Epoxy solid crystal glue for LED packaging

Abstract

The invention discloses an epoxy solid crystal adhesive for LED packaging, which comprises the following components in parts by weight: 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, the curing accelerator is an imidazole derivative having a specific structure. The bisphenol A type epoxy resin and the hydrogenated bisphenol A type epoxy resin are compounded to serve as a resin main body, viscosity controllability is achieved on the premise that a diluent is not used, meanwhile, the curing accelerator of a specific structure is combined, the prepared solid crystal glue has excellent bonding capacity, the room-temperature operation period of about 10 days can be achieved, and the service life of the solid crystal glue is prolonged. The waste of the solid crystal glue can be effectively reduced, and the production efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of adhesive preparation for semiconductor packaging, and specifically relates to an epoxy die-bonding adhesive for LED packaging. Background Art

[0002] Epoxy resin has many advantages, such as corrosion resistance, electrical insulation, excellent adhesion and good processing technology, and is the main adhesive for LED packaging die bonding. The die bonding adhesive for LED packaging is mainly thermosetting, among which the thermal latent epoxy resin die bonding adhesive is widely used in the field of LED small-size chip packaging due to its excellent bonding performance.

[0003] In epoxy resin systems, dicyandiamide is a typical thermal latent curing agent. It is difficult to dissolve in epoxy resin at room temperature, so the resin system has a long storage period. After being heated to a certain temperature, it can be activated by ring opening with epoxy resin, and the epoxy resin can be quickly cross-linked into a three-dimensional network structure. However, as a curing agent for epoxy resin, dicyandiamide has the defect of too high curing temperature, which will greatly limit its scope of use. Curing accelerators can effectively accelerate the curing reaction of dicyandiamide and epoxy resin, reduce the reaction temperature, and increase the reaction rate and completeness.

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

[0005] The purpose of the present invention is to provide an epoxy die-bonding adhesive for LED packaging and a preparation method to meet the needs of LED packaging companies for die-bonding operations. The present invention uses imidazole compounds as accelerators for dicyandiamide-cured epoxy resins to reduce the reaction temperature of the system and promote the reaction process. In order to obtain a highly stable curing accelerator, the imidazole compounds are modified, and the synthesized imidazole derivatives can not only effectively reduce the system reaction temperature of dicyandiamide-cured epoxy resins, but also have high stability, which can meet the long-term stable operation requirements of the die-bonding adhesive at room temperature. At the same time, by compounding bisphenol A epoxy resin and hydrogenated bisphenol A epoxy resin, the viscosity of the bisphenol A epoxy resin system can be controlled without the need for traditional diluents, and an epoxy resin die-bonding adhesive that takes into account both bonding performance and excellent operating performance is developed.

[0006] To achieve the above object, the present invention provides the following technical solution: an epoxy die-bonding adhesive for LED packaging, comprising the following materials in parts by weight:

[0007]

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

[0009]

[0010] The preparation method of the curing accelerator comprises the following steps:

[0011] S1: Add 2-methylimidazole and chloroform solution into a three-necked flask with magnetic stirring and condenser, and stir evenly under nitrogen protection;

[0012] S2: Add a certain amount of p-phenylene diisocyanate and chloroform solution dropwise into the three-necked flask of S1 through a constant pressure funnel, and stir while adding dropwise under nitrogen protection;

[0013] S3: After the addition is completed, the reaction system is raised to a certain temperature, and a continuous reaction is carried out under condensation reflux, and the reaction progress is monitored by detecting the -NCO absorption peak by infrared spectroscopy. When the -NCO absorption peak disappears, the reaction is considered to be completed, and the reaction is stopped and cooled to room temperature;

[0014] S4: All solvents are removed by distillation under reduced pressure to obtain a white solid powder;

[0015] S5: The solid powder obtained in S4 is dissolved in dichloromethane, and then an excess of petroleum ether is added to the solution to stir and precipitate the product. The precipitated product is washed and centrifuged twice, and finally placed in a vacuum drying oven for drying to obtain a curing accelerator product, 2-methylimidazole-blocked p-phenylene diisocyanate.

[0016] The beneficial effects of the previous step are as follows: the isocyanate group (-NCO) is introduced by means of the reactivity of the secondary amino group (-NH) on the imidazole ring, the nucleophilicity of the imidazole part 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 die-bonding adhesive of the present invention at room temperature.

[0017] Preferably, in steps S1 and S2, the molar ratio of -NH groups to -NCO groups 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 in the vacuum drying oven is 35°C to 70°C.

[0020] Preferably, in step S5, the vacuum drying oven is used for drying for 12 hours to 36 hours.

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

[0022]

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

[0024]

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

[0026] Using the beneficial effects of the previous step, compared with bisphenol A epoxy resin, hydrogenated bisphenol A epoxy resin is bisphenol A epoxy resin that has been hydrogenated to remove double bonds, and has the following advantages:

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

[0028] (2) Due to the change in chemical structure, hydrogenated bisphenol A epoxy resin has lower resin viscosity and better production operability;

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

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

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

[0032] Preferably, the curing agent is dicyandiamide.

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

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

[0035] The present invention also provides a method for preparing the above-mentioned epoxy die-bonding adhesive for LED packaging, comprising the following steps:

[0036] T1: First, grind the solid of 2-methylimidazole-blocked phenylene diisocyanate, a curing accelerator, and pass it through a 500-mesh sieve for later use;

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

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

[0039] T4: The mixture obtained in T3 was passed through a three-roll grinding device, with the gap between the three-roll feeding rollers set to 0.08 mm, the gap between the three-roll discharging rollers set to 0.03 mm, and the rotation speed set to 150 rpm / min. The three rollers were repeatedly rolled for 3 times to obtain an epoxy die-bonding adhesive for LED packaging.

[0040] Technical effects and advantages of the present invention:

[0041] (1) The epoxy die-bonding adhesive for LED encapsulation of the present invention adopts a compound of bisphenol A epoxy resin and hydrogenated bisphenol A epoxy resin as the main resin. Compared with a single bisphenol A epoxy resin, the die-bonding adhesive not only maintains excellent adhesion, but also improves its chemical resistance and high temperature resistance, and has good toughness;

[0042] (2) The epoxy die-bonding adhesive for LED encapsulation of the present invention adopts a synthetic imidazole derivative as a curing accelerator, which not only reduces the system reaction temperature of the dicyandiamide-cured epoxy resin, but also greatly improves the room temperature stability of the die-bonding adhesive, and can achieve a room temperature operating cycle of about 10 days, effectively reducing the waste of the die-bonding adhesive and improving production efficiency. DETAILED DESCRIPTION

[0043] The specific embodiments of the present invention are further described below. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in each embodiment 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 2-methylimidazole-blocked p-phenylene diisocyanate

[0045] Add 50 ml of 2.0 mol / L 2-methylimidazole chloroform solution to a three-necked flask with magnetic stirring and a condenser; then, under the protection of nitrogen, add dropwise while stirring, and add 80 ml of 0.5 mol / L chloroform solution of p-phenylene diisocyanate to the 2-methylimidazole and chloroform solution through a constant pressure funnel; after the dropwise addition is completed, heat the reaction system to 45°C, react continuously under condensation reflux, and monitor the reaction progress by detecting the -NCO absorption peak by infrared spectroscopy. When the -NCO absorption peak disappears, it is considered that the reaction has been completed, and the reaction is stopped and cooled to room temperature; remove all solvents after reduced pressure distillation to obtain a white solid powder; dissolve the obtained white solid powder in dichloromethane, then add excess petroleum ether to the solution, stir and precipitate the product, repeat the above operation twice for washing and centrifugation, and finally put it into a vacuum drying oven at 45°C for constant temperature drying for 24 hours to obtain a curing accelerator product 2-methylimidazole blocked p-phenylene diisocyanate.

[0046] (II) Preparation of epoxy die-bonding adhesive for LED packaging

[0047] Experimental Examples 1-5

[0048] The silicone-modified epoxy die-bonding adhesive for LED encapsulation of each experimental example was prepared by the following steps. The specific ingredient list of each experimental example is shown in Table 1:

[0049] (1) Firstly, the solid of 2-methylimidazole-blocked p-phenylene diisocyanate as a curing accelerator is crushed and then passed through a 500-mesh sieve for later use;

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

[0051] (3) Then weighing the silane coupling agent KH560, the curing agent dicyandiamide and the curing accelerator obtained in step (1) and the mixture obtained in step (2) and mixing them uniformly;

[0052] (4) The mixture obtained in step (3) is passed through a three-roll grinding equipment, with the gap between the three-roll feed rollers set to 0.08 mm, the gap between the three-roll discharge rollers set to 0.03 mm, and the rotation speed set to 150 rpm / min. The three rollers are repeatedly rolled three times to obtain an epoxy die-bonding adhesive for LED packaging.

[0053] Table 1 Ingredients of Experimental Examples 1-5

[0054]

[0055] Test 1: Use the epoxy die-bonding adhesive prepared in Experimental Example 1-5 to bond 4×6mil2 The silicon wafer was bonded to the 2835 bracket and then placed in a blast oven for curing at 160°C for 120 min. After curing, the thrust was tested using a bond shear force tester (MFM1200). The results are shown in Table 2 below.

[0056] Table 2 Thrust test

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

[0058] From the results in Table 2, it can be seen that in Experimental Example 4, since no curing accelerator was used, the prepared solid crystal glue required a higher temperature to be completely cured, so the thrust data was too small and had no practical significance; in Experimental Example 2, since hydrogenated bisphenol A epoxy resin had a certain toughening effect, as its usage increased, the hardness of the resin after curing decreased, so the thrust value after curing also decreased; in Experimental Example 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, as its usage increased, the viscosity of the prepared solid crystal glue increased, the workability deteriorated, which was not conducive to production line operation, it was difficult to remove the glue during solid crystal and the wettability of the silver-plated layer of the bracket deteriorated, resulting in a certain decrease in the final thrust value.

[0059] Test 2: Room temperature viscosity change test (Bolefield cone-plate rheometer), 10 g of each of the solid crystal adhesives prepared in Experimental Examples 1-5 were placed in a 40 ml beaker and placed at room temperature. The viscosity was measured 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 Experimental Example 4 Experimental Example 5 time 11 days 11 days 10 days More than 20 days Less than 1 day

[0062] Descriptions not involved in the specific experimental methods of the present invention belong to the well-known techniques in the art and can be implemented with reference to the well-known techniques.

[0063] The invention has been verified through repeated experiments and has achieved satisfactory trial results.

[0064] Although experimental examples of the present invention have been shown and described above, it can be understood that the above experimental examples are illustrative and cannot be construed as limitations of the present invention. Ordinary technicians in the field can change, modify, replace and modify the above experimental examples within the scope of the present invention.

Claims

1. An epoxy die-bonding adhesive for LED packaging, characterized in that: The epoxy die-bonding adhesive comprises, by weight, 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 accelerator is an imidazole derivative having a structure shown in Formula I:

2. The epoxy die-bonding adhesive for LED packaging according to claim 1, characterized in that: The preparation method of the curing accelerator comprises the following steps: S1: Add 2-methylimidazole and chloroform solution into a three-necked flask with magnetic stirring and condenser, and stir evenly under nitrogen protection; S2: a certain amount of p-phenylene diisocyanate and chloroform solution is added dropwise to the three-necked flask of S1 through a constant pressure funnel, and stirred while adding dropwise under nitrogen protection, wherein the molar ratio of -NH group to -NCO group is 0.9:1.0 to 1.5:1.0; S3: After the addition is completed, the reaction system is heated to 35°C to 60°C, and the reaction is continuously carried out under condensation reflux, and the -NCO absorption peak is detected by infrared spectroscopy to monitor the reaction progress. When the -NCO absorption peak disappears, the reaction is considered to be completed, and the reaction is stopped and cooled to room temperature; S4: All solvents are removed by distillation under reduced pressure to obtain a white solid powder; S5: The solid powder obtained in S4 is dissolved in dichloromethane, and then an excess of petroleum ether is added to the solution and stirred to precipitate the product. The precipitated product is subjected to the above operation and washed and centrifuged twice. Finally, the precipitated product is placed in a vacuum drying oven at 35°C to 70°C and dried for 12h to 36h to obtain a curing accelerator product, 2-methylimidazole-blocked p-phenylene diisocyanate.

3. The epoxy die-bonding adhesive for LED packaging according to claim 1, characterized in that: The bisphenol A 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:

4. The epoxy die-bonding adhesive for LED packaging 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:

5. The epoxy die-bonding adhesive for LED packaging according to claim 1, characterized in that: The curing agent is an amine curing agent.

6. The epoxy die-bonding adhesive for LED packaging according to claim 1, characterized in that: The thixotropic agent is any one of fumed silica or a combination of at least two of them.

7. The epoxy die-bonding adhesive for LED packaging according to claim 1, characterized in that: The preparation method of the epoxy die-bonding adhesive comprises the following steps: T1: First, grind the solid of 2-methylimidazole-blocked phenylene diisocyanate, a curing accelerator, and pass it through a 500-mesh sieve for later use; T2: Weigh bisphenol A epoxy resin and hydrogenated bisphenol A epoxy resin, mix them into a transparent solution at 60°C, add thixotropic agent, disperse them in a high-speed disperser at 1500 rpm / min for 30 min, pass through a 100-mesh sieve, and cool to room temperature for use; T3: Then weigh the silane coupling agent, curing agent and the curing accelerator of T1 and mix them evenly with T2; T4: The mixture obtained in T3 was passed through a three-roll grinding device, with the gap between the three-roll feeding rollers set to 0.08 mm, the gap between the three-roll discharging rollers set to 0.03 mm, and the rotation speed set to 150 rpm / min. The three rollers were repeatedly rolled for 3 times to obtain an epoxy die-bonding adhesive for LED packaging.

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