JP2005340699A - Surface mounting electronic component, packaging structure and method of electronic component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface mounting electronic component in which the electronic component element is not cracked easily even when a mounting substrate is bent after packaging, and high precision mounting can be ensured by self-alignment effect due to surface tension of molten solder at the time of reflow soldering. <P>SOLUTION: In the surface mounting electronic component, first and second terminal electrodes 5 and 6 are formed to cover the end faces 2a and 2b of an electronic component element 2 wherein the terminal electrode 5, 6 consists of a first electrode layer 5a, 6a exhibiting relatively low solder wettability, a second electrode layer 5b, 6b formed of a conductive material exhibiting excellent heat resistance on the first electrode layer 5a, 6a only above the end face 2a, 2b, a third electrode layer 5c, 6c formed of a metal material causing solder leaching formed to cover the second electrode layer 5b, 6b and extend to the side face of the electronic component element, and a fourth electrode layer 5d, 6d formed of a metal material exhibiting relatively good solder wettability. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a surface-mounted electronic component having terminal electrodes formed on end faces, and more specifically, a surface-mounted electronic component that can be efficiently mounted by a reflow soldering method, the electronic The present invention relates to a component mounting method and a mounting structure.

  Conventionally, when mounting electronic components on a mounting board such as a printed circuit board, a reflow soldering method has been widely used. An electronic component mounted by the reflow soldering method is usually configured as a surface mount type electronic component formed by forming a terminal electrode on the outer surface of an electronic component element body.

  An example of such a surface-mounted electronic component is disclosed in Patent Document 1 below, for example. FIG. 11 is a front sectional view showing the chip-type positive temperature coefficient thermistor described in Patent Document 1. In the chip type positive temperature coefficient thermistor 101, first and second terminal electrodes 103 and 104 are formed on end faces 102 a and 102 b of the thermistor body 102, respectively. Here, the first and second terminal electrodes 103 and 104 respectively cover the end faces 102a and 102b of the thermistor body 102 and have first electrode layers 103a and 103a having electrode cover portions that reach the side surfaces of the thermistor body. 104a. The first electrode layers 103a and 104a are made of Cr or a Cr alloy.

  Then, second electrode layers 103b and 104b made of Ni or Ni alloy are formed so as to cover the first electrode layers 103a and 104a, and from Ag so as to cover the second electrode layers 103b and 104b. Third electrode layers 103c and 104c are formed. Further, plating films 103d and 104d made of Sn having excellent solderability are formed so as to cover the third electrode layers 103c and 104c.

  The first to third electrode layers 103a to 103c, 104a to 104c and the Sn plating films 103d and 104d are both end surface portions and end surface portions located on the end surfaces 102a and 102b of the electronic component body 102. To an electrode covering portion that extends so as to reach the side surface of the electronic component element body 102.

On the other hand, in the following Patent Document 2, an electronic component 111 shown in FIG. 12 is formed. The electronic component 111 has an electronic component body 112 made of ceramics. First and second terminal electrodes 113 and 114 are formed on end surfaces 112 a and 112 b of the electronic component element body 112. The terminal electrode 113 includes, from the inside, a first electrode layer 113a made of Cr, a second electrode layer 113b made of Ni, a third electrode layer 113c made of Ag, and a fourth electrode layer 113d made of Sn. Each of the first to fourth electrode layers 113a to 113d is located only on the end surface 112a of the electronic component element body 112, and does not have an electrode covering portion reaching the side surface. The second terminal electrode 114 is configured in the same manner as the first terminal electrode 113.
JP 2002-203703 A Japanese Patent Laid-Open No. 5-29176

  In the electronic component 101 described in Patent Document 1, the terminal electrodes 103 and 104 have a structure in which the first to fourth electrode layers 113a to 113c and 114a to 114c and the Sn plating films 113d and 114d are stacked. For example, when mounted on a circuit board by a reflow soldering method or the like, it is said that the chip-type positive temperature coefficient thermistor 101 can be reliably mounted on a printed circuit board with less solder repelling.

  However, when the electronic component 101 is mounted on a printed circuit board using solder, the solder adheres not only to the end face portions of the terminal electrodes 103 and 104 but also to the electrode cover portion. Therefore, for example, when the circuit board is bent so as to protrude upward at the center of the electronic component element body 102, stress due to the bending of the substrate is applied to the electronic component element body 102 through the solder, and the electronic component element body 102 is Cracks sometimes occurred. That is, in the structure in which the electronic component 101 is mounted on the mounting substrate, there is a problem that the bending strength of the electronic component 101 is not sufficient.

  In particular, electronic parts mounted on automobiles are strongly required to have a large bending resistance according to quality standards. In the structure described in Patent Document 1, it is difficult to satisfy such requirements. .

  On the other hand, in the electronic component 111 described in Patent Document 2, the terminal electrodes 113 and 114 are located only on the end surfaces 112 a and 112 b of the electronic component element body 112. That is, the terminal electrodes 113 and 114 do not reach the side surface of the electronic component body 112. Therefore, when mounted on a printed circuit board or the like using molten solder, the solder adheres to the terminal electrodes 113 and 114 only on the end surfaces 112a and 112b of the electronic component element body 112. Therefore, since it is difficult for solder to adhere to the side surface portion of the electronic component element body 112, even if the printed circuit board is bent, stress due to the bending is not applied to the electronic component element body 112 so much. Therefore, cracks in the electronic component body 112 can be suppressed.

  However, when the electronic component 111 is mounted on a printed circuit board by the reflow soldering method, there is a problem that the self-alignment effect cannot be sufficiently obtained. This will be described with reference to FIG. FIGS. 13A and 13B are plan views schematically showing a process of soldering the electronic component 111 by a reflow soldering method. The electronic component 111 is mounted on the electrode lands 122 and 123 provided on the mounting substrate 121 by a reflow soldering method. In this case, solder layers 124 and 125 are formed on the upper surfaces of the electrode lands 122 and 123 in advance. Even if the electronic component 111 is disposed at a slightly shifted position on the electrode lands 122 and 123, when the solder layers 124 and 125 are melted by heating, the electronic component 111 is melted by the surface tension of the molten solder. Close to the center of the solder. That is, as shown in FIG. 13B, the electronic component 111 is brought closer to the center side of the electrode lands 122 and 123.

  However, in the electronic component 111, since the terminal electrode does not exist at the position indicated by the arrow A in FIG. 13B, that is, there is no electrode covering portion that reaches the side surface portion of the electronic component body 112, the molten solder is used in the electronic component. It does not adhere to the side surface of the element body 112. Therefore, the force for attracting the electronic component element 111 due to the surface tension of the molten solder is not sufficient, and the electronic component element 111 is surely attracted to the center in the width direction of the electrode lands 122 and 123 as shown in FIG. I could not. That is, the electronic component 111 could not be accurately positioned using the self-alignment effect due to the surface tension of the molten solder.

  The object of the present invention is to solve the above-mentioned drawbacks of the prior art, and not only is it difficult to cause cracks in the electronic component body and the joint part even when stress is applied due to bending on the mounting substrate side, etc. A surface-mounted electronic component capable of reliably and highly accurately mounting an electronic component by a self-alignment effect using the surface tension of molten solder when surface-mounted by a soldering method, and the surface-mounted electronic component It is an object to provide a mounting structure and mounting method for an electronic component using the above.

  A surface-mount electronic component according to the present invention includes an electronic component element body having at least one end surface and at least one side surface connected to the end surface, and a terminal electrode provided on the end surface of the electronic component element body. The terminal electrode is formed so as to cover an end surface of the electronic component element body, and has a relatively low solder wettability, and the first electrode layer only on the end surface of the electronic component element body. A second electrode layer made of a conductive material that is laminated on the first electrode layer and has a heat resistance superior to that of the first electrode layer; and the second electrode layer so as to cover the second electrode layer; The first electrode layer is formed so as to reach the side surface of the electronic component body, and is formed so as to cover the third electrode layer made of a metal material that causes solder erosion, and the third electrode layer. Metal material with relatively good solder wettability compared to other electrode layers Characterized in that it comprises a Ranaru fourth electrode layer.

  In a specific aspect of the surface mount electronic component according to the present invention, the electronic component body includes first and second end surfaces facing each other and a plurality of side surfaces connecting the first and second end surfaces. And first and second terminal electrodes are formed on the first and second end faces, respectively.

