Patent Publication Number: US-2018047539-A1

Title: Fuse resistor and method of manufacturing the same

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a fuse resistor and a method of manufacturing the same, and more particularly, to a fuse resistor mounted at an electric circuit of an electronic product to prevent the electronic product from breaking down due to inrush current, increase of internal temperature, and continuous overcurrent, and a method of manufacturing the same. 
     Description of the Related Art 
     Generally, in an electric circuit of a large electronic product such as an LCD TV, or a PDP TV, a protector such as a thermal fuse resistor for protecting the electric circuit is provided at an input terminal. Thereby, the protector prevents the electronic product from breaking down due to inrush current, increase of internal temperature, and continuous overcurrent, which are generated when powered on. 
     Such a fuse resistor includes a resistor, a thermal fuse, a lead wire connected between the resistor and the thermal fuse. 
     In addition, when the fuse blows, fragments occur in the fuse resistor. To prevent the fragments from affecting the other electric components, the resistor and the thermal fuse are packaged by a case and the case is filled with a filler. 
     Herein, a slurry type filler including silica (SiO 2 ) is used as the filler in consideration of thermal resistance, conductivity, hardening, and so on. Generally, a case formed of a ceramic material is used as the case. The ceramic case is used as a general resistive case. 
     Furthermore, an end of the lead wire extends to be withdrawn outside the case. In the conventional fuse resistor, the end of the lead wire is soldered to a printed circuit board, and thus the resistor and the thermal fuse are vertically mounted at the printed circuit board. 
     Accordingly, in the case that inrush current is introduced, such a fuse resistor, as provided above, limits the inrush current to a certain current using the resistor. In the case that overcurrent is introduced, heat generated by heating of the resistor is transferred to the thermal fuse through the filler, and then a solid phase lead or a fuse formed of a polymer pellet, which is provided in the thermal fuse, blows to generate a short circuit. As a result, the electric circuit of the electric product is protected. 
       FIGS. 6A and 6B  are views illustrating a conventional fuse resistor. Referring to  FIGS. 6A and 6B , Korean patent No. 10-1060013 discloses a fuse resistor including a resistor 10, a thermal fuse 20 provided to generate a short circuit due to a heating effect, lead wires 31 and 33 connecting the resistor 10 to the thermal fuse 20 in series, a case 40 having an open side to accommodate the resistor 10 and the thermal fuse with grooves 41 formed at one wall of the case 40 with ends of lead wires 31 and 33 poking outside, and a filler 50 filling an inner space of the case 40 to insert the resistor 10 and the thermal fuse 20 into the filler 50 with the filler 50 formed of silica. 
     It is difficult to miniaturize the fuse resistor 10 in described Korean patent No. 10-1060013. Also, a process of manufacturing of the fuse resistor is complicated since a pair of lead wires 31 and 32 and a pair of lead wires 33 and 34 are connected to the resistor 10 and the thermal fuse 20, respectively, and then, the lead wire 31 of the resistor 10 and the lead wire 33 of the thermal fuse 20 are connected to each other. 
     SUMMARY OF THE INVENTION 
     Therefore, the present invention has been made in view of the above problems of the related art, and it is an object of the present invention to provide a thermal fuse capable of simplifying an assembly process by coupling a thermal fuse and a lead wire in a modularized manner and by fixing a fusing lead wire to the lead wire in an integrated manner to form a lower molding unit, and a method of manufacturing the same. 
     It is another object of the present invention to provide a fuse resistor having a simple structure and capable of being miniaturized as an integrated structure of the thermal fuse and the lead wire is inserted, and a method of manufacturing the same. 
     In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of a fuse resistor including a resistor, a fusing lead wire including a first wire part coupled to one side of the resistor, a second wire part connected to a substrate, and a thermal fuse, one end of the thermal fuse being coupled to the first wire part, and the other end of the thermal fuse being coupled to the second wire part, a lead wire connected to the other side of the resistor, a lower molding unit mold-injected in the state that a part of the fusing lead wire and a part of the lead wire are spaced apart a certain distance from each other, and an upper casing having a cylinder shape, the upper casing being provided with an opening at one side thereof, the upper casing accommodating the resistor, a part of the fusing lead wire and a part of the lead wire, and the opening being coupled to the lower molding unit. 
     The upper casing may be filled with a filler, the filler may be formed of cement, and the lower molding unit may be formed of a resin having a thermal conductivity less than that of the filler. 
     The lower molding unit may be formed to have a thickness to accommodate a part of the first wire part, a part of the second wire part and the thermal fuse. 
