COMPOSITE METAL STRIP FOR A FILM CAPER, FILM CAPER AND METHOD FOR MANUFACTURING A COMPOSITE METAL STRIP

Abstract

Composite metal busbar (100) for a film capacitor (1000), comprising a composite metal layer (50) which includes: an aluminum layer (10); a first copper layer (20) which is layered onto one surface of the aluminum layer (10); and a second copper layer (22) layered on the other surface of the aluminum layer (10), wherein the thicknesses of the first and second copper layers (20, 22) are set in the range between 10% and 25% of the total thickness of the composite metal layer (50), and the thickness of the aluminum layer (10) is set in the range between 50% and 70% of the total thickness of the composite metal layer (50), characterized in that the composite metal layer (50) has a percentage thickness reduction of less than 10%; the composite metal layer (50), measured on the basis of ISO 6892, has a stretching percentage of 25% or more;and the bond strength of the composite metal layer (50), measured on the basis of ISO 11339, is greater than or equal to 10 kgf on the basis of a sample width of 25 mm.

Description

BACKGROUND OF THE INVENTIONThe present invention relates to a composite metal bus bar for a foil capacitor and a foil capacitor comprising the same, and to a method for manufacturing a composite metal bus bar for a foil capacitor. More particularly, the present invention relates to a laminated metal bus bar for a foil capacitor, the weight of which can be reduced while having excellent laminated strength and having different characteristics of electric resistance, tightening torque and temperature rise, and a foil capacitor comprising the same.A bus bar refers to a plate-shaped electric component that electrically connects electronic components and that serves as a power conduction path. In the case of vehicle components in which the space is limited, a bus bar is generally used to provide a structure for electrically connecting and holding the components. Specifically, a foil capacitor, which is an inverter component for a hybrid vehicle, uses a bus bar to hold and electrically connect a deposited foil.A hybrid electric vehicle (HEV) requires electrical components that are not used by a general internal combustion engine vehicle or electric vehicle. Further, when a drive motor, a generator, and a battery are added, the HEV needs a power supply system of 12 V to 42 V and a high voltage system of 144 V to 400 V. In particular, when a large amount of power is needed, it is necessary that a high voltage power structure that has not been considered and a high voltage power capacitor used in a power conversion system and a DC-DC inverter circuit be developed. In addition, when the HEV is driven and started, an electric motor supplies power, and when the HEV is braked, an auxiliary energy storage device collects the energy.A foil capacitor, which is an inverter component for a vehicle, uses a plate-shaped bus bar having a large area to hold and electrically connect a deposited foil. Generally, the bus bar is made of copper (Cu) suitable for press working and having high electric conductivity. Normally, tough-poled copper (C1100) is used. This is because Cu has a high melting point at 1,084 °C and an excellent electrical conductivity of 98 IACS% to 100 IACS%, and is suitable for press working. The problems of the bus bar of Cu are that Cu is expensive and has a high specific gravity of 8.94 g / cm 3. Thus, if the bus bar is made of only Cu, the bus bar may be too difficult to handle.A capacitor included in the film capacitor is produced by the following method: a plastic film is used as a dielectric material, a film obtained by depositing a metal on one surface or both surfaces of the plastic film is wound, and zinc, a zinc alloy, arsenic or zinc arsenic is metallized on both sides of the wound deposited film to form metallized surfaces. The plastic film includes various kinds of resins such as polyethylene terephthalate (PET), polypropylene (PP), polyethylene naphthalate (PEN), polycarbonate (PC), polyethylene sulfide (PPS), and the like. Further, according to the use of the capacitor, a plurality of capacitor elements may be connected to an N-pole power line and a P-pole power line and inserted into a case made of plastic or metal. Subsequently, in order to protect and isolate the interior of the capacitor, the capacitor may be filled with a mold material such as epoxy or urethane or a multilayer of heterogeneous mold materials such as epoxy and urethane.When a high voltage or a heavy current is applied to the foil capacitor, the foil capacitor generates heat. The heat generated by the foil capacitor may impair its electrical properties and reduce its life and reliability. Recently, components used in a vehicle are required to have a reduced weight. Thus, a bus bar for a foil capacitor used in a vehicle also needs to have a reduced weight while satisfying a physical property of the bus bar made of Cu.Related art of the present invention is disclosed in Korean Patent Application Laid-Open KR 2006-0035057 A, published on Apr. 26, 2006, entitled "Cu-Al Clad Bus Bar with Ag-Coating and Manufacturing Methods thereof".In addition, KR 10 2014 0 001 290 A discloses a composite metal current rail for a foil capacitor according to the preamble of claim 1.SUMMARY OF THE INVENTIONIt is an object of the invention to provide an improved composite metal busbar for a foil capacitor, and an improved production method therefor.This object is achieved by the subject matter of claim 1 and the subject matter of claim 10, respectively. The dependent claims indicate advantageous further developments of the invention.According to the present invention, a composite metal bus bar for a foil capacitor includes a composite metal layer including: an aluminum layer; a first copper layer laminated on the one surface of the aluminum layer; and a second copper layer laminated on the other surface of the aluminum layer. The thicknesses of the first and second copper layers are set in the range between 10% and 25% of the total thickness of the clad metal layer, and the thickness of the aluminum layer is set in the range between 50% and 70% of the total thickness of the clad metal layer. The bonded metal layer has a percent thickness reduction of less than 10% and an elongation percentage of 25% or more, wherein the bonded strength of the bonded metal layer measured on the basis of ISO 11339 is equal to or greater than 10 kgf on the basis of the sample width of 25 mm.The thickness ratio of the first copper layer to the second copper layer may be set in the range between 1:0.5 and 1:1.5.The thicknesses of the first and second copper layers may be set in the range between 15% and 25% of the total thickness of the clad metal layer, and the cross-sectional thickness of the aluminum layer may be set in the range between 50% and 65% of the total thickness of the clad metal layer.The thickness ratio of the first or second copper layer to the aluminum layer may be set in the range between 1:3 and 1:8.The first and second film thicknesses may have a thickness of 0.05 mm to 0.5 mm, and the aluminum film may have a thickness of 0.3 mm to 2.0 mm.The composite metal bus bar may have a thickness of 0.5 mm to 2.5 mm.The ratio of the thickness reduction percentage to the elongation percentage of the clad metal layer may be set in the range between 1:2 and 1:15.The composite metal bus bar may have an electrical conductivity of 60 IACS% or more.The clad metal layer may have an elongation percentage between 25% and 35%.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 shows a composite metal bus bar according to an embodiment of the present invention. FIG. 2 is an exploded perspective view of a foil capacitor according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of the composite metal bus bar taken along A-A' of FIG. 1. FIGS. 4A to 4D show bending test results of Examples and Comparative Examples when a radius curvature is set to 0.5. FIGS. 5A and 5B are photographs illustrating the cross sections of the bus bars according to the examples before and after a thermal shock test. FIGS. 5C and 5D are photographs showing the cross sections of the bus bars according to the comparative examples before and after the thermal shock test. FIGS. 6A to 6D are photographs showing the transition between the copper layer and the aluminum layer in the bus bars according to the examples and the comparative examples after the heat treatment.DETAILED DESCRIPTIONIn the course of describing the present invention, detailed descriptions related to well-known configurations will be omitted so as not to unnecessarily obscure the subjects of the present invention. Further, the terms as used herein are defined in consideration of the functions of the invention and may be changed according to the need or intention of the users or operators. Thus, the definition of the terms should be made in accordance with the entire disclosure as set forth herein.One aspect of the present invention relates to a composite metal bus bar for a foil capacitor. FIG. 1 shows a composite metal bus bar according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of the composite metal bus bar taken along A-A' of FIG. 1. Referring to FIGS. 1 and 3, the composite metal bus bar may include a composite metal layer 50 including an aluminum layer 10 having a predetermined thickness, a first copper layer 20 laminated to one surface of the aluminum layer 10 in a predetermined thickness, and a second copper layer 22 laminated to the other side of the aluminum layer 10 in a predetermined thickness. When the composite metal bus bar 100 includes an aluminum layer 10 between the first and second copper layers 20 and 22 as described above, the weight of the composite metal bus bar 100 can be reduced.In one embodiment, the clad metal layer 50 may be rolled with a percent thickness reduction of less than 10%. In the present specification, "percent thickness reduction" denotes a difference in thickness of the clad metal layer between before and after rolling. When the clad metal layer 50 is manufactured with the above-described thickness percentage reduction, the bus bar according to the embodiment of the present invention may have excellent formability, hardness, and mechanical strength such as a clad strength. When a percent thickness reduction of 10% or more is applied, moldability, hardness and mechanical strength may be impaired.The clad metal layer may be made, for example, with a percentage thickness reduction of 0% to 10%. In one embodiment, the clad metal layer may be made with a percentage thickness reduction of 0% to 8%. In a particular embodiment, the clad metal layer 50 may be made with a percentage thickness reduction of 0%. The composite metal material may be made, for example, with a percentage thickness reduction of 0% to 8%. In the specification, "the thickness reduction percentage of 0%" may define that a tempered material is used. In a particular embodiment, the composite metal material 50 may be made with a percent thickness reduction of 0, 0.01, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 9.5, or 9.9%.In one embodiment, the clad metal layer 50 may have an elongation percentage of 25% or more. In the above-described range, the hardness and the mechanical strength such as a bond strength can be improved while securing the moldability. When an elongation percentage of 25% or less is applied, the moldability, hardness, and mechanical strength of the bus bar according to the embodiment of the present invention may be impaired. According to the invention, the stretch percentage is measured on the basis of ISO 6892. For example, the clad metal layer 50 may have an elongation percentage of 25% to 35%. In one embodiment, the clad metal layer 50 may have an elongation percentage of 25% to 35%. The clad metal layer 50 may have an elongation percentage of 25, 26, 28, 27, 28, 29, 30, 31, 32, 33, 34, or 35%.In an embodiment, the ratio of the percentage thickness reduction to the stretching percentage of the clad metal layer may be set in a range between 1:2 and 1:15. In the above-described range, the bus bar according to the embodiment of the present invention can have excellent formability and bond strength, bond separation at the junction and cracks during a bending process can be substantially prevented, and a foil capacitor can have an equivalent series resistance (ESR). For example, the ratio of the percentage of thickness reduction to the percentage of elongation of the clad metal layer 50 may be set in the range between 1:2.5 and 1:5. For example, the ratio of the percentage of thickness reduction to the percentage of elongation of the clad metal layer 50 may be set in the range between 1:3 and 1:4.5.In a specific embodiment, the bond strength of the bonded metal layer 50 measured on the basis of ISO 11339 may be greater than or equal to 10 kgf on the basis of a sample width of 25 mm. In the above-described range, the electrical conductivity and the thermal shock resistance of the clad metal layer 50 can be improved while substantially preventing junction disconnection and cracks during a bending process for manufacturing a bus bar of a foil capacitor. In addition, since the junction separation and cracks during the bending process are substantially prevented, the film capacitor according to the embodiment of the present invention can have a low ESR value. If the bonding strength of the bonded metal layer is less than 10 kgf, bonding separation at the interface and cracks may occur during the bending process. The clad metal layer may have, for example, a clad strength of 15 kgf or more. In one embodiment, the composite metal layer may have a composite strength of 10 kgf to 20 kgf. In a particular embodiment, the composite metal layer 50 may have a composite strength of 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 kgf.In a particular embodiment, the cross-sectional thicknesses of the first and second layers 20 and 22 may be set in a range between 10% and 25% of the total thickness of the clad metal layer 50, and the cross-sectional thickness of the aluminum layer 10 may be set in a range between 50% and 70% of the total thickness of the clad metal layer 50. In the above-described range, the clad metal layer 50 can have excellent lightweight property and secure properties such as electric resistance and tightening torque.When the thickness of the first copper layer 20 is less than 10% of the total thickness of the clad metal layer 50, the electrical conductivity and moldability of the bus bar according to the embodiment of the present invention may be impaired, and when the thickness of the first copper layer 20 is more than 25% of the total thickness of the clad metal layer 50, the lightweight property of the bus bar may be impaired.When the thickness of the second copper layer 22 is less than 10% of the total thickness of the composite material 50, the electrical conductivity and moldability of the bus bar according to the embodiment of the present invention may be impaired, and when the thickness of the second copper layer 22 is more than 25% of the total thickness of the composite metal layer 50, the lightweight property of the bus bar may be impaired.When the thickness of the aluminum layer 10 is less than 50% of the total thickness of the clad metal layer 50, the lightweight property and the moldability of the bus bar according to the embodiment of the present invention may be impaired, and when the thickness of the aluminum layer 10 is more than 70% of the total thickness of the clad metal layer 50, the electrical conductivity of the bus bar may be impaired.For example, the cross-sectional thickness of the first and second copper layers 20 and 22 may be set in the range of 15% to 25% of the total thickness of the clad metal layer 50, and the cross-sectional thickness of the aluminum layer 10 may be set in the range of 50% to 65% of the total thickness of the clad metal layer 50.In an embodiment, the cross-sectional thickness of the first and second copper layers 20 and 22 may be set in the range of 22% to 25% of the total thickness of the composite metal material 50, and the cross-sectional thickness of the aluminum layer 10 may be set in the range of 53% to 56% of the total thickness of the composite metal material 50.In an embodiment, the cross-sectional thickness of the first copper layer 20 may be set to 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25% of the total thickness of the clad metal layer 50. Further, the cross-sectional thickness of the second copper layer 22 may be set to 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25% of the total thickness of the clad metal layer 50. Further, the cross-sectional thickness of the aluminum layer 10 may be set to 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 22, 63, 64, 65, 66, 66, 67, 68, 69, or 70% of the total thickness of the clad metal layer 50.In an embodiment of the present invention, the aluminum constituting the aluminum layer 10 is not particularly limited. Pure aluminum such as A1050 or A1100 or an alloy of aluminum and magnesium, manganese or silicon such as A3003, A3004 or A9005m may be used. For example, pure aluminum such as A1050 may be used in consideration of the workability of pressing.In the embodiment of the present invention, the copper forming the first and second copper layers 20 and 22 is not particularly limited. However, pure copper such as C1100 or an alloy of copper and a heterogeneous metal may be used. In a particular embodiment, the first and second copper layers 20 and 22 may be formed of the same material or different materials.In a specific embodiment, the first and second copper layers 20 and 22 may be formed in a thickness ratio of 1:0.5 to 1:1.5. In the above-described range, the bus bar according to the embodiment of the present invention can have excellent electric resistance and tightening torque. For example, the first and second copper layers 20 and 22 may be formed in a thickness ratio of 1:0.8 to 1:1.2. For example, the first and second copper layers 20 and 22 may be formed in a thickness ratio of 1:1 to 1:1.2.The composite metal bus bar 100 according to the embodiment of the present invention may be manufactured by an extrusion method, a drawing method, a rolling method, or a combination thereof. The composite metal bus bar 100 can be manufactured, for example, by the rolling method in consideration of the aluminum material, the copper material, and the adhesion properties thereof.The rolling process can be carried out by a typical heat treatment. At the same time, the temperature of the heat treatment may be between room temperature and the melting points of aluminum and copper. The temperature of the heat treatment may be set in the range between 200° C. and 400° C.In particular, the rolling process may be carried out as follows. First, the copper may be laminated on both sides of an aluminum body so as to form a laminated structure. Subsequently, the laminated structure may be placed in an electric furnace in which a reducing atmosphere, an inert atmosphere or a vacuum atmosphere prevails, and hot-rolled at an appropriate temperature to form a bus bar including a clad metal layer 50. The clad metal layer 50 may include a first copper layer, an aluminum layer, and a second copper layer that are completely attached to each other and integrated with each other.At the same time, an additional heat treatment can be carried out. Specifically, the rolled bus bar may be placed in the electric furnace in which a reducing atmosphere, an inert atmosphere, or a vacuum atmosphere prevails, and heated at an appropriate temperature for a predetermined time. Subsequently, the bond strength at the transition between aluminum and copper may be increased to improve the mechanical property of the busbar. When the composite material including the first copper layer, the aluminum layer, and the second copper layer is manufactured by the rolling method, the rolling method may be performed at room temperature. However, the rolling process may be performed in the range of 200° C. to 400° C., so that the first copper layer, the aluminum layer, and the second copper layer are more easily adhered to each other.In an embodiment, the composite metal bus bar 100 may have a thickness of 0.5 mm to 2.5 mm. Further, based on the total thickness of the composite metal bus bar 100, the thickness of the aluminum layer 10 may be set in the range of 0.3 mm to 2.0 mm, the thickness of the first copper layer 20 may be set in the range of 0.05 mm to 0.5 mm, and the thickness of the second copper layer 22 may be set in the range of 0.05 mm to 0.5 mm.In a particular embodiment, the composite metal bus bar may have an electrical conductivity of 60 IACS% or more. Here, IACS stands for International Annealed Copper Standard and is an electric conductivity unit based on the electric conductivity of pure copper set to 100% IACS at a temperature of 20° C. In the above-described range, the composite metal bus bar can simultaneously ensure corrosion resistance, electric conductivity, and tightening torque while improving light weight property and economicalness thereof. The composite metal bus bar may have, for example, an electrical conductivity of 60 IACS % to 85 IACS %. In one embodiment, the composite metal bus bar may have an electrical conductivity of 65 IACS% to 85 IACS%. In a particular embodiment, the composite metal bus bar may have an electrical conductivity of 60, 61, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, or 85 IACS%.The weight of the composite metal bus bar for a foil capacitor according to the embodiment of the present invention may be reduced by 40% compared to the existing bus bar, and the cost of the composite metal bus bar may be reduced by 15% compared to an existing bus bar.Another aspect of the present invention relates to a foil capacitor comprising the composite metal bus bar. FIG. 2 is an exploded perspective view of a foil capacitor according to an embodiment of the present invention. Referring to FIG. 2, the foil capacitor 100 may include a case 300, a plurality of capacitor elements 200 located in the case 300, a P-pole bus bar 100 aor 100 b, and an N-pole bus bar 100 bor 100 a. The P-pole bus bar and / or the N-pole bus bar may include the composite metal bus bar according to the embodiment of the present invention.The foil capacitor 1000 may be manufactured by a typical method. In a specific embodiment, the plurality of capacitor elements 200 may be connected to the N-pole bus bar 100 aor 100 band the P-pole bus bar 100 bor 100 ahaving different polarities and inserted into the housing 300. Subsequently, in order to protect and isolate the interior of the capacitor, the capacitor may be filled with a mold material such as epoxy or urethane.In a particular embodiment, the capacitor elements 200 may be fabricated using a typical process. For example, a deposited film can be produced by depositing a metal on one or both surfaces of a dielectric plastic film and then laminating or winding. Subsequently, a metal layer may be formed on the laminated or wound deposited film. In a particular embodiment, the plastic dielectric film may comprise one or more of polyethylene terephthalate (PET), polypropylene (PP), polyethylene naphthalate (PEN), polycarbonate (PC), and polyethylene sulfide (PPS). In a particular embodiment, the metal layer may be formed by metallising or spraying one or more of zinc, a zinc alloy, arsenic and zinc arsenic.Subsequently, in order to protect the inside of the film capacitor 1000, the film capacitor 1000 may be filled with a mold molding material such as epoxy or urethane or a multi-chamfer layer of heterogeneous mold molding materials such as epoxy and urethane.The ESR of the foil capacitor 1000, measured at 10 kHz with an automatic current control (LCR) device, may be between 0.1 mΩ and 3.5 mΩ. In the above-described range, the foil capacitor 1000 can have an excellent electrical property. For example, the foil capacitor may have an ESR of 0.5 mΩ to 2.0 mΩ. In a particular embodiment, the foil capacitor 1000 may have an ESR of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.5, 2.0, 2.5, 3.0 and 3.5 mΩ.Hereinafter, the constituent elements and functions of the embodiments of the present invention will be explained in detail with reference to the accompanying drawings. However, the embodiments of the present invention are proposed as preferred embodiments of the present invention, but the present invention is not limited thereto.Since constituent elements and functions not described herein can sufficiently be understood by those skilled in the art, detailed description thereof will be omitted.Examples and Comparative ExamplesExamples 1 to 4A plate of pure copper such as C1100 was laminated on a plate of pure aluminum such as A1050. Subsequently, the laminated structure was placed in an electric furnace in which an atmosphere existed at a temperature of 200°C to 400°C, heated for one hour, and hot-rolled at a percentage reduction in thickness of 0% (tempered material) to 8% to form a material comprising a composite metal layer having a thickness of 1 mm. Thus, a bus bar for a foil capacitor using the material including the compound metal layer was produced. The clad metal layer may include first and second copper layers formed on both surfaces of an aluminum layer in a thickness ratio of the following Table 1.Comparative Example 1A bus bar formed of typical copper such as C1100 was used as the bus bar according to Comparative Example 1. The busbar may have a thickness of 1 mm.Comparative Examples 2 to 6Composite metal bus bars according to Comparative Examples 2 and 6 were produced in the same manner as Example 1, except that a percentage thickness reduction was applied as shown in Table 1, and a composite metal layer including the first and second copper layers formed on both sides of an aluminum layer in the thickness ratio of Table 1 was formed.Experimental ExampleThe following properties were evaluated for the bus bars according to Examples 1 to 4 and Comparative Examples 1 to 6.(1) Stretching percentage (%): Stretching percentages of bus bars according to Examples 1 to 4 and Comparative Examples 1 to 6 were measured on the basis of ISO 6892, and the measurement results are shown in the following Table 1.(2) The bond strengths (kgf / 25 mm): the bond strengths of the bus bars according to Examples 1 and 4 and Comparative Examples 1 to 6 were measured for a 25 mm width sample based on ISO 11339, and the measurement results are shown in the following Table 1.(3) Tensile strength (MPa): The tensile strengths of the bus bars according to Examples 1 to 4 and Comparative Examples 1 to 6 were measured on the basis of ISO 6892, and the measurement results are shown in the following Table 1.(4) Hardness (Hv): The hardnesses of the bus bar according to Examples 1 to 4 and Comparative Examples 1 to 6 were measured with a Vickers hardness tester, and the measurement results are shown in Table 1 below.(5) Bus bar weight (1 set, g): the weights of the bus bars according to Examples 1 to 4 and Comparative Examples 1 to 6 were measured by a typical method, and the measurement results are shown in Table 1 below.(6) Electrical conductivity (IACS%): the electrical conductivities of the bus bars according to Examples 1 to 4 and Comparative Examples 1 to 6 were measured, and the measurement results are shown in the following Table 1. At the same time, IACS stands for International Annealed Copper Standard and is a unit of electric conductivity based on the electric conductivity of pure copper set to 100% at a temperature of 20° C.(7) Electric resistance (μΩ): Electric resistance across bus bars according to Examples 1 to 4 and Comparative Examples 1 to 6 were measured at 10 kHz with an automatic current controller (LCR), the measurement results being shown in Table 1 below.(8) Tightening torque: it was examined whether a crack or damage occurs when a force of 10 N·m acts on the bus bars according to Examples 1 to 4 and Comparative Examples 1 to 6 to tighten a screw. When a bolt without a crack or damage was tightened, it was denoted by ◯, and when a crack or damage occurred, it was denoted by ×. The results of the determination are shown in Table 1 below.(9) Temperature rise test: Foil capacitors comprising the bus bars according to Examples 1 to 4 and Comparative Examples 1 to 6, respectively, were produced, whereby the temperature rises of the bus bars were measured. The results of the measurement are shown in Table 1 below.(10) Bending Test: it was determined whether a crack occurs when an L-shaped bending test, a Z-shaped bending test, and bending tests for radius curvatures of 0.5, 1.0, 1.5, and 2.0 are performed on the bus bars according to Examples 1 to 4 and Comparative Examples 1 to 6. When no crack occurred, it was marked as ◯, and when a crack occurred, it was marked as ×. The results of the determination are shown in Table 1 and Fig. 4.(11) Analysis for the interface between the copper layer and the aluminum layer before and after the thermal shock test: the thermal shock test was carried out for 750 cycles, in each of which the bus bars according to Examples 1 to 4 and Comparative Examples 1 to 6 were left at -40° C. for one hour and then at 105° C. for one hour, thereby checking whether the compound separation occurred at the junction and the crack propagation occurred at another metal junction. When the joint separation at the transition and the propagation of cracks did not occur, it was denoted by ◯, and when the joint separation at the transition and the crack propagation occurred, it was denoted by ×. The determination results are shown in Table 1 and FIG. 5.(12) Analysis of the transition between the copper layer and the aluminum layer after the heat treatment: after the bus bars according to Examples 1 to 4 and Comparative Examples 1 to 6 were heat treated for one hour, a connection layer formed at the transition between the copper layer and the aluminum layer was found, whereby the cross-sectional thickness of the transition was measured. The measurement results are shown in Table 1 and FIG. 6.(13) Equivalent series resistance (ESR): Foil capacitors including the bus bars according to Examples 1 to 4 and Comparative Examples 1 to 6, respectively, were manufactured, a thermal shock test was carried out for 750 cycles, and ESRs of the foil capacitors were measured at 10 kHz with an automatic current controller (LCR meter). The results of the measurement are shown in Table 1 below.As shown in Table 1, the bus bars according to Examples 1 to 4 of the present invention have a lower ESR than Comparative Examples 2 and 6 and a lower weight than the existing bus bar formed of copper, while the electric resistances, the tightening torques, and the temperature rises are similar to those of the existing bus bar formed of copper.Further, Comparative Examples 2 to 4 deviating from the thickness ratio of the aluminum layer to the first or second copper layer in the embodiments of the present invention cannot achieve a lightweight property, or do not have the same electric resistance, tightening torque, and temperature rise as the existing bus bar made of copper. Thus, Comparative Examples 2 to 4 cannot achieve the effect according to the embodiments of the present invention. Comparative Example 1 made of copper has a larger weight than Examples 1 to 4. In the case of Comparative Examples 2 and 3 in which the thickness reduction percentage is different from that of the embodiments of the present invention, the stretching percentages and the bonding strengths thereof were deteriorated, and a crack occurred during the bending test.FIGS. 4A to 4D show bending test results of Examples 1 and 2 and Comparative Examples 2 and 3 when the radius curvature R is set to 0.5. Referring to Table 1 and FIGS. 4A to 4D, no crack occurred during the bending tests on the bus bars according to the embodiments of the present invention. However, cracks occurred in Comparative Examples 2 to 6 in which the thickness ratio of the aluminum layer to the first or second copper layer deviated from those of the embodiments of the present invention or in which the percentage of thickness decrease deviated from those of the embodiments of the present invention.FIGS. 5A and 5B are photographs showing the cross sections of the bus bars according to the embodiments of the present invention before and after the thermal shock test, and FIGS. 5C and 5D are photographs showing the cross sections of the bus bars according to the comparative examples before and after the thermal shock test. Referring to Table 1 and FIGS. 5A to 5D, compound separation occurred at the interface at the interface between the copper layer and the aluminum layer, and a crack propagated to the interface of the other metal layer in the bus bars according to Comparative Examples 2 and 6, in which the thickness ratio of the aluminum layer to the first or second copper layer is different from those of the embodiments of the present invention, or in which the percentage thickness reduction is different from those of the embodiments of the present invention.FIG. 6 is a photograph showing the contact area between the copper layer and the aluminum layer in the bus bar according to Example 1 after the heat treatment, FIG. 6B is a photograph showing the contact area between the copper layer and the aluminum layer according to Example 2 after the heat treatment, FIG. 6C is a photograph showing the contact area between the copper layer and the aluminum layer in the bus bar according to Example 3 after the heat treatment, and FIG. 6D is a photograph showing the contact area between the copper layer and the aluminum layer in the bus bar according to Comparative Example 3 after the heat treatment. Referring to Table 1 and Figs. 6A to 6D, no bonding layer formed at the contact surfaces in Examples 1 to 4 of the present invention. However, a bonding layer was formed in Comparative Examples 2 to 6 in which the thickness ratio of the aluminum layer to the first or second copper layer is different from those of the embodiments of the present invention, or in which the percentage thickness reduction is different from those of the embodiments of the present invention.When the bus bar is heated by resistance heat or used in a high temperature environment, a metal compound made of aluminum and high brittleness copper may form at the interface. In this case, the electrical conductivity, the reliability, and the life of the bus bar may decrease.

