JPH04291903A - Manufacture of thermistor - Google Patents

Abstract

PURPOSE:To manufacture large quantities of thermistor chips whose electric resistance values are scarcely extremely clispersed without requiring a sorting test. CONSTITUTION:A molded body by a metal compound which contains Mn, Co and/or Ni or by its precursor is baked at a temperature at which a spinel phase is not transferred to a to a rock salt phase; a sintered body whose surface layer part includes a rock salt phase is obtained. The surface layer of, preferably, on both ends of the sintered body is removed. Then, a wafer is obtained from it; a thin-film electrode is preferably vapor-deposited; chips are formed; only the chips at the inside are gathered.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thermistor having negative resistance-temperature characteristics. 2. Description of the Related Art A thermistor has the characteristic that its electrical resistance value changes significantly when the temperature changes. Among these thermistors, NTC (Ne
gative Temperature
Thermistors are used in various fields, such as temperature measurement and temperature control. [0003] NTC thermistors currently in practical use include 2- to
There is a four-component spinel metal oxide sintered body, and in order to adjust the resistivity ρ and temperature coefficient α, Ti and A
1 of oxides may be mixed. [0004] In addition, as a thermistor for measurement, for example, a heat-resistant conductive paint is baked on both outer surfaces of a thermistor chip body made of the above-mentioned sintered body as a chip to form electrodes, and metal lead wires are connected to the electrodes. It is composed of [0005] However, the sintered body having the above composition shows a spinel phase as a main component phase in its inner region, but a rock salt phase is present in the surface layer in addition to the spinel phase. exists as a subcomponent. Alternatively, the rock salt phase that existed immediately after firing is reoxidized during cooling and re-dissolved in the spinel phase, forming a spinel phase with high porosity in the surface layer of the sintered body due to reoxidation. . In this case, the rock salt phase on the surface side of the rock salt phase in the surface layer is usually reoxidized, resulting in a layer showing a spinel phase due to reoxidation and a layer containing a mixture of rock salt and spinel phases. They are formed on the surface layer in this order. [0006] A region exhibiting such a rock salt phase or a reoxidized spinel phase has a higher electrical resistivity than a region exhibiting a spinel phase. For this reason, when the sintered body is made into a chip to form a thermistor chip, the resistance value of the chip differs depending on the position at which it is cut out, and variations in electrical resistance value occur between the chips. [0007] Furthermore, when baking electrodes onto a sintered wafer, the electrical resistivity within the wafer varies greatly locally, so positional variations in electrical resistivity also occur within the region exhibiting the spinel phase within the wafer. There is a problem that arises. Therefore, in addition to the influence of the rock salt phase, variations in electrical resistivity occur between the thermistor chips due to variations in electrical resistivity during electrode baking. An object of the present invention is to provide a thermistor manufacturing method for obtaining a thermistor chip with small variations in electrical resistance value and a thermistor body realized by such thermistor chip. [Means for Solving the Problems] Such objects are achieved by the present invention as described in (1) to (5) below. (1) A metal oxide and/or a precursor thereof, wherein the metal consists essentially of Mn, Co and/or N.
After molding the powder i, it is fired at a temperature at which the spinel phase transitions to a rock salt phase to obtain a sintered body having a rock salt phase in the surface layer, and the surface layer of this sintered body is removed, A method for manufacturing a thermistor, characterized by obtaining a thermistor element. (2) Co-precipitation method with Mn, Co and/or N
The method for manufacturing a thermistor according to (1) above, wherein a compound containing i is obtained, and the compound is roasted to create the powder having an average particle size of 1 μm or less. (3) Obtain a wafer from the thermistor body described in (1) or (2) above, form a thin film electrode on the surface of the wafer by vapor deposition, and then divide it into chips to separate the chips in the wafer core. 1. A method for manufacturing a thermistor, the method comprising: collecting a thermistor chip to obtain a thermistor chip having a thin film electrode on the thermistor chip body. (4) The method for manufacturing a thermistor according to (3) above, wherein the density of the thermistor chip body is 99% or more of the theoretical density. (5) The method for manufacturing a thermistor according to (3) or (4) above, wherein the thermistor chip has a porosity of 1% or less. [Operation] In the method for manufacturing a thermistor of the present invention, powder of a predetermined metal oxide or its precursor is molded and then fired at a temperature at which the spinel phase transitions to a rock salt phase, so that the surface layer has a rock salt phase. Obtain a sintered body. [0010] Then, the surface layer portion of the obtained sintered body, that is, the high resistance region where the rock salt phase is mixed, is removed to obtain a thermistor element. Since the entire sintered body does not have to be made into a complete spinel phase, process control becomes extremely easy. Moreover, the sintered body core portion is also densified. Furthermore, by forming thin film electrodes at low temperatures by vapor deposition after obtaining a wafer from the thermistor body, positional variations in electrical resistivity during electrode formation within the wafer are reduced. [0012] Furthermore, when the wafer on which electrodes are formed is made into chips, only the thermistor chips that exhibit a spinel phase throughout and are obtained from a region that substantially does not contain a rock salt phase or a spinel phase due to reoxidation are selected. For this reason,
Variations in electrical resistance values between thermistor chips can be reduced. Furthermore, according to the thermistor manufacturing method of the present invention, it is possible to suppress the variation in electrical resistance between chips within a predetermined range, for example, within a range of ±1%, without conducting a separate screening test. Yield is improved. In addition,
It is advantageous in mass production because it eliminates the sorting process. Furthermore, by using a powder produced by roasting a compound obtained by a coprecipitation method, a dense sintered body can be obtained even if it is fired at a lower temperature. Furthermore, the region having the rock salt phase can be made smaller, and waste of material can be prevented. [Specific Configuration] The specific configuration of the present invention will be explained in detail below. The thermistor element of the thermistor of the present invention is:
It is essentially composed of a spinel-based metal oxide sintered body. The constituent metal elements of the metal oxide sintered body are substantially Mn, Co and/or Ni. According to the present invention, these can reliably control the crystal phase. In this case, when the contents of Mn, Ni, and Co are respectively set as X mol%, Y mol%, and Z mol% (X+Y+Z=100), the composition of Mn, Ni, and Co (X, Y, Z) is a ternary composition diagram as shown in Figure 2,
A(100,0,0), B(0,0,100), C(3
5,35,30), D(65,35,0) and does not include point A or point B. Note that the expression "substantially Mn, Co and/or Ni" also includes cases where unavoidable impurities are contained. Next, a method for manufacturing the thermistor of the present invention will be explained. First, a powder of the metal oxide and/or its precursor, particularly a spinel-structured metal oxide powder, is obtained. [0021] There are no particular restrictions on the method for producing the powder, and various conventionally known dry methods, wet methods, such as solid phase methods, etc. may be used, but in the present invention, Mn, Co and/or It is preferable to prepare a powder by obtaining a compound containing Ni and roasting the compound. In this case, the precipitating agent is preferably an oxalic acid compound or oxalic acid, such as ammonium oxalate. Incidentally, the method for forming the precipitate may be performed according to a conventionally known method. [0022] The roasting temperature is preferably about 300 to 900°C, particularly about 300 to 500°C. If it exceeds the above range, the particle size will become coarse and the time required for pulverization will increase; if it is below the above range, roasting will be insufficient. [0024] The roasting time is preferably about 1 to 2 hours, and is usually roasted in the atmosphere. [0025] By using the coprecipitation method, a spinel structure can be obtained even when roasted at the above-mentioned low temperature, and therefore it can be easily pulverized to the desired particle size as described below. [0026] Next, the roasted product is pulverized to obtain a powder. There are no particular restrictions on the pulverization method; for example, after coarsely pulverizing in a mortar or the like, it may be finely pulverized in a ball mill or the like. The average particle size of the powder is 1 μm or less, particularly 0.0 μm or less.