     A distance from a horizontal central line of the resistor to an upper surface of the lower molding unit may be less than a distance from the horizontal central line of the resistor to an upper surface of the thermal fuse. 
     A distance from a horizontal central line of the resistor to an upper surface of the lower molding unit may be greater than a distance from the horizontal central line of the resistor to a lower surface of the thermal fuse. 
     The lower molding unit may be provided with a seating part at an edge portion thereof, and the seating part may have a width corresponding to a thickness of the upper casing. 
     The resistor may include a wire wound resistor including a ceramic rod, a pair of terminals disposed at both ends of the ceramic rod, and a lead wire wound on the ceramic rod, and silicon may be coated at surfaces of the ceramic rod and the lead wire to form a coating layer. 
     In accordance with another aspect of the present invention, a method of manufacturing a fuse resistor includes preparing a fusing lead wire and a lead wire, coupling both ends of a resistor to the fusing lead wire and the lead wire, respectively, forming a lower molding unit molded by an insert injection, in which a part of the fusing lead wire and a part of the lead wire are inserted into the lower molding unit and are spaced apart a certain distance from each other, filling an inner space of an upper casing with a filler through an opening, in which the upper casing is cylindrical and is provided with the opening at one side thereof, and coupling the upper casing to the lower molding unit with the resistor inserted into the upper casing. 
     The fusing lead wire may include a first wire part coupled to one side of the resistor, a second wire part connected to a substrate and a thermal fuse, one end of the thermal fuse may be coupled to the first wire part, and the other end of the thermal fuse may be coupled to the second wire part, and the first wire part, the second wire part, and the thermal fuse may each have an identical diameter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1A  is a perspective view illustrating a fuse resistor according to an embodiment of the present invention; 
         FIG. 1B  is an exploded perspective view illustrating a fuse resistor according to an embodiment of the present invention; 
         FIG. 2A  is a cross-sectional view of  FIG. 1 ; 
         FIG. 2B  is a cross-sectional view illustrating a coating layer on a resistor according to the present invention; 
         FIG. 2C  is a cross-sectional view illustrating a filling layer on a resistor according to the present invention; 
         FIG. 2D  is a cross-sectional view illustrating a filling layer, different from that of  FIG. 2C , on a resistor according to the present invention; 
         FIG. 3  is a perspective view illustrating a thermal fuse according to the present invention; 
         FIG. 4  is a cross-sectional view illustrating a fuse resistor with a lower molding unit different from a structure of  FIG. 2A ; 
         FIG. 5A  is a view illustrating forming the fusing lead wire according to the present invention; 
         FIG. 5B  is a view illustrating coupling the lead wire to the resistor according to the present invention; 
         FIG. 5C  is a view illustrating forming the lower molding unit by insert injection of the fusing lead wire and the lead wire; 
         FIG. 5D  is a view illustrating coupling the upper casing to the lower molding unit; and 
         FIGS. 6A and 6B  are views illustrating a conventional fuse resistor. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, the embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     Referring  FIGS. 1A, 1B, 2A, 2B, 2C, 2D, and 3 , a fuse resistor, which is designated by reference numeral “ 100 ” according to the present invention, may be provided to be adopted in an electric circuit of an electric product. The fuse resistor may include a resistor  110 , a fusing lead wire  120  and a lead wire  130  coupled to both ends of the resistor  110 , respectively, a lower molding unit  140  mold-injected in the state that a part of the fusing lead wire  120  and a part of the lead wire  130  are spaced apart a certain distance from each other in an inserted manner, an upper casing  150  coupled to the lower molding unit  140 , and a filler  160  filling an inner space of the upper casing  150 . 
     Upon applying overcurrent, the resistor  110  radiates heat such that a thermal fuse  125  mounted at the fusing lead wire  120  may blow. As illustrated in  FIG. 2B , for example, the resistor  110  is a wire wound resistor including a ceramic rod  111 , terminals  117  provided at both ends of the ceramic rod  111 , a wire  113  wound on the ceramic rod  111 . 
     In addition, a coating layer  115  may be formed on a surface of the resistor  110  as illustrated in  FIG. 2B  or a filling layer  115 ′ or  115 ″ may be formed on the surface of the resistor  110  as illustrated in  FIGS. 2C and 2D . 
     The coating layer  115  may function to protect the wire  113  and to improve explosion proofing. As illustrated in  FIG. 2B , the coating layer  115  may be formed by thinly coating silicon on surfaces of the ceramic rod  111  and the wire  113 . 
