Abstract:
A preparation method for an electronic component with an alloy electrode layer includes steps of printing a metal layer on each of the two opposite surfaces of a ceramic substrate with the metal layer made from aluminum, spraying an alloy layer being a copper alloy layer on an outer surface of each metal layer, connecting a pin to each alloy layer, and enclosing the ceramic substrate, the metal layers, the alloy layers and a portion of each pin with an insulating layer. With the adoption of copper alloy for the alloy layer, the preparation method has the advantages of low production cost and high reliability of the electronic component produced by the method.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a preparation method for an electronic component and, more particularly, to a preparation method for an electronic component with an alloy electrode layer. 
         [0003]    2. Description of the Related Art 
         [0004]    Varistor is a delicate electronic ceramic component that is fabricated from a mixture of a base material, which includes electronic grade zinc oxide (ZnO) powder, and various small amount of additives, such as electronic grade bismuth oxide (Bi 2 O 3 ), cobalt oxide (Co 2 O 3 ), manganese dioxide (MnO 2 ), antimony trioxide (Sb 2 O 3 ), titanium dioxide (TiO 2 ), chromium oxide (Cr 2 O 3 ), nickel oxide (Ni 2 O 3 ) and the like added thereto, through mixing, molding and sintering processes, making that the varistor is naturally sensitive to variation of externally applied voltage and it is thus applicable for the varistor to sense and limit all transient overvoltage occurring in circuit and absorb the resulting surge energy. 
         [0005]    To lower the fabrication cost of varistor, China patent application number 201110140236.1, entitled “Copper-electrode zinc-oxide voltage sensitive resistor and preparation method thereof”, discloses a conventional technique of doping and sintering base metal using a chain-belt type tunnel furnace under an oxygen-free atmosphere environment. However, the copper electrode of the varistor fabricated by the conventional technique is prone to oxidation under high-temperature operation, which becomes a durability issue for electronic appliances at home or in industrial area. Additionally, as such conventional technique also needs to consume lots of inert gas, despite the cost down effect arising from the base metal, the varistor produced by the conventional technique is not so cost-effective because of the rising auxiliary production costs. Due to the tendency of oxygen absorption, acceptance rate of mass-produced varistors cannot be guaranteed. 
       SUMMARY OF THE INVENTION 
       [0006]    An objective of the present invention is to provide a preparation method for an electronic component with an alloy electrode layer targeting at enhancing the reliability of base metal copper electrode under a high-temperature environment upon solving the cost issue of an electronic component with the electrode. 
         [0007]    To achieve the foregoing objective, the preparation method for an electronic component with an alloy electrode layer includes steps of: 
         [0008]    preparing a ceramic substrate having two opposite surfaces; 
         [0009]    printing a metal layer on each of the two opposite surfaces of the ceramic substrate, wherein the material of the metal layer is aluminum; 
         [0010]    spraying an alloy layer on an outer surface of each metal layer, wherein the alloy layer is a copper alloy layer, and each metal layer and a corresponding alloy layer stacked on the metal layer form an electrode layer; 
         [0011]    connecting a pin to each alloy layer; and 
         [0012]    enclosing the ceramic substrate, the electrode layers and a portion of each pin with an insulating layer. 
         [0013]    According to the foregoing description of the preparation method, the metal layers and the alloy layers are integrated to form a multilayer structure, which is taken as an electrode layer of the electronic component. In contrast to conventional electrode structure with copper layer only, the present invention employs a copper alloy layer for the electrode layer to keep competitive advantages of being low in production cost and also enhancing reliability of the electronic component at the same time. Given a varistor as an example of the electronic component, the varistor fabricated by the preparation method has a lower varistor voltage variation after the varistor becomes aged and increases the capacity of resisting more combination waves before failure of the varistor. 
         [0014]    Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1A  is a front view in partial section of an electronic component in accordance with the present invention; 
           [0016]      FIG. 1B  is a side view in partial section of the electronic component in  FIG. 1A ; 
           [0017]      FIG. 2  is a flow chart showing a fabrication process of an electronic component; 
           [0018]      FIG. 3  is a schematic diagram showing electric arc spray; and 
           [0019]      FIG. 4  is a flow diagram of a preparation method in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    With reference to  FIGS. 1A and 1B , an electronic component in accordance with the present invention includes a ceramic substrate  1 , two metal layers  21 , two alloy layers  22 , two pins  3  and an insulating layer  4 . 
