JP2019179812A - Manufacturing method of multilayer varistor - Google Patents

Abstract

An object of the present invention is to provide a method for manufacturing a laminated varistor in which steps are simplified. A varistor layer (12) and internal electrodes (13) are alternately laminated and then integrally fired to obtain a sintered body (11), and a first silver paste is formed on a side surface of the sintered body (11) by printing and baked. Forming a first external electrode 14 and applying a second silver paste on the first external electrode 14 and baking to form a second external electrode 15. Wherein the first silver paste is obtained by adding a binder and a plasticizer to a first silver powder, and the second silver paste is obtained by adding a binder, a plasticizer, and a glass frit to a second silver powder. In this case, the 50% particle size of the particle size distribution of the second silver powder is at least three times the 50% particle size of the particle size distribution of the first silver powder. [Selection diagram] Fig. 1

Description

  The present invention relates to a method of manufacturing a laminated varistor for protecting various electronic devices from surges.

  In recent years, a multilayer ceramic varistor has been developed as an electronic component for surface mounting as a circuit protection component. These electronic components have external electrodes, and the external electrodes are electrically and mechanically connected to the wiring board by solder. The wettability of the external electrode with respect to the solder greatly depends on the presence or absence of components other than the metal component on the surface of the external electrode, and various studies have been made in order to make this surface state only the metal component as much as possible.

  As prior art document information related to the invention of this application, for example, Patent Document 1 is known.

Japanese Patent Laid-Open No. 9-27405

  However, if a glass component is present on the surface layer of the external electrode, solder wettability may be reduced. For this reason, a plating layer is formed on the surface of the external electrode. However, if plating is performed on the external electrode of the laminated varistor, the plating also adheres to the element body, so that an insulating film is formed on portions other than the external electrode. It was necessary to provide this, which led to complicated processes.

  In order to solve the above-mentioned problems, the present invention includes a step of alternately laminating varistor layers and internal electrodes and then integrally firing to obtain a sintered body, and forming a first silver paste on the side surface of the sintered body by printing And a step of forming a first external electrode by baking, and a step of applying a second silver paste on the first external electrode and baking to form a second external electrode. The first silver paste is obtained by adding a binder and a plasticizer to the first silver powder, and the second silver paste is obtained by adding a binder, a plasticizer, and a glass frit to the second silver powder. Therefore, the 50% particle size of the particle size distribution of the second silver powder is three times or more than the 50% particle size of the particle size distribution of the first silver powder.

  By performing as described above, the bonding between the first external electrode and the internal electrode can be strengthened, and the silver particle growth rate at the time of firing can be increased by the difference in the particle diameters of the first silver powder and the second silver powder. Unlikely, the glass component in the second silver paste diffuses into the first external electrode. As a result, the glass present on the surface of the second external electrode can be reduced, and the second external electrode can be directly soldered to the second external electrode without forming a plating layer on the second external electrode. In addition, solder dipping can be performed, and the process can be simplified.

Sectional drawing of the lamination | stacking varistor in one embodiment of this invention Sectional drawing of another laminated varistor in one embodiment of the present invention

  Hereinafter, a laminated varistor according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of a laminated varistor according to an embodiment of the present invention.

  The sintered body 11 is obtained by adding bismuth oxide or the like to zinc oxide, mixing a plasticizer, a binder, and the like, forming a sheet, printing an internal electrode paste, laminating, separating, and then about 900 ° C. It is obtained by baking with. The internal electrode paste is a mixture of silver powder mixed with a binder and the like, which is fired simultaneously with the element body to form the internal electrode 13 and the varistor layers 12 and the internal electrodes 13 are alternately laminated. 11 is obtained. By chamfering the sintered body 11 with an abrasive, the corners are chamfered and the internal electrodes 13 are exposed on the side surfaces of the sintered body 11. The size of the sintered body 11 is about 7 mm in width, about 8 mm in length, and about 4 mm in height. The glass component contained in the sintered body 11 is about 0.4 wt%.

  Next, the sintered body 11 is aligned so that the side surface where the internal electrode 13 is exposed, the first silver paste is printed so as to cover the exposed internal electrode 13, and is fired at about 800 ° C. The external electrode 14 is formed. The 1st silver paste uses what added the binder and the plasticizer to the 1st silver powder. The first silver powder is made of silver powder having a 50% particle size distribution of about 0.7 μm.

