MXPA06010303A - Variable watt density layered heater - Google Patents

Abstract

A layered heater is provided that comprises at least one resistive layer comprising a resistive circuit pattern, the resistive circuit pattern defining a length and a thickness, wherein the thickness varies along the length of the resistive circuit pattern for a variable watt density. The present invention also provides layered heaters having a resistance circuit pattern with a variable thickness along with a variable width and/or spacing of the resistive circuit pattern in order to produce a variable watt density. Methods are also provided wherein the variable thickness is achieved by varying a dispensing rate of a conductive ink used to form the resistive circuit pattern, varying the feed rate of a target surface relative to the dispensing of the ink, and overwriting a volume of conductive ink on top of a previously formed trace of the resistive circuit pattern.

Description

STRATIFIED HEATER WITH VARIABLE WAVE DENSITY DESCRIPTION OF THE INVENTION The present invention relates generally to electric heaters and more particularly to devices for and methods for distributing the density in watts of electric heaters. Stratified heaters are typically used in applications where space is limited, when heat output needs to vary across a surface, where rapid thermal response is desirable or in ultra-clean applications where dust or other contaminants They can migrate inside the conventional heater. A stratified heater generally comprises layers of different materials, mainly a dielectric and a resistive material, which are applied to a substrate. The dielectric material is first applied to the substrate and provides electrical insulation between the substrate and the electrically active resistive material and also reduces the leakage of current to ground connection during operation. The resistive material is applied to the dielectric material in a predetermined pattern and provides a resistive heating circuit. The stratified heater also includes conductors connecting the resistive heater circuit to an electric current source, which is typically cycled by a temperature controller. The interconnection of the conductor to the resistive circuit is typically also mechanically and electrically protected from the foreign contact by providing protection against pulls and electrical insulation through a protective layer. Consequently, stratified heaters are highly adaptable for a variety of heating applications. Stratified heaters can be "thick" film, or "thin" film, or "thermally dispersed", among others, wherein the primary difference between these types of stratified heaters is the method in which the layers are formed. For example, layers for thick film heaters are typically formed using processes such as screen printing, adhesive label application, or film supply heads, among others. Layers for thin film heaters are typically formed using deposition processes such as ion plating, cathodic sputtering, chemical vapor deposition (CVD), and physical vapor deposition (PVD), among others. Still another series of different processes of thin and thick film technique are those known as thermal dispersion processes, which may include by way of example flame dispersion, plasma dispersion, arc wire dispersion, and HVOF (High Oxygen Fuel). Speed), among others.

In some electric heater applications, it may be desirable to vary the density in watts of the heater in certain areas in order to adjust the amount of heat distributed to the specific part or device being heated or to justify the variations inherent in the distribution of heat. heat along the stroke or heating element. The known electric heaters typically vary the space of the resistive circuit pattern so that where the space is smaller and the trace of the resistive circuit pattern is closer, the density in watts is greater, for a series of circuit configuration. Conversely, the greater the space between the traces of the resistive circuit pattern, the lower the density in watts in those regions. In other known electric heaters, the stroke width of the resistive circuit pattern varies along its length in order to vary the density in watts, where the wider the stroke the lower the density in watts and the narrower the largest stroke will be the density in watts, again, for a series of circuit configurations. In a preferred form, the present invention provides a stratified heater comprising at least one resistive layer comprising a resistive circuit pattern, wherein the resistive circuit pattern defines a length and a thickness. The thickness of the resistive circuit pattern varies along the length of the resistive circuit pattern for a variable watt density. In other forms, both the thickness and the amplitude of the resistive circuit pattern are varied, the thickness and space are varied, or the thickness and amplitude and space are varied for a variable watt density. In another form, a stratified heater is provided comprising a dielectric layer, a resistive layer formed in the dielectric layer, and a protective layer formed in the resistive layer. The resistive layer comprises a resistive circuit pattern, and the resistive circuit pattern defines a length and a thickness, wherein the thickness of the resistive circuit pattern varies along the length of the resistive circuit pattern for a variable watt density. . In another form, the dielectric layer is formed in a substrate. In yet another form, a resistive circuit pattern for use in a stratified heater providing, wherein the resistive circuit pattern defines a variable length and thickness along the length of the resistive circuit pattern. According to the methods of the present invention, the resistive circuit patterns