  In another specific aspect of the surface mount electronic component according to the present invention, the first and second terminals electrically connected to the first and second terminal electrodes formed on the first and second end faces are provided. Internal electrodes are formed in the electronic component body.

  In a more limited aspect of the surface mount electronic component according to the present invention, the first internal electrode and the second internal electrode are arranged so as to overlap with each other through an electronic component body layer.

  In the surface mount electronic component according to the present invention, preferably, the second electrode layer is made of Ni or a Ni alloy, and the third electrode layer is made of Ag or an Ag alloy.

  In the surface mount electronic component according to the present invention, more preferably, the first electrode layer is made of Cr or a Cr alloy, and the fourth electrode layer is made of Sn.

  An electronic component mounting structure according to the present invention includes a mounting substrate and a surface-mounting electronic component mounted on the mounting substrate by a reflow soldering method and configured according to the present invention.

  An electronic component mounting method according to the present invention includes a step of preparing a mounting substrate on which electrode lands are formed, a step of forming a solder layer on the electrode land of the mounting substrate, and a surface configured according to the present invention. The mounting type electronic component is disposed so that the terminal electrode is positioned on the solder layer on the electrode land, and the solder layer is melted by heating, and the surface mounting type electronic component is formed by a reflow soldering method. And a step of bonding to an electrode land on the substrate.

  In the surface-mount type electronic component according to the present invention, the terminal electrode has a structure in which the first to fourth electrode layers are laminated, on the first electrode layer having low solder wettability, on the end surface of the electronic component element body Is formed on the first electrode layer, and the second electrode layer made of a conductive material having excellent heat resistance is formed, and covers the second electrode layer and the electronic component element. A third electrode layer made of a metal material that causes solder erosion is formed so as to reach the side of the body, and a metal material having relatively good solder wettability so as to cover the third electrode layer The 4th electrode layer which consists of is formed.

  Therefore, since the second electrode layer does not reach the side surface of the electronic component element body and does not have an electrode covering portion, when the surface mount type electronic component of the present invention is mounted on a mounting substrate by molten solder The third electrode layer and the fourth electrode layer are eaten by the solder, and the first electrode layer or the side surface of the electronic component element body is exposed on the side surface of the electronic component element body. Since it is difficult for solder to adhere to the side surface of the first electrode layer or the electronic component element body, the solder adheres only at the end surface portion of the terminal electrode, and the electronic component is joined. Therefore, the stress applied to the electronic component body when the mounting substrate is bent is suppressed, and the bending strength after mounting the surface-mounted electronic component can be increased.

  In mounting using the molten solder, a self-alignment effect due to the surface tension of the molten solder can be expected immediately after the solder is melted. That is, in the electronic component of the present invention, since the third and fourth electrode layers are formed so as to reach the side surface of the electronic component element body, the third and fourth electrode layers immediately after the solder is melted. Therefore, the molten solder wraps around and adheres to the side surface of the electronic component element body. Accordingly, the surface-mounted electronic component is reliably and easily pulled toward the center side of the electrode land of the mounting board by the surface tension of the molten solder. Therefore, it becomes possible to mount the surface mount type electronic component with high accuracy by using the reflow soldering method. In addition, after the electronic component is attracted, the solder erosion proceeds, and as described above, the first electrode layer or the side surface of the electronic component element body is exposed at the side surface portion.

  That is, according to the present invention, the second electrode layer made of the conductive material having excellent heat resistance is located only on the end face of the electronic component body, and the third electrode made of a metal material that causes solder erosion. Since the electrode layer and the fourth electrode layer made of a metal material having good solder wettability have a portion reaching the side surface of the electronic component element body, the surface is improved by the flexural strength after mounting and has a self-alignment effect as described above. It is characterized in that it is possible to simultaneously improve the mounting accuracy of the mounting type electronic component.

  The electronic component element body has first and second end faces facing each other and a plurality of side faces connecting the first and second end faces, and the first and second end faces respectively have first and second end faces. When the second terminal electrode is formed, according to the present invention, it is possible to provide a surface-mount type electronic component having the first and second terminal electrodes facing each other, and the first and second end faces. Even when the mounting substrate is bent so that a force acts in a direction perpendicular to the direction connecting the two, according to the present invention, it is possible to effectively suppress the occurrence of cracks in the surface-mounted electronic component, In surface mounting using molten solder, the electronic component can be reliably pulled toward the center of the corresponding electrode land due to the self-alignment effect.

  When the first and second internal electrodes electrically connected to the first and second terminal electrodes formed on the first and second end faces are formed in the electronic component body, the present invention Accordingly, it is possible to provide a surface-mount type electronic component having an internal electrode that has an increased flexural strength after mounting and can improve mounting accuracy due to a self-alignment effect.

  In the case where the first internal electrode and the second internal electrode are arranged so as to overlap with each other through the electronic component body layer, according to the present invention, a stacked surface mount electronic component is provided. Can do.

  When the second electrode layer is made of Ni or a Ni alloy and the third electrode layer is made of Ag or an Ag alloy, solder adheres to the Ni or Ni alloy surface, but the second electrode layer is an electronic component. Since it does not reach the side surface of the element body, it is possible to effectively increase the flexural strength of the surface-mounted electronic component after mounting. Further, when the third electrode layer is made of Ag or an Ag alloy, solder erosion occurs. However, since the third electrode layer reaches the side surface of the electronic component body, the self-alignment effect The mounted electronic component can be more reliably pulled toward the center side of the electrode land, and the mounting accuracy can be effectively increased.

  When the first electrode layer is made of Cr or a Cr alloy and the fourth electrode layer is made of Sn, the solder hardly adheres to the first electrode layer made of Cr or the Cr alloy, and thus the electronic component Even if the third and fourth electrode layers are eroded by solder on the side surface of the element body and the first electrode layer is exposed, the solder will hardly adhere to the side surface portion. Since the flexural strength of the mounted electronic component can be effectively increased and the fourth electrode layer is made of Sn, the surface-mounted electronic component is more surely correct by the surface tension of the molten solder due to the self-alignment effect. It will be drawn to the mounting position.

  In the mounting structure of the electronic component according to the present invention, the surface mounting type electronic component configured according to the present invention is mounted on the mounting substrate by the reflow soldering method. Therefore, in the mounting structure, the mounting substrate is bent. However, it is difficult for cracks to occur in the surface-mounted electronic component, and when mounted by the reflow soldering method, the surface-mounted electronic component is mounted with high accuracy at the correct position.

  In the mounting method of the surface mount electronic component according to the present invention, a solder layer is formed on the electrode land of the mounting substrate on which the electrode land is formed, and the surface mount electronic component configured according to the present invention is connected to the terminal electrode. Is placed on the solder layer on the electrode land and heated, so that the solder layer is melted and the surface tension of the molten solder is brought to the correct mounting position on the electrode land by the surface tension of the molten solder. Gravitate. Therefore, it is possible to effectively improve the mounting accuracy.

  In addition, after mounting, solder is not bonded to the side surface of the electronic component body, so that the flexural strength of the surface-mounted electronic component after mounting can be increased, and even when the mounting substrate is bent. The occurrence of cracks in the electronic component body can be effectively suppressed.

  Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

  FIGS. 1A and 1B are perspective views showing a chip-type negative characteristic thermistor as a surface-mount electronic component according to the first embodiment of the present invention, and FIG. FIG.

  The laminated negative characteristic thermistor 1 has a thermistor element body 2 as an electronic component element body. The thermistor body 2 is configured using a ceramic sintered body made of semiconductor ceramics having negative resistance temperature characteristics.

  The thermistor body 2 has a rectangular parallelepiped shape and has first and second end faces 2a and 2b facing each other. It has an upper surface 2c, a lower surface 2d, and a pair of side surfaces 2e (the other side surface is not shown) so as to connect the first and second end surfaces 2a, 2b. Note that the electronic component element body only needs to have at least one side surface continuous with the end surface, and thus may be, for example, a cylindrical body.

  In the thermistor body 2, the first internal electrodes 3a and 3b and the second internal electrodes 4a and 4b are arranged so as to overlap each other with a ceramic layer interposed therebetween. The first inner electrodes 3a and 3b are drawn out to the first end face 2a, and the second inner electrodes 4a and 4b are drawn out to the second end face 2b.

