High-contrast transparent display device with hollow-out carrier plate and inverted COB (Chip On Board)

Abstract

The invention discloses high-contrast transparent display equipment with a hollowed-out carrier plate and a COB (Chip On Board) flip chip. The high-contrast transparent display equipment comprises the transparent carrier plate and an LED (Light Emitting Diode) chip array which is welded on the transparent carrier plate through the COB flip chip, the transparent carrier plate adopts a layered structure design and comprises a transparent substrate, a first metal layer, a first insulating layer and a second metal layer, the first metal layer, the first insulating layer and the second metal layer are sequentially stacked, and a hollow structure is formed through etching so as to improve light transmission; the first metal layer and the second metal layer are vertically and electrically connected through a through hole in the first insulating layer, and a bonding pad for welding is formed at the joint; the LED chip is inversely welded on the bonding pad through the solder bump; preferably, the surface of the bonding pad can be provided with an under bump metallization layer to improve the welding reliability, and the periphery of the LED chip can be provided with an enclosure frame packaging layer formed by black enclosure dam glue and a transparent packaging body filled with high-light-transmittance silica gel to absorb stray light and improve the contrast ratio and the light extraction efficiency; the invention combines high light transmittance and high contrast, and is suitable for the field of transparent display.

Description

Technical Field

[0001] This invention belongs to the field of display technology, specifically relating to a transparent display device, and more particularly to a high-contrast transparent display device that employs a hollow carrier board structure combined with chip-level packaging flip-chip bonding technology. Background Technology

[0002] Transparent display technology, with its ability to present information while maintaining background transparency, has shown great application potential in cutting-edge fields such as commercial windows, car windows, and augmented reality. The core challenge in achieving high-performance transparent displays lies in balancing light transmittance and display quality. Traditional solutions often employ the arrangement of micro-light-emitting devices, such as Micro-LEDs, on a transparent substrate. However, the metal layer used to lay out the driving circuitry inevitably blocks some background light, reducing overall light transmittance. Simultaneously, the dense array of light-emitting pixels and their encapsulation structure easily generates internal light reflection and scattering, resulting in a hazy and glare-prone display that severely degrades contrast and color performance.

[0003] In existing technologies, to improve light transmittance, some solutions attempt to reduce metal trace density or use highly transparent conductive materials, but this often comes at the cost of sacrificing circuit driving capability or increasing process complexity. On the other hand, to improve contrast, light-absorbing structures are usually placed on or around the surface of the light-emitting chip, but if these structures are not designed properly, they may further reduce effective light extraction efficiency or increase device thickness.

[0004] Therefore, there is a need to develop a new type of transparent display device structure that can optimize the light transmission path and suppress stray light, thereby achieving excellent display contrast and picture quality while maintaining high transparency. Summary of the Invention

[0005] This invention aims to provide a high-contrast transparent display device with a cutout carrier plate and COB flip-chip design. To solve the technical problem of achieving excellent display contrast while maintaining high transparency, the technical solution provided by this invention is as follows: A COB flip-chip high-contrast transparent display device with a hollowed-out carrier plate includes a transparent carrier plate, wherein the transparent carrier plate includes a transparent substrate and a first metal layer, a first insulating layer and a second metal layer sequentially stacked on the transparent substrate. The first insulating layer has multiple through holes, and the second metal layer is electrically connected to the first metal layer through the filling portion formed by filling the through holes; The transparent substrate is etched to form a hollow portion, which includes at least the transparent substrate and the area on the first insulating layer where no metal layer is disposed; The second metal layer has multiple pads and is electrically connected to the first metal layer through vias; An LED chip array is mounted on a transparent substrate, and the LED chip array is fixed to the pads by COB flip-chip bonding.

[0006] Furthermore, the first metal layer is provided with multiple parallel horizontal wires, and the second metal layer is provided with multiple parallel vertical wires, wherein the horizontal wires and the vertical wires are perpendicular to each other.

