Abstract:
Disclosed is a protecting device for electronic circuit and the manufacturing method thereof. The device is a multi-layered structure which includes a dielectric layer and several electrode layers overlapping in the inner circumference of the substrate. After making up a whole structure, a transverse gap with an appropriate depth is formed by cutting process causing two superposed electrode layers to split into two parts facing to each other with respect to the transverse gap and also split into upper and lower parts with respect to the dielectric layer. With this structure, the gap can serve as a protecting element for electrostatic discharge (ESD) or other elements by filling different materials and with the aid of the dielectric layer of appropriate thickness thereby the whole structure can be used to perform surge protection for various electronic circuits.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a protecting device for electronic circuit and manufacturing method thereof, especially, to a protecting device for an electronic circuit having electrode layers formed on a substrate extending from the two sides of the substrate to its central part with a dielectric layer is interposed therebetween, and a transverse gap is formed by cutting process resulting in a structure that the dielectric layer divides the electrode layers into upper and lower parts and the two electrode parts are respectively separated by the transverse gap. Thus, an electro-static discharge path are formed between the upper and lower electrodes so as to obtain the circuit elements having functions of protecting electronic circuit from a surge voltage. 
         [0003]    2. Description of the Prior Art 
         [0004]    It is known to public that capacitor, resistor, and inductor are three indispensable passive circuit elements of an electronic device. The capacitor, which is formed by intercalating with a dielectric substance between two conducting materials, performs the function of storing electrical energy, and serves as a filter, modulator or oscillator. The capacitor is classified in the categories as a fixed, variable and crystal capacitor by different dielectric substances. 
         [0005]    The resistor performs the function of regulating the circuit voltage and current. The inductor serves to filter out the noise of the current so as to eliminate the magnetic interference. Three of them are associated one another to control the electronic circuits in the field of information, communication, electronic appliances, and other electronic industries. 
         [0006]    In the circuit of electronic communication, an abnormal voltage caused by the electro-static discharge (ESD) may cause a severe damage to the components of the electronic equipment such as a substrate and which further extends to the loss of the whole electronic product. Generally, the electronic apparatus employs the combination of said passive elements (resistor, capacitor, inductor) to protect the electronic products from the attack of the surge voltage arising from ESD. 
         [0007]    Among those ESD protecting devices are Transient Voltage Suppress Diode (TVSD), Multi-Layer Varistor (MLV) etc, while the means for protection of the electronic circuit are shielding, gap discharge, and charging and discharging functions of capacitor etc. 
         [0008]    For protecting the electronic apparatus from ESD attack, in a PCB layout, a gap discharge electrode shown in  FIG. 1A  is provided directly at the place where the ESD protection is needed, and this is included simultaneously during the fabrication of a PCB so as to lower the production cost. 
         [0009]    In  FIG. 1A , on a PCB substrate  10 , a circuit  11  on which an acute discharge electrode  12   a  is formed to serve as an ESD protection means, an a gap  13  is interposed between the discharge electrode  12   a  and the other grounded acute discharge electrode  12   b.    
         [0010]    Referring to  FIG. 1B  together with  FIG. 1A , when an abnormal voltage induced by a surge  15  appears at a circuit  11  with an energy represented by ESD curve  16 , The break down occurs in the gap  13  between the electrodes  12   a  and  12   b , therefore the amplitude of the abnormal voltage should be limited in an acceptable range as shown in curve  17  to protect the circuit  11 . 
         [0011]    However, after a careful study, the aforesaid protecting aspect is deemed incomplete as it has the following shortcomings: 
         [0012]    (1) The gap  13  which is formed by mechanical cutting can not achieve the necessary scale sufficient to protect the surge of ESD. 
         [0013]    (2) As the width of the gap  13  can not reach the required scale, the break down voltage will become high and then is not possible to protect the electronic circuit and device. 
         [0014]    For these defects noticeable on the prior art, an improvement is seriously required. The inventor has dedicated great efforts for years to studying and improving these defects and come up with a novel protecting device for electronic circuit and manufacturing method thereof as provided in this invention. 
       SUMMARY OF THE INVENTION 
       [0015]    Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a protecting device for electronic circuit and manufacturing method thereof such that the electronic circuit can be protected from being damaged due to a surge voltage. 
         [0016]    In order to accomplish the object, there is provided a method of manufacturing a protecting device for electronic circuit to form a stacked structure on a substrate, and to form a dielectric layer thereof using the printing process, and cutting a gap thereof. By utilizing materials of different properties for the dielectric layer, a protecting device can be produced which is able to protect an electronic circuit involving various kinds of resistor, capacitor, and inductor. While the gap may become a protecting element for ESD. by filling a piezoelectrically sensitive material or various gases etc. therein, and then to serve as an element having function of preventing the electronic apparatus from damage by ESD. 
         [0017]    According to the protecting device for electronic circuit and manufacturing method of present invention, a multi-layered structure is formed which includes a dielectric layer and severed electrode layers overlapping one another in the inner circumference of the substrate. After making up a whole structure, a transverse gap with an appropriate depth is formed by cutting process which causes two superposed electrode layers to split into two parts facing to each other with respect to the transverse gap, and also split into upper and lower parts with respect to the dielectric layer. With this structure, the gap can serve as a protecting element for ESD by filling different kinds of materials and with the aid of the dielectric layer of appropriate thickness thereby the whole structure can be used to perform protection for various electronic circuits. 
         [0018]    According to another embodiment of the protecting device for electronic circuit and manufacturing method of present invention, after the electrode layers are formed, a plurality of separated monomer electrodes along the same direction are obtained. Then a transverse gap is formed by the cutting process so as to make each of the said monomer electrode becomes a pair of electrodes having electrodes to face against one another frontward and backward, upward and downward due to the formed transverse gap. Thus a matrix configuration is established in which the plurality of horizontally and vertically arrayed separate monomer electrodes are include thereby forming an arrayed protecting device for ESD. 
         [0019]    According to the protecting device for electronic circuit and manufacturing method of present invention, the distance between the upper and the lower electrode layers is determined by the thickness of the dielectric layer formed by printing process. Accordingly, the high difference between the upper electrode layer and the lower electrode layer can be controlled as small as possible so as to prevent an unappropriate breakdown voltage caused by an improper gap width. 
         [0020]    According to the protecting device for electronic circuit and manufacturing method thereof, the structure of the protecting device is made very simple while having versatile performance, and can be made up with a low production cost. 
         [0021]    The above aspects, and other features and advantages of the present invention will become more apparent after a reading of the following detailed description when taken in conjunction with the drawings, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1A  is a schematic view showing the structure of a conventional gap discharging device; 
           [0023]      FIG. 1B  shows discharge voltage suppressing curve according to the conventional techniques; 
           [0024]      FIG. 2A through 2F  are the plane and side views for illustration of the manufacturing method according to the present invention; 
           [0025]      FIG. 3  is an exploded three dimensional view illustrating the manufacturing method according to a second embodiment of the present invention; 
           [0026]      FIG. 4  is a three dimensional assembly view according to a second embodiment of the present invention; 
           [0027]      FIG. 5  is a cross sectional view according to a second embodiment of the present invention; 
           [0028]      FIG. 6  is a cross sectional view according to a third embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0029]    As shown in  FIG. 2A through 2F , the manufacturing method of the protecting device for electronic circuit of present invention includes the following steps of: 
         [0030]    1. Forming a glass foundation  22  on the surface of a ceramic substrate  21 , wherein the glass foundation  22  is positioned on the central part of the ceramic substrate  21  to avoid contacting it edges with that of the ceramic substrate  21  (please refer to  FIG. 2A ); 
         [0031]    2. Forming a first electrode layer  23  to cover the glass foundation  22 , one side of the first electrode layer  23  is connected with a first side of the ceramic substrate  21 , while the other side thereof is partially covering the upper surface of the glass foundation  22  (please refer to  FIG. 2B ); 
