LED chip CSP packaging method

Abstract

The invention relates to the field of chip packaging, and provides an LED chip CSP packaging method, and the method comprises the steps: carrying out the processing of a conductive layer, so as to expose an electrode region on the back surface of a flip chip in each flip region on a wafer; processing the exposed electrode region to form a connection layer and a solder layer; mounting a fluorescent diaphragm on the front surface of the flip chip to form a flip chip CSP; filling the flip chips on which the fluorescent diaphragms are mounted with white reflective glue, and enabling the white reflective glue to cover the back surface of each flip chip; processing the white reflective glue to expose the solder layer on the back surface of each flip chip; and cutting the flip chip CSP to obtain a CSP processed finished product of a single flip chip. The heat dissipation performance of the packaging structure is remarkably improved, the heat concentration phenomenon is reduced, the stability of electrical connection is optimized through the whole technological process, the reliability and durability of packaging are improved, and therefore the service life of the LED chip is prolonged.

Description

Technical Field

[0001] The invention relates to the field of chip packaging, and in particular to a CSP packaging method for an LED chip. Background Art

[0002] In the current LED chip packaging technology, the flip chip structure is widely used because it can avoid the complexity of the traditional upright chip metal wire bonding process. This structure improves the reliability and efficiency of the package by placing the electrical side of the chip facing down and directly connecting it to the substrate or other connection structures using metal electrodes.

[0003] However, in the CSP packaging of flip-chip LED chips without substrates, the traditional method of preparing tin electrodes and the design of using white glue for fixing and electrical connection have some significant defects; specifically, during the secondary reflow SMT (Surface Mount Technology) process, due to the low melting point of the tin electrode, it is easy to melt. For example, the Chinese utility model patent with the publication number CN220233227U introduces a CSP packaging structure of flip-chip LED chips without substrates, which mentions that the electrode position of the flip-chip LED chip is provided with a tin electrode, which will cause the white glue to expand and lift up the chip pad in actual application, affecting the normal connection between the tin electrode, the chip electrode and the PCB pad, resulting in an incomplete welding surface. More seriously, the poor thermal conductivity of the solder paste causes the heat to be concentrated in the electrode connection area, increasing the junction temperature of the LED chip, thereby reducing the working life of the chip and limiting the use current and conditions of the LED chip. Summary of the invention

[0004] The purpose of the present application is to provide a CSP packaging method for LED chips, which has the advantages of improving packaging reliability, improving heat dissipation performance, extending chip life and enhancing electrical connection stability.

[0005] To solve the above problems, the present invention provides the following technical solutions:

[0006] The present application provides a method for CSP packaging of LED chips, comprising the following steps:

[0007] Processing the back of the wafer to form a conductive layer on the flip chip in each flip chip area; wherein the wafer includes a plurality of flip chip areas, and each flip chip area includes a flip chip;

[0008] Processing the conductive layer to expose an electrode region on the back side of the flip chip of each flip chip region on the wafer;

[0009] processing the exposed electrode area to form a connection layer and a solder layer;

[0010] A fluorescent film is mounted on the front side of the flip chip to form a flip chip CSP;

[0011] Filling the flip chip with white reflective adhesive after the fluorescent film is attached, so that the white reflective adhesive covers the back side of each flip chip;

[0012] Processing the white reflective adhesive to expose the solder layer on the back side of each flip chip;

[0013] The flip chip CSP is cut to obtain a single flip chip CSP finished product.

[0014] Furthermore, the present application also proposes that the processing of the back of the wafer to form a conductive layer on the flip chip in each flip chip area further comprises the following steps:

[0015] placing the wafer in a sputtering device;

[0016] Presetting the parameters of the sputtering device;

[0017] Loading a metal material corresponding to the flip chip into a sputtering device;

[0018] The sputtering device is started to perform sputtering to form a metal seed layer on the entire back side of the flip chip in each flip chip area on the wafer.

[0019] Furthermore, the present application also proposes the following steps of processing the conductive layer to expose the electrode area on the back side of the flip chip of each flip chip area on the wafer:

[0020] Applying photoresist to the conductive layer of each flip chip on the wafer;

[0021] heating the photoresist coated on the conductive layer of each flip chip on the wafer;

[0022] Selecting a mask with a predetermined pattern and covering the pattern position on the electrode area of ​​each flip chip;

[0023] The wafer is placed in an exposure device, and the flip chip on the wafer is exposed through a mask, so that the photoresist on the conductive layer that is not covered by the pattern of the mask becomes soluble;

[0024] The exposed wafer is placed in a developer to dissolve the exposed photoresist and expose the electrode area of ​​each flip chip.

[0025] Furthermore, the present application also proposes that the processing of the exposed electrode area to form a connection layer and a solder layer further comprises the following steps:

[0026] The electrode area of ​​each flip chip on the wafer is immersed in an electroplating solution, and a direct current is applied to deposit copper ions in the electrode area to form a copper layer;

[0027] The copper layer is ground using a grinding device to retain a portion of the copper layer;

[0028] Print solder paste onto the copper layer;

[0029] The copper layer coated with solder paste on the flip chip is heated to combine the solder paste with the copper layer;

[0030] The combined tin layer is ground using a grinding device to retain a portion of the thickness of the tin layer;

[0031] Clean flip chips to remove residues.

[0032] Furthermore, the present application also proposes:

[0033] The thickness of the retained copper layer ranges from 40 to 50 μm;

[0034] The thickness of the retained tin layer ranges from 15 to 30 μm.

[0035] Furthermore, the present application also proposes that the process of attaching a fluorescent film to the front side of the flip chip to form a flip chip CSP further includes the following steps:

[0036] Lay release film on the platform;

[0037] The prepared fluorescent glue is coated on the release film, and the fluorescent glue is heated to form a fluorescent film;

[0038] Apply the prepared transparent adhesive on the fluorescent film to form a protective layer;

[0039] Testing the fluorescent film including the fluorescent film and the protective layer;

[0040] Cut each flip chip on the wafer to form a single flip chip;

[0041] Distribute the fluorescent films that have passed the test evenly on the crystal-making plate, and apply glue to each fluorescent film;

[0042] Press the front side of each flip chip downward relative to the fluorescent film, so that the glue adheres between the flip chip and the fluorescent film and overflows to form an oblique angle;

[0043] Adjust the amount of glue and the viscosity of the adhesive to adjust the bevel and angle.

[0044] Furthermore, the present application also proposes that the process of filling the flip chip with white reflective glue after mounting the fluorescent film so that the white reflective glue covers the back of each flip chip further includes the following steps:

[0045] Set the dispensing volume and dispensing path of the dispensing machine;

[0046] Filling the back and surrounding area of ​​each flip chip on the wafer board with white reflective glue;

[0047] The white reflective adhesive filled on the back and surrounding area of ​​the flip chip on the wafer making plate is dried using a drying device, thereby obtaining a whole CSP of the flip chip.

[0048] Furthermore, the present application also proposes that the processing of the white reflective adhesive so that the solder layer is exposed on the back side of each flip chip further comprises the following steps:

[0049] Fixing the flip chip on a workbench of a grinding device;

[0050] Set the grinding parameters according to the thickness of the white reflective glue and the thickness of the solder layer;

[0051] Start the grinding device according to the preset parameters and grind the white reflective adhesive until the solder layer is exposed;

[0052] Clean flip chips to remove residues.

[0053] Furthermore, the present application also proposes that the cleaning of the flip chip and removal of residues further comprises the following steps:

[0054] Adding a cleaning agent into a cleaning device, and using the cleaning device to clean the flip chip;

[0055] Drying the cleaned flip chip using a drying device;

[0056] Test the electrodes on the back of a single flip chip to determine whether the cleaned flip chip is qualified.

[0057] Furthermore, the present application also proposes that the process of cutting the flip chip CSP to obtain a single flip chip CSP finished product also includes the following steps:

[0058] Place the entire flip chip CSP on the cutting platform;

[0059] Make cutting marks for each flip chip on the entire CSP of the flip chip;

[0060] The cutting device is started according to the cutting mark, and cutting is performed along the cutting mark, so that each flip chip is cut into a single CSP finished product.

[0061] The beneficial effects of the present invention are as follows: by processing the back of the entire flip chip wafer to form a conductive layer and accurately exposing the electrode area, the high-quality formation of the subsequent connection layer and the solder layer is ensured, and the integrity and reliability of the welding surface are improved; and by processing the exposed electrode to form a stable connection layer and a solder layer, the stability of the electrical connection is enhanced, and a fluorescent film is mounted on the front of the flip chip to provide the necessary optical properties, and by filling the mounted chip with white reflective glue, the flip chip is packaged to form a whole CSP, and the white reflective glue is processed to expose the solder layer to achieve conduction. The present invention significantly improves the heat dissipation performance of the packaging structure, reduces the heat concentration phenomenon, and the overall process optimizes the stability of the electrical connection, improves the reliability and durability of the package, thereby extending the service life of the flip chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 This is an overall process flow chart of an LED chip CSP packaging method of the present invention;

[0063] Figure 2 A process flow chart for forming a conductive layer according to the present invention;

[0064] Figure 3 is a process flow chart of exposing the electrode area of ​​the present invention;

[0065] Figure 4 The process flow chart of processing the exposed leakage electrode area of ​​the present invention;

[0066] Figure 5 The present invention is a process flow chart of attaching a fluorescent film to a flip chip;

[0067] Figure 6 The process flow chart of the present invention for filling white reflective glue;

[0068] Figure 7 The present invention is a process flow chart for processing white reflective adhesive;

[0069] Figure 8 A schematic diagram of the structure of one embodiment of the wafer of the present invention;

[0070] Fig. 9 This is a schematic structural diagram of one embodiment of the flip chip of the present invention;

[0071] Fig.10 A schematic diagram of the structure of one embodiment of the conductive layer and the connecting layer of the present invention;

[0072] Fig.11 A side view of one embodiment of a wafer of the present invention;

[0073] Fig.12A schematic diagram of a finished product of one embodiment of a flip chip of the present invention;

[0074] Fig.13 This is a cross-sectional view of a finished product of one embodiment of a flip chip of the present invention.

[0075] Reference numerals:

[0076] 110, flip chip; 200, wafer; 112, conductive layer; 113, electrode area; 114, connection layer; 115, solder layer; 116, fluorescent film; 117, white reflective glue; 121, fluorescent film; 122, protective layer. DETAILED DESCRIPTION

[0077] The technical solutions in the present application will be clearly and completely described below in conjunction with the drawings in the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The components of the present application generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the present application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application.

[0078] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0079] It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. At the same time, in the description of this application, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0080] In the current flip-chip LED chip CSP package without substrate, the traditional tin electrode preparation method and the design of using white glue for fixing and electrical connection have some significant defects; specifically, during the secondary reflow SMT process, due to the low melting point of the tin electrode, melting is likely to occur, for example, causing the white glue to expand and lift the chip pad, affecting the normal connection between the tin electrode, the chip electrode and the PCB pad, resulting in an incomplete soldering surface. More seriously, the poor thermal conductivity of the solder paste causes heat to be concentrated in the electrode connection area, increasing the junction temperature of the LED chip, thereby reducing the working life of the chip and limiting the current and conditions of the lamp bead; these problems seriously affect the performance and reliability of the LED chip. The low melting point tin electrode is prone to deformation or melting in a high temperature environment, resulting in unstable electrical connection. At the same time, since the heat cannot be effectively dissipated, the operating temperature of the chip increases, which not only reduces the luminous efficiency, but also may shorten the chip life. In addition, due to the problem of incomplete soldering surface, the connection strength between the chip and the PCB is reduced, and it is easy to fall off or disconnect in harsh environments such as vibration or thermal cycling.

