FAULTS IN ELECTRICAL INTERCONNECTION IN A BATTERY PACK

FIELD OF THE INVENTION

[0001] The embodiments of the present disclosure relate generally to electrical interconnection and thermal management in a battery pack and particularly to detecting faults in the battery packs.

BACKGROUND OF THE INVENTION

[0002] A battery pack typically includes a plurality of battery cells each with positive and negative terminals and a plurality of interconnects. Each of these battery cells convert chemical energy of substances stored in the battery cell into electrical energy. The plurality of interconnects provides electrical conductivity among the plurality of battery cells. The plurality of battery cells may be configured in a series, parallel or a combination of both arrangements to deliver a desired voltage, capacity, or power to an electrical device. In one of the methods as explained in Indian Patent Application no. 201841032830, a metal core printed circuit board (MCPCB) holds the plurality of battery cells and facilitates interconnection of the battery cells to form a module. Further, a plurality of modules are integrated to form the battery pack.

[0003] A general understanding of the construction of an MCPCB will enable a better understanding of the current invention. As already mentioned, a plurality of battery cells are interconnected within a battery pack through an MCPCB. AN MCPCB typically includes a base layer, a thermally conductive dielectric layer fabricated on top of the base layer and a circuit layer fabricated on top of the thermally conductive dielectric layer. The circuit layer typically includes a plurality of sections. Each of the plurality of sections is electrically insulated from each other. The MCPCB also includes a mask layer fabricated on top of the circuit layer. A plurality of interconnect tabs are electrically coupled to the corresponding plurality of sections of the circuit layer of the MCPCB and they are configured to connect to the plurality of battery cells. One or more through-holes are located within each of the corresponding plurality of the circuit layer sections. Each of these through- holes is configured to facilitate welding of the plurality of interconnect tabs to the battery terminal of the corresponding plurality of battery cells using at least one type of welding method. The circuit layer is made of copper and is normally 0.035 mm, 0.07mm, 0.105 mm thick. The thermally conductive dielectric layer is 0.025mm, 0.075mm or 0.1mm thick. The base layer is made of aluminium and is 1.6mm, 1mm thick. The circuit layer of the MCPCB has various patterns to have voltage terminals, voltage temperature sense lines and tapered sections. Other components, such as, busbars, balancing resistors, temperature sensors are also connected directly to the MCPCB.

[0004] Generally, the manufacturing of an MCPCB goes through two stages. The first stage is the fabrication of a bare MCPCB board. At this stage, it is important to detect and discard the MCPCB with faults in order to provide better battery performance and safety. Also, at this stage, defects, such as, the deep cuts could be developed on the MCPCB. The MCPCB with faults such as deep cuts damage the thermally conductive dielectric layer and provide a path for the electric current to pass through from the circuit layer to the base layer thereby discharging the power/leading to power leakage. The second stage is the assembly of the plurality of interconnect tabs on the MCPCB board, conventionally using a soldering method. The MCPCB also comprises through-holes configured to facilitate welding of the plurality of interconnect tabs to the battery terminal of the corresponding plurality of battery cells using the at least one welding method. During soldering process, there is a tendency that the solder balls get generated and could get lodged between the interconnect tabs and the MCPCB. The presence of solder balls reduces the designed insulation resistance which is normally offered by a dielectric in a fit MCPCB. The reduced insulation resistance leads to conduction of higher current than the allowed leakage current from the circuit layer to the base layer. And the conduction of such high current impacts the overall battery performance. In case the solder balls or some other materials are left behind in the MCPCB of the battery pack, it reduces the gap between the circuit (copper) layer and the base (aluminium) layer. The reduced gap establishes a leakage path between the layers mentioned and leads to a functional problem such as, even when the battery is not being used, the battery cells will keep dissipating/discharging power through the leakage path. The reduced gap between the layers will also lead to a safety problem when the modules are integrated. The voltage difference between the circuit layer and the base layer increases due to the integration of the multiple modules together. The increase in voltage difference leads to ionisation of air, resulting in arcing. The arcing causes burning and damages the dielectric layer further leading to high current flow. Flow of such high current damages the battery cell which overheats and induces other cells to overheat as well causing thermal runway, which eventually leads to battery fire.

