Title of Invention	A PROCESS FOR THE PREPARATION OF AN IMPROVED THICK FILM RESISTOR USEFUL FOR MAKING STRAIN GAUGE WITH ENHANCED GAUGE FATOR UPTO 1000
Abstract	A process for the preparation of an improved thick film resistor useful for making strain gauge with enhanced gauge factor upto 1000, which comprises: a] cleaning and insulating substrate [1] capable of withstanding high temperature by known methods; b] coating the said cleaned substrate by known method with a known non-corrosive conductor thick film [2] of thickness about 10 to 20 microns; drying the coated substrate [1,2] at temperature in the range of 60 to 120°C for 15 minutes; c] coating by known method the thus prepared substrate [1,2] with a known resistor thick film [3] of thickness of about 15 to 20 microns, drying the coated substrate [1, 2, 3] at temperature in the range of 60 to120°C for about 10 to15 minutes; d] coating by known method the resistor thick film [3] with cyanometallic compound [4] of thickness in the range of 10 to 25 microns; drying the coated substrate [1, 2, 3, 4] at temperature in the range of 60 to120°C for about 10 minutes; e] firing the thus prepared substrate [1, 2, 3, 4] to a temperature in the range of 800 to 900°C for a period ranging 10 to 20 minutes to obtain an improved thick film resistor useful for making strain gauge with enhanced gauge factor upto 1000.

Title of Invention

A PROCESS FOR THE PREPARATION OF AN IMPROVED THICK FILM RESISTOR USEFUL FOR MAKING STRAIN GAUGE WITH ENHANCED GAUGE FATOR UPTO 1000

Abstract

A process for the preparation of an improved thick film resistor useful for making strain gauge with enhanced gauge factor upto 1000, which comprises: a] cleaning and insulating substrate [1] capable of withstanding high temperature by known methods; b] coating the said cleaned substrate by known method with a known non-corrosive conductor thick film [2] of thickness about 10 to 20 microns; drying the coated substrate [1,2] at temperature in the range of 60 to 120°C for 15 minutes; c] coating by known method the thus prepared substrate [1,2] with a known resistor thick film [3] of thickness of about 15 to 20 microns, drying the coated substrate [1, 2, 3] at temperature in the range of 60 to120°C for about 10 to15 minutes; d] coating by known method the resistor thick film [3] with cyanometallic compound [4] of thickness in the range of 10 to 25 microns; drying the coated substrate [1, 2, 3, 4] at temperature in the range of 60 to120°C for about 10 minutes; e] firing the thus prepared substrate [1, 2, 3, 4] to a temperature in the range of 800 to 900°C for a period ranging 10 to 20 minutes to obtain an improved thick film resistor useful for making strain gauge with enhanced gauge factor upto 1000.