[0007] Furthermore, the pad is configured as a structure formed by locally widening the area corresponding to the via in the second metal layer.

[0008] Furthermore, it also includes a second insulating layer, which covers the second metal layer and the first insulating layer not covered by the second metal layer, and the second insulating layer has an opening corresponding to the position of the pad.

[0009] Furthermore, the surface of the pad is provided with a metallization layer under the bump, which includes an adhesion layer, a barrier layer and a solderable layer arranged sequentially from bottom to top.

[0010] Furthermore, the material of the adhesion layer is chromium or titanium, the material of the barrier layer is nickel or nickel-vanadium alloy, and the material of the solderable layer is gold or silver.

[0011] Furthermore, the LED chip array includes multiple LED chips, and the bonding surface of each LED chip is provided with solder bumps, which are connected to the pads by a thermo-press bonding process.

[0012] Furthermore, the LED chip array also includes a packaging structure, which is arranged around the outer periphery of the LED chip. The packaging structure includes: a frame packaging layer, which surrounds the LED chip and is connected to the transparent carrier plate at its bottom; and a transparent package, which fills the cavity formed by the frame packaging layer and covers the upper surface and sides of the LED chip.

[0013] Furthermore, the encapsulation layer is made of black dammed adhesive, and the transparent encapsulation body is made of high-transmittance liquid silicone.

[0014] Furthermore, the transparent substrate is made of chemically strengthened glass or transparent polyimide film with low coefficient of thermal expansion and high light transmittance.

[0015] The advantages of this invention are: 1. This invention precisely etches hollow areas onto a transparent substrate, removing the metal and insulating layers that obstruct non-signal traces, thus reducing the obstruction of background light by opaque materials. This allows background light to penetrate the display area with extremely low loss, achieving a superior transparent display effect close to the transmittance of the substrate itself. Simultaneously, the hollow design essentially maximizes the opening area, increasing the optical aperture ratio of the device and enhancing the sense of perspective.

[0016] 2. This invention utilizes a black damming adhesive material to form a frame encapsulation layer surrounding each LED chip. This effectively captures and absorbs scattered light emitted from the sides of the LED chip, preventing it from being mixed into the main outgoing light path after multiple reflections within the encapsulation cavity. Simultaneously, the frame encapsulation layer strongly absorbs reflections and diffusion from ambient light in front of the display panel. This suppresses halos and haze in dark conditions, making the black background appear deeper and purer. Therefore, the contrast ratio is improved by orders of magnitude, and color saturation and layering become more vivid and realistic due to the reduction of background stray light. Attached Figure Description

[0017] Figure 1 This is an overall structural diagram of a COB flip-chip high-contrast transparent display device with a hollowed-out carrier plate.

[0018] Figure 2 An exploded view of a COB flip-chip high-contrast transparent display device with a hollowed-out carrier plate.

[0019] Figure 3 This is an exploded left view of a transparent carrier plate for a COB flip-chip high-contrast transparent display device with a hollowed-out carrier plate.

[0020] Figure 4 This is an exploded right view of a transparent carrier plate for a COB flip-chip high-contrast transparent display device with a hollowed-out carrier plate.

[0021] Figure 5 This is a structural diagram of an LED chip for a COB flip-chip high-contrast transparent display device with a hollowed-out carrier plate.

[0022] Figure 6 This is a cross-sectional view of the packaged LED chip for a COB flip-chip high-contrast transparent display device with a hollow carrier substrate.

[0023] The diagram shows: 1. Transparent carrier plate, 2. LED chip array, 3. Transparent substrate, 4. First metal layer, 5. First insulating layer, 6. Second metal layer, 7. Second insulating layer, 8. Through hole, 9. Pad, 10. Opening, 11. LED chip, 12. Solder bump, 13. Enclosure layer, 14. Transparent package, 15. Filler. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0025] Example 1 A hollowed-out carrier plate COB flip-chip high-contrast transparent display device, such as Figure 1 As shown, it includes a transparent substrate 1 and an LED chip array 2 flip-chip bonded to the transparent substrate 1 via COB. Figure 3 As shown, the transparent substrate 1 features a layered stacked design, including a transparent substrate 3 and, from bottom to top, a first metal layer 4, a first insulating layer 5, and a second metal layer 6 sequentially disposed on the transparent substrate 3. Each layer is precisely positioned and stably connected through specific processes. Simultaneously, an etching process creates a hollow design, and combined with COB flip-chip technology, it achieves a balance between transparent display effects and high contrast performance.

[0026] The transparent substrate 3, as the basic support layer of the entire carrier plate structure, is located at the bottom of the transparent carrier plate 1, and its structural stability directly determines the overall strength of the carrier plate 1. The transparent substrate 3 is made of ultra-thin chemically strengthened glass with low thermal expansion coefficient and high light transmittance. The thickness can be flexibly selected between 0.1mm and 1.1mm according to the size requirements and support strength requirements of the actual application scenario.

[0027] Alternatively, when the equipment has higher requirements for lightweighting and flexibility, transparent substrate 3 can also be made of transparent polyimide film. Transparent polyimide film combines high light transmittance with excellent flexibility, making it suitable for special scenarios such as curved surface mounting.

[0028] The first metal layer 4 is directly fabricated on the upper surface of the transparent substrate 3. The first metal layer 4 is formed by sputtering and then etched to form a tightly bonded structure to the transparent substrate 3. The first metal layer 4 consists of multiple parallel horizontal conductive lines. Since the first metal layer 4 is used to lay scan lines, the horizontal scan lines enable the scan signal to be uniformly transmitted to each pixel unit in the horizontal direction, ensuring the synchronization of signal transmission. To ensure signal transmission efficiency, adjacent horizontal conductive lines maintain an equal spacing. The spacing can be precisely controlled according to the pixel density requirements, avoiding signal crosstalk caused by excessively small spacing and preventing excessively large spacing from affecting the pixel arrangement density.

[0029] The lower surface of the first insulating layer 5 is in close contact with the upper surface of the first metal layer 4 and the exposed upper surface of the transparent substrate 3. The first insulating layer 5 is fully covered on the upper surface of the first metal layer 4, and also extends to cover the exposed areas of the transparent substrate 3 not covered by the first metal layer 4. This achieves electrical isolation between the first metal layer 4 and the upper second metal layer 6, preventing direct contact between the two metal wires and causing a short circuit.

[0030] To ensure the electrical connection requirements of the first metal layer 4 and the second metal layer 6, multiple through holes 8 are uniformly opened on the first insulating layer 5 corresponding to the positions of the conductors in the first metal layer 4.

[0031] The through-holes 8 and the first metal layer 4 are positioned in a one-to-one correspondence. The vertical projection of each through-hole 8 falls on the conductor of the first metal layer 4 below, providing a channel for the subsequent vertical electrical connection between the second metal layer 6 and the first metal layer 4.

[0032] The second metal layer 6 is formed on the upper surface of the first insulating layer 5. The second metal layer 6 is formed by sputtering and then etched to form a film that is tightly bonded to the transparent substrate 3. The second metal layer 6 has multiple parallel vertically arranged wires, and the extension direction of the vertical wires is perpendicular to the horizontal wires of the first metal layer 4. Since the second metal layer 6 is used to lay data lines, the data lines are usually set vertically. The vertical wires transmit data signals to each pixel unit in a vertical direction, and together with the horizontal scan lines, they form a grid-like pixel driving network to achieve precise driving of each LED chip 11.

[0033] like Figure 4 As shown, the second metal layer 6 is partially filled with second metal layer 6 material within the through-hole 8 of the first insulating layer 5, and this filled portion of second metal layer 6 material is designated as a filling portion 15. This allows the metal portion filled into the through-hole 8 to directly contact the upper surface of the lower first metal layer 4, thereby achieving a vertical electrical connection between the second metal layer 6 and the first metal layer 4.