of a stratified heater are formed through the steps of dispersing a conductive ink at a rate on a surface and varying the dispersion rate of the conductive ink to form a resistive circuit pattern of variable thickness. In another method, a feed rate of the surface relative to the dispersion of the conductive ink is varied to form a resistive circuit pattern of varying thickness. Additionally, a method is provided that varies the rate of dispersion and varies the feed rate of the surface relative to the conductive ink dispersion in another form of the present invention. Another method is provided that forms a resistive circuit pattern of a stratified heater through the steps of applying a volume of conductive ink on a substrate to form a trace and applying an additional volume of conductive ink on the line, where produces a resistive circuit pattern of varying thickness. Additional areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and the specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only, and are not intended to limit the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: Figure 1 is a plan view of a stratified heater system with a resistive circuit pattern having a variable space according to a heating system of the prior art; Figure 2 is a plan view of a stratified heater system with a resistive circuit pattern having variable amplitude according to a prior art heating system; Figure 3 is a plan view of a stratified heater system constructed in accordance with the principles of the present invention; Figure 4 is a cross-sectional view taken along line AA of Figure 3 and rotated at 90 °, of a stratified heater system with a resistive circuit pattern having a variable thickness in accordance with the principles of the present invention; Figure 5 is a cross-sectional view, taken along line B-B of Figure 3, of a stratified heater system with a resistive circuit pattern having a variable thickness according to the principles of the present invention; Figure 6 is a cross-sectional view, taken along the line CC of Figure 3, and rotated at 90 °, of a stratified heater system with a resistive circuit pattern having a variable thickness in accordance with the principles of the present invention; Figure 7 is a cross-sectional view, taken along line DD of Figure 3, and rotated at 90 °, of a stratified heater system with a resistive circuit pattern having a variable thickness through a width according to the principles of the present invention; Figure 8 is a plan view of another embodiment of a stratified heater system having a parallel circuit configuration and constructed in accordance with the principles of the present invention; Figure 9 is a cross-sectional view, taken along the line EE of Figure 8, and rotated at 90 °, of a stratified heater system with a resistive circuit pattern in parallel having a varying thickness in accordance with the principles of the present invention; Figure 10 is a cross-sectional view of the resistive trace illustrating the different power densities for a series of circuit configuration versus a parallel circuit configuration in accordance with the principles of the present invention; Figure 11 is a plan view of yet another embodiment of a stratified heater system having a parallel-series-in-parallel circuit configuration and constructed in accordance with the principles of the present invention; Figure 12 is a cross-sectional view, taken along the line FF of Figure 11 and rotated at 90 °, of a stratified heater system with a resistive circuit pattern in parallel-in series-in parallel, with a superimposed graph of the density in watts, which has a variable thickness according to the principles of the present invention; Figure 13 is a cross-sectional view of a stratified heater system with a resistive circuit pattern having a variable thickness and variable amplitude in accordance with the principles of the present invention; Figure 14 is a cross-sectional view of a stratified heater system with a resistive circuit pattern having a variable thickness and a variable space according to the principles of the present invention; Figure 15 is a cross-sectional view of a stratified heater system with a resistive circuit pattern having a varying thickness, a variable amplitude, and a variable space in accordance with the principles of the present invention; Figure 16 is an elevated side view of a high coverage resistive circuit pattern in accordance with the principles of the present invention; Figure 17 is an enlarged cross-sectional view, taken along the line G-G of Figure 16 and rotated at 90 °, of a variable watt density resistive circuit pattern according to the principles of the present invention; Figure 18 is a cross-sectional view along the length of a constant thickness resistive circuit pattern having a variable watt density in accordance with the principles of the present invention; Figure 19a is a cross-sectional view along the length of a continuous resistive circuit pattern according to the principles of the present invention; Figure 19b is a cross-sectional view along the length of a non-continuous resistive circuit pattern according to the principles of the present invention; Figure 20 is a cross-sectional view of a stratified heater system with a plurality of resistive layers, wherein the resistive layers comprise resistive circuit patterns having a variable thickness in accordance with the principles of the present invention; and Figure 21 is a cross-sectional view illustrating a method for forming a resistive circuit pattern of varying thickness by overwriting a previously formed trace of the resistive circuit pattern according to the principles of the present invention; Corresponding reference number indicates corresponding part during