METHOD FOR MICROWELDING FLEXIBLE THIN FILMS, FOR EXAMPLE FOR USE IN ELECTRICAL AND ELECTRONIC DEVICES

Abstract

A method for welding a flexible film (10) to a carrier component (20) having the following steps: 1) pressing the film (10) on the carrier component (20) by a volumetric flow of a fluid, and 2) laser welding the film (10) on the carrier component (20).

Claims

1. A method for welding a flexible film (10) to a carrier component (20), having the following steps: 1) pressing the film (10) on the carrier component (20) by a volumetric flow of a fluid, and 2) laser welding the film (10) on the carrier component (20).

2. The method according to claim 1, characterized in that, in step 1), the fluid is a pressurized fluid, and/or in that, in step 1), the volumetric flow is produced by a nozzle or a nozzle comb.

3. The method according to claim 1, characterized in that, in step 2), a laser radiation in the visible wavelength range, or an NIR laser radiation is used, and/or in that, in step 2), a pulsed laser radiation, a quasi CW laser radiation or a CW laser radiation is used.

4. The method according to claim 1, characterized in that, in step 2), a laser radiation with at least one of the following parameters is used: a wavelength of 500 nm-600 nm, a focus diameter of 20 μm-1 mm, a power output of 1 W-4000 W, a pulse duration of 0.3 ms-50 ms, a scanning rate of 1 mm/s-1 km/s.

5. The method according to claim 1, characterized in that, in step 2), a laser radiation, in particular a pulsed laser radiation, with at least one of the following parameters is used: a wavelength of 1030 nm-1064 nm, a focus diameter of 10 μm-500 μm, a power output of 1 W-2000 W, a frequency of 1 Hz-2000 kHz, pulse duration of: 1 ns-500 ns, a scanning rate of: 1 mm/s-1 km/s.

6. The method according to claim 1, characterized in that, before step 1), a pre-deforming of the film (10) is performed.

7. The method according to claim 1, characterized in that, after step 2), a testing of a weld seam (N) for conductivity, resistance and/or impedance is performed.

8. The method according to claim 1, characterized in that the method is used for welding multiple flexible films (10) to multiple carrier components (20) in the same pass, and/or in that the method is used for welding a flexible film (10) of metal or plastic to a carrier component (20) of metal or plastic.

9. The method according to claim 1, characterized in that the method is used for welding thin metallic traces to electrical carrier components in electronic devices, microprinted components, sensor devices, electrochemical energy converters, or fuel cells.

10. The method according to claim 1, characterized in that the method is used for welding a flexible film (10) in the form of a flexible trace embedded within a flexible circuit board (FPC) to an electrical carrier component (20) in the form of a landing on a rigid circuit board (PCB), and/or in that the method is used for welding a flexible film (10) of a layer thickness of 20 μm-100 μm, to an electrical carrier component (20) of a thickness of 50 μm-500 μm.

11. The method according to claim 2, characterized in that the pressurized fluid is in the form of compressed air, nitrogen and/or shielding gas.

12. The method according to claim 3, characterized in that the laser in the visible wavelength range is in the green wavelength range and/or in the blue wavelength range.

13. The method according to claim 4, characterized in that the laser radiation is a quasi CW laser radiation, with at least one of the following parameters: a wavelength of 515 nm, a focus diameter of 150 μm, a power output of 1 200 W-600 W, a pulse duration of 2 ms-6 ms, a scanning rate of 200 mm/s-300 mm/s.

14. The method according to claim 5, characterized in that the laser radiation is a pulsed laser radiation, with at least one of the following parameters: a wavelength of 1030 nm-1064 nm, a focus diameter of 20 μm-200 μm, a power output of 10 W-500 W, a frequency of 1000 Hz-2000 Hz, a pulse duration of: 120 ns-500 ns, a scanning rate of: 10 mm/s-1000 mm/s.

15. The method according to claim 14, characterized in that the laser radiation is a pulsed laser radiation, with at least one of the following parameters: a power output of 20 W-100 W a scanning rate of: 10 mm/s-100 mm/s.

16. The method according to claim 8, characterized in that the metal is copper.

17. The method according to claim 9, characterized in that the electrochemical energy converters are batteries.

18. The method according to claim 10, characterized in that the method is used for welding a flexible film (10) of a layer thickness of 35 μm, to an electrical carrier component (20) of a thickness of 50 μm-140 μm.

