A method for encapsulating electronic components with polyurethane

Abstract

The present invention discloses a method for encapsulating electronic components with polyurethane. After the thermally conductive polyurethane resin is sealed, it is vacuum-treated to obtain a pretreated thermally conductive polyurethane resin. The electronic components are added into a packaging box, and the thermally conductive polyurethane resin in the loading box extends into the packaging box through a discharge pipe, and the packaging box is subjected to encapsulation molding treatment and curing to obtain the encapsulated and molded electronic components. The thermally conductive polyurethane resin is prepared by the following specific steps: Polyisobutylene is dissolved in tetrahydrofuran and dropped into the polyurethane prepolymer, and stirred at 60-80 °C for 3-6 h under nitrogen protection. 1,3-propanediol is added and stirred for another 2-4 h. Diethylene glycol mono vinyl ether and super-dispersed nano-aluminum oxide microspheres are added and the reaction continues. After defoaming treatment, the thermally conductive polyurethane resin is obtained; the super-dispersed nano-aluminum oxide microspheres are formed by the chelation of aluminum isopropoxide and ethyl acetoacetate to form aluminum sol, which is then compounded with polyvinyl alcohol to form spheres in n-hexane and then formed under the action of ammonia water.

Description

Technical Field

[0001] The present invention relates to the technical field of resin sealing and molding of electronic components, and particularly to a method for encapsulating electronic components with polyurethane. Background Art

[0002] In the electronics industry, encapsulating electronic components is a very necessary step. Encapsulation means assembling various components that make up an electronic device with a grouting material as required to seal the electronic components, isolating the electronic device from the external environment, and effectively preventing moisture, dust, and other chemical harmful substances from entering the electronic components.

[0003] With the continuous development of electronic science and technology, electronic components and integrated circuits are becoming more and more dense and miniaturized, while the usage frequency of electronic devices has increased sharply, resulting in continuous accumulation and increase of heat generated by electronic devices, and the temperature of the working environment of electronic devices has been continuously rising, easily forming local high temperatures, which affects the stability and service life of electronic devices. This poses higher requirements for electronic potting adhesives, requiring that electronic potting adhesives have good sealing performance while also having a high thermal conductivity.

[0004] Polyurethane potting adhesive is a type of block copolymer prepared by reacting polyisocyanate with oligomeric polyol. Polyurethane potting adhesive has a wide range of hardness, excellent wear resistance, elasticity, chemical corrosion resistance and adhesiveness, low gas permeability, and excellent vibration absorption performance. However, polyurethane is a poor conductor of heat, and its thermal conductivity is only 0.18 - 0.20 W / m·K, far from meeting the thermal conductivity requirements.

[0005] Traditional metal oxide thermal conductive materials have good thermal conductivity on the basis of ensuring electrical insulation. When applied to electronic components, they can effectively improve their service life. Nano-aluminum oxide has excellent physical and chemical properties and has extremely wide applications in production and life, especially having good thermal conductivity. When used in the resin sealing of electronic components, it has excellent application prospects. However, due to the small particle size of nano-aluminum oxide, its specific surface area and surface energy are very large, and it is very easy to agglomerate, not only making the thermal conductivity worse, but also easily causing the crystallinity of polyurethane potting adhesive to deteriorate and the thermal stability of electronic components to decrease significantly. Summary of the Invention

[0006] The purpose of the present invention is to solve the deficiencies in the prior art and propose a method for encapsulating electronic components with polyurethane.

[0007] A method for encapsulating electronic components with polyurethane includes the following steps:

[0008] (1) Seal the thermally conductive polyurethane resin and perform vacuum treatment to obtain a pretreated thermally conductive polyurethane resin;

[0009] (2) Add electronic components into the packaging box, extend the pretreated thermally conductive polyurethane resin into the packaging box through the discharge pipe, perform encapsulation molding treatment on the packaging box, and cure to obtain encapsulated and molded electronic components.