all the various views of the drawings. The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its applications, or uses. With reference to Figures 1 and 2, two (2) heater systems 10 and 12 of the prior art are illustrated as providing variable watt density. The two heater systems 10 and 12 of the prior art comprise resistive circuit patterns 14 and 16, respectively, which provide the necessary heating to the part or device that is heated. Generally, the resistive circuit pattern 14 in Figure 1 is formed in a substrate 15 and comprises a variable space (e.g., SI and S2) as shown in order to provide a variable watt density as required. In SI areas, the space is closer and thus the density in watts is higher. Conversely, in the areas of S2, the space is wider and thus the density in watts is smaller. As further shown in Figure 2, the resistive circuit pattern 16 is formed on a substrate 17 and comprises a variable amplitude (e.g., W1 and W2) in order to provide a variable watt density as required. In the areas of Wl, the amplitude is greater and in this way, the density in watts is lower, while in the areas of W2 the amplitude is narrower and the density in watts is higher. Accordingly, these prior art heater systems 10 and 12 employ a variable space or a variable amplitude in order to vary the density in watts as required. More specifically, the density in watts is a result of both a density in watts of the trace, which is the density in watts along the length or stroke of the pattern (14, 16) of resistive circuit, and a density in watts of substrate, which is the amount of coverage or percentage of the total substrate surface area that is covered by the resistive circuit pattern (14, 16), of the resistive circuit pattern (14, 16) across the substrate ( 15, 17) whole. The density in watts of the trace comprises the energy that is dissipated as a function as an area of the individual trace, which, as used herein, is generally defined by times the width of the overall length of the resistive trace. The density in watts of substrate comprises the energy that dissipates along the pattern (14, 16) of the resistive circuit and the energy that is dissipated as a function of the amount of coverage provided by the resistive circuit pattern (14, 16) on the substrate (15, 17). Thus, the watt density of the trace in Figure 1 is constant across the entire substrate 15 since the amplitude of the resistive circuit pattern 14 is constant. However, since the space of the resistive circuit pattern 14 is variable, the coverage amount of the resistive circuit pattern 14 on the substrate 15 varies, resulting in a variable watt density. In Figure 2, the density in watts of the trace varies since the amplitude of the resistive circuit pattern 14 varies, while the coverage amount of the resistive circuit pattern 16 on the substrate 17 remains constant, which results in a density in the resistive circuit. variable watts. Accordingly, a variable watt density is achieved through a density in watts of the variable trace and / or a variable coverage of the pattern (14, 16) of resistive circuit on the substrate (15, 17). Accordingly, as used herein, the term "density in watts" should be interpreted to include either the density in watts of the trace or the density in watts of the substrate. As used herein, the term "coverage" should be interpreted to mean the total circuit area of the resistive circuit pattern when compared to, or as a percentage of, the total area of a substrate. Therefore, the greater the total area of the resistive circuit pattern over a given substrate area, the greater the "coverage". Referring now to Figures 3 and 4, a stratified heater that provides improved design flexibility to achieve variable watt density in accordance with the present invention is illustrated and is generally indicated by the reference number 20. Generally, the heater 20 The laminate comprises a number of layers arranged on a substrate 22, wherein the substrate 22 may be a separate element disposed proximate to the part or device to be heated, or the substrate 22 may be the part or device itself. As best shown in Figure 4, the layers preferably comprise a dielectric layer 24, a resistive layer 26, and a protective layer 28. The dielectric layer 24 provides electrical insulation between the substrate 22 and the resistive layer 26 and is formed on the substrate 22 at a thickness commensurate with the energy output, the applied voltage, the intended application temperature, or combination thereof, of the stratified heater 20. The resistive layer 26 is formed in the dielectric layer 24 and provides a heater circuit for the laminated heater 20, for this reason providing heat to the substrate 22. The protective layer 28 is formed in the resistive layer 26 and is preferably an insulator, however, other materials such as electrical or thermally conductive materials may also be employed according to the requirements of a specific heat application while remaining within the scope of the present invention. As further shown, the terminal pads 30 are preferably arranged in the dielectric layer 24 and are in contact with the resistive layer 26. Accordingly, the electrical conductors (not shown) are in contact with the terminal pads 30 and connect the resistive layer 26 to a power source (not shown). As further shown, the protective layer 28 is formed in the resistive layer 26 and is preferably a dielectric material for insulation and electrical protection of the resistive layer 26 of the operating environment. Additionally, the protective layer 28 may cover a portion of the terminal pads 30 as long as sufficient areas remain to promote an electrical connection to the power source. As used herein, the term "Stratified heater" must be