Full Text	This invention particularly relates to a process for the preparation of an improved I hick film resistor useful for making strain gauge with enhanced gauge factor upto 1000. The (hick film resistor of the present invention is obtained by inducing the strain sensitivity in thick film resistor during its fabrication on substrate by coating it with a formulation capable of gauge factor enhancement and subjecting it to high temperature in furnace. The usage of thick film resistor have industrial applications such as hybrid circuit and thermistors etc. The hitherto known strain gauges are of two types. The first one, makes use of metal foil ( Micro-Measurements, Measurements Group, Vishay Intertechnology, Inc., P.O.Box 306, 38905 Chase Road, Romulus, Michigan 48174) pressed between two insulating laminates and the second one, uses the silicon material ( Kulite Semiconductor International Ltd., One Willow Tree Road, Leonia, New Jersey 07605 ) having diffused layer formed by impurity drive-in at high temperature in an inert gas. The gauges thus formed exhibit 2 - 5 as the gauge factor for the former type and 45-175 for the latter version. Such gauges are fragile and are temperature sensitive too. The substrate is commonly used to mount the gauge onto it. There is a definite need for the enhancement of the gauge factor for improving the signal conditioners and for developing the sensors for medical applications. Our studies have shown that such strain gauge of high gauge factor is not available and is not possible with existing material technology.Our studies have also provided us the experimental fact that it is possible to increase the gauge factor by enhancing the conductive phase size of thick film resistive material. As per our process the surface morphology of the thick film resistor material gets converted to long conductive phases and their tunnel distance get enhanced. This in turn decreases the effective sheet resistance and enhances the gauge factor through geometrical and piezoresistive effects. To the best of our knowledge till date such gauges based on thick film technology having enhanced gauge factor are not available internationally . The main object of the present invention is to provide a process for the preparation of an improved thick film resistor useful for making strain gauge with enhanced gauge factor upto 1000 overcoming the drawbacks of the hitherto known strain gauges. An embodiment of the process steps of the present invention is illustrated in figure 1 of the drawings accompanying this specification. Fig. 1 represents the sectional view of the substrate [1] having conductor thick film [2] resistor thick film [3] and cyanometallic compound formulation [4] formed by silk screen printing and firing process respectively. Accordingly, the present invention provides a process for the preparation of an improved thick film resistor useful for making strain gauge with enhanced gauge factor upto 1000, which comprises: a] cleaning and insulating substrate [1] capable of withstanding high temperature by known methods; b] coating the said cleaned substrate by known method with i a known non-corrosive conductor thick film [2] of thickness abdut 10 to 20 microns; drying the coated substrate [1,2] at temperature in the range of 60 to 120°C for 15 minutes; c] coating by known method the thus prepared substrate [1,2] with a known resistor thick film [3] of thickness of about 15 to 20 microns, drying the coated substrate [1, 2, 3] at temperature in the range of 60 to120°C for about 10 to 15 minutes; d] coating by known method the resistor thick film [3] with cyanometallic compound [4] of thickness in the range of 10 to 25 microns; drying the coated substrate [1, 2, 3, 4] at temperature in the range of 60 to!20°C for about 10 minutes; e] firing the thus prepared substrate [1, 2, 3, 4] to a temperature in the range of 800 to 900°C for a period ranging 10 to 20 minutes to obtain an improved thick film resistor useful for making strain gauge with enhanced gauge factor upto 1000. The substrate [1] used may be such as a ceramic substrate, an alumina, enameled steel, oxidized silicon wafer and any other materials which is an insulator and is capable of withstanding high temperature. The substrate [1] may be cleaned by known methods such as chemical methods, ultrasonic cleaning in acetone, boiling in trylene followed by rinse in methanol. The coating of the substrate [1] with thick films [2, 3, 4] may be effected using standard silk screen printing technique commonly used for thick films. The non-corrosive conductor thick film used may be such as Pt/Au, Pd/Ag, Pt and Au. The resistor thick film used may be such as BIROX formulation etc. The cyanometallic compound used may be such as gold platinium solution, potassiumferrocyanide etc. The drying and firing of the coated substrate may be effected in an air atmosphere. The coated substrate after every heating at high temperature may be cleaned to remove dirt and impurities from it prior to next coating and heating. In the process of the present invention we have prepared and improved thick film resistor capable of being used as a strain gauge with enhanced gauge laclor. This has been possible through modifying the fine conductive phase to long conductive phase with enhanced tunnel distance. The following example is given by way of illustrations and should not be construed to limit the scope of the presen): invention. Example-1 The sample Ug 4(10) was prepared by (a) cleaning the coors alumina substrate (2" x 2" x 0.6 mm) ultrasonically in methanol (b) coating it with Pd/Ag thick film paste of thickness 20 micron by screen printing; drying the coated substrate at 60 C for 15 mins (c) coating the thus prepared substrate with Birox resistor thick film paste of thickness 20 micron by screen prinling; drying the coated substrate at 60 C for 15 mins; (d) coating the thus prepared thick film resistor body with gold plating solution (acidic) 20 micron thick; drying the coated resistor at 60 C for 10 mins.; (e) firing the thus prepared substrate at 850 C for 10 mins. to obtained an improved thick film resistor useful for making strain gauge with enhanced gauge factor upto 1000. Fig. 2. shows the change in resistance with tensile and compressive strains for the sample Ug 4 (10) prepared by the above process. The gauge factor in the linear range for this sample is about 800. The main advantages of the process of the present invention are: 1. The process is very simple as this requires only the cyanometallie compound to be coaled on resistor thick film of the substrate . 2. The process is very easy to monitor as it necessitates the resistance measurement after heating only. 3. The process is highly cost effective as the cyanometallic compound coating requires no extra screen for printing. 4. Since the cyanometallic compound induces mixing therefore it is free from the problem of film peeling and thus increases the yield and the reliability. 5 The substrate is the integral part of the strain gauge. 6. The strain gauge can also be welded /bolted to the object of which the strain behaviour needs to be monitored by metallising the back surface of the strain gauge WE CLAIM: 1. A process for the preparation of an improved thick film resistor useful for making strain gauge with enhanced gauge factor upto 1000, which comprises: a] cleaning and insulating substrate [1] capable of withstanding high temperature by known methods; b] coating the said cleaned substrate by known method with a known non-corrosive conductor thick film [2] of thickness about 10 to 20 microns; drying the coated substrate [1,2] at temperature in the range of 60 to 120°C for 15 minutes; c] coating by known method the thus prepared substrate [1,2] with a known resistor thick film [3] of thickness of about 15 to 20 microns, drying the coated substrate [1, 2, 3] at temperature in the range of 60 to120°C for about 10 to!5 minutes; d] coating by known method the resistor thick film [3] with cyanometallic compound [4] of thickness in the range of 10 to 25 microns; drying the coated substrate [1, 2, 3, 4] at temperature in the range of 60 to120°C for about 10 minutes; e] firing the thus prepared substrate [1, 2, 3, 4] to a temperature in the range of 800 to 900°C for a period ranging 10 to 20 minutes to obtain an improved thick film resistor useful for making strain gauge with enhanced gauge factor upto 1000. 2. A process as claimed in claim 1, wherein the substrate used is ceramic substrate, alumina, enameled steel, oxidized silicon wafer, etc. 3. A process as claimed in claims 1 and 2, wherein the substrate is cleaned by chemical method ultrasonic cleaning in acetone, boiling in trylene and followed by rinse in methanol. 4. A process as claimed in any preceding claim, wherein the coating of substrate with thick films of about 15 to 20 microns is effected by standard silk screen printing techniques commonly use for thick films. 5. A process as claimed in any preceding claim, wherein the non-corrosive conductor thick film used is such as Pd/Ag, Pt/Au etc. 6. A process as claimed in any preceding claim, wherein the resistor thick film used is such as BIROX formulation. 7. A process as claimed in any preceding claim, wherein the cyanometallic compound used is gold plating solution, potassiumferrocyanide solution. 8. A process as claimed in any preceding claim, wherein the drying and firing of the coated substrate is effected in an atmospheric air. 9. A process for the preparation of an improved thick film resistor useful for making strain gauge with enhanced gauge factor upto 1000 substantially as herein described with reference to the foregoing examples and drawings accompanying this specification.

