Electric heating element production method

Abstract

Conductive lines (34) formed by a metal coating deposited on the insulating surface in a thermal spray manner are retreated. In order to compensate for a final resistance deviation caused by a coating thickness difference or a coating structure difference, the line width (36) is adjusted after the line is made. The adjustment of the line width can be carried out on an adjustment section (39) arranged along the length of the conductive line, or over the entire line length.

Description

Technical Field

[0001] Electrical circuits can be formed by applying a pattern of conductive traces made from a metal alloy to an electrically insulating surface. Background Art

[0002] The production of electric heating elements by means of thermal spraying is an industrialized technology widely used in household appliances and electric vehicles. The demand for power density and total power is growing especially in the field of battery electric vehicles due to the increase in size and weight of battery packs. Therefore, the heater power density and the number of wires are increased to increase the total heating power and better control the heat generation and its transfer to the heat transfer liquid. All these factors lead to a reduction in the resistance tolerance and the heating line dimensional tolerance, which in turn is limited by the limitations of the control of the coating thickness used to form the heating circuit / line.

[0003] Currently, the design of heating lines assumes a tight tolerance on the coating thickness of the conductive heating layer (usually 25 to 50 μm of Ni 20Cr alloy). With moderate requirements for total output power and component size, the final resistance tolerance determined by the resistivity of the material (assumed to be a constant value), the line length and the coating thickness can be met. However, as the conditions for meeting higher resistance requirements increase, even small deviations in the range of 1 μm can result in resistance variations that render the component unusable. Summary of the invention

[0004] Embodiments relate to a method in which a heating line is deposited by thermally spraying a conductive material (e.g., Ni 20Cr alloy, Ni 5Al, FeCrAl alloy, or TiO2-based ceramic alloy) onto an insulating surface (e.g., Al2O3, Al2O3 / Cr2O3 blend, Al2O3 3TiO2, Al2O3 / ZrO2 blend, YAG, ZrO2-based ceramic, glass) or an optional bonding coating on a substrate surface, and its resistance is adjusted by reprocessing. Such reprocessing adjustment may, for example, include removing the conductive material from an adjusted section of the deposited heating line. The adjustment section may be a section of the heating line specifically designed for reprocessing adjustment, whereby the resistance of the heating line is increased by removing the conductive material of at least a portion of the adjustment section; the adjustment section may also cover the entire length of the heating line. In this way, the tolerance of the heating line resistance may be reduced during reprocessing adjustment without generating more scrap. In the prior art, the variation in resistance may be ±10%, and not every component can meet this standard. Using the re-trim process, the goal is to bring each part within specification and tighten the tolerance to approximately ±2%.

[0005] In an embodiment, it can be provided that the adjustment or correction section of the heating line (for example, the long straight section located in the single heating line) is 0.5 to 1.0 mm wider than the rest of the heating line. After forming the deposited heating line and before reprocessing adjustment, the resistance of the single heating line is measured to determine whether the resistance is within the target range limit, generally ±10%. At this time, the focus is on the lower limit of the resistance, because re-adjustment can only remove material, thereby increasing the resistance. Therefore, if the target range is, for example, 45-55 ohms (ideal value is 50 ohms), the initial layout will be set to 45 ohms. If the resistance is detected to be within the target range limit, there is no need to reprocess the heating line. However, in the case where the resistance is detected to be too low, that is, when it exceeds the tolerance range limit of this heating line, an appropriate amount of material is removed from the adjustment section by laser ablation, ion sputtering, electron beam sputtering or micro-milling, so that the resistance returns to the tolerance range limit, thereby achieving reprocessing adjustment. Therefore, while focusing on the lower limit during initial formation may result in more parts requiring re-tweaking, nearly all parts will be close to ideal or within a valid ideal range without generating scrap.

[0006] Since the length of the adjustment section of the material to be removed in the reprocessing adjustment has a slightly lower resistance than the rest of the heating line, the length of the removed material is preferably at least about 10% of the length of the single heating line, so that the additional heat generated in the adjustment section can be more evenly distributed on the adjustment section. Otherwise, if the adjustment section length is too short, insufficient heating in the adjustment section may result.

[0007] The layout of the heating line includes an adjustment section of the line, which can be simple in shape, such as an edge of the entire length of a straight heating line, a straight heating line section in a meandering heating line, or a section of increased width in the heating line. In the production of the heating line, the dimensions are set to target a resistance at the lower limit of the target resistance range. After the heating line is produced, the resistance value is measured. If the resistance value is within the predetermined range, no further action is required. If the resistance is below a predetermined minimum level, the resistance is adjusted to within the target range by reducing the width of the adjustment section to a certain extent.

[0008] As an alternative to adjusting the width of the adjustment section, the coating thickness of the entire track can also be reduced, for example by grinding.

[0009] Other embodiments and advantages of the present invention can be determined by studying the specification and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In the following detailed description, the present invention is further described by way of non-limiting embodiments thereof with reference to the several drawings shown, wherein like reference numerals designate similar parts throughout the various views of these drawings, as follows:

[0011] Figure 1 A heating element is shown formed by a coating system on a substrate;

[0012] Figure 2 The resistance of the heating layer is plotted against the number of components prepared according to the prior art without planned reprocessing;

[0013] Figure 3 A graph comparing the relationship between the heating layer resistance and the number of components in the components prepared according to the prior art and not planned for reprocessing and in the components prepared according to the present embodiment and planned for reprocessing;

[0014] Figure 4 A graph comparing the relationship between the heating layer resistance and the number of components in a component prepared according to the prior art without planned reprocessing and in a component prepared according to the present embodiment after reprocessing;

[0015] Figure 5-7 shows an exemplary conditioning section in a heating circuit before reprocessing conditioning according to an embodiment;

[0016] Fig. 8A A heating element showing the meander shape of the design;

[0017] Figure 8B Show Fig. 8A A serpentine heating element with regulated, thin corner traces; and

[0018] Fig. 9 An exemplary flow chart of the method according to this embodiment is shown. DETAILED DESCRIPTION

[0019] The details shown herein are for illustration only and are only used for the purpose of explaining and discussing the embodiments of the present invention, and the purpose is to provide the most useful and understandable description of the principles and concepts of the present invention. In this regard, the structural details of the present invention are not shown in detail, beyond the scope required for basic understanding. The description made in conjunction with the accompanying drawings enables those skilled in the art to clearly understand how several embodiments of the present invention can be implemented in practice.

[0020] Figure 1An electric heating element 1 is shown, wherein a coating system is formed on a substrate 11. The coating system includes an optional metal bonding coating 12, such as Ni 20Cr, Ni 5Al, Ni, Al, AlSi alloys, and FeCr steel and FeCrNi steel, to improve the adhesion between the heating element and the substrate 11, which is preferably made of, for example, low alloy steel, stainless steel, aluminum and aluminum-based alloys. A first insulating layer 13 is composed of an electrically insulating ceramic material, such as Al2O3, Al2O3 / Cr2O3 blends, Al2O3 3TiO2, Al2O3 / ZrO2 blends, YAG, ZrO2-based ceramics, glass, for electrically isolating the conductive heating line 14 from the substrate 11 / bonding layer 12. For example, the conductive heating line 14 formed by a thermal spraying process (such as atmospheric plasma spraying, flame powder spraying, flame wire spraying, arc wire spraying, high-velocity oxygen-fuel spraying or cold spraying) includes a layer of conductive material, such as Ni 20Cr, NiCr, pure Ni, Ni 5Al, FeCrAl alloy or TiO2-based ceramic alloy, that is, in particular a patterned conductive layer, which is preferably applied in a serpentine layout.

[0021] A second insulating layer 15 composed of an electrically insulating ceramic material (such as Al2O3, Al2O3 / Cr2O3 blend, Al2O3 3TiO2, Al2O3 / ZrO2 blend, YAG, ZrO2-based ceramic, glass) is thermally sprayed onto the conductive heating line 14 and therebetween, so that the conductive heating line 14 is electrically isolated from the substrate 11 / bonding layer 12. The conductive layer 16 (such as copper or a copper-based alloy) is patterned at multiple areas by atmospheric plasma spraying, flame powder spraying, flame wire spraying, arc wire spraying, high-velocity oxygen fuel spraying, or cold spraying to allow the conductive heating line 14 to be connected to an external power source (not shown) by welding or the like.

[0022] The width, length and thickness of the conductive heating line 14 are designed to produce a preset / predetermined resistivity to meet the required total power output. For example, at 400 to 800V, the total power per heating line is between 2 and 6kW, and the required total resistance is between 26 and 320Ω, preferably 40 to 53Ω at 3-4kW at 400V. Although the width and length of the heating line 14 applied by the thermal spray process can be precisely controlled, for example, by masking or reprocessing the coating layer, variations in the thickness of the heating line 14, even slight deviations from specific predetermined production parameters, may cause the resistance of the heating line 14 to deviate from its established resistance value.

[0023] According to a non-limiting example, if the heating line is made of a material with a resistivity of 0.002Ωmm, the target resistance of the heating line is 30Ω±3Ω (±10%), and the predetermined coating thickness of the heating line is 0.30mm, and the predetermined width of the heating line is 2.9mm, then according to the specification, the required heating line length is 1300mm, and the resistance of the heating line should be 29.9Ω. If the coating thickness of the heating line material applied by thermal spraying is too large (i.e., exceeds the thickness used when calculating the required size to achieve the target resistance), the resulting heating line resistance may be lower than the target value. In this example, if the coating thickness is less than 0.027mm, the resistance of the corresponding component exceeds the upper limit of 33.2Ω, while a coating thickness of 0.033mm will result in a total resistance below the lower limit (i.e., 27.2Ω).

[0024] In the first example, a layout of a heating circuit 14 in a heating element is described, which can be a straight line or a serpentine pattern with straight or curved sections. The heating circuit 14, to which the conductive material is applied by thermal spraying, is produced according to specific predetermined dimensions to ensure that it meets the target resistance within a predetermined tolerance range. After forming the heating circuit 14, the resistance of the manufactured heating circuit 14 is measured, for example, using a standard commercial multimeter, which is similar to the quality management of resistors, coils, etc. If the measured resistance value is within the tolerance range of the heating circuit (i.e., 27 to 33Ω), the heating element is qualified and no further operation is required. However, if the measured heating circuit resistance exceeds (i.e., is lower than) the tolerance limit of the target minimum value, the width of the adjustment section or correction section is appropriately reduced by removing material from the adjustment section by laser ablation, ion sputtering, electron beam sputtering or micro milling, so that the resistance enters the target range. In this way, the resistance of the heating circuit can be increased to a sufficient degree to return to the tolerance range limit. For example, when the width of the entire circuit needs to be reduced, a linear relationship is followed. For example, if the line resistance is measured to be 26Ω, and it is desired to increase the resistance by 4Ω, the line width should be reduced by 4 / 26=15%.

[0025] Figure 2 A diagram showing the resistance of the heating layer as a function of the number of components when components are produced according to the prior art (i.e. without further modification) is shown. The diagram shows that the target resistance value is 50Ω and the permissible range is ±10%, i.e. the permissible range is between 45Ω and 55Ω. Due to fluctuations in thermal spraying technology, in particular variations in coating thickness, 20% of the components are outside the specified resistance range and are therefore rejected.

[0026] Figure 3The relationship between the heating layer resistance and the number of components is shown in two comparisons: one is a component prepared according to the prior art / without reprocessing, and the other is a component prepared according to the planned reprocessing of this embodiment. As shown in the figure, the distribution curve of the prior art process is concentrated at the target resistance value of 50Ω, while the distribution curve of this embodiment (before reprocessing) is concentrated at the lower limit of the allowable range, i.e. 45Ω. Figure 3 As shown, the tail of the existing process distribution curve exceeds the upper limit of 55Ω, indicating that the scrap rate is 20%, while the tail of the distribution curve of this embodiment exceeds the upper limit of 55Ω, indicating that only a small part (far less than 20%) will exceed the specification and cannot be reprocessed and will be scrapped. Therefore, according to this embodiment, Figure 3 The layout of the heating circuit is designed to make the distribution center be located at the lower limit of the tolerance range. In this way, although there may be more parts that need to be corrected, because the correction can only increase the resistance of the heating circuit, only a small part of the tail will exceed the upper limit and be scrapped.

[0027] Figure 4 The comparison shows the relationship between the resistance of the heating layer and the number of components in two cases: one is a component prepared according to the prior art / without reprocessing, and the other is a component prepared according to the present embodiment with reprocessing. As shown in the figure, the distribution curve of the prior art process is concentrated at the target resistance value of 50Ω, while the distribution curve of the present embodiment (after reprocessing) is also concentrated at the target resistance value of 50Ω. Figure 4 As shown, after reprocessing or re-correction, all parts are within the tolerance range of less than ± 2%, so no scrap is generated. Figure 4 It has been shown that after reprocessing almost all components can meet the tighter tolerance requirements, thereby avoiding scrap.

[0028] Figure 5-7 An exemplary conditioning section of a heating circuit prior to aftertreatment conditioning according to this embodiment is shown.

[0029] Figure 5A top view of an exemplary straight segment of a heating line 24 is shown, including its length 25 and width 26. Before thermally spraying the conductive material onto the substrate or the optional metal bonding coating, the dimensions of the length 25, width 26, and thickness (not shown) of the heating line need to be determined so that the resistance value of the resulting heating line 24 is within the tolerance range of the target resistance. Preferably, for a thermally sprayed heating line 24 made of a material with a known resistivity, the target resistance corresponding to its length 25, width 26, and thickness is set at the lower limit of the allowable range of resistance. When the measured resistance of the heating line 24 is below the lower limit of the allowable range, that is, exceeds the allowable range, the resistance of the heating line 24 can be increased to a value within the allowable range by removing the conductive material at the edge of the heating line 24, such as along the edge of the entire length of the heating line 24 (as shown by the dashed line 27), or only at the edge of at least one section of the heating line 24 (as shown by the dashed line 28). It is preferred to remove the material by laser ablation. Alternative methods include plasma etching and machining.

[0030] Figure 6 Show Figure 5 A top view of a variation of FIG. 3 in which the exemplary heating line 34 is in a serpentine shape. Figure 5 Similar to the embodiment shown, before thermally spraying the conductive material onto the substrate or the optional metal bonding coating, the length and width of the meandering heating line 34 and the thickness (not shown) need to be determined so that the resistance value of the heating line 34 is within the tolerance range of the target resistance. Preferably, during the thermal spraying process, one of the branches 35 of the meandering heating line 34 is formed, and its width 36 is intentionally designed to be larger than the width 37 of the remaining branches 38 of the meandering heating line 34. The width 36 of this wider portion of the branch 35 (i.e., the adjustment section 39) is, for example, 20% wider than the width 37. In this way, if the measured resistance of the heating line 34 is lower than the allowable deviation of the target resistance, according to this embodiment, the material of the adjustment section 39 is removed, such as the edge along the entire length of the adjustment section 39 or along at least a portion of the length of the adjustment section 39, so as to increase the resistance to within the allowable deviation range of the target resistance of the heating line 34.

[0031] By way of the above non-limiting example, if the target resistance of a heating line made of a material with a resistivity of 0.002Ωmm is 100Ω, i.e. the tolerance is ±10%, and the intended coating thickness of the heating line is 0.01mm and the intended width of the heating line is 5mm, then the heating line length should be 2500mm. However, if the heating line thickness is only slightly higher than the target thickness by 5% (equivalent to 0.5μm), the heating line resistance will be proportionally reduced by 5% to 95Ω.

[0032] In this case, the heating line can be divided into two longitudinal sections, for example one section is 2000 mm long and the other section is 500 mm long, for example Figure 5 (As shown by the dotted line 28). The 500 mm long section is designed to be easily accessible and / or adopt a simple geometry, for example, a long straight line can be provided at the edge of the heater. This section may be easier to adjust than the winding section. Therefore, when the target thickness of the heating line is 0.01 mm, the line resistance of the 2000 mm section is 80 Ω, the 500 mm section is 20 Ω, and the entire heating line is 100 Ω. If the thickness of the heating line exceeds the specification by 5% (that is, the coating thickness of the heating line reaches 0.0105 mm), the deviation from the target resistance in the heating line can be compensated by reducing the width of the 500 mm section from 5 mm to 4 mm in a reprocessing step while keeping the width of the 2000 mm section unchanged, so that the device is restored to the target resistance value of 100 Ω (at this time, the line resistance of the 2000 mm section is 76.2 Ω, the 500 mm section is 23.8 Ω, and the entire heating line is 100 Ω). As described above, such reprocessing can be performed by laser ablation, ion sputtering, electron beam sputtering or micro-milling. In addition, because laser ablation is the preferred patterning process for making heating lines and / or heating line patterns for line patterns from metal thermal spray coatings, reprocessing can also be performed using the same process to adjust the resistance of the heating lines.

