Description:FIELD OF INVENTION
The present invention relates generally to the field of printed electronics. More particularly, it relates to a process for achieving low resistance carbon ink traces on ceramic glass substrate, suitable for applications requiring low electrical resistance.

BACKGROUND
Printed electronics is a specialized area of electronic material science that utilizes printing technologies to create electronic circuits and devices on various substrates, including both flexible and rigid surfaces. Ceramic glass, a flexible polycrystalline material formed through the controlled crystallization of glass, merges the advantageous properties of ceramics and glass, such as thermal stability, mechanical strength, and chemical resistance. By printing carbon-based conductive inks onto ceramic glass, it becomes possible to establish reliable electrical pathways, enabling a broad spectrum of electronic and sensing applications. This approach holds significant promise within the expanding domain of printed electronics.
Existing screen-printing methods for applying carbon-based conductive ink onto ceramic glass face several limitations. The carbon ink formulations commonly used in these processes often exhibit poor electrical conductivity, which hampers the effectiveness of the printed circuits. Additionally, these inks tend to generate excess heat during operation, which not only compromises the stability of the printed patterns but also restricts the overall printing speed. Moreover, such inks are generally unsuitable for applications requiring high conductivity, thereby limiting their use in advanced electronic or sensing devices. These challenges collectively lead to increased manufacturing costs and reduced production efficiency, making current methods less viable for scalable or high-performance applications.
PRIOR ART:
WO2009031849A2 discloses a system for conductive ink composition suitable for inkjet printing, comprising metal nanoparticles, a co-solvent, and a nano glass-based component. The nano glass conductive ink is blended with nano glass frit to enhance adhesion between the printed conductive pattern and the substrate. This composition is designed for low-temperature inkjet printing onto glass or ceramic substrates. Following the printing process, the substrate undergoes thermal treatment at elevated temperatures. To ensure high conductivity and minimize defects caused by contraction during the drying and sintering stages, the ink composition incorporates a high concentration of metal nanoparticles. This formulation facilitates the formation of defect-free, highly conductive patterns with improved bonding to the substrate.
WO2018162926A1 discloses a conductive ink composition comprising conductive solids and a medium. Comprised of a percentage by weight of glass flakes coated with an electrically conductive coating less than or equal to 50%. Conductive solids are dispersed evenly within the medium. The glass flakes have average thickness in a range from 0.1 micro metre to 8 micro metre, and an aspect ratio of average diameter divided by average thickness greater than or equal to 3, more preferably 30. The composition additionally comprises filler particles. The filler particles improve the strength and durability of the ink residue and reduce shrinkage. The composition additionally comprises include stabilizers, antioxidants and viscosity modifying compounds.
US8066912B2 discloses conductive pattern forming ink for forming a conductive pattern on a substrate by a droplet discharge method, including metal particles; an aqueous dispersion medium in which the metal particles are dispersed; sugar alcohol derived from a disaccharide; and a polyglycerol compound having a polyglycerol skeleton. Ink prevents the occurrence of cracks and disconnections in a conductive pattern that is to be formed, a conductive pattern and wiring substrate exhibiting high reliability.
Existing prior art on conductive inks predominantly focuses on ink compositions tailored for inkjet printing. These compositions typically include metal nanoparticles, a co-solvent, and a nano glass-based component, specifically formulated to enable low-temperature printing on glass or ceramic substrates. Additionally, such inks often incorporate filler particles to enhance performance. Some formulations also involve a droplet discharge method, comprising metal particles suspended in an aqueous dispersion medium. These are combined with sugar alcohols derived from disaccharides and polyglycerol compounds featuring a polyglycerol backbone, which aid in stability, viscosity control, and uniform droplet formation during printing. However, none of the abovementioned prior arts provide carbon ink that traces on ceramic glass for achieving low resistance and their cost and proper functionality.
Owing to the aforementioned drawbacks, the present invention overcomes the existing challenges by providing low resistance carbon ink traces on ceramic glass substrate, which is advantageous due to its cost effectiveness and environmental stability compared to noble metal inks on ceramic glass. The invention also encompasses the resulting ceramic glass substrate with screen-printed, low-resistance carbon traces and devices incorporating such substrate.

