Method and apparatus for electrically connecting flexible printed circuit board to metal element by ultrasonic welding

Abstract

The invention relates to a method for electrically connecting a flexible printed circuit board (3) to a metal element (5) by means of ultrasonic welding, and to an ultrasonic welding device (1) which can be used to carry out the described method. The flexible printed circuit board has an electrically insulating film-like substrate (9) in a connection region (7) and a metal layer (11) applied to the substrate. The method comprises: applying a connection region of the flexible printed circuit board to the metal element such that the metal layer is in mechanical contact with the metal element; applying an ultrasonic horn (13) to the connection region of the flexible printed circuit board such that the horn surface (15) is in mechanical contact with the film-like substrate; and-generating ultrasonic vibrations at the welding head surface. In order to ensure that soldering can be carried out by means of the film-like substrate and in this case, preferably without damaging the film-like substrate, different measures can be taken.

Description

Technical Field

[0001] This invention relates to a method and apparatus for electrically connecting flexible printed circuit boards to metal components by ultrasonic welding. Background Technology

[0002] Ultrasonic welding has been developed to join at least two weldable materials in a manner that allows them to withstand mechanical loads. If the weldable parts are made of conductive materials, it is often necessary to create a connection between the weldable parts that has good electrical conductivity.

[0003] Typically, the joints are housed within a welding space within an ultrasonic welding apparatus. The welding space is defined on one side by the surface of the anvil and on the opposite side by the surface of the welding head. During the ultrasonic welding process, the joints are held between the anvil and the welding head, and the welding head is configured to vibrate ultrasonically. The ultrasonic vibrations are transmitted through the welding head surface to at least one joint, causing a material bond between the joints at the boundary surfaces, wherein the materials of the joints are typically not heated above their respective melting points.

[0004] To weld two metal joints together using ultrasound and to form a mechanical and electrical connection between them, it is typically necessary to provide relatively high ultrasonic power to the welding head and couple this power to at least one joint through the surface of the welding head. For this purpose, the welding head is usually positioned so that its surface directly abuts against the surface of one of the metal joints and presses it against the joint with sufficient pressure.

[0005] For various applications, it may be necessary to electrically connect flexible printed circuit boards (FPCs) to metal components. Flexible printed circuit boards—sometimes referred to as FPCs or FPC connectors—typically comprise a stack containing an electrically insulating film-like substrate coated with a metal layer. The metal layer is typically configured as one or more electrical conductor traces. The film-like substrate and the metal layer on it have such a small layer thickness that the flexible printed circuit board can be bent without damage. Thus, the flexible printed circuit board is particularly capable of achieving electrical connections with one or more electrical components in at least one degree of freedom. In the connection areas of the flexible printed circuit board, its metal layer is connected to the metal components of the electrical components. The metal components can be any desired metal structure on the electrical components. For example, the metal components can be configured in the form of metal sheets, such as thin, typically self-supporting discs of metal material. However, the metal components can also be deposited as non-self-supporting metal layers, for example, on a carrier layer.

[0006] For example, flexible printed circuit boards are used to form a battery contact system (ZCS) within a battery system consisting of multiple individual battery cells. Here, the battery contact system includes multiple signal lines formed by conductor traces on the flexible printed circuit board. Each of these signal lines is electrically connected to a metal element at an associated connection area, whereby the corresponding metal element is electrically connected to one of the battery cells in the battery system. Using the signal lines, for example, the voltage of each battery cell can be tapped, measured, and, in particular, the state of charge (SOC) can be determined. In particular, all battery cells can be connected to a battery management system (BMS) via the battery contact system, by which the charging and / or discharging processes of the battery system can be controlled or regulated. Optionally, using the battery contact system, particularly with respect to each individual battery cell or group of battery cells, other physical measurements can also be determined at different locations within the battery system, for example, by placing suitable sensors at the corresponding locations, and these sensors can be read by the BMS via the ZCS through the transmission of generated electrical sensor signals.

[0007] To date, relatively complex techniques have been employed to electrically connect the conductor traces of a flexible printed circuit board to metal components that are already connected to a battery cell.

[0008] For example, small metal tabs in the form of nickel sheets (also known as nickel lugs) can be attached to connection areas on a flexible printed circuit board, for example, by soldering them to the metal layer forming the connection area. These metal tabs can protrude beyond the flexible printed circuit board on one side and be electrically connected to metal components on the battery cell from one side, for example, by soldering the metal tabs to the metal components. However, considerable additional expense and cost are required for providing the additional metal tabs and making the necessary electrical connections to the connection areas on the flexible printed circuit board on one side and to the metal components of the battery on the other. Furthermore, it has been observed that, at best, relatively inexpensive nickel lug-type metal tabs can be soldered to metal components using soldering methods that are advantageous in other cases, such as ultrasonic metal welding, for example, because in this case, the welding tools of the ultrasonic welding system may experience accelerated wear.

