Patent Publication Number: US-2015061814-A1

Title: Ferrite circuit board

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Taiwan Patent Application No. 10221672.3 field on Sep. 5, 2013, the entire content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to circuit boards and more particularly, to a ferrite circuit board with firm structure and can be used as an inductor. 
     2. Description of the Related Art 
     A conventional circuit board primarily comprises an insulated substrate and a plurality of wires attached on a surface of the substrate. In the manufacturing process of the circuit board, a conductive material such as nickel-chromium alloy is first coated on the surface of the substrate by sputtering to serve as a seed layer thereon. Subsequently, a photolithography process is performed and a metal material such as copper is electroplated on the seed layer to form the wires. Thereafter, part of the seed layer that is not covered by the wires is removed by etching. 
     However, because the wires of the conventional circuit board protrude from the surface of the substrate, the wires may be easily separated from the substrate in the subsequent manufacturing process of the circuit board. Besides, when the part of the seed layer is etched, the seed layer located between the wires and the substrate is liable to be separated from the substrate due to over-etching. In addition, with the tendency of miniaturized-sized electronic elements, the wire of the circuit board is required to be made thinner, thereby reducing the contact area between the wires and the substrate, which in turn resulting in decrease of the structural stability between the wires and the substrate. Further, because the width and the thickness of the wire are respectively limited by usage requirement and sputtering process, the cross-sectional area of the wire is limited, such that it can only allow a limited amount of current to flow therethrough. 
     SUMMARY OF THE INVENTION 
     In view of the above-mentioned drawbacks of the prior art, it is an objective of the present invention to provide a ferrite circuit board, which has a wire firmly connected with a substrate and is capable of being used as an inductor. 
     To attain the above objective, the present invention provides a ferrite circuit board which comprises a substrate and a wire. The substrate is made of ferrite and has a surface and an elongated groove recessed from the surface. The elongated groove has an inner wall provided with an arithmetic mean roughness (hereinafter referred to as “roughness (Ra)”) of 0.1 μm to 20 μm and accommodates the wire. 
     Because the wire is completely embedded in the elongated groove of the substrate and the inner wall of the elongated groove has a predetermined roughness, the connection strength between the wire and the substrate can be improved in comparison with the prior art. In addition, because the elongated groove has a predetermined depth, the wire having a larger cross-sectional area can be embedded therein so as to allow a relatively large amount of current to flow therethrough. Furthermore, the elongated groove may be designed to have a spiral shape and accommodates the wire having the corresponding shape, so that the ferrite circuit board can also be used as an inductor to provide abundant functionality. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of a ferrite circuit board according to a preferred embodiment of the present invention. 
         FIG. 2  is a cross-sectional view taken along line  2 - 2  of  FIG. 1 . 
         FIGS. 3 to 8  are photographs of real products of the ferrite circuit boards made according to examples 1 to 6 of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The structure and effect of the present invention will become more fully understood from the detailed description given herein below and the accompanying drawings. Referring to  FIG. 1 , a ferrite circuit board  10  according to a preferred embodiment of the present invention comprises a substrate  20  and a wire  30 . 
     The substrate  20  is formed by sintering ferrite powder and the examples of ferrite powder may be Mn—Zn ferrite powder, Ni—Zn ferrite powder, Ni—Cu—Zn ferrite powder, Mn—Mg—Zn ferrite powder, Mn—Mg—Al ferrite powder, Mn—Cu—Zn ferrite powder, Co-ferrite powder, or the combination thereof. In another embodiment, the substrate  20  may be made of ferrite formed by another process. 
     As shown in  FIG. 2 , the substrate  20  has a surface  22  and an elongated groove  24  recessed from the surface  22 . The elongated groove  24  includes an inner wall  241  having a bottom surface  243  and two side surfaces  245 . The bottom surface  243  and the side surfaces  245  of the inner wall  241  are irregular and the inner wall  241  has a roughness (Ra) of 0.1 μm to 20 μm. Specifically speaking, the bottom surface  243  has a plurality of crests  243   a  substantially located in an imaginary plane P that is approximately parallel to the surface  22 . The distance D between the imaginary plane P and the surface  22  is defined as the depth D of the elongated groove  24 , which ranges from 0.9 μm to 70 μm. 
     The wire  30  is made of metal with high electrical conductivity, such as copper (Cu), silver (Ag), gold (Au) and the like, and embedded in the elongated groove  24  of the substrate  20 . The wire  30  has a top surface  32  substantially flush with the surface  22  of the substrate  20 . In other words, the wire  30  has a shape complementary to that of the elongated groove  24  of the substrate  20 . In this embodiment, as shown in  FIG. 1 , the elongated groove  24  is designed in a spiral shape and the wire  30  having a corresponding shape is embedded therein. In another embodiment, the shapes of the elongated groove  24  and the wire  30  may be varied according to an actual condition. In addition, the top surface  32  of the wire  30  may be lower or higher than the surface  22  of the substrate  20 . Further, the numbers of the elongated groove  24  and the wire  30  are not specifically limited and may be varied according to the purpose of using the ferrite circuit board  10 . 
     In the ferrite circuit board  10  of the present invention, because the wire  30  is completely accommodated in the elongated groove  24  of the substrate  20  and does not protrude out of the surface  22  of the substrate  20 , and the bottom surface  243  and side surfaces  245  of the inner wall  241  are provided with a predetermined roughness (Ra) ranging from 0.1 μm to 20 μm, the wire  30  can be firmly fixed in the elongated groove  24 . Therefore, the connection strength between the wire  30  and the substrate  20  is high enough such that the wire  30  is not easily separated from the substrate  20  even though it is very thin. In fact, the roughness (Ra) of bottom surface  243  and side surfaces  245  of the inner wall  241  of the elongated groove  24  is preferably in a range of 0.3 μm to 15 μm, and more preferably in a range of 0.5 μm to 10 μm. In addition, in this embodiment, because the elongated groove  24  of the substrate  20  is designed to have a spiral shape and accommodates the wire  30  having the corresponding shape and the ferrite substrate  20  has magnetism, the ferrite circuit board  10  of the present invention can also be used as an inductor, such that the ferrite circuit board  10  possesses abundant functionality. Moreover, because the elongated groove  24  has a depth D of 0.9 μm to 70 μm, the wire  30  may have a relatively greater thickness to allow a relatively large amount of current to flow therethrough. As such, the ferrite circuit board  10  of the present invention may be widely applied in many fields. 
     Referring to Table 1 below, it shows the ferrite circuit boards according to the examples 1 to 6 respectively, in which the depths D of the elongated grooves  24  of the examples are in the range of 0.9 μm to 20 μm and the roughnesses Ra of the inner walls  241  of the elongated grooves  24  of the examples are in the range of 0.3 μm to 10 μm.  FIGS. 3 to 8  are photographs sequentially showing the real products of the ferrite circuit boards made according to the examples 1 to 6 listed in Table 1. As shown in the photographs, the elongated grooves  24  of the substrates  20  or the wires  30  located in the upper side are wider than those located far away from the upper side. In each of the examples, metal can be firmly embedded in the elongated groove  24  to form the complete wire  30 . According to a further experimental result, in the case that the inner wall  241  of the elongated groove  24  has a roughness (Ra) ranging from 0.1 μm to 20 μm and a depth D ranging from 1 μm to 70 μm, the wire  30  can be firmly disposed in the elongated groove  24 . On the contrary, when the depth D of the elongated groove  24  is less than 0.9 μm or the roughness (Ra) is less than 0.1 μm, a complete wire  30  cannot be easily firmly disposed in the elongated groove  24 . 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                   
                 parameter 
               
            
           
           
               
               
               
            
               
                   
                 depth  
                 roughness  
               
               
                 example 
                 D (μm) 
                 Ra (μm) 
               
               
                   
               
               
                 1 
                  0.9 
                 0.3 
               
               
                 2 
                  1.7 
                 1.2 
               
               
                 3 
                 5  
                 3.7 
               
               
                 4 
                 10   
                 5   
               
               
                 5 
                 15   
                 5-10 
               
               
                 6 
                 20   
                 5-10 
               
               
                   
               
            
           
         
       
     
     It is worth mentioning that, the actual depth D of the elongated groove  24  is extremely thinner than the actual thickness of the substrate  20 ; however, in order to clearly express the technical feature of the present invention, the depth D is shown in exaggerated manner in  FIG. 2 . In another embodiments, the shape of the cross-section of the inner wall  241  of the elongated groove  24  may be semi-ellipse, semi-circle, irregularity, etc. It should be understood that the detailed description and specific example, while indicating preferred embodiment of the invention, are given by way of illustration only, and thus are not limitative of the present invention. The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.