         [0032]    3. Forming a dielectric layer  24  having the area approximately equal to that of the glass foundation  22  to cover the first electrode layer  23  at a position right on the glass foundation  22 , one side of the dielectric layer  24  is connected to one side of the glass foundation  22  (please refer to  FIG. 2C ); 
         [0033]    4. Forming a second electrode layer  25  to cover the dielectric layer  24 , one side of the second electrode layer  25  is connected to a second side of the ceramic substrate  21 , while the other side of the second electrode layer  25  is partially covering the upper surface of the dielectric layer  24  (please refer to  FIG. 2D ); 
         [0034]    5. Forming a protecting glass layer  26  to cover the second electrode layer  25 , one side of the protecting glass layer  26  is connected to the dielectric layer  24  (please refer to  FIG. 2E ); 
         [0035]    6. Finally, by cutting process with a diamond blade or by laser trimming process to cut out in the transverse direction a gap  3  along the overlapped portion of the first electrode layer  23 , the dielectric layer  24  and the second electrode layer  25 . The transverse gap  3  passes through the protecting glass layer  26 , the second electrode layer  25 , the dielectric layer  24 , the first electrode layer  23  and the glass foundation  22  such that the aforesaid five layers are each split into two front and rear parts facing to each other (please refer to  FIG. 2F ); 
         [0036]    With this structure, the thickness of the dielectric layer  24  intercalated between the first and second electrode layers  23 ,  25  serves a discharge gap so that the whole structure becomes a surge protecting device. Further more, the first electrode layer  23  and the second electrode layer  25  are respectively split into a first front electrode layer  231  facing to a first rear electrode layer  232 , and a second front electrode layer  251  also facing to a second rear electrode layer  252  by the transverse gap  3 . Then by filling the gap  3  with a piezoelectrics or gases (for example: an idle gas of He) of different properties, a FSD protecting device of different trigger voltage will result between the first front and the first rear electrode layers  231 ,  232 , and between the second front and the second rear electrode layers  251 ,  252 . 
         [0037]    Referring to  FIG. 3  through  FIG. 5 , the manufacturing method of the protecting device for electronic circuit according to another embodiment of the present invention includes the following steps of: 
         [0038]    1. Preparing a ceramic substrate  4 ; 
         [0039]    2. Forming a buffer layer  41  on the central part of the ceramic substrate  4  with a shape of rectangular parallelepiped elongated in the same direction with the ceramic substrate  4 ; 
         [0040]    3. Forming a π shaped electrode material layer  42  having the same length with that of the ceramic substrate  4  to cover the buffer layer  41 , the two ends thereof are formed into taller billets  421 ,  422  respectively positioned on the right and left sides of the buffer layer  41  and connected to the upper side of the ceramic substrate  4 , the upper end thereof is formed into a flat surface  423  protruded sideward to form a cross bar like figure; 
         [0041]    4. Forming a dielectric layer  43  to cover the electrode material layer  42 ; 
         [0042]    5. Forming an electrode conductor layer  44  to cover the dielectric layer  42 , the electrode conductor layer  44 , which is made of a conducting material consisting of Pd or Pt, is covered partly on the electrode material layer  42 . Several separately disposed monomer electrodes  441 ,  442 ,  443 ,  444  are provided along the longitudinal direction of the ceramic substrate  4 , these monomer electrodes  441 ,  442 ,  443 ,  444  are formed at the upper and the lower sides so as to respectively located on the upper and lower sides of the dielectric layer  43 , the electrode material layer  42  and the buffer layer  41  thereby enabling their upper and lower sides to respectively connect with the upper and lower sides  4 A and  4 B of the ceramic substrate  4 ; 
         [0043]    6. Then afterwards, forming a protecting layer to cover the electrode conductor layer  44 ; 
         [0044]    7. Finally, by the cutting process using a diamond blade or the laser trimming process, a transverse gap  5  is formed along the central part of the structure which passes through the electrode conductor layer  44 , the dielectric layer  43 , the electrode material layer  42 , and partially pierces deeply into the buffer layer  41  so as to split the said layers  44 ,  43  and  42  into two (front and rear) parts facing to each other. Especially for the electrode conductor layer  44 , it is divided into symmetrically separated front and rear monomer electrodes  441 ,  442 ,  443 ,  444  and lower monomer electrodes  44   a ,  44   b ,  44   c ,  44   d.    
