An epoxy molding compound, its preparation method and application

Abstract

This invention relates to the field of encapsulation materials technology, and more particularly to an epoxy molding compound, its preparation method, and its application. The raw materials for preparing the epoxy molding compound include: 40-80 parts epoxy resin, 1-10 parts release agent, 0.1-3 parts catalyst, 50-500 parts filler, 0.1-5 parts silane coupling agent, and 20-60 parts curing agent; the release agent includes at least an alkyd wax; the silane coupling agent includes a methoxysilane coupling agent. This invention explores the selection and synergistic effects of the formulation components of epoxy resin molding compounds, preferably by adding specific alkyd wax release agents and specific methoxysilane coupling agents to the resin / curing agent system, and optimizing the preparation process by using a low-friction mixing and extrusion method. This optimizes the microstructure and interfacial properties of the material, resulting in a novel epoxy molding compound with high CTR, low shrinkage, and excellent release properties, which can well meet the application requirements of optocoupler product encapsulation.

Description

Technical Field

[0001] This invention relates to the field of encapsulation materials technology, and in particular to an epoxy molding compound, its preparation method, and its application. Background Technology

[0002] An optocoupler (or simply optocoupler) is a device that integrates a light-emitting diode (LED) and a photodetector into a single package. It effectively isolates the input and output circuits, severing the direct electrical connection between them. This isolation prevents electrical interference, noise, and high voltage or current from affecting the output, while also preventing output faults from affecting the input, significantly improving circuit stability and reliability. The current transfer ratio (CTR) is a core performance indicator of an optocoupler, defined as the ratio of the current IC of the output photosensitive device (such as a phototransistor or photosensitive IC) to the driving current IF of the input LED, i.e.: CTR = IC / IF × 100%.

[0003] CTR directly reflects the electro-optical-electric conversion efficiency of the optocoupler. Its level directly affects the following performance: 1) Signal transmission reliability. High CTR (>150%) can reduce signal distortion rate and is suitable for high-speed communication (such as CAN bus, USB isolation); 2) Power consumption control. CTR improvement can reduce the LED drive current demand and reduce the overall power consumption of the system (such as photovoltaic inverter, electric vehicle BMS); 3) Lifespan and stability. Low CTR devices need to increase LED current compensation and accelerate LED light decay (CTR decay >30% after aging for 1000 hours). The existing optocoupler CTR is generally limited by the following factors: (1) Optical loss of packaging materials. On the one hand, there is interface scattering. Interface defects such as release agent residue and microcracks cause light scattering, and the transmittance loss in the 450nm band is >15%; on the other hand, there is material absorption. Traditional epoxy resin has intrinsic absorption in the near ultraviolet-visible band, which will reduce the effective light flux; (2) Device offset caused by thermomechanical stress. On the one hand, there is thermal expansion coefficient (CTE) mismatch. The difference in CTE between epoxy molding compound and LED chip Thermal stress is caused, which leads to misalignment of LED and photosensitive device (misalignment > 5 μm) and a decrease in coupling efficiency > 20%; on the other hand, there is curing shrinkage stress, and the curing shrinkage rate of phenolic resin is as high as 0.8-1.0%, and microcracks are formed at the interface after molding; (3) Chemical pollution and interface deterioration, on the one hand, traditional acid release agents decompose to generate carboxylic acids (such as stearic acid) at high temperature molding (> 170℃), which react with epoxy resin to generate light-absorbing salts; on the other hand, there is moisture penetration, and interface defects lead to moisture intrusion (water absorption rate > 0.8% at 85℃ / 85% RH), which causes ion migration (Na⁺, Cl⁻ concentration > 10ppm), and CTR decay is accelerated (decay > 25% after aging for 500 hours).

[0004] Chinese invention patent CN107446316B discloses an epoxy molding compound composition, an epoxy molding compound, and its preparation method. By using isocyanate-modified polyether silicone as a stress absorber in the epoxy molding compound, it solves the problem of increased flexural modulus and decreased glass transition temperature when increasing filler content in existing materials. This achieves a balance between high glass transition temperature and low flexural modulus, improving the material's heat resistance and toughness. Chinese invention patent application CN107868411A discloses an epoxy molding compound for surface mount integrated circuit packaging. By using multi-aromatic epoxy resin, silicone powder, and composite coupling agent in the epoxy molding compound, it solves the delamination problem caused by high-temperature reflow soldering, achieving high reliability and moisture resistance, meeting JEDEC level 1 and UL 94V-0 flame retardant standards.

[0005] However, none of these existing technologies have solved the above-mentioned technical problems or effectively improved the current conversion ratio of the packaging material. Against this background, there is an urgent need to provide a molding compound with high CTR, low shrinkage and excellent release properties to meet the packaging requirements of optocoupler products. Summary of the Invention

[0006] To address the aforementioned issues, this invention explores the selection and synergistic effects of epoxy resin molding compounds in their formulation. Specifically, it incorporates a particular alkyd ester wax release agent and a specific methoxysilane coupling agent into the resin / curing agent system. Furthermore, the preparation process is optimized using a low-friction mixing followed by extrusion, thereby improving the material's microstructure and interfacial properties. This results in a novel epoxy molding compound with high CTR, low shrinkage, and excellent release properties, effectively meeting the packaging requirements of optocoupler products.

[0007] The first aspect of the present invention provides an epoxy molding compound, wherein the raw materials for preparing the epoxy molding compound, by weight, include: 40-80 parts of epoxy resin, 1-10 parts of release agent, 0.1-3 parts of catalyst, 50-500 parts of filler, 0.1-5 parts of silane coupling agent, and 20-60 parts of curing agent.

[0008] The epoxy resin may include one or more combinations of o-cresol-type epoxy resin, bisphenol A-type epoxy resin, and phenol-type epoxy resin.

[0009] To improve the performance of epoxy molding compounds, the epoxy resin may optionally include o-crestoform epoxy resin and bisphenol A epoxy resin; the mass ratio of the o-crestoform epoxy resin to the bisphenol A epoxy resin is (1.5-5):1. The epoxy resin selected in this invention can improve the strength, heat resistance, and chemical stability of the molding compound, and inhibit the shrinkage tendency of the material.

[0010] Optionally, the epoxy equivalent of the o-cresol-formaldehyde epoxy resin is 100-300 g / eq; more preferably 170-190 g / eq; the o-cresol-formaldehyde epoxy resin can be commercially available, such as Nan Ya Plastics NPPN-638.

[0011] Optionally, the epoxy equivalent of the bisphenol A type epoxy resin is 150-400 g / eq; more preferably 238-270 g / eq; the bisphenol A type epoxy resin can be commercially available, such as Huntsman GY-250.

[0012] The phenolic epoxy resin can be commercially available, such as Mitsubishi Chemical YX-4000H.

[0013] The curing agent may include one or more combinations of linear phenolic resin, BPA (bisphenol A) phenolic resin, and acid anhydride.

[0014] Optionally, the linear phenolic resin has a hydroxyl equivalent of 90-200 g / eq; the linear phenolic resin may be commercially available, such as Meiwa Kasei MEW-180.

[0015] The BPA (bisphenol A) phenolic resin can be commercially available, such as Shengquan Group SH-2100.

[0016] The anhydrides mentioned may include tetrahydrophthalic anhydride (THPA), methyltetrahydrophthalic anhydride (MTHPA), hexahydrophthalic anhydride (HHPA), methylhexahydrophthalic anhydride (MHHPA), phthalic anhydride (PA), trimellitic anhydride (TMA), pyromellitic dianhydride (PMDA), etc.

[0017] To increase the crosslinking density, optionally, the equivalent ratio of the active groups in the curing agent to the epoxy groups in the epoxy resin is (0.5-1.5):1; examples include 0.5:1, 1:1, 1.2:1, and 1.5:1.

[0018] The active group is a group that can react with the epoxy groups in the epoxy resin.

[0019] Optionally, the catalyst may include a phosphorus-based catalyst, a modified amine catalyst, or an imidazole catalyst.

[0020] Phosphorus-based catalysts may include triethylphosphine boron trifluoride, triisopropylphosphine boron trifluoride, trimethylphosphine, triphenylphosphine and its derivatives, cyclotriphosphine, and phosphatamine compounds.

[0021] The imidazole catalysts mentioned may include 2-methylimidazole (2MZ), 2-ethyl-4-methylimidazole (2E4MZ), 2-phenylimidazole (2PZ), etc.; the imidazole catalysts may be commercially available, such as products from Shikoku Chemical.

[0022] The modified amine catalyst may be commercially available, such as IDC EH-4360S.

[0023] Optionally, the amount of catalyst added is 0.1-3% of the total amount of epoxy resin and curing agent (e.g., phenolic resin); examples include 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2%, 2.5%, and 3%.

[0024] The release agent may include one or more of the following: oxidized polyethylene wax, carnauba wax, polyolefin wax, alkyd ester wax, carnauba wax, and Montan wax.

[0025] The oxidized polyethylene wax may be commercially available, such as Honeywell AC 316A; the carnauba wax may be commercially available, such as BASF Luwax OA5; the polyolefin wax may be commercially available, such as Mitsui Chemicals Hi-wax 7202P; the alkyd ester wax may be commercially available, such as Clariant Licocene PE 4201.

[0026] Optionally, the release agent includes at least an alkyd wax.

[0027] Further optionally, the release agent may also include oxidized polyethylene wax or acid wax.

[0028] Optionally, the amount of release agent added is 2-8% of the total amount of epoxy resin and curing agent (e.g., phenolic resin); examples include 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, and 8%.

[0029] The fillers may include silica powder, calcium carbonate, barium sulfate, etc.

[0030] Optionally, the filler includes silicon powder with a median particle size of 10-30 μm.

[0031] Optionally, the amount of filler added is 60-80% of the total mass of the epoxy molding compound.

[0032] The silane coupling agents may include methoxysilane coupling agents, allylsilane coupling agents, mercaptosilane coupling agents, etc.

[0033] Optionally, the silane coupling agent includes a methoxysilane coupling agent.

[0034] The methoxysilane coupling agent may be commercially available, such as Dow Chemical Z-6040 (KH560); the allylsilane coupling agent may be commercially available, such as Dow Chemical Z-6310; the mercaptosilane coupling agent may be commercially available, such as Shin-Etsu Chemical KBM-803.

[0035] Optionally, the amount of the silane coupling agent added is 0.05-0.15% of the filler mass.

[0036] Optionally, the CTR of the epoxy molding compound is 195% or higher; more preferably, it is 200% or higher.

[0037] In some embodiments, the total amount of the epoxy resin and curing agent (e.g., phenolic resin) is 100 parts by weight (PPR).

[0038] A second aspect of the present invention provides a method for preparing an epoxy molding compound, wherein the preparation steps of the epoxy molding compound include:

[0039] S1. Pretreatment: The epoxy resin, release agent, catalyst, filler, silane coupling agent and curing agent are pulverized to a particle size of less than 30 mesh.

[0040] S2. Mixing: Mix the pulverized epoxy resin, release agent, catalyst, filler, silane coupling agent and curing agent evenly;

[0041] S3. Extrusion: Transfer the uniformly mixed materials to an extruder, extrude the melt, compress and shape it to obtain epoxy molding compound.

[0042] Optionally, step S2 may be performed using a high-speed mixer.

[0043] In some implementations, to meet the high light transmittance requirements of the optocoupler EMC and minimize the introduction of impurities or pre-precipitation of release agent due to friction, the blades and inner walls of the high-speed mixer may undergo special low-friction surface treatment (such as polishing or coating), or be made of low-friction inert materials (such as specific engineering plastics or stainless steel).

[0044] In some implementations, the pulverizing equipment (such as a pulverizer) used in step S1 is also treated with special low-friction surface treatments (such as polishing or coating), or is made of low-friction inert materials (such as specific engineering plastics or stainless steel).

[0045] Optionally, step S3 involves using a twin-screw extruder to extrude the material and using a calender to press the melt into flakes.

[0046] A third aspect of the present invention provides an application of an epoxy molding compound, wherein the epoxy molding compound is used for the encapsulation of optocoupler products.