Full Text

This invention particularly relates to a process for the preparation of an improved I hick film resistor useful for making strain gauge with enhanced gauge factor upto 1000. The (hick film resistor of the present invention is obtained by inducing the strain sensitivity in thick film resistor during its fabrication on substrate by coating it with a formulation capable of gauge factor enhancement and subjecting it to high temperature in furnace. The usage of thick film resistor have industrial applications such as hybrid circuit and thermistors etc.
The hitherto known strain gauges are of two types. The first one, makes use of metal foil ( Micro-Measurements, Measurements Group, Vishay Intertechnology, Inc., P.O.Box 306, 38905 Chase Road, Romulus, Michigan 48174) pressed between two insulating laminates and the second one, uses the silicon material ( Kulite Semiconductor International Ltd., One Willow Tree Road, Leonia, New Jersey 07605 ) having diffused layer formed by impurity drive-in at high temperature in an inert gas. The gauges thus formed exhibit 2 - 5 as the gauge factor for the former type and 45-175 for the latter version. Such gauges are fragile and are temperature sensitive too. The substrate is commonly used to mount the gauge onto it.
There is a definite need for the enhancement of the gauge factor for improving the signal conditioners and for developing the sensors for medical applications.
Our studies have shown that such strain gauge of high gauge factor is not available and is not possible with existing material technology.Our studies have also provided us the experimental fact that it is possible to increase the gauge factor by enhancing the conductive phase size of thick film resistive material. As per our process the surface morphology of the thick film resistor material gets converted to long conductive phases and their tunnel distance get enhanced. This in turn decreases the effective sheet resistance and enhances the gauge factor through geometrical and piezoresistive effects. To the best of our knowledge till date such gauges based on thick film technology having enhanced gauge factor are not available internationally .
The main object of the present invention is to provide a process for the preparation of an improved thick film resistor useful for making strain gauge with enhanced gauge factor upto 1000 overcoming the drawbacks of the hitherto known strain gauges.