  Since the first external electrode 14 made of silver is directly formed on the exposed internal electrode 13, the electrical connection between the internal electrode 13 and the first external electrode 14 can be stabilized. . The thickness of the first external electrode 14 is about 10 μm. Further, since the first external electrode 14 is formed by printing, it is provided almost only on the side surface of the sintered body 11. The varistor layer 12 sandwiched between the internal electrodes 13 is an important region for determining electrical characteristics. Since a paste obtained by mixing a binder or the like with silver powder is used for the first external electrode 14, it is possible to prevent unnecessary material from diffusing into this region and to stabilize electrical characteristics.

  Next, a second silver paste is applied so as to cover the first external electrode 14, dried, and baked at about 800 ° C. to form the second external electrode 15. The maximum thickness of the second external electrode 15 is about 20 μm. The 2nd silver paste uses what added the binder, the plasticizer, and the glass frit to the 2nd silver powder. The amount of glass frit is about 15 wt%. The second silver powder is made of silver powder having a 50% particle size distribution of about 2.1 μm. Thus, by setting the 50% particle size of the particle size distribution of the second silver powder to three times or more the 50% particle size of the particle size distribution of the first silver powder, the silver particle growth rate at the time of firing differs, and the second The glass component in the silver paste diffuses into the first external electrode 14.

  By doing in this way, the ratio of the glass component of the 1st external electrode 14 observed from the cross section after forming the 2nd external electrode 15 is about 20%, and the ratio of the glass component of the 2nd external electrode 15 Is about 6%. Thus, the glass component on the surface of the second external electrode 15 is almost eliminated by setting the ratio of the glass component of the first external electrode 14 to at least twice the ratio of the glass component of the second external electrode 15. Thus, a laminated varistor with good solderability can be obtained.

  If the sintered body 11 contains too much glass component, the glass in the second silver paste cannot sufficiently move toward the sintered body 11, so the sintered body 11 contains 3 wt% of the glass component. % Or less is desirable.

  FIG. 2 is a cross-sectional view of another laminated varistor according to an embodiment of the present invention.

  Solder dipping is performed on the second external electrode 15 of the multilayer varistor of FIG. 1 to form a layer of solder 16 and lead terminals 18 are connected. The lead terminal 18 is formed by punching an iron or phosphor bronze plate into a predetermined shape and then bending it into an L shape. The lead terminal 18 is formed with a nickel and tin plating layer, and a solder layer 17 is provided in a region in contact with the external electrode. In this way, the lead terminal 18 and the external electrode are brought into contact with each other, heated with a laser or the like to melt the solder layer 17, the lead terminal 18 is connected to the external electrode, and a laminated varistor with a lead terminal can be obtained. . By doing in this way, even if the shape of a laminated varistor becomes large, the laminated varistor strong against a heat cycle can be obtained.

  The method for producing a laminated varistor according to the present invention is industrially useful because a laminated varistor having good solderability can be obtained without forming an insulating film on the surface of the element body.

DESCRIPTION OF SYMBOLS 11 Sintered body 12 Varistor layer 13 Internal electrode 14 1st external electrode 15 2nd external electrode 16 Solder 17 Solder layer 18 Lead terminal

Claims (3)

A step of alternately laminating varistor layers and internal electrodes and then firing them integrally to obtain a sintered body, and forming and baking a first silver paste on the side surface of the sintered body to form a first external electrode Forming a second external electrode by applying and baking a second silver paste on the first external electrode, the manufacturing method of the laminated varistor, 1 silver paste is obtained by adding a binder and a plasticizer to the first silver powder, and the second silver paste is obtained by adding a binder, a plasticizer, and a glass frit to the second silver powder. 2. A method for producing a laminated varistor, wherein the 50% particle size distribution of the silver powder of No. 2 is at least three times the 50% particle size distribution of the first silver powder. The ratio of the glass component of the first external electrode observed from a cross-section after baking of the second external electrode is at least twice the ratio of the glass component of the second external electrode. A method of manufacturing a laminated varistor. The method for producing a laminated varistor according to claim 1, wherein the sintered body has a glass component of 3 wt% or less.