A hybrid packaging micro-led device based on moc and cob process

Abstract

This application discloses a hybrid packaged Micro-LED device based on MOC and COB processes, belonging to the field of Micro-LED display technology. The device includes a substrate assembly, a chip assembly, and an integrated encapsulating layer. The integrated encapsulating layer completely covers the chip assembly and gold wires, including an integrally formed square gold wire protection portion and a light-emitting surface with a preset curvature. It can be formed using various materials such as silicone, epoxy resin, or UV adhesive. This invention solves the problems of poor surface flatness in traditional COB encapsulation and the limited availability of MOC encapsulation materials. The encapsulating surface is flat and aesthetically pleasing, with uniform thickness, allowing for flexible optical design without the need for secondary lenses. The device is thin, compact, and highly reliable, suitable for various Micro-LED display and lighting applications.

Description

Technical Field

[0001] This invention relates to the field of Micro-LED display and packaging technology, specifically to a hybrid packaged Micro-LED device that combines the precision molding characteristics of molded packaging (MOC) with the material flexibility of chip-on-board (COB), and is particularly suitable for applications with high requirements for packaging thickness, optical effect and reliability, such as small-pitch displays, wearable displays and automotive displays. Background Technology

[0002] Micro-LED, as a next-generation display technology, boasts advantages such as high brightness, low power consumption, long lifespan, and fast response speed. However, its packaging process directly determines the optical performance, reliability, and manufacturing cost of the device. Currently, the mainstream Micro-LED packaging structures are mainly divided into two categories: COB packaging structure and MOC molding structure, both of which have significant structural limitations.

[0003] Firstly, the COB packaging structure employs a layered dispensing structure of "damming adhesive + filler adhesive": high-viscosity damming adhesive is first applied around the chip to form a dam, and after the first baking and curing, low-viscosity filler adhesive is then applied inside the dam, followed by a second baking and curing to complete the encapsulation. This structure has the following inherent defects: 1. Due to the difference in step height and the fluidity of the adhesive, the flatness of the adhesive surface after dispensing is poor, and the thickness uniformity error of the adhesive layer usually exceeds ±0.05mm. Multiple layers are prone to collapse and sagging, resulting in poor appearance consistency. 2. The damming adhesive and the filler adhesive are two different materials. After curing, there is a clear material interface. Bubbles, delamination and stress concentration are easily generated at the interface. Moisture can easily penetrate along the interface, leading to gold wire corrosion, chip failure and insufficient airtightness and reliability of the device. 3. The light-emitting surface is a naturally leveled flat or slightly convex surface, which makes it impossible to precisely control the light emission angle and light spot shape. If it is necessary to achieve light collection or large-angle diffused light, a secondary optical lens must be installed, which increases the overall thickness of the device and the assembly cost.

[0004] Secondly, the MOC (Metal-on-Chip) encapsulation structure employs a transfer molding process, using acrylic-based epoxy molding compound (EMC) as raw material, and molding the encapsulation layer in a single step under high temperature and pressure using precision molds. This structure has the following limitations: 1. It has extremely poor material compatibility, only compatible with specific acrylic-based molding compounds, and cannot use silicone, conventional epoxy resin or UV adhesive with better optical properties, making it difficult to achieve high light transmittance, low stress and yellowing resistance. 2. The molding compound is brittle and has a high modulus, which makes it poorly matched with the thermal expansion coefficient of the flexible printed circuit board (FPC). The adhesive layer is prone to cracking when bent or subjected to temperature shock. 3. The investment in molds and equipment is high, and new molds need to be made for product changes, resulting in a long development cycle, which is not suitable for small-batch, multi-variety customized production; 4. After molding, the light-emitting surface is mostly a plane or a simple sphere, which reduces the degree of freedom in optical design and makes it difficult to achieve complex curved surfaces through molding processes.