[0010] Preferably, in step (1), the thermally conductive polyurethane resin is prepared by the following specific steps: Dissolve polyisobutene in tetrahydrofuran, drop it into the polyurethane prepolymer, stir at 60 - 80 °C for 3 - 6 h under nitrogen protection, add 1,3 - propanediol and continue stirring for 2 - 4 h, add diethylene glycol mono vinyl ether and super - dispersed nano - alumina microspheres, continue to react for 3 - 5 h, and perform defoaming treatment to obtain the thermally conductive polyurethane resin;

[0011] The super - dispersed nano - alumina microspheres are formed by chelating aluminum isopropoxide with ethyl acetoacetate to form aluminum sol, then compounding with polyvinyl alcohol to form spheres in n - hexane, and then reacting with ammonia water.

[0012] Preferably, the mass ratio of polyisobutene, polyurethane prepolymer, 1,3 - propanediol, diethylene glycol mono vinyl ether, and super - dispersed nano - alumina microspheres is 0.5 - 1.5:30 - 50:1 - 2:1 - 5:1 - 6.

[0013] Preferably, the specific preparation steps of the polyurethane prepolymer are as follows: Add isophorone diisocyanate and a catalyst to poly(1,4 - butanediol adipate) diol, stir for 2 - 4 h under nitrogen protection to obtain the polyurethane prepolymer.

[0014] Preferably, the mass ratio of poly(1,4 - butanediol adipate) diol, isophorone diisocyanate, and catalyst is 10 - 20:1 - 2:0.1 - 0.2.

[0015] Preferably, the catalyst is at least one of dioctyltin dilaurate, dibutyltin dilaurate, dimethyltin dilaurate, stannous octoate, butyltin oxide, and octyltin oxide.

[0016] Preferably, the super - dispersed nano - alumina microspheres are prepared by the following specific operations: Add aluminum isopropoxide and ethyl acetoacetate to anhydrous ethanol and disperse evenly, adjust the pH of the system to 2 - 6, stir at 80 - 90 °C for 1 - 2 h, add polyvinyl alcohol and continue stirring for 10 - 20 min, drop it into n - hexane and continue stirring to obtain a pre - formed gel system; Under high - speed stirring, continue to drop ammonia water into the pre - formed gel system, stir for 10 - 20 min, stand for 1 - 2 h, filter, wash, and vacuum - dry to obtain the super - dispersed nano - alumina microspheres.

[0017] Preferably, the mass ratio of aluminum isopropoxide, ethyl acetoacetate, and polyvinyl alcohol is 2 - 6:0.1 - 1:1 - 2.

[0018] Preferably, the mass fraction of ammonia water is 4-10%, and the mass ratio of aluminum isopropoxide to ammonia water is 2-6:1-3.

[0019] Preferably, hydrochloric acid with a concentration of 0.1-1 mol / L is used to adjust the pH of the system to 2-6.

[0020] The technical effects of the present invention are as follows:

[0021] In the present invention, a thermally conductive polyurethane resin is used to encapsulate electronic components, which not only has excellent barrier properties to other substances, but also has thermal conductivity, excellent thermal stability and hydrophobicity in addition to the special properties of polyurethane, broadening the scope of use of the sealant. It is used for the encapsulation of electronic devices, which is of great significance for improving the accuracy and service life of electronic devices.

[0022] Specifically, by introducing diethylene glycol mono vinyl ether into polyurethane, a double bond-terminated product is obtained. The hydrogen bonds on it can induce crystallization in the hard segment structure to form a crystallization region, which can not only effectively enhance the thermal stability of the product, but also react with polyisobutylene to further form a large number of chemical cross-linking points, promoting the further increase of intermolecular forces and the further enhancement of thermal stability. At the same time, diethylene glycol mono vinyl ether can also reduce the density of hydrophilic groups on the polyurethane molecular chain, effectively reducing the density of hydrophilic groups, and the excess diethylene glycol mono vinyl ether further combines with the hyperdispersed nano-alumina microspheres to further reduce the surface energy of the product and enhance the hydrophobic effect of the product.