[0034] Furthermore, at the vertical electrical connection between the second metal layer 6 and the first metal layer 4, the second metal layer 6 is locally widened to form a pad 9, the vertical projection of which completely covers the via 8 area. The pad 9 is electrically connected to the first metal layer 4 at the bottom of the via 8 through a metal portion within the via 8, thereby achieving a vertical electrical connection between the second metal layer 6 and the first metal layer 4. The pad 9 can increase the electrical connection contact area, reduce contact resistance, and provide a stable connection point for subsequent COB flip-chip bonding of the LED chip 11.

[0035] In a preferred embodiment, a second insulating layer 7 covers the upper surface of the second metal layer 6, extending to cover the exposed areas of the first insulating layer 5 not covered by the second metal layer 6. An opening 10 is provided on the second insulating layer 7 corresponding to the pads 9 on the second metal layer 6, and the lower surface of the second insulating layer 7 is in close contact with the non-pad areas of the second metal layer 6. This not only protects the second metal layer 6 from corrosion by the external environment but also further enhances the electrical isolation between the first metal layer 4 and the second metal layer 6, ensuring the stability of signal transmission.

[0036] To achieve high structural transparency, the transparent substrate 1 is hollowed out using a precise etching process, forming hollowed-out sections. These hollowed-out sections include areas on the transparent substrate 3 and the first insulating layer 5 where no metal layer is present. The transparent substrate 1 retains the support areas for metal conductors and pads 9, as well as the areas etched away to form the hollowed-out sections. The absence of metal and insulating layers in these hollowed-out sections allows light to freely penetrate the transparent substrate 1, resulting in high light transmittance for the entire substrate.

[0037] like Figure 2 As shown, an LED chip array 2, comprising LED chips 11, is soldered onto pad 9. Each LED chip 11 in the LED chip array 2 is precisely aligned and flip-chip-converted onto its corresponding pad 9, with the soldering surface of the LED chip 11 facing the pad 9 and corresponding to the metal surface of the pad 9. Through flip-chip soldering, heat can be dissipated via the shortest path, resulting in a lower chip junction temperature. The LED chip 11 operates at lower temperatures, exhibiting higher luminous efficacy and less light decay. Under the same current, it emits brighter light; or under the same brightness, it operates more stably and has a longer lifespan.

[0038] like Figure 6 As shown, a solder bump 12 is soldered to the bottom of the LED chip 11. The solder bump 12 protrudes from the soldering surface of the LED chip 11, serving as an intermediate medium for connection with the pad 9. The shape of the solder bump 12 can be columnar or spherical depending on the soldering requirements. The solder bump 12 uses a tin-silver-copper alloy, or eutectic / near-eutectic solders such as SnAg and SnBi. These solders have a low eutectic temperature, enabling melting bonding at a lower temperature and avoiding damage to heat-sensitive structures such as the transparent substrate 3 and the insulating layer caused by high-temperature soldering. At the same time, the resulting solder joint has high mechanical strength and excellent conductivity, ensuring a long-term stable connection between the LED chip 11 and the pad 9.

[0039] In a preferred embodiment, to address the issue of unstable interfacial compounds formed when solder reacts directly with the pad metal, leading to brightness degradation of the LED chip 11, a sub-metallization layer is prepared on the surface of the pad 9 at the bonding positions of the solder bumps 12 of the LED chip 11. This sub-metallization layer is a thin film covering the upper surface of the pad 9. The sub-metallization layer consists of an adhesion layer, a barrier layer, and a solderable layer, stacked sequentially from the surface of the pad 9 upwards.

