JP2003109805A - Method for manufacturing chip type thermistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a chip type thermistor, which has a good property to maintain the shapes of glass layers and baked electrode layers when forming the baked electrode layers and where the surface of the glass layers is flat and excellent in appearance. SOLUTION: At first, a plurality of ceramic greensheets, which have internal electrodes 23 on the upper surfaces, are stacked and then burnt to make a sintered sheet 11. Subsequently, first and second glass pastes are printed on both sides of the sintered sheet and dried and further burned to form a glass layer 14 having a lower glass layer 14a and an upper glass layer 14b. Next, the sintered sheet is cut in a prescribed direction to make a strip thermistor element assembly 13, and the first and second glass pastes are printed sequentially on the cut surfaces of both sides of the thermistor element assembly and dried and then burned to form a glass layer having a lower glass layer and an upper glass layer. Further, the thermistor element assembly is cut in a prescribed direction to make chips 15 and then terminal electrodes 12 are formed at both ends of the chip so as to cover the cut surfaces of the chip.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a chip type thermistor suitable for a temperature compensating thermistor and a surface temperature measuring sensor of various electronic devices. More specifically, the present invention relates to a method for manufacturing a chip thermistor surface-mounted on a printed circuit board or the like. Conventionally, this type of chip thermistor is
Electrodes containing silver-palladium as a main component are baked at both ends of the thermistor body to improve solder heat resistance, and a plating layer is provided on the surface of the baked electrode to improve solder adhesion. In order to prevent the plating from adhering to the surface of the conductive thermistor body during the plating process and changing the resistance value, the applicant of the present invention has set the softening point of the surface of the thermistor body other than the portion where the baked electrode layer is in contact with this electrode. Patent application for a chip type thermistor coated with a glass layer substantially equal to the baking temperature of the layer and having a plating layer formed on the surface of the baked electrode layer has been filed (JP-A-3-250603). In addition, the applicant has made the glass layer a glass, alumina, zirconia,
Patent application for a thermistor made of an inorganic composite material containing an inorganic crystalline material such as magnesia (Japanese Patent Application Laid-Open No. Hei 3-25060).
4). [0003] However, Japanese Patent Laid-Open No. 3-2
In the thermistor disclosed in Japanese Patent No. 50604, since the glass powder and the inorganic crystal powder are difficult to uniformly mix in the paste for forming the glass layer, the paste has poor printability and the surface of the thermistor body after printing is poor. Was not smooth. In addition, bubbles are likely to remain in the inorganic composite material due to the presence of the inorganic crystal during firing of the inorganic composite material. The remaining air bubbles are liable to become open pores, and the plating solution penetrates into the open pores during the plating process in the subsequent process, erodes the thermistor body with the plating solution, and reduces the reliability of the thermistor. there were. In addition, the surface of the glass layer becomes rough after baking of the electrode layer, which impairs the appearance of the thermistor, and when used in a high-temperature and high-humidity environment, the resistance value changes depending on the degree of open pores, thereby lowering product reliability. was there. An object of the present invention is to provide a method for manufacturing a chip type thermistor having good shape retention of a glass layer and a baked electrode layer when the baked electrode layer is formed. Another object of the present invention is to provide a method capable of manufacturing a chip-type thermistor with a smooth glass surface and good appearance. Another object of the present invention is to provide excellent solder heat resistance and solder adhesion, no change in resistance due to plating of a baked electrode layer, and no change in resistance even in an environment such as high temperature and high humidity. It is an object of the present invention to provide a method capable of manufacturing a chip type thermistor with high reliability. Still another object of the present invention is to provide a method for manufacturing a chip type thermistor having high strength against tensile stress caused by thermal stress. According to the first aspect of the present invention, as shown in FIGS. 2 and 3, a ceramic green sheet for a thermistor body is thinly formed and a conductive paste is formed on the upper surface of the sheet. After forming and drying the internal electrode 23, a plurality of ceramic green sheets having the internal electrode 23 are stacked to form a sheet-like laminate, and the laminate is fired to form the ceramic sintered sheet 11, After printing and drying the first glass paste on both sides of the sintered sheet 11, the second glass paste is printed, dried and further fired to form a lower glass layer 14a made of crystallized glass having an insulating property. Forming a glass layer 14 consisting of an upper glass layer 14b made of amorphous glass having sealing and insulating properties; Cutting the ceramic sintered sheet 11 covered with the above into strips in a direction orthogonal to the row direction of the internal electrodes 23 to form a strip-shaped thermistor body 13; Forming a glass layer 14 comprising a lower glass layer 14a and an upper glass layer 14b by sequentially printing, drying and firing the same first and second glass pastes as the first and second glass pastes; The chip 15 is cut by finely cutting the strip-shaped thermistor body 13 in a direction perpendicular to the cut surfaces on both sides of the strip-shaped thermistor body 13 and along the center line in the width direction of the internal electrode 23, and then cutting the chip 15 Baking electrode layer 16, Ni plating layer 18 and Sn / P
forming a terminal electrode 12 made of a b-plated layer 19. The chip type thermistor 10 manufactured by the method of the present invention is, as shown in FIG.