[0023] In the hyperdispersed nano-alumina microspheres, aluminum isopropoxide forms aluminum sol under the chelation of ethyl acetoacetate. After forming spheres in n-hexane, it reacts with ammonia water to form nano-alumina spheres. Polyvinyl alcohol is dispersed in them, which can not only effectively improve the sphericity of the alumina spheres, but also make the obtained hyperdispersed nano-alumina microspheres have excellent dispersion performance in the system after drying. Moreover, the alcohol hydroxyl groups contained on them can form hydrogen bonds with diethylene glycol mono vinyl ether, uniformly disperse in the system and form a thermally conductive network chain. In particular, the hyperdispersed nano-alumina microspheres with small particle size can play a role in filling the microphase separation gap between the hard segment and the soft segment, increasing the probability of forming a thermally conductive network chain and effectively enhancing the thermal conductivity. Description of the Drawings

[0024] Figure 1 It is a comparison chart of the thermal conductivity coefficients of the thermally conductive polyurethane resin films obtained in Example 5 and Comparative Examples 1-2.

[0025] Figure 2 It is a comparison chart of the thermogravimetric curves of the thermally conductive polyurethane resin films obtained in Example 5 and Comparative Examples 1-2.

[0026] Figure 3Comparison chart of static water contact angles of the thermally conductive polyurethane resin films obtained in Example 5 and Comparative Examples 1-2. Detailed implementation manners

[0027] The present invention will be further illustrated below in conjunction with specific embodiments.

[0028] Example 1

[0029] A method for encapsulating electronic components with polyurethane, comprising the following steps:

[0030] (1) Dissolve 0.5 kg of polyisobutylene in 5 kg of tetrahydrofuran, and drop it into 30 kg of polyurethane prepolymer under high-speed stirring. Stir at 60 °C for 3 h under nitrogen protection, add 1 kg of 1,3-propanediol, continue stirring for 2 h, add 1 kg of diethylene glycol mono vinyl ether and 1 kg of super-dispersed nano-alumina microspheres, and continue to react for 3 h. Carry out defoaming treatment by means of vacuum evacuation to obtain a thermally conductive polyurethane resin; seal the thermally conductive polyurethane resin and perform vacuum treatment to obtain a pretreated thermally conductive polyurethane resin.

[0031] The specific preparation steps of the polyurethane prepolymer are as follows: Add 10 kg of poly(butylene adipate) diol to an oven, perform dehydration treatment at 100 °C for 1 h, add 1 kg of isophorone diisocyanate and 0.1 kg of dibutyltin dilaurate, and stir for 2 h under nitrogen protection to obtain a polyurethane prepolymer.

[0032] The following specific operations are adopted for the super-dispersed nano-alumina microspheres: Disperse 2 kg of aluminum isopropoxide and 0.1 kg of ethyl acetoacetate evenly in 20 kg of absolute ethanol. Under stirring, adjust the pH of the system to 2-6 with hydrochloric acid with a concentration of 0.1 mol / L, stir at 80 °C for 1 h, add 1 kg of polyvinyl alcohol and continue stirring for 10 min, drop it into 100 kg of n-hexane under high-speed stirring, continue stirring for 10 min after adding, and the stirring speed is 1000 r / min to obtain a prefabricated gel system; continue to drop 1 kg of ammonia water with a mass fraction of 4% into the prefabricated gel system under high-speed stirring, stir for 10 min, let it stand for 1 h, filter, wash twice with ethanol, and perform vacuum drying to obtain super-dispersed nano-alumina microspheres.

[0033] (2) Add the electronic components into a packaging box, extend the pretreated thermally conductive polyurethane resin into the packaging box through a discharge pipe, perform encapsulation molding treatment on the packaging box, and cure to obtain encapsulated and molded electronic components.

[0034] Example 2

[0035] A method for encapsulating electronic components with polyurethane, comprising the following steps:

[0036] (1) Dissolve 1.5 kg of polyisobutene in 10 kg of tetrahydrofuran, and drop it into 50 kg of polyurethane prepolymer under high-speed stirring. Stir at 80 °C for 6 h under nitrogen protection, add 2 kg of 1,3-propanediol, continue stirring for 4 h, add 5 kg of diethylene glycol mono vinyl ether and 6 kg of super-dispersed nano-aluminum oxide microspheres, and continue reacting for 5 h. Perform degassing treatment by evacuating and releasing gas to obtain thermally conductive polyurethane resin; seal the thermally conductive polyurethane resin and perform vacuum treatment to obtain pretreated thermally conductive polyurethane resin.

[0037] The specific preparation steps of the polyurethane prepolymer are as follows: Add 20 kg of poly(1,4-butylene adipate) diol to an oven, perform dehydration treatment at 120 °C for 2 h, add 2 kg of isophorone diisocyanate and 0.2 kg of stannous octoate, and stir for 4 h under nitrogen protection to obtain the polyurethane prepolymer.

[0038] The following specific operations are adopted for the super-dispersed nano-aluminum oxide microspheres: Add 6 kg of aluminum isopropoxide and 1 kg of ethyl acetoacetate to 40 kg of absolute ethanol and disperse evenly. Under stirring, adjust the pH of the system to 2-6 with 1 mol / L hydrochloric acid, stir at 90 °C for 2 h, add 2 kg of polyvinyl alcohol and continue stirring for 20 min. Drop it into 200 kg of n-hexane under high-speed stirring, and continue stirring for 20 min after adding completely. The stirring speed is 2000 r / min to obtain a prefabricated gel system; Under high-speed stirring, continue to drop 3 kg of 10% ammonia water into the prefabricated gel system, stir for 20 min, let it stand for 2 h, filter, wash 4 times with ethanol, and perform vacuum drying to obtain super-dispersed nano-aluminum oxide microspheres.

[0039] (2) Add the electronic components into the packaging box, extend the pretreated thermally conductive polyurethane resin into the packaging box through the discharge pipe, perform encapsulation and molding treatment on the packaging box, and cure to obtain the encapsulated and molded electronic components.

[0040] Example 3

[0041] A method for encapsulating electronic components with polyurethane, comprising the following steps:

[0042] (1) Dissolve 0.8 kg of polyisobutene in 8 kg of tetrahydrofuran, and drop it into 35 kg of polyurethane prepolymer under high-speed stirring. Stir at 75 °C for 4 h under nitrogen protection, add 1.7 kg of 1,3-propanediol, continue stirring for 2.5 h, add 4 kg of diethylene glycol mono vinyl ether and 2 kg of super-dispersed nano-aluminum oxide microspheres, and continue reacting for 4.5 h. Perform degassing treatment by evacuating and releasing gas to obtain thermally conductive polyurethane resin; seal the thermally conductive polyurethane resin and perform vacuum treatment to obtain pretreated thermally conductive polyurethane resin.

[0043] The specific preparation steps of the polyurethane prepolymer are as follows: Add 12 kg of poly(1,4-butylene adipate) diol to an oven, dehydrate at 115 °C for 1.3 h, add 1.8 kg of isophorone diisocyanate and 0.12 kg of octyltin oxide, and stir for 3.5 h under nitrogen protection to obtain the polyurethane prepolymer.

[0044] The following specific operations are adopted for the super-dispersed nano-aluminum oxide microspheres: Add 3 kg of aluminum isopropoxide and 0.7 kg of ethyl acetoacetate to 25 kg of absolute ethanol and disperse evenly. Under stirring, adjust the pH of the system to 2 - 6 with 0.7 mol / L hydrochloric acid, stir at 82 °C for 1.7 h, add 1.2 kg of polyvinyl alcohol and continue stirring for 17 min, then drop it into 120 kg of n-hexane under high-speed stirring. After complete addition, continue stirring for 17 min with a stirring speed of 1400 r / min to obtain a preformed gel system; Under high-speed stirring, continue to drop 2.5 kg of 6% ammonia water by mass into the preformed gel system, stir for 17 min, let it stand for 80 min, filter, wash with ethanol 3 times, and vacuum dry to obtain the super-dispersed nano-aluminum oxide microspheres.

[0045] (2) Add the electronic components into the packaging box, extend the pretreated thermally conductive polyurethane resin into the packaging box through the discharge pipe, perform encapsulation and molding treatment on the packaging box, and cure to obtain the encapsulated and molded electronic components.

[0046] Example 4

[0047] A method for encapsulating electronic components with polyurethane includes the following steps:

[0048] (1) Dissolve 1.2 kg of polyisobutene in 6 kg of tetrahydrofuran, drop it into 45 kg of polyurethane prepolymer under high-speed stirring, stir at 65 °C for 5 h under nitrogen protection, add 1.3 kg of 1,3-propanediol, continue stirring for 3.5 h, add 2 kg of diethylene glycol mono vinyl ether and 5 kg of super-dispersed nano-aluminum oxide microspheres, and continue to react for 3.5 h. Perform defoaming treatment by evacuating and releasing gas to obtain the thermally conductive polyurethane resin; Seal the thermally conductive polyurethane resin and perform vacuum treatment to obtain the pretreated thermally conductive polyurethane resin.

[0049] The specific preparation steps of the polyurethane prepolymer are as follows: Add 18 kg of poly(1,4-butylene adipate) diol to an oven, dehydrate at 105 °C for 1.7 h, add 1.2 kg of isophorone diisocyanate and 0.18 kg of dimethyltin dilaurate, and stir for 2.5 h under nitrogen protection to obtain the polyurethane prepolymer.

[0050] The specific operation of the super-dispersed nano-aluminum oxide microspheres is as follows: Add 5 kg of aluminum isopropoxide and 0.3 kg of ethyl acetoacetate into 35 kg of absolute ethanol and disperse evenly. Under stirring, adjust the pH of the system to 2-6 with 0.3 mol / L hydrochloric acid, stir at 88 °C for 1.3 h, add 1.8 kg of polyvinyl alcohol and continue stirring for 13 min. Then, dropwise add the mixture into 180 kg of n-hexane under high-speed stirring. After complete addition, continue stirring for 13 min at a stirring speed of 1800 r / min to obtain a pre-gel system. Under high-speed stirring, continue to dropwise add 1.5 kg of 8% ammonia water to the pre-gel system, stir for 13 min, let it stand for 100 min, filter, wash with ethanol three times, and dry in vacuum to obtain the super-dispersed nano-aluminum oxide microspheres.

[0051] (2) Add the electronic components into the packaging box, extend the pretreated thermally conductive polyurethane resin into the packaging box through the discharge pipe, perform encapsulation and molding treatment on the packaging box, and cure to obtain the encapsulated and molded electronic components.

[0052] Example 5

[0053] A method for encapsulating electronic components with polyurethane includes the following steps:

[0054] (1) Dissolve 1 kg of polyisobutene in 7 kg of tetrahydrofuran, and dropwise add it into 40 kg of polyurethane prepolymer under high-speed stirring. Stir at 70 °C for 4.5 h under nitrogen protection, add 1.5 kg of 1,3-propanediol, continue stirring for 3 h, add 3 kg of diethylene glycol mono vinyl ether and 3.5 kg of super-dispersed nano-aluminum oxide microspheres, and continue reacting for 4 h. Perform degassing treatment by evacuating and releasing gas to obtain the thermally conductive polyurethane resin. Seal the thermally conductive polyurethane resin and perform vacuum treatment to obtain the pretreated thermally conductive polyurethane resin.