[0005] In summary, neither existing COB nor MOC packaging structures can simultaneously meet the demands for high-precision molding, multi-material compatibility, flexible optical design, and low-cost manufacturing, becoming key bottlenecks restricting the performance improvement and large-scale application of Micro-LED devices. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a hybrid packaged Micro-LED device based on MOC and COB processes. This invention solves the technical problems of poor adhesive surface flatness, numerous interface defects, and limited optical design in existing COB packaging structures, as well as the single material, high stress, and poor adaptability of MOC molding structures. It achieves a balance between high-precision molding, multi-material compatibility, high reliability, and thinness.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A hybrid packaged Micro-LED device based on MOC and COB processes includes a substrate assembly, a chip assembly, and an integrated encapsulating adhesive layer; The substrate assembly includes a metal heat dissipation substrate, a thermally conductive adhesive layer, and a flexible circuit board. The flexible circuit board is laminated to the upper surface of the metal heat dissipation substrate through the thermally conductive adhesive layer, and conductive lines and chip pads are arranged on the surface of the flexible circuit board. The chip assembly includes a Micro-LED light-emitting chip, a CMOS driver chip, and several gold wires. The Micro-LED light-emitting chip and the CMOS driver chip are both fixed to the chip pad area of ​​the flexible circuit board. The gold wires are bonded between the chip electrodes and the line pads of the flexible circuit board to achieve electrical interconnection. The integrated encapsulating adhesive layer completely covers the chip assembly and gold wires, and the bottom of the adhesive layer is sealed and bonded to the upper surface of the flexible circuit board. The integrated encapsulating adhesive layer includes an integrally formed gold wire protection part and a light-emitting part. The gold wire protection part is a square columnar structure, and the light-emitting part is a curved surface structure with a preset curvature. The integrated encapsulating adhesive layer is an interface-free integral structure formed by a single injection curing of any one of silicone, addition-cured epoxy resin, or UV-curable adhesive.

[0008] In a preferred embodiment, the gold wire protection part and the light-emitting part are independent cavity structures; a horizontal dividing layer is provided between the two, and a light-transmitting hole is opened on the horizontal dividing layer corresponding to the light-emitting area of ​​the Micro-LED light-emitting chip.

[0009] In a preferred embodiment, the gold wire protection part and the light-emitting part are integrated cavity structures; their sidewalls are smoothly transitioned, and their internal cavities are interconnected.

[0010] In a preferred embodiment, the light-emitting surface is a spherical or aspherical convex structure with a light-emitting half-angle of 10° to 30°, forming a small-angle light-receiving optical structure.

[0011] In a preferred embodiment, the light-emitting surface has a free-form structure with a light emission half-angle of 90° to 150°, forming a large-angle diffused optical structure.

[0012] In a preferred embodiment, the integrated encapsulating adhesive layer has a dual-color composite structure; the area surrounding the gold wire protection part and the CMOS driver chip is a black opaque adhesive area, and the light-emitting surface is a transparent adhesive area; the two adhesive materials are cured simultaneously, and there is no delamination interface at the joint.

[0013] In a preferred embodiment, the metal heat dissipation substrate is a copper substrate, an aluminum substrate, or a copper-aluminum alloy substrate, with a thickness of 0.2 mm to 1.0 mm; the thermally conductive adhesive layer is a thermally conductive double-sided adhesive or a thermally conductive film, with a thermal conductivity ≥ 1.0 W / (m·K).

[0014] In a preferred embodiment, the total thickness of the integrated encapsulating adhesive layer is 0.1mm~0.5mm, and the surface flatness error is ≤±0.02mm; the visible light transmittance of the adhesive material is ≥90%, the refractive index is 1.4~1.6, and the Shore hardness is A30~D80.

[0015] In a preferred embodiment, the gold wire is a pure gold wire or a gold-palladium alloy wire with a wire diameter of 18μm to 30μm and a gold wire arch height of 60μm to 120μm; both the Micro-LED light-emitting chip and the CMOS driver chip are fixed to the surface of the flexible circuit board with insulating die-bonding adhesive.

[0016] In a preferred embodiment, the integrated encapsulating adhesive layer is formed by one-time injection and curing using a high-temperature resistant mold strip or a stainless steel fixture cover plate cavity; the adhesive layer has no gaps with the bonding area of ​​the flexible circuit board, forming an airtight encapsulation structure.

[0017] Due to the application of the above technical solution, the beneficial effects of this application compared with the prior art are as follows: 1. High precision of adhesive surface and good consistency of appearance.

[0018] The integrated encapsulation adhesive layer is precisely formed through the mold cavity, and the flatness error of the adhesive surface can be controlled within ±0.02mm, which is far superior to the traditional dispensing process; the curved shape of the light-emitting surface is controllable, without collapse or sagging defects, and the product appearance yield is significantly improved.

[0019] 2. The interface-free integrated structure significantly improves reliability.

