JP6158595B2 - Thermistor element - Google Patents

Description

  The present invention provides a thermistor part, which is a plate-like metal oxide sintered body whose resistance value changes according to temperature, and a first surface of the plate-like thermistor part and a second surface opposite to the first surface. The present invention relates to a thermistor element including a pair of electrode portions formed in each.

  2. Description of the Related Art A thermistor element for detecting the temperature of exhaust gas or the like flowing in an automobile exhaust pipe is known. This type of thermistor element includes, for example, a thermistor portion, an electrode portion, and a lead wire. The thermistor part is a plate-like metal oxide sintered body whose resistance value changes according to temperature. The electrode portion is a layer containing a conductive metal formed on the first surface of the plate-like thermistor portion and the second surface opposite to the first surface. The lead wire is joined to the electrode part. The thermistor element can detect the ambient temperature by taking out the change in the resistance value of the thermistor part through the lead wire.

  When the thermistor element is used in an environment of high thermal shock or high thermal vibration, there is a problem that the electrode part is peeled off from the thermistor part. Therefore, various techniques for increasing the bonding strength between the thermistor part and the electrode part have been studied. For example, in the thermistor element described in Patent Document 1, the thermistor portion and the electrode portion include the same insulating metal oxide that is a common material.

JP 2012-74604 A

  In the thermistor element described in Patent Document 1, the chemical bonding force between the thermistor portion and the electrode portion is improved, but the physical conditions for improving the bonding strength between the thermistor portion and the electrode portion are as follows. It was not examined.

  An object of the present invention is to provide a thermistor element in which peeling is unlikely to occur at a joint portion between a thermistor portion and an electrode portion.

  The thermistor element which concerns on 1 aspect of this invention is a thermistor part which is a plate-shaped metal oxide sintered compact from which resistance value changes according to temperature, the 1st surface of the plate-shaped thermistor part, and the 1st surface A thermistor element comprising a pair of electrode portions formed on each of the second surfaces opposite to each other and a pair of lead wires connected to each of the pair of electrode portions, wherein the thermistor portion Each of the first surface and the second surface is polished, and each of the first surface and the second surface of the thermistor portion is a recess recessed in the thickness direction of the thermistor portion, and is perpendicular to the thickness direction. A plurality of recesses having a portion on the outside of the second projection figure when the first projection figure when projecting the entire depression on a flat surface projects the opening of the depression on the vertical plane Each of the pair of electrode portions has a small number of the recessed portions. A convex portion meet some and also, a plurality have a convex portion having a portion where the third projection figure when projected itself to the plane perpendicular is outside of said second projected figure.

  According to the thermistor element of this aspect, the convex part of the electrode part is formed in the concave part provided in each of the first surface and the second surface of the thermistor part. The shape of the recess is a shape in which the first projection graphic has a portion that is outside the second projection graphic. The shape of the convex portion is a shape in which the third projected graphic has a portion that is outside the second projected graphic. When force is applied to the thermistor element to peel off the thermistor part and the electrode part, the convex part is caught by the concave part because the convex part has a part that is outside the opening of the concave part in a plane perpendicular to the thickness direction. For this reason, a convex part is not pulled out from a recessed part, without a recessed part or a convex part deform | transforming. Therefore, the thermistor element of this aspect has a larger bonding strength between the thermistor part and the electrode part than the conventional thermistor element in which the electrode part is formed on the first and second surfaces of the thermistor part in which only the irregularities are formed, The electrode part is difficult to peel off from the thermistor part.

1 is a schematic perspective view of a thermistor element 1. FIG. 4 is an enlarged perspective view schematically showing a first surface 11 of the thermistor section 10. FIG. FIG. 2 is a diagram corresponding to a section taken along line 3-3 in FIG. It is a figure which shows a response | compatibility with 51-53. Correspondence between a schematic perspective view of the recess 15 and the opening 14 of the first to third modifications, and projections 51 and 52 when the entire recess 15 and the opening 14 are projected on a surface 50 perpendicular to the thickness direction D of the thermistor portion 10. FIG.