         [0021]    The two metal layers  21  are respectively formed on two opposite surfaces of the ceramic substrate  1 . Each alloy layer  22  is stacked on an outer surface of one of the two metal layers  21 , and the multi-layer structure of the metal layers  21  and the alloy layers  22  are taken as an electrode layer of the electronic component. The two pins  3  are electrically connected to the respective alloy layers  22 . The insulating layer  4  encloses the ceramic substrate  1 , the metal layers  21 , the alloy layers  22  and one end of each pin  3  connected to a corresponding alloy layer  22 . 
         [0022]    With reference to  FIG. 2 , a fabrication process of an electronic component is shown. Given varistor as an example of the electronic component, steps of fixing materials, spray granulation, dry-press formation and ceramic sintering that pertain to steps for producing the ceramic substrate  1  are not repeated here. After the ceramic substrate  1  is completed, steps of silk-screen print of the ceramic substrate, electric arc spray of the electrode layer, soldering of the pins, insulating material package and hardening, associated with the present invention can then begin. 
         [0023]    To depict the fabrication process of a first embodiment of the electronic component in accordance with the present invention, varistor 14471 is chosen to elaborate the following embodiment of the electronic component whose diameter and thickness are 14 mm and 1.8 mm respectively. 
       First Embodiment 
       [0024]    Steps of producing the metal layers  21 : 
         [0025]    1. Clean surfaces of the ceramic substrate  1 . 
         [0026]    2. Blend glass powder and a binder with pure aluminum powder to acquire an aluminum slurry with a weight percent of aluminum in a range of 65˜75%. The glass powder includes silicon dioxide (SiO2), bismuth oxide (BiO 2 ) and boron trioxide (B 2 O 3 ) and has a weight percent in a range of 10%˜15%. The binder has a weight percent in a range of 10%˜25% and the contents of the binder include ethylcellulose and terpineol. The aluminum slurry can be coated on a first surface of the ceramic substrate  1  through silk-screen printing. 
         [0027]    3. Place the ceramic substrate  1  printed with the aluminum slurry into an oven for baking for 60 minutes at 100° C., remove the ceramic substrate  1  done with the baking, coat the aluminum slurry on a second surface opposite to the first surface through the same silk-screen printing, and place the ceramic substrate  1  back into the oven and bake for 60 minutes at 100° C. 
         [0028]    4. Place the ceramic substrate  1  with the first surface and the second surface done with the printing into a tunnel furnace in a temperature range 600° C.˜750° C. for sintering in completion of the fabrication of the metal layer  21 . 
         [0029]    Steps of producing the alloy layers  22 : 
         [0030]    Fasten the ceramic substrate  1  with the sintered metal layer  21  on a thermal spray fixture. 
         [0031]    With reference to  FIG. 3 , concepts of electric arc spray are well-known and are thus merely briefly introduced here. The electric arc spray is performed by applying electric arc to melt a pair of electrically conductive wires  51  and using high-speed air flow  52  to atomize the melting pair of electrically conductive wires  51  into small metal particles. The metal particles are propelled by the high speed air flow  52  toward a work piece  53  to form a spray layer  54  on a surface of the work piece  53 . In the present embodiment, the pair of electrically conductive wires is a pair of aluminum bronze wires, and spray parameters associated with the electric arc spray include spray voltage in a range of 20˜35 V, spray current in a range of 100˜200 A, spray pressure in a range of 0.5˜0.6 MPa, wire-feeding voltage in a range of 10˜14 V, and spray thickness in a range of 20˜30 μm. Fabrication of the alloy layer  22  is completed by the electric arc spray. In the present embodiment, the alloy layer  22  of the electrode layer is formed by an alloy made from aluminum and copper. 
         [0032]    The two pins  3  are respectively welded on the alloy layers  22  and then epoxy is used to wrap up the ceramic substrate  1 , the metal layer  21 , the alloy layer  22  and a portion of the pins  3  to form the insulating layer  4 . Electrical characteristics of the finished electronic component are further tested. 
         [0033]    As shown in the following table, the pair of electrically conductive wires from the second embodiment to the fifth embodiment on the basis of the first embodiment can be a pair of wires made from different alloys, namely, silicon bronze, phosphor bronze, tin bronze, tin phosphor bronze, with different percents of metal contents. Detailed spraying steps already introduced are not repeated here. 
         [0034]    Given as an example, an aging test is performed to compare aging characteristics against high-temperature environment among all the embodiments. Test conditions for the high-temperature aging test are 125±2° C., 1000±24 hours and applied voltage VDC=385 V. Varistor voltages before and after the aging test, variation of the varistor voltage, and capacity (times) of combination wave (6 kV/3 kA) resistance are shown in the following table. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Aging test 
                   