[0020] The encapsulating adhesive layer is a single-application, one-time curing integral structure, eliminating the material interface between the damming adhesive and the filler adhesive, thus structurally eliminating interface bubbles, delamination, and moisture intrusion paths; the adhesive layer is sealed and bonded to the substrate, with excellent airtightness, and can pass the dual 85 high temperature and high humidity test for more than 1000 hours, significantly extending the device's lifespan.

[0021] 3. It has strong material compatibility and flexible performance adaptation.

[0022] It breaks through the limitation that the MOC process can only use acrylic molding compound, and is compatible with a variety of mainstream encapsulation materials such as silicone, epoxy resin, and UV adhesive. The optimal material can be matched according to the application scenario: for example, silicone is suitable for flexible and bendable scenarios, epoxy resin is suitable for high hardness and high wear resistance scenarios, and UV adhesive is suitable for fast curing mass production scenarios, balancing performance and cost.

[0023] 4. High optical integration, resulting in thinner and lighter devices.

[0024] The light-emitting face is integrally formed with a curved optical structure on the encapsulating adhesive layer, which can accurately achieve any light emission angle within the range of 10°~150°. It replaces the traditional external secondary lens, reduces the overall thickness of the device by more than 30%, and makes the structure more compact, making it suitable for thin and light terminal devices.

[0025] 5. Low development cost and fast response speed.

[0026] The corresponding molding molds can use low-cost PC mold strips or simple stainless steel fixtures, eliminating the need for expensive precision plastic sealing molds. The mold opening cost is reduced by more than 80%, and the development cycle is shortened to 1 / 5 of the traditional MOC process, making it especially suitable for small-batch customization and rapid prototyping scenarios. Attached Figure Description

[0027] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 This is an exploded view of the independent cavity small-angle light-collecting Micro-LED device described in Embodiment 1 of the present invention; Figure 2 This is a top view of the structure of Embodiment 1 of the present invention; Figure 3 This is a schematic cross-sectional view of the integrated cavity standard light-emitting Micro-LED device described in Embodiment 2 of the present invention; Figure 4 This is a schematic cross-sectional view of the dual-color wide-angle diffused Micro-LED device described in Embodiment 3 of the present invention; The components include: 1. Metal heat dissipation substrate; 2. Thermally conductive adhesive layer; 3. Flexible circuit board; 4. Micro-LED light-emitting chip; 5. CMOS driver chip; 6. Integrated encapsulation adhesive layer; 61. Gold wire protection section; 62. Light-emitting surface. Detailed Implementation

[0029] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0030] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this application described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0031] In this application, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing the invention and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation.

[0032] Furthermore, in addition to indicating direction or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in certain situations to indicate a dependency or connection. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0033] Furthermore, the terms "installation," "setup," "equipped with," "connection," "linking," and "socketing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral structure; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium, or an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0034] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0035] Example 1 like Figure 1 , Figure 2 As shown, this embodiment provides a Micro-LED device with an independent cavity and a small-angle light-receiving type, which is suitable for high-brightness indication and projection display scenarios.

[0036] The device comprises, from bottom to top, a metal heat dissipation substrate 1, a thermally conductive adhesive layer 2, a flexible circuit board 3, a chip assembly, and an integrated encapsulation adhesive layer 6.

[0037] The metal heat dissipation substrate 1 is made of pure copper substrate with a thickness of 0.5 mm and a nickel-gold plating finish, with a thermal conductivity ≥380 W / (m·K). The flexible circuit board 3 is a double-layer PI substrate FPC with a thickness of 0.1 mm and copper lines and gold-plated pads on its surface. The lower surface of the flexible circuit board 3 is bonded to the metal heat dissipation substrate 1 through a thermally conductive adhesive layer 2. The thermally conductive adhesive layer 2 is a thermally conductive double-sided adhesive with a thickness of 0.05 mm and a thermal conductivity of 1.5 W / (m·K).

[0038] The chip assembly includes one Micro-LED light-emitting chip 4 and one CMOS driver chip 5, both of which are fixed to the corresponding pad areas of the flexible circuit board 3 by insulating die bond adhesive. The Micro-LED light-emitting chip 4 is a positive blue light chip with a size of 100μm×100μm. The CMOS driver chip 5 is a silicon-based driver IC with a size of 0.5mm×0.5mm. The gold wire is 99.99% pure gold wire with a wire diameter of 25μm and an arch height of 80μm, which is used to bond the chip electrodes to the FPC pads to achieve electrical interconnection.