     The filling layer  115 ′ or  115 ″ may function to maximize explosion proofing of the resistor  110 . As illustrated in  FIGS. 2C and 2D , the filling layer  115 ′ or  115 ″ may fill a space between a pair of terminals  117  with silicon. At least, the filling layer  115 ′ and  115 ″ may have the same thickness as that of the terminals  117 . Thereby, the wire  113  may be completely sealed. 
     In the case that abnormal current is applied and the resistor  110  is exploded, the coating layer  115  or the filling layer  115 ′ or  115 ″ can initially absorb impact and noise by the exploding. Accordingly, explosion proofing of the product is improved. 
     The fusing lead wire  120  and the lead wire  130  are coupled to each of the terminals  117  of the resistor  110 . 
     The fusing lead wire  120  includes a first wire part  121  coupled to the resistor with the first wire part  121  bent downward, a second wire part  123  connected to a substrate, and the thermal fuse  125 . In this case, one end of the thermal fuse  125  is coupled to the first wire part  121  and the other end of the thermal fuse  125  is coupled to the second wire part  123 . 
     As described above, the thermal fuse  125  is inserted between the first and second wire parts  121  and  123  of the fusing lead wire  120  and, as such, it is possible for the structure to be simplified and miniaturized. 
     The thermal fuse  125  blows by heat radiated from the resistor  110  to generate a short circuit. Thereby, the thermal fuse  125  functions to protect devices mounted on the circuit. 
     In addition, as illustrated in  FIG. 3 , the thermal fuse  125  may include a fusible part  126  and a flex part  127  inserted into a central portion of the fusible part  126 . For example, the fusible part  126  may include tin or a tin alloy. Upon heating, the fusible part  126  blows to block electric connection. 
     The flex part  127  may function to agglomerate the melted fusible part  126 . For example, the flex part  127  may include a chloride, a fluoride, a resin, and so on. 
     Upon coupling the thermal fuse  125  and the first and second wire parts  121  and  123 , an end of the fusible part  126  formed of a metallic material is in contact with each of ends of the first and second wire parts  121  and  123  and then welding is performed. In this case, the thermal fuse  125  may have a diameter identical to each of diameters of the first and second wire parts  121  and  123 . When the diameter of the thermal fuse  125  is greater than each of the diameters of the first and second wire parts  121  and  123 , at least the flex part  127  is formed to have a diameter less than each of the diameters of the first and second wire parts  121  and  123 . Thereby, the fusible part  126  should be in contact with the first and second wire parts  121  and  123 . 
     In the thermal fuse  125 , if the fusible part is formed to be inserted into a central portion of the flex part and heat supplied from the resistor heats the flex part and then heats the fusible part, fusing time is delayed and blowing property is decreased. In addition, as the flex part formed of a dielectric material is disposed on the thermal fuse, the flex part cannot be coupled using a spot welding process. Accordingly, the thermal fuse  125  may preferably have a structure, in which the flex part  127  is inserted into the fusible part  126 . 
     The upper casing  150  may include any one of a thermohardening resin, a thermoplastic resin, and a ceramic material. The upper casing  150  is cylindrical and is provided with an opening  151  at one side. The resistor  110 , a part of the fusing lead wire  120  and the lead wire  130  are inserted into the upper casing  150  through the opening  151 . 
     The opening  151  of the upper casing  150  is sealed by the lower molding unit  140 . The filler  160  providing explosion proofing fills the inner space of the upper case  150 . 
     The filler  160  may absorb impact and noise upon explosion of the resistor  110 . For example, the filler  160  may include cement, silicon, and a resin such as epoxy. 
     As illustrated in  FIG. 2A , the lower molding unit  140  is molded by an insert injection to accommodate interfaces between the thermal fuse  125  and the first and second wire parts  121  and  123 . In this case, the lower molding unit  140  seals the interfaces of both ends of the thermal fuse  125 . Thereby, damage to the thermal fuse  125  or separation of the first and second wire parts  121  and  123  may be prevented during an assembly process. 
     In addition, the resistor  110 , the fusing lead wire  120  and the lead wire  130  are modularized by the lower molding unit in an integrated manner and, as such, it is easy to couple the lower molding unit  140  to the upper casing  150 . Furthermore, the fusing lead wire  120  and the lead wire  130  are spaced apart a certain distance from each other and, as such, defective products may be decreased during surface mounting of the fuse resistor. 