Claims

A composite metal bus bar (100) for a foil capacitor (1000) comprising a composite metal layer (50) including: an aluminum layer (10); a first copper layer (20) laminated on the one surface of the aluminum layer (10); and a second copper layer (22) laminated on the other surface of the aluminum layer (10), wherein the thicknesses of the first and second copper layers (20, 22) are set in the range between 10% and 25% of the total thickness of the composite metal layer (50), and the thickness of the aluminum layer (10) is set in the range between 50% and 70% of the total thickness of the composite metal layer (50), characterized in that the composite metal layer (50) has a percentage thickness decrease of less than 10%; the composite metal layer (50) has an elongation percentage of 25% or more, measured on the basis of ISO 6892; and the bonding strength of the bonded metal layer (50) measured on the basis of ISO 11339 is equal to or greater than 10 kgf on the basis of a sample width of 25 mm.The composite metal bus bar according to claim 1, wherein the thickness ratio of the first copper layer (20) to the second copper layer (22) is set in the range between 1:0.5 and 1:1.5.The composite metal bus bar according to claim 1, wherein the thicknesses of the first and second copper layers (20, 22) are set in the range between 15% and 25% of the total thickness of the composite metal layer (50), and the thickness of the aluminum layer (10) is set in the range between 50% and 65% of the total thickness of the composite metal layer (50).The composite metal bus bar according to claim 1, wherein the first and second copper layers (20, 22) have a thickness of 0.05 mm to 0.5 mm, and the aluminum layer (10) has a thickness of 0.3 mm to 2.0 mm.The composite metal bus bar according to claim 1, wherein the composite metal bus bar (100) has a thickness of 0.5 mm to 2.5 mm.The composite metal bus bar of claim 1, wherein the ratio of the percent thickness reduction to the percent elongation of the composite metal layer (50) is less than 1:2.5 and greater than 1:5.The composite metal bus bar according to claim 1, wherein the composite metal bus bar (100) has an electrical conductivity of 60 IACS% or more.The composite metal bus bar of claim 1, wherein the composite metal layer (50) has an elongation percentage between 25% and 35%.A foil capacitor (1000) comprising the composite metal bus bar (100) according to any one of the preceding claims.A method for manufacturing a composite metal bus bar (100) for a foil capacitor (1000), wherein the composite metal bus bar (100) comprises a composite metal layer (50) comprising an aluminum layer (10), a first copper layer (20) laminated on the one surface of the aluminum layer (10), and a second copper layer (22) laminated on the other surface of the aluminum layer (10), wherein the thicknesses of the first and second copper layers (20, 22) are set in the range between 10% and 25% of the total thickness of the composite metal layer (50), and the thickness of the aluminum layer (10) is set in the range between 50% and 70% of the total thickness of the composite metal layer (50), wherein the composite metal layer (50) has an elongation percentage of 25% or more, as measured on the basis of ISO 6892, and wherein the bond strength of the composite metal layer (50) measured on the basis of ISO 11339 is greater than or equal to 10 kgf on the basis of a sample width of 25 mm, the method comprising the steps of: layering the first copper layer (20) on the one surface of the aluminum layer (10); layering the second copper layer (22) on the other surface of the aluminum layer (10); and making the composite metal layer (50) with a percentage thickness reduction of less than 10%.

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