  That is, the thermistor body 2 can be manufactured according to a known method for manufacturing a multilayer ceramic electronic component. For example, an internal electrode pattern is formed by screen printing of a conductive paste such as an Ag-Pd paste on a mother ceramic green sheet mainly composed of ceramics having negative resistance temperature characteristics, and the mother electrode on which the internal electrode pattern is printed is formed. A plurality of ceramic green sheets are laminated, pressed in the thickness direction, and then cut to obtain a laminate of individual negative characteristic thermistor units. The thermistor body 2 can be obtained by firing this laminate.

  In the negative characteristic thermistor 1, first and second terminal electrodes 5 and 6 are formed so as to cover the end faces 2 a and 2 b of the thermistor body 2. The first terminal electrode 5 has a structure in which first to fourth electrode layers 5a to 5d are stacked in this order from the inside. Similarly, the second terminal electrode 6 has a structure in which a first electrode layer 6a to a fourth electrode layer 6d are stacked in this order from the inside.

  The first electrode layers 5a and 6a have end surface portions located on the end surfaces 2a and 2b, and electrode cover portions reaching the upper surface 2c, the lower surface 2d, and the pair of side surfaces 2e. In the present embodiment, the first electrode layers 5a and 6a are formed by sputtering Cr.

  However, the first electrode layers 5a and 6a may be made of a Cr alloy, and may be made of a conductive material having relatively low solder wettability other than Cr or Cr alloy. The relatively low solder wettability means that the solder wettability is lower than that of fourth electrode layers 5d and 6d described later.

  The first electrode layers 5a and 6a may be formed by a thin film forming method other than sputtering, or may be formed by applying and baking a conductive paste.

  In the present embodiment, the second electrode layers 5b and 6b are formed by sputtering Ni. The second electrode layers 5b and 6b may be made of a Ni alloy, or may be made of a conductive material that is superior in heat resistance compared to the first electrode layer other than Ni or Ni alloy. . As for the method of forming the second electrode layers 5b and 6b, other methods such as a dry thin film forming method other than sputtering, and application / baking of a conductive paste can be used.

  As is apparent from FIG. 1B, the second electrode layers 5b and 6b are formed only at portions located on the end faces 2a and 2b. That is, the second electrode layers 5b and 6b are formed so as not to have electrode cover portions that reach the upper surface 2c, the lower surface 2d, and the pair of side surfaces 2e of the ceramic body 2.

  Third electrode layers 5c and 6c are formed so as to cover second electrode layers 5b and 6b and to have electrode cover portions. In the present embodiment, the third electrode layers 5c and 6c are formed by sputtering Ag. However, the third electrode layers 5c and 6c are made of an appropriate metal that causes solder erosion, and may be made of Ag alloy, Cu, Cu alloy, or the like.

  The third electrode layers 5c and 6c may also be formed by other thin film forming methods or conductive paste application / baking.

  In the present embodiment, the fourth electrode layers 5d and 6d are formed by wet plating Sn. However, the fourth electrode layers 5d and 6d may be formed of an Sn alloy, and have an appropriate solder wettability as compared with the first electrode layers 5a and 6a other than Sn or Sn alloy. You may be comprised with the metal.

  Although the method for forming the terminal electrodes 5 and 6 on the thermistor body 2 is not particularly limited, an example of the electrode forming method will be described with reference to FIGS.

  After the thermistor element body 2 is prepared, a plurality of thermistor element bodies 2 are inserted into the holding jig 21 shown in FIG. The holding jig 21 is made of a flat plate member and has a plurality of through holes 22 provided in a matrix shape. Each through hole 22 has a size capable of holding the thermistor element body 2 when the thermistor element body 2 is inserted. Therefore, the inner peripheral surface of the through hole 22 of the holding jig 21 is made of an elastic material such as rubber. The thermistor element body 2 is press-fitted into the through hole 22, and the thermistor element body 2 is held by the holding jig 21 as shown in FIG. 3. In this state, first by sputtering Cr, the first electrode layer 5a is formed so as to cover the end face 2a of the thermistor body 2 as schematically shown in a front sectional view by a circle Y1 in the upper left of FIG. Form. In addition, the holding jig 21 is turned upside down, and the first electrode layer 6a (see FIG. 1) is similarly formed on the opposite end face 2b side.

