Patent Application
20210046581
This application claims the benefit of European Patent Application Serial No. 19 191 516.4 filed Aug. 13, 2019. The related application is incorporated herein in its entirety by reference.
The present invention concerns a method for connecting a metal sheet at least partially to a busbar and an arrangement of a busbar and a metal sheet realized by such a method.
Laminated busbars typically comprise conductive layers of fabricated copper separated by thin dielectric materials, laminated into a unified structure. For example, busbars can be used for collecting and transferring electrical power from a group of capacitors, connected to such a busbar, and forming a battery package. Typically, such busbars are used in vehicles, driven by electrical motors. In order to use the battery package for signal control, flexible printed circuits (FPC) are connected to the busbar, for instance. Thus, it is possible, to establish a communication between the battery package, including the busbar, and a battery management system. Thereby, flexible printed circuits typically comprise a thin metal sheet.
In general, rivet pins are used for realizing the electrically conductive connection between the busbar and the flexible printed circuit having the thin metal sheet. Further, it is known, for example from US 2018 0 335 060 A1, to use laser welding for realizing the connection between the flexible printed circuit and the busbar, wherein a welding line is realized by a continuous irradiation with a laser light from a fibre laser, while moving the laser light along a welding schedule line.
Considering the above, it is an object of the present invention to provide a method for connecting a thin metal sheet, particularly forming or being part of a flexible printed circuit, to a busbar in an alternative and preferably improved manner compared to the state of the art.
This object is achieved by a method for connecting a metal sheet at least partially to a busbar according to claim 1 and an arrangement of a busbar and a metal sheet according to claim 15. Preferred embodiments are incorporated in the dependent claims, the description, and the figures.
According to a first aspect of the present invention, a method for connecting a metal sheet at least partially to a busbar is provided, comprising
In contrast to the state of the art, it is provided, according to the present invention, to realize the welding joints by laser pulses. It has been discovered that by using laser pulses a sufficient resistance and a strong mechanical connection between the metal sheet and the busbar can be established. Especially, a reliable connection can be realized for thin metal sheets by using laser pulses, in particular without damaging the thin metal sheet. Since the laser welding directly melts the material between the thin metal sheet and the busbar, a connection having a comparable low resistance can be advantageously realized. Further, compared to realizing the connection between the metal sheet and the busbar via a rivet pin, the method for using laser pulses is quicker and more reliable. Thus, the method represents a time efficient way for producing the connection between the metal sheet and the busbar, in particular in a mass production of such connections.
Preferably, the busbar is a flat product extending in a main extension plane. The term flat means that a thickness of the busbar, measured in a direction perpendicular to the main extension plane, is at least 10 times, preferably at least 15 times, smaller than the extensions across the busbar in a plane parallel to the main extension plane. For instance, the busbar is laminated and/or covered with an insulation layer and/or a nickel layer for avoiding corrosion. It is provided according to an embodiment of the present invention that the busbar is made from a bare metal, without any further coating or covering. Further, the busbar is unstructured, i.e., the busbar includes no conductive paths in a common plane that are isolated from each other. to the contrary, the metal sheet, being connected to the busbar, particularly represents at least a part of a conductive or signal path, for example for transferring a signal to a control unit, such as a battery management system. In particular, the contact region is at a top and/or bottom side of the busbar. In another preferred embodiment it is provided that additionally or alternatively the contact region is on the edge of busbar, for example such that the FPC can connect with the terminals or ports of the busbar at said edge. Preferably, the busbar includes aluminum, copper, steel and/or nickel.
It is also provided according to an embodiment of the present invention that the busbar comprises at least one first conductive layer and/or at least one second conductive layer that are separated from each other by a further insulation layer, wherein the at least one first conductive layer, the at least one second conductive layer and the further insulation layer are stacked above each other along a stacking direction, being perpendicular to the main extension plane. Such busbars are particularly intended for collecting and transferring electrical power. For example, a plurality of capacitors is arranged on top of the busbar and the capacitors are connected to the busbar for distributing a total power collected from the plurality of capacitors. It is also provided in a preferred embodiment that the busbar is part of a battery package. In that case the busbar is used to connect battery cells in parallel or in series. The FPC here is used to collect the signal from these busbars, such as the electric potential and temperature of the welding area on busbar. Such busbars are intended for being used in electrical vehicles, for example. Preferably, the at least one first conductive layer and/or the at least second conductive layer is made from a metal, such as copper or aluminum. In particular, the thickness of the busbar, measured in a direction perpendicular to the main extension plane, is between 0.5 mm and 6 mm, more preferably between 0.5 mm and 3 mm, and most preferably between 0.5 mm and 1.5 mm. Especially, the thickness between 0.5 mm and 1.5 mm are favourably for busbars used in battery packs. Because the power transferred in vehicles is not very high as in other busbar applications, thin conductor can be used in such applications.)
Furthermore, it is provided according to an embodiment of the present invention that a ratio of the thickness of the metal sheet to the thickness of the busbar is between 0.005 and 0.02, more preferably between 0.0075 and 0.015 and most preferably about 0.01. In other words: the metal sheet is very thin compared to the thickness of the busbar. Particularly, the welding joints are realized as micro welding joints, i. e. as welding joints, having a comparable small cross section.
According to a preferred embodiment, the metal sheet is at least a part of a flexible printed circuit. Thus, it is possible in an advantageous way to use the metal sheet being part of the flexible printed circuit for signal control. For example, it is possible to use the connection between the flexibly printed circuit and the busbar in a battery package for signal control, in order to communicate with a battery management system. Thereby, it is provided according to an embodiment of the present invention that the flexible printed circuit only comprises the metal sheet or metal film or the metal sheet is at least partially mounted onto or integrated into a flexible plastic substrate, formed for example by a polyamide or transparent conductive polyester film. Another advantage of connecting a flexible metal sheet, in particular as part of the flexibly printed circuit, to a busbar is that this possibly to bend the metal sheet, for example in order to compensate different heights of the busbar on one hand and a further course of the flexible printed circuit outside the region of the busbar on the other hand. It is also conceivable that two separated parts of the FPC are connected via the busbar by just connecting these two parts to the contact region. Preferably an additional tape or glue is used to protect the welding area and/or contact region and enhance the mechanical strength of the welding area and/or contact area.
Preferably, it is provided according to an embodiment of the present invention that the laser pulses have a pulse duration between 0.1 ns and 800 ns, preferably between 20 ns and 500 ns, preferably between 20 ns and 240 ns are used.
Furthermore, it is provided that the contact region comprises a plurality of welding joints, wherein the welding joints are spatially separated from each other. By increasing the number of welding joints, it is advantageously possible to strengthen the mechanical connection between the metal sheet and the bus bar. For example, the number of welding joints lies between 2 and 10, more preferably between 2 and 8, or between 3 and 7. Therefore, by increasing the number of welding joints, the total strength of the connection can be improved. Limiting the number has a positive effect on the time efficiency for realizing the connection. In particular, it was found that realizing 3 to 7 welding joints guarantees a sufficient connection strength for most of potential applications and allows a fast production. Preferably, it is provided that several laser beams, formed each by laser pulses, are simultaneously directed on the contact region for accelerating the production of a group of welding joints.
In a preferred embodiment, it is provided that the plurality of welding joints is grouped, wherein, for example, a two-dimensional pattern is realised by the plurality of welding joints. It is possible to arrange the welding joints of the plurality of the welding joints such that the welding joints are optimized to the loads to the connection to be expected, for example depending on the direction of the expected forces that act on the connection between the busbar and the metal sheet or depending on the geometric form of the contact region.
In another embodiment, it is provided that prior to welding the metal sheet to the busbar, at least the contact region of the metal sheet is fixed to the busbar for forming a gap-free arrangement in the contact region. By guaranteeing a gap-free arrangement of the contact region between the busbar and the metal sheet, a success rate for establishing a strong mechanical connection between the busbar and the metal sheet can be advantageously increased. For example, the busbar and the metal sheet are fixed to each other by a clamp element, which tightens the metal sheet to the busbar, at least in the contact region. It is also conceivable that a frame-like construction presses the metal sheet to the busbar and fixates them together. Preferably, it is provided that a systematic control of the fixating state before the welding process is performed in order to avoid a faulty connection between the busbar and the metal sheet. Thus, a number of insufficient connections can be reduced.
According to a preferred embodiment, it is provided that prior to welding, a surface treatment is carried out on at least one part of the busbar. In particular, the section intended for providing the contact region is surface-treated prior to welding. For example, the surface of the busbar is cleaned for increasing the success rate for establishing the adhesive connection between the busbar and the metal sheet.
According to a preferred embodiment, it is provided that a ratio of the spot size of the welding joint to the size of the contact region is smaller than 0.2, more preferably smaller than 0.1, and most preferred smaller than 0.05. It turned out that even with such small welding joints it is possible to realise a sufficiently strong mechanical connection, which can be used as connection between the metal sheet and the busbar in practice. In particular, the small welding joints realise welding joints that are distributed over the contact region. Preferably, the welding joints are homogeneously distributed over the contact region. It is also conceivable, that the welding joints are distributed statistically across the contact region.
In another embodiment, it is provided that the spot size of the welding joins is between 0.01 mm2 and 5 mm2, preferably between 0.1 mm2 and 1 mm2, and more preferably between 0.2 mm2 and 0.7 mm2. Preferably, the size of the contact region is between 1 mm2 and 80 mm2, more preferably between 5 mm2 and 50 mm2, and most preferably between 10 mm2 and 25 mm2.
In another preferred embodiment, it is provided that the welding joints in the group of welding joints are arranged at least partially in a row. Thus, the several welding joints can easily be realised in the production, for example by a lateral shift of a laser source and repeating the treatment with the laser pulses.
In particular, it is provided that the busbar is coated and/or plated with a metal layer Preferably, it is provided that the busbar is coated, for instance with some nickel for corrosion avoidance. According to another embodiment, it is provided that the welding joints are equidistantly distributed, meaning that the distance between the welding joints—at least those along a line—is equal. It is also conceivable that the welding joints are distributed in-homogenous or even randomly. For example, the distance between the welding joints is not equidistantly distributed. This can be achieved by pre-setting a different welding program. That means a welding device having a corresponding laser source is included in an automatic welding system, which can load different welding program and realize automatic mass production. Thus, a homogeneous connection between the metal sheet and the busbar can be established, in order to provide a reliable connection strength.
According to a preferred embodiment, it is provided that the metal sheet outside the connection region extends slanted relative to the outer surface of the busbar, at least in the finished state of an arrangement including the busbar and the metal sheet. Thus, it is possible in an advantageous manner to adapt the orientation and/or position of the metal sheet depending on the application, i.e. allowing a transfer of the control signal from the busbar to another level in the arrangement, including the busbar and the metal sheet.
Preferably, it is provided that a cross-section of the welding joint is rectangularly, elliptically, triangularly, and/or circularly shaped. By choosing or adapting the geometric form of the welding joint, it is further possible to adapt the mechanical strength of the connection between the busbar and the metal sheet. The circularly and elliptically shaped cross-sections can easily be realised by using laser pulses without requiring additional equipment, such as lenses or other beam forming equipment, which realise the special form of the laser spots used for welding the joints.
Another aspect of the present invention is an arrangement of a busbar and a metal sheet, in particular realised by a method according to the present invention, wherein the metal sheet is connected to the bus bar by welding joints, realized by laser pulses, being spatially separated from each other. All features and benefits described above for the method for realising the connection between the metal sheet and the busbar apply analogously to the arrangement, and vice versa.
Wherever not already described explicitly, individual embodiments or their individual aspects and features can be combined or exchanged with one another without limiting or widening the scope of the described invention, whenever such a combination or exchange is meaningful and in the sense of this invention. Advantages which are described with respect to one embodiment of the present invention are, wherever applicable, also advantageous of other embodiments of the present invention.
