Abstract:
A conductive layer containing gold as a main component is formed on the upper surface of an insulating base. A gap is formed on the conductive layer. A plurality of leader electrodes are formed to oppose one another via the gap. An excess voltage protection material layer is formed to cover some parts of the respective leader electrodes and the gap, so as to obtain an anti-static part. This method enables an accurate formation of a narrow gasp. Thus, it is possible to manufacture an anti-static part having a low peak voltage, stable suppression characteristic of electrostatic discharge (ESD), and a high sulfide resistance.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an electrostatic discharge (ESD) protector for protecting an electronic device from static electricity and to a method for manufacturing the protector. 
       BACKGROUND ART 
       [0002]    Electronic devices, such as portable telephones, have recently had small sizes and high performance, and required electronic components used in the electronic devices to have small sizes. These electronic devices and the electronic components have had low withstanding voltages accordingly. Upon being touched by a human body, an electrostatic pulse applies, to an electronic circuit of an electronic device, a high voltage ranging from several hundred volts to several kilovolts and having a rising time shorter than one nanosecond, and may break an electronic component. 
         [0003]    In order to protect the electronic component from breaking, an electrostatic discharge (ESD) protector is connected between a line receiving the electrostatic pulse and the ground. A signal transmission line has had a high transmission speed higher than several hundred megabits per second. Upon having a large stray capacitance, the ESD protector may degrade signal quality. In order to protect an electronic component operating at a high transmission speed higher than several hundred megabits per second from breaking, the ESD protector is required to have a capacitance equal to or smaller than 1 pF. 
         [0004]    Each of Patent Documents 1 and 2 discloses a conventional ESD protector including an overvoltage protective material filling a gap between two electrodes facing each other. When an excessive voltage caused by static electricity is applied between the electrodes, a current flows between conductive particles or semiconductor particles dispersed in the overvoltage protective material. Thus, the ESD protector allows the current flowing due to the excessive voltage to bypass the electronic component and flow to the ground. 
         [0005]    In the conventional ESD protector, if the applied voltage is higher than 15 kV, an electrostatic discharge generates a large repulsive force, and may chip a protective resin layer covering the overvoltage protective material and cause the protector to break. 
         [0006]    In order to lower a peak voltage applied to the ESD protector and improve characteristics of suppressing electrostatic discharge, it is required that a gap is precisely narrow. In the conventional ESD protector disclosed in Patent Document 1, the gap between the electrodes is formed by a photolithography technique and an etching process based mainly on chemical reactions. This method may cause the gap to have a width smaller than a predetermined width due to foreign matter attached to the gap at light exposure, or insufficient development, or insufficient etching. 
         [0007]    The conventional ESD protector disclosed in Patent Document 1 is provided by forming electrodes and functional elements on an insulating substrate having a sheet shape, and then, dividing the insulating substrate into strips or separate pieces by a dicing technique. This dividing process may produce burrs on the divided surfaces, thus preventing ESD protectors from having small sizes stably. 
         [0008]    In the conventional ESD protector disclosed in Patent Document 2, a gap is formed by cutting an electrode with laser. Since the electrode has a thickness ranging approximately from 10 to 20 μm, a high laser output is necessary for reliably cutting the electrode to form the gap precisely, thus preventing the gap from having a narrow width precisely. 
         [0009]    Patent Document 1: JP 2002-538601A 
         [0010]    Patent Document 2: JP 2002-015831A 
       SUMMARY OF THE INVENTION 
       [0011]    A conductive layer mainly made of gold is formed on an upper surface of an insulating substrate. Plural electrodes facing each other via a gap is formed by forming the gap in the conductive layer. An overvoltage protective layer covering the gap and a portion of each of the plurality of electrodes is formed. 
         [0012]    This method can provide the gap with a narrow width precisely, and thereby, provide an electrostatic (ESD) protector with a low peak voltage, stable characteristics of suppressing electrostatic discharge, and a high resistance to sulfidation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1A  is a perspective view of an electrostatic discharge (ESD) protector in accordance with Exemplary Embodiment 1 of the present invention. 
           [0014]      FIG. 1B  is a sectional view of the ESD protector at line  1 B- 1 B shown in  FIG. 1A . 
           [0015]      FIG. 1C  is a schematic view for illustrating an operation of the ESD protector in accordance with Embodiment 1. 
           [0016]      FIG. 2  is a perspective view of the ESD protector for illustrating a method for manufacturing the ESD protector in accordance with Embodiment 1. 
           [0017]      FIG. 3  is a perspective view of the ESD protector for illustrating a method for manufacturing the ESD protector in accordance with Embodiment 1. 
           [0018]      FIG. 4  is a perspective view of the ESD protector for illustrating a method for manufacturing the ESD protector in accordance with Embodiment 1. 
           [0019]      FIG. 5  is a perspective view of the ESD protector for illustrating a method for manufacturing the ESD protector in accordance with Embodiment 1. 
           [0020]      FIG. 6  is a schematic diagram for illustrating a method for conducting an electrostatic test on the ESD protector in accordance with Embodiment 1. 
           [0021]      FIG. 7  shows results of the electrostatic test on the ESD protector in accordance with Embodiment 1. 
           [0022]      FIG. 8  shows results of the electrostatic test on the ESD protector in accordance with Embodiment 1. 
           [0023]      FIG. 9  shows results of the electrostatic test on the ESD protector in accordance with Embodiment 1. 
           [0024]      FIG. 10  is a sectional view of an ESD protector in accordance with Exemplary Embodiment 2 of the invention. 
           [0025]      FIG. 11  is a perspective view of the ESD protector for illustrating a method for manufacturing the ESD protector in accordance with Embodiment 2. 
           [0026]      FIG. 12  is a perspective view of the ESD protector for illustrating a method for manufacturing the ESD protector in accordance with Embodiment 2. 
           [0027]      FIG. 13  is a perspective view of the ESD protector for illustrating a method for manufacturing the ESD protector in accordance with Embodiment 2. 
           [0028]      FIG. 14  is a perspective view of the ESD protector for illustrating a method for manufacturing the ESD protector in accordance with Embodiment 2. 
           [0029]      FIG. 15  is a perspective view of the ESD protector for illustrating a method for manufacturing the ESD protector in accordance with Embodiment 2. 
