312 , and the substrate  100  is removed from the second guide rail  4312  and dried, as a result, a substrate  100  with uniform plating layer  300  formed on the two opposite surfaces  111 ,  112  is obtained. 
         [0027]    In order to further improve a thickness uniformity of the plating layer  300 , the cathode  410  is connected to a current regulating apparatus (not shown) for regulating an output current of the cathode  410  such that current distribution density on the portion of the two opposite surfaces  111 ,  112  that are immersed in the plating bath  420  remain at a certain valve. For example, when the substrate  100  is elevated in a uniform motion at a velocity of v, cathode  410  has an initial output current of I 0 , and the first portion  100  has a length of L, the current regulating apparatus decreases the output current of the cathode  410  at an acceleration of ΔI wherein ΔI satisfy a equation of ΔI=vI 0 /L. 
         [0028]    The second portion  120  and the metallic layer  200  can be removed according to a practical demand. For example, the substrate  100  can be cut along a boundary between the first portion  110  and the second portion  120  and the second portion  120  is removed. The remained first portion  110  has a very uniform plating layer  300 . 
         [0029]    In the present embodiment, a long contacting boundary exists between the metallic layer  200  and the first portion  110 ; as a result, uniformity of current distribution density in a width direction of the first portion  110  is improved and a deposition speed of plating layer  300  is substantially same in the width direction of the first portion  110 . Furthermore, the substrate  100  is pulled out of the plating bath  420  gradually, the deposited metal particles on the two opposite surfaces  111 ,  112  act as assistant electrode which can improve a current distribution density of the portion of opposite surfaces  111 ,  112  immersed in the plating bath, as a result, a thickness of the plating layer  300  is further improved. 
         [0030]    Finally, it is to be understood that the above-described embodiments are intended to illustrate rather than limit the invention. Variations may be made to the embodiments without departing from the spirit of the invention as claimed. The above-described embodiments illustrate the scope of the invention but do not restrict the scope of the invention.