In
Especially, the busbar 1 comprises a first conductive layer extending in the main extending plane HSE and has a port 9, in particular extending in a direction parallel to the main extending plane HSE from an outer periphery of the first conductive layer, for representing a common pole of the busbar 1 that collects the contributions of several first kind of poles that are each assigned to one capacitor of the several capacitors. Besides the first conductive layer, preferably a second conductive layer is provided, wherein the second conductive layer extends parallel to the first conductive layer. The busbar 1, in particular the first conductive layer and/or the second layer, form a flat or laminated product, i. e. the extension of the busbar 1 in the main extending plane HSE is several times larger than the thickness of the busbar 1 measured in a direction z perpendicular to the main extending plane HSE. Especially, the busbar 1 has a thickness measured in a direction z perpendicular to the main extension plane HSE between 0.5 mm and 6 mm, more preferably between 3 mm and 6 mm and most preferably between 4.5 and 5.5 mm. For busbars 1 used in battery packages it is preferably provided that the thickness measured in a direction z perpendicular to the main extension plane HSE is between 0.5 mm and 3 mm, and most preferably between 0.5 mm and 1.5 mm.) In particular, the material of the first conductive layer and the second conductive layer are configured such that the busbar 1, at least parts of the busbar 1, can be deformed without affecting the functionality of the first and second conductive layer. Thus, the busbar 1 can easily adapted to the space to which the busbar 1 or the assembly including the busbar 1 should be incorporated to, for example by bending a part of the busbar 1. Further, the second conductive layer comprises at is outer periphery another port for representing a common pole of the busbar 1 that collects the contributions of a second kind of poles that are each assigning to one of the several capacitors. Those busbars 1 are used for example in vehicles driven by electrical motors.
Further, it is known to connect a thin metal sheet 2 to the busbar 1 for signal control of a system including the capacitors and the busbar, e.g. in particular the metal sheet 2 is at least part of a flexible printed circuit (FPC). Such a metal sheet 2 is for example used for signal control and has a thickness of less than 300 μm, preferably a thickness between 30 μm and 80 μm. Consequently, the ratio of the thickness of the metal sheet 2 to the thickness of the busbar 1 is between 0.005 and 0.02, more preferably between 0.0075 and 0.15, and most preferred about 0.01. The FPC is for example used to collect the signal from these busbars, such as the electric potential and temperature of the welding area on busbar. In other words, the thickness of the busbar 1 is several times larger than the thickness of the metal sheet 2. In order to realise a connection between the busbar 1 and the thin metal sheet 2 in a time-efficient manner, a welding joint 7 is realised by utilisation of laser light 5. As a consequence of using such laser light 5, material between the thin metal sheet 2 and the busbar 1 is melted, and an adhesive connection between the thin metal sheet 2 and the busbar 1 is formed. Thus, a connection of comparably low resistance is realised. Furthermore, it was found that laser pulses can be used for realising a mechanically strong connection between the busbar 1 and the thin metal sheet 2. By using the laser pulses, it is therefore advantageously possibly to achieve a desired resistance and mechanical strength for the connection between the metal sheet 2 and the busbar 1 in a time-efficient way. In particular, it is provided to realise a micro welding joint 7 by using the laser light 5. It turned out that the use of laser pulses allows the realisation of the welding joints 7, without any damage to the thin metal sheet 2 connected to the busbar 1.
In
Moreover, it is preferably provided that the connection between the busbar 1 and the metal sheet 2 is realised by a plurality of welding joints 7. Especially, the welding joints 7 are grouped and/or represented by micro welding joints 7, i. e. the cross-section of the welding joints 7 is comparably small. As it turns out, it is even possible to establish a mechanically strong connection between metal sheet 2 and the busbar 1 by use of such small welding joints. For example, the cross-section area of the welding joints 7 is about 0.5 mm2.
Preferably, the metal sheet 2 in the example shown in
In
Preferably, a 70 μm-thick gold-plated flexibly printed circuit is welded onto an aluminium busbar 1 of 1 mm thickness, plated with nickel. By using laser pulses, having a pulse duration of 3 ps, a welding joint 7 having a cross-section of about 0.5 mm2 can be realised. In particular, the total duration of illuminating the contact region CR at least partially takes about one second.
In
| Number | Date | Country | Kind |
|---|---|---|---|
| 19 191 516.4 | Aug 2019 | EP | regional |