An embodiment of the process steps of the present invention is illustrated in figure 1 of the drawings accompanying this specification. Fig. 1 represents the sectional view of the substrate [1] having conductor thick film [2] resistor thick film [3] and cyanometallic compound formulation [4] formed by silk screen printing and firing process respectively.
Accordingly, the present invention provides a process for the preparation of an improved thick film resistor useful for making strain gauge with enhanced gauge factor upto 1000, which comprises: a] cleaning and insulating substrate [1] capable of withstanding high temperature by known methods; b] coating the said cleaned substrate by known method with
i
a known non-corrosive conductor thick film [2] of thickness abdut 10 to 20 microns; drying the coated substrate [1,2] at temperature in the range of 60 to 120°C for 15 minutes; c] coating by known method the thus prepared substrate [1,2] with a known resistor thick film [3] of thickness of about 15 to 20 microns, drying the coated substrate [1, 2, 3] at temperature in the range of 60 to120°C for about 10 to 15 minutes; d] coating by known method the resistor thick film [3] with cyanometallic compound [4] of thickness in the range of 10 to 25 microns; drying the coated substrate [1, 2, 3, 4] at temperature in the range of 60 to!20°C for about 10 minutes; e] firing the thus prepared substrate [1, 2, 3, 4] to a temperature in the range of 800 to 900°C for a period ranging 10 to 20 minutes to obtain an improved thick film resistor useful for making strain gauge with enhanced gauge factor upto 1000.
The substrate [1] used may be such as a ceramic substrate, an alumina, enameled steel, oxidized silicon wafer and any other materials which is an insulator and is capable of withstanding high temperature.
The substrate [1] may be cleaned by known methods such as chemical methods, ultrasonic cleaning in acetone, boiling in trylene followed by rinse in methanol.
The coating of the substrate [1] with thick films [2, 3, 4] may be effected using standard silk screen printing technique commonly used for thick films.
The non-corrosive conductor thick film used may be such as Pt/Au, Pd/Ag, Pt and Au.
The resistor thick film used may be such as BIROX formulation etc.
The cyanometallic compound used may be such as gold platinium solution,
potassiumferrocyanide etc.

The drying and firing of the coated substrate may be effected in an air atmosphere.
The coated substrate after every heating at high temperature may be cleaned to remove dirt and impurities from it prior to next coating and heating.
In the process of the present invention we have prepared and improved thick film resistor capable of being used as a strain gauge with enhanced gauge laclor. This has been possible through modifying the fine conductive phase to long conductive phase with enhanced tunnel distance.
The following example is given by way of illustrations and should not be construed to
limit the scope of the presen): invention.
Example-1
The sample Ug 4(10) was prepared by (a) cleaning the coors alumina substrate (2" x 2" x 0.6 mm) ultrasonically in methanol (b) coating it with Pd/Ag thick film paste of thickness 20 micron by screen printing; drying the coated substrate at 60 C for 15 mins (c) coating the thus prepared substrate with Birox resistor thick film paste of thickness 20 micron by screen prinling; drying the coated substrate at 60 C for 15 mins; (d) coating the thus prepared thick film resistor body with gold plating solution (acidic) 20 micron thick; drying the coated resistor at 60 C for 10 mins.; (e) firing the thus prepared substrate at 850 C for 10 mins. to obtained an improved thick film resistor useful for making strain gauge with enhanced gauge factor upto 1000.
Fig. 2. shows the change in resistance with tensile and compressive strains for the sample Ug 4 (10) prepared by the above process. The gauge factor in the linear range for this sample is about 800.
The main advantages of the process of the present invention are:
1. The process is very simple as this requires only the cyanometallie compound to be coaled
on resistor thick film of the substrate .
2. The process is very easy to monitor as it necessitates the resistance measurement
after heating only.
3. The process is highly cost effective as the cyanometallic compound coating requires no
extra screen for printing.