[0040] The adhesion layer is directly bonded to the surface of the pad 9 and is made of materials such as chromium or titanium, which have strong adhesion to both the metal pad 9 and the insulating layer. The adhesion layer enhances the bond strength between the under-bump metallization layer and the pad 9, preventing delamination during subsequent soldering. The barrier layer is located above the adhesion layer and is made of materials with excellent diffusion blocking properties, such as nickel or nickel-vanadium alloys. The barrier layer prevents metal atoms from the solder bump 12 from diffusing into the pad 9 during soldering, avoiding changes in the solder joint composition due to metal diffusion, thereby ensuring the electrical performance and mechanical strength of the solder joint. The solderable layer is located on top of the under-bump metallization layer and is in direct contact with the solder bump 12 of the LED chip 11. The solderable layer is made of materials with low surface energy and low oxidation resistance, such as gold or silver, which improves the wettability of the solder bump 12, allowing the melted solder to spread evenly on the surface of the solderable layer, forming a complete, void-free metallurgical interface.

[0041] COB flip-chip bonding of LED chips 11 to transparent substrate 1 is achieved through a combination of mass transfer and thermocompression bonding processes. The mass transfer process precisely picks up and places a large number of LED chips 11 onto the corresponding pads 9 on the transparent substrate 1, ensuring precise alignment between the solder bumps 12 on the bottom of each LED chip 11 and the metallization layer under the bumps on the surface of the pad 9. The entire LED chip array 2 is heated in an inert protective atmosphere of formic acid vapor or a nitrogen-hydrogen mixture, with the heating temperature controlled above the eutectic temperature of the solder, melting the solder bumps 12 on the bottom of the LED chips 11. Under the pressure applied by the thermocompression device, the molten solder spreads completely under the combined action of surface tension and pressure. After heating is stopped and cooling and solidification are performed, the molten solder re-solidifies, firmly connecting the solder bumps 12 of the LED chips 11 to the pads 9.

[0042] In a preferred embodiment, in order to further highlight the high luminous efficiency of the flip-chip LED 11, a composite packaging structure is integrated on the LED chip 11. The composite packaging structure includes a frame packaging layer 13 and a transparent package 14.

[0043] The frame encapsulation layer 13 is located on the outer layer of the composite encapsulation structure, surrounding the LED chip 11 in an annular frame shape. Its bottom is tightly connected to the second insulating layer 7 of the transparent carrier 1 through a dispensing and curing process. The inner sidewall of the frame maintains a small gap with the side of the LED chip 11, which can both prevent the chip from being squeezed and provide space for the transparent package 14 to fill. The transparent package 14 fills the cavity enclosed by the frame encapsulation layer 13 and completely covers the upper surface and side of the LED chip 11. The bottom of the transparent package 14 forms a tight fit with the upper surface of the LED chip 11, the inner sidewall of the frame encapsulation layer 13, and the upper surface of the second insulating layer 7 of the transparent carrier 1.

[0044] The frame encapsulation layer 13 uses a damming adhesive material. The sealed enclosure formed by the damming adhesive material can separate the encapsulation areas of adjacent LED chips 11 to avoid crosstalk. In a preferred embodiment, the frame encapsulation layer 13 uses black damming adhesive, which can efficiently absorb stray light from the environment and scattered light from the LED chips 11, thereby preventing stray light from being mixed into the effective display light after multiple reflections within the encapsulation area. This helps reduce glare and fogging of the image, thereby improving the contrast of the displayed image, making the details in light and dark clearer and the color levels more distinct.

[0045] like Figure 5 As shown, the transparent encapsulation 14 uses a high-transmittance liquid silicone material. This material has a high optical refractive index matching with the LED chip 11, minimizing light reflection loss at the chip-encapsulation interface, improving light extraction efficiency, and ensuring that the light emitted by the LED chip 11 can penetrate the transparent encapsulation 14 with high brightness. Simultaneously, after the liquid silicone is filled into the frame cavity through a dispensing process, it can cure at room temperature or low temperature to form a bubble-free, fully bonded encapsulation structure. This structure avoids light scattering or refraction distortion caused by encapsulation defects, further ensuring the uniformity and clarity of the displayed image. Furthermore, the material's excellent aging resistance ensures stable light transmittance during long-term use, preventing yellowing, decreased transmittance, and other problems, maintaining a durable high-quality display effect.

[0046] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A COB flip-chip high-contrast transparent display device with a hollowed-out carrier plate, characterized in that, It includes a transparent carrier plate (1), which includes a transparent substrate (3) and a first metal layer (4), a first insulating layer (5) and a second metal layer (6) sequentially stacked on the transparent substrate (3). The first insulating layer (5) is provided with a plurality of through holes (8), and the second metal layer (6) is electrically connected to the first metal layer (4) through the filling portion (15) formed by filling the through holes (8); The transparent substrate (1) is etched to form a hollow portion, which includes at least the transparent substrate (3) and the area on the first insulating layer (5) where no metal layer is provided; The second metal layer (6) is provided with a plurality of pads (9) and is electrically connected to the first metal layer (4) through through holes (8); An LED chip array (2) is provided on a transparent substrate (1), and the LED chip array (2) is fixed on the pad (9) by COB flip soldering.

2. The COB flip-chip high-contrast transparent display device with a hollow carrier plate according to claim 1, characterized in that, The first metal layer (4) is provided with multiple parallel horizontal wires, and the second metal layer (6) is provided with multiple parallel vertical wires, wherein the horizontal wires are perpendicular to the vertical wires.

3. The COB flip-chip high-contrast transparent display device with a hollow carrier plate according to claim 1, characterized in that, The pad (9) is configured as a structure formed by locally widening the area of ​​the second metal layer (6) corresponding to the through hole (8).

4. The COB flip-chip high-contrast transparent display device with a hollow carrier plate according to any one of claims 1 to 3, characterized in that, It also includes a second insulating layer (7), which covers the second metal layer (6) and the first insulating layer (5) not covered by the second metal layer (6), and the second insulating layer (7) has an opening (10) at the position corresponding to the pad (9).

5. The COB flip-chip high-contrast transparent display device with a hollow carrier plate according to claim 1, characterized in that, The surface of the pad (9) is provided with a bump under-metallization layer, which includes an adhesion layer, a barrier layer and a solderable layer arranged sequentially from bottom to top.

6. The COB flip-chip high-contrast transparent display device with a hollow carrier plate according to claim 5, characterized in that, The adhesive layer is made of chromium or titanium, the barrier layer is made of nickel or a nickel-vanadium alloy, and the solderable layer is made of gold or silver.

7. The COB flip-chip high-contrast transparent display device with a hollow carrier plate according to claim 1, characterized in that, The LED chip array (2) includes multiple LED chips (11). The soldering surface of the LED chip (11) is provided with solder bumps (12). The solder bumps (12) are connected to the pads (9) or the metallization layer under the bumps by a hot-press bonding process.

8. The COB flip-chip high-contrast transparent display device with a hollow carrier plate according to claim 1, characterized in that, The LED chip array (2) also includes a packaging structure, which is arranged around the outer periphery of the LED chip (11). The packaging structure includes: a frame packaging layer (13), which surrounds the LED chip (11) and is connected to the transparent carrier plate (1) at the bottom; and a transparent package (14), which fills the cavity formed by the frame packaging layer (13) and covers the upper surface and side surface of the LED chip (11).

9. The COB flip-chip high-contrast transparent display device with a hollow carrier plate according to claim 8, characterized in that, The encapsulation layer (13) is made of black dammed adhesive, and the transparent encapsulation body (14) is made of high-transmittance liquid silicone.

10. The COB flip-chip high-contrast transparent display device with a hollow carrier plate according to claim 1, characterized in that, The transparent substrate (3) is made of chemically strengthened glass or transparent polyimide film with low thermal expansion coefficient and high light transmittance.

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