DEFINITIONS
The expression “resistance” used hereinafter in this specification refers to the property of a material that opposes the flow of electric current. The expression “Substrates” used hereinafter in this specification refers to the foundational material upon which electronic components are fabricated or mounted.
The expression “carbon ink” used hereinafter in this specification refers to a conductive ink made of carbon particles dispersed in a binder, used to create conductive traces, electrodes, and circuits on various substrates like printed circuit boards (PCBs).
The expression “Ohm range” used hereinafter in this specification refers to the range of resistance values measured in ohms (Ω), which is the unit of electrical resistance.
The expression “ceramic glass” used hereinafter in this specification refers to a material that combines the properties of both glass and ceramics.
The expression “off-contact distance” used hereinafter in this specification refers to the distance between the screen-printing frame and the printing substrate when the squeegee passes to deposit ink, where this separation is essential for obtaining sharp and consistent prints.
The expression “screen printing process” used hereinafter in this specification refers to a versatile stencil printing technique used to create conductive patterns, resistors, capacitors, and other components on various substrates. It's a cost-effective method for large-scale production of printed circuit boards (PCBs) and flexible electronics.

OBJECTS OF THE INVENTION
The primary object of the invention is to provide a process for achieving low resistance carbon ink traces on ceramic glass substrates.
Another object of the invention is to provide the process that selects a specific carbon ink composition for high conductivity and adhesion to ceramic glass.
Another object of the invention is to provide the process that prepares the ceramic glass substrate to ensure optimal surface energy and cleanliness.
Yet another object of the invention is to provide a screen printing the carbon ink using precisely controlled parameters, including screen mesh size, emulsion thickness, squeegee hardness, pressure and speed, and potentially multiple print layers.
Yet another object of the invention is to provide the process that dries the printed ink to remove solvents.
Yet another object of the invention is to provide the process that designed thermal curing or firing process at elevated temperatures, which may involve specific ramp rates, dwell times and atmospheric control to densify the carbon particles and form a highly conductive network.

SUMMARY
Before the present invention is described, it is to be understood that the present invention is not limited to specific methodologies and materials described, as these may vary as per the person skilled in the art. It is also to be understood that the terminology used in the description is for the purpose of describing the particular embodiments only and is not intended to limit the scope of the present invention.
The present invention discloses the process for achieving low resistance carbon ink traces on ceramic glass substrates. The invention provides a method for screen printing a carbon-based conductive ink onto a ceramic glass substrate to achieve an electrical resistance of less than 10 Ohms. The method involves selecting a specific carbon ink composition optimized for high conductivity and adhesion to ceramic glass, potentially including conductive carbon nanoparticles, a suitable binder system, and volatile solvents. Preparing the ceramic glass substrate to ensure optimal surface energy and cleanliness. Screen printing the carbon ink using precisely controlled parameters, including screen mesh size, emulsion thickness, squeegee hardness, pressure, and speed, and potentially multiple print layers.
In another aspect, the process includes steps such as drying the printed ink to remove solvents, followed by a carefully designed thermal curing or firing process at elevated temperatures, which may involve specific ramp rates, dwell times, and atmospheric control to densify the carbon particles and form a highly conductive network. The invention also encompasses the resulting ceramic glass substrate with screen-printed, low-resistance carbon traces, and devices incorporating such substrates.

BRIEF DESCRIPTION OF DRAWINGS
A comprehensive understanding of the present invention may be achieved by referring to the following detailed description, which should be read in conjunction with the accompanying drawing. The drawing, which forms an integral part of this specification, provides a visual representation of the invention and, together with the description, elucidates its construction, operation, and key functional aspects.
Fig.1. refers to a flow chart illustrating the steps of the screen printing.
Fig.2. refers to a flow chart illustrating printing glass oven curing standard operating procedure (SOP) or thermal processing method.
Fig.3. illustrates a graph showing the relationship between firing temperature/time and the electrical resistance of the carbon ink trace.

DETAILED DESCRIPTION OF INVENTION
Before the present invention is described, it is to be understood that this invention is not limited to methodologies described, as these may vary as per the person skilled in the art. It is also to be understood that the terminology used in the description is for the purpose of describing the particular embodiments only and is not intended to limit the scope of the present invention. Throughout this specification, the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results. Various embodiments of the present invention are described below. It is, however, noted that the present invention is not limited to these embodiments, but rather the intention is that modifications that are apparent are also included.
The present invention discloses a process for achieving low resistance carbon ink traces on ceramic glass substrate. The process comprises steps of the screen printing as illustrated in Fig. 1.; printing glass oven curing standard operating procedure (SOP) or thermal processing method as illustrated in Fig.2.; and a graph showing the relationship between firing temperature/time and the electrical resistance of the carbon ink trace as illustrated in Fig. 3.
In an embodiment of the invention, the process for achieving low resistance carbon ink traces on ceramic glass substrate, comprises of the ceramic glass substrate and the carbon conductive ink; wherein the ceramic glass substrate can be any commercially available ceramic glass, such as those based on lithium aluminosilicate (LAS) or other glass-substrate composition known for their thermal shock resistance and high-temperature stability. The thickness of the substrate can vary depending on the application, typically ranging from 1millimetre to 6 millimetres. Prior to printing, the substrate surface is cleaned using standard industrial cleaning processes, such as isopropyl alcohol wipe, to remove contamination and enhance surface energy for ink adhesion.
In a next embodiment of the invention, the carbon conductive ink is crucial for achieving low resistance. The ink comprises, a conductive carbon material is high-purity carbon particles, such as specific carbon form e.g., carbon black, graphite, graphene, carbon nanotubes (CNTs), or combination thereof. The particle size distribution is critical, typically in the nanometre to micrometre range, to ensure good packing density and percolation. The carbon content in the solid phase of the ink is typically 65% to 85% by weight. Further a binder system it is a polymeric binder system that provides adhesion to the ceramic glass and structural integrity to the printed trace after firing. The binder content is optimized to balanced adhesion, conductivity and printability. Further comprises a solvent system, a blend of volatile organic solvents chosen for appropriate viscosity, drying rate and compatibility with the carbon and binder. Further comprises an additive such as, dispersants, rheology modifiers and wetting agents may be included to improve ink stability, printing and surface wetting. A preferred embodiment utilizes a carbon ink with a high aspect ratio carbon material dispersed in low-viscosity, fast-drying system with a minimal amount of a high-temperature resistance polymeric binder.
In a preferred embodiment of the invention, screen printing steps as illustrated in Fig. 1. including:
● selecting a mesh for the screen assembly; wherein a polyester screen ranging from 40-360 threads per inch (TPI) with a mesh opening size of 1000-1500 micro meter is used to ensure high resolution and uniform ink deposition;
● employing an emulsion thickness of 100-200 micrometers on the screen; wherein the thickness on the screen dictates the wet film thickness of the printed ink;
● cleaning the glass thoroughly by the user, with Methyl Ethyl Ketone (MEK) to remove oil or particles;
● fixing the glass on the printing machine bed and check level, followed by spreading the ink evenly on the screen, adjusting squeegee with a hardness of 50 to 70 shore A, and an angle of 50 to 75 degrees used to control ink transfer;
● setting the printer speed optimized to 100 to 150 millimetre per second (mm/s) to ensure complete ink transfer without smearing;
● adjusting the print pressure up to 5 to 6 newton per centimetre (N/cm) to achieve full contact between the screen and the substrate, ensuring uniform ink deposition with the help of spreader;
● starting the printing machine in auto mode; wherein the ink transfers and deposits on the glass such that the off-contact distance typically ranging between 15 to 30 mm is maintained to allow for clean snap-off of the screen from the substrate;
● printing multiple layers of carbon ink to achieve single-digit resistance ,wherein each layer is typically dried before the next layer is applied; and the number of layers can range from 1 to 5, depending on the desired resistance and ink properties;
● cleaning the mesh with cleaning agent that is MEK; and
● packing the mesh to avoid dust and it is ready to use for next cycle.
In another preferred embodiment of the invention, the drying and thermal processing also referred to as the glass oven curing standard operating procedure (SOP) as illustrated in Fig. 2. is disclosed. The printed traces undergo a two-stage thermal process after screen printing including the steps as follows:
Stage 1: Drying
● placing the substrate in AC, dust free room for 10 minutes so the wet film levels and begins set before oven work;
● drying the printed substrate at a relatively low temperature; typically ranging between 100 to 200 degrees Celsius for approximately 50 to 60 minutes in a convection oven to remove the volatile solvents, preventing bubbling or cracking during subsequent high- temperature firing;
Stage 2: Firing
● firing the dried substrate where the substrate is subjected to high-temperature in a convection oven; wherein a controlled ramp-up rate of 1 to 2 degrees Celsius per minute is allowed to the peak firing temperature;
● allowing the substrate to cool to ambient temperature (use safety gloves when handling). and preliminary inspecting by visually checking the traces and performing a quick continuity check to catch obvious defects before firing;
● allowing the substrate to undergo a peak firing temperature ranging between of 250 to 300 degree Celsius in ambient air for the densification of carbon particles and the formation of a highly conductive network, as well as for the proper curing of the binder system to ensure strong adhesion to the ceramic glass;
● enabling a dwell time at the peak temperature for 180- 200 minutes (approx. 3 hrs); allowing sufficient time for the carbon particles to coalesce and for the binder to fully cure;
● allowing a controlled cool down rate at 1 to 2 degrees Celsius back to ambient to prevent thermal shock to the ceramic glass and to maintain the integrity of the carbon traces;
● allowing the oven and parts reach room temperature before opening for removal, and final inspection performs resistance measurements and a short check;
● cleaning using lint-free cloth to remove polymers.
It is to be noted that the firing is performed in atmosphere with ambient air. Further, the careful optimization of these parameters, particularly the carbon ink composition and the firing profile, electrical resistance values of less than 10 Ohms, and preferably less than 5 Ohms, can be consistently achieved.
In yet another embodiment, a graph showing the relationship between firing temperature/time and the electrical resistance of the carbon ink trace is disclosed; wherein the graph temperature Vs resistance shows the resistance values of five sample (R1-R5) under three curing conditions; curing at 100 degrees Celsius for 1 hour, curing at 250 degrees Celsius for 3 hours without a copper plate and curing 100 degrees Celsius for 1 hour with copper plate; wherein
- for R1, R2 and R3, the highest resistance is observed after curing at 100 degrees Celsius for 1 hour, followed by lower resistance when cured at 250 degrees Celsius for 3 hours and lowest resistance when cured 100 degrees Celsius for 1 hour with a copper plate;
- for R4 and R5, the difference is more pronounced, with resistance values around 450 Ohms in the 100 degrees Celsius per hour condition, dropping to about 150 Ohms after 250 degrees Celsius per 3-hour cure, and further reducing to roughly 40-50 Ohms with the copper plate method.
Overall, the resistance consistently decreases from the low temperature short duration cure without a copper plate to the high temperature, long duration cure and reaches its lowest values with the copper plate assisted method; indicating that higher cure temperature improves conductivity through better densification and curing of the conductive network, while the copper plate method further enhances thermal transfer and uniformity enabling superior conductivity even at lower temperatures and shorter curing times.
While considerable emphasis has been placed herein on the specific elements of the various embodiments, it will be appreciated that many alterations can be made and that many modifications can be made in the various embodiments without departing from the principles of the invention. These and other changes in the various embodiments of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.
, Claims:CLAIMS

We claim,

1. A process for achieving low resistance carbon ink traces on ceramic glass substrate, suitable for applications requiring low electrical resistance; wherein the process includes a screen-printing process and a two-stage glass oven curing standard operating procedure (SOP) further comprising of drying and firing;

characterized in that:
the screen-printing process steps of;
● selecting a mesh for the screen assembly; wherein a polyester screen is used to ensure high resolution and uniform ink deposition;
● employing an emulsion thickness of 100-200 micrometers on the screen; wherein the thickness on the screen dictates the wet film thickness of the printed ink;
● cleaning the glass thoroughly by the user, with Methyl Ethyl Ketone (MEK) to remove oil or particles;
● fixing the glass on the printing machine bed and check level, followed by spreading the ink evenly on the screen, adjusting squeegee with a hardness of 50 to 70 shore A, and an angle of 50 to 75 degrees used to control ink transfer;
● setting the printer speed optimized to 100 to 150 millimetre per second (mm/s) to ensure complete ink transfer without smearing;
● adjusting the print pressure up to 5 to 6 Newton per centimetre (N/cm) to achieve full contact between the screen and the substrate, ensuring uniform ink deposition with the help of spreader;
● starting the printing machine in auto mode; wherein the ink transfers and deposits on the glass such that the off-contact distance ranging between 15 to 30 mm is maintained to allow for clean snap-off of the screen from the substrate;
● printing multiple layers of carbon ink to achieve single-digit resistance, wherein each layer is dried before the next layer is applied;
● cleaning the mesh with cleaning agent that is MEK; and
● packing the mesh to avoid dust and it is ready to use for next cycle; and
the two-stage glass oven curing standard operating procedure (SOP) further comprising of drying and firing; wherein the drying comprises of;
● placing the substrate in AC, dust free room for 10 minutes so the wet film levels and begins set before oven work;
● drying the printed substrate at a relatively low temperature ranging between 100 to 200 degrees Celsius for approximately 50 to 60 minutes in a convection oven to remove the volatile solvents, preventing bubbling or cracking during subsequent high- temperature firing; and
the firing process comprises of;
● firing the dried substrate wherein a controlled ramp-up rate of 1 to 2 degrees Celsius per minute is allowed to the peak firing temperature;
● allowing the substrate to cool to ambient temperature and preliminarily inspecting by visually checking the traces and performing a quick continuity check to catch obvious defects before firing;
● allowing the substrate to undergo a peak firing temperature ranging between 250 to 300 degrees Celsius in ambient air for the densification of carbon particles and the formation of a highly conductive network, as well as for the proper curing of the binder system to ensure strong adhesion to the ceramic glass;
● enabling a dwell time at the peak temperature for 180- 200 minutes (approx. 3 hrs); allowing sufficient time for the carbon particles to coalesce and for the binder to fully cure;
● allowing a controlled cool down rate at 1 to 2 degrees Celsius back to ambient to prevent thermal shock to the ceramic glass and to maintain the integrity of the carbon traces;
● allowing the oven and parts reach room temperature before opening for removal, and final inspection performs resistance measurements and a short check;
● cleaning using lint-free cloth to remove polymers.

2. The process claimed in claim 1, wherein a polyester screen ranging from 40-360 threads per inch (TPI) with a mesh opening size of 1000-1500 micro meter.

3. The process as claimed in claim 1, wherein the number of layers printed range from 1 to 5, depending on the desired resistance and ink properties.

4. The process as claimed in claim 1, wherein the electrical resistance values of less than 10 Ohms, and preferably less than 5 Ohms are consistently achieved.

5. The process as claimed in claim 1, wherein the ceramic glass substrate includes a ceramic glass based on lithium aluminosilicate (LAS) or other glass-substrate composition known for their thermal shock resistance and high-temperature stability.

6. The process as claimed in claim 1, wherein the thickness of the ceramic glass substrate can vary depending on the application, typically ranging from 1millimetre to 6 millimetres,

7. The process claimed in claim 1, wherein the ink comprises a conductive carbon material with high-purity carbon particles including specific carbon form such as carbon black, graphite, graphene, carbon nanotubes (CNTs), or combination thereof.

8. The process claimed in claim 1, wherein the binder system uses a polymeric binder that provides adhesion to the ceramic glass and structural integrity to the printed trace after firing; and is optimized to balanced adhesion, conductivity and printability.

9. The process claimed in claim 1, wherein the solvent system includes a blend of volatile organic solvents chosen for appropriate viscosity, drying rate and compatibility with the carbon and binder; and additives such as, dispersants, rheology modifiers and wetting agents may be included to improve ink stability, printing and surface wetting.

10. The process as claimed in claim 1, wherein process uses the carbon ink with a high aspect ratio carbon material dispersed in low-viscosity, fast-drying system with a minimal amount of a high-temperature resistance polymeric binder.

Dated this 25th day of August, 2025.