           [0030]      FIG. 16  is a perspective view of the ESD protector for illustrating a method for manufacturing the ESD protector in accordance with Embodiment 2. 
           [0031]      FIG. 17  is a perspective view of the ESD protector for illustrating a method for manufacturing the ESD protector in accordance with Embodiment 2. 
           [0032]      FIG. 18  is a perspective view of the ESD protector in accordance with Embodiment 2. 
           [0033]      FIG. 19A  is a top view of an ESD protector for illustrating a method for manufacturing the ESD protector in accordance with Exemplary Embodiment 3 of the invention. 
           [0034]      FIG. 19B  is a sectional view of the ESD protector at line  19 B- 19 B shown in  FIG. 19A . 
           [0035]      FIG. 19C  is a top view of the ESD protector for illustrating the method for manufacturing the ESD protector in accordance with Embodiment 3. 
           [0036]      FIG. 19D  is a sectional view of the ESD protector at line  19 C- 19 D shown in of  FIG. 19C . 
           [0037]      FIG. 19E  is a top view of the ESD protector for illustrating the method for manufacturing the ESD protector in accordance with Embodiment 3. 
           [0038]      FIG. 19F  is a sectional view of the ESD protector at line  19 F- 19 F shown in  FIG. 19E . 
           [0039]      FIG. 20A  is a top view of the ESD protector for illustrating the method for manufacturing the ESD protector in accordance with Embodiment 3. 
           [0040]      FIG. 20B  is a sectional view of the ESD protector at line  20 B- 20 B shown in  FIG. 20A . 
           [0041]      FIG. 20C  is a top view of the ESD protector for illustrating the method for manufacturing the ESD protector in accordance with Embodiment 3. 
           [0042]      FIG. 20D  is a sectional view of the ESD protector at line  20 D- 2 D shown in  FIG. 20C . 
           [0043]      FIG. 20E  is a top view of the ESD protector for illustrating the method for manufacturing the ESD protector in accordance with Embodiment 3. 
           [0044]      FIG. 20F  is a sectional view of the ESD protector at line  20 E- 20 F shown in  FIG. 20E . 
           [0045]      FIG. 21A  is a bottom view of the ESD protector for illustrating the method for manufacturing the ESD protector in accordance with Embodiment 3. 
           [0046]      FIG. 21B  is a sectional view of the ESD protector at line  21 B- 21 B shown in  FIG. 21A . 
           [0047]      FIG. 21C  is a top view of the ESD protector for illustrating the method for manufacturing the ESD protector in accordance with Embodiment 3. 
           [0048]      FIG. 21D  is a sectional view of the ESD protector at line  21 D- 21 D shown in  FIG. 21C . 
           [0049]      FIG. 21E  is a top view of the ED protector for illustrating the method for manufacturing the ESD protector in accordance with Embodiment 3. 
           [0050]      FIG. 21F  is a sectional view of the ESD protector at line  21 F- 21 F shown in  FIG. 21E . 
           [0051]      FIG. 22A  is a top view of the ESD protector for illustrating the method for manufacturing the ESD protector in accordance with Embodiment 3. 
           [0052]      FIG. 22B  is a sectional view of the ESD protector at line  22 B- 22 B shown in  FIG. 22A . 
           [0053]      FIG. 22C  is a top view of the ESD protector for illustrating the method for manufacturing the ESD protector in accordance with Embodiment 3. 
           [0054]      FIG. 22D  is a sectional view of the ESD protector at line  22 D- 22 D shown in  FIG. 22C . 
           [0055]      FIG. 22E  is a top view of the ESD protector for illustrating the method for manufacturing the ESD protector in accordance with Embodiment 3. 
           [0056]      FIG. 22F  is a sectional view of the ESD protector at line  22 F- 22 F shown in  FIG. 22E . 
       
    
    
     REFERENCE NUMERALS 
       [0000]    
       
           1  Insulating Substrate 
           2 A Electrode 
           2 B Electrode 
           2 C Gap 
           3  Overvoltage Protective Layer 
           4  Intermediate Layer 
           5  Protective Resin Layer 
           101  Insulating Substrate 
           102  Conductive Layer 
           102 A Electrode 
           102 B Electrode 
           10 C Gap 
           104  Overvoltage Protective Layer 
           105  Intermediate Layer 
           106  Protective Resin Layer 
           201  First Dividing Line 
           202  Second Dividing Line 
           203  Insulating Substrate 
           204  Conductive Layer 
           206  Gap 
           205  Resist 
           208  Upper Electrode 
           209  Lower Electrode 
           209 A First Portion of Lower Electrode 
           209 B Second Portion of Lower Electrode 
           210  Overvoltage Protective Layer 
           211  Intermediate Layer 
           212  Protective Resin Layer 
           213  Edge Electrode 
           214  Nickel-Plated Layer 
           215  Tin-Plated Layer 
           1203  Insulating Substrate Strip 
       
     
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Exemplary Embodiment 1 
       [0089]      FIG. 1A  is a perspective view of electrostatic discharge (ESD) protector  1001  in accordance with Exemplary Embodiment 1 of the present invention. 
         [0090]      FIG. 1B  is a sectional view of ESD protector  1001  at line  1 B- 1 B shown in  FIG. 1A . Insulating substrate  1  is made of dielectric ceramic, such as alumina, having a low dielectric constant smaller than 50, preferably smaller than 10. Electrodes  2 A and  2 B are provided on surface (upper surface)  1 A of insulating substrate  1 . Electrode  2 A faces electrode  2 B across gap  2 C having a predetermined interval. Overvoltage protective layer  3  covers portion  12 A of electrode  2 A, portion  12 B of electrode  2 B, and gap  2 C. Overvoltage protective layer  3  contains insulating resin, such as silicone resin, and conductive particles, such as metal powder, dispersed in the insulating resin. Intermediate layer  4  is provided on overvoltage protective layer  3  so as to cover overvoltage protective layer  3 . The intermediate layer contains insulating resin, such as silicone resin, and insulating powder dispersed in the insulating resin. Protective resin layer  5  is provided on intermediate layer  4  so as to completely cover intermediate layer  4 . Terminal electrodes  6 A and  6 B connected to electrodes  2 A and  2 B are provided at both ends of insulating substrate  1 , respectively. 
         [0091]    An operation of ESD protector  1001  will be described below.  FIG. 1C  is a schematic diagram illustrating the operation of ESD protector  1001 . Terminal electrode  6 A of ESD protector  1001  is connected to terminal  2001 A of electronic component  2001 , and terminal electrode  6 B of the ESD protector is connected to ground  2002 . When a voltage applied to terminal  2001 A of electronic component  2001 , i.e. applied between terminal electrodes  6 A and  6 B, is lower than a predetermined rated voltage, the insulating resin of overvoltage protective layer  3  provided in gap  2 C insulates between electrode  2 A and  2 B, thus electrically insulating and opening between terminal electrodes  6 A and  6 B. When a high voltage caused by, e.g. an electrostatic pulse is applied between terminal electrodes  6 A and  6 B, a discharge current flows between the conductive particles dispersed in the insulating resin of overvoltage protective layer  3 , thus drastically decreasing impedance between terminal electrodes  6 A and  6 B. The current generated by the high voltage accordingly flows to ground  2002  via ESD protector  1001 , as the discharge current in ESD protector  1001 . The ESD protector allows the current generated by an abnormal voltage, such as an electrostatic pulse or surge, to bypass electronic component  2001  and flow to ground  2002 . 
         [0092]    A method for manufacturing ESD protector  1001  will be described below.  FIGS. 2 to 5  are perspective views of ESD protector  1001  for illustrating the method for manufacturing ESD protector  1001 . 
         [0093]    First, dielectric ceramic material, such as alumina, having a low dielectric constant smaller than 50, preferably smaller than 10. is fired at a temperature ranging from 900 to 1700° C., thereby providing insulating substrate  1 . Insulating substrate  1  has rectangular surface  1 A. Surface  1 A has long sides  11 B and  1 C facing each other, and short sides  1 D and  1 E being shorter than long sides  11 B and  1 C and facing each other. As shown in  FIG. 2 , metal of Cu, Ag, Au, Cr, Ni, Al, Pd, or an alloy thereof is provided on surface  1 A of insulating substrate  1  by a method, such as sputtering, vapor deposition, printing, or firing, to form electrodes  2 A and  2 B. Electrodes  2 A and  2 B facing each other via gap  2 C have thicknesses ranging from 10 nm to 20 μm. Electrodes  2 A and  2 B extend along long sides  11 B and  1 C of surface  1 A of insulating substrate  1 , respectively. According to Embodiment 1, length L of each of long sides  11 B and  1 C is 2.0 mm, and length W of each of short sides  1 D and  1 E is 1.2 mm. When the metal is provided on surface  1 A to form electrodes  2 A and  2 B, margin  1 F is provided at both ends of each of long sides  11 B and  1 C. According to Embodiment 1, length L 2  of margin  1 F is 0.05 mm. Thus, if each of long sides  11 B and  1 C has length L (mm)=2.0 mm, length L 1  (mm) of each of electrodes  2 A and  2 B along long sides  11 B and  1 C is 1.8 mm. Electrodes  2 A and  2 B facing each other via gap  2 C may be formed by providing the metal on surface  1 A with using a metal mask or a resist mask. 
         [0094]    Alternatively, metal including a portion to be gap  2 C is provided on surface  1 A to form electrodes  2 A and  2 B connected to each other, and then, the metal is etched by a photolithography technique to form gap  2 C. Alternatively, metal including a portion to be gap  2 C is provided on surface  1 A to form electrodes  2 A and  2 B connected to each other, and then, the metal is cut with laser to form gap  2 C. Overvoltage protective layer  3  is more effective when gap  2 C is narrower. The interval of gap  2 C may be preferably equal to or smaller than 50 μm. In order to control gap  2 C to provide gap  2 C with the narrow interval, gap  2 C may be preferably formed by photolithography technique or laser. 
         [0095]    Next, overvoltage protective layer  3  is formed. Metal powder containing spherical particles having an average particle diameter ranging from 0.3 to 10 μm and being made of Ni, Al, Ag, Pd, or Cu is mixed and kneaded with silicone resin, such as methyl silicone resin, and an organic solvent with a three-roll mill to disperse the power in the resin and the solvent, thereby providing overvoltage protective material paste. As shown in  FIG. 3 , this overvoltage protective material paste is applied onto portion  12 A of electrode  2 A, portion  12 B of electrode  2 B, and gap  2 C to have a thickness ranging from 5 to 50 μm by screen printing, and dried at a temperature of 150° C. for a time ranging from 5 to 15 minutes, thereby providing overvoltage protective layer  3 . 
         [0096]    Next, intermediate layer  4  is formed. Insulating powder having an average particle diameter ranging from 0.3 to 10 μm and being made of Al 2 O 3 , SiO 2 , MgO, or composite oxide thereof is prepared. This insulating powder is mixed and kneaded with silicone resin, such as methyl silicone resin, and organic solvent with a three-roll mill to disperse the insulating particles in the resin and the solvent, thereby providing insulating paste. As shown in  FIG. 4 , this insulating paste is applied onto overvoltage protective layer  3  to cover overvoltage protective layer  3 , particularly to completely cover a portion of overvoltage protective layer  3  over gap  2 C, and to have a thickness ranging from 5 to 50 μm by screen printing. The applied insulating paste is dried at a temperature of 150° C. for a time ranging from 5 to 15 minutes, thereby providing intermediate layer  4 . In order to provide a sufficient electrostatic discharge protection, the sum of the thicknesses of overvoltage protective layer  3  and intermediate layer  4  is determined to be equal to or larger than 30 μm. If overvoltage protective layer  3  has a large thickness to provide a predetermined electrostatic discharge protection, intermediate layer  4  may not necessarily be provided. 
         [0097]    Next, protective resin layer  5  is formed. As shown in  FIG. 5 , a resin paste made of epoxy resin or phenol resin is printed by screen printing to completely cover intermediate layer  4  and overvoltage protective layer  3  and to expose ends  22 A and  22 B of electrodes  2 A and  2 B. The applied resin paste is dried at a temperature of 150° C. for a time ranging from 5 to 15 minutes, and then, cured at a temperature ranging from 150 to 200° C. for a time ranging from 15 to 60 minutes, thereby providing protective resin layer  5 . 
         [0098]    Next, as shown in  FIG. 1A , conductive paste containing powder of metal, such as Ag, and a curing resin, such as epoxy resin, is applied onto ends  22 A and  22 B of electrodes  2 A and  2 B to form terminal electrodes  6 A and  6 B, respectively, thereby providing ESD protector  1001 . 
         [0099]    The following test was conducted on samples of ESD protector  1001  fabricated by the above method.  FIG. 6  is a schematic diagram illustrating the method for testing the samples. While terminal electrode  6 B of ESD protector  1001  was grounded to ground  8 , static-electricity generator  10  contacted terminal  9  connected to terminal electrode  6 A to apply an electrostatic pulse. Electrostatic generator  10  included discharge resistance R 1  of 330Ω and discharge capacitance C 1  of 150 pF. 
         [0100]    Five types of samples of ESD protector  1001  were fabricated by the above method so that protective resin layer  5  of the samples after drying had different thicknesses ranging from 15 μm to 35 μm by 5 μm steps. Thirty pieces were fabricated for each type. The above test is conducted on these samples. An electrostatic pulse having a voltage changing from 10 kV to 30 kV by 5 kV steps was applied to each samples of ESD protector  1001 .  FIG. 7  shows the number of broken pieces samples including chipped protective resin layers  5  out of the 30 pieces of each type. 
         [0101]    As shown in  FIG. 7 , some of the samples including protective resin layers  5  having a thickness of 15 μm broke at voltages equal to or higher than 15 kV. The samples having protective resin layers  5  having a thickness of 20 μm did not break even at a voltage of 15 kV. This result shows that protective resin layer  5  has a thickness equal to or larger than 20 μm, in order not to break at a voltage of 15 kV, which exceeds the maximum level defined in the IEC-61000 standard. 
         [0102]    As shown in  FIG. 7 , in order not to be broken at voltages higher than the above voltage, protective resin layer  5  has a thickness equal to or larger than 35 μm. The upper limit of the thickness of protective resin layer  5  is determined by the dimensions of ESD protector  1001  and the upper limit of the thickness of application provided in one printing operation. From this point of view, the thickness of protective resin layer  5  may preferably be 60 μm. 
         [0103]    Thirty pieces of a comparative example of the ESD protector including electrodes  2 A and  2 B extending along short sides  1 D and  1 E of insulating substrate  1 , respectively, were fabricated.  FIG. 8  shows the number of pieces having protective resin layers  5  broken out of the 30 pieces of the comparative example and 30 pieces of ESD protector  1001  according to Embodiment 1. The samples of the comparative example and Embodiment 1 included protective resin layer  5  having a thickness of 35 μm. 
         [0104]    As shown in  FIG. 8 , some of the samples of the comparative example include the protective resin layers chipped by the repulsive force of electrostatic discharge at voltages equal to or higher than 20 kV. In contrast, no sample of ESD protector  1001  was broken even at a high voltage of 30 kV. 
         [0105]    In ESD protector  1001  of Embodiment 1, electrodes  2 A and  2 B extend along long sides  11 B and  1 C, respectively, of insulating substrate  1 , and the thickness of protective resin layer  5  is equal to or larger than 20 μm, preferably larger than 35 μm. This structure has a larger discharge area in gap  2 C covered with overvoltage protective layer  3  when an electrostatic pulse is applied. Further, protective resin layer  5  is thick so that layer  5  can ensure a high physical breaking strength. Thus ESD protector  101  prevents protective resin layer  5  from breaking even if a high-voltage electrostatic pulse is applied. 
         [0106]    When a high-voltage electrostatic pulse is applied, discharge sparks occur between the metal particles in overvoltage protective layer  3 . As the applied voltage increases, the discharge sparks increase, thus breaking intermediate layer  4  and protective resin layer  5 . Intermediate layer  4  prevents insulation property of protective resin layer  5  from deteriorating, and mainly contains resin, such as methyl silicone resin, having side chains of small hydrocarbon radical out of silicone resins. Thus, intermediate layer  4  has a relatively low physical breaking strength. Protective resin layer  5  is made of resin, such as epoxy resin and phenol resin, having a relatively high physical breaking strength, and has a thickness equal to or larger than 20 μm, preferably larger than 35 μm. Electrodes  2 A and  2 B extend along long sides  11 B and  1 C, respectively, of insulating substrate  1 , and allows gap  2 C to be substantially parallel to long sides  11 B and  1 C of insulating substrate  1 . This structure can increase the physical breaking strength of electrodes  2 A and  2 B against a bending stress. 
         [0107]    30 pieces of samples were fabricated for each of four different types of comparative examples of ESD protector  1001 . In these four types, the length W of each of short sides  1 D and  1 E of insulating substrate  1  was 1.1 mm, and the length L of each of long sides  11 B and  1 C ranged from 1.4 mm to 2.0 mm by 0.2 mm steps.  FIG. 9  shows the results of an electrostatic test on these samples. In these samples, electrodes  2 A and  2 B extend along long sides  11 B and  1 C, respectively, of insulating substrate  1 . The length L 2  of margin  1 F from each of both ends of insulating substrate  1  along long sides  11 B and  1 C need be equal to or larger than 0.05 mm. In each of these samples, the length L 2  of each margin  1 F was 0.1 mm, and the width L 1  of each of electrodes  2 A and  2 B along long sides  1 B and  1 C was shown in  FIG. 9 . 
         [0108]    As shown in  FIG. 9 , each of long sides  11 B and  1 C of insulating substrate  1  has a length of L (mm), and each of short sides  1 D and  1 E thereof has a length of W (mm). Samples included protective resin layer  5  which was not broken even if an electrostatic pulse having a voltage of 30 kV was applied, and had a high electrostatic discharge resistance (ESD resistance) if the samples satisfy the following condition. 
         [0000]      ( L− 0.1)/( W− 0.1)≧1.5, 
         [0109]    Metal is provided on surface  1 A of insulating substrate  1  to form electrodes  2 A and  2 B. As described above, margins  1 F are provided for forming the metal. For this reason, the above condition is established not according to a ratio of L to W, but to a ratio of (L−0.1) to (W−0.1). Under this condition, the maximum width W and length L of electrodes  2 A and  2 B in consideration of the margins  1 F can be defined. The length L 2  of margin  1 F along long sides  11 B and  1 C need be set to at least 0.05 mm at each of both ends of insulating substrate  1 . Thus, in consideration of margins  1 F, the length L 1  of each of electrodes  2 A and  2 B along long sides  11 B and  1 C that can be provided on surface  1 A of insulating substrate  1  is (L−0.1) (mm). The width of electrodes  2 A and  2 B and gap  2 C along short sides  1 D and  1 E is (W−0.1) (mm). Margins  1 F can be smaller according to the method for providing the metal. 
         [0110]    In ESD protector  1001  of Embodiment 1, protective resin layer  5  has a large thickness to have a higher physical breaking strength. In ESD protector  1001  of Embodiment 1,surface  1 A of insulating substrate  1  is roughened to have a large anchor effect which increases the junction area between protective resin layer  5  and insulating substrate  1 . This structure can increase the adhesion strength between protective resin layer  5  and insulating substrate  1 , thereby increasing the physical breaking strength of protective resin layer  5 . Alternatively, the amount of fillers in protective resin layer  5  may be increased, or the size of the fillers may be reduced. This can increase the adhesion strength between protective resin layer  5  and insulating substrate  1 , thereby increasing the physical breaking strength of protective resin layer  5 . 
         [0111]    In the comparative example of the ESD protector, the electrodes extend along the short side of the insulating substrate, the long side has a length of 20 mm, and the short side had a length of 12 mm. The comparative example had a capacitance of approximately 0.10 pF. The ESD protector according to Embodiment 1 satisfied the condition, (L−0.1)/(W−0.1)&gt;1.5, and had the same dimensions. The ESD protector according to Embodiment 1 had a capacitance of 0.15 pF, which is larger than higher than that of the comparative example. However, when an ESD protector is used for a transmission line at a relatively low speed in an electronic device, such as an on-vehicle device, to which an electrostatic pulse having an extremely high voltage may be applied, small capacitance is not matter. Thus, ESD protector  1001  according to Embodiment 1 can protect electronic component  2001  from an electrostatic pulse. 
       Exemplary Embodiment 2 
       [0112]      FIG. 10  is a sectional view of ESD protector  1002  in accordance with Exemplary Embodiment 2 of the present invention.  FIGS. 11 to 18  are perspective views of manufacturing ESD protector  1002  for illustrating a method of manufacturing ESD protector  1002 . Insulating substrate  101  is made of low-dielectric ceramic, such as alumina, having a low dielectric constant equal to or smaller than 50, preferably smaller than 10. Electrodes  102 A and  102 B are provided on surface (upper surface)  101 A of insulating substrate  101 . Electrode  102 A faces electrode  102 B across gap  103  having a predetermined spacing. Overvoltage protective layer  104  covers portion  112 A of electrode  102 A, portion  112 B of electrode  102 B, and gap  103 . Overvoltage protective layer  104  contains insulating resin, such as silicone resin, and conductive particles, such as metal powder, dispersed in the insulating resin. Intermediate layer  105  is provided on overvoltage protective layer  104  and covers overvoltage protective layer  104 . Intermediate layer  105  contains insulating resin, such as silicone resin, and at least one kind of insulating powder dispersed in the insulating resin. Protective resin layer  106  is provided on intermediate layer  105  and completely cover intermediate layer  105 . Terminal electrodes  107 A and  107 B are provided at both ends of insulating substrate  101  and are connected to electrodes  102 A and  102 B, respectively. 
         [0113]    A method for manufacturing ESD protector  1002  according to Embodiment 2 will be described below. 
         [0114]    First, as shown in  FIG. 11 , low-dielectric material, such as alumina, having a dielectric constant equal to or smaller than 50, preferably smaller than 10, is fired at temperatures ranging from 900 to 1300° C., thereby providing insulating substrate  101 . Insulating substrate  101  has a rectangular shape, and has long sides  101 B and  101 C which face each other and have lengths L (mm), and short sides  101 D and  101 E which are shorter than long sides  101 B and  101 C and have lengths W (mm). In the actual manufacturing process, an insulating substrate made of low-dielectric ceramic is divided into plural pieces each providing insulating substrate  101 . 
         [0115]    Next, as shown in  FIG. 12 , conductive material containing more than 80 wt % of gold, that is, mainly containing gold is provided on surface  101 A of insulating substrate  101 , thereby providing conductive layer  102 . The conductive material is gold-based organic paste (reginate paste), and conductive layer  102  is formed by printing and firing the material. This method allows conductive layer  102  to be manufactured more inexpensively at higher productivity than other methods, such as the sputtering of gold. The thickness of conductive layer  102  after the firing ranges from 0.2 μm to 2.0 μm. Conductive layer  102  reaches long sides  101  B and  101 C, and is located away from short sides  101 D and  101 E of insulating substrate  101 , thus providing spaces on surface  101 A. The conductive layer may be located away from long sides  101 B and  101 C so as to provide the spaces. 
         [0116]    Next, as shown in  FIG. 13 , a substantially central portion of conductive layer  102  is cut with UV laser to form gap  103  having a width of approximately  10  μm. This provides electrodes  102 A and  102 B facing each other across gap  103 . Conductive layer  102  is formed by applying and firing the gold-based organic paste and is thin, hence forming gap  103  reliably and accurately with the UV laser having a relatively low output. Gap  103  is formed by physically cutting conductive layer  102  with the UV laser, hence having an insulating property prevented from deteriorating. In the case that gap  103  is formed by etching conductive layer  102  by a photolithography technique, glass frit contained in the gold-based organic paste may remain around gap  103  after the etching, and degrade its resistance to humidity. When conductive layer  102  is cut with the UV laser, matter  108 , such as metal particles, may be attached onto gap  103  or surfaces of electrodes  102 A and  102 B around the gap. Gap  103  is substantially parallel to long sides  101 B and  101 C of insulating substrate  101 . Gap  103  may be substantially parallel to short sides  101 D and  101 E of insulating substrate  101 . In this case, conductive layer  102  may preferably be provided on surface  101 A away from long sides  101 B and  101 C of insulating substrate  101 . Gap  103  has a linear shape, and may have a stair shape or a meander shape. 
