Flip-chip LED array and manufacturing method therefor

Abstract

The present invention relates to the technical field of light emitting diodes. Disclosed are a flip-chip LED array and a manufacturing method therefor. The manufacturing method comprises the following steps: (1) fixing one side of a substrate of each flip-chip LED to an adhesive film layer, so as to obtain a chip array; (2) soldering pads of the chip array to solder joints of a packaging substrate; and stripping off the adhesive film layer to obtain a soldered array; (3) removing the substrates and intrinsic semiconductor layers of the flip-chip LEDs of the soldered array, so as to obtain a first intermediate array; (4) forming a reflection layer between adjacent flip-chip LEDs of the first intermediate array, so as to obtain a second intermediate array; and (5) forming a fluorescent layer on the side of the second intermediate array away from the packaging substrate, so as to obtain a finished flip-chip LED array. Implementing the present invention can improve the brightness, the yield and the reliability and prolong the service life of flip-chip LED arrays, and further can shorten the manufacturing process and reduce the product cost.

Description

Flip-chip LED chip array and preparation method thereof Technical Field

[0001] The present invention relates to the technical field of light emitting diodes, and in particular to a flip-chip LED chip array and a preparation method thereof. Background Art

[0002] Light-emitting diodes (LEDs) are solid-state semiconductor devices that convert electrical energy into visible light. As lighting devices, they offer significant advantages over traditional lighting devices: long life, high luminous efficiency, zero radiation, low power consumption, and environmental friendliness. Currently, LEDs are primarily used in display screens, indicator lights, and backlight sources.

[0003] Traditional LED packaging uses a substrate or bracket as the base, with the chip's positive and negative terminals connected via metal wires. The LED is then encapsulated with encapsulant. However, this packaging process requires wire bonding, resulting in low reliability and high overall thermal resistance, which shortens the LED's lifespan. Newer packaging methods, typically based on flip-chip LEDs, significantly reduce the size of the package, lowering packaging costs and making them particularly suitable for high-power devices.

[0004] However, flip-chip LED chips all emit light from the backside, meaning light must pass through the N-type semiconductor layer, the intrinsic semiconductor layer, and the sapphire substrate before escaping from the substrate interface. Sapphire absorbs light and dissipates heat poorly, resulting in low brightness, poor heat dissipation in the LED product, and consequently, LED burnout and a shortened LED lifespan. Furthermore, light inevitably passes through the intrinsic semiconductor layer, which is tightly adhered to the sapphire substrate and has numerous and large defects. This leads to significant light absorption and scattering, resulting in significant light loss, low brightness, and poor yield.

[0005] Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a flip-chip LED chip array and a preparation method thereof, which can improve brightness, yield and reliability, extend service life, shorten the manufacturing process and reduce product cost.

[0007] In order to solve the above technical problems, the present invention provides a method for preparing a flip-chip LED chip array, which comprises the following steps:

[0008] (1) fixing one side of a substrate of a plurality of flip-chip LED chips to a film layer to obtain a chip array; wherein the plurality of flip-chip LED chips are distributed in an array; the flip-chip LED chip comprises a substrate, an intrinsic semiconductor layer, an N-type semiconductor layer, an MQW layer, a P-type semiconductor layer, an electrode, and a pad stacked in sequence;

[0009] (2) soldering the pads of the chip array to the solder joints of the package substrate; wherein the plurality of pads of the chip array are aligned one by one with the plurality of solder joints on the package substrate;

[0010] (3) peeling off the adhesive film layer to obtain a welded array;

[0011] (4) removing the substrate and intrinsic semiconductor layer of the flip-chip LED chip on the soldered array to obtain a first intermediate array;

[0012] (5) forming a reflective layer between adjacent flip-chip LED chips of the first intermediate array to obtain a second intermediate array; wherein the top surface of the reflective layer is flush with or lower than the N-type semiconductor layer of the flip-chip LED chip;

[0013] (6) A fluorescent layer is formed on the side of the second intermediate array away from the packaging substrate, thereby obtaining a finished flip-chip LED chip array.

[0014] As an improvement of the above technical solution, in step (1), the adhesive film layer is a UV film, the viscosity of which is 15000 to 25000 cP, and the high temperature resistance thereof is ≥350°C; and / or

[0015] In step (3), the adhesive film layer is irradiated with UV light to peel off the adhesive film layer.

[0016] As an improvement to the above technical solution, the distance between adjacent flip-chip LED chips in the chip array is a; the packaging substrate includes welding areas and non-welding areas spaced apart, and the width of the non-welding areas is d;

[0017] ad=20~50μm.

[0018] As an improvement of the above technical solution, each flip-chip LED chip in the chip array is provided with two pads, and the distance between the two pads is b;

[0019] The welding area of ​​the package substrate is provided with a welding point group, each welding point group includes two welding points, which are respectively welded to the welding pad; the distance between adjacent welding points is c;

[0020] 20μm<b<50μm, 20μm<c<50μm, b and c are the same or different.

[0021] As an improvement of the above technical solution, in step (2), the pad and the solder joint are eutectic welded, the welding temperature is ≤330° C., and the welding time is 2 to 4 minutes.

[0022] As an improvement of the above technical solution, step (4) includes:

[0023] (4.1) forming a photoresist layer on a side of the welding array away from the packaging substrate;

[0024] (4.2) removing the photoresist layer above the flip-chip LED chip;

[0025] (4.3) Peeling off the substrate of the flip-chip LED chip;

[0026] (4.4) removing the intrinsic semiconductor layer by etching with alkaline solution and roughening the N-type semiconductor layer;

[0027] (4.5) Removing the photoresist layer between adjacent flip-chip LED chips to obtain a first intermediate array.

[0028] As an improvement of the above technical solution, in step (4.4), the alkali solution is a KOH solution with a concentration of 20 to 40 wt %, and the corrosion time is 5 to 15 minutes.

[0029] As an improvement of the above technical solution, in step (5), the reflective layer is a white wall glue layer, the reflectivity of which is ≥95%, and the high temperature resistance is 260-280°C.

[0030] As an improvement of the above technical solution, in step (5), the white wall glue layer is printed by a screen printing process.

[0031] Correspondingly, the present invention also discloses a flip-chip LED chip array, which is prepared by the above-mentioned method for preparing the flip-chip LED chip array.

[0032] The implementation of the present invention has the following beneficial effects:

[0033] In a method for preparing a flip-chip LED chip array of the present invention, the substrate side of a plurality of flip-chip LED chips is first fixed to a film layer to obtain a chip array; then, the chips are welded to a packaging substrate, and after removing the film layer, the substrate and intrinsic semiconductor layer of the flip-chip LED chips are further removed, and then a reflective layer is formed between adjacent flip-chip LED chips, and a fluorescent layer is formed above the flip-chip LED chips. Since the present invention removes the substrate and the intrinsic semiconductor layer, the absorption of light is reduced, thereby improving the brightness and yield of the flip-chip LED chip array, optimizing its heat dissipation, extending its life, and reducing costs. In addition, the present invention integrates the chip end and the packaging end processes together to directly produce lamp beads, greatly shortening the process flow and improving production efficiency; in addition, the use of the chip end semiconductor process for the packaging process greatly improves the process accuracy and product stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG1 is a flow chart of a method for preparing a flip-chip LED chip array according to an embodiment of the present invention;

[0035] FIG2 is a schematic structural diagram of a flip-chip LED chip according to an embodiment of the present invention;

[0036] FIG3 is a schematic structural diagram of a chip array after step S1 is completed in one embodiment of the present invention;

[0037] FIG4 is a schematic top view of the structure of a package substrate in one embodiment of the present invention;

[0038] FIG5 is a schematic structural diagram of a welding array obtained after step S3 in one embodiment of the present invention;

[0039] FIG6 is a schematic structural diagram of the first intermediate array after step S44 is completed in one embodiment of the present invention;

[0040] FIG7 is a schematic structural diagram of a flip-chip LED chip array obtained after step S6 in one embodiment of the present invention;

[0041] In the figure, 1 is a flip-chip LED chip, 11 is a substrate, 12 is an intrinsic semiconductor layer, 13 is an N-type semiconductor layer, 14 is an MQW layer, 15 is a P-type semiconductor layer, 16 is an electrode, 17 is a soldering pad, 18 is a reflective layer, 19 is a passivation layer, 2 is a film layer, 3 is a packaging substrate, 31 is a soldering area, 32 is a non-soldering area, 33 is a soldering point group, 331 is a soldering point, 4 is a photoresist layer, 5 is a reflective layer, and 6 is a fluorescent layer. DETAILED DESCRIPTION

[0042] To make the objectives, technical solutions, and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings. It is hereby stated that any directional terms such as "up," "down," "left," "right," "front," "back," "inside," and "outside" that appear or will appear herein are based solely on the accompanying drawings and are not intended to limit the present invention.