[0005] The current method to detect faults such as presence of defects such as deep cuts or solder balls in the MCPCB includes visually inspecting for the faults. This is a time-consuming and complex process and and there is a probability that such faults could be easily overlooked during visual inspection.

PROBLEM TO BE SOLVED BY INVENTION

[0006] Hence, it is a primary objective of the current invention to provide for an improved fault detection method in a battery pack to avoid causing any safety hazard to the user. Because, if detection of such faults are missed, it leads to a safety hazard.

[0007] It is another objective of the current invention to develop a detection method that is capable of detecting all the faults present in the MCPCB and avoid establishing a leakage path by maintaining the gap between the circuit layer and the base layer. [0008] It is yet another objective of the current invention to develop a detection method that prevents the flow of such high current that damages the battery cell and to prevent battery fire due to the overheated damaged battery cells leading to thermal runaway.

[0009] The above-mentioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.

SUMMARY OF THE INVENTION

[0010] Various embodiments herein describe an unique and improved test method and system for effectively detecting faults in the MCPCB used for electrical interconnection and thermal management in battery. A method for effectively detecting and removing faults in an MCPCB used for electrical interconnection and thermal management in a battery is disclosed. The method comprises of various steps. At the first step, an electrical interconnector connects a positive terminal of a dielectric withstanding voltage source to a circuit layer of the MCPCB and a negative terminal of the dielectric withstanding voltage source to a base layer of the MCPCB. At the second step, the electrical interconnector provides high voltage supply from the dielectric withstanding voltage source to the MCPCB. At the third step, the dielectric withstanding voltage source determines the leakage path between the circuit layer and the base layer due to one or more faults. At the fourth step, the dielectric withstanding voltage source detects one or more faults by checking for arcing as a result of excessive current based on the determined leakage path in the MCPCB. At the last step, one or more detected faults are removed from the determined leakage path in the MCPCB.

[0011] As per first embodiment of the current invention, the method further comprises detecting one or more faults by checking for arcing as a result of excessive current based on the determined leakage path in the MCPCB due to impurities.

[0012] As per second embodiment of the current invention, the method further comprises detecting one or more faults by checking for arcing as a result of excessive current based on the determined leakage path in the MCPCB due to solder balls.

[0013] As per third embodiment of the current invention, the method further comprises detecting one or more faults by checking for arcing as a result of excessive current based on the determined leakage path in the MCPCB due to deep cuts on the MCPCB.

[0014] As per fourth embodiment of the current invention, the method further comprises setting a fault current which is sufficiently high to ignore expected permissible current and low enough to detect one or more faults.

[0015] As per fifth embodiment of the current invention, the method further comprises removing one or more detected faults by clearing the leakage path.

[0016] According to an embodiment of the present invention, a system for effectively detecting and removing faults in a MCPCB used for electrical interconnection and thermal management in a battery is disclosed. The system comprises of an electrical interconnector, a dielectric withstanding source comprising of a positive terminal and a negative terminal, and an MCPCB comprising of a circuit layer and a base layer. The electrical interconnector connects the positive terminal of the dielectric withstanding voltage source to the circuit layer of the MCPCB and the negative terminal of the dielectric withstanding voltage source to the base layer of the MCPCB. The electrical interconnector then provides high voltage supply from the dielectric withstanding voltage source to the MCPCB. The dielectric withstanding voltage source determines the leakage path between the circuit layer and the base layer due to one or more faults. The dielectric withstanding voltage source then detects one or more faults by checking for arcing as a result of excessive current based on the determined leakage path in the MCPCB. And, one or more detected faults are removed from the determined leakage path in the MCPCB.

