Ultrafine and ultrathin nano-silver paste back bonding process

Abstract

This invention relates to an ultra-fine, ultra-thin nano-silver paste back bonding process. This technology involves fabricating an ultra-thin nano-silver paste layer on the front, side, and back of the LTPS (Low Temperature Polycrystalline Silicon) terminals of a display screen, transferring the signal conduction path from the front of the FPC (Flexible Printed Circuit Board) to the back of the display screen for bonding. This significantly reduces the bending radius of the FPC, decreases the bezel width, and increases the screen-to-body ratio. This invention effectively solves the shortcomings of large bezel width and low screen-to-body ratio in existing display modules, providing a superior visual experience for products such as smart wearable displays, smart home displays, and smartphones.

Description

Technical Field

[0001] This invention relates to the field of display module manufacturing technology, and in particular to an ultra-fine and ultra-thin nano silver paste backbonding process. Background Technology

[0002] As consumers' demands for visual experience in electronic products continue to rise, the bezel width (black border) of display modules in products such as smart wearable devices and smartphones is required to be increasingly narrow, and the screen-to-body ratio is also required to be increasingly higher. Currently, the size of the black border in smartphones and wearable devices is typically between 1.1-1.3mm and 1.9-2.1mm, respectively. However, traditional module manufacturing processes have reached their design limits in achieving narrower bezels.

[0003] In the structure of existing modules (such as...) Figure 1 As shown, the FPC is typically bonded on the front of the LTPS terminal. During assembly, the FPC needs to be bent to the back of the screen, requiring a certain bending radius (protrusion), usually between 0.5 and 0.7 mm. This bending radius directly results in the need to increase the black bezel of the lens by 0.6 to 0.7 mm, thus increasing the overall width of the black bezel.

[0004] To address the aforementioned problems, this invention proposes a novel back bonding technology (such as...). Figure 2 (As shown). This technology creates an ultra-thin layer of nano-silver paste lines on the front, sides, and back of the LTPS terminal, enabling the FPC to directly bond with the silver paste lines on the back of the screen, achieving signal transmission and conduction. In this way, the bending radius of the FPC can be significantly reduced, thereby reducing the bezel size by at least 0.5mm. Summary of the Invention

[0005] This invention addresses the technical problems existing in the prior art by providing an ultra-fine, ultra-thin nano-silver paste backbonding process to overcome the shortcomings of large bezel widths and low screen-to-body ratios in existing display modules. By bonding on the back of the display screen, this invention reduces the bending radius of the FPC, thereby reducing the bezel area, increasing the screen-to-body ratio, meeting consumers' higher demands for visual design in mobile phones or wearable devices, and providing users with a superior visual experience.

[0006] The technical solution of this invention to solve the above-mentioned technical problems is as follows: an ultrafine and ultrathin nano silver paste back bonding process; comprising the following steps: S1: Process the three sides of the panel, including: laser cutting the side surface of the LTPS terminal to control the surface roughness to 1.5~2.5 micrometers; and performing plasma cleaning on the front and back of the LTPS terminal; S2: Fabrication of nano-silver paste circuitry on LTPS terminals using EHD equipment; S3: Laser sintering and curing of the sintered nano-silver paste circuit, followed by AOI inspection; S4: Using a dedicated FOG bonding device and a CCD alignment system, the FPC is precisely pressed onto the surface of the nano silver paste circuit. S5: Perform AOI inspection on Bonding's nano silver paste circuitry and FPC, and assemble the products that pass the inspection into ASSY units.

[0007] Furthermore, the ultra-fine and ultra-thin nano silver paste back bonding process includes fabricating nano silver paste lines on the front, side, and back surfaces of LTPS terminals.

[0008] Furthermore, the aforementioned ultra-fine and ultra-thin nano silver paste back bonding process involves fabricating nano silver paste lines on the front and back surfaces of the LTPS terminal, guiding the signal conduction lines to the back of the LTPS terminal, and realizing bonding on the back of the LTPS.

[0009] The beneficial effects of this invention are: Significantly reduce bezel width: By moving the bonding to the back of the screen, the bending space required for the FPC is effectively reduced, thereby directly reducing the physical size of the bezel.

[0010] Increase screen-to-body ratio: Reducing the bezel width directly translates to increasing the screen display area, which in turn increases the screen-to-body ratio and brings a more immersive visual experience.

[0011] Simplify structural design: This may reduce the requirements for some structural components or optimize the dimensions of existing structural components.

[0012] Enhance product competitiveness: Meet market demand for full-screen and narrow-bezel designs to improve product competitiveness in the market. Attached Figure Description

[0013] Figure 1 This is a structural diagram of the existing module.

[0014] Figure 2 This is a schematic diagram of the module structure of the Back Bonding process of the present invention.

[0015] Figure 3 This is a schematic diagram of laser cutting on the side surface of an LTPS terminal in one embodiment.

[0016] Figure 4 This is a schematic diagram of the surface roughness of an LTPS terminal in one embodiment.

[0017] Figure 5 This is a schematic diagram of the process for an ultra-fine, ultra-thin nano silver paste back bonding process according to the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0020] In the description of this application, the term "for example" is used to mean "used as an example, illustration, or description." Any embodiment described as "for example" in this application is not necessarily to be construed as being more preferred or advantageous than other embodiments. The following description is provided to enable any person skilled in the art to make and use the invention. Details are set forth in the following description for purposes of explanation. It should be understood that those skilled in the art will recognize that the invention can be made without using these specific details. In other instances, well-known structures and processes will not be described in detail to avoid obscuring the description of the invention with unnecessary detail. Therefore, the invention is not intended to be limited to the embodiments shown, but is consistent with the broadest scope of the principles and features disclosed in this application.

[0021] like Figures 2-5 As shown, in one embodiment, an ultrafine, ultrathin nano-silver paste back bonding process includes the following steps: S1: Process the three sides of the panel, including: laser cutting the side surface of the LTPS terminal to control the surface roughness to 1.5~2.5 micrometers; and performing plasma cleaning on the front and back of the LTPS terminal; S2: Fabrication of nano-silver paste circuitry on LTPS terminals using EHD equipment; S3: Laser sintering and curing of the sintered nano-silver paste circuit, followed by AOI inspection; S4: Using a dedicated FOGbonding device and a CCD alignment system, the FPC is precisely bonded to the surface of the nano silver paste circuit. S5: Perform AOI inspection on Bonding's nano silver paste circuitry and FPC, and assemble the products that pass the inspection into ASSY units.

[0022] In this embodiment, the LTPS terminal side surface is laser-cut: the LTPS terminals of the display panel are laser-cut in preparation for subsequent circuit fabrication. During the laser cutting process, the cutting parameters need to be precisely controlled so that the surface roughness of the terminal side surface is controlled within the range of 1.5~2.5μm. This roughness range provides a suitable surface morphology for the subsequent adhesion of nano-silver paste, ensuring good conductivity and connection reliability. The front and back of the LTPS terminals are then plasma-cleaned: the front and back of the LTPS terminals are treated with plasma. Plasma cleaning effectively removes organic contaminants, oxide layers, etc., from the terminal surface, improving the activity of the terminal surface and laying the foundation for uniform coating and good adhesion of the nano-silver paste.

[0023] Nano-silver paste circuitry is fabricated on panel terminals using an EHD (Electrophoretic Deposition / Electrospray Deposition) machine. EHD technology precisely fabricates nano-silver paste circuitry on the treated panel terminals. EHD technology enables fine and patterned deposition of nano-silver paste, forming continuous and uniform conductive lines on the front, sides, and back of the LTPS terminals. This circuitry will serve as a conductive bridge between the FPC and the LTPS terminals.

[0024] Laser sintering and curing of nano-silver paste circuits: After the nano-silver paste circuits are fabricated, they are cured by laser sintering. Laser sintering can quickly and efficiently remove the carrier in the nano-silver paste and promote the sintering of silver nanoparticles to form a continuous, highly conductive silver layer. The parameters of laser sintering (such as power, scanning speed, focus, etc.) need to be precisely controlled according to the composition and thickness of the silver paste.

[0025] AOI inspection of sintered nano-silver paste circuits: AOI (Automated Optical Inspection) equipment is used to inspect the sintered and cured nano-silver paste circuits. The inspection includes checking the integrity, conductivity, width, and uniformity of the circuits to ensure that the circuits meet process requirements and are free from defects such as open circuits and short circuits.

[0026] Using specialized FOG bonding equipment and a CCD alignment system, the FPC is precisely bonded to the surface of the silver paste circuitry. A dedicated FOG (Flexible OLED on Glass) bonding device, employing a high-precision CCD (Charge-Coupled Device) alignment system, precisely aligns the contacts on the FPC with the nano-silver paste circuitry fabricated on the back of the panel. Subsequently, appropriate pressure and temperature are applied using the bonding equipment to bond the FPC and silver paste circuitry together, forming a reliable electrical connection.

[0027] AOI inspection of the bonding silver paste lines and FPCs: After bonding is completed, AOI equipment is used again to inspect the silver paste lines and FPCs in the bonding area. The main checks are the reliability of the bonding, continuity, and the presence of issues such as cold solder joints or desoldering.

[0028] Products that pass AOI inspection will be sent to the subsequent ASSY (Assembly) process to complete the assembly of the entire display module.

[0029] Example 1: Using the above process for a narrow bezel display module in a smartphone, a smartphone manufacturer hopes to reduce the black bezel width of the display module of its next-generation flagship phone to less than 1.0mm in order to achieve a full-screen design with a higher screen-to-body ratio.

