Patent Publication Number: US-8994491-B2

Title: Chip resistor and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of Korean Patent Application No. 10-2012-0090322 filed on Aug. 17, 2012, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a chip resistor and a method of manufacturing the same. 
     2. Description of the Related Art 
     As demand for miniaturized, lightweight electronic devices gradually increases, chip shaped electronic components are widely used in order to increase a wiring density of a circuit substrate. 
     With regard to a general resistor formed of a metal foil, the metal foil and a substrate may be adhered to each other via a resin material such as epoxy or the like. 
     In addition, with regard to a general resistor formed of a metal foil, an electrode is formed to have a clad structure or is formed via plating. 
     When a metal foil and a substrate are adhered to each other via a resin material, it may be difficult to transfer heat generated by the metal foil functioning as a resistor of a chip resistor to a material having excellent heat dissipation properties. Thus, heat generated by the chip resistor cannot be rapidly dissipated by the chip resistor. Heat generated by the chip resistor may increase a temperature of the resistor. In addition, a level of resistance can be changed due to an increase in temperature. When the chip resistor is used to detect current, the precision of the chip resistor as a resistor for detecting current may be reduced. 
     In addition, heat generated by the chip resistor may dissolve epoxy used for forming adhesives. Thus, a problem can arise in terms of the adhesion between the metal foil and the resistor. 
     When an electrode is formed to have a clad structure, it may be difficult to precisely control the thickness of the chip resistor. 
     When an electrode is formed via plating, since a current density of an edge of the electrode is increased, a thickness difference between the edge of the electrode and a central portion thereof can be generated. The difference in the thickness of the electrode may affect resistance and may reduce adhesion. 
     RELATED ART DOCUMENT 
     
         
         (Patent Document 1) Japanese Patent Laid-Open Publication No. 2010-114167 
         (Patent Document 2) U.S. Patent Application Publication No. 2009-0000811 
       
    
     SUMMARY OF THE INVENTION 
     An aspect of the present invention provides a chip resistor having improved heat dissipation properties and a method of manufacturing the same. 
     Another aspect of the present invention provides a chip resistor including electrodes, thicknesses of which are precisely controlled and a method of manufacturing the chip resistor. 
     Another aspect of the present invention provides a chip resistor able to accurately adjust a target resistance and a method of manufacturing the chip resistor. 
     According to an aspect of the present invention, there is provided a chip resistor including: a ceramic substrate; an adhesion portion formed on a surface of the ceramic substrate; and a resistor formed on the adhesion portion, wherein the adhesion portion includes at least one of copper (Cu), nickel (Ni), and copper-nickel (Cu—Ni). 
     The resistor may include at least one of copper-nickel (Cu—Ni), copper-nickel-manganese (Cu—Ni—Mn), and nickel-chromium (Ni—Cr). 
     The chip resistor may further include an electrode formed on a surface of the resistor. 
     The chip resistor may further include an additional electrode formed on a surface of the electrode to precisely adjust resistance. 
     The chip resistor may further include a protective layer partially covering the resistor and the electrode. 
     According to another aspect of the present invention, there is provided a method of manufacturing a chip resistor, the method including: preparing a ceramic substrate; printing an adhesive paste including at least one of copper (Cu), nickel (Ni), and copper-nickel (Cu—Ni) on a surface of the ceramic substrate; and forming a resistor on an upper surface of the adhesive paste. 
     The resistor may include at least one of copper-nickel (Cu—Ni), copper-nickel-manganese (Cu—Ni—Mn), and nickel-chromium (Ni—Cr). 
     The method may further include forming an electrode by printing an electrode paste on a surface of the resistor. 
     The method may further include forming an electrode by printing an electrode paste on a surface of the resistor. 
     The method may further include firing the electrode. 
     The firing of the electrode may be performed at a temperature from 800° C. to 1400° C. 
     The method may further include forming an additional electrode on a surface of the electrode to precisely adjust resistance. 
     The method may further include forming a protective layer partially covering the resistor and the electrode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, 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: 
         FIGS. 1A to 1C  are cross-sectional views of chip resistors according to embodiments of the present invention; 
         FIG. 2  is a flowchart of a method of manufacturing a chip resistor according to an embodiment of the present invention; 
         FIGS. 3A to 3F  are cross-sectional views for explaining the method of manufacturing the chip resistor of  FIG. 2 ; 
         FIGS. 4A and 4B  are diagrams of adhesive paste patterns according to embodiments of the present invention; and 
         FIGS. 5A and 5B  are optical microscope images of an adhesion surface between a resistor and an electrode, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
     In the drawings, the shapes and dimensions of elements maybe exaggerated for clarity, and the same reference numerals will be used throughout to designate the same or like elements. 