  Next, the thermistor element body 2 is moved downward from the state shown in FIG. 3, and the protruding height at which the end surface 2 a side of the thermistor element body 2 protrudes from the upper surface 21 a of the holding jig 21 is reduced. In this state, the second electrode layer 5b is formed by dry plating of Ni. As described above, the second electrode layer 5b can be formed only on the end face 2a by reducing the protruding height. The second electrode layer 6b on the second end face 2b side can also be formed in the same manner. That is, the second electrode layer 6b can be formed by performing dry plating in a state where the protruding height of the thermistor body 2 from the lower surface 21b of the holding jig 21 is reduced.

  In forming the third electrode layers 5c and 6c, the protruding height of the thermistor element 2 from the holding jig 21 may be returned to the state shown in FIG. 3 and dry plating may be performed. Thus, as shown in FIG. 5, the 1st-3rd electrode layers 5a-5c are formed.

  Since the formation of the Sn plating film is performed by wet plating such as electrolytic plating and electroless plating, a structure in which the third electrode layers 5c and 6c are formed is put in an appropriate plating tank and wet plating is performed. That's fine.

  The negative characteristic thermistor 1 of the present embodiment is characterized in that, in the terminal electrodes 5 and 6, the first to fourth electrode layers 5a to 5d and 6a to 6d are formed of the above materials, and the second The electrode layers 5b and 6b do not have electrode cover portions but are formed only on portions located on the end faces 2a and 2b of the ceramic body 2. Since it has such a configuration, the negative characteristic thermistor 1 can achieve both the improvement of the bending strength after mounting and the improvement of the mounting accuracy due to the self-alignment effect. This will be described with reference to FIGS. 6A and 6B and FIGS. 7A and 7B.

  FIGS. 6A and 7A are front sectional views for explaining an initial state when the negative characteristic thermistor 1 of the above embodiment is mounted on the mounting substrate 11 by the reflow soldering method. First and second electrode lands 12 and 13 are formed on the upper surface of the mounting substrate 11. Solder layers 14 and 15 are laminated on the electrode lands 12 and 13. Then, the negative characteristic thermistor 1 is placed on the mounting substrate 11 so that the terminal electrodes 5 and 6 of the negative characteristic thermistor 1 are positioned on the solder layers 14 and 15. By heating in this state, the solder layers 14 and 15 and the fourth electrode layers 5d and 6d of the terminal electrodes 5 and 6 are melted. Since the fourth electrode layers 5 d and 6 d reach the side surface of the thermistor body 2, the molten solder also adheres to the fourth electrode layer portion on the side surface of the thermistor body 2. Therefore, the negative characteristic thermistor 1 is quickly drawn toward the center of the electrode lands 12 and 13 due to the surface tension of the molten solder. That is, as shown in FIG. 6B, the negative characteristic thermistor 1 is moved so that the terminal electrodes 5 and 6 of the negative characteristic thermistor 1 are positioned approximately in the center of the electrode lands 12 and 13. Due to this self-alignment effect, the mounting accuracy of the negative characteristic thermistor 1 during soldering by the reflow soldering method can be effectively increased.

  Further, during the heating during the soldering, the solder layers 14 and 15 are melted, and the third electrode layers 5c and 6c made of Ag are also melted. As a result, after the negative characteristic thermistor 1 is moved by the self-alignment effect as described above, the soldering of the third electrode layers 5c and 6c proceeds. Therefore, as shown in a schematic front cross-sectional view in FIG. 7B, in the portion located on the side surface 2e of the thermistor body 2, the third electrode layers 5c and 6c, the fourth electrode layer 5d, 6d disappears due to solder erosion, and the first electrode layers 5a and 6a are exposed. On the other hand, the first electrode layers 5a and 6a do not have good solder wettability. Therefore, the molten solders 14 and 15 do not adhere to the electrode cover portions of the first electrode layers 5a and 6a on the side surface 2e of the thermistor body 2 but only to the terminal electrode portions on the end surfaces 2a and 2b. It becomes.