[0030] Panel three-sided treatment: The LTPS terminal side surface of a 6.5-inch LTPS AMOLED panel was cut using an Nd:YAG laser at a power of 15W and a speed of 500mm / s. After cutting, the surface roughness of the terminal side surface was measured by interferometry, with an average value of 2.0μm, which meets the requirement of 1.5~2.5μm.

[0031] Plasma cleaning was performed using an Ar / O2 mixed gas for 60 seconds at a power of 500W.

[0032] Nano silver paste circuit fabrication: Using a conductive silver paste based on nano-silver particles (approximately 30 nm in diameter) and a polymer binder, nano-silver paste lines with a width of 30 μm and a thickness of approximately 100 nm are precisely printed on the front, side (the part in contact with the FPC), and back (the part that connects with the back contacts of the FPC) of LTPS terminals using an EHD machine.

[0033] A 25W near-infrared laser was used to scan the sintered nano-silver paste circuit at a speed of 2000 mm / s. After sintering, the thickness of the silver paste layer became approximately 70 nm, and the resistivity decreased to 1.5 x 10^-6 Ω·cm.

[0034] AOI testing results showed that all nano-silver paste circuits were complete and continuous, with no open circuits or short circuits.

[0035] Back bonding: A custom FOG bonding device designed for small-sized AMOLED displays is used. The FPC features a double-sided gold finger design, with the rear contacts directly interfaced with the nano-silver paste lines on the back of the panel.

[0036] The contacts on the FPC are aligned with the nano-silver paste lines on the back of the panel with high precision using a CCD alignment system (alignment accuracy ±5μm).

[0037] Apply a temperature of 150°C and a pressure of 0.3 MPa, with a bonding time of 3 seconds, to bond the FPC to the silver paste lines.

[0038] AOI inspection after bonding showed that all bonding points had good contact, the on-resistance was less than 0.5Ω, and the cold solder joint rate was less than 0.01%.

[0039] Qualified modules enter the ASSY process.

[0040] Results: The display module using the technology of this invention successfully controlled the bezel width to 0.95mm, which is about 0.55mm lower than the traditional front bonding technology (bezel of about 1.5mm), and the screen ratio is increased by about 4.5%.

[0041] Example 2: The above technology is used in an ultra-narrow bezel display module for smart wearable devices (smartwatches).

[0042] Panel three-sided treatment: The LTPS terminal side of a 1.5-inch LTPS LCD panel is cut using an ultraviolet laser at 8W power and 300mm / s speed, with the surface roughness controlled at 1.8μm.

[0043] Plasma cleaning was performed using CF4 / O2 gas for 70 seconds.

[0044] Nano silver paste circuit fabrication: Using a nano-silver conductive ink, nano-silver paste lines with a width of 25μm and a thickness of 80nm are fabricated on the front, side and back of LTPS terminals by inkjet printing.

[0045] Photocuring was performed using an LED ultraviolet light source (365nm). After curing, the silver paste layer was 60nm thick and had a resistivity of 2.0 x 10^-6 Ω·cm.

[0046] AOI testing showed that the line quality was good.

[0047] Back bonding: A miniaturized FOG Bonding device for wearable devices is used. The contacts on the back of the FPC are mated to the nano-silver paste lines on the back of the panel.

[0048] CCD alignment accuracy reaches ±3μm.

[0049] Bonding conditions: 130°C, 0.2MPa, 2 seconds.

[0050] AOI testing showed that Bonding's on-resistance was less than 0.3Ω.

[0051] Qualified modules enter ASSY.

[0052] Result: The display module using the technology of this invention successfully controlled the bezel width to 1.4mm, which is about 0.6mm lower than the traditional front bonding (bezel of about 2.0mm), and the screen ratio is significantly improved.

[0053] Example 3: An ultra-narrow bezel display module for smartphones and its manufacturing method; This embodiment uses a smartphone display panel as an example to describe how to use ultra-fine and ultra-thin nano silver paste conductive lines to replace traditional ITO lines to achieve back-side bonding, and combines LIPO vacuum potting technology to manufacture an ultra-narrow bezel display module.

[0054] Panel preparation and processing: Panel type: LTPS TFT-LCD or AMOLED panel, size 6.5 inches.

[0055] Terminal Pad Structure: ITO Pad formed on the LTPSTFT layer, located on the front of the panel.

[0056] Side processing: Using an Nd:YAG laser at 15W power and 500mm / s, the side surface corresponding to the ITO Pad on the front of the panel is precisely cut. After cutting, the surface roughness of the terminal side surface is measured by an interference microscope, with an average value of 2.0μm, which meets the requirement of 1.5~2.5μm.

[0057] Front and Back Cleaning: A Plasma cleaning device using an Ar / O2 mixed gas is used to clean the ITO pad areas on both the front and back of the panel. The cleaning gas is an Ar / O2 mixed gas, with a power of 500W and a cleaning time of 60 seconds, to thoroughly remove surface oil and particles, ensuring good adhesion of the conductive layer.

[0058] Nano silver paste circuit fabrication (S2): Nano silver paste material: Select nano silver paste with uniform particle size distribution (about 30nm), appropriate solid content, and viscosity between 10-20 Pa·s.

[0059] Dispensing equipment: EHD dispensing machine is used and equipped with high-precision printing nozzles.

[0060] Circuit printing: Using a CCD vision system, the Mark points on the panel are accurately identified, and a coordinate system is established. Based on the designed circuit diagram, nano-silver paste circuits are simultaneously printed on the side, front, and back of the panel.

[0061] Front Pad Lead-out: Lead-out from the front ITO Pad area through extremely fine nano-silver paste lines (linewidth approximately 30μm).

[0062] Side guidance: On the side, nano silver paste lines are printed along a preset path to connect the front lead and the back lead.

[0063] Backside lead-out: On the reverse side of the panel (Back side), nano-silver paste lines are printed to form the required contact points for bonding from the back side.

[0064] Precision control: The width of the fabricated nano-silver paste circuit is controlled within 30μm±3μm, and the thickness is controlled within 2~5μm.

[0065] Nano-silver paste circuit curing: Laser sintering: A 25W near-infrared laser was used to scan and sinter the nano-silver paste circuit at a speed of 2000 mm / s. After sintering, the thickness of the silver paste layer became approximately 70 nm, and the resistivity decreased to 1.5 x 10^-6 Ω·cm.

[0066] AOI Inspection: The sintered and cured nano-silver paste circuitry was inspected using AOI (Automated Optical Inspection) equipment. The inspection results showed that all nano-silver paste circuitry were complete and continuous, with no open circuits or short circuits.

[0067] Back bonding: Bonding equipment: A FOG Bonding device customized for small-sized AMOLEDs is used.

[0068] FPC Preparation: The FPC adopts a double-sided gold finger design, with the back contacts directly connecting to the nano silver paste circuitry on the back of the Panel.

[0069] Alignment and bonding: Using a CCD alignment system, the contacts on the FPC are aligned with the nano-silver paste lines on the back of the panel with high precision (alignment accuracy ±5μm). A temperature of 150°C and a pressure of 0.3MPa are applied, and the bonding time is 3 seconds to bond the FPC and the silver paste lines.

[0070] AOI inspection after bonding: AOI inspection after bonding shows that all bonding points have good contact, the on-resistance is less than 0.5Ω, and the cold solder joint rate is less than 0.01%.

[0071] LIPO vacuum encapsulation: Precision Module: Using LSR (Liquid Silicone Rubber) precision molds, which precisely fit around the back of the back-bonded module, especially the boundary area where the FPC connects to the panel.

[0072] Vacuum potting: The module is placed in a low-pressure vacuum potting apparatus. Under vacuum conditions, a ring of epoxy resin (LIPO) is injected into the corresponding area where the FPC and panel are connected through the pre-set injection channel of the LSR mold. Epoxy resin has good flowability and curing properties, which can fill the tiny gaps in the bonding area between the FPC and the back of the panel, and provide a certain degree of support and protection.

[0073] Results: The display module using the technology of this invention successfully controlled the bezel width to 0.95mm, which is about 0.55mm lower than the traditional front bonding technology (bezel of about 1.5mm), and the screen ratio is increased by about 4.5%.

[0074] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0075] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A back bonding process for ultrafine and ultrathin nano silver paste, characterized in that, Includes the following steps: S1: Process the three sides of the panel, including: laser cutting the side surface of the LTPS terminal to control the surface roughness to 1.5~2.5 micrometers; and performing plasma cleaning on the front and back of the LTPS terminal; S2: Fabrication of nano-silver paste circuitry on LTPS terminals using EHD equipment; S3: Laser sintering and curing of the sintered nano-silver paste circuit, followed by AOI inspection; S4: Using a dedicated FOG bonding device and a CCD alignment system, the FPC is precisely pressed onto the surface of the nano silver paste circuit. S5: Perform AOI inspection on Bonding's nano silver paste circuitry and FPC, and assemble the products that pass the inspection into ASSY units.

2. The ultrafine and ultrathin nano silver paste back bonding process according to claim 1, characterized in that, The fabrication of the nano-silver paste circuitry includes fabricating nano-silver paste circuitry on the front, side, and back surfaces of the LTPS terminals.

3. The ultrafine and ultrathin nano silver paste back bonding process according to claim 1, characterized in that, By fabricating nano-silver paste circuits on the front and back surfaces of LTPS terminals, signal conduction circuits are guided to the back of the LTPS terminals, enabling bonding on the back of the LTPS.

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