Capacitive touch screen ultra-fine difficult-to-weld metal wire welding method

Abstract

The application relates to the technical field of capacitive touch screen production, and particularly discloses a capacitive touch screen ultra-micro difficult-to-weld metal wire welding method, which comprises the following steps: S1, wiring base material preparation, the wiring base material being PET+OCA; S2, wiring equipment preparation, the wiring equipment being a precise wiring machine; S3, metal wire preparation, including difficult-to-weld metal wire and base metal wire; S4, base metal wire wiring; S5, difficult-to-weld metal wire wiring; S6, double-sided adhesive tape pasting; S7, shape laser; S8, tinned FPC pre-pasting; S9, welding preparation, using a laser welding machine; S10, welding; by introducing a base conductive metal capable of being combined with tin in good metallurgy as an intermediate bearing transition layer, atomic interdiffusion occurs after liquid tin contacts the base conductive metal, a tin-based intermetallic compound is generated, a high-strength metallurgical transition layer is formed, the ultra-micro difficult-to-weld metal is clamped between the base conductive metal and the tin metallurgical layer, the bonding force is improved, and the welding reliability is improved; the method is suitable for capacitive touch screens using ultra-micro difficult-to-weld metal wires.

Description

Technical Field

[0001] This invention relates to the field of capacitive touchscreen manufacturing technology, specifically to a method for welding ultra-micro and difficult-to-weld metal wires in capacitive touchscreens. Background Technology

[0002] In the production process of printed metal wire capacitive touch screens, ultra-micro diameter metal wires with a diameter of 2μm-30μm are required, such as tungsten wires, tungsten alloy wires, or other high-melting-point refractory metal wires, such as molybdenum, chromium, titanium, platinum, and their corresponding alloys. Tungsten wires and tungsten alloy wires, because their main component is tungsten metal, have relatively stable metallic properties and belong to high-melting-point refractory metals. They cannot form a stable metallurgical bond with tin. During laser welding, the ultra-micro diameter metal wires have extremely poor affinity with tin atoms and will not form a strong interface layer. These ultra-micro diameter metal wires are referred to as ultra-micro difficult-to-solder metal wires. In the existing technology, ultra-micro difficult-to-solder metal wires are usually first laid on an adhesive PET substrate using a wiring machine. Next, tin-plated FPC (flexible printed circuit board) is placed over ultra-fine, difficult-to-solder metal wires. A laser is then used to pass through the PET and adhesive to solder the tin to the ultra-fine, difficult-to-solder metal wires. This production and soldering process relies solely on the molten tin to form a physical contact with the ultra-fine, difficult-to-solder metal wires, and on adhesive bonding. The bonding strength is insufficient, posing a reliability risk for long-term use, and is prone to problems such as weak connections or even detachment. Other improvement methods include modifying the surface of the ultra-fine, difficult-to-solder metal wires or improving the composition of the tin. Both of these methods will change the characteristics of the metal wires or the tin itself. Extensive testing is required to determine the specific modification process while ensuring product performance, which requires a long research and development and verification cycle. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the technical problem solved by this invention is to provide a method for welding ultra-micro difficult-to-weld metal wires in capacitive touch screens, thereby solving the problem of insufficient welding bonding strength of ultra-micro difficult-to-weld metal wires in capacitive touch screens in existing technologies.

[0004] To solve the above problems, the technical solution adopted by the present invention is: a method for welding ultra-micro difficult-to-solder metal wires in a capacitive touch screen, comprising the following steps: S1. Preparation of wiring substrate: Use a cutting machine to cut the substrate according to the corresponding touch screen product size; S2. Preparation of wiring equipment: The wiring equipment is a precision wiring machine. The wiring size of the machine is larger than the size of the substrate. Before printing, check and adjust the diagonal running size of the equipment to 1:1 and set the origin of the machine. S3. Metal wire preparation, including difficult-to-solder metal wires and base metal wires; S4. Base metal wire wiring: Place the PET substrate on the precision wiring machine platform, assemble the base metal wire on the machine table, and pass the base metal wire through the printing needle. The outer diameter of the printing needle is 0.7mm and the inner diameter is 0.2mm. Check the smoothness of the needle. The wiring base metal wire is soldered on the substrate. Only the soldering position of the base metal wire is printed. The starting point of the base metal wire wiring is the origin coordinate point of the machine table. S5. Solderable metal wire wiring: After the base metal wire welding position wiring is completed, the machine replaces the solderable metal wire, checks the smoothness of the needle, and wires the solderable metal wire onto the base material. The solderable metal wire needs to be wired to the functional lines and welding positions of the entire product. The soldering position of the solderable metal wire needs to be wired to cover the base metal wire. S6. Apply double-sided tape. After confirming that the difficult-to-weld metal wires cover the base metal wires, use a flip-type laminating machine to accurately apply the double-sided tape to the substrate after the metal wires are laid. Before applying the double-sided tape, use double-sided release film to stick on the welding position. S7. Shape laser engraving: According to the product model, a laser engraving machine is used to laser engrave the substrate after double-sided tape is applied into the product shape. S8. Pre-attach tin-plated FPC: Separate the double-sided adhesive from the double-sided release film at the welding position of the product after laser engraving. Manually align and attach the tin-plated FPC pads to the metal wire welding position. After the FPC pre-attachment is completed, cover the FPC with double-sided adhesive. S9. Welding preparation: Use a laser welding machine, set the laser energy parameters, and the welding process to spot welding. The parameters are: Point 1: power 28, spot time 50000; Point 2: power 25, spot time 50000; Point 3: power 23, spot time 50000. Place the pre-attached FPC material on the laser welding machine platform with the solder side facing up. The pad image will appear in the window. First, check the simulation processing and observe whether the machine's vision accurately identifies the pad position. Confirm after accurate identification. S10, Welding: Uncheck the simulated processing option, start the machine tool's vision to automatically identify and grab the pads, and use laser energy for processing. The laser energy penetrates PET and OCA, and the energy is concentrated on the tin-plated pads and metal wires. The temperature rises to 200℃, and the tin completely melts. The high temperature causes the copper atoms of the base metal wire to diffuse into the molten tin, forming a Cu-Sn alloy layer. The tin and the base metal wire are metallurgically bonded, fixing the difficult-to-solder metal wires in the middle layer.

[0005] Furthermore, the wiring substrate in step S1 is PET+OCA, specifically 50μm PET+35μm OCA.

[0006] Furthermore, in step S1, the substrate cutting size is 20-30mm larger than the touch screen product size at the edge, making it easier for staff to handle the substrate.

[0007] Furthermore, the base metal wire in step S3 is one of pure copper wire, antimony wire, silver wire, and gold wire, and the wire diameter of the base metal wire is 2μm-50μm, corresponding to the use of difficult-to-solder metal wires with a wire diameter of 2μm-30μm.

[0008] Furthermore, in step S5, the starting point of the difficult-to-solder metal wire wiring is consistent with the starting point of the substrate metal wire wiring.

[0009] Furthermore, the double-sided adhesive in step S6 is PET + double-sided OCA, and the cutting size of the double-sided adhesive is consistent with that of the wiring substrate.

[0010] Furthermore, the double-sided release film in step S6 has a size of 200 mm. 50mm.

[0011] Furthermore, in step S8, the offset between all metal wire soldering positions and the FPC tin-plated pads is less than 0.3 mm.

[0012] Compared to existing technologies, the advantages of this solution are: 1. By introducing a conductive base metal that can form a good metallurgical bond with tin as an intermediate load-bearing transition layer, the liquid tin undergoes atomic interdiffusion after contacting the conductive base metal, generating tin-based intermetallic compounds and forming a high-strength metallurgical transition layer. The ultra-fine hard-to-weld metal is sandwiched between the conductive base metal and the tin metallurgical layer, and is fixed by the dual constraints of metallurgical bonding and physical encapsulation, which enhances the bonding force and greatly improves the welding reliability of the ultra-fine hard-to-weld metal wire. 2. This welding method is suitable for capacitive touch screens using ultra-fine, hard-to-weld metal wires, and can also be applied to products such as heating films made using ultra-fine, hard-to-weld metal wires. The reliability of this method is 10-12 years under normal temperature conditions, which can greatly increase the service life. 3. Welding of difficult-to-weld metals is achieved through metallurgical bonding. Improvements are made to the welding process without altering the product composition or properties. Furthermore, the base metal wires used are common conductive metal materials such as copper, antimony, silver, and gold wires, which can shorten the research and development and verification cycle. Attached Figure Description

[0013] Figure 1 This is a flowchart of the welding method of the present invention; Figure 2 This is a schematic diagram of the wiring of the base metal wire and the difficult-to-solder metal wire in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the pre-attached cross-section of the tin-plated FPC in Embodiment 1 of the present invention; Detailed Implementation The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0014] A method for welding ultra-micro difficult-to-solder metal wires in a capacitive touchscreen, the flowchart of which is shown below. Figure 1 As shown, in this solution, the base metal wire can also be antimony wire, silver wire, or gold wire, as well as other conductive metal materials that can be metallurgically bonded with tin. The PET of the wiring substrate can be replaced with high-temperature resistant polyester (PEN), cyclic olefin polymer (COP / COC), polycarbonate (PC), polyethersulfone (PES), liquid crystal polymer (LCP), colorless transparent polyimide (CPI), thermoplastic polyurethane (TPU), cellulose triacetate (TAC), and ultra-thin reinforced glass, quartz glass inorganic substrates. The OCA of the wiring substrate can also be selected from solid-coated adhesives such as silicone and PU. Among them, the materials of difficult-to-solder metal wires include tungsten, molybdenum, chromium, titanium, platinum and their corresponding alloys, but are not limited to other metals that cannot be metallurgically bonded with tin.

[0015] The following examples illustrate this in detail.

[0016] Example 1 S1. Preparation of wiring substrate: The wiring substrate uses PET+OCA, where PET is polyethylene terephthalate film and OCA is optical adhesive, featuring high transparency. Specifically, it is 50μm PET + 35μm OCA. A cutting machine is used to cut the substrate according to the corresponding touch screen product size. In this embodiment, an 86-inch product is used as an example, and the cutting size is 1200mm. 2000mm, with a 20mm margin at the edge for easy handling by staff; S2. Cabling equipment preparation: The cabling equipment is a precision cabling machine with a cabling size of 1500mm. 2500mm, wiring tolerance is ±0.1mm, check and debug the equipment diagonal running dimension to 1:1 before printing, and set the machine origin (0mm, 0mm). S3. Preparation of metal wires, including difficult-to-solder metal wires, in this embodiment tungsten wires with a diameter of 7μm, and base metal wires, in this embodiment pure copper wires with a diameter of 20μm are selected. S4. Base metal wire wiring: Place the PET substrate on the precision wiring machine platform. The substrate placement coordinates are (-20mm, -20mm). Assemble the pure copper wire on the machine table and pass the pure copper wire through the printing needle. The outer diameter of the printing needle is 0.7mm and the inner diameter is 0.2mm. Check the smoothness of the needle. The wiring base metal wire is soldered on the substrate. Only the soldering position of the base metal wire is printed. The wiring start point is the coordinate point (0mm, 0mm). S5. For difficult-to-solder metal wire routing, after the base metal wire soldering positions are completed, the machine replaces the wire with tungsten wire, checks the needle smoothness, and routes the difficult-to-solder metal wire onto the substrate. The difficult-to-solder metal wire needs to be routed along all functional lines and soldering positions of the entire product. The soldering positions of the difficult-to-solder metal wire need to be covered by routing over the base metal wire. Figure 2 The diagram shows a wiring diagram. Red represents the solderable metal wire and green represents the base metal wire. To ensure the soldering effect between the solderable metal wire, the base metal wire, and the solder, it is necessary to strictly ensure that the solderable metal wire wiring covers the base metal wire. Therefore, the starting point of the solderable metal wire wiring is the same as the starting point of the base metal wire wiring. S6. Apply double-sided tape. After confirming that the difficult-to-solder metal wires completely cover the base metal wires, use a flip-type laminating machine to precisely apply the double-sided tape to the substrate after the metal wires are laid. The double-sided tape is PET + double-sided OCA, and the cut size of the double-sided tape is consistent with the size of the substrate. Before applying the double-sided tape, use a 200mm... A 50mm double-sided release film is applied to the welding position to facilitate subsequent pre-application of FPC; S7. Outline laser engraving: According to the product model, use a laser engraving machine to laser engrave the substrate after applying double-sided tape into the product shape. Specifically, cut off the 20mm width reserved at the edge in step S1. S8. Pre-attach tin-plated FPC: After laser-engraving the product's outline, separate the double-sided adhesive from the double-sided release film at the solder joints. Manually align and attach the tin-plated FPC pads to the metal wire solder joints, ensuring that all metal wire solder joints are misaligned with the tin-plated FPC pads by less than 0.3mm. After pre-attaching the FPC, cover it with double-sided adhesive. The specific structure is as follows... Figure 3 The diagram shows the cross-section after pasting, with the tungsten wire located between the pure copper wire and the tin wire; S9. Welding preparation: Use a laser welding machine, set the laser energy parameters, and select spot welding as the welding process. Use three laser points for welding. The specific parameters are: Point 1: power 28, welding time 50000; Point 2: power 25, welding time 50000; Point 3: power 23, welding time 50000. Place the pre-attached FPC material on the laser welding machine platform with the solder side facing up. The pad image will appear in the window. First, select simulated processing and observe whether the machine's vision accurately identifies the pad position. Confirm after accurate identification. S10. Welding: Uncheck the simulated processing option, start the machine tool's vision system to automatically identify and grab the pads, and use laser energy for processing. The laser energy penetrates PET and OCA, and the energy is concentrated on the tin-plated pads and metal wires. The temperature rises to about 200℃, and the tin completely melts. The high temperature causes the copper atoms of the base metal wire to diffuse into the molten tin, forming a Cu-Sn alloy layer. The tin and the base metal wire are metallurgically bonded, fixing the difficult-to-solder metal wires in the middle layer. This method provides stable and firm welding, and the bonding force far exceeds that of the existing technology that relies solely on melting the tin and fixing the difficult-to-solder metal wires.

[0017] Example 2 The difference between this embodiment and Embodiment 1 is that the difficult-to-solder metal wire in step S3 is a tungsten wire with a diameter of 3μm, and the base metal wire is a pure copper wire with a diameter of 10μm; other process parameters are the same, and the result is a strong weld.

[0018] Example 3 The difference between this embodiment and Embodiment 1 is that the difficult-to-solder metal wire in step S3 is a tungsten wire with a diameter of 10 μm, and the base metal wire is a pure copper wire with a diameter of 25 μm; other process parameters are the same, and the result is a strong weld.

[0019] Example 4 The difference between this embodiment and Embodiment 1 is that the difficult-to-weld metal wire in step S3 is a tungsten wire with a diameter of 2μm, and the base metal wire is a pure copper wire with a diameter of 2μm; other process parameters are the same, and the result is a strong weld.

[0020] Example 5 The difference between this embodiment and Embodiment 1 is that the difficult-to-solder metal wire in step S3 is a tungsten wire with a diameter of 30 μm, and the base metal wire is a pure copper wire with a diameter of 50 μm; other process parameters are the same, and the result is a strong weld.

[0021] This solution is applicable not only to the welding of tin-plated FPCs to difficult-to-solder metal wires, but also to the welding of difficult-to-solder metal wires through the metallurgical bonding of the base metal wire and the tin layer, relying on the dual constraint of metallurgical bonding and physical encapsulation. It can also be used for welding difficult-to-solder metal wires with organic solder mask, chemical silver plating, chemical nickel-plated gold composite layer, chemical nickel-palladium-gold composite layer, electroplated gold layer, tin-bismuth alloy plating, tin-silver-copper alloy plating, chemical tin plating, nickel-palladium-silver composite plating, sputtered aluminum conductive layer, etc.

[0022] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for welding ultra-micro difficult-to-solder metal wires in a capacitive touchscreen, characterized in that, Includes the following steps: S1. Preparation of wiring substrate: Use a cutting machine to cut the substrate according to the corresponding touch screen product size; S2. Preparation of wiring equipment: The wiring equipment is a precision wiring machine. The wiring size of the machine is larger than the size of the substrate. Before printing, check and adjust the diagonal running size of the equipment to 1:1 and set the origin of the machine. S3. Metal wire preparation, including difficult-to-solder metal wires and base metal wires; S4. Base metal wire wiring: Place the PET substrate on the precision wiring machine platform, assemble the base metal wire on the machine table, pass the base metal wire through the printing needle, check the smoothness of the needle, and weld the wiring base metal wire to the substrate. Only print the welding position of the base metal wire. The starting point of the base metal wire wiring is the origin coordinate point of the machine table. S5. Solderable metal wire wiring: After the base metal wire welding position wiring is completed, the machine replaces the solderable metal wire, checks the smoothness of the needle, and wires the solderable metal wire onto the base material. The solderable metal wire needs to be wired to the functional lines and welding positions of the entire product. The soldering position of the solderable metal wire needs to be wired to cover the base metal wire. S6. Apply double-sided tape. After confirming that the difficult-to-weld metal wires cover the base metal wires, use a flip-type laminating machine to accurately apply the double-sided tape to the substrate after the metal wires are laid. Before applying the double-sided tape, use double-sided release film to stick on the welding position. S7. Shape laser engraving: According to the product model, a laser engraving machine is used to laser engrave the substrate after double-sided tape into the product shape. S8. Pre-attach tin-plated FPC: Separate the double-sided adhesive from the double-sided release film at the welding position of the product after laser engraving. Manually align and attach the tin-plated FPC pads to the metal wire welding position. After the FPC pre-attachment is completed, cover the FPC with double-sided adhesive. S9. Welding preparation: Use a laser welding machine, set the laser energy parameters, and select spot welding as the welding process. Use three laser points for welding, each with a different power. Place the pre-attached FPC material on the laser welding machine with the solder side facing up. The solder pad image will appear in the window. First, select simulated processing and observe whether the machine's vision accurately identifies the solder pad position. Confirm after accurate identification. S10, Welding: Uncheck the simulated processing option, start the machine tool's vision to automatically identify and grab the pads, and use laser energy for processing. The laser energy penetrates PET and OCA, and the energy is concentrated on the tin-plated pads and metal wires. The temperature rises to 200℃, and the tin completely melts. The high temperature causes the copper atoms of the base metal wire to diffuse into the molten tin, forming a Cu-Sn alloy layer. The tin and the base metal wire are metallurgically bonded, fixing the difficult-to-solder metal wires in the middle layer.

2. The method for welding ultra-micro difficult-to-solder metal wires in a capacitive touchscreen according to claim 1, characterized in that: The wiring substrate is PET+OCA.

3. The method for welding ultra-micro difficult-to-solder metal wires in a capacitive touchscreen according to claim 1, characterized in that: In step S1, the substrate cutting size is 20-30mm larger than the touch screen product size at the edge.

4. The method for welding ultra-micro difficult-to-solder metal wires in a capacitive touchscreen according to claim 1, characterized in that: The base metal wire in step S3 is one of pure copper wire, antimony wire, silver wire, and gold wire, and the wire diameter of the base metal wire is 2μm-50μm.

5. The method for welding ultra-micro difficult-to-solder metal wires in a capacitive touchscreen according to claim 1, characterized in that: In step S5, the starting point of the difficult-to-solder metal wire wiring is consistent with the starting point of the substrate metal wire wiring.

6. The method for welding ultra-micro difficult-to-solder metal wires in a capacitive touchscreen according to claim 1, characterized in that: The double-sided adhesive used in step S6 is PET + double-sided OCA, and the cutting dimensions of the double-sided adhesive are consistent with those of the wiring substrate.

7. The method for welding ultra-micro difficult-to-solder metal wires in a capacitive touchscreen according to claim 1, characterized in that: The double-sided release film in step S6 has a size of 200mm. 50mm.

8. The method for welding ultra-micro difficult-to-solder metal wires in a capacitive touchscreen according to claim 1, characterized in that: In step S8, the offset between all metal wire soldering positions and the FPC tin-plated pads is less than 0.3 mm.

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