  Therefore, after the molten solder is solidified, the solders 14 and 15 join the terminal electrode portions on the end faces 2a and 2b and the electrode lands 12 and 13 as in the mounting structure shown in FIG. . FIG. 8 is a partially cut end view seen from the direction of arrow X in FIG. As apparent from FIGS. 7B and 8, the solder 14 adheres to the portion of the terminal electrode 5 located on the end face of the thermistor body 2, and the solder 14 is provided with the terminal electrode 5. Although extending outward in the width direction from the portion, it does not adhere to the side surface of the thermistor body 2.

  Therefore, even if the mounting substrate 11 is bent, the stress due to the bending is only applied from the joint portions by the solders 14 and 15 outside the end faces 2a and 2b of the thermistor element body 2. In other words, the thermistor element body 2 Therefore, the thermistor body 2 is unlikely to crack. Therefore, it is possible to increase the bending strength of the negative characteristic thermistor 1 after mounting.

  Next, specific experimental examples will be described.

  According to the above embodiment, a negative characteristic thermistor was manufactured and mounted on a mounting board by a reflow soldering method, and then the mounting board was bent so as to protrude upward between the first and second terminal electrodes. In the negative characteristic thermistor 1 used, the thermistor body 2 was made of Mn—Ni ceramics, and the dimensions were 2 mm long × 1.2 mm wide × 0.9 mm thick. The thicknesses of the first to fourth electrode layers are as follows: first electrode layers 5a, 6a: 0.03 μm to 0.10 μm, second electrode layers 5b, 6b: 0.2 μm to 1.0 μm, The third electrode layers 5c and 6c were 0.2 μm to 0.6 μm and the fourth electrode layers 5d and 6d were 1 μm to 6 μm. Further, the dimension of the electrode covering portion where the terminal electrodes 5 and 6 reach the upper surface 2c, the lower surface 2d and the pair of side surfaces 2e of the ceramic body 2 was 0.30 ± 0.20 mm. In this case, the method of bending the mounting board is varied, and the negative thermistor of this embodiment observes whether or not a crack occurs in the thermistor body, and determines the amount of bending of the mounting board that caused the crack to be the bending strength. It was. The results are shown in FIG.

  For comparison, the negative characteristic thermistor of the comparative example is the same as the negative characteristic thermistor 1 of the above embodiment except that the second electrode layers 5b and 6b are formed to have electrode cover portions. Were prepared and evaluated in the same manner. The results are shown in FIG.

  In FIG. 9, the average value, maximum value, and minimum value of the bending strength of ten negative characteristic thermistors 1 and the average value, maximum value, and minimum value of the bending strength of the negative characteristic thermistor of the comparative example are shown.

  As can be seen from FIG. 9, in the negative characteristic thermistor 1 of the example, the second electrode layer does not have an electrode covering portion, so that the bending strength is effectively increased as compared with the comparative example. .

  FIG. 10 is a front sectional view showing a modified example of the negative characteristic thermistor 1 according to the embodiment of the present invention. In the negative characteristic thermistor 31 according to this modification, the first electrode layers 5a and 6a are formed only on the end faces 2a and 2b of the ceramic sintered body 2, and do not have electrode cover portions. That is, like the second electrode layers 5b and 6b, the first electrode layers 5a and 6a may be formed only on the end surfaces 2a and 2b without having an electrode covering portion. Even in this case, even if the third and fourth electrode layers 5c, 6c, 5d, and 6d are eroded by the reflow soldering method, the side surface portion of the thermistor body 2 is finally soldered. Is difficult to adhere. Therefore, as in the case of the above-described embodiment, it is possible to prevent the solder from adhering to the side surface and improve the flexural strength.

  Although the multilayer negative characteristic thermistor has been described in the above embodiment, the present invention can be applied to various multilayer ceramic electronic components such as a multilayer positive characteristic thermistor and a multilayer ceramic capacitor. Furthermore, the present invention can be applied not only to multilayer ceramic electronic components but also to ceramic electronic components that do not have internal electrodes. For example, the present invention can be applied to a structure in which a terminal electrode is formed on an end face of a ceramic body that does not have an internal electrode as in the conventional electronic component shown in FIG.