An insulating glass layer 14 covering the surface of the thermistor body 11 excluding both end faces thereof;
A pair of terminal electrodes 1 provided at both ends including both end surfaces
2, 12, and these terminal electrodes 12, 12 are formed on the baked electrode layers 16 formed at both ends of the thermistor body 11.
And a Ni plating layer 18 and a Sn or Sn / Pb plating layer 19 formed on the surface of the baked electrode layer 16. Part or all of the glass layer 14 is formed of a lower glass layer 14a made of crystallized glass formed on the surface of the elementary body and an upper glass layer 14 made of amorphous glass having a sealing property formed on the lower glass layer 14a. The glass transition point of the precursor glass of the crystallized glass is in the range of 400 to 1000 ° C., and the crystallization temperature is higher than the glass transition point. Here, "precursor glass of crystallized glass" refers to glass before heat treatment for crystallizing crystallized glass. Further, as shown in FIG. 2, the chip type thermistor has a plurality of resistance adjusting internal electrodes 23 electrically connected to a pair of terminal electrodes 12 inside the thermistor element 11, as shown in FIG. The glass layer 14 is configured to cover the element body surface other than the both end surfaces. Although not shown,
The internal electrode 23 also includes a chip thermistor that is not electrically connected to the pair of terminal electrodes 12. The chip type thermistor 10 shown in FIG.
It is manufactured by the following method. As shown in FIG. 3, first, a ceramic green sheet for a thermistor body is formed extremely thinly, a conductive paste is printed on the upper surface of the sheet and dried to form internal electrodes 23 for resistance value adjustment. These green sheets are stacked to form a sheet-like laminate, and the laminate is fired to produce a sintered sheet (FIG. 3A).
The ceramic green sheet is made of Mn, Fe, Co, N
One, two or more kinds of oxide powders of metals such as i, Cu, and Al are mixed, the mixture is calcined and pulverized, and an organic binder is added and mixed to form a thin rectangular parallelepiped. After calcination and pulverization of the mixture of metal oxides, an organic binder and a solvent were added and kneaded to prepare a slurry, and this slurry was formed into a film by a doctor blade method and dried to form a ceramic green sheet. Is also good. Next, glass layers 14 are formed on both sides of the ceramic sintered sheet 11. This glass layer 14 is formed by first printing and drying the first glass paste, then printing and drying the second glass paste, and then firing, so that the glass layer 14 is formed of crystallized glass having an insulating property. It is composed of a glass layer 14a and an upper glass layer 14b formed of amorphous glass having a sealing property and an insulating property (FIG. 3B). Next, the ceramic sintered sheet 11 having both surfaces covered with the glass layer 14 is cut into strips in a direction orthogonal to the column direction of the internal electrodes 23 using a dicing saw such as a cutting machine with a diamond blade ( FIG.
