Patent Application
20050062585
1. Field of the Invention
The present invention relates to a resistor and an electronic device.
2. Description of the Related Art
Generally, a resistor paste is mainly constituted of a glass material for adjusting a resistance value and giving a bonding property, a conductive material and an organic vehicle (a binder and a solvent). By printing the paste on a substrate and firing, a resistor having a film thickness of 5 to 25 μm or so is formed.
Many of resistor pastes of the related art use lead oxide based glass as a glass material, and a ruthenium oxide or a compound of ruthenium oxide and lead as a conductive material, so that the pastes include lead.
However, use of a resistor paste containing lead is unfavorable in terms of environment contamination, so that there are a variety of proposals made on a lead-free thick resistor paste (refer to patent articles 1 to 5).
Normally, A resistor having a sheet resistance value of 10 kΩ/□ or more uses Pb2Ru2O5 having a high resistivity as a conductive material. Thus, it has been relatively easy to attain high resistance.
When considering the environment as above, however, not to mention PbO based glasses, it is preferable to prevent using Pb2Ru2O5 as a conductive material. As conductive materials having a comparable resistivity as that of Pb2Ru2O5; BaRuO3, CaRuO3, SrRuO3 and Bi2Ru2O7, etc. may be mentioned. But when forming a resistor with these conductive materials and glass not containing lead, particularly deterioration of short time overload (STOL) as one of voltage resistance characteristics became a problem in a resistor having a resistance value of 100 kΩ/□ or more and it was difficult to adjust the characteristics.
As a reason of the difficulty, there is the fact that knowledge of suppressing STOL has not been obtained because history of studying a thick membrane resistor not containing lead is short comparing with a thick membrane resistor containing lead.
Patent Article 1: The Japanese Unexamined Patent Publication No. 8-253342
Patent Article 2: The Japanese Unexamined Patent Publication No. 10-224004
Patent Article 3: The Japanese Unexamined Patent Publication No. 2001-196201
Patent Article 4: The Japanese Unexamined Patent Publication No. 11-251105
Patent Article 5: The Japanese Patent No. 3019136
An object of the present invention is to provide a lead-free resistor having a high resistance value and small short time overload (STOL), and an electronic device, such as a circuit substrate having the resistor.
To attain the above object, according to the present invention, there is provided a resistor, having a resistor layer including a glass material substantially not containing lead but containing CaO and B2O3 and a conductive material substantially not containing lead, wherein:
The present inventors have found when performing TEM observation on the section in a thickness direction of a resistor layer formed on a substrate that a lead-free resistor having a high resistance value and a small STOL was able to be provided in the case where an occupying area of crystalline substances precipitated in a resistor layer of the observation section was less than 30.0% of an area of the resistor layer of the observation section.
A resistor of the present invention is preferably obtained by forming a resistor paste including a glass material substantially not containing lead but containing CaO and B203, a conductive material substantially not containing lead, and an organic vehicle, then, firing at 830 to 870° C. for 5 to 15 minutes.
Preferably, said glass material includes an A group containing CaO, a B group containing B2O3, and a C group containing SiO2; and contents of the respective groups are A group: 25 to 40 mol %, B group: 20 to 40 mol %, and C group: 20 to 40 mol %.
Preferably, said glass material includes an A group containing CaO, a B group containing B2O3, a C group containing SiO2, a D group containing at least one kind of ZrO2, SrO and CuO, and an E group containing NiO; and contents of the respective groups are A group: 25 to 40 mol %, B group: 20 to 40 mol %, C group: 20 to 40 mol %, D group: 0 to 10 mol % (excluding 0 mol %), and E group: 0.1 to 10 mol %.
Preferably, said conductive material contains at least one selected from BaRuO3, SrRuO3, RuO2 and CaRuO3.
Preferably, said resistor layer includes 65 to 93 volume % of said glass material and 7 to 35 volume % of said conductive material.
According to the present invention, there is provided an electronic device having any one of the above resistors.
In the present invention, the expression “substantially not containing lead” means lead is not included by an amount of exceeding an impurity level, and lead may be contained by an amount of an impurity level (for example, a content in a glass material or a conductive material is 0.05 volume % or less). A trace of lead may be sometimes included as an inevitable impurity.
According to the present invention, a lead-free resistor having a high resistance value (for example, 100 kΩ/□ or more, and preferably 1 MΩ/□ Or more) and small STOL (for example, less than ±7%, and preferably less than ±5%) can be provided. Namely, a resistor of the present invention is highly useful due to the capability of maintaining preferable characteristics even when a temperature and an application voltage in the use environment change.
These and other objects and features of the present invention will become clearer from the following description of the preferred embodiments given with reference to the attached drawings, in which:
Resistor
A resistor according to the present invention has a resistor layer on a substrate. Also, when observing a section along the thickness direction of the resistor layer with a transmission electron microscope (TEM), a resistor according to the present invention has an occupying area of a crystal substance CaB2O4 precipitated in the resistor layer of the observation section is less than 30.0%, preferably 28.0% or less, and more preferably 15.0% or less of an area of the resistor layer of the observation section.
The present inventors found that the smaller an occupying area of a crystal substance CaB2O4, the smaller the STOL can be suppressed while maintaining a high resistance value. On the other hand, in the case where the occupying area of the crystal substance CaB2O4 is too small, when a glass material containing ZrO2 is used, the ZrO2 precipitates, consequently, it may cause deterioration of the STOL. Therefore, the lower limit of the occupying area of the crystal substance CaB2O4 is preferably 5% or so.
Substrate
As the substrate, for example, alumina, glass ceramics, dielectric and AIN, etc. may be mentioned.
Resistor Layer
The resistor layer includes a glass material substantially not containing lead but containing CaO and B2O3 and a conductive material substantially not containing lead.
The glass material substantially not containing lead but containing CaO and B2O3 is not particularly limited, but it preferably includes
More preferably, those containing Cao, B2O3 and SiO2 are used as the glass material.
A content of each group is preferably
The glass material may further contains a D group containing at least one kind selected from ZrO2, SrO, CuO, ZnO, MnO, CoO, Li2O, Na2O, K2O, P2O5, TiO2, Bi2O3, V2O5 and Fe2O3 (preferably, at least one kind of ZrO2, SrO and CuO) in addition to the above A to C groups. Preferably, those containing CaO, B2O3, SiO2 and ZrO2 are used as the glass material.
A content of the D group in this case is preferably 0 to 10 mol % (excepting 0 mol %), and more preferably 0 to 7 mol % (excepting 0 mol %).
Preferably, the glass material further includes an E group containing NiO in addition to the above A to D groups. More preferably, those containing CaO, B2O3, SiO2, ZrO2 and NiO are used as the glass material.
As a result that the E group containing NiO is included in the glass material, an occupying area of the crystal substance CaB2O4 precipitated in the resistor layer can be suppressed, the TCR and STOL of a resistor to be obtained are balanced, and a change over time is effectively suppressed.
A content of the E group in this case is preferably 0.1 mol % or more, more preferably 1 mol % or more and further preferably 2 mol % or more; and preferably 10 mol % or less and more preferably 6 mol % or less.
A conductive material substantially not containing lead is not particularly limited, and a ruthenium oxide, an Ag—Pd alloy, TaN, LaB6, WC, MoSiO2, TaSiO2 and metal (Ag, Au, Pd, Pt, Cu, Ni, W and Mo, etc.), etc. may be mentioned. These substances may be used alone or in combination of two or more kinds. Among these, a ruthenium oxide is preferable.
As the ruthenium oxide, ruthenium oxides (RuO2, RuO3 and RuO4), ruthenium based pyrochlore (Bi2Ru2O7-x and Tl2Ru2O7, etc.) and ruthenium composite oxides (SrRuO3, CaRuO3 and BaRuO3, etc.), etc. are included. Among these, ruthenium oxides and ruthenium composite oxides are preferable, and RuO2, SrRuO3, CaRuO3 and BaRuO3, etc. are more preferable.
Contents of the glass material and conductive material in the resistor layer are, the glass material of preferably 65 to 93 volume % and more preferably 68 to 90 volume %; and the conductive material of preferably 7 to 35 volume % and more preferably 8 to 30 volume %.
A film thickness of the resistor layer may be thin, but is normally 1 μm or more, and preferably 10 to 15 μm or so.
Production Method of Resistor
Next, a production method of the resistor will be explained as an example.
(1) First, a resistor paste is prepared.
Resistor Paste
A resistor paste includes the above glass material substantially not containing lead but containing CaO and B2O3, the above conductive material substantially not containing lead, and an organic vehicle.
The organic vehicle is obtained by dissolving a binder in an organic solvent. The binder used in the organic vehicle is not particularly limited, and may be suitably selected from a variety of normal binders, such as ethyl cellulose and polyvinyl butyral.
Also, the organic solvent to be used is not particularly limited, and may be suitably selected from a variety of organic solvents, such as terpineol, butyl carbitol, acetone and toluene.
A content of the glass material in the paste is preferably 65 to 93 volume % and more preferably 68 to 90 volume % when assuming that volume of the powder is 100.
A content of the conductive material in the paste is preferably 7 to 35 volume % and more preferably 8 to 30 volume % when assuming that volume of the powder is 100.
Note that additives may be included in the paste other than the above components.
As the additives, CuO, oxides having the perovskite type crystal structure (crystal structure expressed by ABX3), ZnO and MgO, etc. may be mentioned.
CuO serves as a temperature characteristic (TCR) adjustor of a resistance value. A content of CuO in this case is preferably 0.1 to 2 volume %, and more preferably 0.5 to 2 volume %. When the adding quantity of CuO increases, the STOL tends to deteriorate.
As oxides having the perovskite type crystal structure, simple perovskite, such as CaTiO3, SrTiO3, BaTiO3, CaZrO3 and SrZrO3, defective perovskite and composite perovskite, etc. may be mentioned. Among these, at least any one of CaTiO3, SrTiO3 and BaTiO3 is preferably used, and more preferably, BaTiO3 is used. Oxides having the perovskite type crystal structure have effects of adjusting balance of the TCR and STOL. A content of an oxide having the perovskite type crystal structure is preferably 0.1 to 12 volume %, and more preferably 1 to 10 volume %.
ZnO serves as a TCR adjustor. A content of ZnO in this case is preferably 0.1 to 5 volume %, and more preferably 1 to 4 volume %. When an adding quantity of ZnO increases, the STOL tends to get worse.
MgO serves as a TCR adjuster. A content of MgO in this case is preferably 1 to 8 volume % and more preferably 2 to 6 volume %. When an adding quantity of MgO increases, the STOL tends to get worse.
As other additives serving as a TCR adjustor, for example, MnO2, V2O5, TiO2, Y2O3, Nb2O5, Cr2O3, Fe2O3, CoO, Al2O3, ZrO2, SnO2, HfO2, WO3 and Bi2O3, etc. may be mentioned.
The resistor paste is produced by adding an organic vehicle to a conductive material, a glass material and a variety of additives to be blended in accordance with need, and kneading, for example, with a three-roll mill.
In this case, a ratio (W2/W1) of total weight (W1) of the glass material, conductive material and respective powders of additives to be added in accordance with need and weight of the organic vehicle (W2) is preferably 0.25 to 4, and more preferably 0.5 to 2.
(2) Next, the above resistor paste is formed on a substrate, for example, by a screen printing method, etc., dried, and fired at a predetermined firing temperature for a predetermined time to produce a resistor.
In the present invention, a preferable firing condition is a firing temperature at 830 to 870° C., preferably 840 to 860° C., and the firing temperature holding time is 5 to 15 minutes, preferably 8 to 12 minutes. When observing a section along the thickness direction of the resistor layer with a transmission electron microscope (TEM), an occupying area of the crystal substance CaB2O4 precipitated in a resistor layer on the observation section can be made less than 30.0% of on area of the resistor layer of the observation section by the burning under such conditions. When the occupying area of the crystal substance CaB2O4 is less than 30.0%, it is possible to provide a lead-free resistor having a small STOL of, for example, ±7% or less, preferably less than ±5% while having a high resistance value of, for example, 100 kΩ/□ or more, and preferably 1MΩ/□ or more.
The produced resistor can be applied to an electrode portion of a capacitor and inductor, etc. other than a single-layer or multilayer circuit substrate as an electronic device.
Electronic Device
An electronic device according to the present invention is not particularly limited, and a circuit substrate, a capacitor, an inductor, a chip resistor and isolator, etc. may be mentioned.
Next, the present invention will be explained further in detail by specific examples of the embodiment of the present invention. Note that the present invention is not limited to the examples.
Production of Resistor Paste
A conductive material was produced as below. Predetermined amounts of CaCO3 or Ca(OH)2 powder and RuO2 powder were weighed to be a composition of CaRuO3, mixed by a ball mill and dried. The obtained powder was heated to 1400° C. at a rate of 5° C./min., kept at the temperature for 5 hours, then, cooled to the room temperature at a rate of 5° C./min. Thus obtained CaRuO3 was grinded by a ball mill and CaRuO3 powder was obtained. The obtained powder was confirmed to have a single phase of a desired compound by an XRD.
A glass material was produced as below. Predetermined amounts of CaCO3, B2O3, SiO2, ZrO2, SrO, CuO and NiO were weighed to be final compositions (10 kinds) shown in Table 1, mixed by a ball mill and dried. The obtained powder was heated to 1300° C. at a rate of 5° C./min., kept at the temperature for 1 hour, then, abruptly cooled by being dropped in water to be vitrified. The obtained vitrification was grinded by a ball mill and glass powder was obtained. The obtained glass powder was confirmed to be amorphous by an XRD.
An organic vehicle was produced as below. Terpineol as a solvent was heated while agitated, ethyl cellulose as a resin is dissolved therein to produce an organic vehicle.
The produced conductive material powder and glass powder were weighed to be compositions shown in Table 2, an organic vehicle was added thereto and kneaded by a three-roll mill to obtain a resistor paste. A weight ratio of total weight of the conductive powder and glass material powder and weight of an organic vehicle was suitably adjusted to be in a range of 1:0.25 to 1:4 and made to be a paste, so that an obtained paste has suitable viscosity for screen printing.
Production of Thick Film Resistor
An Ag—Pt conductor paste was printed to be a predetermined shape on a 96% alumina substrate by screen printing and dried. Ag was 95 wt % and Pt was 5 weight % in the Ag—Pt conductor paste. The alumina substrate was put in a belt furnace by a pattern of one hour from feeding to discharging, so that the conductor was burnt on the substrate. The firing temperature was 850° C. and a holding time of the temperature was 10 minutes. The resistor paste produced as explained above was screen printed to be a predetermined shape (1×1 mm) on the alumina substrate formed with the conductor, and dried. Then, the resistor paste was burnt under the same condition as burning of the conductor, so that a thick membrane resistor was obtained. The thickness of the resistor was 12 μm. Samples obtained by changing the burning temperature (firing temperature) were produced.
Evaluation of Thick Membrane Resistor Characteristics
Characteristics evaluations of a resistance value, STOL, crystal substance occupying area (crystal substance area %) and changes over time were performed on the obtained thick film resistors.
A resistance value was measured by using a multimeter 34401A made by Agilent Technologies. The results are shown in Table 2. In Table 2, average values of 36 samples are shown. In the present example, “a resistor value >100kΩ” was used as a reference of the characteristics.
Evaluation on the STOL (short time overload) was made by applying a test voltage to a thick membrane resistor for 5 seconds, letting stand for 30 minutes, and confirming a change rate of the resistance value before and after that. The test voltage was 2.5 times as much as a rated voltage. The rated voltage was {square root}(R/8). Here, R is a resistance value (Ω/□). Note that resistors having a resistance value by which a calculated test voltage thereof exceeds 200V were evaluated with a test voltage of 200V. The results are shown in Table 2. In Table 2, average values of 10 samples are shown. In the present example, “STOL<±5%” was used as a reference of the characteristics.
A crystal substance area percentage was evaluated by sampling a resistor burnt on an alumina substrate by FIB processing and observing the section with a TEM. A TEM picture of a section of a resistor (sample 14) is shown in
Percentage of changes over time was evaluated by measuring a change rate of a resistance value when letting stand for 1000 hours at 85° C. and 85%RH. In Table 2, average values of 10 samples are shown. In the present example, “changes over time ≦±1.0%” was used as a reference of the characteristics.
As shown in Table 2, in samples 1 to 19, it was confirmed that the STOL becomes preferable when an average occupying area of the crystal substance CaB2O4 in each conductive material is less than 30.0% of an area of the resistor layer of its observation section.
In samples 20 to 23, when changing the firing temperature, the higher the temperature, the larger the crystal substance area becomes, and the STOL gets worse at 900° C. However, when the firing temperature is 800° C., the crystal substance area is small but the STOL is unfavorable. It is because the resistor is not sufficiently sintered. It was confirmed that when using CaO—B2O3—SiO2 based glass, it was necessary to burn at approximately 830° C. or more and preferably at 830° C. to 870° C.
In samples 24 to 27, when changing the holding time of the firing temperature, the longer the holding time is, the larger the crystal substance area becomes, and the STOL gets worse with 20 minutes. The crystal substance area does not change much comparing with that in the case of changing the firing temperature. It was confirmed that 5 to 15 minutes or so was preferable.
In samples 28 to 30, by using a glass material containing NiO, it was confirmed that an occupying area of the crystal substance CaB2O4 precipitated in the resistor layer was suppressed, the TCR and STOL were balanced and, moreover, changes over time were suppressed comparing with those in samples 13 to 16 wherein substantially the same quantity of glass material not containing NiO is used, and conditions of a kind and quantity of a conductive material, a firing temperature and firing holding time are approximately the same.
Note that samples 1, 5, 9, 10, 13, 20, 23 and 27 are comparative examples, and the rest are examples.
The embodiments of the present invention were explained above, but the present invention is not at all limited to the embodiments, and may be variously modified within a scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-329968 | Sep 2003 | JP | national |