     The lower molding unit  140  is formed to have a block or plate shape having a size corresponding to the opening  151  of the upper casing  150  to seal the opening  151 . A seating part  141  is provided at an edge region of an upper surface of the lower molding unit  140  to have a width corresponding to a thickness of the upper casing  150 . In this case, the lower molding unit  140  is coupled to the upper casing  150  in an engaged manner. 
     Furthermore, as illustrated in  FIG. 4 , the lower molding unit  140 ′ may be mold-injected such that the thermal fuse  125  is not inserted into the lower molding unit  140 ′ and only one side of the second wire part  123  is inserted therein. 
     Hereinafter, in the case that the filler  160  is formed of cement and the lower molding unit  140  is formed of a resin, fusing characteristics between the lower molding unit  140  of  FIG. 2A  and the lower molding unit  140 ′ of  FIG. 4  will be compared. 
     In the case of the lower molding unit  140  of  FIG. 2A , a distance d 1  from a horizontal central line c of the resistor  110  to the upper surface of the lower molding unit  140  is less than a distance d 2  from the horizontal central line c of the resistor  110  to an upper surface of the thermal fuse  125 . 
     In the case of the lower molding unit  140 ′ of  FIG. 4 , a distance d 1 ′ from the horizontal central line c of the resistor  110  to the upper surface of the lower molding unit  140  is greater than a distance d 3  from the horizontal central line c of the resistor  110  to a lower surface of the thermal fuse  125 . 
     Blowing property of each of the lower molding units  140  and  140 ′ will be given. In  FIG. 4 , a space between the lower molding  140 ′ and the resistor  110  is greater than that of  FIG. 2  and amount of the filler  160  is greater than that of  FIG. 2 . In this case, heat of the resistor  110  is absorbed and is radiated outside at the filler  160  and, as such, heat transferred to the thermal fuse  125  is relatively decreased. 
     Whereas, in  FIG. 2A , the thermal fuse  125  is fully inserted into the lower molding unit  140  having lower thermal conductivity than the filler  160  and a space between the lower molding unit  140  and the resistor  110  is relatively narrow. Thereby, conductive heat transferred from the resistor  110  to the thermal fuse  125  through the first wire part  121  is increased as compared with that of  FIG. 4 . Accordingly, blowing property is improved according to the above description. 
     Hereinafter, a method of manufacturing the fuse resistor will be explained with reference to the accompanying drawings. 
     First, referring to  FIG. 5A , the first wire part  121 , the second wire part  125 , the fusing lead wire  120  coupled to the second wire part  123  and the lead wire  130  are prepared. 
     The thermal fuse  125  is coupled to the first and second wire parts  121  and  123  using a soldering process, a spot welding process or an ultrasonic welding process. 
     Then, referring to  FIG. 5B , after both ends of the resistor  110  are coupled to the fusing lead wire  120  and the lead wire  130 , respectively, the fusing lead wire  120  and the lead wire  130  are bent. 
     Sequentially, referring to  FIG. 5C , the fusing lead wire  120  and the lead wire  130  are molded by an insert injection to form the lower molding unit  140 . Herein, the lower molding unit  140  is injected to accommodate the thermal fuse  125  and a part of the second wire part  123  of the fusing lead wire  120 . 
     Then, referring to  FIG. 5D , the upper casing  150  which is cylindrical and is provided with the opening  151  at one side is prepared. The upper casing  150  is disposed with the opening  151  facing upward. The filler  160  fills the inner space of the upper casing  150 . After the resistor  110  modularized by the lower molding unit  140  is inserted into the upper casing  150 , the lower molding unit  140  is coupled to the upper casing  150 . Thereby, manufacture of the fuse resistor is completed. 
     In conclusion, according to present invention, the thermal fuse  125  is inserted into the fusing lead wire  120  to form a simple structure and, as such, miniaturization of a product may be implemented. The fusing lead wire  120  and the lead wire  130  are fixed in an integrated manner to form the lower molding unit  140 . In this case, the lower molding unit  140  is coupled to the upper casing  150  and, as such, a manufacturing process may be simplified. 
     As apparent from the above description, in accordance with the present invention, the thermal fuse and the lead wire are coupled to form one module and the fusing lead wire and the lead wire are fixed in an integrated manner to form the lower molding unit. Thus, an assembly process is simplified. 
     Furthermore, according to the illustrated embodiment of the present invention, the thermal fuse and the lead wire are formed to be an inserted structure in an integrated manner and, as such, the structure is simple and miniaturized. 
     Although the exemplary embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. Accordingly, the scope of the present invention should not be limited to and defined by the embodiments described herein, and should be construed as including the following claims and equivalents thereof.