       FIGS. 1A to 1C  are cross-sectional views of chip resistors according to embodiments of the present invention. 
       FIG. 1A  is a cross-sectional view of a chip resistor in which electrodes  40  are only formed on portions of an upper surface of a resistor  30 , according to an embodiment of the present invention. 
     Referring to  FIG. 1A , the chip resistor may include a resistor substrate  10 , an adhesion portion  20 , the resistor  30 , and the electrodes  40 . 
     The resistor substrate  10  is a component for mounting the resistor  30  thereon. The resistor substrate  10  may refer to an insulating substrate formed of a ceramic material. The resistor substrate  10  may be, but is not limited to, an alumina (Al 2 O 3 ) substrate. 
     The resistor substrate  10  may not be particularly limited as long as the resistor substrate  10  may be formed of a material having excellent insulating properties, excellent heat dissipation properties, and excellent adhesive properties with the resistor  30 . 
     The adhesion portion  20  may be formed on a surface of the resistor substrate  10 . The adhesion portion  20  is a component for adhering the resistor substrate  10  and the resistor  30  to each other. The adhesion portion  20  may include copper (Cu), nickel (Ni), copper-nickel (Cu—Ni), or the like. The adhesion portion  20  may include a glass material. During a sintering process, the glass material included in the adhesion portion  20  functions as an adhesive for increasing adhesion with the resistor substrate  10 . 
     The adhesion portion  20  may be formed of a similar material to the resistor  30 , and thus, heat generated by the resistor  30  may be easily dissipated by the resistor substrate  10 . For example, since the adhesion portion  20  includes Cu, Ni, Cu—Ni, or the like, heat generated by the resistor  30  may be smoothly dissipated by the resistor substrate  10 . 
     Since the adhesion portion  20  is formed of a similar material to the resistor  30 , adhesion and resistance may be stably maintained, even in a high-temperature environment. 
     Since an adhesive paste, that is, the adhesion portion  20 , includes Cu, Ni, Cu—Ni, or the like, the chip resistor may have improved heat dissipation properties. 
     The resistor  30  may be formed on the adhesion portion  20 . 
     The resistor  30  may be formed of metal foil since the chip resistor is generally used for detection. 
     When the resistor  30  is formed of metal foil, a low level of resistance equal to or less than 100 mΩ may be obtained. In addition, since metal foil is used as the resistor  30 , a high amount of current may be supplied, compared with the size of the chip resistor. 
     According to an embodiment of the present invention, the resistor  30  may include copper-nickel (Cu—Ni), copper-nickel-manganese (Cu—Ni—Mn), nickel-chromium (Ni—Cr), or the like. 
     This is because if the resistor is formed of a material having a low temperature coefficient, such as constantan, manganin, nichrome, or the like, a temperature coefficient of resistivity (TCR) may be increased, in general. 
     When the resistor  30  includes Cu—Ni—Mn, resistance according to temperature maybe improved, compared with a case in which the resistor  30  includes Cu—Ni. 
     When the resistor  30  includes Ni—Cr, a high level of resistance may be obtained, compared with a case in which the resistor  30  includes Cu—Ni. 
     The adhesion portion  20  and the resistor  30  may be alloyed with each other via an ionic diffusion junction to be coupled and adhered to each other. 
     That is, according to the embodiment of the present invention, since the adhesion portion  20  includes Cu, Ni, Cu—Ni, or the like, adhesion may be improved compared with a conventional method of using an epoxy resin. 
     The electrodes  40  may be formed on a surface of the resistor  30 . The electrodes  40  may include Cu or a Cu alloy. This is because it is also necessary to reduce resistance in the electrodes  40  in order to obtain low resistance in the chip resistor. 
     According to the embodiment of the present invention, the electrodes  40  may be formed via electrode paste printing. 
     When the electrodes  40  are formed via electrode paste printing, the thickness of the electrode  40  may be precisely controlled. Also, a target resistance may be easily obtained in the electrode  40 . 
     In addition, when the electrodes  40  are formed via electrode paste printing, a trimming process may be performed on the electrodes  40  formed on the substrate, and thus, a chip resistor having high precision may be manufactured. 
       FIG. 1B  is a cross-sectional view of a chip resistor in which the electrodes  40  are formed on upper and lateral surfaces of the resistor  30 , according to another embodiment of the present invention. 
     Referring to  FIG. 1B , the electrodes  40  may be formed from portions of the upper surface of the resistor  30  and the lateral surface of the resistor  30  to portions of an upper surface of the resistor substrate  10 . 
     The detailed description of the chip resistor shown in  FIG. 1A  is applied to the chip resistor shown in  FIG. 1B  except for the shape of the electrode  40 , and thus, a detailed description of the chip resistor of  FIG. 1B  will be omitted. 
       FIG. 1C  is a cross-sectional view of a chip resistor in which electrodes are formed from portions of the upper surface of the resistor  30  to a lower surface of the resistor substrate  10 , according to another embodiment of the present invention. 
     Referring to  FIG. 1C , the electrodes maybe formed from the portions of the upper surface of the resistor  30  and a lateral surface of the resistor  30  to the lower surface of the resistor substrate  10 . 
     According to the present embodiment, the resistor  30  may be formed on the upper surface of the resistor substrate  10 , upper electrodes  40 - 1  maybe formed on the portions of the upper surface of the resistor  30 , and lower electrodes  40 - 2  may be formed on portions of the lower surface of the resistor substrate  10 . In addition, lateral electrodes  40 - 3  may be formed to electrically connect the upper electrodes  40 - 1  and the lower electrodes  40 - 2  to each other. 
     The detailed description of the chip resistor shown in  FIG. 1A  is applied to the chip resistor shown in  FIG. 1C  except for the shape of the electrode  40 , and thus, a detailed description of the chip resistor of  FIG. 1C  will be omitted. 
     Likewise, according to the above-described embodiments of the present invention, the structure of the electrode  40  and the coupling structure between the resistor substrate  10  and the resistor  30  may be appropriately modified if necessary. 
       FIG. 2  is a flowchart of a method of manufacturing a chip resistor according to an embodiment of the present invention.  FIGS. 3A to 3F  are cross-sectional views for explaining the method of manufacturing the chip resistor of  FIG. 2 . 
     The manufacturing method according to the present embodiment may include preparing the resistor substrate  10  (S 210 ), as shown in  FIG. 3A . 
     The resistor substrate  10  may refer to an insulating substrate formed of a ceramic material. The resistor substrate  10  may be, but is not limited to, an alumina (Al 2 O 3 ) substrate. 
     The manufacturing method according to the present embodiment may include printing an adhesive paste (S 220 ), as shown in  FIG. 3B . 
     The adhesive paste is a component for adhering the resistor substrate  10  and the resistor  30  to each other. 
     The adhesive paste may include Cu, Ni, Cu—Ni, or the like. 
     Due to Cu, Ni, or Cu—Ni included in the adhesive paste, an ionic diffusion junction may occur between the resistor  30  and the adhesive paste, and the resistor  30  and the adhesive paste may be alloyed to be coupled and adhered to each other. 
     The adhesive paste may include a glass material. 
     The glass material included in the adhesive paste increases the adhesion with the resistor substrate  10 . 
       FIGS. 4A and 4B  are diagrams of adhesive paste patterns according to embodiments of the present invention. 
     As shown in  FIG. 4A , the adhesive paste may be printed in a stripe pattern. 
     As shown in  FIG. 4B , the adhesive paste may be printed in a lattice pattern. 
     Likewise, in order to smoothly discharge residue coal generated during firing in a reduction atmosphere, the adhesive paste may be formed in various printing patterns. 
     That is, the printing pattern of the adhesion paste may be appropriately modified if necessary. 
     The manufacturing method according to the present embodiment may include forming the resistor  30  (S 230 ), as shown in  FIG. 3C . 
     The resistor  30  may include Cu—Ni, Cu—Ni—Mn, Ni—Cr, or the like. 
     According to the embodiment of the present invention, the resistor  30  may be stacked on the adhesive paste. 
     In this case, the resulting structure may be fired. In detail, the firing process may be performed in a reduction atmosphere in order to prevent oxidation. 
     According to the embodiment of the present invention, a firing temperature may be in a range of 800° C. to 1400° C. 
     When the firing process is performed, the resistor  30  and the adhesive paste may be alloyed with each other via an ionic diffusion junction to be coupled and adhered to each other, thereby increasing adhesion. 
     The manufacturing method according to the present embodiment may include forming electrodes  40 - 1  (S 240 ), as shown in  FIG. 3D . 
     The electrodes  40 - 1  may include Cu. For example, an electrode paste including Cu may be coated on a surface of the resistor  30  to form the electrodes  40 - 1 . In detail, process efficiency may be increased by using an electrode paste in the same firing conditions as those of the adhesive paste. 
     According to the embodiment of the present invention, the electrode paste may be formed on the surface of the resistor  30  via screen printing to form the electrodes  40 - 1 , and thus, thickness distribution of the electrodes  40 - 1  may be reduced. 
     In addition, the electrodes  40 - 1  may be formed via screen printing using the electrode paste, and thus, a distance between the electrodes  40 - 1  may be easily controlled and the thickness of the electrodes  40 - 1  may be easily controlled. 
     For example, the method of forming the electrodes  40 - 1  via screen printing using the electrode paste may also be used to manufacture a chip resistor having a size of (16×8) mm 2  or less. 
     In this manner, the electrodes  40 - 1  may be formed by coating the electrode paste, such that the film thickness of the electrodes  40 - 1  may be precisely controlled. 
     If a method of forming an electrode via plating is used, since a Cu rack plating process is used, metal foils are inevitably electrically connected to each other. Thus, when components are separated from each other in the form of a chip, additional processes for cutting connectors are required. 
     On the other hand, according to the embodiment of the present invention, since electrodes are separately formed for individual chip resistors, such additional processes may be omitted. 
     In a method of forming an electrode having a clad structure, an additional process for abrading the electrode is required to change resistance. 
     On the other hand, according to the embodiment of the present invention, since a distance between the electrodes may be easily controlled by using a screen mask, such an electrode abrading process may be omitted. 
     According to the embodiment of the present invention, the electrode paste may be printed on the resistor  30  and then the electrode paste may be fired. 
     Conventionally, with regard to a chip resistor using a resin adhesive, when an electrode is fired during the formation of the electrode, the resin may melt. 
     However, according to the embodiment of the present invention, the resistor substrate  10  and the resistor  30  are adhered to each other via the adhesive paste including at least one of Cu and Ni. Thus, even in the case that the electrode paste is fired, a problem may not arise in terms of adhesion between the resistor substrate  10  and the resistor  30 . 
     According to the embodiment of the present invention, since the electrode paste is printed and fired to form electrodes, the resistor  30  and the electrode  40  may be alloyed with each other via the ionic diffusion junction, thereby increasing adhesion. 
     According to the embodiment of the present invention, the firing temperature may be in the range of 800° C. to 1400° C. 
     Since the electrode paste is printed and fired to form the electrodes, recrystallization between the resistor  30  and the electrode  40  proceeds and grain growth occurs, whereby electrical conductivity may be increased. Thus, low resistance may be obtained in the chip resistor. 
     The printing and firing processes of the electrode paste maybe repeated several times in order to obtain a predetermined amount of resistance. 
     Thus, until the predetermined amount of resistance is obtained, the printing and firing processes of the electrode paste may be repeated. 
       FIGS. 5A and 5B  are optical microscope images of adhesion surfaces between the resistor and the electrode, according to an embodiment of the present invention. 
       FIG. 5A  is an optical microscope image of an adhesion surface al between the resistor  30  and the electrode  40  before the electrode  40  is fired. 
       FIG. 5B  is an optical microscope image of an adhesion surface a 2  between the resistor  30  and the electrode  40  after the electrode  40  is fired. 
     As shown in  FIGS. 5A and 5B , the resistor  30  and the electrode  40  maybe integrated with each other via a firing process. That is, since the resistor  30  and the electrode  40  are alloyed with each other via the ionic diffusion junction, the adhesion between the resistor  30  and the electrode  40  may be increased. 
     According to an embodiment of the present invention, as shown in  FIG. 3E , additional electrodes  60  maybe formed on a surface of the electrode  40 . 
     The additional electrodes  60  are provided to precisely control resistance. 
     That is, the resistance of the chip resistor may be precisely controlled by the additional electrodes  60 . In this case, the size and shape of the additional electrodes  60  may be appropriately modified in order to control resistance. 
     The method of forming the electrodes  40  may also be used to form the additional electrodes  60 , and thus, a detailed description of a method of forming the additional electrodes  60  will be omitted. 
     The resistance of the chip resistor may be precisely controlled by repeating the coating/firing process of the electrodes  40  and forming the additional electrodes  60 . 
     After the electrodes  40  are formed, resistance may be adjusted by laser dicing, laser-scribing, sand bursting, or the like. 
     In addition, after the electrodes  40  are formed, as resistance is measured via a probe, the resistance may be adjusted. 
     Likewise, when the resistance is adjusted while being measured, the resistance may be more precisely controlled. 
     According to an embodiment of the present invention, as shown in  FIG. 3F , a protective layer  50  may be formed to partially cover the resistor  30  and the electrodes  40 . 
     The protective layer  50  may be formed of epoxy, a phenol resin, a glass material, or the like. 
     As set forth above, according to embodiments of the present invention, a chip resistor having improved heat dissipation properties and a method of manufacturing the chip resistor may be provided. 
     Moreover, a chip resistor including electrodes, thicknesses of which are precisely controlled and a method of manufacturing the chip resistor may be provided. 
     In addition, a chip resistor able to accurately adjust a target resistance and a method of manufacturing the chip resistor may be provided. 
     While the present invention has been shown and described in connection with the embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.