Patent Publication Number: US-2013233602-A1

Title: Surface treatment structure of circuit pattern

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a surface treatment structure of a circuit pattern, and more particularly to a thin surface treatment structure including a palladium layer, by which the problems occurred in conventional arts can be reduced. 
     2. The Prior Arts 
     After a circuit pattern is formed on a printed circuit substrate, the gold wires used as the soldering wires are often wire-bonded to the circuit pattern which is usually made of copper or aluminum, and however, such a wire bonding is affected by the materials used.  FIG. 1  is a cross sectional view of a conventional surface treatment structure of circuit pattern. The conventional surface treatment structure  30  is formed on a circuit pattern  10  formed on a printed circuit substrate  100 , and the circuit pattern  10  is usually a copper bump. The surface treatment structure of circuit pattern  30  includes a nickel layer  31  and a gold layer  33 , and the strength of wire bonding can be enhanced by using the same gold material for the gold layer  33  and the gold soldering wires, and the nickel layer  31  is mainly used to prevent the diffusion of the copper ions from the circuit pattern  10  into the gold layer  33 , so as to avoid the wiring bonding from being affected. 
     However, with the advances of technology, the demand for high precision of wire width and wire thickness is increased. Conventionally, a thickness of a nickel layer is about 5 μm, and a thickness of a gold layer is about 0.5 μm, and thereby the thickness of a circuit is increased, which limits the circuit density. Furthermore, when the price of gold increases, the manufacture cost becomes higher as the thickness of the gold layer increases. Additionally, due to a characteristic of nickel, the thickness of nickel is not uniform, which may cause the lowerness of line pitch, and short circuit when applied the surface treatment structure in the fine-line circuits. 
     Therefore, there is a need for providing a surface treatment structure of a circuit pattern, which can reduce the manufacture cost, increase the circuit density, and overcome the various problems in the conventional techniques. 
     SUMMARY OF THE INVENTION 
     An objective of the present invention is to provide a surface treatment structure formed on a circuit pattern on a printed circuit board. The circuit pattern is usually a copper circuit. The surface treatment structure formed on a circuit pattern includes a first gold layer, a palladium layer and a second gold layer stacked from bottom to top, respectively, or includes a palladium layer, and a second gold layer stacked from bottom to top, respectively. The thickness of the first gold layer is between 0.01 μm and 0.1 μm, and the thickness of the palladium layer is between 0.03 μm and 0.15 μm, and the thickness of the second gold layer is between 0.03 μm and 0.15 μm. 
     In the present invention, the palladium layer is used to effectively prevent the diffusion of the copper ions from the circuit pattern into the outer layer, so that the strength of wire bonding and tin balls soldering can be enhanced. Only a thin surface treatment structure of the circuit pattern of the present invention is required to achieve excellent wire bonding, so that an overall thickness can be reduced and the manufacture cost is also reduced. Furthermore, the uniformness of the surface treatment structure is improved. Therefore, the surface treatment structure of the circuit pattern of the present invention is suitably used for manufacturing the fine-line circuits, thereby having a wider industrial applicability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be apparent to those skilled in the art by reading the following detailed description of a preferred embodiment thereof, with reference to the attached drawings, in which: 
         FIG. 1  is a cross sectional view of a surface treatment structure of a circuit pattern according to the prior art; 
         FIG. 2  is a cross sectional view of a surface treatment structure of a circuit pattern according to the first embodiment of the present invention; and 
         FIG. 3  is a cross sectional view of a surface treatment structure of a circuit pattern according to the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
       FIG. 2  is a cross sectional view of a surface treatment structure of a circuit pattern according to the first embodiment of the present invention. Referring to  FIG. 2 , a surface treatment structure  20  is formed on a circuit pattern  10  which is formed on a printed circuit board  100 . The circuit pattern  10  is usually the copper circuit. The surface treatment structure  20  formed on the circuit pattern  20  includes a first gold layer  21 , a palladium layer  23  and a second gold layer  25  stacked from bottom to top, respectively. The thickness of the first gold layer is between 0.01 μm and 0.1 μm, and the thickness of the palladium layer is between 0.03 μm and 0.15 μm, and the thickness of the second gold layer is between 0.03 μm and 0.15 μm. The first gold layer  21 , the palladium layer  23 , and the second gold layer  25  are formed by electroplating, electroless plating, evaporation or sputtering method. 
       FIG. 3  is a cross sectional view of a surface treatment structure of a circuit pattern according to the second embodiment of the present invention. The surface treatment structure  22  in the second embodiment is the same as that in the first embodiment except that the surface treatment structure  22  only includes a palladium layer  23 , and a second gold layer  25  stacked from bottom to top, respectively. The thickness of the palladium layer is between 0.03 μm and 0.15 μm, and the thickness of the second gold layer is between 0.03 μm and 0.15 μm. The palladium layer  23  and the second gold layer  25  are formed by electroplating, electroless plating, evaporation or sputtering method. 
     In the present invention, the palladium layer is used to effectively prevent the diffusion of the copper ions from the circuit pattern into the outer layer, so that the strength of wire bonding can be enhanced. Only a thin surface treatment structure of the circuit pattern of the present invention is required to achieve excellent wire bonding, so that an overall thickness can be reduced and the manufacture cost is also reduced. Furthermore, the uniformness of the surface treatment structure is improved. Therefore, the surface treatment structure of the circuit pattern of the present invention is suitably used for manufacturing the fine-line circuits, thereby having a wider industrial applicability. 
     Although the present invention has been described with reference to the preferred embodiments thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims.