Manufacturing method of LED light bar

Abstract

The invention discloses a manufacturing method of an LED light bar. The manufacturing method comprises the following steps that surface pretreatment is conducted on a flexible substrate to form an active area; depositing a copper / silver composite conductive layer through magnetron sputtering; preparing a conductive circuit containing a bonding pad by a photoetching process; bonding the LED chip with the conductive adhesive and curing the LED chip; covering a flexible insulating layer to wrap the chip and the filling gap; and coating a transparent packaging adhesive layer containing fluorescent powder. The traditional wire bonding is replaced by the photoetching process, the welding spot stress concentration is eliminated, the bonding strength of the substrate and the conductive layer is enhanced in combination with surface pretreatment, and the bending fatigue resistance of the light bar is improved; the anisotropic conductive adhesive and the polyimide insulating layer synergistically guarantee the reliability of electric connection and the flexibility of the structure; the fluorescent powder packaging layer optimizes the light emitting uniformity and durability, and is suitable for high-curvature flexible scenes.

Description

Technical Field

[0002] The present invention relates to the technical field of LED strip manufacturing, and particularly to a method for manufacturing an LED strip. Background Art

[0004] An LED strip is a lighting component in which multiple light-emitting diode (LED) chips are arranged at a specific pitch on a flexible or rigid substrate and are connected by a circuit to form a continuous strip-shaped light-emitting body. Due to its energy-saving, high-brightness, bendable and other characteristics, it is widely used in fields such as building decoration, automotive lighting, indoor and outdoor landscape design, etc.

[0005] Currently, the LED strip manufacturing technology mainly involves soldering LED chips on the surface of a substrate with a pre-etched circuit, and then covering it with a packaging adhesive layer to form a protection structure. The key processes involved include chip die bonding, wire bonding, packaging molding and other links. The existing production methods generally adopt the method of welding wires point by point to achieve electrical connection between chips. Although this process can ensure the electrical reliability of a single solder joint, in flexible application scenarios, due to the insufficient ductility of metal wires, stress concentration is likely to occur at the junction of the solder joint and the wire when the strip is repeatedly bent, resulting in solder joint cracking or wire breakage, and further causing problems such as local circuit open circuit and light spot loss. Especially in ultra-thin or high-curvature installation environments, the anti-fatigue performance of the traditional wire bonding structure significantly decreases, seriously restricting the service life and reliability of the strip in dynamic bending scenarios. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for manufacturing an LED strip to solve the problem that in flexible application scenarios, due to the insufficient ductility of metal wires, stress concentration is likely to occur at the junction of the solder joint and the wire when the strip is repeatedly bent, resulting in solder joint cracking or wire breakage, and further causing local circuit open circuit and light spot loss.

[0008] The present invention provides a method for manufacturing an LED strip, including the following steps:

[0009] Step S1: Perform surface pretreatment on the flexible substrate to form an active area with a preset roughness on its surface;

[0010] Step S2: Deposit a conductive layer on the active area by magnetron sputtering technology, and the conductive layer covers the entire surface of the active area;

[0011] Step S3: Pattern the conductive layer by photolithography technology to form a conductive circuit including a series circuit, and the conductive circuit includes a plurality of spaced-apart pads;

[0012] Step S4: Bond the LED chip to the pad with conductive adhesive, and cure the conductive adhesive through a reflow soldering process to form an electrical connection between the electrodes of the LED chip and the pad;

[0013] Step S5: Cover the conductive circuit with a flexible insulating layer, which covers the bottom and side walls of the LED chip and fills the gaps between adjacent LED chips;

[0014] Step S6: Coat a transparent encapsulation adhesive layer on the surface of the flexible insulating layer, and the encapsulation adhesive layer completely covers the light-emitting surface of the LED chip and the outer surface of the flexible insulating layer.

[0015] Furthermore, in step S1, the surface pretreatment includes:

[0016] Step S11: Use a plasma cleaning device to bombard the surface of the flexible substrate to remove impurities;

[0017] Step S12: Form a micron-level groove array on the surface of the substrate by chemical etching;

[0018] Step S13: Deposit nano-scale silicon dioxide particles in the grooves to increase the surface roughness.

[0019] Furthermore, in step S2, the conductive layer is a copper / silver composite metal layer, where the thickness of the copper layer is 50 - 80 nm and the thickness of the silver layer is 20 - 30 nm.

[0020] Furthermore, in step S3, the photolithography process includes:

[0021] Step S31: Spin-coat a positive photoresist on the surface of the conductive layer and perform pre-baking;

[0022] Step S32: Expose the photoresist using a mask, and form a circuit mask pattern after development;

[0023] Step S33: Use the mask pattern as a protective layer to perform wet etching on the conductive layer to obtain the conductive circuit.

[0024] Furthermore, in step S32, the exposure energy is 200 - 250 mJ / cm², and the developer is a 2.38% concentration of tetramethylammonium hydroxide solution.

[0025] Furthermore, in step S4, the conductive adhesive is an anisotropic conductive adhesive, its curing temperature is 180 - 220 °C, and the curing time is 30 - 60 seconds.

[0026] Furthermore, the anisotropic conductive adhesive contains nickel-gold core-shell structured conductive particles with a diameter of 3 - 5 μm, and the volume ratio of the conductive particles is 5 - 8%.

[0027] Further, in step S5, the flexible insulating layer is made of polyimide material with a thickness of 10 - 15 μm, and is bonded to the conductive circuit and the substrate through a hot pressing process.

[0028] Further, in step S6, phosphor particles are dispersed in the transparent encapsulation adhesive layer. The particle size of the phosphor particles is 8 - 12 μm, and the mass ratio is 15 - 20%.

[0029] Further, the total thickness of the conductive layer is 70 - 110 nm, and its grain size is 20 - 30 nm detected by X-ray diffraction.

[0030] Advantages of the present invention: By combining the magnetron sputtering process with the lithography technology, a continuous conductive circuit is directly formed on the flexible substrate, replacing the traditional wire bonding process, fundamentally eliminating the stress concentration problem at the junction of the solder joint and the wire, and significantly improving the anti-fatigue performance of the LED strip in the dynamic bending scenario; By bonding the LED chip with anisotropic conductive adhesive and cooperating with the flexible insulating layer coating structure, while ensuring the electrical connection reliability, the overall mechanical flexibility of the strip is enhanced; In addition, the encapsulation adhesive layer with uniformly dispersed phosphor can optimize the light emission uniformity, and the surface pretreatment and the conductive layer composite structure design further enhance the bonding strength between the substrate and the conductive circuit. The LED strip prepared by this method can still maintain stable electrical performance and light emission effect under repeated bending conditions, and is suitable for the long-term use requirements of high-curvature installation environments and flexible electronic devices. Brief Description of the Drawings

[0032] In order to more clearly illustrate the technical solutions of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0033] Figure 1 It is a flowchart of the manufacturing method of the LED strip provided by the present invention. Detailed Embodiments

[0035] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments. It should be pointed out that the following detailed description is illustrative and is intended to provide further description of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0036] Please refer to Figure 1, the method for manufacturing an LED strip according to an embodiment of the present invention includes:

[0037] Step S1: Perform surface pretreatment on the flexible substrate to form an active area with a preset roughness on its surface.

[0038] The flexible substrate is selected from polyimide or PET materials. First, an argon plasma cleaning device is used to bombard the substrate surface for 5 minutes under the conditions of a power of 300 W and a pressure of 50 Pa to thoroughly remove organic pollutants and oxides. Subsequently, the substrate is immersed in a 10% sodium hydroxide solution and chemically etched at 60°C for 20 seconds to form a groove array with a depth of 2 - 3 μm and a pitch of 10 μm. Finally, silica particles with a particle size of 50 - 100 nm are uniformly filled in the grooves by chemical vapor deposition, so that the Ra value of the substrate surface roughness reaches 0.8 - 1.2 μm. This pretreatment process combines physical cleaning, chemical microstructure construction, and nanoparticle strengthening, significantly increasing the substrate surface area and surface energy, providing a strong anchoring effect for the subsequent conductive layer, and preventing interface peeling between the conductive layer and the substrate during flexible bending.

[0039] Step S2: Deposit a conductive layer on the active area through a magnetron sputtering process, and the conductive layer covers the entire surface of the active area.

[0040] In a vacuum chamber, the conductive layer is deposited by alternately sputtering a copper target and a silver target: First, a copper layer is sputtered to a thickness of 60 nm with a DC power of 1.5 kW, and then a silver layer is sputtered to a thickness of 25 nm with an RF power of 1.2 kW to form a copper / silver bilayer composite structure. The magnetron sputtering process realizes the directional filling of metal atoms in the grooves of the substrate active area, enabling the conductive layer to form a mechanical interlocking structure with the substrate; the silver layer serves as a surface covering layer to reduce the contact resistance, and the copper layer serves as the main layer to balance conductivity and cost economy, and the resistance change rate is less than 5% after 1000 bending tests.

[0041] Step S3: Pattern the conductive layer through a photolithography process to form a conductive circuit including a series circuit, and the conductive circuit includes a plurality of spaced-apart pads.

[0042] A positive photoresist with a thickness of 3 μm is spin-coated on the surface of the conductive layer. After pre-baking at 90 °C for 120 seconds, it is exposed under an ultraviolet light source with an energy of 220 mJ / cm² using a mask plate. After development, the photoresist in the area of the conductive circuit lines is retained; Subsequently, the substrate is immersed in an iron-based etching solution containing 10% nitric acid, and the exposed conductive layer is etched at a rate of 30 μm / min to form a series circuit with a line width of 50 μm and a pitch of 100 μm, and a circular pad with a diameter of 200 μm is reserved at the circuit node. The graphic accuracy error of the lithography process is less than ±2 μm, ensuring the precise alignment of the pad position with the LED chip electrodes, avoiding the additional solder joints required by the traditional wire bonding process, and fundamentally eliminating the risk of stress concentration caused by a large number of solder joints.

[0043] Step S4: Bond the LED chip to the pad through a conductive adhesive, and cure the conductive adhesive through a reflow soldering process to electrically connect the electrodes of the LED chip to the pad.

[0044] An anisotropic conductive adhesive with a volume ratio of nickel-gold core-shell conductive particles of 6% is used. The colloid is coated on the surface of the pad through a precision dispensing device. After mounting the LED chip, a pressure of 5 MPa is applied, and it is cured by heating at 200 °C for 40 seconds under nitrogen protection. The conductive particles in the conductive adhesive rupture under pressure, releasing the core nickel layer and the outer shell gold layer, forming a metal bonding connection between the LED chip electrodes and the pad. The vertical conduction resistance is less than 10 mΩ, while the lateral insulation resistance is greater than 10 MΩ; the thermal gradient control of the reflow soldering process enables uniform curing of the colloid, avoiding defects such as bubbles or voids, and ensuring the long-term stability of the electrical connection.

[0045] Step S5: Cover the conductive circuit with a flexible insulating layer, and the flexible insulating layer covers the bottom and side walls of the LED chip and fills the gaps between adjacent LED chips.

[0046] The liquid polyimide precursor is coated on the conductive circuit, pre-cured at 80 °C for 10 minutes to form an insulating layer with a thickness of 12 μm, and then hot-pressed and formed at 280 °C and a pressure of 0.5 MPa. The polyimide layer completely covers the side walls and the bottom of the LED chip and forms a void-free filling structure between adjacent chips. Its elastic modulus is 3.5 GPa, and the elongation at break is greater than 30%. It can absorb external bending stress and uniformly disperse it to the entire insulating layer, avoiding stress concentration on a single pad or chip; at the same time, the dielectric strength of the insulating layer reaches 200 kV / mm, effectively preventing short circuits in the circuit.

[0047] Step S6: Coat a transparent encapsulation glue layer on the surface of the flexible insulating layer, and the encapsulation glue layer completely covers the light-emitting surface of the LED chip and the outer surface of the flexible insulating layer.

[0048] The silica encapsulation material doped with 10% YAG phosphor (particle size 10 μm) is formed into an encapsulation layer with a thickness of 0.5 mm through a slit coating process and cured at 120 °C for 1 hour. The phosphor shows a gradient distribution in the silica matrix, with a higher concentration in the area close to the LED chip, which improves the blue light excitation efficiency to 85%; the light transmittance of the encapsulation layer is greater than 92%, the haze is less than 3%, and the yellowing index ΔYI is less than 1.5 after 1000 hours of ultraviolet aging test, ensuring that the light bar maintains high brightness and color consistency in the outdoor environment for a long time.

[0049] In summary, the present invention constructs a micro-nano composite rough structure through surface pretreatment, combines the copper / silver double-layer magnetron sputtering process to form a conductive line with high bonding strength and low resistance on a flexible substrate, replaces the traditional metal wire bonding, and completely eliminates the fracture problem caused by stress concentration at the solder joint interface; the directional conduction design of the anisotropic conductive adhesive and the stress dispersion structure of the polyimide insulating layer work together to keep the light bar maintaining stable electrical connection and mechanical integrity under dynamic bending conditions; the encapsulation layer with a gradient distribution of phosphor further optimizes the light efficiency and durability. The whole process breaks through the bottleneck of short bending life and fast light decay of flexible LED light bars in the existing technology through material system innovation and precise process control, and provides a highly reliable light source solution for emerging fields such as wearable devices and flexible displays.

[0050] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A manufacturing method of an LED light strip, characterized in that, It includes the following steps: Step S1: Perform surface pretreatment on the flexible substrate to form an active area with a preset roughness on its surface; Step S2: Deposit a conductive layer on the active area through a magnetron sputtering process, and the conductive layer covers the entire surface of the active area; Step S3: Pattern the conductive layer through a photolithography process to form a conductive circuit including a series circuit, and the conductive circuit includes a plurality of pads distributed at intervals; Step S4: Bond the LED chip to the pad through a conductive adhesive, and cure the conductive adhesive through a reflow soldering process to electrically connect the electrodes of the LED chip to the pad; Step S5: Cover the conductive circuit with a flexible insulating layer, and the flexible insulating layer covers the bottom and side walls of the LED chip and fills the gaps between adjacent LED chips; Step S6: Coat a transparent encapsulation adhesive layer on the surface of the flexible insulating layer, and the encapsulation adhesive layer completely covers the light-emitting surface of the LED chip and the outer surface of the flexible insulating layer.

2. The manufacturing method of the LED light strip according to claim 1, characterized in that In the step S1, the surface pretreatment includes: Step S11: Use a plasma cleaning device to bombard the surface of the flexible substrate to remove impurities; Step S12: Form a micron-level groove array on the substrate surface through chemical etching; Step S13: Deposit nano-scale silica particles in the grooves to increase the surface roughness.

3. The manufacturing method according to claim 1, wherein In the step S2, the conductive layer is a copper / silver composite metal layer, where the thickness of the copper layer is 50 - 80 nm and the thickness of the silver layer is 20 - 30 nm.

4. The manufacturing method of the LED light strip according to claim 1, characterized in that, In the step S3, the photolithography process includes: Step S31: Spin-coat a positive photoresist on the surface of the conductive layer and perform pre-baking treatment; Step S32: Expose the photoresist using a mask plate, and form a circuit mask pattern after development; Step S33: Use the mask pattern as a protective layer to perform wet etching on the conductive layer to obtain the conductive circuit.

5. The manufacturing method of the LED light strip according to claim 4, characterized in that, In the step S32, the exposure energy is 200 - 250 mJ / cm², and the developer is a 2.38% concentration of tetramethylammonium hydroxide solution.

6. The manufacturing method of the LED light strip according to claim 1, characterized in that, In the step S4, the conductive adhesive is an anisotropic conductive adhesive, its curing temperature is 180 - 220 °C, and the curing time is 30 - 60 seconds.

7. The manufacturing method of the LED light strip according to claim 6, wherein, The anisotropic conductive adhesive contains nickel-gold core-shell structure conductive particles with a diameter of 3 - 5 μm, and the volume ratio of the conductive particles is 5 - 8%.

8. The manufacturing method of the LED light strip according to claim 1, wherein, In the step S5, the flexible insulating layer is a polyimide material, its thickness is 10 - 15 μm, and it is bonded to the conductive circuit and the substrate through a hot pressing process.

9. The manufacturing method of the LED light bar according to claim 1, characterized in that, In the step S6, phosphor particles are dispersed in the transparent encapsulation adhesive layer, the particle size of the phosphor particles is 8 - 12 μm, and the mass ratio is 15 - 20%.

10. The manufacturing method of the LED light strip according to claim 3, characterized in that, The total thickness of the conductive layer is 70 - 110 nm, and its grain size is 20 - 30 nm detected by X-ray diffraction.

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