[0033] In another non-limiting example, the adjustment section of the heating circuit can be designed as a wider section, such as Figure 7 As shown. As mentioned above, a wider adjustment section is provided in the heating line in order to provide material that can be removed so as to adjust the resistance of the heating line to within the permissible deviation range of a given resistance. The adjustment section in the heating line can be, for example, 10% wider than the remaining sections of the heating line that do not require reprocessing. In addition, the length of the adjustment section is preferably at least 10% of the length of the heating line. With this design, the risk of local overheating in the heating line caused by reprocessing that makes the line width less than the lower limit can be reduced.

[0034] In yet another non-limiting embodiment, the heating line of the heating element may be produced or formed by a conductive coating. If the resistance of the heating line after forming the heating line by the conductive coating exceeds the tolerance range of the target resistance, the line width may be adjusted over the entire length, for example Figure 5(dashed line 27). For example, assuming that the target resistance of a heating line made of a material with a resistivity of 2x10-6Ωm is 30Ω±10%, the predetermined coating thickness of the heating line is 30μm and the predetermined width of the heating line is 3mm, the length of the heating line should be 1350mm. However, if the thickness of the heating line is only slightly higher than the target thickness by 2μm, the resistance of the heating line is reduced to 28.1Ω. In this case, if the width of the heating line is reduced to 2.81mm over the entire length, for example by removing a 0.19mm edge along the entire length of the heating line, the resistance value of the heating line is increased to within the allowable deviation range of the target resistance value (for example, 31Ω), which avoids unnecessary scrapping of the heating element. Similarly, this reprocessing can be accomplished by laser ablation, ion sputtering, electron beam sputtering or micro-milling. Since laser ablation is the preferred method for making line patterns from metal thermal spray coatings, it is also recommended to use this method for reprocessing to adjust the resistance. In addition, the software can be programmed to implement additional removal of coating material, for example according to the following resistance calculation formula:

[0035]

[0036] However, the reduction of line width should be limited to no more than 20% to avoid hot spot problems caused by the non-uniform structure of the thermal sprayed metal coating (e.g., coating particles with a diameter of 20 to 100 μm and a thickness of 2 to 10 μm, as well as voids, oxides and other defects). In addition, the laser resolution used for material removal is about 0.1 μm in line width.

[0037] In another non-limiting embodiment, the meandering pattern for the heating line formed from the conductive metal coating, for example by laser ablation, can be a wider connecting portion between two adjacent branches. Fig. 8A As shown, the line length of the formed heating line can be selected to produce a given resistance in the heating line at the lower limit of the permissible tolerance range. Fig. 8A The resistance of the heating circuit formed in the process exceeds the allowable deviation range of the target resistance. Fig. 8A The heating line in the second laser ablation process is performed to shorten the width of the connection, such as Figure 8B As shown. In this way, the total length of the resistance line is increased, while the width of the connection is reduced. This reprocessing adjustment increases the resistance of the heating line, thereby avoiding unnecessary scrapping of the heating element due to the resistance of the metal heating line.

[0038] In yet another non-limiting embodiment, in order to increase the resistance of the heating layer to a target resistance, reprocessing may be performed by reducing the coating thickness of the heating line, for example, by grinding.

[0039] Fig. 9An exemplary flow chart 900 for a non-limiting example of producing a heating element is shown. A blank of the heating element can be formed by depositing an entire insulating coating system including an insulating layer and a conductive layer at 901, and the conductive layer can be structured, for example by laser ablation, at 902, or one or more heating lines are formed. By the laser ablation process, the length and width of the heating line to be formed are based on a predetermined thickness and material properties of the conductive material to achieve a target resistance within the line. Alternatively, a mask can be applied to the substrate, the optional bonding layer, and the insulating layer so that one or more heating lines are thermally sprayed onto the insulating layer with a specified length and width based on a predetermined thickness and material properties of the conductive material to achieve a target resistance within the line.