[0009] EP3231033B1 describes an alternative method for connecting battery contact systems. Specifically, this involves electrically soldering a portion of a flexible printed circuit board (PCB) to the contact area of ​​a pluggable connector or power connection, which is connected from one side to the battery terminals of a battery cell. This portion of the PCB is formed by partially omitting its film substrate. This portion is therefore also referred to as a window. In this portion, the metal layer of the PCB is thus partially exposed; that is, it is bare and not covered by the electrically insulating material of the film substrate. In the window region, this portion is then soldered to the contact area of ​​the pluggable connector or power connection with its partially exposed metal layer, wherein ultrasonic welding methods can be used, in particular. However, it has been observed that the described scheme requires considerable processing costs. Summary of the Invention

[0010] An alternative method for electrically connecting flexible printed circuit boards (PCBs) to metal components may be needed. In particular, a method may be required that allows PCBs to be connected to metal components via ultrasonic welding with minimal processing overhead, low cost, low material costs, and / or relatively simple equipment construction. Furthermore, an ultrasonic welding apparatus configured to perform the method may be required.

[0011] This need can be met by the subject matter of the independent claims. Advantageous embodiments are defined in the dependent claims and the following description, or shown in the drawings.

[0012] According to a first aspect of the invention, a method for electrically connecting a flexible printed circuit board to a metal component by ultrasonic welding is described. Here, the flexible printed circuit board has an electrically insulating film-like substrate and a metal layer coated on the substrate in the connection region. The method includes at least the following steps, which may, but do not necessarily, be performed in the order stated:

[0013] The connection area of ​​the flexible printed circuit board is applied to the metal component, such that the metal layer is arranged to make mechanical contact with the metal component;

[0014] An ultrasonic welding head is applied to the connection area of ​​a flexible printed circuit board, such that the surface of the welding head is arranged to make mechanical contact with a film substrate; and

[0015] Ultrasonic vibration is generated (=implemented) on the surface of the welding head.

[0016] According to a second aspect of the invention, an ultrasonic welding apparatus is described for electrically connecting a flexible printed circuit board to a metal component via ultrasonic welding. The ultrasonic welding apparatus has an ultrasonic welding head with a welding head surface. In this case, the ultrasonic welding head is designed as a bending oscillator and configured to generate (=implemented) ultrasonic vibrations at a frequency exceeding 25 kHz on the welding head surface. Furthermore, the welding head surface has a surface texture, wherein the surface texture has a texture depth of less than 0.3 mm.

[0017] As an introduction, the basic concept of the embodiments of the present invention described herein will be briefly explained, wherein this description should be interpreted as general overview and not as limiting the invention:

[0018] As explained above, it has been assumed until now that a reliable conductive connection can be formed between two metal joints by ultrasonic welding only when they are in direct mechanical contact with each other and at least one of the metal joints is in direct contact with the surface of the ultrasonic welding head used in this case. Based on this concept, as also stated in EP3231033B1 cited at the beginning, in order to electrically connect a flexible printed circuit board to metal components in a battery contact system, the metal layers of the flexible printed circuit board must always be exposed in the form of windows before ultrasonic welding can be performed on the exposed metal layers.

[0019] Having overcome this long-held prejudice, it is now recognized that flexible printed circuit boards and their metal layers can be soldered to metal components even if the soldering head is not directly adjacent to the metal layer, but rather applied in a manner where its soldering head surface is in mechanical contact with the film-like substrate covering the metal layer.

[0020] In particular, it has been observed, as will be described in more detail below, that, especially when certain conditions are properly preset and / or parameters are appropriately set within the range of ultrasonic welding, ultrasonic vibrations can be transmitted from the ultrasonic welding head through its welding head surface to the film substrate, and then through the latter to the metal layer of the flexible printed circuit board, so that a reliable and conductive ultrasonic welding connection can be formed between the metal layer and the metal components that are in mechanical contact with the latter by means of these ultrasonic vibrations.

[0021] In this case, the method can be preferably implemented such that the substrate carrying the metal layer is not damaged during the connection process, or remains intact enough to cover the metal layer in an insulating manner even after the metal layer is connected to the metal component. Accordingly, the additional process steps for subsequently insulating the previously windowed portions of the flexible printed circuit board can be eliminated, and thus the cost of establishing electrical connections can be reduced.

[0022] The possible configurations and advantages of the ultrasonic welding apparatus embodiments will be described in more detail below.

[0023] The methods described herein can be used to electrically connect flexible printed circuit boards to metal components that are configured in any desired manner. In one application example described in detail herein, the flexible printed circuit board may, for example, be configured to contact multiple metal components as a battery contact system, which in turn are electrically connected from one side to multiple individual battery cells that are interconnected to form a single battery. However, the method can also be used in a variety of other applications to interconnect electrical or electronic components within electrical devices such as mobile phones, computers, etc., for example, by means of flexible printed circuit boards.

[0024] The flexible printed circuit board can be configured as at least two layers. The first layer is formed from a film substrate. The second layer is formed from a metal layer coated onto the substrate. The metal layer can be connected to the substrate, for example, by means of an intermediate layer consisting of an adhesive or glue. In a more stable, but often more expensive, variant, the metal layer and the film substrate can preferably be pressed together under additional heating. The flexible printed circuit board may also be configured to have more than two layers stacked together. Here, the multiple metal layers can, in each case, be mechanically connected to each other by means of a thin layer of electrically insulating material extending therebetween, but are electrically insulated from each other.

[0025] The film-like substrate has a layered, i.e. planar, quasi-two-dimensional geometry. Lateral dimensions typically range from a few millimeters to tens of centimeters, for example, from 1 millimeter to 500 centimeters, preferably from 5 millimeters to 50 centimeters. The layer thickness of the film-like substrate typically ranges from 5 μm to 300 μm, preferably from 10 μm to 100 μm, or more preferably from 20 μm to 50 μm. The film-like substrate is configured to be at least partially, or preferably entirely, composed of an electrically insulating material. For example, plastics, especially polymers such as polyimide (PI), polyethylene terephthalate (PET), and polyethylene naphthalate (PEN), can be used as materials. Due to its small layer thickness and / or material properties, the film-like substrate can have high mechanical flexibility in the lateral direction relative to its extending plane, for example, and can be bent with radii of curvature of several centimeters or even several millimeters. However, along the extending plane, the film-like substrate can have high strength, especially high tensile strength, and / or negligible elongation. Although called a "substrate," a layer so named does not necessarily have load-bearing properties. Instead, the film-like substrate may simply be configured as a thin layer that covers adjacent metal layers over a large area or the entire region, and acts as an insulating layer to electrically insulate the metal layers from the environment. The flexible printed circuit board may also include multiple film-like substrates, i.e., multiple electrically insulating material layers. They may be arranged on the same side and / or opposite sides of the metal layers.

[0026] The metal layer applied to the film substrate also has a planar geometry. Its lateral dimensions may be similar to those of the substrate. The thickness of the metal layer may also be similar to that of the substrate, wherein, depending on the application, the metal layer may be thinner, the same as, or thicker than the substrate. The metal layer preferably covers the film substrate over a large area, particularly in a partial area or over the entire area. The metal layer may be configured, for example, comprising multiple partial layer regions that are electrically isolated from each other and serve as conductive traces. The metal layer may be applied directly to the substrate. That is, the substrate and the metal layer may have a common boundary surface. Alternatively, one or more intermediate layers may be disposed intermediately between the metal layer and the substrate, for example, as adhesive or glue layers. The metal layer may be adhered to the substrate by material bonding. If appropriate, at least locally, there may also be form-fit connections and / or force-fit connections between the metal layer and the substrate. The metal layer may be configured to have a metal with good conductivity, such as, for example, copper. In this case, the metal layer may be entirely composed of copper, but it may also be composed of a copper alloy and / or have only a copper-containing portion. The metal layer may also include other metals, such as aluminum, silver, etc., or be composed of these metals. Furthermore, the metal layer may be coated with a supplementary metal layer, particularly on exposed surfaces, i.e., on surfaces distant from the film substrate. For example, such a layer may be composed of one or more metal alloys or metal compounds, such as those commonly used as protective layers in electronic applications, especially NiAu, ENIG, ENEPIG, etc. Preferably, such a layer protects the underlying metal layer, i.e., the copper-based metal layer of a flexible printed circuit board, from environmental influences, and particularly serves as corrosion protection.

[0027] The metal element to which the flexible printed circuit board is to be connected can have almost any desired geometry. It can be constructed, for example, as a sheet or connecting lug. In this case, it can have a flat surface, or, where appropriate, a curved, smooth and / or textured surface. The metal element typically has a thickness of at least 0.1 mm, preferably at least 0.2 mm or at least 0.3 mm. Furthermore, the metal element typically has a thickness of up to 10 mm, preferably up to 5 mm or up to 3 mm. The metal element can be constructed as a metal sheet. The metal element is preferably a self-supporting component with high rigidity and low bendability, particularly with significantly higher rigidity and significantly lower bendability than the flexible printed circuit board. The metal element can be configured to have a metal with good electrical conductivity, such as aluminum. In this case, the metal element can be made entirely of aluminum, but it can also be made of an aluminum alloy and / or have only aluminum-containing partial layers. It is possible to utilize the fact that, by selecting appropriate welding parameters, reliable and load-bearing mechanical and electrical connections can be formed between different metals, for example, between a copper-containing metal layer and an aluminum-containing metal element, using the ultrasonic welding proposed herein. However, the metal component may also be made of or include other metals, such as copper, silver, aluminum, gold, nickel, bronze, brass, etc. Furthermore, the metal component may be coated with a metal layer similar to the metal layer described above for flexible printed circuit boards, and this metal layer provides protection, particularly against corrosion.

[0028] As further noted above, it is now recognized that, contrary to previous understanding, in order to solder a flexible printed circuit board to a metal component, it does not appear absolutely necessary to initially remove the electrically insulating substrate in a window-like manner in the area to be formed at the connection point, thereby exposing the metal layer that is otherwise covered by the substrate, before soldering it to the metal component. Instead, it is now recognized that the substrate can remain at the connection point, and it is entirely possible to apply an ultrasonic welding head to the flexible printed circuit board with its surface in contact with the film-like substrate, and then transmit ultrasonic vibrations from the welding head to the underlying metal layer through the substrate, thereby enabling effective soldering of the metal layer to the adjacent metal component. In particular, it is now recognized that, in this configuration, it may be advantageous to specifically adjust the conditions during the ultrasonic welding process to achieve effective soldering by means of ultrasonic vibration, while minimizing undesirable damage to the film-like substrate during the ultrasonic welding process, especially localized opening of the connection area or other disturbance of its electrical insulation properties. Therefore, after the ultrasonic welding process, the film-like substrate preferably also covers the adjacent metal layer over the entire area, and thus protects it, in particular, from corrosion. Therefore, it is preferable to omit the subsequent application of a protective coating, such as a varnish, which is usually necessary in conventional methods to seal the intentionally exposed window-like opening on the substrate.

[0029] According to one embodiment, ultrasonic vibrations with frequencies exceeding 25 kHz, preferably 30 kHz or higher, or even 35 kHz or higher can be generated for this purpose.

[0030] In other words, it is considered advantageous to generate ultrasonic vibrations during ultrasonic welding that are transmitted from the weld head to the joint, with a higher frequency compared to frequencies commonly found during ultrasonic welding of metal joints in other cases. In particular, it is presumed that the higher frequency results in more efficient and / or gentler transmission of the ultrasonic vibrations through the film substrate to the metal layer. Furthermore, due to the higher frequency, the same or even lower ultrasonic power can be transmitted with a lower ultrasonic vibration amplitude, where the likelihood of damage to the film substrate becomes less due to the lower amplitude.

[0031] According to one embodiment, a bending oscillator is used as the ultrasonic welding head.

[0032] In the case of such ultrasonic welding heads designed as bending oscillators (flexible oscillators), ultrasonic vibrations are not generated orthogonally to the boundary surface between the parts to be welded, but rather parallel or tangentially to said boundary surface. Compared to other types of longitudinally vibrating ultrasonic welding heads, bending oscillators typically vibrate with a larger amplitude. In this case, the bending oscillator can vibrate like a whip due to its geometry. Due to the parallel vibration direction and / or large vibration amplitude, ultrasonic vibrations can be transmitted to the film substrate with less destructive force and / or force direction, and / or in a more efficient manner, and through the latter to the metal layer. Furthermore, compared to other types of longitudinally vibrating ultrasonic welding heads, bending oscillators allow for better accessibility to components and / or simpler construction.

[0033] Preferably, the welding head surface has a surface texture, wherein the surface texture is configured such that the texture depth achieved therein is smaller compared to that in the case of conventionally used ultrasonic welding heads.

[0034] Typically, ultrasonic welding heads used for joining metal parts have a textured surface rather than a smooth structure on the surface of the welding head that contacts the welding material. In this case, the textured surface may have textured protrusions projecting towards the welding material, and areas receding from the welding material and laterally adjacent to it. The surface texture can take on a variety of possible configurations. For example, the protruding textured protrusions may have rectangular, triangular, or other types of cross-sectional geometry. For instance, the welding head surface may be provided with a corrugated shape. Such surface textures can help to effectively transmit the ultrasonic vibrations generated by the welding head to the joint.

[0035] Regarding the method proposed in this paper, it is now recognized that although it may be advantageous to add surface texture to the solder head surface, the surface texture should preferably have only a relatively small texture depth compared to conventionally used solder heads. In other words, on the solder head surface, the height difference between the protruding texture protrusions and the laterally adjacent recessed areas of the surface texture—measured along a direction orthogonal to the surface of the printed circuit board to be soldered—should be smaller than that of a conventional solder head.

[0036] Therefore, the risk of damage to the film substrate during ultrasonic welding can be reduced by this surface texture. In particular, the risk that certain areas of the weld head surface may be pressed through the film substrate during ultrasonic welding, and in the worst case, partially expose the underlying metal layer, can be reduced.

[0037] In particular, according to one embodiment, it is considered advantageous that the surface of the welding head has a texture depth of less than 0.4 mm, preferably less than 0.3 mm or less than 0.2 mm. However, the texture depth should preferably be greater than 10 μm or greater than 50 μm. In particular, it is considered advantageous to use a welding head with 0.3 mm, 0.2 mm or even finer ripples on its surface.

[0038] This shallow texture depth allows the solder head to not be pressed too deeply into the surface of the film substrate. On the other hand, such a surface texture is still sufficient to transmit high-frequency ultrasonic vibrations from the solder head to the flexible printed circuit board, and ultimately, especially, to its metal layers.

[0039] In this case, according to a specific embodiment, it is considered advantageous to round off the surface texture at the texture protrusions protruding toward the film substrate, such that the radius of curvature there is greater than 20%, preferably greater than 40%, or even greater than 80% of the thickness of the film substrate layer.

[0040] In other words, it may be advantageous for the applications described herein to not form surface textures with sharp or pointed textured protrusions, but instead to selectively round off the textured protrusions. For this purpose, for example, sharp or pointed textured protrusions may initially be formed on the surface of the welding head, in a manner and forming technique similar to those known for conventional welding heads. These textures can then be selectively rounded off using removal techniques such as sandblasting. Alternatively, they can be formed directly by rounding off during the manufacturing process of the textured protrusions.

[0041] In this configuration, the rounding can be arranged such that the textured protrusions have a sufficiently large radius of curvature on their surface facing the film substrate, so as to distribute the pressure applied from the solder head surface to the flexible printed circuit board in a more planar manner than is typically the case with conventionally used solder heads with sharp-edged textures. In particular, the radius of curvature should be formed such that the local pressure remains small enough to prevent the textured protrusions from penetrating or even piercing the film substrate.

[0042] Therefore, the radius of curvature should be greater than, for example, 5 μm, preferably greater than 10 μm, or greater than 20 μm, or even greater than 50 μm.

[0043] According to one embodiment, the surface of the welding head should be subjected to a force of less than 15 N / mm. 2 Preferably less than 10 N / mm 2 or even less than 7 N / mm 2 The pressure is pressed onto the film substrate. For this purpose, the ultrasonic welding apparatus can be configured such that the ultrasonic welding head is confined to a pressure of less than 15 N / mm² on its surface. 2 Preferably less than 10 N / mm2 Or even less than 7 N / mm 2 The pressure is pressed onto the flexible printed circuit board.

[0044] In other words, especially to avoid damaging the film-like substrate, it can be specified that during ultrasonic welding, the welding head is pressed against the flexible printed circuit board with its surface at a relatively low pressure. For example, for this purpose, a 4×4mm... 2 The welding head surface can be pressed onto the joint with a force of less than 240 N, preferably less than 160 N, or even less than 100 N. In particular, a sensor system can be provided on the ultrasonic welding apparatus to measure the pressure or corresponding force acting on the welding head surface. The measurements from this sensor system can then be used to limit the applied pressure in a desired manner, for example, through targeted open-loop or closed-loop control of the actuator system to move the welding head and press it against the joint. Alternatively or additionally, the mechanism and / or actuator system of the ultrasonic welding apparatus can be configured such that the pressure or corresponding force applied by the welding head is always kept below a predetermined or predeterminable limit value.

[0045] For example, ultrasonic welding apparatuses may be configured with so-called servo presses for moving and / or pressing the ultrasonic welding head. Compared to conventional ultrasonic welding apparatuses—where the welding head is moved and / or pressed toward the workpiece by an actuator in the form of a pneumatic device—ultrasonic welding apparatuses with servo presses can typically position the welding head onto the welding material more precisely, faster, more controllably, and / or more gently, and then press it toward the welding material. In particular, the servo press controls or adjusts the set speed, set depth, and / or set pressure in a targeted and variable manner to achieve, for example, so-called “soft contact.” In this case, the servo press may employ active force adjustment where appropriate. For this purpose, the servo press may have electrically activated and controllable actuators, for example, in the form of servo motors.

[0046] According to one embodiment, during ultrasonic welding, the metal element on the side facing away from the film substrate can be supported solely by a non-metallic support.

[0047] In other words, the method proposed in this paper may eliminate the need for an anvil, which is typically used to form a support in conventional ultrasonic welding.

[0048] In conventional ultrasonic welding, an anvil is typically used to clamp the joints between the anvil and the welding head, such that one joint primarily makes mechanical contact with the anvil, and the other primarily makes mechanical contact with the welding head. The ultrasonic vibrations applied by the welding head are then transmitted to the joints, achieving the desired weld at their abutting interface. In this case, the anvil is usually a robust, heavy component, such as a metal block.

[0049] It is now recognized that providing an anvil may not be necessary in the methods described herein. Instead, supporting the joint only on the side opposite the welding head with a non-metallic support element, such as a plastic component, especially a plastic frame, may suffice. This support element can have a much lower mass compared to a conventional anvil and does not need to be constructed of heavy metals. Such a lightweight support element is possible, especially because, in the case described herein, significantly lower compressive forces can be applied to the joint compared to the previously common practice of ultrasonic welding of metal joints. Using a low-mass and / or stiff support also helps to keep the forces acting on the joint during ultrasonic welding limited, thus allowing the welding process to be performed in a “gentler” manner.

[0050] Eliminating the use of a solid anvil significantly simplifies the welding method and the ultrasonic welding apparatus used for this purpose. In particular, in the case of this method or ultrasonic welding apparatus, there is no need to provide space for a solid anvil in the welding space away from the back of the welding head.

[0051] According to one embodiment, different ultrasonic welding conditions can be achieved in consecutive time phases during the generation of ultrasonic vibrations.

[0052] In other words, ultrasonic welding apparatuses can be specifically configured to not generate the same ultrasonic welding conditions consistently throughout the welding process, but rather to change these conditions over time. This is also known as staged welding. The ultrasonic welding conditions may, in particular, include contact pressure, ultrasonic frequency, ultrasonic amplitude, ultrasonic power, ultrasonic welding energy, welding height, and a welding height spectrum that varies over time. Each welding stage can range in duration from a few milliseconds to up to a few seconds, i.e., from 5 ms to 0.5 s.

[0053] For example, during a first time phase of, say, 50 ms, ultrasonic vibrations with a low contact pressure can be generated to, for example, remove dirt and / or oxide layers from the surfaces at the joint. Subsequently, during a second time phase of, say, 200 ms, a higher contact pressure can be set to perform the actual ultrasonic welding.

[0054] It should be noted that the possible features and advantages of various embodiments of the present invention are described in part with reference to the method configured according to the present invention, and in part with reference to the ultrasonic welding apparatus configured according to the present invention. Those skilled in the art will recognize that features described for a single embodiment can be suitably transferred to other embodiments in a similar manner, adjusted and / or exchanged, thereby obtaining further embodiments of the present invention and potentially producing synergistic effects. Attached Figure Description

[0055] Advantageous embodiments of the present invention will be further described below with reference to the accompanying drawings, which should not be construed as limiting the invention in any way.

[0056] Figure 1 An ultrasonic welding apparatus according to an embodiment of the present invention is shown, which is used to electrically connect a flexible printed circuit board to a metal component by ultrasonic welding.

[0057] Figure 2 Show Figure 1 A magnified view of the local area A marked in the middle.

[0058] The accompanying drawings are highly schematic and not to scale. In all the drawings, the same reference numerals denote the same or equivalent features. Detailed Implementation

[0059] Figure 1 An ultrasonic welding apparatus 1 is shown, which can electrically connect a flexible printed circuit board 3 to a metal component 5 via ultrasonic welding. Figure 2 Shown at magnification Figure 1 The area marked "A" in the middle.

[0060] In the example shown, the flexible printed circuit board 3 comprises an upper film substrate 9, a lower film substrate 37, and a metal layer 11 disposed between the two film substrates 9 and 37. The two film substrates 9 and 37 are made of an electrically insulating material, such as a polymer material, particularly polyimide, and each has a layer thickness 21 in the range of 40 μm ± 20 μm. The metal layer 11 is made of copper and has a layer thickness similar to that of the film substrates 9 and 37.

[0061] The metal element 5 may be, for example, a connecting plate, which may be configured as part of a battery contact system within a battery (not shown). The metal element 5 may be made of aluminum, for example, and have a thickness significantly greater than that of the flexible printed circuit board 3, or greater than the thickness of the film substrates 9, 37 and / or the metal layer 11 contained therein. For example, the thickness of the metal element 5 may range from 1.5 mm ± 0.3 mm.

[0062] In the connection area 7 where the flexible printed circuit board 3 and the metal component 5 are to be connected, there is no lower film substrate 37. Therefore, the metal layer 11 is exposed downward in the connection area 7, but is covered upward by the upper film substrate 9.

[0063] In order to electrically connect the flexible printed circuit board 3 to the metal component 5 at its connection area 7, the two components need to be welded together by ultrasonic welding using an ultrasonic welding device 1.

[0064] For this purpose, the ultrasonic welding apparatus 1 has an ultrasonic welding head 13. During the welding process, the ultrasonic welding head 13 has a surface texture 19, for example, in the form of corrugations, particularly cross-corrugations, on the welding head surface 15 facing the connection area 7 of the flexible printed circuit board 3. This surface texture 19 has a texture depth 23 significantly smaller than that of conventionally used welding heads. For example, the surface texture 19 can be configured to have a texture depth 23 in the range of 100 μm to 200 μm. In other words, the welding head surface 15 can be configured to have 0.2 corrugations or finer corrugations. In this case, as... Figure 2 The surface texture 19 shown can be rounded on the texture protrusions 25 facing the printed circuit board 3. The radius of curvature on the texture protrusions 25 can be in the range of 5 μm to 50 μm, for example.