(A) And (b) is the perspective view and front sectional drawing which show the negative characteristic thermistor as an electronic component which concerns on one Embodiment of this invention. The perspective view for demonstrating the process of forming an electrode in the thermistor body of the negative characteristic thermistor shown in FIG. The perspective view for demonstrating the process of forming a 1st electrode layer in the end surface of the thermistor body of the negative characteristic thermistor of embodiment shown in FIG. The perspective view for demonstrating the process of forming a 2nd electrode layer in the end surface of the thermistor body of the negative characteristic thermistor of embodiment shown in FIG. FIG. 4 is a schematic partial cross-sectional view for explaining a state in which a third electrode layer is formed on the end face of the thermistor element body of the negative characteristic thermistor of the embodiment shown in FIG. 1. (A) And (b) is each typical top view for demonstrating the improvement of the mounting precision by the self-alignment effect in the negative characteristic thermistor of embodiment shown in FIG. (A) And (b) is each front sectional drawing which shows the initial state at the time of mounting the negative characteristic thermistor of embodiment shown in FIG. 1, and the state after mounting. The partial notch end view seen from the X direction of FIG.7 (b). The figure which shows the result of having measured the bending strength of the negative characteristic thermistor of the Example and comparative example of this invention. The front sectional view showing the modification of the negative characteristic thermistor of one embodiment of the present invention. Front sectional drawing which shows an example of the conventional electronic component. Front sectional drawing which shows the other example of the conventional electronic component. (A) And (b) is each typical top view which shows the state which cannot improve the mounting precision by the self-alignment effect in the conventional electronic component shown in FIG.

Explanation of symbols

1. Negative thermistor (electronic component)
2 ... Thermistor body 2a, 2b ... First and second end faces 2c ... Upper surface 2d ... Lower surface 2e ... Side surface 3a, 3b ... First internal electrodes 4a, 4b ... Second internal electrodes 5, 6 ... First, 2nd terminal electrode 5a, 6a ... 1st electrode layer 5b, 6b ... 2nd electrode layer 5c, 6c ... 3rd electrode layer 5d, 6d ... 4th electrode layer 11 ... Mounting substrate 12, 13 ... Electrode Land 14, 15 ... Solder layer 21 ... Holding jig 21a ... Upper surface 21b ... Lower surface 22 ... Through hole 31 ... Negative characteristic thermistor

Claims (8)

An electronic component element body having at least one end surface and at least one side surface connected to the end surface;
A terminal electrode provided on the end face of the electronic component body,
The terminal electrode is formed so as to cover the end face of the electronic component body, and the first electrode layer having relatively low solder wettability;
A second electrode layer that is laminated on the first electrode layer only on the end face of the electronic component element body and is made of a conductive material superior in heat resistance compared to the first electrode layer;
A third electrode layer that is formed so as to cover the second electrode layer and to reach the side surface of the electronic component body, and is made of a metal material that causes solder erosion;
And a fourth electrode layer made of a metal material which is formed so as to cover the third electrode layer and has relatively good solder wettability as compared with the first electrode layer. Surface mount electronic components.   The electronic component element body has first and second end faces facing each other and a plurality of side faces connecting the first and second end faces, and the first and second end faces each have a first side. The surface mount electronic component according to claim 1, wherein a second terminal electrode is formed.   The first and second internal electrodes that are electrically connected to the first and second terminal electrodes formed on the first and second end faces are formed in the electronic component body. The surface mount electronic component as described.   The surface-mount type electronic component according to claim 3, wherein the first internal electrode and the second internal electrode are arranged so as to overlap with each other through an electronic component element layer.   The surface-mount type electronic component according to claim 1, wherein the second electrode layer is made of Ni or an Ni alloy, and the third electrode layer is made of Ag or an Ag alloy.   The surface mount electronic component according to claim 5, wherein the first electrode layer is made of Cr or a Cr alloy, and the fourth electrode layer is made of Sn. A mounting board;
The mounting structure of an electronic component provided with the surface mounting type electronic component of any one of Claims 1-6 mounted by the reflow soldering method on the said mounting board | substrate. Preparing a mounting substrate with electrode lands formed on the surface;
Forming a solder layer on the electrode land of the mounting substrate;
A step of disposing the surface mount electronic component according to any one of claims 1 to 6 so that the terminal electrode is positioned on a solder layer on the electrode land;
And a step of melting the solder layer by heating and bonding the surface-mounted electronic component to an electrode land on the substrate by a reflow soldering method.

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