[0039] The integrated encapsulating adhesive layer 6 is made of high-refractive-index addition-cured silicone with a refractive index of 1.54, visible light transmittance of 92%, Shore hardness A50, total thickness of 0.3mm, and surface flatness error of ±0.015mm. This embodiment adopts an independent cavity structure, with the adhesive layer divided into a lower gold wire protection part 61 and an upper light-emitting part 62.

[0040] The gold wire protection part 61 is a square columnar structure with a side length of 1.2mm and a height of 0.12mm. It completely encloses the gold wire, the Micro-LED light-emitting chip 4, and the CMOS driver chip 5. The sidewalls are perpendicular to the substrate surface, and the bottom is tightly bonded to the flexible circuit board 3. The light-emitting part 62 is a spherical convex structure with a radius of curvature of 2.0mm and a light emission half-angle of 15°, achieving a small-angle light collection effect. The center brightness is improved by more than 45% compared with the planar package. A horizontal dividing layer is provided between the gold wire protection part 61 and the light-emitting part 62. A circular light-transmitting hole with a diameter of 0.8mm is opened in the dividing layer corresponding to the light-emitting area of ​​the Micro-LED chip.

[0041] In this embodiment, the device is formed by one-time injection molding and curing of high-temperature resistant PC mold strips. The mold strip cavity and the shape of the adhesive layer are perfectly matched. After molding, the device can be demolded to obtain a high-precision encapsulation surface.

[0042] Example 2 like Figure 3 As shown, this embodiment provides a standard light-emitting hybrid packaged Micro-LED device with an integrated cavity, suitable for conventional display modules.

[0043] The structure of the substrate assembly and chip assembly in this embodiment is basically the same as that in Embodiment 1, except that: the metal heat dissipation substrate 1 is made of aluminum alloy substrate with a thickness of 0.3mm; the flexible circuit board 3 is a single-layer FPC with a thickness of 0.08mm.

[0044] The integrated encapsulation layer 6 is made of bisphenol A type epoxy resin, with a heat distortion temperature of 120℃, Shore hardness of D60, total thickness of 0.2mm, and surface flatness error of ±0.02mm. In this embodiment, a one-piece cavity structure is adopted, with a smooth transition between the sidewalls of the gold wire protection part 61 and the light-emitting part 62, and the internal cavity is connected without a dividing layer.

[0045] The square cavity of the gold wire protection part 61 has a side length of 1.0mm and a height of 0.1mm; the light-emitting part 62 has a gently convex structure with a curvature radius of 5.0mm, a light emission half angle of 30°, and a light emission uniformity of ≥90%, balancing brightness and viewing angle, making it suitable for use in conventional display panels.

[0046] In this embodiment, the device is formed by injection molding and curing using a combination of stainless steel fixture and cover plate. The fixture carries the substrate and chip, and the cover plate cavity forms the light-emitting curved surface. During demolding, the product is ejected through the ejection hole at the bottom of the fixture, resulting in high molding efficiency and suitability for small to medium batch production.

[0047] Example 3 like Figure 4 As shown, this embodiment provides a dual-color, wide-angle diffused hybrid packaged Micro-LED device, suitable for backlight and surface light source scenarios.

[0048] The structure of the substrate assembly and chip assembly in this embodiment is basically the same as that in Embodiment 1. The difference is that the metal heat dissipation substrate 1 uses a thick copper substrate with a thickness of 0.8mm to meet the heat dissipation requirements of high-power chips.

[0049] The integrated encapsulation adhesive layer 6 has a dual-color composite structure with a total thickness of 0.4mm and a surface flatness error of ±0.01mm. Among them, the area around the gold wire protection part 61 and the CMOS driver chip 5 is a black opaque adhesive area, which uses epoxy resin filled with carbon black and has a light-blocking rate OD≥5, which can effectively absorb side stray light and prevent cross-light and light leakage between pixels. The light-emitting surface 62 is a transparent adhesive area, which uses high-transmittance UV adhesive with a light transmittance of 93% and a refractive index of 1.48.

[0050] This embodiment employs a one-piece cavity structure, with the light-emitting surface 62 designed as a peanut-shaped freeform surface. The light emission half-angle is 120°, achieving uniform light dispersion over a large angle and good Lambertian light characteristics. It achieves a surface light source effect without the need for an additional diffusion film. The black adhesive area and the transparent adhesive area are injected into the cavity in stages and then simultaneously UV-cured, resulting in a tight, non-delaminating bond.