  Embodiments of the present invention will be described with reference to the drawings. Note that the drawings to be referred to are used for explaining technical features that can be adopted by the present invention, and the configuration of the apparatus described is merely an illustrative example. The upper side, the lower side, the left side, the right side, the lower left diagonal side, and the upper right diagonal side of FIG. 1 are respectively defined as the upper side, lower side, left side, right side, front side, and rear side of the thermistor element 1.

The thermistor element 1 is an element incorporated in a temperature sensor, for example, and used for applications such as detecting the temperature of a fluid to be measured such as automobile exhaust gas. The thermistor element 1 mainly includes a thermistor portion 10, a pair of electrode portions 20, a pair of lead wires 40 and a joint portion 30. The thermistor portion 10 is a plate-shaped (cuboid) metal oxide sintered body whose resistance value changes according to temperature. The thermistor portion 10 includes a conductor which is a metal oxide having a perovskite crystal structure having a composition of (Y _0.9 Sr _0.1 ) (Al _0.60 Mn _0.38 Cr _0.02 ) O ₃ Insulating metal oxide for adjusting the resistance value of the thermistor element 1 is included. The first surface 11 and the second surface 12 of the thermistor portion 10 are each polished to adjust the degree of unevenness. Each of the first surface 11 and the second surface 12 preferably has a maximum height roughness Rz of 0.8 (μm) or less.

  As schematically shown in FIG. 2, the first surface 11 and the second surface 12 (see FIG. 1) of the thermistor portion 10 having a plate shape each have a first specific shape recessed in the thickness direction D of the thermistor portion 10. A plurality of recesses 15 are provided. The second surface 12 is a surface opposite to the first surface 11. As shown in FIG. 3, the first specific shape means that the first projection graphic 51 when the entire recess 15 is projected on the surface 50 perpendicular to the thickness direction D of the thermistor portion 10 is the recess on the surface 50. This is a shape having a portion that is outside the second projected figure 52 when 15 apertures 14 are projected. That is, the first projected graphic 51 has a portion that is outside the second projected graphic 52 in a part or all of the direction perpendicular to the thickness direction D. The first projected graphic 51 of the present embodiment is outside the second projected graphic 52 in all directions perpendicular to the thickness direction D. The first projected pattern 51 of the recess 15 of the present embodiment is equal to the cut surface having the largest area among the cut surfaces perpendicular to the thickness direction D of the recess 15.

  As will be described later, the concave portion 15 of this embodiment is formed by circular or elliptical bubbles (pores) formed in the process of sintering the metal oxide sintered body constituting the thermistor portion 10 by polishing. It is exposed on the surface of the sintered product. Therefore, the first surface 11 and the second surface 12 may be each formed with a recess 18 that does not have the first specific shape. Although not shown, in the concave portion 18 not having the first specific shape, the first projection view is equal to the second projection view. That is, the concave portion 18 has no portion that is outside the opening 17 in any direction perpendicular to the thickness direction D.

  The pair of electrode portions 20 is formed on the first surface 11 and the second surface 12 of the thermistor portion 10 having a plate shape. As schematically shown in FIG. 3, the pair of electrode portions 20 has a second specific shape that fills at least part of the recess 15 on the surface 21 and the surface 22 (see FIG. 1) on the side facing the thermistor portion 10. Convex part 23 is provided. The second specific shape is a shape having a portion where the third projection graphic 53 is outside the second projection graphic 52 when projected onto the surface 50 perpendicular to the thickness direction D of the thermistor section 10. That is, the third projected figure 53 has a portion that is outside the second projected figure 52 in a part or all of the direction perpendicular to the thickness direction D. The third projected figure 53 of the present embodiment is outside the second projected figure 52 in all directions perpendicular to the thickness direction D. The convex portion 23 of the present embodiment is formed so as to follow the shape of the concave portion 15. That is, the convex portion 23 fills the concave portion 15. The third projected figure 53 of the present embodiment is equal to the cut surface having the largest area among the cut surfaces perpendicular to the thickness direction D of the convex portion 23. From the viewpoint of the bonding strength between the thermistor portion 10 and the pair of electrode portions 20, it is preferable that the ratio of the convex portion 23 filling the concave portion 15 is larger than the case where the proportion of the convex portion 23 filling the concave portion 15 is small. . This is because the contact area between the thermistor portion 10 and the pair of electrode portions 20 is reduced when there is a gap between the convex portion 23 and the concave portion 15. The concave portions 15 and the convex portions 23 are preferably distributed substantially uniformly on each of the first surface 11 and the second surface 12. In this case, the bonding strength is substantially uniform over the entire first surface 11 and the second surface 12, and it is possible to avoid peeling of the electrode portion 20 from the thermistor portion 10 due to uneven bonding strength. .

  The right ends of the pair of lead wires 40 are each joined to the vicinity of the center of the pair of electrode parts 20 by the joining part 30. As the lead wire 40, for example, a jumet wire or a wire made of Pt or Pt alloy can be used. The pair of lead wires 40 are substantially parallel to each other and extend in the left-right direction.

  A method for manufacturing the thermistor element 1 will be described. The manufacturing method of the thermistor element 1 includes a metal oxide sintered body forming step, a polishing step, a coating step, a heat treatment step, a cutting step, and a joining step, and each step is performed in this order. Hereinafter, each process with which the manufacturing method of the thermistor element 1 is provided is explained in full detail.

(1) Metal oxide sintered body forming step Y, Sr, Cr, Mn, oxide of Al, or a carbonate of said element, included in the thermistor 10, the chemical formula _(Y 0.9 _{Sr 0.1)} A conductor calcined powder is obtained by weighing the mixture to have a composition of a conductor having a perovskite-type crystal structure of (Al _0.60 Mn _0.38 Cr _0.02 ) O ₃ , and mixing and calcining. The conductor calcined powder is pulverized, and a predetermined amount of an insulating metal oxide is added to the obtained powder, and a binder and the like are appropriately added, and then the mold is filled, and the diameter is 40 mm using a single screw press. And formed into a disk shape having a thickness of 1.5 (mm). A powder (in other words, a molded body) formed into a disk shape is fired at a predetermined temperature in an air atmosphere to obtain a conductive metal oxide sintered body. The predetermined temperature is higher than the firing temperature of the conventional metal oxide sintered body forming step. When firing at a conventional firing temperature, bubbles (pores) are hardly generated in the thermistor wafer after firing. When the powder (molded body) formed into a disk shape is fired at a predetermined temperature, a part of the material melts and a plurality of pores are irregularly formed during solidification. The pores are, for example, spherical and elliptical. The firing temperature and firing time are preferably set so that the maximum diameter of the pores is about 5 to 20 (μm). For example, a disk-shaped powder (molded body) is fired under conditions of 1570 (° C.) and 4 hours.

(2) Polishing Step The first surface 11 and the second surface 12 of the disk-shaped metal oxide sintered body are polished to obtain a thermistor wafer having a thickness of 0.5 (mm). The first surface 11 and the second surface 12 of the disk-shaped metal oxide sintered body of the present embodiment are the circular surfaces having the largest area among the surfaces of the disk-shaped metal oxide sintered body. It is. In the polishing step, a part of the plurality of irregularly formed pores formed in the metal oxide sintered body by the above-described firing is polished, and the recessed pores exposed to the outside of the metal oxide sintered body are polished. It becomes an open pore. Thereby, a recess 15 is formed in each of the first surface 11 and the second surface 12. The first surface 11 and the second surface 12 are preferably polished so that the maximum height roughness Rz is 0.8 (μm) or less. When each of the first surface 11 and the second surface 12 has a maximum height roughness Rz, the electrode portion 20 is formed on each of the first surface 11 and the second surface 12 of the thermistor portion 10. The metal paste, which is the material of the portion 20, can easily reach the recess 15. That is, the convex portion 23 tends to have a shape that fills the concave portion 15.

(3) Application process A metal paste containing a conductive metal is applied to each of the first surface 11 and the second surface 12 of the plate-like metal oxide sintered body that has undergone the polishing process. Specifically, first, a conductive metal powder is kneaded with a binder to obtain a metal paste. The conductive metal powder is, for example, a Pt powder having an average particle diameter of 2 (μm). The binder is, for example, etosel or terpineol. The viscosity of the metal paste is determined in consideration of the surface roughness of the conductive oxide that has undergone the polishing process. Thereafter, a metal paste is screen-printed on each of the first surface 11 and the second surface 12 of the thermistor wafer that has undergone the polishing process. The metal paste reaches the recesses 15 formed in each of the first surface 11 and the second surface 12.

(5) Heat treatment step The thermistor wafer that has undergone the coating step is heat treated, and the electrode portion 20 is baked. The reaction is carried out at 1250 ° C. for 48 hours. By the heat treatment step, the electrode portion 20 made of a metal paste is formed on the first surface 11 and the second surface 12 of the metal oxide sintered body.

(6) Cutting step The metal oxide sintered body and the metal layer that have undergone the heat treatment step are cut into a plurality of thermistor chips having the metal oxide sintered body as the thermistor portion 10 and the metal layer as the pair of electrode portions 20. To do. The thermistor chip has, for example, a rectangular parallelepiped shape of 0.50 (mm) × 0.50 (mm) × 0.35 (mm).
(7) Joining process A pair of lead wires 40 are joined to the pair of electrode portions 20 included in the thermistor chip cut out in the cutting process using a metal paste. The metal paste is obtained by kneading a conductive metal powder and a binder. The conductive metal is, for example, Au, and the binder is, for example, etosel and terpineol. The thermistor element 1 is obtained through the above steps.

  According to the thermistor element 1, when a force in the thickness direction D is applied to the thermistor element 1 to peel off the thermistor portion 10 and the electrode portion 20, the convex portion 23 is a concave portion on the surface 50 perpendicular to the thickness direction D. Since it has a part which becomes outside the opening 14 of 15, it is caught in the recess 15. For this reason, the convex part 23 is not pulled out from the concave part 15 without the concave part 15 or the convex part 23 being deformed. Therefore, the thermistor element 1 has a larger bonding strength between the thermistor part 10 and the electrode part 20 than the conventional thermistor element in which the electrode part is formed on the first surface and the second surface of the thermistor part where only the irregularities are formed, The electrode part 20 is difficult to peel off from the thermistor part 10. Even when the thermistor element 1 cannot obtain a sufficient bonding strength only by the chemical bonding force between the thermistor portion 10 and the pair of electrode portions 20, The bonding strength between the electrode part 20 and the thermistor part 10 can be increased.

  The method for manufacturing the thermistor element 1 of the present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the scope of the present invention. For example, the following modifications (A) to (E) may be added as appropriate.

(A) The thermistor portion 10 of the thermistor element 1 of the present embodiment has a perovskite type having a composition of (Y _0.9 Sr _0.1 ) (Al _0.60 Mn _0.38 Cr _0.02 ) O ₃ . A conductor which is a metal oxide having a crystal structure is included, but is not limited thereto. Specifically, Y, Nd, Sm, Gd, Yb, Sr, Ca, Mg, or the like may be included as the A site of the chemical formula ABO ₃ showing a perovskite crystal structure. Further, the thermistor element 1 may be configured by including Al, Cr, Mn, Fe, Co or the like as the B site in the thermistor section 10. Even in such a case, the same effect can be obtained.

  (B) As shown in FIG. 3 of Japanese Patent Application Laid-Open No. 2012-74604, the thermistor element 1 has a thermistor portion 10, an electrode portion 20, a joint portion 30, and a lead wire 40 partially covered with a glass layer. Also good. The material of the glass layer may be crystallized glass or amorphous glass. In this case, when the thermistor element 1 is actually used, it is possible to effectively suppress the thermistor portion 10 from changing its characteristics due to the influence of the external atmosphere. Moreover, since the junction part 30 is coat | covered with a glass layer, the connection state of the lead wire 40 and the electrode part 20 can be maintained stably. In this case, in the manufacturing process of the thermistor element 1, a step of forming a known glass layer may be performed after the bonding step of S7.

  (C) The shape of the recess 15 may be any shape as long as it is the first specific shape described above. Therefore, for example, an elliptical shape inclined with respect to the thickness direction D may be used like the concave portion 15 of the first modification of FIG. In another example, shapes other than a circular shape and an elliptical shape may be used, such as the concave portion 15 of the modified examples 2 and 3 in FIG. As in the modified examples 1 and 2, the first projected graphic 51 of the recess 15 having the first specific shape is the second projected graphic 52 in a part of the directions perpendicular to the thickness direction D of the thermistor section 10. You may have the site | part which becomes outside. The shape of the first projected graphic 51 indicates the position of the outermost portion with respect to the opening 14 in each direction perpendicular to the thickness direction D.

  As in the first modification, the second projected pattern 52 of the recess 15 having the first specific shape may be a cut surface having the maximum area among the cut surfaces perpendicular to the thickness direction D of the recess 15. That is, the first projected graphic 51 of the concave portion 15 having the first specific shape may not be a cut surface having the largest area among the cut surfaces perpendicular to the thickness direction D of the concave portion 15. In the first modification, when all of the plurality of recesses 15 have the same shape, it is preferable that at least some of the plurality of recesses 15 are inclined in different directions with respect to the thickness direction D.

  (D) The shape of the convex portion 23 may be any shape as long as it has the above-described second specific shape. The convex portion 23 may have a shape that satisfies a part of the concave portion 15. The convex portions 23 having the second specific shape need not be formed in all the concave portions 15. From the viewpoint of increasing the bonding strength between the thermistor portion 10 and the pair of electrode portions 20, the larger the convex portion forming ratio, which is the number of convex portions 23 relative to the number of concave portions 15, is preferable than the case where the convex portion forming ratio is small. .

  (E) The manufacturing method of the thermistor element 1 may be changed as appropriate. For example, the metal oxide sintered body that is the precursor of the thermistor portion 10 of the present embodiment is obtained in the above-described (1) metal oxide sintered body step by obtaining a molded body obtained using a uniaxial press machine. The molded body is fired, but is not limited to this. For example, an insulating metal oxide, an appropriate binder, and the like are added to the calcined conductor powder to perform sheet molding, and the obtained sheet molded body (for example, thickness 1.0 mm) is fired at a predetermined temperature. A plurality of pores may be formed in the metal oxide sintered body. In other examples, the formation method of the recessed part 15 may be changed suitably.

DESCRIPTION OF SYMBOLS 1 Thermistor element 10 Thermistor part 11 1st surface 12 2nd surface 14 Opening 15 Concave part 20 Electrode part 23 Convex part 30 Joint part 40 Lead wire 50 Surface 51 First projection figure 52 Second projection figure 53 Third projection figure

Claims (1)

A thermistor part which is a plate-like metal oxide sintered body whose resistance value changes according to temperature;
A pair of electrode portions formed on each of the first surface of the plate-like thermistor portion and the second surface opposite to the first surface;
A thermistor element comprising a pair of lead wires connected to each of the pair of electrode portions,
Each of the first surface and the second surface of the thermistor portion is polished,
Each of the first surface and the second surface of the thermistor part is a recessed part that is recessed in the thickness direction of the thermistor part, and is the first when the entire recessed part is projected on a surface perpendicular to the thickness direction. The projection figure includes a plurality of recesses having a portion that is outside the second projection figure when the opening of the recess is projected onto the vertical plane,
Each of the pair of electrode parts is a convex part that fills at least a part of the concave part, and a third projection figure when projecting itself onto the vertical plane is outside the second projection figure. A thermistor element comprising a plurality of convex portions having portions.

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