Epoxy die bonding adhesive for LED package

Abstract

The application discloses an epoxy die bonding adhesive for LED packaging, which comprises, by weight, a combination of bisphenol A type epoxy resin, hydrogenated bisphenol A type epoxy resin, a curing agent, a curing accelerator, a silane coupling agent and a thixotropic agent; and the curing accelerator is an imidazole derivative with a specific structure. The epoxy die bonding adhesive is prepared by using the combination of the bisphenol A type epoxy resin and the hydrogenated bisphenol A type epoxy resin as a main resin body, and under the premise of not using a diluent, viscosity can be controlled, and the specific structure of the curing accelerator is combined, so that the prepared die bonding adhesive not only has excellent bonding capacity, but also can achieve a room temperature operation period of about 10 days, can effectively reduce waste of the die bonding adhesive and improve production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor packaging adhesive preparation technology, specifically relating to an epoxy die bond adhesive for LED packaging. Background Technology

[0002] Epoxy resin has many advantages, such as corrosion resistance, electrical insulation, excellent adhesion, and good processability, making it the main adhesive for LED encapsulation die bonding. Thermosetting adhesives are the primary type used for LED encapsulation die bonding, among which thermosetting epoxy resin die bonding adhesives are widely used in the field of small-size LED chip packaging due to their excellent bonding properties.

[0003] In epoxy resin systems, dicyandiamide, as a typical heat-latent curing agent, is poorly soluble in epoxy resin at room temperature, thus resulting in a long shelf life. However, when heated to a certain temperature, it can ring-open and activate the epoxy resin, rapidly crosslinking it into a three-dimensional network structure. But dicyandiamide's high curing temperature significantly limits its application. Curing accelerators can effectively accelerate the curing reaction between dicyandiamide and epoxy resin, lowering the reaction temperature and increasing the reaction rate and completeness.

[0004] Imidazole compounds are widely used as curing agents or curing accelerators in epoxy resin curing due to their inherent high reactivity. However, imidazole compounds exhibit volatility and hygroscopicity, resulting in poor stability when used as curing accelerators for dicyandiamide-cured epoxy resins. Therefore, it is necessary to develop and synthesize imidazole derivatives with excellent stability for use in dicyandiamide-cured epoxy resin curing, thereby improving the long-term stability of epoxy resin adhesives at room temperature. Summary of the Invention

[0005] The purpose of this invention is to provide an epoxy die-bonding adhesive for LED packaging and its preparation method, to meet the die-bonding requirements of LED packaging companies. This invention uses imidazole compounds as accelerators for dicyandiamide-cured epoxy resins to lower the system reaction temperature and accelerate the reaction process. To obtain a highly stable curing accelerator, the imidazole compounds are modified, and imidazole derivatives are synthesized. These derivatives not only effectively lower the system reaction temperature of dicyandiamide-cured epoxy resins but also possess high stability, meeting the requirement for long-term stable operation of the die-bonding adhesive at room temperature. Simultaneously, by compounding bisphenol A type epoxy resin and hydrogenated bisphenol A type epoxy resin, the viscosity of the bisphenol A type epoxy resin system can be controlled without traditional diluents, developing an epoxy resin die-bonding adhesive that balances adhesive performance and excellent workability.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an epoxy die bond for LED encapsulation, comprising the following components by weight:

[0007]

[0008] The curing accelerator is an imidazole derivative having the structure shown in Formula I:

[0009]

[0010] The method for preparing the curing accelerator includes the following steps:

[0011] S1: Add 2-methylimidazole and chloroform solution to a three-necked flask equipped with a magnetic stirrer and a condenser, and stir until homogeneous under nitrogen protection;

[0012] S2: A certain amount of terephthalic diisocyanate and chloroform solution is added dropwise to the three-necked flask of S1 above through a constant pressure funnel, and stirred while being added under nitrogen protection;

[0013] S3: After the addition is complete, raise the reaction system to a certain temperature and carry out the continuous reaction under reflux. The reaction process is monitored by detecting the -NCO absorption peak by infrared spectroscopy. When the -NCO absorption peak disappears, the reaction is considered to be complete. Stop the reaction and cool to room temperature.

[0014] S4: Remove all solvent by vacuum distillation to obtain a white solid powder;

[0015] S5: Dissolve the solid powder obtained in S4 in dichloromethane, then add excess petroleum ether to the solution and stir to precipitate the product. Repeat the above operation twice to wash and centrifuge the precipitated product, and finally put it into a vacuum drying oven to dry, to obtain the curing accelerator product 2-methylimidazolium-blocked terephthalic acid diisocyanate.

