Inverted COB packaging structure and packaging method thereof

Abstract

The flip COB packaging structure comprises a substrate, a copper circuit is arranged on the substrate, and the copper circuit comprises a plurality of chip bonding pads and wires electrically connected with the adjacent chip bonding pads; each chip bonding pad is welded with a flip LED chip electrically connected with the chip bonding pad through a die bonding solder; the outer contour size of the chip bonding pad is larger than the outer contour size of the flip LED chip corresponding to the chip bonding pad and the outer contour size of the solid crystal welding flux, so that the outer edge of the chip bonding pad protrudes out of the outer edge of the flip LED chip and the outer edge of the solid crystal welding flux. High-reflection white glue is filled between the adjacent chip bonding pads, the top of the high-reflection white glue protrudes upwards, and the highest point of the high-reflection white glue is higher than the top surfaces of the chip bonding pads; the substrate is further provided with fluorescent powder glue used for sealing the copper circuit, the flip LED chip and the high-reflection white glue. The invention has the advantage of improving the lighting effect and reliability of the light source.

Description

Technical Field

[0001] The present invention relates to the technical field of COB packaging, and in particular to a flip-chip COB packaging structure and a packaging method thereof. Background Art

[0002] Chip-on-Board (COB) packaging technology has become one of the mainstream technologies in the field of high-power LED applications due to its excellent heat dissipation performance and compact packaging structure.

[0003] However, the existing flip-chip COB packaging technology still faces some challenges. The traditional flip-chip COB packaging process usually uses solder paste printing for die bonding, that is, printing solder paste on the chip pad of the substrate, and then placing the flip-chip LED chip on the solder paste, melting the solder paste through reflow soldering, and soldering the chip to the substrate together. In this method, the flux in the solder paste will volatilize during the high-temperature reflow soldering process and remain in the light source area between the chips. These residues will discolor when exposed to light and high temperature for a long time, which will not only affect the aesthetics of the COB light source, but also reduce its luminous efficiency and have an adverse effect on long-term reliability. In addition, in order to prevent short circuits, traditional flip-chip COB packaging usually uses white oil spraying to insulate the non-electrode pad area of ​​the substrate. However, the reflectivity of white oil is low and its long-term stability is poor, which further limits the improvement of the luminous efficiency of the flip-chip COB light source.

[0004] Therefore, it is necessary to further improve and perfect the prior art to overcome these shortcomings, and the present invention is made based on this situation. Summary of the invention

[0005] The object of the present invention is to overcome the deficiencies of the prior art and to provide a flip-chip COB packaging structure and a packaging method thereof that can improve the light efficiency and reliability of a light source.

[0006] The present invention can be implemented by the following technical solutions:

[0007] In order to solve the above technical problems, the present invention provides a flip-chip COB packaging structure, including a substrate, on which a copper circuit is arranged, and the copper circuit includes a plurality of chip pads and wires electrically connecting adjacent chip pads; each of the chip pads is soldered with a flip-chip LED chip electrically connected thereto by a solid crystal solder; the outer contour dimensions of the chip pads are larger than the outer contour dimensions of the corresponding flip-chip LED chip and the solid crystal solder, so that the outer edges of the chip pads protrude from the outer edges of the flip-chip LED chip and the outer edges of the solid crystal solder; highly reflective white glue is filled between adjacent chip pads, the top of the highly reflective white glue protrudes upward, and its highest point is higher than the top surface of the chip pad; the substrate is also provided with a phosphor glue for sealing the copper circuit, the flip-chip LED chip and the highly reflective white glue.

[0008] In order to further solve the technical problem to be solved by the present invention, the present invention provides a flip-chip COB packaging structure, in which the chip pad includes two oppositely arranged electrode pads, the flip-chip LED chip spans between the two electrode pads, and an electrode gap is provided between the two electrode pads, and no high-reflective white glue is provided in the electrode gap.

[0009] In order to further solve the technical problem to be solved by the present invention, in a flip-chip COB packaging structure provided by the present invention, the high-reflective white glue is formed by dispensing liquid high-reflective white glue in the gap between the chip pads through a dispensing process, and after dispensing, it is quickly cured by high-temperature baking at not less than 150°C; when dispensing, the chip pads are first facing upward, and glue is dispensed in the gaps between the chip pads to allow the high-reflective white glue to diffuse. When the high-reflective white glue flows to the side of the chip pad, the chip pad is turned over and facing downward, and finally a baking device is placed under the chip pad for rapid curing by high-temperature baking at not less than 150°C.

[0010] In order to further solve the technical problem to be solved by the present invention, in a flip-chip COB packaging structure provided by the present invention, a circle of dam glue surrounding the copper circuit is provided on the substrate, and the height of the dam glue is consistent with the height of the phosphor glue, forming a cavity for accommodating the phosphor glue to prevent the phosphor glue from overflowing.

