CA1056026A - Resistor composition and method for its manufacture - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
This invention relates to and discloses a novel resistor composition and a process for manufacturing the composition. The composition comprises a conductive material, a glass frit and a vehicle therefor, or a conductive material, a glass frit, an insulating or semiconductive metal oxide and a vehicle therefor. The weight ratio of the conductive material, the glass frit and the metal oxide (when the latter is present) is maintained substantially constant. The resistance value of the composition is established by varying the total surface area of the conductive material and the glass frit and when applicable, the metal oxide, without changing the temperature coefficient of resistance of the composition. The resistor has an excellent, definite and easily obtainable temperature coefficient of resistance whereas in the prior art, it had been impossible to obtain certain definite resistance values without varying the temperature coefficient of resistance.

Description

BACXGR~UND A~D SVMMARY OF THE INVENTION
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The present invention relates to a novel resistor c~mp~sition having an excellent temperature coefficient of ; resistance (TCR) and its method of preparation. More particularly, the present invention is directed to a resistor comp~sition con--taining a conductive material and a glass frit or a conductive material, a glass frit and an insulating or semiconductive metal oxide wherein the weight ratio of said conductive material and said glass frit or said conductive material, said glass frit and 10 said metal oxide is maintained constant and the resistance value --of the resistor composition is determined by varying the total surface area of said conductive material and said glass frit or by varying the total surface area of said conductive material, ,~ said glass frit and said metal oxide without substantially changing the temperature coefficient of resistance of the I resisto~ composition.
In the precious, well-known techniques, the preparation of a resistor composition containing a series of varied resistance values was obtained by controlling the weight ratio of the 20 components of the resistor composition, that is, the weight ratio o-f the conductive material and the resistive material. However, in following the well-known techniques for the preparation of j resistor compositions, the variation of the resistance value was always accompanied by a simultaneous deviation in the temperature coefficient of resistance. Therefore, in the prior art resistor compositions and method of manufacture, it was impossible to obtain certain definite resistance values without varying the temperature coefficient of resistance~
In addition, although an even surface film resistor 30 with higher resistance value is obtainable, adoption of some .

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1 special devices are inevitably required in the preparation processes of the resistor composition. With respect to resistors having a lower resistance value, although composi-tions having satisfactory printing ability are obtainable, the yiel~ed resistors normally have uneven surfaces and also unstable resis-tance values.
The present invention is directed to a resistor composition comprising a conductive material and a glass frit, or a conductive material, a glass frit and an insulating or semi-tO conductive metal oxide, wherein the weight ratio of the conductivematerial and the glass frit and, when present, the said metal oxide is constant and the resistance value of the composition is ` determined by varying the total surface area of the conductive material, the glass frit and, when present, the said metal oxide, -without changing the temperature coefficient of resistance of the composition. In the process for manufacturing the resistor ~
composition of thq present in~ention, conducti~e materials, glass -frit and insulating or semiconductive metal oxides having known ;~ specific areas are utilized and the resistance value of the

2~0 resistor comp~sition is determined by increasing or decreasing the total surface area of said conductive material, said glass ~rit and, when present, said metal oxide, while maintaining the weight ratio of said conductive material, glass frit and said : :
metal oxide constant. Alternatively, the specific surface area of one or two components selected from the above two or three . .
~ components can be either increased or decreased while maintaining .
the specific surface area of the residual component constant -~

and while maintaining the weight ratio of said two components or said three components constant. Advantageously, a vehicle is provided for said two-component or three-component resistor - .

~OS60Z6 1 composition of the present invention.
Thus, according ~o the present invention, the problems encountered in the prior art resistor compositions and processes have been overcome by the teachings of the present invention whicl are summarized as follows:
1. A resistor composition comprising a cond~ctive material, a glass frit and a vehicle therefor wherein the weight ratio of said conductive material to said glass frit is constant and the resistance value of said composition i5 established by varying the total surface area of said conductive material and said glass frit without changing the TCR of said composition.
; 2. A resistor composition comprising a conductive material, a glass frit, an insulating or semiconductive metal oxide and a vehicle therefor, wherein the weight ratio of said conductive material, said glass frit, and said insulating or semi-conductive metal oxide is cons~ant and the resistance value of said composition is established by varying the total surface area of said conductive material, said glass frit and said insulating ox semiconductive metal oxide without changing the TCR of said composition.