3 to 0.9 μm is preferable. If the temperature exceeds the above range, a dense sintered body cannot be obtained when fired at the desired temperature described below, and if the temperature falls below the above range, pulverization is difficult. The average particle size may be measured by laser diffraction. Next, the obtained powder is mixed with a binder and then molded to obtain a molded body. The binder used is preferably polyvinyl alcohol, to which ion-exchanged water or the like is added if necessary. [0031] There are no particular restrictions on the shape or dimensions of the molded product, but when molded into a cylindrical shape, for example, the dimensions are usually about 50 to 60 mm in diameter and about 15 to 20 mm in thickness. Next, the molded body is fired at a temperature at which the spinel phase transitions to the rock salt phase. [0033] In this case, since the phase transition temperature differs depending on the composition of the sintered body, the firing temperature cannot be unambiguously determined, but it is preferably selected appropriately within the range of about 1000 to 1400°C. For example, Mn (65 to 70
mol%), Co (15-20 mol%) and Ni (15
When obtaining a metal oxide sintered body of 20 mol %), the firing temperature is preferably higher than 1200°C and lower than 1350°C. If the firing temperature is below 1200 degrees, a dense sintered body cannot be obtained;
When the temperature exceeds 50°C, the phase transition to rock salt phase becomes significant. [0035] The firing time is preferably about 1 to 2 hours, and is usually fired in the atmosphere. The sintered body thus obtained has a rock salt phase in the surface layer, a spinel phase throughout the interior, and substantially no rock salt phase. The surface layer usually has a reoxidized spinel phase produced by reoxidation of the rock salt phase after sintering, and a phase in which the rock salt phase and spinel phase are mixed, in this order from the surface side. In order to confirm the crystal structure of the thermistor sintered body, a composition image of a cross section of the sintered body is obtained using a scanning electron microscope (SEM).
It can be observed by In this case, the spinel phase and the reoxidized spinel phase can be determined, for example, by the size of the porosity, and if there is no area where the rock salt phase and spinel phase coexist in the surface layer, the reoxidized spinel phase is substantially present in the surface layer. It may be determined that it does not exist. Note that the porosity of the reoxidized spinel phase is about 2% or more. Note that the porosity of a sintered body or the like can be determined by observing a cross section with a scanning electron microscope (SEM) and calculating the pore area ratio. The sintered body thus sintered has an extremely dense and homogeneous spinel phase core inside the surface layer. Therefore, in the next step, the surface layer of the sintered body,
That is, the thermistor body is obtained by removing the region exhibiting the reoxidized spinel phase and the region in which the rock salt phase and the reoxidized spinel phase are mixed. In this case, the thermistor element is sliced into a wafer shape in a later step and further made into chips, so in the present invention, in this step, the slice start end and slice end point when slicing into a wafer shape are determined. Just remove it. For example, it is preferable to obtain a cylindrical sintered body and remove the surface layer portions on both end faces thereof. Removal thickness is generally 1-2m
Let it be m. The removed thickness may be determined experimentally in advance depending on the sintering conditions. [0041] Through such a removal step, it is possible to stably obtain a sintered body having a homogeneous and dense core portion inside. On the other hand, if the entire sintered body is made to have a spinel phase, a slight variation in the sintering conditions will result in defective products, which will require effort in process control. The thermistor element manufactured in this way is sliced into wafer shapes by slicing or the like.
Considered to be a wafer. There is no particular limit to the thickness of the wafer, but it is usually finished to a thickness of about 0.15 to 0.5 mm. Next, thin film electrodes are formed on the surface of the wafer by vapor deposition. The metal film formed by vapor deposition is T
1 selected from i, Cr, Ni, Cu, Ag and Au
The number of laminated metal layers may be one or more than one layer. In addition, during vapor deposition, in order to prevent positional variations in electrical resistivity within the wafer, it is preferable not to heat the wafer.
It is preferable to perform the vapor deposition at about 0 to 150°C. Since the metal is evaporated without heating, the temperature inside the device increases, and as a result, the temperature of the wafer can reach about 150°C. In addition, there are no particular restrictions on the vapor deposition conditions, and the pressure is 10-6P.
It may be carried out by a normal method at a temperature below about a. The thickness of the thin film electrode is usually about 0.5 to 2 μm. Next, the wafer on which the electrodes have been formed is divided into chips by dicing or the like. At this time, only the thermistor chips having a thin film electrode on the thermistor chip body obtained from a region (inner region excluding the outer periphery) that exhibits a spinel phase and does not substantially contain rock salt phase and reoxidized spinel phase in the wafer are used. select. In this way, almost all thermistor chips obtained from one sintered body or thermistor element have a crystal structure in which the entire thermistor chip is substantially composed of a spinel phase. In the present invention, the coefficient of variation CV of the electrical resistance value of the thermistor chip obtained from one thermistor element is set to 0.33% or less, further 0.3% or less, particularly about 0.1 to 0.3%. can. The density of the thermistor chip body is preferably 99% or more of the theoretical density, particularly 99.2 to 100%. If it is less than the above range, there will be a local difference in the density of the sintered body, and the resistance value between chips will vary. Further, the porosity of the thermistor chip body is 1
% or less, more preferably 0.8% or less, particularly 0.5% or less, for example 0.1 to 0.5%. [0049] If the above range is exceeded, the resistance value becomes high in some parts, and the resistance value varies between chips. The porosity may be measured in the same manner as described above. Note that the average grain size of the thermistor chip body is approximately 1 to 30 μm. [0052] The dimensions of the thermistor chip body are not particularly limited and may be determined appropriately depending on the purpose and use, but are usually 1.0 to 3.0 mm x 1.0 to 3.0 mm x
It is about 0.15 to 0.5 mm. [0053] When obtaining chip bodies from the wafer, only chips obtained from the area excluding the area of 1 to 2.5 mm from the outer circumference of the wafer are selected. The excluded region can be easily determined experimentally based on the sintered body manufacturing conditions, similar to the region where both ends are removed, so it is possible to mechanically perform the sorting based on the geometric conditions without conducting a separate sorting test. can. The thermistor chip of the present invention has a lead body connected to a thin film electrode, and is further sealed with glass or molded with resin to form a thermistor element. [Examples] The present invention will be explained in more detail below with reference to specific examples. Example 1 The following solutions A and B were prepared. Solution A An aqueous solution of a sulfuric acid compound (1 mol/l) containing a total of 2.0 mol of Mn, Ni, and Co ions and having a liquid volume of 2000 ml. The content ratio of metal ions in the aqueous solution is Mn: 66 mol%,
Ni: 16.5 mol%, Co: 17.5 mol%. Ion-exchanged water was added to 2.0 mol of solution B (NH4)2C2O4.H2O, and the liquid volume was adjusted to 6667ml. (0.3 mol/l). Next, while stirring Solution A, Solution B was added to Solution A, and the mixture was stirred at 25° C. for 20 minutes. The obtained precipitate was filtered, washed with ion-exchanged water, and then dried at 50° C. for 24 hours. [0061] Next, it was roasted in a sagger at 500°C for 2 hours. When the obtained roasted product was subjected to X-ray diffraction, the following peaks were observed, and it was confirmed that it exhibited a spinel phase. [0063] Plane index Plane spacing (A) (111) 4.809 (220) 2.945 (311) 2.512 (222) 2.405 (400) 2.082 [0064] Next, the roasted product is roughly ground in a mortar. After pulverizing, the mixture was pulverized for 7 hours using a ball mill under the following conditions. [1 liter pot] Roasted product: 120 g Ion exchange water: 180 ml 3φ zirconia balls: 1800 g [0066] And a laser diffraction particle size distribution measuring device
At HELOS & RODOS (SYMPA TEC
A powder with an average particle size of 0.9 μm was obtained using a method of Next, the obtained powder was placed in a mortar, ion-exchanged water was added, mixed, and then molded into a cylinder having a thickness of 15 mm and a diameter of 2 inches. [0068] Next, the molded body was fired in the atmosphere at 1350°C for 2 hours to obtain a sintered body. A composition image of the cross section of the obtained sintered body is shown in FIG. In the figure, the white dots are the rock salt phase, and it can be seen that there is a region where the spinel phase and the rock salt phase coexist at a depth of about 0.3 to 2.5 mm from the surface. It is also found that the spinel phase above the mixed region has many pores and is a reoxidized rock salt phase, and that the interior of the mixed region shows a spinel phase. Furthermore, the molar ratio of Mn, Co and Ni in the sintered body was determined by EMPA and was found to be Mn:Co:Ni.