(C)) The same first and second glass pastes as described above are sequentially printed on the cut surfaces on both sides of the strip-shaped thermistor body 13, dried, and then fired to form the lower glass layer 14a and the upper glass layer 14b. Forming a glass layer 14 (FIG. 3)
(D)). Next, the strip-shaped thermistor element body 13 is finely cut in a direction perpendicular to the cut surface and along the center line in the width direction of the internal electrode 23 to form a chip 15 (FIG. 3).
(E)). A conductive paste containing a noble metal powder and an inorganic binder is applied to both ends of the chip so as to surround the cut surface of the chip 15 and fired to form an electrode layer. Further, a chip type having the baked electrode layer 16 as a base electrode layer, a Ni plating layer and a Sn / Pb plating layer 19 formed on the surface thereof, and a terminal electrode 12 composed of a baked electrode layer, a Ni plating layer and a Sn / Pb plating layer. A thermistor 10 is obtained (FIGS. 1, 2 and 3 (f)). The above-described glass layer 14 will be described in detail. This glass layer is partially or entirely composed of two layers, a lower glass layer and an upper glass layer. The lower glass layer is made of crystallized glass formed on the ceramic body, and the upper glass layer is made of hermetically sealed amorphous glass formed on the lower glass layer. The lower glass layer is printed or coated with a glass paste described later, dried, and then baked to form a glass paste.
It is formed to a thickness of about 20 μm. When the lower glass layer is partially crystallized glass, the crystallization ratio is required to be 10% or more to achieve the object of the present invention. Here, the crystallized glass is a glass ceramic produced by firing uniform amorphous glass in the vicinity of its softening point in accordance with a controlled schedule to change into a collection of fine crystals. In order to obtain crystallized glass, an amorphous glass powder (raw glass powder) contained in a glass paste is selected and compounded so as to be crystallizable, and the glass contained in the glass paste is crystallized. It is necessary to bake the dried paste under a predetermined temperature condition. The precursor glass of the crystallized glass has a glass transition point in the range of 400 to 1000 ° C. and a crystallization temperature of the glass so that the density of the lower glass layer after firing the glass paste becomes good. It must be higher than the transition point. The range of the glass transition point is determined in consideration of the firing temperature of the electrode layer. When Ag is used for this electrode layer, the sintering temperature is 600 to 850 ° C., and when the glass transition point is significantly lower than that temperature, for example, when the glass transition point of the precursor glass of the crystallized glass is less than 400 ° C. May have a crystallization temperature lower than 600 ° C., and the crystallized glass may be deteriorated during firing of the electrode layer. When the glass transition point of the precursor glass exceeds 1000 ° C., the crystallization temperature becomes higher than 1000 ° C., and the thermistor element may be deteriorated. On the other hand, the upper glass layer needs to be selected and blended so that the amorphous glass powder (raw glass powder) contained in the glass paste does not crystallize under the above-described firing conditions for the lower glass layer. It is. The upper glass layer is formed to a thickness of about 5 to 20 μm by printing or applying and drying a glass paste containing such a raw material glass powder, followed by firing. In order to achieve the object of the present invention, the crystallization ratio of the lower glass layer is 10% or less, and it is necessary to seal the lower glass layer. The crystallized glass of the lower glass layer has a coefficient of thermal expansion of 40% to 100% of the coefficient of thermal expansion of the thermistor body.