         [0045]    With this structure obtained by the process described above, the dielectric layer  43 , which is intercalated between the electrode conductor layer  44  and the electrode material layer  42 , can be made by the thick film printing process to control its thickness as thin as possible, and further by employing various kinds of dielectric substance, and filling the transverse gap  5  with a piezoelectrically sensitive material, a perfect ESD protecting device can be obtained to protect the electronic circuit containing register, inductor, capacitor of different values. 
         [0046]    The protecting device formed of plural monomer electrodes arrayed in a matrix pattern can be provided with a plurality of pins for connection with several circuits when used on a circuit board, while the billets  421 ,  422  formed at the two sides of the electrode material layer  42  can be used to serve as ground terminals. By doing this way, because of the fact that the dielectric layer  42  which will affect the characteristics of resistor and capacitor is able to be well controlled so that the conventional disadvantages of troubles to connect individually different protecting devices for different electronic circuits can be rectified, and through filling the gap  5  with a material to avoid lowering break down voltage that results in improving the surge protection and stability of the protected electronic circuit. 
         [0047]    With the above mentioned steps to manufacture the protecting device, the electronic circuit will sure be well protected from the surge attack. 
         [0048]    Referring to  FIG. 6 , according to one more embodiment of the present invention, a buffer layer  61 . a first electrode layer  62 , a dielectric layer  63 , a second electrode layer  64 , a protecting layer  65 , a first insulation layer  66  and a second insulation layer  67  are sequentially formed on a substrate. By cutting process, a transverse gap  68  is formed to split the above layers into two parts facing to each other. Different gases and piezoelectrically sensitive materials are filled into the gap  68  by the technique of air discharging, so as to obtain the structure on the substrate having properties of the ESD protection. Meanwhile, by the thick film printing process, a first electrode layer  71 , a second electrode layer  72 , a dielectric layer  73 , a protecting layer  74 , a first insulation layer  75  and a second insulation layer  76  can be formed on the reverse surface of the substrate so as to obtain a similar structure as the former one to perform ESD protection. Afterward, by electroplating process, two external electrodes  81 ,  82  are provided on outside of the structure, and further forms a two-face protecting device for the electronic circuit by making an electrical connection between the upper and lower structures. 
         [0049]    In the embodiment shown in  FIG. 6 , the upper part of the substrate may serve as an ESD protecting device while the lower part thereof may serve as a RC or EMI circuit therefore a two-functional structure, for example, a multi-functional device having ESD protection function and RC circuit, or, a multi-functional device having ESD protection function and EMI circuit, is realized. 
         [0050]    The above mentioned resistor and capacitor arrayed in matrix pattern as a whole structure is able to play a roll of a versatile protecting device applicable to all electronic products so as to reduce the cost of circuit construction. It fulfills the requirements of light, thin, short and compact especially suitable for the high frequency or sophisticated electronic devices. 
         [0051]    With multi-layered dielectric and electrode unit associated with a gap filled with a certain material, a structure containing various capacitors and resistors can be constructed to meet various requirement about abnormal voltage protection only varying the material filled in the gap. 
         [0052]    The outstanding features of the present invention are as follows: 
         [0053]    1. The gap width can be easily controlled at 10˜30 μm through diamond blade cutting or the laser trimming. 
         [0054]    2. The vertically stacked structure facilitates controlling the gap width at 5˜25 μm through printing process. 
         [0055]    3. Extremely minimized gap with aids to effectively bring down the break down voltage so as to improve the ESD protection for the low voltage device using a simply constructed protecting structure. 
         [0056]    The above aspects, and other features and advantages of the present invention will become more apparent after a reading of the following detailed description when taken in conjunction with the drawings.