[0040] Once the one or more heating lines are formed, the resistance of the formed heating lines is measured at 903, and a determination is made as to whether the measured resistance is within tolerance at 904. If the resistance of the heating lines is within tolerance, the method determines that the heating element is good, and continues processing of the next element at 905. However, if the resistance of the heating lines is outside of tolerance, the method calculates a new line width at 906 and generates a new CAD layout at 907.

[0041] Based on this new CAD layout, the out-of-tolerance heating line width is adjusted at 908, the resistance of the adjusted heating line (or all heating lines) is measured at 909, and it is determined at 910 whether the measured resistance is within the tolerance range. If the resistance of the heating line is within the tolerance range, the method determines that the heating element is qualified and continues processing of the next element at 911. However, if the resistance of the heating line is out of tolerance, the method determines at 912 whether the resistance of the heating line is too low. If the resistance is not too low, the heating element is discarded at 913. If the resistance is determined to be too low at 912, the method returns to 906, recalculates the line width and continues the method.

[0042] It should be noted that the above examples are for illustration only and should never be interpreted as limiting the present invention. Although the present invention has been described with reference to the embodiments, it should be understood that the terms used herein are for descriptive and illustrative purposes, rather than restrictive terms. Without departing from the scope and spirit of the present invention, the present invention may be adjusted according to the attached claims and their modifications. Although the specific means, materials and embodiments mentioned herein are helpful for understanding the present invention, the present invention is not limited to these specific details, and any functionally equivalent structures, methods and applications within the scope of the attached claims are included in the scope of protection of the present invention.

Claims

1. A circuit forming method, comprising: forming at least one conductive line on the substrate by thermally spraying a conductive material; determining whether a resistance of the at least one conductive line is within a predetermined tolerance range; as well as At least a portion of the at least one conductive layer is adjusted so that the resistance of the at least one conductive line is within the predetermined tolerance range.

2. The method according to claim 1, wherein: The electrical circuit is a heating element and the at least one electrically conductive trace is at least one heating trace.

3. The method according to claim 1 or 2, wherein: The at least one heating line is straight or in a serpentine form.

4. The method according to any one of the preceding claims, wherein: The conditioning includes removing conductive material from edges of the at least one conductive trace.

5. The method according to any one of the preceding claims, wherein: The conductive material is removed from at least a portion of the overall length of the at least one conductive trace, preferably by adjusting the width of the conductive trace.

6. The method according to claim 5, wherein: The conductive material is removed from the entire length of the at least one conductive trace.

7. The method according to any one of the preceding claims, wherein: The conductive material is removed from the at least one conductive trace by laser ablation.

8. The method according to claim 1, wherein: The step of forming at least one conductive circuit on the substrate comprises: thermally spraying the conductive material on the substrate to form a conductive layer having a predetermined target thickness; and removing a portion of the conductive material from the conductive layer to obtain at least one conductive line having a predetermined length and width, The predetermined length, width and target thickness of the at least one conductive line are selected based on the material properties of the conductive material to achieve a predetermined resistance of the at least one conductive line.

9. The method according to claim 1, wherein: The step of forming at least one conductive circuit on the substrate comprises: applying a mask on the substrate, the mask defining a predetermined length and width of the at least one conductive trace; thermally spraying the conductive material onto the substrate covered by the mask to a specified target thickness; and removing the mask to obtain at least one conductive line having a predetermined length and width, The predetermined length, width and target thickness of the at least one conductive line are selected based on the material properties of the conductive material to achieve a predetermined resistance of the at least one conductive line.

10. The method according to claim 1, wherein: The at least one conductive trace includes an adjustment section having a width greater than a remaining width of the at least one conductive trace.

11. The method according to claim 10, wherein: The conditioning includes removing conductive material from the conditioning section.

12. The method according to claim 1, further comprising: determining whether the resistance of the at least one conductive path is within a predetermined tolerance range after at least a portion thereof has been adjusted, and At least one second portion of the at least one conductive layer is adjusted so that the resistance of the at least one conductive line is within the predetermined tolerance.

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