Preparation method of epoxy molding compound for patch bridge rectifier

Abstract

The invention discloses a preparation method of an epoxy molding compound for a patch bridge rectifier. The filling amount of the silica powder is designed to be 80-88% (preferably 84%), and the optimal ratio of the fused silica powder (with the particle sizes of 800 meshes and 2500 meshes) to the crystalline silicon powder (with the particle sizes of 325 meshes, 400 meshes, 600 meshes and 2000 meshes) is optimized, so that the dispersity and fluidity of the filler are remarkably improved. Specifically, the weight ratios of the 800-mesh fused silica powder and the 2500-mesh fused silica powder are 23.5% and 7.6% respectively; the weight ratios of the crystalline silicon micro powder of 325 meshes, 400 meshes, 600 meshes and 2000 meshes are 21%, 16%, 9.2% and 6.7% respectively. In addition, a double mixing process is adopted and comprises the steps of ball milling, high-speed shearing dispersion and the like, so that the raw materials are uniformly mixed. According to the invention, the mechanical, electrical and flame-retardant properties of the epoxy molding compound can be effectively improved, the application potential of the epoxy molding compound in a high-temperature environment is expanded, and the epoxy molding compound has a good market prospect.

Description

Technical Field

[0001] The invention relates to the field of electronic packaging materials, in particular to a method for preparing an epoxy molding compound for a patch bridge stack. Background Art

[0002] Epoxy molding compound (EMC) is an important electronic packaging material and the main material that determines the final packaging performance. It is mainly composed of epoxy resin, filler, curing agent, curing accelerator, flame retardant, etc. The components are mixed evenly in a certain proportion and then hot mixed. Epoxy molding compound is widely used in electronic packaging materials. It has the advantages of low cost, simple process, good electrical insulation, etc. At present, its usage accounts for more than 90% of the entire packaging material market. Today, the world is ushering in an era of electronic information technology with electronic computers and digital home appliances as the core. Electronic products are also developing towards high performance, multi-function, high reliability, thinness, lightness, and portability. At the same time, electronic products are also required to have the characteristics of popularization, popularization, and low cost. This requires electronic packaging products to develop in the direction of lighter, thinner, high density, strong reliability, and outstanding cost performance. Therefore, meeting the requirements of ultra-thin, miniaturization, high performance, multi-function, low cost, and green environmental protection packaging is the primary problem facing the development of microelectronic packaging materials.

[0003] The SMD bridge stack is an electronic component that plays a rectifying role. It is mainly used in various power products and has a huge market demand. Nowadays, the SMD bridge stack is also developing towards miniaturization, but there is currently no epoxy molding compound product for SMD bridge stack packaging. Most companies temporarily use integrated circuit packaging products as a substitute, which has the disadvantages of high price, poor sealing, pores, flash and other quality problems during the packaging process. Research has found that the core of the above problems lies mainly in the mismatch of the particle size of the silicon micropowder filler and the poor mixing of the raw materials. Summary of the invention

[0004] Silica powder is mainly used as filler in epoxy molding compounds. The higher the filling amount, the smaller the thermal expansion coefficient of the epoxy molding compound and the higher the thermal conductivity. However, it is not easy to achieve a high filling rate with a single size of silica powder during use. It is necessary to match silica powders of various shapes and sizes to achieve the above purpose. In addition, at a high filling rate, silica powder will also cause problems such as poor filler dispersion and increased viscosity. Therefore, how to ensure the matching of different silica powder particles while still having good fluidity is a key issue.

[0005] The present invention aims at the packaging problem caused by the defects of the existing epoxy molding compound formula for patch bridge stacks, utilizes the matching of different silicon micropowder characteristics and particles, and a double mixing preparation method to solve the process problems caused by the mismatch between the currently used products and the packaging performance.