[0055] The specific preparation steps of the polyurethane prepolymer are as follows: Add 15 kg of poly(1,4-butylene adipate) diol into the oven, perform dehydration treatment at 110 °C for 1.5 h, add 1.5 kg of isophorone diisocyanate and 0.15 kg of dioctyltin dilaurate, and stir for 3 h under nitrogen protection to obtain the polyurethane prepolymer.

[0056] The specific operation of the super-dispersed nano-aluminum oxide microspheres is as follows: Add 4 kg of aluminum isopropoxide and 0.5 kg of ethyl acetoacetate to 30 kg of absolute ethanol and disperse evenly. Under stirring, adjust the pH of the system to 2-6 with 0.5 mol / L hydrochloric acid, stir at 85 °C for 1.5 h, add 1.5 kg of polyvinyl alcohol and continue stirring for 15 min. Then drip it into 150 kg of n-hexane under high-speed stirring. After complete addition, continue stirring for 15 min at a stirring speed of 1600 r / min to obtain a preformed gel system. Under high-speed stirring, continue to drip 2 kg of 7% ammonia water into the preformed gel system, stir for 15 min, let it stand for 90 min, filter, wash with ethanol 3 times, and vacuum dry to obtain the super-dispersed nano-aluminum oxide microspheres.

[0057] (2) Add the electronic components into the packaging box, extend the pretreated thermally conductive polyurethane resin into the packaging box through the discharge pipe, perform encapsulation and molding treatment on the packaging box, and cure to obtain the encapsulated and molded electronic components.

[0058] Comparative Example 1

[0059] A method for encapsulating electronic components with polyurethane includes the following steps:

[0060] (1) Dissolve 1 kg of polyisobutene in 7 kg of tetrahydrofuran, drip it into 40 kg of polyurethane prepolymer under high-speed stirring, stir at 70 °C for 4.5 h under nitrogen protection, add 1.5 kg of 1,3-propanediol, continue stirring for 3 h, add 3 kg of diethylene glycol mono vinyl ether and 3.5 kg of nano-aluminum oxide, and continue to react for 4 h. Perform degassing treatment by evacuating and releasing gas to obtain the thermally conductive polyurethane resin. Seal the thermally conductive polyurethane resin and perform vacuum treatment to obtain the pretreated thermally conductive polyurethane resin.

[0061] The specific preparation steps of the polyurethane prepolymer are as follows: Add 15 kg of poly(1,4-butylene adipate) diol to the oven, perform dehydration treatment at 110 °C for 1.5 h, add 1.5 kg of isophorone diisocyanate and 0.15 kg of dioctyltin dilaurate, and stir for 3 h under nitrogen protection to obtain the polyurethane prepolymer.

[0062] (2) Add the electronic components into the packaging box, extend the pretreated thermally conductive polyurethane resin into the packaging box through the discharge pipe, perform encapsulation and molding treatment on the packaging box, and cure to obtain the encapsulated and molded electronic components.

[0063] Comparative Example 2

[0064] A method for encapsulating electronic components with polyurethane includes the following steps:

[0065] (1) Dissolve 1 kg of polyisobutene in 7 kg of tetrahydrofuran, and drop it into 40 kg of polyurethane prepolymer under high-speed stirring. Stir at 70 °C for 4.5 h under nitrogen protection, add 1.5 kg of 1,3-propanediol, continue stirring for 3 h, add 3 kg of diethylene glycol mono vinyl ether and 3.5 kg of hyperdispersed nano-alumina microspheres, and continue reacting for 4 h. Perform defoaming treatment by evacuating and releasing gas to obtain thermally conductive polyurethane resin; seal the thermally conductive polyurethane resin and perform vacuum treatment to obtain pretreated thermally conductive polyurethane resin.