[0011] In order to further solve the technical problem to be solved by the present invention, in a flip-chip COB packaging structure provided by the present invention, the height difference H between the highest point of the high-reflective white glue and the top surface of the chip pad is not less than 50 μm.

[0012] In order to further solve the technical problem to be solved by the present invention, in a flip-chip COB packaging structure provided by the present invention, the distance M between the outer edge of the flip-chip LED chip and the outer edge corresponding to the chip pad is 50-150 μm.

[0013] In order to further solve the technical problem to be solved by the present invention, in a flip-chip COB packaging structure provided by the present invention, no high-reflective white glue is provided at the wire, and the width T of the wire is not greater than 200 μm.

[0014] In order to further solve the technical problem to be solved by the present invention, in a flip-chip COB packaging structure provided by the present invention, the spacing L1 between two adjacent chip pad edges in the horizontal direction is equal to the spacing L2 between two adjacent chip pad edges in the vertical direction.

[0015] The present invention can also be implemented by the following technical solutions:

[0016] In order to solve the above technical problems, the present invention provides a flip-chip COB packaging method for packaging a flip-chip COB packaging structure as described above, comprising the following steps:

[0017] S1. Soldering: placing the substrate upright so that the chip pad on the substrate faces upward, applying a solid crystal solder on the chip pad, placing the flip-chip LED chip (3) on the solid crystal solder (4), and applying temperature so that the flip-chip LED chip (3) and the chip pad (21) are firmly soldered, wherein the outer contour of the chip pad is larger than the outer contour of the corresponding flip-chip LED chip and the solid crystal solder;

[0018] S2, the first glue dispensing, using a fine glue dispensing head to dispense liquid high-reflective white glue in the gaps between the chip pads, wherein the high-reflective white glue is not provided at the wires; after dispensing, the high-reflective white glue is allowed to diffuse, and when the high-reflective white glue is observed to flow to the side of the chip pad, the substrate is turned over so that the chip pad on the substrate faces downward;

[0019] S3, first baking, after the substrate is turned over, the baking device is placed under the chip pad for high temperature baking at not less than 150°C for more than 5 minutes, so that the highly reflective white glue in the gap of the chip pad is quickly solidified and a stable micro-convex morphology is formed;

[0020] S4, dispense glue for the second time, then put the substrate upright, and use the dispensing head to dispense liquid high-reflective white glue on the blank area of ​​the substrate outside the chip pad;

[0021] S5, second baking, using a baking device to bake the high-reflective white glue on the front side to solidify it;

[0022] S6, sealing glue, coating the phosphor glue used to seal the copper circuit, flip-chip LED chip and high-reflective white glue on the substrate, and baking and curing, completing the entire packaging process.

[0023] In order to further solve the technical problem to be solved by the present invention, a flip-chip COB packaging method provided by the present invention further comprises the following steps between step S1 and step S2:

[0024] Step S1.5, coating a circle of dam glue surrounding the copper circuit on the substrate, and baking to fix the dam.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] The flip-chip COB packaging structure provided by the present invention is formed by filling highly reflective white glue between the chip pads, and the outer edge of the chip pad protrudes from the outer edge of the flip-chip LED chip and the outer edge of the solid crystal solder, so that the highly reflective white glue forms a slightly convex top morphology due to surface tension. Such a structure effectively improves the light efficiency and reliability of the COB light source. The structure can effectively shield the low-reflectivity substrate and solid crystal residues, while avoiding blocking the light from the side of the chip, thereby achieving higher light output efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings, wherein:

[0028] Figure 1 is a cross-sectional schematic diagram of the present invention;

[0029] Figure 2 is a cross-sectional schematic diagram of another embodiment;

[0030] Figure 3 It is a top view schematic diagram of the present invention. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0032] The present invention provides a flip-chip COB packaging structure, such as Figures 1 to 3 As shown. The structure includes a substrate 1 and a copper circuit 2 thereon. The substrate 1 is a supporting structure that provides mechanical support and electrical insulation, and different materials and structures can be selected according to different application requirements. For example, an insulating ceramic substrate with excellent thermal conductivity can be used, such as an alumina ceramic substrate (Al2O3) or an aluminum nitride ceramic substrate (AlN), such as Figure 1 As shown. These ceramic substrates can effectively dissipate heat and improve the reliability of the device. In addition, a more economical solution can also be adopted, that is, a layer of insulating layer 11 is covered on the commonly used aluminum substrate, such as Figure 2 The insulating layer 11 can be made of materials such as epoxy resin and polyimide, and its thickness needs to be selected according to the actual application to ensure sufficient insulation performance.

[0033] On the substrate 1, a copper circuit 2 is provided. Preferably, the thickness of the copper circuit 2 is not less than 50 μm to ensure sufficient current carrying capacity and mechanical strength. This thickness can be achieved by a variety of processes, such as a printed circuit board process, a sputtering process or an electroplating process. The copper circuit 2 consists of a plurality of chip pads 21 and wires 22 connecting these pads. The chip pads 21 provide electrical connection and mechanical support for the flip-chip LED chip 3. The wires 22 are responsible for connecting adjacent chip pads 21 to form a complete circuit.

[0034] A flip-chip LED chip 3 is soldered to each chip pad 21 by a die-bonding solder 4. The function of the die-bonding solder 4 is to fix the flip-chip LED chip 3 on the chip pad 21 and provide electrical connection. Commonly used die-bonding solder 4 is solder paste, which contains a flux component to facilitate the soldering process. The active light-emitting surface of the flip-chip LED chip 3 faces downward and directly contacts the substrate 1 or the insulating layer 11, thereby achieving a shorter heat dissipation path and improving heat dissipation efficiency.

[0035] Highly reflective white glue 5 is filled between adjacent chip pads 21, which not only plays the role of electrical insulation and mechanical protection, but more importantly, it has a significant contribution to improving the light efficiency. More importantly, the top of the highly reflective white glue 5 bulges upward to form a slightly convex lens-like structure, the highest point of which is higher than the top surface of the chip pad 21. This unique shape design, as well as its high reflective properties, is the key to achieving efficient light output.

[0036] Highly reflective white glue 5 usually refers to epoxy resin used for filling around the chip and the bottom of the package. In order to achieve the requirement of high reflectivity, the epoxy resin is added with high reflectivity fillers, such as titanium oxide (TiO2), barium sulfate (BaSO4) or other similar materials, so that it appears white and has excellent light reflection performance, and the reflectivity is required to be greater than 98%.

[0037] Since the light-emitting area of ​​the flip-chip LED chip is close to the substrate, the light emitted from the side of the chip is easily absorbed by the adjacent chip or other low-reflectivity areas, thereby reducing the overall light output efficiency. To solve this problem, the present invention creatively utilizes the convex structure of the highly reflective white glue 5.

[0038] Specifically, in the present invention, the height difference H between the highest point of the highly reflective white glue 5 and the top surface of the chip pad 21 is not less than 50μm, and is further preferably greater than half of the total thickness of the chip pad 21 and the die-bonding solder 4. The reason for selecting 50μm as the minimum value is that the thickness of the chip pad 21 is usually around 100μm, or even thicker. The highly reflective white glue 5 is flush with the pad at the edge close to the chip pad 21, and due to the effect of surface tension, it bulges upward in the center area to form the highest point. When the height difference H is greater than half of the total thickness of the chip pad 21 and the die-bonding solder 4 (about 50μm), the light emitted from the side of the chip can almost be blocked and reflected by the highly reflective white glue 5, changing the propagation direction to emit upward, thereby minimizing the loss of light absorbed by adjacent chips.

[0039] This raised, highly reflective white glue 5 has multiple functions:

[0040] 1) Improve substrate reflectivity: Shield the substrate area with low reflectivity, effectively improving the overall reflectivity of the substrate.

[0041] 2) Shielding residues: Covering organic matter such as flux remaining on the substrate after die bonding, preventing these residues from changing color or deteriorating during long-term use, affecting light efficiency and reliability.

[0042] 3) Improve the side light output efficiency: By reflecting the light on the side of the chip, the light absorbed by the adjacent chip is reduced, which significantly improves the light output efficiency of the chip.

[0043] 4) Forming a microlens effect: The raised white glue surface is similar to a microlens, which can converge part of the light and further improve the light extraction efficiency.

[0044] Through the above design, the present invention effectively utilizes the characteristics of the highly reflective white glue 5, realizes the effective utilization of the light from the side of the chip, and thus significantly improves the overall light efficiency of the flip-chip COB package. This micro-convex structure design not only improves the light efficiency, but also simplifies the manufacturing process and reduces the manufacturing cost, and has important practical value.

[0045] In order to achieve the expected characteristics of the highly reflective white glue 5 and effectively apply it to the flip-chip COB packaging structure, the present invention has carried out a series of innovative design and process improvements:

[0046] First, precise control of pad, chip and solder dimensions:

[0047] In the present invention, the design of the size and relative position relationship of the chip pad 21, the flip-chip LED chip 3 and the die-bonding solder 4 is crucial to achieve the best performance of the highly reflective white glue 5. The design mainly focuses on the following key aspects:

[0048] The outer contour size of the chip pad 21 is designed to be larger than the outer contour size of the corresponding flip-chip LED chip 3 and the die-bonding solder 4. This makes the outer edge of the chip pad 21 protrude from the outer edge of the flip-chip LED chip 3 and the outer edge of the die-bonding solder 4. Such a design creates a circle of vital exposed area between the chip pad 21 and the flip-chip LED chip 3. This circle of exposed area lays the foundation for the subsequent high-reflection white glue 5 to form a slightly convex shape.

[0049] The micro-convex structure of the highly reflective white glue 5 relies on the surface tension generated at the side wall of the chip pad 21. In order to ensure the effective formation of surface tension, the area of ​​the chip pad 21 must be larger than the area of ​​the solidified die-bonding solder 4. If the die-bonding solder 4 overflows to the edge of the chip pad 21, due to its inherent fluidity, it will spread along the side wall of the chip pad 21 to form a slope, thereby eliminating the sharp edge angle required to form surface tension. This will make it difficult for the highly reflective white glue 5 to form an ideal micro-convex shape at the side wall, thereby affecting its light reflection performance. Therefore, the present invention particularly emphasizes that the outer edge of the die-bonding solder 4 cannot exceed the outer edge of the chip pad 21. Figure 1 As shown, a certain distance N needs to be maintained between the two. This design effectively ensures that the highly reflective white glue 5 can form an ideal micro-convex shape at the side wall of the chip pad 21, thereby maximizing its optical performance.

[0050] In addition, in order to maximize the coverage area of ​​the highly reflective white glue 5 to improve the lighting effect, ideally the area of ​​the chip pad 21 should be as small as possible. However, a chip pad area that is too small will increase the difficulty of chip mounting and may affect the welding quality. Therefore, the present invention seeks a balance in the size design of the chip pad 21. Specifically, the distance M between the outer edge of the flip-chip LED chip 3 and the corresponding outer edge of the chip pad 21 is controlled within the range of 50-150μm, and the more preferred range is 95-105μm. The setting of this range not only ensures sufficient white glue filling space, but also takes into account the processability and reliability of chip mounting.

[0051] In summary, the present invention creates necessary conditions for filling with highly reflective white glue and forming a micro-convex structure by precisely controlling the sizes of the chip pad, flip-chip LED chip and die-bonding solder, and carefully designing their relative positions, thereby ultimately achieving a significant improvement in the lighting efficiency of the flip-chip COB package.

[0052] Second, the dispensing and rapid curing process of high-reflective white glue:

[0053] The application and curing process of the highly reflective white glue 5 has a crucial impact on the performance of the final device. The present invention adopts an optimized dispensing and rapid curing process to ensure the formation of an ideal micro-convex morphology and maximize the optical properties of the highly reflective white glue.

[0054] 1) Precision dispensing: The filling of the highly reflective white glue 5 adopts a precision dispensing process. The liquid highly reflective white glue is precisely dispensed into the gaps between the chip pads 21 using a fine needle. This method can accurately control the filling amount and position of the white glue, ensure that the white glue is evenly distributed, and form the required initial micro-convex shape. The use of a fine needle helps to improve the accuracy and consistency of dispensing, especially when the chip spacing is small.

[0055] 2) Rapid high temperature curing: The curing process of the highly reflective white glue 5 is a key innovation of the present invention. After the highly reflective white glue is dispensed, it will naturally form a slightly convex shape due to the effect of surface tension. However, the traditional baking process (low temperature first and then high temperature) is not suitable for the present invention. This is because during the heating process, the viscosity of the white glue will decrease and the fluidity will increase, causing its slightly convex shape to change or even collapse.

[0056] In order to avoid this problem, the present invention adopts a rapid high temperature curing process. Specifically, the substrate after dispensing is directly placed in a high temperature environment for rapid curing. There are two feasible solutions:

[0057] High temperature reflow soldering: Place the substrate directly in a high temperature reflow oven and use a high temperature of over 150°C for rapid shaping.

[0058] High temperature oven: Place the substrate in a high temperature oven at not less than 150°C and bake for more than 5 minutes to quickly solidify the surface of the white glue and form a stable micro-convex morphology. After that, according to the characteristics of the white glue, use conventional baking conditions to complete the complete curing of the white glue.

[0059] This rapid high-temperature curing process can make the surface of the white glue cure quickly to form a stable micro-convex structure. Even if the temperature is lowered and the fluidity of the white glue is increased during the subsequent curing process, it will not affect its formed shape.

[0060] When performing the glue dispensing operation, the following key steps need to be noted: First, place the chip pad 21 upward. Then, accurately apply the highly reflective white glue 5 in the gap between adjacent chip pads 21. After dispensing, let the glue spread. When the colloid is observed to flow and contact the side of the chip pad 21, turn the chip pad 21 over so that it faces downward. At this time, place a preheated baking device (such as a radiant heating light source) under the chip pad 21 for high-temperature baking to achieve rapid solidification of the colloid, thereby forming it.