[0047] Beneficial effects:

[0048] This invention provides an epoxy molding compound, its preparation method, and its application, which have the following advantages:

[0049] (1) The present invention introduces a multifunctional alkyd ester wax as a release agent in the epoxy resin curing system. Its unique amphiphilic molecular structure (epoxy-loving end: hydroxyl-OH; mold-retardant end: long-chain alkyl) can promote the formation of a high-strength hydrogen bond network, effectively reduce interfacial voids, and achieve low release force and extremely low chemical residue through van der Waals forces. Compared with epoxy molding compounds made from traditional acid waxes, it has better performance, especially with a higher CTR.

[0050] (2) The hydrogen bond network formed by the multifunctional alkyd ester wax and curing agent of the present invention can moderately delay the curing reaction rate, reduce the curing shrinkage rate from 0.5% to 0.4%, effectively reduce the alignment misalignment of LED and photosensitive device caused by shrinkage stress; at the same time, the gel time is extended, the curing rate of epoxy resin is delayed, which is conducive to stress release.

[0051] (3) In this invention, the preferred silane coupling agent is a methoxysilane coupling agent, which preferentially occupies the active sites on the surface of the filler (silica powder), greatly improving the interfacial bonding strength between the filler and the resin. The dense siloxane network formed effectively anchors the release agent molecules, significantly inhibiting the release agent from agglomerating and precipitating at the interface, thereby reducing light scattering centers, reducing light transmission loss, and further improving the CTR of the epoxy molding compound.

[0052] (4) The present invention further optimizes the preparation process of epoxy molding compound by pre-treating the raw materials to reduce the particle size to below 30 mesh before mixing. This can minimize shear friction and optimize the overall performance of epoxy molding compound while ensuring that the materials are fully melted and mixed evenly.

[0053] (5) The raw materials of the present invention are readily available, the preparation process is simple and highly operable, and high-quality products can be prepared efficiently. The resulting epoxy molding compound has high CTR and low shrinkage characteristics, and excellent release properties, which can well meet the packaging requirements of optocoupler products and has broad application prospects. Detailed Implementation

[0054] The raw material information for the following examples and comparative examples is shown in Table 1 below.

[0055] Table 1

[0056]

[0057] Unless otherwise specified, all raw materials, equipment and other consumables used in this invention are commercially available.

[0058] Examples 1-3 and Comparative Examples 1-8

[0059] Examples 1-3 and Comparative Examples 1-8 each provide an epoxy molding compound, the formulation of which is shown in Table 2; the values ​​in Table 2 are parts by weight.

[0060] Table 2

[0061]

[0062] The preparation steps of the epoxy molding compound all include:

[0063] S1. Pretreatment: Use a pulverizer to pulverize the epoxy resin, release agent, catalyst, filler, silane coupling agent and curing agent respectively, until the particle size is below 30 mesh;

[0064] S2. Mixing: Transfer the pulverized epoxy resin, release agent, catalyst, filler, silane coupling agent, and curing agent to a high-speed mixer and mix them evenly;

[0065] S3. Extrusion: Transfer the uniformly mixed materials to a twin-screw extruder to extrude the melt. Use a calender to press the melt into sheets to obtain epoxy molding compound.

[0066] Performance testing

[0067] 1. Processing performance

[0068] The epoxy resin molding compounds prepared in the examples and comparative examples were used to determine the spiral flow length, gel time and thermal hardness of the epoxy resin molding compounds according to the national standard GB / T 40564-2021 Test Method for Epoxy Molding Compounds for Electronic Packaging; the test results are recorded in Table 3.

[0069] 2. Curing performance

[0070] The epoxy resin molding compounds prepared in the examples and comparative examples were injected into the mold and cured at 175°C. After curing, they were cooled to room temperature for curing performance testing. The test indicators included flexural strength, CTR and continuous molding properties. The test results are recorded in Table 3.

[0071] Table 3

[0072]

[0073] Comparing the test data of Examples 1-3 and Comparative Examples 1-2, it can be seen that compared with the use of traditional release agents (acid wax or oxidized polyethylene wax), the introduction of multifunctional alkyd ester wax (which can be used alone or in combination with other release agents) into the epoxy resin curing system achieves a breakthrough improvement in the overall performance of the epoxy molding compound for photocouplers. In particular, the CTR of Example 1 increased to 214%, which is 15% higher than that of the traditional release agent (the CTR of Comparative Example 1 is 186%). Furthermore, the release force of the epoxy molding compound in Example 1 decreased to 2N, which is 81% lower than that of the acid wax control group (Comparative Example 1: 10.8N) and 72% lower than that of the oxidized polyethylene wax group (Comparative Example 2: 7.2N). The release force ranking is Example 1 (2N) < Example 2 (4N) < Example 3 (6.5N) << traditional release agent group. The experimental data proves that the complete replacement effect of multifunctional alkyd ester wax is the best, and the release force of the epoxy molding compound is the lowest. Meanwhile, Example 1 exhibits industry-leading low shrinkage characteristics (Comparative Examples 1 and 2 show even higher shrinkage rates), further verifying that the hydrogen bond network constructed by the alkyd ester wax-curing agent possesses excellent stress suppression capabilities, effectively reducing the shrinkage tendency of the epoxy molding compound. The gel time of the epoxy molding compound in Example 1 can be extended to 16 seconds, while the gel time using traditional release agents (Comparative Examples 1 and 2) is 12-13 seconds, indicating that the introduction of alkyd ester wax slows down the curing rate of the resin, which is beneficial for stress release.

[0074] Comparative Examples 3-8 used different silane coupling agents while maintaining the same total amount of silane coupling agent added, resulting in differences in the performance of the epoxy molding compounds. Comparative Example 3, using a single methoxysilane coupling agent, showed better release performance and significantly higher flexural strength at room temperature compared to epoxy molding compounds prepared with other silane coupling agents. This demonstrates that methoxysilane coupling agents can improve interfacial bonding strength, anchor the release agent through the siloxane network, inhibit release agent aggregation, and further reduce light scattering and light transmission loss. Other types of silane coupling agents did not achieve similar effects.

Claims

1. An epoxy molding compound, characterized in that, The raw materials for preparing the epoxy molding compound, by weight, include: 40-80 parts epoxy resin, 1-10 parts release agent, 0.1-3 parts catalyst, 50-500 parts filler, 0.1-5 parts silane coupling agent, and 20-60 parts curing agent. The release agent includes at least alkyd ester waxes; The silane coupling agent includes a methoxysilane coupling agent; The CTR of the epoxy molding compound is above 195%.

2. The epoxy molding compound according to claim 1, characterized in that, The release agent also includes oxidized polyethylene wax or acid wax.

3. The epoxy molding compound according to claim 1, characterized in that, The epoxy resin includes o-cresol-type epoxy resin and bisphenol A-type epoxy resin; the mass ratio of the o-cresol-type epoxy resin and the bisphenol A-type epoxy resin is (1.5-5):

1.

4. The epoxy molding compound according to claim 3, characterized in that, The curing agent includes one or more of linear phenolic resin, BPA phenolic resin, and acid anhydride.

5. The epoxy molding compound according to claim 3, characterized in that, The equivalent ratio of the active groups in the curing agent to the epoxy groups in the epoxy resin is (0.5-1.5):

1.

6. The epoxy molding compound according to claim 1, characterized in that, The filler includes silicon powder with a median particle size of 10-30 μm; the amount of filler added is 60-80% of the total mass of the epoxy molding compound.

7. A method for preparing the epoxy molding compound according to claim 1, characterized in that, The preparation steps of the epoxy molding compound include: S1. The epoxy resin, release agent, catalyst, filler, silane coupling agent, and curing agent are pulverized separately. S2. Mix the pulverized epoxy resin, release agent, catalyst, filler, silane coupling agent, and curing agent evenly; S3. Transfer the uniformly mixed material to an extruder, extrude the melt, compress and shape it to obtain epoxy molding compound.

8. The method for preparing epoxy molding compound according to claim 7, characterized in that, In step S1, the particles are pulverized to a particle size of less than 30 mesh.

9. An application of the epoxy molding compound according to any one of claims 1-6, characterized in that, The epoxy molding compound is used for the encapsulation of optocoupler products.

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