Or less, particularly preferably 50% or more and 90% or less. In the case of the above 40 to 100%, the bending strength of the chip type thermistor is increased as compared with the case where the glass layer is not provided, and the glass layer is made of uncrystallized glass and the coefficient of thermal expansion is It also increases compared to those in the range. In particular, when it is 50 to 90%, the bending strength is increased by 20 to 70%, respectively, as compared with those without the glass layer and those with the glass layer made of uncrystallized glass. On the other hand, if it is outside the range of 40 to 100%, the transverse rupture strength is reduced as compared with those without the glass layer and those with the glass layer made of uncrystallized glass. The transverse rupture strength is defined as 2
This refers to the breaking strength when both ends of a chip thermistor are placed on a single table and a load is applied to the center of the chip thermistor. This is due to the stress (mechanical stress) caused by the mounting machine when the chip-type thermistor is surface-mounted on a printed circuit board, or the stress distortion (thermal stress) caused by heat due to solder or the thermal cycle after mounting. It is a measure of whether you can endure. The increase in the bending strength of the chip type thermistor manufactured by the method of the present invention is considered to be due to the residual compressive stress in the glass layer on the thermistor body surface. That is, when the thermistor element and the glass layer that have been thermally expanded at the time of firing the glass are cooled, the thermistor element having a larger thermal expansion coefficient shrinks more, and the glass layer is in a compressed state. When a bending force is applied to the chip-type thermistor in this state, a compressive stress is generated inside the bend and a tensile stress is generated outside the bend. Both the thermistor body and the glass layer are characterized by being strong in compressive stress and weak in tensile stress. For this reason, if a larger compressive stress is applied to the glass layer in advance, compared to the case where the glass layer is not provided and the case where the glass layer is made of non-crystallized glass, when the bending force is applied, the outside of the bending is reduced. Cracks are less likely to occur due to tensile stress. Like the crystallized glass of the lower glass layer, the thermal expansion coefficient of the amorphous glass of the upper glass layer is 4 times the thermal expansion coefficient of the thermistor body.
It is preferably 0% or more and 100% or less, especially 50% or less.
% Or more and 90% or less. As shown in FIG. 3, first, a plurality of internal electrodes 23 for adjusting a resistance value are formed inside a ceramic sintered sheet 11, and first and second glass sheets are formed on both surfaces of the sintered sheet 11. The paste is printed, dried and further baked to form a glass layer 1 having a lower glass layer 14a and an upper glass layer 14b.
4 is formed. Next, the sintered sheet 11 is cut in a predetermined direction to form a strip-shaped thermistor body 13, and the same first and second glass pastes as described above are sequentially printed on cut surfaces on both sides of the thermistor body 13. After drying and firing, a glass layer 14 having a lower glass layer 14a and an upper glass layer 14b is formed. Furthermore, the strip-shaped thermistor body 13
Is cut in a predetermined direction to form a chip 15, and after baking electrode layers 16 are provided on both ends of the chip so as to wrap the cut surface of the chip 15, plating layers 18 and 19 are provided. The chip thermistor 10 shown is made. The lower glass layer 14a of the glass layer 14 is crystallized glass, and since the glass paste to be the crystallized glass does not contain an inorganic crystal as in the related art, the printability is good and the lower glass layer is formed. Since the crystallization temperature is reached sometimes through the glass transition point, the density of the glass itself after firing is good. The upper glass layer 14 of the glass layers 14
Since b is an amorphous glass and seals the lower glass layer 14a, even if there are fine open pores in the lower glass layer 14a, these open pores are covered and the surface of the glass layer 14 is smoothed. I do. Therefore, the thermistor body 11 is completely covered, and only the baked electrode layer 16 is plated. The two glass layers prevent erosion of the plating solution on the thermistor body 11 and adhesion of the plating to the body 11 during the plating process, and the resistance value of the thermistor does not fluctuate from the expected value. The Ni plating layer 18 improves the solder heat resistance, and prevents the electrode layer 16 from being eroded by the solder when the thermistor is soldered to the substrate. In addition, Sn or Sn /
The Pb plating layer 19 improves the solder adhesion of the terminal electrode 12. Since these plating layers 18 and 19 cover the surface of the baked electrode layer 16 of the noble metal, ion migration of the noble metal hardly occurs. In addition, since the lower glass layer 14a is crystallized glass, the viscosity of the glass itself is less reduced during the formation of the baked electrode layer 16, and the glass layer at the edge of the thermistor body and the baked electrode layer 16 at the edge disappear. No trace of fusion or contact with the firing jig or the like remains on the glass layer 14 after the formation of the electrode layer. Furthermore, if the coefficient of thermal expansion of the crystallized glass is made appropriately smaller than the coefficient of thermal expansion of the thermistor body, a larger compressive stress is given to the glass layer of the manufactured chip-type thermistor, and the chip-type thermistor has no glass layer. Compared to a thermistor or a chip-type thermistor having only a glass layer of uncrystallized glass, cracks are less likely to occur when a bending force is applied to tensile stress outside the bending. As described above, according to the present invention, a glass comprising a lower glass layer and an upper glass layer on both sides of a ceramic sintered sheet having a plurality of internal electrodes for adjusting a resistance value inside. Since the lower glass layer was made of crystallized glass, the glass layer was not softened and deformed during the formation of the baked electrode layer and did not fuse to a firing jig or the like. Since it does not dissolve into the glass layer, the shape retention of the glass layer and the baked electrode layer is improved. By forming an upper glass layer made of amorphous glass on the lower glass layer and sealing the open pores of the crystallized glass, the surface of the glass layer is smooth and the appearance of the thermistor is improved. Further, since the thermistor body is completely protected by the double-layered glass layer, first, after the electrode layer is formed, the resistance value of the thermistor changes due to erosion of the plating solution during plating. Absent. Second, the resistance value does not change in an environment such as high temperature and high humidity after mounting the thermistor. As a result, a highly reliable chip thermistor having plating solution resistance and weather resistance can be obtained. Further, by appropriately selecting the coefficient of thermal expansion, the glass layer can have a higher bending strength than the chip thermistor made of uncrystallized glass.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an external perspective view of a chip thermistor of the present invention. FIG. 2 is a sectional view taken along line AA of FIG. FIG. 3 is a diagram illustrating a manufacturing process of the chip thermistor of FIG. 1; DESCRIPTION OF SYMBOLS 10 Chip type thermistor 11 Thermistor element 12 Terminal electrode 14 Glass layer 14a Lower glass layer 14b Upper glass layer 16 Baked electrode layer 18 Ni plating layer 19 Sn / Pb plating layer 23 Internal electrode for resistance value adjustment

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Yoshihiko Ishikawa             3270 Yokoze, Yokoze, Yokoze-cho, Chichibu-gun, Saitama             Ryo Materials Co., Ltd. Ceramics Laboratory             Inside (72) Inventor Hideto Kataoka             3270 Yokoze, Yokoze, Yokoze-cho, Chichibu-gun, Saitama             Ryo Materials Co., Ltd. Ceramics Laboratory             Inside (72) Inventor Masaki Koshimura             3270 Yokoze, Yokoze, Yokoze-cho, Chichibu-gun, Saitama             Ryo Materials Co., Ltd. Ceramics Laboratory             Inside F term (reference) 5E034 BA09 BB06 DA07 DB04 DC01                       DE01 DE07

Claims (1)

Claims 1. A ceramic green sheet for a thermistor body is thinly formed, a conductive paste is printed on the upper surface of the sheet, dried to form an internal electrode (23), and then the internal electrode (23) is formed. A) stacking a plurality of the ceramic green sheets having a) to form a sheet-like laminate, and firing the laminate to produce a ceramic sintered sheet (11); After printing and drying the glass paste, the second glass paste is printed, dried and further baked to have a sealing and insulating property with the lower glass layer (14a) formed of crystallized glass having insulating properties. Upper glass layer made of amorphous glass
(14b) forming a glass layer (14), and the ceramic sintered sheet (11), both surfaces of which are covered with the glass layer (14), are orthogonal to the row direction of the internal electrodes (23). Forming a strip-shaped thermistor element body (13) by cutting the strip-shaped thermistor element body (13) in the direction; and forming the same first and second glass pastes on the cut surfaces on both sides of the strip-shaped thermistor element body (13). A step of forming a glass layer (14) composed of a lower glass layer (14a) and an upper glass layer (14b) by sequentially printing and drying the second glass paste, followed by firing, and the strip-shaped thermistor body (13) The strip thermistor body (13) is finely cut in a direction perpendicular to the cut surfaces on both sides of the inner electrode and along the center line in the width direction of the internal electrode (23).
After making (15), bake electrode layer (16), Ni plating layer on both ends of chip (15) so as to wrap the cut surface of chip (15)
Terminal electrode (12) consisting of (18) and Sn / Pb plating layer (19)
Forming a chip-type thermistor.