=66.8:16.3:16.9 (mol%). Next, 2 mm of the surface layer at both ends of the cylindrical sintered body was removed using a slicer to obtain a thermistor element, which was then sliced into wafer shapes and finished to a predetermined thickness using a precision flat lapping machine. Seven wafers each having a thickness of 0.5 mm were obtained. Next, after cleaning the wafer with acetone,
Installed in a vacuum evaporator, the pressure was set to 10-6 Pa or less, and Ti was deposited at 300% without heating the wafer.
A, Cu at 3000A, Ni at 1μm, Au at 30A
00A Films were formed in this order to form four-layer thin film electrodes on both surfaces of each wafer. Note that the temperature during vapor deposition was 150°C. [0072] Then, the wafer on which the thin film electrodes were formed was cut into chips by dicing, and
Only the thermistor chips obtained from the region exhibiting a spinel phase (excluding the surface layer up to 2.5 mm in the outer circumference) were selected. [0073] The dimensions of the thermistor chip are 2.4 mm x
It is 2.4mm x 0.5mm, and 12
60 pieces were obtained. [0074] When the electrical resistance value at 25°C of each of the obtained thermistor chips was measured, the average value of electrical resistivity and the coefficient of variation CV were as follows. Average value: 472.5Ω・cmCV
: 0.3% The relative density of the thermistor chip body to the theoretical density was 99.5%, and the porosity calculated from the pore area determined by cross-sectional SEM observation was 0.5%. Comparative Example 1 Using the sintered body of Example 1, ten wafers each having a thickness of 0.5 mm were obtained in the same manner except that the surface layer portion was not removed from the sintered body. Next, thin film electrodes were formed on each wafer in the same manner as described above, and the wafers were cut into chips by dicing to obtain thermistor chips. However, chips were not selected as in Example 1. [0079] In this way, 2.4 mm x 2.4 mm
A total of 2000 thermistor chips with a size of 0.5 mm were obtained. 25.0°C of each thermistor chip obtained
When the electrical resistance value was measured, the average electrical resistivity value and the coefficient of variation CV were as follows. Average value: 538.1Ω・cmCV
: 40% [Effects of the Invention] In the present invention, a dense thermistor sintered body can be obtained because the firing is carried out at a relatively high temperature at which the spinel phase undergoes a phase transition to the rock salt phase. At this time, variations in electrical resistance values between thermistor chips obtained from one sintered body can be reduced. Moreover, since the surface layer portions of both end faces of the sintered body are mechanically removed, and the chips formed from the sliced wafer can be removed as they are, a sorting process is not necessary, which is advantageous in terms of mass production.

[Brief explanation of the drawing]

FIG. 1 is a photograph substituted for a drawing showing a crystal structure, and is a composition image of a cross section of a thermistor sintered body.

FIG. 2 is a ternary diagram showing preferred composition ranges of Mn, Ni, and Co in the thermistor of the present invention.

Claims (5)

[Claims] 1. After shaping a powder of a metal oxide and/or its precursor, the metal being substantially Mn, Co and/or Ni, a spinel phase undergoes a phase transition to a rock salt phase. 1. A method for manufacturing a thermistor, which comprises firing at a high temperature to obtain a sintered body having a rock salt phase in the surface layer, and removing the surface layer of the sintered body to obtain a thermistor element. 2. A compound containing Mn, Co and/or Ni is obtained by a coprecipitation method, and the compound is roasted to produce the powder having an average particle size of 1 μm or less.
The method for manufacturing a thermistor described in . 3. Obtaining a wafer from the thermistor body according to claim 1 or 2, forming a thin film electrode on the surface of the wafer by a vapor deposition method, dividing the wafer into chips, and collecting the chips in the wafer core. A method for producing a thermistor, comprising obtaining a thermistor chip having a thin film electrode on the thermistor chip body. 4. The method for manufacturing a thermistor according to claim 3, wherein the density of the thermistor chip body is 99% or more of the theoretical density. 5. The thermistor chip body has a porosity of 1.
% or less. 5. The method for manufacturing a thermistor according to claim 3, wherein