[0017] The foregoing has outlined, in general, the various aspects of the invention and serves as an aid to better understanding the more complete detailed description which is to follow. In reference to such, there is to be a clear understanding that the present invention is not limited to the method or application of use described and illustrated herein. It is intended that any other advantages and objects of the present invention that become apparent or obvious from the detailed description or illustrations contained herein are within the scope of the present invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0018] The other objects, features and advantages will occur to those skilled-in- the-art from the following description of the preferred embodiments and the accompanying drawings in which:

[0019] Figure 1 is a cross sectional view of a diagram illustrating layers of the MCPCB connected to the dielectric withstanding voltage source according to an embodiment of the present invention.

[0020] Figure 2 is a cross sectional view of a diagram illustrating presence of deep cuts on the MCPCB according to an embodiment of the present invention.

[0021] Figure 3 is a cross sectional view of a diagram illustrating presence of solder balls in the MCPCB according to an embodiment of the present invention. [0022] Further, those skilled-in-the-art will appreciate that elements in the figures are illustrated for simplicity and may not have necessarily been drawn to scale. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the figures by conventional symbols, and the figures may show only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the figures with details that will be readily apparent to those skilled in the art having the benefit of the description herein.

DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention provides an unique test method and system for effectively detecting faults in the MCPCB used for electrical interconnection and thermal management in battery. In the following detailed description of the embodiments of the invention, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled-in-the-art to practice the invention, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.

[0024] The specification may refer to “an”, “one” or “some” embodiment(s) in several locations. This does not necessarily imply that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments. [0025] As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms “includes”, “comprises”, “including” and/or “comprising” when used in this specification, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations and arrangements of one or more of the associated listed items.

[0026] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure pertains. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0027] Embodiments of the present invention will be described below in detail with reference to the accompanying figures.

[0028] According to an embodiment of the present invention, a dielectric withstanding voltage test is performed to detect the faults in the MCPCB (102). A minimum of 750V of alternating current (AC) or 1000V of direct current (DC) high voltage is applied, which leads to ionization of air and when the electric current is passed, it results in an arc (70) on detecting the faults. The applied voltage is chosen such that the distance between the circuit layer (30) and the base layer (10) in a fit MCPCB (102) does not result in an arc (70). The dielectric withstanding voltage test is applied for 20 seconds or more. [0029] According to an embodiment of the present invention, first stage is the fabrication of the MCPCB (102) and at this stage deep cuts (60) on the MCPCB (102) could creep in. Upon applying the high voltage to the MCPCB (102) after the first stage of fabrication, if there is no arc (70) that is generated, it indicates that the MCPCB (102) is fit and ready for the next stage of assembly. In case, an arc (70) is detected at an area of MCPCB (102), then that particular MCPCB (102) is replaced with another one. Second stage is the assembly of the interconnect tabs (90) on the MCPCB (102) and at this stage solder balls (100) could be left on the MCPCB (102). Upon applying the high voltage to the MCPCB (102) after the second stage which is after the assembly of the interconnect tabs (90) on the MCPCB (102), the arc (70) generation is checked. If there is no arc (70) that is generated, it indicates that the assembled MCPCB (102) is fit and is safe. In case, an arc (70) is detected at an area in the assembled MCPCB (102), that particular area is deeply analysed to detect and remove the faults. The arcing (70) is visually detected during the presence of faults. The faults could be deep cuts (60) on the MCPCB (102), insufficient dielectric layer thickness, impurities or the solder balls (100) generated during the soldering (80) process. Once the faults are removed, the dielectric withstanding voltage test is performed again until the MCPCB (102) is found to be fit and safe.