[0081] For the above technical issues, please refer to Figure 1-8 , Figure 9-13 As shown, the present application proposes a LED chip CSP packaging method, comprising the following steps: processing the back of the entire wafer 200 of the flip chip 110 to form a conductive layer 112; wherein the wafer 200 includes a plurality of flip-chip regions, each of which is provided with a flip chip 110; processing the conductive layer 112 to expose an electrode region 113 on the back of the flip chip 110 of each flip-chip region; processing the exposed electrode region to form a connecting layer 114 and a solder layer 115; attaching a fluorescent film 116 to the front side of the flip chip 110 to form a flip chip CSP; filling the flip chip 110 with the fluorescent film 116 with a white reflective adhesive 117 so that the white reflective adhesive 117 covers the back side of each flip chip 110; processing the white reflective adhesive 117 so that the solder layer 115 is exposed on the back side of each flip chip 110, and cutting the entire CSP of the flip chip 110 to obtain a CSP processed product of a single flip chip 110.

[0082] According to the above scheme, specifically, the technical scheme solves the problem of electrode exposure and connection of the flip chip 110 during the packaging process through a series of processing steps, including forming a conductive layer 112 on the back of the whole wafer 200 of the flip chip 110, exposing the electrode area 113, forming a connection layer 114 and a solder layer 115, attaching a fluorescent film 116, filling with white reflective glue 117, and processing to expose the solder layer 115. Among them, the role played by each technical feature is as follows: forming a conductive layer 112 to ensure effective conduction of current; exposing the electrode area 113 to provide a basis for the subsequent formation of the connection layer 114 and the solder layer 115; forming the connection layer 114 and the solder layer 115 to ensure reliable connection between the electrode and the external circuit; attaching the fluorescent film 116 to provide optical performance; filling with white reflective glue 117 to protect the chip and ensure structural stability; processing to expose the solder layer 115 to facilitate subsequent electrical connection. Through these steps, the reliability and stability of electrode exposure and connection of the flip chip 110 during the packaging process are ensured.

[0083] Please refer to Figure 1-2 , Figure 9-13 As shown, according to the above scheme, specifically, in this embodiment, the back of the entire wafer 200 of the flip chip 110 is processed to form a conductive layer 112: the wafer 200 is placed in a sputtering device; the parameters of the sputtering device are preset; the metal material corresponding to the flip chip 110 is loaded into the sputtering device; the sputtering device is started to sputter to form a metal seed layer on the entire back of the flip chip 110.

[0084] Optionally, the sputtering seed layer in this embodiment is made of metal titanium.

[0085] It can be understood that the technical solution of the present application forms a uniform metal seed layer on the back of the entire wafer 200 of the flip chip 110 through a sputtering process, thereby realizing the formation of the conductive layer 112. Metal sputtering is a physical vapor deposition (PVD) method that uses high-energy particles (usually argon ions) to bombard a solid material (target material) so that atoms on the surface of the target material are sputtered out and deposited on the surface of the wafer 200 to form a thin film. By controlling the sputtering conditions (such as power, pressure and time), the thickness and uniformity of the film can be accurately controlled; further, the seed layer refers to a thin metal film pre-deposited on the substrate, and its main function is to serve as the starting point for metal growth in the subsequent electroplating or chemical plating process. The seed layer must have good conductivity and good adhesion to the substrate and subsequent metal layers. For the flip chip 110, the seed layer is usually composed of one or more layers of different metals, such as titanium / platinum / gold (Ti / Pt / Au) or chromium / gold (Cr / Au), to ensure good adhesion and conductivity.

[0086] Specifically, an inert gas is introduced into the vacuum chamber. In this embodiment, argon gas is selected, and high pressure is applied to ionize the gas to form plasma. The positive ions in the plasma are accelerated to hit the surface of the target material, so that the target atoms are sputtered out and deposited on the surface of the wafer 200. The thickness of the metal seed layer finally formed is adjusted by adjusting the sputtering parameters (sputtering time, power and gas pressure). The optimization of these parameters can ensure the uniformity and adhesion of the metal seed layer. The metal material can be selected from metals with good conductivity such as titanium, silver, and gold. The specific selection can be adjusted according to the application requirements of the flip chip 110.

[0087] Please refer to Figure 3-4 , Figure 9-13 As shown, according to the above scheme, specifically, photoresist is coated on the back of the entire flip chip 110, the flip chip 110 coated with photoresist is heated, a mask with a predetermined pattern is selected, and the pattern position covers the electrode position, the wafer 200 is placed in an exposure device, and the flip chip 110 is exposed through the mask to make the photoresist of the exposed part soluble, and the exposed flip chip 110 is placed in a developer to dissolve the exposed photoresist and expose the electrode area 113.

[0088] Specifically, first, a layer of photoresist is evenly coated on the back of the flip chip 110, and then the flip chip 110 coated with the photoresist is heated to make the photoresist reach appropriate hardness and adhesion. Next, a mask with a predetermined pattern is selected, and the pattern position of the mask is covered on the electrode position of the flip chip 110. The wafer 200 is placed in an exposure device, and the flip chip 110 is exposed through the mask, so that the photoresist part under the mask pattern is irradiated with light and becomes soluble. The exposed flip chip 110 is placed in a developer, and the developer dissolves the exposed photoresist, and finally exposes the electrode area 113 of the flip chip 110.

[0089] Specifically, a liquid photoresist is evenly coated on the back of a wafer 200 with a metal seed layer using a spin coater, and the solvent is removed through soft baking to solidify the photoresist layer. The wafer 200 coated with the photoresist is placed under a mask having a pre-designed pattern corresponding to the electrode position to be retained, and ultraviolet (UV) light is used to chemically change the photoresist through the transparent part of the mask, so that the photoresist layer in the exposed area becomes soluble; the exposed wafer 200 is placed in a developer to dissolve the exposed photoresist, and after development, the electrode area 113 originally covered with the photoresist is exposed, while other areas that do not require metallization are still protected by the photoresist, and after development, a hard bake is performed again to stabilize the photoresist pattern and reduce residual stress.

[0090] As a preferred embodiment, the photoresist is applied by spin coating, the temperature and time of the heating treatment are adjusted according to the characteristics of the photoresist, the predetermined pattern of the mask is prepared by photolithography technology, and the choice of developer should match the solubility characteristics of the photoresist.

[0091] Furthermore, the present application also proposes that processing the exposed electrodes to form a connecting layer 114 and a solder layer 115 also includes the following steps: immersing the electrode portion of the flip chip 110 in an electroplating solution, applying a direct current, and causing copper ions to be deposited in the electrode area 113 to form a copper layer; using a grinding device to grind the copper layer, leaving a portion of the copper layer with a thickness of L1; using a steel mesh to print solder paste onto the copper layer; heating the flip chip 110 coated with solder paste to combine the solder paste with the copper layer; using a grinding device to grind the combined tin layer, leaving a portion of the tin layer with a thickness of L2; it can be understood that the thickness L1 of the copper layer is the thickness of the connecting layer 114, and the thickness L2 of the tin layer is the thickness of the solder layer; cleaning the flip chip to remove residues.

[0092] Please refer to Figure 3-4 , Figure 9-13 As shown, the technical solution immerses the electrode portion of the flip chip 110 in an electroplating solution and applies a direct current to deposit copper ions in the electrode region 113 to form a copper layer, thereby forming a high-quality copper connection layer 114 in the electrode region 113. Then, the copper layer is ground using a grinding device, and a portion of the copper layer with a thickness of L1 is retained to ensure the uniformity and appropriateness of the thickness of the connection layer 114. Next, the solder paste is printed on the copper layer using a steel mesh, and the flip chip 110 coated with the solder paste is heated to combine the solder paste with the copper layer to form a solder layer 115. Finally, the combined tin layer is ground again using a grinding device, and a portion of the tin layer with a thickness of L2 is retained to ensure the uniformity and appropriateness of the thickness of the solder layer 115. Through these steps, the problem of forming a high-quality connection layer 114 and solder layer 115 during the electrode processing process is solved, and the reliability and efficiency of the package are improved.

[0093] Please refer to Figure 3-4 , Figure 9-13 As shown, preferably, the deposition of the copper layer is achieved by an electroplating process. Specifically, the electrode portion of the flip chip 110 is immersed in an electroplating solution containing copper ions, and a direct current is applied to deposit the copper ions in the electrode region 113 to form a copper layer.

[0094] Preferably, the grinding step uses precision grinding equipment to ensure that the thickness L1 of the copper layer is uniform and meets the requirements.

[0095] Preferably, the solder paste is printed using a steel screen printing technique, and the solder paste is evenly printed onto the copper layer through the steel screen.

[0096] Preferably, the heating step uses a reflow soldering device to melt the solder paste at a high temperature and combine with the copper layer.

[0097] Understandably, the final grinding step also requires precision grinding equipment.

[0098] Furthermore, the present application also proposes that the thickness L1 of the retained portion of the copper layer is in the range of 40 to 50 μm; the thickness L2 of the retained portion of the tin layer is in the range of 15 to 30 μm; it can be understood that the electroplated copper layer is ground using chemical mechanical polishing equipment, and the grinding pressure, rotation speed and grinding time are precisely adjusted according to the required thickness L1 of the copper layer to be retained (40 to 50 μm), and the grinding pressure, rotation speed and grinding time are precisely adjusted according to the required thickness L2 of the tin layer to be retained (15 to 30 μm); by adopting the above-mentioned technical solution, the present application retains copper and tin layers of appropriate thickness in the electrode part of the flip chip 110, ensuring the structural stability and conductivity of the electrode part, and avoiding the occurrence of tin layer melting during the secondary reflow SMT process.

[0099] Please refer to Figure 5-6 , Figure 9-13 As shown, specifically, mounting the fluorescent film 116 on the front side of the flip chip 110 also includes the following steps: laying a release film on the platform, preparing fluorescent glue by mixing fluorescent powder and transparent silica gel, and coating the prepared fluorescent glue on the release film, and then heating the fluorescent glue to form a fluorescent film 121; further, preparing transparent glue according to the type of the fluorescent film 121, and coating it on the fluorescent film 121 to form a protective layer 122; further, testing the fluorescent film 116 including the fluorescent film 121 and the protective layer 122. These steps ensure the quality and performance of the fluorescent film 116. Through the above scheme, the problem of how to ensure the quality and performance of the fluorescent film 116 when mounting the fluorescent film 116 on the front side of the flip chip 110 can be effectively solved.

[0100] A release film is laid on the platform, which can be a glass platform, or a metal platform or a marble platform. In this embodiment, a glass platform is preferred. The purpose of this step is to facilitate the peeling of the formed fluorescent film 121 from the platform during the subsequent fluorescent glue coating and heating process. The release film should have good heat resistance and peeling performance. Fluorescent glue is configured and coated on the release film. In this step, the configuration of the fluorescent glue needs to be adjusted according to the specific application requirements. The composition and proportion of the fluorescent glue will directly affect the quality and performance of the final fluorescent film 121. The fluorescent glue is heated to form the fluorescent film 121. The heating temperature and time need to be set according to the characteristics of the fluorescent glue to ensure that the fluorescent glue can be uniformly cured into a film. Transparent glue is configured according to the type of fluorescent film 121, and it is coated on the fluorescent film 121 to form a protective layer 122. In this step, the configuration of the transparent glue needs to take into account the compatibility with the fluorescent film 121 and the protective effect. The coating of the transparent glue should be uniform to ensure the integrity of the protective layer 122. The fluorescent film 116 including the fluorescent film 121 and the protective layer 122 is tested. The test items include color parameters, brightness output, color rendering, luminous flux output and other indicators. Through the test, it can be determined whether the fluorescent film 116 meets the application requirements.

[0101] Further, each flip chip on the wafer 200 is cut, and the wafer 200 is placed on a cutting platform; a cutting mark is made for each flip chip area on the wafer 200 as a reference for subsequent cutting by a cutting device; the cutting device is started according to the cutting mark, and cutting is performed along the cutting mark on the wafer 200, so that each flip chip 110 becomes a single flip chip; further, the fluorescent film sheets that have passed the test are evenly distributed on the crystal making board, and each fluorescent film sheet 116 is glued; the fluorescent film sheet 116 that has passed the test is attached to the crystal making board, with the protective layer facing the adhesive layer of the crystal making board. It can be understood that the adhesive layer is designed to be transparent, so that during the testing of the fluorescent film sheet, the light of the flip chip 110 can pass through the fluorescent film sheet 116 and the adhesive layer between the crystal making board and the fluorescent film sheet 116 to irradiate the integrating sphere, thereby completing the test.

[0102] It is understandable that the adhesive layer in this embodiment adopts a thermal release film. The thermal release tape (Thermal Release Tape or Thermal Debonding Adhesive) is a special tape or adhesive, which has the characteristic of having good adhesion properties at room temperature, but significantly reducing its adhesion when heated, thereby allowing the bonded objects to be easily removed or separated. This material is widely used in semiconductor manufacturing, electronic assembly, LED packaging and other processes that require temporary fixation and subsequent precise disassembly. It is understandable that the temperature of the thermal release film usually needs to reach 180-200°C before the viscosity of the thermal release film will be reduced, and the viscosity of the thermal release film will not be reduced due to the curing of the fluorescent film and other heating operations.

[0103] Specifically, the present application includes measuring the color parameters, brightness output, color rendering, and luminous flux output of the fluorescent film 116, and judging whether it is qualified according to the set standards. These technical features ensure that the quality and performance of the fluorescent film 116 meet the requirements by testing the different performance parameters of the fluorescent film 116. Through these testing methods, the quality of the fluorescent film 116 can be effectively detected to ensure that the fluorescent film 116 used in the LED chip CSP packaging process has good performance, thereby solving the problem of quality detection of the fluorescent film 116; the color parameters are measured using a spectrophotometer, and the color coordinate values ​​are obtained by analyzing the reflection and transmission spectra of the fluorescent film 116 under different wavelength light sources. The brightness output is measured using a brightness meter to measure the brightness value of the fluorescent film 116 under different light sources. The color rendering is measured using a CRI (color rendering index) instrument to evaluate the color restoration ability of the fluorescent film 116 under different light sources. The luminous flux output is measured using an integrating sphere to measure the total luminous flux of the fluorescent film 116 under different light sources.

[0104] It is understandable that these measurement methods can be used independently or in combination to comprehensively evaluate the performance of the fluorescent film 116 .

[0105] Specifically, by setting the glue dispensing amount, glue dispensing path and glue dispensing angle of the glue machine, ensure that the glue can be evenly distributed on the fluorescent film 116; attach the front side of the flip chip 110 to the fluorescent film 116, so that the glue is evenly distributed between the flip chip 110 and the fluorescent film 116 and overflows to form a bevel, and the bevel angle is 45 degrees; preferably, the upper edge of the glue is just pressed to the intersection of the copper electrode and the tin electrode to form a larger transparent silicone bevel, and then dried to ensure the stability and uniformity of the bonding. It can be understood that the bevel and angle are adjusted by adjusting the amount of glue and the viscosity of the adhesive, so that the bevel can expand the irradiation angle of the light when the flip chip is illuminated; further, use white reflective glue 117 to cover the entire flip chip 110 and the surrounding area. In this embodiment, the white reflective glue 117 is made of insulating protective material to provide additional protection. Through the cooperation of these technical features, the problem of uneven glue distribution during the filling process of the white reflective glue 117 is effectively solved, ensuring the packaging quality and reliability of the flip chip 110.

[0106] It can be understood that by introducing a 45° bevel design in this solution, the light propagation path within the package can be replanned. When light is emitted from the flip chip 110, part of the light will first contact the bevel area. Due to the existence of the bevel, these light rays will no longer follow the rule of straight-line propagation, but will be refracted or reflected, thereby changing their original propagation direction. This causes more light to be scattered outward at a wider angle, thereby effectively increasing the irradiation range; in addition, the bevel design also helps to improve the overall thermal performance of the package. Since the bevel glue is integrally formed with the glue between the fluorescent film and the flip chip, and the other side is in contact with the copper layer and the tin layer, the heat generated by the flip chip during operation can be transferred through the bevel, so that the bevel formed by the overflow of the glue can be used as an additional heat dissipation path, which can help to conduct the heat generated by the chip during operation more quickly, thereby maintaining a lower operating temperature. This is very important for extending the life of the LED and maintaining stable light output characteristics.

[0107] When setting the dispensing amount and dispensing path of the glue machine, the glue dispenser is programmed through the control system to achieve accurate dispensing. When the glue is distributed on the fluorescent film 116, a multi-point step-by-step dispensing method is adopted to ensure that the glue evenly covers the entire fluorescent film 116. When attaching the front side of the flip chip 110 to the fluorescent film 116, a vacuum adsorption device is used to ensure the flatness and uniformity during the attachment process. When using white reflective glue 117 to cover the entire flip chip 110 and the surrounding area, select a material with good insulation and heat resistance, such as epoxy resin or silicone, and cover it by spraying or dipping.

[0108] Please refer to Figure 7-8 , Figure 9-13As shown, specifically, in this embodiment, the flip chip 110 is fixed on the workbench of the grinding device; the grinding parameters are set according to the thickness of the insulating protective material and the thickness of the solder layer 115; the grinding device is started according to the preset parameters, and the insulating protective material is ground until the solder layer 115 is exposed; the flip chip 110 is cleaned to remove the residue; it can be understood that by selecting a suitable grinding device, fixing the flip chip 110, setting the grinding parameters, starting the grinding device for grinding, and cleaning the flip chip 110, these technical features work together to ensure that the solder layer 115 can be exposed during the processing of the white reflective glue 117 by accurately controlling the grinding process, and the residue is removed by the cleaning step, thereby ensuring the cleanliness of the chip and the smooth progress of the subsequent process. Through the above technical means, the problem of how to expose the solder layer 115 during the processing of the white reflective glue 117 is solved, and the integrity and cleanliness of the solder layer 115 are ensured, thereby improving the reliability of the chip package and the quality of the electrical connection.

[0109] Specifically, a cleaning agent is added to a cleaning device, and the cleaning device is used to clean the flip chip 110; a drying device is used to dry the cleaned flip chip 110; and a performance test is performed on the flip chip 110 to determine whether the cleaned flip chip 110 is qualified (OK or NG).

[0110] The present application includes a cleaning device, a drying device and a performance testing step. The cleaning device is used to clean the flip chip 110 and remove impurities and contaminants remaining during the processing. The drying device is used to dry the flip chip 110 after cleaning to prevent residual moisture from affecting subsequent processes. The performance testing step is used to detect the flip chip 110 after cleaning and drying to ensure that it meets the predetermined quality standards. Through the combination of the cleaning device, the drying device and the performance testing step, the solution of the present application effectively solves the problem of exposure and performance testing of the solder layer 115 of the flip chip 110 during the cleaning and drying process. The cleaning step ensures the cleanliness of the solder layer 115, the drying step prevents residual moisture, and the performance testing step ensures the quality of the flip chip 110 after cleaning and drying, thereby improving the reliability and production efficiency of the package.

[0111] Specifically, in this embodiment, the cleaning device uses an ultrasonic cleaning machine, which can effectively remove tiny particles and pollutants on the surface of the flip chip 110 through the cavitation effect generated by ultrasonic vibration, and the drying device uses a hot air circulation dryer, which accelerates the evaporation of water on the surface of the flip chip 110 through hot air circulation to ensure that the chip is completely dry. The performance test step uses automated testing equipment to test the electrical and optical properties of the flip chip 110 through electrical and optical testing to ensure that it meets the predetermined quality standards.

[0112] Preferably, after completing the above steps, the wafer 200 is placed on a cutting platform; a cutting mark is made on each flip-chip area on the wafer 200 as a reference for subsequent cutting by a cutting device; the cutting device is started according to the cutting mark, and cutting is performed along the cutting mark on the wafer 200, so that each flip-chip 110 becomes a single processed finished product; further, the present embodiment also includes the following steps, and according to the test result of each flip-chip, each flip-chip after cutting is graded; it can be understood that the grading is performed according to the test result, and the electrodes on the back of each flip-chip are energized to perform optical and electrical energy tests, and the grading is performed according to the test results. Since each chip emits light in a different wavelength band, the brightness, color and excitation color area of ​​the light are also different, so they can be divided into different grades, and each flip-chip CSP is sorted according to the different grades of the flip-chip CSP, so as to sort out the same type of CSP finished products.

[0113] In a specific embodiment, a method for forming a copper electrode on the back of a flip chip 110 is provided, wherein the entire wafer 200 of the flip chip 110 is placed in a sputtering device, the power of the sputtering device is set to 300 W, the argon pressure is set to 0.5 Pa, and the sputtering time is adjusted to 2 minutes, titanium is selected as the sputtering material, and it is loaded into the sputtering device, and the sputtering device is started to form a uniform metal seed layer with a thickness of 0.5 μm on the entire back of the flip chip 110; a layer of positive photoresist is uniformly coated on the back of the flip chip 110 using a spin coater, and a soft baking treatment is performed at a temperature of 90° C. for 90 seconds; a mask having a predetermined pattern is used to cover the wafer 200, and the wafer 200 is exposed to ultraviolet light through the mask, and the exposure energy is 200 mJ / cm2, and the exposed wafer 200 is placed in a developer to dissolve the exposed portion of the photoresist to expose the electrode region 113, and the development time is 60 seconds. , the developed wafer 200 is hard-baked at a temperature of 120°C for 120 seconds to stabilize the photoresist pattern; the patterned wafer 200 is immersed in a plating solution containing copper ions, and a DC current density of 1A / dm2 is applied to deposit copper ions in the electrode area 113 to form a 70μm thick copper layer, and the copper layer is ground using a chemical mechanical polishing (CMP) device to retain a 50μm thick copper layer; further, the photoresist and the sputtered metal titanium layer outside the pad are removed by etching technology, leaving only the conductive layer 112 on the electrode; further, Sn63Pb37 solder paste is printed on the copper layer using a steel mesh to ensure that each electrode position is evenly covered, and the wafer 200 coated with solder paste is placed in a reflow oven and heated with a peak temperature of 240°C to melt the solder paste and combine with the copper layer to form a tin layer about 50μm thick, and the tin layer is ground again using a grinding device to finally retain a tin layer about 30μm thick.