4. Since the cyanometallic compound induces mixing therefore it is free from the problem
of film peeling and thus increases the yield and the reliability.
5 The substrate is the integral part of the strain gauge.
6. The strain gauge can also be welded /bolted to the object of which the strain behaviour needs
to be monitored by metallising the back surface of the strain gauge

WE CLAIM:
1. A process for the preparation of an improved thick film resistor useful for making strain gauge with enhanced gauge factor upto 1000, which comprises: a] cleaning and insulating substrate [1] capable of withstanding high temperature by known methods; b] coating the said cleaned substrate by known method with a known non-corrosive conductor thick film [2] of thickness about 10 to 20 microns; drying the coated substrate [1,2] at temperature in the range of 60 to 120°C for 15 minutes; c] coating by known method the thus prepared substrate [1,2] with a known resistor thick film [3] of thickness of about 15 to 20 microns, drying the coated substrate [1, 2, 3] at temperature in the range of 60 to120°C for about 10 to!5 minutes; d] coating by known method the resistor thick film [3] with cyanometallic compound [4] of thickness in the range of 10 to 25 microns; drying the coated substrate [1, 2, 3, 4] at temperature in the range of 60 to120°C for about 10 minutes; e] firing the thus prepared substrate [1, 2, 3, 4] to a temperature in the range of 800 to 900°C for a period ranging 10 to 20 minutes to obtain an improved thick film resistor useful for making strain gauge with enhanced gauge factor upto 1000.
2. A process as claimed in claim 1, wherein the substrate used is ceramic substrate, alumina,
enameled steel, oxidized silicon wafer, etc.
3. A process as claimed in claims 1 and 2, wherein the substrate is cleaned by chemical
method ultrasonic cleaning in acetone, boiling in trylene and followed by rinse in
methanol.
4. A process as claimed in any preceding claim, wherein the coating of substrate with thick
films of about 15 to 20 microns is effected by standard silk screen printing techniques
commonly use for thick films.
5. A process as claimed in any preceding claim, wherein the non-corrosive conductor thick
film used is such as Pd/Ag, Pt/Au etc.
6. A process as claimed in any preceding claim, wherein the resistor thick film used is such
as BIROX formulation.

7. A process as claimed in any preceding claim, wherein the cyanometallic compound used
is gold plating solution, potassiumferrocyanide solution.
8. A process as claimed in any preceding claim, wherein the drying and firing of the coated
substrate is effected in an atmospheric air.
9. A process for the preparation of an improved thick film resistor useful for making strain
gauge with enhanced gauge factor upto 1000 substantially as herein described with
reference to the foregoing examples and drawings accompanying this specification.

Documents:

1108-del-1998-abstract.pdf

1108-del-1998-claims.pdf

1108-del-1998-correspondence-others.pdf

1108-del-1998-correspondence-po.pdf

1108-del-1998-description (complete).pdf

1108-del-1998-drawings.pdf

1108-del-1998-form-1.pdf

1108-del-1998-form-19.pdf

1108-del-1998-form-2.pdf

1108-del-1998-form-5.pdf

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Patent Number

215172

Indian Patent Application Number

1108/DEL/1998

PG Journal Number

10/2008

Publication Date

07-Mar-2008

Grant Date

21-Feb-2008

Date of Filing

27-Apr-1998

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110001.

Inventors:

#	Inventor's Name	Inventor's Address
1	DR. AWATAR SINGH, SCIENTIST	CENTRAL ELECTRONICS ENGINEERING RESEARCH INSTITUTE, PILANT, INDIA.

PCT International Classification Number

H01C 7/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA