WO2022021389A1 - Underfill and preparation method therefor, and dispensing method applied to an led display screen - Google Patents

Abstract

An underfill and a preparation method therefor, and a dispensing method applied to an LED display screen (100). The underfill comprises the following raw materials in percentage by mass: epoxy resin: 50%-70%; latent curing agent: 1%-20%; filler: 5%-20%; diluent: 1%-20%; toughening agent: 1%-10%; coupling agent: 0.1%-2%; and defoaming agent: 0.1%-3%. The light transmittance of the underfill is greater than 80%.

Description

A kind of bottom filling glue and preparation method thereof and glue dispensing method applied to LED display screen technical field

The application relates to the technical field of LED display screens, in particular to an underfill adhesive and a preparation method thereof, and a glue dispensing method applied to an LED display screen.

Background technique

LED display has the characteristics of high luminous brightness, bright colors and low energy consumption, and is widely used in cultural performances, advertising media, securities trading and other fields. Among them, LED lamp beads, as an important component of LED display, directly affect the use effect of LED display. Usually, LED lamp beads are soldered on the substrate (such as PCB board) by surface mount technology, but due to the small pad area, the connection force between the LED lamp beads and the substrate is small, and it is easy to transport the LED display during the handling process. The LED lamp beads fall off, which greatly affects the display quality of the LED display.

In order to solve the problem of the lamp beads falling off of the LED display, the industry has begun to use underfill for reinforcement. Based on capillary action, the underfill fills the gap between the bottom of the LED lamp beads and the substrate. However, the current underfills are mostly black products directly transplanted from the field of integrated circuits. If the black underfill is smeared on the lamp surface of the LED lamp bead, after curing, it will block/absorb the light of the lamp bead, greatly reducing the Reduce the display effect of the LED display.

SUMMARY OF THE INVENTION

In view of this, the present application provides an underfill adhesive that can be applied to an LED display screen, which has high transparency and can not only solve the problem of falling off of the LED lamp beads, but also does not affect the display effect of the LED display screen.

In a first aspect, the application provides an underfill adhesive, and the underfill adhesive includes the following raw materials by mass percentage:

Epoxy resin: 50%～70%;

Latent curing agent: 1% to 20%;

Filler: 5%～20%;

Thinner: 1%～20%;

Toughening agent: 1%～10%;

Coupling agent: 0.1%～2%;

Defoamer: 0.1%～3%;

Wherein, the light transmittance of the underfill is greater than 80%.

In this application, the light transmittance of the underfill adhesive is relatively high. When it is applied to an LED display screen, even if it is attached to the lamp surface of the LED lamp bead during the dispensing process, the light transmittance of the adhesive layer formed by its curing will The rate is also high, which will not affect the luminescence of the LED lamp beads, and thus will not affect the display effect of the LED display.

Optionally, the viscosity of the underfill of the present application at 25° C. is 1000 mPa·s˜2000 mPa·s. The viscosity of the underfill is suitable, and it can flow out smoothly through the dispensing needle of the dispensing machine, and it will not spread excessively on the LED display, which will affect the filling performance.

Optionally, the light transmittance of the underfill in the present application may be greater than 85%, greater than 90%, greater than 95%, greater than 98%, and even greater than 99%. Preferably, the light transmittance of the underfill may be greater than 90%.

Optionally, the linear expansion coefficient of the underfill in this application is ≤50×10 ⁻⁶ /°C.

Optionally, the tensile shear strength of the underfill in this application is ≥8Mpa. Preferably it is ≥20Mpa.

Optionally, the glass transition temperature of the underfill of the present application is above 110°C. In this way, the underfill has good high temperature resistance and is not easy to soften and fall off.

In this application, fillers can increase the strength of the underfill. Preferably, the filler is a white filler with a size in nanometer level. Optionally, the particle size of the filler ranges from 15 nm to 100 nm. The white filler with a particle size of nanometer can not only ensure the smooth flow of the underfill from the dispensing needle, but also ensure that the underfill has a high light transmittance. Further optionally, the filler is regular spherical particles. Specifically, the material of the filler may include one or more of silicon dioxide, titanium dioxide, aluminum oxide, and calcium carbonate. Further, the surface of the filler can also be modified by a surfactant (such as sodium dodecylbenzenesulfonate, sodium laurate, etc.) and/or a coupling agent, so as to avoid the filler agglomeration caused by too small particle size. Wherein, the particle size of the modified filler can also be in the range of 15 nm to 100 nm.

In this application, epoxy resin is used as the base resin of the underfill. In order to keep the viscosity of the underfill in the above range, the viscosity of the epoxy resin at 25°C can be 1000mPa·s～3000mPa·s, for example, 1200mPa·s ~2800mPa·s. Optionally, the total chlorine content of the epoxy resin is less than or equal to 500 ppm, which can ensure that the above-mentioned underfill will have less corrosive effect on the metal material on the substrate when it is applied to the LED display screen.

Optionally, epoxy resins include bisphenol A type epoxy resins, bisphenol F type epoxy resins, aliphatic epoxy resins, alicyclic epoxy resins, polycyclic aromatic epoxy resins and novolac type epoxy resins one or more of.

In the present application, the latent curing agent can be cross-linked with the epoxy resin to form a three-dimensional network structure. The latent curing agent has a certain storage stability at room temperature, and after heating and heating, the reactivity of the curing agent can be quickly released, so as to achieve the purpose of rapid curing of the epoxy resin. Optionally, the stability of the latent curing agent at 40° C. is 3 weeks to 4 weeks, which can maintain relatively stable fluidity during the dispensing process of the underfill and ensure higher dispensing quality.

Further optionally, the D50 particle size of the latent curing agent is 200 nm to 500 nm. Latent curing agents are relatively light in color, such as white or transparent. The latent curing agent of suitable size and light color can not only ensure the smooth flow of the underfill from the dispensing tip, but also ensure the high light transmittance of the underfill.

Optionally, the latent curing agent may include one or more of modified amine curing agents, imidazole curing agents and dicyandiamide curing agents. The modified amine curing agent may include one or more of boron trifluoride monoethylamine, boron trifluoride aniline, boron trifluoride benzylamine and boron trifluoride pyridine. Preferably, the modified amine curing agent is white boron trifluoride monoethylamine. The imidazole-based curing agent may include one or more of imidazole, 2-methylimidazole, 2-ethylimidazole, 2, 4-dimethylimidazole, and 2-ethyl 4-methylimidazole. The dicyandiamide curing agent may include one or more of dicyandiamide and aniline-modified dicyandiamide.

In the present application, the toughening agent can improve the toughness of the underfill, increase its elastic modulus, and reduce the thermal expansion coefficient, so that the underfill has high impact resistance and good heat resistance. Optionally, the toughening agent may comprise one or one of liquid silicone rubber, liquid carboxyl-terminated nitrile rubber, liquid hydroxyl-terminated nitrile rubber, liquid hydroxyl-terminated polybutadiene rubber and epoxy-terminated polybutadiene rubber. variety. Wherein, the liquid silicone rubber includes at least one of methyl vinyl silicone rubber, dimethyl vinyl silicone rubber, methyl phenyl vinyl silicone rubber and methyl diphenyl vinyl silicone rubber.

Further, the liquid toughening agent also helps to ensure that the viscosity of the underfill is in an appropriate range. Optionally, the viscosity of the toughening agent at 25° C. is 5 mPa·s˜100 mPa·s. For example, it is 15 mPa·s to 80 mPa·s.

In this application, the coupling agent has both reactive groups that can be chemically combined with inorganic materials (such as fillers) and reactive groups that can be chemically combined with organic materials (such as epoxy resins), which can improve the interface properties of epoxy resins and fillers , make the dispersibility and compatibility of the inorganic filler in the organic matrix, reduce the viscosity of the system, and also enhance the bonding strength of the glue on different substrates.

Optionally, the coupling agent includes one or more of silane-based coupling agents, titanate-based coupling agents and aluminate-based coupling agents. Wherein, the silane coupling agent may include aminopropyltriethoxysilane, aminopropyltrimethoxysilane, 2-aminoethyl-aminopropyltrimethoxysilane and diethylenetriaminopropyltrimethoxysilane one or more of. The titanate coupling agent may include isopropyl dioleic acid acyloxy (dioctyl phosphoric acid acyloxy) titanate, isopropyl tris (dioctyl phosphoric acid acyloxy) titanate, triisopropyl One or more of isopropyl stearate titanate, isopropyl triisostearate titanate and tetraisopropyl bis(dioctylphosphiteoxy) titanate. Aluminate coupling agents can include one or more of distearoyloxyisopropylaluminate, DL-411, DL-411AF, DL-411D, DL-411DF, anti-settling aluminate ASA, etc. kind.

In this application, the diluent can reduce the viscosity of the underfill and improve the fluidity. Alternatively, the diluent may include cyclohexane-1,2-dicarboxylate diglycidyl ester, tetrahydrophthalate diglycidyl ester, tolyl glycidyl ether, o-tolyl glycidyl ether, neopentyl One or more of glycol diglycidyl ether, hexylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and ethylene glycol diglycidyl ether.

In the present application, the defoaming agent can effectively reduce the probability of generating bubbles during the preparation and use of the underfill, and improve the reliability of the adhesive layer. Optionally, the antifoaming agent may include one or more of a silicone antifoaming agent and a non-silicone antifoaming agent. Among them, silicone defoamer can include BYK-077, BYK-322, BYK-323, BYK-320, and non-organic silicon defoamer can include BYK-051, BYK-052, BYK-053, BYK-054, BYK -055, BYK-057, BYK-A550, BYK-1790.

The underfill provided in the first aspect of the present application has high light transmittance and high transparency. When it is applied to an LED display, the connection strength between the LED lamp beads and the substrate can be greatly improved, even if The underfill glue sticks to the lamp surface of the LED lamp beads during the dispensing process, and will not affect the light emission of the LED lamp beads, and thus will not affect the display effect of the LED display screen.

Correspondingly, a second aspect of the present application provides a method for preparing an underfill, comprising the following steps:

At a temperature of less than or equal to 45°C, mix the epoxy resin, latent curing agent, filler, toughening agent, diluent, defoamer and coupling agent uniformly to obtain a mixed slurry, and vacuum the mixed slurry After defoaming, an underfill with a light transmittance greater than 80% is obtained; wherein, the underfill includes the following components by mass percentage:

Epoxy resin: 50%～70%;

Latent curing agent: 1% to 20%;

Filler: 5%～20%;

Thinner: 1%～20%;

Toughening agent: 1%～10%;

Coupling agent: 0.1%～2%;

Defoamer: 0.1% to 3%.

In an embodiment of the present application, the mixed slurry is prepared by the following method: at a temperature less than or equal to 45°C, the epoxy resin, the latent curing agent and the toughening agent are first mixed to obtain a first mixture, and then add diluent, defoaming agent, coupling agent and filler to the first mixture, and carry out the second mixing to obtain a mixed slurry. The above-mentioned mixed slurry is prepared by step-by-step mixing, so that the components in the obtained underfill can be dispersed relatively uniformly.

Optionally, the stirring speed used for the first mixing is 800 r/min to 1000 r/min, and the stirring time is 20 min to 60 min. Optionally, the stirring speed used for the second mixing is 1000r/min～1200r/min, and the stirring time is 60min～120min. The temperature of the first mixing and the second mixing can be the same or different, as long as it does not exceed 45°C, for example, 20°C to 35°C, so as to avoid excessively high temperature during the preparation of the glue, making the latent type The curing agent cures and affects subsequent dispensing.

Optionally, the degree of vacuum during vacuum degassing is 0.06-0.1 MPa. Optionally, the time for vacuum defoaming is 5 min to 30 min, for example, 5 min to 15 min.

The preparation method of the underfill provided by the second aspect of the present application is simple and easy to implement, and the prepared underfill has high transparency, high light transmittance and stable performance.

A third aspect of the present application also provides a glue dispensing method applied to an LED display screen. The dispensing method adopts the underfill of the first aspect of the present application, and the underfill can be used to strengthen the welding force between the LED lamp bead and the substrate.

In an embodiment of the present application, the glue dispensing method specifically includes: providing an LED display screen, the LED display screen including a substrate and a matrix of LED lamp beads arranged on the substrate; placing the LED display screen on an operating table, and making the LED lights The LED lamp beads in the bead matrix are far away from the operating table; the underfill glue provided in the first aspect of the present application is applied to the gap between the LED lamp beads through a glue dispenser, and after curing, a transparent glue layer is formed on the substrate to obtain Reinforced LED display.

Optionally, the underfill glue is applied to the gap between the LED lamp beads by at least one of the following methods, and the method b) and the method c) are not performed simultaneously:

a) On the periphery of the LED lamp bead matrix, at the gap between any two adjacent LED lamp beads, apply underfill glue;

b) Apply underfill glue at the position corresponding to the LED lamp bead between any two adjacent rows of LED lamp beads; wherein, the two adjacent rows of underfill glue are separated by a row of LED lamp beads;

c) Apply underfill glue at positions corresponding to the LED lamp beads between any two adjacent rows of LED lamp beads; wherein, the two adjacent rows of underfill glue are separated by two rows of LED lamp beads.

Among them, the above-mentioned method a) can be referred to as "outer ring spot painting"; mode b) can be referred to as "every line spot painting", and mode c) can be referred to as "interlaced spot painting". In some embodiments, the mode a), the mode b) or the mode c) can be adopted alone, or the mode a) and the mode b) can be adopted at the same time, or the mode a) and the mode c) can be adopted at the same time.

Optionally, the curing temperature is 80° C.˜130° C., and the curing time is 20 min˜60 min. The curing temperature may be 80°C, 90°C, 100°C, 110°C or 120°C.

Optionally, after curing, the glass transition temperature of the formed transparent adhesive layer is above 110°C. During the use of the LED display, high heat may be generated, and the transparent adhesive layer with a high glass transition temperature is not easy to soften and fall off in such an environment, which can improve the service life of the LED display.

Optionally, in the reinforced LED display screen, the LED lamp beads can withstand a thrust of 2.5Kg to 5.0Kg. Preferably, the LED lamp beads can withstand a thrust of 4.0Kg-5.0Kg. The larger thrust of the LED lamp beads can effectively solve the problem of the LED display lamp beads falling off during the handling process.

Applying the underfill adhesive provided by this application to the LED display screen for dispensing can greatly improve the connection force between the LED lamp beads and the substrate, and the LED lamp beads are not easy to fall off the substrate; and the underfill adhesive does not affect the LED lamp beads. It emits light and will not affect the display effect of the LED display.

Description of drawings

Fig. 1 is a kind of glue dispensing effect diagram of the underfill glue on the LED display screen according to the embodiment of the application;

FIG. 2 is another effect diagram of the dispensing effect of the underfill glue on the LED display screen according to the embodiment of the application;

FIG. 3 is another effect diagram of the dispensing effect of the underfill glue on the LED display screen according to the embodiment of the application;

FIG. 4 is another effect diagram of the dispensing effect of the underfill glue on the LED display screen according to the embodiment of the application;

FIG. 5 is another effect diagram of the dispensing effect of the underfill glue on the LED display screen according to the embodiment of the application;

FIG. 6 is a comparison of the luminous effect of the LED display screen after using the underfill of the embodiment of the present application and the existing black underfill to reinforce the LED display.

detailed description

Before the application is further described with specific examples, the above-mentioned dispensing method in the application will be described in detail.

Referring to Fig. 1, the dispensing effect shown in Fig. 1 corresponds to the dispensing method a) in this application - "outer ring dispensing". The LED display screen 100 in FIG. 1 includes a substrate 10 and 64 LED lamp beads 21 arranged on the substrate 10 . The 64 LED lamp beads 21 are arranged in an 8×8 matrix on the substrate 10 to form an LED lamp bead matrix. 20. The periphery of the LED lamp bead matrix 20 is surrounded by 28 LED lamp beads 21 . The gap between any two adjacent lamp beads between the 28 lamp beads is coated with the underfill glue of the present application, and there are 28 glue dispensing positions shown by the numeral 3 in FIG. 1 .

The dispensing effect shown in FIG. 2 corresponds to the mode b) in this application—“dispensing per row”. In the LED display screen 100 of FIG. 2 , the LED lamp bead matrix on the substrate 10 includes N lamp bead rows, wherein the first lamp bead row and the second lamp bead row are any two adjacent lamps in the N lamp bead rows. In the bead row, the underfill adhesive of the embodiment of the present application is applied between the lamp bead located in the Mth column in the first lamp bead row and the lamp bead in the Mth column in the second lamp bead row, wherein the Mth The column is any column of the lamp bead row. The above-mentioned M and N are integers of 2 or more. It can be seen that in the dispensing method b), N-1 rows of underfill are dispensed on the substrate 10 in total, and two adjacent rows of underfill are separated by a row of LED lamp beads. It can be seen from Figure 2 that the underfill forms a 7×8 matrix arrangement.

The dispensing effect shown in FIG. 3 corresponds to the method c) in this application—“interlaced dispensing”. In the LED display screen 100 of FIG. 3 , the LED lamp bead matrix on the substrate 10 includes N lamp bead rows, wherein the N lamp bead rows are divided into N/2 pairs of lamp bead rows, and the first pair of lamp bead rows is divided into N/2 pairs of lamp bead rows. It is any one of N/2 pairs of lamp bead rows, the first pair of lamp bead rows includes the adjacent first lamp bead row and the second lamp bead row, and the lamp bead in the first lamp bead row is located in the Mth column. The underfill adhesive of the embodiment of the present application is applied between the second lamp bead row and the lamp beads located in the M-th column; wherein, the M-th column is any column of the lamp bead row. The above-mentioned M is an integer greater than or equal to 2, and N is an even number greater than 2. It can be seen that, in the dispensing method c), N/2 rows of underfill are dispensed on the substrate 10 in total, and the two adjacent rows of underfill are separated by two rows of LED lamp beads. Dispensing method c) is suitable for dispensing of LED lamp beads with even rows.

In addition, the dispensing effect shown in FIG. 4 corresponds to the combination of dispensing method a) and dispensing method c) in this application. The dispensing effect shown in FIG. 5 corresponds to the combination of dispensing method a) and dispensing method b) in this application.

The present application will be further described below through specific examples.

Example 1

An underfill adhesive comprising the following raw materials in the following mass ratios:

Bisphenol A epoxy resin (viscosity at 25℃ is 2000mPa·s, total chlorine content≤500ppm): 55%;

Latent curing agent (specifically micronized dicyandiamide, D50 particle size is 300nm): 10%;

Toughening agent (specifically, liquid hydroxy-terminated nitrile rubber, its viscosity at 25°C is 50mPa·s): 10%;

Diluent (specifically cyclohexane-1,2-dicarboxylate diglycidyl ester): 17%;

Defoamer (specifically BYK-077): 1.5%;

Coupling agent (specifically aminopropyltriethoxysilane): 1.5%;

Filler (specifically, spherical nano-silica modified with aminopropyltriethoxysilane, with a particle size of 20 nm): 5%.

The preparation method of the above-mentioned underfill comprises: 1) weighing each raw material according to the component ratio of the above underfill; 2) first mixing the weighed epoxy resin with a curing agent and a toughening agent, and at a time less than or equal to Stir evenly at a temperature of 45 ° C, the stirring speed is 800 r/min, and the stirring time is 50 min to obtain the first mixture; 3) At a temperature of less than or equal to 45 ° C, then weigh the diluted diluent, defoamer, The coupling agent and the filler are added to the first mixture, stirred at a speed of 1200 r/min for 70 minutes to obtain a second mixture; 4) the second mixture is degassed under vacuum for 10 minutes to obtain the above-mentioned underfill with high transparency .

The glue dispensing method for applying the above-mentioned underfill to an LED display screen specifically includes: 1) providing an LED display screen 100 (see FIG. 5 ), the LED display screen 100 includes a substrate 10 and a plurality of LED lamp beads arranged on the substrate 10 21. A plurality of LED lamp beads 21 are arranged in a matrix on the substrate 10 to form an LED lamp bead matrix 20; the substrate 10 of the LED display screen 100 is placed on the console to keep the LED lamp beads 21 away from the console;

2) Place the above-mentioned underfill glue in the liquid storage chamber of a glue dispenser with a pneumatically driven or piezoelectrically driven glue dispensing valve, and dispense it on the substrate 10. The dispensing effect is shown in Figure 5 (the symbol in Figure 5). 3 shows the dispensing position of the underfill); after that, the substrate 10 with the underfill is heated and cured (the temperature is 110° C. and the time is 40 minutes), and the underfill is cured to form a transparent adhesive layer, obtaining Reinforced LED display.

Example 2

An underfill adhesive comprising the following raw materials in the following mass ratios:

Bisphenol F-type epoxy resin (viscosity at 25°C is 1800mPa·s, total chlorine content≤500ppm): 60%;

Latent curing agent (specifically 2-methylimidazole, D50 particle size is 300nm): 7%;

Toughening agent (specifically, methyl vinyl silicone rubber, whose viscosity at 25° C. is 30 mPa·s): 10%;

Diluent (specifically diglycidyl tetrahydrophthalate): 13%;

Defoamer (specifically BYK-051): 1.5%;

Coupling agent (specifically 2-aminoethyl-aminopropyltrimethoxysilane): 1.5%;

Filler (specifically, spherical nano-calcium carbonate modified with sodium dodecylbenzenesulfonate, with a particle size of 30 nm): 7%.

The preparation method of the above-mentioned underfill comprises: 1) weighing each raw material according to the component ratio of the above underfill; 2) first mixing the weighed epoxy resin with a curing agent and a toughening agent, and at a time less than or equal to Stir evenly at a temperature of 45 ° C, the stirring speed is 900 r/min, and the stirring time is 40 min to obtain the first mixture; 3) At a temperature of less than or equal to 45 ° C, then weighed diluent, defoamer, The coupling agent and the filler are added to the first mixture, and stirred at a speed of 1100 r/min for 85 minutes to obtain a second mixture; 4) the second mixture is degassed under vacuum for 15 minutes to obtain the above-mentioned underfill with high transparency .

Example 3

An underfill adhesive comprising the following raw materials in the following mass ratios:

Aliphatic epoxy resin (viscosity at 25°C is 1600mPa·s, total chlorine content≤500ppm): 65%;

Latent curing agent (specifically, boron trifluoride monoethylamine, D50 particle size is 400nm): 5%;

Toughening agent (specifically, liquid hydroxy-terminated nitrile rubber, whose viscosity at 25° C. is 40 mPa·s): 5%;

Diluent (specifically cyclohexane-1,2-dicarboxylate diglycidyl ester): 5%;

Defoamer (specifically BYK-077): 1%;

Defoamer (specifically BYK-051): 1%;

Coupling agent (specifically aminopropyltriethoxysilane): 1.5%;

Coupling agent (specifically, isopropyl dioleic acid acyloxy (dioctyl phosphoric acid acyloxy) titanate): 1.5%;

Filler (specifically, spherical nano-silica modified with aminopropyltriethoxysilane, with a particle size of 20 nm): 7%;

Filler (specifically, spherical nano-calcium carbonate modified with sodium dodecylbenzenesulfonate, with a particle size of 30 nm): 8%.

The preparation method of the above-mentioned underfill comprises: 1) weighing each raw material according to the component ratio of the above underfill; 2) first mixing the weighed epoxy resin with a curing agent and a toughening agent, and at a time less than or equal to Stir evenly at a temperature of 45 ° C, the stirring speed is 1000 r/min, and the stirring time is 30 min to obtain the first mixture; 3) At a temperature of less than or equal to 45 ° C, then weighed diluent, defoamer, The coupling agent and filler are added to the first mixture, and stirred at a speed of 1000 r/min for 105 minutes to obtain a second mixture; 4) the second mixture is degassed under vacuum for 20 minutes to obtain the above-mentioned underfill with high transparency .

In order to strongly support the beneficial effects brought by the technical solutions of the embodiments of the present application, the performance test results of the highly transparent underfill adhesives of each embodiment are provided (see Table 1).

Table 1 Performance test results of highly transparent underfill in each embodiment

Test items	Example 1	Example 2	Example 3
Viscosity (mPa s)	1500	1200	1800
Use time (25℃)	≥48h	≥48h	≥48h
Transmittance(%)	93	95	90

Glass transition temperature (℃)	120	125	140
Linear expansion coefficient (10 -6 /℃)	30	40	25
Tensile shear strength (45# steel) (Mpa)	16	14	18

In Table 1, the two test items of viscosity and service time are for uncured high transparent underfill, and the four tests of light transmittance, glass transition temperature, coefficient of linear expansion, and tensile shear strength are for For cured highly transparent underfill.

It can be seen from Table 1 that the highly transparent underfill provided by the examples of the present application has high light transmittance, high glass transition temperature, good high temperature resistance, is not easy to expand and fall off, and has good tensile shear performance, it is very suitable for application to the LED display that emits light and heat.

This application also tested the LED lamp beads on the reinforced LED display screen by using a thrust meter to test the LED lamp beads on the reinforced LED display screen after the highly transparent underfill provided in Example 1 was used to reinforce the LED display screen according to the dispensing method shown in FIG. 5 . Thrust, it is measured that the peripheral and middle LED lamp beads can withstand a thrust of 4.5Kg, which indicates that the highly transparent underfill provided by the embodiment of this application can greatly avoid the problem of lamp beads falling off during the handling of the LED display screen. In addition, the present application also provides a comparison of the luminous effect after the use of black underfill commonly used in the field of integrated circuits and the reinforcement of the LED display screen. The results are shown in FIG. 6 . It can be seen from Figure 6 that the LED lamp beads in the high transparent glue reinforced area emit light normally, while the LED lamp beads in the black glue reinforced area greatly reduce the luminous brightness. It can be seen that the application of the underfill adhesive provided in the present application to the LED display screen can not only greatly improve the bonding force between the LED lamp beads and the substrate, but also does not affect the luminous effect of the LED display screen.

In addition, if the highly transparent underfill provided in Example 1 is applied to the LED display screen according to the dispensing method shown in Figure 1, it is measured that on the reinforced LED display screen, the peripheral LED lamp beads can withstand 2.5Kg The thrust of the LED lamp bead in the middle is not reinforced by the above-mentioned underfill glue, and its thrust is only 1.5Kg; on the LED display screen reinforced by the dispensing method shown in Figure 2, the peripheral LED lamp beads can withstand 2.5Kg thrust, the middle LED lamp bead can withstand 4.5Kg thrust; on the LED display screen reinforced by the dispensing method shown in Figure 3, the peripheral and middle LED lamp beads can withstand 2.5Kg thrust; On the LED display screen reinforced by the dispensing method shown in Figure 4, the peripheral LED lamp beads can withstand a thrust of 4.5Kg, and the middle LED lamp beads can withstand a thrust of 2.5Kg.

The above examples only represent several embodiments of the present application, and the descriptions thereof are relatively specific and detailed, but should not be construed as a limitation on the scope of the patent of the present application. It should be pointed out that for those skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which all belong to the protection scope of the present application. Therefore, the scope of protection of the patent of the present application shall be subject to the appended claims.

Claims (14)

1. An underfill, characterized in that the underfill comprises the following raw materials by mass percentage:

   Epoxy resin: 50%～70%;

   Latent curing agent: 1% to 20%;

   Filler: 5%～20%;

   Thinner: 1%～20%;

   Toughening agent: 1%～10%;

   Coupling agent: 0.1%～2%;

   Defoamer: 0.1%～3%;

   Wherein, the light transmittance of the underfill is greater than 80%.
2. The underfill of claim 1, wherein the underfill has a viscosity of 1000 mPa·s˜2000 mPa·s at 25°C.
3. The underfill adhesive according to claim 1, wherein the color of the filler is white, and the particle size of the filler is in nanometer level.
4. The underfill adhesive according to claim 1, wherein the material of the filler comprises one or more of silicon dioxide, titanium dioxide, aluminum oxide and calcium carbonate.
5. The underfill adhesive according to claim 1, wherein the epoxy resin has a viscosity of 1000 mPa·s˜3000 mPa·s at 25° C., and the total chlorine content of the epoxy resin is less than or equal to 500 ppm.
6. The underfill adhesive according to claim 1, wherein the D50 particle size of the latent curing agent is 200 nm to 500 nm.
7. The underfill adhesive according to claim 6, wherein the latent curing agent comprises one or more of a modified amine curing agent, an imidazole curing agent and a dicyandiamide curing agent.
8. The underfill rubber according to claim 1, wherein the viscosity of the toughening agent at 25° C. is 5 mPa·s˜100 mPa·s.
9. The underfill rubber according to claim 8, wherein the toughening agent comprises liquid silicone rubber, liquid carboxy-terminated nitrile rubber, liquid hydroxy-terminated nitrile rubber, liquid hydroxy-terminated polybutadiene rubber and end rings One or more of oxypolybutadiene rubbers; wherein, the liquid silicone rubber includes methyl vinyl silicone rubber, dimethyl vinyl silicone rubber, methyl phenyl vinyl silicone rubber and methyl diethyl silicone rubber At least one of phenyl vinyl silicone rubber.
10. A glue dispensing method applied to an LED display screen, comprising:

    An LED display screen is provided, the LED display screen includes a substrate and an LED lamp bead matrix arranged on the substrate; the LED display screen is placed on an operation table, and the LED lamp beads in the LED lamp bead matrix are away from said console;

    The underfill glue according to any one of claims 1-9 is applied to the gap between the LED lamp beads by a glue dispenser, and after curing, a transparent glue layer is formed on the substrate, Reinforced LED display.
11. The glue dispensing method according to claim 10, wherein the dispensing of the underfill glue in the gap between the LED lamp beads is performed by at least one of the following methods, and the method is b ) is different from mode c):

    a) On the periphery of the LED lamp bead matrix, at the gap between any two adjacent LED lamp beads, apply the underfill glue;

    b) Apply the underfill glue at the position corresponding to the LED lamp bead between any two adjacent rows of LED lamp beads; wherein, the two adjacent rows of the underfill glue are separated by a row of LED lamp beads open;

    c) Apply the underfill glue at the position corresponding to the LED lamp bead between any two adjacent rows of LED lamp beads; wherein, two rows of LED lamp beads are placed between the two adjacent rows of the underfill glue separated.
12. The glue dispensing method according to claim 10, wherein the curing temperature is 80°C to 130°C, and the curing time is 20min to 60min.
13. The glue dispensing method according to claim 10, wherein the glass transition temperature of the transparent glue layer is above 110°C.
14. A preparation method of underfill, characterized in that the preparation method comprises the following steps:

    The epoxy resin, latent curing agent, filler, toughening agent, diluent, defoamer and coupling agent are mixed uniformly at a temperature less than or equal to 45°C to obtain a mixed slurry. After vacuum defoaming, an underfill is obtained; wherein, the underfill includes the following components by mass percentage:

    Epoxy resin: 50%～70%;

    Latent curing agent: 1% to 20%;

    Filler: 5%～20%;

    Thinner: 1%～20%;

    Toughening agent: 1%～10%;

    Coupling agent: 0.1%～2%;

    Defoamer: 0.1%～3%;

    Wherein, the light transmittance of the underfill is greater than 80%.

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