[0114] In a specific embodiment, a method for preparing a fluorescent film 116 is provided, wherein the proportion of fluorescent powder and the type of adhesive are adjusted as needed, a release film is laid on a glass platform, and a mixed fluorescent glue is prepared, a jig is used to control the gap width to be 100 μm, and a uniform layer of fluorescent powder film with a thickness of about 100 μm is coated on the release film by moving at a uniform speed, and the film is baked and cured at a temperature of 120°C for 30 minutes; transparent silica gel is prepared, and a layer of transparent silica gel is coated on the fluorescent powder film again as a protective layer 122 with a thickness of about 100 μm, and the film is baked and cured at a temperature of 120°C for 30 minutes; the color and color area coordinates, brightness output, color rendering, luminous flux output and other parameters of the fluorescent film 116 are measured, and according to the set standards, whether the fluorescent film 116 is qualified (OK or NG) is judged, and the fluorescent film 116 that meets the quality standards is selected for subsequent processes.

[0115] In a specific embodiment, a method for preparing a CSP (Chip Scale Package) with an inverted cup structure is provided. Specifically: a prepared double-layer fluorescent film is coated on a silicone crystal plate, ensuring that one side faces the glass carrier and the other side faces the transparent silicone layer of the fluorescent film, and the dispensing amount of the high-precision dispensing machine is set to 0.5 ml / chip, the dispensing path is circular, and the dispensing angle is 45 degrees to ensure that the glue is evenly distributed and appropriate; the glue is distributed on the fluorescent film 116, and the front side of the flip chip 110 is attached to the fluorescent film 116, so that the glue is distributed between the flip chip 110 and the fluorescent film 116 and overflows to form an oblique angle, and the oblique angle is 45 degrees; preferably, the upper edge of the glue is just pressed to the junction of the copper electrode and the tin electrode to form a larger transparent silicone bevel, and then the glue is dried. Use a spraying method to cover the entire flip chip 110 and the surrounding area with white insulating protective material (such as white wall glue), and perform a curing treatment at a temperature of 120°C for 30 minutes; select a suitable grinding device (such as a CMP device or a grinding wheel machine), set the grinding parameters according to the type of insulating protective material and the thickness of the solder layer 115, set the grinding depth to 15μm, fix the crystal board containing the flip chip 110 on the workbench of the grinding device, start the grinding device according to the preset parameters, and grind the insulating protective material until the solder layer 115 is completely exposed; further, use deionized water to thoroughly clean the flip chip 110 to remove residues, and use a nitrogen gun or a rotary drying device to blow dry the crystal board to ensure that the moisture is completely removed.

[0116] Finally, the whole CSP after grinding is cut into a single CSP with copper-tin electrodes. At this time, the film is inverted to become a finished CSP product.

[0117] It can be understood that in a specific embodiment, a method for cutting a wafer is provided. In order to obtain a single flip chip from a whole LED chip CSP package wafer, we adopt a set of precise and efficient cutting process. First, the whole wafer is thoroughly cleaned with deionized water and a special cleaning agent, and a microscopic inspection is performed to ensure that there are no cracks or contaminants on its surface. Then, the cleaned wafer is placed on the workbench of a fully automatic wafer cutting machine, and the wafer is fixed with a vacuum adsorption device to ensure that it is stable and motionless during the entire cutting process. To protect the front of the wafer, we evenly coat a layer of photoresist on its surface and cure it by baking to prevent the debris generated during the cutting process from damaging the chip surface.

[0118] Subsequently, the cutting path is set according to the chip layout diagram, and a laser scribing machine is used to make precise cutting marks on the wafer. A high-precision diamond tool cutter is selected as the cutting device, and the cutting speed is adjusted to 80mm / s, the feed rate is 25μm / step, and the cutting depth is to completely penetrate the thickness of the wafer without damaging the solder layer on the back. The cutter is started and cuts along the preset path, while providing a coolant spray to avoid high temperature caused by friction and damage to the chip. After the cutting is completed, an ultrasonic cleaner is used to remove the debris generated during the cutting process, and the wafer is blown dry with a nitrogen gun.

[0119] Next, a special solvent is used to strip the photoresist on the front of the wafer to restore the original state of the chip surface. Then, the appearance of each chip is checked one by one under a microscope to ensure that there are no cracks, missing corners or other physical damage, and basic electrical characteristics tests are performed on each chip to verify whether its performance meets the design requirements. Finally, the single flip chip that has passed the inspection is carefully removed, placed in an anti-static tray, and labeled with batch number, production date and other information for subsequent traceability and quality control.

[0120] Through the above specific embodiments, a complete LED chip CSP packaging method is demonstrated, ensuring that the operating details and process parameters of each step are strictly controlled, providing a solid foundation for the performance and reliability of the final product. This embodiment is only an example, and the specific parameters and conditions of each step can be adjusted according to specific needs in actual applications.

[0121] In summary, the present invention provides a CSP packaging method for LED chips, which gradually solves these problems by forming a conductive layer on the back of the flip chip, exposing the electrode area, forming a connection layer and a solder layer, mounting a fluorescent film, and performing the steps of filling with white reflective glue and processing to expose the solder layer. By forming a conductive layer, effective conduction of current is ensured; exposing the electrode area provides a basis for the formation of the connection layer and the solder layer; forming the connection layer and the solder layer ensures reliable connection between the electrode and the external circuit; mounting the fluorescent film to provide optical performance; filling with white reflective glue to protect the chip and ensure structural stability; processing to expose the solder layer provides convenience for subsequent electrical connection. In this way, the reliability and stability of electrode exposure and connection of the flip chip during the packaging process are ensured.

[0122] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for packaging LED chips CSP, characterized in that: The following steps are involved: Processing the back of the wafer to form a conductive layer on the flip chip in each flip chip area; wherein the wafer includes a plurality of flip chip areas, and each flip chip area includes a flip chip; Processing the conductive layer to expose an electrode region on the back side of the flip chip of each flip chip region on the wafer; processing the exposed electrode area to form a connection layer and a solder layer; A fluorescent film is mounted on the front side of the flip chip to form a flip chip CSP; Filling the flip chip with white reflective adhesive after the fluorescent film is attached, so that the white reflective adhesive covers the back side of each flip chip; Processing the white reflective adhesive to expose the solder layer on the back side of each flip chip; The flip chip CSP is cut to obtain a single flip chip CSP finished product.

2. The LED chip CSP packaging method according to claim 1, characterized in that: The processing of the back of the wafer to form a conductive layer on the flip chip in each flip chip area also includes the following steps: placing the wafer in a sputtering device; Presetting the parameters of the sputtering device; Loading a metal material corresponding to the flip chip into a sputtering device; The sputtering device is started to perform sputtering to form a metal seed layer on the entire back side of the flip chip in each flip chip area on the wafer.

3. The LED chip CSP packaging method according to claim 1, characterized in that: The conductive layer is processed to expose the electrode area on the back side of the flip chip of each flip chip area on the wafer in the following steps: Applying photoresist to the conductive layer of each flip chip on the wafer; heating the photoresist coated on the conductive layer of each flip chip on the wafer; Selecting a mask with a predetermined pattern and covering the pattern position on the electrode area of ​​each flip chip; The wafer is placed in an exposure device, and the flip chip on the wafer is exposed through a mask, so that the photoresist on the conductive layer that is not covered by the pattern of the mask becomes soluble; The exposed wafer is placed in a developer to dissolve the exposed photoresist and expose the electrode area of ​​each flip chip.

4. The LED chip CSP packaging method according to claim 1, characterized in that: The step of processing the exposed electrode area to form a connection layer and a solder layer further comprises the following steps: The electrode area of ​​each flip chip on the wafer is immersed in an electroplating solution, and a direct current is applied to deposit copper ions in the electrode area to form a copper layer; The copper layer is ground using a grinding device to retain a portion of the copper layer; Print solder paste onto the copper layer; The copper layer coated with solder paste on the flip chip is heated to combine the solder paste with the copper layer; The combined tin layer is ground using a grinding device to retain a portion of the thickness of the tin layer; Clean flip chips to remove residues.

5. The LED chip CSP packaging method according to claim 4, characterized in that: The thickness of the retained copper layer ranges from 40 to 50 μm; The thickness of the retained tin layer ranges from 15 to 30 μm.

6. The LED chip CSP packaging method according to claim 1, characterized in that: The method of attaching a fluorescent film to the front side of the flip chip to form a flip chip CSP further comprises the following steps: Lay release film on the platform; The prepared fluorescent glue is coated on the release film, and the fluorescent glue is heated to form a fluorescent film; Apply the prepared transparent adhesive on the fluorescent film to form a protective layer; Testing the fluorescent film including the fluorescent film and the protective layer; Cut each flip chip on the wafer to form a single flip chip; Distribute the fluorescent films that have passed the test evenly on the crystal-making plate, and apply glue to each fluorescent film; Press the front side of each flip chip downward relative to the fluorescent film, so that the glue adheres between the flip chip and the fluorescent film and overflows to form an oblique angle; Adjust the amount of glue and the viscosity of the adhesive to adjust the bevel and angle.

7. The LED chip CSP packaging method according to claim 6, characterized in that: The method of filling the flip chip with white reflective glue after mounting the fluorescent film so that the white reflective glue covers the back side of each flip chip further comprises the following steps: Set the dispensing volume and dispensing path of the dispensing machine; Filling the back and surrounding area of ​​each flip chip on the wafer board with white reflective glue; The white reflective adhesive filled on the back and surrounding area of ​​the flip chip on the wafer making plate is dried using a drying device, thereby obtaining a whole CSP of the flip chip.

8. The LED chip CSP packaging method according to claim 1, characterized in that: The processing of the white reflective adhesive to expose the solder layer on the back side of each flip chip further comprises the following steps: Fixing the flip chip on a workbench of a grinding device; Set the grinding parameters according to the thickness of the white reflective glue and the thickness of the solder layer; Start the grinding device according to the preset parameters and grind the white reflective adhesive until the solder layer is exposed; Clean flip chips to remove residues.

9. The LED chip CSP packaging method according to claim 4 or 8, characterized in that: The cleaning of the flip chip and removal of residues also includes the following steps: Adding a cleaning agent into a cleaning device, and using the cleaning device to clean the flip chip; Drying the cleaned flip chip using a drying device; Test the electrodes on the back of a single flip chip to determine whether the cleaned flip chip is qualified.

10. The LED chip CSP packaging method according to claim 1, characterized in that: Cutting the flip chip CSP to obtain a single flip chip CSP finished product also includes the following steps: Place the entire flip chip CSP on the cutting platform; Make cutting marks for each flip chip on the entire CSP of the flip chip; The cutting device is started according to the cutting mark, and cutting is performed along the cutting mark, so that each flip chip is cut into a single CSP finished product.

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