[0065] In this context, it should be clearly pointed out that, Figure 1 and Figure 2 The dimensional proportions shown do not correspond to the actual structure, and the dimensions of the surface texture 19 and its rounding are not shown in the correct proportions, especially relative to the thickness of the film substrates 9, 37 and the metal layer 11.

[0066] The ultrasonic welding device 1, which has its own welding head 13, is designed as a bending oscillator 29. In the case of such a bending oscillator 29, ultrasonic vibrations are generated such that the welding head surface 15 moves only or at least primarily along the bending vibration direction 17, which is parallel or tangential to the surface of the flexible printed circuit board 3 to be welded in its connection area 7.

[0067] The ultrasonic welding apparatus 1 can be configured as a servo press. In this case, the ultrasonic welding apparatus 1 has a sensor system 31, an actuator system 33, and a controller 35 (shown only very schematically in the figure). In this case, the force or pressure acting on the welding head surface 15 can be measured by means of the sensor system 31. In particular, the ultrasonic welding head 13 can be displaced by means of the actuator system 33, which can move in the direction toward the flexible printed circuit board 3. The controller 35 can control the actuator system 33, taking into account the signal from the sensor system 31 in the process. In particular, by means of the controller 35, the ultrasonic welding head 13 can be displaced in the direction toward the flexible printed circuit board 3 so that the contact pressure between the welding head surface 15 and the flexible printed circuit board 3 can be limited to the maximum pressure or the maximum force associated therewith by targeted open-loop or closed-loop control of the actuator system 33.

[0068] Furthermore, the controller 35, and if appropriate, the actuator system 33 and / or sensor system 31, can be configured to achieve different ultrasonic welding conditions in successive time phases during the ultrasonic welding process, such as time-varying ultrasonic frequency, ultrasonic amplitude, contact pressure, ultrasonic power or energy, welding height, etc.

[0069] To solder the flexible printed circuit board 3 to the metal element 5, the two components are mechanically supported against each other. In this case, the metal layer 11 of the flexible printed circuit board 3 in its connection region 7 directly contacts the opposite surface of the metal element 5 with its surface facing the metal element 5. The welding head surface 15 of the ultrasonic welding head 13 is then applied to the opposite surface of the flexible printed circuit board 3, that is, to the upper film substrate 9 covering the metal layer 11 in the connection region 7. At the same time or subsequently, ultrasonic vibrations are generated by the ultrasonic welding head 13 at its welding head surface 15. These ultrasonic vibrations are transmitted to the flexible printed circuit board 3, particularly to its film substrate 9 in the connection region 7, and through the substrate 9 to the metal layer 11.

[0070] In this case, the ultrasonic welding apparatus 1 and its operating mode are selected such that ultrasonic vibrations can reach the metal layer 11 through the film substrate 9 as effectively as possible, and the desired welding effect can be guaranteed there.

[0071] For this purpose, ultrasonic vibrations are generated at a frequency of at least 25 kHz. Furthermore, the ultrasonic vibrations are generated along the bending vibration direction 17. The contact pressure of the ultrasonic welding head 13 can also be limited in a targeted manner. In this case, the metal element 5 on the side facing away from the film substrate 9 can be supported solely by the non-metallic support element 27.

[0072] Because the surface texture 19 has a small texture depth 23 and possibly rounded texture protrusions 25 on the surface 15 of the welding head, efficient transmission of ultrasonic vibrations from the ultrasonic welding head 13 to the flexible printed circuit board 3 can be achieved. On the other hand, it prevents the surface texture 19 from being pressed too deeply into the flexible printed circuit board 3, especially into its upper film substrate 9. Furthermore, the welding process can be configured as so-called staged welding, for example, generating different ultrasonic welding conditions in the initial and subsequent time stages.

[0073] Some or all of the above-described characteristics of the ultrasonic welding apparatus 1, as well as the measures and / or conditions employed during the welding process, contribute to the fact that, in the case of the method described herein, the flexible printed circuit board 3 does not need to have its connection area 7 exposed from the film substrate 9; rather, the underlying metal layer 11 can be effectively welded to the metal element 5 substantially through the non-metallic film substrate 9.

[0074] In this context, the aforementioned characteristics, measures, and / or conditions particularly contribute to the fact that the film substrate 9 undergoes at most minimal deformation during ultrasonic welding, and especially is not partially penetrated and partially opened by the ultrasonic welding head 13. Therefore, after welding, the film substrate 9 can still cover the metal layer 11 in the connection region 7, thereby ensuring effective electrical insulation, mechanical protection, and / or protection against chemical reagents.