[0016] The beneficial effects of the previous step are: by utilizing the reactivity of the secondary amino group (-NH) on the imidazole ring to introduce an isocyanate group (-NCO), the nucleophilicity of the imidazole moiety is reduced, the high activity of imidazole is passivated, and the stability of imidazole derivatives is improved, which helps to improve the long-term stability of the epoxy crystal fixative of the present invention at room temperature.

[0017] Preferably, in steps S1 and S2, the molar ratio of -NH group to -NCO group is 0.9:1.0 to 1.5:1.0.

[0018] Preferably, in step S3, the reaction system is heated to 35°C to 60°C.

[0019] Preferably, in step S5, the drying temperature of the vacuum drying oven is 35℃~70℃.

[0020] Preferably, in step S5, the drying time in the vacuum drying oven is 12h to 36h.

[0021] The bisphenol A type epoxy resin has an epoxy equivalent of 178-182 and a viscosity of 8000-11000 mPa·s, and its structure is as shown in Formula II:

[0022]

[0023] The hydrogenated bisphenol A type epoxy resin has an epoxy equivalent of 205-225 and a viscosity of 2000-3500 mPa·s, and its structure is as shown in Formula III:

[0024]

[0025] Preferably, the weight ratio of bisphenol A type epoxy resin to hydrogenated bisphenol A type epoxy resin is 1.0:1.0 to 4.0:1.0.

[0026] Based on the beneficial effects of the previous step, compared with bisphenol A type epoxy resin, hydrogenated bisphenol A type epoxy resin, which removes double bonds through hydrogenation treatment, has the following advantages:

[0027] (1) In terms of chemical structure, hydrogenated bisphenol A type epoxy resin exhibits superior chemical resistance due to the hydrogenation of double bonds.

[0028] (2) Hydrogenated bisphenol A type epoxy resin has a lower resin viscosity due to the change in chemical structure, and has better production operability.

[0029] (3) Hydrogenated bisphenol A type epoxy resin exhibits better flexibility.

[0030] By compounding bisphenol A type epoxy resin and hydrogenated bisphenol A type epoxy resin as the main resin, the disadvantages of bisphenol A type epoxy resin, such as high viscosity at room temperature and difficulty in handling, can be improved. At the same time, it also helps to improve the chemical resistance and high temperature resistance of the die bond adhesive.

[0031] The curing agent is an amine-based curing agent.

[0032] Preferably, the curing agent is dicyandiamide.

[0033] Preferably, the silane coupling agent is any one or a combination of at least two of commercially available KH550, KH560, and KH570.

[0034] The thixotropic agent is any one or a combination of at least two of fumed silica.

[0035] This invention also provides a method for preparing the above-mentioned epoxy die bond for LED encapsulation, comprising the following steps:

[0036] T1: First, pulverize the solid 2-methylimidazolium-blocked terephthalic acid diisocyanate and pass it through a 500-mesh sieve for later use;

[0037] T2: Weigh out bisphenol A type epoxy resin and hydrogenated bisphenol A type epoxy resin, mix them at 60°C to form a transparent solution, add thixotropic agent, disperse in a high-speed disperser at 1500 rpm / min for 30 min, pass through a 100-mesh sieve, and cool to room temperature for later use.

[0038] T3: Then weigh out the mixture of silane coupling agent, curing agent and curing accelerator of T1 and mix it evenly with T2;

[0039] T4: Pass the mixture obtained in T3 through a three-roll mill. The gap between the feeding rollers is set to 0.08 mm, the gap between the discharge rollers is set to 0.03 mm, and the rotation speed is set to 150 rpm / min. Repeat the rolling process 3 times to obtain epoxy die bond for LED packaging.

[0040] The technical effects and advantages of this invention are as follows:

[0041] (1) The epoxy die bond adhesive for LED packaging of the present invention uses a compound of bisphenol A type epoxy resin and hydrogenated bisphenol A type epoxy resin as the resin body. Compared with single bisphenol A type epoxy resin, it not only maintains the excellent adhesion of the die bond adhesive, but also improves its chemical resistance and high temperature resistance, and also has good toughness.

[0042] (2) The epoxy die bond adhesive for LED packaging of the present invention uses a synthetic imidazole derivative as a curing accelerator, which not only reduces the reaction temperature of the system of dicyandiamide curing epoxy resin, but also greatly improves the room temperature stability of the die bond adhesive, and can achieve a room temperature operation cycle of about 10 days, effectively reducing the waste of die bond adhesive and improving production efficiency. Detailed Implementation

[0043] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0044] (I) Preparation of Curing Accelerator-Blocked Te-Phenyl Isocyanate by 2-Methylimidazolium

[0045] 50 ml of a 2.0 mol / L chloroform solution of 2-methylimidazole was added to a three-necked flask equipped with a magnetic stirrer and a condenser. Then, under nitrogen protection, 80 ml of a chloroform solution of 0.5 mol / L terephthalic acid diisocyanate was added dropwise to the 2-methylimidazole and chloroform solution through a constant-pressure funnel while stirring. After the addition was complete, the reaction system was heated to 45°C and continuously reacted under reflux. The reaction progress was monitored by detecting the -NCO absorption peak using infrared spectroscopy. When the -NCO absorption peak disappeared, the reaction was considered complete, and the reaction was stopped and cooled to room temperature. All solvents were removed by vacuum distillation to obtain a white solid powder. The obtained white solid powder was dissolved in dichloromethane, and then excess petroleum ether was added to the solution with stirring to precipitate the product. The precipitated product was washed and centrifuged twice, and finally placed in a vacuum drying oven at 45°C for 24 hours to obtain the curing accelerator product, 2-methylimidazole-blocked terephthalic acid diisocyanate.

[0046] (II) Preparation of epoxy die bond for LED packaging

[0047] Experimental Examples 1-5

[0048] The silicone-modified epoxy die bond for LED encapsulation in each experimental example was prepared through the following steps. See Table 1 for the specific ingredient list for each experimental example:

[0049] (1) First, pulverize the solid 2-methylimidazolium-blocked curing accelerator terephthalic acid diisocyanate and pass it through a 500-mesh sieve for later use;

[0050] (2) Weigh out bisphenol A type epoxy resin and hydrogenated bisphenol A type epoxy resin, mix them at 60°C to form a transparent solution, add commercially available Japanese Tokuyama DM30, disperse in a high-speed disperser at 1500 rpm / min for 30 min, pass through a 100-mesh sieve, and cool to room temperature for later use.

[0051] (3) Then weigh out the silane coupling agent KH560, the curing agent dicyandiamide, and the curing accelerator obtained in step (1) and mix them evenly with the mixture obtained in step (2);

[0052] (4) Pass the mixture obtained in step (3) through a three-roll mill. The gap between the feeding rollers is set to 0.08 mm, the gap between the discharge rollers is set to 0.03 mm, and the rotation speed is set to 150 rpm / min. Repeat the rolling process 3 times to obtain epoxy die bond for LED packaging.

[0053] Table 1 Ingredients list for Experiment Examples 1-5

[0054]

[0055] Test 1: Using the epoxy die bond prepared in Examples 1-5, 4×6mil...2 The silicon wafer was bonded to the 2835 support and then placed in a forced-air oven to cure at 160°C for 120 minutes. After curing, the thrust was tested using a bonding shear force tester (MFM1200), and the results are shown in Table 2 below.

[0056] Table 2 Thrust Test

[0057] Experimental Example 1 Experimental Example 2 Experimental Example 3 Experiment Example 4 Experimental Example 5 <![CDATA[4×6mil 2 ]]> 285g 265g 250g --- 255g

[0058] As shown in Table 2, in Experiment 4, since no curing accelerator was used, the prepared die-bonding adhesive required a higher temperature to fully cure, so the thrust data was too small to be practically meaningful. In Experiment 2, since hydrogenated bisphenol A epoxy resin has a certain toughening effect, the increased amount of bisphenol A used would lead to a decrease in the hardness of the resin after curing, thus the thrust value after curing would also decrease. In Experiment 3, since the viscosity of bisphenol A epoxy resin was too high and the present invention did not use conventional diluents to reduce the viscosity, the increased amount of bisphenol A used would lead to an increase in the viscosity of the prepared die-bonding adhesive, which would worsen the workability and be unfavorable for production line operations. It would also make it difficult to remove the adhesive during die bonding and worsen the wettability of the silver plating layer on the support, resulting in a certain degree of decrease in the final thrust value.

[0059] Test 2: Viscosity change test at room temperature (Bollerfeld cone plate rheometer). Take 10g of each of the solidification adhesives prepared in Experiments 1-5 and place them in a 40ml beaker. Place them at room temperature and measure them every 24 hours to test the time required for the viscosity to increase by 50%. The test results are shown in Table 3 below.

[0060] Table 3 Viscosity Change Test

[0061] Experimental Example 1 Experimental Example 2 Experimental Example 3 Experiment Example 4 Experimental Example 5 time 11 days 11 days 10 days More than 20 days Less than 1 day

[0062] Any descriptions of the specific experimental methods of this invention that are not covered herein are techniques known in the art and can be implemented with reference to such techniques.

[0063] This invention has been repeatedly tested and verified, and has achieved satisfactory trial results.

[0064] Although experimental examples of the present invention have been shown and described above, it is understood that the above experimental examples are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above experimental examples within the scope of the present invention.

Claims

1. An epoxy die bond for LED encapsulation, characterized in that, The epoxy resin, by weight, comprises 100 parts of bisphenol A epoxy resin, 25-100 parts of hydrogenated bisphenol A epoxy resin, 10-25 parts of curing agent, 2.5-10 parts of curing accelerator, 2.5-10 parts of silane coupling agent, and 1-10 parts of thixotropic agent. The curing agent is dicyandiamide; The curing accelerator is an imidazole derivative having the structure shown in Formula I: (Formula I).

2. The epoxy die bond for LED encapsulation according to claim 1, characterized in that, The preparation method of the curing accelerator includes the following steps: S1: Add 2-methylimidazole and chloroform solution to a three-necked flask equipped with a magnetic stirrer and a condenser, and stir until homogeneous under nitrogen protection; S2: A certain amount of terephthalic diisocyanate and chloroform solution is added dropwise to the three-necked flask of S1 above through a constant pressure funnel. The mixture is added dropwise while stirring under nitrogen protection. The molar ratio of -NH groups to -NCO groups is 0.9:1.0 to 1.5:1.

0. S3: After the addition is complete, heat the reaction system to 35℃~60℃ and carry out the continuous reaction under reflux. The reaction process is monitored by detecting the -NCO absorption peak by infrared spectroscopy. When the -NCO absorption peak disappears, the reaction is considered to be complete. Stop the reaction and cool to room temperature. S4: Remove all solvent by vacuum distillation to obtain a white solid powder; S5: Dissolve the solid powder obtained in S4 in dichloromethane, then add excess petroleum ether to the solution and stir to precipitate the product. Repeat the above operation twice to wash and centrifuge the precipitated product, and finally put it in a vacuum drying oven at 35℃~70℃ for 12h~36h to obtain the curing accelerator product 2-methylimidazolium-blocked terephthalic acid diisocyanate.

3. The epoxy die bond for LED encapsulation according to claim 1, characterized in that, The bisphenol A type epoxy resin has an epoxy equivalent of 178-182 g / eq and a viscosity of 8000-11000 mPa·s, and its structure is as shown in Formula II: (Formula II).

4. The epoxy die bond for LED encapsulation according to claim 1, characterized in that, The hydrogenated bisphenol A type epoxy resin has an epoxy equivalent of 205-225 g / eq and a viscosity of 2000-3500 mPa·s, and its structure is as shown in Formula III: (Formula III).

5. The epoxy die bond for LED encapsulation according to claim 1, characterized in that, The thixotropic agent is fumed silica.

6. The epoxy die bond for LED encapsulation according to claim 1, characterized in that, The preparation method of the epoxy crystal fixative includes the following steps: T1: First, pulverize the solid 2-methylimidazolium-blocked terephthalic acid diisocyanate and pass it through a 500-mesh sieve for later use; T2: Weigh out bisphenol A type epoxy resin and hydrogenated bisphenol A type epoxy resin, mix them at 60°C to form a transparent solution, add thixotropic agent, disperse at 1500 rpm in a high-speed disperser for 30 min, pass through a 100-mesh sieve, and cool to room temperature for later use. T3: Then weigh out the mixture of silane coupling agent, curing agent and curing accelerator of T1 and mix it evenly with T2; T4: Pass the mixture obtained in T3 through a three-roll mill. Set the gap between the feeding rollers to 0.08mm, the gap between the discharge rollers to 0.03mm, and the rotation speed to 150rpm. Repeat the process 3 times to obtain epoxy die bond for LED encapsulation.

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