3. A process for manufacturing a resistor composition characterized by using a conductive material and a glass frit having known specific surface areas, respectively, and establishing the resistance value of said resistor composition by increasing or decreasing the total surface area of said conductive material and said glass frit while maintaining the weight ratio of said conductive material to said glass frit constant

4. A process for manufacturing a resistor composition characterized by using a conductive matérial, a g7ass frit and an insulating or semiconductive metal oxide having known specific .

lOS6026 1 surEace areas, respectively, and establishing the resistor value of said resistor composition by increasing or decreasing the total surface area of said conductive material, glass frit and insula-ting or semiconductive metal oxide while keeping the weight ratio of said conductive material, glass frit and insulating or semi-conductive metal oxide constant.

5. A process for manufacturing a resistor composition characterized by using a conductive material and a glass frit having known specific areas, respectively, and establishing the resistance value of said resistor composition by increasing or decreasing the specific surface area of ~ne component and main-taining the specific surface area of the other component constant while keeping the weight ratio of said conductive material to said glass frit constant. -

6. A process for manufacturing a resistor composition characterized by using a conductive material, a glass frit and an insulating or semiconductive metal oxide having known speci~ic surface areas, respectively, and esta~lishing the resistance value of said resistor composition by increasing or decreasing the specific surface area of ;one or two components and maintaining the specific surface area of the residual compon~nt or components constant while keeping the weight ratio of said conductive : . .
material, glass frit and insulatlng or semiconductive metal oxide ~; constant.
As mentioned above, one of the main features of the present invention is that a definite resistance value is easily obtained by controlling the total surface area while the tempera-ture coefficient of resistance is maintained substantially constant.
However, the theoretical reasons why this phenomena exists is uncertain. One possible assumption in this connection is an ~ 4 ~ ~
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1 explanation based upon the contact area between the resistive material and the conductive material. But the effects cannot be fully understood from only the above assumption. In any event, the amount of reproducibility involved in the present invention suggests that this is an entirely novel and widely applicable technical contribution which has not yet been fully supported by theoretical bases.
The term "specific surface area" as referred to herein-above shall be defined as the surface area of each l-gram of finely divided particles, and accordingly, the "total surface area"
can be defined by the following equation:
Total surface area = specific surface area X total wt. of particles.
The conductive ma~erial or component which can be utilized in the present invention can be, for example, Au (gold), Ag (silver), Pt (platinum), Rh (rhodium), Ru (ruthenium), Os (osmium), Ir (iridium), V (vanadium), Sn (tin), W (tungsten), C ~carbon), and alloys mixtures, and oxides thereof. These con-ductive materials, after the composition has been fired, become highly conductive particles.

The glass frits which can be used in the resistor composition of the present invention are, generally speaXing, conventional glass frits. Examples of such glass frits include ~-~ the borosilicates and particularly the lead-borosilicates.
The insulating or semiconductive metal oxide which can be used in the resistor composition of the present invention should be capable of producing, after firing, finely divided particles with insulating or semiconductive properties. Exemplary ;~ of suitable insulating or semiconductive metal oxides include palladium oxidej copper oxide, aluminum oxide, zinc oxide, iron oxide, chromium oxide, cobalt oxide, tantalum oxide, nickel oxide, ' , ~