[0030] According to an embodiment of the present invention, the path for the fault current to flow is from the circuit layer (30) to the solder ball (100) to the air and to the base layer (10). If the presence of solder ball (100) is directly shorting the circuit layer (30) with the base layer (10), then such solder ball (100) will be detected even with the low voltage method such as checking continuity using a multimeter. In most cases, the solder balls (100) do not form a direct connection between the circuit layer (30) and the base layer (10), and also there is an air gap around the solder balls (100). [0031] According to Figure 1, a method for effectively detecting and removing faults in an MCPCB (102) used for electrical interconnection and thermal management in a battery (101) is disclosed. The method comprises of various steps. At the first step, an electrical interconnector (110) connects a positive terminal of a dielectric withstanding voltage source (50) to a circuit layer (30) of the MCPCB (102) and a negative terminal of the dielectric withstanding voltage source (50) to a base layer (10) of the MCPCB (102). At the second step, the electrical interconnector (110) provides high voltage supply from the dielectric withstanding voltage source (50) to the MCPCB (102). At the third step, the dielectric withstanding voltage source (50) determines the leakage path between the circuit layer (30) and the base layer (10) due to one or more faults. At the fourth step, the dielectric withstanding voltage source (50) detects one or more faults by checking for arcing (70) as a result of excessive current based on the determined leakage path in the MCPCB (102). At the last step, one or more detected faults are removed from the determined leakage path in the MCPCB (102). According to Figure 2, the method further comprises detecting one or more faults by checking for arcing (70) as a result of excessive current based on the determined leakage path in the MCPCB (102) due to deep cuts on the MCPCB (102). According to Figure 3, the method further comprises detecting one or more faults by checking for arcing (70) as a result of excessive current based on the determined leakage path in the MCPCB (102) due to solder balls.

[0032] As per first embodiment of the current invention, the method further comprises detecting one or more faults by checking for arcing (70) as a result of excessive current based on the determined leakage path in the MCPCB (102) due to impurities.

[0033] As per second embodiment of the current invention, the method further comprises detecting one or more faults by checking for arcing (70) as a result of excessive current based on the determined leakage path in the MCPCB (102) due to solder balls.

[0034] As per third embodiment of the current invention, the method further comprises detecting one or more faults by checking for arcing (70) as a result of excessive current based on the determined leakage path in the MCPCB (102) due to deep cuts on the MCPCB (102).

[0035] As per fourth embodiment of the current invention, the method further comprises setting a fault current which is sufficiently high to ignore expected permissible current and low enough to detect one or more faults.

[0036] As per fifth embodiment of the current invention, the method further comprises removing one or more detected faults by clearing the leakage path.

[0037] According to an embodiment of the present invention, a system for effectively detecting and removing faults in a MCPCB (102) used for electrical interconnection and thermal management in a battery (10) is disclosed. The system comprises of an electrical interconnector (110), a dielectric withstanding source (105) comprising of a positive terminal and a negative terminal, and an MCPCB (102) comprising of a circuit layer (30) and a base layer (10). The electrical interconnector (110) connects the positive terminal of the dielectric withstanding voltage source (105) to the circuit layer (30) of the MCPCB (102) and the negative terminal of the dielectric withstanding voltage source (105) to the base layer (10) of the MCPCB (102). The electrical interconnector (110) then provides high voltage supply from the dielectric withstanding voltage source (105) to the MCPCB (102). The dielectric withstanding voltage source (105) determines the leakage path between the circuit layer (30) and the base layer (10) due to one or more faults. The dielectric withstanding voltage source (105) then detects one or more faults by checking for arcing as a result of excessive current based on the determined leakage path in the MCPCB (102). And, one or more detected faults are removed from the determined leakage path in the MCPCB (102).

FURTHER ADVANTAGES OF THE INVENTION

[0038] The current invention solves the problem of overlooking faults in an MCPCB during visual inspection. The faults are detected by checking for arcing as a result of excessive current based on the determined leakage path in the MCPCB by the dielectric withstanding voltage source.

[0039] The current invention further prevents formation of a leakage path by maintaining the gap between the circuit layer and the base layer. The proposed method further helps to minimize the temperature gradient inside the battery pack during a charging and a discharging of the battery pack thus improving battery cell capacity, life and performance.

[0040] The current invention further prevents the flow of high current that damages the battery cell, which eventually leads to battery fire as the method described in the present invention helps to prevent thermal runaway and maintain battery cells within a narrow range of ambient temperatures.

[0041] Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the claims. It is also to be understood that the following claims are intended to cover all the generic and specific features of the embodiments described herein and all the statements of the scope of the embodiments which as a matter of language might be said to fall there between. REFERENCE TABLE: