Flexible circuit board pre-contact by means of ultrasound for subsequent laser radiation welding

Abstract

The invention relates to a method for welding a flexible film (10) to a carrier part (20), comprising the following steps: 1) pre-contacting the film (10) on the carrier part (20) by means of ultrasound, 2) laser welding the film (10) on the carrier part (20).

Description

Technical Field

[0001] The invention relates to a method for welding a flexible film to a carrier part. Background Art

[0002] Laser welding of metal films (e.g. FPC, English: flexible printed circuit) to substrates requires a suitable clamping solution that ensures an admissible gap height between the bonding pairs. In this case, mechanical solutions are usually used, such as the use of clamping hoods. In addition, clamping methods with the aid of pneumatic devices and clamping methods using force control of gravity are also known. All of these solutions require mechanical pretreatment, which causes the conductor circuits of the flexible circuit board to undergo plastic deformation in the welding area, thereby producing a defined embossing geometry. Summary of the invention

[0003] The invention provides a method for welding a flexible film to a carrier part having the features of the independent method claim. Further advantages, features and details of the invention are derived from the dependent claims, the description and the drawings. Here, features and details described in different claims with respect to embodiments of the invention naturally also apply to other claims of the same embodiment and vice versa, so that the disclosure of the various aspects of the invention always refers to each other or can refer to each other.

[0004] The present invention provides a method for welding (joining or material-locking connection) a flexible film to a carrier component (or substrate), the method comprising the following steps:

[0005] 1) pre-contacting the film on a carrier member by means of ultrasound,

[0006] 2) Laser welding the film to the carrier component.

[0007] The method can be used to weld flexible films with layer thicknesses in the micrometer range. In other words, the method can be referred to as a micro-welding method. As laser welding, heat conduction welding or welding processes close to the deep welding threshold of the elements to be connected (film and carrier part) can preferably be used.

[0008] A flexible film can be understood as a film made of metal, such as copper, silver, gold or the like, or plastic, with a layer thickness in the micrometer range, in particular between 20 μm and 100 μm, preferably 35 μm. A flexible film can be understood as a flexible conductor track embedded in a flexible circuit board, a so-called flexible printed circuit board or FPC for short, for example.

[0009] A carrier component can be understood as a carrier component made of metal, for example copper or a copper alloy, ceramic or plastic, with a layer thickness in the micrometer range. A carrier component made of metal, for example copper or a copper alloy, can have a layer thickness of 5-500 μm, preferably 300-500 μm. A carrier component made of ceramic can have a layer thickness of 100-1000 μm, preferably 300-700 μm. For example, an electrical carrier component in the form of pads (landings) on, for example, a rigid circuit board, a so-called printed circuit board or PCB for short, can be used as a carrier component. A carrier component can be understood as an electrical carrier component in the form of, for example, DBC (English: directly bonded copper) or AMB (English: active metal brazed copper).

[0010] The method advantageously enables the elimination of mechanical pretreatment of the flexible printed circuit board and the elimination of clamping solutions. For this purpose, the invention proposes the use of an ultrasonic process before laser radiation welding. This process is not a joining process in the true sense. Here, an ultrasonic tool or an ultrasonic oscillation unit is preferably used without a wire guide or a belt guide to introduce energy into the joining zone by means of ultrasound. Then, a material-locking connection between the film and the substrate is produced in the pre-contact zone by means of laser radiation.

[0011] This approach offers several advantages:

[0012] - Robust pre-contacting of flexible circuit boards even with large component tolerances,

[0013] - The elimination of mechanical pre-processing (e.g. embossing) and complex clamping technology has the potential for cost savings,

[0014] - Ultrasound can be applied with the aid of an inexpensive ultrasonic machine or ultrasonic oscillator,

[0015] - reliable and reproducible operation of the pre-contact as welding preparation, for which the ultrasonic tool can be tactilely placed against the component,

[0016] - the requirements for the ultrasonic welding process are advantageously low, since the contact does not have to meet any requirements for the service life of the product,

[0017] - Especially compared to pure ultrasonic welding, the advantages of laser radiation welding can be fully utilized, such as:

[0018] ○The requirements for surface cleanliness are relatively low.

[0019] ○ The requirements for surface roughness are relatively low (Rz<=15μm, Rmax<=25μm),

[0020] ○Can weld a wide variety of substrate materials, such as: Cu, CuSn0.15, CuNiSi, CuSn6, FeNi36, Ag, Au...,

[0021] ○Multiple coatings can be applied on substrate / flexible film, such as: Ag, Au, Sn, ENiG...,

[0022] ○The requirements for surface oxidation state are relatively low.

[0023] ○Reliable, material-locked connections with a long service life, etc.

[0024] Furthermore, the method for welding the flexible film to the carrier part can provide that in step 1), the film is contacted by means of an ultrasonic oscillator. In this way, the film can be held in place. Thus, a reliable and reproducible pre-contact can be achieved as a welding preparation.

[0025] Furthermore, the method for welding the flexible film to the carrier part can provide that in step 1), thermal energy is introduced into the joining region between the film and the carrier part by means of ultrasound. Thus, a reliable material-locking pre-contact can be achieved as a welding preparation.

[0026] Advantageously, the method can be carried out for welding components with a low surface roughness, for example components with a surface roughness below 25 μm, in particular below 15 μm. Thus, the advantages of laser radiation welding can be fully utilized in the second step. In this way, even very thin and / or smooth films with very smooth surfaces can be reliably connected to one another.

[0027] In principle, it is conceivable that the carrier part can include one of the following materials: copper (Cu), copper alloys (CuSn0.15, CuNiSi, CuSn6), iron-nickel alloys (FeNi36), silver (Ag), gold (Au), etc. It is also conceivable that the film can include one of the following materials: copper (Cu), silver (Ag), gold (Au), tin (Sn) and / or immersion nickel gold (ENiG), etc.

[0028] In step 2), laser radiation can be used, for example pulsed laser radiation, quasi-CW laser radiation or CW laser radiation.

[0029] It is also conceivable that the method can be extended to the connection of non-metallic films (e.g. made of plastic) to metallic or non-metallic carrier materials (e.g. for the packaging industry, medical technology, sensors, etc.) by using laser radiation with low radiation quality (e.g. with the aid of a diode laser).

[0030] In principle, the method can be used for contacting thin metal conductor circuits with any kind of electronic device. For example, the method can be used for contacting conductor bridges in micro-printed components, for example in the construction of MEMS devices, for example by combining the laser induced forward transfer method (LIFT) with the proposed ultrasound step. The method can also be used in battery management systems (for example in lithium-ion batteries), specifically for contacting thin metal flat conductors with circuit boards (for example in battery cell voltage monitoring, for example for voltage taps). The method can also be used for contacting thin current carrier films or plates with terminals of battery cells (for example round battery cells in lithium-ion batteries).

[0031] Furthermore, the method for welding the flexible film to the carrier part can be provided that laser radiation or NIR laser radiation in the visible wavelength range, preferably in the green wavelength range (approximately 490 nm-560 nm) and / or in the blue wavelength range (approximately 380 nm-480 nm) is used in step 2). Laser radiation in the green wavelength range and in part in the blue wavelength range has proven to be advantageous for achieving heat conduction welding of the elements to be connected (film and carrier part), even without tinning. NIR laser radiation enables welding processes close to the deep welding threshold of the elements to be connected. It is thus possible to join or connect elements at the contour of the weld seam.

[0032] Furthermore, the method for welding a flexible film to a carrier component can be provided that pulsed laser radiation, quasi-CW laser radiation or CW laser radiation is used in step 2). Pulsed laser radiation can provide peak power within the pulse. In the case of using NIR laser radiation, pulsed laser radiation can be advantageous for achieving sufficient adhesion between components along the contour of a plurality of, for example, spot-shaped welds. In addition to a narrow spectrum, quasi-CW laser radiation also enables the application of peak power. In the case of using green and blue laser radiation, quasi-CW laser radiation can be advantageous. CW laser radiation enables precise adjustment of the welding depth.

[0033] Furthermore, the method for welding a flexible film to a carrier part can provide that, in step 2), a 2D galvo scanner, a 1D / 2D polygon scanner or a diode laser is used to generate the laser radiation. 2D galvo scanners and 1D / 2D polygon scanners can be advantageous for producing the weld seam and also for checking or scanning the weld seam. Diode lasers can be advantageous for providing laser radiation with low radiation quality, which can be advantageous for welding non-metallic films (e.g. made of plastic) to metallic or non-metallic carrier parts, for example in the packaging industry, medical technology or sensors.

[0034] Furthermore, the method for welding a flexible film to a carrier part can provide that in step 2) a weld seam with an adjustable depth is produced. Since the depth can be adjusted, the method can be flexibly adapted to films of different thicknesses. In some cases, the adjustable depth can even dispense with an auxiliary coating of the elements to be connected, for example tinning. In particular, the heat conduction can be adjusted in such a way that the material of the carrier part is heated sufficiently in the desired weld seam region to form a material-locking connection with the film, but without damaging or even tearing the film.

[0035] Furthermore, the method for welding the flexible film to the carrier part can provide that in step 2) heat conduction welding or a process close to the deep welding threshold for the carrier part is used. In this way, the method can achieve welding of thin metal elements as reliably as possible and at the same time process thinner elements to be connected gently. In addition, no spatter is generated during heat conduction welding, which is advantageous for electronic components.

[0036] Furthermore, the method for welding a flexible film to a carrier part can provide that in step 2), laser radiation, in particular quasi-CW laser radiation, is used, which has at least one of the following parameters:

[0037] -500nm-600nm, especially 515nm wavelength,

[0038] - a focal spot diameter of 20 μm-1 mm, in particular 150 μm,

[0039] -1W-4000W, especially 200W-600W power,

[0040] -0.3ms-50ms, especially 2ms-6ms pulse duration,

[0041] - A scanning speed of 1 mm / s to 1 km / s, in particular 200 mm / s to 300 mm / s.

[0042] The conductor tracks are usually made of copper. The use of such preferably green laser radiation increases the absorption in the copper components (film and carrier part) by at least 35% compared to the processing of copper using conventional laser radiation sources, for example in the near infrared range. The use of such laser radiation thus makes it possible to carry out heat conduction welding of copper components, for example by means of green quasi-CW laser radiation, even without an auxiliary coating made of tin. Thus, thinner copper components can be micro-welded in this way.

[0043] It is also conceivable to produce a circular weld seam preferably with a diameter of 0.1 mm to 10 mm, in particular 0.1 mm to 0.4 mm, or a linear weld seam in step 2). It is also conceivable to produce a weld seam with a length of 0.1 mm to 5 mm, in particular 0.5 mm, in step 2). Such a weld seam allows a gentle and reliable connection of the film to the carrier part.

[0044] Furthermore, the method for welding a flexible film to a carrier part can provide that in step 2), laser radiation, in particular pulsed laser radiation, is used, which has at least one of the following parameters:

[0045] - Wavelength of 1030nm-1064nm,

[0046] - a focal spot diameter of 10 μm to 500 μm, in particular 20 μm to 200 μm,

[0047] - a power of 1 W to 2000 W, in particular 10 W to 500 W, preferably 20 W to 100 W,

[0048] -1Hz-2000kHz, especially 1000Hz-2000Hz,

[0049] -1ns-500ns, especially 120ns-500ns pulse duration,

[0050] - a scanning speed of 1 mm / s to 1 km / s, in particular 10 mm / s to 1000 mm / s, in particular 10 mm / s to 100 mm / s,

[0051] and / or in step 2) a linear weld seam or a plurality of linear weld seams, in particular parallel, is produced,

[0052] And / or in step 2) a weld seam having a length of 0.1 mm to 5 mm, in particular 0.4 mm, is produced.

[0053] The use of such laser radiation, preferably NIR laser radiation, for example pulsed laser radiation, makes it possible to weld copper components at the weld seam edge.

[0054] Furthermore, the method for welding a flexible film to a carrier part can provide that after step 2), the weld seam (N) is tested, in particular optically, for conductivity, resistance and / or impedance, wherein in particular re-welding can be performed based on this test. In this way, the scrap rate of the finished product can be significantly reduced.

[0055] Furthermore, it can be provided that the method is used to solder a plurality of flexible films to a plurality of carrier parts in the same operation, so that a plurality of functional components can be connected simultaneously to corresponding carrier parts, for example on a circuit board.

[0056] It is also conceivable that the method is used to weld a flexible film made of metal or plastic to a carrier part made of metal or plastic. In this way, the field of application of the method can be advantageously expanded.

[0057] It is also conceivable that the method can be used in electronic devices, microprinted components, sensor devices, electrochemical energy converters, in particular batteries or fuel cells, for soldering thin metallic conductor tracks to electrical carrier components, for example in the form of solder pads on a circuit board.

[0058] Advantageously, the method can be used to solder a flexible film in the form of a flexible conductor track embedded in a flexible circuit board to an electrical carrier component in the form of a soldering pad on a rigid circuit board. In particular, the method can be used to solder a flexible film with a layer thickness of 20 μm-100 μm, in particular 35 μm, to an electrical carrier component (20) with a thickness of 5 μm-500 μm, 300 μm-500 μm. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] The present invention and its improved solutions and advantages are described in detail below with reference to the accompanying drawings, wherein the corresponding schematic diagrams are shown:

[0060] Figure 1 An exemplary clamping method is shown;

[0061] Figure 2 Additional exemplary clamping methods are shown;

[0062] Figure 3 An exemplary pre-processing is shown; and

[0063] Figure 4 An exemplary sequence of a method within the meaning of the present invention is shown.

[0064] Figures 1 to 3 Used to explain the basis of the present invention. DETAILED DESCRIPTION

[0065] like Figure 1 and Figure 2 As shown, according to the prior art, laser radiation welding of a metal film (such as FPC, English: flexible printed circuit) to a substrate requires a suitable clamping solution 1*). Figure 1 As shown by way of example, a clamping cap 30 can be used for this purpose, for example. Figure 2 As shown, a clamping method 1*) with the aid of a pneumatic device 40 and a force-controlled clamping method 1*) utilizing gravity using a guide 50 and a counterweight 51 are conceivable. Figure 3As shown, all these clamping methods require a mechanical pretreatment 2*) which plastically deforms the conductor tracks of the flexible printed circuit board in the soldering area, so that a defined embossing geometry is produced.

[0066] With the help of Figure 4 Explain the present invention.

[0067] The present invention provides a method for welding (joining or material-locking connection) a flexible film 10 to a carrier component 20 (or a substrate), the method comprising the following steps:

[0068] 1) pre-contacting the film 10 on the carrier part 20 by means of ultrasound,

[0069] 2) Laser welding the film 10 to the carrier component 20 .

[0070] The method can be used to weld flexible films 10 with layer thicknesses in the micrometer range. In other words, the method can be referred to as a micro-welding method. As laser welding, heat conduction welding or welding processes close to the deep welding threshold of the elements to be connected (film 10 and carrier part 20) can preferably be used.

[0071] The flexible film 10 can be understood as a film made of metal, such as copper, silver, gold or the like, or plastic, with a layer thickness in the micrometer range, in particular between 20 μm and 100 μm, preferably 35 μm. The flexible film 10 can be understood as a flexible conductor track embedded in a flexible circuit board, a so-called flexible printed circuit board or FPC for short.