niobium oxide, silicon oxide and the like. Th~ finely divided particles of the said c~nductive material, glass frit and metal oxide are those containing a diameter of about 100 ~ to 50Jff.
The vehicle which can be used in combination with the conductive material, glass frit and the insulating or semiconduc-tive metal oxide in forming the resistor composition of the present inven~ion can be an organic binder, such as, for example, ethyl cellulose, alkyd resins, butyral resins, nitrocellulose, and the like. Any vehicles which are normally used in the resistor field of technology are applicable to the resistor composition and method of the present in~ention.
Examples of suitable solve~ts which can be included in the resistor composition of the present invention include organic solvents such as butyl carbitol, butyl carbitol acetate, terpineol, tetralin, and the like~
In the resistor composition of the present invention, ' the conductive material can be present in an amount of about 10 to 60 parts by weight and the resistive material, which includes the glass frit alone or the glass frit and the insulating or ; 20 semiconductive metal oxide can be present in an amoun~ of about 40 ` to 90 parts by weight.
The specific surface area of the conductive material, - glass frit and insulating or semiconductive metal oxide can be varied from 0.02 to about 270 m2/g. Within this range, the specific surface area of the conductive material can vary from about 0.02 to about 85; the specific surface area of the glass frit can vary from about 0.05 to 2.0, and the specific surface area of the insulating or semiconductive metal oxide can vary from about 0.5 to 265.

- 6 - ~ -l~S60Z6 DESCRIPTION OF TE:~E PREFERRED EMBODIMENTS
The following examples are given merely as being illustrative of the presen-t invention and thus are not to be considered as limiting.

Parts by weight Ag (specific surface area, 0.1 m2/g) 24 RuO2 (specific surface area, 0.1 m2/g) 36 Glass frit (specific surface area, 2.0 m2/g) 40 10 Ethylcellulose 10 Tetraline 40 The above composition was well milled to make a homogeneous paste which was then printed onto an alumina substrate in an area of 5 mm x 5 mm. After the composition was dried at a temperature of 150C for 10 minutes, it was gradually heated up to 800C and maintained at that temperature for 10 minutes. Then ! the composite was slowly cooled to room temperature. Silver electrodes were formed on the cooled substrate to produce a composite resistor.

With the use of the same components, and utilizing a similar treatment as in Example 1, a series of resistors were obtained according to the composition ratio given in the table shown on page 11.
EXAMPhE 12 Parts b~ weight RuO2(specific surface area, 4 m /g) 25 Glass frit (specific surface axea, 0.3 m2/g) 75 Ethylcellulose 7 -~
30 Terpineol 19 .

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1 The above composition was milled to make a homogeneous paste and was then printed onto an alumina substrate, on which Ag-Pd electrodes (ag; Pd = 70:30) were previously formed in a desired pattern, in an area of 4 mm x 2 mm. After the composition was dried at a temperature of 150C for 10 minutes, it was ~radually heated up to 760C and maintained at that temperature for 10 min-utes. Then the composition was slowly co~led to room temperature to produce a composite resistor.

With the use of the same components, and utilizing a similar treatment as in Example 12, a series of resistors were o~tained according to the composition ratio given in the table shown on page 10~

Parts hy we_~ht ~U2 (specific surface area, 10 m2/g) 10 Glass frit (specific surface area, 0.3 m2/g) 67 A1203 lspecific surface area, 20 m2/g) 23 Ethyl cellulose 5.5 20 Terpineol 22 The above composition was well milled to make a homo-geneous paste and was then printed on an alumina substrate, on which Ag-Pd electrodes (Ag:Pd = 70:30) were previously formed in a desired pattern, in an area of 4 mm x 2 mm. After the composi-tion was dried at a temperature of 150C for 10 minutes, it was gradually heated up to 760C and maintained at that temperature for 10 minutes. Then the composite was slowly cooled to room temperature to produce a composite resistor.

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EX~MPLES 17 - 21 With the use of the same components and utilizing a ~- ~
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similar treatment as in Example 16, a series of resistors wexe obtained according to the composition ratio given in the table shown on page 10.