         [0117]    Next, as shown in  FIG. 14 , insulating substrate  101 , particularly gap  103 , is cleaned with acidic solution, such as sulfuric acid, hydrofluoric acid, nitric acid, or mixed acid thereof, so as to remove attached matter  108 . Since electrodes  102 A and  102 B contain more than 80 wt. % of gold, i.e. mainly containing gold, conductive components of the electrodes do not dissolve in the acidic solution even if contacting the solution. Therefore, attached matter  108  can be removed while gap  103  is not enlarged. Attached matter  108  contains metal particles that may cause an insulation failure. Then, insulating substrate  101  may be cleaned with ultrasonic waves, thereby having the attached matter  108  removed reliably. Alternatively, attached matter  108  may be physically removed by another method, such as blowing air, sucking air, or grinding, after the cleaning with the acidic solution, thereby having attached matter  108  removed reliably. 
         [0118]    Next, overvoltage protective layer  104  is formed. Metal particles, such as metal powder having spherical shapes and an average particle diameter ranging from 0.3 to 10 μm and made of Ni, Al, Ag, Pd, or Cu, is prepared. The metal particles, silicone-resin-based insulating resin, such as methyl silicone resin, and organic solvent are kneaded with a three-roll mill to have the particles dispersed in the solvent, thereby providing overvoltage protective material paste. As shown in  FIG. 15 , this overvoltage protective material paste is applied by screen printing to have a thickness ranging from 5 to 50 μm so as to cover portion  112 A of electrode  102 A, portion  112 B of electrode  102 B, and gap  103 . The applied paste is dried at 150° C. for 5 to 15 minutes, thereby providing overvoltage protective layer  104 . 
         [0119]    Next, intermediate layer  105  is formed. Insulating powder having an average particle diameter ranging from 0.3 to 10 μm and made of Al 2 O 3 , SiO 2 , MgO, or composite oxide thereof is prepared. This insulating powder, silicone-resin-based insulating resin, such as methyl silicone resin, and organic solvent are kneaded with a three-roll mill to disperse the insulating powder in the solvent, thereby providing insulating paste. As shown in  FIG. 16 , this insulating paste is applied by screen printing to have a thickness ranging from 5 to 50 μm so as to cover overvoltage protective layer  104 . The insulating paste is applied to completely cover overvoltage protective layer  104  above gap  103 . The applied insulating paste is dried at 150° C. for 5 to 15 minutes, thereby providing intermediate layer  105 . In order to provide a sufficient resistance to electrostatic discharge, the sum of the thicknesses of overvoltage protective layer  104  and intermediate layer  105  after the drying is equal to or larger than  30  μm. If overvoltage protective layer  104  has a thickness large enough to provide the sufficient resistant to electrostatic discharge, the device does not necessarily include intermediate layer  105 . 
         [0120]    Next, as shown in  FIG. 17 , resin paste made of resin, such as epoxy resin or phenol resin, is applied by screen printing to completely cover intermediate layer  105  such that ends  122 A and  122 B of electrodes  102 A and  102 B are exposed. The applied resin paste is dried at 150° C. for 5 to 15 minutes, and then cured at a temperature ranging from 150 to 200° C. for 15 to 60 minutes, thereby providing protective resin layer  106 . The thickness of protective resin layer  106  after the drying ranges from 15 to 35 μm. 
         [0121]    Next, as shown in  FIG. 18 , conductive paste containing powder of metal, such as Ag, and curing resin, such as epoxy resin, is applied onto long sides  101 B and  101 C of insulating resin  101 , and dried and cured, thereby providing terminal electrodes  107 A and  107 B. Terminal electrodes  107 A and  107 B are connected to ends  122 A and  122 B of electrodes  102 A and  102 B, respectively, thus providing ESD protector  1002  according to Embodiment 2. ESD protector  1002  operates similarly to ESD protector  1001  according to Embodiment 1 shown in  FIG. 1C . When a voltage applied between terminal electrodes  107 A and  107 B is lower than a predetermined rated voltage, the insulating resin in overvoltage protective layer  104  existing in gap  103  insulates between electrode  102 A and  102 B, thus electrically insulating between terminal electrodes  107 A and  107 B and opening the circuit between the terminals. When a high voltage caused by, e.g. an electrostatic pulse is applied between terminal electrodes  107 A and  107 B, a discharge current flows between the conductive particles dispersed in the insulating resin of overvoltage protective layer  104 , thus drastically decreasing impedance between terminal electrodes  107 A and  107 B. The current generated by the high voltage accordingly flows to a ground via ESD protector  1002 , as the discharge current in ESD protector  1002 . The ESD protector allows the current generated by an abnormal voltage, such as an electrostatic pulse or surge, to bypass an electronic component and flow to the ground. 
         [0122]    Fifty pieces of a comparative example of an ESD protector having gaps formed by a photolithography technique were fabricated. While a voltage of DC 15V is applied, insulation resistances of the samples of the comparative example and fifty samples of ESD protector  1001  according to Embodiment 2 were measured for finding out insulation resistance failure. Further, for the samples of the comparative example of the device and the device according to Embodiment 2, peak voltages were measured under conditions of experiment corresponding to human body model in accordance with IEC61000 (a discharge resistance of 33052, a discharge capacitance of 150 pF, and the applied voltage of 8 kV). 
         [0123]    Two samples out of the fifty samples of the comparative example exhibited the insulation resistance failures. In contrast, none of the samples of ESD protector  1002  according to Embodiment 2 exhibited insulation resistance failure, thus improving a yield rate. The average value of peak voltages applied to the samples of the comparative example was 345 V. The average value of peak voltages applied to the samples of ESD protector  1002  according to Embodiment 2 was 330V, which is lower than that of the comparative example. Thus, ESD protector  1002  having more stable characteristics of suppressing electrostatic discharge (ESD) is provided. In ESD protector  1002  according to Embodiment 2, electrodes  102 A and  102 B are made of material containing more than 80 wt % of gold, i.e. mainly containing gold, and gap  103  is formed by cutting conductive layer  102  with laser. This method provides gap  103  reliably and precisely. 
       Exemplary Embodiment 3 
       [0124]      FIGS. 19A ,  19 C, and  19 E are top views of an ESD protector according to Exemplary Embodiment 3 for illustrating a method of manufacturing the ESD protector.  FIGS. 19B ,  19 D, and  19 F are sectional views of the ESD protector at lines  19 B- 19 B,  19 D- 19 D, and  19 F- 19 F shown in  FIGS. 19A ,  19 C, and  19 E, respectively. 
         [0125]    Low-dielectric material, such as alumina, having a dielectric constant equal to or smaller than 50, preferably smaller than 10, is fired at a temperature ranging from 900 to 1600° C., thereby providing insulating substrate  203  having a sheet shape. 
         [0126]    As shown in  FIGS. 19A and 19B , plural first dividing lines  201  and plural second dividing lines  202  crossing first dividing lines  201  perpendicularly to lines  201  are defined on upper surface  203 A of insulating substrate  203  having the sheet shape. First dividing lines  201  are parallel to each other. Second dividing lines  202  are parallel to each other. Dividing grooves may be formed in upper surface  203 A of insulating substrate  203  along first dividing lines  201  and second dividing lines  202 . Conductive paste made of gold resinate is applied onto upper surface  203 A of insulating substrate  203  by screen printing to have a strip shape, and fired, thereby providing conductive layer  204 . Conductive layer  204  is located away from second dividing lines  202 , and crosses first dividing lines  201 . Conductive layer  204  has a thickness ranging from 0.2 μm to 2.0 μm, thus being thin. 
         [0127]    Next, as shown in  FIGS. 19C and 19D , photosensitive resist  205  is applied to cover upper surface  203 A of insulating substrate  203  and conductive layer  204 . According to Embodiment 3, novolac-based positive photoresist is used for photosensitive resist  205 . 
         [0128]    Next, as shown in  FIGS. 19E and 19F , resist  205  applied to insulating substrate  203  is exposed through a mask pattern and developed so as to remove an unnecessary portion of the resist, thereby forming a pattern for forming the electrodes in resist  205 . This pattern includes gaps  206 A. 
         [0129]      FIGS. 20A ,  20 C, and  20 E are top views of the ESD protector according to Embodiment 3 for illustrating the method for manufacturing the ESD protector.  FIGS. 20B ,  20 D, and  20 F are sectional views of the ESD protector at lines  20 B- 20 B,  20 D- 20 D, and  20 E- 20 F shown in  FIGS. 20A ,  20 C, and  20 E, respectively. 
         [0130]    Next, as shown in  FIGS. 20A and 20B , the unnecessary portion of conductive layer  204  are removed by etching layer  204  through resist  205  with etching solution mainly containing iodine and potassium iodine, thereby providing electrodes  207 . Electrodes  207  face each other across gaps  206  each having a width of approximately 10 μm. If portions of conductive layer  204  along second dividing lines  202  remains, electrodes  207  are electrically connected to each other and thus short-circuited. In the case that the dividing grooves are formed in upper surface  203 A of insulating substrate  203  along dividing lines  201  and  202 , portions of conductive layer  204  in the dividing grooves along first dividing lines  201  may not be removed completely by the etching. However, conductive layer  204  is located away from second dividing lines  202  and does not cross second dividing lines  202 , thus allowing conductive layer  204  not to exist in the dividing grooves along second dividing lines  202 . This prevents short circuits between electrodes  207 . 
         [0131]    Next, as shown in  FIGS. 20C and 20D , resist  205  is removed from insulating substrate  203  with resist-removing agent so as to expose electrodes  207 . Then, appearance of electrodes  207  is checked particularly in whether or not the widths of gaps  206  have variations. 
         [0132]    Next, as shown in  FIGS. 20E and 20F , resin silver paste is applied, by screen printing to have a thickness ranging from 3 to 20 μm, onto a portion of each electrode  207  away from first dividing lines  201  and second dividing lines  202 , and dried at a temperature ranging from 100 to 200° C. for 5 to 15 minutes, thereby providing upper electrodes  208 . Ends  2207  of electrodes  207  contacting first dividing lines  201  are exposed from upper electrodes  208 . 
         [0133]      FIG. 21A  is a bottom view of the ESD protector according to Embodiment 3 for illustrating the method for manufacturing the ESD protector.  FIG. 21B  is a sectional view of the ESD protector at line  21 B- 21 B shown in  FIG. 21A . Insulating substrate  203  has lower surface  1203 B opposite to upper surface  203 A. Resin silver paste is applied to lower surface  1203 B of insulating substrate  203  by screen printing to have a thickness ranging from 3 to 20 μm, and dried at a temperature ranging from 100 to 200° C. for 5 to 15 minutes, thereby providing lower electrodes  209 . Lower electrodes  209  face electrodes  207  across insulating substrate  203 . Lower electrodes  209  cross first dividing lines  201  and second dividing lines  202 . Each of lower electrodes  209  includes first portion  209 A which crosses second dividing lines  202 , and second portion  209 B which is connected to first portion  209 A and which crosses first dividing line  201 . First portion  209 A bridges between second dividing lines  202  adjacent to each other. The width of second portion  209 B of lower electrodes  209  is narrower than the width of first portion  209 A, and thus, lower electrode  209  has a T-shape. In other words, lower electrode  209  is located away from a portion of first dividing line  201 . This shape prevents lower electrodes  209  from having burrs protruding therefrom when insulating substrate  203  is divided along first dividing lines  201 . 
         [0134]      FIGS. 21C and 21E  are top views of the ESD protector in accordance with Embodiment 3 for illustrating the method for manufacturing the ESD protector.  FIGS. 21D and 21F  are sectional views of the ESD protector at line  21 D- 21 D and  21 F- 21 F shown in  FIGS. 21C and 21E , respectively. 
         [0135]    Conductive particles having spherical shapes having an average particle diameter ranging from 0.3 to 10 μm and made of metal powder, such as Ni, Al, Ag, Pd, or Cu, is prepared. The conductive particles, silicone-based resin, such as methyl silicone resin, and organic solvent are kneaded with a three-roll mill to disperse the conductive particles, thereby providing overvoltage protective material paste. As shown in  FIGS. 21C and 21D , the overvoltage protective material paste is applied by screen printing to have a thickness ranging from 5 to 50 μm so as to cover gaps  206  and portions  1207  of electrodes  207 , and dried at 150° C. for 5 to 15 minutes, thereby providing overvoltage protective layer  210 . 
         [0136]    Insulating powder having an average particle diameter ranging from 0.3 to 10 μm and made of Al 2 O 3 , SiO 2 , MgO, or composite oxide thereof is prepared. This insulating powder, silicone-based resin, such as methyl silicone resin, and organic solvent are kneaded with a three-roll mil to disperse the insulating powder, thereby providing insulating paste. As shown in  FIGS. 21E and 21F , this insulating paste is applied by screen printing to have a thickness ranging from 5 to 50 μm so as to cover overvoltage protective layer  210 , and dried at 150° C. for 5 to 15 minutes, thereby providing intermediate layer  211 . Intermediate layer  211  completely covers portions of overvoltage protective layer  210  over gaps  206 . In order to provide a sufficient resistance to electrostatic discharge, the sum of the thicknesses of overvoltage protective layer  210  and intermediate layer  211  is preferably equal to or larger than  30  gm after the drying. In the case that overvoltage protective layer  210  has a thickness enough to allow resistance to electrostatic discharge to satisfy predetermined conditions, intermediate layer  211  is not necessarily be formed. 
         [0137]      FIGS. 22A ,  22 C, and  22 E are top views of the ESD protector in accordance with Embodiment 3 for illustrating the method for manufacturing the ESD protector.  FIGS. 22B ,  22 D, and  22 F are sectional views of the ESD protector at lines  22 B- 22 B,  22 D- 22 D, and  22 F- 22 F shown in  FIGS. 22A ,  22 C, and  22 E, respectively. 
         [0138]    Next, as shown in  FIGS. 22A and 22B , resin paste made of insulating resin, such as epoxy resin or phenol resin, is applied by screen printing to completely cover overvoltage protective layer  210  and intermediate layer  211 . The applied resin paste is dried at 150° C. for 5 to 15 minutes, and then, cured at a temperature ranging from 150 to 200° C. for 15 to 60 minutes, thereby providing protective resin layer  212 . The thickness of protective resin layer  212  ranges from 15 to 35 μm. End  2207  of electrode  207  contacting first dividing lines  201  and portion  2208  of upper electrode  208  are exposed from protective resin layer  212 . 
         [0139]    Next, as shown in  FIGS. 22C and 22D , substrate  203  is divided into insulating substrate strips  1203  by dicing substrate  203  along first dividing lines  201 . Resin silver paste is applied onto edge surfaces  1203 C along first dividing lines  201  of each insulating substrate strip  1203 , thereby providing edge electrodes  213  electrically connected to electrodes  207 , upper electrodes  208 , and lower electrodes  209 . 
         [0140]    Next, as shown in  FIGS. 22E and 22F , insulating substrate strip  1203  is divided along second dividing lines  202  into insulating substrate pieces  2203 . Then, nickel-plated layers  214  are formed by barrel plating to cover edge electrodes  213 , lower electrodes  209 , and upper electrodes  208  so that these electrodes are not exposed. Then, tin-plated layers  215  covering nickel-plated layers  214  are formed by barrel plating to provide terminal electrodes  216 , thus providing ESD protector  1003  according to Embodiment 3. 
         [0141]    ESD protector  1003  operates similarly to ESD protector  1001  according to Embodiment 1 shown in  FIG. 1C . When a voltage applied between terminal electrodes  216  is lower than a predetermined rated voltage, the insulating resin of overvoltage protective layer  210  existing in gap  206  insulates between electrodes  207 , thus electrically insulating between terminal electrodes  216  and opening the circuit between the terminal electrodes. When a high voltage caused by, e.g. an electrostatic pulse is applied between terminal electrodes  216 , a discharge current flows between the conductive particles dispersed in the insulating resin of overvoltage protective layer  210 , thus drastically decreasing impedance between terminal electrodes  216 . The current generated by the high voltage accordingly flows to a ground via ESD protector  1003 , as the discharge current in ESD protector  1003 . The ESD protector allows the current generated by an abnormal voltage, such as an electrostatic pulse or surge, to bypass an electronic component and flow to the ground. 
         [0142]    In ESD protector  1003  according to Embodiment 3, conductive layer  204  is formed by applying gold resinate paste onto insulating substrate  203  so that the paste crosses first dividing lines  201 . Since conductive layer  204  for forming electrodes  207  is made of gold-based material, the electrodes are more resistant to sulfidation than electrodes made of silver or copper, providing ESD protector  1003  with high resistance to sulfidation. Further, the gold resinate paste is applied and fired to provide thin conductive layer  204  for forming electrodes  207 . Thus, when insulating substrate  203  is divided into insulating substrate strips  1203  by dicing the substrate along first dividing lines  201 , insulating substrate  203  is prevented from producing burrs on electrodes  207 , accordingly providing ESD protector  1003  with a small size and a stable shape. 
         [0143]    In ESD protector  1003  according to Embodiment 3, overvoltage protective layer  210  is covered with intermediate layer  211 , and intermediate layer  211  and overvoltage protective layer  210  are completely covered with protective resin layer  212 . This structure prevents insulation of protective resin layer  212  from deteriorating due to an electrostatic pulse applied thereto. 
         [0144]    Further, in ESD protector  1003  according to Embodiment 3, a portion of electrode  207  is covered with upper electrode  208 . When ESD protector  1003  is mounted on a circuit board, solder may flow into a gap between tin-plated layer  215  and protective resin layer  212 . The solder reaches upper electrode  208  and stops. If the solder reaches electrode  207 , metallic components of electrode  207  may flow to the solder and increase the resistance of electrode  207 . Upper electrode  208  prevents the solder from reaching electrode  207 , and thus prevents a decrease in the effect of suppressing electrostatic electricity caused by the increased resistance of electrode  207 , thus providing ESD protector  1003  with a stable effect of suppressing static electricity. 
         [0145]    According to Embodiment 3, the sides of insulating substrate  2203  along first dividing lines  201  and second dividing lines  202  are the short sides and long sides, respectively. Electrodes  207  reach the short sides of insulating substrate  2203 . In the case that the sides along first dividing lines  201  and second dividing lines  202  are the long sides and short sides, respectively, the method of manufacturing ESD protector  1003  according to Embodiment 3 can provide ESD protectors  1001  and  1002  according to Embodiments 1 and 2 shown in  FIGS. 1A and 18 . 
       INDUSTRIAL APPLICABILITY 
       [0146]    A manufacturing method forms a gap with a narrow width precisely, and provides an ESD protector having a low peak voltage, stable characteristics of suppressing electrostatic discharge (ESD), and a high resistance to sulfidation, and is useful particularly to a method for manufacturing a component for protecting an electronic device to which an electrostatic pulse having a high voltage is applied.