[0072] A carrier part can be understood as a carrier part made of metal, for example copper or a copper alloy, ceramic or plastic, with a layer thickness in the micrometer range. A carrier part made of metal, for example copper or a copper alloy, can have a layer thickness of 5-500 μm, preferably between 300-500 μm. A carrier part made of ceramic can have a layer thickness of 100-1000 μm, preferably between 300-700 μm.

[0073] For example, an electrical carrier component in the form of a soldering pad on a rigid circuit board, a so-called printed circuit board or PCB for short, can be used as a carrier component. A carrier component can be understood to be, for example, an electrical carrier component in the form of a DBC (English: direct bonded copper) or an AMB (English: active metal brazed copper).

[0074] This method advantageously makes it possible to dispense with mechanical pretreatment 2*) of the flexible printed circuit board and to dispense with clamping concepts 1*).

[0075] The invention proposes to use an ultrasonic process 1) before the laser radiation welding 2). In this case, an ultrasonic tool or ultrasonic oscillation unit 11 is preferably used without a wire guide or a belt guide to introduce energy into the joining region 12 by means of ultrasound. Then, a material-locking connection 22 or a weld seam between the film 10 and the carrier part 20 is produced in the pre-contact region or joining region 12 by means of laser radiation 21. This Figure 4 It is schematically shown in FIG.

[0076] This approach offers several advantages:

[0077] - Robust pre-contacting of flexible circuit boards even with large component tolerances,

[0078] - No mechanical pre-treatment (e.g. embossing, see Figure 3 ) and complex clamping technology (see Figure 1 and Figure 2 ),

[0079] - Save costs,

[0080] - the ultrasound can be applied by means of an inexpensive ultrasound machine or ultrasound oscillation unit 11,

[0081] - reliable and reproducible operation of the pre-contact as welding preparation, for which the ultrasonic tool can be tactilely placed against the component,

[0082] - the requirements for the ultrasonic welding process are advantageously low, since the contact does not have to meet any requirements for the service life of the product,

[0083] - Especially compared to pure ultrasonic welding, the advantages of laser radiation welding can be fully utilized, such as:

[0084] ○The requirements for surface cleanliness are relatively low.

[0085] ○ The requirements for surface roughness are relatively low (Rz<=15μm, Rmax<=25μm),

[0086] ○Can weld a wide variety of substrate materials, such as: Cu, CuSn0.15, CuNiSi, CuSn6, FeNi36, Ag, Au...,

[0087] ○Multiple coatings can be applied on substrate / flexible film, such as: Ag, Au, Sn, ENiG...,

[0088] ○The requirements for surface oxidation state are relatively low.

[0089] ○Reliable, material-locked connections with a long service life, etc.

[0090] like Figure 4As shown, in step 1), the film 10 can be contacted by means of the sonotrode 11. In this way, the film 10 can be held in position. Thus, a reliable and reproducible pre-contact can be achieved in the joining region 12 as a welding preparation.

[0091] also Figure 4 It is shown that in step 1), thermal energy is introduced into the joining region 12 between the film 10 and the carrier part 20. As a welding preparation, a reliable material-locking preliminary contact can thus be achieved.

[0092] The method can be carried out for welding components with low surface roughness, for example components with a surface roughness below 25 μm, in particular below 15 μm. Thus, the advantages of laser radiation welding can be fully utilized in the second step 2). In this way, even very thin and / or smooth films 10 with very smooth surfaces can be reliably connected to one another.

[0093] In step 2), laser radiation can be used, for example pulsed laser radiation, quasi-CW laser radiation or CW laser radiation.

[0094] The method can be extended to the joining of non-metallic films (eg made of plastic) to metallic or non-metallic carrier materials (eg for the packaging industry, medical technology, sensors, etc.) by using laser radiation with low radiation quality (eg by means of a diode laser).