Parts by weiqht Ru02 (specific surface area, 10 m /g) 21 Glass frit (specific surface area, 0.3 m2/g) 74 SiO2 (specific surface area, 265 m2/g) 5 Ethyl cellulose 5.5 10 Terpineol 22 The above composition was well milled to make a homo-geneous paste and was then printed on an alumina substrate, on which Ag-Pd electrodes (Ag:Pd = 70:30) were previously formed in a desired pattern, in an area of 4 mm x 2 mm. After the composi-tion was dried at a temperature of 150C for 10 minutes, it was gradually heated up to 760C and maintained at that temperature ! for 10 minutes Then the composite was slowly cooled to room temperature to produce a composite resistor.

With the use of the same components and utilizing a similar treatment as in Example 22, a series of resistors were obtained according to the composition ratio given in the table ~:
shown on page 10.

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1 Measurement of the specific surface area referred to in the Examples was performed by following the Blaine Permeability Method and the BET Method. The resistance value, R, was obtained by using a conventional Wheatstone bridge apparatus. The TCR is represented in ppm/C) unit according to resistance values measured in the range from 25C - 125C.
The weight ratio of the conductor, glass frit and the insulating or semiconductive metal oxide, based on total of 100 parts by weight. of either the two or three components, the specific area (m2/g), the resistance (Q /~), and the TCR (ppm/C) in each of the examples are shown in the table where the results of the present invention are cleverly shown.

In the table, WA , WR , W W
. g uO2, glass, A1203, and SiO
.re.present.pa~.ts by weight of the Ag, Ru02, glass frit, ~ :.

: A1203, and SiO2 and furthermore S S , S S
Ag, Ru02 glass' A12o3' and SSiO , represent specific surface area of Ag, Ru02, glass ~.
frit, A1203, and SiO2.
As can be seen from the table, the following.
~:~ conclusions.can be readily understood from Examples 1, 4 and 8. ::
In these Examples, the specific surface areas of Ag, Ru02, and glass frit are maintained constant but the weight ratio of these components are varied: 24, 36, 40; 12, 18, 70;
and 8, 12, 80. Such variations in the weight ratio result in resistance values l~L , lOk ~L and lOOk Q , and greatly varied ..
TCR, ~300, ~10, and -100. ~ariations in resistance values were inevitably accompanied by a considerable variation in ,~, .
~` : TCR. The above phenomena is representative of the prior art.
However, in Examples 1, 2 and 3, where the weight ratio is maintained constant, the resistance value varies, only ~30 depending upon the variation of the specific surface area, .

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1 with the TCR being maintained substantially constant.
In these Examples, the resistance value greatly varied from l~L/~ , lO~L/ D , 80~/L~ , but the TCR varied little from +300 ppm/C,to +290 ppm/C to +305 ppm/C.
In the prior art, when the contact area was varied by con~rolling the weight ratio of the resisti~e material and the conductive material, the variation in the resistance value was always accompanied by a simultaneous variation deviation in the TCR. With respect to TCR, it should be known that the TCR ,~
increases with an increase in the amount of conductive material and decreases with an increase in the amount of glass frit and insulating or semiconductive metal oxide. In previous techniques, the addition of a small amount of semiconductive metal oxide was employed in order to minimize the de~iation of the TCR. However, satisfactory results in reproduc,ibility and and stability could not he obtained by following the previous technique and thus the complicated process ~o obtain a definite resistance could not be avoided.
In the case of our lnvestigations which were aimed at the ' ~-settlement of the above-mentioned difficulties, it was found that appropriate adjustment of both conductor and resistor components could exhibit desired resistance values depending upon the nature ~ ~' of the components. The above Examples have shown that a wide range of resistance values from ~RL to M~ with low TCR are more easily attained by only modifying and adjusting the specific surface area of the binary or occasionally ternary components. The "resistor composition" in the present invention implies a composite material which produces a firm resistor film on an insulating substrate, by firing.
The invention being thus described, it will be obvious '~

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1056C~26 1 that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

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Claims (16)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for manufacturing a resistor composition com-prising a conductive material and a glass frit having previously measured specific surface areas, respectively, and establishing the resistance value of said resistor composition by increasing or decreasing the total surface area of said conductive material and the total surface area of said glass frit while maintaining the weight ratio of said conductive material to said glass frit constant.