[0066] The specific preparation steps of the polyurethane prepolymer are as follows: Add 15 kg of poly (1,4-butylene adipate) diol to an oven, dehydrate at 110 °C for 1.5 h, add 1.5 kg of isophorone diisocyanate and 0.15 kg of dioctyltin dilaurate, and stir for 3 h under nitrogen protection to obtain the polyurethane prepolymer.

[0067] The following specific operations are adopted for the hyperdispersed nano-alumina microspheres: Disperse 4 kg of aluminum isopropoxide and 0.5 kg of ethyl acetoacetate evenly in 30 kg of absolute ethanol. Under stirring, adjust the pH of the system to 2-6 with 0.5 mol / L hydrochloric acid, stir at 85 °C for 1.5 h, and drop it into 150 kg of n-hexane under high-speed stirring. After adding, continue stirring for 15 min, and the stirring speed is 1600 r / min to obtain a preformed gel system; continue to drop 2 kg of 7% ammonia water by mass fraction into the preformed gel system under high-speed stirring, stir for 15 min, let it stand for 90 min, filter, wash with ethanol 3 times, and perform vacuum drying to obtain hyperdispersed nano-alumina microspheres.

[0068] (2) Add the electronic components into the packaging box, extend the pretreated thermally conductive polyurethane resin into the packaging box through the discharge pipe, perform encapsulation and molding treatment on the packaging box, and cure to obtain the encapsulated and molded electronic components.

[0069] Transfer the thermally conductive polyurethane resins obtained in Example 5 and Comparative Examples 1-2 to a template with a polytetrafluoroethylene surface, let it stand at room temperature to air dry naturally, place it in a vacuum drying oven and dry at 50 °C for 8 h, and put the obtained film into a desiccator for storage and standby.

[0070] Use a DRP-II type thermal conductivity tester to measure the thermal conductivity of each group of specimens obtained above. The set temperature of the heating plate is 50 °C, and the temperature is stabilized for 30-40 min. The sample size is 80 mm in diameter and 3 mm in height.

[0071] As Figure 1 shown, the thermally conductive polyurethane resin film obtained in Example 5 has the highest thermal conductivity and the best thermal performance.

[0072] The applicant believes that this is because the hyper-dispersed nano-alumina microspheres not only have excellent dispersion performance in the system, but also the alcohol hydroxyl groups contained therein can form hydrogen bonds with diethylene glycol mono vinyl ether, are uniformly dispersed in the system and form a heat conduction network chain. In particular, the hyper-dispersed nano-alumina microspheres with small particle sizes can fill the micro-phase separation gaps between the hard segments and the soft segments, increase the probability of forming the heat conduction network chain, and effectively enhance the thermal conductivity.

[0073] An automatic differential thermal gravimetric analyzer was used to analyze the thermal stability of each group of the above-obtained specimens.

[0074] As Figure 2 shown, the thermal stability of the thermally conductive polyurethane resin film obtained in Example 5 is the best.

[0075] The applicant believes that this is because the present invention introduces diethylene glycol mono vinyl ether into polyurethane to obtain a product capped with double bonds, and the hydrogen bonds thereon can induce crystallization in the hard segment structure and form a crystallization region, which can not only effectively enhance the thermal stability of the product, but also react with polyisobutylene to further form a large number of chemical cross-linking points, promoting the intermolecular force to increase further and the thermal stability to be further enhanced.

[0076] A water contact angle tester was used to measure the static water contact angle (CA) existing on the surfaces of each group of the above-obtained specimens at room temperature.

[0077] As Figure 3 shown, the static water contact angle of the thermally conductive polyurethane resin film obtained in Example 5 is the largest, forming a hydrophobic structure.

[0078] The applicant believes that this is because the present invention introduces diethylene glycol mono vinyl ether into polyurethane to obtain a product capped with double bonds, which reduces the density of hydrophilic groups on the polyurethane molecular chain, can effectively reduce the density of hydrophilic groups, and the excess diethylene glycol mono vinyl ether further combines with the hyper-dispersed nano-alumina microspheres to further reduce the surface energy of the product and enhance the hydrophobic effect of the product.

[0079] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A method for encapsulating electronic components with polyurethane, characterized in that, It includes the following steps: (1) Dissolve polyisobutylene in tetrahydrofuran, drop it into the polyurethane prepolymer, stir at 60 - 80 °C for 3 - 6 h under nitrogen protection, add 1,3 - propanediol and continue stirring for 2 - 4 h, then add diethylene glycol mono vinyl ether and hyperdispersed nano - alumina microspheres, continue the reaction for 3 - 5 h, conduct degassing treatment to obtain the thermally conductive polyurethane resin, seal the thermally conductive polyurethane resin, and conduct vacuum treatment to obtain the pretreated thermally conductive polyurethane resin; Among them, the mass ratio of polyisobutylene, polyurethane prepolymer, 1,3 - propanediol, diethylene glycol mono vinyl ether, and hyperdispersed nano - alumina microspheres is 0.5 - 1.5:30 - 50:1 - 2:1 - 5:1 - 6; The hyperdispersed nano - alumina microspheres are obtained by chelating aluminum isopropoxide with ethyl acetoacetate to form an aluminum sol, then compounding with polyvinyl alcohol to form spheres in n - hexane, and then reacting with ammonia water; (2) Add the electronic components into the packaging box, extend the pretreated thermally conductive polyurethane resin into the packaging box through the discharge pipe, conduct encapsulation molding treatment on the packaging box, and cure to obtain the encapsulated and molded electronic components.

2. The method for encapsulating electronic components with polyurethane according to claim 1, wherein The specific preparation steps of the polyurethane prepolymer are as follows: Add isophorone diisocyanate and a catalyst to poly(1,4 - butanediol adipate) diol, stir for 2 - 4 h under nitrogen protection to obtain the polyurethane prepolymer.

3. The method for encapsulating electronic components with polyurethane according to claim 2, characterized in that, The mass ratio of poly(1,4 - butanediol adipate) diol, isophorone diisocyanate, and the catalyst is 10 - 20:1 - 2:0.1 - 0.

2.

4. The method for encapsulating electronic components with polyurethane according to claim 2, wherein, The catalyst is at least one of dibutyltin dilaurate, dimethyltin dilaurate, dioctyltin dilaurate, stannous octoate, butyltin oxide, and octyltin oxide.

5. The method for encapsulating electronic components with polyurethane according to claim 1, wherein The following specific operations are adopted for the hyperdispersed nano - alumina microspheres: Disperse aluminum isopropoxide and ethyl acetoacetate evenly in absolute ethanol, adjust the pH of the system to 2 - 6, stir at 80 - 90 °C for 1 - 2 h, add polyvinyl alcohol and continue stirring for 10 - 20 min, drop it into n - hexane and continue stirring to obtain a pre - formed gel system; Under high - speed stirring, continue to drop ammonia water into the pre - formed gel system, stir for 10 - 20 min, stand for 1 - 2 h, filter, wash, and conduct vacuum drying to obtain the hyperdispersed nano - alumina microspheres.

6. The method for encapsulating electronic components with polyurethane according to claim 5, characterized in that, The mass ratio of aluminum isopropoxide, ethyl acetoacetate, and polyvinyl alcohol is 2 - 6:0.1 - 1:1 - 2.

7. The method for encapsulating electronic components with polyurethane according to claim 5, characterized in that, The mass fraction of ammonia water is 4 - 10%, and the mass ratio of aluminum isopropoxide to ammonia water is 2 - 6:1 - 3.

8. The method for encapsulating electronic components with polyurethane according to claim 5, characterized in that, Adjust the pH of the system to 2 - 6 with hydrochloric acid with a concentration of 0.1 - 1 mol / L.

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