[0061] In addition, it should be emphasized that the highly reflective white glue 5 located in the gap between adjacent chip pads 21 needs to form a specific micro-convex structure. As for the highly reflective white glue 5 in the large gap outside the chip, there is no need to deliberately pursue the micro-convex structure, and it can be operated according to the conventional glue dispensing process. This differentiated treatment is intended to ensure the performance and stability of the final product. The main reason is that the highly reflective white glue 5 in the gap between the chips will have the light from the side of the chip absorbed by the adjacent chip, while the highly reflective white glue 5 in the area outside that is not between the chips does not have this problem, so it is only necessary to make the middle high-reflective white glue 5 into a micro-convex structure, and the outside does not need it, which can simplify the process. In the specific operation, after the fine glue in the gap between the chip pads 21 is fixed, the outside area that needs to be glued can be coated by glue dispensing.

[0062] 3) Chip pad thickness control: In order to ensure the uniformity and controllability of glue dispensing, the thickness of the chip pad 21 needs to be controlled. A chip pad that is too thin will make glue dispensing difficult, and it will be difficult to control the filling amount and shape of the white glue. A chip pad that is too thick will increase the manufacturing cost. In the present invention, the thickness range of the chip pad 21 is set to 30-150μm. This thickness range is determined after comprehensively considering the feasibility of the glue dispensing process, the manufacturing cost, and the performance of the final device. The chip pad 21 can be made by a variety of methods, such as etching a pattern after hot pressing a copper sheet on a substrate, or directly electroplating or sputtering on the substrate.

[0063] In summary, the present invention achieves precise control of the shape and performance of the highly reflective white glue 5 by adopting precision dispensing and rapid high-temperature curing processes, combined with control of the chip pad thickness, thereby significantly improving the light efficiency and reliability of the flip-chip COB package.

[0064] Third, the design of electrode pads and wires:

[0065] In the present invention, the design of the chip pad 21 and the wire 22 is also carefully considered to optimize the electrical and optical performance of the device.

[0066] 1) Electrode pads and gaps: Each chip pad 21 includes two electrode pads 211 arranged opposite to each other. The flip-chip LED chip 3 spans between the two electrode pads 211 and is electrically connected thereto through the die-bonding solder 4. An electrode gap 212 is provided between the two electrode pads 211. Importantly, the electrode gap 212 is not filled with highly reflective white glue 5. This is because the main function of the highly reflective white glue 5 is to increase light reflectivity, not conduct electricity. If the white glue is filled into the electrode gap, it may affect the electrical connection between the flip-chip LED chip 3 and the electrode pad 211, thereby reducing the performance of the device and even causing the device to fail.

[0067] 2) Wire width control: The wire 22 is usually at the same height as the chip pad 21. In order to prevent the highly reflective white glue 5 from flowing from the wire 22 to the chip pad 21, causing overflow and affecting the performance of the device, the present invention is specially designed not to set the highly reflective white glue 5 at the wire 22. The highly reflective white glue 5 also forms a micro-convex structure on the side of the wire 22 due to surface tension. This design can effectively isolate the excessive contact between the white glue and the wire, prevent the white glue from diffusing along the wire to the chip pad 21, thereby ensuring the cleanliness of the chip pad 21 and the reliability of the electrical connection.

[0068] In addition, since the reflectivity of the copper wire 22 is low, in order to minimize its absorption of light, the width T of the wire 22 is controlled within the smallest possible range, no greater than 200 μm, and a more preferred range is 100-150 μm. A narrower wire width can reduce its shielding of light, thereby improving light output efficiency. At the same time, the width range also needs to take into account the current carrying capacity of the wire to ensure the normal operation of the device.

[0069] In summary, the present invention minimizes the risk of light absorption and white glue overflow while ensuring the electrical performance of the device by designing and sizing the electrode pads, electrode gaps, and wires, thereby further improving the overall light efficiency and reliability of the flip-chip COB package.

[0070] Fourth, other optimizations:

[0071] In addition to the above key designs, the present invention also makes a series of other optimizations to further improve the performance and reliability of flip-chip COB packaging:

[0072] 1) Eutectic welding process: The present invention preferably uses eutectic welding process to weld the flip-chip LED chip 3. Compared with other welding methods, eutectic welding has the following advantages:

[0073] Thinner chip electrodes: Eutectic welding can use thinner chip electrodes, thereby reducing the obstruction of light on the side of the chip and improving light extraction efficiency.

[0074] Less solder overflow: During eutectic soldering, there is less solder overflow and it is easier to control, which is very important for the subsequent filling and molding of high-reflective white glue.

[0075] Higher reliability: Eutectic soldering can form more reliable solder connections and improve the long-term stability of the device.

[0076] 2) Uniform chip spacing: In order to achieve stable and reliable white glue dispensing, the present invention designs a uniform chip spacing. Figure 3 As shown, the spacing L1 between the edges of two adjacent chip pads 21 in the horizontal direction is equal to the spacing L2 between the edges of two adjacent chip pads 21 in the vertical direction. This uniform spacing design can ensure that the white glue is filled more uniformly between the chips, thereby forming a more ideal micro-convex shape and improving the light effect.