[0075] Overall, in this case, with the aid of the method described herein and the ultrasonic welding apparatus 1 that can be used for this purpose, the electrical connection between the flexible printed circuit board 3 and any desired metal element 5 can be significantly simplified, reliably configured, and / or cost-effective.

[0076] Finally, it should be noted that terms such as "having" or "comprising" do not exclude other elements or steps, and terms such as "a" or "an" do not exclude multiple. Furthermore, it should be noted that the features or steps described with reference to any of the exemplary embodiments described above may also be used in combination with other features or steps of the other exemplary embodiments described above. Reference numerals in the claims should not be considered limiting.

[0077] List of reference numerals

[0078] 1. Ultrasonic welding device

[0079] 3 Flexible Printed Circuit Board (FPC) 5 Metal Components

[0080] 7 Connecting Area

[0081] 9. Film substrate

[0082] 11 Metal Layer

[0083] 13 Ultrasonic welding head

[0084] 15 Weld head surface

[0085] 17. Direction of bending vibration

[0086] 19 Surface Texture

[0087] 21. Substrate thickness

[0088] 23 Texture Depth

[0089] 25 textured protrusions

[0090] 27 Support element

[0091] 29 Bending Oscillator

[0092] 31 Sensor System

[0093] 33 Actuator System

[0094] 35 Controller 37 Film Substrate

Claims

1. A method for electrically connecting a flexible printed circuit board (3) to a metal component (5) by ultrasonic welding, The flexible printed circuit board (3) has an electrically insulating film substrate (9) and a metal layer (11) coated on the substrate (9) in the connection area (7); The method includes: The connection area (7) of the flexible printed circuit board (3) is applied to the metal element (5) such that the metal layer (11) is arranged to be in mechanical contact with the metal element (5); An ultrasonic welding head (13) is applied to the connection area (7) of the flexible printed circuit board (3) such that the surface (15) of the welding head is arranged to make mechanical contact with the film substrate (9); Ultrasonic vibrations are generated on the surface (15) of the welding head.

2. The method according to claim 1, The ultrasonic vibrations are generated at a frequency of 25 kHz or higher.

3. The method according to any one of the preceding claims, The ultrasonic welding head (13) is configured as a bending oscillator (29).

4. The method according to any one of the preceding claims, The welding head surface (15) has a surface texture (19), and the surface texture (19) has a texture depth (23) of less than 0.4 mm.

5. The method according to claim 4, The surface texture (19) is rounded on the texture protrusions (25) protruding toward the film substrate (9) such that the radius of curvature is greater than 20% of the layer thickness (21) of the film substrate (9).

6. The method according to any one of the preceding claims, The welding head surface (15) has a strength of less than 15 N / mm. 2 The pressure is pressed onto the film substrate (9).

7. The method according to any one of the preceding claims, The metal element (5) is supported only on the side opposite to the film substrate (9) by a non-metallic support element (27).

8. The method according to any one of the preceding claims, Different ultrasonic welding conditions are generated during a continuous time phase during which ultrasonic vibrations are produced.

9. The method according to any one of the preceding claims, The film substrate (9) has a layer thickness (21) of 5 μm to 300 μm; and / or The film substrate (9) therein has a material selected from the group consisting of: polyimide, polyethylene terephthalate, and polyethylene naphthalate.

10. The method according to any one of the preceding claims, wherein the metal layer (11) has a layer thickness of 10 μm to 100 μm; and / or The metal layer (11) therein comprises copper.

11. The method according to any one of the preceding claims, The metal element (5) has a layer thickness of 0.1 mm to 10 mm; and / or The metal element (5) mentioned therein includes aluminum.

12. An ultrasonic welding apparatus (1) for electrically connecting a flexible printed circuit board (3) to a metal component (5) by ultrasonic welding, comprising: An ultrasonic welding head (13) having a welding head surface (15); The ultrasonic welding head (13) is designed as a bending oscillator (29) and configured to generate ultrasonic vibrations with a frequency of 25 kHz or higher at the surface (15) of the welding head; and The welding head surface (15) has a surface texture (19), and the surface texture (19) has a texture depth (23) of less than 0.4 mm.

13. The ultrasonic welding apparatus (1) according to claim 12, The ultrasonic welding device (1) is configured to be limited to 15 N / mm. 2 The following pressure presses the ultrasonic welding head (13) onto the flexible printed circuit board (3) with its welding head surface (15).

14. The ultrasonic welding apparatus (1) according to any one of claims 12 and 13, The ultrasonic welding apparatus is equipped with a servo press for moving and / or pressing the ultrasonic welding head.

15. The ultrasonic welding apparatus (1) according to any one of claims 12 to 14, The ultrasonic welding apparatus (1) is configured to generate different ultrasonic welding conditions during a continuous time phase during the generation of ultrasonic vibrations.

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