[0006] To achieve the above object, the technical solution provided by the present invention is as follows:

[0007] The weight percentages of the components in the formula are as follows: silica fume 80 - 88% (preferably 84%), epoxy resin 8 - 12% (preferably 9%), curing agent 2.3 - 3.2% (preferably 2.8%), curing accelerator 1.8 - 2.1% (preferably 2%), release agent 1.0 - 1.5% (preferably 1.2%), flame retardant 0.4 - 0.6% (preferably 0.5%), coupling agent 0.4 - 0.6% (preferably 0.5%).

[0008] One of the core technical contents of the present invention is the optimal ratio between different fillers. The fillers selected are fused silica fume and crystalline silica fume. The former has two particle sizes (800 mesh and 2500 mesh), and the latter has four particle sizes (325 mesh, 400 mesh, 600 mesh, 2000 mesh). On the basis of the preferred formula, the optimal dosages of each silica fume are as follows: the weight ratios of 800 - mesh and 2500 - mesh fused silica fume are 23.5% and 7.6% respectively, while the weight ratios of 325 - mesh, 400 - mesh, 600 - mesh, and 2000 - mesh crystalline silica fume used in combination are 21%, 16%, 9.2%, and 6.7% respectively.

[0009] The epoxy resin used is tetramethylbiphenol - type epoxy resin; the curing agent is 4,4 - diaminodiphenyl sulfone (DDS); the curing accelerator is boron trifluoride monoethylamine complex (BF3 - MEA); the release agent uses wax - type release agent; the flame retardant selects zinc borate; the coupling agent uses 3 - mercaptopropyltrimethoxysilane.

[0010] Another core technical content of the present invention is a two - stage mixing process. The overall brief process is as follows: the raw materials metered according to the formula are subjected to ball milling (the first - stage mixing), high - speed shear dispersion (the second - stage mixing), kneading, cooling, pulverizing, magnetic separation, tablet pressing, etc.

[0011] In summary, the present invention has the following beneficial effects: (1) Although the particle sizes of the fused silica fume and the crystalline silica fume are different, the matching of the silica fume particle sizes is achieved through the dosages of different silica fumes, which can significantly increase the proportion of the filler in the product, is beneficial to enhancing the mechanical properties of the product, and reducing the thermal expansion coefficient of the product; (2) The two - stage mixing process can improve the dispersibility of the filler and ensure the consistency of the material properties; (3) The two - stage mixing process can mix the raw materials more evenly, improve the production efficiency, and reduce the defective product rate during the production process. Specific Embodiments

[0012] During implementation, the optimized component ratio is adopted, namely, 84% silica powder, 9% epoxy resin, 2.8% curing agent, 2% curing accelerator, 1.2% mold release agent, 0.5% flame retardant, and 0.5% coupling agent. First, mix the components other than epoxy resin in a ball mill (about 4 - 6 h), which is the first mixing. After the ball milling is completed, mix the ball - milled material and epoxy resin by high - speed shear dispersion (15 - 30 min), which is the second mixing.

[0013] After two - stage mixing, the mixture is then kneaded. Kneading can be carried out using hot rolling or a screw extruder, but it is necessary to ensure that the heating temperature reaches at least the softening point of the resin, preferably about 110 - 135 °C. This process can soften the resin and uniformly impregnate fillers, etc., and achieve a certain degree of prepolymerization.

[0014] After kneading, it is necessary to quickly cool to terminate the prepolymerization reaction.

[0015] After cooling, it is crushed and sieved. Generally, it is required that the diameter after crushing is less than 2 mm.

[0016] After that, magnetic separation is carried out to remove possible metal impurities in the product.

[0017] Finally, after pressing into cakes according to customer requirements, it can be packaged and stored refrigerated.

[0018] Examples

[0019] The preparation of the examples is generally carried out according to the foregoing steps. The weight ratios of the epoxy resin, curing agent, curing accelerator, silica powder, coupling agent, flame retardant, and mold release agent used are: 9%, 2.8%, 2%, 84%, 0.5%, 0.5%, 1.2% respectively. The present invention lists 3 examples, which differ in the ratios of 6 kinds of silica powder used, while the ratios of other components are the same. The specific ratios are implemented according to the formulations in Table 1.

[0020] Table 1 Formulations of Examples

[0021]

[0022] Properties of Examples

[0023] Performance tests were carried out on the above 3 examples. The specific test methods are as follows:

[0024] (1) Spiral flow length: Measured according to GB / T 40564 - 2021 under the conditions of a temperature of 175 °C, an injection pressure of 6.9 MPa, and a curing time of 90 s to test the length of the epoxy molding compound flowing along the spiral cavity path.

[0025] (2) Gelation time: Place the epoxy molding compound on a curing plate heated to 175°C, start the stopwatch, and use a spatula to stir the sample evenly. Stop the stopwatch when the sample gels, and record this time as the gelation time.

[0026] (3) Flexural strength: According to GB / T 40564-2021, make a sample piece (80 mm long, 15 mm wide, 4 mm thick) from the epoxy molding compound and test it using a materials testing machine.

[0027] (4) Glass transition temperature: According to GB / T 40564-2021, test using dynamic thermomechanical analysis (bending mode). Before testing, the sample needs to be preformed at 175°C to obtain a sample block (60 mm long, 13 mm wide, 3 mm thick), then the sample block is placed in an oven at 175°C and cured for 6 h, and then cooled to room temperature in a desiccator. The specific test conditions are: probe pressure 0.01 N, starting temperature 40°C, heating rate 5°C / min, termination temperature 300°C, amplitude 20 μm, vibration frequency 1 Hz, bending fixture span 50 mm.

[0028] (5) Water absorption: According to GB / T 40564-2021, make a circular sample piece (50 mm in diameter, 3 mm thick) from the epoxy molding compound. During testing, first dry the sample piece in an oven (125°C, 24 h), then place the sample piece in a thermostatic and humidistatic chamber (121°C, relative humidity 100%, 24 h) to absorb moisture, and finally calculate the water absorption based on the weight before and after moisture absorption.

[0029] According to the weight difference before and after drying.

[0030] (6) Flame retardancy: According to GB / T 2408-2021, conduct a flame retardancy test using the vertical burning method.

[0031] It can be seen from the test results in Table 2 that there are certain differences in the properties of the epoxy molding compounds obtained from the formulations of the 3 examples. Among them, the fluidity of Example 1 is the best, and it has the highest mechanical strength, the lowest water absorption, and a moderate gelation time. Therefore, the comprehensive performance is outstanding, which indicates that the matching of different silicon micro-powder particle sizes in Example 1 is better. At the same time, it can also be seen that the particle size ratio of silicon micro-powder has an obvious effect on the product performance. Therefore, in the actual production process, suitable products can be designed according to the different cavity structures of the molds used by customers.

[0032] Table 2 Performance test results of examples

[0033]

[0034] The above embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation to the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention.

Claims

1. An epoxy molding compound for patch bridge stack, characterized in that: The invention comprises the following raw material proportions: 80-88% (preferably 84%) of silicon micropowder, 8-12% (preferably 9%) of epoxy resin, 2.3-3.2% (preferably 2.8%) of curing agent, 1.8-2.1% (preferably 2%) of curing accelerator, 1.0-1.5% (preferably 1.2%) of release agent, 0.4-0.6% (preferably 0.5%) of flame retardant and 0.4-0.6% (preferably 0.5%) of coupling agent.

2. The epoxy molding compound for patch bridge stack according to claim 1, characterized in that: The matching between different silicon micropowder fillers specifically uses molten silicon micropowder and crystalline silicon micropowder. The former has two particle sizes (800 mesh and 2500 mesh), and the latter has four particle sizes (325 mesh, 400 mesh, 600 mesh, and 2000 mesh).

3. The epoxy molding compound for patch bridge stack according to claim 1, characterized in that: The raw materials are mixed and formed by a double mixing process of ball milling and high-speed shear dispersion.

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