constructed to include heaters comprising at least one functional layer (eg, dielectric layer 24, resistive layer 26, and protective layer 28, among others), wherein the layer is formed through application or accumulation of a material to a substrate or another layer using processes associated with thick film, thin film, thermal dispersion or sol-gel, among others. These processes are also referred to as "stratified processes", "stratified processes", or "stratified heat processes". Such processes and functional layers are described in greater detail in the co-pending application entitled "Combined Stratification Technologies for Electric Heaters," filed January 6, 2004, which is commonly assigned with the present application and the contents of which are incorporated in the present for reference in its entirety. As further shown in Figure 3, the resistive layer 26 defines a resistive circuit pattern 40, which comprises a length (shown as the distance along the pattern 40 of the resistive circuit between the terminal pads 30), an amplitude W, and a space S. As illustrated in Figure 4, the resistive circuit pattern 40 further comprises a variable thickness along the length L as shown by way of example in the areas having a thickness TI, thickness T2, and thickness T3. As shown, the thickness TI is greater than the thickness T2, and the thickness T2 is greater than the thickness T3. In this example, a greater density in watts is required in the area of T3 against the areas of T2 and TI, and higher density in watts is required in the area of T2 than IT, generally due to the loss of heat through the edges of the substrate 22 for a typical heater application. Accordingly, the thickness of the resistive circuit pattern 40 is thinner in areas where higher density in watts is required (higher resistance, higher heat transfer and thicker areas where lower density in watts is required (lower resistance, lower heat transfer) during the operation of the stratified heater 20. Accordingly, as the thickness varies along the length of the resistive circuit pattern 40, the resistance of the resistive circuit pattern 40 varies along its length, which results in a density in watts of the variable trace. Methods for producing the resistive circuit pattern 40 of variable thickness are described in greater detail in the following, with reference now to Figures 5 and 6, a thickness T4 is shown through a curved portion or "race track" of the resistive circuit pattern 40, which is thicker than an adjacent area having a thickness T5 along a linear portion of the resistive circuit pattern 40. This portion of the racetrack has traditionally included a wider resistive circuit pattern due to the inherent buildup of current "current overcrowding" in these areas during operation. The "overcrowding of current" will result in high density in watts of the trace in the region adjacent to the inner portion of the race track, leading to a higher operating temperature and subsequently a degradation of reliability. To maintain a constant voltage, the pattern of the heaters of the prior art has been designed to be wider to reduce the resistance where a current increase occurs. Unfortunately, this wider race track consumes additional space and to some degree dictates the space between the resistive circuit pattern 40 along the linear portions. The present invention overcomes this disadvantage by increasing the thickness T4 along the race track portion rather than increasing the amplitude of the resistive circuit pattern 40 such that no additional space is consumed and a resistive circuit pattern 40 is provided. more compact In another form of the present invention as shown in Figure 7, the resistive circuit pattern 40 comprises a variable thickness across the width of the race track portion. Along the inner portion of the race track where current overcrowding occurs more specifically, the resistive circuit pattern 40 comprises a thickness T6, which is thicker and has more strength than the outer portion of the track. races comprising a thickness T7. As a result, the inner portion of the race track at T6 has a density in watts less than the outer portion of the race track at T7 in order to accommodate the overcrowding of current, which promotes a more uniform temperature across the race track. the entire portion of the race track. Accordingly, the thickness varies across the width of the resistive circuit pattern 40 from T6 to T7 in order to provide a variable watt density. It should be understood that the specific application of a variable thickness across the width of the resistive circuit pattern 40 for a racing track configuration is not intended to limit the scope of the present invention. The variable thickness across the width as illustrated and described herein may be applied in any application where such a variable watt density is desired as long as it remains within the teachings of the present invention. With reference to Figures 8 and 9, the variable thickness according to another form of the present invention is employed in a parallel circuit configuration of a laminated heater 42, before a series circuit configuration as previously described. As shown, a resistive circuit pattern 44 comprises a series of resistive traces 46 that are connected to power buses 48. In a parallel circuit, assuming a constant voltage, the current in each resistive trace 46 is a function of the resistance and is not constant as with the series circuit illustrated previously. Since the power is equal to the square of the current multiplied by the resistance, (P = I2R), an increase in the power is best achieved by an increase in current, which is accompanied by an increase in the thickness of the trace 46 corresponding resistive. Therefore, in