[0043] Referring to FIG1 , the present invention provides a method for preparing a flip-chip LED chip array, which includes the following steps:

[0044] S1: Fixing one side of the substrate of multiple flip-chip LED chips to the adhesive film layer to obtain a chip array;

[0045] 2 , the flip-chip LED chip 1 includes a substrate 11 and an intrinsic semiconductor layer 12, an N-type semiconductor layer 13, an MQW layer 14, a P-type semiconductor layer 15, an electrode 16, and a pad 17 sequentially stacked on the substrate 11. The intrinsic semiconductor layer 12 may be a U-GaN layer or a U-AlGaN layer, but is not limited thereto. The N-type semiconductor layer 13 may be an N-type GaN layer, an N-type AlGaN layer, or an N-type GaAs layer, but is not limited thereto. The MQW layer 14 may be an InGaN-GaN type MQW layer, an InGaN-AlGaN type MQW layer, or an AlGaN-AlGaN type MQW layer, but is not limited thereto. The P-type semiconductor layer 15 may be a P-type GaN layer, a P-type AlGaN layer, or a P-type GaAs layer, but is not limited thereto.

[0046] Preferably, in some embodiments, the flip-chip LED chip 1 further includes a buffer layer disposed between the substrate 11 and the intrinsic semiconductor layer 12 , a reflective layer 18 and a passivation layer 19 disposed on the P-type semiconductor layer, but is not limited thereto.

[0047] Specifically, the electrodes 16 of the flip-chip LED chip 1 include an N electrode and a P electrode. Accordingly, the flip-chip LED chip 1 is provided with two solder pads 17 electrically connected to the N electrode and the P electrode, respectively. The distance between the two solder pads 17 is b. Here, 20 μm < b < 50 μm. If b is too small, the soldering process window is insufficient. If b is too large, there is an excessive amount of unsolderable area, resulting in waste. Preferably, b is 25 μm to 45 μm, and more preferably 30 μm to 40 μm.

[0048] Among them, the adhesive film layer 2 can be a polyurethane adhesive layer or an epoxy resin adhesive layer, but is not limited thereto. The adhesive film layer 2 can undergo a viscosity change under the conditions of heating or light irradiation, thereby realizing the separation of the adhesive film layer 2 and the flip-chip LED chip 1. Preferably, in one embodiment of the present invention, the adhesive film layer 2 is a UV film, and its viscosity is 12000~30000cP (25℃). If the viscosity of the UV film is too high, it is not easy to demold; if the viscosity is too low, it is easy to cause the flip-chip LED chip to shift and rotate, resulting in abnormal spacing, causing the flip-chip LED chip 1 and the packaging substrate 3 to shift in alignment. Preferably, the viscosity of the UV film is 15000~25000cP. The high temperature resistance of the UV film is ≥350℃, so that it will not wrinkle or carbonize during subsequent welding, affecting the packaging accuracy. Preferably, the high temperature resistance of the UV film is 370℃~400℃. It should be noted that the high temperature resistance temperature here refers to the maximum temperature at which the UV film does not carbonize or wrinkle when heated in an air environment.

[0049] Specifically, referring to FIG3 , a plurality of flip-chip LED chips are arrayed on the adhesive film layer 2 , with the spacing between adjacent flip-chip LED chips 1 being the same or different. Preferably, the spacing a between adjacent flip-chip LED chips 1 is the same. More specifically, a is 40 to 80 μm, and more preferably, a is 50 to 80 μm.

[0050] It should be noted that the chip array in the present invention may contain 3 flip-chip LED chips, 6 flip-chip LED chips, or multiple (>6) flip-chip LED chips.

[0051] S2: Solder the pads of the chip array to the solder joints of the package substrate;

[0052] 4 , a soldering area 31 and a non-soldering area 32 are provided on the package substrate 3. The width of the non-soldering area 32 is d. Multiple solder joint groups 33 are provided in the soldering area 31. Each solder joint group 33 includes two solder joints 331. The two solder joints 331 are respectively soldered to the two pads in the flip-chip LED chip 1. Specifically, the spacing between the two solder joints 331 is c, and 20μm < c < 50μm. b is the same as or different from c, that is, the size of the solder joint 331 is the same as or different from the pad 17. Preferably, c is 25μm to 45μm, and more preferably 30μm to 40μm.

[0053] The width d of the non-welding area 32 is 20-40 μm. If it is too small, the soldering window is insufficient, which can easily cause soldering shorts. If it is too large, a wide dark area will appear during subsequent packaging, resulting in poor light distribution and low brightness. Preferably, the width d of the non-welding area 32 is 20-30 μm.