2. A process for manufacturing a resistor composition as claimed in claim 1, said resistor composition further containing an insulating or semiconductive metal oxide, said conductive material, glass frit and insulating or semiconductive metal oxide having previously measured specific surface areas, respectively, wherein the resistance value of said resistor composition is established by increasing or decreasing the total surface area of said conductive material, the total surface area of said glass frit, and the total surface area of the insulating or semicon-ductive metal oxide while maintaining the weight ratio of said conductive material, glass frit and insulating or semiconductive metal oxide constant.

3. A process as claimed in claim 1, wherein the specific surface area of one of the components is increased or decreased and the specific surface area of the other component is maintained constant while keeping the weight ratio of said conductive material to said glass frit constant.

4. A process as claimed in claim 2, wherein the specific surface area of one or two components is increased or decreased whereas the specific surface area of the residual component or components is maintained constant while keeping the weight ratio of said conductive material, glass frit and insulating or semiconductive metal oxide constant.

5. A process as claimed in claims 1, 2 or 3 wherein the conductive material is selected from the group consisting of gold, silver, platinum, rhodium, ruthenium, osmium, iridium, vanadium, tin, tungsten, carbon and alloys, mixtures and oxides thereof.

6. A process as claimed in claim 4, wherein the conductive material is selected from the group consisting of gold, silver, platinum, rhodium, ruthenium, osmium, iridium, vanadium, tin, tungsten, carbon and alloys, mixtures and oxides thereof.

7. A process as claimed in claims 1, 2 or 3, wherein the glass frit is selected from the group consisting of borosilicates and lead-borosilicates.

8. A process as claimed in claim 4, wherein the glass frit is selected from the group consisting of borosilicates and lead-borosilicates.

9. A process as claimed in claims 2 or 4, wherein the insulating or semiconductive metal oxide is selected from the group consisting of palladium oxide, copper oxide, aluminum oxide, zinc oxide, iron oxide, chromium oxide, cobalt oxide, tantalum oxide, nickel oxide, niobium oxide and silicon oxide.

10. A process as claimed in claims 1, 2 or 3, wherein the specific surface area of the conductive material, glass frit and the insulating or semiconductive metal oxide, when the latter is present, varies from 0.02 to about 270 m2/g.

11. A process as claimed in claim 4, wherein the specific surface area of the conductive material, glass frit and the insulating or semiconductive metal oxide varies from 0.02 to about 270 m2/g.

12. A process for manufacturing a resistor composition of claim 1, 2 or 3, wherein the conductive material, the glass frit and the insulating or semiconductive metal oxide, when the latter is present, have a diameter of about 100 .ANG. to 50 microns.

13. A process for manufacturing a resistor composition of claim 4, wherein the conductive material, the glass frit and the insulating or semiconductive metal oxide have a diameter of about 100 .ANG. to 50 microns.

14. A resistor composition comprising a conductive material and a glass frit having previously measured specific surface area respectively, wherein the weight ratio of said conductive material to said glass frit is constant and the resistance value of said composition is established by varying the total surface area of said conductive material and the total surface area of said glass frit without changing the temperature coefficient of resistance of the composition calculated by the following equation namely, the total surface area = specific surface area x total weight of particles.

15. A resistor composition as claimed in claim 14 which further contains an insulating or semiconductive metal oxide having previously measured specific surface area, wherein the weight ratio of said conductive material, glass frit and insulating or semiconductive metal oxide is constant and the resistance value of said composition is established by varying the total surface area of said conductive material, the total surface area of the glass frit and the total surface area of the insulating or semiconductive metal oxide.

16. A resistor composition as claimed in claims 14 or 15 wherein the conductive material is selected by the group con-sisting of Ag(silver), Pt(platinum), Rh(rhodium), Ru(ruthenium), Os(osmium), Ir(iridium), V(vanadium), Sn(tin), W(tungsten), C(carbon), alloys and mixtures and oxides thereof.