               
             
          
           
               
                   
                   
                 Varistor 
                 Varistor 
                   
                 Combination 
               
               
                   
                   
                 voltage 
                 voltage 
                 Voltage 
                 wave 
               
               
                 Electronic 
                 Contents of 
                 before test 
                 after test 
                 variation 
                 (6 kV * 3 kA) 
               
               
                 component 
                 spray material 
                 (V1mA) 
                 (V1mA) 
                 (%) 
                 (times) 
               
               
                   
               
             
          
           
               
                 Conventional 1 
                 Conventional 
                 453 
                 432 
                 4.60% 
                 62 
               
               
                   
                 printing + silver 
               
               
                   
                 spray 
               
               
                 Conventional 2 
                 Silk-screen 
                 476 
                 441 
                 7.40% 
                 109 
               
               
                   
                 printing with 
               
               
                   
                 aluminum + 
               
               
                   
                 purple bronze 
               
               
                   
                 spray (99.90% 
               
               
                   
                 copper) 
               
               
                 First 
                 Silk-screen 
                 468 
                 453 
                 3.20% 
                 106 
               
               
                 embodiment 
                 printing with 
               
               
                   
                 aluminum + 
               
               
                   
                 aluminum 
               
               
                   
                 bronze spray 
               
               
                   
                 (7.5% aluminum + 
               
               
                   
                 remaining % 
               
               
                   
                 copper) 
               
               
                   
                 Silk-screen 
                 458 
                 449 
                 2.00% 
                 103 
               
               
                   
                 printing with 
               
               
                   
                 aluminum + 
               
               
                   
                 aluminum 
               
               
                   
                 bronze spray 
               
               
                   
                 (7.9% aluminum + 
               
               
                   
                 remaining % 
               
               
                   
                 copper) 
               
               
                   
                 Silk-screen 
                 466 
                 458 
                 1.70% 
                 107 
               
               
                   
                 printing with 
               
               
                   
                 aluminum + 
               
               
                   
                 aluminum 
               
               
                   
                 bronze spray 
               
               
                   
                 (8.4% aluminum + 
               
               
                   
                 remaining % 
               
               
                   
                 copper) 
               
               
                 Second 
                 Silk-screen 
                 485 
                 469 
                 3.30% 
                 112 
               
               
                 embodiment 
                 printing with 
               
               
                   
                 aluminum + 
               
               
                   
                 silicon bronze 
               
               
                   
                 spray (2.8% 
               
               
                   
                 silicon + 
               
               
                   
                 remaining % 
               
               
                   
                 copper) 
               
               
                   
                 Silk-screen 
                 474 
                 463 
                 2.30% 
                 109 
               
               
                   
                 printing with 
               
               
                   
                 aluminum + 
               
               
                   
                 silicon bronze 
               
               
                   
                 spray (3.2% 
               
               
                   
                 silicon + 
               
               
                   
                 remaining % 
               
               
                   
                 copper) 
               
               
                   
                 Silk-screen 
                 462 
                 457 
                 1.10% 
                 112 
               
               
                   
                 printing with 
               
               
                   
                 aluminum + 
               
               
                   
                 silicon bronze 
               
               
                   
                 spray (4.0% 
               
               
                   
                 silicon + 
               
               
                   
                 remaining % 
               
               
                   
                 copper) 
               
               
                 Third 
                 Silk-screen 
                 442 
                 436 
                 1.40% 
                 98 
               