[0054] In one embodiment, pad 17 is bonded to solder joint 331 via eutectic bonding at a temperature of ≤330°C to prevent damage to adhesive film layer 2. The bonding time is 2 to 5 minutes. If the bonding time is too short, the eutectic effect is poor, and abnormalities such as voids are likely to occur. If the bonding time is too long, the flip-chip LED chip may be damaged. Preferably, the bonding temperature is 260°C to 320°C, and the bonding time is 2 to 4 minutes. More preferably, the bonding temperature is 280°C to 300°C, and the bonding time is 3 to 4 minutes.

[0055] In one embodiment of the present invention, the package substrate is cleaned before the pad is bonded to remove impurities on the surface of the package substrate. Specifically, isopropyl alcohol and / or acetone may be used for cleaning.

[0056] S3: peeling off the film layer to obtain the welded array;

[0057] According to the specific material of the adhesive film layer 2 , the adhesive film layer 2 can be peeled off by heating or light irradiation, but is not limited thereto.

[0058] Preferably, in one embodiment of the present invention, UV light is used to irradiate the adhesive film layer 2 to reduce its viscosity, thereby allowing the adhesive film layer 2 to be peeled off.

[0059] S4: removing the substrate and intrinsic semiconductor layer of the flip-chip LED chips on the soldered array to obtain a first intermediate array;

[0060] The substrate 11 and the intrinsic semiconductor layer 12 may be removed by laser lift-off, etching or other processes, but are not limited thereto. Preferably, in one embodiment of the present invention, step S4 includes the following steps:

[0061] S41: forming a photoresist layer on a side of the welding array away from the package substrate;

[0062] The photoresist may be a positive photoresist or a negative photoresist, but is not limited thereto. The photoresist may be applied to the surface of the soldering array by spin coating, spray coating, inkjet printing, etc., to form a photoresist layer 4, but is not limited thereto.

[0063] S42: removing the photoresist layer above the flip-chip LED chip;

[0064] Among them, by exposing and developing the photoresist layer, the photoresist layer 4 above the flip-chip LED chip can be accurately removed. At the same time, the photoresist N layer in other areas that has not been removed by development will protect the side walls of the flip-chip LED chip, preventing impurities generated by subsequent laser stripping from entering, and also preventing subsequent alkaline solution etching from damaging the side walls of the flip-chip LED chip.

[0065] S43: peeling off the substrate of the flip-chip LED chip;

[0066] The laser lift-off process removes the substrate 11, which also removes the buffer layer, but does not remove the intrinsic semiconductor layer. The laser lift-off depth is 100 to 300 μm. Excessive lift-off depth can easily burn the flip-chip LED chip, while too shallow a lift-off depth can hinder effective separation. Preferably, the laser lift-off depth is 200 to 300 μm. By lifting off the substrate, the brightness of the flip-chip LED chip array can be increased and heat dissipation can be enhanced.

[0067] S44: removing the intrinsic semiconductor layer by etching with alkaline solution, and roughening the N-type semiconductor layer;

[0068] Because the intrinsic semiconductor layer has many large defects and absorbs and scatters light, removing this layer can effectively improve brightness and yield. Furthermore, at the end of the alkaline solution removal of the intrinsic semiconductor layer, part of the N-type semiconductor layer is also removed, further optimizing light extraction efficiency.

[0069] Specifically, the alkali solution may be a KOH solution, but is not limited thereto, with a concentration of 20 to 40 wt %, and a corrosion time of 5 to 15 minutes.

[0070] S45: removing the photoresist layer between adjacent flip-chip LED chips to obtain a first intermediate array;

[0071] The photoresist layer may be removed by mechanical stripping or chemical stripping, but is not limited thereto.

[0072] S5: forming a reflective layer between adjacent flip-chip LED chips in the first intermediate array to obtain a second intermediate array;

[0073] In one embodiment of the present invention, a reflective layer 5 is placed between adjacent flip-chip LED chips to enhance light reflection. Specifically, to prevent any impact on light pattern and brightness, the top surface of the reflective layer 5 is aligned with or slightly below the N-type conductor layer 13. Preferably, the top surface of the reflective layer 5 is aligned with the N-type semiconductor layer 13.

[0074] The reflective layer 5 can be a white wall glue layer, that is, it is obtained by curing white wall glue, the reflectivity of the white wall glue is ≥95%, and its high temperature resistance is 260°C to 280°C to prevent carbonization damage during later application.

[0075] Preferably, in one embodiment, the white wall glue is formed by a screen printing process, and its precision can reach 2 μm, which can effectively prevent the white wall glue from covering the flip-chip LED chip and causing the problem of reduced brightness.

[0076] S6: forming a fluorescent layer on the side of the second intermediate array away from the packaging substrate, thereby obtaining a finished flip-chip LED chip array.

[0077] The fluorescent layer 6 can be obtained by injecting fluorescent glue and curing it, or the fluorescent layer 6 can be a laminated fluorescent glue film.

[0078] Preferably, in one embodiment, the method further includes the step of cutting the flip-chip LED chip array and the step of board pasting, but is not limited thereto.

[0079] The above is a preferred embodiment of the invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing an inverted LED chip array, characterized in that, It includes the following steps: (1) Fix one side of the substrates of multiple flip-chip LED chips to a film layer to obtain a chip array; wherein, the multiple flip-chip LED chips are arranged in an array; the flip-chip LED chip includes a substrate, an intrinsic semiconductor layer, an N-type semiconductor layer, an MQW layer, a P-type semiconductor layer, an electrode, and a pad that are stacked in sequence; (2) Weld the pads of the chip array to the solder joints of a packaging substrate; wherein, the multiple pads of the chip array are aligned with the multiple solder joints on the packaging substrate one by one; (3) Peel off the film layer to obtain a welded array; (4) Remove the substrates and intrinsic semiconductor layers of the flip-chip LED chips on the welded array to obtain a first intermediate array; (5) Form a reflective layer between adjacent flip-chip LED chips in the first intermediate array to obtain a second intermediate array; the top surface of the reflective layer is flush with or lower than the N-type semiconductor layer of the flip-chip LED chip; (6) Form a fluorescent layer on the side of the second intermediate array away from the packaging substrate to obtain a finished flip-chip LED chip array.

2. The manufacturing method of the flip-chip LED chip array according to claim 1, characterized in that, In step (1), the film layer is a UV film, its viscosity is 15000 - 25000 cP, and its high-temperature resistance temperature ≥ 350 °C; and / or In step (3), irradiate the film layer with UV light to peel off the film layer.

3. The manufacturing method of the flip-chip LED chip array according to claim 1, characterized in that The distance between adjacent flip-chip LED chips in the chip array is a; the packaging substrate includes a welding area and a non-welding area arranged at intervals, and the width of the non-welding area is d; a - d = 20 - 50 μm.

4. The manufacturing method of the flip-chip LED chip array according to claim 3, wherein Each flip-chip LED chip in the chip array is provided with two pads, and the distance between the two pads is b; The welding area of the packaging substrate is provided with a solder joint group, and each solder joint group includes two solder joints, which are respectively welded corresponding to the pads; the distance between adjacent solder joints is c; 20 μm < b < 50 μm, 20 μm < c < 50 μm, and b and c are the same or different.

5. The manufacturing method of the flip-chip LED chip array according to claim 1 or 2, characterized in that In step (2), eutectic weld the pads and the solder joints, the welding temperature ≤ 330 °C, and the welding time is 2 - 4 min.

6. The manufacturing method of the flip-chip LED chip array according to claim 1, characterized in that, Step (4) includes: (4.1) Form a photoresist layer on the side of the welded array away from the packaging substrate; (4.2) Remove the photoresist layer above the flip-chip LED chip; (4.3) Peel off the substrate of the flip-chip LED chip; (4.4) Use an alkali solution to corrode and remove the intrinsic semiconductor layer, and roughen the N-type semiconductor layer; (4.5) Remove the photoresist layer between adjacent flip-chip LED chips to obtain a first intermediate array.

7. The manufacturing method of the flip-chip LED chip array according to claim 6, characterized in that, In step (4.4), the alkali solution is a KOH solution, its concentration is 20 - 40 wt%, and the corrosion time is 5 - 15 min.

8. The manufacturing method of the flip-chip LED chip array according to claim 1, characterized in that, In step (5), the reflective layer is a white wall glue layer, its reflectivity ≥ 95%, and its high-temperature resistance temperature is 260 - 280 °C.

9. The manufacturing method of the flip-chip LED chip array according to claim 8, characterized in that, In step (5), print the white wall glue layer by a screen printing process.

10. A flip-chip LED chip array, characterized in that: It is prepared by the preparation method of the flip-chip LED chip array according to any one of claims 1 - 9.

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