[0077] 3) Application of phosphor glue and powder deposition scheme:

[0078] In order to convert the blue light emitted by the flip-chip LED chip 3 into white light and provide protection while encapsulating, the present invention sets a phosphor glue 6 on the substrate 1. The phosphor glue 6 is used to seal the copper circuit 2, the flip-chip LED chip 3 and the highly reflective white glue 5. There are two methods for preparing the phosphor glue:

[0079] Mixing phosphor and silica gel: Evenly mix the phosphor and transparent encapsulating silica gel.

[0080] Powder deposition solution: The phosphor is deposited at the bottom of the COB light source phosphor glue.

[0081] Although the difference in luminous efficacy between the two solutions is not large, the powder deposition solution has better heat dissipation performance. Since the phosphor is deposited near the bottom of the substrate 1, the heat generated during the phosphor conversion process can be more effectively conducted through the substrate, thereby reducing the temperature of the phosphor and improving the reliability and service life of the device.

[0082] 4) Design of dam glue:

[0083] In order to confine the phosphor glue 6 and the highly reflective white glue 5 to a specific light source area (for example, Figure 3 In order to prevent the phosphor glue from overflowing, a circle of dam glue 7 is provided on the substrate 1. The height of the dam glue 7 is consistent with the height of the phosphor glue 6, forming a cavity for accommodating the phosphor glue 6. This design can effectively control the flow and distribution of the phosphor glue, prevent it from contaminating other areas, and improve the manufacturing yield of the device.

[0084] In general, the present invention sets a copper circuit 2 layer on the COB substrate 1, and the thickness of the copper circuit layer is not less than 50μm. Ensure that the chip pad 21 of the copper circuit 2 is only slightly larger than the flip-chip LED chip 3, and then use a fine glue dispensing head to perform fine glue dispensing according to the area of ​​the gap between the chip pad 21, to ensure that the amount of glue of the high-reflective white glue 5 can be filled in the gap between the chip pad 21, and is only slightly higher than the copper circuit 2 layer. Being only slightly higher than the copper circuit 2 layer can ensure that the high-reflective white glue 5 will not diffuse to the copper circuit 2 layer due to the existence of surface tension. In this way, the COB light source with white glue that presents a slightly convex surface tension is placed in an oven for baking, and the baking oven temperature is set to high temperature to ensure that the surface of the white glue can be quickly solidified due to high temperature, and to avoid the low temperature process causing the entire white glue to increase in fluidity and cause insufficient surface tension and flow to the side wall of the chip. Because the white glue has a very high reflectivity, and the light source of the flip-chip LED chip 3 is at the bottom of the chip, if the side of the chip is covered by white glue, the light on the side cannot go out, which will affect the chip light emission and reduce the light efficiency. The micro-convex morphology of the white glue can be preserved after the surface is quickly micro-cured, so that the light from the side of the chip can be emitted normally.

[0085] The flip-chip COB packaging structure provided by the present invention is formed by filling highly reflective white glue between the chip pads, and the outer edge of the chip pad 21 protrudes from the outer edge of the flip-chip LED chip 3 and the outer edge of the die-bonding solder 4, so that the highly reflective white glue forms a slightly convex top morphology due to surface tension. Such a structure effectively improves the light efficiency and reliability of the COB light source. The structure can effectively shield the low-reflectivity substrate and die-bonding residues, while avoiding blocking the light from the side of the chip, thereby achieving higher light output efficiency.

[0086] In addition, the present invention also provides a flip-chip COB packaging structure and a packaging method thereof, which can effectively improve light efficiency, reduce costs and enhance reliability. The present invention is described in detail below in conjunction with specific embodiments.

[0087] Substrate preparation: A ceramic substrate of appropriate thickness is selected as the substrate material, which has good thermal conductivity and mechanical strength. A copper circuit 2 of appropriate thickness is deposited on the ceramic substrate, and the copper circuit includes a plurality of chip pads 21 and wires 22 for electrically connecting adjacent chip pads. The size of the chip pad 21 is designed to be slightly larger than the size of the flip-chip LED chip 3 and the size of the die-bonding solder 4. The width of the wire 22 is designed to be 150 μm to minimize light blocking.

[0088] Flip-chip LED chip welding (step S1): Place the substrate 1 upright so that the chip pad 21 faces upward. Apply an appropriate amount of solid crystal solder 4 on each chip pad 21, for example, use a dispenser to accurately apply eutectic solder flux. Then, the flip-chip LED chip 3 is accurately placed on the solid crystal solder 4. Using a vacuum eutectic welding process, under a vacuum and nitrogen protection atmosphere, the temperature is raised to above 280°C and maintained for a period of time to melt the solid crystal solder 4, thereby firmly welding the flip-chip LED chip 3 to the chip pad 21.

[0089] Dam glue coating (step S1.5): On the substrate 1, a circle of dam glue 7 is coated along the periphery of the copper circuit 2, for example, using silica gel. The height of the dam glue 7 is designed to be consistent with the thickness of the phosphor glue 6 to be subsequently coated. The substrate coated with the dam glue is placed in an oven for baking to solidify the dam glue 7 and form a cavity for accommodating the phosphor glue 6.

[0090] High-reflective white glue filling – first stage (step S2): Use a fine glue dispensing head to dispense liquid high-reflective white glue 5 in the gaps between adjacent chip pads 21. High-reflective white glue is not filled at the wires 22. The amount of glue dispensed is controlled so that the high-reflective white glue 5 just fills the gaps between the chip pads 21 and is slightly higher than the surface of the chip pads 21. Due to the effect of surface tension, the high-reflective white glue 5 will form a slightly raised liquid surface between the chip pads 21. After dispensing, when it is observed that the high-reflective white glue 5 diffuses to the side of the chip pad 21, turn the substrate 1 over so that the chip pad 21 faces downward.

[0091] High-reflective white glue curing – first stage (step S3): The flipped substrate 1 is placed in an oven and baked at 150°C for 5 minutes. The heating light source in the oven shines on the high-reflective white glue 5 from bottom to top. High-temperature baking can quickly cure the surface of the high-reflective white glue 5 to form a stable micro-convex morphology, while preventing the high-reflective white glue 5 from flowing to the side of the flip-chip LED chip 3, thereby avoiding affecting the light effect.

[0092] Highly reflective white glue filling - second stage (step S4): The substrate 1 is turned over again so that the chip pad 21 faces upward. The blank area on the substrate 1 outside the chip pad 21 is filled with highly reflective white glue 5 using a dispensing head.

[0093] High-reflective white glue curing - second stage (step S5): the substrate 1 is placed in an oven for baking to completely cure the high-reflective white glue 5.

[0094] Phosphor glue coating (step S6): A layer of phosphor glue 6 is coated on the substrate 1 to completely seal the copper circuit 2, the flip-chip LED chip 3 and the highly reflective white glue 5. The thickness of the phosphor glue 6 is controlled to be about 0.5 mm and is limited to a predetermined area by the dam glue 7. The substrate coated with the phosphor glue is placed in an oven for baking to completely cure the phosphor glue 6.

[0095] The present invention may also use other types of substrate materials, die-bonding solder, highly reflective white glue and phosphor glue, and different process parameters, such as baking temperature and time, etc. The specific implementation method may be adjusted according to actual needs without departing from the core idea of ​​the present invention.

[0096] It is worth noting that the flipping operation is performed after dispensing glue in the gap between the chip pads 21, and then baking is performed, mainly based on the following two key reasons:

[0097] ① Enhance the formation of micro-convex structure: After dispensing, the highly reflective white glue 5 is in liquid state, and under the action of surface tension, a preliminary, slightly convex liquid surface will be formed between the chip pads 21. However, the degree of convexity formed by surface tension alone is limited, and the shape is not stable enough. By turning the substrate 1 over so that the uncured liquid highly reflective white glue 5 faces downward, the gravity can be used to cause the highly reflective white glue 5 to flow further downward and concentrate, thereby enhancing its convexity and forming a more obvious micro-convex lens structure. This micro-convex structure can effectively converge and reflect the light emitted by the flip-chip LED chip 3, improve the light emission efficiency, and ultimately improve the light efficiency of the COB light source.

[0098] ② Prevent white glue from contaminating the side of the chip: The light-emitting surface of the flip-chip LED chip 3 is located at the bottom, and there is also a certain amount of light emitted from the side. If the highly reflective white glue 5 flows to the side of the chip 3, it will hinder the light emission and reduce the light efficiency. Although the white glue can be quickly cured by baking immediately after dispensing, due to the viscosity and surface tension of the white glue, some of the white glue may still flow to the side of the chip during the baking process. By flipping the substrate so that the chip pad 21 faces downward, under the action of gravity, the liquid highly reflective white glue 5 will tend to flow downward and away from the side of the chip, thereby effectively preventing the white glue from contaminating the side of the chip, ensuring that the light can be smoothly emitted from the side of the chip, and maximizing the light efficiency.

[0099] In summary, the operation of flipping and baking after dispensing the glue cleverly utilizes gravity, which not only enhances the micro-convex structure of the highly reflective white glue, but also prevents the white glue from contaminating the side of the chip, which is crucial to improving the light efficiency of the COB light source. This step reflects the ingenuity of the process design of the present invention and effectively solves the shortcomings of the prior art.

Claims

1. A flip-chip COB packaging structure, characterized in that: The invention comprises a substrate (1), on which a copper circuit (2) is arranged, wherein the copper circuit (2) comprises a plurality of chip pads (21) and wires (22) electrically connecting adjacent chip pads (21); a flip-chip LED chip (3) electrically connected thereto is soldered to each chip pad (21) via a solid crystal solder (4); the outer contour dimensions of the chip pad (21) are larger than the outer contour dimensions of the corresponding flip-chip LED chip (3) and the solid crystal solder (4), so that the outer edge of the chip pad (21) protrudes from the outer edge of the flip-chip LED chip (3) and the outer edge of the solid crystal solder (4); highly reflective white glue (5) is filled between adjacent chip pads (21), the top of the highly reflective white glue (5) protrudes upward, and its highest point is higher than the top surface of the chip pad (21); and a fluorescent powder glue (6) for sealing the copper circuit (2), the flip-chip LED chip (3) and the highly reflective white glue (5) is also arranged on the substrate (1).

2. The flip-chip COB packaging structure according to claim 1, characterized in that: The chip pad (21) comprises two electrode pads (211) arranged opposite to each other, the flip-chip LED chip (3) spans between the two electrode pads (211), an electrode gap (212) is provided between the two electrode pads (211), and no high-reflective white glue (5) is provided in the electrode gap (212).

3. The flip-chip COB packaging structure according to claim 1, characterized in that: The highly reflective white glue (5) is formed by dispensing liquid highly reflective white glue (5) in the gaps between chip pads (21) through a dispensing process, and then rapidly solidifying by baking at a high temperature of not less than 150°C. When dispensing, the chip pads (21) are first facing upwards, and dispensing is performed in the gaps between the chip pads (21) to allow the highly reflective white glue (5) to diffuse. When the highly reflective white glue (5) flows to the side of the chip pads (21) that contacts the chip pads (21), the chip pads (21) are turned upside down so that the chip pads (21) face downwards, and finally a baking device is placed under the chip pads (21) to perform rapid baking at a high temperature of not less than 150°C to rapidly solidify.

4. The flip-chip COB packaging structure according to claim 1, characterized in that: The substrate (1) is provided with a circle of dam glue (7) surrounding the copper circuit (2); the height of the dam glue (7) is consistent with the height of the fluorescent glue (6), forming a cavity for accommodating the fluorescent glue (6) to prevent the fluorescent glue (6) from overflowing.

5. The flip-chip COB packaging structure according to claim 1, characterized in that: The height difference H between the highest point of the highly reflective white glue (5) and the top surface of the chip pad (21) is not less than 50 μm.

6. The flip-chip COB packaging structure according to claim 1, characterized in that: The distance M between the outer edge of the flip-chip LED chip (3) and the corresponding outer edge of the chip pad (21) is 50-150 μm.

7. The flip-chip COB packaging structure according to claim 1, characterized in that: The conductive line (22) is not provided with high-reflective white glue (5), and the width T of the conductive line (22) is not greater than 200 μm.

8. The flip-chip COB packaging structure according to claim 1, characterized in that: The spacing L1 between the edges of two adjacent chip pads (21) in the transverse direction is equal to the spacing L2 between the edges of two adjacent chip pads (21) in the longitudinal direction.

9. A flip-chip COB packaging method, used for packaging a flip-chip COB packaging structure according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. Soldering: placing the substrate (1) upright so that the chip pad (21) on the substrate (1) faces upward, applying a solid crystal solder (4) to the chip pad (21), placing the flip-chip LED chip (3) at the position of the solid crystal solder (4), and applying temperature so that the flip-chip LED chip (3) and the chip pad (21) are firmly soldered, wherein the outer contour dimensions of the chip pad (21) are larger than the outer contour dimensions of the corresponding flip-chip LED chip (3) and the solid crystal solder (4); S2, dispensing glue for the first time, using a fine dispensing head to dispense liquid high-reflective white glue (5) in the gaps between the chip pads (21), wherein the high-reflective white glue (5) is not provided at the wires (22); after dispensing glue, the high-reflective white glue (5) is allowed to diffuse, and when the high-reflective white glue (5) is observed to flow to the side of the chip pads (21), the substrate (1) is turned over so that the chip pads (21) on the substrate (1) face downward; S3, first baking, after the substrate (1) is turned over, a baking device is placed under the chip pad (21) to perform high temperature baking at not less than 150° C. for more than 5 minutes, so that the highly reflective white glue (5) in the gap of the chip pad (21) is quickly solidified and forms a stable micro-convex morphology; S4, dispensing glue for the second time, placing the substrate (1) upright again, and using a dispensing head to dispense liquid highly reflective white glue (5) on the blank area of ​​the substrate (1) outside the chip pad (21); S5, second baking, using a baking device to bake the high-reflective white glue (5) on the front side to solidify it; S6, sealing glue, coating the phosphor glue (6) for sealing the copper circuit (2), the flip-chip LED chip (3) and the high-reflective white glue (5) on the substrate (1), and baking and curing, thereby completing the entire packaging process.

10. A flip-chip COB packaging method according to claim 9, characterized in that: There are also the following steps between step S1 and step S2: Step S1.5, coating a circle of dam glue (7) surrounding the copper circuit (2) on the substrate (1), and baking to fix the dam.

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