               
                 embodiment 
                 printing with 
               
               
                   
                 aluminum + 
               
               
                   
                 phosphor bronze 
               
               
                   
                 spray (7.5% 
               
               
                   
                 phosphor + 
               
               
                   
                 remaining % 
               
               
                   
                 copper) 
               
               
                   
                 Silk-screen 
                 446 
                 439 
                 1.60% 
                 104 
               
               
                   
                 printing with 
               
               
                   
                 aluminum + 
               
               
                   
                 phosphor bronze 
               
               
                   
                 spray (8.1% 
               
               
                   
                 phosphor + 
               
               
                   
                 remaining % 
               
               
                   
                 copper) 
               
               
                   
                 Silk-screen 
                 442 
                 432 
                 2.30% 
                 111 
               
               
                   
                 printing with 
               
               
                   
                 aluminum + 
               
               
                   
                 phosphor bronze 
               
               
                   
                 spray (8.5% 
               
               
                   
                 phosphor + 
               
               
                   
                 remaining % 
               
               
                   
                 copper) 
               
               
                 Fourth 
                 Silk-screen 
                 490 
                 475 
                 3.10% 
                 110 
               
               
                 embodiment 
                 printing with 
               
               
                   
                 aluminum + tin 
               
               
                   
                 bronze spray 
               
               
                   
                 (4% tin + 
               
               
                   
                 remaining % 
               
               
                   
                 copper) 
               
               
                   
                 Silk-screen 
                 480 
                 468 
                 2.50% 
                 100 
               
               
                   
                 printing with 
               
               
                   
                 aluminum + tin 
               
               
                   
                 bronze spray 
               
               
                   
                 (5% tin + 
               
               
                   
                 remaining % 
               
               
                   
                 copper) 
               
               
                   
                 Silk-screen 
                 484 
                 475 
                 1.90% 
                 101 
               
               
                   
                 printing with 
               
               
                   
                 aluminum + tin 
               
               
                   
                 bronze spray 
               
               
                   
                 (6% tin + 
               
               
                   
                 remaining % 
               
               
                   
                 copper) 
               
               
                 Fifth 
                 Silk-screen 
                 471 
                 460 
                 2.30% 
                 113 
               
               
                 embodiment 
                 printing with 
               
               
                   
                 aluminum + tin 
               
               
                   
                 phosphor bronze 
               
               
                   
                 spray (phosphor 
               
               
                   
                 7.1%, 5.8% tin + 
               
               
                   
                 remaining % 
               
               
                   
                 copper) 
               
               
                   
               
             
          
         
       
     
         [0035]    As can be seen from the foregoing table, the electronic components with the multi-layer electrode structure produced by printing with aluminum and spraying with copper alloys wires have lower voltage variation after the aging test than the electronic component with the conventional silver printed electrode, and the voltage variation of all the embodiments is lower than 4%. The capacity (times) of combination wave resistance of the electronic components relative to that of the electronic component with the conventional silver printed electrode is increased by 40%. 
         [0036]    The shape of the multi-layer electrode in accordance with the present invention includes, but is not limited to, square-shaped, round, oval, tubular, cylindrical and conic. The types of the electronic components in accordance with the present invention may be voltage-sensitive components, gas-sensitive components, positive temperature coefficient (PTC) thermally sensitive components, negative temperature coefficient (NTC) thermally sensitive components, piezoelectric ceramic, ceramic capacitors and the like. 
         [0037]    With reference to  FIG. 4 , a preparation method for an electronic component with an alloy electrode layer in accordance with the present invention includes steps of: 
         [0038]    Step S 401 : Prepare a ceramic substrate  1  having two opposite surfaces. 
         [0039]    Step S 402 : Print a metal layer  21  on each of the two opposite surfaces of the ceramic substrate  1 . The material of the metal layer  21  is aluminum. 
         [0040]    Step S 403 : Spray an alloy layer  22  on an outer surface of each metal layer  21 . The alloy layer  22  is a copper alloy layer. Each metal layer  21  and a corresponding alloy layer  22  stacked on the metal layer  21  form an electrode layer. 
         [0041]    Step S 404 : Connect a pin  3  to each alloy layer  22 . 
         [0042]    Step S 405 : Enclose the ceramic substrate  1 , the electrode layers and a portion of each pin  3  with an insulating layer  4 . 
         [0043]    Even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only. Changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.