a similar application as previously described where a higher watt density is required near the edges 45 and 47 of the substrate 22, the thickness TI 'is less than the thickness T2', and the thickness T2 'is less than T3'. Consequently, the thickness of the resistive circuit pattern 44 is thicker in areas where a higher and thinner density is required in areas where a lower watt density is required during the operation of the stratified heater 42 in a parallel circuit . Accordingly, as the thickness varies in each of the resistive trace 46 of the resistive circuit pattern 44, the current varies within each trace 46 resistive, which results in a density in watts of the variable trace through the substrate 22 (i.e., density in watts of variable substrate). Thus, depending on whether the resistive circuit pattern comprises a series circuit configuration or in parallel, the thickness of the resistive line varies differentially. As illustrated in Figure 10, for a parallel circuit configuration, the thickness of the resistive trace is thicker in areas where a higher and thinner density in watts is required where a lower density in watts is required. Conversely, for a series circuit configuration, the thickness of the resistive trace is thicker where a lower and thinner density in watts is required where higher density in watts is required. Therefore, the configuration of the circuit, whether in series or in parallel, dictates whether the thickness should be increased or decreased according to the density requirements in watts of the specific application. In addition to the individual circuits in series and in parallel as previously described, another form of the present invention comprises a parallel-series-in-parallel circuit as illustrated in Figures 11 and 12, wherein a laminated heater 48 comprises a circuit 49 in series and in parallel with a circuit 50 in parallel. As shown, a resistive circuit pattern 51 comprises the traces 52 in parallel and a tracing 53 in series, which are connected through power terminals 61 and power buses 63. In an application where a higher watt density is required near the edges 54 and 55 of the substrate 22, the thickness of the resistive circuit pattern 51 near the edges within the traces 52 in parallel is thicker for a density in watts. greater, and the thickness of the resistive circuit pattern 51 within the series trace 53 is also thicker for a lower density in watts. Accordingly, the parallel and series circuits can be combined with varying thicknesses according to the teachings of the present invention to achieve the desired density distribution in watts. Accordingly, the term "in series-in parallel" or "in parallel-in series" should be interpreted to mean a circuit that includes one or more circuits in series and in parallel within the same power circuit, notwithstanding the order of each one of the circuits in series and in parallel within the power circuit. As further shown in Figure 12, a graph of the density in watts across the substrate 22 is superimposed over the traces 52 in parallel and the tracing 53 in series to further illustrate the different effect of the variable thickness based on the type of circuit, that is, in parallel or in series. As the thickness decreases through the traces 52 in parallel, the corresponding density in watts decreases, however, with shape increasing the thickness through the trace 53 in series, the density in watts continues to decrease. Accordingly, the magnitude and direction (i.e., increase and decrease in thickness) of the variable thickness according to the teachings of the present invention depend on the circuit configuration and the desired density in watts across the substrate 22. In addition to varying the thickness of resistive circuit pattern 40, width and / or space may also be varied for additional design flexibility to achieve a desired distribution of density in watts across the length of the substrate. Consequently, Figure 13 illustrates a resistive circuit pattern 57 having both a variable thickness (T8 and T9) and a variable width (W3 and W4), with a constant space in a series circuit configuration. In the areas of T8 and W4, the resistive circuit pattern 57 is relatively thin and narrow, while in the areas of T9 and W3, the resistive circuit pattern 57 is relatively thick and broad. As a result, a higher density in watts is provided in the areas of T8 and W4, and a lower density in watts is provided in the areas of T9 and W3. With reference to Figure 14, a resistive circuit pattern 58 is illustrated in another form of the present invention which comprises both a variable thickness (UNCLE and TIL) and variable space (S3 and S4), with a constant width in a configuration of series circuit. As shown, in the areas of UNCLE and 33, the pattern 58 of the resistive circuit is relatively thin and has more closed space, while in the areas of Til and S4, the pattern 58 of the resistive circuit is relatively thick and has more space. large. As a result, a higher density in watts is provided in the areas of UNC and S3, and a lower density in watts is provided in the areas of Til and S4. Even another form of the present invention is illustrated in Figure 15, wherein a resistive circuit pattern 59 comprises a variable thickness (T12 and T13), a variable width (W5 and W6), and a variable space (S5 and S6). in a series circuit configuration. In the areas of T12, W5 and S5, the resistive circuit pattern 59 is relatively thin, narrow, and has a more closed space. In the areas of T13, W6 and S6, the resistive circuit pattern 59 is relatively thick, broad, and has a wider space. In this way, a higher density in watts is provided in the areas of T12, W5 and S5, while a lower density in watts is provided in the areas of T13, W6 and S6. It should be understood that combinations of variable thickness and variable width, a variable thickness and a variable space, and a variable thickness, a variable width, and a variable space as described herein may also be applied in parallel circuit configuration or a series-parallel circuit configuration while remaining within the scope of the present invention. Figure 16 illustrates another form of the present invention, while a resistive circuit pattern 50 has a relatively high amount of coverage on the substrate 62. Such an application may exist where the size of the substrate 62 is limited due to the part or device relatively small target to be heated, or where space is limited for the stratified heater within the specific application. An example of an application where a high density in a relatively compact size is required is a quartz tube heater in chemical applications, which is illustrated and is generally indicated by reference number 64. Generally, a chemical solution it enters an inlet port 66 at a proximal end 68, flows through the quartz tube heater 64 for heating, and then flows through the outlet port 70 to a disk end 72. In this way, the chemical solution is at a lower temperature at the inlet port 66 than at the outlet port 70, which results in a relatively wide temperature distribution through the quartz tube heater 64. To create a more uniform temperature distribution, the density in watts at the proximal end 68 must be greater than the density in watts at the distal end 72. However, since the coverage of the resistive circuit pattern 60 is relatively greater, there is little to no place to adjust the space or width of the resistive circuit pattern 60. Accordingly, the thickness of the resistive circuit pattern 60 is thinner at the proximal end 68 and is thicker at the distal end 72 according to a form of the present invention as shown in Figure 17, which results in a pattern 60 of resistive circuit density in watts variable. In addition to a variable thickness and other variable geometries as previously described, another form of the present invention provides a variable watt density through a change in composition of the resistive circuit pattern material along its length. As shown in Figure 18, a resistive circuit pattern 80 defines a constant thickness T14 along its length. However, the composition of the resistive circuit pattern 80 material changes along its length, for example, changing from a high strength composition in the portion 82 and a low strength composition in the portion 84. As a result, the Watt density is greater in the 82 portion than the density in watts in the 84th portion, resulting in a 80 resistive density pattern in variable watts. Accordingly, varying the material composition of the resistive circuit pattern 80 provides additional design flexibility in providing a variable watt density stratified heater according to another form of the present invention. It should be understood that such variation in material composition can be combined with variable thickness and other variable geometries while remaining within the scope of the present invention.

In yet another form of the present invention, the variable thickness and other geometries as previously described may be either continuous as shown in Figure 19a or not continuous as shown in Figure 19b. A pattern 90 of continuous resistive circuit, which is formed by the processes described in more detail below, defines a gradual change in thickness from T15 to T16. As a result, a gradual dimension in the density in watts occurs along the length of the resistive circuit pattern 90 from T15 to T16. Alternatively, a non-continuous resistive circuit pattern 92 can be produced which defines a stage change in thicknesses from T17 to T18 to T19. Consequently, a change of stage in the density in watts from high to low results along the length of the resistive circuit pattern 92 from T17 to T19. Processes for pattern 92 of non-continuous resistive circuit are also described in more detail below. These continuous and non-continuous configurations can be applied not only to the thicknesses as illustrated herein, but also to the width of the resistive circuit patterns while remaining within the scope of the present invention. With reference to Figure 20, another form of the present invention includes a stratified heater 110 comprising a plurality of resistive layers 112 and 114, wherein each of resistive layers 112 and 114 defines at least one resistive circuit pattern with the resistive lines 16 and 18 of variable thickness, respectively. For the purposes of this embodiment, the circuit configuration is serial, although it should be understood that parallel and / or series-parallel configurations within the plurality of resistive layers may also be employed. Accordingly, in applications where the substrate 120 defines an insufficient surface area to accommodate a resistive circuit pattern to produce the required density in watts in a single layer, a plurality of resistive circuit patterns are employed in a plurality of layers as shown in FIG. sample. Additionally, the thickness is varied as shown according to the density requirements in watts, where a higher density in watts is required near the edges 122 and 124 of the substrate 120. Accordingly, the thickness varies according to the teachings of the present invention is employed within multiple resistive layers to provide the density in watts required when the surface area of the substrate is limited. It should also be understood that the thickness may vary across the width in addition along the length as shown and that a variable width and / or space may also be employed as long as it remains within the scope of the present invention.

It should further be understood that the thickness of the resistive circuit patterns as shown and described herein are varied according to specific heating application requirements and the modalities illustrated above are only exemplary and should not be construed as limiting the scope of the present invention. Consequently, different patterns with different areas and configurations of variable thickness, together with variable width and / or space, within series and / or parallel circuits, and arranged within a plurality of resistive layers, among other configurations, are also they may be employed while they remain within the scope of the present invention. According to a method of the present invention, the variable watt density resistive circuit patterns as described herein are formed by varying the rate at which an electrically conductive ink is distributed over a surface, for example, over the dielectric layer 24. The conductive ink can be dispensed using precision line driver writing equipment, which is described in greater detail in US Pat. No. 5., 973,296 and commonly assigned with the present application, the contents of which is incorporated herein by reference in its entirety. With the precision scriber writing equipment, the conductive ink is distributed through a hole in a writing tip while the tip and / or the target substrate is moved in order to produce a predetermined resistive circuit pattern. In order to achieve a variable thickness where desired, the rate at which the conductive ink is distributed, or the flow rate of the electrically conductive ink through the orifice of the tip, is varied. For example, in areas where a thicker resistive circuit pattern is desired, the rate at which the conductive ink is distributed is increased. Conversely, in areas where a thinner resistive circuit pattern is desired, the rate at which the conductive ink is distributed is reduced. Consequently, a resistive circuit pattern of varying thickness is produced by varying the rate at which the conductive ink is distributed over the target surface. According to another method of the present invention, the rate at which the target surface moves relative to the writing line (i.e., feed rate) is varied in order to produce a thickness resistive circuit pattern variable. In areas where a thicker resistive circuit pattern is desired, the feed rate of the target surface is reduced relative to the writing line while the rate at which the conductive ink is distributed remains constant. Alternatively, in area where a thinner resistive circuit pattern is desired, the feed rate of the target surface is increased relative to the writing line, again while the rate at which the conductive ink is distributed remains constant. In yet another form of the present invention, both the rate of distribution of the conductive ink and the feed rate of the target surface may vary in order to reproduce a resistive circuit pattern of variable thickness. Both the rate of distribution and the feed rate can vary whether continuously or not continuously to produce the continuous and non-continuous resistive circuit patterns as previously described while remaining within the scope of the present invention. In yet another method as shown in Figure 21, the present invention produces a resistive circuit pattern of varying thickness by overwriting a volume of conductive ink at the top of a previously formed trace of the resistive circuit pattern. More specifically, the method includes the steps of distributing a volume of conductive ink from a lantern 94 on a surface 96 to form a trace 98 and then selectively distributing an additional volume 100 of conductive ink onto the previously formed trace 98, where it is produced a resistive circuit pattern of variable thickness.

Accordingly, in an area where a thicker resistive circuit pattern is desired, an additional volume 100 of conductive ink is formed on a trace 98 previously formed in accordance with the principles of the present invention. In addition, either the line 94 and / or the surface 96 move relative to one or the other during the distribution of the conductive ink to form the desired resistive circuit pattern. Alternatively, the conductive ink volumes may be applied using different processes than the precision line writing equipment while remaining within the scope of the present invention. Other laminating processes associated with thick film, thin film, thermal dispersion, or sol-gel can be used to apply the volumes of conductive ink. For example, the coarse film process of screen printing can be employed to apply the volumes of conductive ink in an alternative form of the present invention. It should be understood that the application of additional volumes of conductive ink is not limited to sequential applications after the original volume is applied within a manufacturing process. More specifically, the additional volume can be applied at any stage of the manufacturing process such as, by way of example, after the drying operation or after the firing operation.

The description of the invention is merely exemplary in nature and in this way, variations that are not separated from the main aspect of the invention are intended to be within the scope of the invention. For example, heating systems as described herein may be employed with a two wire controller as shown and described in copending application Serial No. 10/719327, entitled "Two Wire Stratified Heater System," submitted on November 21, 2003, and the co-pending applications entitled "Laminating Technologies of Combined Material for Electric Heaters" and "Stratified Heat Transfer Layer System Adjusted to the Measure", both filed on January 6, 2004 and which will all be commonly assigned with the present application and the contents of which are incorporated herein by reference in their entirety. In addition, the cross section of the resistive circuit patterns are not limited to rectangular shapes as illustrated herein. The ink leveling qualities may not produce such a shape after processing, and other shapes may be desired such as varying width and thickness through the portions of race tracks as previously described and illustrated. In addition, the resistive circuit patterns herein are illustrated in relatively flat and rectangular substrate for clarity purpose, and it should be understood that other substrate geometries such as cylinders and other three-dimensional shapes, such as those illustrated in the heater mode of quartz, are within the scope of the present invention. In addition, the circuits as illustrated herein are in series or in parallel, and it should be understood that the various embodiments of the present invention may also be employed with serial-parallel circuits as long as they remain within the scope of the present invention. . Such variations will not be considered as a separation of the spirit and scope of the invention.

Claims (18)

1. CLAIMS 1. A stratified heater characterized in that it comprises: a dielectric layer; at least one resistive layer formed in the dielectric layer, the resistive layer comprises a resistive circuit pattern, the resistive circuit pattern defines a stroke having a width and a space; and a protective layer formed in at least one resistive layer, wherein a thickness of the resistive circuit pattern varies across the width of the trace of the resistive circuit pattern for a variable watt density.
2. 2. A stratified heater characterized in that it comprises: a dielectric layer; a resistive layer formed in the dielectric layer, the resistive layer comprises a resistive circuit pattern, the resistive circuit pattern defines a trace having a length, a thickness and a space; and a protective layer formed in the resistive layer, wherein the thickness of the resistive circuit pattern varies along the length of the trace of the resistive circuit pattern for a variable watt density.
3. 3. The stratified heater according to claim 2, characterized in that the space is constant.
4. The stratified heater according to claim 2, characterized in that the space is variable
5. 5. The stratified heater according to claim 2, characterized in that the resistive circuit pattern also comprises a width that is constant.
6. 6. The stratified heater according to claim 2, characterized in that the resistive circuit pattern further comprises a width that is variable.
7. The stratified heater according to claim 2, characterized in that the stratified heater is selected from the group consisting of thick film, thin film, thermal spray, and sol-gel.
8. The stratified heater according to claim 2, characterized in that the resistive circuit pattern is selected from a group consisting of series, parallel, and series-in parallel.
9. 9. The stratified heater according to claim 2, characterized in that the variable thickness is continuous.
10. 10. The stratified heater according to claim 2, characterized in that the variable thickness is non-continuous.
11. 11. A stratified heater characterized in that it comprises: a substrate; a dielectric layer formed in the substrate; a resistive layer formed in the dielectric layer, the resistive layer comprises a resistive circuit pattern, the resistive circuit pattern defines a trace having a length and a thickness; and a protective layer formed in the resistive layer, wherein the thickness of the resistive circuit pattern varies along the length of the trace of the resistive circuit pattern for a variable watt density.
12. 12. A method for forming a resistive circuit pattern of a stratified heater, the method comprising the steps of: (a) distributing a conductive ink at a rate on a surface; and (b) varying the distribution rate of the conductive ink to form a resistive circuit pattern of variable thickness.
13. 13. A method for forming a resistive circuit pattern of a stratified heater, the method is characterized in that it comprises the steps of: (a) distributing a conductive ink at a rate on a surface; and (b) varying the feed rate of the substrate relative to the distribution of the conductive ink to form a resistive circuit pattern of variable thickness.
14. 14. A method for forming a resistive circuit method of a stratified heater, the method comprising the steps of: (a) distributing a conductive ink at a rate on a surface, (b) varying the rate of distribution of the conductive ink; and (c) varying a feed rate of the substrate relative to the distribution of the conductive ink, wherein a resistive circuit pattern of varying thickness is produced.
15. 15. A method for forming a resistive circuit pattern of a stratified heater, the method is characterized in that it comprises the steps of: (a) applying a volume of conductive ink on a surface to form a trace; and (b) applying an additional volume of conductive ink on a line, where a resistive circuit pattern of varying thickness is produced.
16. The method according to claim 14, characterized in that the volumes of conductive ink are applied by a lamination process selected from the group consisting of thick film, thin film, thermal spray, and sol-gel.
17. 17. The method according to claim 14, characterized in that the volumes of conductive ink are applied using precision scriber writing equipment.
18. 18. The method according to claim 14, characterized in that the volumes of conductive ink are applied using screen printing processes.