[0051] The device in this embodiment is formed by high-hardness epoxy resin molding strips, which can be reused more than 500 times, and the overall cost is lower than that of traditional MOC process.

[0052] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A hybrid packaged Micro-LED device based on MOC and COB processes, characterized in that, This includes substrate components, chip components, and an integrated encapsulation adhesive layer; The substrate assembly includes a metal heat dissipation substrate, a thermally conductive adhesive layer, and a flexible circuit board. The flexible circuit board is laminated to the upper surface of the metal heat dissipation substrate through the thermally conductive adhesive layer, and conductive lines and chip pads are arranged on the surface of the flexible circuit board. The chip assembly includes a Micro-LED light-emitting chip, a CMOS driver chip, and several gold wires. The Micro-LED light-emitting chip and the CMOS driver chip are both fixed to the chip pad area of ​​the flexible circuit board. The gold wires are bonded between the chip electrodes and the line pads of the flexible circuit board to achieve electrical interconnection. The integrated encapsulating adhesive layer completely covers the chip assembly and gold wires, and the bottom of the adhesive layer is sealed and bonded to the upper surface of the flexible circuit board. The integrated encapsulating adhesive layer includes an integrally formed gold wire protection part and a light-emitting part. The gold wire protection part is a square columnar structure, and the light-emitting part is a curved surface structure with a preset curvature. The integrated encapsulating adhesive layer is an interface-free integral structure formed by a single injection curing of any one of silicone, addition-cured epoxy resin, or UV-curable adhesive.

2. The hybrid packaged Micro-LED device according to claim 1, characterized in that, The gold wire protection part and the light-emitting part are independent cavity structures; a horizontal dividing layer is provided between the two, and a light-transmitting hole is opened on the horizontal dividing layer corresponding to the light-emitting area of ​​the Micro-LED light-emitting chip.

3. The hybrid packaged Micro-LED device according to claim 1, characterized in that, The gold wire protection part and the light-emitting part are integrated cavity structures; their sidewalls are smoothly transitioned, and their internal cavities are interconnected.

4. The hybrid packaged Micro-LED device according to claim 1, characterized in that, The light-emitting surface has a spherical or aspherical convex structure with a light-emitting half-angle of 10° to 30°, forming a small-angle light-receiving optical structure.

5. The hybrid packaged Micro-LED device according to claim 1, characterized in that, The light-emitting surface has a free-form structure with a light emission half-angle of 90°~150°, forming a large-angle diffused optical structure.

6. The hybrid packaged Micro-LED device according to claim 1, characterized in that, The integrated encapsulation adhesive layer has a dual-color composite structure; the area around the gold wire protection part and the CMOS driver chip is a black opaque adhesive area, and the light-emitting part is a transparent adhesive area; the two adhesive materials are cured simultaneously, and there is no delamination interface at the joint.

7. The hybrid packaged Micro-LED device according to claim 1, characterized in that, The metal heat dissipation substrate is a copper substrate, an aluminum substrate, or a copper-aluminum alloy substrate, with a thickness of 0.2mm to 1.0mm; the thermally conductive adhesive layer is a thermally conductive double-sided adhesive or a thermally conductive film, with a thermal conductivity ≥1.0W / (m·K).

8. The hybrid packaged Micro-LED device according to claim 1, characterized in that, The total thickness of the integrated encapsulating adhesive layer is 0.1mm~0.5mm, and the flatness error of the adhesive surface is ≤±0.02mm; the visible light transmittance of the adhesive material is ≥90%, the refractive index is 1.4~1.6, and the Shore hardness is A30~D80.

9. The hybrid packaged Micro-LED device according to claim 1, characterized in that, The gold wire is pure gold wire or gold-palladium alloy wire, with a wire diameter of 18μm~30μm and a gold wire arch height of 60μm~120μm; the Micro-LED light-emitting chip and the CMOS driver chip are both fixed to the surface of the flexible circuit board by insulating die bond adhesive.

10. The hybrid packaged Micro-LED device according to claim 1, characterized in that, The integrated encapsulation adhesive layer is formed by one-time injection and curing of adhesive through a high-temperature resistant mold strip or a stainless steel fixture cover plate cavity; there is no gap between the adhesive layer and the bonding area of ​​the flexible circuit board, forming an airtight encapsulation structure.

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