19. The method according to claim 18, characterized in that the method is used for welding a flexible film (10) of a layer thickness of 35 μm, to an electrical carrier component (20) of a thickness of 135 μm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The invention and developments thereof as well as advantages thereof are explained in more detail below on the basis of drawings, in which schematically:

[0048] FIG. 1 shows a representation by way of example of the elements to be connected within the context of the invention,

[0049] FIG. 2 shows a representation by way of example of a first method step within the context of the invention,

[0050] FIG. 3 shows a representation by way of example of a second method step within the context of the invention,

[0051] FIG. 4 shows a representation by way of example of an optional preparation method step within the context of the invention,

[0052] FIG. 5 shows a representation by way of example of an elastic film within the context of the invention,

[0053] FIG. 6 shows a representation by way of example of a carrier component within the context of the invention,

[0054] FIG. 7 shows an absorption diagram of a laser radiation for copper,

[0055] FIG. 8 shows an example of a weld seam within the context of the invention, and

[0056] FIG. 9 shows a further example of a weld seam within the context of the invention.

DETAILED DESCRIPTION

[0057] In the various figures, the same parts of the invention are always provided with the same designations, for which reason they are generally only described once.

[0058] FIGS. 1 to 4 are intended to serve the purpose of illustrating a method according to the invention for welding a flexible film 10 to a carrier component 20.

[0059] FIGS. 1 to 4 show a basic construction for carrying out the method according to the invention.

[0060] FIGS. 1 to 4 show a possible film 10 within the context of the invention, which may be configured in the form of a flexible trace embedded within a flexible circuit board (flexible-printed circuit or FPC for short).

[0061] FIG. 5 shows hereafter a flexible circuit board FPC with multiple embedded flexible traces as possible flexible films 10 within the context of the invention. In this case, each flexible trace may be formed from copper Cu and have a thickness or layer thickness of 20 μm-100 μm, in particular 35 μm. The surfaces of the recessed flexible traces may be configured in a chemically tinned or untinned manner. According to FIG. 5, the flexible circuit board FPC may have the following construction: [0062] base film 25 μm, polyamide; [0063] adhesive 28 μm; [0064] signal layer 35/70 μm Cu, chem. Sn; [0065] adhesive 60 μm; [0066] top film 25 μm, polyamide.

[0067] Furthermore, FIGS. 1 to 4 show a possible carrier component 20 in the form of an electrical carrier component 20, in particular in the form of a landing on a rigid circuit board (printed-circuit board or PCB for short).

[0068] FIG. 6 shows hereafter multiple electrical carrier components 20 in the form of multiple landings on a rigid circuit board PCB. The carrier components 20 (known as landings) may have thicknesses of 50 μm-500 μm, for example 50 μm-140 μm, in particular 135 μm. Of this, about 30 μm-120 μm may be attributable to the Cu base layer itself and about 20 μm respectively to an electrodeposited Cu layer (see the dashed separating line T given by way of example in the lower sectional representation of FIG. 6). The landing surface may be chemically tinned, but may also be configured in an untinned manner.

[0069] It is conceivable however that the method according to the invention can be used for the contacting of thin metallic traces with respect to electronic devices of all kinds, such as for example microprinted components, sensor devices, electrochemical energy converters, in particular batteries or fuel cells.

[0070] FIG. 2 shows the first step of the method according to the invention:

[0071] pressing the film 10 on the carrier component 20 by a volumetric flow of a fluid.

[0072] A pressurized fluid, preferably in the form of compressed air, nitrogen or shielding gas (Ar, He, CO2, . . . ), etc. may be used here as the fluid.

[0073] FIG. 3 shows the second step of the method according to the invention:

[0074] laser welding the film 10 on the carrier component 20.

[0075] A heat conduction welding or a welding process close to the deep welding threshold of the elements to be connected 10, 20 (films 10 and carrier components 20) may for example be used as laser welding within the context of the invention.

[0076] FIG. 4 also shows that, before step 1), a pre-deforming, in particular trench-shaped pre-deforming, of the film 10 can be carried out by an embossing punch S and a negative mold M for the deliberate overstretching of the film 10, for example by means of microdeforming and/or deep drawing.

[0077] FIG. 7 shows by means of a diagram the absorption rate of laser radiation of different wavelengths in copper Cu, in particular for green laser radiation and for NIR laser radiation. It is evident from FIG. 7 that, by using green laser radiation, the degree of absorption in copper Cu increases by 35% in contrast with working copper Cu with classic laser beam sources in the near infrared range NIR. Therefore, the use of green laser radiation makes the microwelding of Cu connections possible.

[0078] The green laser radiation, in particular in the form of quasi CW laser radiation, that is used in step 2) of the method according to the invention may have at least one of the following parameters and/or properties: [0079] wavelength: 500 nm-600 nm, specifically 515 nm, [0080] focus diameter: 20 μm-1 mm, specifically 150 μm, [0081] focal position: z=0 mm to z=+/−2 zR, specifically z=+/−1 zR, [0082] power output: 1 W-4000 W, specifically 200 W-600 W, [0083] pulse duration: 0.3 ms-50 ms, specifically 2 ms-6 ms, [0084] pulse shape: rectangle, ramp(s), [0085] scanning rate: 1 mm/s-1 km/s, specifically 200 mm/s-300 mm/s, [0086] scanner equipment: 2D galvoscanner, 1D/2D polygon scanner, [0087] length of the weld seam: 0.1 mm-5 mm, specifically 0.5 mm, [0088] geometry of the weld seam: circle with a diameter of 0.1 mm-10 mm, specifically 0.1 mm-0.4 mm or line with a length of 0.1 mm-5 mm, specifically 0.5 mm.

[0089] FIG. 8 shows a circular weld seam, which can be created by means of the green laser radiation, in particular in the form of quasi CW laser radiation. The welding process between the flexible circuit board FPC and a rigid circuit board PCB according to FIG. 8 may be carried out within one laser pulse. Within the scope of the invention, this laser pulse may have a duration of about 2 ms-5 ms. In this time, the laser beam in the form of a circle or in the form of lines is passed over the surface of the flexible circuit board FPC on a rigid circuit board PCB (known as long pulse welding or quasi CW welding). Consequently, annular or linear microwelded seams with a seam length s are created during a pulse. The depth of the weld seam can be advantageously controlled by what is known as the energy input per unit length L (quotient of laser power output & traversing speed).

[00001]$L=\frac{\mathrm{power}.Math..Math.\mathrm{output}.Math..Math.P}{\mathrm{speed}.Math..Math.v}\left[\frac{\mathrm{Ws}}{m}=\frac{J}{m}\right]$

[0090] In a certain process regime (dependent on Cu/Sn layer thicknesses of the flexible circuit boards FPCs and the rigid circuit boards PCBs), with a constant working speed and laser focus area, the welding-in-depth increases with increasing laser power output, without the elements 10, 20 that are to be connected being damaged.

[0091] FIG. 9 shows multiple linear weld seams which can be created by means of the NIR laser radiation, in particular in the form of pulsed laser radiation. By using pulsed NIR laser radiation, energy/heat can be deposited in the material in spite of a low degree of absorption, since the pulsed NIR laser radiation has a small focus diameter and the resultant high intensity causes a deep welding effect. By the use of pulsed NIR laser radiation, the microwelding within the context of the invention of Cu connections therefore likewise becomes possible.

[0092] The NIR laser radiation, in particular in the form of pulsed laser radiation, that is used in step 2) of the method according to the invention may have at least one of the following parameters and/or properties: [0093] laser focus diameter 10 μm-500 μm, specifically 20 μm-200 μm, [0094] wavelength: 1030 nm-1064 nm; [0095] power output: 1 W-2000 W, specifically 10 W-500 W, specifically 20 W-100 W; [0096] rep. rate: 1 Hz-2000 kHz, specifically 1000 Hz-2000 Hz; [0097] pulse duration: 1 ns-500 ns, specifically 120 ns-500 ns; [0098] geometry: lines (0.4 mm length, 100 μm hatch, others conceivable); [0099] scanning rate: 1 mm/s-1 km/s, specifically 10 mm/s-1000 mm/s, specifically 10 mm/s-100 mm/s; [0100] scanner equipment: 2D galvanoscanner, 1D/2D polygon scanner.

[0101] The welding process between the flexible circuit board FPC and a rigid circuit board PCB according to FIG. 9 can be carried out by means of a multiplicity of laser pulses. A single laser pulse may in this case have a typical duration of about 120 ns (possibly longer pulses of up to 500 ns are conceivable). Within the welding time, the laser beam in the form of lines is passed over the surface of the flexible circuit board FPC on a rigid circuit board PCB. Consequently, multiple linear microwelded seams with the seam length s, consisting of a multiplicity of pulses, are created. The heat input into the material that is required for the welding process may be controlled by what is known as heat accumulation of individual laser pulses, whereby an average heating ΔT is obtained.

[00002]$\Delta .Math.T=\left(1-R\right).Math.\frac{2.Math.I_0}{\lambda }.Math.v_{\mathrm{rep}}.Math.\tau .Math.\sqrt{\alpha .Math.t}.Math.i.Math..Math.\mathrm{erfc}\left(\frac{z}{\sqrt{4.Math.\alpha .Math.t}}\right)$$i..Math.\stackrel{}{.Math.\frac{1}{\sqrt{\pi }}.Math..Math.\mathrm{for}.Math..Math.z=0}$

[0102] In the center of the laser beam, the material is vaporized, along the lateral surface of the deposition there forms the weld seam. Tin Sn can thereby melt, and in thin marginal zones so can copper Cu.

[0103] In addition, it is conceivable that the method according to the invention can be extended to the attachment of nonmetallic films (for example of plastic) to metallic or nonmetallic carrier materials (for example for the packaging industry, medical technology, sensors, etc.) by means of the use of a laser radiation with a low beam quality (for example by means of a diode laser).

[0104] The above description of the figures describes the present invention exclusively by way of examples. It goes without saying that it is possible for individual features of the embodiments to be freely combined with one another, where technically expedient, without departing from the scope of the invention.