[0095] In principle, the method can be used for contacting thin metal conductor circuits with any kind of electronic device. For example, the method can be used for contacting conductor bridges in micro-printed components, for example in the construction of MEMS devices, for example by combining the laser induced forward transfer method (LIFT) with the proposed ultrasound step. The method can also be used in battery management systems (for example in lithium-ion batteries), specifically for contacting thin metal flat conductors with circuit boards (for example in battery cell voltage monitoring, for example for voltage taps). The method can also be used for contacting thin current carrier films or plates with terminals of battery cells (for example round battery cells in lithium-ion batteries).

[0096] The preceding description of the figures describes the invention only within the scope of examples. Of course, individual features of the embodiments can be freely combined with one another, if technically meaningful, without departing from the scope of the invention.

Claims

1. A method for welding a flexible film (10) to a carrier component (20), the method comprising the following steps: 1) pre-contacting the film (10) on the carrier component (20) by means of ultrasound, 2) Laser welding the film (10) to the carrier component (20).

2. The method according to claim 1, It is characterized in that In step 1), the film (10) is contacted by means of an ultrasonic oscillation unit (11) and / or in step 1), thermal energy is introduced into the joining region (12) between the film (10) and the carrier part (20).

3. The method according to claim 1 or 2, It is characterized in that The method is carried out for welding components (10, 20) having a surface roughness of less than 25 μm, in particular less than 15 μm.

4. The method according to any one of the preceding claims, It is characterized in that The carrier part (20) can include one of the following materials: copper (Cu), a copper alloy (CuSn0.15, CuNiSi, CuSn6), an iron-nickel alloy (FeNi36), silver (Ag) and / or gold (Au). And / or the film (10) can include one of the following materials: copper (Cu), silver (Ag), gold (Au), tin (Sn) and / or immersion nickel gold (ENiG).

5. The method according to any one of the preceding claims, It is characterized in that In step 2), laser radiation, in particular quasi-CW laser radiation, is used, which has at least one of the following parameters: -500nm-600nm, especially 515nm wavelength, - a focal spot diameter of 20 μm-1 mm, in particular 150 μm, -1W-4000W, especially 200W-600W power, -0.3ms-50ms, especially 2ms-6ms pulse duration, - A scanning speed of 1 mm / s to 1 km / s, in particular 200 mm / s to 300 mm / s.

6. The method according to any one of the preceding claims 1 to 3, It is characterized in that In step 2), laser radiation, in particular pulsed laser radiation, is used, which has at least one of the following parameters: - Wavelength of 1030nm-1064nm, - a focal spot diameter of 10 μm to 500 μm, in particular 20 μm to 200 μm, - a power of 1 W to 2000 W, in particular 10 W to 500 W, preferably 20 W to 100 W, -1Hz-2000kHz, especially 1000Hz-2000Hz, -1ns-500ns, especially 120ns-500ns pulse duration, - A scanning speed of 1 mm / s to 1 km / s, in particular 10 mm / s to 1000 mm / s, in particular 10 mm / s to 100 mm / s.

7. The method according to any one of the preceding claims, It is characterized in that After step 2), the weld (N) is tested for conductivity, resistance and / or impedance.

8. The method according to any one of the preceding claims, It is characterized in that The method is used for welding a plurality of flexible films (10) to a plurality of carrier parts (20) in the same operation run, And / or the method is used for welding a flexible film (10) made of metal or plastic to a carrier part (20) made of metal or plastic.

9. The method according to any one of the preceding claims, It is characterized in that The method is used for welding thin metallic conductor tracks to electrical carrier components in electronic devices, microprinted components, sensor devices and / or electrochemical energy converters, in particular batteries or fuel cells.

10. The method according to any one of the preceding claims, It is characterized in that The method is used to solder a flexible film (10) in the form of a flexible conductor circuit embedded in a flexible printed circuit (FPC) to an electrical carrier component (20) in the form of a soldering pad on a rigid printed circuit board (PCB). And / or the method is used for welding a flexible film (10) having a layer thickness of 20 μm-100 μm, in particular 35 μm, to an electrical carrier component (20) having a thickness of 50 μm-500 μm, in particular 50 μm-140 μm, preferably 135 μm.

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